A method and device for preparing alkyl carbonate from alkyl oxalate

Abstract

The invention discloses a method and device for preparing alkyl carbonate from alkyl oxalate, comprising the following steps: S1, preheating the raw material alkyl oxalate and entering the decarbonylation reactor, contacting with the catalyst under the conditions of 190-230°C and 0.1-0.9MPaG to produce alkyl carbonate, carbon monoxide and a small amount of by-products, and the generated products are all discharged from the decarbonylation reactor in a gas phase state and enter the alkyl oxalate absorption tower directly connected to the reactor. In the present invention, the decarbonylation reaction products all leave the reactor in a gas phase state and enter the oxalate absorption tower directly connected to the reactor, and the oxalate absorption tower outlet gas phase is recovered by waste heat, condensed and cooled, and the liquid phase product obtained by gas-liquid separation, the content of the target product alkyl carbonate exceeds 97.5wt% and does not contain unreacted raw material alkyl oxalate, the subsequent alkyl carbonate distillation system is simplified to a single tower distillation process, and the alkyl carbonate content in the decarbonylation reaction product is very high, which greatly reduces the energy consumption of the distillation system.

Description

Technical Field

[0001] The invention belongs to the technical field of alkyl carbonate preparation, and particularly relates to a method and a device for preparing alkyl carbonate from alkyl oxalate. Background Art

[0002] The structural formula of alkyl carbonate is R1-O-CO-O-R2. The molecule contains multiple active groups such as carbonyl and ester groups. Therefore, alkyl carbonate has multiple activities and is an important chemical with great application prospects. Taking common alkyl carbonate as an example, dimethyl carbonate (DMC) has the structural formula of C3H6O3. It is a colorless and transparent liquid at room temperature with a slight fragrance. It has an appearance similar to general alcohols, esters and ketones. It can be mixed with organic solvents such as alcohols, esters and ketones in any proportion and is non-corrosive. DMC molecules contain groups such as -CO, -COOCH3, and -CH3, so it has multiple activities and can be used for carbonylation, carbonyl methoxylation and methylation reactions. DMC is currently mainly used as a raw material for the non-phosgene production of polycarbonate and as a solvent. DMC is also a component of the solvent in lithium battery electrolyte, accounting for the largest proportion, and other solvents such as ethyl methyl carbonate and alkyl carbonate are produced by DMC through ester exchange reactions. With the increase in the installation of lithium batteries, the demand for DMC is also increasing year by year.

[0003] The industrial production methods of DMC mainly include transesterification, gas phase carbonylation, liquid phase carbonylation, and urea alcoholysis. The raw material of the transesterification method is ethylene oxide, which reacts with CO2 to produce ethylene carbonate, which then reacts with methanol to produce DMC and ethylene glycol, or propylene oxide reacts with CO2 to produce propylene carbonate, which then reacts with methanol to produce DMC and 1,2-propylene glycol. The liquid phase carbonylation method uses methanol, oxygen and CO as raw materials, cuprous chloride or cupric chloride as the active component of the catalyst, and reacts in a slurry bed reactor. The catalyst has a short life and needs to be continuously supplemented with chlorine. There are many impurities in the product and it can affect the quality of the DMC product. The gas phase carbonylation method is an original method of Ube Industries, Ltd. of Japan. It uses CO, O2 and methanol as raw materials. It cleverly divides the reaction into two steps: the first step is the reaction of CO with methyl nitrite (MN) to produce DMC and NO, and the second step is the reaction of NO with oxygen and methanol to produce MN and water. The DMC product of this method is of high quality and low impurity content, and electronic grade DMC products can be obtained only through distillation. However, chlorine needs to be continuously supplemented during the reaction process, and some equipment, pipeline materials, and tower internals have high requirements. Ube's gas phase carbonylation DMC process technology has complete intellectual property protection and is relatively strict in technology transfer to domestic customers.

[0004] The structural formula of alkyl oxalate is R1-O-COCO-O-R2, among which dimethyl oxalate is the most representative and largest alkyl oxalate chemical. Dimethyl oxalate (DMO) in China is mainly an intermediate product of the two-step synthesis gas process for producing ethylene glycol, that is, CO, oxygen, and methanol are used to produce DMO, and DMO is hydrogenated to produce ethylene glycol. With the development of domestic synthesis gas-based ethylene glycol technology and the release of production capacity, DMO has grown from scratch in China in just over a decade. At present, it has a production capacity of more than 10 million tons. The main raw materials of DMO are only CO, O2 and methanol, and the consumption of utilities such as steam is small, so the variable cost of DMO is relatively low. The DMO downstream technology with low development cost and large production capacity has broad development prospects. It is also an effective way to reduce costs and increase efficiency for domestic synthesis gas-based ethylene glycol enterprises, and it is of great significance to the development of the domestic synthesis gas-based ethylene glycol industry.

[0005] As early as the 1980s and 1990s, Celanese of the United States and Ube Industries of Japan had studied the technology of decarbonylation of oxalate to produce carbonate. For example, US4544507 uses a liquid phase oxalate decarbonylation process to produce carbonate, the reaction temperature is 50-150°C, the reaction raw materials and reaction products (except CO) are in liquid phase, and the catalyst is alcohol salt, such as sodium methoxide.

[0006] EP0916645B1 adopts a gas phase oxalate decarbonylation process to produce carbonates, that is, the raw material oxalate passes through a catalyst bed in a gas phase under reaction temperature and pressure, and the catalyst is an organic acid salt, inorganic acid salt, hydroxide or oxide of an alkali metal.

[0007] JP10-330323 adopts a liquid phase process for producing carbonates by decarbonylating alkyl oxalate, i.e., the oxalate raw material and the reaction product (except CO) are in the liquid phase under the reaction temperature and pressure conditions, and the catalyst is a carbonate of potassium, rubidium or cesium, or a metal halide, carboxylate or phosphate of potassium, rubidium or cesium.

