A continuous rectification method and system for crude succinic anhydride

Abstract

The present application belongs to the field of maleic anhydride rectification and separation, and particularly relates to a crude maleic anhydride continuous rectification method and a crude maleic anhydride continuous rectification system. The continuous rectification system comprises an absorption unit, a desorption unit, a light component removal unit, a refining unit, a solvent purification unit, a gas-liquid separation unit and a tail gas washing unit. The crude maleic anhydride continuous rectification method is reasonable in design, reduces the operating temperature of the refining unit, and can further improve the purity of the maleic anhydride product under the same yield.

Description

Technical Field

[0001] This invention belongs to the field of maleic anhydride distillation and separation, specifically, it relates to a continuous distillation method and system for crude maleic anhydride. Background Technology

[0002] Maleic anhydride, also known as maleic acid anhydride, is the third largest acid anhydride after phthalic anhydride and acetic anhydride. Currently, the main industrial methods for producing maleic anhydride are the n-butane oxidation method and the benzene oxidation method. Globally, 80% of maleic anhydride production capacity uses n-butane as a raw material. The benzene method involves oxidizing benzene in a fixed-bed reactor using a vanadium-molybdenum-oxygen silicon carbide catalyst, generating maleic anhydride gas. This gas is then absorbed by water, undergoes azeotropic dehydration using xylene as an azeotropic agent, and is followed by continuous distillation under reduced pressure to obtain the final maleic anhydride product. The technology of the n-butane method for producing maleic anhydride mainly lies in the reactor bed design and the recovery and refining technology. The n-butane oxidation method has advantages such as low environmental pollution, high carbon atom utilization, and a wide availability and low price of raw materials, and in recent years it has gradually replaced the benzene oxidation method as the dominant production process for maleic anhydride. With the development of large-scale intensive production of maleic anhydride, the post-treatment of maleic anhydride is increasingly inclined to adopt solvent absorption-desorption technology. Typical solvent absorption-desorption processes include the Huntsman process, the Conser process, and the ALMA process. The former two use dibutyl phthalate (DBP) as a solvent, while the latter uses diisobutyl hexahydrophthalate (DIBE) as a solvent.

[0003] The crude maleic anhydride material after absorption and desorption contains impurities such as acetic acid, acrylic acid, maleic acid, fumaric acid, absorbent, n-butanol, dibutyl maleate, phthalic anhydride, and tar. Acetic acid and acrylic acid are byproducts of n-butane oxidation, maleic acid is a hydration product of maleic anhydride, fumaric acid is an isomer of maleic acid, phthalic anhydride and n-butanol are solvent hydrolysis products, phthalic acid is a hydrolysis product of phthalic anhydride, and tar is generated by fine catalyst particles entering the absorption unit, causing esterification of the absorbent, and then undergoing complex chemical reactions with the byproducts.

[0004] Currently, continuous distillation is commonly used in industry to remove acetic acid and acrylic acid, which have boiling points lower than maleic anhydride, after absorption and desorption. Then, heavier components are removed to obtain purified maleic anhydride. Numerous research findings on oxidation and absorption-desorption processes have been reported, and industrial applications have yielded relatively stable results. In existing butane-based methods for producing maleic anhydride, the crude maleic anhydride product after desorption has a low maleic anhydride content, affecting the purity of the final product. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a reasonably designed continuous distillation method and system for crude maleic anhydride, which can guarantee the yield of maleic anhydride products, further improve the purity of maleic anhydride products, and has the characteristics of good economic performance.

[0006] To achieve the above objectives, a first aspect of the present invention provides a continuous distillation method for crude maleic anhydride, the method comprising:

[0007] 1) The absorbent and reaction products enter the absorption unit to absorb maleic anhydride in the reaction products. After absorption, one stream of liquid phase is sent to the desorption unit to regenerate the absorbent, and the other stream is cooled and used as a circulating absorbent.

[0008] 2) After desorption, the product enters the light component removal unit to remove components lighter than maleic anhydride gas. After light component removal, one part of the product returns to the upper part of the desorption unit, and the other part is sent to the refining unit for refining.

[0009] 3) One stream of the desorbed solvent is returned to the lower part of the desorption unit, another stream is sent to the tail gas washing unit to recover maleic anhydride from the tail gas of the light removal unit and the purification unit, and then returned to the desorption unit after absorption. The third stream is purified and recycled.

