DE1543175B - Process for the production and recovery of acetic acid - Google Patents

Description

The invention relates to a method of manufacture and recovery of acetic acid.

The art already knows a large number of processes by which acetic acid is produced. Most of the known processes have one or more disadvantages, which consist in the fact that oxidation catalysts, Initiators, critical feed quantities of the reactants, expensive or dangerous Starting materials, excessively high reaction temperatures or difficult to operate Separation procedures are required. The invention therefore aims to provide a method for Production and recovery of acetic acid by non-catalytic, direct oxidation of propene with molecular oxygen in a liquid phase that contains fully esterified polyacyl esters of polyols.

Another purpose of the invention is the production and recovery of acetic acid in one Process in which mechanical loss of solvent can be replaced by products of oxidation.

In addition, the process of the invention is simple, economical and convenient and does not require any expensive, dangerous and difficult to obtain raw materials.

The invention therefore relates to a process for the production of acetic acid by oxidation of Propene and distillative recovery of acetic acid from the reaction product, characterized in that that he

a) propene with oxygen in the liquid phase in the presence of at least 25 percent by weight, based on the liquid reaction mixture, a fully acylated polyoxyalkane, polyoxycycloalkane or polyglycol, preferably propylene glycol diacetate, containing solvent in a temperature range from 160 to 250 ° C, preferably 180 to 230 ° C, and a pressure range from 0.5 to 350 at, preferably 5 to 200 at, converts

b) and the reaction product with the aid of a flash evaporator and a stripper into a the gas phase containing the acetic acid and low-boiling products and a main amount the solvent, high-boiling products and the liquid phase containing the residue are broken down,

c) the liquid phase is returned to the oxidation zone via an adsorber, while adhering to a residue concentration below 60 percent by weight in the reaction mixture,

d) the gas phase is subjected to condensation by cooling, the non-condensed vapors over the adsorber is returned to the oxidation zone and propene and propane are distilled off from the condensate and the propene and the acetaldehyde obtained from a side stream are returned to the oxidation zone and the remaining Condensate in a distillation residue and in one containing the total amount of acetic acid Distilled distillate,

e) first of all the low-boiling components are distilled off from this, the acetic acid by azeotropic Freed from water and formic acid by distillation with benzene and then by distillation cleans

f) and the distillation residue of the condensate together with the distilled, low-boiling,

Propylene glycol and glycol monoester-containing constituents of an ester concentration column feeds whose vapors together with the acetic acid from the bottom stream of the acetic acid refining column and the bottom stream of the azeotropic distillation in the presence of a catalyst, preferably toluenesulfonic acid, esterified or transesterified to give fully acylated polyoxyalkanes and these to the oxidation process feeds again.

The solvents used according to the invention are very resistant to attack by free ones Radicals generated in the oxidation process; they also mitigate the disturbing effects, those of acidic components, especially formic acid and, to a lesser extent, acetic acid, be exercised on commercially valuable, non-acidic by-products, for example propylene oxide, formed by the oxidation of olefins. Fully esterified polyacyl esters serve as solvents of polyoxyalkanes, polyoxycycloalkanes, polyglycols and their mixtures. According to the invention Applicable polyacyl esters generally contain 1 to 18 carbon atoms in each acyl group and from 2 to 18 carbon atoms in each alkylene or cycloalkylene moiety. The best However, results are achieved when the acyl group contains 1 to 6 carbon atoms and the Alkylene and cycloalkylene groups each contain 2 to 6 carbon atoms. These esters can be used without further can be produced by known processes. For example, U.S. patent describes 1 534 752 a process in which the corresponding Glycol ester is produced. Acid anhydrides can also be used in place of the acids.

Suitable glycols include straight-chain glycols, for example ethylene glycol and hexylene glycol or octadecylene glycol. Branched chain glycols such as the iso-, primary, secondary and tertiary isomers of the aforementioned straight chain glycols are also suitable, for example isobutylene glycol, primary, secondary and tertiary amylene glycol or 2,3-dimethyl-2,3-dodecanediol. The polyalkylene glycols (polyols) include diethylene glycol or dihexylene glycol.

In addition to straight and branched chain glycols, alicyclic glycols can also be used, for example 1,2-cyclopentanediol or 1-methyl-1,2-cyclohexanediol.

Further suitable hydroxyl compounds are the polyoxyalkanes, for example glycerol and erythritol or pentaerythritol.

Suitable carboxylic acids include the fatty acids, for example formic acid, acetic acid, Propionic acid or stearic acid, the naphthenic acids, for example cyclopentanecarboxylic acid, as well as aromatic acids, for example benzoic acid.

