WO2002051784A1 - Method for producing acrylic acid - Google Patents

Method for producing acrylic acid Download PDF

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Publication number
WO2002051784A1
WO2002051784A1 PCT/EP2001/015207 EP0115207W WO02051784A1 WO 2002051784 A1 WO2002051784 A1 WO 2002051784A1 EP 0115207 W EP0115207 W EP 0115207W WO 02051784 A1 WO02051784 A1 WO 02051784A1
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Prior art keywords
acrylic acid
tert
butyl
column
weight
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PCT/EP2001/015207
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German (de)
French (fr)
Inventor
Ulrich Hammon
Gerhard Nestler
Jürgen Schröder
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Basf Aktiengesellschaft
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Publication of WO2002051784A1 publication Critical patent/WO2002051784A1/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
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
    • 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
    • C07C51/50—Use of additives, e.g. for stabilisation

Definitions

  • the invention describes a process for the production of acrylic acid, by heterogeneously catalyzed gas phase partial oxidation of at least one C 3 precursor with molecular oxygen, the resulting product gas mixture containing acrylic acid being cooled and subsequently subjected to either a fractional condensation or a rectification process.
  • Acrylic acid is a valuable monomer because of its acid function and the very reactive double bond, e.g. is used in the production of acrylic acid esters, superabsorbents or polymer dispersions, which are used, for example, as adhesives or paint dispersions.
  • acrylic acid is obtainable by heterogeneously catalyzed gas phase partial oxidation of C 3 precursors of acrylic acid with molecular oxygen on catalysts in the solid state at elevated temperature.
  • C 3 precursor of acrylic acid summarizes those chemical compounds which are formally obtainable by reducing acrylic acid.
  • Known C 3 precursors of acrylic acid are, for example, propane, propene and acrolein. Compounds such as propionaldehyde or propionic acid are also among the C 3 precursors.
  • the heterogeneously catalyzed gas phase partial oxidation with molecular oxygen is at least partially an oxidative dehydrogenation.
  • inert gases such as nitrogen, carbon monoxide, carbon dioxide and / or water vapor
  • DE-OS 2 241 714 Absorption of acrylic acid in high-boiling solvents is described, for example, in DE-OS 2 241 714 and DE-Al 43 08 087.
  • DE-OS 2 241 714 describes the use of esters of aliphatic or aromatic mono- or dicarboxylic acids which have a melting point below 30 ° C and a boiling point at normal pressure above 160 ° C.
  • DE-Al 43 08 087 recommends the use of a high-boiling mixture of 0.1 to 25% by weight of ortho-dimethylphthalate based on a mixture consisting of 70 to 75% by weight of diphenyl ether for the separation of acrylic acid from reaction gases of catalytic oxidation by countercurrent absorption and 25 to 30% by weight diphenyl.
  • the processes consist essentially in that the acrylic acid contained in the reaction gas mixture and the condensable by-products are largely absorbed in the solvent or solvent mixture, for which purpose countercurrent absorption is preferably used, followed by the low-boiling components, e.g. low-boiling aldehydes, such as acetaldehyde, propionaldehyde or acrolein, acetone, acetic acid or propionic acid, are partially stripped, for which purpose countercurrent desorption is preferably used, and finally the acrylic acid is separated off from the solvent by distillation.
  • the low-boiling components e.g. low-boiling aldehydes, such as acetaldehyde, propionaldehyde or acrolein, acetone, acetic acid or propionic acid
  • Phenothiazine is recommended as a stabilizer in the above applications.
  • a disadvantage of the processes described is that when the acrylic acid is separated off, polymer formation occurs, which severely limits the running time of the separation devices, that is to say columns and evaporators, by the formation of deposits.
  • EP-A 1 041 062 attempts to prevent the formation of polymer during purification by distillation in that the mixture to be cleaned, acrylic acid-containing mixture, contains not more than 2000 ppm, based on acrylic acid, of C - C 4 aldehydes and acetone ,
  • N-oxyl compounds e.g. 4-hydroxy-2, 2,6, 6-tetramethyl-piperidine-N-oxyl, 4-oxo-2, 2,6, 6-tetramethyl-piperidine-N- oxyl, 4-acetoxy-2, 2,6, 6-tetramethyl-piperidine-N-oxyl, 2,2,6, 6-tetramethyl-piperidine-N-oxyl, 4,4 ', 4' 'tris (2,2,6, 6-tetramethyl-piperidine-N-oxyl) phosphite, 3-oxo-2, 2, 5, 5-tetramethyl-pyrrolidine-N-oxyl), aromatic amines (e.g.
  • Phenols e.g. hydroquinone or hydroquinone monomethyl ether
  • the object was achieved by a process for the production of acrylic acid, by heterogeneously catalyzed gas phase partial oxidation of at least one C 3 precursor with molecular oxygen, the resulting product gas mixture containing acrylic acid being subsequently cooled, either subjected to a fractional condensation or a rectification process , if phenothiazine and at least one phenolic compound are introduced into the column head or in the area of the column head of the rectification or condensation column (s)
  • the product gas mixture is obtainable in a manner known per se by heterogeneously catalyzed gas phase partial oxidation of at least one C 3 precursor of acrylic acid with molecular oxygen at elevated temperature.
  • the starting gas is generally diluted with gases which are inert under the selected reaction conditions, such as nitrogen (N), C0, saturated C 1 -C 6 -hydrocarbons and / or water vapor, and mixed with molecular oxygen (0 2 ) or an oxygen-containing gas at elevated temperatures (usually 200 to 450 ° C.) and, if appropriate, increased pressure, passed over solid, transition-metallic (containing Mo and V or Mo, W, Bi and Fe) mixed oxide catalysts and converted oxidatively into the acrylic acid ,
  • gases which are inert under the selected reaction conditions, such as nitrogen (N), C0, saturated C 1 -C 6 -hydrocarbons and / or water vapor, and mixed with molecular oxygen (0 2 ) or an oxygen-containing gas at elevated temperatures (usually 200 to 450 ° C.) and, if appropriate, increased pressure, passed over solid, transition-metallic (containing Mo and V or Mo, W, Bi and Fe) mixed oxide catalysts and converted oxidatively into the acrylic acid ,
  • the product gas mixture used according to the invention is preferably obtained from the partial oxidation of propane or propene and / or acrolein.
  • the hot product gas mixture generally has a temperature between 200 and 400 ° C. and can be cooled to a temperature between 100 and 180 ° C. in a manner known per se.
  • the cooling can take place partially or completely indirectly, for example with tube bundle or plate heat exchangers with a suitable cooling medium, but mainly takes place as a rule by direct cooling with a high-boiling liquid in a quench, which may be preceded by a pre-quench.
  • the temperature of the quench liquid is usually 70 to 200 ° C, often 100 to 150 ° C.
  • Suitable cooling media in heat exchangers for indirect cooling or for recooling the quench liquid are air in the case of corresponding air coolers and cooling liquids, in particular water, in the other cooling devices.
  • a high-boiling liquid can at least partially be a rectification process sequence, optionally after distillation, containing high-boiling substances (see below) or an absorbent known per se for separating acrylic acid from the product gas mixture.
  • the latter can be, for example, tri (n-butyl) phosphate (US Pat. No.
  • High-boiling here means boiling higher than acrylic acid, ie boiling higher than 141 ° C under normal pressure, preferably boiling at least at 151 ° C under normal pressure.
  • the acrylic acid-containing liquid thus obtained is rectified, that is to say fed to a rectification process which consists of at least one rectification column.
  • the acrylic acid contained in the liquid is essentially separated as a medium boiler from higher and lower boiling components.
  • the higher-boiling components essentially comprise the high-boiling liquid mentioned above, as well as the components which have a boiling point above the medium boilers at normal pressure, for example above 151 ° C. and in particular above 141 ° C.
  • These can include polymeric acrylic acid, Michael addition products of acrylic acid, such as di-, tri- and tetraacrylic acid, etc., higher mono- and dicar- be bonic acids and their anhydrides and stabilizers, and of course also incompletely separated, lower-boiling components.
  • the lower-boiling components essentially comprise those components which have a boiling point below the medium boiler fraction at normal pressure, for example in the temperature interval from about 30 to 120 ° C., in particular 30 to 131 ° C.
  • This low boiler fraction can partly be returned to the top of the column and partly but also completely removed. It usually consists of
  • the non-condensable constituents of the product gas mixture i.e. those with a boiling point at normal pressure below approx. 30 ° C. and, for example, those which are stripped out by the gaseous constituents, for example nitrogen, oxygen, propane, propene or carbon monoxide, carbon dioxide etc. discharged at the top of the column or via a quench system or, if appropriate after purification, at least partly recycled as cycle gas into the gas phase oxidation if they have not already been substantially removed in the absorption step (see above).
  • the temperature in the bottom of the column is typically 90 to 130 ° C., the top temperature depends on the type of discharge of the low boilers. If this separation takes place via a side draw, it is normally 15 to 70 ° C, often 20 to 50 ° C. If the separation takes place via a quench, e.g. can be operated with acid water, it is usually 50 - 90 ° C, preferably 60 - 80 ° C.
  • the withdrawal temperature of the crude acrylic acid in the side hood is usually 80 to 110 ° C.
  • the return temperature of the acid water to the column is usually 25 to 35 ° C.
  • the rectification column which in this case is operated as fractional condensation, as described for example in the German application with the file number 100 53 086.9 or DE-A 197 40 253, is operated, for example, at a pressure between 500 and 1200 hPa, preferably between 800 and 1100 hPa and particularly preferably at atmospheric pressure.
  • the isolation of the acrylic acid by distillation is preferably carried out as follows:
  • Acrylic acid is generally contained in the feed to 5 to 30% by weight, preferably to 10 to 20% by weight.
  • columns with separating internals are suitable as rectification columns.
  • Column internals are all common internals, in particular trays, packings and / or packing. Of the trays, bubble trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays or any combination thereof are preferred.
  • the rectification is preferably carried out in a tray column with, for example, 25 to 50 trays, preferably with 30 to 40 trays, with external circulation evaporators, the feed generally being in the lower quarter of the column.
  • the acrylic acid is discharged in liquid form via a side draw in the upper half of the column.
  • the low boilers still present e.g. water, acetic acid
  • the low boilers are separated in gaseous form via the top of the column and condensed, whereby part of the condensate can be returned to the column as reflux.
  • the acrylic acid is preferably removed by distillation under reduced pressure. It is expedient to work at a head pressure of at most 500 hPa, usually at 10-200 hPa, preferably at 10-100 hPa.
  • the associated temperatures in the bottom of the column are generally 100-230 ° C and 30-80 ° C at the top of the column.
  • an oxygen-containing gas preferably air
  • a rectification column can be flowed through the rectification column.
  • the crude acrylic acid taken off as a medium boiler fraction which essentially comprises the components which, at normal pressure, have a boiling point in the temperature interval, for example from 120 to 160 ° C., in particular in the range of +/- 10 ° C. around that of the product of value
  • Acrylic acid ie about 131 to 151 ° C.
  • Such crude acrylic acid taken off as a middle boiler, usually also contains acrylic acid
  • low molecular weight carbonyl compounds such as e.g. Furfural, formaldehyde, acrolein, acetaldehyde, propionaldehyde, acetone
  • the crystallization is generally carried out without the addition of a solvent, in particular without the addition of an organic solvent.
  • the crystallization method to be used is not limited.
  • the crystallization can be carried out continuously or discontinuously, in one or more stages up to almost any degree of purity.
  • water can be added to the crude acrylic acid to be crystallized before crystallization (based on the amount of acrylic acid contained up to 10% by weight or more, preferably up to 5% by weight).
  • Such an addition facilitates the separation of lower carboxylic acid contained as a by-product in the crude acrylic acid, e.g. Acetic acid, because it is incorporated to a lesser extent in the acrylic acid crystals in the presence of water.
  • the presence of water reduces the tendency to crust in the crystallizer.
  • the pure acrylic acid obtained in this way generally contains significantly less of the impurities specified above for the crude acrylic acid, for example up to a total of 2000 ppm by weight.
  • the column is stabilized by adding a stabilizer solution in a suitable solvent in the area of the column top This includes the addition of the stabilizer solution into the reflux mentioned or directly into the column.
  • the stream provided with stabilizer solution or the direct feed of the stabilizer solution into the column in the area of the column head is fed, which for example comprises the area of the upper quarter of the separation stages, preferably the upper 20% and particularly preferably the upper 15%.
  • the area of the column head can also mean a cooling device, for example quench or condenser, for cooling the low boilers, into which stabilizer solution can likewise be metered in, and of course also the column head itself.
  • the stabilizer solution can be added at one point or at several points in the area of the column top, it being possible for the composition of the stabilizer solution supplied at the various points in the column to be the same or different.
  • Stabilizers are understood to be those compounds which delay and / or inhibit the polymerization of acrylic acid or methacrylic acid. These can be inhibitors, for example.
  • the stabilization takes place according to the invention with phenothiazine and at least one phenolic component.
  • the phenolic component can e.g. an alkyl phenol, for example 2-tert-butyl-4-methylphenol, 6-tert-butyl-2, 4-dimethyl-phenol, 2, 6-di-tert. -Butyl-4-methylphenol, 2-methylhydroquinone or 2, 2 '-methylene-bis- (6-tert-butyl-4-methylphenol) to a hydroxyphenol, for example hydroquinone, pyrocatechol or benzoquinone an aminophenol, such as para-aminophenol, a nitrosophenol, such as para-nitrosophenol, or a methoxyphenol, for example 4-methoxyphenol, mono- or di-tert-butyl-4-methoxyphenol. Methoxyphenol (hydroquinone monomethyl ether) used.
  • an alkyl phenol for example 2-tert-butyl-4-methylphenol, 6-tert-butyl-2, 4-dimethyl-phenol, 2, 6-di-tert. -Butyl
  • butylphenol nonylphenol [11066-49-2], Octylphenol [140-66-9], 2, 6-dimethylphenol, bisphenol A, bisphenol F, bisphenol B, bisphenol S, bisphenol C, 3,3 ', 5, 5'-tetrabromo-bisphenol A, 3, 5 -Di-tert-butyl-4-hydroxyanisole, Koresin® from BASF AG, 3, 5-di-tert-butyl-4-hydroxybenzoic acid methyl ester, 4-tert-butylpyrocatechol, 2-hydroxybenzyl alcohol,
  • 1,1,4-Tris (5'-butyl-4'-hydroxy-2'-methylphen-1'-yl) utane, 2-methoxyphenol (guaiacol, pyrocatechol onomethyl ether), 2-ethoxyphenol , 2-isopropoxyphenol, 4-ethoxyphenol, 4-butoxyphenol, hydroquinone monobenzyl ether, p-phenoxyphenol, 4,4'-oxydiphenyl, 3, 4-methylenedioxydiphenol (sesamol), 3, 4-dimethylp ⁇ enol,
  • Phenothiazine and the phenolic component can be metered in together in a mixture or separately, preferably as solutions.
