WO2003095411A1 - Method for the production of acrylic acid and/or the esters thereof and propionic acid and/or the esters thereof in a compound - Google Patents

Method for the production of acrylic acid and/or the esters thereof and propionic acid and/or the esters thereof in a compound Download PDF

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Publication number
WO2003095411A1
WO2003095411A1 PCT/EP2003/004710 EP0304710W WO03095411A1 WO 2003095411 A1 WO2003095411 A1 WO 2003095411A1 EP 0304710 W EP0304710 W EP 0304710W WO 03095411 A1 WO03095411 A1 WO 03095411A1
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WIPO (PCT)
Prior art keywords
acrylic acid
weight
acid
column
ppm
Prior art date
Application number
PCT/EP2003/004710
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German (de)
French (fr)
Inventor
Christoph Adami
Ralf Böhling
Otto Machhammer
Peter Zehner
Claus Hechler
Volker Schliephake
Joachim Thiel
Original Assignee
Basf Aktiengesellschaft
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Publication date
Priority claimed from DE2002120752 external-priority patent/DE10220752A1/en
Priority claimed from DE2002124341 external-priority patent/DE10224341A1/en
Application filed by Basf Aktiengesellschaft filed Critical Basf Aktiengesellschaft
Priority to AU2003224144A priority Critical patent/AU2003224144A1/en
Publication of WO2003095411A1 publication Critical patent/WO2003095411A1/en

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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
    • C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
    • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
    • C07C51/25—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring
    • C07C51/252—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring of propene, butenes, acrolein or methacrolein
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/347—Preparation of carboxylic acids or their salts, halides or anhydrides by reactions not involving formation of carboxyl groups
    • C07C51/36—Preparation of carboxylic acids or their salts, halides or anhydrides by reactions not involving formation of carboxyl groups by hydrogenation of carbon-to-carbon unsaturated bonds
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C67/00—Preparation of carboxylic acid esters
    • C07C67/30—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group
    • C07C67/303—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group by hydrogenation of unsaturated carbon-to-carbon bonds

Definitions

  • the present invention relates to a process for the preparation of acrylic acid and / or its esters and of propionic acid and / or their esters in combination.
  • Acrylic acid either by itself or in the form of its salts or its esters, is particularly important for the preparation of polymers for a wide variety of applications (e.g. adhesives, superabsorbents, binders).
  • Acrylic acid esters can be obtained by direct esterification of acrylic acid with the corresponding alcohol, e.g. Alkanol available.
  • Propionic acid is e.g. used in the form of their Ca or Na salts for the preservation of feed and food or used as a starting material for the production of herbicides.
  • esters of propionic acid are used as a solvent, plasticizer or comonomer (vinyl propionate).
  • acrylic acid is by selective heterogeneously catalyzed gas phase partial oxidation of propane, propene and / or
  • Acrolein available are generally diluted with inert gases such as nitrogen, CO, water vapor, molecular hydrogen, noble gases, other saturated and / or unsaturated hydrocarbons, in a mixture with molecular oxygen at elevated temperatures and, if appropriate, increased pressure via transition metals
  • Mixed oxide catalysts passed and oxidatively converted into a product gas mixture containing acrylic acid (e.g. EP-A 1090684, DE-A 10122027, DE-A 10101695, DE-A 10059713, DE-A 10028582, DE-A 19955168, DE-A 19955176, EP-A 1159247, DE-A 19948248 and DE-A 19948241).
  • a disadvantage of the aforementioned partially oxidative method of producing acrylic acid is that not only the main product, acrylic acid, but also secondary components typical of the gas-phase catalytically oxidative method of production are formed in its framework. These are, in particular, Al carboxylic acids (such as formic acid, acetic acid and / or propionic acid) and / or aldehydes (such as acrolein, methacrolein, propionaldehyde, n-butyraldehyde, benzaldehyde, furfural and crotonaldehyde) and allyl acrylate.
  • Al carboxylic acids such as formic acid, acetic acid and / or propionic acid
  • aldehydes such as acrolein, methacrolein, propionaldehyde, n-butyraldehyde, benzaldehyde, furfural and crotonaldehyde
  • allyl acrylate such as acro
  • the secondary components mentioned can be formed in total amounts of up to 5% by weight (in the case of aldehydes (including allyl acrylate)) and 5% by weight (in the case of alkane carboxylic acids).
  • esters from C 1 -C 6 -alkanols and acrylic acid the corresponding formic, acetic and / or propionic esters would also be formed in side reactions, which relates to the yield of the desired acrylic ester to the amount of alkanol used.
  • the aldehyde content usually has an effect, e.g. disadvantageous in that it e.g. the induction time of polymerization reactions, i.e. affects the period between reaching the polymerization temperature and the actual start of the polymerization. Furthermore, it usually influences the degree of polymerization and can also cause discoloration in the polymers. Allyl acrylate has the same disadvantageous effect. Allyl acrylate is therefore to be understood in this document as aldehyde.
  • the procedure is to this end so that one component acrylic acid, accompanied by a portion of the relevant side, optionally after direct 'and / or indirect cooling of the product gas mixture of the gas phase oxidation of this product gas mixture by absorption initially in a suitable absorbent (in the Usually water or a high-boiling organic solvent) and subsequently largely separates the acrylic acid from the absorption medium and the secondary components by distillative, rectificative, extractive and / or crystallizing processes (cf. e.g. DE-A 10115277, EP-A 982289, EP-A 982288, EP-A 982287, DE-A 19606877, DE-A 19631645 and DE-A 10218419 and the prior art cited in these documents).
  • a suitable absorbent in the Usually water or a high-boiling organic solvent
  • the product gas mixture of the selective heterogeneously catalyzed gas phase partial oxidation can also be subjected to fractional condensation, as is the case e.g. describe DE-A 19740253, DE-A 19627847 and DE-A 19924532.
  • the condensation is the case e.g. describe DE-A 19740253, DE-A 19627847 and DE-A 19924532.
  • processing zone The sum of all processing steps is referred to as processing zone in this document. You (this also applies to that
  • an acrylic acid quality is generally removed, the acrylic acid content of which is 90% by weight.
  • the boiling point of several aldehydic secondary components at normal pressure is in the range T S ⁇ 60 ° C or in the range T S ⁇ 50 ° C or ⁇ 40 ° C, where T s is the boiling point of acrylic acid at normal pressure 45 (1 at) , Similarly, the boiling point of acrylic acid and propionic acid almost coincide at normal pressure, whereas acetic acid, for example, clings to acrylic acid in a crystallisative separation.
  • the aforementioned fractions are therefore generally not led directly out of the processing zone, but are at least partially returned to the processing zone at another location in the processing zone which differs from the place where they were formed.
  • fractions containing secondary components enriched in the processing zone are also not always desirable from a different point of view. Namely, if you take into account that the corrosion effect of e.g. lower alkane carboxylic acids is considerable, which is why their local accumulation, especially in the case of formic acid, should be avoided.
  • Acrylic acid target product quality separates a substance mixture containing secondary components and acrylic acid without significantly impairing the economics of the process due to acrylic acid losses.
  • Such a process would also be a process for the production of acrylic acid esters, since acrylic acid can be converted into the associated acrylic acid ester in the same way by direct reaction with the corresponding alcohol.
  • a method is provided as a solution to the problem, in which one produces acrylic acid and / or its ester and propionic acid and / or its ester in combination and is characterized in that
  • a by-substance mixture containing acrylic acid which is characterized in that either its total content (in mol%) of aldehydes based on the amount of acrylic acid contained and / or its total content based on the amount of acrylic acid contained (in mol %) of alkane carboxylic acids is greater than the respective al ehydric and / or alkane carboxylic acid content, obtained in the same way, of the acrylic acid quality separated off under i),
  • the method according to the invention is based, inter alia, on the fact that propionic acid and / or its ester can be obtained from acrylic acid and / or its ester by hydrogenation with molecular hydrogen.
  • DE-A 2310754 recommends a heterogeneously catalyzed (a supported catalyst is recommended as the catalyst to which palladium is applied as the catalytically active material), which is carried out under pressure in the liquid phase.
  • the process of DE-A 2310754 is preferably carried out in a fluidized bed.
  • the basis of the liquid phase is a Solvent. As such, water comes into consideration.
  • preferred solvent is propionic acid.
  • the aforementioned hydrogenation is expediently carried out at moderate temperatures (e.g. 20 to 80 ° C) and moderate hydrogen pressures (e.g. 1 to 10 atm).
  • Polish patent PL-94748 recommends producing propionic acid by heterogeneously catalyzed hydrogenation in the gas phase.
  • a copper-zinc catalyst which is applied to aluminum oxide is considered appropriate as the catalyst.
  • the hydrogenation process takes place e.g. Temperatures of 250 to 350 ° C in the fixed catalyst bed at pressures from normal pressure to 6 atm with propionic acid selectivities of at least 95 mol%.
  • the acrylic acid is advantageously diluted in the gas phase by means of water vapor.
  • the finished product can be obtained directly by liquefying the propionic acid vapors in coolers.
  • DE-A 2834691 discloses e.g. a process for the preparation of ethyl propionate by catalytic hydrogenation of ethyl acrylate. Rhodium complex compounds are used as catalysts.
  • EP-A 408338 recommends similar catalysts for the catalytic hydrogenation of acrylic acid derivatives.
  • Electroanalytical Chemistry and Interfacial Electrochemistry, 60 (1975) 75-80 teaches a cathodic reduction of acrylic acid to propionic acid on a platinized platinum electrode.
  • the method according to the invention is also based on the fact that the presence of small amounts of formic acid or acetic acid is only slightly disruptive in most uses of propionic acid.
  • the problem of separating propionic acid from acrylic acid, which can hardly be achieved by distillation, is virtually eliminated when the hydrogenation variant according to the invention is used. Since propionic acid and its esters are not used for the purposes of radical polymerizations, any aldehydes contained in them cannot adversely affect them.
  • a first design variant is based on the procedure of EP-A 982288.
  • a selective heterogeneously catalyzed gas-phase partial oxidation of propane, propene and / or acrolein is first carried out in a reaction zone, as described, for example, in column 3 of EP-A 982288.
  • the resulting product gas mixture A usually contains, based in each case on the total reaction gas mixture, 1 to 30% by weight of acrylic acid, 0.05 to 1% by weight of propene, 0.05 to 1% by weight of acrolein, 0.05 to 10 wt .-% molecular 'oxygen, 0.05 to 2 wt .-% formic acid, 0.05 to 2 wt .-% acetic acid is 0.01 to 2 wt .-% propionic acid, 0.05 to 1 weight % Formaldehyde, 0.05 to 2% by weight of other aldehydes such as furfural and benzaldehyde, 0.01 to 0.5% by weight (as a total) of maleic acid and maleic anhydride and 20 to 97% by weight, preferably 50 to 97% by weight of inert diluent gases.
  • the latter can, in particular, saturated C 1 -C 6 -hydrocarbons, for example 0 to 95% by weight ⁇ % methane ' and / or propane, in addition 1 to 30% by weight water vapor, 0.05 to 15% by weight carbon dioxide and 0 to 95 % By weight of nitrogen, in each case based on 100% by weight of product gas mixture A.
  • saturated C 1 -C 6 -hydrocarbons for example 0 to 95% by weight ⁇ % methane ' and / or propane, in addition 1 to 30% by weight water vapor, 0.05 to 15% by weight carbon dioxide and 0 to 95 % By weight of nitrogen, in each case based on 100% by weight of product gas mixture A.
  • the acrylic acid and some of the secondary components are initially absorbed from product mixture A in a high-boiling organic solvent in a first process step.
  • the boiling point of the high-boiling organic solvent at normal pressure is preferably at least 20 ° C., in particular 50 ° C., more preferably 70 ° C. above the boiling point of the acrylic acid.
  • Preferred solvents, the term solvent also comprising solvent mixtures in the present application have boiling points (at atmospheric pressure) from 180 to 400 ° C., in particular from 220 to 360 ° C.
  • solvents are high-boiling, hydrophobic organic solvents which do not contain any polar group acting outwards, such as, for example, aliphatic or aromatic hydrocarbons, for example middle oil fractions from paraffin ' distillation, or ethers with bulky groups on the O atom, or mixtures thereof, a polar solvent such as the 1, 2-dimethylphthalate disclosed in DE-A-43 08 087 is advantageously added to these.
  • Esters of benzoic acid and phthalic acid with straight-chain, 1 to 8 are also suitable
  • Alkanols containing carbon atoms such as benzoic acid n-butyl ester, methyl benzoate, ethyl benzene, ethyl phthalate, diethyl phthalate, and so-called heat transfer oils, such as diphenyl, diphenyl ether or their chlorine derivatives and triarylalkanes, e.g. 4-methyl-4 '-benzyl-diphenylmethane and its isomers 2-methyl-2'-benzyl-diphenylmethane, 2-methyl-4' -benzyl-diphenyleneethane and 4-methyl-2'-benzyl-diphenylmethane.
  • a particularly preferred solvent is a solvent mixture of diphenyl and diphenyl ether, preferably in the azeotropic composition, in particular from about 25% by weight of diphenyl (biphenyl) and about 75% by weight of diphenyl ether, for example the commercially available Diphyl®.
  • This solvent mixture preferably also contains a polar solvent such as dimethyl phthalate in an amount of 0.1 to 25% by weight, based on the total solvent mixture.
  • high and low boilers, medium and low boilers as well as corresponding adjective terms refer to compounds that have a higher boiling point than normal acrylic acid (high boilers) or those that have approximately the same boiling point as acrylic acid (middle low boilers) or those that have a low boiling point as acrylic acid (low boilers).
  • the hot product gas mixture A is advantageously cooled by partial evaporation of the solvent in a direct condenser or quench apparatus before absorption.
  • a direct condenser or quench apparatus are suitable for this especially venturi washers, bubble columns or spray condensers.
  • the high-boiling secondary components of the reaction gas condense into the non-evaporated solvent.
  • a partial stream of the unevaporated solvent preferably 1 to 10% by weight of the mass stream fed to the absorption column, is drawn off and subjected to solvent cleaning.
  • the solvent is distilled over and the high-boiling secondary components remain, which - if necessary further thickened - can be disposed of, eg burned. This solvent distillation is used to avoid an excessive concentration of high boilers in the solvent stream.
  • the distilled solvent is preferably fed to the loaded solvent stream from the absorption column.
  • the absorption takes place in a countercurrent absorption column, which is basically equipped with any type of column internals, preferably with packing or structured packing, and which is charged with solvent from above.
  • the gaseous reaction product and any evaporated solvent from the quench apparatus are introduced into the column from below and then cooled to the absorption temperature.
  • the cooling is advantageously carried out by cooling circuits, i.e. heated, loaded solvent is drawn off from the column, cooled in heat exchangers and fed back to the column at a point above the point of withdrawal. After absorption, all of the high boilers, most of the acrylic acid and some of the low boilers are in the solvent.
  • the remaining, not absorbed remainder of the product gas mixture A is further cooled in order to separate the condensable part of low-boiling secondary components such as water, formaldehyde and acetic acid contained therein by condensation.
  • This condensate is called acid water in the following.
  • the gas stream then remaining consists predominantly of nitrogen, carbon oxides and unreacted starting materials. Preferably, this is partly fed back into the reaction zone as a diluent gas, hereinafter referred to as circulating gas.
  • the other part is discharged as waste gas and preferably burned.
  • the acrylic acid is separated from the solvent together with the low-boiling components and the low-boiling secondary components contained. This separation takes place by means of rectification, whereby basically every rectification column can be used. A column with dual-flow trays is advantageously used for this purpose.
  • the acrylic acid is largely freely distilled from the solvent and the medium-boiling secondary components, such as maleic anhydride.
  • the buoyancy part of the column is advantageously lengthened and the acrylic acid is withdrawn as a side draw from the column in a quality of 95% by weight acrylic acid.
  • the secondary substance mixture carried away in this way contains:
  • the .. acrylic acid separated as the target product usually contains:
  • a stream is drawn off from the bottom of the rectification column which predominantly contains solvents. Before being returned to the absorption stage, the solvent stream is largely cleaned of acrylic acid in order to be able to absorb acrylic acid from product gas mixture A again.
  • the solvent of acrylic acid is preferably depleted by stripping with inert gas, particularly preferably with a partial stream of the circulating gas, or in the case that propane is diluent gas, with propane.
  • the stripping is generally carried out at pressures of about 1.1 to 2.0 bar, preferably at pressures of 1.3 to 1.6 bar and at temperatures of about 80 to 120 ° C., preferably from 110 to 120 ° C.
  • the solvent stream to be cleaned is added to the top of a stripping column; it flows over the internals towards the swamp.
  • the stripping gas is introduced into the bottom of the stripping column in countercurrent. While the stripping gas flows in the direction of the column top, it absorbs acrylic acid from the liquid solvent stream, so that a purified solvent stream can be drawn off from the bottom of the stripping column, which has an acrylic acid concentration of at most 1% by weight, preferably of at most 0.5%. -% contains. This largely acrylic acid-free solvent can then be recirculated to the absorption stage.
  • the stripping gas loaded with acrylic acid is expediently recirculated to the stage in which the partial evaporation of the solvent takes place or to the absorption column.
