Fixed bed reaction process for continuously producing dimethyl carbonate

Abstract

The invention relates to a reaction process for continuously producing dimethyl carbonate, which takes carbon monoxide, oxygen and methanol as main reaction raw materials, and is characterized by comprising the following steps: mixing and preheating the reaction raw materials, feeding the reaction raw materials into a fixed bed reactor, carrying out oxidative carbonylation reaction under the reaction conditions of 90-160 DEG C and 0.5-5.0 MPa to generate dimethyl carbonate, cooling the reaction product, and carrying out gas-liquid separation, a liquid-phase dimethyl carbonate crude product is obtained. The dimethyl carbonate crude product is further rectified, separated and purified to obtain a dimethyl carbonate product meeting the industrial purity requirement, and meanwhile, separated methanol which does not participate in the reaction and a gas-phase component obtained by gas-liquid separation of a reaction product are used as reaction raw materials and are returned to the reactor for continuous reaction. The reaction process provided by the invention has the advantages of high selectivity and space-time yield of dimethyl carbonate, good catalyst activity and stability, continuous and stable reaction process and the like.

Description

Technical Field

[0001] The invention belongs to the field of chemical catalytic synthesis, and relates to a process for synthesizing dimethyl carbonate by using carbon monoxide, oxygen and methanol as raw materials, specifically a fixed bed reaction process for continuously producing dimethyl carbonate by using carbon monoxide, oxygen and methanol as main reaction raw materials. Background Art

[0002] Dimethyl carbonate (DMC) is a widely used, low-toxic, environmentally friendly, green and safe chemical raw material, which is widely used in the preparation of high-performance resins, dye intermediates, drugs, coatings, power battery electrolytes and fuel additives. At present, the synthesis methods of dimethyl carbonate mainly include phosgene method, ester exchange method, urea alcoholysis method and oxidative carbonylation method. Among them, the oxidative carbonylation method includes methanol gas phase oxidative carbonylation method and methanol liquid phase oxidative carbonylation method.

[0003] The technology of producing dimethyl carbonate by methanol gas phase oxidation carbonylation is relatively mature and has been widely studied. This method mainly involves first allowing the raw materials methanol, O2 and NO to enter the catalyst bed in gas phase, generating methyl nitrite under the catalytic action, and then reacting with CO under the action of the catalyst to generate dimethyl carbonate. At the same time, the generated NO is separated and purified from the tail gas and recycled. This method uses a two-step gas phase reaction, NO is recycled, chloride salt is used as a catalyst, and the main by-product is dimethyl oxalate. This method has the problems of complex reaction process, difficulty in closed-loop circulation of NO, poor heat and mass transfer, catalyst corrosion equipment, rapid deactivation, short service life, etc., and low methanol conversion rate and DMC space-time yield, and high production cost.

[0004] At present, many researchers are committed to the research of direct liquid phase oxidation carbonylation of methanol to synthesize dimethyl carbonate. Bubble tower reactor or stirred tank reactor is mainly used. The catalyst is dissolved or suspended in the reactor. Methanol is preheated and fed in liquid form. CO and O2 mixed gas are preheated and bubbled into the reactor. Under the action of the catalyst, a reaction occurs to generate dimethyl carbonate. The product is discharged with the tail gas. After gas-liquid cooling and separation, the liquid phase product is further distilled and separated to obtain a dimethyl carbonate product that meets the quality requirements. Unreacted methanol and gas are further circulated into the reactor. In this process, methanol reacts directly with CO and O2 to generate dimethyl carbonate in one step. The process is simple and the cost is low. However, the disadvantage is that the back mixing phenomenon in the bubbling bed reactor is very serious, the reaction efficiency is low, and the product is taken out of the reactor with the gas phase, resulting in a large gas phase flow rate, a large gas circulation volume, a large amount of low-boiling methanol in the crude product, and high subsequent separation energy consumption. In addition, the selectivity of CO conversion to dimethyl carbonate is low, and a large amount of CO raw material is consumed. This process uses chloride-containing copper salt as a catalyst. Not only is it difficult to separate the catalyst, but the presence of chloride ions during the reaction causes serious problems of equipment corrosion and catalyst deactivation. The use of special materials resistant to chloride ion corrosion is costly, which greatly limits the application of this process. Summary of the invention

[0005] In order to overcome the problems that the existing methanol gas phase oxidation carbonylation method for producing dimethyl carbonate has a complicated process, the use of environmentally unfriendly NO gas circulation increases energy consumption, and the production efficiency is low, while the methanol direct liquid phase oxidation carbonylation method for producing dimethyl carbonate has a simple process, but has the problems of difficulty in catalyst separation, chloride ion corrosion equipment, high production device manufacturing cost, high product separation energy consumption, high production cost, etc. The present invention provides a fixed bed reaction process for continuously producing dimethyl carbonate.

