MXPA00005086A - Method for separating maleic anhydride from maleic anhydride-containing mixtures by stripping - Google Patents

Abstract

The invention relates to a method for separating maleic anhydride from the maleic anhydride-containing reactor waste gases resulting from maleic anhydride production by hydrocarbon oxidation. According to said method the gas stream is placed into contact with a high-boiling inert absorption agent for maleic anhydride and maleic anhydride is separated from the resulting liquid absorbate phase by steam stripping. An alcohol is used as desorption agent and maleicanhydride at least partly reacts with the alcohol to yield an ester.

Description

SEPARATION OF MALEIC ANHYDRIDE FROM MIXTURES CONTAINING MALEIC ANHYDRIDE, BY DRAGGING The present invention relates to a process for the separation of maleic anhydride from a gaseous stream containing maleic anhydride, to a process for the preparation of maleic esters and to a process for the preparation of hydrogenation products of maleic acid derivatives , which includes the separation of maleic anhydride from a gaseous stream containing maleic anhydride. Maleic anhydride is produced on an industrial scale by catalytic oxidation of hydrocarbons, such as benzene, butenes or butane, using air. In addition to maleic anhydride, the resulting gaseous reaction mixture contains mainly water, carbon monoxide and carbon dioxide. Typically, the maleic anhydride is washed from the reactor exhaust gases containing maleic anhydride from the oxidation of hydrocarbons by extinction with high-boiling aliphatic alcohols. A process of this type is described, for example, in DE-A-31 06 819. This process has the disadvantage that, in the extinguishing process, some of the alcohol is lost with the exhaust gases. This loss causes high costs.

The maleic anhydride which can be obtained from the reactor discharge gases from the oxidation of hydrocarbons and the maleic acid derivatives, such as the maleic esters obtained from the maleic anhydride by reaction with absorbents are frequently subjected to hydrogenation Subsequent to butanol, tetrahydrofuran or? -butyrolactone. WO 97/43234 describes a process for the preparation of β-butyrolactone, butan-1,4-diol and tetrahydrofuran in which the maleic anhydride is separated from the discharge gases of the maleic anhydride reactor from the oxidation of hydrocarbons using an inert organic solvent of high boiling point as an absorbent, and the maleic anhydride is separated from the resulting absorption product by stripping using a stream of hydrogen gas. The separated maleic anhydride then passes to a gas phase hydrogenation for the preparation of butanediol, tetrahydrofuran and β-butyrolactone. This process has the disadvantage of the formation of free maleic acid or fumaric acid. In the presence of still small amounts of water as are frequently present in the reactor discharge gases from the oxidation of hydroparbins, the maleic anhydride forms free maleic acid which is corrosive. In addition, the free maleic acid tends to be isomerized into fumaric acid, which has only poor solubility and can cause considerable problems in the subsequent hydrogenation step due to deposit on the hydrogenation catalyst. Moreover, the maleic or fumaric acid forms succinic acid in the hydrogenation step. This has extremely low volatility, which may sooner or later give rise to catalyst cake formation. An object of the present invention is to provide a process for the separation of maleic anhydride from the reactor discharge gases containing maleic anhydride from the oxidation of hydrocarbons, which is suitable for the preparation of maleic acid derivatives or products of hydrogenation thereof and avoids the aforementioned disadvantages. We have found that this objective is achieved by a process for the separation of maleic anhydride from a gaseous stream containing maleic anhydride, in which the gaseous stream containing maleic anhydride is contacted with a liquid absorbent phase containing at least one high-boiling inert absorbent for maleic anhydride, and the maleic anhydride is separated from the resulting liquid absorbent phase by steam entrainment, where the separating agent used is an alcohol, at least some of the maleic anhydride reacting with the alcohol . For the purposes of the present invention, the term absorbent phase is taken to mean the liquid mixture of absorbents. The phase of the substance absorbed or absorbed is the absorbent phase charged with the absorptive or absorbent, in this case maleic anhydride or the reaction products thereof. In the presence of alcohol as the separating agent, at least partial alcoholysis of the maleic anhydride is carried out with formation of the monoester, and further esterification is carried out with diester formation. The hydrolysis of the anhydride to free maleic acid is thus suppressed by traces of water absorbed from the gas stream in favor of ester formation. Any maleic acid formed by hydrolysis will then react to obtain monoesters or maleic diesters. The proportion of free acid in the absorbed phase is consequently low. The absorbent or liquid absorbed phase contains at least one high boiling inert absorbent for maleic anhydride. The high boiling point inert absorbent generally has a boiling point which is at least 30 ° C, preferably at least 50 ° C, particularly preferably at least 70 ° C, higher than the boiling point of the maleic anhydride. Suitable absorbers are described, for example, in WO 97/43234. Examples are high-boiling esters of italic acid, terephthalic acid or maleic acid such as dimethyl, diethyl or dibutyl phthalate, dimethyl terephthalate or dibutyl maleate, aromatic hydrocarbons such as diynylbenzene, esters of cycloaliphatic acids such as dibutyl hexahydrophthalate. , in addition polymethylbenzophenols, ethylene glycol ethers and polysiloxane ethers. Preferred absorbers are esters of aromatic and cycloaliphatic dicarboxylic acids, particularly preferably esters of italic acid and terephthalic acid. The high boiling point absorber is generally present in excess in the absarving phase. The weight ratio between the absorbent and the maleic anhydride is generally from 1: 1 to 100: 1, preferably from 2: 1 to 100: 1, particularly preferably from 4: 1 to 100: 1. The maleic anhydride is separated from the absorbed phase by steam entrainment using an alcohol as the buffering agent. The term "entrainment" is taken to mean the separation of the absorptive or absorber present in the absorbed phase with the aid of a desorption aid (separating agent), with the absorptive accumulating in the separating agent. The absorptive concentration in the absorbed phase is correspondingly reduced, and the absorbed phase is regenerated in the process. In addition to the mass transfer of the absorbed phase, the present process also includes at least partial reaction of the absorber with the separating agent.