[0008] CN112028771A discloses a method for preparing alkyl carbonate, comprising subjecting molten alkyl oxalate or a solution of alkyl oxalate to a decarbonylation reaction with a catalyst at a temperature between 50 and 160°C and a pressure between 0.5 bar and 5 bar to obtain a reaction gas and a reaction liquid containing alkyl carbonate, and then distilling the reaction liquid to obtain the product alkyl carbonate.

[0009] The inventors have systematically studied the technology of preparing alkyl carbonate by decarbonylation of alkyl oxalate. The inventors have found that: in the liquid phase process for preparing alkyl carbonate by decarbonylation of alkyl oxalate, such as disclosed in US4544507, JP10-330323 and CN112028771A, under the reaction temperature and pressure conditions, the reaction product (except CO) is in liquid phase. Due to the limitation of residence time and reaction kinetics, the conversion rate of the raw material alkyl oxalate is low, and the proportion of unreacted alkyl oxalate in the product is high. If the conversion rate of alkyl oxalate is to be increased, the reaction time of the raw material needs to be increased, which is limited by the scale of reactor and equipment in industrial application. In addition, the content of the target product carbonate in the reaction product is low. In the subsequent distillation, a large amount of unreacted raw material needs to be distilled and separated, and the consumption of utilities such as steam is high, which is not economical.

[0010] Therefore, it is necessary to invent a method and device for preparing alkyl carbonate from alkyl oxalate to solve the above problems. Summary of the invention

[0011] In view of the above problems, the present invention provides a method and apparatus for preparing alkyl carbonate from alkyl oxalate, wherein the decarbonylation reaction products all leave the reactor in a gaseous state and enter an oxalate absorption tower directly connected to the reactor, and the gas phase at the outlet of the oxalate absorption tower is subjected to waste heat recovery, condensation cooling and gas-liquid separation to obtain a liquid phase product, in which the content of the target product alkyl carbonate exceeds 97.5wt% and does not contain unreacted raw material alkyl oxalate, and the subsequent alkyl carbonate distillation system can be simplified to a single-tower distillation process, and the alkyl carbonate content in the decarbonylation reaction product is very high, which can greatly reduce the energy consumption of the distillation system, thereby solving the problems raised in the above background technology.

[0012] To achieve the above object, the present invention provides the following technical solution: a method for preparing alkyl carbonate from alkyl oxalate, comprising the following steps:

[0013] S1. Preheat the raw material alkyl oxalate and then enter the decarbonylation reactor. Under the conditions of 190-230° C. and 0.1-0.9 MPaG, the raw material alkyl oxalate is contacted with the catalyst to undergo a decarbonylation reaction to produce alkyl carbonate, carbon monoxide and a small amount of by-products. The generated products are all discharged from the decarbonylation reactor in a gas phase state and enter an alkyl oxalate absorber directly connected to the reactor. The gas phase at the top outlet of the alkyl oxalate absorber is subjected to waste heat recovery, condensation cooling and gas-liquid separation to obtain gas phase components and liquid phase products. The gas phase component is mainly carbon monoxide and discharged from the device for recycling. The content of the target product alkyl carbonate in the liquid phase product can exceed 97.5wt%, and the rest is by-products generated by the decarbonylation reaction. A small part of the obtained liquid phase product is returned to the top of the alkyl oxalate absorber as an absorption medium, and the rest of the liquid phase product enters the subsequent alkyl carbonate distillation system;

[0014] S2. The alkyl carbonate distillation system can be simplified into a single-tower distillation process. The above-mentioned liquid products enter the alkyl carbonate distillation tower, the light components are separated out at the top of the tower, and the alkyl carbonate products are obtained through the side outlet. The heavy components in the bottom of the tower are returned to the decarbonylation reactor to continue the reaction.

[0015] Further, the decarbonylation reactor is a kettle reactor with a stirring and heating module, the heating module of the decarbonylation reactor is in the form of a built-in plate group, a coil or a jacket, preferably a built-in plate group, the built-in plate group is composed of one or more groups of plates, the built-in plate group is arranged in parallel in a vertical direction, and the angle with the tangent direction of the outer surface of the decarbonylation reactor is 15-90°; each plate group in the built-in plate group is composed of two plates, and the spacing between the two plates is 5-80mm; the plate width is 100-800mm;

[0016] Steam is introduced between the two plates of each built-in plate group as a heat source for decarbonylation reaction, the steam pressure level is 1.5-3.8MPaG, and the stirring form of the decarbonylation reactor is paddle type, propeller type, turbine type, anchor type, and frame type.

[0017] Furthermore, the catalyst is loaded in a catalyst cage, the interior of the catalyst cage has a structural skeleton with supporting strength, and the exterior is covered with a wire mesh or a grid, and the reaction raw materials and products can freely enter and exit the catalyst cage to contact and react with the catalyst, while the catalyst cannot enter the reactor through the wire mesh or the grid covering the exterior of the catalyst cage;

[0018] The catalyst cage is cylindrical and vertically installed. The upper part of the catalyst cage passes through the upper end surface of the decarbonylation reactor and is connected to the catalyst feeding system; the lower part of the catalyst cage passes through the lower end surface of the decarbonylation reactor and is connected to the catalyst recovery and separation system; the catalyst can be continuously or intermittently extracted and replenished, so that the decarbonylation reactor can react continuously.

[0019] Furthermore, the catalyst feeding system can be transported by gas or liquid, the gas transport medium is nitrogen or carbon monoxide, and the liquid transport medium is the raw material alkyl oxalate or the target product alkyl carbonate, preferably alkyl carbonate;

[0020] The function of the catalyst recovery and separation system is to separate the spent catalyst particles from the liquid material in the decarbonylation reactor, and return the separated liquid material to the decarbonylation reactor for recovery and treatment of the spent catalyst; the recovery and separation system is a basket filter device, a filter press device or a suction filter device, preferably a basket filter device;

[0021] The catalyst is a supported catalyst, including a support and an alkali metal carbonate, wherein the alkali metal carbonate loading is 5-15wt%, the alkali metal carbonate is one of sodium carbonate, potassium carbonate, cesium carbonate or a mixture thereof, and the support has a specific surface area greater than 1300m 2 / g of activated carbon.

