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 and a tail gas washing unit. The present application avoids the solvent tank corrosion problem possibly caused by the solvent returned to the solvent tank after washing the tail gas, and further reduces the energy consumption on the basis of improving the 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 adsorption tower, 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 solvent after washing the tail gas contains maleic anhydride, acetic acid, acrylic acid, maleic acid, fumaric acid, etc., and has a lower absorbent content compared to the solvent in the solvent tank. Directly returning it to the solvent tank would reduce the absorbent concentration and increase the difficulty of solvent purification. Furthermore, the solvent after absorbing the tail gas contains some acetic acid and acrylic acid, and directly returning it to the solvent tank could lead to corrosion problems. 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 avoid the corrosion problem of solvent tanks that may be caused by the return of solvent from the tail gas after washing, and further reduce energy consumption while improving yield.

[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 and the absorption 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, a circulating absorbent inlet, and a washing tail gas solvent 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 circulating absorbent inlet of the desorption unit and the absorption unit.

[0020] The beneficial effects of this invention are:

[0021] The continuous distillation method for crude maleic anhydride of the present invention is reasonably designed. The solvent after washing the tail gas is divided into two parts, which avoids the corrosion problem of the solvent tank that may be caused by returning the solvent after washing the tail gas to the solvent tank. This further reduces energy consumption while improving the yield. After washing the tail gas, part of the solvent enters the lower part of the absorption unit to continue to absorb maleic anhydride. This can effectively utilize the coldness and absorption capacity of the solvent after absorbing the tail gas, and further improve the product yield and product output without changing the product purity.

[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 and the absorption 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 embodiment, in step 3), after the exhaust gas is absorbed by the exhaust gas scrubbing unit, 10%-90% of the gas returns to the desorption unit and 10%-90% enters the absorption unit. More preferably, in step 3), after the exhaust gas is absorbed by the exhaust gas scrubbing unit, 30%-70% of the gas returns to the desorption unit and 30%-70% enters the absorption unit.

[0060] As a preferred option, in step 1), another stream is cooled to below 70°C and used as a circulating absorbent.

[0061] 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.

[0062] 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.

[0063] A second aspect of the present invention provides a continuous crude maleic anhydride distillation system, the system comprising:

[0064] Absorption unit, desorption unit, light component removal unit, refining unit, exhaust gas scrubbing unit;

[0065] The absorption unit includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, a lower outlet, a circulating absorbent inlet, and a washing tail gas solvent inlet;

[0066] 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;

[0067] The light-weight removal unit includes a feed inlet, an upper discharge outlet, and a lower discharge outlet;

[0068] The refining unit includes a liquid phase inlet, an upper outlet, and a lower outlet;

[0069] 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.

[0070] The exhaust gas scrubbing unit includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, and a lower outlet;

[0071] 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.

[0072] The lower outlet of the exhaust gas scrubbing unit is connected to the circulating absorbent inlet of the desorption unit and the absorption unit.

[0073] 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.

[0074] 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.

[0075] 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;

[0076] 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;

[0077] 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.

[0078] As a preferred embodiment, the circulating absorbent inlet is located above the lower gas phase inlet of the absorption unit, and the washing tail gas solvent inlet is located between the circulating absorbent inlet and the lower gas phase inlet of the absorption unit. In this case, maleic anhydride is further absorbed in the area with a higher concentration of maleic anhydride in the lower part of the absorption unit, resulting in higher yield.

[0079] 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.

[0080] In the embodiments and comparative examples of this invention, the absorbent used is dibutyl phthalate (DBP).

[0081] 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.

[0082] 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.

[0083] 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.

[0084] Example 1

[0085] This embodiment provides a method and system for continuous distillation of crude maleic anhydride.

[0086] 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.

[0087] See Figure 2 The 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.

