System and method for preparing succinic anhydride from maleic anhydride and application

Abstract

The invention discloses a system and a method for preparing butanedioic anhydride from maleic anhydride and application of the system and the method. According to the system for preparing succinic anhydride from maleic anhydride, a liquid phase feeding tank, a first-stage reactor, a first-stage high-pressure gas-liquid separation tank, a second-stage reactor, a second-stage high-pressure gas-liquid separation tank and a low-pressure separation tank are sequentially connected through pipelines; wherein an outlet of the liquid-phase feeding tank is connected with a liquid-phase material inlet of the first-stage reactor through a pipeline, an outlet of the first-stage reactor is connected with an inlet of the first-stage high-pressure gas-liquid separation tank through a pipeline, and a liquid-phase outlet of the first-stage high-pressure gas-liquid separation tank is connected with a liquid-phase material inlet of the second-stage reactor through a pipeline; an outlet of the second-stage reactor is connected with an inlet of the second-stage high-pressure gas-liquid separation tank through a pipeline, and a liquid phase outlet of the second-stage high-pressure gas-liquid separation tank is connected with an inlet of the low-pressure separation tank through a pipeline. The pressure difference of liquid phases of the first-stage high-pressure gas-liquid separation tank and the low-pressure separation tank is utilized, pressure can be further recovered, energy is saved, consumption is reduced, and recovered and discharged hydrogen has good economical efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of succinic anhydride, and specifically relates to a system, a method and an application for preparing succinic anhydride from maleic anhydride. Background Art

[0002] Succinic anhydride, also known as amber anhydride, is a fine chemical product, mainly used in industries such as medicine, pesticides and petrochemicals. The current mainstream industrial production methods of succinic anhydride mainly include the dehydration method of succinic acid, the direct catalytic hydrogenation method of maleic anhydride and the biological fermentation method. Comparing the three technical routes, the advantages of the direct catalytic hydrogenation method of maleic anhydride are as follows: First, the processing cost is low, the process flow is short, and the equipment is relatively few; Second, the product quality is good and the production efficiency is high; Third, it is environmentally friendly and the environmental pollution is the smallest.

[0003] At present, the existing direct catalytic hydrogenation method of maleic anhydride to prepare succinic anhydride mainly uses two-stage hydrogenation reactors. For example, Chinese Patent CN116041289A proposes a production process for preparing succinic anhydride by hydrogenating maleic anhydride. The process includes: the first liquid-phase mixed feed enters from the bottom of the up-flow fixed-bed reactor I, and undergoes a rapid liquid-phase hydrogenation reaction with the hydrogenation catalyst bed layer arranged inside from bottom to top. The rapid hydrogenation reaction product leaves from the top of the up-flow fixed-bed reactor, and after heat removal, it is mixed evenly with the supplementary hydrogen to form the second liquid-phase mixed feed, which enters the up-flow fixed-bed reactor II, and undergoes a mild liquid-phase hydrogenation reaction with the hydrogenation catalyst bed layer arranged inside from bottom to top. The mild hydrogenation reaction product flows out from the top of the reactor, and after heat removal and gas-phase separation, a part is recycled back to the up-flow fixed-bed reactor I and / or II, and the other part is fractionated. Chinese Patent CN105801536A proposes a method for preparing succinic anhydride by liquid-phase selective hydrogenation of maleic anhydride. The liquid-phase hydrogenation reaction uses a two-stage low-temperature and low-pressure reaction process to prepare succinic anhydride, and two reactors are used, namely a first-stage reactor and a second-stage reactor, which are used in series; maleic anhydride, a solvent and hydrogen enter the first-stage reactor for partial catalytic selective hydrogenation. After the reaction, the remaining maleic anhydride, the formed succinic anhydride and the solvent mixture material enter the second-stage reactor for complete catalytic selective hydrogenation. The product of the second-stage reactor is obtained as a succinic anhydride product after gas-liquid separation and rectification.

[0004] However, in the current existing technology, the process of preparing succinic anhydride by the direct catalytic hydrogenation method of maleic anhydride using two-stage hydrogenation reactors still has problems such as high energy consumption, easy entry of hydrogen into the downstream product separation section and low hydrogen recovery rate. Therefore, there is an urgent need for a process for preparing succinic anhydride by the direct catalytic hydrogenation method of maleic anhydride with lower energy consumption and higher hydrogen recovery rate. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a system, a method and an application for preparing succinic anhydride from maleic anhydride.

[0006] One of the objectives of the present invention is to provide a system for preparing succinic anhydride from maleic anhydride, which includes two-stage reactors and is successively connected by pipelines to a liquid-phase feed tank, a first-stage reactor, a first-stage high-pressure gas-liquid separation tank, a second-stage reactor, a second-stage high-pressure gas-liquid separation tank, and a low-pressure separation tank; wherein, the outlet of the liquid-phase feed tank is connected by a pipeline to the liquid-phase material inlet of the first-stage reactor, the outlet of the first-stage reactor is connected by a pipeline to the inlet of the first-stage high-pressure gas-liquid separation tank, the liquid-phase outlet of the first-stage high-pressure gas-liquid separation tank is connected by a pipeline to the liquid-phase material inlet of the second-stage reactor, the outlet of the second-stage reactor is connected by a pipeline to the inlet of the second-stage high-pressure gas-liquid separation tank, and the liquid-phase outlet of the second-stage high-pressure gas-liquid separation tank is connected by a pipeline to the inlet of the low-pressure separation tank.