[0022] Furthermore, under the above reaction temperature and pressure, the products obtained by decarbonylation of alkyl oxalate are all in gas phase. The gas phase products enter the alkyl oxalate absorption tower directly connected to the reactor for absorption and separation, and then the waste heat is recovered. The waste heat recovery includes a waste boiler and an inlet and outlet heat exchanger. The waste boiler can produce 0.5-1.5MPaG grade steam as a by-product, thereby recovering the latent heat contained in the gas phase products to the greatest extent and reducing steam consumption.

[0023] Furthermore, the alkyl oxalate absorption tower may be a packed tower or a plate tower, the number of theoretical plates being 2-22, and the mass ratio of the reflux amount of the liquid phase product returning to the top of the alkyl oxalate absorption tower to the output amount of the alkyl carbonate distillation system is 0.05-0.2;

[0024] The operating pressure of the alkyl carbonate distillation tower is 0-50 KPaG, the alkyl carbonate distillation tower can be a packed tower or a plate tower, and the side outlet of the alkyl carbonate distillation tower is located above the feed inlet, with a distance of 20-60 theoretical plates;

[0025] The molecular formula of the alkyl oxalate is R1-O-COCO-O-R2, wherein R1 and R2 are alkyl groups with 1 to 4 carbon atoms; the molecular formula of the alkyl carbonate is R1-O-CO-O-R2, wherein R1 and R2 of the alkyl oxalate are the same as R1 and R2 of the alkyl carbonate.

[0026] Furthermore, the basket filter device comprises an outer frame, a sealing cover is provided on the top of the outer frame, a discharge port is provided on one side of the bottom surface of the outer frame, a first filter plate and a second filter plate are provided inside the outer frame, the first filter plate is located on the top of the second filter plate, a vertical bar is provided on the inner side wall of the circumference of the outer frame, and the circumferential sides of the first filter plate and the second filter plate are provided with grooves corresponding to and matching the vertical bars, the first filter plate is arranged in a truncated cone shape, the second filter plate is arranged horizontally, the aperture of the leakage hole on the surface of the second filter plate is smaller than the aperture of the surface of the first filter plate, and a A rotating rod is provided, the bottom end of the rotating rod passes through the center of the bottom surface of the outer frame, the top end of the rotating rod passes through the center of the top surface of the cover, and the rotating rod is spirally matched with the center of the first filter plate, and a liquid inlet and a liquid outlet are respectively provided at the top and bottom of one side of the outer frame, the inner end of the liquid inlet corresponds to the top of the first filter plate, and the inner end of the liquid outlet corresponds to the bottom of the second filter plate, and a plurality of rotating rings are equidistantly arranged on the inner bottom surface of the outer frame in an annular shape, and the plurality of rotating rings are annularly located on the outside of the rotating rod, and the surface of the rotating ring is tightly fitted with the surface of the rotating rod, and the rotating ring is rotatably matched with the rotating rod by means of a fixed rod, and the bottom end of the fixed rod is fixedly connected to the inner bottom surface of the outer frame.

[0027] Furthermore, a plurality of vertical rods are fixedly connected to the bottom surface of the first filter plate, the bottom ends of the vertical rods penetrate the surface of the second filter plate, the surface of the vertical rods is sleeved with springs, slides are provided on both sides of the bottom of the second filter plate, the two slides are arranged opposite to each other, the slides slide with the vertical bars, both sides of the slides are rotatably connected to the top of the rotating plate, the bottom end of the rotating plate is rotatably connected to the sliding frame, two parallel corresponding cross frames are provided on the inner side of the outer frame, and the slides are slidably sleeved on the surface of the cross frames, and the two opposite slides are correspondingly connected by elastic plates.

[0028] The present invention also provides a device for preparing alkyl carbonate from alkyl oxalate, comprising a decarbonylation reactor, a catalyst feeding system, a catalyst recovery and separation system, a waste heat recovery system and an alkyl carbonate distillation system;

[0029] The decarbonylation reactor is used for the raw material alkyl oxalate to undergo a decarbonylation reaction with a catalyst at a certain temperature and pressure to produce alkyl carbonate, carbon monoxide and a small amount of by-products; wherein the decarbonylation reactor is also provided with an alkyl oxalate absorption tower directly connected thereto, for absorbing and separating the alkyl oxalate in the reaction product;

[0030] The catalyst feeding system adopts gas or liquid transportation, the medium of gas transportation is nitrogen or carbon monoxide, and the medium of liquid transportation is raw material alkyl oxalate or product alkyl carbonate, preferably alkyl carbonate;

[0031] The catalyst recovery and separation system is used to separate and recover the deactivated catalyst from the liquid material in the decarbonylation reactor; the catalyst is loaded in the catalyst cage, the catalyst can be continuously or intermittently extracted and replenished, the separated liquid material is returned to the decarbonylation reactor, and the spent catalyst is recovered and processed, the recovery and separation system is a basket filter device, a filter press device or a suction filter device, preferably a basket filter device;

[0032] The waste heat recovery system is used to recover the waste heat of the gas phase product obtained by the decarbonylation reactor, including a waste boiler and an inlet and outlet heat exchanger. The waste boiler can produce 0.5-1.5MPaG grade steam as a by-product. The waste heat recovery system can recover the latent heat and sensible heat contained in the gas phase product to the greatest extent, thereby reducing the steam consumption of the device;

[0033] The alkyl carbonate distillation system is simplified to a single-tower distillation process, wherein the liquid product enters the alkyl carbonate distillation tower, the light component is separated from the tower top, the alkyl carbonate product is obtained from the side outlet, and the heavy component in the tower bottom is returned to the decarbonylation reactor for further reaction.

[0034] Furthermore, the alkyl carbonate distillation system also includes auxiliary equipment of the alkyl oxalate distillation tower, including but not limited to an overhead condenser, an overhead reflux tank, a side sampling tank, a reboiler, a reflux pump and other auxiliary equipment.

