A production system and process for dimethyl succinate

Abstract

This application discloses a production system and process for dimethyl succinate. The system includes a monoesterification reactor, a diesterification pre-reactor, a diesterification reactive distillation column, a methanol recovery column, a compressor, and a hydrogenation unit. The diesterification reactive distillation column has a bottom vapor inlet, a bottom outlet, a middle inlet, and a top vapor outlet. The methanol recovery column has a mixed steam inlet and a methanol vapor outlet. The outlet of the monoesterification reactor is connected to the inlet of the diesterification pre-reactor, and the outlet of the diesterification pre-reactor is connected to the middle inlet of the diesterification reactive distillation column. The top vapor outlet of the diesterification reactive distillation column is connected to the mixed steam inlet of the methanol recovery column, the methanol vapor outlet of the methanol recovery column is connected to the compressor inlet, and the compressor outlet is connected to the bottom vapor inlet of the diesterification reactive distillation column. Using the system described in this application to produce dimethyl succinate can reduce the energy consumption for methanol recovery.

Description

Technical Field

[0001] This application relates to the technical field of dimethyl succinate preparation, and more particularly to a production system and process for dimethyl succinate. Background Technology

[0002] Dimethyl maleate is an important chemical product. It is typically produced using a maleic anhydride esterification and hydrogenation process. This process first involves the esterification of maleic anhydride with methanol under a catalyst to produce dimethyl maleate. Then, a high-pressure hydrogenation process is used to hydrogenate the dimethyl maleate to a mixture of dimethyl maleate, 1,4-butanediol, γ-butyrolactone, tetrahydrofuran, etc., requiring complex separation and purification to obtain dimethyl maleate. The esterification of maleic anhydride to dimethyl maleate involves two steps: the first step is the monoesterification of maleic anhydride with methanol to produce monomethyl maleate; the second step is the further diesterization of monomethyl maleate with methanol to produce dimethyl maleate.

[0003] In some existing technologies, in the monoesterification reaction, to ensure the conversion rate of maleic anhydride, maleic anhydride is usually reacted with excess methanol, and the water generated by the reaction is removed by vaporizing methanol to promote the forward reaction. The diesterification reaction is usually carried out by distillation. In order to ensure the complete conversion of maleic acid monomethyl ester, a large amount of methanol is also required. A large amount of methanol at the top and bottom of the reactive distillation column needs to be separated, purified and recycled. Excess methanol needs to be continuously heated, vaporized and condensed, resulting in high energy consumption from methanol recycling. Summary of the Invention

[0004] To reduce the energy consumption of methanol recovery during the production of dimethyl succinate, this application proposes a production system and process for dimethyl succinate, and adopts the following technical solution:

[0005] In a first aspect, this application discloses a production system for dimethyl succinate, the system comprising a monoesterification reactor, a diesterification reactive distillation column, a methanol recovery column, and a hydrogenation unit. The monoesterification reactor is provided with an inlet and an outlet. The diesterification reactive distillation column is provided with a bottom gas phase inlet, a bottom outlet, a middle inlet, and a top gas phase outlet. The methanol recovery column is provided with a mixed steam inlet and a methanol steam outlet.

[0006] The dimethyl succinate production system also includes a compressor, which has an air inlet and an air outlet.

[0007] The outlet of the monoesterification reactor is connected to the middle inlet of the diesterification distillation column; the top vapor outlet of the diesterification distillation column is connected to the mixed vapor inlet of the methanol recovery column; the methanol vapor outlet of the methanol recovery column is connected to the inlet of the compressor; the outlet of the compressor is connected to the bottom vapor inlet of the diesterification distillation column; and the hydrogenation unit is connected to the bottom outlet of the diesterification distillation column.

[0008] The compressor is used to pressurize the methanol vapor extracted from the methanol recovery tower;

[0009] The hydrogenation unit is used to hydrogenate the dimethyl maleate to produce dimethyl succinate.

[0010] Optionally, the dimethyl succinate production system further includes a diesterization pre-reactor, which is provided with an inlet and an outlet.

[0011] The outlet of the esterification reactor is connected to the inlet of the diester pre-reactor, and the outlet of the diester pre-reactor is connected to the middle inlet of the diester reactive distillation column.

[0012] The diesterization pre-reactor is used to completely convert maleic anhydride into monomethyl maleate, and to react a portion of the monomethyl maleate with methanol to generate dimethyl maleate.

[0013] Optionally, the system further includes a diester feed preheater, which is provided with a feed inlet, a discharge outlet and a heat source inlet;

[0014] The feed inlet of the diester feed preheater is connected to the discharge outlet of the esterification reactor, the heat source inlet of the diester feed preheater is connected to the air outlet of the compressor, and the discharge outlet of the diester feed preheater is connected to the feed inlet of the diester pre-reactor.

