CN111871373B

CN111871373B - Adsorbent for separating nitrogen and methane and preparation method and application thereof

Info

Publication number: CN111871373B
Application number: CN202010758061.XA
Authority: CN
Inventors: 沈俊; 赵燕
Original assignee: Ningxia Boshi Technology Co ltd
Current assignee: Ningxia Boshi Technology Co ltd
Priority date: 2020-07-31
Filing date: 2020-07-31
Publication date: 2022-06-21
Anticipated expiration: 2040-07-31
Also published as: CN111871373A

Abstract

The invention relates to an adsorbent for separating nitrogen and methane, a preparation method and application thereof, and belongs to the technical field of adsorbents. The invention aims to provide a preparation method of an adsorbent for separating nitrogen and methane. The method comprises the following steps: soaking the carbon molecular sieve by using a high molecular solution, performing solid-liquid separation, and drying the solid to obtain the carbon molecular sieve; the polymer solution contains polyvinyl alcohol and polyethylene glycol, and the weight ratio of the polyvinyl alcohol to the polyethylene glycol is 1: 0.5-10. The invention adopts polyvinyl alcohol and polyethylene glycol to carry out impregnation modification on the carbon molecular sieve, successfully prepares the adsorbent for separating nitrogen and methane, has simple and controllable preparation method, low energy consumption and low cost, and the obtained modified molecular sieve can be used as N₂/CH₄、O₂/CH₄Or N₂/O₂In particular in the separation of N₂/CH₄When is in contact with CH₄The adsorption capacity of the method is extremely low, the separation ratio of nitrogen to methane is large, and the method can also be applied to methane purification in coal bed gas, oil field gas or landfill gas.

Description

Adsorbent for separating nitrogen and methane and preparation method and application thereof

Technical Field

The invention relates to an adsorbent for separating nitrogen and methane, a preparation method and application thereof, and belongs to the technical field of adsorbents.

Background

Methane (CH)₄) Can be used as fuel, such as natural gas and coal gas, and is widely applied to civil use and industry; can also be used as chemical raw materials for producing acetylene, hydrogen, synthetic ammonia, carbon black, nitrochloromethane, carbon disulfide, methane chloride, dichloromethane, trichloromethane, carbon tetrachloride, hydrocyanic acid and the like; furthermore, methane is a greenhouse gas with a significant greenhouse effect, CH₄Is CO₂Molecular greenhouse effect is 21 times, ozone layer destruction capability is 7 times of that of carbon dioxide, and CH₄The emission into the atmosphere causes, on the one hand, a serious waste of resources and, on the other hand, a greenhouse effect. Therefore, for oil field gas (oil field)d gas), Coal Bed Methane (CBM), landfill gas (LFG), and other resources₄The utilization of the energy-saving and environment-friendly energy-saving agent has double meanings of energy conservation and environmental protection.

To concentrate and utilize low CH₄The concentration resources are mainly developed and researched by membrane separation technology, low-temperature cryogenic separation technology, pressure swing adsorption separation technology and the like. Among them, the Pressure Swing Adsorption (PSA) technology is a novel gas adsorption separation technology, has the advantages of simple equipment, flexible operation, simple and convenient maintenance, low operation energy consumption, low investment, good performance and the like, and is considered to be the most possible way to fully utilize CH₄Gas separation technology of resources.

The core of PSA is the adsorbent, the performance of which determines whether or not it can achieve separation of the mixed gas and the separation effect. Theoretically, the main component of coal bed gas, natural gas, oil field gas and the like is CO₂、CH₄And N₂Etc. CO₂And CH₄The molecules have widely different physical properties and are easy to separate, but N is₂And CH₄The critical temperature of the two is very low, the two are close in physical property and kinetic diameter, and are not easy to separate, so that CH₄The core technology of gas separation lies in CH₄And N₂The separation is efficient.

Carbon Molecular Sieves (CMS) are a new adsorbent developed in the seventies of the 20 th century, are excellent nonpolar Carbon materials, have more pore diameters between 0.3nm and 1nm, and are mainly used for separating various mixed gases. At present, the adsorbent is the first pressure swing adsorption air separation nitrogen-rich adsorbent in engineering, but CH₄And N₂In the separation of (2), the separation efficiency of the conventional CMS is not high, and improvement thereof is required.