  • the amount of stabilizer is chosen so that the phenothiazine concentration in the isolated acrylic acid 50-1000 ppm by weight, preferably 100-600 ppm by weight, and the concentration of the phenolic component 10-1000 ppm by weight, preferably 50-500 Ppm by weight.
  • Suitable solvents are both components that are contained in the system and components that are external to the system, preferably components that are contained in the system.
  • the stabilizers can be dissolved in acrylic acid, water, aqueous acrylic acid solution or the acid water obtained, preferably in acrylic acid or acid water.
  • the concentration of the solution for phenothiazine is 0.1-1% by weight and for the phenolic components 0.01-1% by weight in a suitable solvent.
  • At least one metal salt can also be added as a stabilizer.
  • This can include, for example, a manganese, cerium or copper salt, preferably manganese acetate, cerium acetate, copper acetate, copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper di-butyldithiocarbamate and / or copper salicylate.
  • Manganese acetate is particularly preferred.
  • Nickel and chromium salts are also suitable as metal salts.
  • Suitable anions of the metal salts are acetates, dithiocarbamates and salicylates and also the sulfates of the metals mentioned.
  • the metal salt can be dissolved in a suitable one of the abovementioned solvents and metered in together with or separately from in the region of the column top.
  • the metal salt can be added at any point in the entire column, for example below the withdrawal of the acrylic acid and / or at the top of the column.
  • the metal salt is generally added in an amount of 0.5 to 30% by weight, based on the amount of phenothiazine added, preferably 1 to 20% by weight, particularly preferably 1 to 10% by weight.
  • the metal salt is added in a suitable solvent, preferably in water, acid water, aqueous acrylic acid or acrylic acid.
  • a suitable solvent preferably in water, acid water, aqueous acrylic acid or acrylic acid.
  • concentration in the solution is usually 0.01 to 0.5% by weight, preferably 0.05 to 0.1% by weight.
  • N-oxyl compounds i.e. those compounds which have at least one> N-0 group, e.g. the N-oxyl compounds mentioned at the beginning. This means that no N-oxyl compounds are detectable in the rectification column.
  • the reaction gas mixture which is cooled and contains acrylic acid is subjected to an absorption process with the high-boiling liquid.
  • This absorption process can take place both in cocurrent and in countercurrent, preferably in countercurrent.
  • Thormann, valve or sieve trays, with ordered or unordered packings and / or fillings, venturi washers or film washers, bottom columns are preferably used.
  • the absorption process is generally carried out at a top temperature of 15 to 50 ° C and a bottom temperature of 120 to 180 ° C. Since non-condensable constituents are removed overhead in the absorption process, they no longer enter the subsequent rectification process, so that they do not occur there or only to a small extent.
  • the liquid discharge of the absorption process containing acrylic acid is additionally subjected to a desorption process in which low boilers, such as low-boiling aldehydes, such as acetaldehyde, propionaldehyde or acrolein, acetone, acetic acid or propionic acid, are at least partially separated off.
  • low boilers such as low-boiling aldehydes, such as acetaldehyde, propionaldehyde or acrolein, acetone, acetic acid or propionic acid
  • the acrylic acid-containing solution is treated with a gas in cocurrent or countercurrent, preferably in countercurrent to desorb the low boilers.
  • a gas which is inert under the reaction conditions can be used as the gas.
  • Desorption can be carried out both in the presence and in the absence of oxygen (0). If they are carried out in the presence of oxygen, an oxygen-containing gas can be used, in which the oxygen may be mixed with an inert gas such as carbon dioxide (CO 2 ), nitrogen (N) or noble gases, such as helium or argon, or mixtures thereof is diluted. Nitrogen is preferably used for dilution.
  • the oxygen content of the oxygen-containing gas can be between 1 and 100 vol%, preferably between 2 and 80 vol%, particularly preferably between 5 and 50 vol% and in particular between 10 and 30 vol%.
  • air is used as the oxygen-containing gas.
  • any of the inert gases listed above can be used individually or in a mixture, but the process is preferably carried out in the presence of an oxygen-containing gas.
  • the apparatuses known per se are suitable for such a desorption process, as described, for example, in Ulimann's Encyclopedia of Industrial Chemistry (6 th ed, 1999 Electronic Release. Chapter: Absorption), for example columns with bell, Thorman, valve or sieve trays, with ordered or unordered packings and / or fillings, venturi washers, film washers, Stripping or flash devices, preferably column columns, stripping or flash devices are used.
  • a high-boiling substance sequence of the rectification process e.g. the high boilers, subjected to a reclassification.
  • the high boilers separated off in the rectification process are subjected to thermal and / or catalytic cleavage, as described, for example, in US Pat. No. 4,317,926, DE-C2 240 72 36 and US Pat. No. 3,086,046 and WO 00/53560, the oligomeric acrylic acids being known Be split into acrylic acid.
  • the cleavage products are advantageously returned to the rectification process.
  • Oligomeric acrylic acids are Michael adducts of acrylic acid, optionally several times, on themselves and not by free-radical polymerization resulting acrylic acid polymers.
  • Polymers are formed by an essentially radical polymerization with the formation of carbon-carbon linkages. As a rule, these products cannot be split back.
  • the products cleaved in such a cleavage can be introduced at any point in the process according to the invention, preferably into the rectification process, particularly preferably there together with the feed into the rectification column.
  • acidic catalysts include, for example, sulfuric acid, organic sulfonic acids, such as para-toluenesulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, xylenesulfonic acid or dodecylbenzenesulfonic acid, acidic ion exchangers or acidic metal oxides are suitable.
  • the temperature in the cleavage is generally 100 to 220 ° C, preferably 120 to 200 ° C, particularly preferably 140 to 180 ° C and in particular 150 to 180 ° C.
  • the removal of the low boilers can be supported by passing a gas stream (stripping) which is essentially inert under the reaction conditions, such as nitrogen, water vapor, but also an oxygen-containing gas, such as air.
  • a gas stream which is essentially inert under the reaction conditions, such as nitrogen, water vapor, but also an oxygen-containing gas, such as air.
  • the remaining residue can, for example, be partially discharged, distilled or subjected to a further cleavage.
  • a high-boiling substance in particular a run of the rectification process containing one of the abovementioned absorbents, is subjected to a distillation.
  • This process is particularly preferably subjected to a distillation as described in the simultaneous application with the German file number 100 64 642.5 and the title "Process for the Production of (Meth) Acrylic Acid” from BASF AG with the same filing date as the present application ,
  • the outflow is passed into a distillation apparatus and a low-boiler stream is removed from it in gaseous form, which stream may contain, in addition to acrylic acid and / or the absorbent present, further components such as, for example, diacrylic acid or stabilizer.
  • This low-boiling stream can, if appropriate after condensation and possibly further cooling, be fed to the work-up process at any point, for example the quench, absorption or rectification process, preferably the quench or absorption process, particularly preferably the absorption process.
  • Suitable distillation apparatus are all distillation apparatus known to the person skilled in the art, e.g. Circulation evaporator, thin film evaporator, falling film evaporator, wiper blade evaporator, if necessary, each with attached rectification columns and stripping columns.
  • a stripping current can also be applied, e.g. with nitrogen or an oxygen-containing gas, preferably with air.
  • the distillation apparatus can be operated at temperatures between 80 and 350 ° C, preferably between 100 and 280 ° C, particularly preferably between 120 and 200 ° C and in particular between 130 and 200 ° C and independently at pressures between 5 and 2000 hPa, preferably between 5 and 1200 hPa, particularly preferably between 20 and 500 hPa, very particularly preferably between 50 and 400 hPa and in particular between 50 and 300 hPa.
  • the stabilizers listed in Table 1 were dissolved in stabilizer-free acrylic acid (2 x distilled) and 20 ml of the solution were stored at 120 ° C. in air in a sealed 50 ml test vessel which was completely immersed in a heating bath. The time until the onset of polymerization (induction period) was determined.
  • MEHQ hydroquinone monomethyl ether
  • Example 2 A catalytic gas phase oxidation of propene or acrolein according to DE-A 43 02 991 produced a reaction mixture containing acrylic acid. 2.2 Nm3 / h of this reaction mixture were obtained in a gas cooler (quench) by injecting a coolant mixture which had been taken from the bottom of the rectification column (see below) from 58.8% by weight diphenyl ether, 21.2% by weight Diphenyl and 20 wt .-% o-dimethylphthalate cooled to 170 ° C.
  • a gas cooler quench
  • reaction gases cooled to 170 ° C.
  • 3 l / h was also composed of 58.8% by weight of diphenyl ether, 21.2% by weight of diphenyl and 20% by weight .-% o-Dimethylphthalat composite, applied to the column head at a temperature of 45 ° C, exposed to absorbent.
  • the outlet of the absorption column was indirectly heated to 105 ° C. in a heat exchanger and placed on the top of a desorption column which was designed as a bubble tray column with 20 trays.
  • the rectification column was operated at a bottom temperature of 160 ° C. and a bottom pressure of 130 mbar and a top pressure of 80 mbar. Between the fifteenth and sixteenth trays (counted from the evaporator), 1500 ml of liquid acrylic acid were removed continuously in a purity of 99.7% by weight per side draw, with 970 ml / h of the acrylic acid discharged again immediately below the side draw were fed.
  • the vaporous top product was condensed (600 ml / h), mixed with 100 ml / h of a solution of phenothiazine (5 g / 1) and hydroquinone monomethyl ether (2 g / 1) in acrylic acid and again up to 60 ml / h above the top of the column returned to the rectification column.
  • the operating time of the rectification column was at least 700 hours.
  • the evaporator was only slightly occupied.
  • Example 3 (comparison) The procedure was as in Example 2. The stabilization was carried out with 100 ml / h of a solution of 7 g / l phenothiazine in acrylic acid. The distillation had to be stopped after 400 hours of operation due to the formation of polymer in the rope and strong fouling in the stripping section of the column. The evaporator was very busy.
  • Example 2 The procedure was as in Example 2. The stabilization was carried out with 100 ml / h of a solution of 5 g / 1 phenothiazine, 1 g / 1 hydroquinone monomethyl ether and 1 g / 1 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl in acrylic acid.
  • Example 2 The procedure was as in Example 2. The stabilization was carried out with 100 ml / h of a solution of 6 g / 1 phenothiazine and 1 g / 1 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl in acrylic acid. The distillation had to be stopped after about 450 hours of operation due to polymer formation in the rectifying section and the formation of a black coating in the stripping section of the column. The evaporator was very busy.
  • Example 2 The procedure was as in Example 2. The stabilization was carried out with 100 ml / h of a solution of 5 g / 1 phenothiazine, 2 g / 1 hydroquinone monomethyl ether and 0.1 g / 1 manganese diacetate (2% based on phenothiazine) in acrylic acid.
  • Example 7 The procedure was as in Example 2, but 2000 ppm of acetone were added to the feed to the rectification column.

Abstract

The invention relates to a method for producing acrylic acid by heterogeneously catalysed gas phase partial oxidation of at least one C3 precursor with molecular oxygen. The product gas mixture containing acrylic acid is cooled and subsequently subjected to either fractionating condensation or a rectification process. Phenothiazine and at least one phenolic composition is introduced into the column head or in the vicinity of the column head the rectification or condensation column (n).

Description

Verfahren zur Herstellung von AcrylsaureProcess for the production of acrylic acid
Beschreibungdescription
Die Erfindung beschreibt ein Verfahren zur Herstellung von Acrylsaure, durch heterogen katalysierte Gasphasen-Partialoxidation mindestens eines C3-Vorläufers mit molekularem Sauerstoff wobei man das entstehende, Acrylsaure enthaltende Produktgasgemisch ab- kühlt und in der Folge entweder einer fraktionierenden Kondensation oder einem Rektifikationsprozeß unterwirft.The invention describes a process for the production of acrylic acid, by heterogeneously catalyzed gas phase partial oxidation of at least one C 3 precursor with molecular oxygen, the resulting product gas mixture containing acrylic acid being cooled and subsequently subjected to either a fractional condensation or a rectification process.
Acrylsaure ist wegen ihrer Säurefunktion und der sehr reaktiven Doppelbindung ein wertvolles Monomer, das z.B. bei der Herstel- lung von Acrylsäureestern, Superabsorbern oder Polymerdispersionen, die beispielsweise als Klebstoff oder Anstrichdispersionen Anwendung finden, eingesetzt wird.Acrylic acid is a valuable monomer because of its acid function and the very reactive double bond, e.g. is used in the production of acrylic acid esters, superabsorbents or polymer dispersions, which are used, for example, as adhesives or paint dispersions.
Unter anderem ist Acrylsaure durch heterogen katalysierte Gaspha- sen-Partialoxidation von C3-Vorläufern der Acrylsaure mit molekularem Sauerstoff an im festen Aggregatzustand befindlichen Katalysatoren bei erhöhter Temperatur erhältlich. Unter dem Begriff "C3-Vorläufer" von Acrylsaure werden dabei solche chemischen Verbindungen zusammengefaßt, die formal durch Reduktion von Acryl- säure erhältlich sind. Bekannte C3-Vorläufer von Acrylsaure sind z.B. Propan, Propen und Acrolein. Aber auch Verbindungen wie Pro- pionaldehyd oder Propionsäure sind zu den C3-Vorläufern zu zählen. Von ihnen ausgehend handelt es sich bei der heterogen katalysierte Gasphasen-Partialoxidation mit molekularem Sauerstoff we- nigstens teilweise um eine oxidative Dehydrierung.Among other things, acrylic acid is obtainable by heterogeneously catalyzed gas phase partial oxidation of C 3 precursors of acrylic acid with molecular oxygen on catalysts in the solid state at elevated temperature. The term “C 3 precursor” of acrylic acid summarizes those chemical compounds which are formally obtainable by reducing acrylic acid. Known C 3 precursors of acrylic acid are, for example, propane, propene and acrolein. Compounds such as propionaldehyde or propionic acid are also among the C 3 precursors. Based on these, the heterogeneously catalyzed gas phase partial oxidation with molecular oxygen is at least partially an oxidative dehydrogenation.
Bei den erfindungsrelevanten heterogen katalysierten Gasphasen- Partialoxidationen wird mindestens einer der genannten C3-Vorläu- fer der Acrylsaure, in der Regel mit inerten Gasen wie z.B. Stickstoff, Kohlenstoffmonoxid, Kohlenstoffdioxid und/oder Wasserdampf verdünnt, im Gemisch mit molekularem Sauerstoff bei erhöhten Temperaturen sowie gegebenenfalls erhöhtem Druck über übergangsmetallische Mischoxidkatalysatoren geleitet und oxidativ in ein Acrylsaure enthaltendes Produktgasgemisch umgewandelt.In the heterogeneously catalyzed gas phase partial oxidations relevant to the invention, at least one of the C 3 precursors of acrylic acid mentioned, as a rule diluted with inert gases such as nitrogen, carbon monoxide, carbon dioxide and / or water vapor, in a mixture with molecular oxygen at elevated temperatures and optionally increased pressure passed over transition metal mixed oxide catalysts and converted oxidatively into a product gas mixture containing acrylic acid.
