Study On Preparation Of Carbon Materials From Deoxidized Low Concentration Gas

China has abundant coal-bed methane reserves,but because the methane content in some coal-bed methane is too low to be used,the utilization rate of coal-bed methane is still at a low level,and more than half of the low-concentration gas is directly drained,resulting in a large amount of resource waste and serious environmental pollution.In this thesis,a research idea is proposed to separate and concentrate low-concentration gas through vacuum swing adsorption process and use the product gas for the preparation of carbon materials,so as to complete the green and efficient utilization of low-concentration gas and avoid causing a large amount of energy waste and environmental pollution.The main research content of this thesis includes the adsorption and separation performance test of adsorbent,exploring the adsorption characteristics of gas components on the adsorbent and the separation ability of the adsorbent.The single column vacuum pressure swing adsorption device was used to deoxidize and concentrate low concentration gas,and the influence of working conditions on the separation effect was studied,so as to optimize the process to get better separation effect.The separation and concentration of the product gas was used to prepare carbon materials.The influence of different preparation conditions on the quality of carbon materials was explored,and the possibility of its application was found.The product gas after separation and concentration was used for cracking catalysis to produce carbon materials and hydrogen.The influences of different cracking conditions on methane conversion and carbon sediment quality were explored to seek greater utilization value.The following conclusions are reached:（1）In the separation performance test,the penetration time of CH₄,N₂ and O₂ was CH₄<N₂<O₂ from small to large,indicating that the adsorbent did have separation effect on the mixed gas,and the increase of CH₄ concentration reduced the separation effect,while the increase of back pressure improved the separation effect.By using a single tower vacuum swing adsorption device set up in the laboratory for deoxidation and concentration of low concentration gas,raw gas containing 4.3%CH₄ and 19%O₂can be treated to produce gas containing 24.7%CH₄ and 1.6%O₂.The recovery rate of CH₄ is 86%.The concentration,deoxidation rate and recovery rate decreased with the increase of CH₄ concentration in raw gas.The best inlet flow rate of low concentration raw gas is 2L/min,and the best bed length is 2m.The best inlet flow rate of high concentration raw gas is 1L/min and 1.5L/min,and the best bed length is 1.8m.The decrease of desorption pressure can improve the concentration and deoxidation rate,but can reduce the recovery rate of CH₄ and increase energy consumption.For feed gas with high concentration of CH₄,increasing adsorption pressure can improve the adsorption separation performance.（2）The processed gas mixture was used as carbon source and copper foil as matrix to prepare carbon materials,and the influence of deposition conditions on the structure of carbon materials was explored.With the increase of deposition temperature（950℃～1050℃）,deposition time（20min～40min）and CH₄ concentration in raw gas（10%-20%）,the content of structural defects in the prepared carbon sediments decreased first and then increased,and the degree of crystallization increased first and then decreased.The optimal sedimentary conditions obtained by screening are:The concentration of CH₄ in the raw gas is 15%,the total intake flow rate is 110sccm,H₂ flow rate is 10sccm,deposition temperature is 1000℃,deposition time is 30min,the ratio of I_D/I_G in the Raman spectrum of the material is only 0.207,the half-peak width of G peak is29.980cm^-1.It shows that pyrolytic carbon materials with low defect degree are obtained.（3）Copper foam was used as catalyst to crack the treated gas mixture at high temperature to prepare carbon material and hydrogen,and the influence of cracking conditions on methane conversion was explored.The methane conversion rate decreases with the increase of methane concentration in feed gas（10%-20%）,with the increase of pyrolysis temperature（950℃～1050℃）,and with the increase of intake flow rate（50sccm～100sccm）.Under the pyrolysis temperature of 1050℃,methane and nitrogen mixed gas was injected at 50sccm,and the methane conversion rate reached53.44%after high temperature catalytic pyrolysis.The methane conversion rate remained at a high level 20h after pyrolysis and did not decrease.The solid carbon deposits obtained by cracking reaction have more defects and less crystallization.This thesis has 38 figures,13 tables and 78 references.