KR102580160B1 - Method and apparauts for preparing syntheitc nautral gas - Google Patents

Abstract

The present invention relates to a production method and production equipment for producing synthetic natural gas using carbon monoxide, and includes a first methane synthesis reaction step in which methane is synthesized by supplying reactants containing carbon monoxide and hydrogen to a first methane synthesis reactor, a first methane synthesis reaction step, A synthesis comprising a cooling step of cooling the effluent flowing out of the methane synthesis reactor, passing the cooled effluent through a separation membrane contactor to remove water and CO ₂ from the effluent, and recovering the effluent containing carbon dioxide. A method for producing natural gas, and a catalytic reactor for methane synthesis in which a reactant stream containing carbon monoxide and hydrogen reacts to synthesize methane, a cooler for cooling the effluent of the catalytic reactor for methane synthesis, and a shell side and tube separated by a porous membrane It includes a side, the cooled effluent flows into the tube side, water flows into the shell side, and water and carbon dioxide in the cooled effluent pass through the porous separation membrane and are removed by dissolving in water on the shell side. A synthetic natural gas production facility comprising a phosphorus membrane contactor is provided.

Description

Synthetic natural gas manufacturing process and manufacturing equipment {METHOD AND APPARAUTS FOR PREPARING SYNTHEITC NAUTRAL GAS}

The present invention relates to a production method and production equipment for producing synthetic natural gas using carbon monoxide.

Synthetic natural gas (SNG) can be synthesized through the methane synthesis reaction of carbon monoxide and hydrogen, and the methane synthesis reaction can be expressed in the following equation (1).

Methane synthesis reaction of CO: 3H ₂ + CO → CH ₄ + H ₂ O, ΔH _rxn = -206 kJ/mol (1)

As can be seen from equation (1), when producing synthetic natural gas by methane synthesis reaction with carbon monoxide, when one molecule of methane is produced, one molecule of H ₂ O is produced. Meanwhile, the methane synthesis reaction is an exothermic reaction (ΔH _rxn = -206 kJ/mol), and the temperature of the catalyst layer increases due to the heat of reaction, so there is a limit to the equilibrium conversion rate.

Therefore, the SNG synthesis process by methane synthesis of carbon monoxide usually consists of several reactors. The temperature of the product produced by reaction in the first reactor is lowered, the produced water is removed, and the remaining carbon monoxide is injected into the second reactor. Everyone is reacting.

A schematic diagram of this SNG synthesis process is schematically shown in Figure 1. The SNG synthesis process usually consists of several reactors, and Figure 1 shows a process using two reactors as an example.

According to Figure 1, the catalyst reactor for methane synthesis includes a methane synthesis reactor (2, 6), a cooler (3, 7), and a separator (4, 8). A methane synthesis reaction is performed by injecting reactants containing carbon monoxide and hydrogen into the methane synthesis reactor (2), a catalyst reactor for methane synthesis. Thereafter, in the cooler (3), the effluent from the methane synthesis reactor and the catalyst reactor for methane synthesis are cooled to lower the temperature, and then the cooled effluent passes through the separator (4), where water is converted into gas-liquid. separated.

Next, using the effluent from which water has been removed, a methane synthesis reaction is performed in the second methane synthesis reactor, a catalyst reactor for methane synthesis (6), in the same process as the first methane synthesis reaction, followed by cooling by the cooler (7). And through a water removal process by the separator 8, the desired synthetic natural gas is generated.

As can be seen from the above equation (1), water is produced by the hydrogenation reaction of carbon monoxide, and a water gas conversion reaction such as equation (2) is also generated as a side reaction in each reactor.

Water gas shift reaction: CO + H ₂ O → CO ₂ + H ₂ (2)

Through this water-gas shift reaction, carbon monoxide, a carbon source of methane, is converted to carbon dioxide, and this water-gas shift reaction can reduce the yield of methane synthesis by carbon monoxide.

Additionally, a portion of the carbon dioxide produced in the side reaction may be converted to methane, as shown in equation (3).

CO ₂ methanation reaction: 4H ₂ + CO ₂ → CH ₄ + 2H ₂ O

However, this methane synthesis reaction using carbon dioxide requires more hydrogen and generates more water as a by-product. Furthermore, CO ₂ may remain in the final product, which causes the problem of reduced methane purity.

In the conventional methane synthesis reaction technology using carbon monoxide, mainly water is separated from the reaction product of the first methane synthesis reaction through gas-liquid separation, and then it is preheated and injected into the second reactor. At this time, because the methane synthesis process is in a high-pressure atmosphere, some carbon dioxide may be dissolved in water, but the flow of reactants and reaction products continues, and the carbon dioxide does not dissolve as much as it can dissolve in water at equilibrium, so a sufficient amount of carbon dioxide is not removed. can not do it.

