CN116082112A - A method for producing olefins through oxidative coupling of natural gas - Google Patents

Abstract

The invention discloses a method for producing olefins through oxidative coupling of natural gas. The present invention mainly includes the following steps: converting methane into product gas with an ethylene content of more than 25% through a two-stage oxidative coupling reaction, and then separating methane from CO, CO ₂ , H ₂ , etc. into a cycle and Methanation unit, the remaining part is refined and removed through the product separation unit. The method of the invention couples the oxidative coupling process, methanation and product separation process, makes full use of the reaction heat to by-produce high-temperature steam, and at the same time recycles the over-reacted carbon resources through methanation, and the product separation unit fully separates and refines the product gas. The invention can improve the carbon utilization efficiency of the system, reduce the emission of carbon dioxide, and have high comprehensive benefits.

Description

A method for producing olefins through oxidative coupling of natural gas

technical field

The invention relates to a method for producing olefins through oxidative coupling of natural gas, which belongs to the technical field of natural gas chemical industry

Background technique

The high-value utilization of natural gas has always been the focus of research in the chemical industry. In 1982, Keller and Bhasin of UCC Company first proposed the process of oxidative coupling of natural gas to olefins, which immediately attracted the attention of people in the field of catalysis. For natural gas conversion, the oxidative coupling of methane (abbreviated as OCM) reaction to produce olefins is the most direct and effective method. It can not only convert the abundant natural gas into the most important and basic raw material in the organic chemical industry -- Ethylene, and opened up a non-petroleum route to olefins, a strategic research field, has great theoretical significance.

Chinese patent application (CN 110386853 A) discloses a coupling process of methane oxidative coupling to ethylene and methane dry reforming to synthesis gas. This process introduces the raw material gas containing methane and oxygen into the methane oxidation coupling reactor, and the gas after the catalytic reaction of methane and oxygen passes through the cooling and separation unit to separate C ₂ H ₄ , and the tail gas is preheated and then introduced into the dry reforming reactor , to catalytically convert _CO2 and _CH4 into synthesis gas. In the invention, the methane oxidation coupling reactor is wrapped outside the methane dry reforming reactor, the reaction space is independent, and the two reaction heat requirements are fully utilized at the same time. However, this process is not enough for the product gas separation unit, and the purity of the product is relatively coarse. In addition, the reactor equipment is complex and difficult to process, which is not practical. Chinese patent application (CN 111450779 A) discloses a methane oxidative coupling reaction device and process. The characteristics of this technology are a special reaction barrel, with a feed pipe on the top of the barrel, and evenly distributed sloping plates on the inner wall of the pipe. Arrangement, below the feed pipe, and the refining reaction layer on the inner wall of the reaction barrel, this structure is designed to solve the problems of reaction hot spots and catalyst sintering. But the overall structure of the device is complicated, the manufacturing cost is high, the difficulty is large, and it is difficult to maintain. Chinese patent application (CN 113976048 A) discloses a reaction device for oxidative coupling of methane to olefins, which is characterized in that two fluidized bed reactors are set up to reduce the hot spots caused by the reaction, and the gas-solid is separated by a cyclone separator. , to ensure that the reaction proceeds fully. The fluidized bed reactor consumes a lot of catalyst, and the temperature of the oxidative coupling reaction is high, which puts forward higher requirements for the high temperature resistance of the subsequent equipment. Chinese patent application (CN 111747821 A) discloses a process for oxidative coupling of methane to olefins. This technical feature divides the catalytic bed of the oxidative coupling reactor into multiple sections in series, and each section has a fixed height, so as to realize the control of temperature rise and heat dissipation. use efficiently. The big problem with this technology is that the removal of heat leads to complex processing of the fixed bed reactor, the difficulty of heat preservation control of the equipment is increased, and the separation technology of the subsequent product gas is unknown.

The natural gas oxidative coupling process is a highly exothermic, multi-reaction, and multi-separation process. Although the above-mentioned patent provides a partial methane oxidative coupling process, there is still a big gap from the industrial application of this technology. Therefore, it is necessary to propose A more feasible method that can be applied in industry.

Contents of the invention

The purpose of the present invention is to provide a method for producing olefins through oxidative coupling of natural gas.