Disclosure of Invention

The invention aims to obtain the adsorbent for separating nitrogen and methane by modifying the carbon molecular sieve, thereby reducing the adsorption quantity of the adsorbent on methane and effectively separating nitrogen and methane.

The invention solves the first technical problem of providing a preparation method of an adsorbent for separating nitrogen and methane.

The preparation method of the adsorbent for separating nitrogen and methane comprises the following steps: after a carbon molecular sieve is impregnated by a high molecular solution, carrying out solid-liquid separation, and drying the solid to obtain an adsorbent for separating nitrogen and methane; the polymer solution contains polyvinyl alcohol and polyethylene glycol, and the weight ratio of the polyvinyl alcohol to the polyethylene glycol is 1: 0.5-10.

In some embodiments of the invention, the weight ratio of polyvinyl alcohol to polyethylene glycol is 1:1 to 8. In specific embodiments, the weight ratio of polyvinyl alcohol to polyethylene glycol is 1:3 or 1:1 or 1:8 or 1: 4.

In one embodiment of the present invention, the polymerization degree of the polyvinyl alcohol is 300 to 2400, and the number average molecular weight of the polyethylene glycol is 300 to 1800. In one embodiment, the polyvinyl alcohol has a number average molecular weight of 500 to 1800, and the polyethylene glycol has a number average molecular weight of 400 to 1000.

For sufficient impregnation, preferably, the impregnation is an equal volume impregnation or an excess impregnation.

In one embodiment of the present invention, the polymer solution has a polymer concentration of 0.05 to 10 wt%.

The second technical problem solved by the invention is to provide an adsorbent for separating nitrogen and methane.

The adsorbent for separating nitrogen and methane is prepared by the preparation method of the adsorbent for separating nitrogen and methane, and is based on a carbon molecular sieve, and the pore size distribution of the carbon molecular sieve mainly has two intervals: 0.3-0.4nm and 0.42-0.7nm, the pores of 0.3-0.4nm can be reduced after the pore is adjusted by the method, the pore distribution of 0.42-0.7nm changes, the pore diameter tends to shrink, and the adsorbent for separating nitrogen and methane is used for separating N₂/CH₄Compared with unmodified methane, the methane adsorption capacity is sharply reduced, so that the methane can be effectively separated and purified, the separation ratio is high, and the yield of the methane is high.

The invention also provides the adsorbent for separating nitrogen and methane as N₂/CH₄、O₂/CH₄Or N₂/O₂The use of a selective adsorbent according to (1).

The molecular sieve of the invention can be used as a selective adsorbent by adjusting the aperture through process parameters. For separating N₂/CH₄Can selectively adsorb N₂(ii) a And for separating O₂/CH₄When adsorbing O selectively₂(ii) a For separating N₂/O₂When adsorbing O selectively₂Thereby achieving the purpose of separating the mixed gas.

The invention also provides application of the adsorbent for separating nitrogen and methane in methane purification in coal bed gas, oil field gas or landfill gas. Because the modified molecular sieve hardly adsorbs methane, the modified molecular sieve can be used as an adsorbent for purifying methane from coal bed gas, oil field gas or landfill gas, and achieves the purposes of energy conservation and environmental protection.

Compared with the prior art, the invention has the following beneficial effects:

the carbon molecular sieve is subjected to impregnation modification by adopting the polyvinyl alcohol and the polyethylene glycol, the adsorbent for separating nitrogen and methane is successfully prepared, the preparation method is simple and controllable, the energy consumption is low, the cost is low, and the obtained modified molecular sieve can be used as N₂/CH₄、O₂/CH₄Or N₂/O₂In particular in the separation of N₂/CH₄When is CH₄The adsorption capacity of the method is extremely low, the separation ratio of nitrogen to methane is large, and the method can also be applied to methane purification in coal bed gas, oil field gas or landfill gas.