Accordingly, an embodiment of the present invention seeks to provide a method and equipment that can simultaneously reduce water generated during methane synthesis reaction by carbon monoxide and carbon dioxide generated by water gas shift reaction, which is a side reaction between the water and carbon monoxide.

From one perspective, the present invention relates to a production method for producing synthetic natural gas using carbon monoxide, which includes a first methane synthesis reaction step of supplying reactants containing carbon monoxide and hydrogen to a first methane synthesis reactor to synthesize methane, 1 A cooling step of cooling the effluent flowing out of the methane synthesis reactor, passing the cooled effluent through a separation membrane contactor to remove water and CO ₂ from the effluent, and recovering the effluent containing carbon dioxide. Provides a method for producing synthetic natural gas.

The membrane contactor includes a shell side and a tube side separated by a porous membrane, the cooled effluent flows into the tube side, water flows into the shell side, and water and carbon dioxide in the cooled effluent contact the separation membrane. It can pass through and be removed by dissolving in water on the shell side.

It further includes recovering carbon dioxide by depressurizing the removed carbon dioxide-containing water and degassing at least a portion of the CO ₂ dissolved in the water.

The effluent contains unreacted carbon monoxide and hydrogen, and further includes a second methane synthesis reaction step of supplying the effluent to a second methane synthesis reactor to synthesize methane.

A second cooling step of cooling the second effluent flowing out of the second methane synthesis reactor and introducing the cooled second effluent into the tube side of the membrane contactor including the shell side and tube side separated by a porous membrane, Water is introduced into the shell side, water and carbon dioxide in the cooled effluent are passed through a porous separation membrane and dissolved in water on the shell side to remove water and carbon dioxide in the effluent, and water containing carbon dioxide is recovered to recover the second effluent. Additional steps may be included.

At least one of the carbon dioxide-containing water removed from the effluent and the carbon dioxide-containing water removed from the second effluent, or a mixture thereof, is depressurized and at least a portion of the carbon dioxide dissolved in the carbon dioxide-containing water is degassed to obtain carbon dioxide. It may further include a step of recovering.

The recovered carbon dioxide can be supplied to the second methane synthesis reactor.

The recovered carbon dioxide can be pressurized and supplied to the second methane synthesis reactor.

The membrane contactor or the second membrane contactor can be operated at a pressure ranging from normal pressure to 50 bar.

The separator contactor or the second separator contactor may be made of a type of polymer selected from the group consisting of polypropylene, polyethylene, and polymethyl methacrylate, or a composite of two or more of these polymers.

It is preferable to preheat the reactant and supply it to the first methane synthesis reactor.

It is preferable to preheat the effluent and supply it to the second methane synthesis reactor.

In another aspect, the present invention provides a synthetic natural gas production facility, which includes a catalytic reactor for methane synthesis in which a reactant stream containing carbon monoxide and hydrogen reacts to synthesize methane, and a cooler for cooling the effluent of the catalytic reactor for methane synthesis. and a shell side and a tube side separated by a porous separation membrane, wherein the cooled effluent flows into the tube side, water flows into the shell side, and water and carbon dioxide in the cooled effluent pass through the porous separation membrane. Provided is a synthetic natural gas production facility including a separation membrane contactor that is removed by dissolving in water on the shell side.

The effluent passing through the tube side is supplied, and may further include a second methane synthesis reactor for synthesizing methane by reacting unreacted carbon monoxide and hydrogen in the effluent.

It may further include a preheater for preheating the effluent and supplying it to a second methane synthesis reactor.

It includes a shell side and a tube side separated by a second cooler and a porous separator for cooling the second effluent discharged from the second catalytic reactor for methane synthesis, and the cooled second effluent flows into the tube side. , water flows into the shell side, and the water and carbon dioxide in the cooled second effluent pass through the porous membrane and are dissolved in the water on the shell side and removed.

It may further include a reduced pressure degassing device that recovers carbon dioxide by depressurizing carbon dioxide-containing water discharged from the shell side and degassing at least a portion of the carbon dioxide dissolved in the water.

It further includes a pipe for mixing carbon dioxide-containing water discharged through the shell side of the membrane contactor with carbon dioxide-containing water discharged through the shell side of the second membrane contactor, and the mixed carbon dioxide-containing water can be transferred to the reduced pressure degassing device. .

A carbon dioxide supply pipe may be provided to supply carbon dioxide recovered from the reduced pressure degassing device to the second methane synthesis reactor.

The carbon dioxide supply pipe may be equipped with a pressurizing device to pressurize the carbon dioxide supplied to the second methane synthesis reactor.

According to one embodiment of the present invention, by using a membrane contactor, a large amount of carbon dioxide can be removed along with water, thereby improving the yield of methane and also improving the purity of the finally obtained synthetic natural gas.