  • the acidic water which can also still contain acrylic acid in solution, is treated extractively with a partial stream of the solvent fraction which has been almost completely freed from acrylic acid as described above.
  • the aqueous stream from the acid water extraction can still be concentrated and subsequently disposed of.
  • the organic stream is also returned to the absorption stage.
  • the bottom stream from the countercurrent absorption column which, in addition to the solvent, contains about 10 to 40% by weight of acrylic acid, essentially all the high boilers and part of the low boilers, in the upper region of a first rectification column I is added, and in the rectification column I at a bottom temperature of 165 to 210 ° C., preferably from 180 to 200 ° C., particularly preferably from 190 to 195 ° C.
  • the top stream is passed on for the rectificative recovery of the target product acrylic acid quality, and the bottom stream is returned to the absorption stage, that is to say fed into the upper region of the countercurrent absorption column (in a special embodiment, the acid water, which may still contain acrylic acid in solution, is mixed with a treated small extract stream of the bottom stream extractive.
  • the aqueous stream of acid water extraction can then be disposed of while the organic stream is also returned to the absorption stage).
  • the target product acrylic acid quality is preferably obtained from the top stream in the following process steps:
  • a separating plate rectification column with two condensers and one evaporator is preferably used for this separation problem. Dual-flow floors are particularly suitable as internals.
  • the top stream coming from the rectification column I is first condensed and then runs downward in the left-hand sub-column (stripping column) of the separating plate column used.
  • steam predominantly vaporous acrylic acid
  • a stream rich in low boilers is then drawn off at the top of this partial column after condensation.
  • this stream still contains significant amounts of acrylic acid, it is normally returned to the absorption stage and / or the quenching apparatus.
  • this stream rich in low boilers, containing acrylic acid, on the other hand, is passed out of the work-up zone as a by-product mixture and fed to the hydrogenation according to the invention, if appropriate after esterification of the acrylic acid beforehand.
  • the secondary substance mixture carried away in this way has the following contents:
  • the target product acrylic acid quality is obtained from the liquid stream arriving in the sump in the right-hand partial column (buoyancy column) of the separating plate column (this could also be replaced by a crystallizing separation step).
  • the stripping column and the lifting column have a common sump. This contains predominantly the solvent which, if necessary after cleaning, for example by evaporation in a quench, recirculates into the absorption stage.
  • the substantially free low-boiling acrylic acid vapor rises, the medium boilers and high boilers being washed out of the steam by the liquid reflux.
  • the vapor is condensed at the top of the column Part is subtracted from the head as the target product acrylic acid quality and the rest forms liquid reflux.
  • the target product acrylic acid quality usually has the following contents:
  • the removal of the secondary substance mixture from the workup zone results in reduced polymer formation in the workup zone, in which the individual working steps are of course in a known manner in the presence of polymerization inhibitors such as e.g. Phenothiazine or monomethyl ether of hydroquinone (MEHQ) can be performed.
  • polymerization inhibitors such as e.g. Phenothiazine or monomethyl ether of hydroquinone (MEHQ) can be performed.
  • FIGS. 4, 5 and 6 of DE-A 19 606 877 can also refrain from recirculating the top stream from column K30 into the absorption column and instead supply this top stream as a by-product mixture to the hydrogenation according to the invention.
  • the measure according to the invention results in an extended running time in the processing zone.
  • a third design variant lies in the documents DE-A 19 833 049, DE-A 19 814 375, DE-A 19 814 421,
  • DE-A 19 814 449, DE-A 10053086, DE-A 19 740 252, DE-A 19 814 387, DE-A 19 740 253 and DE-A 19 924 532 disclose the procedure for the fractional condensation of the, in advance optionally the rectified and / or indirectly cooled product gas mixture A.
  • this target product acrylic acid quality will be fed to further distillation and / or crystallization purification stages and at least some of the bottom liquids and / or mother liquor obtained in the course of these distillations and / or crystallizations will be returned to the fractionating condensation column.
  • a disadvantage of the procedure of fractional condensation is that the medium-boiling secondary components (e.g. acetic acid) form concentration bellies over their length in the condensation column. In other words, they accumulate over certain column lengths (heights) until they leave the column either overhead or at the bottom, depending on the boiling point.
  • the medium-boiling secondary components e.g. acetic acid
  • concentration bellies over their length in the condensation column.
  • water forms a high-boiling azeotrope with formic acid, which boils between water and acrylic acid at normal pressure, so that a concentration belly of formic acid is formed above the side deduction of the target product quality, which contains up to 30% by weight can be.
  • This leads to corrosion problems which the application of complex measures such as require the use of corrosion inhibitors, catalytic decomposition of formic acid or esterification of formic acid.
  • the accumulation of other secondary components puts a strain on subsequent cleaning stages.
  • the procedure according to the invention can also remedy this. This is done in a simple manner in that it allows the secondary component antinodes to be pierced in the condensation column without significant economic disadvantage. That is, at the level of the respective concentration belly, the respective secondary components and the liquid phase containing acrylic acid are partially carried up from the condensation column and the acrylic acid contained therein, if appropriate after its esterification, is converted into propionic acid and / or ester by hydrogenation using molecular hydrogen. This measure reduces the amplitude of the concentration bellies and makes it easier to separate the secondary components from the acrylic acid (Subsequent cleaning stages can be dimensioned smaller). The latter is a very general advantage of the procedure according to the invention.
  • fractional condensation can be carried out in detail as in the cited prior art documents (in particular DE-A 19 924 532). The same applies to the polymerization inhibition in fractional condensation.
  • hydrogenations of acrylic acid to propionic acid in the gas phase are generally preferred over liquid phase processes, since the problem of acrylic acid polymerization arises less with gas phase processes.
  • liquid substance mixtures that have been removed must be converted into the gas phase by evaporation.
  • the target esters are, in particular, methyl acrylate, ethyl acrylate, n-butyl acrylate and tert. -Butyl acrylate into consideration.
  • An optionally desired separation of propionic acid and / or its ester from the hydrogenation product mixture can be carried out in a manner known per se, e.g. by rectification.
  • the process according to the invention is particularly suitable when the propene used as the starting material for the selective heterogeneously catalyzed gas phase oxidation, as in WO 01/96270, EP-A 11 71 146, DE-A 33 13 573 and US Pat 31 61 670 described, was generated by catalytic pre-dehydrogenation of propane.
  • the molecular hydrogen formed in the process can subsequently be used for the hydrogenation in step c) of the process according to the invention.
  • the product gas mixture (3600 g / h) was cooled to a temperature of 136 ° C. in a spray cooler (2).
  • 750 g / h (7) of a total of 7000 g / h via the collecting tray (5) (with a temperature of 100 ° C.) of the high boiler fraction (6) removed from the separating column (3) were used as spray liquid (bottom liquid 4 did not occur)
  • the spray liquid was circulated over the tube bundle heat exchanger (8) described with heat transfer oil. 40 g / h high boilers were continuously removed from the circuit (9).
  • the product gas mixture cooled to a temperature of 136 ° C. was fed to the separation column (10) below the tray (5).
  • the column was a tray column with, viewed from bottom to top, first 25 dual-flow trays and then 50 bubble trays (1 bell per tray). The bottom diameter was 49 mm.
  • the dual flow floors had 6 holes per floor.
  • the hole diameter of the first five dual-flow trays was 9.5 mm.
  • the subsequent 10 trays had a hole diameter of 9 mm and the hole diameter of the last 5 dual-flow trays was 8.7 mm.
  • the floor above floor 15 was another collecting floor (11). staltet. Above it were 1800 g / h containing a temperature of 97 ° C acrylic acid quality (12)
  • the crystallizer was a stirred tank (3 1 internal volume) with a spiral stirrer. The heat of crystallization was removed via the double jacket of the container. The equilibrium temperature of the solution was 9.7 ° C.
  • the suspension produced during crystallization (solids content approx. 25% by weight) was discontinuously separated into crystals and mother liquor on a centrifuge at 2000 rpm (centrifuge diameter 300 mm) and a centrifuging time of 3 min. The crystals were then washed with melted (previously washed) crystals (80 g) for 20 seconds at 2000 rpm.
  • a gaseous mixture (17) was removed from the top of the column and subjected to a partial condensation in the spray cooler (18).
  • 480 g / h of the resulting acid water were at the top of Ko ⁇ lonne with a temperature of 30 ° C thereinto recycled (26).
  • 220 g / h of the sour water were continuously removed (the Sour water contained 3% by weight of acrylic acid and 2.6% by weight of acetic acid).
  • 90 g / h of the acid water removed were mixed with MEHQ (22) and as a 0.5% by weight aqueous stabilizer solution (21) together with the remaining amount of acid water (23) via the water-cooled tube bundle heat exchanger (24) to 18 ° C cooled used as spray liquid (25).
  • a 0.5% by weight aqueous solution of 4-hydroxy-TEMPO (4-hydroxy-2, 2,6, 6-tetramethyl-piperidine-1-oxyl) was prepared, which in an amount of 18 g / h at a temperature of 20 ° C was fed to the 75th tray of the separation column (27).
  • the separation device described could be operated for 40 days without any appreciable polymer formation.
  • the formic acid belly By removing a liquid side stream of 10 g / h at this column height, the formic acid belly could be reduced to 13% by weight.
  • the stationary composition of the liquid side stream removed was essentially:
  • the side stream removed is fed to a hydrogenation according to DE-A 23 10 754.
  • the purity of the crystals was slightly improved.
  • the gas phase which was at a temperature of approx. 150 ° C, was led into the lower part of a packed column 2 (3 m high; double jacket made of glass; inner diameter 50 mm, three packed zones of lengths (from bottom to top) 90 cm, 90 cm and 50 cm; the packing zones were thermostated from bottom to top as follows:
  • the penultimate and the last packing zone were separated by a chimney floor;
  • the packing elements were metal helices made of stainless steel with a helix diameter of 5 mm and a helix length v ⁇ n 5 mm; immediately above the middle packing zone, the absorbent was fed and the counterflow of 2900 g / h of 57.4% by weight of diphenyl ether, 20.7% by weight of diphenyl, 20% by weight of o-dimethylphthalate and the rest from others Components composite absorbent applied at a temperature of 50 ° C, exposed.
  • the non-absorbed gas mixture leaving the second packed zone in the absorption column 2 was cooled further in the third packed zone in order to separate off the condensable part of the secondary components contained therein, for example water and acetic acid, by condensation.
  • This condensate is called sour water.
  • part of the acid water above the third packing zone of the absorption column 2 was returned to the absorption column 2 at a temperature of 20 ° C.
  • the sour water was removed below the uppermost packing zone from the chimney floor attached there.
  • the ratio of recycled to withdrawn acid water was 200 g / g.
  • the acid water removed also contained 0.8% by weight of acrylic acid. If necessary, this can be recovered as described in DE-A 19 600 955. 1600 Nl / h of the gas stream ultimately leaving the absorption column 2 were recycled as recycle gas into the propene oxidation. The rest were burned.
  • a solvent stream loaded with acrylic acid of 5230 g / h (main components, each in% by weight or ppm by weight: solvent 61, acrylic acid 30, acetic acid 8118 ppm, maleic anhydride 200 ppm) was introduced into a first partial stream IIIA of 2160 g / h, which predominantly contained acrylic acid (main components, each in% by weight: solvent 20, acrylic acid 77 and acetic acid 0.22) and a second partial stream IIIB of 3070 g / h, which predominantly contained the solvent (main components each in wt. -% or ppm by weight: solvent 83, acrylic acid 5, and acetic acid 636 ppm) separated '.
  • Partial stream IIIB was fed to the top of stripping column 3. An air flow of 600 Nl / h was used as the stripping gas. Partial stream IIB from the evaporator was added to the top of stripping column 3; the stripping column 3 was used here to purify the solvent from acrylic acid. The solvent removed from acrylic acid was withdrawn from the bottom of the stripping column 3 and recirculated to the top of the absorption column 2. The diacrylic acid content in the solvent was 2.0% by weight.
  • the partial stream IIIA occurring in the evaporator 5 was condensed in a heat exchanger 6 at 100 mbar and the condensate was fed to the 28th tray of the two-part rectification column 4, namely its stripping section.
  • the low boilers were stripped from the partial stream IIIA with acrylic acid vapor in countercurrent, whereas the medium boilers and high boilers were predominantly dissolved in the liquid. remained.
  • an almost low-boiler-free stream b main components in% by weight or ppm by weight: solvent 28, acrylic acid 71, acetic acid 721 ppm, maleic anhydride 4026 ppm was removed.
  • the partial stream b was taken from the common evaporator 7 of the stripping section and the lifting section of the rectification column 4, a residual stream c was drawn off from the evaporator 7 (480 g / h, main components, in% by weight or ppm by weight: solvent 87, acrylic acid 10, maleic anhydride 700 ppm) and the Venturi quench 1.
  • the vapor stream from the evaporator 7 was fed to the lifting section of the rectification column 4 in order to obtain the desired acrylic acid quality and was cleaned of medium boilers and high boilers by the acrylic acid return flow.
  • a stream of 420 g / was at the top of the lifting section of the rectification column 4 h deducted from the target product, which still contained 1500 ppm acetic acid and 50 ppm maleic anhydride lt (otherwise the total aldehyde content (including allyl acrylate) was ⁇ 300 ppm by weight and the total alkane carboxylic acid content was also ⁇ 300 ppm by weight).
  • the vapor from the stripping section of the rectification column 4 was treated as a residual stream a with 87% by weight acrylic acid, 200% by weight solvent, 1510% by weight aldehydes, 1000% by weight allyl acrylate, 6% by weight acetic acid and 7% by weight of formic acid condensed, mixed with phenothiazine and likewise fed to the Venturi quench 1.
  • the diacrylic acid content of the acid water which was fed to the combustion was 2.6% by weight.
  • the residual stream a from comparative example 2 from c) was removed from the work-up zone and fed to a hydrogenation according to the invention of the acrylic acid contained.
  • the run-up time of the processing zone was increased to 28 days.

Abstract

A target-product acrylic acid quality and an acrylic acid/secondary constituent mixture are separated from a product gas mixture containing acrylic acid and secondary constituents of a heterogeneously catalyzed gas phase partial oxidation in a treatment area. The target-product quality has a lower secondary-constituent content than the secondary-constituent mixture. The acrylic acid contained in the latter is converted into propionic acid and/or the esters thereof, optionally after prior esterification, by means of hydrogenation.

Description

Verfahren zur Herstellung von Acrylsaure und/oder deren Ester sowie von Propionsäure und/oder deren Ester im VerbundProcess for the production of acrylic acid and / or its esters as well as propionic acid and / or its esters in combination
Beschreibungdescription
Vorliegende Erfindung betrifft ein Verfahren zur Herstellung von Acrylsaure und/oder deren Ester sowie von Propionsäure und/oder deren Ester im Verbund.The present invention relates to a process for the preparation of acrylic acid and / or its esters and of propionic acid and / or their esters in combination.
Acrylsaure, entweder für sich oder in Form ihrer Salze oder ihrer Ester, ist insbesondere zur Herstellung von Polymerisaten für die verschiedensten Anwendungsgebiete (z.B. Klebstoffe, Super- absorber, Bindemittel) von Bedeutung. Acrylsäureester sind durch direkte Veresterung von Acrylsaure mit dem entsprechenden Alkohol, z.B. Alkanol , erhältlich.Acrylic acid, either by itself or in the form of its salts or its esters, is particularly important for the preparation of polymers for a wide variety of applications (e.g. adhesives, superabsorbents, binders). Acrylic acid esters can be obtained by direct esterification of acrylic acid with the corresponding alcohol, e.g. Alkanol available.
Propionsäure wird z.B. in Form ihrer Ca- bzw. Na-Salze zur Konservierung von Futter- und Lebensmitteln eingesetzt oder als Ausgangsstoff zur Herstellung von Herbiziden verwendet. Ester der Propionsäure werden u.a. als Lösungsmittel, Weichmacher oder Comono ere (Vinylpropionat) angewendet.Propionic acid is e.g. used in the form of their Ca or Na salts for the preservation of feed and food or used as a starting material for the production of herbicides. Among other things, esters of propionic acid are used as a solvent, plasticizer or comonomer (vinyl propionate).
Unter anderem ist Acrylsaure durch selektive heterogen kataly- sierte Gasphasenpartialoxidation von Propan, Propen und/oderAmong other things, acrylic acid is by selective heterogeneously catalyzed gas phase partial oxidation of propane, propene and / or
Acrolein erhältlich. Dabei werden diese Ausgangsgase, in der Regel mit inerten Gasen wie Stickstoff, C0 , Wasserdampf, molekularem Wasserstoff, Edelgasen, anderen gesättigten und/oder ungesättigten Kohlenwasserstoffen verdünnt, im Gemisch mit mole- kularem Sauerstoff bei erhöhten Temperaturen sowi.e gegebenenfalls erhöhtem Druck über übergangsmetallische Mischoxidkatalysatoren geleitet und oxidativ in ein Acrylsaure enthaltendes Produktgasgemisch umgewandelt (z.B. EP-A 1090684, DE-A 10122027, DE-A 10101695, DE-A 10059713, DE-A 10028582, DE-A 19955168, DE-A 19955176, EP-A 1159247, DE-A 19948248 und DE-A 19948241) .Acrolein available. These starting gases are generally diluted with inert gases such as nitrogen, CO, water vapor, molecular hydrogen, noble gases, other saturated and / or unsaturated hydrocarbons, in a mixture with molecular oxygen at elevated temperatures and, if appropriate, increased pressure via transition metals Mixed oxide catalysts passed and oxidatively converted into a product gas mixture containing acrylic acid (e.g. EP-A 1090684, DE-A 10122027, DE-A 10101695, DE-A 10059713, DE-A 10028582, DE-A 19955168, DE-A 19955176, EP-A 1159247, DE-A 19948248 and DE-A 19948241).