[0015] Optionally, the system further includes an esterification delighting tower for removing light components from the crude dimethyl maleate product and an esterification deheavying tower for removing heavy components from the crude dimethyl maleate product.

[0016] The bottom outlet of the diester reaction distillation column is connected to the inlet of the esterification light-weight removal column, and the outlet of the esterification light-weight removal column is connected to the inlet of the esterification heavy-weight removal column.

[0017] Optionally, the esterification reactor is a tubular reactor.

[0018] Optionally, the diesterization prereactor is a tubular reactor or a fixed-bed reactor.

[0019] Optionally, the hydrogenation unit includes a first-stage hydrogenation reactor, a first-stage gas-liquid separator, a second-stage hydrogenation reactor, and a second-stage gas-liquid separator connected in sequence.

[0020] Both the first-stage hydrogenation reactor and the second-stage hydrogenation reactor are provided with a feed inlet and a discharge outlet, and both the first-stage gas-liquid separator and the second-stage gas-liquid separator are provided with a feed inlet, a liquid outlet, and a gas outlet.

[0021] The feed inlet of the first-stage hydrogenation reactor is connected to the discharge outlet of the esterification deweighting tower, and the gas outlet of the second-stage gas-liquid separator is connected to the gas inlet of the first-stage hydrogenation reactor.

[0022] Secondly, this application discloses a production process for dimethyl succinate, wherein the process is implemented through the production system described in the first aspect, and the process includes:

[0023] Maleic anhydride and methanol are added to a monoesterification reactor to carry out a monoesterification reaction to produce monomethyl maleate.

[0024] The monomethyl maleate, unreacted maleic anhydride and methanol are further mixed and heated and then added to the diester pre-reactor for diester pre-reaction. All maleic anhydride is converted into monomethyl maleate and some monomethyl maleate is converted into dimethyl maleate.

[0025] The pre-esterification product is sent to a diester distillation column for diesterization reaction, whereby monomethyl maleate is completely converted into dimethyl maleate, and a mixed vapor containing methanol and water is separated out, outputting crude dimethyl maleate product.

[0026] The mixed steam containing methanol and water is sent to the methanol recovery tower for separation, and methanol vapor is collected from the methanol recovery tower;

[0027] The methanol vapor is sent to a compressor for pressurization, and the pressurized methanol vapor is returned to the bottom of the diester reaction distillation column as the circulating gaseous methanol of the diester reaction distillation column;

[0028] The crude dimethyl maleate product is purified and sent to the hydrogenation unit for hydrogenation to produce dimethyl succinate.

[0029] Optionally, in the feed of the esterification reactor, the mass ratio of methanol to maleic anhydride is 1.2:1 to 1.5:1.

[0030] Optionally, the reaction temperature in the monoesterification reactor is 70–78°C, the reaction temperature in the diesterification pre-reactor is 104–110°C, the top temperature of the diesterification reaction distillation column is 74–84°C, the bottom temperature is 140–160°C, and the top temperature of the methanol recovery column is 64–74°C.

[0031] Optionally, the pressure range at the methanol vapor outlet of the methanol recovery tower is 1 to 1.5 bar, and the compressor pressurizes the methanol vapor to 2.5 to 3 bar.

[0032] Optionally, the hydrogenation temperature range of the dimethyl maleate is 40–80°C, and the hydrogenation pressure range is 20–30 bar.

[0033] Optionally, the ratio of hydrogen to dimethyl maleate in the hydrogenation unit is in the range of 300:1 to 350:1.

[0034] Based on the above technical solution, the beneficial effects of this application compared with the prior art are as follows:

[0035] 1. In the production system of this application embodiment, when recovering and reusing methanol, a compressor is set up to directly extract the gaseous methanol at the top of the diester distillation column for secondary use, avoiding the liquefaction and re-vaporization of the methanol at the top of the column. This simplifies the operation process and significantly reduces the energy consumption of methanol recovery. By directly pressurizing the gaseous methanol for secondary use, the requirements of the bottom heat source can be met without increasing the operating pressure of the distillation column, further reducing the operating energy consumption of the diester distillation column.

[0036] 2. The production system in this application embodiment converts most of the monomethyl maleate into dimethyl maleate by setting up a diester pre-reactor. The diester pre-reaction mainly involves the reaction between liquid monomethyl maleate and methanol, resulting in low energy consumption. Since the pre-reaction consumes most of the monomethyl maleate, it reduces the gas-phase processing load of the diester distillation column, achieving energy savings. Furthermore, the pre-reaction allows for the conversion of almost all maleic anhydride, improving the conversion rate of the reactants.

[0037] 3. In the production system of this application embodiment, a portion of the gaseous methanol from the top of the diester distillation column is collected and used as a heat source for the diester feed preheater to preheat the monoesterification reaction product, thereby reusing the heat in the recovered methanol and reducing the system's energy consumption.