[0006] In order to achieve the above object, the present invention adopts carbon monoxide, oxygen and methanol as raw materials to continuously produce dimethyl carbonate in a fixed bed reaction process, and the process steps are as follows:

[0007] S1: Loading a proper amount of granular supported metal catalyst into the reactor, and then starting preheating to preheat the catalyst to a reaction temperature of 90-160°C;

[0008] S2: After the raw material liquid is preheated, it is passed into the reactor from the raw material feeding port at the top of the reactor at a certain flow rate. At the same time, after the raw material gas is preheated, it is passed into the reactor from the raw material gas inlet at the top of the reactor; the raw material liquid is industrial methanol, and the raw material gas is a mixed gas composed of CO and O2.

[0009] S3: The raw gas and the raw liquid pass through the supported metal catalyst bed from top to bottom to carry out a gas-liquid-solid three-phase reaction, and a certain reaction temperature and a certain reaction pressure are controlled;

[0010] S4: The reaction product is discharged from the bottom of the reactor, and after condensation and gas-liquid separation, the obtained liquid product is a crude dimethyl carbonate product; the obtained gas product is used as a circulating gas, purified and compressed, and mixed with the raw gas and returned to the reactor to continue the reaction;

[0011] S5: The crude dimethyl carbonate product is further separated by distillation to obtain a dimethyl carbonate product that meets industrial purity requirements; the separated unreacted methanol is mixed with the raw material liquid and recycled, and finally all the methanol is converted.

[0012] The fixed-bed reaction process for continuously producing dimethyl carbonate is further characterized in that the supported metal catalyst is expressed as M / S, M is the active component, S is the carrier, and the loading amount of the active component is 5 to 15%; wherein M is any one or more of Cu, Zn, Co, Pd, and Rh, and S is any one or more of porous carbon, Al2O3, Al2O3-SiO2, and molecular sieve materials.

[0013] The fixed bed reaction process for continuous production of dimethyl carbonate is characterized in that the unreacted methanol solution separated from the liquid phase product is mixed with the raw material methanol to form a reaction raw material liquid, and the liquid phase volume space velocity for the catalyst is 0.5h -1 ~10h -1 .

[0014] The fixed bed reaction process for continuously producing dimethyl carbonate is characterized in that the circulating gas separated from the reaction tail gas is mixed with the raw gas to form the reaction raw gas, and the gas volume space velocity for the catalyst is 250h -1 ~5000h -1 .

[0015] The fixed bed reaction process for continuously producing dimethyl carbonate is further characterized in that the reaction temperature in the reactor is 90-160° C. and the reaction pressure is 0.5 MPa-5.0 MPa.

[0016] The fixed-bed reaction process for continuously producing dimethyl carbonate is further characterized in that when the reaction unit is started up, the raw material liquid is methanol; after the production of the reaction unit is stable, the unreacted methanol solution separated from the liquid product and the raw material methanol are mixed to form a reaction liquid, which is a mixture of methanol, dimethyl carbonate and water, and the mass ratio thereof is 70-100:0-15:0-10.

[0017] The fixed-bed reaction process for continuously producing dimethyl carbonate is further characterized in that when the reaction unit is started up, the raw gas is a mixture of CO and O2; after the production of the reaction unit is stable, the tail gas obtained by cooling and separating the product is purified and compressed and then mixed with the raw gas, and the mixed gas composed of CO, CO2 and O2 is used as the reaction gas, and the volume ratio thereof is 65-95:0-30:1-20.

[0018] Furthermore, the fixed bed reaction process for continuously producing dimethyl carbonate is characterized in that the reactor is a fixed bed reactor, and the bed layer is composed of solid particle catalysts.

