A process design method for separating dimethyl carbonate / methanol by pressure swing distillation

Abstract

The present application comprises a process design method of energy-saving process for separating dimethyl carbonate / methanol by pressure swing rectification, and the process flow is as follows: the mixture of dimethyl carbonate and methanol to be separated is pretreated and then enters a high-pressure tower, the raw material is rectified and separated and purified in the high-pressure tower, high-purity dimethyl carbonate product is obtained at the bottom of the tower, the overhead product enters a reflux tank, part of the product refluxes, the rest of the product enters a low-pressure tower for further separation, and finally high-purity methanol product is obtained at the bottom of the low-pressure tower. The process flow adopts a pressure swing rectification process design flow, which maximizes the purity requirement of the product and reduces energy consumption. The process has many advantages such as good product separation effect, high quality, short production route, simple operation, easy industrialization and the like.

Description

Technical Field

[0001] This invention relates to a process design for separating dimethyl carbonate / methanol by pressure swing distillation, belonging to the field of dimethyl carbonate and methanol production. Background Technology

[0002] With the development and progress of human society, the consumption of traditional fossil fuels has continued to rise, bringing increasingly serious environmental pollution and carbon emission problems. Therefore, developing a new, green, low-carbon, and widely available alternative energy source has significant strategic value. Methanol, as a high-quality clean fuel and basic chemical raw material, is receiving widespread attention and is being promoted intensively. Methanol is a low-carbon oxygenated fuel that can be produced through various pathways, including coal, natural gas, biomass, and carbon dioxide hydrogenation. It can be used directly as a clean fuel or to produce high-value-added chemicals such as olefins and aromatics, effectively alleviating dependence on petroleum resources and reducing pollutant and greenhouse gas emissions, possessing enormous application potential and market space. As an important component of the low-carbon energy system, methanol fuel and related industrial chains can promote energy structure transformation, facilitate the achievement of carbon emission reduction targets, and drive related technological innovation and industrial upgrading, which is of great significance to my country's energy security and sustainable economic and social development. Optimizing and upgrading existing methanol production and application facilities not only meets the national "dual-carbon" requirements but also significantly reduces energy and material consumption, achieving the goals of energy conservation, emission reduction, cost reduction, and efficiency improvement.

[0003] Mature separation methods include atmospheric distillation, extractive distillation, azeotropic distillation, and membrane separation. However, these methods involve complex equipment and high energy consumption. Furthermore, in the refining of the dimethyl carbonate-methanol azeotropic system, they suffer from low separation accuracy and susceptibility to introducing impurities. Therefore, there is an urgent need to research a novel, efficient separation method and its supporting equipment. Currently, a highly efficient separation method and apparatus for dimethyl carbonate and methanol has been disclosed in China. Compared to traditional distillation techniques, this separation apparatus offers advantages such as a simpler process, higher separation purity, higher degree of automation, milder requirements for equipment operating conditions, and no introduction of third components such as extractants / azeotropic agents. Simultaneously, energy consumption can be reduced by more than 50%.

[0004] Therefore, developing a pressure swing distillation separation process for refined methanol to reduce energy consumption and improve energy utilization is a key issue that urgently needs to be addressed in methanol production. Summary of the Invention

[0005] The purpose of this invention is to propose a process design for separating dimethyl carbonate / methanol using pressure swing distillation, addressing the problems of high energy consumption and low product separation efficiency in the production of high-concentration methanol in my country. This invention, while ensuring the desired methanol concentration, utilizes a dual-tower coupling of a high-pressure tower and a low-pressure tower to fully utilize the heat of the material, thereby reducing production energy consumption and significantly lowering production costs. Simultaneously, it also increases the methanol yield, achieving substantial economic benefits.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A process design for separating dimethyl carbonate / methanol by pressure swing distillation, comprising the following steps: S1. The mixed raw materials used enter the raw material processing device through pipelines to reach the feed temperature and pressure of the distillation column. The heated material enters the high-pressure column for distillation separation to complete the feeding. S2. After the feed liquid enters the high-pressure tower, the mixture enters the distillation tower at a fixed flow rate. Part of it enters the separator to achieve gas-liquid separation. The liquid part of the separator is returned to the high-pressure tower as reflux liquid, and the rest is used as feed to the low-pressure tower for high-purity separation of methanol. S3. After the system maintains stable operation, the mixture formed at the top of the high-pressure tower enters the compressor. The compressor processes the temperature and pressure of the steam at the top of the tower to meet the feed standard of the low-pressure tower, and then sends it to the low-pressure tower for distillation and separation. S4. After the top product of the high-pressure tower enters the low-pressure tower for further purification, the high-purity methanol water vapor formed at the bottom of the low-pressure tower enters the compressor. The compressor restores the temperature and pressure at the bottom of the tower to atmospheric pressure to meet the transportation requirements of the product. S5. The product generated at the top of the low-pressure tower enters the flash tank for gas-liquid separation. The liquid portion is used as reflux liquid and returned to the low-pressure tower for reflux operation. The product at the top of the low-pressure tower is pressurized and then circulated to the high-pressure tower, realizing the recycling of materials and high-purity purification.