[0038] 4. In the production system of this application embodiment, in the hydrogenation unit, the outlet of the second-stage gas-liquid separator is connected to the inlet of the first-stage hydrogenation reactor, so that the recycled hydrogen separated in the second-stage hydrogenation process reacts fully with the first-stage fresh raw material again, thereby improving the hydrogen utilization rate and reducing the hydrogen consumption cost. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the dimethyl succinate production system in the embodiments of this application;

[0040] Figure 2This is a process flow diagram of the production of dimethyl succinate in the embodiments of this application.

[0041] Explanation of reference numerals in the attached figures:

[0042] 101. Esterification reactor; 102. Diesterification feed preheater; 103. Diesterification feed heater; 104. Diesterification pre-reactor; 105. Diesterification reactive distillation column; 106. Methanol recovery column; 107. Compressor; 108. Esterification light component removal column; 109. Esterification heavy component removal column; 110. First-stage hydrogenation reactor; 111. First-stage gas-liquid separator; 112. Second-stage hydrogenation reactor; 113. Second-stage gas-liquid separator; 114. Condenser; 115. Reboiler; I. ​​Gas phase methanol; II. Methanol-water solution; III. Light component; IV. Heavy component; V. Hydrogen. Detailed Implementation

[0043] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0044] The inventors discovered in their research that the esterification reaction of maleic anhydride and methanol requires a large amount of methanol to promote the reaction, and that the water generated in the reaction is removed by vaporizing the methanol to promote the forward reaction. The energy consumption for methanol vaporization and dehydration accounts for a high proportion of the total energy consumption in the entire production process. In particular, when recovering methanol from the mixed steam at the top of the diester distillation column, the methanol at the top is typically condensed, recovered, and then reheated and vaporized before finally entering the bottom of the diester distillation column for recycling. In this process, repeated cooling and heating consume a large amount of cooling water and steam. Furthermore, due to the significant difference in boiling points between methanol and water, when using heat pumps or multi-effect distillation technology for methanol recovery, the operating pressure of the distillation column needs to be increased to meet the heat source requirements at the bottom of the column.

[0045] Based on the above problems, in order to reduce the energy consumption of methanol recovery during the production of dimethyl succinate, the inventors further developed and made this invention.

[0046] In the first aspect, this application discloses a production system for dimethyl succinate, referring to... Figure 1The system includes a monoesterification reactor 101, a diesterification pre-reactor 104, a diesterification reactive distillation column 105, a methanol recovery column 106, a compressor 107, and a hydrogenation unit. The monoesterification reactor 101 and the diesterification pre-reactor 104 are equipped with inlets and outlets; the compressor 107 is equipped with an inlet and an outlet; the diesterification reactive distillation column 105 is equipped with a bottom vapor inlet, a bottom outlet, a middle inlet, and a top vapor outlet; and the methanol recovery column 106 is equipped with a mixed steam inlet and a methanol vapor outlet. The outlet of the monoesterification reactor 101 is connected to the inlet of the diesterification pre-reactor 104, and the outlet of the diesterification pre-reactor 104 is connected to the middle inlet of the diesterification reactive distillation column 105. The bottom gas phase inlet of the diester reaction distillation column 105 is connected to the gas phase outlet of the monoesterification reactor 101, the top gas phase outlet of the diester reaction distillation column 105 is connected to the mixed steam inlet of the methanol recovery column 106, the methanol vapor outlet of the methanol recovery column 106 is connected to the air inlet of the compressor 107, and the air outlet of the compressor 107 is connected to the bottom gas phase inlet of the diester reaction distillation column 105.

[0047] Specifically, in this embodiment, the monoesterification reactor 101 reacts maleic anhydride and methanol to produce monomethyl maleate, and the diesterification pre-reactor 104 completely converts maleic anhydride into monomethyl maleate, and reacts a portion of the monomethyl maleate with methanol to produce dimethyl maleate. The pre-reaction product, dimethyl maleate, along with the remaining unreacted monomethyl maleate and methanol, enters the diesterification reaction distillation column 105 for further reaction. Within the diesterification reaction distillation column 105, the remaining monomethyl maleate is completely converted into dimethyl maleate, yielding crude dimethyl maleate and separating methanol. At this point, the crude dimethyl maleate contains light components (III) such as dimethyl maleate and methanol, and heavy components (IV) such as monomethyl maleate. After purification, the crude dimethyl maleate is sent to a hydrogenation unit to hydrogenate dimethyl maleate, producing dimethyl succinate, thus completing the entire production process of dimethyl succinate. Throughout the production process, methanol recovery tower 106 separates and recovers the mixed vapor containing methanol and water collected from diester distillation tower 105, and collects methanol vapor. The collected methanol vapor is then further fed into compressor 107 to pressurize the methanol vapor collected from methanol recovery tower 106, so as to serve as the circulating gaseous methanol I in diester distillation tower 105.