[0010] A second aspect of the present invention provides a continuous crude maleic anhydride distillation system, the system comprising:

[0011] Absorption unit, desorption unit, light component removal unit, refining unit, exhaust gas scrubbing unit;

[0012] The absorption unit includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, a lower outlet, and a circulating absorbent inlet;

[0013] The desorption unit includes a liquid phase inlet, an upper outlet, a lower outlet, a circulating absorbent inlet, an absorbent return outlet, and a light product return outlet;

[0014] The light-weight removal unit includes a feed inlet, an upper discharge outlet, and a lower discharge outlet;

[0015] The refining unit includes a liquid phase inlet, an upper outlet, and a lower outlet;

[0016] The absorption unit, the desorption unit, the light component removal unit, and the refining unit are connected in sequence, and the lower discharge port of the light component removal unit is connected to the desorption unit.

[0017] The exhaust gas scrubbing unit includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, and a lower outlet;

[0018] The lower outlet of the desorption unit is connected to the desorption unit, and the upper outlets of the deionization unit, the light-removal unit, and the refining unit are respectively connected to the exhaust gas washing unit.

[0019] The lower outlet of the exhaust gas scrubbing unit is connected to the inlet of the circulating absorbent of the desorption unit.

[0020] The beneficial effects of this invention are:

[0021] The continuous distillation method for crude maleic anhydride of the present invention is rationally designed. By diverting a stream of maleic anhydride from the bottom of the light-light-removal unit column back to the top of the desorption unit column, a stream with a higher concentration of maleic anhydride can be obtained at the top of the desorption unit column. At the same time, the operating temperature of the purification unit is reduced. Under the same yield, the purity of maleic anhydride product can be further improved. To a certain extent, this promotes the extension of maleic anhydride to downstream industries such as pharmaceuticals and pesticides, which have high purity requirements and high added value. This is of great significance to the adjustment of the industrial structure of maleic anhydride in my country.

[0022] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0023] Exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0024] Figure 1 A simplified schematic diagram of one embodiment of a crude maleic anhydride continuous distillation system of the present invention is shown.

[0025] Figure 2 A schematic diagram of one embodiment of a crude maleic anhydride continuous distillation system of the present invention is shown.

[0026] Figure 3 A simplified schematic diagram of the crude maleic anhydride distillation system used in Comparative Example 1 is shown.

[0027] Figure 4 A schematic diagram of the crude maleic anhydride distillation system used in Comparative Example 1 is shown.

[0028] Explanation of reference numerals in the attached figures:

[0029] 1-Absorbent; 2-Reaction product; 3-Tail gas treatment system; 4-Vacuum system; 5-Mastic anhydride product; 6-Heavy component; 7-Absorption unit; 8-Desorption unit; 9-Light weight removal unit; 10-Purification unit; 11-Solvent purification unit; 12-Gas-liquid separation unit; 13-Light weight removal unit reflux tank; 14-Purification unit reflux tank; 15-Tail gas scrubbing unit. Detailed Implementation

[0030] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0031] A first aspect of the present invention provides a continuous distillation method for crude maleic anhydride, the continuous distillation method for crude maleic anhydride comprising:

[0032] 1) The absorbent and reaction products enter the absorption unit to absorb maleic anhydride in the reaction products. After absorption, one stream of liquid phase is sent to the desorption unit to regenerate the absorbent, and the other stream is cooled and used as a circulating absorbent.

[0033] 2) After desorption, the product enters the light component removal unit to remove components lighter than maleic anhydride gas. After light component removal, one part of the product returns to the upper part of the desorption unit, and the other part is sent to the refining unit for refining.

[0034] 3) One stream of the desorbed solvent is returned to the lower part of the desorption unit, another stream is sent to the tail gas washing unit to recover maleic anhydride from the tail gas of the light removal unit and the purification unit, and then returned to the desorption unit after absorption. The third stream is purified and recycled.

[0035] As a preferred embodiment, the continuous distillation method for crude maleic anhydride further includes:

[0036] After the gas phase of the absorption unit is separated by the gas-liquid separation unit, the gas phase enters the tail gas treatment system; the liquid phase of the gas-liquid separation unit is sent to the desorption unit for absorbent regeneration.

[0037] As a preferred embodiment, the absorption unit operates under slightly positive pressure; the desorption unit, light-weight gas removal unit, tail gas washing unit, purification unit, and vacuum system are connected and operate under negative pressure.

[0038] More preferably, the operating conditions satisfied by each unit include:

[0039] Absorption unit:

[0040] The working pressure at the top of the column is 101-200 kPaA, and the working pressure at the bottom of the column is 105-230 kPaA.

[0041] The operating temperature at the top of the column is 70-100℃, and the operating temperature at the bottom of the column is 90-110℃.

[0042] Desorption unit:

[0043] The working pressure at the top of the column is 1-10 kPaA, and the working pressure at the bottom of the column is 1-30 kPaA.