Suitable polyacyl esters include polyacyl esters of polyoxyalkanes, for example triacyl esters of glycerine, tetraacyl esters of erythritol and pentaerythritol and polyacyl esters of polyalkylene glycols, for example diethylene glycol diacetate. These are polyacyl esters which can be used as solvents compatible with one another, so that they can be used alone or in admixture with one another. At-

3 4

For example, you can use a mixture of different conditions up to 75 percent by weight of the liquid

Proportions of a diacyl ester of an oxyalkane, e.g. B. make up the reaction medium,

of the propylene glycol diacetate, with a polyacyl ester in the practice of these less preferred

of a polyglycol, for example the dipropylene embodiment, the amount of in the liquid

use glycol diacetate. In the present Ver 5 reaction medium contained polyacyl ester solution

drive, which in the following execution means at least 25 percent by weight of this

Examples is explained, can be used as a solution medium, so that the above

medium also a mixture of a polyacyl ester of one of advantages can be achieved, which for this olefin

Polyglycol, for example of the dibutylene glycol oxidizing solvent, are characteristic,

dibutyrate, with a polyacyl ester of a polyoxy ίο In further embodiments of the invention

alkane, for example the glycerol trivalerate or according to the method, the polyacyl ester

use the pentaerythritol tetrapropionate. Solvent suitable in combination with

Of particular interest in the thinners of the invention or auxiliary solvents used, According to processes, the vicinal diacyl esters are the high ones with respect to volatile reaction products of alkylene glycols, for example the diformates, have 15 boiling points and, under the reaction conditions, diacetates, Distearates of the abovementioned conditions are chemically relatively indifferent and relatively indifferent to them Alkylene and polyalkylene glycols and their compounds are resistant to oxidative and thermal attack mix. Of particular interest are the diacetates. In this case too, the polyacyl ester des Ethylene glycol and propylene glycol. These solvents in an amount of at least 25 can 20 percent by weight of the liquid reaction medium mixed alone or in any proportions be used. . be turned. The liquid reaction

Polyacyl esters with mixed acyl groups are medium that proportion of the total content of the

also suitable, for example called ethylene glycol, which is in the liquid

formate butyrate, tetraethylene glycol butyrate caprylate, phase.

Erythritol diacetatdipropionat, Pentaerythritdibutyrat- 25 Among the suitable diluents, which in the

divaleriate or cyclohexanediol acetate valerate. Framework of the invention together with the polyacyl

Monoacyl esters of polyoxylalkanes and polyglyester solvents can be used, kolen are heard for use as a reaction medium, for example, hydrocarbon solvents unsuitable in the present process. The same as xylenes, kerosene, biphenyl, and the like, halogenated applies to other oxy compounds or hydroxylated benzenes such as chlorobenzene, dicarboxylic acid esters, such as Compounds, for example glycerol, glycols, dialkyl phthalates, sebazates, aromatic ethers, such as Polyglycols and oxycarboxylic acids. This is diphenyl ether on it; halogenated aryl ethers, e.g. B. the due to the fact that a large amount of reactive 4,4'-dichlorodiphenyl ether, also diarylsulfoxides, capable hydroxyl groups are present, such as diphenyl sulfoxide; Dialkyl and diary sulfones, are subject to auto-oxidative attack, so that oxidative 35 z. B. the dimethyl sulfone and the dixylyl sulfone, and Side reactions occur which result in the desired nitroalkanes, e.g. B. nitrohexane. The foregoing condemnations Affect oxidation of the olefin. bonds are examples of diluents

In the preferred embodiment, those specified form the within the scope of the invention with the Polyacyl esters are used over all other constituents polyacyl ester solvents; of the reaction mixture, including those contained therein, however, this list is not exhaustive. the dissolved reactants, oxidation products and the advantages that can be achieved with the help of these polyacyl esters By-products, most of the reaction, can also be practical when combined with mixed. This means that the weight of the solvent determines each chemically inert diluent is always higher than the total weight of everyone will hold.

other components. In a less preferred 45 As stated above, need at

Embodiment of the invention, however, the present oxidation process cannot be cata-

work that the total weight of all but the lysers to be added. As a result of the versatile

Polyacyl esters present in the liquid phase usability of the solutions described above

Components is higher than the weight of the poly-solvent used in the oxidation of propene

acyl esters of existing solvents. For example, however, the usual oxidation catalysts are tolerated

can be used as a hydrocarbon feedstock, although they do not produce significant benefits

in refinery quality or a raw hydrocarbon lead. For example, catalysts can be used

material starting material, the z. B. to 50 weight metal basis, such as platinum, selenium, vanadium, iron, nickel,

percent of the olefin to be oxidized and cobalt, cerium, chromium, manganese, silver, cadmium,

50 percent by weight of saturated hydrocarbons 55 mercury and its compounds, preferably in

substances, e.g. B. an alkane, such as propane, in oxidic form, etc. undistributed, on a carrier

in an amount of up to 50 percent by weight, on or without a carrier, or as finely divided suspensions

on the solvent. After the oxy- be present.