[0088] The absorption unit 7 includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, a lower outlet, a circulating absorbent inlet, and a washing tail gas solvent inlet. The circulating absorbent inlet is located above the lower gas phase inlet of the absorption unit 7, and the washing tail gas solvent inlet is located between the circulating absorbent inlet and the lower gas phase inlet of the absorption unit 7. The desorption unit includes a liquid phase inlet, an upper outlet, a lower outlet, a circulating absorbent inlet, an absorbent return inlet, and a light product return inlet. The light product removal unit includes an inlet, an upper outlet, and a lower outlet. The refining unit includes a liquid phase inlet, an upper outlet, and a lower outlet. The tail gas washing unit includes an upper liquid phase inlet, a lower gas phase inlet, an upper outlet, and a lower outlet.

[0089] 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.

[0090] The top of the desorption unit 8 is connected to the light-weight 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 washing unit 15 and the solvent purification unit 11 respectively through the second cooling device; 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.

[0091] 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.

[0092] 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;

[0093] The bottom of the tail gas scrubbing unit 15 is connected to the scrubbing tail gas solvent inlet of the absorption unit 7 and the lower part of the desorption unit 8 via pipes.

[0094] The crude maleic anhydride continuous distillation system also includes a light-light-removal reflux tank 13 and a refining reflux tank 14;

[0095] 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.

[0096] 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.

[0097] 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 pipelines 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.

[0098] See Figure 2The 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 absorption unit 7. The gas at the top of absorption unit 7 undergoes flash evaporation and then enters the tail gas treatment system 3. The liquid phase from the gas-liquid separation unit 12, along with a portion of the liquid at the bottom of absorption unit 7, is sent to desorption unit 8 for absorbent regeneration. The remaining portion of the liquid at the bottom of absorption unit 7 is cooled to below 70°C and then recycled back to absorption unit 7. The maleic anhydride-rich gas at the top of desorption unit 8 enters the light-duty removal unit 9 to remove impurities such as acetic acid and acrylic acid. The lean solvent at the bottom of desorption unit 8 is divided into three parts: one part returns to the lower part of desorption unit 8 for re-desorption; another part is cooled to below 70°C and sent to the tail gas washing unit 15 to recover the maleic anhydride from the gas phase at the top of the light-duty removal unit; and the remaining part is purified in the solvent purification unit 11 and then returned to absorption unit 7 for reuse. The liquid in the bottom of the light-light-removal unit 9 is divided into two parts. One part is returned to the top of the desorption unit 8 to increase the maleic anhydride content in the top gas of the desorption unit 8, and the other part is sent to the purification unit 10 for purification, from which maleic anhydride product is obtained. The non-condensable gas from the top of the light-light-removal unit 9 and the purification unit 10 enters the tail gas scrubbing unit 15 to recover the maleic anhydride. After scrubbing, the tail gas is connected to the vacuum system 4. The solvent after scrubbing the tail gas is divided into two parts. One part is returned to the desorption unit 8 for desorption, and the other part enters the lower part of the absorption unit 7 to continue absorbing maleic anhydride.

[0099] The crude maleic anhydride product generated in the reaction section is 38,8903 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 89,138.87 kg / h (of which 23.05 kg / h originates from the gas-liquid separation unit 12 and 89,115.82 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; one part is sent to the tail gas scrubbing unit to recover maleic anhydride from the top gas phase of the light component removal unit, at a rate of 15,000 kg / h; and the remaining part is sent to the solvent purification unit for refining and then returned to the absorption unit, at a rate of 67,552.18 kg / h. The bottom liquid of the light-weight removal unit is divided into two parts. One part is returned to the top of the desorption unit to increase the maleic anhydride content at the top of the desorption unit, at a rate of 1000 kg / h. The other part is sent to the purification unit for purification, from which maleic anhydride product is obtained at a rate of 12684.86 kg / h. The solvent after washing the tail gas is divided into two parts. One part is returned to the desorption unit for desorption, at a rate of 7718.84 kg / h. The other part enters the lower part of the absorption unit to continue absorbing maleic anhydride, at a rate of 7718.84 kg / h.

[0100] The temperature of the absorber bottom liquid was 101.7℃, and the pressure was 0.3 MPa.G. The composition of the absorber bottom liquid (by mass) was: water 1.27%, nitrogen 0.02%, n-butane 0.006%, acetic acid 0.03%, acrylic acid 0.08%, maleic anhydride 14.54%, maleic acid 0.57%, fumaric acid 0.009%, phthalic anhydride 0.13%, absorbent 83.85%, phthalic acid 0.02%, dibutyl maleate 0.009%, and tar 1.1%. The operating conditions for each piece of equipment are shown in Table 1.

