GB1593610A

GB1593610A - Process for recovering maleic anhydride by condensation

Info

Publication number: GB1593610A
Application number: GB23605/78A
Authority: GB
Original assignee: Chevron Research and Technology Co; Chevron Research Co
Current assignee: Chevron USA Inc
Priority date: 1977-06-24
Filing date: 1978-05-26
Publication date: 1981-07-22
Also published as: FR2395265B1; JPS5412318A; DE2826919A1; BE868363A; FR2395265A1; NL7806705A; CA1091678A; IT7824854A0; IT1096763B; DE2826919C2; JPS5747194B2

Description

(54) A PROCESS FOR RECOVERING MALEIC ANHYDRIDE BY CONDENSATION (71) We, CHEVRON RESEARCH COMPANY, a corporation duly organized under the laws of the State of Delaware, United States of America, of 525 Market Street, San Francisco, California, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns a process for recovering maleic anhydride from gaseous compositions which comprise water as well as maleic anhydride. The process is carried out by condensing the gas under select temperature and pressure conditions. In this way, maleic anhydride is collected as a condensate while light impurities such as water and acids remain in the vapor phase.

This process is particularly adaptable to the recovery of maleic anhydride which is normally lost during the light stripping of crude maleic anhydride. Crude maleic anhydride is produced by the vapor phase oxidation of a hydrocarbon feed, and is recovered by absorption from the oxidation effluent using a liquid solvent followed by distillation of the anhydride-rich absorbent. U.S. Patent 3,818,680 thoroughly describes a typical process for producing crude maleic anhydride using a liquid intramolecular carboxylic acid absorbent.

Other organic absorbents can be used such as those disclosed in U.S. Patents 2,574,644; 3,040,059; 2,893,924; 3,891,680 and 3,850,758.

It is conventional practice to further refine the crude maleic anhydride by stripping off low-boiling impurities using reduced pressure distillation. In general, the low-boiling impurities comprise carboxylic acids such as acetic and acrylic acids and water. However, under even the best of operating conditions, the overhead vapor will also contain some maleic anhydride which is either lost through the vacuum system or recovered through an elaborate absorption and recycle process. Thus, the overhead vapor comprises maleic anhydride and water. Conventional absorption processing has been tried as a method of recovering the anhydride, but has several drawbacks. In particular, a significant proportion of the impurities must also be absorbed and recycled to insure complete anhydride recovery. Thus, using absorption to recover the anhydride from the light stripper overhead vapor is a relatively inefficient process.

Accordingly, it would be advantageous to provide a process for recovering maleic anhydride from gaseous mixtures also containing water and low-boiling impurities which while recovering the anhydride leaves the water and other impurities in the gas.

Several U.S. patents discuss the recovery of maleic anhydride from gaseous compositions also containing water. In general, these methods use partial condensation of maleic anhydride effected by cooling the gaseous composition to temperatures above 50 so as to minimize condensation of water. Such practice, however, results in only partial recovery of maleic anhydride contaminated with some maleic acid, since any attempt at complete recovery requires cooling the gas below the water dew point. If the water dew point is reached, the maleic anhydride will hydrolyze to maleic and fumaric acids. Thus, for example, British Patent 822,612 teaches diluting the effluent gas from the oxidation reactor with an inert gas until the anhydride partial pressure is less than 2.24 millimeters of mercury and cooling the gas to about 20"C. Similarly, U.S. Patent 2,762,449; U.S. Patent 2,812,037; and French Patent 1,303,126 teach partial condensation processes for recovering maleic anhydride by cooling the gas to temperatures between 50"-60"C from gas compositions comprising the anhydride and relatively low concentrations of water. In summary, prior art teaches recovery of maleic anhydride by cooling maleic anhydride gases at about one atmosphere pressure.

The prior art partial condensations are particularly useful where the concentration of anhydride is relatively high and concentration of water relatively low, usually less than 5 volume %, such that the over-all efficiency of the recovery is not significantly reduced by leaving minor amounts of anhydride in the gas. However, it is still desirable to provide a process which provides essentially complete recovery of anhydride even where the concentration of water is relatively high, typically more than 10 volume %.

According to the present invention, there is provided a process for recovering maleic anhydride from gaseous compositons comprising maleic anhydride and water, comprising cooling said composition to a temperature in the range of from 20"C to 50"C at a pressure less than 200 millimeters of mercury.

The composition is preferably condensed at a temperature of from 25"C to 400C and at a pressure of from 25 mm to 100 mm of mercury, more preferably less than 50 mm of mercyry.

Maleic anhydride can be recovered from gaseous mixtures with water by the process of this invention without appreciable loss of efficiency by condensing the gas containing water and maleic anhydride at reduced pressure. Generally, gas streams containing both water and maleic anhydride cannot be condensed because of the possibility that enough water will condense with the anhydride to cause hydrolysis of the anhydride to maleic acid. Maleic acid readily isomerizes to solid fumaric acid which is insoluble. However, it has been found that under the select conditions of this invention, such gaseous mixtures can be condensed to recover maleic anhydride without consequent water condensation. Condensation of the mixtures can be carried out at a temperature between 20"C and 50"C at a reduced pressure of less than 200 mm of mercury.

In a preferred embodiment, the process is used to recover residual maleic anhydride contained in the gaseous overheads from the distillation of crude maleic anhydride. Such compositions generally comprise from 1 to 30 per cent by volume maleic anhydride and from 10 to 70 per cent by volume water. In accordance with this invention, the overhead vapor containing residual maleic anhydride and low-boiling impurities is passed to a condenser system. The condenser system is maintained at a temperature of from 20"C to 50"C at a pressure of less than 200 millimeters of mercury. The condensate from the condenser system, containing liquid maleic anhydride, can be recycled and the vaporous impurities can be vented through the vacuum system.