[0007] In a preferred embodiment of the present invention,

[0008] the system further includes a hydrogen feed tank, and the outlet of the hydrogen feed tank is respectively connected by pipelines to the gas-phase material inlet of the first-stage reactor and the gas-phase material inlet of the second-stage reactor; and / or,

[0009] the liquid-phase feed tank is provided with a liquid-phase raw material inlet, preferably a maleic anhydride feed port and a solvent feed port are respectively provided; and / or,

[0010] a first centrifugal pump for pumping liquid-phase feed and / or a first heat exchanger are further provided on the pipeline connecting the liquid-phase feed tank and the first-stage reactor; preferably, a first centrifugal pump for pumping the reaction discharge mixture is connected before the first heat exchanger; and / or,

[0011] a second heat exchanger is further provided on the pipeline connecting the first-stage reactor and the first-stage high-pressure gas-liquid separation tank; and / or,

[0012] a turbocharging device is further provided on the pipeline connecting the first-stage high-pressure gas-liquid separation tank and the second-stage reactor; and / or,

[0013] the system further includes a high-pressure scrubbing tower, which is provided with a gas-phase inlet at the bottom and a scrubbing solvent inlet at the upper part; the gas-phase outlet of the first-stage high-pressure gas-liquid separation tank and / or the gas-phase outlet of the second-stage high-pressure gas-liquid separation tank are connected by pipelines to the gas-phase inlet of the high-pressure scrubbing tower; and / or,

[0014] the low-pressure separation tank is provided with a liquid-phase outlet, and the liquid-phase outlet of the low-pressure separation tank is connected by a pipeline to the subsequent product separation section; preferably, a second centrifugal pump for pumping liquid-phase feed is further provided on the pipeline connecting the liquid-phase outlet of the low-pressure separation tank and the subsequent product separation section; the subsequent product separation section includes conventional product separation devices in the art, such as a light component removal tower, a solvent evaporation tower, a heavy component removal tower, and a product tower, etc., and those skilled in the art can select according to actual situations, and no limitation is made in the present invention; and / or,

[0015] The low-pressure separation tank is provided with a gas-phase outlet, and the gas-phase outlet of the low-pressure separation tank is connected to a low-pressure washing tank. The low-pressure washing tank is further provided with a water-washing inlet, a gas-phase outlet and a liquid-phase outlet.

[0016] In a preferred embodiment of the present invention,

[0017] The liquid-phase outlet of the high-pressure washing tower is connected to the liquid-phase raw material inlet of the liquid-phase feed tank, preferably connected to the solvent feed port; and / or,

[0018] The gas-phase outlet of the high-pressure washing tower is connected to the inlet of the hydrogen feed tank by a pipeline. Preferably, a hydrogen compressor buffer tank and / or a hydrogen recycle compressor are further provided on the pipeline connecting the gas-phase outlet of the high-pressure washing tower to the inlet of the hydrogen feed tank. More preferably, the hydrogen compressor buffer tank is connected before the hydrogen recycle compressor; and / or,

[0019] A branch is further provided on the pipeline connecting the turbocharging device to the secondary reactor and is connected to the liquid-phase raw material inlet of the liquid-phase feed tank, preferably connected to the solvent feed port; and / or,

[0020] A branch is further provided on the pipeline connecting the second centrifugal pump to the subsequent product separation section and is connected to the liquid-phase raw material inlet of the liquid-phase feed tank, preferably connected to the solvent feed port.

[0021] In a preferred embodiment of the present invention,

[0022] The primary reactor and the secondary reactor are the same or different, and are independently one of an upflow liquid-phase hydrogenation reactor, a fixed-bed reactor, and a shell-and-tube reactor.

[0023] The second object of the present invention is to provide a method for preparing succinic anhydride using the system of the first object of the present invention, including contacting maleic anhydride solution with hydrogen in a primary reactor for hydrogenation, feeding the liquid-phase product obtained by primary high-pressure gas-liquid separation into the secondary reactor to continue contacting with hydrogen for hydrogenation, and subjecting the liquid phase obtained by secondary high-pressure gas-liquid separation to low-pressure gas-liquid separation.

[0024] In a preferred embodiment of the present invention,

[0025] The method includes:

[0026] 1) Mix maleic anhydride with a solvent in a liquid-phase feed tank and contact with hydrogen fed from a hydrogen feed tank in a primary reactor to perform a primary hydrogenation reaction to obtain a primary hydrogenation reaction product;

[0027] 2) The gas phase obtained by subjecting the primary hydrogenation reaction product to primary high-pressure gas-liquid separation is sent to a high-pressure washing tower, and the liquid phase obtained by primary high-pressure gas-liquid separation is fed into the secondary reactor to continue contacting with hydrogen to perform a secondary hydrogenation reaction to obtain a secondary hydrogenation reaction product;

[0028] 3) The gas phase obtained by secondary high-pressure gas-liquid separation of the secondary hydrogenation reaction product is sent to the high-pressure scrubbing tower. After the liquid phase obtained by secondary high-pressure gas-liquid separation is further separated at low pressure, the low-pressure separated liquid phase is sent to the subsequent product separation section for product separation, and the non-condensable gas separated at low pressure is sent to the low-pressure scrubbing tank for water washing;

[0029] 4) The liquid phase obtained from the high-pressure scrubbing tower is optionally returned to the liquid-phase feed tank for recycling; and / or, the gas phase obtained from the high-pressure scrubbing tower is optionally returned to the hydrogen feed tank for recycling.

