KR102580498B1 - Carbon dioxide to hydrocarbon conversion system and its conversion process - Google Patents

Abstract

The present invention relates to a system for converting carbon dioxide into hydrocarbons and a conversion process thereof, and more specifically, to increase the overall energy efficiency and carbon reduction efficiency of the process while further maximizing the yield of high value-added products among the conversion products of carbon dioxide. It relates to a system for converting carbon dioxide into hydrocarbons and the conversion process.

Description

Carbon dioxide to hydrocarbon conversion system and its conversion process}

The present invention relates to a system for converting carbon dioxide into hydrocarbons and a conversion process thereof. More specifically, in the process of converting carbon dioxide into useful products, the energy efficiency and carbon reduction efficiency of the process are greatly increased, while the high added value of carbon dioxide is achieved. It relates to a conversion system and process for converting carbon dioxide into hydrocarbons, which can maximize the conversion rate to products.

Carbon dioxide (CO ₂ ) is a representative greenhouse gas, and immobilization and reduction technologies through carbon dioxide capture, storage, and conversion are being actively proposed. Among them, the GTL (Gas-to-liquid) process is an important technology for supplying hydrocarbons obtained from petroleum resources, and is receiving more attention along with the recent development of shale gas.

The Fischer-Tropsch synthesis (FTS) process, a core process of GTL technology, is a process for producing hydrocarbons from synthesis gas containing carbon monoxide produced through a reforming reaction of natural gas, using carbon dioxide as a raw material instead of carbon monoxide. When used, changes are required in the catalyst, etc.

As an example, Korean Patent Publication No. 2018-0004165 includes a process of separating CO ₂ from the product mixture of the RWGS reaction and/or the product mixture of the FT reaction and recycling it to the RWGS reaction to produce light olefins from the conversion of CO ₂ A method for producing hydrocarbons is disclosed.

In addition, in Korean Patent No. 1626800, the Fischer-Tropsch (FT) synthesis reaction and reverse water gas conversion reaction are simultaneously performed to produce synthetic liquid fuel from carbon dioxide-containing synthesis gas, and then the product is separated from the synthesis gas. A method for producing synthetic liquid fuel containing hydrocarbons such as light olefins (C ₂ ~ C ₄ ) and liquid hydrocarbons (C ₅₊ ) is disclosed.

However, the above prior arts do not have a concept for recycling unreacted products or FTS off-gas, or even if recycling occurs, the methane contained in the off-gas is reformed again and converted into synthesis gas before being returned. This has the disadvantage of lowering energy efficiency or carbon reduction efficiency.

From the perspective of this process energy efficiency and carbon reduction efficiency, Korean Patent No. 2230155 combines the FTS process and the methane synthesis process, significantly increasing energy efficiency and carbon reduction efficiency by merging the FTS and methane synthesis processes depending on the situation. An integrated process is presented.

However, in Korea Patent No. 2230155, there is still a need to further improve energy efficiency and carbon reduction efficiency, and there is also a need to improve the economic feasibility of the process by maximizing products with higher added value in the distribution of carbon dioxide conversion products. .

Korean Patent Publication No. 2018-0004165 (Publication Date: 2018.01.10) Korean Patent No. 1626800 (Publication Date: 2016.01.26) Korean Patent No. 2230155 (Publication Date: 2020.08.10)

The main purpose of the present invention is to solve the above-mentioned problems. In the process of converting carbon dioxide into useful materials, energy efficiency is increased by reducing the overall energy cost of the process, and carbon dioxide emissions are further reduced, thereby reducing carbon dioxide. The goal is to provide a system and process for converting carbon dioxide into hydrocarbons that can increase efficiency while also allowing the products produced by the conversion of carbon dioxide to have higher added value.

In order to achieve the above object, one embodiment of the present invention includes: a first reaction unit that introduces an incoming gas containing carbon dioxide and hydrogen to perform a reverse water gas conversion reaction and a Fischer-Tropsch synthesis reaction; a second reaction unit that receives the effluent from the first reaction unit and performs an oligomerization reaction; A separation unit that receives the effluent from the second reaction unit and separates C ₅₊ hydrocarbons having 5 or more carbon atoms from the mixture of lower hydrocarbons having 1 to 4 carbon atoms and unreacted substances; a recirculation unit that receives the mixture of lower hydrocarbons and unreacted substances separated from the separation unit and re-supplies some of them to the first reaction unit, and supplies the remainder to the third reaction unit; And a third reaction unit that generates synthetic natural gas by injecting hydrogen into the feed supplied from the recirculation unit, wherein the second reaction unit performs an oligomerization reaction at 220 ° C. to 280 ° C. in the presence of ZSM-5 zeolite. A system for converting carbon dioxide into hydrocarbons is provided.

In a preferred embodiment of the present invention, the Si/Al molar ratio of the ZSM-5 catalyst in the second reaction unit may be 5 or more, preferably 10 to 100, and the Si/Al molar ratio may be in the range of 10 to 35. By further limiting it, the selectivity for hydrocarbons with 8 to 10 carbon atoms can be further increased.

In a preferred embodiment of the present invention, the first reaction unit may be characterized in that it performs a reverse water gas conversion reaction and a Fischer-Tropsch synthesis reaction at 200°C to 500°C at 3 bar to 100 bar.

In a preferred embodiment of the present invention, the inlet gas may have a molar ratio of hydrogen to carbon dioxide of 1 to 5.

In a preferred embodiment of the present invention, it may further include a reverse water gas conversion reaction unit that introduces carbon dioxide and hydrogen into the front end of the first reaction unit to perform a reverse water gas conversion reaction.

In a preferred embodiment of the present invention, it may further include a thermal energy supply device that supplies thermal energy generated in the first reaction unit and/or the third reaction unit to the reverse water gas shift reaction unit.

Another embodiment of the present invention includes: (a) a first reaction step of introducing an incoming gas containing carbon dioxide and hydrogen to perform a reverse water gas shift reaction and a Fischer-Tropsch synthesis reaction; (b) a second reaction step of receiving the effluent of the first reaction step and performing an oligomerization reaction; (c) a separation step of receiving the effluent from the second reaction step and separating C ₅₊ hydrocarbons having 5 or more carbon atoms from the mixture of lower hydrocarbons having 1 to 4 carbon atoms and unreacted substances; (d) a recycling step of receiving the mixture of lower hydrocarbons and unreacted substances separated from the separation step, resupplying some of them to the first reaction step, and supplying the remainder to the third reaction step; and (e) a third reaction step of generating synthetic natural gas by adding hydrogen to the feed supplied from the recycling step, wherein the second reaction step is to produce oligomer at 220°C to 280°C in the presence of ZSM-5 zeolite. A process for converting carbon dioxide into hydrocarbons is provided, characterized in that a conversion reaction is performed.