[0044] The operating temperature at the top of the tower is 90-130℃, and the operating temperature at the bottom of the tower is 190-230℃.

[0045] Lightweight unit removal:

[0046] The working pressure at the top of the column is 1-10 kPaA, and the working pressure at the bottom of the column is 1-30 kPaA.

[0047] The operating temperature at the top of the tower is 60-90℃, and the operating temperature at the bottom of the tower is 70-100℃.

[0048] Refining Unit:

[0049] The working pressure at the top of the column is 1-10 kPaA, and the working pressure at the bottom of the column is 1-30 kPaA.

[0050] The operating temperature at the top of the column is 70-100℃, and the operating temperature at the bottom of the column is 150-210℃.

[0051] Exhaust gas scrubbing unit:

[0052] The working pressure at the top of the column is 1-10 kPaA, and the working pressure at the bottom of the column is 1-30 kPaA.

[0053] The working temperature at the top of the tower is 45-75℃, and the working temperature at the bottom of the tower is 45-80℃.

[0054] In this invention, the crude maleic anhydride comprises acetic acid, acrylic acid, maleic acid, fumaric acid, and an absorbent. In one specific embodiment, the crude maleic anhydride further comprises at least one of n-butanol, dibutyl maleate, phthalic anhydride, and tar.

[0055] As a preferred embodiment, the solvent used in the absorption unit is dibutyl phthalate and / or diisobutyl phthalate.

[0056] As a preferred embodiment, in step 2), the portion returned to the upper part of the desorption unit after light removal is 3%-11%, and the portion sent to the refining unit for refining is 89%-97%. More preferably, in step 2), the portion returned to the upper part of the desorption unit after light removal is 5%-10%, and the portion sent to the refining unit for refining is 90%-95%.

[0057] As a preferred embodiment, in step 1), 10%-50% of the absorbed liquid phase is sent to the desorption unit for regeneration of the absorbent, and 50%-90% is cooled and used as a circulating absorbent. More preferably, in step 1), 10%-30% of the absorbed liquid phase is sent to the desorption unit for regeneration of the absorbent, and 70%-90% is cooled and used as a circulating absorbent.

[0058] As a preferred embodiment, in step 3), 1%-30% of the solvent returned to the lower part of the desorption unit, and 1%-20% of the solvent after desorption is returned to the desorption unit after being absorbed by the tail gas washing unit to recover maleic anhydride from the tail gas of the light oxidizing unit and the refining unit, and 50%-98% is recycled after purification. More preferably, in step 3), 1%-25% of the solvent returned to the lower part of the desorption unit, and 5%-20% of the solvent after desorption is returned to the desorption unit after being absorbed by the tail gas washing unit to recover maleic anhydride from the tail gas of the light oxidizing unit and the refining unit, and 55%-94% is recycled after purification.

[0059] As a preferred option, in step 1), another stream is cooled to below 70°C and used as a circulating absorbent.

[0060] As a preferred option, in step 3), one stream of the desorbed solvent is returned to the lower part of the desorption unit, which can reduce the absorption of excessive water in the absorbent, reduce the generation of impurities and the frequency of equipment blockage due to impurities, as well as maintenance costs and labor costs; another stream is sent to the tail gas scrubbing unit to recover maleic anhydride from the tail gas of the light removal unit and the refining unit, and then returned to the lower part of the desorption unit for desorption after absorption. The advantages of this are: the absorbent is at a lower temperature after absorption in the tail gas scrubbing unit, and enters the higher temperature part of the lower part of the desorption unit, which enhances heat exchange, makes the concentration of maleic anhydride in the feed and the bed closer, and increases the utilization rate of the absorbent through small circulation; the other stream is recycled after purification.

[0061] As a preferred option, one stream of the desorbed solvent is cooled to below 70°C and sent to the tail gas washing unit to recover maleic anhydride from the tail gas of the light removal unit and the refining unit. After absorption, it is returned to the desorption unit. The other stream is cooled to below 70°C and then purified before being recycled.

[0062] A second aspect of the present invention provides a continuous crude maleic anhydride distillation system, the system comprising:

[0063] Absorption unit, desorption unit, light component removal unit, refining unit, exhaust gas scrubbing unit;

[0064] The absorption unit includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, a lower outlet, and a circulating absorbent inlet;

[0065] The desorption unit includes a liquid phase inlet, an upper outlet, a lower outlet, a circulating absorbent inlet, an absorbent return outlet, and a light product return outlet;

[0066] The light-weight removal unit includes a feed inlet, an upper discharge outlet, and a lower discharge outlet;

[0067] The refining unit includes a liquid phase inlet, an upper outlet, and a lower outlet;

[0068] The absorption unit, the desorption unit, the light component removal unit, and the refining unit are connected in sequence, and the lower discharge port of the light component removal unit is connected to the desorption unit.

