Composition for separating methane in coal bed gas by hydrate method

Abstract

The invention discloses a composition for separating methane in coal bed gas by a hydrate method, the composition is composed of a hydrate formation kinetic accelerator and a hydrate formation thermodynamic accelerator, the hydrate formation kinetic accelerator is an N-acylamino acid type surfactant, and the hydrate formation thermodynamic accelerator is an N-acylamino acid type surfactant. The hydrate generation thermodynamic accelerant is at least one of tetrahydrofuran, cyclopentane and 1, 3-dioxolane. According to the invention, the N-acylamino acid type surfactant is used as a hydrate generation kinetic accelerant, and the N-acylamino acid type surfactant is matched with a thermodynamic accelerant to form a composition which can promote rapid generation of the coal bed gas hydrate at low temperature and high pressure, so that the induction time of formation of the coal bed gas hydrate is remarkably shortened, and the separation effect of coal bed gas is enhanced; good application prospects are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of coalbed methane purification, and specifically relates to a composition composed of a hydrate formation kinetic promoter and a thermodynamic promoter, and a method for separating methane from coalbed methane by using the composition. Background Art

[0002] Coalbed methane is a mineral resource associated with coal in coal seams with methane as the main component. It is an unconventional natural gas. Coalbed methane is mainly extracted underground, and is often mixed with air during the process. Coalbed methane with a methane content of less than 30% is called low-concentration coalbed methane. Due to its low calorific value, it cannot meet the demand for utilization and is often discharged directly into the atmosphere. On a century-long scale, the global warming potential of methane is 27.9 times that of carbon dioxide, so direct emission will lead to waste of resources and environmental problems. The main impurity in low-concentration coalbed methane is nitrogen. Since the boiling point, polarizability and kinetic size of nitrogen are similar to those of methane, the purification of methane in low-concentration coalbed methane has become a difficulty in the utilization of coalbed methane. Currently, the commonly used methods such as low-temperature distillation, membrane separation and pressure swing adsorption have not been widely used due to problems such as high energy consumption, poor safety and complex operation. The hydrate-based coalbed methane separation technology has good application prospects due to its advantages in the above aspects.

[0003] Gas hydrates are crystalline cage compounds formed by gas molecules and water molecules under high pressure and low temperature conditions. The principle of hydrate separation of coalbed methane is based on the obvious pressure difference between methane hydrates and nitrogen hydrates under phase equilibrium conditions. Under appropriate pressure, methane molecules will be wrapped by the cage structure of the hydrate, while nitrogen molecules will remain in the gas phase. Therefore, the gas phase and the hydrate phase can be separated, and then high-purity methane gas can be obtained through the decomposition process of the hydrate. At present, the development of hydrates is mainly restricted by more stringent formation conditions and slower formation speed, so the current research focuses on thermodynamics and kinetics.

[0004] Thermodynamic research mainly focuses on using different thermodynamic promoters to reduce the phase equilibrium conditions required for the reaction. Therefore, current kinetic research mainly focuses on improving the hydrate formation rate. Since the hydrate reaction rate is usually slow, which leads to a decrease in separation efficiency, and a longer reaction time will also increase energy consumption, kinetic research is of paramount importance. There are mechanical and chemical methods to increase the hydrate formation rate. The mechanical method is to increase the gas-liquid contact area by stirring, bubbling, spraying and other methods, so that the hydrate formation shows a faster reaction rate; while the chemical method is to enhance the reaction by adding hydrate kinetic promoters to the solution. These promoters will change the interfacial properties of the gas-liquid interface and accelerate the reaction. However, the commonly used kinetic promoters have adverse effects on the environment, so it is still necessary to find an efficient and environmentally friendly promoter to enhance the formation of hydrates.

[0005] N-acyl amino acid type surfactant is an amino acid surfactant, usually in the form of white powder. As a biomass-based surfactant, its raw material source is wide, its toxic side effects on organisms are small, and it can be degraded quickly and safely. The present invention uses N-acyl amino acid type surfactant as a kinetic promoter for coalbed methane separation, and forms a composition with a hydrate formation thermodynamic promoter, which can significantly improve the hydrate formation efficiency and enhance the separation effect, providing an environmentally friendly, low-cost, and safe way and solution for coalbed methane separation, and has good application prospects. Summary of the invention

[0006] The object of the present invention is to provide a composition for separating methane from coalbed methane by a hydrate method, and a method for separating methane from coalbed methane by using the composition.

[0007] To achieve the above object, the present invention adopts the following technical solutions: One of the purposes of the present invention is to protect a composition for separating methane from coalbed methane by the hydrate method, which is composed of a hydrate formation kinetic promoter and a hydrate formation thermodynamic promoter.