In another preferred embodiment of the present invention, the first reaction step may be characterized in that a reverse water gas shift reaction and a Fischer-Tropsch synthesis reaction are performed at 200°C to 500°C at 3 bar to 100 bar.

In another preferred embodiment of the present invention, the inlet gas may have a molar ratio of hydrogen to carbon dioxide of 1 to 5.

In another preferred embodiment of the invention, the Si/Al molar ratio of ZSM-5 in the second reaction step may be 10 to 35.

In another preferred embodiment of the present invention, a reverse water gas conversion step of introducing carbon dioxide and hydrogen to convert carbon dioxide into carbon monoxide may be further included before the first reaction step.

In another preferred embodiment of the present invention, the reaction heat generated in the first reaction step and/or the third reaction step may be used for the reaction in the reverse water gas conversion step.

The system and process for converting carbon dioxide into hydrocarbons according to the present invention directly oligomerize the product produced after the Fischer-Tropsch reaction without separation and recycling, making it difficult to liquefy the unreacted material recycled in the conventional carbon dioxide conversion process. By reducing the overall amount of low-grade hydrocarbons, it improves process operating costs and energy efficiency, and at the same time prevents low-grade hydrocarbons, which act as inert substances in the Fischer-Tropsch reaction, from accumulating in the reaction system, improving reaction efficiency and producing high value-added products. It has the effect of increasing yield.

In addition, the present invention converts carbon dioxide to carbon monoxide through a reverse water gas shift reaction prior to the Fischer-Tropsch reaction, and uses the reaction heat generated from synthetic natural gas production as part or all of the energy required for the reaction, thereby converting carbon monoxide into carbon monoxide. It has the effect of maximizing efficiency and reducing energy use while increasing the content of high value-added products among the products of the overall reaction.

Figure 1 is a schematic diagram of a system for converting carbon dioxide according to the prior art.
Figure 2 is a schematic diagram of a carbon dioxide conversion system with improved energy efficiency and carbon reduction efficiency by improving the prior art of Figure 1.
Figure 3 is a flow chart schematically showing a system and process for converting carbon dioxide into hydrocarbons according to an embodiment of the present invention.
Figure 4 is a diagram illustrating the configuration of a system for converting carbon dioxide into hydrocarbons according to an embodiment of the present invention.
Figure 5 is a flow chart schematically showing a system and process for converting carbon dioxide into hydrocarbons according to another embodiment of the present invention.
Figure 6 is a graph showing the conversion rate and selectivity measured in the system according to the examples and comparative examples of the present invention.
Figure 7 is a graph showing the conversion rate and selectivity (a) measured in systems according to examples and comparative examples of the present invention.
Figure 8 is a graph showing selectivity according to the number of hydrocarbon carbons measured in systems according to examples and comparative examples of the present invention.
Figure 9 is a graph showing (a) synthetic crude oil production, (b) SNG production, and (c) flow rate of the FTS reactor measured in the system according to the examples and comparative examples of the present invention.
Figure 10 is a graph showing (a) energy efficiency and (b) net CO ₂ emission measured in systems according to examples and comparative examples of the present invention.

Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

'Stream' as used herein may refer to the flow of fluid within a process, or may also refer to the fluid itself flowing within a pipe. The 'stream' may refer to both the fluid itself and the flow of the fluid flowing within the pipes connecting each device. Additionally, the fluid may refer to gas or liquid.

Terms such as 'comprises', 'includes', 'contains', or 'has' used in the specification indicate the presence of features, values, steps, operations, components, parts, or combinations thereof described in the specification. It refers to, and does not exclude the possibility that other features, values, steps, operations, components, parts, or combinations thereof not mentioned may exist or be added.

In addition, throughout this specification, the names of the components are divided into first, second, etc. for the purpose of clearly explaining the configuration, and to distinguish them because the names of the components are the same. It is not limited to order.

Hereinafter, a system for converting carbon dioxide into hydrocarbons according to the present invention and preferred embodiments of the process will be described in detail with reference to the attached drawings.

Figure 1 is a schematic diagram of a carbon dioxide conversion system according to the prior art, and Figure 2 is a schematic diagram of a carbon dioxide conversion system with increased energy efficiency and carbon reduction efficiency by improving the conventional technology of Figure 1.

Referring to FIG. 1, in a conventional carbon dioxide conversion system for obtaining polymer hydrocarbons from carbon dioxide, carbon dioxide and hydrogen are mixed with the gas recycled in the first mixer 101, and then converted to an appropriate amount for the conversion reaction in the first compressor 102. compressed by pressure. Afterwards, the compressed mixed gas undergoes heat exchange in the first heat exchanger 103 and then flows into the carbon dioxide conversion reactor 104, where a carbon dioxide conversion reaction proceeds.

The effluent discharged from the carbon dioxide conversion reactor 104 is again heat-exchanged in the second heat exchanger 105 and then flows into the first separator 201. The effluent from the carbon dioxide conversion reactor 104 in the first separator 201 is a stream of lower hydrocarbons (C ₁ to C ₄ ) with 1 to 4 carbon atoms including unconverted reactants (carbon monoxide, carbon dioxide, hydrogen), and 5 carbon atoms. The above C ₅₊ hydrocarbon streams are separated, and the separated C ₅₊ hydrocarbons are introduced into the water separator 204 through the pipe 202, where water is removed and the final product, C ₅₊ hydrocarbons, is obtained. In addition, the low-grade hydrocarbons and unconverted reactants separated from the top in the first separator 201 are separated from moisture in the second separator 402, and then are recycled back to the mixer 101 through the pipe 404. Through the above process, a carbon dioxide conversion reaction proceeds.

At this time, low-grade hydrocarbons contained in the recirculated stream do not participate in the reaction process in the carbon dioxide conversion reactor 104 and act as inert gases, or even if they participate in the reaction process, they act as a factor in reducing reaction efficiency. When hydrocarbons are introduced into the first separator 201 as is, low-grade hydrocarbons generated in the carbon dioxide conversion reactor are continuously added to the recycled low-grade hydrocarbons, causing accumulation.

In order to prevent such low-grade hydrocarbons from accumulating through recirculation, conventionally, a reforming reactor 401 is placed at the top of the first separator 201 to perform a reforming reaction to reform the low-grade hydrocarbons present in the recirculated stream back into synthesis gas. did.

However, since the low-grade hydrocarbon is a product created from carbon dioxide and hydrogen by inputting energy, returning it to the state before synthesis is a waste of energy, and due to the nature of the reforming reaction, a strong endothermic reaction causes a serious decrease in energy efficiency. I do it.