[0069] The exhaust gas scrubbing unit includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, and a lower outlet;

[0070] The lower outlet of the desorption unit is connected to the desorption unit, and the upper outlets of the deionization unit, the light-removal unit, and the refining unit are respectively connected to the exhaust gas washing unit.

[0071] The lower outlet of the exhaust gas scrubbing unit is connected to the inlet of the circulating absorbent of the desorption unit.

[0072] As a preferred embodiment, the desorption unit, the light-weight removal unit, the refining unit, and the exhaust gas washing unit are connected to a vacuum system.

[0073] As a preferred embodiment, the crude maleic anhydride continuous distillation system further includes a gas-liquid separation unit, with the upper outlet of the absorption unit connected to the gas-liquid separation unit and the lower part of the gas-liquid separation unit connected to the desorption unit.

[0074] As a preferred embodiment, the crude maleic anhydride continuous distillation system further includes a light-light-removal unit reflux tank and / or a refining unit reflux tank;

[0075] The light-duty removal unit, the light-duty removal unit return tank, and the exhaust gas scrubbing unit are connected in sequence, and the light-duty removal unit and the light-duty removal unit return tank form a loop;

[0076] The refining unit, the refining unit return tank, and the exhaust gas scrubbing unit are connected in sequence, and the refining unit and the refining unit return tank form a loop.

[0077] The present invention will be further described below with reference to the embodiments, but the scope of the present invention is not limited to these embodiments.

[0078] In the embodiments and comparative examples of this invention, the absorbent used is dibutyl phthalate (DBP).

[0079] In the embodiments and comparative examples of this invention, the connection methods not shown are all pipe connections, or other conventional connection methods that can be selected by those skilled in the art.

[0080] In the embodiments and comparative examples of this invention, the transportation method of the logistics is "pumping" or other methods well known to those skilled in the art.

[0081] In the embodiments and comparative examples of this invention, the absorption unit adopts an absorption tower; the desorption unit adopts a desorption tower; the light-weight removal unit adopts a light-weight removal tower; the purification unit adopts a purification tower; and the gas-liquid separation unit adopts a flash tank.

[0082] Example 1

[0083] This embodiment provides a method and system for continuous distillation of crude maleic anhydride.

[0084] Figure 1 A simplified schematic diagram of one embodiment of a crude maleic anhydride continuous distillation system of the present invention is shown. Figure 2 A schematic diagram of one embodiment of a crude maleic anhydride continuous distillation system of the present invention is shown.

[0085] See Figure 2The crude maleic anhydride continuous distillation system includes: an absorption unit 7, a desorption unit 8, a light component removal unit 9, a purification unit 10, a solvent purification unit 11, a gas-liquid separation unit 12, and a tail gas washing unit 15.

[0086] Absorption unit 7 includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, a lower outlet, and a circulating absorbent inlet; desorption unit 8 includes a liquid phase inlet, an upper outlet, a lower outlet, a circulating absorbent inlet, an absorbent return outlet, and a light product return outlet; light product removal unit 9 includes an inlet, an upper outlet, and a lower outlet; refining unit 10 includes a liquid phase inlet, an upper outlet, and a lower outlet; and exhaust gas scrubbing unit 15 includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, and a lower outlet.

[0087] The top of the absorption unit 7 is connected to the gas-liquid separation unit 12, and then to the tail gas treatment system 3. The bottom of the gas-liquid separation unit 12 is connected to the liquid outlet pipe of the bottom liquid of the absorption unit 7 to the desorption unit 8. The liquid outlet pipe of the bottom liquid of the absorption unit 7 is connected to the circulating absorbent inlet of the absorption unit 7 through the first cooling device.

[0088] The top of the desorption unit 8 is connected to the light component removal unit 9; the bottom of the desorption unit 8 is connected to a second cooling device, and the bottom of the desorption unit 8 is connected to the tail gas scrubbing unit 15 and the solvent purification unit 11 through the second cooling device; the bottom of the tail gas scrubbing unit 15 is connected to the desorption unit 8; the liquid outlet of the solvent purification unit 11 is connected to the circulating absorbent inlet of the absorption unit 7; the bottom of the bottom of the desorption unit 8 is connected to the lower part of the desorption unit 8 through a pipe.