In addition, the removed carbon dioxide can be separately recovered and used to promote additional methanation reaction, thereby improving the purity of synthetic natural gas. Furthermore, the recovered carbon dioxide can be used as a raw material in other chemical synthesis processes, or as a stabilizer to adjust the pH of a solution.

Figure 1 is a diagram schematically showing a conventional synthetic natural gas manufacturing process.
Figure 2 is a diagram schematically showing a process for producing synthetic natural gas according to an embodiment of the present invention, and shows an example of removing water and carbon dioxide using a membrane contactor.
Figure 3 is a diagram schematically showing a process for producing synthetic natural gas according to an embodiment of the present invention, showing an example in which carbon dioxide is separated and recovered at the rear of the first methane synthesis reactor and supplied to the second methane synthesis reactor.
Figure 4 is a diagram schematically showing the manufacturing process of synthetic natural gas according to an embodiment of the present invention, showing another example in which carbon dioxide separated and recovered at the rear of each methane synthesis reactor is separated and recovered and supplied to the second methane synthesis reactor. indicates.
Figure 5 is a graph showing the results of the methane production reaction according to temperature changes in the methane synthesis reactor of Example 4.
Figure 6 is a graph showing the results of carbon dioxide removal rate according to the pressure and flow rate of the membrane contactor in Example 5.
Figure 7 is a graph showing the H ₂ removal rate results according to the pressure and flow rate of the membrane contactor in Example 3.

The present invention provides a manufacturing method and manufacturing equipment for producing synthetic natural gas using carbon monoxide.

Hereinafter, the present invention will be described in detail with reference to the attached drawings. The attached drawings are exemplary drawings showing one embodiment of the present invention, and are not intended to limit the present invention thereby.

The synthetic natural gas production method of the present invention relates to a method of producing synthetic natural gas by methanating carbon monoxide and hydrogen. Figure 2 schematically shows an embodiment of the present invention.

According to Figure 2, the method for producing synthetic natural gas of the present invention includes a methane synthesis reaction process including a preheating step of reactants by a preheater, a methane synthesis reaction step, a reaction effluent cooling step, and a carbon dioxide and water removal step.

However, the preheating step can be performed as needed and does not necessarily have to be included. In addition, the attached drawing is shown as including a two-step methane synthesis reaction process, but it is shown as an example, and not only can synthetic natural gas be produced through a one-step methane synthesis reaction process, but also three or more methane synthesis reaction processes. It can be performed by a reaction process, and simply 'methane synthesis reaction' and 'methane synthesis reactor' refer to 'first methane synthesis reaction' and 'first methane synthesis reactor' unless otherwise specified.

In the methane synthesis reaction for producing synthetic natural gas of the present invention, the methane synthesis reaction can be performed by supplying reactants containing carbon monoxide and hydrogen to a methane synthesis reactor.

The reactants supplied to the methane synthesis reactor are not particularly limited as long as they contain carbon monoxide and hydrogen. Sources of carbon monoxide and hydrogen can mainly be produced through reforming reactions, and examples include reaction products obtained by reforming methanol, methane, ethylene glycol, and glycerol.

The methane synthesis reaction using carbon monoxide can be expressed as the following equation (1).

Methane synthesis reaction of carbon monoxide: 3H ₂ +CO → CH ₄ +H ₂ O, ΔH _rxn =-206 kJ/mol (1)

The reactant stream contains 1 to 5 hydrogen per 1 carbon monoxide by volume, for example, more preferably, the volume ratio of carbon monoxide:hydrogen ranges from 1:2.5 to 4.

It is preferable to preheat the reactants containing carbon monoxide and hydrogen before supplying them to the methane synthesis reactor. At this time, preheating of the reactant may be performed at 100 to 300°C. If the temperature of the reactant before injection into the reactor is too low, the reaction may not occur because it does not have the activation energy for the reaction to proceed. If the injection temperature is too high, the equilibrium conversion rate may decrease due to the exothermic nature of the reaction, which may lower the degree of reaction. You can.

Therefore, as shown in FIG. 2, the reactant can be preheated by passing through the preheater 11 and then supplied to the methane synthesis reactor 12. As long as the reactant can be preheated to the above temperature range, the means for preheating the reactant is not particularly limited and can be used in various ways. For example, it can be preheated through a preheating means such as an electric heater, boiler, steam, etc. there is.

The methane synthesis reaction of carbon monoxide and hydrogen can usually be carried out in a temperature range of 200 to 800°C, preferably in the temperature range of 200 to 600°C. Before injecting the reactant into the methane synthesis reactor 12, methane synthesis It is desirable to preheat to the above temperature range where the reaction can occur.

