A method for recovering maleic anhydride

Abstract

The present invention discloses a method for recovering maleic anhydride. The method comprises an absorption flash tower, a stripping flash tower, and a scrubbing tower. The absorption flash tower comprises an absorption section (A) and a flash section (B). The stripping flash tower comprises a stripping section (C) and a flash section (D). The maleic anhydride reaction product passes through the absorption section (A), where most of the maleic anhydride is absorbed by a lean solvent within the tower. The absorbed rich solvent then enters the flash section (B) for further water removal before entering the stripping section (C). Crude maleic anhydride is withdrawn from a sideline above the stripping section (C). The overhead gas from the stripping flash tower is sent to a scrubbing tower for further maleic anhydride recovery. The bottoms of the stripping section (C) enter the flash section (D) for further maleic anhydride recovery. The present invention features a simple process setup, a high maleic anhydride recovery rate, low energy consumption in the solvent absorption and desorption stages, and flexible process operation.

Description

Technical Field

[0001] The invention belongs to the field of chemical industry, and particularly relates to a method for recovering maleic anhydride by using a solvent. Background Art

[0002] Maleic anhydride is widely used in synthetic plastics, coatings, food additives, and pharmaceuticals, and is an important organic chemical and chemical intermediate. The production process for maleic anhydride can be divided into two types, depending on the raw materials: benzene oxidation and n-butane oxidation. With the rapid development of my country's petrochemical industry, the comprehensive utilization of C4 resources will make the n-butane oxidation process more resource-efficient and cost-effective. Furthermore, the n-butane oxidation process generates a large amount of water, making the water absorption refining process more difficult than the benzene absorption process. In recent years, solvent absorption has become more widely used. The organic solvent absorption post-processing process utilizes the solubility differences between different solutes in the organic solvent to absorb the maleic anhydride in the product, and then desorbs the maleic anhydride-rich solvent to obtain the crude maleic anhydride product.

[0003] However, during the solvent absorption post-processing process, water is present in the gaseous product composition, which can lead to a series of side reactions during the subsequent solvent absorption desorption and solvent refining. The most important side reactions are the hydrolysis of water with the solvent and the reaction of water with maleic anhydride to form maleic acid and fumaric acid. Because these impurities have high melting points, they easily crystallize and precipitate in equipment and pipelines, leading to equipment and system blockages. In severe cases, this can cause production cuts or shutdowns, impacting plant operation. Consequently, the solvent absorption post-processing process presents numerous challenges.

[0004] CN 102558113 B discloses an improved method for recovering maleic anhydride using an organic solvent. This technology primarily involves an absorption tower, a desorption tower, and a scrubbing tower for anhydride recovery. The process setup is relatively complex, with the temperature of the reaction gas product entering the absorption tower being 130-140°C. The temperature at the top of the absorption tower is relatively high, and compressed air is introduced at the bottom of the absorption tower for stripping. This method effectively reduces the light component content in the rich solvent at the bottom of the absorption tower. Due to the high temperature at the top of the absorption tower, the loss of maleic anhydride in the gas phase at the top of the absorption tower is high. This technology has complex process facilities, and controlled air stripping effectively reduces the water content in the rich solvent. However, the harsh operating conditions of the vacuum flash tank and the multi-stage heat extraction method in the middle of the absorption tower result in high energy consumption during the absorption process. Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art in which solvents are used to recover maleic anhydride, such as high energy consumption, and to propose a new method for recovering maleic anhydride using a solvent. The method of the present invention has the advantages of simple process setting, high maleic anhydride recovery rate, low energy consumption in the solvent absorption and desorption sections, and flexible process operation.