[0035] Technical effects and advantages of the present invention:

[0036] 1. In the present invention, the decarbonylation reaction products all leave the reactor in a gas phase state and enter an oxalate absorption tower directly connected to the reactor. The oxalate absorption tower outlet gas phase is subjected to waste heat recovery, condensation cooling and gas-liquid separation to obtain a liquid phase product, in which the target product alkyl carbonate has a content of more than 97.5wt% and does not contain unreacted raw material alkyl oxalate. The subsequent alkyl carbonate distillation system is simplified to a single-tower distillation process, and the alkyl carbonate content in the decarbonylation reaction product is very high, which greatly reduces the energy consumption of the distillation system.

[0037] 2. The present invention filters the liquid material through the first filter plate and the second filter plate, and the rotation of the rotating rod and the spiral effect of the first filter plate make the first filter plate move down inside the outer frame, and when the first filter plate slides on the surface of the vertical bars by utilizing the groove, the first filter plate drives the second filter plate to move down synchronously by utilizing the spring, and when the second filter plate drives the slide frame to move down, the slide frame drives the top end of the rotating plate to move down, and when the rotating plate rotates, the bottom end of the rotating plate drives the sliding frame to slide on the surface of the horizontal frame, and the two relative sliding frames gradually approach each other during the sliding process, and the two sliding frames gradually squeeze the elastic plate, and the downward moving speed of the second filter plate decreases. At this time, the first filter plate and gradually approach the second filter plate, and when the first filter plate and the second filter plate approach each other, they gradually squeeze the solid catalyst between the two, so as to squeeze out the liquid material remaining on the surface of the solid catalyst. If the solid catalyst is a flocculent material, the extrusion of the first filter plate and the second filter plate can ensure the drying effect of the solid catalyst between the two.

[0038] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 A partial schematic flow chart of the reaction of decarbonylating alkyl oxalate to prepare alkyl carbonate according to an embodiment of the present invention is shown;

[0041] Figure 2 A schematic flow chart of an alkyl carbonate distillation system according to an embodiment of the present invention is shown;

[0042] Figure 3 The overall structure schematic diagram of the basket filter device according to the embodiment of the present invention is shown;

[0043] Figure 4 A schematic diagram of the internal structure of the outer frame of an embodiment of the present invention is shown;

[0044] Figure 5 It shows the corresponding schematic diagram of the first filter plate and the second filter plate of the embodiment of the present invention;

[0045] In the figure: 1. outer frame; 2. sealing cover; 3. discharge port; 4. first filter plate; 5. second filter plate; 6. vertical bar; 7. groove; 8. rotating rod; 9. liquid inlet; 10. liquid outlet; 11. rotating ring; 12. fixed rod; 13. vertical rod; 14. spring; 15. slide; 16. rotating plate; 17. sliding frame; 18. horizontal frame; 19. elastic plate. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Embodiment 1:

[0048] The present invention provides a method for preparing alkyl carbonate from alkyl oxalate, such as Figure 1 As shown, the following steps are included:

[0049] S1. Preheat the raw material alkyl oxalate and then enter the decarbonylation reactor. Under the conditions of 190-230°C and 0.1-0.9MPaG, the raw material alkyl oxalate is contacted with the catalyst to undergo a decarbonylation reaction to produce alkyl carbonate, carbon monoxide and a small amount of by-products. The generated products are all discharged from the decarbonylation reactor in a gaseous state and enter an alkyl oxalate absorber directly connected to the reactor. The gas phase at the outlet of the top of the alkyl oxalate absorber is subjected to waste heat recovery, condensation cooling and gas-liquid separation to obtain gas phase components and liquid phase products. The gas phase component is mainly carbon monoxide and discharged from the device for recycling. The content of the target product alkyl carbonate in the liquid phase product can exceed 97.5wt%, and the rest is by-products generated by the decarbonylation reaction. A small part of the obtained liquid phase product is returned to the top of the alkyl oxalate absorber as an absorption medium, and the rest of the liquid phase product enters the subsequent alkyl carbonate distillation system.

[0050] Before adding the alkyl oxalate to the decarbonylation reactor, the alkyl oxalate needs to be preheated. The treatment process includes: passing the raw alkyl oxalate through the inlet and outlet heat exchangers in the waste heat recovery unit to recover the heat of the alkyl oxalate at the outlet of the decarbonylation reactor, and preheating the alkyl oxalate to 120°C before entering the decarbonylation reactor.

[0051] The internal configuration of the decarbonylation reactor is as follows:

[0052] The decarbonylation reactor is a kettle reactor with a stirring and heating module. The heating module of the decarbonylation reactor is in the form of a built-in plate group, a coil or a jacket, preferably a built-in plate group. The built-in plate group consists of one or more groups of plates. The built-in plate groups are arranged in parallel in a vertical direction, and the angle with the tangent direction of the outer surface of the decarbonylation reactor is 15-90°; each plate group in the built-in plate group consists of two plates, and the spacing between the two plates is 5-80mm; the plate width is 100-800mm; steam is introduced between the two plates of each built-in plate group as a heat source for the decarbonylation reaction, and the steam pressure level is 1.5-3.8MPaG. The stirring form of the decarbonylation reactor is paddle type, propeller type, turbine type, anchor type, and frame type.

[0053] Exemplarily, the decarbonylation reactor is a kettle reactor with stirring and built-in plate group heating module, wherein the stirring form is pusher type; the built-in plate group consists of 8 groups, the plate width is 200mm, the angle between the plate group and the tangent direction of the decarbonylation reactor facade is 30°, and the distance between the two plates is 25mm. 3.8MPaG medium-pressure saturated steam is introduced between the two plates of each plate group as a heat source for the decarbonylation reaction.

[0054] When a catalyst is used to accelerate the reaction of alkyl oxalate in a decarbonylation reactor, the catalyst is loaded in a catalyst cage, the interior of the catalyst cage has a structural skeleton with supporting strength, and the exterior is covered with a wire mesh or a grid, the reaction raw materials and products can freely enter and exit the catalyst cage to contact and react with the catalyst, but the catalyst cannot enter the reactor through the wire mesh or the grid covering the exterior of the catalyst cage; the catalyst cage is cylindrical and vertically installed, the upper part of the catalyst cage passes through the upper end face of the decarbonylation reactor and is connected to the catalyst feeding system; the lower part of the catalyst cage passes through the lower end face of the decarbonylation reactor and is connected to the catalyst recovery and separation system; the catalyst can be continuously or intermittently extracted and replenished, so that the decarbonylation reactor can react continuously.