[0030] In a preferred embodiment of the present invention,

[0031] In step 1),

[0032] The mixed solution obtained by mixing maleic anhydride and the solvent in the liquid-phase feed tank is cooled and then sent to the primary reactor, preferably cooled to 40 - 60 °C; and / or,

[0033] The maleic anhydride is in a molten state; and / or,

[0034] The solvent is one or more of γ-butyrolactone, tetrahydrofuran, dioxane, acetic anhydride, ethyl acetate, four-carbon dibasic acid ester, ethanol, isopropanol, straight-chain or branched-chain alkane, aromatic hydrocarbon, cycloalkane, preferably one or two of γ-butyrolactone and tetrahydrofuran; and / or,

[0035] The mass ratio of maleic anhydride to the solvent is 1:(6 - 15); and / or,

[0036] The volume ratio of hydrogen to the mixed solution of maleic anhydride and the solvent is (30 - 65):1, where the volume of hydrogen is the volume under standard conditions; and / or,

[0037] The operating conditions of the primary reactor include: temperature is 40 - 130 °C; and / or, pressure is 1.8 - 4.2 MpaG; and / or, volume space velocity is 1.8 - 4.2 h -1 .

[0038] In a preferred embodiment of the present invention,

[0039] In step 2),

[0040] The primary hydrogenation reaction product is cooled before primary high-pressure gas-liquid separation, preferably cooled to 40 - 60 °C; and / or,

[0041] The operating pressure of the primary high-pressure gas-liquid separation is 2.8 - 4.0 MpaG; and / or,

[0042] The liquid phase obtained from the first-stage high-pressure gas-liquid separation is sent into the second-stage reactor through turbocharging, preferably pressurized to 2.8 - 3.8 MpaG before being sent into the second-stage reactor; and / or,

[0043] The operating conditions of the second-stage reactor include: temperature of 40 - 130 °C; and / or, pressure of 1.8 - 4.2 MpaG; and / or, volume space velocity of 1.8 - 4.2 h -1 .

[0044] In a preferred embodiment of the present invention,

[0045] In step 2),

[0046] The liquid phase obtained from the first-stage high-pressure gas-liquid separation is divided into two parts. One part of the liquid phase is recycled back to the liquid feed tank, and the other part of the liquid phase is sent into the second-stage reactor to continue contacting with hydrogen for the second-stage hydrogenation reaction to obtain the second-stage hydrogenation reaction product; preferably, the liquid phase recycled to the liquid feed tank accounts for 0 - 60% of the liquid phase obtained from the first-stage high-pressure gas-liquid separation, preferably 30 - 50%.

[0047] In a preferred embodiment of the present invention,

[0048] In step 3),

[0049] The operating pressure of the second-stage high-pressure gas-liquid separation is 2.8 - 4.0 MpaG; and / or,

[0050] The operating pressure of the low-pressure separation tank is 0.3 - 3 MpaG, preferably 0.3 - 1.5 MpaG; preferably,

[0051] The pressure difference between the liquid phases of the low-pressure separation tank and the first-stage high-pressure gas-liquid separation tank is 1.0 - 3.2 MpaG, preferably 2.5 - 3.2 MpaG, more preferably 2.7 MpaG.

[0052] The non-condensable gas separated at low pressure is sent to the low-pressure washing tank for water washing. After water washing, the liquid phase is sent out to the wastewater treatment plant, and the gas phase after water washing enters the downstream plant for application.

[0053] Functions of the low-pressure separation tank: ① Since the subsequent product separation system (section) mainly consists of several vacuum towers, the mixing of high-pressure gas (hydrogen) and oxygen is likely to cause an explosion. Therefore, the low-pressure separation tank can serve as a safety isolation for the subsequent product separation section to prevent high-pressure gas (hydrogen) from surging into the downstream product separation system. ② Prevent maleic anhydride from entering the downstream separation tower. Maleic anhydride is prone to polymerization at high temperatures, which can block pipelines or equipment ports, resulting in shutdown and production suspension. When problems occur during reactor shutdown, the liquid phase outlet of the low-pressure separation tank has a withdrawal line that returns to the liquid phase feed tank for further reaction until the maleic anhydride reaction is complete, and then it enters the downstream product separation system. ③ The low-pressure separation tank is set up to remove hydrogen more thoroughly. This part of hydrogen can carry away some impurities in the reaction system and can also be discharged into the fuel gas pipeline network or recycled and utilized in other devices of downstream factories. ④ The low-pressure washing tank connected to the gas phase outlet of the low-pressure separation tank can wash away the acid anhydride to prevent acidic media from corroding the flare system, fuel gas pipeline network or other devices.

[0054] In a preferred embodiment of the present invention,

[0055] In step 3),

[0056] The low-pressure separation liquid phase is divided into two parts. One part of the liquid phase is recycled back to the liquid phase feed tank, and the other part of the liquid phase is sent to the subsequent product separation section for product separation. Preferably, the liquid phase recycled to the liquid phase feed tank accounts for 0-60% of the low-pressure separation liquid phase, preferably 30-50%. The external circulation line for the liquid phase to be recycled back to the liquid phase feed tank is opened during startup or shutdown interlock. The function of the external circulation line is to ensure that there is no reaction dead zone in the reactor, so that the reactant maleic anhydride reacts completely, and to ensure that maleic anhydride will not be carried into the subsequent product separation section.

[0057] In the present invention, the first-stage reactor and the second-stage reactor are filled with a hydrogenation catalyst. The hydrogenation catalyst is any conventional hydrogenation catalyst in the art, and its dosage is also a conventional dosage, which can be selected by those skilled in the art according to actual situations. For example, the filling ratio (volume ratio) of the catalyst in the first-stage reactor can be 0.4-0.6; the filling ratio (volume ratio) of the catalyst in the second-stage reactor can be 0.5-0.75; the hydrogenation catalyst can be the catalyst described in Chinese Patent Application CN114433127A.