[0006] The present invention provides a method for recovering maleic anhydride, characterized in that the method comprises the following steps:

[0007] 1. A method for recovering maleic anhydride, characterized in that the method comprises the following steps:

[0008] 1) The maleic anhydride reaction product enters an absorption flash tower, which includes an absorption section in zone A and a flash section in zone B. The maleic anhydride reaction product first contacts a lean solvent in the absorption section in zone A. The lean solvent absorbs the maleic anhydride component in the maleic anhydride reaction product to become a rich solvent. The rich solvent then enters the flash section in zone B for flash evaporation to further remove water contained in the rich solvent by flash evaporation, and then enters step 2). The tail gas from the top of the absorption flash tower is discharged through the top of the absorption flash tower, wherein the middle and upper sideline extract from the absorption section in zone A is returned to the absorption section in zone A after heat removal. The absorption flash tower includes an air ejector section, and the gas phase of the flash section in zone B and air enter the absorption section in zone A together through the ejector of the absorption flash tower;

[0009] 2) The rich solvent from step 1) after being dehydrated is sent to a stripping flash tower after heat exchange and heating. The stripping flash tower includes a stripping part in zone C and a flash part in zone D. The rich solvent first enters the stripping part in zone C from the lower part of the stripping part in zone C for stripping. The crude maleic anhydride obtained after stripping in the stripping part in zone C is extracted from the side line at the upper part of the stripping part in zone C. The gas coming out of the top of the stripping flash tower is cooled. After cooling, the liquid is divided into two parts. One part is returned to the stripping part in zone C as the top reflux of the stripping flash tower, and the other part is returned to the stripping part in zone C. The top of the absorption flash evaporation tower is used as reflux to the upper part of the absorption part of zone A for recycling. After cooling, the gas is sent to the subsequent scrubbing tower. The bottom liquid of the stripping part of zone C enters the flash evaporation part of zone D. After flash evaporation in the flash evaporation part of zone D, it is divided into two parts. One part is returned to the lower part of the stripping part of zone C, and the other part is used as the lean solvent after heat exchange with the rich solvent in step 1). The stripping flash evaporation tower includes an air ejector part. The gas phase of the flash evaporation part of zone D and air pass through the stripping flash evaporation tower ejector and then enter the stripping part of zone C.

[0010] 3) The gas entering the scrubber in step 2) is countercurrently contacted with the lean solvent entering from the top of the scrubber. The rich solvent at the bottom of the scrubber is returned to the absorption part of the absorption flash tower A. The non-condensable gas at the top of the scrubber is discharged to the discharge device.

[0011] The method for recovering maleic anhydride of the present invention is further characterized in that: in the step 2), the rich solvent from the step 1) after dehydration is divided into two parts, one part is returned to the lower part of the flash part of zone B after passing through the reboiler of the absorption flash tower, and the other part is sent to the stripping flash tower after heat exchange and heating.

[0012] The method for recovering maleic anhydride described in the present invention is further technically characterized in that: in the step 1), the rich solvent discharged from the bottom of the absorption part of zone A is divided into two parts, one part is used as feed to the flash evaporation part of zone B for flash evaporation, and the other part is used as circulating cold liquid of the absorption flash evaporation tower and returned to the absorption part of zone A after cooling; preferably, the other part is mixed with the rich solvent at the bottom of the washing tower obtained from the bottom of the washing tower, and is used as circulating cold liquid of the absorption flash evaporation tower and returned to the absorption part of zone A after cooling.

[0013] The method for recovering maleic anhydride described in the present invention is further technically characterized in that: in the above step 1), a side line extraction pipeline for the middle section of zone A is provided in the upper middle portion of the absorption part of zone A, and the middle section extract of zone A is extracted through the side line extraction pipeline, and then after heat removal, it is returned to the absorption part of zone A as the cold liquid in the middle section of zone A of the absorption flash tower.

[0014] The method for recovering maleic anhydride described in the present invention is further technically characterized in that: the extract from the middle section of zone A is extracted through the side line extraction pipeline of the middle section of zone A and is divided into two parts, a small part is used as the return liquid extracted from the middle section of zone A of the absorption flash tower, and is returned to the absorption part of zone A of the absorption flash tower under the control of the return liquid regulating valve of the middle section of the absorption flash tower, and the other part is used as the cold liquid of the middle section of zone A of the absorption flash tower after heat is removed and is returned to the absorption part of zone A of the absorption flash tower.