Absorption von Acrylsaure in hochsiedenden Lösemitteln ist z.B. in der DE-OS 2 241 714 und DE-Al 43 08 087 beschrieben. DE-OS 2 241 714 beschreibt die Verwendung von Estern aliphati- scher oder aromatischer Mono- oder Dicarbonsäuren, die einen Schmelzpunkt von unter 30°C und einen Siedepunkt bei Normaldruck oberhalb von 160°C aufweisen. DE-Al 43 08 087 empfiehlt für die Abtrennung von Acrylsaure aus Reaktionsgasen der katalytischen Oxidation durch Gegenstromab- sorption die Verwendung eines hochsiedenden Gemisches aus 0,1 bis 25 Gew% ortho-Dimethylphthalat bezogen auf ein Gemisch, bestehend aus 70 bis 75 Gew% Diphenylether und 25 bis 30 Gew% Diphenyl.Absorption of acrylic acid in high-boiling solvents is described, for example, in DE-OS 2 241 714 and DE-Al 43 08 087. DE-OS 2 241 714 describes the use of esters of aliphatic or aromatic mono- or dicarboxylic acids which have a melting point below 30 ° C and a boiling point at normal pressure above 160 ° C. DE-Al 43 08 087 recommends the use of a high-boiling mixture of 0.1 to 25% by weight of ortho-dimethylphthalate based on a mixture consisting of 70 to 75% by weight of diphenyl ether for the separation of acrylic acid from reaction gases of catalytic oxidation by countercurrent absorption and 25 to 30% by weight diphenyl.
Die Verfahren bestehen im wesentlichen darin, daß die im Reaktionsgasgemisch enthaltene Acrylsaure und die kondensierbaren Nebenprodukte im Lösemittel beziehungsweise Lösemittelgemisch weit- gehend absorbiert werden, wofür bevorzugt eine Gegenstromabsorp- tion eingesetzt wird, anschließend die leichtsiedenden Komponenten, z.B. niedrigsiedende Aldehyde, wie Acetaldehyd, Propionalde- hyd oder Acrolein, Aceton, Essigsäure oder Propionsäure, teilweise gestrippt werden, wofür bevorzugt eine Gegenstromdesorption eingesetzt wird, und schließlich die Acrylsaure destillativ vom Lösemittel abgetrennt wird.The processes consist essentially in that the acrylic acid contained in the reaction gas mixture and the condensable by-products are largely absorbed in the solvent or solvent mixture, for which purpose countercurrent absorption is preferably used, followed by the low-boiling components, e.g. low-boiling aldehydes, such as acetaldehyde, propionaldehyde or acrolein, acetone, acetic acid or propionic acid, are partially stripped, for which purpose countercurrent desorption is preferably used, and finally the acrylic acid is separated off from the solvent by distillation.
In den obigen Anmeldungen wird als Stabilisator Phenothiazin empfohlen.Phenothiazine is recommended as a stabilizer in the above applications.
Nachteilig bei den beschriebenen Verfahren ist, daß es bei der Abtrennung der Acrylsaure zur Polymerisatbildung kommt, die die Laufzeit der Trennvorrichtungen, also Kolonnen und Verdampfer, durch Bildung von Ablagerungen stark einschränkt.A disadvantage of the processes described is that when the acrylic acid is separated off, polymer formation occurs, which severely limits the running time of the separation devices, that is to say columns and evaporators, by the formation of deposits.
Es ist allgemein bekannt, daß Acrylsaure sehr leicht, besonders unter Einwirkung von Hitze, polymerisiert . Diese spontane Polymerisation ist hochexotherm und extrem gefährlich (siehe z.B. Ulimann' s Encyclopedia of Industrial Chemistry, 6th ed, 1999 Elec- tronic Release, Kapitel: Acrylic Acid and Derivatives). So ist beispielsweise sogar beim Schmelzen von Acrylsaure (Schmelzpunkt 13.5 °C) eine lokale Überhitzung zu vermeiden.It is well known that acrylic acid polymerizes very easily, especially when exposed to heat. This spontaneous polymerization is highly exothermic and extremely dangerous (see e.g. Ulimann's Encyclopedia of Industrial Chemistry, 6th ed, 1999 Electronic Release, chapter: Acrylic Acid and Derivatives). For example, local overheating should be avoided even when melting acrylic acid (melting point 13.5 ° C).
Vor allem bei der Herstellung und der destillativen Reinigung ist Acrylsaure Temperaturen ausgesetzt, die leicht eine unerwünschte Polymerisation auslösen können. Diese Polymerisatbildung führt dann zu einer Belegung der Wärmetauscherflächen und Kolonnenböden, dem sogenannten Fouling, sowie zu einem Verstopfen von Leitungen, Pumpen, Ventilen etc. (EP-A 522 709, Seite 2, Zeilen 9-18; US 5 171 888, Spalte 1, Zeilen 19-38).Especially during production and cleaning by distillation, acrylic acid is exposed to temperatures that can easily trigger undesired polymerization. This polymer formation then leads to a covering of the heat exchanger surfaces and column trays, the so-called fouling, and to clogging of lines, pumps, valves, etc. (EP-A 522 709, page 2, lines 9-18; US 5 171 888, column 1 , Lines 19-38).
Die Folge sind teure Abstellungen und aufwendige Reinigungsopera- tionen, wie z.B. das in der DE-A 195 36 179 beschriebene Kochen mit basischen Lösungen, die anschließend aufwendig entsorgt wer- den müssen. In der EP-A 1 041 062 wird versucht, die Bildung von Polymerisat bei der destillativen Reinigung dadurch zu verhindern, daß das zu reinigende, acrylsäurehaltige Gemisch nicht mehr als 2000 ppm, bezogen auf Acrylsaure, an C - C4-Aldehyden und Aceton enthält.The result is expensive shutdowns and complex cleaning operations, such as cooking with basic solutions described in DE-A 195 36 179, which subsequently have to be disposed of in a complex manner. EP-A 1 041 062 attempts to prevent the formation of polymer during purification by distillation in that the mixture to be cleaned, acrylic acid-containing mixture, contains not more than 2000 ppm, based on acrylic acid, of C - C 4 aldehydes and acetone ,
Zur Reduzierung der Polymerisation wird allgemein die Verwendung verschiedener Inhibitoren beziehungsweise InhibitorSysteme vorgeschlagen.To reduce the polymerization, the use of various inhibitors or inhibitor systems is generally proposed.
Besonders empfohlen werden unter anderem N-Oxyl-Verbindungen (z.B. 4-Hydroxy-2 ,2,6, 6-tetramethyl-piperidin-N-oxyl , 4-Oxo-2 ,2,6, 6-tetramethyl-piperidin-N-oxyl , 4-Acetoxy-2 ,2,6, 6-te- tramethyl-piperidin-N-oxyl , 2,2,6, 6-tetramethyl-piperidin-N-oxyl , 4,4' ,4' '-Tris (2,2,6, 6-tetramethyl-piperidin-N-oxyl) -phosphit, 3-Oxo-2 , 2, 5, 5-tetramethyl-pyrrolidin-N-oxyl) , aromatische Amine (z.B. Derivate des Diphenylamins oder Phenothiazin), Phenole (z.B. Hydrochinon oder Hydrochinonmonomethylether) oder Gemische aus Nitroxylradikalen und Diheterosubstituierten Benzolderivaten mit mindestens einem übertragbaren Wasserstoffatom, aus N-Oxyl- Verbindungen, Phenolen und Phenothiazin oder aus Phenothiazin und sterisch gehinderten Aminen (siehe z.B. EP-A 620 206, EP-A 765 856 und dort zitierte Literatur) .Among others, N-oxyl compounds (e.g. 4-hydroxy-2, 2,6, 6-tetramethyl-piperidine-N-oxyl, 4-oxo-2, 2,6, 6-tetramethyl-piperidine-N- oxyl, 4-acetoxy-2, 2,6, 6-tetramethyl-piperidine-N-oxyl, 2,2,6, 6-tetramethyl-piperidine-N-oxyl, 4,4 ', 4' 'tris (2,2,6, 6-tetramethyl-piperidine-N-oxyl) phosphite, 3-oxo-2, 2, 5, 5-tetramethyl-pyrrolidine-N-oxyl), aromatic amines (e.g. derivatives of diphenylamine or phenothiazine ), Phenols (e.g. hydroquinone or hydroquinone monomethyl ether) or mixtures of nitroxyl radicals and diheterosubstituted benzene derivatives with at least one transferable hydrogen atom, of N-oxyl compounds, phenols and phenothiazine or of phenothiazine and sterically hindered amines (see for example EP-A 620 206, EP- A 765 856 and literature cited there).
Gesucht wurde ein einfaches und wirtschaftliches Verfahren zur Herstellung der Acrylsaure mit verringerter Polymerisationsproblematik.A simple and economical process for the production of acrylic acid with reduced polymerization problems was sought.
Die Aufgabe wurde gelöst durch ein Verfahren zur Herstellung von Acrylsaure, durch heterogen katalysierte Gasphasen-Partialoxida- tion mindestens eines C3-Vorläufers mit molekularem Sauerstoff, wobei man das entstehende, Acrylsaure enthaltende Produktgasgemisch abkühlt in der Folge entweder einer fraktionierenden Kondensation oder einem Rektifikationsprozeß unterwirft, wenn man im Kolonnenkopf oder im Bereich des Kolonnenkopfes der Rektifika- tions- beziehungsweise Kondensationskolonne (n) Phenothiazin und mindestens eine phenolische Verbindung einbringtThe object was achieved by a process for the production of acrylic acid, by heterogeneously catalyzed gas phase partial oxidation of at least one C 3 precursor with molecular oxygen, the resulting product gas mixture containing acrylic acid being subsequently cooled, either subjected to a fractional condensation or a rectification process , if phenothiazine and at least one phenolic compound are introduced into the column head or in the area of the column head of the rectification or condensation column (s)
Stabilitätsversuche (s. Bsp. 1, Tabelle 1) konnten die besondere Wirksamkeit der empfohlenen bekannten Gemische aus N-Oxyl-Verbin- düngen, Phenothiazin und/oder Phenolen im Falle der Stabilisierung von reiner Acrylsaure bestätigen.Stability tests (see Example 1, Table 1) were able to confirm the particular effectiveness of the recommended known mixtures of N-oxyl compounds, phenothiazine and / or phenols in the case of the stabilization of pure acrylic acid.
Überraschenderweise wurden jedoch andere Ergebnisse bei der kontinuierlich betriebenen Aufreinigung der Acrylsaure aus einem hochsiedenden Lösungsmittelgemisch erzielt (s. Bsp. 2). Das bei den stationären Stabilitätstests (Bsp. 1) nur mäßig wirksame Stabilisatorgemisch aus Hydrochinonmonomethylether und Phenothiazin lieferte dabei die besten Ergebnisse. Dies ist umso überraschender, da allgemein bekannt ist, Hydrochinonmonomethylether wäre nur bei Raumtemperatur und nur in Gegenwart von Sauerstoff als Polymerisationsinhibitor wirksam (Journal of Polymer Science: Po- lymer Chemistry Edition, Vol. 23, 1505-1515 (1985)).Surprisingly, however, other results were obtained in the continuous purification of the acrylic acid from a high-boiling solvent mixture (see Example 2). The stabilizer mixture of hydroquinone monomethyl ether and phenothiazine, which is only moderately effective in the stationary stability tests (Example 1) delivered the best results. This is all the more surprising since it is generally known that hydroquinone monomethyl ether would only be effective as a polymerization inhibitor at room temperature and only in the presence of oxygen (Journal of Polymer Science: Polymer Chemistry Edition, Vol. 23, 1505-1515 (1985)).
Demgegenüber wird die Wirkung von 4-Hydroxy-2 , 2 , 6, 6-tetramethyl- piperidin-N-oxyl im stationären Stabilitätstest im kontinuierlichen Betrieb nicht erreicht (siehe Beispiel 4) .In contrast, the effect of 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl is not achieved in the steady-state stability test in continuous operation (see Example 4).
Diese Wirkung wird noch verstärkt durch eine optionale Zugabe mindestens eines Metallsalzes.This effect is reinforced by the optional addition of at least one metal salt.
Das erfindungsgemäße Verfahren wird im allgemeinen wie folgt durchgeführt :The process according to the invention is generally carried out as follows:
Das Produktgasgemisch ist in an sich bekannter Weise durch eine heterogen katalysierte Gasphasenpartialoxidation von mindestens einem C3-Vorläufer der Acrylsaure mit molekularem Sauerstoff bei erhöhter Temperatur erhältlich.The product gas mixture is obtainable in a manner known per se by heterogeneously catalyzed gas phase partial oxidation of at least one C 3 precursor of acrylic acid with molecular oxygen at elevated temperature.
Dazu wird bei der Herstellung der Acrylsaure in der Regel das Ausgangsgas mit unter den gewählten Reaktionsbedingungen inerten Gasen wie z.B. Stickstoff (N ), C0 , gesättigten Cι-C6-Kohlenwas- serstoffen und/oder Wasserdampf verdünnt und im Gemisch mit molekularem Sauerstoff (02) oder einem sauerstoffhaltigen Gas bei erhöhten Temperaturen (üblicherweise 200 bis 450 °C) sowie gegebenenfalls erhöhtem Druck über feste, übergangsmetallische (z.B. Mo und V beziehungsweise Mo, W, Bi und Fe enthaltende) Mischoxidka- talysatoren geleitet und oxidativ in die Acrylsaure umgewandelt. Diese Umsetzungen können mehrstufig oder einstufig durchgeführt werden.For this purpose, the starting gas is generally diluted with gases which are inert under the selected reaction conditions, such as nitrogen (N), C0, saturated C 1 -C 6 -hydrocarbons and / or water vapor, and mixed with molecular oxygen (0 2 ) or an oxygen-containing gas at elevated temperatures (usually 200 to 450 ° C.) and, if appropriate, increased pressure, passed over solid, transition-metallic (containing Mo and V or Mo, W, Bi and Fe) mixed oxide catalysts and converted oxidatively into the acrylic acid , These implementations can be carried out in several stages or in one stage.
Bevorzugt wird das erfindungsgemäß eingesetzte Produktgasgemisch aus der Partialoxidation von Propan oder Propen und/oder Acrolein erhalten.The product gas mixture used according to the invention is preferably obtained from the partial oxidation of propane or propene and / or acrolein.
