CN110773125B

CN110773125B - Organic modified molecular sieve and preparation method and application thereof

Info

Publication number: CN110773125B
Application number: CN201911088455.2A
Authority: CN
Inventors: 敬方梨; 王荣; 罗仕忠; 沈俊; 李映春; 黄显波
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2019-11-08
Filing date: 2019-11-08
Publication date: 2021-06-04
Anticipated expiration: 2039-11-08
Also published as: CN110773125A

Abstract

The invention relates to an organic modified molecular sieve and a preparation method and application thereof, belonging to the technical field of adsorbents. The invention solves the technical problem of providing a preparation method of an organic modified molecular sieve. The method comprises the steps of impregnating a molecular sieve with an organic matter solution, carrying out solid-liquid separation, and drying the solid to obtain the modified molecular sieve. The organic modified molecular sieve is successfully prepared by carrying out impregnation modification on the molecular sieve, 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/CH₄、(N₂+O₂)/CH₄Isosystem selective adsorbents, especially in the separation of N₂/CH₄When is CH₄Low adsorption amount of (2), N₂/CH₄The separation ratio of the catalyst is large, and the catalyst can be applied to purifying CH in coal bed gas, oil field gas or biogas₄。

Description

Organic modified molecular sieve and preparation method and application thereof

Technical Field

The invention relates to an organic modified molecular sieve and a preparation method and application thereof, belonging to the technical field of adsorbents.

Background

Methane (CH)₄) As a main energy source and chemical raw material, the material is widely applied to civil use and industry; the methane can be used 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, the CH is contained in Oil field gas (Oil field gas), coal bed gas (CBM) and Biogas (Biogas)₄The utilization of the energy-saving and environment-friendly energy-saving agent has double meanings of energy conservation and environmental protection.

Oil field gas, coal bed gas and biogas usually contain nitrogen and oxygen with certain concentrations, so that the purity and the calorific value of methane are low and cannot reach the industrial standard, and meanwhile, the existence of oxygen increases the risk of explosion. Using this CH fraction for concentration₄Less concentrated resources, need to be on N₂、O₂And CH₄The mixed gas of (2) is separated. The technologies developed and researched at present mainly include a membrane separation technology, a low-temperature cryogenic separation technology, a 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 coal seamThe main component of gas, oil field gas, etc. is CO₂、CH₄And N₂Etc. CO₂And CH₄The physical properties of the molecules are very different and 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.

Patent CN101596445A discloses a preparation method of a carbon molecular sieve adsorbent, which takes a high molecular polymer as a raw material, and prepares the adsorbent for separating CH from low-concentration gas by pressure swing adsorption through the preparation processes of solidification, dry distillation, fine crushing, molding, carbonization and activation and carbon deposition pore regulation₄Carbon molecular sieve of gas, the carbon molecular sieve being paired with CH₄Has high adsorption capacity, large selective adsorption coefficient, good strength, low cost and no pollution, and the performance of the catalyst reaches or exceeds the level of a carbon molecular sieve of a Japanese sample. However, the adsorbent is mainly used for adsorbing CH₄Also, desorption is required to achieve CH₄The purpose of effective utilization.

Patent CN109179369A discloses a preparation method of a carbon molecular sieve for adsorbing and separating methane and nitrogen by using a phenolic resin matrix. According to the method, carbonization and deposition hole adjustment are integrated in the preparation process, energy loss is reduced, energy is saved, the influence of heat on the change of the aperture of the substrate in the carbonization cooling and deposition heating processes is reduced, the aperture is stable, the aperture of the obtained substrate is small, the deposition time is reduced, the nitrogen adsorption capacity is 6.5-7.5 ml/g, and the methane adsorption capacity is 7-10 ml/g of a deposited sample under the atmospheric pressure of 25 degrees/1. Although the molecular sieve prepared by the method can be used for kinetic separation of nitrogen and methane, the separation ratio is not high, and nitrogen and methane cannot be effectively separated.

Patent CN101935032A discloses a method for preparing a carbon molecular sieve by using a chemical activator KOH or a physical activator CO₂The conventional carbon molecular sieve is subjected to secondary activation and pore expansion for an activating agent, the carbon molecular sieve subjected to secondary activation is used as an adsorbent to perform pressure swing adsorption operation, the preferential selectivity of nitrogen adsorption is shown, and the adsorbent is used for performing pressure swing adsorption separation of methane-nitrogen to realize the purpose of directly purifying methane. Although this method can separate and adsorb nitrogen, the adsorption of methane is also increased, and the methane yield is not high. In addition, CO is used₂The activation reaming has the defects of high-temperature energy consumption, complex process and the like.