[0055] The catalyst feeding system can be transported by gas or liquid, the gas transport medium is nitrogen or carbon monoxide, the liquid transport medium is raw material alkyl oxalate or target product alkyl carbonate, preferably alkyl carbonate; the catalyst recovery and separation system is used to separate the spent catalyst particles from the liquid material in the decarbonylation reactor, and the separated liquid material is returned to the decarbonylation reactor for spent catalyst recovery and treatment; the recovery and separation system is a basket filter, a filter press or a suction filter, preferably a basket filter; the catalyst is a supported catalyst, including a carrier and an alkali metal carbonate, the alkali metal carbonate loading is 5-15wt%, the alkali metal carbonate is one of sodium carbonate, potassium carbonate, cesium carbonate or a mixture thereof, and the carrier is a catalyst with a specific surface area greater than 1300m2 / g of activated carbon.

[0056] Exemplarily, the catalyst is activated carbon loaded with a mixture of sodium carbonate and cesium carbonate, wherein the sodium carbonate content is 5 wt %, the cesium carbonate content is 6 wt %, and the specific surface area of ​​the activated carbon is 1500 m 2 / g. The catalyst is transported to the catalyst cage through the catalyst feeding system, and the transport medium is alkyl carbonate. There are 6 groups of catalyst cages in total, which are evenly distributed vertically in the decarbonylation reactor.

[0057] S2. The alkyl carbonate distillation system can be simplified into a single-tower distillation process. The above-mentioned liquid phase product enters the alkyl carbonate distillation tower, the light component is separated from the top of the tower, and the alkyl carbonate product is obtained from the side outlet. The bottom of the tower is the heavy component and returns to the decarbonylation reactor to continue the reaction. The alkyl carbonate distillation system is a single-tower distillation process, and only a product tower needs to be set up, and the product tower is a packed tower.

[0058] The above liquid products enter the product tower, and the operating pressure at the top of the tower is 0.005MPaG. The process gas at the top of the tower is condensed to 50°C through the top condenser and enters the reflux tank of the product tower. After being pressurized by the product tower reflux pump, a part of it returns to the product tower, and the other part is cooled to 40°C through the cooler and sent to outside the boundary for treatment as light components; the light components mainly include by-products of decarbonylation: methyl formate, methylal, methanol, etc.

[0059] When utilizing waste heat recovery to recover heat, under the above-mentioned reaction temperature and pressure, the products obtained from the decarbonylation of alkyl oxalate are all in gas phase. The gas phase products enter the alkyl oxalate absorption tower directly connected to the reactor for absorption and separation, and then the waste heat is recovered. The waste heat recovery includes a waste boiler and an inlet and outlet heat exchanger. The waste boiler can produce 0.5-1.5MPaG grade steam as a by-product, thereby recovering the latent heat contained in the gas phase products to the greatest extent and reducing steam consumption.

[0060] The alkyl oxalate absorption tower can be a packed tower or a plate tower, with a theoretical plate number of 2-22, and the mass ratio of the reflux of the liquid product returning to the top of the alkyl oxalate absorption tower to the output of the alkyl carbonate distillation system is 0.05-0.2. The operating pressure of the alkyl carbonate distillation tower is 0-50KPaG, the alkyl carbonate distillation tower can be a packed tower or a plate tower, and the side output port of the alkyl carbonate distillation tower is located at the upper part of the feed port, with a distance of 20-60 theoretical plates; the molecular formula of the alkyl oxalate is R1-O-COCO-O-R2, wherein R1 and R2 are alkyl groups with 1-4 carbon atoms, the molecular formula of the alkyl carbonate is R1-O-CO-O-R2, and R1 and R2 of the alkyl oxalate are the same as R1 and R2 of the alkyl carbonate.

[0061] Exemplarily, the raw material alkyl oxalate is contacted with a catalyst under the conditions of 220°C and 0.6MPaG to undergo a decarbonylation reaction to produce alkyl carbonate, carbon monoxide and a small amount of by-products. The generated products are discharged from the decarbonylation reactor in a gaseous state and enter an alkyl oxalate absorption tower directly connected to the reactor for absorption and separation. The alkyl oxalate absorption tower adopts a packed tower with 18 theoretical plates. The outlet gas at the top of the alkyl oxalate absorption tower is passed through the feed and discharge heat exchanger and the waste boiler of the waste heat recovery unit to recover the latent heat and sensible heat in the product, and the by-product 0.5MPaG steam is sent to the whole The steam pipe network of the plant; then it enters the condensation cooling and gas-liquid separation unit, and is cooled to 40-60℃ by a water cooler, and then the gas-liquid separation is carried out to obtain gas phase components and liquid phase products. The gas phase component is mainly carbon monoxide and discharged from the device for recycling. The content of the target product alkyl carbonate in the liquid phase product is 98.2wt%, and the rest is the by-product generated by the decarbonylation reaction, which does not contain the raw material alkyl oxalate; a small amount of liquid phase product returns to the top of the alkyl oxalate absorption tower as reflux, and the remaining liquid phase products enter the subsequent alkyl carbonate distillation system, and the mass ratio of reflux to production is 0.08. The side sampling port of the product tower is located at the 45th theoretical plate above the feed port. The side sampling port directly obtains the high-grade alkyl carbonate product, which is cooled to 40℃ by a water cooler and sent to the high-grade alkyl carbonate storage tank. The product tower kettle is equipped with a thermal siphon reboiler, and the reboiler uses 1.5MPaG saturated steam as a heat source. The product tower kettle is a heavy component, which returns to the decarbonylation reactor for re-reaction.