Das heiße Produktgasgemisch weist in der Regel eine Temperatur zwischen 200 und 400 °C auf und kann in an sich bekannter Weise auf eine Temperatur zwischen 100 und 180 °C abgekühlt werden. Die Kühlung kann dabei teilweise oder vollständig indirekt, z.B. mit Rohrbündel- oder Plattenwärmetauschern mit einem geeigneten Kühlmedium, erfolgen, hauptsächlich erfolgt sie jedoch in der Regel durch direkte Kühlung mit einer hochsiedenden Flüssigkeit in einem Quench, dem gegebenenfalls ein Vorquench vorgeschaltet sein kann. Die Temperatur der Quenchflüssigkeit beträgt normalerweise 70 bis 200°C, häufig 100 bis 150°C.The hot product gas mixture generally has a temperature between 200 and 400 ° C. and can be cooled to a temperature between 100 and 180 ° C. in a manner known per se. The cooling can take place partially or completely indirectly, for example with tube bundle or plate heat exchangers with a suitable cooling medium, but mainly takes place as a rule by direct cooling with a high-boiling liquid in a quench, which may be preceded by a pre-quench. The temperature of the quench liquid is usually 70 to 200 ° C, often 100 to 150 ° C.
Geeignete Kühlmedien in Wärmetauschern für die indirekte Kühlung oder für die Rückkühlung der Quenchflüssigkeit sind Luft bei entsprechenden Luftkühlern und Kühlflüssigkeiten, insbesondere Wasser, bei den anderen Kühlvorrichtungen.Suitable cooling media in heat exchangers for indirect cooling or for recooling the quench liquid are air in the case of corresponding air coolers and cooling liquids, in particular water, in the other cooling devices.
Als Quenchvorrichtung können alle im Stand der Technik für diesen Zweck bekannten Vorrichtungen (z.B. Sprühkühler, Venturiwäscher, Blasensäulen oder sonstige Apparate mit berieselten Oberflächen) eingesetzt werden, wobei vorzugsweise Venturi-Waseher oder Sprühkühler verwendet werden.All devices known in the prior art for this purpose (e.g. spray coolers, venturi washers, bubble columns or other apparatuses with sprinkled surfaces) can be used as the quench device, preferably venturi washers or spray coolers being used.
Als hochsiedende Flüssigkeit kann dabei zumindest teilweise ein hochsiedende Stoffe enthaltender Ablauf des Rektifikationsprozesses, gegebenenfalls nach Destillation, (siehe unten) verwendet werden oder ein an sich bekanntes Absorptionsmittel zur Abtrennung von Acrylsaure aus dem Produktgasgemisch. Bei Letzterem kann es sich beispielsweise um Tri- (n-Butyl) -Phosphat handeln (US 4 219 389) oder um ein Gemisch aus Diphenylether und Biphenyl (siehe z.B. DE-PS 21 36 396), beispielsweise im Gewichtsverhältnis von 10:90 bis 90:10, oder um ein solches Gemisch, dem zusätzlich 0,1 bis 25 Gew% mindestens eines ortho-Phthalsäureesters, wie z.B. ortho-Phthalsäuredimethylester, ortho-Phthalsäurediethy- lester oder ortho-Phthalsäuredibutylester, zugesetzt sind, oder um Wasser.A high-boiling liquid can at least partially be a rectification process sequence, optionally after distillation, containing high-boiling substances (see below) or an absorbent known per se for separating acrylic acid from the product gas mixture. The latter can be, for example, tri (n-butyl) phosphate (US Pat. No. 4,219,389) or a mixture of diphenyl ether and biphenyl (see, for example, DE-PS 21 36 396), for example in a weight ratio of 10:90 to 90:10, or such a mixture, which additionally 0.1 to 25% by weight of at least one ortho-phthalic acid ester, such as ortho-phthalic acid dimethyl ester, ortho-phthalic acid diethyl ester or ortho-phthalic acid dibutyl ester, or water.
Hochsiedend bedeutet hier höher als Acrylsaure siedend, also hö- her als 141 °C bei Normaldruck siedend, bevorzugt mindestens bei 151°C bei Normaldruck siedend.High-boiling here means boiling higher than acrylic acid, ie boiling higher than 141 ° C under normal pressure, preferably boiling at least at 151 ° C under normal pressure.
Die so erhaltene, Acrylsäure-enthaltende Flüssigkeit wird rektifiziert, also einem Rektifikationsprozeß zugeführt, der aus min- destens einer Rektifikationskolonne besteht.The acrylic acid-containing liquid thus obtained is rectified, that is to say fed to a rectification process which consists of at least one rectification column.
In diesem Rektifikationsprozeß wird die in der Flüssigkeit enthaltene Acrylsaure als Mittelsieder im wesentlichen von höherund niedrigersiedenden Komponenten abgetrennt.In this rectification process, the acrylic acid contained in the liquid is essentially separated as a medium boiler from higher and lower boiling components.
Die höhersiedenden Komponenten (Schwersieder) umfassen im wesentlichen die oben angeführte hochsiedende Flüssigkeit, sowie die Komponenten, die bei Normaldruck einen Siedepunkt oberhalb der Mittelsieder, also beispielsweise oberhalb von 151 °C und insbe- sondere oberhalb von 141 °C, aufweisen. Dies können beispielsweise polymere Acrylsaure, Michael-Additionsprodukte der Acrylsaure, wie Di-, Tri- und Tetraacrylsäure usw., höhere Mono- und Dicar- bonsäuren sowie deren Anhydride und Stabilisatoren sein, sowie selbstverständlich auch unvollständig abgetrennte, niedriger siedende Komponenten.The higher-boiling components (high boilers) essentially comprise the high-boiling liquid mentioned above, as well as the components which have a boiling point above the medium boilers at normal pressure, for example above 151 ° C. and in particular above 141 ° C. These can include polymeric acrylic acid, Michael addition products of acrylic acid, such as di-, tri- and tetraacrylic acid, etc., higher mono- and dicar- be bonic acids and their anhydrides and stabilizers, and of course also incompletely separated, lower-boiling components.
Die niedrigersiedenden Komponenten (Leichtsiederfraktion, Sauerwasser) umfassen im wesentlichen diejenigen Komponenten, die bei Normaldruck einen Siedepunkt unterhalb der Mittelsiederfraktion, beispielsweise im Temperaturintervall von etwa 30 bis 120 °C, insbesondere 30 bis 131 °C aufweisen. Daneben liegen selbstverständ- lieh auch unvollständig abgetrennte Komponenten außerhalb dieses Temperaturintervalls vor und solche, die mit dem enthaltenen Wasser ausgewaschen wurden. Diese Leichtsiederfraktion kann teilweise auf den Kopf der Kolonne zurückgeführt und teilweise, aber auch vollständig ausgeschleust werden. Sie besteht in der Regel ausThe lower-boiling components (low boiler fraction, acid water) essentially comprise those components which have a boiling point below the medium boiler fraction at normal pressure, for example in the temperature interval from about 30 to 120 ° C., in particular 30 to 131 ° C. In addition, there are of course also incompletely separated components outside of this temperature interval and those that have been washed out with the water they contain. This low boiler fraction can partly be returned to the top of the column and partly but also completely removed. It usually consists of
80 - 95 Gew.% Wasser80-95% by weight water
5 - 15 Gew.% Essigsäure5 - 15% by weight acetic acid
1 - 5 Gew.% Acrylsaure 0,05 - 1 Gew.% Aldehyde (Acrolein, Formaldehyd)1 - 5% by weight acrylic acid 0.05 - 1% by weight aldehydes (acrolein, formaldehyde)
Die nicht kondensierbaren Bestandteile des Produktgasgemisches, also solche mit einem Siedepunkt bei Normaldruck unter ca. 30 °C und beispielsweise solche, die durch die gasförmigen Bestandteile ausgestrippt werden, beispielsweise Stickstoff, Sauerstoff, Propan, Propen, beziehungsweise Kohlenmonoxid, Kohlendioxid etc., können beispielsweise am Kopf der Kolonne oder über ein Quenchsy- stem ausgeschleust oder, gegebenenfalls nach einer Reinigung, zumindest zum Teil als Kreisgas in die Gasphasenoxidation rückge- führt werden, wenn sie nicht bereits im wesentlichen im Absorptionsschritt (siehe oben) entfernt wurden.The non-condensable constituents of the product gas mixture, i.e. those with a boiling point at normal pressure below approx. 30 ° C. and, for example, those which are stripped out by the gaseous constituents, for example nitrogen, oxygen, propane, propene or carbon monoxide, carbon dioxide etc. discharged at the top of the column or via a quench system or, if appropriate after purification, at least partly recycled as cycle gas into the gas phase oxidation if they have not already been substantially removed in the absorption step (see above).
Wird die Acrylsaure gasförmig der Rektifikationskolonne zugeführt, so liegt die Temperatur im Sumpf der Kolonne in typischer Weise bei 90 bis 130°C, die Kopf emperatur hängt von der Art der Ausschleusung der Leichtsieder ab. Erfolgt diese Abtrennung über einen Seitenabzug so beträgt sie normalerweise 15 bis 70 °C, häufig 20 bis 50°C. Erfolgt die Abtrennung über einen Quench, der z.B. mit Sauerwasser betrieben werden kann, so beträgt sie in der Regel 50 - 90 °C, vorzugsweise 60 - 80 °C.If the acrylic acid is fed in gaseous form to the rectification column, the temperature in the bottom of the column is typically 90 to 130 ° C., the top temperature depends on the type of discharge of the low boilers. If this separation takes place via a side draw, it is normally 15 to 70 ° C, often 20 to 50 ° C. If the separation takes place via a quench, e.g. can be operated with acid water, it is usually 50 - 90 ° C, preferably 60 - 80 ° C.
Die Entnahmetemperatur der Rohacrylsäure im Seitenabzug liegt meist bei 80 bis 110°C.The withdrawal temperature of the crude acrylic acid in the side hood is usually 80 to 110 ° C.
Die Rückführtemperatur des Sauerwassers in die Kolonne liegt in der Regel bei 25 bis 35°C. Die Rektifikationskolonne, die in diesem Fall als fraktionierende Kondensation betrieben wird, wie z.B. in der deutschen Anmeldung mit dem Aktenzeichen 100 53 086.9 oder der DE-A 197 40 253 beschrieben, wird beispielsweise bei einem Druck zwischen 500 und 1200 hPa betrieben, bevorzugt zwischen 800 und 1100 hPa und besonders bevorzugt bei Atmosphärendruck.The return temperature of the acid water to the column is usually 25 to 35 ° C. The rectification column, which in this case is operated as fractional condensation, as described for example in the German application with the file number 100 53 086.9 or DE-A 197 40 253, is operated, for example, at a pressure between 500 and 1200 hPa, preferably between 800 and 1100 hPa and particularly preferably at atmospheric pressure.
Wird die Acrylsaure dagegen in einem Absorptionsmittel gelöst der Rektifikationskolonne zugeführt, so erfolgt die destillative Iso- lierung der Acrylsaure vorzugsweise folgendermaßen:If, on the other hand, the acrylic acid dissolved in an absorbent is fed to the rectification column, the isolation of the acrylic acid by distillation is preferably carried out as follows:
In dem Zulauf ist Acrylsaure in der Regel zu 5 bis 30 Gew% enthalten, bevorzugt zu 10 bis 20 Gew% .Acrylic acid is generally contained in the feed to 5 to 30% by weight, preferably to 10 to 20% by weight.
Grundsätzlich eignen sich alle Kolonnen mit trennwirksamen Einbauten als Rektifikationskolonnen. Als Kolonneneinbauten kommen alle gängigen Einbauten in Betracht, insbesondere Böden, Packungen und/oder Füllkörper. Von den Böden sind Glockenböden, Siebböden, Ventilböden, Thormannböden und/oder Dual-Flow-Böden oder be- liebige Kombinationen davon bevorzugt.Basically, all columns with separating internals are suitable as rectification columns. Column internals are all common internals, in particular trays, packings and / or packing. Of the trays, bubble trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays or any combination thereof are preferred.
Vorzugsweise erfolgt die Rektifikation in einer Bodenkolonne mit beispielsweise 25 bis 50 Böden, bevorzugt mit 30 bis 40 Böden, mit außenliegenden UmlaufVerdampfern, wobei der Zulauf in der Re- gel im unteren Viertel der Kolonne liegt.The rectification is preferably carried out in a tray column with, for example, 25 to 50 trays, preferably with 30 to 40 trays, with external circulation evaporators, the feed generally being in the lower quarter of the column.
Die Acryls ure wird flüssig über einen Seitenabzug in der oberen Hälfte der Kolonne ausgeschleust. Die noch vorhandenen Leichtsie- der (z.B. Wasser, Essigsäure) werden gasförmig über den Kopf der Kolonne abgetrennt und kondensiert, wobei ein Teil des Kondensats als Rücklauf wieder in die Kolonne zurückgeführt werden kann.The acrylic acid is discharged in liquid form via a side draw in the upper half of the column. The low boilers still present (e.g. water, acetic acid) are separated in gaseous form via the top of the column and condensed, whereby part of the condensate can be returned to the column as reflux.
Die destillative Abtrennung der Acrylsaure erfolgt vorzugsweise bei vermindertem Druck. Es wird zweckmäßigerweise bei einem Kopf- druck von höchstens 500 hPa, üblicherweise bei 10 - 200 hPa, vorzugsweise bei 10 - 100 hPa gearbeitet. In entsprechender Weise betragen die zugehörigen Temperaturen im Sumpf der Kolonne in der Regel 100 - 230 °C und am Kolonnenkopf 30 - 80 °C.The acrylic acid is preferably removed by distillation under reduced pressure. It is expedient to work at a head pressure of at most 500 hPa, usually at 10-200 hPa, preferably at 10-100 hPa. Correspondingly, the associated temperatures in the bottom of the column are generally 100-230 ° C and 30-80 ° C at the top of the column.
Um den Trennprozeß zu unterstützen und zur Stabilisierung kann die Rektifikationskolonne mit einem sauerstoffhaltigen Gas, bevorzugt mit Luft, durchströmt werden.To support the separation process and for stabilization, an oxygen-containing gas, preferably air, can be flowed through the rectification column.
Die als Mittelsiederfraktion entnommene Rohacrylsäure, die im we- sentlichen die Komponenten umfaßt, die bei Normaldruck einen Siedepunkt im Temperaturintervall beispielsweise von 120 bis 160 °C, insbesondere im Bereich von +/- 10 °C um den des Wertproduktes Acrylsaure, d.h. etwa 131 bis 151 °C, aufweisen, wird entweder direkt verestert oder zum Zwecke der Weiterreinigung einer Kristallisation zugeführt, so daß Kolonne und Kristallisation gemeinsam den Reinigungsprozeß darstellen, wobei in diesem Falle die anfal- lende Mutterlauge vorteilhaft wieder der Kolonne als Rücklauf zugeführt wird, bevorzugt unterhalb des Abzugs der Mittelsieder- fraktion.The crude acrylic acid taken off as a medium boiler fraction, which essentially comprises the components which, at normal pressure, have a boiling point in the temperature interval, for example from 120 to 160 ° C., in particular in the range of +/- 10 ° C. around that of the product of value Acrylic acid, ie about 131 to 151 ° C., is either esterified directly or fed to a crystallization for the purpose of further purification, so that column and crystallization together represent the purification process, in which case the mother liquor obtained advantageously returns to the column as reflux is fed, preferably below the deduction of the medium boiler fraction.