[0101] Table 1. Main operating conditions of each device in Example 1

[0102]

[0103] Example 1: The maleic anhydride product had a purity of 99.97%, a yield of 12556.51 kg / h, a recovery rate of 99.92%, and a desorption unit heat load of 4655 kW.

[0104] Comparative Example 1

[0105] 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.

[0106] 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 11. 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.

[0107] 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 is sent to the desorption unit 8 for absorbent regeneration, at a rate of 81,368.04 kg / h (of which 24.07 kg / h originates from the gas-liquid separation unit 12 and 81,343.97 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 15,000 kg / h; and the remaining part is sent to the solvent purification unit for refining and then returned to the absorption unit for use, at a rate of 67,586 kg / h.

[0108] 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 12651.73 kg / h.

[0109] 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 1.27%, nitrogen 0.02%, n-butane 0.006%, acetic acid 0.03%, acrylic acid 0.07%, maleic anhydride 15.75%, maleic acid 0.57%, fumaric acid 0.09%, phthalic anhydride 0.18%, absorbent 82.84%, 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.

[0110] Table 2 Main operating conditions of each piece of equipment in Comparative Example 1

[0111]

[0112] The comparative calculations showed that the maleic anhydride product purity was 99.97%, the yield was 12551.35 kg / h, the recovery rate was 99.88%, and the heat load of the desorption unit was 5046 kW.

[0113] A comparison of the examples and comparative examples reveals that the method of dividing the solvent after washing the tail gas into two parts—one part returning to the desorption unit for desorption, and the other part entering the lower part of the absorption unit to continue absorbing maleic anhydride—effectively utilizes the cooling capacity and absorption capacity of the solvent after absorbing the tail gas, allowing for further absorption of maleic anhydride in the region with a higher concentration in the lower part of the absorption unit. With the product purity remaining unchanged, the maleic anhydride yield can be increased from 12551.35 kg / h to 12556.51 kg / h, and the yield can be increased from 99.88% to 99.92%. The heat load of the desorption unit is reduced by 8%, while simultaneously avoiding the solvent tank corrosion problems that might occur if the solvent after washing the tail gas is returned to the solvent tank.

[0114] 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 from 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. 10%-50% of the liquid phase after absorption is sent to the desorption unit for absorbent regeneration, and 50%-90% is cooled and used as a circulating absorbent. 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 returns to the lower part of the desorption unit, and another stream goes to the tail gas scrubbing unit to recover maleic anhydride from the tail gas of the light removal unit and the purification unit. After absorption, it returns to the desorption unit and the absorption unit. The other stream is purified and recycled. After absorption by the tail gas scrubbing unit, 10%-90% of the solvent returns to the desorption unit and 10%-90% enters the absorption unit.

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 or 2, 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 7, 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.

9. The continuous distillation method for crude maleic anhydride according to claim 1, wherein, In step 3), after the exhaust gas is absorbed by the exhaust gas scrubbing unit, 30%-70% of it returns to the desorption unit and 30%-70% enters the absorption unit.

10. 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.

11. 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, a circulating absorbent inlet, and a washing tail gas solvent 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 circulating absorbent inlet of the desorption unit and the absorption unit.

12. The continuous distillation system for crude maleic anhydride according to claim 11, wherein, The desorption unit, the light component removal unit, the refining unit, and the exhaust gas washing unit are connected to the vacuum system.

13. The continuous distillation system for crude maleic anhydride according to claim 11, 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.

14. The continuous distillation system for crude maleic anhydride according to claim 11, 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.

15. The continuous distillation system for crude maleic anhydride according to claim 11, wherein, The circulating absorbent inlet is located above the lower gas phase inlet of the absorption unit, and the washing tail gas solvent inlet is located between the circulating absorbent inlet and the lower gas phase inlet of the absorption unit.

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