The preheated reactant is put into the methane synthesis reactor 12 to perform a methane synthesis reaction. The methane synthesis reaction is carried out in the presence of a catalyst, and the catalyst may be a catalyst commonly used in methane synthesis. The catalyst is not particularly limited, but for example, a catalyst in which nickel as a catalyst and magnesium, barium, manganese, etc. as cocatalysts are supported on an alumina support can be used.

The methane synthesis reaction in the methane synthesis reactor may be performed in a temperature range of 200 to 800°C. If the temperature of the methane synthesis reaction is less than 200°C, the reaction does not occur because the reaction does not have the activation energy to proceed, and if it exceeds 800°C, the equilibrium conversion rate may decrease due to the exothermic nature of the methane synthesis reaction. This may lower the degree of reaction. Preferably, it may be performed in a temperature range of 200 to 600°C.

Meanwhile, the methane synthesis reaction can be performed in a wide range from normal pressure to 100 bar. In general, the methane synthesis reaction is a reaction in which the number of molecules is reduced, so the higher the pressure, the more advantageous it is, and the methane synthesis reaction is usually performed at high pressure rather than normal pressure. However, when performed at high pressure, the use of devices such as a compressor is required, which requires the use of a large amount of energy, and it is preferably performed in a pressure range of 5 to 30 bar.

Under these conditions, carbon monoxide and hydrogen react to synthesize methane according to the reaction equation (1) above.

Synthetic natural gas containing methane can be obtained from the reaction effluent flowing out of the methane synthesis reactor 12.

On the other hand, as can be seen from the above equation (1), when the methane synthesis reaction occurs, methane is synthesized and water is produced as a by-product, and the methane synthesis reaction as described above is an exothermic reaction, and reaction heat is generated. do. As the temperature of the catalyst layer rises due to the heat of reaction, the equilibrium conversion rate is limited. As a result, unreacted carbon monoxide and hydrogen may exist in the reaction effluent along with the reactants.

Therefore, by cooling the reaction effluent, the temperature is lowered to separate water and carbon dioxide present in the reaction effluent and to synthesize more methane through injection into the secondary reactor.

For this purpose, a cooler 13 is provided to cool the temperature of the reaction effluent flowing out of the rear end of the methane synthesis reactor. The cooling means for cooling the effluent is not particularly limited, but may be a cooler 13 such as a heat exchanger. The heat exchanger is not limited to this, but may be cooled through air or cooling water, and may also be cooled through an electric cooler.

The cooling temperature of the reaction effluent is not particularly limited, but it is preferable to cool the effluent to a temperature of 100° C. or lower in order to remove water. Specifically, it can be cooled to a range of 0 to 100°C, more preferably 5 to 65°C.

Meanwhile, it is preferable to additionally perform a methane synthesis reaction using unreacted carbon monoxide and hydrogen present in the reaction effluent. However, the remaining unreacted carbon monoxide may react with water produced by the methane synthesis reaction to produce carbon dioxide, resulting in a water gas conversion reaction as shown in equation (2).

Water gas shift reaction: CO + H ₂ O → CO ₂ + H ₂ (2)

When this water gas conversion reaction occurs, carbon monoxide, a carbon source of methane, is converted to carbon dioxide, which may reduce methane yield. Some carbon dioxide can be converted to methane through a methanation reaction of carbon dioxide that reacts with hydrogen to synthesize methane, as shown in Equation 3 below, but a lot of hydrogen is required and more water is produced.

Methane synthesis reaction from carbon dioxide: 4H ₂ + CO ₂ → CH ₄ + 2H ₂ O (3)

Furthermore, if carbon dioxide remains in the final product, methane purity decreases.

Therefore, it is desirable to remove water and carbon dioxide from the reaction effluent. In one embodiment of the present invention, the water and carbon dioxide in the effluent are removed using a membrane contactor (14). The separation membrane contactor 14 is one that can be suitably used in the present invention as long as it is commonly used. There is no particular limitation, but there is a boundary between the porous membrane and the gas inside, that is, the tube side through which the reaction effluent flows, and the liquid outside. , Specifically, it may be composed of a shell side through which water is supplied and flows.

At this time, the porous separator of the separator contactor 14 may be formed of polymers such as PP, PE, PMMA, and composites of these polymers.

The liquid on the shell side cannot move to the tube side through the porous separator, but the gas on the tube side can pass through the porous separator to the shell side, which causes water and carbon dioxide in the reaction effluent flowing through the tube side. By contacting the liquid side with a flowing liquid, it can be dissolved in the liquid and removed.

Furthermore, the membrane contactor 14 can be operated in a pressure range of normal pressure to 50 bar. Preferably, the reaction effluent flowing through the membrane contactor 14 is operated at the same pressure as the pressure inside the reactor, whereby water and carbon dioxide can be easily removed from the reaction effluent.