Solche als Mittelsieder entnommene Rohacrylsäure enthält neben Acrylsaure in der Regel nochSuch crude acrylic acid, taken off as a middle boiler, usually also contains acrylic acid
0,1 bis 2 Gew. -% Niedere Carbonsäuren, zum Beispiel0.1 to 2% by weight of lower carboxylic acids, for example
Essigsäureacetic acid
0,5 bis 5 Gew.-% Wasser 0,05 bis 1 Gew.-% niedermolekulare CarbonylVerbindungen, wie z.B. Furfural, Formaldehyd, Acrolein, Acetaldehyd, Propionalde- hyd, Aceton0.5 to 5% by weight of water 0.05 to 1% by weight of low molecular weight carbonyl compounds, such as e.g. Furfural, formaldehyde, acrolein, acetaldehyde, propionaldehyde, acetone
0,01 bis 1 Gew.-% Maleinsäure und/oder deren Anhydrid0.01 to 1 wt .-% maleic acid and / or its anhydride
1 bis 500 Gew.ppm Stabilisator, jeweils bezogen auf das Gewicht der Rohacrylsäure.1 to 500 ppm by weight of stabilizer, in each case based on the weight of the crude acrylic acid.
Die Kristallisation wird in der Regel ohne Zusatz eines Lösungsmittels, insbesondere ohne Zusatz eines organischen Lösungsmit- tels durchgeführt. Das zu verwendende Kristallisationsverfahren unterliegt keiner Beschränkung. Die Kristallisation kann kontinuierlich oder diskontinuierlich, einstufig oder mehrstufig bis zu nahezu beliebigen Reinheitsgraden durchgeführt werden. Bei Bedarf kann der kristallisativ zu reinigenden Rohacrylsäure vor einer Kristallisation Wasser zugesetzt werden (bezogen auf die enthaltene Menge an Acrylsaure bis zu 10 Gew.-% oder mehr, vorzugsweise bis zu 5 Gew.-%). Ein solcher Zusatz erleichtert die Abtrennung von in der Rohacrylsäure als Nebenprodukt enthaltener niederer Carbonsäure, wie z.B. Essigsäure, da diese im Beisein von Wasser in geringerem Ausmaß in die Acrylsäurekristalle eingebaut wird. Außerdem mindert ein Beisein von Wasser die Verkrustungsneigung im Kristaller.The crystallization is generally carried out without the addition of a solvent, in particular without the addition of an organic solvent. The crystallization method to be used is not limited. The crystallization can be carried out continuously or discontinuously, in one or more stages up to almost any degree of purity. If necessary, water can be added to the crude acrylic acid to be crystallized before crystallization (based on the amount of acrylic acid contained up to 10% by weight or more, preferably up to 5% by weight). Such an addition facilitates the separation of lower carboxylic acid contained as a by-product in the crude acrylic acid, e.g. Acetic acid, because it is incorporated to a lesser extent in the acrylic acid crystals in the presence of water. In addition, the presence of water reduces the tendency to crust in the crystallizer.
Die so erhaltene Rein-Acrylsäure enthält in der Regel deutlich weniger der oben für die Roh-Acrylsaure angegebenen Verunreinigungen, beispielsweise bis zu insgesamt 2000 Gew.ppm.The pure acrylic acid obtained in this way generally contains significantly less of the impurities specified above for the crude acrylic acid, for example up to a total of 2000 ppm by weight.
Die Stabilisierung der Kolonne erfolgt durch Zugabe einer Stabilisatorlösung in einem geeigneten Lösemittel im Bereich des Ko- lonnenkopfes Dies umfaßt hier die Zugabe der Stabilisatorlösung in den genannten Rücklauf oder direkt in die Kolonne. Dabei wird der mit Stabilisatorlösung versehene Strom oder die direkte Einspeisung der Stabilisatorlösung in die Kolonne im Bereich des Kolonnenkopfes zugeführt, was beispielsweise den Bereich des oberen Viertels der Trennstufen, bevorzugt die oberen 20% und besonders bevorzugt die oberen 15% umfaßt. Weiterhin kann der Bereich des Kolonne - kopfes auch eine Kühlvorrichtung, z.B. Quench oder Kondensator, zur Abkühlung der Leichtsieder bedeuten, in die ebenfalls Stabi- lisatorlösung eindosiert werden kann, sowie selbstverständlich auch der Kolonnenkopf selbst.The column is stabilized by adding a stabilizer solution in a suitable solvent in the area of the column top This includes the addition of the stabilizer solution into the reflux mentioned or directly into the column. The stream provided with stabilizer solution or the direct feed of the stabilizer solution into the column in the area of the column head is fed, which for example comprises the area of the upper quarter of the separation stages, preferably the upper 20% and particularly preferably the upper 15%. Furthermore, the area of the column head can also mean a cooling device, for example quench or condenser, for cooling the low boilers, into which stabilizer solution can likewise be metered in, and of course also the column head itself.
Die Zugabe der Stabilisatorlösung kann an einer Stelle oder an mehreren Stellen im Bereich des Kolonnenkopfes erfolgen, wobei die Zusammensetzung der an den verschiedenen Stellen der Kolonne zugeführten Stabilisatorlösung gleich oder verschieden sein kann.The stabilizer solution can be added at one point or at several points in the area of the column top, it being possible for the composition of the stabilizer solution supplied at the various points in the column to be the same or different.
Als Stabilisatoren werden dabei solche Verbindungen verstanden, die die Polymerisation von Acrylsaure oder Methacrylsäure verzö- gern und/oder hemmen. Dies können beispielsweise Inhibitoren sein.Stabilizers are understood to be those compounds which delay and / or inhibit the polymerization of acrylic acid or methacrylic acid. These can be inhibitors, for example.
Die Stabilisierung erfolgt erfindungsgemäß mit Phenothiazin und mindestens einer phenolischen Komponente.The stabilization takes place according to the invention with phenothiazine and at least one phenolic component.
Bei der phenolischen Komponente kann es sich z.B. um ein Alkyl- phenol, beispielsweise 2-tert.-Butyl-4-methylphenol, 6-tert.-Bu- tyl-2 , 4-dimethyl-phenol, 2, 6-Di-tert. -Butyl-4-methylphenol, 2-Me- thylhydrochinon oder 2, 2' -Methylen-bis- (6-tert . -butyl-4-methyl- phenol, um ein Hydroxyphenol, beispielsweise Hydrochinon, Brenz - catechin oder Benzochinon, um ein Aminophenol, wie z.B. para-Ami- nophenol, um ein Nitrosophenol, wie z.B. para-Nitrosophenol, oder um ein Methoxyphenol, beispielsweise 4-Methoxyphenol, Mono- oder Di-tert .-Butyl-4-methoxyphenol handeln. Vorzugsweise wird 4-Me- thoxyphenol (Hydrochinonmonomethylether) eingesetzt.The phenolic component can e.g. an alkyl phenol, for example 2-tert-butyl-4-methylphenol, 6-tert-butyl-2, 4-dimethyl-phenol, 2, 6-di-tert. -Butyl-4-methylphenol, 2-methylhydroquinone or 2, 2 '-methylene-bis- (6-tert-butyl-4-methylphenol) to a hydroxyphenol, for example hydroquinone, pyrocatechol or benzoquinone an aminophenol, such as para-aminophenol, a nitrosophenol, such as para-nitrosophenol, or a methoxyphenol, for example 4-methoxyphenol, mono- or di-tert-butyl-4-methoxyphenol. Methoxyphenol (hydroquinone monomethyl ether) used.
Als phenolische Komponenten können beispielsweise weiterhin auch folgende Verbindungen eingesetzt werden:The following compounds, for example, can also be used as phenolic components:
o-, m- oder p-Kresol (Methylphenol), 2, 5-Di-tert.-Butylhydrochi- non, 2, 5-Di-tert.-Amylhydroch.inon, 2-tert . -Butylphenol, 4-tert.- Butylphenol, 2, 4-di-tert. -Butylphenol, 2-Methyl-4-tert. -Butylphenol, 4-tert.-Butyl-2,6-dimethylphenol, 2- oder 4- (1' -Phenyl- eth-l'-yl) -phenol, 2- (1' -Methylcyclohex-1' -yl) -4, 6-dimethyl- phenol, 2-tert-Butyl-β-methylphenol, 2, 4, 6-Tris-tert-Butylphenol, 2,6-Di-tert-butyl-p-kresol, 2, 6-Di-tert. -butylphenol, 2,4-Di- tert. -butylphenol, 4-tert .Butylphenol, Nonylphenol [11066-49-2] , Octylphenol [140-66-9] , 2, 6-Dimethylphenol, Bisphenol A, Bisphenol F, Bisphenol B, Bisphenol S, Bisphenol C, 3,3', 5, 5'-Tetra- bromo-bisphenol A, 3 , 5-Di-tert-butyl-4-hydroxyanisol, Koresin® der BASF AG, 3 , 5-Di-tert-butyl-4-hydroxybenzoesäuremethylester, 4-tert-Butylbrenzcatechin, 2-Hydroxybenzylalkohol,o-, m- or p-cresol (methylphenol), 2, 5-di-tert-butylhydroquinone, 2, 5-di-tert-amylhydroquinone, 2-tert. -Butylphenol, 4-tert-butylphenol, 2, 4-di-tert. -Butylphenol, 2-methyl-4-tert. -Butylphenol, 4-tert-butyl-2,6-dimethylphenol, 2- or 4- (1 '-phenyl-eth-l'-yl) -phenol, 2- (1' -methylcyclohex-1 '-yl) -4, 6-dimethylphenol, 2-tert-butyl-β-methylphenol, 2, 4, 6-tris-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, 2, 6-di tert. -butylphenol, 2,4-di- tert. -butylphenol, 4-tert. butylphenol, nonylphenol [11066-49-2], Octylphenol [140-66-9], 2, 6-dimethylphenol, bisphenol A, bisphenol F, bisphenol B, bisphenol S, bisphenol C, 3,3 ', 5, 5'-tetrabromo-bisphenol A, 3, 5 -Di-tert-butyl-4-hydroxyanisole, Koresin® from BASF AG, 3, 5-di-tert-butyl-4-hydroxybenzoic acid methyl ester, 4-tert-butylpyrocatechol, 2-hydroxybenzyl alcohol,
2-Methoxy-4-methylphenol, 2, 3 , 6-Trimethylphenol, 2,4,5-Tri- methylphenol, 2 , 4, 6-Trimethylphenol, 2-Isopropylphenol, 4-Iso- propylphenol, 6-Isopropyl-m-Kresol, 4-tert-Butylbrenzcatechin, n- Octadecyl-ß- (3 , 5-di-tert-butyl-4-hydroxyphenyl)propionat , 1,1, 3-Tris- (2-methyl-4-hydroxy-5-tert-butylphenyl)butan, 1,3, 5-Trimethyl-2 , 4 , 6-tris- (3 , 5-di-tert-butyl4-hydroxy- benzyl)benzol, 1,3,5, -Tris- (3 , 5-di-tert-butyl-4-hydroxy- benzyl) isocyanurat, 1,3,5, -Tris- (3, 5-di-tert-butyl-4-hydroxy- phenyl ) -propionyloxyethyl-isocyanurat, 1,3, 5-Tris-(2, 6-dimethyl-3-hydroxy-4-tert-butylbenzyl) -isocyanurat, Pentaerythrit-tetrakis- [ß- (3 , 5, -di-tert-butyl-4-hydroxy- phenyl) -propionat] , 2, 6-Di-tert. -butyl-4-dimethylaminomethyl-phe- nol, 6-seJ.-Butyl-2, 4-dinitrophenol, Irganox® 245, 259, 565, 1141, 1192, 1222, 1330, 1425 und MD1024 der Firma Ciba Speziali- tätenchemie, 3-(3 ' , 5 '-Di-tert.-butyl-4 ' -hydroxyphenyl)propionsäu- reoctadecylester, 3- (3 ' , 5 '-Di-tert.-butyl-4 '-hydroxyphenyl)pro- pionsäurehexadecylester, 3- (3 ' , 5 '-Di-tert. -butyl-4 '-hydroxyphenyl )propionsäureoctylester, 3-Thia-l, 5-pentandiol- bis- [ (3 ' , 5 '-di-tert. -butyl-4 '-hydroxyphenyl)propionat] , 4, 8-Dioxa-l, 11-undecandiol-bis- [ (3 ' , 5 '-di-tert. -butyl-4 '-hydroxyphenyl ) propionat] , 1, 7-Heptandiamin-bis [3- (3 ' , 5 '-di-tert. -butyl-4 '-hydroxyphenyl )propionsäureamid] , 3- (3' , 5 '-di-tert. -Butyl-4 ' -hydroxyphenyl) ropionsäurehydrazid, 3- (3 ' , 5 '-Dimethyl-4' -hydroxyphenyl)propionsäurehydrazid, Bis (3-tert.-Butyl-5-ethyl-2-hydroxy-phen-l-yl)methan, Bis (3 , 5-di- tert. -Butyl-4-hydroxy-phen-l-yl)methan, Bis [3- (1 '-methylcyclo- hex-l'-yl) -5-methyl-2-hydroxy-phen-l-yl] methan, Bis (3-tert.-Bu- tyl-2-hydroxy-5-methyl-phen-l-yl)methan, 1, 1-Bis (5-tert. -Butyl-4-hydroxy-2-methyl-phen-l-yl ) ethan, Bis ( 5-tert . -Bu- tyl-4-hydroxy-2-methyl-phen-l-yl) sulfid, Bis (3-tert.-Bu- tyl-2-hydroxy-5-methyl-phen-l-yl) sulfid,2-methoxy-4-methylphenol, 2, 3, 6-trimethylphenol, 2,4,5-trimethylphenol, 2, 4, 6-trimethylphenol, 2-isopropylphenol, 4-isopropylphenol, 6-isopropyl-m- Cresol, 4-tert-butylpyrocatechol, n-octadecyl-ß- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,1,3-tris (2-methyl-4-hydroxy-5-) tert-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris- (3,5-di-tert-butyl4-hydroxybenzyl) benzene, 1,3,5, -Tris- (3rd , 5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5, -Tris- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionyloxyethyl isocyanurate, 1, 3, 5-tris (2, 6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate, pentaerythritol tetrakis [ß- (3, 5, -di-tert-butyl-4-hydroxyphenyl ) propionate], 2, 6-di-tert. -butyl-4-dimethylaminomethyl-phenol, 6-seJ.-butyl-2, 4-dinitrophenol, Irganox® 245, 259, 565, 1141, 1192, 1222, 1330, 1425 and MD1024 from Ciba Specialty Chemicals, 3- (3 ', 5' -di-tert-butyl-4'-hydroxyphenyl) propionic acid octadecyl ester, 3- (3 ', 5' -di-tert-butyl-4'-hydroxyphenyl) propionic acid hexadecyl ester, 3- (3 ', 5'-di-tert-butyl-4' -hydroxyphenyl) propionic acid octyl ester, 3-thia-l, 5-pentanediol-bis- [(3 ', 5' -di-tert-butyl- 4'-hydroxyphenyl) propionate], 4,8-dioxa-l, 11-undecanediol-bis- [(3 ', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate], 1,7-heptanediamine -bis [3- (3 ', 5' -di-tert-butyl-4'-hydroxyphenyl) propionic acid amide], 3- (3 ', 5' -di-tert-butyl-4'-hydroxyphenyl) ropionic acid hydrazide, 3- (3 ', 5' -Dimethyl-4'-hydroxyphenyl) propionic acid hydrazide, bis (3-tert-butyl-5-ethyl-2-hydroxy-phen-l-yl) methane, bis (3, 5-di tert-butyl-4-hydroxy-phen-1-yl) methane, bis [3- (1 '-methylcyclo-hex-1'-yl) -5-methyl-2-hydroxy-phen-1-yl] me than, bis (3-tert-butyl-2-hydroxy-5-methyl-phen-1-yl) methane, 1, 1-bis (5-tert. -Butyl-4-hydroxy-2-methyl-phen-l-yl) ethane, bis (5-tert. -Butyl-4-hydroxy-2-methyl-phen-l-yl) sulfide, bis (3- tert-butyl-2-hydroxy-5-methyl-phen-1-yl) sulfide,