The oxidation of propene according to the invention cannot do this with this starting material converted olefin, the alkane and the oxygen together rapidly after a short introduction period with oxidation products including the equip, are also no initiators or auxiliary acetic acid, Low-boiling compounds, such as acetal catalysts, are required, but these can do so dehyde, propylene oxide, acetone, and methyl acetate, and · used to make the short introductory period high-boiling substances (components whose boiling point should be shortened or eliminated. After this period Point above that of the polyacyl ester solvent 65 do not need initiators or auxiliary catalysts is) that were formed during the reaction and / or more to be added.

recycled to the reaction vessel. Suitable initiators include organic ones

are, depending on the reaction or circulation peroxides, for example benzoyl peroxide, further

organic peroxides, for example hydrogen and sodium peroxide, as well as peracids such as peracetic acid and perbenzoic acid, ketones, e.g. B. acetone; Ether, e.g. B. diethyl ether, and aldehydes, e.g. B. that Acetaldehyde, propionaldehyde and isobutyraldehyde. When carrying out the method according to the invention the reaction mixture can be prepared in various ways. For example, you can the propene and the oxygen with the solution

The pressure can range from 0.5 to 350 at. However, the oxidation reaction is facilitated by higher temperatures and pressures, so that the pressure is preferably in the range from 5 to 5,200 at, in particular in the range from 25 to 75 at. The pressure and the temperature must of course be chosen so that the liquid Phase is maintained.
The oxidation of propene takes place autocatalytically

Mix the medium and pour the mixture into the reaction vessel. One can also use propene (expediently proceed very quickly. A typical oxidation of propene moderately in an amount of up to 50 percent by weight,
preferably in an amount of 5 to 30 weight

percent, based on the solvent) with the

in a batch process takes about 0.1 to 20 minutes.

The reaction vessel can be made from the various

Premix the solvent. Preferably the 15 most keen materials will be made up. For example are Propene premixed with the solvent and the aluminum, silver, nickel, almost all ceramic oxygen-containing gas introduced in partial amounts or continuously into the propene-solvent mixture.

You can also use propene and oxygen

The temperature and pressure conditions specified below are initiated. Suitable volume ratios between propene and

per hour or more and are mainly dependent on the size of the reaction vessel. the Oxygen supply is adjusted so that an acidic

Materials, porcelain, glass, silica and various stainless steels are suitable.

The removal of the oxidation products from the

Gas simultaneously through separate or common 20 reaction vessels is preferably in the form of one Feed lines into a body of the solvent are a mixture of a liquid and a gas. bring, which is in a suitable solvent. According to the invention, the oxidation is carried out, which is described below. In a liquid reaction mixture containing products in Embodiment is a mixture of propene and a work-up plant, which a separation device oxygen-containing gas in the in a con- 25 in which a high-speed evaporator and a continuously stirred reaction vessels are combined under the scraper. This arrangement in

Combination with the preceding propene oxidation reaction and subsequent separation steps creates a new, safe, simple, oxygen range from 1: 5 to 15: 1. 30 economical and convenient process for the quantities supplied can be from 0.014 to 42 m ³ large-scale production and extraction of

Acetic acid.

Significant advantages of using the separation device with the high-speed evaporator and

Substance excess (over 1%) in the exhaust gas or above the scraper consists in the fact that, firstly, the one-half of the reaction mixture is prevented because the heat of the oxidation reaction leads to an otherwise dangerous concentration of explosive separation between the gaseous and the liquid Gases is present. If too large a _gene product is supplied, and secondly the amount of oxygen (or air), the total amount of solvent transferred to propene is also stripped from the mixture, so that the concentration is reduced to a minimum, so that the solution rate of the propene in the liquid phase, the oxy-medium load of the downstream distillation rate of propene and the circulating columns become smaller. This reduction in the rate of change can be reduced. Solvent pollution has the advantage that for

An intimate touch of the reactants, d. H. Separating the products smaller columns required Propene and molecular oxygen in which are 45 tfch. Through the said facility will Third, solvent, is known by various the amount of acidic components, above Measures brought about. especially formic acid, in which the

AIs starting materials pure propylene guided solvents can be reduced to traces and mixtures of propylene with other olefins, fourthly, the mass examples of the non-condensable gases game as ethylene or olefinic materials, the overall so _unc j _se h _r volatile components removed so that saturated compounds, for example propane, in the pressure, to prevent excessive

high product loss is required in the downstream work-up stages, is reduced. A special feature of the separating device ⁵⁵ with the high-speed evaporator and stripper is that in the high-speed evaporator about a third of the acids formed during the reaction are separated off and transferred. The treatment of the reactive oxygen leaving the bottom of the flash evaporator results in considerable decomposition; the polymerization mixture in a stripping column results in the remaining reaction and excessively strong side reactions in the circulating solvent. In general, temperature acids are used essentially completely, with the exception of about doors in the range from about 160 to 250 ° C. The temperature should lead to 0.05 to 0.2 percent by weight of that in the circuit for safe operation Removed solvent. This extensive temperature should be so high that dangerous peroxides cannot accumulate in considerable amounts. Corrosive formic acid, of which a temperature in the range from 180 to running solvent is preferred, has the advantage that 230.degree. C., in particular in the range from 190 to 210.degree. C., all devices for working up the bottom stream

an amount of 50% or more can be used. This can be done by cracking Hydrocarbon oils, paraffin wax or other petroleum fractions are produced.