[0019] Furthermore, the fixed bed reaction process for continuously producing dimethyl carbonate is characterized in that the fixed bed reactor is a tubular reactor, and a temperature sensor and a pressure sensor are arranged in the tubular reactor.

[0020] Furthermore, the fixed-bed reaction process for continuously producing dimethyl carbonate is characterized in that the temperature sensor is a thermocouple or a thermal resistor temperature sensor; the pressure sensor is any one of a pointer pressure gauge, a digital pressure gauge or a pressure sensor.

[0021] Compared with the prior art, the present invention has the following significant technical advances:

[0022] (1) The present invention fully absorbs the advantages of the existing methanol gas phase oxidation carbonylation method and the methanol liquid phase oxidation carbonylation method, and on this basis, proposes a novel fixed bed reaction process for the continuous production of dimethyl carbonate. Compared with the existing methanol gas phase oxidation carbonylation method, the reaction process of the present invention adopts a one-step direct reaction of oxidation carbonylation, which reduces the operation process, simplifies the production process, and reduces energy consumption and production costs. Compared with the existing methanol liquid phase oxidation carbonylation method, the reaction process of the present invention adopts a continuous fixed bed reaction process, and there is almost no back-mixing problem in the reactor, the production operation is stable, the dimethyl carbonate content in the crude product is high, the tail gas circulation is less, the production efficiency is high, and the use of chlorine-free supported catalysts does not cause deactivation of the catalyst and equipment corrosion due to the loss of chloride ions, and there is no catalyst separation problem, etc., and the production energy consumption is low, and the cost of product separation and refining is low.

[0023] (2) The reaction process of the present invention is easy to operate, can be continuously fed and discharged, uses chlorine-free catalyst particles with a wide diameter range, a small amount, low wear, and a fluid flow close to a piston flow. The production efficiency is very high, and a higher reaction conversion rate and selectivity can be obtained. In addition, the reaction liquid and gas space velocity is large, which effectively inhibits a series of side reactions and improves product selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1The figure is a schematic diagram of a specific reaction process device of the reaction process of the present invention.

[0025] Markings in the figure are: 1-first preheater, 2-second preheater; 3-reactor; 4-condenser; 5-gas-liquid separator; 6-circulation compression equipment; 7-distillation separation equipment; 8-liquid circulation pump. DETAILED DESCRIPTION

[0026] The concept and technical solution of the present invention are described in detail below through a specific implementation method of the reaction process of the present invention and a corresponding reaction process device diagram.

[0027] like Figure 1 As shown, first, the granular supported metal catalyst is loaded into the fixed bed reactor 3, then the first preheater 1 and the second preheater 2 are opened, and the supported metal catalyst in the reactor 3 is preheated to a reaction temperature of 90 to 160°C. Then, the upper feed port control valve of the reactor 3 is opened, and the raw gas fully mixed with the circulating gas compressed by the circulating compression device 6 and the 0.5MPa to 5.0MPa high-pressure CO raw gas, high-pressure O2 raw gas and gas phase products is preheated to a reaction temperature of 90 to 160°C by the first preheater 1 and then enters the reactor 3 from the reactor 3 feed port. At the same time, the raw liquid methanol and the light components at the top of the tower separated by rectification of the liquid phase product are fully mixed with the circulating reaction liquid pressurized by the liquid circulation pump 8, and are preheated to a reaction temperature of 90 to 160°C by the second preheater 2 as the raw liquid, and are added to the reactor 3 from the upper raw liquid feed port of the fixed bed reactor 3 at a certain flow rate. The methanol and CO / O2 in the raw gas and raw liquid undergo oxidative carbonylation reaction under the action of a supported metal catalyst in the reactor 3 at a temperature of 90 to 160°C and a pressure of 1MPa to 10MPa to generate dimethyl carbonate product. The gas-liquid mixed product formed after the reaction is discharged from the lower discharge port of the reactor 3, cooled and condensed by the condenser 4, and enters the gas-liquid separator 5 to obtain the top gas phase product and the bottom liquid phase product. The top gas phase product mainly contains CO, CO2 and O2, which are pressurized to 0.5MPa to 5.0MPa by the circulating compression device 6, and then fully mixed with the raw gas CO and O2. After being preheated to 90 to 160°C by the first preheater 1, it enters the reactor 3 again to react to synthesize dimethyl carbonate. The liquid phase product discharged from the gas-liquid separator 5 enters the distillation separation device 7, and after separation, a dimethyl carbonate product that meets the quality requirements is obtained. The liquid phase heavy components mainly composed of process water are discharged from the bottom of the tower, while the liquid phase light components mainly composed of unreacted methanol discharged from the top of the tower are pressurized by the liquid circulation pump 8, fully mixed with the raw methanol liquid and preheated to 90-160°C, and then enter the reactor 3 again as the reaction liquid to participate in the catalytic chemical reaction to achieve a continuous circulation reaction.