Nachteilig an der vorgenannten partiell oxidativen Herstellweise von Acrylsaure ist, dass in ihrem Rahmen nicht nur das Hauptprodukt Acryls ure sondern zusätzlich für den gasphasen- katalytisch oxidativen Herstellungsweg typische Nebenkomponenten gebildet werden. Diese sind insbesondere Al ancarbonsäuren (wie Ameisensäure, Essigsäure und/oder Propionsäure) und/oder Aldehyde (wie Acrolein, Methacrolein, Propionaldehyd, n-Butyraldehyd, Benzaldehyd, Furfurale und Crotonaldehyd) sowie Allylacrylat . Bezogen auf die gebildete Menge an Acrylsaure können die genannten Nebenkomponenten in Gesamtmengen von bis zu 5 Gew.-% (im Falle der Aldehyde (einschließlich Allylacrylat) ) und 5 Gew.-% (im Fall der Alkancarbonsäuren) gebildet werden.A disadvantage of the aforementioned partially oxidative method of producing acrylic acid is that not only the main product, acrylic acid, but also secondary components typical of the gas-phase catalytically oxidative method of production are formed in its framework. These are, in particular, Al carboxylic acids (such as formic acid, acetic acid and / or propionic acid) and / or aldehydes (such as acrolein, methacrolein, propionaldehyde, n-butyraldehyde, benzaldehyde, furfural and crotonaldehyde) and allyl acrylate. Based on the amount of acrylic acid formed, the secondary components mentioned can be formed in total amounts of up to 5% by weight (in the case of aldehydes (including allyl acrylate)) and 5% by weight (in the case of alkane carboxylic acids).
Nachteilig an diesen Nebenkomponenten ist, dass sich ein Beisein der meisten von ihnen im Rahmen einer AcrylsäureVerwendung als nachteilig erweist.A disadvantage of these secondary components is that the presence of most of them in the context of acrylic acid use proves to be disadvantageous.
Würde beispielsweise eine Alkancarbonsäuren als Nebenkomponenten enthaltende Acrylsaure zur Herstellung von Estern aus Cl-Cs-Alkanolen und Acrylsaure verwendet, würden in Nebenreaktionen auch die entsprechenden Ameisensäure-, Essigsäure- und/oder Propionsäureester gebildet, was die Ausbeute an ge- wünschtem Acrylsäureester, bezogen auf die eingesetzte Menge an Alkanol , mindert .If, for example, an acrylic acid containing alkane carboxylic acids as secondary components were used for the production of esters from C 1 -C 6 -alkanols and acrylic acid, the corresponding formic, acetic and / or propionic esters would also be formed in side reactions, which relates to the yield of the desired acrylic ester to the amount of alkanol used.
Setzt man die im Beisein der Aldehyde gebildeten Acrylsäureester oder solche Aldehyde enthaltende Acrylsaure selbst zu radika- lischen Polymerisationen ein, wirkt sich der Aldehydgehalt in der Regel z.B. insofern nachteilig aus, als er z.B. die Induktionszeit von Polymerisationsreaktionen, d.h. den Zeitraum zwischen dem Erreichen der Polymerisationstemperatur und dem tatsächlichen Beginn der Polymerisation, beeinflußt. Ferner beeinflußt er in der Regel den Polymerisationsgrad und kann in den Polymerisaten auch Verfärbungen verursachen. Allylacrylat wirkt in gleicher Weise nachteilig. Allylacrylat soll deshalb in dieser Schrift als Aldehyd aufgefaßt werden.If the acrylic acid esters formed in the presence of the aldehydes or acrylic acid containing such aldehydes are themselves used for radical polymerizations, the aldehyde content usually has an effect, e.g. disadvantageous in that it e.g. the induction time of polymerization reactions, i.e. affects the period between reaching the polymerization temperature and the actual start of the polymerization. Furthermore, it usually influences the degree of polymerization and can also cause discoloration in the polymers. Allyl acrylate has the same disadvantageous effect. Allyl acrylate is therefore to be understood in this document as aldehyde.
Bei der Gewinnung von Acrylsaure aus dem Produktgasgemisch einer selektiven heterogen katalysierten Gasphasenoxidation von Propan, Propen und/oder Acrolein ist es daher im Hinblick auf eine Weiterverwendbarkeit der gewonnenen Acrylsaure nicht nur erforderlich, die Acrylsaure aus der Gasphase abzutrennen, sondern die Acrylsaure muss gleichzeitig möglichst weitgehend von den vorstehend aufgeführten Nebenkomponenten abgetrennt werden.When recovering acrylic acid from the product gas mixture of a selective heterogeneously catalyzed gas phase oxidation of propane, propene and / or acrolein, it is therefore not only necessary to separate the acrylic acid from the gas phase with a view to the reusability of the acrylic acid obtained, but at the same time the acrylic acid must be as largely as possible be separated from the secondary components listed above.
Üblicherweise wird zu diesem Zweck so vorgegangen, dass man die Acrylsaure in Begleitung eines Teils der relevanten Neben- komponenten, gegebenenfalls nach vorheriger direkter 'und/oder indirekter Kühlung des Produktgasgemisches der Gasphasenoxidation, aus diesem Produktgasgemisch durch Absorption zunächst in ein geeignetes Absorptionsmittel (in der Regel Wasser oder ein hochsiedendes organisches Lösungsmittel) aufnimmt und nachfolgend die Acrylsaure durch destillative, rektifikative, extraktive und/oder kristallisative Verfahren sowohl vom Absorptions ittel als auch von den Nebenkomponenten weitestgehend abtrennt (vgl. z.B. DE-A 10115277, EP-A 982289, EP-A 982288, EP-A 982287, DE-A 19606877, DE-A 19631645 und DE-A 10218419 sowie der in diesen Schriften zitierte Stand der Technik) .Typically, the procedure is to this end so that one component acrylic acid, accompanied by a portion of the relevant side, optionally after direct 'and / or indirect cooling of the product gas mixture of the gas phase oxidation of this product gas mixture by absorption initially in a suitable absorbent (in the Usually water or a high-boiling organic solvent) and subsequently largely separates the acrylic acid from the absorption medium and the secondary components by distillative, rectificative, extractive and / or crystallizing processes (cf. e.g. DE-A 10115277, EP-A 982289, EP-A 982288, EP-A 982287, DE-A 19606877, DE-A 19631645 and DE-A 10218419 and the prior art cited in these documents).
'5 Alternativ dazu kann das Produktgasgemisch der selektiven heterogen katalysierten Gasphasenpartialoxidation, gegebenenfalls nach vorab erfolgter Kühlung, auch einer fraktionierenden Kondensation unterworfen werden, wie es z.B. die DE-A 19740253, die DE-A 19627847 und die DE-A 19924532 beschreiben. Die der Kondensati-'5 Alternatively, the product gas mixture of the selective heterogeneously catalyzed gas phase partial oxidation, if necessary after cooling beforehand, can also be subjected to fractional condensation, as is the case e.g. describe DE-A 19740253, DE-A 19627847 and DE-A 19924532. The condensation
10 onskolonne dabei entnommene Acrylsäurequalität kann bei Bedarf z.B. kristallisativ weiter aufgearbeitet werden.10 oncolumns of acrylic acid taken off can, if necessary, e.g. be worked up crystallisatively.
Die Summe aller Aufarbeitungsschritte wird in dieser Schrift als Aufarbeitungszone bezeichnet. Ihr (dies gilt auch für dasThe sum of all processing steps is referred to as processing zone in this document. You (this also applies to that
15 erfindungsgemäße Verfahren) wird in der Regel eine Acrylsäurequalität entnommen, deren Gehalt an Acrylsaure 90 Gew.-% beträgt. Häufig liegt der AcrylSäuregehalt der der Aufarbeitungszone (dies gilt auch für das erfindungsgemäße Verfahren) entnommenen Acrylsäurequalität bei 3=95 Gew.-%, oft bei 3=98 Gew.-%, vielfach bei15 methods according to the invention), an acrylic acid quality is generally removed, the acrylic acid content of which is 90% by weight. The acrylic acid content of the acrylic acid quality removed from the workup zone (this also applies to the process according to the invention) is frequently 3 = 95% by weight, often 3 = 98% by weight
20 99 Gew.-% und teilweise sogar bei 3=99,5 Gew.-%. Der Gesamt- gehalt der vorgenannten Acrylsäurequalitäten (auch der erfindungsgemäß entnommenen) an aldehydischen Nebenkomponenten beträgt üblicherweise 2000 Gew.pp , oft IOOO Gew.ppm, vielfach =5500 Gew.ppm, teilweise =S250 Gew.ppm oder s≤lOO Gew.ppm und in20 99% by weight and sometimes even 3 = 99.5% by weight. The total content of the above-mentioned acrylic acid qualities (including those extracted according to the invention) of aldehydic secondary components is usually 2000 ppm by weight, often 100 ppm by weight, in many cases = 5500 ppm by weight, partially = S250 ppm by weight or s≤100 ppm by weight and in
25 günstigen Fällen sogar 50 Gew.ppm bzw. =520 Gew.ppm oder =510 Ge .ppm.25 favorable cases even 50 ppm by weight or = 520 ppm by weight or = 510 ppm by weight.
In entsprechender Weise liegt der Gesamtgehalt der vorgenannten Acrylsäurequalitäten (auch der erfindungsgemäß entnommenen) an 30 Alkancarbonsäuren in der Regel gleichzeitig bei =55000 Gew.ppm, oft =53000 Gew.ppm, vielfach =52000 Gew.ppm, in güstigen Fällen bei =5500 Gew.ppm oder =5250 Gew.ppm sowie manchmal bei =5200 Gew.ppm oder = 100 Gew.ppm.In a corresponding manner, the total content of 30 alkane carboxylic acids in the above-mentioned acrylic acid qualities (including those extracted according to the invention) is generally at the same time = 55,000 ppm by weight, often = 53,000 ppm by weight, in many cases = 52,000 ppm by weight, in some cases = 5500 ppm by weight .ppm or = 5250 ppm by weight and sometimes at = 5200 ppm by weight or = 100 ppm by weight.
35 Problematisch an der skizzierten Art und Weise der Aufarbeitung des Produktgasgemisches der selektiven heterogen katalysierten Gasphasenpartialoxidation zur Gewinnung von Acrylsaure ist jedoch, dass das Siede- und/oder Kristallisationsverhalten eines Teils der unerwünschten Nebenkomponenten demjenigen von Acryl-35 The problem with the outlined way of working up the product gas mixture of the selective heterogeneously catalyzed gas phase partial oxidation for the production of acrylic acid is, however, that the boiling and / or crystallization behavior of some of the undesired secondary components to that of acrylic
40 säure ähnelt.40 acidity.
So liegt der Siedepunkt mehrerer aldehydischer Nebenkomponenten bei Normaldruck im Bereich TS±60°C bzw. im Bereich TS±50°C, bzw. ±40°C, wobei Ts der Siedepunkt von Acrylsaure bei Normaldruck 45 (1 at ) ist. In ähnlicher Weise fallen bei Normaldruck der Siedepunkt von Acrylsaure und Propionsäure nahezu zusammen, wohingegen z.B. Essigsäure sich bei einer kristallisativen Trennung an Acrylsaure klammer .The boiling point of several aldehydic secondary components at normal pressure is in the range T S ± 60 ° C or in the range T S ± 50 ° C or ± 40 ° C, where T s is the boiling point of acrylic acid at normal pressure 45 (1 at) , Similarly, the boiling point of acrylic acid and propionic acid almost coincide at normal pressure, whereas acetic acid, for example, clings to acrylic acid in a crystallisative separation.
Eine signifikante Abtrennung der Nebenkomponenten von Hauptprodukt Acrylsaure ist deshalb nur unter Ausbildung von Fraktionen möglich, die zwar einerseits die Nebenkomponenten angereichert, andererseits, infolge der Schwere der Trennung, aber auch noch nennenswerte Anteile an Acrylsaure enthalten.A significant separation of the secondary components from the main product acrylic acid is therefore only possible with the formation of fractions, which on the one hand enriched the secondary components, on the other hand, due to the difficulty of the separation, also contain significant amounts of acrylic acid.
Um in der Aufarbeitungszone zu hohe Acrylsäureverluste zu vermeiden, werden vorgenannte Fraktionen daher in der Regel nicht unmittelbar aus der Aufarbeitungszone herausgeführt, sondern wenig- stens teilweise an einem anderen Ort der Aufarbeitungszone, der vom Ort ihrer Bildung verschieden ist, in die Aufarbeitungszone rückgeführ .In order to avoid excessive acrylic acid losses in the processing zone, the aforementioned fractions are therefore generally not led directly out of the processing zone, but are at least partially returned to the processing zone at another location in the processing zone which differs from the place where they were formed.
Die ist jedoch insofern von Nachteil als sich als Ergebnis einge- hender Forschung gezeigt hat, dass wenigstens ein Teil der Nebenkomponenten die Polymerisationsneigung von Acrylsaure zu erhöhen vermag, weshalb mit einer solchen Rückführung im Regelfall eine erhöhte Polymerisatbildung in, der Aufarbeitungszone einhergeht.However, this is disadvantageous insofar as the result of in-depth research has shown that at least some of the secondary components can increase the tendency of acrylic acid to polymerize, which is why such recycling generally results in increased polymer formation in the work-up zone.
Die Ausbildung von Nebenkomponenten angereichert enthaltenden Fraktionen in der Aufarbei ungszone ist auch unter einem anderen Blickwinkel nicht immer wünschenswert. Nämlich dann, wenn man berücksichtigt, dass die Korrosionswirkung von z.B. niederen Alkancarbonsäuren beträchtlich ist, weshalb ihre lokale Anhäufung, insbesondere im Fall von Ameisensäure, vermieden werden sollte.The formation of fractions containing secondary components enriched in the processing zone is also not always desirable from a different point of view. Namely, if you take into account that the corrosion effect of e.g. lower alkane carboxylic acids is considerable, which is why their local accumulation, especially in the case of formic acid, should be avoided.
Wünschenswert wäre daher ein Verfahren zur Herstellung von Acrylsaure, das von einer selektiven heterogen katalysierten Gasphasenpartialoxidation von Propan, Proben und/oder Acrolein ausgeht und bei dem man aus der Aufarbeitungszone neben einerIt would therefore be desirable to have a process for the preparation of acrylic acid which starts from a selective heterogeneously catalyzed gas-phase partial oxidation of propane, samples and / or acrolein and in which, in addition to a
Acrylsäurezielproduktqualität ein Nebenkomponenten und Acrylsaure enthaltendes Stoffgemisch abtrennt, ohne die Wirtschaftlichkeit des Verfahrens aufgrund von Acrylsäureverlusten ausgeprägt zu beeinträchtigen. Ein solches Verfahren wäre gleichzeitig ein Ver- fahren zur Herstellung von Acrylsäureestern, läßt sich Acrylsaure doch in gleicher Weise durch direkte Umsetzung mit dem entsprechenden Alkohol in den zugehörigen Acrylsäureester überführen. Als Problemlösung wird ein Verfahren zur Verfügung gestellt, bei dem man Acrylsaure und/oder deren Ester und Propionsäure und/oder deren Ester im Verbund herstellt und das dadurch gekennzeichnet ist, dass manAcrylic acid target product quality separates a substance mixture containing secondary components and acrylic acid without significantly impairing the economics of the process due to acrylic acid losses. Such a process would also be a process for the production of acrylic acid esters, since acrylic acid can be converted into the associated acrylic acid ester in the same way by direct reaction with the corresponding alcohol. A method is provided as a solution to the problem, in which one produces acrylic acid and / or its ester and propionic acid and / or its ester in combination and is characterized in that
a) in einer ersten Zone, der Reaktionszone, Propan, Propen und/ oder Acrolein einer selektiven heterogen katalysierten Gasphasenpartialoxidation unter Bildung eines Produktgas- gemisches A, das als Hauptprodukt Acrylsaure und als Neben- komponenten Aldehyde und/oder gesättigte Alkancarbonsäuren enthält, unterwirft,a) in a first zone which subjects the reaction zone, propane, propene and / or acrolein to a selective heterogeneously catalyzed gas phase partial oxidation to form a product gas mixture A which contains acrylic acid as the main product and aldehydes and / or saturated alkane carboxylic acids as secondary components,
b) in einer zweiten Zone, der Aufarbeitungszone, aus dem Produktgasgemisch Ab) in a second zone, the work-up zone, from the product gas mixture A
i) einerseits als Zielprodukt eine Acrylsäurequalität abtrennt, deren Gehalt an Acrylsaure 3=90 Gew.-% beträgt, und gleichzeitigi) on the one hand, separates an acrylic acid quality as target product, the acrylic acid content of which is 3 = 90% by weight, and at the same time
ii) andererseits ein Acrylsaure enthaltendes Neben-Stoffgemisch abtrennt, das dadurch charakterisiert ist, dass entweder sein auf die enthaltene Menge an Acrylsaure bezogener Gesamtgehalt (in mol-%) an Aldehyden und/oder sein auf die enthaltene Menge an Acrylsaure bezogener Gesamtgehalt (in mol-%) an Alkancarbonsäuren größer ist, als der jeweilige, in gleicher Weise bezogene, Al ehyd- und/oder Alkancarbonsäuregehalt der unter i) abgetrennten Acrylsäurequalität,ii) on the other hand, separates a by-substance mixture containing acrylic acid, which is characterized in that either its total content (in mol%) of aldehydes based on the amount of acrylic acid contained and / or its total content based on the amount of acrylic acid contained (in mol %) of alkane carboxylic acids is greater than the respective al ehydric and / or alkane carboxylic acid content, obtained in the same way, of the acrylic acid quality separated off under i),
undand
c) die im unter ii) abgetrennten Neben-Stoffgemisch enthaltene Acrylsaure, gegebenenfalls nach erfolgter Veresterung, durch Hydrierung mittels molekularem Wasserstoff in Propionsäure und/oder deren Ester überführt.c) the acrylic acid contained in the secondary substance mixture separated off under ii), if appropriate after esterification, is converted into propionic acid and / or its ester by hydrogenation using molecular hydrogen.