For the reaction temperature and the reaction pressure, only those limits are to be complied with, at which Exceeded in the oxidation of propene with molecular in the liquid phase

the wiper now contains low-cost, unalloyed functional groups, including carboxyl, Carbon steel can be made while carbonyl, alkoxy and oxy groups. previously very expensive, corrosion-resistant, stainless steel. If this residue is returned to the reactor-

Steels were required. is carried out, its oxidation takes place there in the first place

The separation device according to the invention with 5 lines to acetic acid instead of carbon oxides a flash evaporator and a stripper is and water if the reaction conditions are right cleaning devices are also chosen for various reasons. However, this residue material can Considerations that several high-speed vaporizers only within certain concentration limits exhibit. First, a combination ensures that it is returned to and returned to the reaction zone of a flash evaporator with a scraper an io for the production of acetic acid can be evaluated, better control and greater adaptability The upper limit is critical. The overriding Procedure, since with one scraper there is a lot of this upper limit leads to several more easily is to 'change the separation conditions as other related effects. the with a fast vaporizer. This is the first of these effects is a viscosity effect. Line by controlling the flow from a reboiler to 15 as a result of too high a viscosity of the bottom stream heat given off by the wiper reaches. Since one of the reaction vessel is the scraper in the Rapid evaporator only a single equal product processing plant clogged and overweight condition has, a scraper enlarges each wash, so that the amount of in the circuit increases constantly according to the number and the efficiency of its solvents returned to the reactor Soils the degree of 20 achieved with high-speed evaporators. Along with the decrease of the in Kreisder Product separation. Another advantage of the run-out solvent decreases the acetic acid according to the invention Arrangement of a Schnellverdamp- yield, because together with the in the circuit gefers and a wiper versus use solvent also resulted in lower amounts of the several high-speed evaporators consists in the fact that in the case of a residue that can be oxidized to acetic acid Use of a separator, e.g. B. be returned with two 25 reaction vessels. Because the crowd High-speed evaporators produce an undesirably large amount of the propylene oxide solution returned to the reaction vessel (about 7 to 8% of the amount produced) by means of and residue decreases, decreases as a result of the circulated back to the reactor and decreasing dilution the concentration so that the overall yield is reduced. In the case of the unreacted propene. As a result, leads Use of the combination according to the invention 30 the oxidation of propene to produce even greater High-speed evaporator with a scraper will reduce the amount of residue, which will increase the viscosity on the other hand, the propylene oxide is practically completely increased by further, so that the normal oxygen defenders The solvent removal recirculated in the circuit is even more disturbed and the complete oxide is separated. Another advantage of using a tion of the residue to acetic acid is prevented. Wiper instead of a second flash evaporator. 35 In the absence of excess residue in It also consists in the fact that the acids formed in the reactor are the result of these phenomena from the circulating solvent to the procedure soon impracticable, removed to a small residue which should be about 0.05 to The residue concentration in the reactor

0.2 percent by weight of the total in the circuit, therefore less than 60 percent by weight, preferably in returned current is. When using 40 a range from 25 to 50 percent by weight, be quick evaporators remain on the other hand about 1 to 2 drawn on the reaction mixture, are held, weight percent acids in the back in the cycle. Procedure can also be carried out in the case of residues Solvent. concentrations up to about 75% carried out

The bottom stream of the scraper will contain the mass, but will increase with residue concentrations the solvent and residues, d. H. of the 45 over 60% the load on the downstream components, which boil higher than the solution processing facilities due to the viscosity of the medium. This bottoms stream will progressively towards the top of the reaction mixture. fed to an absorber. Non-condensed gases In the present process, the concentration

in the vapor of the flash evaporator and the removal of the residue in the reactor as a result the lower area of the absorber 50 controls the amount of oxidized residue fed and flow in this against the soil and the amount of that formed during the oxidation electricity. Residue within the above specified

An important feature of the present ver limits are coordinated. This driving consists in the controlled oxidation of controlling the residue concentration in the reactor Residue material that is formed in the reactor is caused by a combination of factors. Through this oxidation the yield becomes particular to the temperature, the movement, the spoilage acetic acid generated in the process increased. residence time and the proportion of the reaction

The Oxyda partner carried out in the liquid phase. When a steady state of hydrocarbons is reached, the residue concentration in the solvent that is returned to a complete mixture of oxidation products is determined. If th. For example, in the present case the residue concentration is too high, leading to the oxidation of propene in the liquid phase with problems discussed above, it can be exposed to more than forty individual molecules by enhancing the agitation compounds. In addition to these individual additions and / or reductions in (1) the reaction temperature, a polymeric residue is also generated (2) the residence time in the reactor and (3) the ratio material, which is a complex combination between the propene and propene supplied Settlement has and has not yet been fully described O ₂ quantities. When applying the measures (1), (2) has been. It is known, however, that there are different or (3) the other two factors must be so