[0089] The bottom of the light-light removal unit 9 is connected to the top of the purification unit 10 and the desorption unit 8, respectively; the non-condensable gas pipelines at the top of the light-light removal unit 9 and the purification unit 10 are connected to the tail gas scrubbing unit 15.

[0090] The desorption unit 8, the light component removal unit 9, the refining unit 10, and the exhaust gas washing unit 15 are connected to the vacuum system 4.

[0091] The crude maleic anhydride continuous distillation system also includes a light-light-removal reflux tank 13 and a refining reflux tank 14;

[0092] The gas phase discharge pipeline at the top of the light-light removal unit 9 is connected to the light-light removal unit reflux tank 13, the non-condensable gas pipeline of the light-light removal unit reflux tank 13 is connected to the tail gas scrubbing unit 15, and the liquid phase discharge pipeline of the light-light removal unit reflux tank 13 is connected to the top of the light-light removal unit 9.

[0093] The gas phase discharge pipeline at the top of the refining unit 10 is connected to the refining unit reflux tank 14, the non-condensable gas pipeline of the refining unit reflux tank 14 is connected to the tail gas scrubbing unit 15, and the liquid phase discharge pipeline of the refining unit reflux tank 14 is connected to the top of the refining unit 10.

[0094] The bottom of the desorption unit 8 is connected to the upper part of the tail gas scrubbing unit 15, and the non-condensable gas pipes at the top of the light gas removal unit 9 and the refining unit 10 are connected to the lower part of the tail gas scrubbing unit 15.

[0095] See Figure 2 The crude maleic anhydride product containing impurities such as acetic acid, acrylic acid, maleic acid, fumaric acid, absorbent, n-butanol, dibutyl maleate, phthalic anhydride, and tar enters the absorption unit 7. The absorbent enters the absorption unit 7 through the absorbent feed inlet. The gas at the top of the absorption unit 7 is flashed by the gas-liquid separation unit 12 and then enters the tail gas treatment system 3. The liquid phase of the gas-liquid separation unit 12 is combined with a portion of the liquid at the bottom of the absorption unit 7 and sent to the desorption unit 8 for absorbent regeneration. The other portion of the liquid at the bottom of the absorption unit 7 is cooled to below 70°C by the first cooling device and then recycled back to the absorption unit 7. The maleic anhydride-rich gas from the top of desorption unit 8 enters light component removal unit 9 to remove components lighter than maleic anhydride, such as acetic acid, acrylic acid, water, carbon monoxide, nitrogen, oxygen, carbon dioxide, and n-butane. The lean solvent at the bottom of desorption unit 8 is divided into three parts: the first part is returned to the bottom of desorption unit 8 for re-desorption; the second part is cooled to below 70°C by a second cooling device and sent to tail gas scrubbing unit 15 to recover maleic anhydride from the non-condensable gas at the top of light component removal unit 9 and purification unit 10, and after absorption, it is returned to the lower part of desorption unit 8 for desorption; the third part is cooled to below 70°C by a second cooling device and sent to solvent purification unit 11 for purification before being returned to absorption unit 7 for use. The liquid at the bottom of light component removal unit 9 is divided into two parts: one part is returned to the top of desorption unit 8 to increase the maleic anhydride content in the top gas of desorption unit 8, and the other part is sent to purification unit 10 for purification. Maleic anhydride product 5 is obtained from the top of purification unit 10, and heavy component 6 is obtained from the bottom of purification unit 10. The non-condensable gas from the top of the light-light removal unit 9 and the refining unit 10 enters the tail gas scrubbing unit 15 to recover maleic anhydride. After scrubbing, the tail gas is connected to the vacuum system 4.

[0096] The crude maleic anhydride product generated in the reaction section is 388,903 kg / h, of which the maleic anhydride mass flow rate is 12,562.12 kg / h. A portion of the liquid phase from the gas-liquid separation unit 12 and the bottom liquid from the absorption unit 7 are combined and sent to the desorption unit 8 for absorbent regeneration, at a rate of 81,369 kg / h (of which 24.07 kg / h originates from the gas-liquid separation unit 12 and 81,344.93 kg / h originates from the bottom liquid of the absorption unit 7). Another portion of the bottom liquid from the absorption unit is cooled and recycled back to the absorption unit, at a rate of 300,000 kg / h. The lean solvent from the bottom of the desorption unit is divided into three parts: one part is returned to the bottom of the desorption unit for re-desorption, at a rate of 1,000 kg / h; another part is sent to the tail gas scrubbing unit to recover maleic anhydride from the top gas phase of the light component removal unit and then returned to the desorption unit for desorption after absorption, at a rate of 10,000 kg / h; and the remaining part is sent to the solvent purification unit for purification and then returned to the absorption unit for use, at a rate of 67,587.26 kg / h. The bottom liquid of the light-light unit column is divided into two parts. One part is returned to the top of the desorption unit column to increase the maleic anhydride content at the top of the desorption unit column, which is 1000 kg / h. The other part is sent to the purification unit for purification, and maleic anhydride product is obtained from the top of the purification unit column, which is 12662.48 kg / h.