[0058] The third object of the present invention is to provide an application of the system of the first object of the present invention or the method of the second object of the present invention in the field of succinic anhydride preparation.

[0059] The present invention utilizes the pressure difference between the liquid phases of the primary high-pressure gas-liquid separation tank and the low-pressure separation tank. This pressure difference can drive the hydraulic turbocharger online pressure energy recovery device to replace the traditional multi-stage centrifugal pump and regulating valve pressure reduction combination system, further recovering pressure and saving energy and reducing consumption. Compared with the relatively complex multi-stage pump in structure, the turbocharger online pressure energy recovery device has the advantages of high integration and compactness, small floor area, high flexibility, short installation time. Compared with the multi-stage pump, it can save at least 50% of the electricity consumption, achieving the effect of energy conservation and emission reduction.

[0060] By reasonably setting the pressures of the primary high-pressure gas-liquid separation tank and the low-pressure separation tank, the pressure difference generated by the setting of the high- and low-pressure separation tanks makes the recovered and discharged hydrogen have good economy. The recycled hydrogen and the externally-supplemented hydrogen enter the hydrogen circulation compressor again, making the compression ratio of the circulation compressor reach a suitable value, and the compression ratio range is 1.5 - 2.5:1. The functions of the circulation hydrogen compressor and the tail gas recovery compressor in the conventional process are integrated into one.

[0061] Both the primary reactor and the secondary reactor of the present invention have external circulation pipelines, which can be used as start-up lines and emergency disposal lines for circulating the reaction products, achieving the effect of energy conservation and emission reduction. Brief Description of the Drawings

[0062] Figure 1 is a simplified process flow diagram of the present invention.

[0063] Among them, 1 is the maleic anhydride feed tank; 2 is the solvent feed tank; 3 is the liquid-phase feed tank; 4 is the first centrifugal pump; 5 is the first heat exchanger; 6 is the primary reactor; 7 is the second heat exchanger; 8 is the primary high-pressure gas-liquid separation tank; 9 is the secondary reactor; 10 is the secondary high-pressure gas-liquid separation tank; 11 is the high-pressure scrubbing tower; 12 is the hydrogen compressor buffer tank; 13 is the hydrogen circulation compressor; 14 is the hydrogen feed tank; 15 is the turbocharging device; 16 is the third centrifugal pump; 17 is the low-pressure separation tank; 18 is the low-pressure scrubbing tank; 19 is the second centrifugal pump; 20 is the molten maleic anhydride; 21 is the solvent; 22 is the fresh hydrogen; 23-1 is the primary reaction circulating liquid phase; 23-2 is the secondary reaction circulating liquid phase; 24 is water; 25 is the liquid phase sent to the subsequent product separation section; 26 is the liquid phase sent to the wastewater treatment plant; 27 is the gas phase sent to the downstream factory for application; 28 is the maleic anhydride solution; 29 is the primary hydrogenation reaction product; 30 is the primary high-pressure gas-liquid separation gas phase; 31 is the primary high-pressure gas-liquid separation liquid phase; 32 is the secondary hydrogenation reaction product; 33 is the secondary high-pressure gas-liquid separation gas phase; 34 is the secondary high-pressure gas-liquid separation liquid phase; 35 is the low-pressure separation liquid phase; 36 is the low-pressure separation non-condensable gas; 37 is the high-pressure scrubbing liquid phase; 38 is the high-pressure scrubbing gas phase. Detailed Embodiments

[0064] The present invention will be specifically described below in conjunction with specific embodiments and the accompanying drawings. It is necessary to point out here that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0065] Take Figure 1 as an example to illustrate the method for preparing succinic anhydride of the present invention: The molten maleic anhydride (20) in the maleic anhydride feed tank (1) and the solvent (21) from the solvent feed tank (2) are configured into a maleic anhydride solution 28 in the liquid-phase feed tank (3). The maleic anhydride solution 28 is pumped into the first heat exchanger (5) by the first centrifugal pump (4) and cooled, and then fed into the first-stage reactor (6) from below the first-stage reactor (6). High-pressure hydrogen also enters the first-stage reactor (6) from below the first-stage reactor (6) through the hydrogen feed tank (14) for the first-stage hydrogenation reaction. Hydrogen converts 50% - 60% of the maleic anhydride into succinic anhydride in the first-stage reactor (6). The first-stage hydrogenation reaction product 29 at the outlet of the first-stage reactor (6) is first cooled in the second heat exchanger (7), and then sent to the first-stage high-pressure gas-liquid separation tank (8) for gas-liquid separation. The obtained first-stage high-pressure gas-liquid separation gas phase 30 goes to the high-pressure scrubbing tower (11), and the first-stage high-pressure gas-liquid separation liquid phase 31 is sent to the second-stage reactor (9) by the turbocharging device (15). High-pressure hydrogen and the first-stage high-pressure gas-liquid separation liquid phase are secondarily distributed at the bottom of the second-stage reactor (9) and undergo a second-stage hydrogenation reaction. In the second-stage reactor, maleic anhydride is completely converted into succinic anhydride and part of γ-butyrolactone. The second-stage hydrogenation reaction product 32 undergoes gas-liquid separation in the second-stage high-pressure gas-liquid separation tank (10). The obtained second-stage high-pressure gas-liquid separation gas phase 33 enters the high-pressure scrubbing tower (11), and the obtained second-stage high-pressure gas-liquid separation liquid phase 34 enters the low-pressure separation tank (17). The low-pressure separation liquid phase 35 obtained from the low-pressure separation tank (17) is pumped into the subsequent product separation section by the second centrifugal pump (19) to further separate succinic anhydride and γ-butyrolactone. The non-condensable gas 36 separated from the low-pressure separation tank (17) is sent to the wastewater treatment plant after the liquid phase (26) is washed with water in the low-pressure scrubbing tank (18), and the gas phase (27) enters the downstream factory for application. The high-pressure scrubbing liquid phase 37 obtained from the high-pressure scrubbing tower (11) is sent back to the liquid-phase feed tank (3) by the third centrifugal pump (16), and the obtained high-pressure scrubbing gas phase 38 is sent back to the hydrogen compressor buffer tank (12) and then sent to the hydrogen feed tank (14) through the hydrogen circulation compressor (13) for recycling in the first-stage reactor. Optionally, part of the liquid phase (23-1) of the first-stage high-pressure gas-liquid separation liquid phase 31 is recycled back to the liquid-phase feed tank (3) after being pressurized by the turbocharging device (15), and part of the liquid phase (23-2) pumped by the second centrifugal pump (19) is recycled back to the liquid-phase feed tank (3).