The method of the present invention couples the oxidative coupling process, methanation and product separation process, makes full use of reaction heat to by-produce high-temperature steam, and simultaneously recycles over-reacted carbon resources through methanation, and the product separation unit fully separates and refines product gas. The present invention converts methane into ethane, ethylene, C3 alkanes or alkenes, CO ₂ , CO, H ₂ , H ₂ O, etc. through a two-stage oxidative coupling reaction; through rapid cooling and separation of products, methane and CO, CO ₂ , _H2 , etc. are separated and enter the circulation and methanation unit, and the remaining part is refined and removed through the product separation unit.

The invention provides a method for producing olefins through oxidative coupling of natural gas, comprising the steps of:

S1. The methane feed gas after desulfurization is passed into the OCM primary reactor and merged with the oxygen feed gas into the reaction bed for an oxidative coupling reaction to convert methane and oxygen into a mixed product gas;

S2. The mixed product gas flows out from the outlet of the OCM first-stage reactor, passes through the second-stage superheater heat exchanger, and then merges with oxygen into the OCM second-stage reactor. After oxidative coupling reaction, it passes through the first-stage steam superheater and steam generation Reduce the temperature of the device to obtain product gas with an ethylene content of more than 25%;

S3. The product gas with an ethylene content of more than 25% is recovered from heat, then enters the OCM product quenching tower, and is cooled to room temperature. At the same time, the water vapor is condensed and separated to obtain a dry product gas;

S4, the dried product gas is cooled by low-temperature heat exchange, enters the demethanizer, separates the light component gas from the outlet at the top of the tower, and separates the heavy component from the outlet at the bottom of the tower; the light component gas includes methane , CO, CO ₂ and H ₂ ;

S5. The light component gas obtained in step S4 is pressurized by a compressor, and undergoes a methanation reaction after self-heat exchange to obtain a methanation cycle gas. After heat exchange to the inlet temperature of the raw material gas, it is mixed with the The methane raw material gas is mixed into the OCM primary reactor for circulation;

S6. The heavy component obtained in step S4 enters the deethanizer tower and undergoes heat exchange separation to obtain ethylene ethane mixed product gas and tower bottom product separated from the top of the tower;

S7. The ethylene and ethane mixed product gas described in step S6 enters the deethylene tower for separation. The product ethylene is separated from the top of the tower, and the ethane is separated from the bottom of the tower. The ethane enters the OCM described in step S2 through heat exchange and pressure. The secondary reactor carries out the dehydrogenation reaction;

S8. The tower bottom product described in step S6 enters the depropanizer for separation, the C3 alkane or olefin product is separated at the top of the tower, and the alkane or olefin product with a carbon number ≥ 4 is separated at the bottom of the tower.

Further, the mixed product gas includes ethane, ethylene, C3 alkanes or alkenes, alkanes or alkenes with carbon number ≥ 4, CO ₂ , CO, H ₂ and H ₂ O.

Further, in step S1, the volume ratio of the desulfurized methane feed gas to the oxygen feed is 2-5:1;

After the methane raw material gas described in step S1 is mixed with the methanation cycle gas described in step S5, the inlet pressure of the OCM primary reactor is 1 bar to 3 Mpa;

The temperature of the oxidative coupling reaction is 400-750°C.

Further, the temperature of the mixed product gas flowing out from the outlet of the OCM primary reactor in step S2 is 700-900°C, and the temperature is lowered to 600-700°C;

The inlet oxygen fraction of the OCM secondary reactor is less than 20%, and the pressure is 0.5bar～2.9MPa;

The temperature drops to 200-300° C. through the first-stage steam superheater and steam generator.

Further, the product gas with an ethylene content of more than 25% in step S3 comprehensively recovers heat through process gas heat exchange, boiler feed water preheating, and cold process gas heat exchange;

The temperature of the product gas with an ethylene content of more than 25% is 300-400°C after heat exchange with the process gas, and 200-300°C after heat exchange with the boiler feed water and cold process gas. The temperature of the product quenching tower after heat exchange is 30-60°C.

Further, the dried product gas described in step S4 is cooled to -80～-110°C through low-temperature heat exchange;

The outlet temperature at the top of the demethanizer is -100 to -110°C; the outlet gas at the top of the demethanizer is heated to -5 to 30°C through heat exchange to separate the light component gas.

Further, the light component gas described in step S5 is pressurized to 3-5MPa; the temperature is 200-300°C after self-heat exchange;

The methanation reaction includes a secondary methanation reaction.