[0015] The method for recovering maleic anhydride of the present invention is further technically characterized in that the stripping part of zone D of the stripping flash tower is composed of a packing section, wherein the packing section is composed of structured packing or random packing.

[0016] The method for recovering maleic anhydride described in the present invention is further technically characterized in that: the operating pressure of the absorption part in zone A of the absorption flash tower is 100-300KPa and the temperature is 50-130°C; the operating pressure of the flash part in zone B is 30-80KPa and the temperature is 50-130°C.

[0017] The method for recovering maleic anhydride of the present invention is further technically characterized in that the operating pressure of the stripping part in zone C of the stripping flash tower is 1-8 kPa and the temperature is 20-90°C; the operating pressure of the flash part in zone D is 1-8 kPa and the temperature is 20-90°C.

[0018] The method for recovering maleic anhydride of the present invention is further characterized in that the solvent is one of dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisobutyl hexahydrophthalate and dibutyl sebacate; preferably dimethyl phthalate or diethyl phthalate.

[0019] The method for recovering maleic anhydride of the present invention can be used for recovering maleic anhydride reaction products, especially for recovering and purifying products produced by n-butane oxidation process.

[0020] The advantages of the method for recovering maleic anhydride described in the present invention over the prior art are as follows: 1) The absorption tower and flash tower are combined into one tower, namely, the absorption flash tower, operating in different zones. The flash evaporation section further removes moisture from the rich solvent under low-pressure conditions, thereby reducing the coking rate and extending the stable operation time of the device. 2) The stripping tower and post-flash tower are combined into one tower, namely, the stripping flash tower, operating in different zones. The post-flash section further recovers maleic anhydride from the lean solvent, effectively improving the recovery rate of maleic anhydride. 3) Both the flash section in zone B of the absorption flash tower and the flash section in zone D of the stripping flash tower use air ejectors for pressure reduction. On the one hand, air is used as the working medium, and the working medium is used to generate high speed. The air pressure energy is converted into velocity energy, and the gas in the pressure reduction zone is drawn into the mixing chamber. The air and the gas in the pressure reduction zone are continuously withdrawn to ensure the pressure reduction operation requirements. On the other hand, the air serves to strip the gas and reduce the partial pressure in the absorption flash tower and the stripping flash tower, respectively. 4) The rich solvent from the bottom of the absorption / flash column is preheated by the hot lean solvent produced from the bottom of the stripping flash column to recover heat before entering the stripping flash column.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of the present invention is not limited thereto. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a schematic flow diagram of a method for recovering maleic anhydride.

[0023] The reference numerals shown in the figures are:

[0024] 1-maleic anhydride reaction product; 2-air; 3-air; 4-absorption flash tower top tail gas; 5-absorption flash tower middle section cold liquid; 6-absorption flash tower middle section extraction return liquid; 7-B zone tower bottom liquid extraction pipeline; 8-absorption flash tower reboiler return pipeline; 9-A zone absorption part tower bottom extraction pipeline; 10-B zone flash part feed; 11-absorption flash tower circulating cold liquid; 12-stripping flash tower top reflux; 13-stripping flash tower top gas; 14-wash tower feed; 15- Oil extraction pipeline at the bottom of tower C; 16-reboiler return pipeline for stripping flash tower; 17-liquid extraction pipeline at the bottom of tower D; 18-lean solvent for washing tower; 19-side extraction pipeline for the middle section of tower A; 20-lean solvent for absorption flash tower; 21-rich solvent at the bottom of washing tower; 22-gas phase at the top of washing tower; 23-non-condensable gas; 24-supplementary lean solvent; 25-crude maleic anhydride; 26-regulating valve for return liquid extraction from the middle section of absorption flash tower; 27-reflux at the top of stripping flash tower; 28-absorption flash tower; 29-middle section of absorption flash tower Condenser; 30-absorption flash tower ejector; 31-absorption flash tower reboiler; 32-cooler; 33-heat exchanger; 34-heater; 35-stripping flash tower; 36-condenser; 37-reflux tank; 38-stripping flash tower reboiler; 39-stripping flash tower ejector; 40-washing tower; 41-lean solvent cooler; 42-lean solvent tank; 43-vacuum system; 44-washing tower lean solvent cooler; 45-absorption flash tower zone B gas phase; 46-stripping flash tower zone D gas phase. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings.