[0066] In the present invention, the primary reactor and the secondary reactor are both up-flow liquid-phase hydrogenation reactors.

[0067] In the embodiments of the present invention, the raw materials used are all conventional commercially available raw materials. Among them,

[0068] The specifications of hydrogen and maleic anhydride are as follows:

[0069] Table 1 Hydrogen Specification Table

[0070] Item Index Volume fraction of hydrogen, v% ≥99.9 Volume fraction of C2 and hydrocarbons with carbon number greater than or equal to 2, v% ≤0.1 Sum of volume fractions of carbon monoxide and carbon dioxide / (μL / L) ≤20 Volume fraction of carbon monoxide / (μL / L) ≤5 Volume fraction of chlorine (calculated as Cl) / (μL / L) ≤0.1 Volume fraction of oxygen (calculated as O2) / (μL / L) ≤10 Volume fraction of hydrogen sulfide (calculated as H2S) / (μL / L) ≤0.1

[0071] Table 2 Maleic Anhydride Specification Table

[0072] Item Index Mass fraction of maleic anhydride (calculated as C4H2O3), wt% ≥99.5 Appearance Transparent, molten state Melting chromaticity / Hazen unit (platinum-cobalt color number) ≤25 Crystallization point / °C ≥52.5 Mass fraction of sulfur (calculated as S) / (μg / g) ≤1 Mass fraction of chlorine (calculated as Cl) / (μg / g) ≤1 Mass fraction of phosphorus (calculated as P) / (μg / g) ≤1 Mass fraction of ash / (μg / g) ≤10 Mass fraction of iron (calculated as Fe) / (μg / g) ≤2

[0073] Example 1

[0074] Adopt Figure 1 The method shown, the solvent is γ-butyrolactone, the content of maleic anhydride in the maleic anhydride solution (a mixture of maleic anhydride and γ-butyrolactone) is 10%, and this maleic anhydride solution is pumped into the first heat exchanger through the first centrifugal pump and cooled to 55 °C, and continuously fed into the primary reactor. The volume ratio of hydrogen to the maleic anhydride solution is 35:1, and the volume space velocity of the primary reactor is 3.6 h -1 , the reaction temperature is 80 °C, and the reaction pressure is 3.5 MPaG. The primary hydrogenation reaction product (maleic anhydride conversion rate of 55%) is cooled to 55 °C. After primary high-pressure gas-liquid separation (operating pressure 3.4 MpaG), the gas phase of the primary high-pressure gas-liquid separation enters the high-pressure scrubbing tower, and the liquid phase of the primary high-pressure gas-liquid separation is pressurized to 3.2 MpaG through a turbocharger and enters the secondary reactor. The volume space velocity of the secondary reactor is 3.6 h -1 , the reaction temperature is 85 °C, and the reaction pressure is 3.5 MPaG. After the secondary hydrogenation reaction product (maleic anhydride conversion rate of 100%) undergoes secondary high-pressure gas-liquid separation (operating pressure 3.4 MpaG), the gas phase of the secondary high-pressure gas-liquid separation enters the high-pressure scrubbing tower, and the liquid phase of the secondary high-pressure gas-liquid separation enters the low-pressure separation tank for low-pressure separation (operating pressure 0.3 MpaG). The low-pressure separation liquid phase obtained from the low-pressure separation is pumped into the subsequent product separation section through the second centrifugal pump, and the non-condensable gas from the low-pressure separation is sent to the low-pressure scrubbing tank. The catalysts filled in the primary and secondary reactors are both the catalysts of Example 1 in Chinese Patent Application CN114433127A; the filling ratio (volume ratio) of the catalyst in the primary reactor is 0.55; the filling ratio (volume ratio) of the catalyst in the secondary reactor is 0.58; after calculation, the total hydrogen recovery rate is 40%. In the present invention, the total hydrogen recovery rate = (the amount of hydrogen recovered from the primary high-pressure separator + the amount of hydrogen recovered from the secondary high-pressure separator + the amount of hydrogen recovered from the low-pressure separation tank) / (the amount of fresh hydrogen + the amount of high-pressure scrubbing gas phase recycle) × 100%.