[0048] The production system in this embodiment converts most of the monomethyl maleate into dimethyl maleate by setting up a diester pre-reactor 104. The diester pre-reaction mainly involves the reaction between liquid monomethyl maleate and methanol, resulting in low energy consumption. By setting up the diester pre-reactor 104, most of the monomethyl maleate is consumed, reducing the gaseous processing load of the diester reactive distillation column 105 and achieving energy saving. Furthermore, the pre-reaction allows for the conversion of almost all maleic anhydride, improving the conversion rate of the reactants. Moreover, when recovering methanol, a compressor 107 is used to directly collect the gaseous methanol I from the top of the diester distillation column for secondary use, avoiding the liquefaction and re-vaporization of the methanol at the top of the column. This simplifies the operation process and significantly reduces the energy consumption for methanol recovery. Finally, by directly pressurizing the gaseous methanol I, the operating pressure of the distillation column can be increased to meet the requirements of the bottom heat source, further reducing the operating energy consumption of the diester reactive distillation column 105.

[0049] In an optional embodiment, the monoesterification reactor 101 is a tubular reactor, with methanol introduced between the tubes. By adjusting the pressure, the methanol between the tubes is vaporized, thereby precisely controlling the reaction temperature inside the tubes. The diesterification pre-reactor 104 is a tubular reactor or a fixed-bed reactor. The diesterification pre-reactor 104 is filled with a catalyst, which can be a resin catalyst. Under the action of the catalyst, most of the monomethyl maleate is converted into dimethyl maleate.

[0050] In an optional embodiment, the dimethyl succinate production system further includes a diesterization feed preheater 102 and a diesterization feed heater 103, both of which are equipped with an inlet, an outlet, and a heat source inlet. The inlet of the diesterization feed preheater 102 is connected to the outlet of the monoesterification reactor 101, and the heat source inlet of the diesterization feed preheater 102 is connected to the outlet of the compressor 107. The inlet of the diesterization feed heater 103 is connected to the outlet of the diesterization feed preheater 102, and the outlet of the diesterization feed heater 103 is connected to the inlet of the diesterization pre-reactor 104. Therefore, the monoesterification reaction product first enters the diesterization feed preheater 102, where it exchanges heat with the high-temperature, high-pressure methanol vapor from the compressor 107. After the heat exchange, a certain amount of methanol is added before the product enters the diesterization feed heater 103 and is heated to the required temperature. During this process, the diester feed preheater 102 can recover a portion of methanol, thereby increasing the temperature of the monoesterification product, improving the utilization rate of recovered methanol, and reducing system energy consumption.

[0051] In an optional embodiment, the diesterization distillation column 105 includes a rectification section, a catalyst section, and a stripping section distributed sequentially from top to bottom. The pre-reaction product enters the catalyst section in the middle of the distillation column through the feed inlet in the middle of the distillation column 105. Gaseous methanol I enters the stripping section through the gaseous inlet at the bottom of the distillation column 105. Part of the gaseous methanol I comes from the compressor 107, and the other part comes from the monoesterification reactor 101. A reboiler 115 is further connected to the bottom of the column to re-vaporize most of the liquid methanol in the bottom of the column, so that the gaseous methanol I comes into countercurrent contact with monomethyl maleate during its upward movement along the distillation column, thereby ensuring a sufficiently large contact area between the gaseous methanol I and monomethyl maleate.

[0052] In an optional embodiment, a condenser 114 is further connected to the top of the methanol recovery tower 106 to achieve bubble point reflux. Most of the liquid methanol is refluxed to the top of the tower, and a portion of the liquid methanol can also be flexibly collected, with methanol vapor collected at the top two trays of the methanol recovery tower 106. Correspondingly, a reboiler 115 is also connected to the bottom of the methanol recovery tower 106 to re-vaporize the liquid methanol.

[0053] In an optional embodiment, the system further includes an esterification stripping column 108 for removing light component III and an esterification stripping column 109 for removing heavy component IV. The bottom outlet of the diester reactive distillation column 105 is connected to the inlet of the esterification stripping column 108, and the outlet of the esterification stripping column 108 is connected to the inlet of the esterification stripping column 109. Accordingly, the tops of the esterification stripping columns 108 and 109 are also connected to condensers 114 for bubble point reflux, and the bottoms are also connected to reboilers 115, which will not be described in detail here.

[0054] In an optional embodiment, the hydrogenation unit includes a first-stage hydrogenation reactor 110, a first-stage gas-liquid separator 111, a second-stage hydrogenation reactor 112, and a second-stage gas-liquid separator 113 connected in sequence. Both the first-stage hydrogenation reactor 110 and the second-stage hydrogenation reactor 112 have inlets and outlets; both the first-stage gas-liquid separator 111 and the second-stage gas-liquid separator 113 have inlets, liquid outlets, and gas outlets. The inlet of the first-stage hydrogenation reactor 110 is connected to the outlet of the esterification de-heavyweight tower 109. Both the first-stage gas-liquid separator 111 and the second-stage gas-liquid separator 113 are used to separate dimethyl succinate and hydrogen V.