[0028] In the reaction process of the present invention, the sulfur content of CO raw gas and O2 raw gas is required to be less than 1 mg / m 3 , and fully mixed with the reaction circulating gas to form a uniformly mixed reaction gas, wherein the volume ratio of CO, CO2 and O2 is 65-95:0-30:1-20. The methanol raw material liquid is industrial grade methanol with a sulfur content of less than 1 mg / m 3 , fully mixed with the reaction circulating liquid to form a uniformly mixed reaction liquid, wherein the mass ratio of methanol, dimethyl carbonate and water is 70-100:0-15:0-10. The reaction temperature in reactor 3 is maintained at 90-160°C, and the reaction pressure in reactor 3 is adjusted to 0.5MPa-5.0MPa. The reaction gas and reaction liquid pass through the supported metal catalyst bed from top to bottom to carry out a gas-liquid-solid three-phase reaction. The gas phase space velocity of the reaction gas is controlled to be 250-5000h -1 The liquid phase space velocity of the reaction liquid is controlled to be 0.5~10h -1 , in order to ensure the continuity and stability of the entire production process.

[0029] It should be noted that, in the initial stage of the operation of the device, the raw material liquid adopts industrial-grade methanol liquid feed, and after the reaction device is stably operated, the mixture of the light component methanol, dimethyl carbonate and water separated by the liquid product distillation and the mixture of industrial-grade methanol liquid is used as liquid feed, so that the methanol that does not participate in the reaction is circulated and fed, and finally a 100% conversion rate of methanol is achieved. At the same time, in the initial stage of the operation of the device, the raw gas of this reaction process adopts industrial-grade CO and O2, and the gas feed is mixed and preheated. After the reaction device is stably operated, the CO / CO2 / O2 circulating gas separated and compressed by the reaction tail gas product and the raw gas industrial-grade CO and O2 mixed material are used as gas feed, so that the gas that does not participate in the reaction can be circulated back to the reaction system to continue the reaction, and finally a high conversion rate of the effective components of the gas is achieved. In addition, in the reaction process device of the present invention, during the circulation compression process of the gas phase product, it may be necessary to further purify and separate, release part of the purge gas, and reach gas equilibrium. The distillation and separation equipment of the liquid product preferably adopts an azeotropic distillation separation device, and the parameter performance of the equipment is determined according to the separation requirements.

[0030] The following further describes the implementation of the present invention in detail through specific examples. It should be noted that the protection scope of the present invention is not limited to the description of the examples of the present invention.

[0031] [Example 1]

[0032] In this embodiment, the reactor adopts a fixed bed reactor, and methanol, CO and O2 are used as raw materials for reaction. The gas phase and liquid phase circulating materials separated by cooling and condensation of the product are not circulated. First, the Cu / C copper-based activated carbon catalyst is loaded in the catalyst bed of the reactor 3 and preheated to 120°C. The methanol raw material liquid is sent into the second preheater 2 through the raw material liquid delivery pump at a certain flow rate and preheated to 120°C, and then continuously added to the reactor 3 through the raw material liquid feeding port at the top of the reactor 3. At the same time, carbon monoxide and oxygen with a volume ratio of 95:5 are fully mixed, and introduced into the reactor 3 from the raw material gas inlet at the top of the reactor 3, and dimethyl carbonate synthesis reaction is carried out under the action of the catalyst. During the reaction process, the volume space velocity of the methanol raw material liquid in the reactor is controlled to be 0.5h -1 The gas volume space velocity of the mixed gas is 250h -1 The reaction pressure in the reactor 3 is maintained at about 2.5 MPa by adjusting the pressure regulator, and the temperature control regulator is adjusted to stabilize the catalyst bed temperature at 120°C. The reacted material is discharged from the discharge port at the bottom of the reactor 3, and then after condensation and gas-liquid separation, the obtained liquid product is the crude dimethyl carbonate product, and the gas product is the reaction cycle tail gas.