Accordingly, the present inventor configured the process as shown in FIG. 2 in the previous application (Korean Patent No. 2230155) to obtain 1 to 4 carbon atoms including the unconverted reactants (carbon monoxide, carbon dioxide, and hydrogen) separated in the first separator 201. A stream of low-grade hydrocarbons (C ₁ to C ₄ ) is returned from the splitter 206 to the first mixer 101 through a pipe 203 (207) and a stream 205 sent to the second mixer 301. Divided into, the stream 205 branched from the splitter 206 is mixed with hydrogen added in the second mixer 301, exchanges heat through the third heat exchanger 302, and is then sent to the synthetic natural gas production reactor 303. By introducing synthetic natural gas, it prevents low-grade hydrocarbons such as methane, which acts as an inert material in the Fischer-Tropsch reaction, from accumulating in the reaction system, while increasing the energy efficiency and carbon reduction efficiency of the overall process. There is a bar.

In view of the above, the applicant conducted further research and found that the product produced in the Fischer-Tropsch reaction was obtained without separation of lower hydrocarbons containing unreacted products produced in the Fischer-Tropsch reaction and C ₅₊ hydrocarbons with 5 or more carbon atoms. When going through a direct oligomerization process, energy efficiency and carbon reduction efficiency are further increased while the yield of high value-added products is increased, and the economic feasibility of the process can also be improved, leading to the completion of the present invention.

In the present invention, some or all of the low-grade hydrocarbon stream containing unconverted reactants recycled after the oligomerization step is branched from the recycled stream to produce synthetic natural gas through a methanation reaction to prevent low-grade hydrocarbons from accumulating during the system or process. While doing so, low-grade hydrocarbons in the recycle stream can be utilized effectively.

Specifically, as shown in FIGS. 3 and 4, the system for converting carbon dioxide into hydrocarbons according to the present invention uses a first reaction unit 510 to produce liquid hydrocarbons and synthetic natural gas from incoming gas containing carbon dioxide and hydrogen. , a second reaction unit 520, a separation unit 530, a recirculation unit 540, and a third reaction unit 550.

The first reaction unit 510 introduces an incoming gas containing carbon dioxide and hydrogen to perform a reverse water gas conversion reaction and a Fischer-Tropsch synthesis reaction. At this time, the inlet gas flowing into the first reaction unit 510 is a raw material containing hydrogen and carbon dioxide, and can be supplied as a mixed gas of hydrogen and carbon dioxide, or hydrogen and carbon dioxide can be supplied separately.

A suitable source of carbon dioxide in the incoming gas is a carbon oxide emission plant that emits carbon dioxide, especially a plant that needs to reduce its carbon oxide emission. Examples of such plants include blast furnaces used to produce steel, and thermal power plants that produce electricity using fossil fuels such as coal or gas. Carbon dioxide, carbon monoxide, or carbon oxides, or mixtures, may be provided by any method, including but not limited to, provided from any source.

Additionally, the hydrogen may be hydrogen produced by electrolyzing water using electricity generated by hydropower, solar power, ocean waves, wind power, tidal currents, or a combination of two or more of these. The electrolyzer may require significant amounts of heat to operate, which heat may be supplied by water vapor generated elsewhere in the plant along with the water for operation. Hydrogen can also be produced by conventional electrolysis of water using electrodes, but other methods can also be used, including thermochemical processes by thermal decomposition of water using waste heat from nuclear reactors, and combinations of these methods.

In the inlet gas, the molar ratio of hydrogen to carbon dioxide may be in the range of 1 to 5, preferably 3 to 4, and when the molar ratio of hydrogen to carbon dioxide is less than 1, carbon dioxide is converted to carbon monoxide. Because the reaction is insufficient, the effect of maximizing carbon efficiency, which is the goal of the present invention, cannot be obtained, and when the molar ratio of hydrogen to carbon dioxide exceeds 5, hydrogenation reaction is preferred over the chain bonding reaction of the FTS reaction, rather than liquid hydrocarbons. A lot of low-grade hydrocarbons are produced, and more hydrogen than necessary is supplied, which can lead to problems of low economic feasibility.

The incoming gas flowing into the first reaction unit may include carbon monoxide in addition to carbon dioxide as a carbon source. In this case, the molar ratio of carbon monoxide/carbon dioxide may be in the range of 0 to 1.

The first reaction unit 510 can supply carbon dioxide and hydrogen at various flow rates, and the flow rate and gas hourly space velocity (GHSV) can be varied as known in the art.

Additionally, the first reaction unit 510 may be provided with one or more reactors filled with a catalyst to perform a reverse water gas conversion reaction and a Fischer-Tropsch synthesis reaction of the introduced gas. In the reactor, a catalyst that simultaneously promotes the reverse water gas shift reaction and the Fischer-Tropsch synthesis reaction or a catalyst for the reverse water gas shift reaction and a catalyst for the Fischer-Tropsch synthesis reaction can be uniformly mixed or placed in layers, 2 When using more than one reactor, different types of catalysts may be charged and used for each reactor.

The catalyst for the reverse water gas shift reaction can be used without limitation as long as it is a catalyst active in the reverse water gas shift reaction. For example, it may be a metal oxide or a mixed metal oxide. The metal oxide may include copper, zinc, lithium, and rhodium. , molybdenum, platinum, palladium, etc. may be included.

In addition, the catalyst for the Fischer-Tropsch synthesis reaction can be used without limitation as long as it is a catalyst active in the Fischer-Tropsch synthesis reaction. For example, it may be a metal oxide or a mixed metal oxide, and the metal oxides include iron and copper. , manganese, cobalt, nickel, zinc, aluminum, potassium, sodium, etc. may be included.

The catalyst for the reverse water gas shift reaction and the catalyst for the Fischer-Tropsch synthesis reaction may be solid-supported catalysts. In one embodiment of the invention, the solid support is a variety of metal salts, metalloid oxides and/or metal oxides, such as titania (titanium oxide), zirconia (zirconium oxide), silica (silicon oxide), alumina (aluminum oxide). , magnesia (magnesium oxide), and magnesium chloride. In one specific embodiment of the present invention, the solid support is alumina (Al2O3), silica (SiO2), magnesia (MgO), titania (TiO2), zirconia (ZrO2), cerium (IV) oxide (CeO2), or a combination thereof. It can be included.

