Preparation And Application Of Carbon Molecular Sieves

The main objective of this thesis is composed of three parts:The exploration of new binder for carbon molecular sieves(CMS)preparation,pore size modification of CMS with Chemical Vapor Dipositon(CVD)and CMS application in nitrogen/methane separation.In the process of CMS preparation,coconut shell was adopted as the raw material and acrylamide as the binder.Acrylamide pyrolysised between 220 and 400℃,with 26% pyrolytic carbon left.CO,H₂ and NH₃ are the main gaseous phase products of the acrylamide pyrolysis,which make it more environmental friendly compared with phenol-formaldehyde resin and coal tar.The binder influences CMS mechanical strength intensively.CMS with acrylamide,methyl cellulose and phenol-formaldehyde resin as main binders are prepared respectively,and their intension are compared as well.Some accessorial components are added to consummate the function of binder.The result turned out that CMS with 20% acrylamide as main binder and 5%amylum and 0.5%triethanolamine as accessorial binders has the best intension.Finally,coconut shell based CMS are prepared with such binders.The air separation capability of CMS are characterized by pressure swing adsorption(PSA),N₂ concentration in the product can reaches 96%after proper pore size modification.Chemical vapor dipostion is the most commonly used pore size modification method during CMS preparation.This thesis adopted the CVD pore size modification in three parts: One-step CVD to prepare CMS under mild conditions,tow-step CVD process to modification CMS pore size and excessive-CVD-reopenning process to prepare CMS.The influence of CVD concentration and CVD time to the CMS pore structures have been examined in detail. After one-step CVD,CMS air separation capability of CMS are improved,N₂ concentration in the PSA product can reaches 99%.This thesis put forward and experienced two-step CVD pore size modification process.Deposition agent concentrtion and deposition time and temperature in the second stage CVD are investigated.The recovery rate of N₂ in the CMS air separation PSA process are greatly improved.Excessive CVD reopenning process prepared the most excellent air separation CMS,N₂ concentration in the PSA product is greater than 99%and O₂ in PSA desorption gas can reaches 32%.To proof the mechanism of the CVD, the pore size distribution,SEM and diffusion of oxygen and nitrogen on different CMS samples is characterized.The result is that CMS pore size decreased after CVD while the selective adsorption of O₂ on CMS is increased,which makes CMS have excellent air separation capability.CMS air separation exhibits great economic efficiency,especially in middle and small scale nitrogen product plant.The mechanism of CMS air separation is depended on diffusion dynamics.The smaller molecular diffuses much faster into CMS pores,and the larger molecular is left in the gas phase and flow out the tower as product.If the diffusion kinetic mechanism of CMS can be used in N₂/CH₄ separation for coalbed methane recovery,it will produce great social and economic benefits.The breakthrough curves of CH₄ and N₂ on CMS are tested,effects of operating conditions on CH₄ and N₂ separation such as:operation pressure,temperature and outlet gas flow rat are systematically investigated.To proof the feasibility of CMS kinetic separation CH₄/N₂,breakthrough curves of CH₄/N₂ on CMS and activated carbon are tested respectively.Finally,some proposals are listed to produce suitable CMS for CH₄/N₂ separation.