[0097] The temperature of the absorber bottom liquid was 101.8℃, and the pressure was 0.3 MPa.G. The composition of the absorber bottom liquid (by mass) was: water 1.25%, nitrogen 0.02%, n-butane 0.01%, acetic acid 0.03%, acrylic acid 0.08%, maleic anhydride 15.44%, maleic acid 0.57%, fumaric acid 0.09%, phthalic anhydride 0.18%, absorbent 81.21%, phthalic acid 0.02%, dibutyl maleate 0.01%, and tar 1.1%. The operating conditions for each piece of equipment are shown in Table 1.

[0098] Table 1. Main operating conditions of each device in Example 1

[0099]

[0100] Example 1 shows that the maleic anhydride product has a purity of 99.99%, a yield of 12550.33 kg / h, and a recovery rate of 99.88%.

[0101] Comparative Example 1:

[0102] Figure 3 A simplified schematic diagram of the crude maleic anhydride distillation system used in Comparative Example 1 is shown. Figure 4 A schematic diagram of the crude maleic anhydride distillation system used in Comparative Example 1 is shown.

[0103] See Figure 4The crude maleic anhydride product containing impurities such as acetic acid, acrylic acid, maleic acid, fumaric acid, absorbent, n-butanol, dibutyl maleate, phthalic anhydride, and tar enters the absorption unit 7. The absorbent enters the absorption unit 7 through the absorbent feed inlet. The gas at the top of the absorption unit 7 is flashed by the gas-liquid separation unit 12 and then enters the tail gas treatment system 3. The liquid phase of the gas-liquid separation unit 12 is combined with a portion of the liquid at the bottom of the absorption unit 7 and sent to the desorption unit 8 for absorbent regeneration. The other portion of the liquid at the bottom of the absorption unit 7 is cooled to below 70°C by the first cooling device and then recycled back to the absorption unit 7. The maleic anhydride-rich gas from the top of desorption unit 8 enters light component removal unit 9 to remove components lighter than maleic anhydride, such as acetic acid, acrylic acid, water, carbon monoxide, nitrogen, oxygen, carbon dioxide, and n-butane. The lean solvent from the bottom of desorption unit 8 is divided into three parts: the first part returns to the bottom of desorption unit 8 for re-desorption; the second part is cooled to below 70°C by a second cooling device and sent to tail gas scrubbing unit 15 to recover maleic anhydride from the non-condensable gas at the top of light component removal unit 9 and purification unit 10, and after absorption, returns to the lower part of desorption unit 8 for desorption; the third part is cooled to below 70°C by a second cooling device and sent to solvent purification unit 11 for purification before returning to absorption unit 7 for use. The liquid from the bottom of light component removal unit 9 is sent to purification unit 10 for purification, yielding maleic anhydride product 5 from the top of purification unit 10 and heavy component 6 from the bottom of purification unit 10. The non-condensable gas from the top of light component removal unit 9 and purification unit 10 enters tail gas scrubbing unit 15 to recover maleic anhydride, and after scrubbing, the tail gas is connected to vacuum system 4.

[0104] The crude maleic anhydride produced in the reaction section is 388,903 kg / h, of which the maleic anhydride mass flow rate is 12,562.12 kg / h. The liquid phase from the gas-liquid separation unit 12 and a portion of the liquid from the bottom of the absorption unit 7 are combined and sent to the desorption unit 8 for absorbent regeneration, at a rate of 81,369 kg / h (of which 24.07 kg / h comes from the gas-liquid separation unit 12 and 81,344.93 kg / h comes from the liquid from the bottom of the absorption unit 7). The remaining portion of the liquid from the bottom of the absorption unit 7 is cooled and recycled back to the absorption unit 7, at a rate of 300,000 kg / h. The lean solvent in the bottom of the desorption unit 8 is divided into three parts. The first part is returned to the bottom of the desorption unit 8 for re-desorption, with a capacity of 1000 kg / h. The second part is sent to the tail gas washing unit 15 to recover maleic anhydride from the non-condensable gas at the top of the light volatile organic compound removal unit 9 and then returned to the desorption unit 8 for desorption after absorption, with a capacity of 10000 kg / h. The third part is sent to the solvent purification unit 11 for purification and then returned to the absorption unit 7 for use, with a capacity of 67140.26 kg / h.