9 10

be made to achieve optimal results. Drawn steam contains all amounts of acid, entire

If, however, it turns out that the residue water and all low-boiling components and

concentration for maximum acetic acid production is fed to an acid-low boiler separating column,

If the supply is too low, the residue concentration can be that of the low boilers and a small amount of water

tion in the reaction vessel can be withdrawn as vapor by reversing the figure 5. These _ low boilers

above for the reduction of the residue can be divided into fractions that are

concentration indicated increases various uses suitable as a solvent

will. are. These low boilers can also be divided into individual components

When difficult-to-melt components are divided in the process as mentioned above

Forming residues that do not oxidize and that have become in io, with the help of various

As they accumulate in the system, they can be easily removed using methods such as selective adsorption and extraction

by removing part of the desorption, solvent extraction,

recycled solvent through a small extractive distillation or azeotropic distillation

Distillation column leads, for example, with the tion, using a suitable extractant

Bottom stream of the scraper described here is used,

is fed. The bottom stream of the acid-low boiler separating

The vapor phase of the flash evaporator and column contains acetic acid, formic acid and

streifers is fed to coolers. That of these water and becomes an azeotrope distillation column

released non-condensable material containing benzene is supplied. In this column

agrees and fed to a primary product separator, 20 forms azeotropic mixtures with water and benzene

from the unreacted propene and propane than with formic acid. These mixtures go over and

Steam is drawn to a separator for these components- are fed to a cooler, which is filled with cooling water

leads to be. From this propene is cooled as steam. After condensing, these will be

withdrawn and returned to the reaction vessel - water and formic acid in a separator

guided. One can also cleanly separate and collect all the vapor of the 25 from the benzene. from

Primary product separator in an absorber and this separator is the benzene in the circuit to the

Work up desorber, as described below, recycled azeotropic distillation column while

will. Water and formic acid as the bottom stream of the

Can be withdrawn from an upper area of a primary product separator. The bottom stream of the separator is withdrawn from a side stream that contains mainly low boilers upstream of the azeotropic distillation column, i.e. products that have an acetic acid and a boiling point lower than acetic acid refining than acetic acid, two-column, in which the purified acetic acid transfers propylene oxide, methyl formate, acetal goes and is obtained as an end product,
dehyde, acetone, methyl acetate and methanol. This stream of the solvent-acid separator from which acetaldehyde is withdrawn as vapor is an important feature of the present process. It and recirculated to the reactor have been found to be various components. The remaining products are withdrawn as the bottom stream of this mixed stream, for example the propylene. The recirculated acetal glycol and various of its monoesters, in particular dehyde, increase the acetic acid yield, based on the propylene glycol monoacetate and monoformate of which the propene consumption is disrupted by oxidation with additional course of the reaction in the reactor. This lichem oxygen to acetic acid. disturbing effects are mainly due to

The acetic acid produced and other valuable pro-

Products of the present oxidation process are oxidized to undesired oxidation products

from the bottom stream of the aforementioned 45.

Primary product separator won. This ground- The disadvantage that in the presence of the upstream contains the total amount of the solvent, listed, harmful components in the which consists of the cleaning device with the high-speed solvent returned in the circuit, Evaporator and stripper as steam is withdrawn by the present process in one was, furthermore, the acid, the water, which was not transformed with great advantage. This is done with the help of a the secondary stream of the primary product separator is achieved by solvent treatment, which follows remote, low-boiling components, including to the solvent-acid separation column Methanol, methyl acetate, acetone, isopropanol, will lead. The bottom stream of this column consists Allyl alcohol, biacetyl and others, as well as some predominantly, at about 88 to 92 percent by weight higher boiling components including from the solvent that is in the primary reactor Propylene glycol and various forms formed in situ is used, e.g. B. from propylene glycol diacetate, too high-boiling Esters of propylene glycol, for example together with about 8 to 12 percent by weight Propylene glycol monoacetate, propylene glycol pylene glycol, d. H. a polymeric material that has a monoformate and propylene glycol acetate formate. has a higher boiling point than the solvent. This

^{The soil 6} ° stream containing the substances mentioned is fed to an ester concentration device.

stream of the primary product separator is led to a Lö-, which consists of a distillation column,

Solvent-acid separator supplied, from which all of which the propylene glycol and the glycol ester

higher boiling components including that in the form of a vapor with a high content of

Solvent, the propylene glycol and the pro these components are stripped off while

pylene glycol esters are withdrawn as a bottom stream. 65 the bottom stream, the remaining residue and

Treat and use this soil- containing most of the solvent, first

Stroms is discussed below. to the absorber and then to the reaction vessel

Which is returned from the solvent-acid separator.