[0075] Example 2

[0076] Adopt Figure 1 the method shown, using γ-butyrolactone as the solvent, with the maleic anhydride content in the maleic anhydride solution (a mixture of maleic anhydride and γ-butyrolactone) being 10%. This maleic anhydride solution is pumped into the first heat exchanger by a first centrifugal pump and cooled to 55°C, and then continuously fed into the first-stage reactor. The volume ratio of hydrogen to the maleic anhydride solution is 35:1, and the volume space velocity of the first-stage reactor is 3.6 h -1 , the reaction temperature is 80°C, and the reaction pressure is 3.5 MPaG. The product of the first-stage hydrogenation reaction (maleic anhydride conversion rate of 55%) is cooled to 55°C. After the first-stage high-pressure gas-liquid separation (operating pressure 3.4 MpaG), the gas phase of the first-stage high-pressure gas-liquid separation enters the high-pressure scrubbing tower, and the liquid phase of the first-stage high-pressure gas-liquid separation is pressurized to 3.2 MpaG by a turbocharger and enters the second-stage reactor. The volume space velocity of the second-stage reactor is 3.6 h -1 , the reaction temperature is 85°C, and the reaction pressure is 3.5 MPaG. The product of the second-stage hydrogenation reaction (maleic anhydride conversion rate of 100%) is separated by the second-stage high-pressure gas-liquid separation (operating pressure 3.4 MpaG). The gas phase of the second-stage high-pressure gas-liquid separation enters the high-pressure scrubbing tower, and the liquid phase of the second-stage high-pressure gas-liquid separation enters the low-pressure separation tank for low-pressure separation (operating pressure 0.8 MpaG). The low-pressure separation liquid obtained from the low-pressure separation is pumped into the subsequent product separation section by a second centrifugal pump, and the non-condensable gas from the low-pressure separation is sent to the low-pressure scrubbing tank. The catalysts filled in the first-stage and second-stage reactors are both the catalysts of Example 1 in Chinese Patent Application CN114433127A; the filling ratio (volume ratio) of the catalyst in the first-stage reactor is 0.55; the filling ratio (volume ratio) of the catalyst in the second-stage reactor is 0.58; after calculation, the total hydrogen recovery rate is 39.3%.

[0077] Example 3

[0078] Adopt Figure 1 the method shown, using γ-butyrolactone as the solvent, with the maleic anhydride content in the maleic anhydride solution (a mixture of maleic anhydride and γ-butyrolactone) being 10%. This maleic anhydride solution is pumped into the first heat exchanger by a first centrifugal pump and cooled to 55°C, and then continuously fed into the first-stage reactor. The volume ratio of hydrogen to the maleic anhydride solution is 35:1, and the volume space velocity of the first-stage reactor is 3.6 h -1 , the reaction temperature is 80°C, and the reaction pressure is 3.5 MPaG. The product of the first-stage hydrogenation reaction (maleic anhydride conversion rate of 55%) is cooled to 55°C. After the first-stage high-pressure gas-liquid separation (operating pressure 3.4 MpaG), the gas phase of the first-stage high-pressure gas-liquid separation enters the high-pressure scrubbing tower, and the liquid phase of the first-stage high-pressure gas-liquid separation is pressurized to 3.2 MpaG by a turbocharger and enters the second-stage reactor. The volume space velocity of the second-stage reactor is 3.6 h -1, the reaction temperature is 85 °C, and the reaction pressure is 3.5 MPaG. After the secondary hydrogenation reaction product (maleic anhydride conversion rate of 100%) undergoes secondary high-pressure gas-liquid separation (operating pressure 3.4 MpaG), the gas phase of the secondary high-pressure gas-liquid separation enters the high-pressure scrubbing tower, and the liquid phase of the secondary high-pressure gas-liquid separation enters the low-pressure separation tank for low-pressure separation (operating pressure 1.9 MpaG). The low-pressure separation liquid phase obtained from the low-pressure separation is pumped into the subsequent product separation section through the second centrifugal pump, and the non-condensable gas from the low-pressure separation is sent to the low-pressure scrubbing tank. The catalysts filled in the primary and secondary reactors are both the catalysts of Example 1 in Chinese Patent Application CN114433127A; the filling ratio (volume ratio) of the catalyst in the primary reactor is 0.55; the filling ratio (volume ratio) of the catalyst in the secondary reactor is 0.58; after calculation, the total hydrogen recovery rate is 33.5%.

[0079] Comparative Example 1

[0080] Adopt Figure 1 The method shown, the solvent is γ-butyrolactone, the maleic anhydride content in the maleic anhydride solution (mixed solution of maleic anhydride and γ-butyrolactone) is 12%, and this maleic anhydride solution is pumped into the first heat exchanger by the first centrifugal pump and cooled to 55 °C, and continuously fed into the primary reactor. The volume ratio of hydrogen to the maleic anhydride solution is 35:1, and the volume space velocity of the primary reactor is 3.6 h -1 , the reaction temperature is 80 °C, and the reaction pressure is 3.5 MPaG. The primary hydrogenation reaction product (maleic anhydride conversion rate of 55%) is cooled to 55 °C. After primary high-pressure gas-liquid separation (operating pressure 3.4 MpaG), the gas phase of the primary high-pressure gas-liquid separation enters the high-pressure scrubbing tower, and the liquid phase of the primary high-pressure gas-liquid separation is pressurized to 3.2 MpaG by turbocharging and enters the secondary reactor. The volume space velocity of the secondary reactor is 3.6 h -1 , the reaction temperature is 85 °C, and the reaction pressure is 3.5 MPaG. After the secondary hydrogenation reaction product (maleic anhydride conversion rate of 100%) undergoes secondary high-pressure gas-liquid separation (operating pressure 3.4 MpaG), the gas phase of the secondary high-pressure gas-liquid separation enters the high-pressure scrubbing tower, and the liquid phase of the secondary high-pressure gas-liquid separation is pumped into the subsequent product separation section through the second centrifugal pump. The catalysts filled in the primary and secondary reactors are both the catalysts of Example 1 in Chinese Patent Application CN114433127A; the filling ratio (volume ratio) of the catalyst in the primary reactor is 0.55; the filling ratio (volume ratio) of the catalyst in the secondary reactor is 0.58; after calculation, the total hydrogen recovery rate is 31.2%. In addition, when there are problems during reactor shutdown, since there is no subsequent low-pressure separation tank, maleic anhydride will enter the subsequent product separation section. Maleic anhydride is prone to polymerization at high temperatures and will block pipelines or equipment ports, so it is easy to cause shutdown and production suspension.