Das erfindungsgemäße Verfahren fußt unter anderem darauf, dass Propionsäure und/oder deren Ester aus Acrylsaure und/oder deren Ester durch Hydrierung mit molekularem Wasserstoff erhältlich ist.The method according to the invention is based, inter alia, on the fact that propionic acid and / or its ester can be obtained from acrylic acid and / or its ester by hydrogenation with molecular hydrogen.
Beispielsweise empfiehlt die DE-A 2310754 ein heterogen katalysiertes (als Katalysator wird ein Trägerkatalysator empfohlen, auf den als katalytisch aktives Material Palladium aufgebracht ist) Verfahren, das unter Druck in der Flüssigphase durchgeführt wird. Bevorzugt wird das Verfahren der DE-A 2310754 in einem Flüssigwirbelbett ausgeführt. Grundlage der Flüssigphase ist ein Lösungsmittel. Als solches kommt z.B. Wasser in Betracht. Bevorzugtes Lösungsmittel ist jedoch Propionsäure.For example, DE-A 2310754 recommends a heterogeneously catalyzed (a supported catalyst is recommended as the catalyst to which palladium is applied as the catalytically active material), which is carried out under pressure in the liquid phase. The process of DE-A 2310754 is preferably carried out in a fluidized bed. The basis of the liquid phase is a Solvent. As such, water comes into consideration. However, preferred solvent is propionic acid.
Um eine Kontrolle der natürlichen Polymerisationsneigung der Acrylsaure zu ermöglichen, wird die vorgenannte Hydrierung in zweckmäßiger Weise bei mäßigen Temperaturen (z.B. 20 bis 80°C) sowie mäßigen Wasserstoffdrucken ( z.B. 1 bis 10 atm) durchgeführt.In order to enable control of the natural tendency of acrylic acid to polymerize, the aforementioned hydrogenation is expediently carried out at moderate temperatures (e.g. 20 to 80 ° C) and moderate hydrogen pressures (e.g. 1 to 10 atm).
Aus Polyhydron, Vol. 15, No. 8, 1241-1251 (1966) ist bekannt, Propionsäure durch homogene katalytische (an Ruthenium-Phosphin- Komplexen) Hydrierung in der Flüssigphase (bevorzugtes Lösungsmittel ist Methanol) zu erzeugen. Typische Reaktionstemperaturen betragen dabei 60°C und der Wasserstoffdruck kann z.B. bei 3 MPa liegen.Made of polyhydron, vol. 15, no. 8, 1241-1251 (1966) is known to produce propionic acid by homogeneous catalytic (on ruthenium-phosphine complexes) hydrogenation in the liquid phase (preferred solvent is methanol). Typical reaction temperatures are 60 ° C and the hydrogen pressure can e.g. are around 3 MPa.
Das polnische Patent PL-94748 empfiehlt, Propionsäure durch heterogen katalysierte Hydrierung in der Gasphase herzustellen. Als Katalysator wird dabei ein Kupfer-Zink-Katalysator als zweckmäßig erachtet, der auf Aluminiumoxid aufgebracht ist. Der Hydrierungs- prozess verläuft bei z.B. Temperaturen von 250 bis 350°C im Katalysatorfestbett bei Drucken von Normaldruck bis 6 atm mit Propionsäureselektivitäten von wenigstens 95 mol-% . Mit Vorteil wird die Acrylsaure in der Gasphase mittels Wasserdampf verdünnt. Durch Verflüssigen der Propionsäuredämpfe in Kühlern kann unmit- telbar das fertige Produkt gewonnen werden.Polish patent PL-94748 recommends producing propionic acid by heterogeneously catalyzed hydrogenation in the gas phase. A copper-zinc catalyst which is applied to aluminum oxide is considered appropriate as the catalyst. The hydrogenation process takes place e.g. Temperatures of 250 to 350 ° C in the fixed catalyst bed at pressures from normal pressure to 6 atm with propionic acid selectivities of at least 95 mol%. The acrylic acid is advantageously diluted in the gas phase by means of water vapor. The finished product can be obtained directly by liquefying the propionic acid vapors in coolers.
In Che . Prum. , 37 (1987) 651 bis 653 wird die Möglichkeit der Herstellung von Propionsäure durch katalytische Hydrierung von Acrylsaure in der Gasphase an geträgerten Metallkatalysatoren (Pd, Ni, Cu, Zn) offenbart.In Che. Prum. , 37 (1987) 651 to 653 discloses the possibility of producing propionic acid by catalytic hydrogenation of acrylic acid in the gas phase over supported metal catalysts (Pd, Ni, Cu, Zn).
Die DE-A 2834691 offenbart z.B. ein Verfahren zur Herstellung von Propionsäureethylester durch katalytische Hydrierung von Acryl- säureethylester . Als Katalysatoren werden dabei Rhodiumkomplex- Verbindungen eingesetzt.DE-A 2834691 discloses e.g. a process for the preparation of ethyl propionate by catalytic hydrogenation of ethyl acrylate. Rhodium complex compounds are used as catalysts.
Ähnliche Katalysatoren empfiehlt auch die EP-A 408338 zur kataly- tischen Hydrierung von Acrylsäurederivaten.EP-A 408338 recommends similar catalysts for the catalytic hydrogenation of acrylic acid derivatives.
Electroanalytical Chemistry and Interfacial Electrochemistry, 60 (1975) 75-80 lehrt eine kathodische Reduzierung von Acrylsaure zu Propionsäure an einer platinisierten Platinelektrode.Electroanalytical Chemistry and Interfacial Electrochemistry, 60 (1975) 75-80 teaches a cathodic reduction of acrylic acid to propionic acid on a platinized platinum electrode.
Gemäß J. Electroanalytical Chem., M. Byrne, A. Kuhn; 60 (1975), 75-80 kann die Hydrierung von Acrylsaure zu Propionsäure sogar bakteriell erfolgen. Prinzipiell können alle vorgenannten Verfahrensweisen für den Schritt c) des erfindungsgemäßen Verfahrens angewendet werden.According to J. Electroanalytical Chem., M. Byrne, A. Kuhn; 60 (1975), 75-80, the hydrogenation of acrylic acid to propionic acid can even take place bacterially. In principle, all of the aforementioned procedures can be used for step c) of the method according to the invention.
Das erfindungsgemäße Verfahren fußt aber auch darauf, dass bei den meisten Verwendungen von Propionsäure ein Beisein geringer Mengen an Ameisensäure bzw. Essigsäure nur wenig störend ist. Auch das Problem der destillativ kaum zu bewerkstelligenden Abtrennung von Propionsäure aus Acrylsaure ist bei Anwendung der erfindungsgemäßen Hydrierungsvariante so gut wie aufgehoben. Da Propionsäure und ihre Ester nicht für Zwecke von radikalischen Polymerisationen verwendet werden, vermögen gegebenenfalls in ihnen enthaltene Aldehyde eine solche auch nicht negativ zu beeinträchtigen.However, the method according to the invention is also based on the fact that the presence of small amounts of formic acid or acetic acid is only slightly disruptive in most uses of propionic acid. The problem of separating propionic acid from acrylic acid, which can hardly be achieved by distillation, is virtually eliminated when the hydrogenation variant according to the invention is used. Since propionic acid and its esters are not used for the purposes of radical polymerizations, any aldehydes contained in them cannot adversely affect them.
Nachfolgend seien zwei bzw. drei Gestaltungsvarianten von im erfindungsgemäßen Verfahren anwendbaren Aufarbeitungszonen, einschließlich der aus diesen in zweckmäßiger Weise erfindungsgemäß abzutrennenden, Acrylsaure und Nebenkomponenten enthaltenden, und nachfolgend für Hydrierzwecke zu verwendenden Nebenstoffgemische, näher ausgeführt.Two or three design variants of work-up zones which can be used in the process according to the invention, including the acrylic acid and secondary components which are expediently separated from them in accordance with the invention and which are subsequently used for hydrogenation purposes, are explained in more detail below.
Einer ersten Gestaltungsvariante liegt die Verfahrensweise der EP-A 982288 zugrunde.A first design variant is based on the procedure of EP-A 982288.
In an sich bekannter Weise wird zunächst in einer Reaktionszone eine selektive heterogen katalysierte Gasphasenpartialoxidation von Propan, Propen und/oder Acrolein durchgeführt, wie es die EP-A 982288 beispielsweise in Spalte 3 beschreibt.In a manner known per se, a selective heterogeneously catalyzed gas-phase partial oxidation of propane, propene and / or acrolein is first carried out in a reaction zone, as described, for example, in column 3 of EP-A 982288.
Das dabei anfallende Produktgasgemisch A enthält blicherweise, jeweils bezogen auf das gesamte Reaktionsgasgemisch, 1 bis 30 Gew.-% Acrylsaure, 0,05 bis 1 Gew.-% Propen, 0,05 bis 1 Gew.-% Acrolein, 0,05 bis 10 Gew.-% molekularen 'Sauerstoff , 0,05 bis 2 Gew.-% Ameisensäure, 0,05 bis 2 Gew.-% Essigsäure, 0,01 bis 2 Gew.-% Propionsäure, 0,05 bis 1 Gew.-% Formaldehyd, 0,05 bis 2 Gew.-% sonstige Aldehyde wie Furfurale und Benzaldehyd, 0,01 bis 0,5 Gew.-% (als Gesamtmenge) an Maleinsäure und Maleinsäureanhydrid sowie 20 bis 97 Gew.-%, vorzugsweise 50 bis 97 Gew.-% inerte Verdünnungsgase. Letztere können insbesondere gesättigte Cι-C6-Kohlenwasserstoffe, z.B. 0 bis 95 Gew.~% Methan' und/oder Propan, daneben 1 bis 30 Gew.-% Wasserdampf, 0,05 bis 15 Gew.-% Kohlendioxide und 0 bis 95 Gew.-% Stickstoff, jeweils bezogen auf 100 Gew.-% Produktgasgemisch A, enthalten. In der Aufarbeitungszone werden die Acrylsaure und ein Teil der Nebenkomponenten zunächst in einer ersten Verfahrensstufe aus dem Produktgemisch A in einem hochsiedenden organischen Lösungsmittel absorbiert .The resulting product gas mixture A usually contains, based in each case on the total reaction gas mixture, 1 to 30% by weight of acrylic acid, 0.05 to 1% by weight of propene, 0.05 to 1% by weight of acrolein, 0.05 to 10 wt .-% molecular 'oxygen, 0.05 to 2 wt .-% formic acid, 0.05 to 2 wt .-% acetic acid is 0.01 to 2 wt .-% propionic acid, 0.05 to 1 weight % Formaldehyde, 0.05 to 2% by weight of other aldehydes such as furfural and benzaldehyde, 0.01 to 0.5% by weight (as a total) of maleic acid and maleic anhydride and 20 to 97% by weight, preferably 50 to 97% by weight of inert diluent gases. The latter can, in particular, saturated C 1 -C 6 -hydrocarbons, for example 0 to 95% by weight ~% methane ' and / or propane, in addition 1 to 30% by weight water vapor, 0.05 to 15% by weight carbon dioxide and 0 to 95 % By weight of nitrogen, in each case based on 100% by weight of product gas mixture A. In the work-up zone, the acrylic acid and some of the secondary components are initially absorbed from product mixture A in a high-boiling organic solvent in a first process step.
Vorzugsweise liegt der Siedepunkt des hochsiedenden organischen Lösungsmittels bei Normaldruck wenigstens 20°C, insbesondere 50°C, stärker bevorzugt 70°C über dem Siedepunkt der Acrylsaure. Bevorzugte Lösungsmittel, wobei in vorliegender Anmeldung der Begriff Lösungsmittel auch Lösungsmittelgemische umfaßt, haben Siedepunkte (bei Normaldruck) von 180 bis 400°C, insbesondere von 220 bis 360°C. Günstige Lösungsmittel sind hochsiedende, hydrophobe organische Lösungsmittel, die keine nach außen wirkende polare Gruppe enthalten, wie z.B. aliphatische oder aromatische Kohlen- Wasserstoffe, z.B. Mittelölfraktionen aus der Paraffin-' destillation, oder Äther mit sperrigen Gruppen am O-Atom, oder Gemische davon, wobei diesen vorteilhafterweise ein polares Lösungsmittel, wie das in der DE-A-43 08 087 offenbarte 1, 2-Dimethylphthalat, zugesetzt wird. Weiterhin eignen sich Ester der Benzoesäure und Phthalsäure mit geradkettigen, 1 bis 8The boiling point of the high-boiling organic solvent at normal pressure is preferably at least 20 ° C., in particular 50 ° C., more preferably 70 ° C. above the boiling point of the acrylic acid. Preferred solvents, the term solvent also comprising solvent mixtures in the present application, have boiling points (at atmospheric pressure) from 180 to 400 ° C., in particular from 220 to 360 ° C. Favorable solvents are high-boiling, hydrophobic organic solvents which do not contain any polar group acting outwards, such as, for example, aliphatic or aromatic hydrocarbons, for example middle oil fractions from paraffin ' distillation, or ethers with bulky groups on the O atom, or mixtures thereof, a polar solvent such as the 1, 2-dimethylphthalate disclosed in DE-A-43 08 087 is advantageously added to these. Esters of benzoic acid and phthalic acid with straight-chain, 1 to 8 are also suitable
Kohlenstoffatome enthaltenden Alkanolen, wie Benzoesäure-n-buty- lester, Benzoesäuremethylester , Benzolsäureethylester , Phthalsäu- redimethylester, Phthalsäurediethylester, sowie sogenannte Wärmeträgeröle, wie Diphenyl, Diphenylether oder deren Chlorderivate und Triarylalkane, z.B. 4-Methyl-4 ' -benzyl-diphenylmethan und dessen Isomere 2-Methyl-2 ' -benzyl-diphenylmethan, 2-Methyl-4 ' -benzyl-diphenylenethan und 4-Methyl-2 ' -benzyl-diphenylmethan. Ein besonders bevorzugtes Lösungsmittel ist ein Lösungsmittelgemisch aus Diphenyl und Diphenylether, bevorzugt in der azeotropen Zusammensetzung, insbesondere aus etwa 25 Gew.-% Diphenyl (Biphenyl) und etwa 75 Gew.-% Diphenylether, beispielsweise das im Handel erhältliche Diphyl®. Vorzugsweise enthält dieses Lösungsmittelgemisch weiterhin ein polares Lösungsmittel wie Dimethylphthalat in einer Menge von 0,1 bis 25 Gew.-%, bezogen auf das gesamte Lösungsmittelgemisch.Alkanols containing carbon atoms, such as benzoic acid n-butyl ester, methyl benzoate, ethyl benzene, ethyl phthalate, diethyl phthalate, and so-called heat transfer oils, such as diphenyl, diphenyl ether or their chlorine derivatives and triarylalkanes, e.g. 4-methyl-4 '-benzyl-diphenylmethane and its isomers 2-methyl-2'-benzyl-diphenylmethane, 2-methyl-4' -benzyl-diphenyleneethane and 4-methyl-2'-benzyl-diphenylmethane. A particularly preferred solvent is a solvent mixture of diphenyl and diphenyl ether, preferably in the azeotropic composition, in particular from about 25% by weight of diphenyl (biphenyl) and about 75% by weight of diphenyl ether, for example the commercially available Diphyl®. This solvent mixture preferably also contains a polar solvent such as dimethyl phthalate in an amount of 0.1 to 25% by weight, based on the total solvent mixture.