The separating agents suitable for the novel process are in principle all the alcohols which are volatile under the process conditions (separating alcohols). Preference is given to methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, n-pentanol and isopentanol, particularly preferably methanol, ethanol and n-butanol. The molar ratio between alcohol and maleic anhydride is generally from 1: 1 to 300: 1, preferably from 1.5 to 200: 1, particularly preferably from 3: 1 to 50: 1. The entrainment or separation is generally carried out countercurrently, in which the absorbed phase charged with maleic anhydride moves in the opposite direction to the separating agent in vapor form, with intense mass and heat exchange taking place between the descending phase, of the absorbed liquid and the ascending vapor phase. The liquid absorbed phase is generally depleted in maleic anhydride, while the vapor phase is enriched in correspondence with maleic anhydride or the reaction products thereof. The preferred drag is carried out countercurrently in a column, preferably a packed column or a bubble cap column. The alcohol used as the separating agent is preferably introduced into the lower section of the column, and the absorbed phase charged with maleic anhydride is preferably introduced into the upper section of the column. The phase of the depleted absorbed maleic anhydride is obtained in the lower part of the column, and the alcohol used as separating agent together with the maleic acid derivatives are obtained in the head of the column. For the purposes of the present invention, the term maleic acid derivatives is taken to mean maleic anhydride, maleic acid, maleic monoesters, maleic diesters, fumaric acid, fumaric monoesters and fumaric diesters, the esters being based on the alcohol used for the separation. It is also possible to carry out the separation of maleic anhydride from the absorbed phase in a holding tank with the attached distillation head, it being possible for the alcohol to be transported to the tank together with or separately from the absorbed phase. The maleic acid derivatives are passed over the distillation head together with the evaporating alcohol. The countercurrent method is a preferred embodiment of the invention, in a particularly preferred embodiment, other separation steps for retaining the high boiling inert absorbent are located between the feed point for the absorbed phase and the column head. Some of the separating alcohol can be added to the absorbed phase before feeding to the column. The spent absorbed phase is obtained in the lower part of the column and can be fed to a new absorption operation. A high degree of exhaustion is not necessary, but it is desirable. Based on the maleic anhydride content of the feed in the head, this is generally from 80 to 100%, preferably from 95 to 100%. The drag is generally carried out at above 100 ° C, preferably from 150 to 300 ° C, particularly preferably from 170 to 300 ° C. The pressure during the drag is generally from 10 mbar to 10 bar, preferably from 100 mbar to 6 bar, particularly preferably from 300 mbar to 5 bar. During separation or entrainment, the maleic anhydride is at least partially esterified by means of alcohol. A mixture consisting mainly of maleic anhydride, maleic acid, fumaric acid, maleic monoesters, maleic diesters, fumaric monoesters and fumaric diesters is formed. In general, a high excess of spacer alcohols promotes the formation of the ester. The novel process has the advantage of a small proportion of free maleic or fumaric acid in the superior product. In general, the proportion of free acid in the superior product, based on the total amount of maleic acid derivatives, depends on the amount of water present. Furthermore, it is advantageous if the proportion of fumaric esters in the upper product is low. The proportion of fumaric monoesters and fumaric diesters is from 0 to 10% by weight, preferably from 0 to 5% by weight, based on the total amount of maleic acid derivatives. The present invention also relates to a process for the preparation of maleic esters comprising the following steps: contacting a gaseous stream containing maleic anhydride with a liquid absorbent phase containing at least one high boiling, inert absorbent having a boiling point which is at least 30 ° C higher than that of the maleic anhydride, separation of the anhydride maleic by entrainment with alcohol as the separating agent, where at least some of the maleic anhydride reacts with alcohol, c) if desired, in addition esterification using alcohol.