[0055] Furthermore, it should be noted that after the product of the first-stage hydrogenation reactor 110 undergoes gas-liquid separation, a portion of the liquid is returned to the first-stage hydrogenation reactor 110 for further hydrogenation, while the other portion enters the second-stage hydrogenation reactor 112 for hydrogenation, thus achieving a cooling-cycle hydrogenation process. Simultaneously, the outlet of the second-stage gas-liquid separator 113 is connected to the inlet of the first-stage hydrogenation reactor 110, allowing the separated hydrogen V to fully react with the fresh feedstock, thereby improving the utilization rate of hydrogen V and reducing its consumption.

[0056] Secondly, referring to Figure 2 This application discloses a production process for dimethyl succinate, which is implemented through the production system of the first aspect, and includes the following steps:

[0057] S1: Maleic anhydride and methanol are added to the esterification reactor 101 in a certain proportion to generate monomethyl maleate. Specifically, the feed rate is 25-30 t / h, preferably 25 t / h, and the mass ratio of methanol to maleic anhydride is 1.2:1-1.5:1, so that methanol is in excess to promote the forward reaction. The reaction temperature range of the esterification reactor 101 is 70-78℃.

[0058] S2: Maleic monomethyl ester, unreacted maleic anhydride, and methanol are further mixed and heated before being added to the diesterization pre-reactor 104. The remaining small amount of maleic anhydride is completely converted into maleic monomethyl ester, and most of the maleic monomethyl ester is converted into dimethyl maleate. Specifically, the monoesterification product is first heated to 90-100°C via the diesterization feed preheater 102. After heat exchange, a certain amount of methanol is added, and then the product is heated to 100-110°C, preferably 105-108°C, via the diesterization feed heater 103. Finally, the product enters the diesterization pre-reactor 104, where the reaction temperature range is 104-110°C, completing the diesterization pre-reaction.

[0059] S3: The output material from the diester pre-reactor 104 is sent to the middle of the diester reactive distillation column 105, and the vaporous methanol I from the monoesterification reactor 101 is sent to the bottom of the diester reactive distillation column 105. Monomethyl maleate is completely converted to dimethyl maleate. The top vapor outlet of the diester reactive distillation column 105 outputs a mixed vapor containing methanol and water, and the bottom outlet outputs crude dimethyl maleate product. Specifically, the top temperature of the diester reactive distillation column 105 is 74–84℃, and the bottom temperature is 140–160℃.

[0060] S4: The mixed steam containing methanol and water is sent to the methanol recovery tower 106 for separation, and methanol vapor is collected from the methanol recovery tower 106. Specifically, the top temperature of the methanol recovery tower 106 is 64-74°C, and the pressure at the methanol vapor outlet of the methanol recovery tower 106 is 1-1.5 bar, preferably 1.2 bar.

[0061] S5: Methanol vapor collected from methanol recovery tower 106 is sent to compressor 107 for pressurization. The pressurized methanol vapor is then returned to the bottom of diesterization reactive distillation tower 105 as circulating gaseous methanol. Specifically, compressor 107 pressurizes the methanol vapor to 2.5–3 bar.

[0062] S6: After purification, the crude dimethyl maleate product is sent to the hydrogenation unit for hydrogenation to produce dimethyl succinate. Specifically, light component III and heavy component IV are separated by a distillation column during purification. Light component III is refluxed from the top of the esterification light component removal column 108, and a portion of the methanol-water solution II is collected and returned to the methanol recovery column 106 for methanol recovery. Heavy component IV and dimethyl maleate enter the esterification heavy component removal column 109 from the bottom of the esterification light component removal column 108. Heavy component IV flows out of the system from the bottom of the esterification heavy component removal column 109, while dimethyl maleate is refluxed from the top, and the dimethyl maleate product is collected.

[0063] Furthermore, a two-stage hydrogenation process is employed to circulate hydrogenation for 80% of the material. In the second stage of hydrogenation, excess fresh hydrogen is replenished. Hydrogen gas V, after gas-liquid separation in the second stage, enters the first stage hydrogenation reaction, allowing it to fully react with the fresh feedstock, thus improving hydrogen utilization and reducing hydrogen consumption. The hydrogenation temperature range for dimethyl maleate is 40–80°C, the hydrogenation pressure range is 20–30 bar, and the molar ratio of hydrogen to dimethyl maleate product ranges from 300:1 to 350:1.

[0064] It should be noted that the above steps are for ease of description and do not strictly reflect the order. For example, steps S4 and S5 do not actually have a specific order; the two processes are carried out simultaneously and do not interfere with each other.