[0081] As can be seen from Examples 1-3 and Comparative Example 1, by specially arranging a low-pressure separation tank after the secondary high-pressure gas-liquid separation tank in the present invention, hydrogen can be removed more thoroughly. Moreover, this part of hydrogen can carry away some impurities in the reaction system and be discharged into the downstream factory for recycling. Therefore, the low-pressure separation tank can serve well as a safety isolation for the subsequent product separation section, preventing high-pressure gas (hydrogen) from surging into the subsequent product separation section. And when problems occur during the reactor shutdown, there is a material return line at the liquid phase outlet of the low-pressure separation tank to return to the liquid phase feed tank and continue the reaction until the maleic anhydride reaction is complete, and then enter the subsequent product separation section to prevent maleic anhydride from polymerizing and blocking pipelines or equipment ports at high temperatures in the subsequent product separation section. In addition, when the pressure difference between the low-pressure separation tank and the liquid phase of the primary high-pressure gas-liquid separation tank is preferably in the range of 2.5-3.2 MpaG, hydrogen can be removed more thoroughly, and thus the total recovery rate of hydrogen will be better improved. Additionally, the low-pressure washing tank connected to the gas phase outlet of the low-pressure separation tank is used to wash off the acid anhydride with water to prevent acidic media from corroding the flare system, fuel gas pipeline network or other devices.

Claims

1. A system for preparing succinic anhydride from maleic anhydride, comprising two-stage reactors, characterized in that A liquid-phase feed tank, a first-stage reactor, a first-stage high-pressure gas-liquid separation tank, a second-stage reactor, a second-stage high-pressure gas-liquid separation tank, and a low-pressure separation tank are sequentially connected by pipelines; wherein, the outlet of the liquid-phase feed tank is connected to the liquid-phase material inlet of the first-stage reactor by a pipeline, the outlet of the first-stage reactor is connected to the inlet of the first-stage high-pressure gas-liquid separation tank by a pipeline, the liquid-phase outlet of the first-stage high-pressure gas-liquid separation tank is connected to the liquid-phase material inlet of the second-stage reactor by a pipeline, the outlet of the second-stage reactor is connected to the inlet of the second-stage high-pressure gas-liquid separation tank by a pipeline, and the liquid-phase outlet of the second-stage high-pressure gas-liquid separation tank is connected to the inlet of the low-pressure separation tank by a pipeline.

2. The system according to claim 1, wherein: The system further includes a hydrogen feed tank, and the outlet of the hydrogen feed tank is respectively connected to the gas-phase material inlet of the first-stage reactor and the gas-phase material inlet of the second-stage reactor by pipelines; and / or, The liquid-phase feed tank is provided with a liquid-phase raw material inlet, preferably a maleic anhydride feed port and a solvent feed port are respectively provided; and / or, A first centrifugal pump for pumping liquid-phase feed and / or a first heat exchanger are further provided on the pipeline connecting the liquid-phase feed tank and the first-stage reactor; preferably, a first centrifugal pump for pumping the reaction product mixture is connected before the first heat exchanger; and / or, A second heat exchanger is further provided on the pipeline connecting the first-stage reactor and the first-stage high-pressure gas-liquid separation tank; and / or, A turbocharging device is further provided on the pipeline connecting the first-stage high-pressure gas-liquid separation tank and the second-stage reactor; and / or, The system further includes a high-pressure scrubbing tower, which is provided with a gas-phase inlet at the bottom and a scrubbing solvent inlet at the upper part; the gas-phase outlet of the first-stage high-pressure gas-liquid separation tank and / or the gas-phase outlet of the second-stage high-pressure gas-liquid separation tank are connected to the gas-phase inlet of the high-pressure scrubbing tower by pipelines; and / or, The low-pressure separation tank is provided with a liquid-phase outlet, and the liquid-phase outlet of the low-pressure separation tank is connected to the subsequent product separation section by a pipeline; preferably, a second centrifugal pump for pumping liquid-phase feed is further provided on the pipeline connecting the liquid-phase outlet of the low-pressure separation tank and the subsequent product separation section; and / or, The low-pressure separation tank is provided with a gas-phase outlet, and the gas-phase outlet of the low-pressure separation tank is connected to a low-pressure scrubbing tank.

3. The system according to claim 2, wherein: The liquid-phase outlet of the high-pressure scrubbing tower is connected to the liquid-phase raw material inlet of the liquid-phase feed tank, preferably connected to the solvent feed port; and / or, The gas-phase outlet of the high-pressure scrubbing tower is connected to the inlet of the hydrogen feed tank by a pipeline, preferably, a hydrogen compressor buffer tank and / or a hydrogen recycle compressor are further provided on the pipeline connecting the gas-phase outlet of the high-pressure scrubbing tower and the inlet of the hydrogen feed tank, and further preferably, the hydrogen recycle compressor is connected to the hydrogen compressor buffer tank before; and / or, A branch is further provided on the pipeline connecting the turbocharging device and the second-stage reactor and is connected to the liquid-phase raw material inlet of the liquid-phase feed tank, preferably connected to the solvent feed port; and / or, A branch is further provided on the pipeline connecting the second centrifugal pump and the subsequent product separation section and is connected to the liquid-phase raw material inlet of the liquid-phase feed tank, preferably connected to the solvent feed port.