Drawings

FIG. 1 is a schematic view of a static adsorption experimental apparatus in example 1 of the present invention; in the figure: 1-a PLC module; 2-a pressure sensor; 3-a reference cell; 4-an adsorption tank; 5-constant temperature water bath; 6-a vacuum pump; 7-CH₄A gas cylinder; 8-N₂A gas cylinder; 9-He gas cylinder.

Detailed Description

Researches show that polyvinyl alcohol and polyethylene glycol are used as modifiers for modification, PVA and PEG are mutually matched and have synergistic effect, the aperture of the carbon molecular sieve can be adjusted, partial pore adjusting effect is achieved, and the carbon molecular sieve has the shape selection effect when separating gas, particularly when separating N₂/CH₄When is CH₄Has a molecular dynamic diameter of 0.38nm, N₂Has a molecular dynamics diameter of 0.364nm, and can selectively adsorb N₂To CH₄The adsorption capacity is low, and the purpose of separating the mixed gas is achieved.

The solvent of the polymer solution can be water, or various organic solvents such as ethanol, acetone, benzene, toluene, chlorobenzene, cyclohexane, ethyl acetate, glycerol, propylene oxide, dimethyl sulfoxide and the like or mixed solutions thereof, and only the organic matters can be dissolved. For cost saving, the polymer solution is preferably an aqueous solution. The molecular weight of the polymer is such that it can be dissolved.

Specifically, the invention adopts the following operations: stirring, mixing and soaking the carbon molecular sieve and the polymer solution for a certain time, filtering and separating, and drying the filtered molecular sieve at 60-200 ℃ to obtain the adsorbent for separating nitrogen and methane.

Wherein, the macromolecular solution can be prepared by the following method: mixing a certain amount of polyvinyl alcohol and polyethylene glycol with a solvent at a certain temperature, and then stirring for a certain time until the polyvinyl alcohol and the polyethylene glycol are completely dissolved, thereby obtaining a high molecular solution.

In the present invention, "/" is "and", for example, N₂/CH₄Is a mixed gas system of nitrogen and methane, O₂/CH₄Is a mixed gas system of oxygen and methane.

CH₄Has a molecular dynamic diameter of 0.38nm, N₂Has a molecular kinetic diameter of 0.364nm, O₂Has a molecular kinetic diameter of 0.346 nm. The molecular sieve of the invention can be used as a selective adsorbent by adjusting the aperture through process parameters. For separating N₂/CH₄Can selectively adsorb N₂(ii) a And for separating O₂/CH₄When adsorbing O selectively₂(ii) a For separating N₂/O₂When adsorbing O selectively₂Thereby achieving the purpose of separating the mixed gas.

The following examples are provided to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention. In the examples, the polymerization degree of polyvinyl alcohol (PVA) was 500, and the molecular weight of polyethylene glycol (PEG) was 600.

Example 1

The adsorbent for separating nitrogen and methane is prepared by the following method:

1) preparing a mixed solution with a certain concentration: mixing a certain amount of PVA and PEG with deionized water at the temperature of 90 ℃, wherein the weight ratio of the PVA to the PEG is 1:3, then stirring the mixture to ensure that the mixture is completely dissolved in water to obtain a mixed solution, and controlling the adding amount of the deionized water to ensure that the total concentration of the PVA and the PEG in the mixed solution is 1 wt%;

2) and fully mixing and stirring the ground carbon molecular sieve (40-60 meshes) and the mixed solution, then carrying out suction filtration and separation, and drying the filtered solid at 150 ℃ overnight to obtain the final adsorbent sample for separating nitrogen and methane.