[0065] In summary, the system and process in this application embodiment achieve continuous production of dimethyl succinate from methanol and maleic anhydride. This system reduces the amount of vaporized methanol in the diesterization reaction distillation by more than 10% by employing a diesterization pre-reactor 104, thus reducing overall methanol recovery energy consumption. By collecting and compressing vaporized methanol I directly into the diesterization reaction distillation column 105, instead of collecting the liquid phase and reusing it through vaporization, the energy consumption of methanol recycling is significantly reduced. Simultaneously, the heat from the recovered methanol is fully utilized to heat the monoesterification product, promoting heat reuse. Finally, a two-stage hydrogenation technology with low temperature, low pressure, and low agent-to-oil ratio is employed to improve hydrogen utilization and reduce hydrogen consumption, while simultaneously increasing the conversion rate of maleic anhydride. The purity of dimethyl succinate reaches over 99%, resulting in low operating costs and high product yield.

[0066] The present application will be described in detail below through specific embodiments:

[0067] Example 1

[0068] The maleic anhydride feed rate is 28 t / h. Methanol and maleic anhydride are mixed at a mass ratio of 1.2:1 and fed into monoesterification reactor 101. The temperature of monoesterification reactor 101 is 78℃. The monoesterification reaction product is heated to 98℃ by heat exchange with compressed methanol, and then heated to 100℃. The heated monoesterification reaction product enters diester pre-reactor 104 to complete the diester pre-reaction at a temperature of 104℃. The diester pre-reaction product enters diester reactive distillation column 105 for diesterization to obtain dimethyl maleate. The top temperature of diester reactive distillation column 105 is 84℃, and the bottom temperature is 160℃. The mixed vapor at the top of the column enters methanol recovery column 106. The top temperature of methanol recovery column 106 is 74℃, and the pressure is 1.5 bar. Bubble point reflux is used at the top of the column. The vapor phase at the top of the column is compressed to 3 bar by compressor 107. After purification, dimethyl maleate was subjected to two-stage hydrogenation to obtain dimethyl succinate. Each hydrogenation stage was carried out at a pressure of 30 bar and a temperature of 80°C, with a hydrogen-to-dimethyl maleate molar ratio of 300:1. In this example, the conversion rate of maleic anhydride was 99.4%, and the purity of dimethyl succinate reached 99.8%. The flow rate of vaporized methanol (I) in the diesterization reaction distillation column 105 was 30 t / h, the circulating water consumption was 811 t / h, the hydrogen utilization rate was 99.8%, and the energy consumption, after conversion, was 236 kg standard oil / h.

[0069] Example 2

[0070] The maleic anhydride feed rate is 25 t / h. Methanol and maleic anhydride are mixed at a mass ratio of 1.5:1 and fed into monoesterification reactor 101. The temperature of monoesterification reactor 101 is 70℃. The monoesterification reaction product is heated to 100℃ by heat exchange with compressed methanol, and then further heated to 108℃. The heated monoesterification reaction product enters diester pre-reactor 104 to complete the diester pre-reaction at a temperature of 110℃. The diester pre-reaction product enters diester reactive distillation column 105 for diester reaction to obtain dimethyl maleate. The top temperature of diester reactive distillation column 105 is 75℃, and the bottom temperature is 140℃. The mixed vapor at the top of the column enters methanol recovery column 106. The top temperature of methanol recovery column 106 is 65℃, and the pressure is 1 bar. Bubble point reflux is used at the top of the column. The vapor phase collected at the top of the column is compressed and pressurized to 2.5 bar by compressor 107. After purification, dimethyl maleate was subjected to two-stage hydrogenation to obtain dimethyl succinate. Each hydrogenation stage was conducted at a pressure of 20 bar and a temperature of 40°C, with a hydrogen-to-dimethyl maleate molar ratio of 350:1. In this example, the conversion rate of maleic anhydride was 99.6%, and the purity of dimethyl succinate reached 99.5%. The methanol flow rate in the diesterization reaction distillation column 105 was 34 t / h, the circulating water consumption was 780 t / h, the hydrogen utilization rate was 98.3%, and the energy consumption, after conversion, was 234 kg standard oil / h.

