Process for preparing succinic acid through succinic anhydride steam hydrolysis

Abstract

The invention discloses a process for producing succinic acid by a succinic anhydride steam hydrolysis method, and solves the problems of high equipment investment, high operation cost, high energy consumption, further improvement of product quality and the like in the existing crystallization process. According to the technical scheme, the method comprises the following steps: feeding butanedioic anhydride into a steam hydrolysis reactor to be in contact with steam for hydrolysis reaction to generate succinic acid, and controlling the reaction pressure in the steam hydrolysis reactor to be 0.02-0.3 MPaG and the reaction temperature to be 190-210 DEG C. The method is simple in process, high in product yield, good in quality, small in equipment occupied space, easy to overhaul and maintain and low in investment and operation cost.

Description

Technical Field

[0001] The invention relates to the technical field of degradable plastics, in particular to a process for preparing succinic acid by steam hydrolysis of succinic anhydride. Background Art

[0002] In the field of biodegradable plastics, PBS has attracted much attention and praise for its excellent biodegradability, mechanical properties close to PP, excellent machining performance, heat resistance over 100°C and good light stability. The raw materials for producing PBS are 1,4-butanediol and succinic acid or succinic anhydride. The production technology of 1,4-butanediol is mature and stable, while the production technology of succinic anhydride / succinic acid is still a restrictive technology that restricts the development of the PBS industry.

[0003] At present, the production technologies of succinic acid include electrochemical method, biological fermentation method, paraffin oxidation method and maleic anhydride hydrogenation method. The electrochemical method has mature technology, but it has the disadvantages of high power consumption, serious equipment corrosion, large investment and land occupation; the biological fermentation method has cheap raw materials and low energy consumption, but it has the disadvantages of low product yield, difficult product purification, and large wastewater output; the paraffin oxidation method has mature technology, but the product is complex, difficult to separate, and the product yield is low. Maleic anhydride hydrogenation method has received extensive attention from domestic and foreign research institutions, and has made relevant experimental results. It is considered to be the most promising technology for producing PBS raw materials.

[0004] Maleic anhydride hydrogenation process is divided into maleic anhydride direct hydrogenation process and maleic anhydride hydrogenation process with solvent. Due to the large heat release of the direct hydrogenation process, the reaction temperature is difficult to accurately control, there are relatively more by-products, separation is difficult, and the yield of the target product is low. Maleic anhydride hydrogenation process with solvent is convenient for raw material storage and transportation, the reaction temperature is easy to control, and the bed is not easy to form hot spots, so there are fewer side reactions and the product yield is high. Maleic anhydride hydrogenation process with solvent is hereinafter referred to as maleic anhydride hydrogenation process.

[0005] The solvent used in the maleic anhydride hydrogenation method can be tetrahydrofuran or γ-butyrolactone. The maleic anhydride hydrogenation process of the two solvents has been successfully used in industry and can produce succinic anhydride on a large scale. To convert succinic anhydride into succinic acid, hydrolysis and crystallization are required.

[0006] The existing succinic anhydride hydrolysis crystallization technology still has the following problems:

[0007] (1) The hydrolysis of succinic anhydride releases a large amount of heat. During the hydrolysis process, the solution has a strong corrosive ability and will cause corrosion of equipment and pipelines. More importantly, iron ions dissolve into the solution, which will cause the iron ion content in the succinic acid product to be high (20-60ppm). A high iron ion content will make the PBS product yellowish in color.

[0008] (2) Existing hydrolysis crystallization processes are mostly intermittent processes, especially the crystallization process. There is no mature industrial device for continuous crystallization in China. Intermittent kettle crystallizers are difficult to operate, pipelines are easily blocked, and production capacity is limited. Industrial devices often require many crystallizers for intermittent operation. This makes the device investment high, occupies a large area, and has high energy consumption.

[0009] (3) The existing hydrolysis crystallization process requires the discharge of mother liquor, which contains about 5%wt of succinic acid in addition to iron ions and needs to be sent to a sewage treatment plant for treatment.

[0010] (4) The existing hydrolysis crystallization process requires the consumption of utilities such as deionized water, steam, chilled water, and circulating water.

[0011] Therefore, how to efficiently convert the succinic anhydride produced by the maleic anhydride hydrogenation to succinic anhydride device into succinic acid is a difficult problem that technicians in this field need to solve. Summary of the invention

[0012] The purpose of the present invention is to solve the above technical problems and to provide a process for preparing succinic acid by steam hydrolysis of succinic anhydride which has the advantages of simple process, low equipment investment and operating cost, low operation difficulty, high product purity, low energy consumption, environmental friendliness and can meet the requirements of continuous or intermittent production.