The reaction in the first reaction section is preferably carried out at 200°C to 500°C at 3 bar to 100 bar, and preferably at 200°C to 400°C at 15 bar to 50 bar. If the reaction proceeds at temperatures and pressures below the lower limit, the conversion reaction of carbon dioxide is insufficient and the production rate of hydrocarbons is low, which is undesirable, and if the reaction proceeds above the upper limit, the amount of low molecular weight hydrocarbons produced increases, and There is a problem that energy efficiency decreases.

Since exothermic reactions mainly occur in the first reaction section and product selectivity is sensitive to reaction temperature, a cooling device (not shown) is required to remove heat generated in the first reaction section for stable operation. The cooling device may be installed separately in the form of a heat exchanger at the rear of the first reaction unit or may be in a form that cools the first reaction unit itself.

When a heat exchanger is installed separately at the rear of the first reaction unit, it is preferable to use a multi-stage reaction system in which the first reaction unit and the heat exchanger are continuous. In the case of cooling the first reaction unit itself, a cooling device is used. 1 It is preferable to use an isothermal reactor or quasi-isothermal reactor mounted inside the reaction unit.

It is a type of isothermal or quasi-isothermal reactor. A catalyst is installed inside the tube, reactants flow to the catalyst layer to cause a reaction, and a cooling medium (mainly water or steam) flows to the outside (shell), generating heat from the reaction tube. A tube-and-shell type multi-tube reactor can be used to remove the , or conversely, a cooling medium flows through the tube and a catalyst layer is placed on the outside to allow reactants to flow and cause a reaction.

In another type of isothermal or quasi-isothermal reactor, a cooling pipe is installed inside the cylindrical reactor and a cooling medium flows through the cooling pipe to recover reaction heat. Cooling tubes can be in the form of coils or multi-tubes and can be installed only in certain areas of the reaction tube. It is desirable to select the partial region close to the outlet of the reactor (i.e., the lower region in the downward flow type and the upper region in the upward flow type).

Meanwhile, the second reaction unit 520 receives the product of the first reaction unit 510 from the first reaction unit without a separate separation process and performs an oligomerization reaction. Without _the separation process of C ₅₊ hydrocarbons with 5 or more carbon atoms _, higher-carbon _hydrocarbons ( C ₅₊ or more), preferably can be converted into hydrocarbons and paraffinic hydrocarbons having 5 to 11 carbon atoms.

In the present invention, the oligomerization reaction is a reaction in which lower C ₁ to C ₄ hydrocarbons, including unconverted reactants, are oligomerized and converted into hydrocarbons with a high carbon number that can exist mainly in the liquid phase, and the oligomerization reaction is performed in a reactor type. , the selectivity of the product can be adjusted depending on the reaction temperature, reaction pressure, catalyst type, etc.

The second reaction unit 520 may use one or more reactors filled with a catalyst to perform an oligomerization reaction, and the one or more reactors in which the oligomerization reaction is performed are not limited in form, and include a fixed bed reactor, a fluidized bed reactor, A known reaction process using a mobile bed reactor or the like can be applied. In addition, the second reaction unit 520 may be performed in any of the forms of batch, semi-continuous, or continuous, but is preferably performed in a continuous manner. Furthermore, a single reactor may be used, but it may be performed in series or parallel. A plurality of reactors arranged may be used. However, since the oligomerization reaction is an exothermic reaction, it is preferable to use a reactor that can easily control the reaction heat. Therefore, even a fixed bed reactor can be used as an adiabatic quenching reactor. In addition, coke is generated during the reaction, and the generated coke deactivates the catalyst, so a system that can regenerate the catalyst by periodically burning the coke during the reaction is needed. Therefore, a swing bed reactor can be used.

In addition, the catalyst charged in the reactor of the second reaction section is a catalyst for oligomerization reaction that can promote the oligomerization reaction, and a ZSM-5 zeolite catalyst having a Bransted acid site can be used. At this time, it was unexpectedly discovered that by adjusting the Si/Al molar ratio of ZSM-5, hydrocarbons with a specific carbon number among the C ₅₊ produced could be more selectively produced.

When the molar ratio of Si/Al is set to 5 or more, preferably in the range of 10 to 100, the production of C ₅₊ increases. If the Si/Al range is further narrowed to 10 to 35, preferably 15 to 25, the overall C ₅₊ yield slightly decreases, but the selectivity for C ₈ to C ₁₀ hydrocarbons among C ₅₊ hydrocarbons increases. appears even higher. Since the hydrocarbons of C ₈ to C ₁₀ have more diverse uses than hydrocarbons of other carbon numbers and may have higher added value, the Si/Al molar ratio can be adjusted to the range of 10 to 35, if necessary, to increase the production of hydrocarbons of C ₈ to C ₁₀ . can also be increased.

The oligomerization reaction in the second reaction unit may be performed at 220°C to 280°C, preferably at 230°C to 250°C. If the reaction temperature is less than 220 ℃, the effect of the oligomerization reaction may be minimal, and if it exceeds 280 ℃, the oligomerization reaction decreases, the aromatization reaction is promoted, the yield of long-chain hydrocarbons decreases, and at the same time, the catalyst phase This may cause problems such as increased coke production, faster catalyst deactivation speed, and shorter catalyst regeneration cycle.

The reaction conditions of the second reaction section identify the optimal reaction conditions and catalysts that can maximize the production of high-value products, preventing overload of the separation section 530, which will be described later, and reducing operating costs. there is.

The separation unit 530 is disposed at the rear of the second reaction unit 520 to separate the products produced in the second reaction unit into lower hydrocarbons of C ₁ to C ₄ containing unconverted reactants (carbon monoxide, carbon dioxide, hydrogen) and Separation is carried out with C ₅₊ hydrocarbons having 5 or more carbon atoms. These separations can be performed through various techniques known in the art, and non-limiting examples may include distillation columns, flash drums, etc.

In one embodiment, an inlet (not shown) is formed on one side of the separation unit 530 to allow the product of the second reaction unit to flow in, and water and/or higher hydrocarbons of C ₅₊ or higher are separated from the introduced reaction product to the lower outlet ( (not shown), etc., and the remaining light products (lower hydrocarbons of C ₁ to C ₄ ) and unconverted reactants can be discharged to the upper outlet (not shown) and supplied to the recirculation unit 540. .

The recirculation unit 540 receives light products (lower hydrocarbons of C ₁ to C ₄ ) and unconverted reactants 541 from the separation unit 530, resupplies some of the stream 543 to the first reaction unit, and supplies the remainder ( 544) supplies synthetic natural gas to the third reaction unit 550 that generates it. The ratio of the stream 543 resupplied to the first reaction unit among the streams 541 flowing from the recirculation unit is defined as the recirculation ratio, and this recirculation ratio may be 0 to 0.9 in volume ratio.