4. The system according to claim 1, wherein: The first-stage reactor and the second-stage reactor are the same or different, and are each independently one of an upflow liquid-phase hydrogenation reactor, a fixed-bed reactor, and a shell-and-tube reactor.

5. A method for preparing succinic anhydride using the system according to any one of claims 1-4, comprising subjecting a maleic anhydride solution to hydrogenation by contacting it with hydrogen in a first-stage reactor, feeding the liquid-phase product obtained by first-stage high-pressure gas-liquid separation into a second-stage reactor for further hydrogenation by contacting it with hydrogen, and subjecting the liquid phase obtained by second-stage high-pressure gas-liquid separation to low-pressure gas-liquid separation.

6. The method according to claim 5, wherein The method comprises: 1) Mixing maleic anhydride with a solvent in a liquid-phase feed tank and contacting the mixture with hydrogen fed from a hydrogen feed tank in a first-stage reactor to carry out a first-stage hydrogenation reaction to obtain a first-stage hydrogenation reaction product; 2) Sending the gas phase obtained by first-stage high-pressure gas-liquid separation of the first-stage hydrogenation reaction product to a high-pressure scrubbing tower, and feeding the liquid phase obtained by first-stage high-pressure gas-liquid separation into a second-stage reactor for further hydrogenation by contacting it with hydrogen to obtain a second-stage hydrogenation reaction product; 3) Sending the gas phase obtained by second-stage high-pressure gas-liquid separation of the second-stage hydrogenation reaction product to a high-pressure scrubbing tower, subjecting the liquid phase obtained by second-stage high-pressure gas-liquid separation to low-pressure separation, feeding the low-pressure separated liquid phase into a subsequent product separation section for product separation, and feeding the non-condensable gas separated at low pressure into a low-pressure scrubbing tank for water washing; 4) Optionally returning the liquid phase obtained from the high-pressure scrubbing tower to the liquid-phase feed tank for recycling; and / or, optionally returning the gas phase obtained from the high-pressure scrubbing tower to the hydrogen feed tank for recycling.

7. The method according to claim 6, wherein: In step 1), the mixed solution obtained by mixing maleic anhydride with a solvent in a liquid-phase feed tank is cooled and then fed into the first-stage reactor, preferably cooled to 40-60°C; and / or, the maleic anhydride is in a molten state; and / or, the solvent is one or more of γ-butyrolactone, tetrahydrofuran, dioxane, acetic anhydride, ethyl acetate, four-carbon dibasic acid ester, ethanol, isopropanol, straight-chain or branched-chain alkane, aromatic hydrocarbon, cycloalkane, preferably one or two of γ-butyrolactone and tetrahydrofuran; and / or, the mass ratio of maleic anhydride to the solvent is 1:(6-15); and / or, the volume ratio of hydrogen to the mixed solution of maleic anhydride and the solvent is (30-65):1; and / or, The operating conditions of the primary reactor include: the temperature is 40 - 130 °C; and / or, the pressure is 1.8 - 4.2 MpaG; and / or, the volume space velocity is 1.8 - 4.2 h -1 .

8. The method according to claim 6, wherein: In step 2), the first-stage hydrogenation reaction product is cooled before first-stage high-pressure gas-liquid separation, preferably cooled to 40-60°C; and / or, the operating pressure of the first-stage high-pressure gas-liquid separation is 2.8-4.0 MpaG; and / or, the liquid phase obtained by first-stage high-pressure gas-liquid separation is fed into the second-stage reactor by turbocharging, preferably pressurized to 2.8-3.8 MpaG and then fed into the second-stage reactor; and / or, the operating conditions of the second-stage reactor include: temperature of 40-130°C; and / or, pressure of 1.8-4.2 MpaG; and / or, the space velocity on volume basis is 1.8 - 4.2 h -1 .

9. The method according to claim 6, wherein: In step 2), The liquid phase obtained by the first-stage high-pressure gas-liquid separation is divided into two parts. One part of the liquid phase is recycled to the liquid-phase feed tank, and the other part of the liquid phase is sent into the second-stage reactor to continue to contact with hydrogen for the second-stage hydrogenation reaction to obtain the second-stage hydrogenation reaction product.

10. The method according to claim 6, wherein: In step 3), the operating pressure of the second-stage high-pressure gas-liquid separation is 2.8 - 4.0 MpaG; and / or, the operating pressure of the low-pressure separation tank is 0.3 - 3 MpaG, preferably 0.3 - 1.5 MpaG; preferably, the pressure difference between the low-pressure separation tank and the liquid phase of the first-stage high-pressure gas-liquid separation tank is 1.0 - 3.2 MpaG, preferably 2.5 - 3.2 MpaG.

11. The method according to claim 6, wherein: In step 3), the low-pressure separated liquid phase is divided into two parts. One part of the liquid phase is recycled to the liquid-phase feed tank, and the other part of the liquid phase is sent to the subsequent product separation section for product separation.

12. An application of the system according to any one of claims 1 - 4 or the method for preparing succinic anhydride according to any one of claims 5 - 11 in the field of succinic anhydride preparation.

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