In summary, most of the existing methods for improving carbon molecular sieves are to increase N by deposition pore blocking or activation pore-expanding process₂The adsorption quantity is increased while the CH is inevitably increased₄So that the separation of nitrogen and methane is relatively low; in addition, when the adsorbent preferentially adsorbs methane, the methane can be enriched and utilized only by carrying out secondary desorption and recompression on the methane, and the separation energy consumption is higher.

Disclosure of Invention

In view of the above defects, the present invention aims to modify a molecular sieve, thereby reducing the adsorption amount of the molecular sieve to methane, effectively enriching and purifying methane, and removing nitrogen, oxygen, etc.

The invention solves the first technical problem by providing a preparation method of an organic modified molecular sieve.

The preparation method of the organic modified molecular sieve comprises the following steps: impregnating the molecular sieve with an organic solution, carrying out solid-liquid separation, and drying the solid to obtain an organic modified molecular sieve; the structural general formula of the organic matter is as follows:

m is any integer of 0-4, n is polymerization degree, R is-OH, -COOH, -CONH₂、-COOCH₃or-COOCH₂CH₃。

Preferably, n is 500-5000, and more preferably, n is 1200-1700.

Preferably, the molecular sieve is a carbon molecular sieve, an A-type molecular sieve, an X-type molecular sieve, a Y-type molecular sieve, a ZSM molecular sieve, an SAPO molecular sieve, a silicon-titanium molecular sieve or activated carbon; preferably, the molecular sieve is a carbon molecular sieve.

Preferably, the molecular sieve is a carbon molecular sieve.

Preferably, the organic substance is polyvinyl alcohol.

Preferably, the impregnation is an equal volume impregnation or an excess impregnation.

Preferably, the concentration of the organic solution is 0.001-40 wt%; preferably, the concentration of the organic solution is 0.01-20 wt%; more preferably, the concentration of the organic solution is 1 to 10 wt%.

The present invention preferably employs the following operations: stirring and uniformly mixing the molecular sieve and the organic matter solution, soaking, filtering and separating, and drying the filtered molecular sieve at 60-200 ℃ to obtain the organic modified molecular sieve.

The second technical problem solved by the invention is to provide an organic modified molecular sieve.

The organic modified molecular sieve is prepared by the preparation method of the organic modified molecular sieve. The modified molecular sieve 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 organic modified molecular sieve of the invention as N₂/CH₄、O₂/CH₄Or (N)₂+O₂)/CH₄Use of a selective adsorbent for a system.

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 separation (N)₂+O₂)/CH₄While selectively adsorbing N₂And O₂Thereby achieving the purpose of separating the mixed gas.

The invention also provides application of the organic modified molecular sieve in purifying methane in coal bed gas, oil field gas or biogas. 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 biogas, thereby achieving the purposes of energy conservation and environmental protection.

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

the organic modified molecular sieve is successfully prepared by carrying out impregnation modification on the molecular sieve, 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 (N)₂+O₂)/CH₄In 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 biogas.

Drawings

FIG. 1 shows BET characterization patterns of carbon molecular sieves used as raw materials in examples 1 to 6 of the present invention and samples in example 1.

FIG. 2 is a schematic view of a static adsorption experimental apparatus in test 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.

FIG. 3 is a graph showing adsorption isotherms of the raw material carbon molecular sieves used in examples 1 to 6 of the present invention.

FIG. 4 is the adsorption isotherm of the modified carbon molecular sieve obtained in example 2 of the present invention.

FIG. 5 is the adsorption isotherm of the modified carbon molecular sieve obtained in example 3 of the present invention.

FIG. 6 is the adsorption isotherm of the modified carbon molecular sieve obtained in example 4 of the present invention.

FIG. 7 is the adsorption isotherm of the modified carbon molecular sieve obtained in example 5 of the present invention.

FIG. 8 is the adsorption isotherm of the modified carbon molecular sieve obtained in example 6 of the present invention.