[0062] Embodiment 2:

[0063] The method described in Example 1 is the same, except that the raw material is diethyl oxalate (DEO), and the decarbonylation reaction produces diethyl carbonate (DEC) and carbon monoxide. The catalyst is activated carbon loaded with cesium carbonate, wherein the cesium carbonate content is 8wt% and the specific surface area of ​​the activated carbon is 1400m 2 / g. The decarbonylation reaction temperature is 225°C and the reaction pressure is 0.4MPaG. The theoretical number of plates of the alkyl oxalate absorption tower is 15, and the mass ratio of the reflux volume to the withdrawal volume is 0.12.

[0064] The alkyl carbonate distillation system adopts a single-tower distillation process, and the DEC product is directly withdrawn from the side sampling port, which is located at the 40th theoretical plate above the feed inlet.

[0065] Comparative Example 1:

[0066] According to the method described in Example 1, the difference is that DMO is heated to 60°C and enters the decarbonylation reactor in a molten state, the decarbonylation reaction temperature is reduced to 100°C, the reaction pressure is 0.15MPaG, and the alkyl oxalate absorption tower directly connected to the decarbonylation reactor is cancelled; the catalyst uses a carbonyl rhodium catalyst, and at this reaction temperature and reaction pressure, the reaction raw material DMO and the target product DMC are both in a liquid phase state, and the reaction gas and reaction liquid obtained by the decarbonylation reaction, wherein the reaction gas components are CO and a small amount of DMO and DMC entrained, and the reaction liquid is the target product. Due to the limitations of residence time and reaction kinetics, the DMC content in the reaction liquid is only 35wt%, and the rest is mainly unreacted DMO. The above-mentioned reaction gas cannot be recovered from waste heat, and can only be sent to the DMC distillation system for distillation separation after cooling and gas-liquid separation to obtain a superior grade DMC product.

[0067] The key parameters of the method for preparing alkyl carbonate by decarbonylation of alkyl oxalate are shown in Table 1.

[0068] Table 1

[0069]

[0070] exist Figure 3 and Figure 4In the invention, the basket filter device comprises an outer frame 1, a sealing cover 2 is arranged on the top of the outer frame 1, a discharge port 3 is arranged on one side of the bottom surface of the outer frame 1, a first filter plate 4 and a second filter plate 5 are arranged inside the outer frame 1, the first filter plate 4 is at the top of the second filter plate 5, a vertical bar 6 is arranged on the inner side wall of the circumference of the outer frame 1, and the circumferential sides of the first filter plate 4 and the second filter plate 5 are both provided with grooves 7 corresponding to and matching the vertical bars 6, the first filter plate 4 is arranged in a truncated cone shape, the second filter plate 5 is arranged horizontally, the aperture of the leakage hole on the surface of the second filter plate 5 is smaller than the aperture of the surface of the first filter plate 4, and a rotating rod 8 is arranged at the center of the first filter plate 4 and the second filter plate 5, and the rotating rod 8 is arranged at the center of the first filter plate 4 and the second filter plate 5. The bottom end of the rod 8 passes through the center of the bottom surface of the outer frame 1, the top end of the rotating rod 8 passes through the center of the top surface of the cover 2, and the rotating rod 8 is spirally matched with the center of the first filter plate 4. The top and bottom of one side of the outer frame 1 are respectively provided with a liquid inlet 9 and a liquid outlet 10, the inner end of the liquid inlet 9 corresponds to the top of the first filter plate 4, and the inner end of the liquid outlet 10 corresponds to the bottom of the second filter plate 5. A plurality of rotating rings 11 are equidistantly arranged in an annular shape on the inner bottom surface of the outer frame 1. The plurality of rotating rings 11 are annularly located on the outside of the rotating rod 8, and the surface of the rotating ring 11 is tightly fitted with the surface of the rotating rod 8. The rotating ring 11 is rotatably matched with the rotating rod 8 by means of a fixing rod 12, and the bottom end of the fixing rod 12 is fixedly connected to the inner bottom surface of the outer frame 1. When the catalyst needs to be filtered out, the liquid material in the decarbonylation reactor is passed into the basket filter device, and the liquid material carrying the catalyst is passed into the outer frame 1 through the liquid inlet 9. The liquid material will pass through the first filter plate 4 and the second filter plate 5 in turn, and the catalyst in the liquid material is filtered out by using the first filter plate 4 and the second filter plate 5. After the filtered liquid material falls on the bottom of the inner side of the outer frame 1, the liquid material flows out through the liquid outlet 10, and the first filter plate 4 and the second filter plate 5 are used to perform double filtration on the liquid material, thereby ensuring the separation of the liquid material and the solid catalyst.

[0071] When the liquid material is filtered using the first filter plate 4 and the second filter plate 5, the discharge port 3 needs to be blocked, and the filtered liquid material falls into the inner part of the outer frame 1. At this time, the fine materials that cannot be filtered in the liquid material will gradually accumulate at the inner bottom of the outer frame 1. When the filtration of the liquid material is completed, the discharge port 3 is used for water backwashing to discharge the fine materials accumulated inside the outer frame 1, thereby ensuring the cleanliness of the outer frame 1.