Meanwhile, methane, the reaction product, has low solubility in water and is almost insoluble in the liquid flowing to the shellside. However, the solubility of hydrogen in water is very low compared to carbon dioxide, but as the pressure increases, some of the hydrogen may dissolve in water. Therefore, in order to prevent hydrogen from dissolving in water, it is desirable to increase the flow rate of the gas flowing through the membrane contactor 14. In other words, the faster the gas flow rate and the lower the pressure, the higher the hydrogen recovery rate can be. For this purpose, the reaction effluent passing through the membrane contactor 14 is preferably 0.03 to 1 m/s at a pressure of 5 to 50 bar in the reactor. The higher the linear speed, the more hydrogen can be recovered without loss, but since the removal of carbon dioxide is not easy, it is preferable to flow the reaction effluent within the above range. Under the above conditions, more than 90% of hydrogen can be recovered.

As a result, it is possible to suppress the loss of reactants while selectively removing carbon dioxide and water from the reaction effluent, and to recover methane as a product from the reaction effluent discharged through the tube side of the membrane contactor 14. Depending on the method, methane may be synthesized by further reacting the carbon monoxide and hydrogen remaining in the reaction effluent.

The water and carbon dioxide removed from the reaction effluent are dissolved in the liquid flowing through the shell side of the membrane contactor 14 and discharged. As shown in FIG. 2, the carbon dioxide-containing water discharged from the membrane contactor 14 is transferred to a reduced pressure degassing device 19, and the pressure is lowered to degas the carbon dioxide dissolved in the water. It may include a separation step. . The pressure reduction device 19 can separate carbon dioxide from water by lowering the pressure by opening and closing the pressure reduction valve 20. As a result, carbon dioxide and water are separated, and the separated carbon dioxide can be stored separately and used as a raw material for other chemical synthesis processes or as a stabilizer to adjust the pH of the solution. Furthermore, the recovered carbon dioxide may be used as a reactant in the methane synthesis reaction within the process.

Hereinafter, a second methane synthesis reaction process using the reaction effluent generated in the first methane synthesis reaction process will be described. The second methane synthesis reaction process includes steps and equipment that overlap with the first methane synthesis reaction process, and detailed descriptions thereof will be omitted. Furthermore, the expressions 'first' and 'second' are used to distinguish between the first methane synthesis reaction process and the second methane synthesis reaction process.

The first reaction effluent passing through the first membrane contactor 14 during the first methane synthesis reaction process is subjected to second methane synthesis to further synthesize methane using unreacted carbon monoxide and hydrogen along with methane, which is a reaction product. may be introduced into reactor 16. Since the first reaction effluent is cooled in the first cooler (13) after being discharged from the first methane synthesis reactor (12), it is performed in the first methane synthesis reaction step before being introduced into the second methane synthesis reactor (16). In the same way as, it may include a preheating process in the second preheater 15.

The first reaction effluent preheated in the second preheater 15 is introduced into the second methane synthesis reactor 16 as a reactant of the second methane synthesis reaction, whereby carbon monoxide and hydrogen are converted into reaction formula (1). Methane can be synthesized by reaction.

The reaction conditions of the second methane synthesis reactor 16 are the same as those of the first methane synthesis reactor 12, and detailed descriptions are omitted.

As shown in FIG. 3, carbon dioxide recovered in the first methane synthesis reaction process can be supplied to the second methane synthesis reactor 16 as a reactant for methane synthesis. The supplied carbon dioxide can synthesize methane according to the reaction formula shown in Equation 3. As a result, methane can be additionally synthesized and the methane purity of the reaction product can be improved.

When supplying the carbon dioxide to the second methane synthesis reactor 16, the first reaction effluent supplied into the second methane synthesis reactor 16 is pressurized to a pressure equivalent to the pressure in order to avoid lowering the pressure within the reactor. It is desirable to supply it. For this purpose, as shown in FIG. 3, a pressurizing device 21 may be provided in the supply pipe through which the carbon dioxide is supplied. The pressurizing device 21 is not particularly limited, and any device that can increase the pressure of the fluid can be suitably used in the present invention.

The second reaction effluent flowing out after the methane synthesis reaction in the second methane synthesis reactor 16 contains water and carbon dioxide like the first reaction effluent, and the same as in the first methane synthesis reaction step. 2 After the reaction effluent is cooled by the second cooler 17, it passes through the second membrane contactor 18 to remove water and carbon dioxide from the second reaction effluent to recover the reaction product.