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The discharged from the ester concentration device are operated, the reaction draws Steam is fed with the acetic acid from the mixture of these reactors in the bottom stream below the acetic acid refining column and the described separation device are introduced, the column for removing water and that from a flash evaporator and a waste formic acid united. This combined stream will consist of 5 more closely.

fed to a reaction vessel in which the pro- The reaction product is partly gaseous, partly pylene glycol and the glycol ester in the presence of a wise liquid and is continuously a rapid acid catalyst, eg. B. of toluenesulfonic acid, supplied to the evaporator, in which a pressure of 16 at esters and to a certain extent are unesterified. and at the bottom a temperature of 190 ⁰ C and the stream of the esterification vessel is pylenglykoldiacetat maintaining a temperature of 17O ⁰ C and the product io above, the were used in this procedure. From this high-speed evaporator, the solvent preferred for oxidation, greatly increasing the majority of all low boilers, including the whole, was enriched and, with regard to the above-mentioned unreacted propene, CO ₂ and at least half of the harmful components, was in substantially half this example about 60%, the other depleted. 15 low boilers together with about a quarter of the. By treating the solvent, acids, e.g. B. formic and acetic acid, all dissolved therefore certain harmful products of the primary gases and about 6 to 8% of the solvent removed as an oxidation reaction in an excellent solvent vapor. The bottom stream of the rapid agent can be converted for oxidation. Furthermore, the steam was fed to a stripping column, in which a pressure of about 1.74 at and a solvent loss at the bottom, which was maintained in the process instead of temperature of 200 ° C., can be compensated for, due to mechanical causes, while at the same time which contained six distillation trays. The rest of the efficiency and controllability of the Oxyda low boilers, generally between 40 and 50% of the eruption reaction, can be increased. amount produced, in the present example about The ester mixture is fed to a stripping column to 25 33%, furthermore essentially the total amount in which the excess acetic acid and other acids and lighter components and small amounts of water, formic acid and other 10 to 15 % of the solvent was withdrawn as vapor products of the esterification and / or transesterification. The bottom stream of the stripper contained the bulk of the solvent and the vapor from the solvent and was fed to a medium-acid separator for further treatment. 3 ° Absorber. That are cleaned up by the scraper. The bottom stream of the stripping column drawn solvent contained about 55 weight consists predominantly of propylene glycol diesters, percent residue, ie reaction products with which the in the present process preferably a higher boiling point than the solvent,
th solvent, and a small amount of that from the flash evaporator and the off of propylene glycol and its monoesters. This steam withdrawn more thinly became the partial condensation bottom stream and is fed to the ester concentration device in each case to a cooler, which was returned with cooling water and was operated there again as above. In the cooler that deals with the described. In the following exemplary embodiment, the direct non-condensable substances, including the non-oxidation of propene in continuous working condensable gases, most of the CO ₂ , are described in a wise manner. Furthermore, a novel process is about 7% of the total amount of low boilers, for example for separating and purifying acetic acid and 74% of the unconverted propene and propane that was generated by the reaction. separated from the condensable substances and expedient modifications of the work-up countercurrent to that as the bottom flow from the dismantling facilities are also given. 45 stripped off solvent to the absorber. fed. The removed from the cooler, which is connected to the Ab example, not in this example, an autoclave with a condensable substance containing CO ₂ , propane and a capacity of 1 1 as a reaction vessel in propene and are either disposed of or can be used continuously System used. 5 ° also compressed in a compressor and the solvent, propene and oxygen were fed to the absorber so that the propene is recovered through a floor passage directly into the room. In the absorber a pressure was introduced into a turbine stirrer, which circulated at 900 rpm of 10.5 atmospheres, a temperature of about 75 ° C. at the top. The reaction vessel was heated electrically. and below a temperature of 95 ° C.-The temperature regulation was obtained by control 55. He had 25 floors. The non-condensing water flow in internal cooling coils. The free gases O ₂ , H ₂ , N ₂ , CH ₄ , CO and CO ₂ , the reaction temperature, was drawn off on a measuring strip from the upper end of the absorber. Propane recorded continuously. Propene and other soluble components are dissolved in the operation, the reactants, consisting of the solvent, which is returned to the reaction vessel of 92% propene and 99% oxygen, or for purification with propylene glycol acetate, a preferred supply of propene further worked up, as after solvent, fed to a reactor in which a. is described standing.

Pressure of 60 atü and a temperature of 210 ° C The condensate from the cooler, which was kept down. The molar ratio between the streamer and the added amounts of C ₃ H ₆ and O ₂ was 0.8 with the condensate. 65 from the condenser, the one after the flash evaporator. The total residence time was 8 minutes. One can be switched, united. This combined stream also provide two or more reactors, which held 95% of the low boilers produced, most of them are connected in parallel and under identical conditions the acids and about 20% of the solvent and

was fed to a primary product separator. This consists of a distillation column with 40 floors in which a pressure of 2.8 at, a temperature of about -16 ° C above and a temperature below maintained at 145 ° C and operated at a reflux ratio of 6.0.