Further, the process of the methanation reaction is as follows: the light component gas enters the primary methanation reactor after self-heat exchange, and carbon monoxide is subjected to a primary methanation reaction under the environment of excess hydrogen, and the methanation primary The outlet gas of the primary reactor enters the secondary methanation reactor after being heated, and continues the secondary methanation reaction of carbon dioxide and hydrogen;

The inlet temperature of the secondary methanation reactor is 300-500° C., and the pressure is 2.9-4.9 MPa.

Further, the temperature at the top outlet of the deethanizer described in step S6 is -70-～-80°C;

The outlet temperature at the top of the deethylene tower described in step S7 is -90～-100°C;

The outlet temperature at the top of the depropanizer in step S8 is -40 to -45°C.

In step S7 of the present invention, the ethane enters the OCM secondary reactor described in step S2 through heat exchange and pressurization for dehydrogenation reaction in order to increase the yield of ethylene products.

The inventive method has the following beneficial effects:

1. Realize the high-value utilization of natural gas, provide a process path for methane conversion into high industrial value-added products, avoid the reforming process of natural gas, realize high-value utilization of natural gas, and have good economy.

2. Coupling the carbon monoxide and carbon dioxide methanation process improves the carbon utilization efficiency of the system, reduces carbon dioxide emissions, and has high comprehensive benefits.

3. The environmental benefit is good, and the carbon emission in the utilization process of natural gas can be reduced through the present invention, and the environmental impact can be reduced.

4. Realized the refining of product gas and improved the economic benefits of the product. Through the cascaded utilization of cold energy, ethylene, ethane, C3 alkanes or olefins, and alkanes or alkenes with carbon atoms ≥ 4 in the product can be separated to further improve the product gas. industrial added value.

Description of drawings

Figure 1 is a schematic diagram of the process flow of the present invention for oxidative coupling of natural gas to olefins.

Detailed ways

The experimental methods used in the following examples are conventional methods unless otherwise specified.

The materials and reagents used in the following examples can be obtained from commercial sources unless otherwise specified.

The method of the invention is coupled with the oxidative coupling process, the methanation process of carbon monoxide and carbon dioxide, and the product gas refining and separation process, and can realize methane to generate high value-added industrial olefin products. An important way to use value.

The method for producing olefins by oxidative coupling of natural gas of the present invention comprises the following steps:

The desulfurized methane gas merges with the circulating methane gas and enters the OCM primary reactor. Oxygen from the air atmosphere enters the OCM primary reactor through another inlet for oxidative coupling reaction to generate ethylene ethane and C3 alkanes. Or olefins, alkanes or alkenes with carbon number ≥ 4, CO ₂ , H ₂ O, H ₂ , CO, after heat exchange, mix with another stream of oxygen and circulating ethane, and then enter the OCM secondary reactor to increase the olefins, The content of alkane components; the product gas goes through multi-stage heat exchange to recover heat and the quench tower to room temperature, condenses and separates the water vapor in it, and then enters the demethanizer through low-temperature heat exchange, and the top gas enters the circulating methanation unit, and the bottom group into the product refining separation unit; the top gas is compressed by the compressor and enters the methanation primary reactor after self-heat exchange, and then enters the methanation secondary reactor after heat exchange to obtain the methanation cycle gas. After heat exchange to the feed gas inlet temperature, it is mixed with the methane feed gas described in step S1 and entered into the OCM primary reactor for circulation; after the demethanizer bottom component passes through the deethanizer, it is The light component gas is separated at the outlet, and the heavy component is separated from the outlet at the bottom of the tower; the light component gas is pressurized by the compressor, and enters the primary methanation reactor after self-heat exchange. The carbon monoxide is subjected to a primary methanation reaction, the outlet gas of the primary methanation reactor is heated and then enters the secondary methanation reactor, and carbon dioxide and hydrogen are continuously subjected to a secondary methanation reaction to obtain a methanation cycle gas, After heat exchange to the inlet temperature of the raw material gas, it is mixed with the methane raw material gas and entered into the OCM primary reactor for circulation; the heavy component enters the deethanizer tower and is separated by heat exchange to obtain a mixture of ethylene and ethane separated from the top of the tower. Product gas and tower bottom product; the mixed product gas of ethylene and ethane enters the deethylene tower for separation, the product ethylene is separated at the top of the tower, and the ethane is separated at the bottom of the tower, and the ethane enters the step S2 through heat exchange and pressurization. The OCM secondary reactor is used for dehydrogenation reaction; the bottom product enters the depropanizer for separation, the C3 alkane or olefin product is separated at the top of the tower, and the alkane or olefin product with carbon number ≥ 4 is separated at the bottom of the tower.