Carbon dioxide in the stream supplied to the first reaction unit through the recirculation unit 540 is reused as a reactant in the first reaction unit 510 along with carbon dioxide and hydrogen injected from the outside, thereby improving overall carbon efficiency.

Additionally, part or all of the stream flowing out of the recirculation unit can be supplied to the third reaction unit 550 and converted into synthetic natural gas through a methanation reaction.

The third reaction unit 550 is provided with one or more catalytic reactors, and a synthetic natural gas production reaction is performed within the catalytic reactor. The catalytic reactor in the third reaction section can be variably changed in size or shape depending on production capacity, supply amount, catalyst, etc., and a fixed bed reactor, a fluidized bed reactor, etc. may be preferably used.

In the catalytic reactor of the third reaction unit _, methane or low hydrocarbons (C ₁ to C _{4 4} ) and water, etc. are produced.

At this time, the catalytic reactor of the third reaction section may be mainly used in the form of an isothermal or adiabatic reactor, and the reaction temperature of the isothermal reactor is usually maintained at a temperature of 200 ℃ ~ 450 ℃, and in the case of an adiabatic reactor, the temperature may be raised to 700 ℃. there is.

In addition, the H ₂ / (3CO + 4CO ₂ ) molar ratio in the third reaction section may be 0.9 to 1.1, preferably 0.95 to 1.0, and the reaction may be mainly carried out in the presence of a Ni-based catalyst, and the catalyst is a pellet. It may include solid pellets, granules, plates, tablets, or rings.

Since a very severe exothermic reaction occurs in the third reaction section, a cooling device is required to remove the heat generated in the reaction section for stable operation. The cooling device may be installed separately in the form of a heat exchanger at the rear of the reactor, or may be in the form of cooling the reactor itself. When a separate heat exchanger is installed at the rear of the reactor, it is preferable to use a multi-stage reaction system in which the reactor and heat exchanger are connected in succession. In the case of cooling the reactor itself, it is preferable to use an isothermal reactor or quasi-isothermal reactor in which a cooling device is installed inside the reactor. A tube and shell type multi-tube reactor can be used as a type of isothermal or quasi-isothermal reactor. A catalyst is installed inside the tube of the tube and shell type multi-tube reactor, reactants flow to the catalyst layer and a reaction occurs, and a cooling medium (mainly water or steam) flows to the outside (shell) to react. Be sure to remove the heat generated in the pipe. Or, conversely, a cooling medium can flow through the pipe and a catalyst layer can be placed on the outside, and reactants can flow through it to cause a reaction. In another type of isothermal or quasi-isothermal reactor, a cooling pipe is installed inside the cylindrical reactor and a cooling medium flows through the cooling pipe to recover reaction heat. Cooling tubes can be in the form of coils or multi-tubes and can be installed only in certain areas of the reaction tube. It is desirable to select the partial region close to the outlet of the reactor (i.e., the lower region in the downward flow type and the upper region in the upward flow type).

Meanwhile, the third reaction unit 550 may additionally include a separation device (not shown), where the separation device is a device that separates and removes water, etc. in the product of the synthetic natural gas production reaction, and is known in the relevant technical field. Separation can be achieved through a variety of techniques, and non-limiting examples may include a condenser that cools and separates the reaction product.

The synthetic natural gas produced according to the present invention contains low-grade hydrocarbons (C ₁ to C ₄ ) generated in the first reaction unit, and can be directly connected to the LNG city gas piping network without a separate heat quantity adjustment process, thereby replacing the existing synthetic natural gas. It is much more economical than the gas generation process.

Hereinafter, a specific embodiment of the system for converting carbon dioxide into hydrocarbons according to the present invention will be described in more detail with reference to FIG. 4.

Carbon dioxide and hydrogen, which are raw material gases, are mixed with the recycled stream 543 in the first mixer 501 and then compressed in the first compressor 502 to an appropriate pressure for the conversion reaction. At this time, the pressure may be in the range of 3 bar to 100 bar, and preferably 15 bar to 50 bar. The compressed mixed gas is then heat-exchanged in the first heat exchanger 503 and then flows into the first reaction unit 510, where a water-gas conversion reaction and a Fischer-Tropsch synthesis reaction occur. At this time, the temperature of the mixed gas after heat exchange in the first heat exchanger 503 is appropriately maintained at 200°C to 500°C, preferably 250°C to 400°C.

The product flowing out of the first reaction unit 510 is again heat-exchanged in the second heat exchanger 511 to maintain the mixed gas temperature after heat exchange at 220 ℃ to 280 ℃, and then flows into the second reaction unit 520. and performs an oligomerization reaction to convert it into a higher carbon number hydrocarbon. The product converted into a high-carbon hydrocarbon in this way is introduced into the third heat exchanger 521 for heat exchange and then supplied to the separation unit 530 at the rear.

The effluent from the second reaction unit flowing into the separation unit 530 is a C ₁ to C ₄ low hydrocarbon stream 541 including unconverted reactants (carbon monoxide, carbon dioxide, hydrogen), and a C ₅₊ hydrocarbon stream with 5 or more carbon atoms ( 531). Thereafter, the separated C ₅₊ hydrocarbon stream 531 flows into the decanter 532 through a pipe, and after the mixed water is removed, the final product, C ₅₊ hydrocarbon, is obtained.

Meanwhile, the low-grade hydrocarbon stream 541 of C ₁ to C ₄ containing unconverted reactants (carbon monoxide, carbon dioxide, hydrogen) separated in the separation unit 530 is returned to the first mixer 501 through the splitter 542. It is divided into a stream 543 and a stream 544 sent to the second mixer 545. The stream 544 sent to the second mixer 545 separated by the splitter 542 is mixed with the hydrogen added in the second mixer 545 and exchanged heat through the fourth heat exchanger 546, and then the third mixer 545 is mixed with hydrogen. It is introduced into the reaction unit 550 to generate synthetic natural gas.

Since the reaction in the third reaction unit 550 is converted to 100%, the reaction gas is completely converted and unconverted reactants no longer exist. Thereafter, the effluent from the third reaction unit 550 is introduced into the synthetic natural gas separator 560 to remove water, and then discharged as synthetic natural gas.

Meanwhile, the stream 543 branched from the splitter 542 is returned to the first mixing device 501, mixed with newly introduced carbon dioxide and hydrogen, and then transferred to the first compressor 502 and the first heat exchanger 503. A reaction is performed in the first reaction unit to produce hydrocarbons.