[0105] The bottom liquid temperature of absorption unit 7 is 101.8℃, and the pressure is 0.3 MPa.G. The composition of the bottom liquid in the absorption unit (by mass) is: water 1.25%, nitrogen 0.02%, n-butane 0.01%, acetic acid 0.03%, acrylic acid 0.08%, maleic anhydride 15.44%, maleic acid 0.57%, fumaric acid 0.09%, phthalic anhydride 0.18%, absorbent 81.21%, phthalic acid 0.02%, dibutyl maleate 0.01%, and tar 1.1%. The operating conditions for each piece of equipment are shown in Table 2.

[0106] Table 2 Main operating conditions of each piece of equipment in Comparative Example 1

[0107]

[0108] Comparative Example 1 yielded a maleic anhydride product purity of 99.97%, a yield of 12551.39 kg / h, and a recovery rate of 99.88%.

[0109] By comparing the examples and comparative examples, it was found that the method of returning part of the liquid from the bottom of the light-light unit column to the top of the desorption unit column to increase the maleic anhydride content in the top gas of the desorption unit column, and sending part of it to the purification unit for purification, and obtaining maleic anhydride product from the top of the purification unit column, can increase the purity of maleic anhydride product from 99.97% to 99.99% under the same yield.

[0110] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A continuous distillation method for crude maleic anhydride, characterized in that, The continuous distillation method for crude maleic anhydride includes: 1) The absorbent and reaction products enter the absorption unit to absorb maleic anhydride in the reaction products. After absorption, one stream of the liquid phase is sent to the desorption unit to regenerate the absorbent, and the other stream is cooled and used as a circulating absorbent. The solvent used in the absorption unit is dibutyl phthalate and / or diisobutyl phthalate. The working pressure at the top of the absorption unit is 101-200 kPaA, and the working pressure at the bottom of the unit is 105-230 kPaA. 2) After desorption, the product enters the light-weight removal unit to remove components lighter than maleic anhydride gas. After light-weight removal, one portion of the product returns to the upper part of the desorption unit, and the other portion is sent to the purification unit for purification. The portion returning to the upper part of the desorption unit after light-weight removal is 3%-11%, and the portion sent to the purification unit for purification is 89%-97%. 3) One stream of the desorbed solvent is returned to the lower part of the desorption unit, another stream is sent to the tail gas scrubbing unit to recover maleic anhydride from the tail gas of the light nitrate removal unit and the purification unit, and then returned to the desorption unit after absorption. The third stream is purified and recycled. The portion returned to the lower part of the desorption unit is 1%-30%, the portion of the desorbed solvent sent to the tail gas scrubbing unit to recover maleic anhydride from the tail gas of the light nitrate removal unit and the purification unit, and the portion returned to the desorption unit after absorption is 1%-20%, and the portion recycled after purification is 50%-98%.

2. The continuous distillation method for crude maleic anhydride according to claim 1, wherein, The continuous distillation method for crude maleic anhydride also includes: After the gas phase of the absorption unit is separated by the gas-liquid separation unit, the gas phase enters the tail gas treatment system; the liquid phase of the gas-liquid separation unit is sent to the desorption unit for absorbent regeneration.

3. The continuous distillation method for crude maleic anhydride according to claim 1 or 2, wherein, The absorption unit operates under slightly positive pressure; the desorption unit, light volatile matter removal unit, tail gas washing unit, purification unit, and vacuum system are connected and operate under negative pressure.

4. The continuous distillation method for crude maleic anhydride according to claim 3, wherein, The operating conditions that each unit must meet include: Absorption unit: The operating temperature at the top of the column is 70-100℃, and the operating temperature at the bottom of the column is 90-110℃. Desorption unit: The working pressure at the top of the column is 1-10 kPaA, and the working pressure at the bottom of the column is 1-30 kPaA. The operating temperature at the top of the tower is 90-130℃, and the operating temperature at the bottom of the tower is 190-230℃. Lightweight unit removal: The working pressure at the top of the column is 1-10 kPaA, and the working pressure at the bottom of the column is 1-30 kPaA. The operating temperature at the top of the tower is 60-90℃, and the operating temperature at the bottom of the tower is 70-100℃. Refining Unit: The working pressure at the top of the column is 1-10 kPaA, and the working pressure at the bottom of the column is 1-30 kPaA. The operating temperature at the top of the column is 70-100℃, and the operating temperature at the bottom of the column is 150-210℃. Exhaust gas scrubbing unit: The working pressure at the top of the column is 1-10 kPaA, and the working pressure at the bottom of the column is 1-30 kPaA. The working temperature at the top of the tower is 45-75℃, and the working temperature at the bottom of the tower is 45-80℃.