1, 1-Bis(3, 4-Dimethyl-2-hydroxy-phen-l-yl)-2-methylpropan, 1, 1-Bis (5-tert.-Butyl-3-methyl-2-hydroxy-phen-l-yl) -butan, 1,3, 5-Tris[l'-(3 ' ' ,5' ' -di-tert. -Butyl-4 ' '-hydroxy- phen-1' '-yl) - eth-l'-yl] -2 , 4, 6-trimethylbenzol,1,1-bis (3,4-dimethyl-2-hydroxy-phen-l-yl) -2-methylpropane, 1,1-bis (5-tert-butyl-3-methyl-2-hydroxy-phen- l-yl) -butane, 1,3, 5-tris [l '- (3 ", 5" -di-tert. -butyl-4 "-hydroxy-phen-1" -yl) - eth -l'-yl] -2, 4, 6-trimethylbenzene,
1,1, 4-Tris (5 '- ert. -Butyl-4 ' -hydroxy-2 ' -methyl-phen-1 '-yl ) utan, 2-Methoxyphenol (Guajacol, Brenzcatechin onomethylether) , 2-Eth- oxyphenol, 2-Isopropoxyphenol, 4-Ethoxyphenol , 4-Butoxyphenol, Hydrochinonmonobenzylether, p-Phenoxyphenol, 4,4'-Oxydiphenyl, 3, 4-Methylendioxydiphenol (Sesamol) , 3 , 4-Dimethylpϊιenol ,1,1,4-Tris (5'-butyl-4'-hydroxy-2'-methylphen-1'-yl) utane, 2-methoxyphenol (guaiacol, pyrocatechol onomethyl ether), 2-ethoxyphenol , 2-isopropoxyphenol, 4-ethoxyphenol, 4-butoxyphenol, hydroquinone monobenzyl ether, p-phenoxyphenol, 4,4'-oxydiphenyl, 3, 4-methylenedioxydiphenol (sesamol), 3, 4-dimethylpϊιenol,
3-Hydroxy-4-methoxybenzylalkohol, 2 , 5-Dimethoxy-4-hydroxybenzyl- alkohol (Syringaalkohol) , 4-Hydroxy-3-methoxybenzaldehyd (Vanil- lin) , 4-Hydroxy-3-ethoxybenzaldehyd (Ethylvanillin) , 3-Hydroxy-4-methoxybenzaldehyd (Isovanillin) , 1- (4-Hydroxy-3-me- thoxy-phenyl ) ethanon (Acetovanillon) , Eugenol, Isoeugenol, Dihy- droeugenol, 2, 5-Di-tert.-Butylhydrochinon, 2-Methyl-p-hydrochi- non, 2, 3-Dimethylhydrochinon, Trimethylhydrochinon, 4-Methyl - brenzcatechin, tert-Butylhydrochinon, 3-Methylbrenzcatechin, p- Nitroso-o-Kresol, sowie Tocopherole, wie z.B. α-, ß-, γ-, δ- und ε-Tocopherol, Tocol, α-Tocopherolhydrochinon, sowie 2,3-Di- hydro-2 , 2-dimethyl-7-hydroxybenzofuran (2, 2-Dimethyl-7-hydroxycu- maran) .3-hydroxy-4-methoxybenzyl alcohol, 2, 5-dimethoxy-4-hydroxybenzyl alcohol (syringa alcohol), 4-hydroxy-3-methoxybenzaldehyde (vanilla lin), 4-hydroxy-3-ethoxybenzaldehyde (ethylvanillin), 3-hydroxy-4-methoxybenzaldehyde (isovanillin), 1- (4-hydroxy-3-methoxyphenyl) ethanone (acetovanillon), eugenol, isoeugenol, dihy - droeugenol, 2, 5-di-tert-butylhydroquinone, 2-methyl-p-hydroquinone, 2, 3-dimethylhydroquinone, trimethylhydroquinone, 4-methyl-catechol, tert-butylhydroquinone, 3-methylcatechol, p-nitroso o-cresol, as well as tocopherols, such as α-, β-, γ-, δ- and ε-tocopherol, tocol, α-tocopherol hydroquinone, and 2,3-dihydro-2, 2-dimethyl-7-hydroxybenzofuran ( 2,2-dimethyl-7-hydroxycu- maran).
Phenothiazin und die phenolische Komponente können gemeinsam im Gemisch oder getrennt voneinander zudosiert werden, bevorzugt als Lösungen.Phenothiazine and the phenolic component can be metered in together in a mixture or separately, preferably as solutions.
Die Stabilisatormenge wird so gewählt, daß die Phenothiazin-Kon- zentration in der isolierten Acrylsaure 50 - 1000 Gew.ppm, vorzugsweise 100 - 600 Gew.ppm, und die Konzentration an der phenolischen Komponente 10 - 1000 Gew.ppm, vorzugsweise 50 - 500 Gew.ppm, beträgt.The amount of stabilizer is chosen so that the phenothiazine concentration in the isolated acrylic acid 50-1000 ppm by weight, preferably 100-600 ppm by weight, and the concentration of the phenolic component 10-1000 ppm by weight, preferably 50-500 Ppm by weight.
Als Lösungsmittel geeignet sind sowohl im System enthaltene als auch systemfremde Komponenten, bevorzugt im System enthaltene. Beispielsweise können die Stabilisatoren in Acrylsaure, Wasser, wäßriger Acrylsäurelösung oder dem anfallenden Sauerwasser gelöst werden, bevorzugt in Acrylsaure oder Sauerwasser.Suitable solvents are both components that are contained in the system and components that are external to the system, preferably components that are contained in the system. For example, the stabilizers can be dissolved in acrylic acid, water, aqueous acrylic acid solution or the acid water obtained, preferably in acrylic acid or acid water.
Die Konzentration der Lösung beträgt bei Phenothiazin 0,1 - 1 Gew.% und bei den phenolischen Komponenten 0,01 - 1 Gew.% in ei- nem geeigneten Lösungsmittel.The concentration of the solution for phenothiazine is 0.1-1% by weight and for the phenolic components 0.01-1% by weight in a suitable solvent.
Optional kann als Stabilisator noch mindestens ein Metallsalz zugegeben werden. Dies kann beispielsweise ein Mangan-, Cer- oder Kupfersalz, bevorzugt Manganacetat, Ceracetat, Kupferacetat, Kup- ferdimethyldithiocarbamat, Kupferdiethyldithiocarbamat, Kupferdi - butyldithiocarbamat und/oder Kupfersalicylat umfassen. Besonders bevorzugt ist Manganacetat.Optionally, at least one metal salt can also be added as a stabilizer. This can include, for example, a manganese, cerium or copper salt, preferably manganese acetate, cerium acetate, copper acetate, copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper di-butyldithiocarbamate and / or copper salicylate. Manganese acetate is particularly preferred.
Als Metallsalze geeignet sind weiterhin Nickel- und Chromsalze.Nickel and chromium salts are also suitable as metal salts.
Als Anionen der Metallsalze geeignet sind Acetate, Dithio- carbamate und Salicylate sowie weiterhin die Sulfate der genannten Metalle. Das Metallsalz kann in einem geeigneten der oben genannten Lösungsmittel gelöst und zusammen mit oder getrennt von im Bereich des Kolonnenkopfes zudosiert werden.Suitable anions of the metal salts are acetates, dithiocarbamates and salicylates and also the sulfates of the metals mentioned. The metal salt can be dissolved in a suitable one of the abovementioned solvents and metered in together with or separately from in the region of the column top.
Die Zugabe des Metallsalzes kann an jedem beliebigen Punkt in der gesamten Kolonne erfolgen, beispielsweise unterhalb des Abzuges der Acrylsaure und/oder am Kopf der Kolonne.The metal salt can be added at any point in the entire column, for example below the withdrawal of the acrylic acid and / or at the top of the column.
Das Metallsalz wird im allgemeinen in einer Menge von 0,5 bis 30 Gew% bezogen auf die hinzugefügte Phenothiazinmenge zugegeben, bevorzugt 1 bis 20 Gew%, besonders bevorzugt 1 bis 10 Gew%.The metal salt is generally added in an amount of 0.5 to 30% by weight, based on the amount of phenothiazine added, preferably 1 to 20% by weight, particularly preferably 1 to 10% by weight.
Das Metallsalz wird in einem geeigneten der oben genannten Lösungsmittel zugegeben, bevorzugt in Wasser, Sauerwasser, wäßriger Acrylsaure oder Acrylsaure. Die Konzentration in der Lösung beträgt in der Regel 0,01 bis 0,5 Gew%, bevorzugt 0,05 bis 0 , 1 Gew%.The metal salt is added in a suitable solvent, preferably in water, acid water, aqueous acrylic acid or acrylic acid. The concentration in the solution is usually 0.01 to 0.5% by weight, preferably 0.05 to 0.1% by weight.
Das erfindungsgemäße Verfahren wird in Abwesenheit von N-Oxylver- bindungen durchgeführt, d.h. solche Verbindungen, die eine wenigstens eine >N-0- -Gruppe aufweisen, wie z.B. die eingangs erwähnten N-Oxyl erbindungen. Dies bedeutet, daß in der Rektifikations - kolonne keine N-Oxylverbindungen nachweisbar sind.The process according to the invention is carried out in the absence of N-oxyl compounds, i.e. those compounds which have at least one> N-0 group, e.g. the N-oxyl compounds mentioned at the beginning. This means that no N-oxyl compounds are detectable in the rectification column.
In einer bevorzugten Ausführungsform bei der Verwendung eines der genannten Absorptionsmittel als hochsiedender Flüssigkeit im Quench bgekühlte, Acrylsaure enthaltende Reaktionsgasgemisch einem Absorptionsprozeß mit der hochsiedenden Flüssigkeit unterworfen. Dieser Absorptionsprozeß kann sowohl im Gleichstrom als auch im Gegenstrom, bevorzugt im Gegenstrom erfolgen.In a preferred embodiment, when one of the absorbents mentioned is used as the high-boiling liquid in the quench, the reaction gas mixture which is cooled and contains acrylic acid is subjected to an absorption process with the high-boiling liquid. This absorption process can take place both in cocurrent and in countercurrent, preferably in countercurrent.
Geeignet für einen solchen Absorptionsprozeß sind die an sich bekannten Apparate, wie z.B. in Ulimann' s Encyclopedia of Indu- strial Chemistry (6th ed, 1999 Electronic Release. Kapitel: Ab- Sorption) beschrieben, beispielsweise Kolonnen mit Glocken-,The apparatuses known per se are suitable for such an absorption process, as described, for example, in Ulimann's Encyclopedia of Industrial Chemistry (6 th ed, 1999 Electronic Release. Chapter: Absorption), for example columns with bell,
Thormann-, Ventil- oder Siebböden, mit geordneten oder ungeordneten Packungen und/oder Schüttungen, Venturiwäscher oder Filmwäscher, bevorzugt werden Bodenkolonnen verwendet.Thormann, valve or sieve trays, with ordered or unordered packings and / or fillings, venturi washers or film washers, bottom columns are preferably used.
Der Absorptionsprozeß wird im allgemeinen bei einer Kopftemperatur von 15 bis 50 °C und einer Sumpftemperatur von 120 bis 180 °C durchgeführt . Da bei dem Absorptionsprozeß nicht kondensierbare Bestandteile über Kopf abgetrennt werden, gelangen diese nicht mehr in den nachfolgenden Rektifikationsprozeß, so daß diese dort nicht oder nur in geringem Maß anfallen.The absorption process is generally carried out at a top temperature of 15 to 50 ° C and a bottom temperature of 120 to 180 ° C. Since non-condensable constituents are removed overhead in the absorption process, they no longer enter the subsequent rectification process, so that they do not occur there or only to a small extent.
In einer weiteren bevorzugten Ausführungsform wird der acrylsäu- rehaltige, flüssige Austrag des Absorptionsprozesses zusätzlich einem Desorptionsprozeß unterworfen, in dem Leichtsieder, wie niedrigsiedende Aldehyde, wie Acetaldehyd, Propionaldehyd oder Acrolein, Aceton, Essigsäure oder Propionsäure, zumindest teilweise abgetrennt werden. In der Regel beträgt nach der Desorption der Gesamtgehalt an niederen Aldehyden und Aceton höchstens 10000 Gew.ppm, bevorzugt höchstens 5000 Gew.ppm.In a further preferred embodiment, the liquid discharge of the absorption process containing acrylic acid is additionally subjected to a desorption process in which low boilers, such as low-boiling aldehydes, such as acetaldehyde, propionaldehyde or acrolein, acetone, acetic acid or propionic acid, are at least partially separated off. As a rule, after the desorption, the total content of lower aldehydes and acetone is at most 10,000 ppm by weight, preferably at most 5000 ppm by weight.
Dazu wird die acrylsäurehaltige Lösung im Gleich- oder Gegenstrom, bevorzugt im Gegenstrom zur Desorption der Leichtsieder mit einem Gas behandelt.For this purpose, the acrylic acid-containing solution is treated with a gas in cocurrent or countercurrent, preferably in countercurrent to desorb the low boilers.
Als Gas kann dazu ein unter den Reaktionsbedingungen reaktions- träges Gas verwendet werden.A gas which is inert under the reaction conditions can be used as the gas.