[0007] Preferably, in the process of the present invention, the raw material entering the pretreatment device can be a low-concentration dimethyl carbonate / methanol mixture or a high-concentration dimethyl carbonate / methanol mixture.

[0008] Preferably, in the process of the present invention, the raw material processing device includes processes such as heating, pressurizing, and pre-separation.

[0009] Preferably, in the process of the present invention, the concentration of dimethyl carbonate in the mixture obtained by the raw material processing device is 10-20%.

[0010] Preferably, in the process of the present invention, the high-pressure tower and the low-pressure tower are plate towers or packed towers.

[0011] Preferably, in the process of the present invention, the absolute pressure range of the high-pressure tower is 0.1~0.3MPa; the temperature range of the top of the high-pressure tower is 65~75℃, and the temperature range of the bottom of the tower is 95~105℃; the absolute pressure range of the low-pressure tower is 0.01~0.1MPa; the temperature range of the top of the low-pressure tower is 14~30℃, and the temperature range of the bottom of the tower is 35~55℃. Preferably, in the process of the present invention, the reflux ratio at the top of the high-pressure tower is 1.5 to 1.8; and the reflux ratio of the low-pressure tower is 4 to 5.

[0012] Preferably, in the process of the present invention, the reboiler is a kettle-type reboiler.

[0013] Preferably, in the process of the present invention, the molar concentration of dimethyl carbonate entering the low-pressure tower is above 60%.

[0014] Preferably, the process of the present invention is applicable to the refining of various methanol products, including fuel methanol, medical methanol, and industrial methanol.

[0015] Compared with existing technologies, the present invention has the following advantages: 1. The process of this invention uses a dual-tower coupling of a high-pressure tower and a low-pressure tower for separation and purification. The process is simple, the production route is short, the energy utilization rate is high, it is environmentally friendly and energy-saving, and the safety factor is high, which fully ensures the safety of personnel and thus significantly improves the economic benefits of enterprises.

[0016] 2. The reboiler device of the process of this invention adopts a kettle-type reboiler, which has the advantages of simple operation, low operating cost, high degree of equipment automation, low pollution to the external environment, and wide application. Compared with other methanol separation devices, it has obvious technical advantages, reduces external energy consumption, improves the economic benefits of production enterprises, and has broad application prospects. Attached Figure Description

[0017] Figure 1 This is a process flow diagram for the separation of dimethyl carbonate / methanol by pressure swing distillation. The names of the equipment in the diagram are as follows: 1-Raw material pretreatment unit; 2-High-pressure tower; 3-High-pressure tower condenser; 4-Reflux tank 1; 5-Valve 1; 6-Low-pressure tower compressor; 7-High-pressure tower reboiler; 8-DMC product compressor; 9-Valve 2; 0-Valve 3; 11-Low-pressure tower; 12-Low-pressure tower condenser; 13-Reflux tank 2; 14-Valve 4; 15-Reflux liquid compressor pump; 16-Valve 5; 17-Low-pressure tower reboiler; 18-MeOH product compressor; 19-Valve 5; 20-Circulating stream pressurization pump.

[0018] The technical solution of the present invention will be further described clearly and accurately below with reference to the implementation examples of the present invention. However, the described implementation examples are only a part of the present invention and not all of it.