Embodiment 1,

As shown in Figure 1, it is a flow chart of the inventive method, and concrete steps are as follows:

After the desulfurized methane feed gas is combined with the methanation cycle gas, it is passed into the oxidation coupling (OCM) primary reactor at 5 bar and 650 ° C. After being merged with the oxygen feed gas, it enters the reaction bed layer, and the methane and oxygen feed into the reaction bed. The gas volume ratio is 3. After oxidative coupling reaction, methane and oxygen are converted into ethane, ethylene, C3 alkanes or alkenes, alkanes or alkenes with carbon number ≥ 4, CO ₂ , CO, H ₂ , H ₂ O.

After the product gas comes out of the OCM primary reactor outlet, the temperature is 900°C. After passing through the secondary superheater, high-pressure steam is generated, and the temperature is reduced to 700°C. The ethane produced by the ethylene tower merges into the OCM secondary reactor. After oxidative coupling reaction and ethane deethylene reaction, the ethylene content in the product reaches 40%, and the temperature drops to 300°C through the primary steam superheater and steam generator . After the treatment, the product gas is heat-exchanged with process gas, boiler feed water preheated, and heat-exchanged with cold process gas to recover heat comprehensively, and then enters the OCM product quenching tower, where it is cooled to 20°C. At the same time, the water vapor in the product gas is condensed and separated. After treatment, the product gas is cooled to -103°C by low-temperature heat exchange, and enters the demethanizer. The gas separated from the outlet at the top of the tower is cooled to normal temperature by low-temperature heat exchange, and then enters the circulation and methanation unit. The heavy component separated from the outlet at the bottom of the tower enters the subsequent product separation and purification process. The product gas produced at the top of the demethanizer is pressurized to 3.6MPa by the compressor, and after self-heat exchange, the temperature reaches 270°C and enters the primary methanation reactor. The carbon monoxide is fully reacted in the environment of excess hydrogen, and the outlet gas After being heated to 460°C, it enters the secondary methanation reactor, continues the methanation reaction of carbon dioxide and hydrogen, and after the hydrogen is consumed, it is mixed with methane after heat exchange to the inlet temperature range of the raw material gas and enters the OCM primary reactor. The bottom product of the demethanizer enters the deethanizer and is separated by heat exchange. The temperature at the top of the deethanizer is controlled at -80°C. The product ethylene and ethane mixture gas is separated from the top of the tower, and the bottom product enters the depropanizer for refining. . The product gas from the top of the deethanizer enters the deethylene tower for separation, and the temperature at the top of the tower is controlled at -94°C to produce ethylene at the top of the tower, and ethane is separated from the bottom of the tower, and enters the OCM secondary reactor for deethanization through heat exchange and pressure. The hydrogen reaction increases the ethylene product yield. The product gas from the bottom of the deethanizer enters the depropanizer, and the temperature at the top of the tower is controlled at -45°C. After separation, the C3 alkane or olefin product is separated from the top of the tower, and the alkane or olefin product with a carbon number ≥ 4 is separated from the bottom of the tower. .

The entire process of the above method, through the coupling of carbon monoxide and carbon dioxide to carry out a two-stage methanation reaction process, improves the carbon utilization efficiency of the system, reduces carbon dioxide emissions, and has high comprehensive benefits. Through the cascade utilization of cold energy, ethylene, ethane, C3 alkanes or alkenes, and alkanes or alkenes with a carbon number ≥ 4 in the product can be separated, which realizes the refining of the product gas, improves the economic benefit of the product, and further improves the industry of the product gas. added value.