Detailed Description

Research shows that the R group in the organic matter can produce hydrogen bond with hydroxyl in the molecular sieve to regulate the pore size of the molecular sieve and form and select during gas separation, especially during separation (N)₂+O₂)/CH₄When is CH₄Has a molecular dynamic diameter of 0.38nm, N₂The molecular kinetic diameter of the molecular sieve is 0.364nm, the kinetic diameter of the oxygen is 0.346nm, and the molecular sieve can selectively adsorb N₂And O₂To CH₄The adsorption capacity is low, and the purpose of separating the mixed gas is achieved.

The solvent of the organic 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 can be dissolved. The molecular weight of the organic substance is determined to be soluble.

In order that the organic matter can be well prepared into a solution, a better hole adjusting effect is generated, the diffusion coefficient and the mass transfer rate of different gas components in the holes of the adsorbent are changed, and preferably, the polymerization degree n of the organic matter is 500-5000. More preferably, n is 1200 to 1700.

Molecular sieves commonly used in the art are suitable for use in the present invention, and preferably, the molecular sieve is Carbon Molecular Sieve (CMS), a type a molecular sieve (e.g., 4A molecular sieve, 5A molecular sieve), an X type molecular sieve, a Y type molecular sieve, a ZSM molecular sieve (e.g., ZSM-5 molecular sieve), a SAPO molecular sieve (e.g., SAPO-34 molecular sieve, SAPO-11 molecular sieve), a silicon titanium molecular sieve, activated carbon, or the like.

Preferably, the molecular sieve is a carbon molecular sieve. Research shows that 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 is changed, the pore diameter tends to shrink, thereby further separating N₂/CH₄。

Preferably, the organic substance is polyvinyl alcohol (PVA).

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

Specifically, the present invention preferably employs the following operations: stirring, mixing and soaking the molecular sieve and the organic matter solution for a certain time, filtering and separating, and drying the filtered molecular sieve at 60-200 ℃ to obtain the organic modified molecular sieve.

Wherein, the organic solution can be prepared by the following method: mixing a certain amount of organic matters with a solvent at a certain temperature, and then stirring for a certain time until the organic matters are completely dissolved to obtain an organic matter solution.

The invention also provides the organic modified molecular sieve of the invention as N₂/CH₄、O₂/CH₄Or (N)₂+O₂)/CH₄Selectivity of the systemUse of an adsorbent.

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, (N)₂+O₂)/CH₄Is a mixed gas system of nitrogen, 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 separation (N)₂+O₂)/CH₄While selectively adsorbing N₂And O₂Thereby 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.

Example 1

The PVA modified carbon molecular sieve is prepared by the following method:

1) preparing a PVA aqueous solution: mixing a certain amount of PVA with deionized water at the temperature of 90 ℃, and then stirring for a certain time until foams in the PVA aqueous solution gradually disappear, wherein the solution is clear and transparent, and the PVA solution with the concentration of 1 wt% is obtained;

2) and fully mixing and stirring the ground carbon molecular sieve (40-60 meshes) and a PVA solution, then carrying out suction filtration and separation on the modified carbon molecular sieve solid impregnated with the organic polymer, and drying the filtered solid at 150 ℃ overnight to obtain a final PVA modified carbon molecular sieve sample.

The BET method is adopted to determine the specific surface area of the raw material carbon molecular sieve and the modified carbon molecular sieve sample, and the map of the specific surface area is shown in figure 1.

As can be seen from FIG. 1, the pore size distribution of the carbon molecular sieve is obviously changed after the modification by the invention.

Examples 2 to 6

By adopting the method of example 1, only the concentration of the PVA solution is changed to obtain a series of PVA solution modified carbon molecular sieves with different concentrations, and the specific changed parameters are shown in Table 1.

TABLE 1

Example numbering	PVA solution concentration (%)
		Example 1	1
Example 2	2
		Example 3	3
Example 4	4
		Example 5	5
Example 6	10

Test example 1

And (3) measuring the adsorption capacity of the raw material carbon molecular sieve and the modified samples obtained in the embodiments 2-6 on nitrogen and methane by using a static adsorption method. The specific measurement method is as follows:

as shown in fig. 2, the static adsorption apparatus is composed of 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, an electromagnetic valve, a needle stop valve, a thermocouple, an electromagnetic relay, and the like. Utilize constant temperature water bath 5 to keep the adsorption process constancy of temperature, utilize reference cell 3 to calculate the free volume, realize gaseous adsorption process through the switching of adsorption cell 4, reference cell 3, solenoid valve, aciculiform stop valve, realize the record of pressure and the transmission of signal of telecommunication through pressure sensor 2, realize gaseous automatic adsorption process through the coordinated control of PLC module 1, electromagnetic relay, solenoid 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. And (5) vacuumizing by using a vacuum pump to regenerate the adsorbent.