Nachfolgend bezeichnen die Begriffe Hoch- oder Schwersieder , Mit- telsieder und Leichtsieder sowie entsprechend adjektivisch gebrauchte Begriffe Verbindungen, die bei Normaldruck einen höheren Siedepunkt als die Acrylsaure besitzen (Hochsieder) bzw. solche, die in etwa den gleichen Siedepunkt wie Acrylsaure besitzen (Mit- telsieder) bzw. solche, die einen niedrigen Siedepunkt als Acrylsaure besitzen (Leichtsieder) .In the following, the terms high and low boilers, medium and low boilers as well as corresponding adjective terms refer to compounds that have a higher boiling point than normal acrylic acid (high boilers) or those that have approximately the same boiling point as acrylic acid (middle low boilers) or those that have a low boiling point as acrylic acid (low boilers).
Vorteilhafterweise wird das heiße Produktgasgemisch A durch Teilverdampfen des Lösungsmittels in einem Direktkondensator oder Quenchapparat vor der Absorption abgekühlt. Hierfür eignen sich insbesondere Venturiwäscher, Blasensäulen oder Sprühkondensatoren. Dabei kondensieren die schwersiedenden Nebenkomponenten des Reaktionsgases in das nicht verdampfte Lösungsmittel. In einer bevorzugten Ausführungsform der Erfindung wird ein Teilstrom des nicht verdampften Lösungsmittels, vorzugsweise 1 bis 10 Gew.-% des der Absorptionskolonne zugeführten Massenstroms, abgezogen und einer Lösungsmittelreinigung unterworfen. Hierbei wird das Lösungsmittel überdestilliert und zurück bleiben die schwer- siedenden Nebenkomponenten, die - bei Bedarf weiter eingedickt - entsorgt, z.B. verbrannt, werden können. Diese Lösungsmitteldestillation dient der Vermeidung einer zu hohen Konzentration an Schwersiedern im Lösungsmittelstrom. Das überdestillierte Lösungsmittel wird vorzugsweise dem beladenen Lösungsmittelstrom aus der Absorptionskolonne zugeführt .The hot product gas mixture A is advantageously cooled by partial evaporation of the solvent in a direct condenser or quench apparatus before absorption. Are suitable for this especially venturi washers, bubble columns or spray condensers. The high-boiling secondary components of the reaction gas condense into the non-evaporated solvent. In a preferred embodiment of the invention, a partial stream of the unevaporated solvent, preferably 1 to 10% by weight of the mass stream fed to the absorption column, is drawn off and subjected to solvent cleaning. Here, the solvent is distilled over and the high-boiling secondary components remain, which - if necessary further thickened - can be disposed of, eg burned. This solvent distillation is used to avoid an excessive concentration of high boilers in the solvent stream. The distilled solvent is preferably fed to the loaded solvent stream from the absorption column.
Die Absorption erfolgt in einer Gegenstromabsorptionskolonne, die grundsätzlich mit jeder Art von Kolonneneinbauten, vorzugsweise mit Füllkörpern oder strukturierten Packungen, bestückt ist, und die von oben mit Lösungsmittel beaufschlagt wird. Das gasförmige Reaktionsprodukt und gegebenenfalls verdampftes Lösungsmittel aus dem Quenchapparat werden von unten in die Kolonne eingeleitet und anschließend auf Absorptionstemperatur abgekühlt. Die Abkühlung erfolgt vorteilhafterweise durch Kühlkreise, d.h. erwärmtes bela- denes Lösungsmittel wird aus der Kolonne abgezogen, in Wärmetau- schern abgekühlt und wieder an einer Stelle oberhalb der Abzugs- stelle der Kolonne zugeführt. Nach der Absorption befinden sich im wesentlichen alle Schwersieder, der größte Teil der Acrylsaure sowie ein Teil der Leichtsieder im Lösungsmittel.The absorption takes place in a countercurrent absorption column, which is basically equipped with any type of column internals, preferably with packing or structured packing, and which is charged with solvent from above. The gaseous reaction product and any evaporated solvent from the quench apparatus are introduced into the column from below and then cooled to the absorption temperature. The cooling is advantageously carried out by cooling circuits, i.e. heated, loaded solvent is drawn off from the column, cooled in heat exchangers and fed back to the column at a point above the point of withdrawal. After absorption, all of the high boilers, most of the acrylic acid and some of the low boilers are in the solvent.
Der verbleibende, nicht absorbierte Rest des Produktgasgemisches A wird weiter abgekühlt, um den darin enthaltenen kondensierbaren Teil an leichtsiedenden Nebenkomponenten wie Wasser, Formaldehyd und Essigsäure, durch Kondensation davon abzutrennen. Dieses Kondensat wird im folgenden Sauerwasser genannt. Der dann noch ver- bleibende Gasstrom besteht überwiegend aus Stickstoff, Kohlenoxiden und nicht umgesetzten Edukten. Vorzugsweise wird dieser teilweise wieder als Verdünnungsgas, im folgenden Kreisgas genannt, der Reaktionszone zugeführt. Der andere Teil wird als Ab-' gas ausgeschleust und vorzugsweise verbrannt.The remaining, not absorbed remainder of the product gas mixture A is further cooled in order to separate the condensable part of low-boiling secondary components such as water, formaldehyde and acetic acid contained therein by condensation. This condensate is called acid water in the following. The gas stream then remaining consists predominantly of nitrogen, carbon oxides and unreacted starting materials. Preferably, this is partly fed back into the reaction zone as a diluent gas, hereinafter referred to as circulating gas. The other part is discharged as waste gas and preferably burned.
In der nächsten Verfahrensstufe der Aufarbeitungszone wird die Acrylsaure zusammen mit den ittelsiedenden Komponenten sowie enthaltenen leichtsiedenden Nebenkomponenten vom Lösungsmittel abgetrennt . Diese Abtrennung erfolgt mittels Rektifikation wobei grundsätzlich jeder Rektifkationskolonne verwendet werden kann. Vorteilhafterweise wird hierzu eine Kolonne mit Dual-flow-Böden verwendet. Im Auftriebsteil der Kolonne wird die Acrylsaure vom Lösungsmittel und den mittelsiedenden Nebenkomponenten , wie Maleinsäureanhydrid, weitgehend frei destilliert. Um den Leicht- siederanteil in der Acrylsaure zu reduzieren, wird vorteilhafterweise der Auftriebsteil der Kolonne verlängert und die Acrylsaure als Seitenabzug aus der Kolonne in einer Qualität von 95 Gew.-% Acrylsaure abgezogen.In the next stage of the processing zone, the acrylic acid is separated from the solvent together with the low-boiling components and the low-boiling secondary components contained. This separation takes place by means of rectification, whereby basically every rectification column can be used. A column with dual-flow trays is advantageously used for this purpose. In the lifting section of the column, the acrylic acid is largely freely distilled from the solvent and the medium-boiling secondary components, such as maleic anhydride. In order to reduce the low boiler content in the acrylic acid, the buoyancy part of the column is advantageously lengthened and the acrylic acid is withdrawn as a side draw from the column in a quality of 95% by weight acrylic acid.
Am Kopf der Kolonne wird dann nach einer Partialkondensation ein an Leichtsiedern reicher Strom abgezogen. Da dieser Strom aber noch signifikante Mengen an Acrylsaure enthält, würde er normalerweise in die Absorptionsstufe rückgeführt.A stream rich in low boilers is then drawn off at the top of the column after a partial condensation. However, since this stream still contains significant amounts of acrylic acid, it would normally be returned to the absorption stage.
Erfindungsgemäß wird er jedoch zweckmäßig als Neben-Stoffgemisch aus der Aufarbeitungszone herausgeführt und der Hydrierung der darin enthaltenen Acrylsaure, gegebenenfalls nach vorher erfolg- ter Veresterung der Acrylsaure, zugeführt. In typischer Weise enthält das solchermaßen weggeführte Neben-Stoffgemisch:According to the invention, however, it is expediently led out of the work-up zone as a by-product mixture and fed to the hydrogenation of the acrylic acid contained therein, optionally after esterification of the acrylic acid has taken place beforehand. Typically, the secondary substance mixture carried away in this way contains:
98 Gew.-% Acrylsaure,98% by weight acrylic acid,
0,94 Gew.-% Essigsäure, 0,98 Gew.-% Wasser,0.94% by weight of acetic acid, 0.98% by weight of water,
57 Gew.-ppm Acrolein,57 ppm by weight of acrolein,
327 Gew.-ppm Propionsäure,327 ppm by weight of propionic acid,
35 Gew.-ppm Furfurale,35 ppm by weight furfural,
303 Gew.-ppm Allylacrylat, 11 Gew.-ppm Maleinsäureanhydrid und303 ppm by weight of allyl acrylate, 11 ppm by weight of maleic anhydride and
350 Gew.-ppm Diacrylsäure .350 ppm by weight of diacrylic acid.
Im Unterschied dazu enthält die als Zielprodukt abgetrennte .. Acrylsaure in der Regel:In contrast, the .. acrylic acid separated as the target product usually contains:
> 99 Gew.-% Acrylsaure,> 99% by weight acrylic acid,
< 2000 Gew.-ppm Essigsäure,<2000 ppm by weight of acetic acid,
< 15 Gew.-ppm Acrolein,<15 ppm by weight of acrolein,
< 350 Gew.-ppm Propionsäure, < < 1 155 Gew.-% Furfurale,<350 ppm by weight propionic acid, <<1 155% by weight furfural,
< 150 Gew.-ppm Allylacrylat,<150 ppm by weight of allyl acrylate,
< 20 Gew.-ppm Maleinsäureanhydrid,<20 ppm by weight maleic anhydride,
< 550 Gew.-ppm Diacrylsäure und<550 ppm by weight of diacrylic acid and
< 100 Gew.-ppm Wasser. Aus dem Sumpf der Rektifikationskolonne wird ein Strom abgezogen, der vorwiegend Lösungsmittel enthält. Vor der Rückführung in die Absorptionsstufe wird der Lösungsmittelstrom weitgehend von Acrylsaure abgereinigt, um erneut Acrylsaure aus Produktgas- gemisch A aufnehmen zu können. Die Abreicherung des Lösungsmittels von Acrylsaure erfolgt vorzugsweise durch Strippen mit Inertgas, besonders bevorzugt mit einem Teilstrom des Kreisgases, oder für den Fall, daß Propan Verdünnungsgas ist, mit Propan.<100 ppm water. A stream is drawn off from the bottom of the rectification column which predominantly contains solvents. Before being returned to the absorption stage, the solvent stream is largely cleaned of acrylic acid in order to be able to absorb acrylic acid from product gas mixture A again. The solvent of acrylic acid is preferably depleted by stripping with inert gas, particularly preferably with a partial stream of the circulating gas, or in the case that propane is diluent gas, with propane.
Das Strippen erfolgt in der Regel bei Drücken von etwa 1,1 bis 2,0 bar, bevorzugt bei Drücken von 1,3 bis 1,6 bar sowie bei Temperaturen von ca. 80 bis 120°C, bevorzugt von 110 bis 120°C. Beim Strippen wird der zu reinigende Lösungsmittelstrom am Kopf einer Strippkolonne aufgegeben; er fließt über die Einbauten in Rich- tung Sumpf. Im Gegenstrom wird in den Sumpf der Strippkolonne das Strippgas eingeleitet. Während das Strippgas in Richtung Kolonnenkopf strömt, nimmt es Acrylsaure aus dem flüssigen Lösungsmittelstrom auf, so daß aus dem Sumpf der Strippkolonne ein gereinigter Lösungsmittelstrom abgezogen werden kann, der eine Acrylsäurekonzentration von maximal 1 Gew.-%, bevorzugt von maximal 0,5 Gew.-% enthält. Dieses weitgehend acrylsäurefreie Lösungsmittel kann anschließend wieder zur Absorptionsstufe rezirkuliert werden.The stripping is generally carried out at pressures of about 1.1 to 2.0 bar, preferably at pressures of 1.3 to 1.6 bar and at temperatures of about 80 to 120 ° C., preferably from 110 to 120 ° C. , When stripping, the solvent stream to be cleaned is added to the top of a stripping column; it flows over the internals towards the swamp. The stripping gas is introduced into the bottom of the stripping column in countercurrent. While the stripping gas flows in the direction of the column top, it absorbs acrylic acid from the liquid solvent stream, so that a purified solvent stream can be drawn off from the bottom of the stripping column, which has an acrylic acid concentration of at most 1% by weight, preferably of at most 0.5%. -% contains. This largely acrylic acid-free solvent can then be recirculated to the absorption stage.
Das mit Acrylsaure beladene Strippkreisgas- wird zweckmäßigerweise in die Stufe, in der die TeilVerdampfung des Lösungsmittels erfolgt, oder in die Absorptionskolonne rezirkuliert.The stripping gas loaded with acrylic acid is expediently recirculated to the stage in which the partial evaporation of the solvent takes place or to the absorption column.
In einer bevorzugten Ausführungsform der Erfindung wird das Sau- erwasser, das ebenfalls noch Acrylsaure gelöst- enthalten kann, mit einem Teilstrom des wie vorstehend beschrieben von Acrylsaure nahezu befreiten Lösungsmittelanteils extraktiv behandelt. Der wäßrige Strom aus der Sauerwasserextraktion kann noch eingeengt und nachfolgend entsorgt werden. Der organische Strom wird eben- falls in die Absorptionsstufe rückgeführt.In a preferred embodiment of the invention, the acidic water, which can also still contain acrylic acid in solution, is treated extractively with a partial stream of the solvent fraction which has been almost completely freed from acrylic acid as described above. The aqueous stream from the acid water extraction can still be concentrated and subsequently disposed of. The organic stream is also returned to the absorption stage.
Die konkreten Verfahrensbedingungen für die eben beschriebene Aufarbeitungszone können der EP-A 982 288 entnommen werden.The specific process conditions for the processing zone just described can be found in EP-A 982 288.
Das Herausführen des Neben-Stoffgemisches aus der Aufarbeitungs- zone (verglichen mit seiner Rückführung in die Absorptionsstufe) bewirkt eine verringerte Polymerisatbildung in der Aufarbeitungszone, in welcher die einzelnen Arbeitsschritte selbstredend in an sich bekannter Weise im Beisein von Polymerisationsinhibitoren wie z.B. Phenothiazion oder Monomethylether des Hydrochinons durchgeführt werden. Einer zweiten Gestaltungsvariante liegt die Verfahrensweise der DE-A 10115277 zugrunde. Im Unterschied zum Aufarbeitungsverfahren der EP-A 982 288 wird im Aufarbeitungsverfahren der DE-A 10115277 der Sumpfström aus der Gegenstromabsorptionskolonne, der neben dem Lösungsmittel etwa 10 bis 40 Gew.-% Acrylsaure, im wesentlichen alle Schwersieder sowie einen Teil der Leichtsieder enthält, in den oberen Bereich einer ersten Rektifkationskolonne I aufgegeben, und in der Rektifikationskolonne I bei einer Sumpftemperatur von 165 bis 210°, bevorzugt von 180 bis 200°C, beson- ders bevorzugt von 190 bis 195°C und entsprechenden Drücken von 100 bis 500 mbar, bevorzugt 180 bis 350 mbar und besonders bevorzugt 250 bis 290 mbar in einen Kopfstrom, der überwiegend, d.h. zu etwa 70 bis 95 Gew.-%, Acrylsaure, im wesentlichen alle Leichtsieder, einen Teil der Schwersieder sowie Reste des Lösungsmittels enthält, und in einen Sumpfström aufgetrennt, wobei letzterer überwiegend das Lösungsmittel und nur in geringen Anteilen, zu etwa 0,1 bis 1,5 Gew.-%, Acrylsaure enthält. Der Kopfstrom wird zur rektifikativen Gewinnung der Zielproduktacryl- säurequalität weitergeleitet, und der Sumpfström wird in die Ab- sorptionsstufe rückgeführt, d.h., in den oberen Bereich der Gegenstromabsorptionskolonne aufgegeben (in einer speziellen Ausführungsform wird das Sauerwasser, das noch Acrylsaure gelöst enthalten kann, mit einem kleinen Teilstrom des Sumpfstroms extraktiv behandelt. Der wäßrige Strom der Sauerwasserextraktion kann dann entsorgt werden, während der organische Strom ebenfalls in die Absorptionsstufe rückgeführt wird) .The removal of the secondary substance mixture from the work-up zone (compared with its return to the absorption stage) results in reduced polymer formation in the work-up zone, in which the individual working steps are of course in a manner known per se in the presence of polymerization inhibitors such as phenothiazione or monomethyl ether of hydroquinone be performed. A second design variant is based on the procedure of DE-A 10115277. In contrast to the work-up process of EP-A 982 288, in the work-up process of DE-A 10115277, the bottom stream from the countercurrent absorption column, which, in addition to the solvent, contains about 10 to 40% by weight of acrylic acid, essentially all the high boilers and part of the low boilers, in the upper region of a first rectification column I is added, and in the rectification column I at a bottom temperature of 165 to 210 ° C., preferably from 180 to 200 ° C., particularly preferably from 190 to 195 ° C. and corresponding pressures from 100 to 500 mbar, preferably 180 to 350 mbar and particularly preferably 250 to 290 mbar in a top stream which contains predominantly, ie approximately 70 to 95% by weight, acrylic acid, essentially all low boilers, part of the high boilers and residues of the solvent, and in one Bottom stream separated, the latter mainly containing the solvent and only in small proportions, about 0.1 to 1.5 wt .-%, acrylic acid. The top stream is passed on for the rectificative recovery of the target product acrylic acid quality, and the bottom stream is returned to the absorption stage, that is to say fed into the upper region of the countercurrent absorption column (in a special embodiment, the acid water, which may still contain acrylic acid in solution, is mixed with a treated small extract stream of the bottom stream extractive. The aqueous stream of acid water extraction can then be disposed of while the organic stream is also returned to the absorption stage).