Meanwhile, water in which carbon dioxide is dissolved, removed from the second reaction effluent by the membrane contactor 18, is supplied in liquid form to a reduced pressure degassing device, and carbon dioxide can be separated from water and recovered by reducing the pressure in the reduced pressure degassing device. . At this time, the reduced pressure degassing device can be used as a separate pressure degassing device from the reduced pressure degassing device 19 in the first methane synthesis reaction stage, and as shown in FIG. 4, the shell side of the second membrane contactor 18 After mixing water containing carbon dioxide discharged through the pipe with water containing carbon dioxide discharged through the shell side of the membrane contactor 14 of the first methane synthesis reaction stage, the mixed water containing carbon dioxide is depressurized. Carbon dioxide can be separated at the same time by supplying it to the degassing device 19.

Conventionally, only water was removed from the reaction effluent by simple gas-liquid separators (4, 8), but according to the present invention as described above, carbon dioxide and water can be removed simultaneously by using membrane contactors (14, 18). Furthermore, carbon dioxide can be further separated from water, and high concentration carbon dioxide can be recovered. The carbon dioxide recovered here can be used in other processes as well as as a reactant for methane synthesis within the methane synthesis process, thereby increasing the production of methane and producing high purity methane.

Example

Hereinafter, the present invention will be described in more detail through examples. However, the following example corresponds to a specific example of the present invention and is not intended to limit the present invention thereby.

Example 1

In order to confirm the reaction efficiency of methane synthesis through the methane synthesis reaction of CO and CO ₂ , CO and H ₂ preheated to 200°C as reaction gases were used as reaction gases in a methane synthesis reactor containing a catalyst of 40% by weight Ni/Al ₂ O ₃ . Methane synthesis reaction was performed by continuously supplying H ₂ at a supply rate of 1,000 mL/min and 3,000 mL/min.

While changing the temperature of the methane synthesis reactor from 250 to 650°C, the CO conversion rate and CH ₄ selectivity according to temperature were confirmed, and the results are shown in FIG. 5.

As can be seen from Figure 5, the CH ₄ synthesis reaction is an exothermic reaction, and the equilibrium conversion rate tended to decrease as the reaction temperature increased, resulting in a decrease in the conversion rates of CO and CO ₂ .

On the other hand, when the temperature is 400°C or lower, the CO and CO ₂ conversion rates are more than 90%, and the CH ₄ selectivity is 100%. Therefore, it can be seen that it is desirable to perform the methane synthesis reaction by maintaining the reaction temperature below 400°C.

Example 2

To check the CO ₂ removal and H ₂ recovery efficiency in the membrane contactor according to the gas flow rate, a gas with a composition of 12.8% N ₂ , 43.6% H ₂ , and 43.6% CO ₂ was used at a flow rate of 8.5 L/min and 12.5 L/min. It was adjusted to min and passed through the tube side of the membrane contactor. At this time, the pressure was adjusted from 4 bar to 8 bar.

Water was supplied to the shell side at a fixed flow rate of 3 L/min.

The composition of the gas discharged from the membrane contactor was analyzed, the remaining CO ₂ content was measured, and the CO ₂ removal rate from the membrane contactor is shown in FIG. 6. In addition, the content of remaining H ₂ was measured and the H ₂ recovery rate in the membrane contactor is shown in FIG. 7.

As can be seen from Figure 6, as pressure increases, CO ₂ solubility increases and CO ₂ removal rate tends to increase. Even when the gas flow rate was as high as 12.5 L/min, the CO ₂ removal rate increased from 72% to 94%, showing a tendency for CO ₂ solubility to increase with pressure increase. On the other hand, when the gas flow rate is low, the contact time with the membrane contactor becomes longer, so even if the pressure is low, the CO ₂ removal rate only decreases to about 89% when the gas flow rate is 8.5 L/min, resulting in high CO ₂ removal efficiency. You can see that

The solubility of _H2 in water is very low compared to _CO2 . However, as can be seen from Figure 7, as the pressure increases, some H ₂ dissolves in water, but the higher the gas flow rate, the less the recovery rate of H ₂ decreases, and the membrane contactor is operated at a low pressure of 8 bar. Even when driving, an H ₂ recovery rate of over 90% could be obtained.

From this, the faster the gas flow rate and the lower the pressure, the lower the rate at which H ₂ is lost.

Example 3

Based on the results of Examples 1 and 2, CO and H ₂ preheated to 200°C as reaction gases were supplied at a rate of 1,000 mL/min of CO and 3,000 mL/min of H ₂ , with a CO conversion rate of 90% and methane selectivity of 95%. It was simulated to carry out the first methane synthesis reaction by continuously supplying the catalyst of Example 1 with the performance of the first methane synthesis reactor. At this time, the temperature was set at 250 to 350°C and the pressure was 20 bar.

The composition of the first effluent discharged from the first methane synthesis reactor was CO ₂ 45 mL/min, CH ₄ 855 mL/min, and H ₂ O 810 mL/min, H ₂ 480 mL/min, and CO 100 mL/min. appeared to remain.

Based on the results of Example 2, the first effluent was passed through a membrane contactor to remove H ₂ O and CO ₂ .