[0072] exist Figure 4 and Figure 5In the figure, a plurality of vertical rods 13 are fixedly connected to the bottom surface of the first filter plate 4, and the bottom ends of the vertical rods 13 penetrate the surface of the second filter plate 5. A spring 14 is sleeved on the surface of the vertical rods 13. Slides 15 are provided on both sides of the bottom of the second filter plate 5. The two slides 15 are arranged opposite to each other, and the slides 15 slide with the vertical bars 6. Both sides of the slides 15 are rotatably connected to the top of the rotating plate 16, and the bottom end of the rotating plate 16 is rotatably connected to the sliding frame 17. Two parallel corresponding cross frames 18 are provided on the inner side of the outer frame 1, and the slides 15 are slidably sleeved on the surface of the cross frames 18, and the two opposite slides 15 are correspondingly connected by elastic plates 19. After the liquid material is filtered by the first filter plate 4 and the second filter plate 5, the catalyst gradually accumulates on the top surfaces of the first filter plate 4 and the second filter plate 5, and the rotating rod 8 is rotated. The rotating rod 8 rotates inside the outer frame 1 by means of the rotating ring 11 and the cover 2. The rotation of the rotating rod 8 and the spiral effect of the first filter plate 4 make the first filter plate 4 move down inside the outer frame 1. When the first filter plate 4 slides on the surface of the vertical bar 6 by means of the groove 7, the first filter plate 4 drives the second filter plate 5 to move down synchronously by means of the spring 14. When the second filter plate 5 drives the slide 15 to move down, the slide 15 drives the top of the rotating plate 16 to move down. When the rotating plate 16 rotates, the rotating plate 16 The bottom end of plate 16 drives the sliding frame 17 to slide on the surface of the cross frame 18. The two relative sliding frames 17 gradually approach each other during the sliding process, and the two sliding frames 17 gradually squeeze the elastic plate 19. The downward movement speed of the second filter plate 5 decreases. At this time, the first filter plate 4 gradually approaches the second filter plate 5. When the first filter plate 4 and the second filter plate 5 approach each other, they gradually squeeze the solid catalyst between the two, which is convenient for squeezing out the liquid material remaining on the surface of the solid catalyst. If the solid catalyst is a flocculent material, the extrusion of the first filter plate 4 and the second filter plate 5 can ensure the drying effect of the solid catalyst between the two.

[0073] The present invention also provides a device for preparing alkyl carbonate from alkyl oxalate, comprising a decarbonylation reactor, a catalyst feeding system, a catalyst recovery and separation system, a waste heat recovery system and an alkyl carbonate distillation system;

[0074] The decarbonylation reactor is used for the raw material alkyl oxalate to undergo a decarbonylation reaction with a catalyst at a certain temperature and pressure to produce alkyl carbonate, carbon monoxide and a small amount of by-products; wherein the decarbonylation reactor is also provided with an alkyl oxalate absorption tower directly connected thereto, for absorbing and separating the alkyl oxalate in the reaction product;

[0075] The catalyst feeding system adopts gas or liquid transportation, the medium of gas transportation is nitrogen or carbon monoxide, and the medium of liquid transportation is raw material alkyl oxalate or product alkyl carbonate, preferably alkyl carbonate;

[0076] The catalyst recovery and separation system is used to separate and recover the deactivated catalyst from the liquid material in the decarbonylation reactor; the catalyst is loaded in the catalyst cage, the catalyst can be continuously or intermittently extracted and replenished, the separated liquid material is returned to the decarbonylation reactor, and the spent catalyst is recovered and processed, the recovery and separation system is a basket filter device, a filter press device or a suction filter device, preferably a basket filter device;

[0077] The waste heat recovery system is used to recover the waste heat of the gas phase product obtained by the decarbonylation reactor, including a waste boiler and an inlet and outlet heat exchanger. The waste boiler can produce 0.5-1.5MPaG grade steam as a by-product. The waste heat recovery system can recover the latent heat and sensible heat contained in the gas phase product to the greatest extent, thereby reducing the steam consumption of the device;

[0078] The alkyl carbonate distillation system is simplified to a single-tower distillation process, wherein the liquid product enters the alkyl carbonate distillation tower, the light component is separated from the tower top, the alkyl carbonate product is obtained from the side outlet, and the heavy component in the tower bottom is returned to the decarbonylation reactor for further reaction.

[0079] The alkyl carbonate distillation system also includes auxiliary equipment of the alkyl oxalate distillation tower, including but not limited to an overhead condenser, an overhead reflux tank, a side sampling tank, a reboiler, a reflux pump and other auxiliary equipment.

[0080] The method of the present invention uses alkyl oxalate as a raw material to produce alkyl carbonate with high added value. The greatest advantage is that when the alkyl oxalate is decarbonylated to produce the target product, the alkyl carbonate content in the obtained crude alkyl carbonate product can reach more than 97.5wt%, and the target product content is relatively high, which can greatly reduce the steam consumption in the subsequent distillation process, thereby reducing the variable cost. The method of the present invention is a continuous reaction with a short process flow. Taking the decarbonylation of dimethyl oxalate to produce dimethyl carbonate as an example, the method of the present invention can fully utilize the huge domestic dimethyl oxalate production capacity with low cost, and has excellent practicality and economy.