In addition, Figure 5 shows another embodiment of the carbon dioxide to hydrocarbon conversion system 500 according to the present invention, a reverse water gas conversion reaction unit 560 that performs a reverse water gas conversion reaction in front of the first reaction unit 510. ) has a configuration that further installs. According to this configuration, the carbon dioxide to hydrocarbon conversion system 500 includes a reverse water gas conversion reaction unit 560 that introduces carbon dioxide and hydrogen to perform a reverse water gas conversion reaction; A first reaction unit 510 that receives the effluent from the reverse water gas conversion reaction unit and generates hydrocarbons; a second reaction unit 520 that receives the effluent from the first reaction unit and performs an oligomerization reaction; A separation unit 530 that receives the effluent from the second reaction unit and separates C ₅₊ hydrocarbons having 5 or more carbon atoms from the mixture of lower hydrocarbons having 1 to 4 carbon atoms and unreacted substances; A recirculation unit 540 that receives the mixture of lower hydrocarbons and unreacted substances separated from the separation unit, re-supplies some of them to the first reaction unit, and supplies the remainder to the third reaction unit at the rear of the recirculation unit; And a third reaction unit 550 that generates synthetic natural gas by adding hydrogen to the feed supplied from the recirculation unit at the rear end of the recirculation unit.

The reverse water gas conversion reaction unit 560 performs a reverse water gas conversion reaction by introducing carbon dioxide and hydrogen, and may be equipped with one or more reactors filled with a catalyst to perform a reverse water gas conversion reaction of the introduced gas. and the catalyst for the reverse water gas shift reaction is as described above.

In addition, the system includes a thermal energy supply device (not shown) that supplies the reaction heat of the synthetic natural gas production reaction generated in the first reaction unit 510 and the third reaction unit 550 to the reverse water gas conversion reaction unit 560. ) may further include, at the rear end of the reverse water gas conversion reaction unit 560, water is removed from the product and then supplied to the first reaction unit 510, or carbon dioxide is separated from the product of the reverse water gas conversion reaction unit. It is returned to the reverse water gas conversion reaction unit 560, and a carbon dioxide separator (not shown) that supplies the product from which carbon dioxide has been separated and removed to the first reaction unit may be further added.

The heat energy required in the reverse water gas conversion reaction unit 560 may be supplied from the first reaction unit 510 and/or the third reaction unit 550. The reaction heat generated in the reaction unit is recovered through a heat exchanger (not shown) installed in each reaction unit, and the recovered heat is formed outside the reverse water gas conversion reaction unit through a heat energy supply pipe (not shown) using a heat medium. As it is supplied to the flow path, the recovered reaction heat can be supplied to the reverse water gas conversion reaction unit. To this end, the heat transfer medium in which the reaction heat generated in the first reaction unit 510 and/or the third reaction unit is recovered is flowed to a reaction raw material gas preheater in the form of a heat exchanger mounted in front of the reverse water gas conversion reaction unit, or It can also be flowed to a heat exchanger in the form of a heating tube mounted inside the gas conversion reaction unit.

Alternatively, the reaction raw material gas injected into the reverse water gas conversion reaction unit 560 may be directly used as a heat medium to recover the reaction heat of the first reaction unit 510 and/or the third reaction unit 550. .

The above two methods may be used in combination to efficiently receive the heat energy required by the reverse water gas conversion reaction unit 560 from the first reaction unit 510 and/or the third reaction unit.

A relatively high temperature of 300 ℃ or higher is thermodynamically advantageous for the reverse water gas conversion reaction, but since the synthetic natural gas production reaction can proceed even at a reaction temperature of 300 ℃ or higher, it is better to use the reaction heat from the synthetic natural gas production reaction for the reverse water gas conversion reaction. It is advantageous.

Thereafter, the stream discharged from the reverse water gas conversion reaction unit 560 is heat-exchanged through a heat exchanger, etc., and then introduced into the above-described first reaction unit 510, and goes through the same flow process as in the description of FIGS. 3 and 4. It is again introduced into the second reaction unit 520 and the third reaction unit 550 and converted into hydrocarbons with 5 or more carbon atoms and synthetic natural gas.

One of the differences between the process of FIG. 3 and the process of FIG. 5 described above is that in the process of FIG. 5, carbon dioxide has already been converted to carbon monoxide and is introduced into the first reaction unit with a high carbon monoxide concentration, so C ₅ compared to the process of FIG. 3. ₊ More hydrocarbons can be produced.

In addition, since the reverse water gas shift reaction has a high yield at high temperatures, and the Fischer-Tropsch conversion reaction has a high yield at low temperatures, the operating temperature of the first reaction unit in FIG. 3 is the same as the reverse water gas shift reaction and the Fischer-Tropsch synthesis reaction. There was no choice but to use an appropriate intermediate temperature between the optimal temperatures of There is room to maintain the reaction temperature at an appropriately low temperature. For this reason, in the process of FIG. 5 in which the reversible gas conversion reaction unit is introduced in front of the first reaction unit, the process of FIG. 3 without the reversible gas conversion reaction unit Compared to this, the production rate of C ₅₊ hydrocarbons may be higher.

Hereinafter, a method for converting carbon dioxide into hydrocarbons using the above-described carbon dioxide to hydrocarbon conversion system according to the present invention will be described in detail.

The method for converting carbon dioxide into hydrocarbons according to the present invention includes a first reaction step of introducing an incoming gas containing carbon dioxide and hydrogen to perform a reverse water gas conversion reaction and a Fischer-Tropsch synthesis reaction; A second reaction step of receiving the effluent from the first reaction step and performing an oligomerization reaction under a ZSM-5 catalyst; A separation step of receiving the effluent from the second reaction step and separating C ₅₊ hydrocarbons having 5 or more carbon atoms from the mixture of lower hydrocarbons having 1 to 4 carbon atoms and unreacted substances; A recycling step of receiving the mixture of lower hydrocarbons and unreacted substances separated from the separation step, resupplying some of them to the first reaction step, and supplying the remainder to the third reaction step; And a third reaction step of generating synthetic natural gas by adding hydrogen to the feed supplied from the recirculation step. After the third reaction step, a synthetic natural gas separation step may be added in which the synthetic natural gas generated in the third reaction step is supplied and water and high boiling point hydrocarbons are further separated.

At this time, the first reaction step can perform the reverse water gas conversion reaction and Fischer-Tropsch synthesis reaction at 200 ℃ ~ 400 ℃ at 10 bar ~ 30 bar, and the second reaction step can be performed at 1 bar ~ 20 bar, reaction temperature The oligomerization reaction can be performed at 220°C to 280°C.

The Si/Al molar ratio of the ZSM-5 catalyst in the second reaction step may be 5 or more, preferably 10 to 100. In order to increase the yield of C8 to C10 in the product, the Si/Al range can be adjusted to 10 to 35, preferably 15 to 25.