[0013] The technical scheme is: succinic anhydride is sent into a steam hydrolysis reactor to contact with steam to undergo a hydrolysis reaction to generate succinic acid, and the reaction pressure in the steam hydrolysis reactor is controlled at 0.02-0.3 MPaG and the reaction temperature is 190-210°C.

[0014] The upper section of the steam hydrolysis reactor is provided with a distributor, and the middle section is a shell and tube heat exchange section; the succinic anhydride is evenly distributed by the distributor in the upper section, and then sent to the heat exchange tubes of the shell and tube heat exchange section to contact with the steam in reverse to undergo a hydrolysis reaction; the generated succinic acid is drawn out from the bottom of the steam hydrolysis reactor after exiting the heat exchange tubes, and after being pressurized by a circulating pump, all or part of it is mixed with succinic anhydride as a circulating liquid and then circulated into the steam hydrolysis reactor, and the rest is sent out as a product.

[0015] The circulating liquid flow rate is 10-15 times the succinic anhydride feed flow rate entering the steam hydrolysis reactor.

[0016] Circulating hot water is introduced into the shell side of the shell and tube heat exchange section to remove the reaction heat, and the circulating hot water after heat exchange is sent to the steam generator to flash out low-pressure steam. The consumed boiler water is replenished into the steam generator through the water replenishment control valve and then returned to the shell side of the shell and tube heat exchange section for heat exchange.

[0017] The low-pressure steam flashed out by the steam generator is partially sent back to the lower section of the steam hydrolysis reactor and then enters the heat exchange tube to contact with succinic anhydride in reverse to produce a hydrolysis reaction, and the rest is sent out.

[0018] A steam flow feed control valve is provided at the steam inlet of the lower section of the steam hydrolysis reactor, and the reaction pressure in the steam hydrolysis reactor is controlled within 0.02-0.3 MPaG by controlling the flow rate of steam injected into the steam hydrolysis reactor.

[0019] An exhaust control valve is provided on the top of the steam hydrolysis reactor. When the reaction pressure in the steam hydrolysis reactor exceeds a set pressure range, the exhaust control valve is opened to reduce the pressure to the set pressure range.

[0020] In view of the problems existing in the background technology, the inventors have overcome the conventional understanding and proposed a process route for preparing succinic acid by steam hydrolysis using succinic anhydride as raw material, which has the following characteristics:

[0021] 1) Instead of using deionized water or deionized water mixed with succinic anhydride for hydrolysis, low-pressure steam is used to contact succinic anhydride to achieve the hydrolysis reaction. Although the rate of steam hydrolysis of succinic anhydride is slightly slower, no free water appears in the system and no aqueous solution of succinic acid is formed. Therefore, the corrosion performance of the material is greatly reduced, and the ion content in the obtained succinic acid product will be greatly reduced, which is more suitable for large-scale industrial production.

[0022] 2) Hydrolysis is an exothermic reaction. In the original hydrolysis crystallization process, the reaction heat needs to be removed by circulating water and chilled water. However, the present invention ingeniously uses circulating hot water in the shell and tube heat exchange section to recover the reaction heat, which is all used for by-product low-pressure steam, and no longer consumes circulating water and chilled water; the by-product low-pressure steam can be returned to the steam hydrolysis reactor for hydrolysis of succinic anhydride, and the excess steam can be sent out. The entire reaction process does not require the consumption of external steam, but instead recovers by-product steam, with significant economic benefits.

[0023] 3) The hydrolysis process of the present invention needs to control the reaction temperature and pressure. Considering that too high a reaction pressure will increase equipment investment and operating energy consumption, the reaction pressure is controlled at 0.02-0.3MPaG, preferably 0.03-0.1MPaG. If the reaction pressure is too low, the rate and degree of hydrolysis of the hydrolysis reaction will decrease; if the reaction pressure is too high, although the reaction rate and degree of hydrolysis are improved, the water content of succinic acid will increase, and the equipment investment and operating energy consumption will also increase. The hydrolysis reaction is an exothermic process. The melting point of succinic anhydride is 120°C, the melting point of succinic acid is 185°C, and the decomposition temperature of succinic acid is 235°C. When a shell-and-tube reaction is used, in order to ensure the efficiency of the hydrolysis reaction in the heat exchange tube, the reaction temperature needs to be controlled at 185-210°C, preferably 190-210°C. If the temperature is too low, succinic acid will solidify, and if the temperature is too high, succinic acid will decompose into succinic anhydride and water. Furthermore, in the present invention, the succinic acid drawn out from the bottom of the hydrolysis reactor is pressurized by a circulating pump and then partially used as a circulating liquid to mix with the raw material succinic anhydride and feed, and the circulating liquid is used to mix with the raw material succinic anhydride. Circulation has multiple effects: a. The reaction temperature can be well controlled by using the circulating liquid. Preferably, the circulating liquid flow rate is 10-15 times the succinic anhydride feed flow rate entering the steam hydrolysis reactor; b. There may still be some unhydrolyzed succinic anhydride in the liquid phase drawn out from the bottom of the hydrolysis reactor. By mixing the circulating liquid with the raw materials and sending it into the steam hydrolysis reactor for hydrolysis again, a small amount of unreacted succinic anhydride in the circulating liquid can be further hydrolyzed, greatly improving the purity of the product; c. Due to the existence of material circulation, continuous or intermittent operation can be flexibly switched according to actual needs. Furthermore, the pressure in the reactor can be controlled by the amount of steam returned. If it is overpressured, the pressure can be reduced through the exhaust control valve at the top, and the control of reaction temperature and pressure becomes simple and easy to operate.