[0008] Furthermore, the hydrate formation kinetics promoter is an N-acylamino acid type surfactant, and its general structural formula is as follows: , Wherein, R is selected from one of lauroyl, coconut oil acyl and oleic acid; R1 and R2 are independently selected from one of glutamic acid, glycine, alanine and sarcosine.

[0009] Furthermore, the hydrate formation thermodynamic promoter is at least one of tetrahydrofuran, cyclopentane and 1,3-dioxolane.

[0010] Furthermore, the mass ratio of the hydrate formation kinetic promoter to the hydrate formation thermodynamic promoter is 1:176-1:3935.

[0011] The second purpose of the present invention is to protect a method for separating methane from coalbed methane using the composition, which comprises mixing coalbed methane and water with the composition, and controlling the pressure and temperature during the mixing process so that the methane in the coalbed methane and the water form coalbed methane hydrates, then separating and collecting the generated coalbed methane hydrates, and then decomposing them to obtain methane.

[0012] Furthermore, the amount of the composition in the solution is converted based on the concentration of the hydrate formation kinetics promoter therein being 50 ppm-1000 ppm.

[0013] Furthermore, the methane content in the coalbed methane is 20% to 90%.

[0014] Furthermore, the pressure range used in the formation process of coalbed methane hydrate is 3 MPa-5 MPa and the temperature is 0-20°C.

[0015] Furthermore, the formation time of coalbed methane hydrate is 1-24 hours.

[0016] Traditional coalbed methane separation has problems such as high energy consumption, low efficiency, and environmental pollution. The present invention provides an efficient, safe, and pollution-free hydrate promoter composition, which can greatly increase the hydrate formation rate by using a low dose, and can achieve efficient separation of methane in coalbed methane through hydrate separation technology. As a safe and reliable bio-based material, the solubilization effect of N-acylamino acid type surfactant can increase the solubility of gas in the aqueous phase. At the same time, its change in the surface tension of the aqueous phase enables better mass transfer at the gas-liquid interface during the growth of hydrates, which is beneficial to the initial nucleation of hydrates and the growth of hydrate crystals, and has a good effect on improving the generation efficiency of hydrates. Therefore, by forming a composition of N-acylamino acid type surfactant and hydrate formation thermodynamic promoter, the generation rate of coalbed methane hydrates can be significantly increased under high pressure and low temperature conditions, and a higher methane recovery rate can be obtained.

[0017] Compared with the traditional separation method and the commonly used hydrate promoter, the present invention has the following advantages: (1) Low energy consumption: Compared with traditional separation methods, hydrate separation technology can effectively reduce energy consumption and thus reduce production costs.

[0018] (2) High separation efficiency: The addition of N-acyl amino acid type surfactant improves the kinetic efficiency of the hydrate formation process, significantly reduces the induction time and growth phase of hydrate formation, and at the same time enhances the selectivity of hydrates for methane and improves the separation efficiency of methane, thereby improving the purity and economic value of coalbed methane.

[0019] (3) Environmentally friendly: The N-acylamino acid surfactant used in the present invention has a wide range of sources and good biodegradability, has little impact on the environment, and meets the requirements of sustainable development.

[0020] (4) Easy to operate: The method of separating coalbed methane using hydrates is easy to operate, avoiding complex equipment and cumbersome operating procedures, and is more suitable for industrial production. It has important practical significance for recovering low-concentration coalbed methane, optimizing energy structure and reducing greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the transparent sapphire high-pressure reaction system used.

[0022] Figure 2 It is a comparison chart of the induction time of Examples 1 to 6 and Comparative Examples 1 to 5.

[0023] Figure 3 For Examples 1 to 6 and Comparative Examples 1 to 5 T 90 Comparison chart.

[0024] Figure 4 It is a comparison chart of methane recovery rates of Examples 1 to 6 and Comparative Examples 1 to 5.

[0025] Figure 5 It is a comparison chart of the coalbed methane absorption kinetic curves of Examples 1 to 6 and Comparative Examples 1 to 5. DETAILED DESCRIPTION

[0026] The technical scheme and implementation effects of the present invention are further described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of implementation of the present invention.

[0027] Taking sodium lauroyl glutamate as an example, the effect of the promoter composition on the growth of hydrates was studied. Figure 1 The experiment was carried out in a transparent sapphire high-pressure reaction system. The system mainly consists of six parts: high-pressure sapphire reactor, equilibrium reactor, constant temperature water bath, temperature measuring instrument, pressure measuring instrument, gas chromatograph and computer data automatic acquisition system. The maximum working volume of the high-pressure sapphire reactor is 425 cm 3 (including stirring paddle), the maximum working pressure is 20 MPa, and the working temperature range is -80-150 ℃.