[0033] The products were collected and the molar compositions of the liquid products and gas products were analyzed by gas chromatograph. According to the test data, the conversion rate C of methanol was calculated to be 13.5%, the selectivity S1 of dimethyl carbonate based on methanol conversion was 99.6%, and the selectivity S2 of dimethyl carbonate product based on CO conversion was 95.6%.

[0034] [Example 2]

[0035] The difference between this embodiment and embodiment 1 is that the reaction process uses Rh / SiO2 catalyst, and the CO:O2 in the raw gas is different, so the reaction process space velocity and reaction condition parameter settings are slightly different. The reaction process operation steps are exactly the same as those in embodiment 1. The specific reaction condition parameter control and product results are shown in Table 1. [Example 3]

[0036] In this embodiment, the reactor adopts a fixed bed reactor, and the gas phase and liquid phase circulating materials separated by the product cooling and condensation are mixed with the raw materials and then mixed and fed. First, the Cu / C copper-based activated carbon catalyst is loaded in the catalyst bed of the reactor 3 and preheated to 140°C. The methanol solution raw material liquid is sent into the second preheater 2 through the raw material liquid delivery pump at a certain flow rate and preheated to 140°C, and then continuously added to the reactor 3 through the raw material liquid feeding port at the top of the reactor 3. At the same time, the reaction gas with a volume ratio of 95:5 of carbon monoxide and oxygen fully mixed is passed into the reactor 3 from the raw material gas inlet at the top of the reactor 3, and the reaction gas and reaction liquid are subjected to dimethyl carbonate synthesis reaction in the reactor 3. The reaction pressure in the reactor 3 is maintained at about 5.0MPa by adjusting the pressure regulator, and the temperature control regulator is adjusted to stabilize the catalyst bed temperature at 140°C. The reacted material is discharged from the discharge port at the bottom of the reactor 3, and then after condensation and gas-liquid separation, the obtained liquid product is the crude dimethyl carbonate product, and the gas product is the reaction cycle tail gas.

[0037] The liquid product is separated by distillation to obtain dimethyl carbonate product, heavy components at the bottom of the tower (mainly process water) and light components at the top of the tower (mainly unreacted methanol). The light components at the top of the tower and the methanol raw liquid are fully mixed and preheated to the reaction temperature of 140°C. The reaction liquid is formed, and its mass composition is controlled to be methanol: dimethyl carbonate: water = 90:5:5, and the liquid space velocity is controlled to be 3h -1 .

[0038] The main components of the gas product are CO / CO2 / O2. After compression and purification, it is fully mixed with CO raw gas and O2 raw gas and preheated to the reaction temperature of 140°C to form a reaction gas. The volume composition is controlled to be CO:CO2:O2=90:5:5, and the space velocity is 2000h -1 .

[0039] The molar composition of the liquid product and the gas product was analyzed by gas chromatograph. According to the detection and analysis data, the conversion rate C of methanol was calculated to be 16.1%, the selectivity S1 of dimethyl carbonate based on methanol conversion was 96.1%, and the selectivity S2 of dimethyl carbonate product based on CO conversion was 92.4%.

[0040] [Example 4] to [Example 13]

[0041] The difference between Examples 4 to 13 and Example 3 is that different catalysts are used in the reaction process, CO:CO2:O2 in the reaction gas is different, and the mass ratios of methanol, dimethyl carbonate and water in the reaction liquid are different, so the reaction process space velocity and reaction condition parameter settings are slightly different. The reaction process operation steps are exactly the same as in Example 3. The specific reaction condition parameter control and product results are shown in Table 1.

[0042] Table 1 Example reaction conditions control and experimental results

[0043]

[0044] Note: In Table 1, M represents gas feed; N represents liquid feed; D represents dimethyl carbonate; W represents water; C represents methanol; S1 represents the selectivity of dimethyl carbonate based on methanol conversion; S2 represents the selectivity of dimethyl carbonate based on CO conversion; M:D:W mass ratio represents the mass ratio of methanol, dimethyl carbonate and water

[0045] The above embodiments are only for further explanation of the present invention and are not intended to limit the patent of the present invention. All equivalent implementations of the present invention should be included in the scope of the claims of the patent of the present invention.