[0024] 4) The method of the present invention adopts the principle of steam hydrolysis, and there is no distillation or separation process. Under normal circumstances, there is no tail gas emission and no wastewater generation. It is environmentally friendly and has high purity. The purity of the succinic acid product can reach more than 99.95%. The obtained succinic acid product can be directly sliced ​​or granulated, and the solid product will not stick together into blocks. The water content of the product succinic acid is ≯0.4wt%.

[0025] 5) Compared with the hydrolysis crystallization process, taking the succinic acid production of 10,000 tons / year as an example, the process of the present invention only requires one steam hydrolysis reactor, while the hydrolysis crystallization process requires at least 10 reactors, and the equipment investment and operation costs are low.

[0026] The invention has the advantages of simple process, low equipment investment and operation cost, low operation difficulty, high product purity, low energy consumption, environmental friendliness, ability to meet continuous or intermittent production, and good product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a process flow chart of the present invention.

[0028] Figure 1 In the figure, R01 is a steam hydrolysis reactor, P01 is a circulation pump, and V01 is a steam generator;

[0029] 1-upper section, 2-distributor, 3-shell and tube heat exchange section, 3.1-heat exchange tube, 4-lower section, 5-steam flow feed control valve, 6-exhaust control valve, 7-water make-up control valve, 8-discharge valve, 9-circulation valve, 10-steam delivery valve, 11-flow control valve. DETAILED DESCRIPTION

[0030] The process of the present invention is further explained below in conjunction with the accompanying drawings:

[0031] The raw material in this example is succinic anhydride, with a purity of 99.8-99.9%wt, and the impurities mainly contain a small amount of γ-butyrolactone. The feed flow rate is 1.25 t / h, the feed temperature is 125°C, and the feed pressure is 0.4 MPaG.

[0032] Another raw material in this embodiment is deionized water (boiler feed water), the feed flow rate is 0.35 t / h, the feed pressure is 1.0 MPaG, and the temperature is 104°C.

[0033] Succinic anhydride is mixed with the circulating liquid through the flow control valve 11 and enters the upper section of the steam hydrolysis reactor R01. After being distributed by the distributor 2, it enters the multiple heat exchange tubes 3.1 that evenly enter the shell and tube heat exchange section 3, and contacts the steam from the lower section in reverse direction to undergo a hydrolysis reaction. After succinic acid is generated, it enters the lower section of the steam hydrolysis reactor R01 and is finally drawn out from the bottom. After being pressurized by the circulating pump P01, it is mixed with the raw material succinic anhydride as a circulating liquid in whole or in part as needed and then sent to the steam hydrolysis reactor R01. The flow rate of the circulating liquid is 10-15 times the feed flow rate of succinic anhydride entering the steam hydrolysis reactor R01, so as to control the reaction temperature of the steam hydrolysis reactor R01 to be maintained at 190-210°C. The flow rate of the circulating liquid is controlled by the circulating valve 9. If the flow rate of the circulating liquid is large, the temperature of the steam hydrolysis reactor R01 will be lower. If the circulating flow rate is small, the temperature of the steam hydrolysis reactor R01 will be higher.

[0034] The material circulation method can not only discharge materials continuously, but also discharge materials intermittently. For example, most of the succinic acid discharged from the circulation pump P01 is returned as the circulation liquid, and a small part is continuously discharged as the product; or all of the succinic acid discharged from the circulation pump P01 is returned as the circulation liquid, and when intermittent discharge is required, the corresponding discharge valve 8 is opened to discharge materials, which has good flexibility.