And (3) measuring the adsorption capacity of the modified sample to nitrogen and methane by using a static adsorption method. The specific measurement method is as follows:

as shown in figure 1, the static adsorption device comprises a PLC module 1, a pressure sensor 2, a reference tank 3, an adsorption tank 4, a constant temperature water bath 5, a vacuum pump 6 and CH₄ Gas steel cylinder 7, N₂A gas steel cylinder 8, a He gas steel cylinder 9, an electromagnetic valve, a needle stop valve, a thermocouple, an electromagnetic relay and the like. The constant temperature water bath is utilized to keep the temperature constant in the adsorption process, the reference tank 3 is utilized to calculate the free volume, the gas adsorption process is realized through the opening and closing of the adsorption tank 4, the reference tank 3, the electromagnetic valve and the needle-shaped stop valve, the pressure recording and the transmission of electric signals are realized through the pressure sensor,the automatic gas adsorption process is realized through the linkage control of the PLC module 1, the electromagnetic relay and the electromagnetic valve. And (4) obtaining the adsorption capacity of the adsorbate gas on the adsorbent by iteration of the RK state equation according to the equilibrium pressure data after the adsorption process under different initial pressures. The adsorbent is regenerated by vacuum pumping by a vacuum pump 6.

The static adsorption device comprises the following operation steps:

weighing a certain amount of samples, putting into the adsorption tank, then adjusting the constant temperature water bath to the experiment temperature, starting the experiment after the water bath temperature is stable, guaranteeing that helium, nitrogen, methane steel cylinder main valve is the open mode before the experiment, the relief pressure valve is opened to a little more than the required maximum pressure of experiment:

1. instrument leak detection

And opening the helium valve to observe whether the pressure changes, if not, slowly opening the adsorption tank valve to observe whether the pressure continuously drops, and if the pressure is stable to a certain pressure after the pressure drops, the instrument is normal and the air tightness is good.

2. Test procedure

And opening the programmed PLC program, and automatically carrying out the instrument according to preset steps. That is, after the apparatus is evacuated, the valves are opened and closed in a matched manner, and He gas dead volume test and N are sequentially performed₂Adsorption test, CH₄And (5) testing gas adsorption. The He gas steel cylinder and the N are respectively controlled by adopting a valve₂Gas cylinder, CH₄The gas steel cylinder is opened and closed, so that the gas pressure of the system is increased, the valve controls the opening and closing of the adsorption tank and the vacuum pump, and the adsorption and desorption processes are respectively realized. The PLC module 1 records the initial pressure and the balance pressure data after each boosting.

3. Data computation

After the experimental data are obtained through the PLC control program, the RK state equation is sequentially used for iterative calculation to obtain the free volume of the adsorption system and the ethane-ethylene gas adsorption capacity, and the calculation process is as follows:

from the RK state equation:

the above formula is modified to an iterative formula:

wherein a and b are respectively RK state equation constants as follows:

the ideal state equation is then used to provide the initial value V0:

will be an initial value V₀The adsorption amount of nitrogen and methane can be obtained by iteration in the formula (2), and the result is shown in table 1.

TABLE 1

Example 2

1) preparing a mixed solution with a certain concentration: mixing a certain amount of PVA and PEG with deionized water at the temperature of 90 ℃, wherein the weight ratio of the PVA to the PEG is 1:1, then stirring the mixture to ensure that the mixture is completely dissolved in water to obtain a mixed solution, and controlling the adding amount of the deionized water to ensure that the total concentration of the PVA and the PEG in the mixed solution is 0.5 wt%;

The adsorption amounts of nitrogen and methane of the modified samples were measured by the static adsorption method in example 1, and the results are shown in Table 2.

TABLE 2

Example 3

1) preparing a mixed solution with a certain concentration: mixing a certain amount of PVA and PEG with deionized water at 90 ℃, wherein the weight ratio of the PVA to the PEG is 1:8, stirring the mixture to completely dissolve the mixture in water to obtain a mixed solution, and controlling the adding amount of the deionized water to ensure that the total concentration of the PVA and the PEG in the mixed solution is 4 wt%;

The adsorption amounts of nitrogen and methane of the modified samples were measured by the static adsorption method in example 1, and the results are shown in Table 3.

TABLE 3

Example 4

1) preparing a mixed solution with a certain concentration: mixing a certain amount of PVA and PEG with deionized water at the temperature of 90 ℃, wherein the weight ratio of the PVA to the PEG is 1:4, then stirring the mixture to ensure that the mixture is completely dissolved in water to obtain a mixed solution, and controlling the adding amount of the deionized water to ensure that the total concentration of the PVA and the PEG in the mixed solution is 5 wt%;

The adsorption amounts of nitrogen and methane of the modified samples were measured by the static adsorption method in example 1, and the results are shown in Table 4.