Die Desorption kann sowohl in Gegenwart als auch in Abwesenheit von Sauerstoff (0 ) durchgeführt werden. Führt man sie in Anwesenheit von Sauerstoff aus, so ist ein Sauerstoffhaltiges Gas ver- wendbar, in dem der Sauerstoff gegebenenfalls mit einem reaktionsträgen Gas wie Kohlenstoffdioxid (C02) , Stickstoff (N ) oder Edelgase, wie z.B. Helium oder Argon, oder Gemischen davon verdünnt wird. Bevorzugt wird Stickstoff zur Verdünnung verwendet. Der Sauerstoffanteil am sauerstoffhaltigen Gas kann zwischen 1 und 100 Vol% betragen, bevorzugt zwischen 2 und 80 Vol% besonders bevorzugt zwischen 5 und 50 Vol% und insbesondere zwischen 10 und 30 Vol%.Desorption can be carried out both in the presence and in the absence of oxygen (0). If they are carried out in the presence of oxygen, an oxygen-containing gas can be used, in which the oxygen may be mixed with an inert gas such as carbon dioxide (CO 2 ), nitrogen (N) or noble gases, such as helium or argon, or mixtures thereof is diluted. Nitrogen is preferably used for dilution. The oxygen content of the oxygen-containing gas can be between 1 and 100 vol%, preferably between 2 and 80 vol%, particularly preferably between 5 and 50 vol% and in particular between 10 and 30 vol%.
In einer bevorzugten Ausführungsform wird Luft als sauerstoffhal- tiges Gas verwendet.In a preferred embodiment, air is used as the oxygen-containing gas.
Führt man das Verfahren in Abwesenheit von Sauerstoff aus, so sind beliebige der oben aufgeführten reaktionsträgen Gase einzeln oder im Gemisch verwendbar, bevorzugt wird das Verfahren jedoch in Gegenwart eines sauerstoffhaltigen Gases durchgeführt.If the process is carried out in the absence of oxygen, any of the inert gases listed above can be used individually or in a mixture, but the process is preferably carried out in the presence of an oxygen-containing gas.
Geeignet für einen solchen Desorptionsprozeß sind die an sich bekannten Apparate, wie z.B. in Ulimann' s Encyclopedia of Indu- strial Chemistry (6th ed, 1999 Electronic Release. Kapitel: Absorption) beschrieben, beispielsweise Kolonnen mit Glocken-, Thormann-, Ventil- oder Siebböden, mit geordneten oder ungeordneten Packungen und/oder Schüttungen, Venturiwäscher, Filmwäscher, Stripp- oder Flashapparate, bevorzugt werden Bodenkolonnen, Stripp- oder Flashapparate verwendet.The apparatuses known per se are suitable for such a desorption process, as described, for example, in Ulimann's Encyclopedia of Industrial Chemistry (6 th ed, 1999 Electronic Release. Chapter: Absorption), for example columns with bell, Thorman, valve or sieve trays, with ordered or unordered packings and / or fillings, venturi washers, film washers, Stripping or flash devices, preferably column columns, stripping or flash devices are used.
In einer weiteren bevorzugten Ausführungsform wird ein hochsie- dende Stoffe enthaltender Ablauf des Rektifikationsprozesses, wie z.B. die Schwersieder, einer Rückspaltung unterworfen.In a further preferred embodiment, a high-boiling substance sequence of the rectification process, e.g. the high boilers, subjected to a reclassification.
Dazu werden die im Rektifikationsprozeß abgetrennten Schwersieder einer thermischen und/oder katalytischen Spaltung unterworfen, wie beispielsweise in US 4 317 926, DE-C2 240 72 36 und US 3 086 046 sowie in der WO 00/53560 beschrieben, wobei die oligomeren Acrylsäuren auf bekannte Weise in Acrylsaure gespalten werden. Die Spaltprodukte werden vorteilhaft wieder dem Rektifikations - prozeß zugeführt.For this purpose, the high boilers separated off in the rectification process are subjected to thermal and / or catalytic cleavage, as described, for example, in US Pat. No. 4,317,926, DE-C2 240 72 36 and US Pat. No. 3,086,046 and WO 00/53560, the oligomeric acrylic acids being known Be split into acrylic acid. The cleavage products are advantageously returned to the rectification process.
Oligomere Acrylsäuren sind dabei Michael-Addukte von Acrylsaure, gegebenenfalls mehrfach, an sich selbst und nicht durch radikalische Polymerisation entstehende Acrylsäurepolymere.Oligomeric acrylic acids are Michael adducts of acrylic acid, optionally several times, on themselves and not by free-radical polymerization resulting acrylic acid polymers.
Polymere entstehen durch eine im wesentlichen radikalische Polymerisation unter Ausbildung von Kohlenstoff-Kohlenstoff-Verknüpfungen. Diese Produkte sind in der Regel nicht rückspaltbar. Die bei einer solchen Spaltung, beispielsweise nach der Lehre der WO 00/53560 und der darin zitierten Literatur, rückgespaltenen Produkte können in den erfindungsgemäßen Prozeß an beliebigen Stellen eingeleitet werden, bevorzugt in den Rektifikationsprozeß, besonders bevorzugt dort zusammen mit dem Zulauf in die Rektifikationskolonne .Polymers are formed by an essentially radical polymerization with the formation of carbon-carbon linkages. As a rule, these products cannot be split back. The products cleaved in such a cleavage, for example according to the teaching of WO 00/53560 and the literature cited therein, can be introduced at any point in the process according to the invention, preferably into the rectification process, particularly preferably there together with the feed into the rectification column.
Der der Rückspaltung zugeführte Strom kann, gegebenenfalls unter Zusatz von saurem Katalysator, zur Rückspaltung der enthaltenen Oligomere thermisch behandelt werden. Dazu sind als saure Katalysatoren beispielsweise Schwefelsäure, organische Sulfonsäuren, wie z.B. para-Toluolsulfonsäure, Methansulfonsäure, Trifluorme- thansulfonsäure, Xylolsulfonsäure oder Dodecylbenzolsulfonsäure, saure Ionentauscher oder saure Metalloxide geeignet.The stream fed to the cleavage can, if appropriate with the addition of acid catalyst, be thermally treated to cleave the oligomers contained. For this purpose, acidic catalysts include, for example, sulfuric acid, organic sulfonic acids, such as para-toluenesulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, xylenesulfonic acid or dodecylbenzenesulfonic acid, acidic ion exchangers or acidic metal oxides are suitable.
Die Temperatur in der Rückspaltung beträgt im allgemeinen 100 bis 220 °C, bevorzugt 120 bis 200 °C, besonders bevorzugt 140 bis 180 °C und insbesondere 150 bis 180 °C.The temperature in the cleavage is generally 100 to 220 ° C, preferably 120 to 200 ° C, particularly preferably 140 to 180 ° C and in particular 150 to 180 ° C.
Die Abtrennung der Leichtsieder kann durch das Durchleiten eines unter den Reaktionsbedingungen im wesentlichen inerten Gasstromes (Strippen), wie z.B. Stickstoff, Wasserdampf, aber auch ein sau- erstoffhaltiges Gas, wie z.B. Luft, unterstützt werden. Der verbleibende Rückstand kann beispielsweise teilweise ausgeschleust, destilliert oder nochmals einer Rückspaltung unterworfen werden.The removal of the low boilers can be supported by passing a gas stream (stripping) which is essentially inert under the reaction conditions, such as nitrogen, water vapor, but also an oxygen-containing gas, such as air. The remaining residue can, for example, be partially discharged, distilled or subjected to a further cleavage.
In einer weiteren bevorzugten Ausführungsform wird ein hochsiedende Stoffe, insbesondere ein eines der genannten Absorptions- mittel enthaltender Ablauf des Rekti ikationsprozesses einer Destillation unterworfen. Besonders bevorzugt wird dieser Ablauf einer Destillation unterworfen, wie sie in der zeitgleichen An- meidung mit dem deutschen Aktenzeichen 100 64 642.5 und dem Titel "Verfahren zur Herstellung von (Meth) acrylsaure" der BASF AG mit dem gleichen Anmeldetag wie die vorliegende Anmeldung beschrieben ist.In a further preferred embodiment, a high-boiling substance, in particular a run of the rectification process containing one of the abovementioned absorbents, is subjected to a distillation. This process is particularly preferably subjected to a distillation as described in the simultaneous application with the German file number 100 64 642.5 and the title "Process for the Production of (Meth) Acrylic Acid" from BASF AG with the same filing date as the present application ,
Dazu wird der Ablauf in einen Destillationsapparat geleitet und aus diesem gasförmig ein Leichtsiederstrom entnommen, der neben Acrylsaure und/oder dem vorhandenen Absorptionsmittel noch weitere Komponenten, wie beispielsweise Diacrylsäure oder Stabilisator, enthalten kann.For this purpose, the outflow is passed into a distillation apparatus and a low-boiler stream is removed from it in gaseous form, which stream may contain, in addition to acrylic acid and / or the absorbent present, further components such as, for example, diacrylic acid or stabilizer.
Dieser Leichtsiederstrom kann, gegebenenfalls nach Kondensation und gegebenenfalls noch weiterer Abkühlung, dem Aufarbeitungsprozeß an beliebigen Stellen zugeführt werden, beispielsweise dem Quench-, Absorptions- oder Rektifikationsprozeß, bevorzugt dem Quench- oder Absorptionsprozeß, besonders bevorzugt dem Absorptionsprozeß.This low-boiling stream can, if appropriate after condensation and possibly further cooling, be fed to the work-up process at any point, for example the quench, absorption or rectification process, preferably the quench or absorption process, particularly preferably the absorption process.
Als Destillationsapparat geeignet sind sämtliche dem Fachmann bekannte Destillationsapparate, z.B. Umlaufverdampfer, Dünnfilmver- dampfer, Fallfilmverdampfer, Wischblattverdampfer, gegebenenfalls jeweils mit aufgesetzten Rektifikationskolonnen sowie Strippkolonnen.Suitable distillation apparatus are all distillation apparatus known to the person skilled in the art, e.g. Circulation evaporator, thin film evaporator, falling film evaporator, wiper blade evaporator, if necessary, each with attached rectification columns and stripping columns.
Zusätzlich kann ein Strippstrom angelegt werden, z.B. mit Stick- stoff oder einem sauerstoffhaltigen Gas, bevorzugt mit Luft.A stripping current can also be applied, e.g. with nitrogen or an oxygen-containing gas, preferably with air.
Der Destillationsapparat kann bei Temperaturen zwischen 80 und 350 °C, bevorzugt zwischen 100 und 280 °C, besonders bevorzugt zwischen 120 und 200 °C und insbesondere zwischen 130 und 200 °C und unabhängig davon bei Drücken zwischen 5 und 2000 hPa, bevorzugt zwischen 5 und 1200 hPa, besonders bevorzugt zwischen 20 und 500 hPa, ganz besonders bevorzugt zwischen 50 und 400 hPa und insbesondere zwischen 50 und 300 hPa betrieben werden.The distillation apparatus can be operated at temperatures between 80 and 350 ° C, preferably between 100 and 280 ° C, particularly preferably between 120 and 200 ° C and in particular between 130 and 200 ° C and independently at pressures between 5 and 2000 hPa, preferably between 5 and 1200 hPa, particularly preferably between 20 and 500 hPa, very particularly preferably between 50 and 400 hPa and in particular between 50 and 300 hPa.
Das erfindungsgemäße Verfahren wird durch die nachfolgenden Beispiele näher erläutert. Beispiel 1The process according to the invention is explained in more detail by the following examples. example 1
Die in Tabelle 1 aufgeführten Stabilisatoren wurden in stabilisatorfreier Acrylsaure (2 x destilliert) gelöst und 20 ml der Lösung unter Luft in einem verschlossenen 50 ml Prüfgefäß, das vollkommen in ein Heizbad eingetaucht war, bei 120 °C gelagert. Bestimmt wurde die Zeit bis zur eintretenden Polymerisation (Induktionsperiode) .The stabilizers listed in Table 1 were dissolved in stabilizer-free acrylic acid (2 x distilled) and 20 ml of the solution were stored at 120 ° C. in air in a sealed 50 ml test vessel which was completely immersed in a heating bath. The time until the onset of polymerization (induction period) was determined.
Tabelle 1:Table 1:
Figure imgf000017_0001
MEHQ: Hydrochinonmonomethylether PTZ: Phenothiazin HT: 4-Hydroxy-2 ,2,6, 6-tetramethyl-piperidin-N-oxyl
Figure imgf000017_0001
MEHQ: hydroquinone monomethyl ether PTZ: phenothiazine HT: 4-hydroxy-2, 2,6, 6-tetramethyl-piperidine-N-oxyl
Beispiel 2 Durch katalytische Gasphasenoxidation von Propen beziehungsweise Acrolein gemäß DE-A 43 02 991 wurde ein Acrylsaure enthaltendes Reaktionsgemisch erzeugt. 2,2 Nm3/h dieses Reaktionsgemisches wurden in einem Gaskühler (Quench) durch Einspritzen eines Kühlmittelgemisches, das aus dem Sumpf der Rektifikationskolonne (siehe unten) entnommen wurde, aus 58,8 Gew.-% Diphenylether, 21,2 Gew.-% Diphenyl und 20 Gew.-% o-Dimethylphthalat auf 170 °C gekühlt. Diese auf 170°C abgekühlten Reaktionsgase wurden unterhalb des ersten Bodens in eine Glockenbodenkolonne mit 27 Böden geleitet und dem Gegenstrom von 3 1/h des gleichfalls aus 58,8 Gew.-% Diphenylether, 21,2 Gew.-% Diphenyl und 20 Gew.-% o-Dimethylphthalat zusammengesetzten, am Kolonnenkopf mit einer Temperatur von 45°C aufgegebenen, Absorptionsmittels ausgesetzt. Der Ablauf der Absorptionskolonne wurde in einem Wärmetauscher indirekt auf 105°C erwärmt und auf den Kopf einer Desorptionskolonne gegeben, die als Glockenbodenkolonne mit 20 Böden ausgeführt war. In der Desorptionskolonne wurden im Vergleich zu Acrylsaure leichtsiedende Komponenten, z.B. Essigsäure und Aldehyde, durch Strippen mit Stickstoff (400 1/h, Gegenstrom) weitgehend aus dem Gemisch entfernt, der Restgehalt betrug 0,2 Gew% Essigsäure und 0,15 Gew% Aldehyde. Der Ablauf der Desorptionskolonne enthielt 15,4 Gew.-% Acrylsaure. Dieser wurde mit einer Temperatur von 25 °C in einer Menge von 3 1/h zwischen dem fünften und sechsten Boden (vom Verdampfer aus gezählt) in eine 20 Glockenböden umfassende, luftdurchströmte Rektifikationskolonne geleitet.Example 2 A catalytic gas phase oxidation of propene or acrolein according to DE-A 43 02 991 produced a reaction mixture containing acrylic acid. 2.2 Nm3 / h of this reaction mixture were obtained in a gas cooler (quench) by injecting a coolant mixture which had been taken from the bottom of the rectification column (see below) from 58.8% by weight diphenyl ether, 21.2% by weight Diphenyl and 20 wt .-% o-dimethylphthalate cooled to 170 ° C. These reaction gases, cooled to 170 ° C., were passed below the first tray into a bubble tray column with 27 trays and the countercurrent of 3 l / h was also composed of 58.8% by weight of diphenyl ether, 21.2% by weight of diphenyl and 20% by weight .-% o-Dimethylphthalat composite, applied to the column head at a temperature of 45 ° C, exposed to absorbent. The outlet of the absorption column was indirectly heated to 105 ° C. in a heat exchanger and placed on the top of a desorption column which was designed as a bubble tray column with 20 trays. In the desorption column, low-boiling components, for example acetic acid and aldehydes, were largely removed from the mixture by stripping with nitrogen (400 l / h, countercurrent), the residual content was 0.2% by weight of acetic acid and 0.15% by weight of aldehydes , The outlet of the desorption column contained 15.4% by weight of acrylic acid. This was passed at a temperature of 25 ° C. in an amount of 3 l / h between the fifth and sixth plate (counted from the evaporator) into a rectification column with air flowing through it and comprising 20 bubble plates.