[0071] Comparative Example 1

[0072] The maleic anhydride feed rate is 28 t / h. Methanol and maleic anhydride are mixed at a mass ratio of 1.2:1 and fed into monoesterification reactor 101. The temperature of monoesterification reactor 101 is 78℃. The monoesterification reaction product is heated to 98℃ by heat exchange with compressed methanol, and then further heated to 100℃. The heated monoesterification reaction product enters diester pre-reactor 104 to complete the diester pre-reaction at a temperature of 110℃. The diester pre-reaction product enters diester reactive distillation column 105 for diesterization to obtain dimethyl maleate. The top temperature of diester reactive distillation column 105 is 84℃, and the bottom temperature is 160℃. The mixed vapor at the top of the column enters methanol recovery column 106. The methanol recovery tower 106 has a top temperature of 74℃ and a pressure of 1.5 bar. Liquid methanol is collected from the top of the tower and heated to vaporize at 88℃. The vaporized methanol is then returned to the bottom of the diesterization reactive distillation tower 105. Dimethyl maleate is purified and then subjected to two-stage hydrogenation to obtain dimethyl succinate. Each hydrogenation stage has a pressure of 30 bar and a temperature of 80℃, with a molar ratio of hydrogen to dimethyl maleate of 300:1. In this embodiment, the conversion rate of maleic anhydride is 99.5%, and the purity of dimethyl succinate reaches 99.7%. The flow rate of vaporized methanol in the diesterization reactive distillation tower 105 is 29 t / h, the circulating water consumption is 1750 t / h, the heating steam consumption for vaporizing liquid methanol is 11.4 t / h, the hydrogen utilization rate is 99%, and the energy consumption is equivalent to 1103 kg standard oil / h.

[0073] Comparative Example 2

[0074] The maleic anhydride feed rate is 25 t / h. Methanol and maleic anhydride are mixed at a mass ratio of 1.5:1 and fed into a monoesterification reactor 101. The temperature of the monoesterification reactor 101 is 70℃. The monoesterification reaction product is heated to 100℃ by heat exchange with compressed methanol, and then further heated to 108℃. The heated monoesterification reaction product directly enters a diester distillation column 105 for diesterization to obtain dimethyl maleate. The top temperature of the diester distillation column 105 is 75℃, and the bottom temperature is 140℃. The mixed vapor at the top of the column enters a methanol recovery column 106. The top temperature of the methanol recovery column 106 is 65℃, and the pressure is 1 bar. Bubble point reflux is used at the top of the column. The vapor phase collected at the top of the column is compressed and pressurized to 2.5 bar by compressor 107. After purification, the dimethyl maleate product undergoes two-stage hydrogenation to obtain dimethyl succinate. Each stage of hydrogenation is carried out at a pressure of 20 bar and a temperature of 40°C. The molar ratio of hydrogen V to dimethyl maleate is 350:1. In this example, the conversion rate of maleic anhydride is 97.2%, and the purity of dimethyl succinate reaches 96.4%. The vapor methanol flow rate of the diesterization reaction distillation column 105 is 38 t / h, the circulating water consumption is 2293 t / h, the hydrogen utilization rate is 97.9%, and the energy consumption after conversion is 1452 kg standard oil / h.

[0075] Based on the above embodiments and comparative examples, firstly, Embodiment 1 adds a compressor compared to Comparative Example 1. By collecting the gaseous methanol from the methanol recovery tower 106 and compressing it through the compressor 107, it is directly recycled. Compared to Comparative Example 1, which collects the liquid methanol and then regasifies it, this reduces the heating steam consumption by 11.4 t / h, the circulating water consumption by 939 t / h, and the overall energy consumption of the production system by 1055 kg standard oil / h. It can be seen that directly recycling the gaseous methanol collected from the methanol recovery tower 106 after compression can effectively reduce system energy consumption.

[0076] Secondly, in Example 2, a diester pre-reactor 104 was added compared to Comparative Example 2. Correspondingly, the amount of vapor methanol in the diester reactive distillation column 105 was reduced by 10%, and the energy consumption of the diester reactive distillation and methanol recovery section could be reduced by 1218 kg standard oil / h, while the maleic anhydride conversion rate was increased by 2.4%. It can be seen that adding the diester pre-reactor 104 can effectively reduce the vapor methanol processing load of the diester reactive distillation column 105, reduce the overall energy consumption of the system, and improve the maleic anhydride conversion rate.

[0077] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments, but those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," just as "comprising" is interpreted as a conjunction in the claims. Additionally, the use of any term "or" in the specification of the claims is intended to mean "non-exclusive or."

Claims

1. A production system for dimethyl succinate, comprising a monoesterification reactor, a diesterification distillation column, a methanol recovery column, and a hydrogenation unit, wherein the monoesterification reactor is provided with an inlet and an outlet, the diesterification distillation column is provided with a bottom gas phase inlet, a bottom outlet, a middle inlet, and a top gas phase outlet, and the methanol recovery column is provided with a mixed steam inlet and a methanol steam outlet; It is characterized in that The dimethyl succinate production system also includes a compressor, which has an air inlet and an air outlet. The outlet of the monoesterification reactor is connected to the middle inlet of the diesterification distillation column; the top vapor outlet of the diesterification distillation column is connected to the mixed vapor inlet of the methanol recovery column; the methanol vapor outlet of the methanol recovery column is connected to the inlet of the compressor; the outlet of the compressor is connected to the bottom vapor inlet of the diesterification distillation column; and the hydrogenation unit is connected to the bottom outlet of the diesterification distillation column. The compressor is used to pressurize the methanol vapor extracted from the methanol recovery tower; The hydrogenation unit is used to hydrogenate dimethyl maleate to produce dimethyl succinate. The dimethyl succinate production system also includes a diesterization pre-reactor, which is equipped with an inlet and an outlet. The outlet of the esterification reactor is connected to the inlet of the diester pre-reactor, and the outlet of the diester pre-reactor is connected to the middle inlet of the diester reactive distillation column. The diesterization pre-reactor is used to completely convert maleic anhydride into monomethyl maleate, and to react a portion of the monomethyl maleate with methanol to generate dimethyl maleate. The system also includes a diester feed preheater, which is provided with a feed inlet, a discharge outlet and a heat source inlet; The feed inlet of the diester feed preheater is connected to the discharge outlet of the esterification reactor, the heat source inlet of the diester feed preheater is connected to the air outlet of the compressor, and the discharge outlet of the diester feed preheater is connected to the feed inlet of the diester pre-reactor.