The composition of the first effluent that passed through the first membrane contactor was: all water was removed and did not exist, CO ₂ was removed by 90% and decreased from 45 mL/min to 4.5 mL/min, and H ₂ was recovered by 90%. , it was confirmed that it decreased from 480 mL/min to 432 mL/min.

The first effluent that passed through the first membrane contactor is injected into a second methane synthesis reactor with a methane synthesis reaction conversion rate and selectivity of CO and CO ₂ of 90% and a methane selectivity of 95% to perform a second methane synthesis reaction. carried out.

The composition of the second effluent discharged from the second methane synthesis reactor is CH ₄ 948 mL/min, CO ₂ 1 mL/min, H ₂ O 97 mL/min, CO 10 mL/min, and H ₂ 149 mL/min. confirmed to exist.

Based on the results of Example 2, the second effluent was passed through a second separator contactor to remove H ₂ O and CO ₂ .

In the second effluent that passed through the second membrane contactor, all water was removed and did not exist.

The composition of the final product was confirmed to include CH ₄ 948 mL/min, CO 10 mL/min, and H ₂ 134 mL/min.

Therefore, it can be seen that the CH ₄ purity of the final product is 87%.

Example 4

It was carried out in the same manner as Example 1, except that the following process was additionally included:

In Example 1, the solution containing carbon dioxide and water (carbon dioxide-containing water) removed from the first effluent through the first membrane contactor was recovered, and then the pressure was reduced to normal pressure to recover CO ₂ in a gaseous state.

The recovered CO ₂ was pressurized to a pressure of 20 bar and then injected into the second methane synthesis reactor along with the first effluent that passed through the first separation membrane contactor to perform a second methane synthesis reaction.

The composition of the second effluent discharged from the second methane synthesis reactor is CH ₄ 981 mL/min, CO 12 mL/min, CO ₂ 5 mL/min, H ₂ 15 mL/min, H ₂ O 164 mL/min. It was confirmed that

Based on the results of Example 2, the second effluent was passed through a second membrane contactor to remove H ₂ O and CO ₂ .

In the second effluent that passed through the second membrane contactor, all water was removed and did not exist.

The composition of the final product was confirmed to include CH ₄ 981 mL/min, CO 12 mL/min and H ₂ 14 mL/min.

Therefore, it can be seen that the CH ₄ purity of the final product is 97%.

Example 5

It was carried out in the same manner as Example 2, except that the following process was additionally included:

In Example 2, a solution containing carbon dioxide and water (first carbon dioxide-containing water) removed from the first effluent through the first membrane contactor was recovered.

Meanwhile, a solution containing carbon dioxide and water (second carbon dioxide-containing water) removed from the second effluent through the second membrane contactor of Example 2 was recovered.

After mixing the first carbon dioxide-containing water and the second carbon dioxide-containing water, the pressure was reduced to normal pressure to recover CO ₂ in a gaseous state.

The recovered CO ₂ was pressurized to a pressure of 20 bar and then injected into the second methane synthesis reactor along with the first effluent that passed through the first separation membrane contactor to perform a second methane synthesis reaction.

The composition of the second effluent discharged from the second methane synthesis reactor is CH ₄ 985 mL/min, CO 12 mL/min, CO ₂ 5 mL/min, H ₂ 1 mL/min, H ₂ O 171 mL/min. It existed.

The second effluent was passed through a second membrane contactor to remove H ₂ O and CO ₂ .

The second effluent that passed through the second membrane contactor did not exist because all of the water was removed.

The composition of the final product was confirmed to include CH ₄ 985 mL/min, CO 12 mL/min and H ₂ 1 mL/min.

Therefore, it can be seen that the CH ₄ purity of the final product is 99%.

Comparative Example 1

In Example 3, water was removed from the first effluent using a gas-liquid separator instead of a membrane contactor, and the composition of the first effluent that passed through the gas-liquid separator was analyzed. As a result, all water was removed, but CO ₂ was removed from the first methane synthesis reaction. It was confirmed that only a portion was dissolved in the produced water, but a significant amount remained.

The first effluent that passed through the gas-liquid separator was injected into a methane synthesis reactor of CO and CO ₂ in the same manner as in Example 3 to perform a methane synthesis reaction, and the composition of the second effluent flowing out from the second methane synthesis reactor was analyzed. did.

The second effluent is CH ₄ 959 mL/min, CO 11 mL/min, H ₂ 152 mL/min, and CH ₄ purity is 85%.