[0028] Before the reaction begins, the entire experimental system is cleaned with deionized water. After vacuum drying, 120 ml of the prepared aqueous solution is placed in a sapphire kettle, and the temperature of the constant temperature water bath is set to the experimental temperature. After the system temperature stabilizes for 2 hours, the experimental gas (the gas simulates a low-concentration coalbed methane combination, and its composition is 30 mol% CH4+70 mol% N2) is introduced to replace the air in the kettle 3-4 times, and an experimental gas of a certain pressure (less than the equilibrium pressure of hydrate formation at this temperature, and the hydrate equilibrium pressure is calculated using the Chen-Guo hydrate model) is introduced to achieve dissolution equilibrium. Then, the experimental gas is introduced from the equilibrium kettle to raise the system pressure to the test pressure, the air inlet valve is closed, and the agitator is turned on. The stirring speed remains constant during the entire experimental process. As the reaction proceeds, the gas is continuously consumed, and relevant data in the kettle are obtained through pressure and temperature measuring instruments. After the reaction is completed, the gas after the reaction is completed is measured by gas chromatograph to measure the content of each component in it.

[0029] Example 1 The initial liquid of the reaction system was prepared by 0.006 g of sodium lauroyl glutamate, 23.61 g of 1,3-dioxolane and 97.43 g of deionized water, that is, the content of sodium lauroyl glutamate in the system was 50 ppm, and the content of 1,3-dioxolane was 5.56 mol%. Then the solution was sent into the reactor, and simulated low-concentration coalbed methane was introduced. The experimental pressure was 3 MPa, the experimental temperature was 276.15 K, and the stirring rate was 500 r / min for reaction.

[0030] The results showed that hydrates were formed rapidly during the entire experiment, indicating that the hydrate promoter had a good effect in promoting hydrate formation. After the reaction was completed, the gas phase components were measured, and the methane content decreased significantly.

[0031] Example 2 The initial liquid of the reaction system was prepared by 0.06 g of sodium lauroyl glutamate, 23.61 g of 1,3-dioxolane and 97.43 g of deionized water, that is, the content of sodium lauroyl glutamate in the system was 500 ppm, and the content of 1,3-dioxolane was 5.56 mol%. Then the solution was sent into the reactor, and simulated low-concentration coalbed methane was introduced. The experimental pressure was 3 MPa, the experimental temperature was 276.15 K, and the stirring rate was 500 r / min for reaction.

[0032] The results showed that hydrates were formed rapidly during the entire experiment, indicating that the hydrate promoter had a good effect in promoting hydrate formation. After the reaction was completed, the gas phase components were measured, and the methane content decreased significantly.

[0033] Example 3 The initial liquid of the reaction system is prepared by 0.06 g of sodium lauroyl glutamate, 22.37 g of tetrahydrofuran and 94.86 g of deionized water, that is, the content of sodium lauroyl glutamate in the system is 500 ppm, and the content of tetrahydrofuran is 5.56 mol%. Then the solution is sent into the reactor, and the simulated low-concentration coalbed methane is introduced. The experimental pressure is 3 MPa, the experimental temperature is 276.15K, and the stirring rate is 500 r / min for reaction.

[0034] The results showed that hydrates were formed rapidly during the entire experiment, indicating that the hydrate promoter had a good effect in promoting hydrate formation. After the reaction was completed, the gas phase components were measured, and the methane content decreased significantly.

[0035] Example 4 The initial liquid of the reaction system is prepared by 0.006 g of sodium lauroyl glutamate, 21.09 g of cyclopentane and 91.92 g of deionized water, that is, the content of sodium lauroyl glutamate in the system is 50 ppm, and the content of cyclopentane is 5.56 mol%. Then the solution is sent into the reactor, and the simulated low-concentration coalbed methane is introduced. The experimental pressure is 3 MPa, the experimental temperature is 283.15K, and the stirring rate is 500 r / min for reaction.

[0036] The results showed that hydrates were formed rapidly during the entire experiment, indicating that the hydrate promoter had a good effect in promoting hydrate formation. After the reaction was completed, the gas phase components were measured, and the methane content decreased significantly.

[0037] Example 5 The initial liquid of the reaction system was prepared by 0.011 g of sodium lauroyl glutamate, 21.09 g of cyclopentane and 91.92 g of deionized water, that is, the content of sodium lauroyl glutamate in the system was 100 ppm, and the content of cyclopentane was 5.56 mol%. The solution was then sent into the reactor, and simulated low-concentration coalbed methane was introduced. The experimental pressure was 3 MPa, the experimental temperature was 283.15 K, and the stirring rate was 500 r / min for reaction.

[0038] The results showed that hydrates were formed rapidly during the entire experiment, indicating that the hydrate promoter had a good effect in promoting hydrate formation. After the reaction was completed, the gas phase components were measured, and the methane content decreased significantly.