[0035] The heat released by the reaction in the shell and tube heat exchange section 3 is recovered by the circulating hot water on the shell side, and enters the steam generator V01 through the thermal siphon effect to flash low-pressure steam. The consumed boiler water (DW) is replenished into the steam generator V01 through the water replenishment control valve 7 and is returned to the shell side of the shell and tube heat exchange section 3 with the cooled circulating hot water to recover the reaction heat. The low-pressure steam flashed out of the steam generator V01 is fed into the lower section of the steam hydrolysis reactor R01 through the steam flow feed control valve 11, and then enters the heat exchange tube 3.1 of the shell and tube heat exchange section 3 to react with the raw material succinic anhydride in reverse to generate succinic acid, and the excess low-pressure steam (LS) is sent out through the steam delivery valve 10. The amount of steam fed into the steam hydrolysis reactor R01 is controlled by the steam flow feed control valve 5. The larger the amount of steam fed, the higher the reactor pressure and the faster the hydrolysis reaction. If the amount of steam fed is less than the amount of steam consumed by the reaction, the reactor pressure will decrease. It is advisable to control the reactor pressure at 0.02-0.3MPaG. Under normal operation, the reactor is not vented. If a special overpressure occurs, it is adjusted through the exhaust control valve 6 at the top of the steam hydrolysis reactor R01.

[0036] Taking 1.25 t / h of succinic anhydride feed as an example, the circulating liquid flow rate is 15 t / h, the reactor temperature is 210°C, the boiler feed water consumption is 0.35 t / h, the 1.0 MPaG steam production is 0.12 t / h, the succinic acid production is 1.48 t / h, the succinic acid product purity is over 99.95%, the water content in succinic acid is 0.33% wt, and the iron ion content + titanium ion content is less than 10 ppm.

[0037] The method of the invention can produce high-purity succinic acid with good product quality, simple process flow, low investment, small land occupation, low operating energy consumption, environmental friendliness, no waste water, waste gas and waste solid generation, and solves the technical problem of preparing succinic acid from succinic anhydride.

Claims

1. A process for preparing succinic acid by steam hydrolysis of succinic anhydride, characterized in that: Succinic anhydride is fed into a steam hydrolysis reactor to contact with steam to undergo a hydrolysis reaction to generate succinic acid. The reaction pressure in the steam hydrolysis reactor is controlled at 0.02-0.3 MPaG and the reaction temperature is controlled at 190-210°C.

2. The process for preparing succinic acid by steam hydrolysis of succinic anhydride as claimed in claim 1, characterized in that: The upper section of the steam hydrolysis reactor is provided with a distributor, and the middle section is a shell and tube heat exchange section; the succinic anhydride is evenly distributed by the distributor in the upper section, and then sent to the heat exchange tubes of the shell and tube heat exchange section to contact with the steam in reverse to undergo a hydrolysis reaction; the generated succinic acid is drawn out from the bottom of the steam hydrolysis reactor after exiting the heat exchange tubes, and after being pressurized by a circulating pump, all or part of it is mixed with succinic anhydride as a circulating liquid and then circulated into the steam hydrolysis reactor, and the rest is sent out as a product.

3. The process for preparing succinic acid by steam hydrolysis of succinic anhydride as claimed in claim 2, characterized in that: The circulating liquid flow rate is 10-15 times the succinic anhydride feed flow rate entering the steam hydrolysis reactor.

4. The process for preparing succinic acid by steam hydrolysis of succinic anhydride as claimed in claim 2, characterized in that: Circulating hot water is introduced into the shell side of the shell and tube heat exchange section to remove the reaction heat, and the circulating hot water after heat exchange is sent to the steam generator to flash out low-pressure steam. The consumed boiler water is replenished into the steam generator through the water replenishment control valve and then returned to the shell side of the shell and tube heat exchange section for heat exchange.

5. The process for preparing succinic acid by steam hydrolysis of succinic anhydride as claimed in claim 4, characterized in that: The low-pressure steam flashed out by the steam generator is partially sent back to the lower section of the steam hydrolysis reactor and then enters the heat exchange tube to contact with succinic anhydride in reverse to produce a hydrolysis reaction, and the rest is sent out.

6. The process for preparing succinic acid by steam hydrolysis of succinic anhydride as claimed in claim 5, characterized in that: A steam flow feed control valve is provided at the steam inlet of the lower section of the steam hydrolysis reactor, and the reaction pressure in the steam hydrolysis reactor is controlled within 0.02-0.3 MPaG by controlling the flow rate of steam injected into the steam hydrolysis reactor.

7. The process for preparing succinic acid by steam hydrolysis of succinic anhydride as claimed in claim 6, characterized in that: An exhaust control valve is provided on the top of the steam hydrolysis reactor. When the reaction pressure in the steam hydrolysis reactor exceeds a set pressure range, the exhaust control valve is opened to reduce the pressure to the set pressure range.

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