The static adsorption device comprises the following operation steps:

weighing a certain amount of sample, placing into an adsorption tank 4, adjusting a constant temperature water bath 5 to an experimental temperature, starting an experiment after the temperature of the water bath is stable, and ensuring He gas steel cylinders 9 and N before the experiment₂Gas cylinder 8, CH₄The main valve of the gas steel cylinder 7 is in an open state, and the pressure reducing valve is opened to a pressure slightly higher than the highest pressure required by the experiment:

1. instrument leak detection

And opening a valve for controlling the He gas steel cylinder, observing whether the pressure changes, slowly opening the valve for controlling the adsorption tank if the pressure does not change, observing whether the pressure continuously drops, and if the pressure is stable to a certain pressure after the pressure drops, ensuring that 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 performed₂And (3) performing an adsorption test on the mixture,CH₄and (5) testing gas adsorption. Respectively controlling He gas steel cylinder and N₂Gas cylinder, CH₄The gas steel cylinder is opened and closed, so that the gas pressure of the system is increased; the adsorption tank and the vacuum pump are controlled to be opened and closed, and the adsorption process and the desorption process are respectively realized. And the PLC module 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 an initial value V₀：

Will be an initial value V₀And (3) substituting the formula (2) for iteration to obtain the adsorption quantity of nitrogen and methane.

The isothermal adsorption curves of the raw material carbon molecular sieve and the modified samples obtained in examples 2 to 6 on nitrogen and methane are shown in fig. 3 to 8.

As is evident from FIGS. 3 to 8, the carbon molecular sieve obtained by modification by the modification method of the present invention retains the original molecular sieve N₂CH with substantially constant adsorption capacity₄The 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. For selective adsorption of N₂/CH₄In the system N₂The preparation method of the organic modified molecular sieve is characterized by comprising the following steps:

impregnating the molecular sieve with an organic solution, carrying out solid-liquid separation, and drying the solid to obtain an organic modified molecular sieve; the organic matter is polyvinyl alcohol, the polymerization degree n of the polyvinyl alcohol is 500-5000, the molecular sieve is a carbon molecular sieve, and the concentration of the organic matter solution is 0.001-40 wt%.

2. The process of claim 1 for the selective adsorption of N₂/CH₄In the system N₂The preparation method of the organic modified molecular sieve is characterized by comprising the following steps: the polymerization degree n is 1200-1700.

3. The process of claim 1 for the selective adsorption of N₂/CH₄In the system N₂The preparation method of the organic modified molecular sieve is characterized by comprising the following steps: the impregnation is equal volume impregnation or excess impregnation.

4. The process of claim 1 for the selective adsorption of N₂/CH₄In the system N₂The preparation method of the organic modified molecular sieve is characterized by comprising the following steps: the concentration of the organic solution is 0.01-20 wt%.

5. The process of claim 4 for the selective adsorption of N₂/CH₄In the system N₂The preparation method of the organic modified molecular sieve is characterized by comprising the following steps: the concentration of the organic matter solution is 1-10 wt%。

6. The process according to any one of claims 1 to 5 for the selective adsorption of N₂/CH₄In the system N₂The preparation method of the organic modified molecular sieve is characterized by comprising the following steps: uniformly mixing and soaking the molecular sieve and the organic matter solution, filtering and separating, and drying the filtered molecular sieve at 60-200 ℃ to obtain the organic modified molecular sieve.

7. An organically modified molecular sieve, characterized in that: use of a catalyst according to any one of claims 1 to 6 for the selective adsorption of N₂/CH₄In the system N₂The organic modified molecular sieve is prepared by the preparation method.

8. Organically modified molecular sieve as claimed in claim 7 as N₂/CH₄Selective adsorption of N to the System₂The use of (1).

9. Use of the organically modified molecular sieve of claim 7 for purifying methane in coal bed gas, oil field gas or biogas.