Bezüglich der trennwirksamen Einbauten in die Rektifikationskolonne I gibt es grundsätzlich keine Einschränkungen. Es können gleichermaßen Siebböden, Dual-Flow-Böden, Ventilböden, Füllkörper oder Packungen eingesetzt werden. Bevorzugt werden jedoch Dual- Flow-Böden.There are basically no restrictions with regard to the separating internals in the rectification column I. Sieve trays, dual-flow trays, valve trays, packing elements or packings can be used in the same way. However, dual-flow trays are preferred.
Die Gewinnung der Zielproduktacrylsäurequalität aus dem Kopfstrom erfolgt bevorzugt in folgenden Verfahrensschritten:The target product acrylic acid quality is preferably obtained from the top stream in the following process steps:
Abtrennung eines Reststroms, der neben Acrylsaure die Leichtsieder, sowie einen Teil der Mittelsieder und einen Teil der Schwersieder enthält sowie eines Teilstroms, der im wesentli- chen frei von Leichtsiedern ist undSeparation of a residual stream which, in addition to acrylic acid, contains the low boilers and also part of the middle boilers and part of the high boilers, and also a partial stream which is essentially free of low boilers and
Gewinnung der Zielproduktacrylsäurequalität aus dem Teilstrom. Bevorzugt wird für dieses Trennproblem eine Trennblechrektifika- tionskolonne mit zwei Kondensatoren und einem Verdampfer verwendet. Als Einbauten eignen sich in besonderem Maß Dual-Flow- Böden .Obtaining the target product acrylic acid quality from the partial stream. A separating plate rectification column with two condensers and one evaporator is preferably used for this separation problem. Dual-flow floors are particularly suitable as internals.
Der aus der Rektifikationskolonne I kommende Kopfstrom wird zunächst kondensiert und läuft dann in der linken Teilkolonne (Abtriebskolonne) der verwendeten Trennblechkolonne abwärts. Im Gegenzug steigt Dampf, vorwiegend dampfförmige Acrylsaure, aus dem Sumpf nach oben und strippt dabei die Leichtsieder aus der Flüssigkeit, so daß der im Sumpf ankommende Flüssigkeitsstrom nahezu leichtsiederfrei ist. Am Kopf dieser Teilkolonne wird dann nach Kondensation ein an Leichtsiedern reicher Strom abgezogen. Da dieser Strom aber noch signifikante Mengen an Acrylsaure ent- hält, wird er normalerweise in die Absorptionsstufe und/oder in den Quenchapparat zurückgefahren. Erfindungsgemäß wird dieser an Leichtsiedern reiche, Acrylsaure enthaltende Strom dagegen als Neben-Stoffgemisch aus der Aufarbeitungszone heraus- und der erfindungsgemäßen Hydrierung, gegebenenfalls nach vorab erfolgter Veresterung der Acrylsaure, zugeführt.The top stream coming from the rectification column I is first condensed and then runs downward in the left-hand sub-column (stripping column) of the separating plate column used. In return, steam, predominantly vaporous acrylic acid, rises from the sump and strips the low boilers out of the liquid, so that the liquid stream arriving in the sump is almost free from low boilers. A stream rich in low boilers is then drawn off at the top of this partial column after condensation. However, since this stream still contains significant amounts of acrylic acid, it is normally returned to the absorption stage and / or the quenching apparatus. According to the invention, this stream, rich in low boilers, containing acrylic acid, on the other hand, is passed out of the work-up zone as a by-product mixture and fed to the hydrogenation according to the invention, if appropriate after esterification of the acrylic acid beforehand.
In der Regel weist das so weggeführte Neben-Stoffgemisch folgende Gehalte auf:As a rule, the secondary substance mixture carried away in this way has the following contents:
8 877 G Geeww..-% Acrylsaure,8 877 G wt.% Acrylic acid,
6 Gew . -% Essigsäure,6 wt. -% acetic acid,
5 Gew . -% Wasser,5 wt. -% Water,
0 , 7 Gew . -% Ameisensäure0.7 wt. -% formic acid
1500 Gew . -ppm Acrolein, 1 1000000 G Geeww..- -ppppmm Allylacrylat,1500 wt. -ppm acrolein, 1 1000000 g wt. - -ppppmm allyl acrylate,
400 Gew . -ppm Maleinsäureanhydrid,400 wt. -ppm maleic anhydride,
150 Gew . -ppm Propionsäure und150 wt. -ppm propionic acid and
10 Gew . -ppm Furfurale.10 wt. -ppm furfural.
Die Gewinnung der Zielproduktacrylsäurequalität aus dem im Sumpf ankommenden Flüssigkeitsstrom erfolgt in der rechten Teilkolonne (Auftriebskolonne) der Trennblechkolonne (diese könnte auch durch einen kristallisativen Trennschritt ersetzt werden) . Die Abtriebskolonne und die Auftriebskolonne haben dabei einen ge- meinsamen Sumpf. Dieser enthält vorwiegend das Lösungsmittel, das, gegebenenfalls nach einer Reinigung, z.B. durch Verdampfung in einem Quench, in die Absorptionsstufe rezirkuliert. In der Auftriebskolonne steigt der im wesentlichen an Leichtsiedern freie Acrylsäuredampf nach oben, wobei die Mittelsieder und Schwersieder durch den flüssigen Rücklauf aus dem Dampf ausgewaschen werden. Am Kolonnenkopf wird der Brüden kondensiert, ein Teil wird am Kopf als Zielproduktacrylsäurequalität abgezogen und der Rest bildet flüssigen Rücklauf.The target product acrylic acid quality is obtained from the liquid stream arriving in the sump in the right-hand partial column (buoyancy column) of the separating plate column (this could also be replaced by a crystallizing separation step). The stripping column and the lifting column have a common sump. This contains predominantly the solvent which, if necessary after cleaning, for example by evaporation in a quench, recirculates into the absorption stage. In the lifting column, the substantially free low-boiling acrylic acid vapor rises, the medium boilers and high boilers being washed out of the steam by the liquid reflux. The vapor is condensed at the top of the column Part is subtracted from the head as the target product acrylic acid quality and the rest forms liquid reflux.
Die Zieproduktacrylsäurequalität weist dabei üblicherweise fol- gende Gehalte auf:The target product acrylic acid quality usually has the following contents:
> 99 Gew.-% Acrylsaure,> 99% by weight acrylic acid,
< 2000 Gew. -ppm Essigsäure,<2000 ppm by weight acetic acid,
< 100 Gew.-ppm Wasser, < 10 Gew.-ppm Ameisensäure,<100 ppm by weight water, <10 ppm by weight formic acid,
< 100 Gew.-ppm Allylacrylat,<100 ppm by weight of allyl acrylate,
< 100 Gew.-ppm Maleinsäureanhydrid,<100 ppm by weight of maleic anhydride,
< 250 Gew.-ppm Propionsäure und<250 ppm by weight propionic acid and
< 260 Gew.-ppm Furfurale.<260 ppm by weight furfural.
Die neuen Verfahrensbedingungen für die oben beschriebene Aufarbeitungszone können der DE-A 101152779 entnommen werden.The new process conditions for the processing zone described above can be found in DE-A 101152779.
Das Herausführen des Neben-Stoffgemisches aus der Aufarbeitungs- zone (verglichen mit seiner Rückführung in die Absorptionsstufe) bewirkt eine verringerte Polymerisatbildung in der Aufarbeitungszone, in welcher die einzelnen Arbeitsschritte selbstredend in an sich bekannter Weise im Beisein von Polymerisationsinhibitoren wie z.B. Phenothiazin oder Monomethylether des Hydrochinons (MEHQ) durchgeführt werden.The removal of the secondary substance mixture from the workup zone (compared to its return to the absorption stage) results in reduced polymer formation in the workup zone, in which the individual working steps are of course in a known manner in the presence of polymerization inhibitors such as e.g. Phenothiazine or monomethyl ether of hydroquinone (MEHQ) can be performed.
In völlig entsprechender Weise kann auch in den Figuren 4, 5 und 6 der DE-A 19 606 877 die Rückführung des Kopfstromes aus der Kolonne K30 in die Absorptionskolonne unterlassen und statt dessen dieser Kopfström als Neben-Stoffgemisch der erfindungsgemäßen Hydrierung zugeführt werden. Auch in diesem Fall bewirkt die erfindungsgemäße Maßnahme eine verlängerte Laufzeit in der Aufarbeitungszone.In a completely corresponding manner, FIGS. 4, 5 and 6 of DE-A 19 606 877 can also refrain from recirculating the top stream from column K30 into the absorption column and instead supply this top stream as a by-product mixture to the hydrogenation according to the invention. In this case too, the measure according to the invention results in an extended running time in the processing zone.
Das Gleiche gilt im Fall des Kopfstromes der Kolonne VI-I aus Figur 2 der EP-A 982 289, der erfindungsgemäß ebenfalls nicht mehr in die Aufarbeitung rückgeführt sondern einer erfindungsgemäßen Hydrierung zugeführt werden würde.The same applies in the case of the top stream of column VI-I from FIG. 2 of EP-A 982 289, which according to the invention would also no longer be recycled to the workup but would be fed to a hydrogenation according to the invention.
Einer dritten Gestaltungsvariante liegt die in den Schriften DE-A 19 833 049, DE-A 19 814 375, DE-A 19 814 421,A third design variant lies in the documents DE-A 19 833 049, DE-A 19 814 375, DE-A 19 814 421,
DE-A 19 814 449, DE-A 10053086, DE-A 19 740 252, DE-A 19 814 387, DE-A 19 740 253 und DE-A 19 924 532 offenbarte Verfahrensweise der fraktionierenden Kondensation des, vorab gegebenenfalls di- rekt und/oder indirekt abgekühlten, Produktgasgemisches A zugrunde . Aus vorgenannten Schriften ist bekannt, daß eine Grundabtrennung der im Produktgasgemisch A enthaltenen Acrylsaure nicht nur durch Absorption in ein geeignetes Absorptionsmittel und nachfolgende Trennung vom Absorptionsmittel über extraktive und/oder rektifi- kative Trennverfahren sondern auch dadurch möglich ist, daß man das Produktgasgemisch A, gegebenenfalls nach direkter und/oder indirekter Vorkühlung, in einer mit trennwirksamen Einbauten versehenen Trennkolonne in sich selbst aufsteigend einer fraktionierenden Kondensation unterwirft und eine Zielproduktacrylsäure- qualität über einen Seitenabzug der Trennkolonne entnimmt, deren AcrylSäuregehalt üblicherweise > 95 Gew.-% beträgt. Normalerweise wird man diese Zielproduktacrylsäurequalität weiteren destillativen und/oder kristallisativen Reinigungsstufen zuführen und wenigstens einen Teil der im Rahmen dieser Destillationen und/oder Kristallisationen anfallenden Sumpfflüssigkeiten und/ oder Mutterlauge in die fraktionierende Kondensationskolonne rückführen .DE-A 19 814 449, DE-A 10053086, DE-A 19 740 252, DE-A 19 814 387, DE-A 19 740 253 and DE-A 19 924 532 disclose the procedure for the fractional condensation of the, in advance optionally the rectified and / or indirectly cooled product gas mixture A. From the abovementioned documents it is known that a basic separation of the acrylic acid contained in product gas mixture A is possible not only by absorption in a suitable absorption medium and subsequent separation from the absorption medium by means of extractive and / or rectification separation processes, but also in that product gas mixture A, if appropriate after direct and / or indirect pre-cooling, in a separating column provided with separating internals, is subjected to ascending fractional condensation in itself and removes a target product acrylic acid quality via a side draw of the separating column, the acrylic acid content of which is usually> 95% by weight. Normally, this target product acrylic acid quality will be fed to further distillation and / or crystallization purification stages and at least some of the bottom liquids and / or mother liquor obtained in the course of these distillations and / or crystallizations will be returned to the fractionating condensation column.
Nachteilig an der Verfahrensweise der fraktionierenden Konden- sation ist jedoch, daß die mittelsiedenden Nebenkomponenten (z.B. Essigsäure) in der Kondensationskolonne über deren Länge Konzentrationsbäuche ausbilden. D.h., sie akkumulieren auf bestimmten Kolonnenlängen (höhen) , bis sie die Kolonne je nach Siedepunkt über Kopf oder Sumpf verlassen. Besonders problematisch ist in diesem Zusammenhang die Tatsache, dass Wasser mit Ameisensäure ein Schwersieder-Azeotrop bildet, das bei Normaldruck zwischen Wasser und Acrylsaure siedet, so dass sich oberhalb des Seitenabzugs der Zielproduktqualität ein Konzentrationsbauch der Ameisensäure ausbildet, der bis zu 30 Gew.-% betragen kann. Dies führt zu Korrosionsproblemen, die die Anwendung aufwendiger Maßnahmen wie z.B. den Einsatz von Korrosionsinhibitoren, katalytische Zersetzung der Ameisensäure oder Veresterung der Ameisensäure erforderlich machen. Die Akkumulation anderer Nebenkomponenten belastet nachfolgende Reinigungsstufen.A disadvantage of the procedure of fractional condensation, however, is that the medium-boiling secondary components (e.g. acetic acid) form concentration bellies over their length in the condensation column. In other words, they accumulate over certain column lengths (heights) until they leave the column either overhead or at the bottom, depending on the boiling point. Particularly problematic in this connection is the fact that water forms a high-boiling azeotrope with formic acid, which boils between water and acrylic acid at normal pressure, so that a concentration belly of formic acid is formed above the side deduction of the target product quality, which contains up to 30% by weight can be. This leads to corrosion problems, which the application of complex measures such as require the use of corrosion inhibitors, catalytic decomposition of formic acid or esterification of formic acid. The accumulation of other secondary components puts a strain on subsequent cleaning stages.
Die erfindungsgemäße Verfahrensweise vermag auch hier Abhilfe zu leisten. Dies in einfacher Weise dadurch, daß sie es ohne signifikanten wirtschaftlichen Nachteil gestattet, die Nebenkomponen- tenkonzentrationsbäuche in der Kondensationskolonne anzustechen. D.h., auf der Höhe des jeweiligen Konzentrationsbauches wird die jeweilige Nebenkomponenten sowie Acrylsaure enthaltende Flüssigphase partiell aus der Kondensationskolonne heraufgeführt und die darin enthaltene Acrylsaure, gegebenenfalls nach ihrer Veresterung, durch Hydrierung mittels molekularem Wasserstoff in Propionsäure und/oder Ester überführt. Durch diese Maßnahme wird die Amplitude der Konzentrationsbäuche gemindert und die Abtrennung der Nebenkomponenten von der Acrylsaure erleichtert (nachfolgende Reinigungsstufen können kleiner dimensioniert werden) . Letzteres ist ein ganz genereller Vorteil der erfindungs- gemäßen Verfahrenweise.The procedure according to the invention can also remedy this. This is done in a simple manner in that it allows the secondary component antinodes to be pierced in the condensation column without significant economic disadvantage. That is, at the level of the respective concentration belly, the respective secondary components and the liquid phase containing acrylic acid are partially carried up from the condensation column and the acrylic acid contained therein, if appropriate after its esterification, is converted into propionic acid and / or ester by hydrogenation using molecular hydrogen. This measure reduces the amplitude of the concentration bellies and makes it easier to separate the secondary components from the acrylic acid (Subsequent cleaning stages can be dimensioned smaller). The latter is a very general advantage of the procedure according to the invention.
Die detaillierte Ausführung der fraktionierenden Kondensation kann wie in den genannten Schriften des Standes der Technik (insbesondere der DE-A 19 924 532) erfolgen. Desgleichen gilt für die Polymerisationsinhibierung bei der fraktionierenden Kondensation.The fractional condensation can be carried out in detail as in the cited prior art documents (in particular DE-A 19 924 532). The same applies to the polymerization inhibition in fractional condensation.
Erfindungsgemäß werden ganz generell Hydrierungen von Acrylsaure zu Propionsäure in der Gasphase gegenüber Flüssigphasenverfahren bevorzugt, da sich bei Gasphasenverfahren die Problematik der Acrylsäurepolymerisation weniger stellt. Zu diesem Zweck müssen flüssig entnommene Neben-Stoffgemische durch Verdampfen in die Gasphase überführt werden.According to the invention, hydrogenations of acrylic acid to propionic acid in the gas phase are generally preferred over liquid phase processes, since the problem of acrylic acid polymerization arises less with gas phase processes. For this purpose, liquid substance mixtures that have been removed must be converted into the gas phase by evaporation.