[0019] Implementation Case 1: 30,000-ton / year dimethyl carbonate and methanol project like Figure 1 As shown, the process features include a raw material processing unit, a high-pressure distillation column, a low-pressure distillation column, a reboiler, and a condenser. The raw material processing unit is connected to the high-pressure column via pipelines. The top of the high-pressure column is connected to its top heat exchanger via pipelines, and the top heat exchanger is connected to its reflux tank via pipelines. Valves of the high-pressure and low-pressure columns are connected via pipelines. The reflux tank at the top of the high-pressure column is connected to the feed valves of both the high-pressure and low-pressure columns via pipelines. The bottom of the high-pressure column is connected to its reboiler via pipelines. After distillation in the high-pressure column, the top product is... The excess distillate is fed into the high-pressure column as reflux, while the remainder becomes the feed product for the low-pressure column. The bottom product then enters the reboiler for gas-liquid separation, producing a high-purity dimethyl carbonate. After distillation in the low-pressure column, a portion of the top product is refluxed back into the low-pressure column via pipeline, while the remaining product is recycled back into the high-pressure column for further purification. The bottom product then enters the reboiler for gas-liquid separation, and the liquid distillate separated in the flash evaporator is a high-purity methanol product. Ultimately, this process achieves high-purity separation of dimethyl carbonate and methanol from the feed.

[0020] A process design for separating dimethyl carbonate / methanol by pressure swing distillation, characterized by the following steps: S1. The mixed raw materials used enter the raw material processing device through pipelines to reach the feed temperature and pressure of the distillation column. The heated material enters the high-pressure column for distillation separation to complete the feeding. In this step, the raw material entering the pretreatment unit can be a low-concentration dimethyl carbonate / methanol mixture or a high-concentration dimethyl carbonate / methanol mixture. The raw material treatment unit includes processes such as heating, pressurization, and pre-separation. The dimethyl carbonate concentration in the mixture obtained by the raw material treatment unit is 10-20%. S2. After the feed liquid enters the high-pressure tower, the mixture enters the distillation tower at a fixed flow rate. Part of it enters the separator to achieve gas-liquid separation. The liquid part of the separator is returned to the high-pressure tower as reflux liquid, and the rest is used as feed to the low-pressure tower for high-purity separation of methanol. In this step, the absolute pressure range of the high-pressure tower is 0.1~0.3MPa; the temperature range of the top of the high-pressure tower is 65~75℃, and the temperature range of the bottom of the tower is 95~105℃; the absolute pressure range of the low-pressure tower is 0.01~0.1MPa; the temperature range of the top of the low-pressure tower is 14~30℃, and the temperature range of the bottom of the tower is 35~55℃.

[0021] S3. After the system maintains stable operation, the mixture formed at the top of the high-pressure tower enters the compressor. The compressor processes the temperature and pressure of the steam at the top of the tower to meet the feed standard of the low-pressure tower, and then sends it to the low-pressure tower for distillation and separation. The absolute pressure range of the low-pressure tower is 0.01~0.1MPa; the temperature range of the top of the low-pressure tower is 14~30℃, and the temperature range of the bottom of the tower is 35~55℃.

[0022] S4. After the top product of the high-pressure tower enters the low-pressure tower for further purification, the high-purity methanol water vapor formed at the bottom of the low-pressure tower enters the compressor. The compressor restores the temperature and pressure at the bottom of the tower to atmospheric pressure to meet the transportation requirements of the product. The reflux ratio at the top of the high-pressure tower is 1.5 to 1.8; the reflux ratio of the low-pressure tower is 4 to 5.

[0023] S5. The product generated at the top of the low-pressure tower enters the flash tank for gas-liquid separation. The liquid portion is used as reflux liquid and returned to the low-pressure tower for reflux operation. The product at the top of the low-pressure tower is pressurized and then circulated to the high-pressure tower, realizing the recycling of materials and high-purity purification.

[0024] In this step, the reboiler of the membrane is a batch reboiler; the molar concentration of dimethyl carbonate entering the low-pressure tower is above 60%; the process of the present invention is applicable to the refining of various methanol products, including fuel methanol, medical methanol and industrial methanol, etc.

[0025] Compared with traditional processes, this implementation case significantly reduces energy consumption, requiring only external steam heat supply to the high-pressure and low-pressure towers, further improving the yield of methanol products.