In addition, among the streams introduced in the recycling step, it is preferable that the stream recycled back to the first reaction step has a volume ratio of 0 to 0.9 in terms of maximizing carbon efficiency and energy efficiency and reducing carbon dioxide emissions.

At this time, the proportion of the stream supplied to the third reaction step is high in that low-grade hydrocarbon (C ₁ to C ₄ ) compounds account for a large proportion of the total hydrocarbon compounds, and the proportion of by-products re-supplied to the first reaction step through the recycling process is As it increases, the content of higher hydrocarbon (C ₅₊ ) compounds increases.

Since the calorific value of the synthetic natural gas produced in the third reaction step is related to the content of lower hydrocarbon (C ₁ to C ₄ ) compounds included, the operating conditions in the first separation step and/or the second separation step, for example, By adjusting the process temperature and/or pressure, the calorific value of the finally produced synthetic natural gas can be adjusted by adjusting the content of hydrocarbon compounds (C ₂₊ ) with two or more carbon atoms among the lower hydrocarbon (C ₁ to C ₄ ) compounds.

The pressure in the first separation step and/or the second separation step is 10 barg to 50 barg and the temperature is -50 ° C to 0 ° C, preferably the pressure is 20 barg to 30 barg and the temperature is -30 ° C to - When the temperature is 10°C, the calorific value of the synthetic natural gas produced in the third reaction step may be similar to that of typical city gas.

The calorific value of the synthetic natural gas produced can also be adjusted by adjusting the pressure and/or temperature in the synthetic natural gas separation step. In this case, the pressure in the second separation step is 10 barg to 50 barg and the temperature is -50 ℃. It may be ~0 ℃, preferably the pressure is 20 barg ~ 30 barg, and the temperature is -30 ℃ ~ -10 ℃.

Meanwhile, a water separation step may be further included to separate the water produced before the first separation step and/or the second separation step, and the conditions may be 30° C. to 50° C. at 10 barg to 50 barg. there is

In the method for converting carbon dioxide into hydrocarbons according to the present invention, a reverse water gas conversion reaction step may be additionally performed before the first reaction step. At this time, part or all of the heat supplied in the reverse water gas conversion reaction step can be replaced with reaction heat generated in the first reaction step and/or the third reaction step.

In addition, a carbon dioxide separation step of separating carbon dioxide from the product in the reverse water gas conversion step and returning the separated carbon dioxide to the reverse water gas conversion step is further included, and after the carbon dioxide is separated and removed in the carbon dioxide separation step, A flow may be introduced into the first reaction stage.

Since the method of converting carbon dioxide into hydrocarbons according to the present invention is the same as mentioned in the corresponding conversion system of carbon dioxide into hydrocarbons, a person skilled in the art will be able to clearly understand the method of converting carbon dioxide into hydrocarbons, as follows. To avoid duplication of explanation, it will be omitted.

Hereinafter, the present invention will be described in more detail through examples. These examples are merely for illustrating the present invention, and the scope of the present invention should not be construed as limited by these examples.

<Example 1>

1 g of an iron-based catalyst with a composition ratio of 4K/100Fe-6Cu-16Al was charged into a 1/2-inch stainless steel fixed bed reactor, and the incoming gas containing carbon dioxide, carbon monoxide, and hydrogen was mixed at a molar ratio of carbon dioxide: carbon monoxide: hydrogen of 1:1. :5 was supplied at a flow rate of 1,800 mL/gcat.h, and then the reverse water gas shift reaction and Fischer-Tropsch synthesis reaction (first reaction step) were performed under the conditions of a reaction temperature of 320 °C and a reaction pressure of 20 bar.

Afterwards, the product generated from the reverse water gas shift reaction and Fischer-Tropsch synthesis reaction was placed in a 1/2 inch stainless steel fixed bed reactor filled with 0.6 g of zeolite catalyst (NH ₄ -ZSM5, Si/Al=25 mole ratio, Zeolyst). It was supplied at a flow rate of 3,000 mL/gcat.h, and an oligomerization reaction (second reaction step) was performed under the conditions of a reaction temperature of 250 °C and a reaction pressure of 20 bar to prepare hydrocarbons. The produced hydrocarbons were analyzed using on-line GC (TCD, FID), and the results are shown in Figures 6 to 8.

<Examples 2 to 4>

Hydrocarbons were prepared in the same manner as in Example 1, except that the reaction was performed under the conditions shown in Table 1 below. The produced hydrocarbons were analyzed using on-line GC (TCD, FID), and the results are shown in Figures 6 to 8.

<Comparative Example 1>

Hydrocarbons were prepared in the same manner as in Example 1, but without performing the second reaction step. The produced hydrocarbons were analyzed using on-line GC (TCD, FID), and the results are shown in Figures 6 to 8.

<Comparative Example 2>

Hydrocarbons were prepared and analyzed in the same manner as in Example 1, except that the temperature of the second reaction step was set to 300°C, and the results are shown in Figures 6 to 8.

division first reaction step second reaction step Temperature (℃) pressure (bar) Temperature (℃) pressure (bar) catalyst
(Si/Al molar ratio) Example 1 320 20 250 20 NH ₄ -ZSM5 (25) Example 2 320 20 230 20 NH ₄ -ZSM5 (25) Example 3 320 20 250 20 NH ₄ -ZSM5 (15) Example 4 320 20 250 20 NH ₄ -ZSM5 (40) Comparative Example 1 320 20 - - - Comparative Example 2 320 20 300 20 NH ₄ -ZSM5 (25)

As shown in Figures 6 to 8, in the case of Examples 1 to 4, Comparative Example 1 in which the second reaction step was not performed, and the second reaction step in which the second reaction step was performed at 300° C., which is higher than the temperature range according to the present invention. It can be seen that the selectivity for hydrocarbons with 5 or more carbon atoms is high compared to Comparative Example 2.

In particular, among Examples 1, 3, and 4 in which the reaction was performed at the same temperature, when the Si/Al ratio was in the range of 10 to 35 as in Examples 1 and 3, the selectivity for hydrocarbons with 8 to 10 carbon atoms increased, It can be confirmed that oil with higher added value is produced (see Figure 8).