The unreacted propene and propane were withdrawn as vapor from the primary product separator and fed to a separator for these components. From this, propane is used as the bottom stream and propene withdrawn as vapor. The propene is recycled to the reaction vessel. The propene-propane separator has 75 floors. A pressure of 21 at is maintained in it, and it is heated at the top to 50 ° C. and at the bottom to 55 ° C. and operated at a reflux ratio of 11.7. If you increase the temperature at the lower end of the separator, some propane can also escape.

In another method for separating propane from the circulated propene, the steam from the primary product separator is mixed with the steam that is fed from the coolers to the absorber. As mentioned above, the bottom stream containing the solvent, propene and propane from the absorber can be returned directly to the reactor or further worked up to purify the propene, ie to separate off the propane. When the propane concentration in the reaction vessel rises to a value , in which the propene oxidation is disturbed, a return of additional or excess propane to the reactor is prevented by the fact that the bottom stream of the absorber is wholly or partly conducted in a side stream branched off from the bottom stream of the absorber, for example by means of a controllable distributor, into a desorber (not shown) in which a pressure of 21 at and above a temperature of 50 ° C and below a temperature of 100 ° C was maintained. Here, solvent is drawn off as a bottom stream and returned to the reactor. Propane and propene are drawn off as vapor and _{fed to a C 3} H ₆ -C ₃ H ₈ separator, in which a pressure of 21 atm is maintained and which is heated to about 50 ° C. at the top and to 55 ° C. at the bottom. Propane is withdrawn as a bottom stream. Propene in essentially the same composition as the starting material is circulated into the flow of the propene starting material fed to the reaction vessel.

The primary product separator was about the fifth tray, from the top of the column calculated from a side stream withdrawn, which is fed to an acetaldehyde separation column. from acetaldehyde was withdrawn as vapor and recycled to the main reactor. The other low boilers were withdrawn as the bottom stream. This can expediently be separated into fractions which can be used as a solvent for various purposes or optionally can also be further separated into individual components. In the acetaldehyde separation column a temperature of about 22 ° C was maintained at the top and a temperature of 60 ° C at the bottom. It had 70 trays and was operated at a pressure of 1.05 atmospheres and a reflux ratio of 6.0.

Now is the recovery of the acetic acid produced and of other valuable oxidized by-products treated. The bottom stream of the primary product separator described above contains the Total amount of solvent used by the flash evaporator and wiper Separation device was withdrawn as steam, further acid, water, in the side stream low-boiling components not removed from the primary product separator, including methanol, Methyl acetate, acetone, isopropanol, allyl alcohol, biacetyl and other, various high-boiling components, including acetonylacetate, propylene glycol and various esters thereof, for example Propylene glycol monoacetate, propylene glycol monoformate and propylene glycol acetate formate, as well as a small amount of residue. This stream is fed to a solvent-acid separator. This column had 10 trays, at the top a temperature of about 105 ° C and at the bottom End a temperature of 192 ° C and was under a pressure of 1.05 at and with a reflux ratio operated by 3. The total amount of solvent and high-boiling components was withdrawn as a bottoms stream and fed to a solvent treatment system, which follows is described. The vapor withdrawn from the solvent-acid separator contains the total amount the acid, the water and the low-boiling components and became a distillation column for the separation of acids and low boilers, from which the low boilers, a small one Amount of water and traces of high boilers were withdrawn as steam.

The bottom stream of this column contained about 74% acetic acid, about 8.5% formic acid, about 6.5% water and traces of other components and was fed to an azeotropic distillation column. This had about 70 floors and had a temperature of about 77 ° C. at the top and a temperature of 125 ° C. below and was operated under a pressure of 1.05 at. Benzene was used to form the azeotropic mixture, which was introduced into the column at a point above the top tray. The amount of benzene corresponded to 9 parts by weight of benzene per part of the product withdrawn as vapor from the column. In this system, the benzene forms two distinct azeotropic mixtures, one with water and one with formic acid, rather than a ternary azeotropic mixture of these three components. In operation, an azeotropic mixture of benzene and water and an azeotropic mixture of benzene and formic acid were drawn off as vapor and fed to a water circulation cooler. After the condensation, a mixture of benzene, water and formic acid was fed to a collector, in which the mixture separated into an upper benzene phase and a lower phase which contained about 42% water, 55 % formic acid and about 3% acetic acid. These components have been removed from the bottom of the collector. The benzene of the upper phase was supplemented with further benzene and recycled to the azeotrope distillation column.

The bottom stream of this column consisted for the most part (more than 86 percent by weight) Acetic acid and also contained small amounts of higher boiling components. He became an acetic acid refining column fed, the 40 floors

sat, above a temperature of about 118 ° C, below had a temperature of 130 ° C and under a pressure of 1.05 at and with a reflux ratio operated by 5.0. Purified acetic acid was withdrawn as vapor. . .