Bei Flüssigphasenhydrierverfahren wird empfhohlen, mit Inhibitoren wie Hydrochinon oder Hydrochinonmonomethylether zu stabilisieren.In liquid phase hydrogenation processes, it is recommended to stabilize with inhibitors such as hydroquinone or hydroquinone monomethyl ether.
Wird die im erfindungsgemäß abgetrennten Nebenstoffgemisch enthaltene Acrylsaure vorab ihrer Hydrierung wenigstens teilweise verestert, so kommen als Zielester insbesondere Methylacrylat, Ethylacrylat, n-Butylacrylat und tert . -Butylacrylat in Betracht.If the acrylic acid contained in the by-product mixture separated according to the invention is at least partially esterified beforehand, the target esters are, in particular, methyl acrylate, ethyl acrylate, n-butyl acrylate and tert. -Butyl acrylate into consideration.
Eine gegebenenfalls erwünschte Abtrennung von Propionsäure und/ oder deren Ester aus dem Hydrierproduktgemisch kann in an sich bekannter Weise, z.B. auf rektifikativem Weg, erfolgen.An optionally desired separation of propionic acid and / or its ester from the hydrogenation product mixture can be carried out in a manner known per se, e.g. by rectification.
Das erfindungsgemäße Verfahren ist insbesondere dann geeignet, wenn das für die selektive heterogen katalysierte Gasphasenoxidation als Ausgangsstoff verwendete Propen, wie in der WO 01/96270, der EP-A 11 71 146, der DE-A 33 13 573 und der - US-A 31 61 670 beschrieben, durch katalytische Vorabdehydrierung von Propan erzeugt wurde. Der dabei gebildete molekulare Wasserstoff kann nachfolgend für die Hydrierung in Schritt c) des erfindungsgemäßen Verfahrens verwendet werden. BeispieleThe process according to the invention is particularly suitable when the propene used as the starting material for the selective heterogeneously catalyzed gas phase oxidation, as in WO 01/96270, EP-A 11 71 146, DE-A 33 13 573 and US Pat 31 61 670 described, was generated by catalytic pre-dehydrogenation of propane. The molecular hydrogen formed in the process can subsequently be used for the hydrogenation in step c) of the process according to the invention. Examples
a) Vergleichsbeispiel 1a) Comparative Example 1
Alle Adressen beziehen sich auf die Figur der DE-A 19 924 532.All addresses refer to the figure of DE-A 19 924 532.
Aus einer heterogen katalysierten Gasphasenoxidation wurde ein eine Temperatur von 270°C aufweisendes Produktgasgemisch (1) der nachfolgenden Zusammensetzungsgehalte erhalten:A product gas mixture (1) of the following composition contents, which had a temperature of 270 ° C., was obtained from a heterogeneously catalyzed gas phase oxidation:
11,5 Gew.-% Acryls ure,11.5% by weight of acrylic acid,
0,3 Gew.-% Essigsäure,0.3% by weight of acetic acid,
280 Gew.-ppm Ameisensäure,280 ppm by weight of formic acid,
30 Gew.-ppm Propionsäure, 0,09 Gew.-% Maleinsäureanhydrid,30 ppm by weight of propionic acid, 0.09% by weight of maleic anhydride,
0,01 Gew.-% Acrolein,0.01% by weight of acrolein,
0,1 Gew.-% Formaldehyd,0.1% by weight of formaldehyde,
30 Gew.-ppm Furfurale,30 ppm by weight furfural,
0,001 Gew.-% Benzaldehyd, 0,3 Gew.-% Propen,0.001% by weight of benzaldehyde, 0.3% by weight of propene,
3,4 Gew.-% Sauerstoff,3.4% by weight oxygen,
5,3 Gew.-% Wasser5.3% by weight of water
1,7 Gew.-% Kohlenoxide, und als Restmenge N2.1.7 wt .-% carbon oxides, and as a residual amount of N 2 .
Das Produktgasgemisch (3600 g/h) wurde in einem Sprühkühler (2) auf eine Temperatur von 136°C abgekühlt. Als Sprühflüssigkeit wurden 750 g/h (7) von insgesamt 7000 g/h über den Fangboden (5) (mit einer Temperatur von 100°C) aus der Trennkolonne (3) entnommener Schwersiederfraktion (6) verwendet (Sumpfflüssigkeit 4 trat nicht auf) . Über den mit Wärmeträgeröl beschriebenen Rohrbündelwärmetauscher (8) wurde die Sprühflüssigkeit im Kreis geführt. 40 g/h Schwersieder wurden dem Kreislauf kontinuierlich entnommen (9) .The product gas mixture (3600 g / h) was cooled to a temperature of 136 ° C. in a spray cooler (2). 750 g / h (7) of a total of 7000 g / h via the collecting tray (5) (with a temperature of 100 ° C.) of the high boiler fraction (6) removed from the separating column (3) were used as spray liquid (bottom liquid 4 did not occur) , The spray liquid was circulated over the tube bundle heat exchanger (8) described with heat transfer oil. 40 g / h high boilers were continuously removed from the circuit (9).
Das auf eine Temperatur von 136°C abgekühlte Produktgasgemisch wurde unterhalb des Fangbodens (5) der Trennkolonne zugeführt (10) .The product gas mixture cooled to a temperature of 136 ° C. was fed to the separation column (10) below the tray (5).
Die Kolonne war eine Bodenkolonne mit, von unten nach oben be- trachtet, zunächst 25 Dual-Flow- und anschließend 50 Glockenböden (1 Glocke pro Boden) . Der Bodendurchmesser betrug 49 mm. Die Dual-Flow-Böden wiesen 6 Löcher pro Boden auf. Der Lochdurch- messer der ersten fünf Dual-Flow-Böden betrug 9,5 mm. Die darauffolgenden 10 Böden hatten einen Lochdurchmesser von 9 mm und der Lochdurchmesser der letzten 5 Dual-Flow-Böden betrug 8,7 mm. Der Boden oberhalb von Boden 15 war als weiterer Fangboden (11) ge- staltet. Über ihm wurden 1800 g/h einer eine Temperatur von 97°C aufweisenden Acrylsäurequalität (12) enthaltendThe column was a tray column with, viewed from bottom to top, first 25 dual-flow trays and then 50 bubble trays (1 bell per tray). The bottom diameter was 49 mm. The dual flow floors had 6 holes per floor. The hole diameter of the first five dual-flow trays was 9.5 mm. The subsequent 10 trays had a hole diameter of 9 mm and the hole diameter of the last 5 dual-flow trays was 8.7 mm. The floor above floor 15 was another collecting floor (11). staltet. Above it were 1800 g / h containing a temperature of 97 ° C acrylic acid quality (12)
Acrylsaure 97,3 Gew.-%, Essigsäure 0,8 Gew.-%, Ameisensäure 154 Gew.-ppm, Propionsäure 600 Gew.-ppm, Furfural 700 Gew.-ppm, Maleinsäureanhydrid 40 Gew.-ppm, Benzaldehyd 200 Gew.-ppm und Wasser 1,3 Gew.-%Acrylic acid 97.3% by weight, acetic acid 0.8% by weight, formic acid 154% by weight, propionic acid 600% by weight, furfural 700% by weight, maleic anhydride 40% by weight, benzaldehyde 200% by weight. -ppm and water 1.3% by weight
abgezogen und einem Suspensionskristaller (13) zugeführt. Ein Teil (6250 g/h) der entnommenen Schwersiederfraktion (14) wurde in einem mit Wärmeträgeröl beschriebenen Rohrbündelwärmetauscher auf 105°C erwärmt und auf den 5ten Boden in die Kolonne rückgeführt (16) .withdrawn and fed to a suspension crystallizer (13). A portion (6250 g / h) of the high boiler fraction (14) removed was heated to 105 ° C. in a tube bundle heat exchanger described with heat transfer oil and returned to the fifth tray in the column (16).
Der Kristaller war ein Rührbehälter (3 1 Innenvolumen) mit Wen- delrührer. Die Kristallisationswärme wurde über den Doppelmantel des Behälters abgeführt. Die Gleichgewichtstemperatur der Lösung betrug 9,7°C. Die bei der Kristallisation erzeugte Suspension (Feststoffgehalt ca. 25 Gew.-%) wurde auf einer Zentrifuge bei 2000 U/min (Zentrifugendurchmesser 300 mm) und einer Schleuder- zeit von 3 min diskontinuierlich in Kristalle und Mutterlauge getrennt. Die Kristalle wurden anschließend mit aufgeschmolzenem (zuvor gewaschenem) Kristallisat (80 g) 20 sec lang bei 2000 U/ min gewaschen. Die Mutterlauge wurde zusammen mit der Waschflüssigkeit auf den 15ten Boden in die Trennkolonne rückgeführt (28) .The crystallizer was a stirred tank (3 1 internal volume) with a spiral stirrer. The heat of crystallization was removed via the double jacket of the container. The equilibrium temperature of the solution was 9.7 ° C. The suspension produced during crystallization (solids content approx. 25% by weight) was discontinuously separated into crystals and mother liquor on a centrifuge at 2000 rpm (centrifuge diameter 300 mm) and a centrifuging time of 3 min. The crystals were then washed with melted (previously washed) crystals (80 g) for 20 seconds at 2000 rpm. The mother liquor, together with the washing liquid, was returned to the 15th tray in the separation column (28).
Die Analyse der Kristalle (370 g/h) ergab folgende Gehalte:The analysis of the crystals (370 g / h) showed the following contents:
Acrylsaure 99,5 Gew.-%, Essigsäure 0,2 Gew.-%,Acrylic acid 99.5% by weight, acetic acid 0.2% by weight,
Ameisensäure 0,1 Gew.-%,Formic acid 0.1% by weight,
Propionsäure 200 Gew.-ppm,Propionic acid 200 ppm by weight,
Maleinsäureanhydrid 60 Gew.-ppm,Maleic anhydride 60 ppm by weight,
Furfural 200 Gew.-ppm, Benzaldehyd 30 Gew.-ppm, undFurfural 200 ppm by weight, benzaldehyde 30 ppm by weight, and
Wasser 1000 Gew.-ppm.Water 1000 ppm by weight.
Am Kopf der Kolonne wurde ein gasförmiges Gemisch (17) entnommen und im Sprühkühler (18) einer Partialkondensation unterworfen. 480 g/h des dabei anfallenden Sauerwassers wurden am Kopf der Ko¬ lonne mit einer Temperatur von 30°C in selbige zurückgeführt (26) . 220 g/h des Sauerwassers wurden kontinuierlich entnommen (das Sauerwasser enthielt 3 Gew.-% Acrylsaure und 2,6 Gew.-% Essigsäure) . 90 g/h des entnommenen Sauerwassers wurden mit MEHQ (22) versetzt und als 0,5 gew.-%ige wässrige Stabilisatorlösung (21) gemeinsam mit der Restmenge des Sauerwassers (23) über den was- sergekühlten Rohrbündelwärmetauscher (24) auf 18°C abgekühlt als Sprühflüssigkeit (25) verwendet. Mit einem anderen Teil des entnommenen Sauerwassers wurde eine 0,5 gew.-%ige wässrige Lösung von 4-Hydroxy-TEMPO (4-Hydroxy-2 ,2,6, 6-tetramethyl- piperidin-1-oxyl) hergestellt, die in einer Menge von 18 g/h mit einer Temperatur von 20°C auf dem 75ten Boden der Trennkolonne zugeführt wurde (27) .A gaseous mixture (17) was removed from the top of the column and subjected to a partial condensation in the spray cooler (18). 480 g / h of the resulting acid water were at the top of Ko ¬ lonne with a temperature of 30 ° C thereinto recycled (26). 220 g / h of the sour water were continuously removed (the Sour water contained 3% by weight of acrylic acid and 2.6% by weight of acetic acid). 90 g / h of the acid water removed were mixed with MEHQ (22) and as a 0.5% by weight aqueous stabilizer solution (21) together with the remaining amount of acid water (23) via the water-cooled tube bundle heat exchanger (24) to 18 ° C cooled used as spray liquid (25). With another part of the acid water removed, a 0.5% by weight aqueous solution of 4-hydroxy-TEMPO (4-hydroxy-2, 2,6, 6-tetramethyl-piperidine-1-oxyl) was prepared, which in an amount of 18 g / h at a temperature of 20 ° C was fed to the 75th tray of the separation column (27).
Die beschriebene Trennvorrichtung konnte 40 Tage ohne nennenswerte Polymerisatbildung betrieben werden.The separation device described could be operated for 40 days without any appreciable polymer formation.
b) Beispiel 1b) Example 1
Im Vergleichsbeispiel 1 aus a) bildete sich auf der Höhe des 30ten Glockenbodens (von unten) ein Ameisensäurebauch aus (die Rücklaufflüssigkeit enthielt auf dieser Kolonnenhöhe 28 Gew.-% Ameisensäure) .In comparative example 1 from a), a formic acid belly formed at the height of the 30th bell bottom (from below) (the reflux liquid contained 28% by weight of formic acid at this column height).
Durch Entnahme eines flüssigen Seitenstro s von 10 g/h auf dieser Kolonnenhöhe konnte der Ameisensäure-Bauch auf 13 Gew.-% gesenkt werden.By removing a liquid side stream of 10 g / h at this column height, the formic acid belly could be reduced to 13% by weight.
Die stationäre Zusammensetzung des entnommenen flüssigen Seiten- stromes war im wesentlichen:The stationary composition of the liquid side stream removed was essentially:
38 Gew.-% Acrylsaure,38% by weight acrylic acid,
13 Gew.-% Ameisensäure,13% by weight of formic acid,
12 Gew.-% Essigsäure und12% by weight of acetic acid and
37 Gew.-% Wasser.37 wt% water.
Der entnommene Seitenstrom wird einer Hydrierung gemäß DE-A 23 10 754 zugeführt.The side stream removed is fed to a hydrogenation according to DE-A 23 10 754.
Die Reinheit der Kristalle war leicht verbessert.The purity of the crystals was slightly improved.
c) Vergleichsbeispiel 2c) Comparative Example 2
Die nachfolgende Beschreibung bezieht sich auf die Fig. 1 der DE-A 10115277 bzw. Fig. 2 der EP-A 982 289. Ein Gasstrom aus der Gasphasenoxidation zu Acrylsaure vonThe following description refers to FIG. 1 of DE-A 10115277 and FIG. 2 of EP-A 982 289. A gas stream from gas phase oxidation to acrylic acid from
2900 Nl/h, einer Temperatur von 270°C und einem Druck von 1,6 bar mit den Hauptkomponenten (jeweils in Gew.-%)2900 Nl / h, a temperature of 270 ° C and a pressure of 1.6 bar with the main components (each in% by weight)
Stickstoff (75) , Sauerstoff (3 ) , Acrylsaure (12), Wasser (5) , CO (1), C02 (3) ,Nitrogen (75), oxygen (3), acrylic acid (12), water (5), CO (1), C0 2 (3),
Rest, d.h. weitere Komponenten (1),Rest, i.e. further components (1),
wurde in einem Venturi uench 1 durch direkten Kontakt mit im Bereich des .engsten Querschnitts des Venturi-Rohres angebrachten Schlitzen eingedüster Quenchflüssigkeit (140 - 150°C) auswas created in a Venturi uench 1 by direct contact with in the area of the . narrowest cross-section of the venturi tube made slots of injected quench liquid (140 - 150 ° C)
57,4 Gew.-% Diphenylether, 20,7 Gew.-% Diphenyl, 20 Gew.-% o-Di- methylphthalat , Rest andere Komponenten, auf eine Temperatur von 150°C abgekühlt. Anschließend wurde in einem nachgeschalteten Tropfenabschneider (Vorlagebehälter mit oben weggeführtem Gas- röhr) der tropfenförmig flüssig gebliebene Anteil der Quenchflüssigkeit von der aus Reaktionsgas und verdampfter Quenchflüssigkeit bestehenden Gasphase abgetrennt und in einem Kreislauf zum Venturiwäscher rückgeführt. Ein Teilstrom der rückgeführten Quenchflüssigkeit wurde dabei einer Lösungsmitteldestillation un- terzogen, wobei die Quenchflüssigkeit überdestilliert wurde und schwersiedende Nebenkomponenten, die verbrannt wurden, zurückblieben .57.4% by weight of diphenyl ether, 20.7% by weight of diphenyl, 20% by weight of o-dimethylphthalate, the rest of other components, cooled to a temperature of 150 ° C. The drop-shaped portion of the quench liquid, which remained in the form of a drop of liquid, was separated from the gas phase consisting of reaction gas and vaporized quench liquid in a downstream droplet cutter (storage container with the gas tube removed at the top) and returned to the venturi scrubber in a circuit. A partial stream of the recycled quench liquid was subjected to a solvent distillation, the quench liquid being distilled over and high-boiling secondary components which were burned up remaining.