[0026] like Figure 1 As shown, a method for recovering maleic anhydride includes an absorption flash tower 28, a stripping flash tower 35, and a washing tower 40. The absorption flash tower 28 includes an absorption section in zone A and a flash section in zone B, wherein the absorption section in zone A is located above the flash section in zone B. The stripping flash tower 35 includes a stripping section in zone C and a flash section in zone D, wherein the stripping section in zone C is located above the flash section in zone D. The specific steps of the method for recovering maleic anhydride are as follows:

[0027] 1) The maleic anhydride reaction product 1 enters the lower part of the absorption part of zone A, and the absorption flash tower lean solvent 20 enters the upper part of the absorption part of zone A through a pipeline. The maleic anhydride reaction product 1 and the absorption flash tower lean solvent 20 are in countercurrent contact in the absorption part of zone A. The absorption flash tower lean solvent 20 absorbs the maleic anhydride component in the maleic anhydride reaction product to become a rich solvent. The rich solvent is extracted from the bottom of the absorption part of zone A through a pipeline 9 and then divided into two parts. One part of the rich solvent is used as the feed 10 of the flash part of zone B to enter the flash part of zone B for flash evaporation to further flash evaporation and remove the water contained in the rich solvent. After that, it is extracted from the bottom liquid extraction pipeline 7 of zone B and divided into two parts. One part is returned to the lower part of the flash part of zone B through the absorption flash tower reboiler 31 through the absorption flash tower reboiler 8, and the other part is sent to the stripping part of zone C of the stripping flash tower 35 after passing through the heat exchanger 33 and the heater 34, and is extracted from the bottom of the absorption part of zone A through a pipeline 9 The other part of the rich solvent is used as the circulating cold liquid 11 of the absorption flash tower and is cooled by the cooler 32 and then returned to the absorption part of zone A. The tail gas 4 at the top of the absorption flash tower is discharged through the top of the absorption flash tower. The middle-upper part of the absorption part of zone A is provided with a side line extraction pipeline 19 for the middle section of zone A. The middle section extract of zone A is extracted through the side line extraction pipeline 19 for the middle section of zone A, and then returns to the absorption part of zone A as the middle section cold liquid 5 of zone A of the absorption flash tower after heat is removed through the middle section condenser 29 of the absorption flash tower. In order to facilitate the control of the liquid level and temperature, the preferred solution is that the middle section extract of zone A is divided into two parts after being extracted through the middle section side line extraction pipeline 19 of zone A. Under the control of the middle section extract return liquid regulating valve 26 of the absorption flash tower, a small part is returned to zone A of the absorption flash tower as the middle section extract return liquid of zone A of the absorption flash tower, and the other part is returned to the absorption part of zone A as the middle section cold liquid 5 of zone A of the absorption flash tower after heat is removed through the middle section condenser 29 of the absorption flash tower. The absorption flash tower 28 includes an air ejector section, and the absorption flash tower B zone gas phase 45 from the B zone flash section and air 2 enter the A zone absorption section through the absorption flash tower ejector 30;