[0081] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing alkyl carbonate from alkyl oxalate, characterized in that: The following steps are involved: S1. Preheat the raw material alkyl oxalate and then enter the decarbonylation reactor. Under the conditions of 190-230° C. and 0.1-0.9 MPaG, the raw material alkyl oxalate is contacted with the catalyst to undergo a decarbonylation reaction to produce alkyl carbonate, carbon monoxide and a small amount of by-products. The generated products are all discharged from the decarbonylation reactor in a gas phase state and enter an alkyl oxalate absorber directly connected to the reactor. The gas phase at the top outlet of the alkyl oxalate absorber is subjected to waste heat recovery, condensation cooling and gas-liquid separation to obtain gas phase components and liquid phase products. The gas phase component is mainly carbon monoxide and discharged from the device for recycling. The content of the target product alkyl carbonate in the liquid phase product exceeds 97.5wt%, and the rest is by-products generated by the decarbonylation reaction. A small part of the obtained liquid phase product is returned to the top of the alkyl oxalate absorber as an absorption medium, and the rest of the liquid phase product enters the subsequent alkyl carbonate distillation system; S2. The alkyl carbonate distillation system is simplified to a single-tower distillation process. The liquid product enters the alkyl carbonate distillation tower, the light component is separated from the top of the tower, and the alkyl carbonate product is obtained from the side outlet. The heavy component in the bottom of the tower is returned to the decarbonylation reactor to continue the reaction; The decarbonylation reactor is a kettle reactor with a stirring and heating module. The heating module of the decarbonylation reactor is in the form of a built-in plate group, a coil or a jacket. The built-in plate group consists of one or more groups of plates. The built-in plate groups are arranged in parallel in a vertical direction, and the angle with the tangent direction of the outer surface of the decarbonylation reactor is 15-90°; each plate group in the built-in plate group consists of two plates, and the spacing between the two plates is 5-80mm; the plate width is 100-800mm; Steam is introduced between the two plates of each built-in plate group as a heat source for decarbonylation reaction, the steam pressure level is 1.5-3.8MPaG, and the stirring form of the decarbonylation reactor is paddle type, propeller type, turbine type, anchor type, frame type; The catalyst is loaded in a catalyst cage, which has a structural framework with supporting strength inside and is covered with a wire mesh or grid outside. The reaction raw materials and products can freely enter and exit the catalyst cage to contact and react with the catalyst, while the catalyst cannot enter the reactor through the wire mesh or grid covering the outside of the catalyst cage. The catalyst cage is cylindrical and vertically installed. The upper part of the catalyst cage passes through the upper end surface of the decarbonylation reactor and is connected to the catalyst feeding system; the lower part of the catalyst cage passes through the lower end surface of the decarbonylation reactor and is connected to the catalyst recovery and separation system; the catalyst can be continuously or intermittently extracted and replenished, so that the decarbonylation reactor can react continuously; The catalyst feeding system adopts gas delivery or liquid delivery, the gas delivery medium is nitrogen or carbon monoxide, and the liquid delivery medium is raw material alkyl oxalate or target product alkyl carbonate; The function of the catalyst recovery and separation system is to separate the spent catalyst particles from the liquid material in the decarbonylation reactor, and return the separated liquid material to the decarbonylation reactor for recovery and treatment of the spent catalyst; the recovery and separation system is a basket filter device; The catalyst is a supported catalyst, including a support and an alkali metal carbonate, wherein the alkali metal carbonate loading is 5-15wt%, the alkali metal carbonate is one of sodium carbonate, potassium carbonate, cesium carbonate or a mixture thereof, and the support has a specific surface area greater than 1300m 2 / g of activated carbon; The basket filter device comprises an outer frame (1), a cover (2) is arranged on the top of the outer frame (1), a discharge port (3) is arranged on one side of the bottom surface of the outer frame (1), a first filter plate (4) and a second filter plate (5) are arranged inside the outer frame (1), the first filter plate (4) is located on the top of the second filter plate (5), a vertical bar (6) is arranged on the inner circumferential side wall of the outer frame (1), and grooves (7) corresponding to the vertical bar (6) are arranged on the circumferential sides of the first filter plate (4) and the second filter plate (5), the first filter plate (4) is arranged in a truncated cone shape, the second filter plate (5) is arranged horizontally, the aperture of the leakage hole on the surface of the second filter plate (5) is smaller than the aperture of the surface of the first filter plate (4), and a rotating rod (8) is arranged at the center of the first filter plate (4) and the second filter plate (5), and the rotating rod (8) 8) the bottom end of which passes through the center of the bottom surface of the outer frame (1), the top end of the rotating rod (8) passes through the center of the top surface of the cover (2), and the rotating rod (8) is spirally matched with the center of the first filter plate (4), the top and bottom of one side of the outer frame (1) are respectively provided with a liquid inlet (9) and a liquid outlet (10), the inner end of the liquid inlet (9) corresponds to the top of the first filter plate (4), and the inner end of the liquid outlet (10) corresponds to the bottom of the second filter plate (5), a plurality of rotating rings (11) are equidistantly arranged in an annular manner on the inner bottom surface of the outer frame (1), the plurality of rotating rings (11) are annularly located outside the rotating rod (8), and the surface of the rotating ring (11) is tightly fitted with the surface of the rotating rod (8), the rotating ring (11) is rotatably matched with the rotating rod (8) by means of a fixing rod (12), and the bottom end of the fixing rod (12) is fixedly connected to the inner bottom surface of the outer frame (1); The bottom surface of the first filter plate (4) is fixedly connected to a plurality of vertical rods (13), the bottom ends of the vertical rods (13) penetrate the surface of the second filter plate (5), the surface of the vertical rods (13) is sleeved with a spring (14), and both sides of the bottom of the second filter plate (5) are provided with slides (15), the two slides (15) are arranged opposite to each other, the slides (15) and the vertical bars (6) are slidably matched, both sides of the slides (15) are rotatably connected to the top of a rotating plate (16), the bottom end of the rotating plate (16) is rotatably connected to a sliding frame (17), and two parallel corresponding horizontal frames (18) are arranged on the inner side of the outer frame (1), and the slides (15) are slidably sleeved on the surface of the horizontal frame (18), and the two opposite slides (15) are correspondingly connected by an elastic plate (19).

2. The method for preparing alkyl carbonate from alkyl oxalate according to claim 1, characterized in that: At the above reaction temperature and pressure, the products obtained by decarbonylation of alkyl oxalate are all in gas phase. The gas phase products enter the alkyl oxalate absorption tower directly connected to the reactor for absorption and separation, and then the waste heat is recovered. The waste heat recovery includes a waste boiler and an inlet and outlet heat exchanger. The waste boiler can produce 0.5-1.5MPaG grade steam as a by-product, thereby recovering the latent heat contained in the gas phase products to the greatest extent and reducing steam consumption.

3. The method for preparing alkyl carbonate from alkyl oxalate according to claim 1, characterized in that: The alkyl oxalate absorption tower is a packed tower or a plate tower with a theoretical plate number of 2-22, and the mass ratio of the reflux amount of the liquid phase product returning to the top of the alkyl oxalate absorption tower to the output amount of the alkyl carbonate distillation system is 0.05-0.2; The operating pressure of the alkyl carbonate distillation tower is 0-50 KPaG, the alkyl carbonate distillation tower is a packed tower or a plate tower, and the side outlet of the alkyl carbonate distillation tower is located above the feed inlet, with a distance of 20-60 theoretical plates; The molecular formula of the alkyl oxalate is R1-O-COCO-O-R2, wherein R1 and R2 are alkyl groups with 1 to 4 carbon atoms; the molecular formula of the alkyl carbonate is R1-O-CO-O-R2, wherein R1 and R2 of the alkyl oxalate are the same as R1 and R2 of the alkyl carbonate.

Images