Step a) is preferably carried out using a gaseous stream containing reactor discharge gases containing maleic anhydride from the preparation of maleic anhydride by the oxidation of hydrocarbons.

Step b) of the separation generally gives a mixture containing, based on the total amount of maleic esters, from 5 to 95% by weight, preferably from 10 to 90% by weight of the maleic diester. Step b) of preference separation is followed by step c) in which the proportion of maleic monoesters and, where appropriate, maleic anhydride or maleic acid or fumaric acid and fumaric monoesters is reduced by another esterification to maleic diesters or diesters fumáricos. The preferred esterification is carried out using the separating alcohol. The esterification of maleic anhydride, maleic acid, maleic monoesters or carboxylic acids is generally described in EP-A 0 255 399, EP-A 0 454 719, DE-A 5 543 673, DE-A 19 607 953 or in "Organikum", VEB Deutscher Verlag der Wissenschaften, 15th edition, Berlin, 1977, pp. 498-502. The novel process of preference is used for the preparation of maleic diesters. The mixture obtained in separation step b) or the mixture obtained by another esterification using the separating alcohol in step c) of the process described above or the maleic acid derivatives obtained from this mixture by distillation can then be subjected to hydrogenation. Depending on the reaction conditions, preference is given to 1,4-butanediol, tetrahydrofuran and / or β-butyrolactone. The present invention also relates to a process for the preparation of at least one compound selected from the group consisting of 1,4-butanediol, β-butyrolactone and tetrahydrofuran, comprising the following steps: a) contacting a gaseous stream containing maleic anhydride with a liquid absorbent phase containing at least one high-boiling, inert absorbent having a boiling point which is at least 30 ° C higher than that of the maleic anhydride, b) the separation of maleic anhydride by entrainment with alcohol as the separating agent, where at least some of the maleic anhydride reacts with the alcohol, c) if desired, in addition another esterification using the alcohol, d) if desired, the separation of the alcohol from from the resulting mixture containing the maleic acid derivatives, e) the hydrogenation of the resulting maleic acid derivatives.

Step a) is preferably carried out using a gaseous stream consisting of the reactor discharge gases containing maleic anhydride from the preparation of maleic anhydride by the oxidation of hydrocarbons. The maleic acid derivatives obtained in step b) of separation can be directly hydrogenated. These may be in the form of a mixture with the alcohol separator. Advantageous, but not crucial to the success of the hydrogenation, is a high degree of esterification of the resultant maleic acid derivatives. In general, at least 50% by weight, preferably at least 70% by weight, particularly preferably at least 90% by weight, especially preferably at least 95% by weight, in particular at least 97% by weight of the derivatives of maleic acid that are going to be hydrogenated are in the form of maleic diesters. To obtain a high degree of esterification, the mixture obtained in step b) of the separation preferably is subjected to another esterification using alcohol. The mixture obtained in separation step b) or by another esterification as in step c) can be subjected to hydrogenation directly or after separation of the alcohol employed as the separating agent. Preferably, the hydrogenation proceeds by separating the alcohol from the resulting mixture as in step d). The hydrogenation of the resulting maleic acid derivatives can be carried out in the liquid phase or in the gas phase. The hydrogenation can be carried out using homogeneously dissolved catalysts, using suspended catalysts or using fixed bed catalysts. In general, the hydrogenation catalysts used contain one or more of the following elements: Copper, palladium, platinum, ruthenium, rhenium, cobalt, manganese, nickel, molybdenum and chromium. These hydrogenation catalysts and the hydrogenations are carried out using them as described, for example, in WO 97/43234, EP-A 0 552 463, EP-A 0 724 908, DE-A 2 501 499, BE 851 227, US 4,115,919 , EP-A 0 147 219, EP-A 0 417 867, US 5,115,086 and EP-A 0 382 050. During hydrogenation in gas phase, the temperature is generally from 150 to 250 ° C and the pressure is generally from 5 to 100 bar In the case of hydrogenation in the liquid phase, the temperature preferably is from 100 to 3Q0 ° C and the pressure is preferably from 60 to 300 bar. The alcohol bound in the maleic esters is released into the hydrogenation and can be recovered and reused for entrainment. The novel process is distinguished by the fact that the formation of corrosive acids is virtually eliminated. In addition, the maleic and fumaric esters formed and the succinic esters formed therefrom by hydrogenation have greater solubility and higher volatility than the free acids, which means that the problems caused by the deposit in the hydrogenation catalyst are avoided.

The invention is illustrated in more detail by the following examples.