The bottom stream of the solvent-acid separator contained about 90% propylene glycol diester, mainly the diacetate (about 88%) and a small amount of acetate formate (about 2%), the remainder mainly propylene glycol and its monoesters, propylene glycol morroacetate and monoformate, and a small amount Acetonylacetate and residue. This stream was fed to a distillation column for Esterkonzentration which had 50 trays, the top having a temperature of 186 ° C and below a temperature of 195 ⁰ C and was operated at a reflux ratio of 7.0. The bottom stream of this column consisted of more than 97% of the propylene glycol diesters, which can be used as solvents for the oxidation reaction, the remainder being essentially residue. This stream was combined with the stream from the stripper and fed to the absorber, the stream of which was returned to the main reactor. This absorber stream contained about 50 percent by weight of residue on entry into the reaction vessel. In this embodiment, the reaction conditions were previously set so that, with the predetermined product distribution, the amount of the oxidized residue and the amount of the residue formed in the reaction are matched to one another so that the residue concentration in the reaction vessel is kept relatively constant.

The vapor withdrawn from the ester concentration column, which is about 20 percent by weight of the opposite an oxidation attack of volatile propylene glycol, its monoesters and acetonylacetate was fed to an esterification vessel in which, with the help of an acid catalyst (e.g. toluene sulfonic acid) the components mentioned have been esterified and transesterified to form useful propylene glycol diesters. Before entering the esterification vessel the steam stream was combined with the stream obtained from a mixture of the bottoms stream the acetic acid refining column and one of the bottoms stream of the water-formic acid separation column The stream branched off existed, so that in the esterification reaction there was an excess of acetic acid was guaranteed. This combined stream now contained about 61% propylene glycol ester, about 17% of the above-mentioned, inconsistent components and residue, about 21% acetic acid, remainder undesignated High boilers. This stream was fed to the esterification vessel, in which a temperature of 170 ° C and a pressure of 1.05 at would. After completion of the reaction, the esterification product contained about 70% useful propylene glycol diesters (about 14 weight percent more than in the reactor feed stream), about 6% acetonylacetate, propylene glycol and its monoesters (about 62 percent by weight less than in the feed stream of the reactor), about 18% acetic acid, the remainder esterification by-products and persistent High boilers.

The ester mixture of the esterifier was fed to a solvent stripping column which had 20 plates, had a temperature of 150 ° C. at the top, a temperature of 200 ° C. below and was operated under a pressure of 1.76 at and with a reflux ratio of 7.0. The vapor withdrawn from this stripper contained over 77% acetic acid, about 6% water and small amounts of formic acid, lower and higher boiling components and was fed to the acid intermediate boiler column for further treatment. The bottom stream of the scraper was about -92% solvent usable diester oil. enriched, remainder volatile components, and was recycled to the ester concentrator so that the volatile components were converted to persistent solvent esters. These useful, persistent solvent esters were recycled to the absorber and ultimately to the reaction vessel.

In a typical oxidation process according to this embodiment, the main reaction vessel the starting materials are supplied in approximately the following quantities per hour: 575 g propene, 700g oxygen, 4600g solvent (e.g. propylene glycol diacetate). In the steady state (residence time in the reaction vessel about 8.0 minutes) the propene conversion was about 50% and the oxygen conversion 99.95%. Acetic acid is obtained in a yield of about 40 mol percent as well as smaller ones Quantities of other oxidation products.

Claims (1)

Claim: Process for the production of acetic acid by oxidation of propene and distillative Obtaining acetic acid from the reaction product, characterized in that one a) propene with oxygen in the liquid phase in the presence of at least 25 percent by weight, based on the liquid reaction mixture, a fully acylated polyoxyalkane, polyoxycycloalkane or polyglycol, preferably Propylene glycol diacetate, containing solvent in a temperature range of 160 to 250 ° C, preferably 180 to 230 ° C, and a pressure range of 0.5 to 350 at, preferably 5 to 200 at, implements b) and the reaction product with the aid of a flash evaporator and a stripper in a gas phase containing the acetic acid and low-boiling products and a gas phase Most of the solvent, high-boiling products and the residue containing it Liquid phase decomposed, c) the liquid phase is returned to the oxidation zone via an adsorber, while adhering to a residue concentration below 60 percent by weight in the reaction mixture, d) the gas phase is subjected to condensation by cooling, the non-condensed Vapors are returned to the oxidation zone via the adsorber, propene and propane are distilled off from the condensate and that Propene and the acetaldehyde obtained from a bypass flow are returned to the oxidation zone and the remaining con- 009 532/282 Densate is broken down into a distillation residue and ¹ into a distillate containing the total amount of acetic acid, e) from this first the. low-boiling components are distilled off, the acetic acid through . . azeotropic distillation. with; benzene from what -... ser and formic acid freed and intestine. Purifies by distillation. f f) and the distillation residue of the condensate; sows together with the distilled, deep feeds boiling, propylene glycol and glycol monoester containing constituents of an ester concentration column, the vapors of which together with the acetic acid from the bottom stream of the acetic acid refining column and the bottom stream of the azeotropic distillation in the presence of a. Catalyst, preferably toluene sulfonic acid, esterified to give fully acylated polyoxyalkanes or esterified to _T and these fed back to the oxidation process. . , ';