1, 5, 11, 15: Preheater
2, 6, 12, 16: Methane synthesis reactor
3, 7, 13, 17: Cooler
4, 8: Gas-liquid separator
14, 18: Separator contactor
19: Reduced pressure deaerator
20: Pressure reducing valve
21: Pressurizing device

Claims (15)

A first methane synthesis reaction step of synthesizing methane by supplying reactants containing carbon monoxide and hydrogen to a first methane synthesis reactor;
A cooling step of cooling the first effluent flowing out of the first methane synthesis reactor;
A carbon dioxide-containing water removal step of passing the cooled first effluent through a first membrane contactor to remove water and CO ₂ from the first effluent and recovering the first effluent containing unreacted carbon monoxide and hydrogen;
Recovering carbon dioxide by depressurizing the removed carbon dioxide-containing water and degassing at least a portion of the CO ₂ dissolved in the water;
A second methane synthesis reaction step of synthesizing methane by supplying the recovered carbon dioxide and the first effluent to a second methane synthesis reactor;
A second cooling step of cooling the second effluent flowing out of the second methane synthesis reactor;
The cooled second effluent is introduced into the tube side of the second membrane contactor, which includes a shell side and a tube side separated by a porous membrane, water is introduced into the shell side, and water and carbon dioxide in the cooled second effluent are introduced. A carbon dioxide-containing water removal step of removing water and carbon dioxide in the second effluent by passing it through a porous separation membrane and dissolving it in water on the shell side, and recovering the second effluent;
Recovering carbon dioxide by depressurizing the carbon dioxide-containing water removed from the second effluent and degassing at least a portion of the carbon dioxide dissolved in the carbon dioxide-containing water; and
A synthetic natural gas production method comprising supplying the recovered carbon dioxide to a second methane synthesis reactor. The method of claim 1, wherein the first membrane contactor includes a shell side and a tube side separated by a porous membrane, the cooled first effluent flows into the tube side, water flows into the shell side, and cooling. A method of producing synthetic natural gas in which water and carbon dioxide in the first effluent pass through a porous separation membrane and are removed by dissolving in water on the shell side. delete delete delete The method of claim 1, wherein the recovered carbon dioxide is pressurized and supplied to a second methane synthesis reactor. The method of producing synthetic natural gas according to any one of claims 1, 2, and 6, wherein the first membrane contactor or the second membrane contactor is operated at a pressure of normal pressure to 50 bar. The method of any one of claims 1, 2, and 6, wherein the first separator contactor or the second separator contactor is a polymer selected from the group consisting of polypropylene, polyethylene, and polymethyl methacrylate, or any of these. A method of producing synthetic natural gas made of a composite of two or more types of polymers. The method of producing synthetic natural gas according to any one of claims 1, 2, and 6, wherein the reactants are preheated and supplied to the first methane synthesis reactor. The method of producing synthetic natural gas according to any one of claims 1, 2, and 6, wherein the first effluent is preheated and supplied to a second methane synthesis reactor. a first methane synthesis reactor in which a reactant stream containing carbon monoxide and hydrogen reacts to synthesize methane;
A first cooler for cooling the first effluent of the first methane synthesis reactor;
It includes a shell side and a tube side separated by a porous separator, the cooled first effluent flows into the tube side, water flows into the shell side, and water and carbon dioxide in the cooled first effluent flow into the porous separator. A first membrane contactor that passes through and is removed by dissolving in water on the shell side;
a second methane synthesis reactor to which the first effluent passing through the tube side is supplied and which synthesizes methane by reacting unreacted carbon monoxide and hydrogen in the first effluent;
a reduced pressure degassing device that recovers carbon dioxide by depressurizing carbon dioxide-containing water discharged from the shell side of the first membrane contactor and degassing at least a portion of the carbon dioxide dissolved in the water; and
A carbon dioxide supply pipe supplying the carbon dioxide recovered from the reduced pressure degassing device to the second methane synthesis reactor.
Including, synthetic natural gas manufacturing equipment. The synthetic natural gas production facility of claim 11, further comprising a second preheater for preheating the first effluent and supplying the first effluent to a second methane synthesis reactor. According to clause 12,
a second cooler for cooling the second effluent flowing out of the second methane synthesis reactor; and
It includes a shell side and a tube side separated by a porous separator, the cooled second effluent flows into the tube side, water flows into the shell side, and water and carbon dioxide in the cooled second effluent flow into the porous separator. A second membrane contactor that passes through and is removed by dissolving in water on the shell side.
Synthetic natural gas manufacturing equipment including. The method of claim 13, further comprising a pipe for mixing carbon dioxide-containing water discharged through the shell side of the first membrane contactor with carbon dioxide-containing water discharged through the shell side of the second membrane contactor, and the mixed carbon dioxide-containing water. A synthetic natural gas production facility that transfers gas to a pressure degassing device. The synthetic natural gas production facility of claim 11, wherein the carbon dioxide supply pipe is provided with a pressurizing device to pressurize the carbon dioxide supplied to the second methane synthesis reactor.