<Example 5 and Comparative Examples 3 to 5>

In order to confirm the effectiveness of the process according to the present invention, process simulation was performed using the Aspen Plus (Aspen Tech.) program, and the results are shown in Figures 9 and 10. In the process simulation, the process corresponding to FIG. 3 was configured, and the conditions for each unit reaction step were those listed in Table 2 below. In Comparative Examples 3 and 4, a process simulation was performed in which synthetic natural gas was produced by methanation after the reverse water gas conversion reaction and Fischer-Tropsch synthesis reaction without the second reaction step. At this time, Energy Efficiency is the sum of the LHV (Lower Heat Value) of the product divided by the LHV (Lower Heat Value) of hydrogen and the total energy required for process operation, and the net amount of _CO2 generated is determined by the process. It was calculated by subtracting the amount of CO ₂ consumed by the process from the CO ₂ generated. At this time, CO ₂ generated by the process included the amount of CO ₂ generated when burning city gas to produce energy used in the process.

division Inflow gas (raw material) first reaction step
(RWGS and FTS reactions) second reaction step
(Oligomerization reaction) Third reaction step
(Methanation reaction) temperature
(℃) enter
(bar) temperature
(℃) enter
(bar) temperature
(℃) enter
(bar) Example 5 _CO2 / _H2 300 30 250 20 450 10 Comparative Example 3 CO/ _H2 300 10 - - 450 10 Comparative Example 4 _CO2 / _H2 300 30 - - 450 10 Comparative Example 5 CO/ _H2 300 10 250 20 450 10

As shown in Figure 9, when comparing Example 5 and Comparative Examples 3 to 5 in terms of synthetic crude oil production or reactor flow rate of the first reaction step, the second reaction step is performed using carbon dioxide as a raw material. It was found that Example 5 according to the present invention was advantageous for the production of synthetic fuel (Syncrude), and it was confirmed that the reactor flow rate in the first reaction step was also reduced, making it possible to reduce the size of the reactor.

In addition, as shown in Figure 10, in terms of energy efficiency and carbon dioxide emissions, Example 5 according to the present invention is supplied to the first reaction step and the third reaction step as the second reaction step is performed using carbon dioxide as a raw material. , the amount of the recycled gas stream is small, so that the energy efficiency is high and the net carbon dioxide emissions are low compared to Comparative Examples 3 to 5 in which the second reaction step is not performed or carbon monoxide rather than carbon dioxide is used as the input gas. I was able to.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and this is also the present invention. It is natural that it falls within the scope of .

500: System for converting carbon dioxide into hydrocarbons
510: first reaction unit
520: second reaction unit
530: separation part
540: Recirculation unit
550: third reaction unit
560: Reverse water gas conversion reaction unit

Claims (12)

a first reaction unit that introduces incoming gas containing carbon dioxide and hydrogen to perform a reverse water gas conversion reaction and a Fischer-Tropsch synthesis reaction;
a second reaction unit that receives the effluent from the first reaction unit and performs an oligomerization reaction;
A separation unit that receives the effluent from the second reaction unit and separates C ₅₊ hydrocarbons having 5 or more carbon atoms from the mixture of lower hydrocarbons having 1 to 4 carbon atoms and unreacted substances;
a recirculation unit that receives the mixture of lower hydrocarbons and unreacted substances separated from the separation unit and re-supplies some of them to the first reaction unit, and supplies the remainder to the third reaction unit; and
It includes a third reaction unit that generates synthetic natural gas by injecting hydrogen into the feed supplied from the recirculation unit,
The second reaction unit performs an oligomerization reaction at 220°C to 280°C in the presence of ZSM-5 zeolite, and the effluent from the first reaction unit is supplied to the second reaction unit as is without separation of lower hydrocarbons and C5+ hydrocarbons having 5 or more carbon atoms. A system for converting carbon dioxide into hydrocarbons, characterized in that:
In paragraph 1
A system for converting carbon dioxide into hydrocarbons, wherein the first reaction unit performs a reverse water gas conversion reaction and a Fischer-Tropsch synthesis reaction at 200 ° C to 500 ° C at 3 bar to 100 bar.
According to paragraph 1,
A system for converting carbon dioxide into hydrocarbons, wherein the inlet gas has a molar ratio of hydrogen to carbon dioxide of 1 to 5.
According to paragraph 1,
A system for converting carbon dioxide into hydrocarbons, characterized in that the Si/Al molar ratio of the ZSM-5 catalyst in the second reaction section is 10 to 35.
According to paragraph 1,
A system for converting carbon dioxide into hydrocarbons, further comprising a reverse water gas conversion reaction unit that introduces carbon dioxide and hydrogen into the front end of the first reaction unit to perform a reverse water gas conversion reaction.
According to clause 5,
A system for converting carbon dioxide into hydrocarbons, further comprising a thermal energy supply device that supplies thermal energy generated in the first reaction unit and/or the third reaction unit to the reverse water gas conversion reaction unit.
(a) a first reaction step of introducing an incoming gas containing carbon dioxide and hydrogen to perform a reverse water gas shift reaction and a Fischer-Tropsch synthesis reaction;
(b) a second reaction step of receiving the effluent of the first reaction step and performing an oligomerization reaction;
(c) a separation step of receiving the effluent from the second reaction step and separating C ₅₊ hydrocarbons having 5 or more carbon atoms from the mixture of lower hydrocarbons having 1 to 4 carbon atoms and unreacted substances;
(d) a recycling step of receiving the mixture of lower hydrocarbons and unreacted substances separated from the separation step, resupplying some of them to the first reaction step, and supplying the remainder to the third reaction step; and
(e) a third reaction step of generating synthetic natural gas by adding hydrogen to the feed supplied from the recirculation step,
In the second reaction step, an oligomerization reaction is performed at 220°C to 280°C in the presence of ZSM-5 zeolite, and the effluent of the first reaction step is directly subjected to the second reaction without separation of lower hydrocarbons and C5+ hydrocarbons having 5 or more carbon atoms. A process for converting carbon dioxide into hydrocarbons, characterized in that it is supplied in stages.
In clause 7,
The first reaction step is a process for converting carbon dioxide into hydrocarbons, characterized in that performing a reverse water gas conversion reaction and a Fischer-Tropsch synthesis reaction at 200 ° C to 500 ° C at 3 bar to 100 bar.
In clause 7,
A process for converting carbon dioxide into hydrocarbons, wherein the inlet gas has a molar ratio of hydrogen to carbon dioxide of 1 to 5.
In clause 7,
A process for converting carbon dioxide into hydrocarbons, characterized in that the Si/Al molar ratio of the ZSM-5 catalyst in the second reaction step is 10 to 35.
In clause 7,
A process for converting carbon dioxide into hydrocarbons, further comprising a reverse water gas conversion step of converting carbon dioxide into carbon monoxide by introducing carbon dioxide and hydrogen before the first reaction step.
According to clause 11,
A process for converting carbon dioxide into hydrocarbons, characterized in that the heat of reaction generated in the first reaction step and/or the third reaction step is used in the reaction of the reverse water gas conversion step.