Die Rektifikationskolonne wurde mit einer Sumpftemperatur von 160°C und einem Sumpfdruck von 130 mbar sowie einem Kopfdruck von 80 mbar betrieben. Zwischen dem fünfzehnten und sechzehnten Boden (vom Verdampfer aus gezählt) wurden über Seitenabzug pro Stunde 1500 ml Acrylsaure flüssig in einer Reinheit von 99,7 Gew.-% kontinuierlich entnommen, wobei unmittelbar unterhalb des Seitenabzugs 970 ml/h der ausgeschleusten Acrylsaure wieder der Kolonne zugeführt wurden. Das dampfförmige Kopfprodukt wurde kondensiert (600 ml/h) , mit 100 ml/h einer Lösung von Phenothiazin (5 g/1) und Hydrochinonmonomethylether (2 g/1) in Acrylsaure versetzt und bis auf 60 ml/h oberhalb des obersten Kolonnenbodens wieder in die Rektifikationskolonne zurückgeführt.The rectification column was operated at a bottom temperature of 160 ° C. and a bottom pressure of 130 mbar and a top pressure of 80 mbar. Between the fifteenth and sixteenth trays (counted from the evaporator), 1500 ml of liquid acrylic acid were removed continuously in a purity of 99.7% by weight per side draw, with 970 ml / h of the acrylic acid discharged again immediately below the side draw were fed. The vaporous top product was condensed (600 ml / h), mixed with 100 ml / h of a solution of phenothiazine (5 g / 1) and hydroquinone monomethyl ether (2 g / 1) in acrylic acid and again up to 60 ml / h above the top of the column returned to the rectification column.
Das ausgeschleuste Kopfprodukt (60 ml/h) wurde wieder dem Ablauf der Absorptionskolonne zugegeben.The discharged top product (60 ml / h) was again added to the outlet of the absorption column.
Ein Teil des stabilisatorhaltigen Kolonnensumpfes wurde entnommen und teilweise, nach Abkühlung, als Absorptionsmittel in der vorhergehenden Absorption verwendet, der Rest wurde ausgeschleust.A part of the column bottom containing stabilizer was removed and partly, after cooling, used as an absorbent in the previous absorption, the rest was discharged.
Die Betriebsdauer der Rektifikationskolonne betrug mindestens 700 Stunden. Der Verdampfer war nur leicht belegt.The operating time of the rectification column was at least 700 hours. The evaporator was only slightly occupied.
Beispiel 3 (Vergleich) Es wurde wie in Beispiel 2 verfahren. Die Stabilisierung erfolgte mit 100 ml/h einer Lösung von 7g/l Phenothiazin in Acrylsaure. Die Destillation mußte nach 400 Stunden Betriebsdauer wegen Polymerisatbildung im Vers ärker eil und starkem Fouling im Abtrieb- steil der Kolonne abgebrochen werden. Der Verdampfer war stark belegt.Example 3 (comparison) The procedure was as in Example 2. The stabilization was carried out with 100 ml / h of a solution of 7 g / l phenothiazine in acrylic acid. The distillation had to be stopped after 400 hours of operation due to the formation of polymer in the rope and strong fouling in the stripping section of the column. The evaporator was very busy.
Beispiel 4 (Vergleich)Example 4 (comparison)
Es wurde wie in Bsp. 2 verfahren. Die Stabilisierung erfolgte mit 100 ml/h einer Lösung von 5 g/1 Phenothiazin, 1 g/1 Hydrochinon- monomethylether und 1 g/1 4-Hydroxy-2 , 2, 6, 6-tetramethylpiperidin- N-oxyl in Acrylsaure.The procedure was as in Example 2. The stabilization was carried out with 100 ml / h of a solution of 5 g / 1 phenothiazine, 1 g / 1 hydroquinone monomethyl ether and 1 g / 1 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl in acrylic acid.
Die Destillation mußte nach ca. 500 Stunden Betriebsdauer wegen Polymerisatbildung im Verstärkerteil und der Bildung eines schwarzen Belags im Abtriebsteil der Kolonne abgebrochen werden. Der Verdampfer war stark belegt. Beispiel 5 (Vergleich)The distillation had to be stopped after about 500 hours of operation due to polymer formation in the rectifying section and the formation of a black coating in the stripping section of the column. The evaporator was very busy. Example 5 (comparison)
Es wurde wie in Bsp. 2 verfahren. Die Stabilisierung erfolgte mit 100 ml/h einer Lösung von 6 g/1 Phenothiazin und 1 g/1 4-Hy- droxy-2, 2, 6, 6-tetramethylpiperidin-N-oxyl in Acrylsaure. Die Destillation mußte nach ca. 450 Stunden Betriebsdauer wegen Polymerisatbildung im Verstärkerteil und der Bildung eines schwarzen Belags im Abtriebsteil der Kolonne abgebrochen werden. Der Verdampfer war stark belegt.The procedure was as in Example 2. The stabilization was carried out with 100 ml / h of a solution of 6 g / 1 phenothiazine and 1 g / 1 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl in acrylic acid. The distillation had to be stopped after about 450 hours of operation due to polymer formation in the rectifying section and the formation of a black coating in the stripping section of the column. The evaporator was very busy.
Beispiel 6Example 6
Es wurde wie in Bsp. 2 verfahren. Die Stabilisierung erfolgte mit 100 ml/h einer Lösung von 5 g/1 Phenothiazin, 2 g/1 Hydrochinonmonomethylether und 0,1 g/1 Mangandiacetat (2% bezogen auf Phenothiazin) in Acrylsaure.The procedure was as in Example 2. The stabilization was carried out with 100 ml / h of a solution of 5 g / 1 phenothiazine, 2 g / 1 hydroquinone monomethyl ether and 0.1 g / 1 manganese diacetate (2% based on phenothiazine) in acrylic acid.
Nach ca. 700 Stunden Betriebsdauer zeigten weder Kolonne noch Verdampfer Anzeichen von Polymerisatbildung.After approximately 700 hours of operation, neither the column nor the evaporator showed any signs of polymer formation.
Beispiel 7 Es wurde wie in Bsp. 2 verfahren, jedoch wurden dem Zulauf der Rektifikationskolonne 2000 ppm Aceton zugesetzt.Example 7 The procedure was as in Example 2, but 2000 ppm of acetone were added to the feed to the rectification column.
Nach ca. 700 Stunden Betriebsdauer zeigten weder Kolonne noch Verdampfer Anzeichen von Polymerisatbildung.After approximately 700 hours of operation, neither the column nor the evaporator showed any signs of polymer formation.
Dieses Beispiel zeigt, daß bei erfindungsgemäßer Stabilisierung der Gehalt an Aceton und Aldehyden keinen Einfluß auf die Polymerisatbildung hat. This example shows that with the stabilization according to the invention the content of acetone and aldehydes has no influence on the formation of the polymer.

Claims

Patentansprüche claims
1. Verfahren zur Herstellung von Acrylsaure, durch heterogen ka- talysierte Gasphasen-Partialoxidation mindestens eines1. Process for the preparation of acrylic acid, by heterogeneously catalyzed gas phase partial oxidation of at least one
C3-Vorläufers mit molekularem Sauerstoff wobei man das entstehende, Acrylsaure enthaltende Produktgasgemisch abkühlt und in der Folge entweder einer fraktionierenden Kondensation oder einem Rektifikationsprozeß unterwirft, dadurch gekenn- zeichnet, daß man im Kolonnenkopf oder im Bereich des Kolonnenkopfes der Rektifikations- beziehungsweise Kondensationskolonne (n) Phenothiazin und mindestens eine phenolische Verbindung einbringt .C 3 precursor with molecular oxygen, cooling the resulting product gas mixture containing acrylic acid and subsequently subjecting it either to fractional condensation or a rectification process, characterized in that the rectification or condensation column (n ) Introduces phenothiazine and at least one phenolic compound.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man zusätzlich zu Phenothiazin und mindestens einer phenolischen Verbindung mindestens ein Metallsalz einbringt.2. The method according to claim 1, characterized in that in addition to phenothiazine and at least one phenolic compound at least one metal salt is introduced.
3. Verfahren nach einem der vorstehenden Ansprüche, dadurch ge- kennzeichnet, daß das heiße, Acrylsaure enthaltende Produktgasgemisch nach Abkühlung in einen Absorptionsprozeß und die so erhaltene Acrylsaure enthaltende Flüssigkeit rektifiziert wird.3. The method according to any one of the preceding claims, characterized in that the hot product gas mixture containing acrylic acid after cooling is rectified in an absorption process and the liquid containing acrylic acid thus obtained is rectified.
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, daß die aus dem Absorptionsprozeß erhaltene Acrylsaure enthaltende Lösung einem Desorptionsprozeß unterworfen wird und die so erhaltene Acrylsaure enthaltende Flüssigkeit rektifiziert wird.4. The method according to claim 3, characterized in that the solution containing acrylic acid obtained from the absorption process is subjected to a desorption process and the acrylic acid-containing liquid thus obtained is rectified.
5. Verfahren nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, daß als Quench und/oder Absorptionsmittel ein Gemisch aus Diphenylether und Biphenyl verwendet wird.5. The method according to any one of the preceding claims, characterized in that a mixture of diphenyl ether and biphenyl is used as the quench and / or absorbent.
6. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß das6. The method according to claim 5, characterized in that the
Gemisch zusätzlich 0,1 bis 25 Gew% eines ortho-Phthalsäuree- sters enthält.Mixture additionally contains 0.1 to 25% by weight of an orthophthalic ester.
7. Verfahren nach einem der vorstehenden Ansprüche, dadurch ge- kennzeichnet, daß als phenolische Verbindung mindestens ein7. The method according to any one of the preceding claims, characterized in that at least one as the phenolic compound
Mitglied der Gruppe bestehend aus Hydrochinon, Hydrochinonmonomethylether, 2-tert . -Butyl-4-methyl henol, 2 , 6-di-tert .-Bu- tyl-4-methylphenol, 2-Methylhydrochinon und 6-tert.-Bu- tyl-2 , 4-dimethyl-phenol sowie 2 , 5-di-tert .-Butylhydrochinon, 2-tert.Butylphenol, 4-tert .butylphenol, 2, 4-Di-tert. -Butylphenol , 4-tert . -Butyl-2 , 6-dimethylphenol , 2-tert . -Bu- tyl-6-methylphenol, 4-Ethoxyphenol oder 4-Butoxyphenol verwendet wird.Member of the group consisting of hydroquinone, hydroquinone monomethyl ether, 2-tert. -Butyl-4-methylhenol, 2, 6-di-tert-butyl-4-methylphenol, 2-methylhydroquinone and 6-tert-butyl-2, 4-dimethylphenol and 2, 5- di-tert-butyl hydroquinone, 2-tert-butylphenol, 4-tert-butylphenol, 2, 4-di-tert. -Butylphenol, 4-tert. -Butyl-2, 6-dimethylphenol, 2-tert. -Bu- tyl-6-methylphenol, 4-ethoxyphenol or 4-butoxyphenol is used.
8. Verfahren nach einem der vorstehenden Ansprüche, dadurch ge- 5 kennzeichnet, daß als phenolische Verbindung Hydrochinonmonomethylether verwendet wird.8. The method according to any one of the preceding claims, character- 5 indicates that hydroquinone monomethyl ether is used as the phenolic compound.
9. Verfahren nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, daß man die Stabilisatormenge so wählt, daß die9. The method according to any one of the preceding claims, characterized in that one chooses the amount of stabilizer so that the
10 Phenothiazin-Konzentration in der isolierten Acrylsaure 50 - 1000 Gew.ppm und die Konzentration an der phenolischen Komponente 10 - 1000 Gew.ppm beträgt.10 phenothiazine concentration in the isolated acrylic acid 50-1000 ppm by weight and the concentration of the phenolic component is 10-1000 ppm by weight.
10. Verfahren nach einem der Ansprüche 2 bis 9, dadurch gekenn- 15 zeichnet, daß als Metallsalz mindestens eine Mangan-, Cer-,10. The method according to any one of claims 2 to 9, characterized in that the metal salt is at least one manganese, cerium,
Nickel-, Chrom- oder Kupferverbindung verwendet wird.Nickel, chrome or copper compound is used.
11. Verfahren nach einem der Ansprüche 2 bis 10, dadurch gekennzeichnet, daß als Metallsalz mindestens eine Verbindung der11. The method according to any one of claims 2 to 10, characterized in that at least one compound of the metal salt
20 Gruppe bestehend aus Manganacetat, Ceracetat, Kupferacetat, Kupferdimethyldithiocarbamat, Kupferdiethyldithiocarbamat, Kupferdibutyldithiocarbamat und Kupfersalicylat verwendet wird.20 group consisting of manganese acetate, cerium acetate, copper acetate, copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dibutyldithiocarbamate and copper salicylate is used.
25 12. Verfahren nach einem der Ansprüche 2 bis 11, dadurch gekennzeichnet, daß als Metallsalz Manganacetat verwendet wird.25 12. The method according to any one of claims 2 to 11, characterized in that manganese acetate is used as the metal salt.
13. Verfahren nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, daß es in Abwesenheit einer N-OxylVerbindung 30 durchgeführt wird.13. The method according to any one of the preceding claims, characterized in that it is carried out in the absence of an N-oxyl compound 30.
3535
4040
45 45
PCT/EP2001/015207 2000-12-22 2001-12-21 Method for producing acrylic acid WO2002051784A1 (en)

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DE2000164641 DE10064641A1 (en) 2000-12-22 2000-12-22 Production of acrylic acid by catalytic gas-phase oxidation of propene or acrolein involves fractional condensation or rectification with addition of phenothiazine and phenolic stabilizers at the column head

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JP4440518B2 (en) 2002-07-16 2010-03-24 株式会社日本触媒 Acrylic acid production method

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