5. The continuous distillation method for crude maleic anhydride according to claim 1 or 2, wherein, The crude maleic anhydride comprises acetic acid, acrylic acid, maleic acid, fumaric acid, and an absorbent.

6. The continuous distillation method for crude maleic anhydride according to claim 5, wherein, The crude maleic anhydride also includes at least one of n-butanol, dibutyl maleate, phthalic anhydride, and tar.

7. The continuous distillation method for crude maleic anhydride according to claim 1, wherein, In step 2), 5%-10% of the portion after desorption is returned to the upper part of the desorption unit, and 90%-95% is sent to the refining unit for refining.

8. The continuous distillation method for crude maleic anhydride according to claim 1 or 2, wherein, In step 1), 10%-50% of the absorbed liquid phase is sent to the desorption unit to regenerate the absorbent, and 50%-90% is cooled and used as a circulating absorbent.

9. The continuous distillation method for crude maleic anhydride according to claim 8, wherein, In step 1), 10%-30% of the absorbed liquid phase is sent to the desorption unit to regenerate the absorbent, and 70%-90% is cooled and used as a circulating absorbent.

10. The continuous distillation method for crude maleic anhydride according to claim 1, wherein, In step 3), 1%-25% of the solvent is returned to the lower part of the desorption unit. After desorption, the solvent is sent to the tail gas washing unit to recover maleic anhydride from the tail gas of the light removal unit and the purification unit. After absorption, 5%-20% of the solvent is returned to the desorption unit. After purification, 55%-94% of the solvent is recycled.

11. The continuous distillation method for crude maleic anhydride according to claim 1 or 2, wherein, In step 1), another stream is cooled to below 70°C and used as a circulating absorbent; In step 3), one stream of the desorbed solvent is returned to the lower part of the desorption unit, and another stream is sent to the tail gas washing unit to recover maleic anhydride from the tail gas of the light removal unit and the purification unit. After absorption, it is returned to the lower part of the desorption unit for desorption. The other stream is purified and recycled.

12. The continuous distillation method for crude maleic anhydride according to claim 1 or 2, wherein, After desorption, one stream of solvent is cooled to below 70°C and sent to the tail gas washing unit to recover maleic anhydride from the tail gas of the light removal unit and the refining unit. After absorption, it is returned to the desorption unit. The other stream is cooled to below 70°C and then purified before being recycled.

13. A continuous distillation system for crude maleic anhydride, characterized in that, The system includes: Absorption unit, desorption unit, light component removal unit, refining unit, exhaust gas scrubbing unit; The absorption unit includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, a lower outlet, and a circulating absorbent inlet; The desorption unit includes a liquid phase inlet, an upper outlet, a lower outlet, a circulating absorbent inlet, an absorbent return outlet, and a light product return outlet; The light-weight removal unit includes a feed inlet, an upper discharge outlet, and a lower discharge outlet; The refining unit includes a liquid phase inlet, an upper outlet, and a lower outlet; The absorption unit, the desorption unit, the light component removal unit, and the refining unit are connected in sequence, and the lower discharge port of the light component removal unit is connected to the desorption unit. The exhaust gas scrubbing unit includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, and a lower outlet; The lower outlet of the desorption unit is connected to the desorption unit, and the upper outlets of the deionization unit, the light-removal unit, and the refining unit are respectively connected to the exhaust gas washing unit. The lower outlet of the exhaust gas scrubbing unit is connected to the inlet of the circulating absorbent of the desorption unit.

14. The continuous distillation system for crude maleic anhydride according to claim 13, wherein, The desorption unit, the light component removal unit, the refining unit, and the exhaust gas washing unit are connected to the vacuum system.

15. The continuous distillation system for crude maleic anhydride according to claim 13, wherein, The crude maleic anhydride continuous distillation system also includes a gas-liquid separation unit, with the upper outlet of the absorption unit connected to the gas-liquid separation unit and the lower part of the gas-liquid separation unit connected to the desorption unit.

16. The continuous distillation system for crude maleic anhydride according to claim 13, wherein, The crude maleic anhydride continuous distillation system also includes a light-light-removal unit reflux tank and / or a refining unit reflux tank; The light-duty removal unit, the light-duty removal unit return tank, and the exhaust gas scrubbing unit are connected in sequence, and the light-duty removal unit and the light-duty removal unit return tank form a loop; The refining unit, the refining unit return tank, and the exhaust gas scrubbing unit are connected in sequence, and the refining unit and the refining unit return tank form a loop.

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