Research On The Preparation Of Modified Clinoptilolite Molecular Sieve And Its Adsorption Separation Properties For CH₄/N₂

With the country's increasing demand for energy,the development and utilization of low-concentration coalbed methane is imminent.The physical properties of methane?CH₄?and nitrogen?N₂?,the main components in coalbed methane,are very close and difficult to separate,which severely restricts the development and utilization of low concentration coalbed methane.Concentration and purification of CH₄in CH₄/N₂mixed gas by pressure swing adsorption separation technology is one of the effective methods to solve the problem of development and utilization of low concentration coalbed methane.In this paper,natural clinoptilolite with abundant reserves and low processing cost is selected as the raw material.Using its unique ion adsorption and exchange performance,modified clinoptilolite adsorbents with good selectivity to N₂,large equilibrium separation coefficient,good selectivity to CH₄and large equilibrium separation coefficient are respectively prepared by adjusting the pore size,pore diameter and pore volume.The modified clinoptilolite adsorbents can be effectively used for pressure swing adsorption separation of CH₄/N₂mixture.1.This paper select the representativeness clinoptilolite mine to test.Based on the Based on the difference of hardness and particle size about clinoptilolite,feldspar and quartz,we put forward the scheme of grind/screening-grind/centrifugation/screening.It reduces the influence of impurity minerals on the process of centrifugal beneficiation,it effectively increases the content of the clinoptilolite from 75%to 89%and reached the quality standard of the zeolite deposit evaluation index,and this technology may provide support for the development and application of local natural clinoptilolite ore in gas purification field.2.The adsorption selectivity coefficient of N₂and CH₄is further optimized via the adjust of cation exchange degree and the ratio of cations in the structure and modified cations.In this paper,the Ca²⁺of Clinoptilolite itself is exchanged by a certain amount Na⁺in short time,resulting in the change of the content of Na⁺and Ca²⁺in it,and the pore size and polarity of the channel are regulated.After the modification,we get the modified clinoptilolite adsorbents with good selectivity to N₂,large equilibrium separation coefficient to N₂/CH₄.Experiments show adsorption N₂capacity of it can reach 12 cm³/g,and the equilibrium separation coefficient of N₂/CH₄can reach more than 12.This kind of molecular sieve can be used for separation CH₄/N₂,and it has good regeneration capability.By controlling the adsorption time and pressure,we can get directly the gas of CH₄when the raw gas of 20%CH₄and 80%N₂flow through a single tower pressure swing adsorption device with it,its concentration is 96.87%,the recovery is 41.2%.The molecular sieve can be regenerated by pumping vacuum,we do the test three time repeatedly,the penetration curve of CH₄is basically unchanged.Its effect is better than the Carbon molecular sieve under the same test conditions.3.The modified Clinoptilolite is prepared by NH₄⁺and another cation,it has large specific surface area and abundant micropores with good adsorption capacity of CH₄and high equilibrium separation coefficient to CH₄/N₂.The experimental results show the specific surface area and pore volume of N-Cu reach 253 m²/g and 0.225 m³/g which was modified with ammonium copper double ion,and the equilibrium separation coefficient of CH₄/N₂is from 1.07 to 2.26.The specific surface area and pore volume of N-Ba reach 97.84 m²/g and 0.105 m³/g which was modified with ammonium barium double ion,and the equilibrium separation coefficient of CH₄/N₂is from 1.17 to 5.52.This type of zeolite molecular sieve is expected to be another new material for adsorption CH₄.The N-Ba is used in a single tower pressure swing adsorption device for separation CH₄/N₂.By controlling the adsorption time and pressure,we can get the gas of CH₄by pumping vacuum of adsorption tower when the raw gas of 50%CH₄and50%N₂flow through the device and the CH4 penetration concentration reaches 95%of the raw gas,its concentration is 63.88%,the recovery is 67.78%.we can get the gas of CH₄by pumping vacuum of adsorption tower when the raw gas of 20%CH₄and 80%N₂flow through the device and the CH₄penetration concentration reaches 95%of the raw gas,its concentration is 41.46%,the recovery is 68.97%.Its effect is better than the zeolite molecular sieve 5A and 13X under the same test conditions.4.Pressure swing adsorption test device was set up and the dynamic separation effect of modified clinoptilolite molecular sieve,commercial molecular sieves 5A,13X and carbon molecular sieve on CH₄/N₂mixture was analyzed and studied.The adsorption and separation effects of molecular sieve adsorbents on CH₄in low concentration feed gas under different pressures and flow rates were observed and analyzed.The experimental results show that appropriate system pressure made the gas stay in the adsorption tower for sufficient time,increased the penetration time difference between the two components of gas,which is conducive to concentration and separation of CH₄.The lower CH₄concentration in the feed gas resulted in the lower CH₄concentration and recovery in the product and more difficult separation.Comprehensive analysis of the dynamic breakthrough curve of modified clinoptilolite,isotherms of adsorption of CH₄and N₂and molecular dynamics simulation results show that the mechanism of separation of CH₄/N₂by modified clinoptilolite molecular sieve is based on the equilibrium adsorption difference of the two components of gas.Through molecular dynamics simulation analysis,it has been found that the clinoptilolite system with different modified cations has different energy.The larger energy of clinoptilolite and its easier interaction force with CH₄of high polarizability than N₂will lead to the selective adsorption of CH₄.The smaller energy of clinoptilolite and its easier interaction force with N₂of quadrupole moment than CH₄will lead the selective adsorption of N₂.