2. The dimethyl succinate production system according to claim 1, characterized in that, The esterification reactor is a tubular reactor.

3. The dimethyl succinate production system according to claim 1, characterized in that, The diesterization prereactor is a tubular reactor or a fixed-bed reactor.

4. The dimethyl succinate production system according to claim 1, characterized in that, The system also includes an esterification delighting tower for removing light components from the crude dimethyl maleate product and an esterification deheavying tower for removing heavy components from the crude dimethyl maleate product. Both the esterification tower for removing light particles and the esterification tower for removing heavy particles are provided with a feed inlet and a discharge outlet; The bottom outlet of the diester reaction distillation column is connected to the inlet of the esterification light-weight removal column, and the outlet of the esterification light-weight removal column is connected to the inlet of the esterification heavy-weight removal column.

5. The dimethyl succinate production system according to claim 4, characterized in that, The hydrogenation unit includes a first-stage hydrogenation reactor, a first-stage gas-liquid separator, a second-stage hydrogenation reactor, and a second-stage gas-liquid separator; Both the first-stage hydrogenation reactor and the second-stage hydrogenation reactor are equipped with inlets and outlets; Both the first-stage gas-liquid separator and the second-stage gas-liquid separator are equipped with a feed inlet, a liquid outlet, and a gas outlet. The feed inlet of the first-stage hydrogenation reactor is connected to the outlet of the esterification deweighting tower, the outlet of the first-stage hydrogenation reactor is connected to the feed inlet of the first-stage gas-liquid separator, the liquid outlet of the first-stage gas-liquid separator is connected to the feed inlet of the esterification deweighting tower, the outlet of the esterification deweighting tower is connected to the feed inlet of the second-stage gas-liquid separator, and the gas outlet of the second-stage gas-liquid separator is connected to the feed inlet of the first-stage hydrogenation reactor.

6. A production process for dimethyl succinate, characterized in that, The process is implemented using the production system according to any one of claims 1-5, and the process includes: Maleic anhydride and methanol are added to a monoesterification reactor to carry out a monoesterification reaction to produce monomethyl maleate. The monomethyl maleate, unreacted maleic anhydride and methanol are mixed and heated and then added to the diester pre-reactor for diester pre-reaction. All maleic anhydride is converted into monomethyl maleate and some monomethyl maleate is converted into dimethyl maleate. The pre-esterification product is sent to a diester distillation column for diesterization reaction, whereby monomethyl maleate is completely converted into dimethyl maleate, and a mixed vapor containing methanol and water is separated out, outputting crude dimethyl maleate product. The mixed steam containing methanol and water is sent to a methanol recovery tower for separation, and methanol vapor is collected from the methanol recovery tower. The methanol vapor is sent to a compressor for pressurization, and the pressurized methanol vapor is returned to the bottom of the diester reaction distillation column as circulating gaseous methanol of the diester reaction distillation column; The crude dimethyl maleate product is purified and sent to a hydrogenation unit for hydrogenation to produce dimethyl succinate.

7. The production process according to claim 6, characterized in that, The methanol vapor outlet pressure range of the methanol recovery tower is 1 to 1.5 bar, and the compressor pressurizes the methanol vapor to 2.5 to 3 bar.

8. The production process according to claim 6, characterized in that, In the feed of the esterification reactor, the mass ratio of methanol to maleic anhydride is 1.2:1 to 1.5:

1.

9. The production process according to claim 6, characterized in that, The reaction temperature range in the esterification reactor is 70–78°C, the reaction temperature range in the diester pre-reactor is 104–110°C, the top temperature range in the diester reactive distillation column is 74–84°C, the bottom temperature range is 140–160°C, and the top temperature range in the methanol recovery column is 64–74°C.

10. The production process according to claim 6, characterized in that, The hydrogenation temperature range of the dimethyl maleate is 40–80°C, and the hydrogenation pressure range is 20–30 bar.

11. The production process according to claim 6, characterized in that, The molar ratio of hydrogen to dimethyl maleate in the hydrogenation unit ranges from 300:1 to 350:1.

Images