Claims

1. A fixed bed reaction process for continuously producing dimethyl carbonate, using carbon monoxide, oxygen and methanol as reaction raw materials, and the process steps are as follows: S1: Loading a proper amount of granular supported metal catalyst into the reactor, and then starting preheating to preheat the catalyst to a reaction temperature of 90-160°C; S2: preheating the raw material liquid and passing it into the reactor from the raw material feeding port at the top of the reactor at a certain flow rate, and preheating the raw material gas and passing it into the reactor from the raw material gas inlet at the top of the reactor; S3: The raw gas and the raw liquid pass through the supported metal catalyst bed from top to bottom to carry out a gas-liquid-solid three-phase reaction, and a certain reaction temperature and a certain reaction pressure are controlled; S4: The reaction product is discharged from the bottom of the reactor, and after condensation and gas-liquid separation, the obtained liquid product is the crude dimethyl carbonate product; the obtained gas product is used as circulating gas, which is purified and compressed, mixed with the raw gas and returned to the reactor to continue the reaction; S5: the crude dimethyl carbonate product is further separated by rectification to obtain a dimethyl carbonate product that meets industrial purity requirements; the separated unreacted methanol is mixed with the raw material liquid and recycled; In the above steps, the raw material liquid is methanol, and the raw material gas is a mixed gas composed of CO and O2.

2. The fixed bed reaction process for continuously producing dimethyl carbonate according to claim 1, characterized in that: The supported metal catalyst is expressed as M / S, where M is the active component and S is the carrier, and the loading amount of the active component is 5-15%; wherein M is any one or more of Cu, Zn, Co, Pd, and Rh, and S is any one or more of porous carbon, Al2O3, Al2O3-SiO2, and molecular sieve materials.

3. The fixed bed reaction process for continuously producing dimethyl carbonate according to claim 1, characterized in that: The unreacted methanol solution separated from the liquid product is mixed with the raw methanol to form the reaction raw liquid. The liquid phase volume space velocity of the raw liquid is 0.5h -1 ~10h -1 .

4. The fixed bed reaction process for continuously producing dimethyl carbonate according to claim 1, characterized in that: The circulating gas separated from the reaction tail gas is mixed with the raw gas to form the reaction raw gas. The gas volume space velocity of the raw gas is 250h -1 ~5000h -1 .

5. The fixed bed reaction process for continuously producing dimethyl carbonate according to claim 1, characterized in that: The reaction temperature in the reactor is 90-160°C, and the reaction pressure is 0.5MPa-5.0MPa.

6. The fixed bed reaction process for continuously producing dimethyl carbonate according to claim 1, characterized in that: When the reaction device is started up, the raw material liquid is methanol; after the production of the reaction device is stable, the unreacted methanol solution separated from the liquid phase product and the raw material methanol are mixed to form a reaction liquid, which is a mixture of methanol, dimethyl carbonate and water, and the mass ratio of methanol, dimethyl carbonate and water in the reaction product is 70-100:0-15:0-10.

7. The fixed bed reaction process for continuously producing dimethyl carbonate according to claim 1, characterized in that: When the reaction unit is started up, the initial raw gas is a mixture of CO and O2; after the production of the reaction unit is stable, the tail gas obtained by cooling and separating the products is purified and compressed and mixed with the raw gas as reaction gas, and the reaction gas is a mixture of CO, CO2 and O2, and the volume ratio of the three is 65-95:0-30:1-20.

8. The fixed bed reaction process for continuously producing dimethyl carbonate according to any one of claims 1 to 7, characterized in that: The reactor is a fixed bed reactor, and the bed layer is composed of solid particle catalyst.

9. The fixed bed reaction process for continuously producing dimethyl carbonate according to claim 8, characterized in that: The fixed bed reactor is a tubular reactor, and a temperature sensor and a pressure sensor are arranged in the tubular reactor.

10. The fixed bed reaction process for continuously producing dimethyl carbonate according to claim 9, characterized in that: The temperature sensor is a thermocouple or a thermal resistor temperature sensor; the pressure sensor is any one of a pointer pressure gauge, a digital pressure gauge or a pressure sensor.

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