Synthesis Of Starch-Derived Microporous Carbon For The CH₄ Separation&Enrichment From Low Concentration Coalbed Methane

Separation and enrichment of CH₄/N₂ in coalbed methane is of great significance for Guizhou Province to make full use of existing energy sources and reducing environmental pollution.Adsorption separation method is a suitable method for the separation and enrichment of low-concentration coalbed methane CH₄/N₂ especially in Guizhou.The adsorbent is primary element in industrial production process of this technology.Activated carbon is considered as a hight-quality absorbent due to the rich pore structure,low price and improved recyclability.The molecular dynamics diameter of CH₄ is 0.382 nm,and when the pore size of the adsorbent is1.3-3 times of the adsorbate molecule the adsorbent is most conducive to adsorption.Therefore,in order to increase the adsorption capacity of activated carbon for CH₄,the pore size of the adsorbent should be micropores and the distributed of these microspores is around 0.5-1.3nm.Moreover,the microspores volume should be as large as possible.However,activated carbon that is available on the market has uneven distribution pores and low microporosity,which results in poor adsorption performance for CH₄.Therefore,it is very necessary to synthesis microporous carbon materials with large micropore volume and suitable pore size distribution.Accordingly,in this dissertationstarch is used as carbon source to prepare a series of carbon materials through hydrothermal carbonization,K₂CO₃ activation and ion activation.N₂ adsorption/desorption method is used for analyzing the pore structure of starch-based carbon materials.And FITR and Boehm titration were used to determinate the surface chemical properties of carbon materials Furthermore a fixed bed device to determine the effect of carbon materials on simulated coalbed methane?CH₄ 20%,N₂ 64%,O₂ 16%?was explored by a fixed bed device.The main research results could be conclude as follows:The hydrothermal preparation conditions on the adsorption performance of carbon materials?SAC_x?has great effect.It isfound that the hydrothermal carbonization of starch has a narrower pore size distribution and better CH₄adsorption performance than carbon materials prepared by direct carbonization.As the hydrothermal time and the amount of?-amylase increase,the adsorption performance of carbon materials increases first and then decreases.The optimized carbon material SAC_10-10-0.1 which was prepared under conditions of hydrothermalsolution concentration of 10g/60mL,hydrothermal time of 10 h,and?-amylaseaddition of 0.1 g,has the highest CH₄ content in simulated coalbed methane.The unit adsorption capacity reached 29.77m L/g.The influence of mixing method and activation condition of K₂CO₃ activated hydrothermal carbon on the adsorption performance of carbon materials are also essential.The specific surface area and micropore volume of the carbon material prepared after K₂CO₃ activated hydrothermal is nearly doubled than that of the hydrothermal carbon.This post-processing carbon materials showimproved CH₄adsorption performance.Besides the activation time and activation temperature during the activation process have a certain effect on the adsorption performance of the prepared carbon materials.The carbon material WAC_k-1.5-850 prepared under the best process?Ball milling,activation temperature of 850?,activation time of 1.5 h?has the largest microspores specific surface area and micropore volume,which are1596.19 m²/g and 0.67 cm³,respectively/g.It has the highest unit adsorption capacity of CH₄ in the simulated coalbed methane,reaching 49.17 m L/g.This adsorption rate is increased by 55.8%comparing with the non-K₂CO₃ activated hydrothermal carbon WAC.The the addition amount of acrylic acid and the ion exchange ratio of K₂CO₃solution in the ion activation method on the adsorption performance of the prepared carbon material Ax-WAC_k-y also an important factor.With the increase of the ion exchange ratio and added amount of acrylic acid,the micropore specific surface area and micropore volume of Ax-WAC_k-y raised first and then dropped down.Under the optimal process conditions?Acrylic acid concentration is 6 wt%,ion exchange ratio is3?the carbon material A6-WAC_k-3 show the largest micropore specific surface area and micropore volume,which reach 1826.81 m²/g and 0.77 cm³/g,respectively.It has the highest unit adsorption capacity for CH₄ in simulated coalbed methane,reaching63.12 mL/g.