Claims (9)

1. A method for producing olefins through oxidative coupling of natural gas, comprising the steps of: S1. The methane feed gas after desulfurization is passed into the OCM primary reactor and merged with the oxygen feed gas into the reaction bed for an oxidative coupling reaction to convert methane and oxygen into a mixed product gas; S2. The mixed product gas flows out from the outlet of the OCM first-stage reactor, passes through the second-stage superheater heat exchanger, and then merges with oxygen into the OCM second-stage reactor. After oxidative coupling reaction, it passes through the first-stage steam superheater and steam generation Reduce the temperature of the device to obtain product gas with an ethylene content of more than 25%; S3. The product gas with an ethylene content of more than 25% is recovered from heat, then enters the OCM product quenching tower, and is cooled to room temperature. At the same time, the water vapor is condensed and separated to obtain a dry product gas; S4, the dried product gas is cooled by low-temperature heat exchange, enters the demethanizer, separates the light component gas from the outlet at the top of the tower, and separates the heavy component from the outlet at the bottom of the tower; the light component gas includes methane , CO, CO ₂ and H ₂ ; S5. The light component gas obtained in step S4 is pressurized by a compressor, and undergoes a methanation reaction after self-heat exchange to obtain a methanation cycle gas. After heat exchange to the inlet temperature of the raw material gas, it is mixed with the The methane raw material gas is mixed into the OCM primary reactor for circulation; S6. The heavy component obtained in step S4 enters the deethanizer tower and undergoes heat exchange separation to obtain ethylene ethane mixed product gas and tower bottom product separated from the top of the tower; S7. The ethylene and ethane mixed product gas described in step S6 enters the deethylene tower for separation. The product ethylene is separated from the top of the tower, and the ethane is separated from the bottom of the tower. The ethane enters the OCM described in step S2 through heat exchange and pressure. The secondary reactor carries out the dehydrogenation reaction; S8. The tower bottom product described in step S6 enters the depropanizer for separation, the C3 alkane or olefin product is separated at the top of the tower, and the alkane or olefin product with a carbon number ≥ 4 is separated at the bottom of the tower. 2. The method according to claim 1, characterized in that: the mixed product gas comprises ethane, ethylene, C3 alkanes or alkenes, alkanes or alkenes with carbon number ≥ 4, CO ₂ , CO, H ₂ and _H2O . 3. The method according to claim 1 or 2, characterized in that: in step S1, the volume ratio of the desulfurized methane feed gas to the oxygen feed is 2-5:1; After the methane raw material gas described in step S1 is mixed with the methanation cycle gas described in step S5, the inlet pressure of the OCM primary reactor is 1 bar to 3 Mpa; The temperature of the oxidative coupling reaction is 400-750°C. 4. The method according to any one of claims 1-3, characterized in that: the temperature of the mixed product gas flowing out from the outlet of the OCM primary reactor in step S2 is 700-900°C, and the temperature is lowered to 600-700°C ℃; The inlet oxygen fraction of the OCM secondary reactor is less than 20%, and the pressure is 0.5bar～2.9MPa; The temperature drops to 200-300° C. through the first-stage steam superheater and steam generator. 5. The method according to any one of claims 1-4, characterized in that: the product gas with an ethylene content of more than 25% in step S3 is heat exchanged through process gas, boiler feed water preheating, and cold process gas heat exchange Comprehensive heat recovery; The temperature of the product gas with an ethylene content of more than 25% is 300-400°C after heat exchange with the process gas, and 200-300°C after heat exchange with the boiler feed water and cold process gas. The temperature of the product quenching tower after heat exchange is 30-60°C. 6. The method according to any one of claims 1-5, characterized in that: the dried product gas in step S4 is cooled to -80～-110°C through low-temperature heat exchange; The outlet temperature at the top of the demethanizer is -100 to -110°C; the outlet gas at the top of the demethanizer is heated to -5 to 30°C through heat exchange to separate the light component gas. 7. The method according to any one of claims 1-6, characterized in that: the light component gas in step S5 is pressurized to 3-5MPa; the temperature after self-heat exchange is 200-300°C; The methanation reaction includes a secondary methanation reaction. 8. according to the method described in claim 7, it is characterized in that: described methanation reaction process is as follows: described light component gas enters methanation primary reactor after self-heat exchange, under the environment of excess hydrogen, carbon monoxide Carry out a primary methanation reaction, the outlet gas of the primary methanation reactor is heated and then enters the secondary methanation reactor, and continue the secondary methanation reaction with carbon dioxide and hydrogen; The inlet temperature of the secondary methanation reactor is 300-500° C., and the pressure is 2.9-4.9 MPa. 9. The method according to any one of claims 1-8, characterized in that: the temperature at the top outlet of the deethanizer described in step S6 is -70-～-80°C; The outlet temperature at the top of the deethylene tower described in step S7 is -90～-100°C; The outlet temperature at the top of the depropanizer in step S8 is -40 to -45°C.

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