Die eine Temperatur von ca. 150°C aufweisende Gasphase wurde in den unteren Teil einer Füllkörperabsorptionskolonne 2 geführt (3 m hoch; Doppelmantel aus Glas; Innendurchmesser 50 mm, drei Füllkörperzonen der Längen (von unten nach oben) 90 cm, 90 cm und 50 cm; die Füllkörperzonen waren von unten nach oben wie folgt thermostatiert :The gas phase, which was at a temperature of approx. 150 ° C, was led into the lower part of a packed column 2 (3 m high; double jacket made of glass; inner diameter 50 mm, three packed zones of lengths (from bottom to top) 90 cm, 90 cm and 50 cm; the packing zones were thermostated from bottom to top as follows:
90°C, 60°C, 20°C; die vorletzte und die letzte Füllkörperzone waren durch einen Kaminboden getrennt; die Füllkörper waren Metallwendeln aus Edelstahl mit einem Wendeldurchmesser von 5 mm und einer Wendellänge vσn 5 mm; unmittelbar oberhalb der mittleren Füllkörperzone wurde das Absorptionsmittel zugeführt und dem Gegenstrom von 2900 g/h des gleichfalls aus 57,4 Gew.-% Diphenylether, 20,7 Gew.-% Diphenyl, 20 Gew.-% o-Dimethylphthalat und Rest aus anderen Komponenten zusammengesetzten, mit einer Temperatur von 50°C aufgegebenen Absorptionsmittels, ausgesetzt. Das in der Absorptionskolonne 2 die zweite Füllkörperzone nach oben verlassende nicht abbsorbierte Gasgemisch wurde in der dritten Füllkörperzone weiter abgekühlt, um den kondensierbaren Teil der darin enthaltenen Nebenkomponenten z.B. Wasser und Essig- säure, durch Kondensation abzutrennen. Dieses Kondensat wird Sau- erwasser genannt. Zur Erhöhung der Trennwirkung wurde ein Teil des Sauerwassers oberhalb der dritten Füllkörperzone der Absorpi- tonskolonne 2 mit einer Temperatur von 20°C in die Absorptionskolonne 2 rückgeführt. Die Entnahme des Sauerwassers erfolgte un- terhalb der obersten Füllkörperzone vom dort angebrachten Kaminboden. Das Verhältnis von rückgeführtem zu abgezogenem Sauerwasser betrug 200 g/g. Das entnommene Sauerwasser enthielt neben 97,5 Gew.-% Wasser auch noch 0,8 Gew.-% Acrylsaure. Diese kann bei Bedarf wie in DE-A 19 600 955 beschrieben rückgewonnen wer- den. 1600 Nl/h des die Absorptionskolonne 2 letztlich verlassenden Gasstromes wurden als Kreisgas in die Propenoxidation rückgeführt. Der Rest wurde verbrannt.90 ° C, 60 ° C, 20 ° C; the penultimate and the last packing zone were separated by a chimney floor; the packing elements were metal helices made of stainless steel with a helix diameter of 5 mm and a helix length vσn 5 mm; immediately above the middle packing zone, the absorbent was fed and the counterflow of 2900 g / h of 57.4% by weight of diphenyl ether, 20.7% by weight of diphenyl, 20% by weight of o-dimethylphthalate and the rest from others Components composite absorbent applied at a temperature of 50 ° C, exposed. The non-absorbed gas mixture leaving the second packed zone in the absorption column 2 was cooled further in the third packed zone in order to separate off the condensable part of the secondary components contained therein, for example water and acetic acid, by condensation. This condensate is called sour water. To increase the separation effect, part of the acid water above the third packing zone of the absorption column 2 was returned to the absorption column 2 at a temperature of 20 ° C. The sour water was removed below the uppermost packing zone from the chimney floor attached there. The ratio of recycled to withdrawn acid water was 200 g / g. In addition to 97.5% by weight of water, the acid water removed also contained 0.8% by weight of acrylic acid. If necessary, this can be recovered as described in DE-A 19 600 955. 1600 Nl / h of the gas stream ultimately leaving the absorption column 2 were recycled as recycle gas into the propene oxidation. The rest were burned.
Der Ablauf der Absorptionskolonne 2 wurde auf einen Zwangsumlau- fentspannungsverdampfer 5 gegeben, der bei 60 mbar und 105°C betrieben wurde. Dabei wurde ein mit Acrylsaure beladener Lösungsmittelstrom von 5230 g/h (Hauptkomponenten, jeweils in Gew.-% bzw. Gew.-ppm : Lösungsmittel 61, Acrylsaure 30, Essigsäure 8118 ppm, Maleinsäureanhydrid 200 ppm) in einen ersten Teilstrom IIIA von 2160 g/h, der überwiegend Acrylsaure enthielt (Hauptkomponenten, jeweils in Gew.-% : Lösungsmittel 20, Acrylsaure 77 und Essigsäure 0,22) sowie einen zweiten Teilstrom IIIB von 3070 g/h, der überwiegend das Lösungsmittel enthielt (Hauptkomponenten jeweils in Gew.-% bzw. Gew.-ppm : Lösungsmittel 83, Acrylsaure 5, und Essigsäure 636 ppm) aufgetrennt'.The outlet of the absorption column 2 was placed on a forced-circulation flash evaporator 5, which was operated at 60 mbar and 105 ° C. A solvent stream loaded with acrylic acid of 5230 g / h (main components, each in% by weight or ppm by weight: solvent 61, acrylic acid 30, acetic acid 8118 ppm, maleic anhydride 200 ppm) was introduced into a first partial stream IIIA of 2160 g / h, which predominantly contained acrylic acid (main components, each in% by weight: solvent 20, acrylic acid 77 and acetic acid 0.22) and a second partial stream IIIB of 3070 g / h, which predominantly contained the solvent (main components each in wt. -% or ppm by weight: solvent 83, acrylic acid 5, and acetic acid 636 ppm) separated '.
Der Teilstrom IIIB wurde auf den Kopf der Strippkolonne 3 aufgegeben. Als Strippgas wurde ein Luftstrom von 600 Nl/h eingesetzt. Auf den Kopf der Strippkolonne 3 wurde der Teilstrom IIB aus dem Verdampfer gegeben; die Strippkolonne 3 diente hier zur Abreini- gung des Lösungsmittels von Acrylsaure. Das von Acrylsaure gereinigte Eosungsmittel wurde aus dem Sumpf der Strippkolonne 3 abgezogen und zum Kopf der Absorptionskolonne 2 rezirkuliert . Der Diacrylsäuregehalt im Lösungsmittel betrug 2,0 Gew.-%.Partial stream IIIB was fed to the top of stripping column 3. An air flow of 600 Nl / h was used as the stripping gas. Partial stream IIB from the evaporator was added to the top of stripping column 3; the stripping column 3 was used here to purify the solvent from acrylic acid. The solvent removed from acrylic acid was withdrawn from the bottom of the stripping column 3 and recirculated to the top of the absorption column 2. The diacrylic acid content in the solvent was 2.0% by weight.
Der im Verdampfer 5 anfallende Teilstrom IIIA wurde in einem Wärmetauscher 6 bei 100 mbar kondensiert und das Kondensat wurde auf den 28. Boden der zweigeteilten Rektifikationskolonne 4, und zwar deren Abtriebsteil, zugeführt. Im Abtriebsteil der Rekti- fikationskolonne 4 wurden aus dem Teilstrom IIIA mit Acrylsäure- dampf im Gegenstrom die Leichtsieder ausgestrippt , wogegen die Mittelsieder und Schwersieder überwiegend in der Flüssigkeit ver- blieben. Aus dem Sumpf des Abtriebsteils der Rektifikationskolonne 4 wurde ein nahezu leichtsiederfreier Strom b (Hauptkomponenten in Gew.-% bzw. Gew.-ppm : Lösungsmittel 28, Acrylsaure 71, Essigsäure 721 ppm, Maleinsäureanhydrid 4026 ppm entnommen. Der Teilstrom b wurde dem gemeinsamen Verdampfer 7 des Abtriebsteils und des Auftriebsteils der Rektifikationskolonne 4 zugeführt, aus dem Verdampfer 7 wurde ein Reststrom c abgezogen (480 g/h, Hauptkomponenten, in Gew.-% bzw. Gew.-ppm : Lösungsmittel 87, Acrylsaure 10, Maleinsäureanhydrid 700 ppm) und dem Venturiquench 1 zugeführt. Der Brüdenstrom aus dem Verdampfer 7 wurde zwecks Gewinnung der angestrebten Acrylsäurequalität dem Auftriebsteil der Rektifikationskolonne 4 zugeführt und durch den Acrylsäurerück- lauf von Mittelsiedern und Schwersiedern gereinigt. Am Kopf des Auftriebsteils der Rektifikationskplonne 4 wurde ein Strom von 420 g/h an Zielprodukt abgezogen, das noch 1500 ppm Essigsäure und 50 ppm Maleinsäureanhydrid enthielt (im übrigen betrug der Gesamtaldehydgehalt (einschließlich Allylacrylat) < 300 Gew.-ppm und der Gesamtalkancarbonsauregeha.lt ebenfalls < 300 Gew.-ppm). Der Brüden aus dem Abtriebsteil der Rektifikationskolonne 4 wurde als Reststrom a mit 87 Gew.-% Acrylsaure, 200 Gew.-ppm Lösungsmittel, 1510 Gew.-ppm Aldehyden, 1000 Gew.-ppm Allylacrylat, 6 Gew.-% Essigsäure und 0,7 Gew.-% Ameisensäure kondensiert, mit Phenothiazin versetzt und ebenfalls dem Venturiquench 1 zugeführt .The partial stream IIIA occurring in the evaporator 5 was condensed in a heat exchanger 6 at 100 mbar and the condensate was fed to the 28th tray of the two-part rectification column 4, namely its stripping section. In the stripping section of the rectification column 4, the low boilers were stripped from the partial stream IIIA with acrylic acid vapor in countercurrent, whereas the medium boilers and high boilers were predominantly dissolved in the liquid. remained. From the bottom of the stripping section of the rectification column 4, an almost low-boiler-free stream b (main components in% by weight or ppm by weight: solvent 28, acrylic acid 71, acetic acid 721 ppm, maleic anhydride 4026 ppm was removed. The partial stream b was taken from the common evaporator 7 of the stripping section and the lifting section of the rectification column 4, a residual stream c was drawn off from the evaporator 7 (480 g / h, main components, in% by weight or ppm by weight: solvent 87, acrylic acid 10, maleic anhydride 700 ppm) and the Venturi quench 1. The vapor stream from the evaporator 7 was fed to the lifting section of the rectification column 4 in order to obtain the desired acrylic acid quality and was cleaned of medium boilers and high boilers by the acrylic acid return flow. A stream of 420 g / was at the top of the lifting section of the rectification column 4 h deducted from the target product, which still contained 1500 ppm acetic acid and 50 ppm maleic anhydride lt (otherwise the total aldehyde content (including allyl acrylate) was <300 ppm by weight and the total alkane carboxylic acid content was also <300 ppm by weight). The vapor from the stripping section of the rectification column 4 was treated as a residual stream a with 87% by weight acrylic acid, 200% by weight solvent, 1510% by weight aldehydes, 1000% by weight allyl acrylate, 6% by weight acetic acid and 7% by weight of formic acid condensed, mixed with phenothiazine and likewise fed to the Venturi quench 1.
Nach der Extraktion des Sauerwassers mit einem Teilstrom des rezirkulierten Lösungsmittelstroms betrug der Diacrylsäuregehalt des Sauerwassers, das der Verbrennung zugeführt wurde, 2, 6 Gew.-%.After extraction of the acid water with a partial stream of the recirculated solvent stream, the diacrylic acid content of the acid water which was fed to the combustion was 2.6% by weight.
Alle flüssigen Acrylsaure enthaltenden Ströme waren mit Phenothiazin polymerisationsinhibiert . Nach 14tägiger Betriebsdauer mußte die Aufarbeitung wegen Polymerisatbildung unterbrochen -werden.All streams containing liquid acrylic acid were polymerization inhibited with phenothiazine. After 14 days of operation, the workup had to be interrupted due to polymer formation.
d) Beispiel 2d) Example 2
Der Reststrom a aus Vergleichsbeispiel 2 aus c) wurde aus der Aufarbeitungszone heraus und einer erfindungsgemäßen Hydrierung der enthaltenen Acrylsaure zugeführt. Die Laufzeit der Aufarbeitungszone konnte so auf 28 Tage erhöht werden. The residual stream a from comparative example 2 from c) was removed from the work-up zone and fed to a hydrogenation according to the invention of the acrylic acid contained. The run-up time of the processing zone was increased to 28 days.

Claims

Patentanspruch claim
1. Verfahren zur Herstellung von Acrylsaure und/oder deren Ester sowie von Propionsäure und/oder deren Ester im Verbund, dadurch gekennzeichnet, dass man1. A process for the preparation of acrylic acid and / or its esters and propionic acid and / or their esters in combination, characterized in that
a) in einer ersten Zone, der Reaktionszone, Propan, Propen, und/oder Acrolein einer selektiven heterogen katalysier- ten Gasphasenpartialoxidation unter Bildung einesa) in a first zone, the reaction zone, propane, propene, and / or acrolein of a selective heterogeneously catalyzed gas phase partial oxidation to form a
Produktgasgemisches A, das als Hauptprodukt Acrylsaure und als Nebenkomponenten Aldehyde und/oder gesättigte Alkancarbonsäuren enthält, unterwirft,Subjecting product gas mixture A, which contains acrylic acid as the main product and aldehydes and / or saturated alkane carboxylic acids as secondary components,
b) in einer zweiten Zone, der Aufarbeitungszone, aus dem Produktgasgemisch Ab) in a second zone, the work-up zone, from the product gas mixture A
i) einerseits als Zielprodukt eine Acrylsäurequalität abtrennt, deren Gehalt an Acrylsaure >90 Gew.-% be- trägt, und gleichzeitigi) on the one hand, separates an acrylic acid quality as target product, the acrylic acid content of which is> 90% by weight, and at the same time
ii) andererseits ein Acrylsaure enthaltendes Neben-Stoffgemisch abtrennt, das dadurch charakterisiert ist, dass entweder sein auf die enthaltene Menge an Acryl- säure bezogener Gesamtgehalt (in mol.-%) an Aldehyden und/oder sein auf die enthaltene Menge an Acrylsaure bezogener Gesamtgehalt (in mol.-%) an Alkancarbonsäuren größer ist, als der jeweilige, in gleicher Weise bezogene, Aldehyd- und/oder Alkancarbonsäurege- samtgehalt der unter i) abgetrennten. Acrylsäurequalität,ii) on the other hand, separates a by-substance mixture containing acrylic acid, which is characterized in that either its total content (in mol%) of aldehydes based on the amount of acrylic acid contained and / or its total content based on the amount of acrylic acid contained (in mol%) of alkane carboxylic acids is greater than the respective total aldehyde and / or alkane carboxylic acid content obtained in the same way, that of those separated under i). Acrylic acid quality,
undand
c) die im unter ii) abgetrennten Neben-Stoffgemisch enthaltene Acrylsaure, gegebenenfalls nach erfolgter Veresterung, durch Hydrierung mittels molekularem Wasserstoff in Propionsäure und/oder deren Ester überführt. c) the acrylic acid contained in the secondary substance mixture separated off under ii), if appropriate after esterification, is converted into propionic acid and / or its ester by hydrogenation using molecular hydrogen.
PCT/EP2003/004710 2002-05-08 2003-05-06 Method for the production of acrylic acid and/or the esters thereof and propionic acid and/or the esters thereof in a compound WO2003095411A1 (en)

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DE2002120752 DE10220752A1 (en) 2002-05-08 2002-05-08 Production of propionic acid (ester), useful e.g. as an intermediate for herbicides, comprises hydrogenation of acrylic acid (ester) using hydrogen obtained from dehydrogenation of propane in a prior stage of the process
DE2002124341 DE10224341A1 (en) 2002-05-29 2002-05-29 Production of acrylic and propionic acid and/or their esters, useful as intermediates for e.g. adhesives, comprises catalytic gas-phase oxidation, and work-up to give pure acrylic acid and an acrylic acid by-product which is hydrogenated
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WO2008090190A1 (en) * 2007-01-26 2008-07-31 Basf Se Method for the production of acrylic acid
US7566804B2 (en) 2007-01-26 2009-07-28 Basf Aktiengesellschaft Process for preparing acrylic acid
RU2472768C2 (en) * 2007-01-26 2013-01-20 Басф Се Method of producing acrylic acid
WO2008135676A1 (en) * 2007-03-19 2008-11-13 Arkema France Improved method for producing acrolein and/or acrylic acid from propylene
WO2010010298A2 (en) * 2008-07-22 2010-01-28 Arkema France Method for producing bioresourced propionic acid from glycerol
WO2010010298A3 (en) * 2008-07-22 2011-08-18 Arkema France Method for producing bioresourced propionic acid from glycerol
CN102216252A (en) * 2008-07-22 2011-10-12 阿肯马法国公司 Method for producing bioresourced propionic acid from glycerol
DE102011076931A1 (en) 2011-06-03 2012-12-06 Basf Se Aqueous solution containing acrylic acid and its conjugate base
WO2012163931A1 (en) 2011-06-03 2012-12-06 Basf Se Aqueous solution comprising acrylic acid and the conjugate base thereof
US9150483B2 (en) 2011-06-03 2015-10-06 Basf Se Aqueous solution comprising acrylic acid and the conjugate base thereof

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