The following example further illustrates the process of this invention applied to the recovery of maleic anhydride from the light stripper overhead vapors of a crude maleic anhydride distillation process, and suggests additional embodiments within the scope of the following claims.

Example A crude maleic anhydride product stream was obtained by oxidising n-butane according to the process described in U.S. Patent 3,864,280. The concentrations of components in the product stream are shown in Table I. For such a composition, the dew points of water and maleic anhydride at various total pressures are given in Table II. The stream was condensed by passing it through a condenser cooled by a countercurrent flow of air through the jacket.

In a typical run, for example, 2 gmols/hr of this stream was passed through a condenser with a heat transfer area of 0.3 sq.ft.

As condensation proceeded, crystals of maleic anhydride were formed on the heat exchanger walls. The exhaust from the condenser was scrubbed and analyzed for its composition by potentiometric titration for organic acids and by gas chromatography for complete composition.

The condensed maleic anhydride was then analyzed for trace impurities such as maleic acid, fumaric acid, light organic acids and other organic impurities by various methods such as freezing point, preferential solubility in chloroform, infra-red spectrometry and gas chromatography.

Table III lists the run conditions and the results of these analyses. Efficiency of maleic anhydride recovery by this condensation process was obtained from analyses of the condensed maleic anhydride and the exhaust gas composition leaving the condenser in operation. Data in Table III shows that maintaining a temperature of more than about 20"C, preferably more than about 30"C, and a pressure of less than about 50 mm Hg results in undetectably small amount of water condensation or hydration of condensed maleic anhydride to maleic acid of fumaric acid. Other organic impurities were also rejected under these conditions to provide high quality of maleic anhydride shown by increased color stability.

TABLE I Typical Composition of Crude Maleic Anhydride Distillation Overhead Component Volume % n-butane 0.69 water 49.39 oxygen 5.13 nitrogen 21.87 carbon oxides 1.84 acetic acid 6.68 acrylic acid 5.56 butyric acid 0.18 maleic anhydride 8.66 Total 100.00 TABLE II Dew Points for Water and Maleic Anhydride in Stream with Composition of Table I Condenser Pressure Dew Point Temperature, "F mm Hg Water Maleic Anhydride 20 52 118 25 58 126 30 63 129 50 78 145 70 89 156 TABLE 111 ppm Maleic Condenser Wt. % Organic & Fumaric Run Condenser Pressure MA Condenser Acids in Acids in No. Temp. ("C) (mm Hg) Efficiency Wo Condensed MA Condensed MA 1 37.8 20 86 0.3 < 300 2 37.8 25 82 0.42 < 300 3 37.8 30 79 0.49 < 300 4 37.8 50 78 0.8 < 300 5 32.2 30 82 0.7 < 300 6 23.9 30 85 1.88 1000-2000 7 21.1 30 94 2.7 2500-5000 WHAT WE CLAIM IS: 1. A process for recovering maleic anhydride from gaseous compositions comprising maleic anhydride and water, comprising cooling said composition to a temperature in the range of from 20"C to 50"C at a pressure less than 200 millimeters of mercury.

2. A process according to claim 1, wherein the gaseous composition comprises from 1 to 30 percent by volume maleic anhydride and from 10 to 70 percent by volume water.

3. A process according to claim 1, wherein the composition is cooled to a temperature of from 25"C to 400C at a pressure less than 50 millimeters of mercury.

4. A process according to claim 3, wherein the composition is cooled to a temperature of about 30"C.

5. A process for stripping low-boiling impurities from crude maleic anhydride produced

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. TABLE I Typical Composition of Crude Maleic Anhydride Distillation Overhead Component Volume % n-butane 0.69 water 49.39 oxygen 5.13 nitrogen 21.87 carbon oxides 1.84 acetic acid 6.68 acrylic acid 5.56 butyric acid 0.18 maleic anhydride 8.66 Total 100.00 TABLE II Dew Points for Water and Maleic Anhydride in Stream with Composition of Table I Condenser Pressure Dew Point Temperature, "F mm Hg Water Maleic Anhydride 20 52 118 25 58 126 30 63 129 50 78 145 70 89 156 TABLE 111 ppm Maleic Condenser Wt. % Organic & Fumaric Run Condenser Pressure MA Condenser Acids in Acids in No. Temp. ("C) (mm Hg) Efficiency Wo Condensed MA Condensed MA

1 37.8 20 86 0.3 < 300

2 37.8 25 82 0.42 < 300

3 37.8 30 79 0.49 < 300

4 37.8 50 78 0.8 < 300

5 32.2 30 82 0.7 < 300

6 23.9 30 85 1.88 1000-2000

7 21.1 30 94 2.7 2500-5000 WHAT WE CLAIM IS: 1. A process for recovering maleic anhydride from gaseous compositions comprising maleic anhydride and water, comprising cooling said composition to a temperature in the range of from 20"C to 50"C at a pressure less than 200 millimeters of mercury.

by the vapor phase oxidation of a hydrocarbon feedstock, which includes the step of passing the lights stripper overhead vapor through a condenser system maintained at a temperature in the range of from 20"C to 500C at less than 200 millimeters of mercury pressure.

6. A process according to claim 5, wherein maleic anhydride recovered in the condenser system is recycled to the lights stripper.

7. A process for recovering maleic anhydride, substantially as described in the foregoing Example.

8. Maleic anhydride whenever obtained by the process claimed in any preceding claim.