[0039] Example 6 The initial liquid of the reaction system was prepared by 0.06 g of sodium lauroyl glutamate, 21.09 g of cyclopentane and 91.92 g of deionized water, that is, the content of sodium lauroyl glutamate in the system was 500 ppm and the content of cyclopentane was 5.56 mol%. The solution was then sent into the reactor, and simulated low-concentration coalbed methane was introduced. The experimental pressure was 3 MPa, the experimental temperature was 283.15 K, and the stirring rate was 500 r / min for reaction.

[0040] The results showed that hydrates were formed rapidly during the entire experiment, indicating that the hydrate promoter had a good effect in promoting hydrate formation. After the reaction was completed, the gas phase components were measured, and the methane content decreased significantly.

[0041] Comparative Example 1 The reaction system was prepared by 23.61 g of 1,3-dioxolane and 97.43 g of deionized water. The solution was fed into the reactor, and simulated low-concentration coalbed methane was introduced. The experimental pressure was 3 MPa, the experimental temperature was 276.15 K, and the stirring rate was 500 r / min for reaction.

[0042] Comparative Example 2 The reaction system was prepared by 22.37 g of tetrahydrofuran and 94.86 g of deionized water. The solution was fed into the reactor, and simulated low-concentration coalbed methane was introduced. The experimental pressure was 3 MPa, the experimental temperature was 276.15 K, and the stirring rate was 500 r / min for reaction.

[0043] Comparative Example 3 The reaction system was prepared by 21.09 g of cyclopentane and 91.92 g of deionized water. The solution was fed into the reactor, and simulated low-concentration coalbed methane was introduced. The experimental pressure was 3 MPa, the experimental temperature was 283.15 K, and the stirring rate was 500 r / min for reaction.

[0044] Comparative Example 4 The reaction system was prepared by 0.06 g of sodium lauroyl glutamate and 120 g of deionized water. The solution was fed into the reactor, and simulated low-concentration coalbed methane was introduced. The experimental pressure was 3 MPa, the experimental temperature was 276.15 K, and the stirring rate was 500 r / min for reaction.

[0045] Comparative Example 5 The reaction system was prepared by 0.06 g of sulfonated castor oil, 23.61 g of 1,3-dioxolane and 97.43 g of deionized water, that is, the content of sulfonated castor oil in the system was 500 ppm, and the content of 1,3-dioxolane was 5.56 mol%. Then the solution was sent into the reactor, and the simulated low-concentration coalbed methane was introduced. The experimental pressure was 3 MPa, the experimental temperature was 276.15 K, and the stirring rate was 500 r / min for reaction.

[0046] Table 1 shows the induction time of the embodiments and comparative examples. T 90 (reaction proceeds 90% of the time) and methane recovery.

[0047] Table 1 Summary of results

[0048] As can be seen from Table 1, the combination of N-acylamino acid surfactant as a hydrate formation kinetic promoter and a hydrate formation thermodynamic promoter as a composition can promote the rapid formation of coalbed methane hydrates, significantly shorten the induction time of coalbed methane hydrate formation, and enhance the separation effect of coalbed methane. If the thermodynamic promoter is missing during the experiment, hydrates are basically not generated at 3 MPa, and higher phase equilibrium conditions are required.

[0049] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A composition for separating methane from coalbed methane by hydrate method, characterized in that: The composition is composed of a hydrate formation kinetics promoter and a hydrate formation thermodynamics promoter; The hydrate formation kinetics promoter is an N-acylamino acid type surfactant, and its general structural formula is as follows: ， Wherein, R is selected from one of lauroyl, cocoyl, and oleyl; R1 and R2 are independently selected from one of glutamic acid, glycine, alanine, and sarcosine; The hydrate formation thermodynamic promoter is at least one of tetrahydrofuran, cyclopentane and 1,3-dioxolane.

2. The composition according to claim 1, characterized in that The mass ratio of the hydrate formation kinetic promoter to the hydrate formation thermodynamic promoter is 1:176-1:3935.

3. A method for separating methane from coalbed methane using the composition of claim 1, characterized in that: Water and the composition are formulated into a solution, which is then mixed with coalbed methane. During the mixing process, the pressure and temperature are controlled to allow the methane in the coalbed methane to form coalbed methane hydrate with water. The generated coalbed methane hydrate is then separated and collected, and then decomposed to obtain methane.

4. The method according to claim 3, characterized in that The amount of the composition in the solution is calculated based on the concentration of the hydrate formation kinetics promoter in the solution being 50 ppm to 1000 ppm.

5. The method according to claim 3, characterized in that: The methane content in the coalbed methane is 20% to 90%.

6. The method according to claim 3, characterized in that The pressure range used in the formation process of coalbed methane hydrate is 3 MPa-5 MPa and the temperature is 0-20℃.

7. The method according to claim 3, characterized in that The formation time of coalbed methane hydrate is 1-24 hours.

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