[0028] 2) The stripping flash tower 35 includes a stripping section in zone C and a flash section in zone D. In the stripping section in zone C, the rich solvent from the stripping section in zone B of the absorption flash tower, which has been dehydrated and heated, is stripped under the action of a stripping gas (such as air). The crude maleic anhydride 25 obtained after stripping in the stripping section in zone C is withdrawn from the upper side line of the stripping section in zone C. The stripping flash tower overhead gas 13 coming out of the top of the stripping flash tower is cooled by a condenser 36 and then enters a reflux tank 37 for liquid separation. The liquid in the reflux tank 37 is divided into two parts. One part is returned to the stripping section in zone C as the stripping flash tower overhead reflux 27, and the other part is returned to the upper part of the absorption section in zone A for recycling as the absorption flash tower overhead reflux 12. The gas in the reflux tank 37 is sent to the subsequent washing tower as the washing tower feed 14. The washing tower 40 further recovers maleic anhydride. The bottom liquid of the stripping part of zone C enters the flash evaporation part of zone D through the bottom oil extraction pipeline 15 of zone C. After flash evaporation in the flash evaporation part of zone D, it exits through the bottom liquid extraction pipeline 17 of zone D and is divided into two parts. One part is returned to the lower part of the stripping part of zone C through the stripping flash tower reboiler return pipeline 16, passes through the stripping flash tower reboiler 38, and then exchanges heat with the rich solvent in step 1) in the heat exchanger 33. The other part is then cooled in the lean solvent cooler 41 and sent to the lean solvent tank 42 for use as the lean solvent. The stripping flash tower 35 includes an air ejector part. The stripping flash tower zone D gas phase 46 from the flash evaporation part of zone D and the stripping gas (preferably air) enter the stripping part of zone C together through the stripping flash tower ejector 39.

[0029] 3) Step 2) The scrubber feed 14 enters the scrubber 40 and is countercurrently contacted with the scrubber lean solvent 18 entering from the upper portion of the scrubber 40. A scrubber bottom rich solvent 21 is obtained at the scrubber bottom. The scrubber bottom rich solvent 21 is returned to the absorption portion of the absorption flash tower section A. Preferably, the scrubber bottom rich solvent 21 is mixed with the absorption flash tower circulating cold liquid 11, and then cooled in the cooler 32 before returning to the absorption portion of the absorption flash tower section A. The scrubber top gas phase 22 exits the scrubber top and enters the vacuum system 43 to obtain a non-condensable gas 23 discharge device.

[0030] The stripping section of zone C of the stripping flash column 35 of the present invention is usually composed of a packing section, wherein the packing section is composed of structured packing or random packing to obtain high separation efficiency.

[0031] The absorption part of zone A in the absorption flash tower of the present invention has an operating pressure of 100-300 KPa and a temperature of 50-130°C; the flash part of zone B has an operating pressure of 30-80 KPa and a temperature of 50-130°C.

[0032] The operating pressure of the stripping part in zone C of the stripping flash tower of the present invention is 1-8KPa and the temperature is 20-90°C; the operating pressure of the flash evaporation part in zone D is 1-8KPa and the temperature is 20-90°C.

[0033] The solvent of the present invention can be selected from one of dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisobutyl hexahydrophthalate and dibutyl sebacate, preferably dimethyl phthalate or diethyl phthalate.

[0034] The lean solvent tank 42 can provide lean solvent for the present invention. When the amount of lean solvent cannot meet the use of the present invention, the supplementary lean solvent 24 can be added to the lean solvent tank 42 through a pipeline. The lean solvent tank 42 can provide the washing tower lean solvent 18 to the washing tower 40 and provide the absorption flash tower lean solvent 20 to the absorption flash tower 28 through pipelines.