TABLE 4

Comparative example 1

1) preparing a PVA solution with a certain concentration: mixing a certain amount of PVA with deionized water at 90 ℃, then stirring the mixture to ensure that the mixture is completely dissolved in water to obtain a PVA solution, and controlling the addition of the deionized water to ensure that the concentration of the PVA in the PVA solution is 1 wt%;

2) and (3) fully mixing and stirring the ground carbon molecular sieve (40-60 meshes) and a PVA solution, then performing suction filtration and separation, and drying the filtered solid overnight at 150 ℃ to obtain a final adsorbent sample for separating nitrogen and methane.

The adsorption amounts of nitrogen and methane were measured for the modified sample by the static adsorption method in example 1, and the results are shown in table 5.

TABLE 5

Comparative example 2

1) preparing a PEG solution with a certain concentration: mixing a certain amount of PEG and deionized water at room temperature, then stirring to completely dissolve the PEG in water to obtain a PEG solution, and controlling the addition of the deionized water to ensure that the concentration of the PEG in the PEG solution is 1 wt%;

2) and (3) fully mixing and stirring the ground carbon molecular sieve (40-60 meshes) and the PEG solution, then performing suction filtration and separation, and drying the filtered solid overnight at 150 ℃ to obtain a final adsorbent sample for separating nitrogen and methane.

The adsorption amounts of nitrogen and methane of the modified samples were measured by the static adsorption method in example 1, and the results are shown in table 6.

TABLE 6

Therefore, compared with the molecular sieve modified by only PVA or PEG, the modified molecular sieve obtained by mixing and modifying PVA and PEG and mutually synergically modifying the PVA and the PEG keeps the original molecular sieve N₂While the adsorption amount is basically unchanged, CH₄The adsorption capacity is sharply reduced, the nitrogen-methane separation ratio is high, and the method can be applied to the separation of nitrogen-methane.

Claims

1. The preparation method of the adsorbent for separating nitrogen and methane is characterized by comprising the following steps of: after a carbon molecular sieve is impregnated by a high molecular solution, carrying out solid-liquid separation, and drying the solid to obtain an adsorbent for separating nitrogen and methane; the polymer solution contains polyvinyl alcohol and polyethylene glycol, and the weight ratio of the polyvinyl alcohol to the polyethylene glycol is 1: 0.5-10.

2. The method for producing an adsorbent for separating nitrogen and methane according to claim 1, characterized in that: the weight ratio of the polyvinyl alcohol to the polyethylene glycol is 1: 1-8.

3. The method for producing an adsorbent for separating nitrogen and methane according to claim 2, characterized in that: the weight ratio of polyvinyl alcohol to polyethylene glycol is 1:3 or 1:1 or 1:8 or 1: 4.

4. The method for producing an adsorbent for separating nitrogen and methane according to claim 1, characterized in that: the polymerization degree of the polyvinyl alcohol is 300-2400, and the number average molecular weight of the polyethylene glycol is 300-1800.

5. The method for producing an adsorbent for separating nitrogen and methane according to claim 4, characterized in that: the polyvinyl alcohol has a number average molecular weight of 500-1800, and the polyethylene glycol has a number average molecular weight of 400-1000.

6. The method for producing an adsorbent for separating nitrogen methane according to claim 1, characterized in that: the impregnation is equal volume impregnation or excess impregnation.

7. The method for producing an adsorbent for separating nitrogen and methane according to claim 1, characterized in that: in the polymer solution, the concentration of the polymer is 0.05-10 wt%.

8. The adsorbent for separating nitrogen and methane prepared by the method for preparing the adsorbent for separating nitrogen and methane according to any one of claims 1 to 7.

9. The adsorbent for separating nitrogen methane as set forth in claim 8 as N₂/CH₄、O₂/CH₄Or (N)₂+O₂)/CH₄Use of a selective adsorbent for a system.

10. Use of the adsorbent for separating nitrogen and methane according to claim 8 for purifying methane in coal bed gas, oil field gas or biogas.