Claims

1. A process design method for separating dimethyl carbonate / methanol by pressure swing distillation, the process comprising a feed processing unit, a high-pressure distillation column, a low-pressure distillation column, a reboiler, and a condenser unit. The feed processing unit is connected to the high-pressure column via pipelines. The top of the high-pressure column is connected to its top heat exchanger via pipelines. The top heat exchanger is connected to its reflux tank via pipelines. Valves of the high-pressure and low-pressure columns are connected via pipelines. The reflux tank at the top of the high-pressure column is connected to the feed valves of both the high-pressure and low-pressure columns via pipelines. The bottom of the high-pressure column is connected to its reboiler via pipelines. After distillation, the top product is partially refluxed into the high-pressure column, while the remaining portion becomes the feed to the low-pressure column. The bottom product enters the reboiler for gas-liquid separation, and the resulting distillate is high-purity dimethyl carbonate. After distillation in the low-pressure column, part of the top product is refluxed back into the low-pressure column via pipeline, while the remaining product is recycled back into the high-pressure column for further purification. The bottom product enters the reboiler for gas-liquid separation, and the liquid distillate separated in the flash evaporator is high-purity methanol. Ultimately, high-purity separation of dimethyl carbonate and methanol from the feed is achieved. The process includes the following steps: S1. The mixed raw materials used enter the raw material processing device through pipelines to reach the feed temperature and pressure of the distillation column. The heated material enters the high-pressure column for distillation separation to complete the feeding. S2. After the feed liquid enters the high-pressure tower, the mixture enters the distillation tower at a fixed flow rate. Part of it enters the separator to achieve gas-liquid separation. The liquid part of the separator is returned to the high-pressure tower as reflux liquid, and the rest is used as feed to the low-pressure tower for high-purity separation of methanol. S3. After the system maintains stable operation, the mixture formed at the top of the high-pressure tower enters the compressor. The compressor processes the temperature and pressure of the steam at the top of the tower to meet the feed standard of the low-pressure tower, and then sends it to the low-pressure tower for distillation and separation. S4. After the top product of the high-pressure tower enters the low-pressure tower for further purification, the high-purity methanol water vapor formed at the bottom of the low-pressure tower enters the compressor. The compressor restores the temperature and pressure at the bottom of the tower to atmospheric pressure to meet the transportation requirements of the product. S5. The product generated at the top of the low-pressure tower enters the flash tank for gas-liquid separation. The liquid portion is used as reflux liquid and returned to the low-pressure tower for reflux operation. The product at the top of the low-pressure tower is pressurized and then circulated to the high-pressure tower, realizing the recycling of materials and high-purity purification.

2. The process design for separating dimethyl carbonate / methanol by pressure swing distillation as described in claim 1, characterized by the following features: The feedstock entering the fermentation unit can be a low-concentration dimethyl carbonate / methanol mixture or a high-concentration dimethyl carbonate / methanol mixture.

3. The process design for separating dimethyl carbonate / methanol by pressure swing distillation as described in claim 1, characterized by the following features: The raw material processing equipment includes processes such as heating, pressurization, and pre-separation.

4. The process design for separating dimethyl carbonate / methanol by pressure swing distillation as described in claim 1, characterized by the following features: The concentration of dimethyl carbonate in the mixture obtained from the raw material processing device is 10-20%.

5. The process design for separating dimethyl carbonate / methanol by pressure swing distillation as described in claim 1, characterized by the following features: In the process of this invention, the high-pressure tower and the low-pressure tower are plate towers or packed towers.

6. The process design for separating dimethyl carbonate / methanol by pressure swing distillation as described in claim 1, characterized by the following features: In the process of this invention, the absolute pressure range of the high-pressure tower is 0.1~0.3MPa; the temperature range of the top of the high-pressure tower is 65~75℃, and the temperature range of the bottom of the tower is 95~105℃; the absolute pressure range of the low-pressure tower is 0.01~0.1MPa; the temperature range of the top of the low-pressure tower is 14~30℃, and the temperature range of the bottom of the tower is 35~55℃.

7. The process design for separating dimethyl carbonate / methanol by pressure swing distillation as described in claim 1, characterized in that: In the process of this invention, the reflux ratio at the top of the high-pressure tower is 1.5 to 1.8; The reflux ratio of the low-pressure tower is 4~5.

8. The process design for separating dimethyl carbonate / methanol by pressure swing distillation as described in claim 1, characterized in that: In the process of this invention, the reboiler is a kettle-type reboiler.

9. The process design for separating dimethyl carbonate / methanol by pressure swing distillation as described in claim 1, characterized in that: In the process of this invention, the molar concentration of dimethyl carbonate entering the low-pressure tower is above 60%.

10. The process design for separating dimethyl carbonate / methanol by pressure swing distillation as described in claim 1, characterized in that: The process of this invention is applicable to the refining of various methanol products, including fuel methanol, medical methanol, and industrial methanol.

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