Study On The Enrichment Of Oxygen-Bearing Low-Concentration Methane Using The Method Of Column Chromatography

Coalbed methane is one of the unconventional natural gas,which is an efficient and clean energy,with hugely reserved amount in China.However,large amount of oxygen-bearing low-concentration gas(C_CH4<30%)is formed,due to the air mixed in the extraction process.The low methane concentration has resulted in the difficulty of utilization for low-concentration methane,therefore,the utilization amount of coalbed methane is much lower than its extraction amount.And numerous low-concentration methane is directly discharged into the atmosphere,which can not only cause huge energy waste,but also result in serious environmental pollution.Therefore,the enrichment and utilization of oxygen-bearing low-concentration methane is of great significance to economy and environment.There are some great challenges in the purification of oxygen-bearing low-concentration methane,because of the similar physical properties of CH₄,O₂and N₂.At present,pressure swing adsorption is considered as the most promising method in methane enrichment,but which has not been studied much in the purification of oxygen-bearing low-concentration methane.Based on the methods of pressure swing adsorption and principle of gas chromatography,an separation method of elution column chromatography（ECC）is proposed in this work.And some properties of the method in methane enrichment vital to industrial application were studied further.In this work,carbon molecular sieve（CMS-3KT）and 5A zeolite are selected as adsorbents for the adsorption separation methods.And the main contents are as follows:The microstructure,specific surface area and pore size distribution of the both adsorbents were analyzed by scanning electron microscope（SEM）,nitrogen physical adsorption/desorption test.The adsorption isotherms and curves of single gas（CH₄,N₂and O₂）on the two adsorbents were tested by the static volumetric method,and the equilibrium separation coefficients and diffusion time constants of each component were calculated.As for CMS-3KT,the equilibrium separation coefficients of methane and nitrogen over oxygen are nearly equal to 1.while the diffusion time constants of oxygen and nitrogen are much higher than that of methane.Therefore,it is feasible that CMS-3KT can efficiently separate CH₄,N₂and O₂according to the results of adsorption kinetics.In term of 5A zeolite,the equilibrium separation coefficients of methane and nitrogen are about 4 and 2 times as that of oxygen,and the diffusion time of methane and nitrogen is slightly longer than that of oxygen.Thus,the feasibility that 5A zeolite can separate CH₄,N₂and O₂could be concluded from adsorption equilibrium performance and kinetic behaviour.And it is an suitable adsorbent of two adsorption separation methods,while CMS-3KT is only suitable for the method of pressure swing adsorption.The breakthrough experiment of CH₄/N₂/O₂mixture with methane concentration of 1-30%on the CMS-3KT was measured.The results indicated that the adsorbent can enrich the methane efficiently,and the results of adsorption kinetics were verified further.While the upper limit value of methane concentration is around 5%,in which the methane can be enriched feasibly but difficultly.Therefore,the oxygen removal and methane enrichment performance of ultra-low concentration methane(C_CH4<5%)was studied using the proposed method of micro-positive VPSA.And the method has been successfully used in coal mine to enrich the methane concentration from 0.25 to10%with several circulation.The results indicated that the proposed method is promising for enriching O₂-bearing ultra-low concentration CBM.The separation method of ECC with 5A zeolite as the adsorbent was used to enrich methane in this work.And the results revealed that the methane enrichment effect is much better than that of the method of PSA.The experimental results of carrier gas types and flow rates were studied in this work.And the result indicated that methane is the optimal carrier gas.Meanwhile,an increase can be observed in production efficiency and the purification effect is almost unchanged with the growth of carrier gas flow velocity in some degree.Also,the relationship between the initial concentration of methane and the critical volume of feed gas was studied.The growth rate of critical volume for feed gas is lower than that of initial methane concentration.In addition,the influence of column diameter and length on production efficiency and adsorbent efficiency was studied.A slight decrease can be observed in the adsorbent efficiency,but the production efficiency increased greatly with the rise of chromatographic column diameter.While the efficiency of adsorbent and production both increased with the growth in the chromatographic column length.In addition,the energy consumption of the two methods for purifying low-concentration methane was calculated respectively.It is noticeably that there is a reduction in it with the increase in initial methane concentration.A slight growth occurred in energy consumption with the rise of chromatographic column diameter and length.Therefore,the method of ECC is promising in enrichment of oxygen-bearing low-concentration method for industrial application,which can result in the novel approach in oxygen-bearing low-concentration methane enrichment.36 figure,13 tables and 82 references can be found in the thesis.