Examples The experiments described below are carried out in an apparatus consisting of a 250 ml distillation flask, which can be heated, with distillation inlet and outlet, a heatable packed column with a length of 50 cm and a width of 3 cm attached to it, and a distillation union with a head point. The feed for the absorbed, a mixture of dimethyl phthalate as an absorbent and maleic anhydride, is located between the upper end of the heatable column and the distillation union. The methanol as the separating alcohol is introduced over the distiller. The feed and discharge streams are continuous, and the distillation level is released in batches. After a process time of 5 hours, the samples of the distillation discharge and the head discharge are taken and analyzed by gas chromatography. The percentages refer to percent of the CG area.

Example 1 150 g of dimethyl phthalate are introduced into the distiller and heated to 220 ° C. 100 ml / h of methanol are then fed continuously into the distiller and evaporated. The packed column is heated to 220 ° C producing a temperature above 65 ° C at the head of the column. 100 ml / h of a mixture of 80% by weight of dimethyl phthalate and 20% by weight of maleic anhydride are then introduced continuously as the feed to the head, during which the temperature at the top of the column rises to 140. at 150 ° C. The discharge of the distillation contains from 98% to 99% dimethyl phthalate, approximately 0.3% methanol, approximately 0.3% maleic anhydride and approximately 0.28% monomethyl maleate and dimethyl. The discharge from the head contains about 0.8% maleic anhydride, about 20% monomethyl maleate, about 14% dimethyl maleate and about 62% methanol. Free maleic acid or fumaric acid can not be detected.

Example 2 The procedure is as described in Example 1, but the overhead feed consists of 100 ml / h of a mixture of 78.5% by weight of dimethyl phthalate, 19.5% by weight of maleic anhydride and 2% by weight of water, and the distillation feed consists of 200 ml / h of methanol. The temperature at the head of the column is approximately 150 ° C. The distillation discharge contains 99% dimethyl phthalate, about 0.5% methanol, < 0.05% monomethyl and dimethyl maleate and traces (< 0.05%) of maleic anhydride. The head discharge contains < 0.05% maleic anhydride, about 18% monomethyl maleate, about 1% dimethyl maleate and about 77% methanol. The rest consists of monomethyl fumarate (approximately 1%) and maleic acid (0.4%) and fumaric acid «0.05%).

Example 3 The procedure is as described in Example 1, but the overhead feed consists of 100 ml / h of a mixture of 79.7% by weight of dimethyl phthalate, 19.9% by weight of maleic anhydride and 0.4% by weight of water , and the distillation feed consists of 100 ml / h of methanol. The temperature at the head of the column is approximately 150 ° C. The discharge from the distillation contains approximately 99.2% dimethyl phthalate, approximately 0.3% methanol < 0.05% monomethyl and dimethyl maleate and < 0.05% maleic anhydride. The head discharge contains < 0.05% maleic anhydride, about 14% monomethyl maleate, about 11% dimethyl maleate, about 2% monomethyl fumarate and about 72% methanol. Free maleic acid (approximately 0.5%) and fumaric acid (< 0.05%) were only present in small amounts.

Claims (4)

1. A process for the separation of maleic anhydride from a gaseous stream containing maleic anhydride, in which: a) the gaseous stream containing maleic anhydride is contacted with a liquid absorbent phase containing at least one inert absorbent of boiling point for the maleic anhydride, and b) the maleic anhydride is separated from the phase of the resulting liquid absorbed by steam entrainment, wherein the separating agent used is an alcohol, at least some of the maleic anhydride reacting with the alcohol.

2 . The process as recited in claim 1, wherein the high boiling point inert absorbent has a boiling point which is at least 30 ° C higher than that of the maleic anhydride.

3. The process as recited in claim 1 or 2, wherein the alcohol employed as a separating agent is selected from the group consisting of methanol, ethanol and n-butanol.

4. The process as mentioned in any of claims 1 to 3, wherein the gas stream used is a reactor discharge stream containing maleic anhydride from the separation of maleic anhydride by the oxidation of hydrocarbons. The process as mentioned in claim 2, consists of the additional steps of: c) in addition the esterification of the resulting mixture using alcohol, where esters of maleic acid are obtained. The process as recited in claim 5, wherein step a) is carried out using the reactor discharge gases containing maleic anhydride from the preparation of the maleic anhydride by the oxidation of hydrocarbons. The process as mentioned in claim 5, for the preparation of maleic acid diesters. The process as mentioned in claim 2, comprises the following additional steps: c) optionally, another esterification using the alcohol, d) optionally, the separation of the alcohol from the resulting mixture containing maleic acid derivatives, e) the hydrogenation of the resulting maleic acid derivatives, wherein at least one compound selected from the group consisting of 1,4-butanediol, β-butyrolactone and tetrahydrofuran is obtained. The process as mentioned in claim 8, wherein step a) is carried out using exhaust gases of the reactor containing maleic anhydride and coming from the preparation of maleic anhydride by oxidation of hydrocarbons.