Claims

1. A method for recovering maleic anhydride, characterized in that The method comprises the following steps: 1) The maleic anhydride reaction product enters an absorption flash tower, which includes an absorption section in zone A and a flash section in zone B. The maleic anhydride reaction product first contacts a lean solvent in the absorption section in zone A. The lean solvent absorbs the maleic anhydride component in the maleic anhydride reaction product to become a rich solvent. The rich solvent then enters the flash section in zone B for flash evaporation to further remove water contained in the rich solvent by flash evaporation, and then enters step 2). The tail gas from the top of the absorption flash tower is discharged through the top of the absorption flash tower, wherein the middle and upper sideline extract from the absorption section in zone A is returned to the absorption section in zone A after heat removal. The absorption flash tower includes an air ejector section, and the gas phase of the flash section in zone B and air enter the absorption section in zone A together after passing through the absorption flash tower ejector; 2) The rich solvent from step 1) after being dehydrated is sent to a stripping flash tower after heat exchange and heating. The stripping flash tower includes a stripping part in zone C and a flash part in zone D. The rich solvent first enters the stripping part in zone C from the lower part of the stripping part in zone C for stripping. The crude maleic anhydride obtained after stripping in the stripping part in zone C is extracted from the side line at the upper part of the stripping part in zone C. The gas coming out of the top of the stripping flash tower is cooled. After cooling, the liquid is divided into two parts. One part is returned to the stripping part in zone C as the top reflux of the stripping flash tower, and the other part is returned to the stripping part in zone C as the top reflux of the stripping flash tower. The top of the absorption flash tower is used as reflux to return to the upper part of the absorption part of zone A for recycling. After cooling, the gas is sent to the subsequent washing tower. The bottom liquid of the stripping part of zone C enters the flash evaporation part of zone D again. After flash evaporation in the flash evaporation part of zone D, it is divided into two parts. One part returns to the lower part of the stripping part of zone C, and the other part is used as the lean solvent after heat exchange with the rich solvent in step 1). The stripping flash tower includes an air ejector part. The gas phase of the flash evaporation part of zone D and air enter the stripping part of zone C together after passing through the stripping flash tower ejector; 3) The gas entering the scrubber in step 2) is countercurrently contacted with the lean scrubber solvent entering from the top of the scrubber, and the rich scrubber bottom solvent obtained at the bottom of the scrubber is returned to the absorption part of zone A of the absorption flash tower, and the non-condensable gas discharged from the top of the scrubber is discharged to the discharge device; The operating pressure of the absorption part in zone A of the absorption flash tower is 100-300 KPa and the temperature is 50-130°C; the operating pressure of the flash part in zone B is 30-80 KPa and the temperature is 50-130°C; the operating pressure of the stripping part in zone C of the stripping flash tower is 1-8 KPa and the temperature is 20-90°C; the operating pressure of the flash part in zone D is 1-8 KPa and the temperature is 20-90°C.

2. A method for recovering maleic anhydride according to claim 1, characterized in that: In the step 2), the rich solvent from step 1) after dehydration is divided into two parts, one part is returned to the lower part of the flash part of zone B after passing through the reboiler of the absorption flash tower, and the other part is sent to the stripping flash tower after heat exchange and heating.

3. A method for recovering maleic anhydride according to claim 1, characterized in that: In the step 1), the rich solvent coming out of the bottom of the absorption part of zone A is divided into two parts, one part is fed into the flash evaporation part of zone B for flash evaporation, and the other part is used as circulating cold liquid of the absorption flash tower and returned to the absorption part of zone A after cooling.

4. A method for recovering maleic anhydride according to claim 1, characterized in that: In the step 1), a side line extraction pipeline for the middle section of zone A is provided in the upper middle portion of the absorption part of zone A. The middle section extraction liquid of zone A is extracted through the side line extraction pipeline for the middle section of zone A, and then returns to the absorption part of zone A as the cold liquid of the middle section of zone A of the absorption flash tower after heat removal.

5. A method for recovering maleic anhydride according to claim 4, characterized in that: The extract from the middle section of zone A is extracted through the side line extraction pipeline of the middle section of zone A and is divided into two parts. A small part is used as the return liquid extracted from the middle section of zone A of the absorption flash tower and is returned to the absorption part of zone A of the absorption flash tower under the control of the return liquid regulating valve of the middle section of the absorption flash tower. The other part is used as the cold liquid of the middle section of zone A of the absorption flash tower and is returned to the absorption part of zone A after heat removal.

6. A method for recovering maleic anhydride according to claim 1, characterized in that: The stripping part of zone D of the stripping flash tower is composed of a packing section, wherein the packing section is composed of structured packing or random packing.

7. A method for recovering maleic anhydride according to claim 1 or 3, characterized in that: The rich solvent coming out of the bottom of the absorption part of zone A is divided into two parts, one part is used as feed to the flash evaporation part of zone B for flash evaporation, and the other part is mixed with the rich solvent at the bottom of the washing tower obtained at the bottom of the washing tower, and is returned to the absorption part of zone A after being cooled as circulating cold liquid of the absorption flash evaporation tower.

8. A method for recovering maleic anhydride according to claim 1, characterized in that: The solvent is one of dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisobutyl hexahydrophthalate and dibutyl sebacate.

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