论文部分内容阅读
Biomethane route uses inferior biomass as a raw material which possess abilities of both energy saving and emission reduction.It generated during anaerobic digestion of biological wastes(e.g.kitchen waste,landfill sites,animal waste),typically consists of 55–60%methane,38–40%carbon dioxide and smaller amounts of hydrogen sulfide.Natural gas upgrading is a main problem.As a key technology of biogas purification,membrane processes have gained a lot of attention for the separation of biogas.Therefore,transport mechanism of biogas in the selected membrane cannot wait to figure out.Carbon nanotube(CNT)membranes are studied to separate the mixture of CO2 and CH4.The gas permeabilities of CNT membranes are several orders of magnitude higher than those of commercial polycarbonate membranes,despite having pore sizes an order of magnitude smaller.Meanwhile the CNTs demonstrate a higher selectivity of CO2 than other materials(activated carbons,zeolites 13X,and metal-organic frameworks)reported in the literature.CNTs are easy to be modified and modeled due to their simple structure at the same time.Molecular simulation methods include Grand canonical Monte Carlo(GCMC)and equilibrium molecular dynamics simulations(EMD)were used to compute adsorption loadings and self-diffusivities of CH4/CO2 in CNTs modified with hydrophilic carboxylic groups.Equimolar CO2/CH4 mixture was simulated in a range of temperature and pressure which cover the critical point of the gases.The diameters of CNTs are about 1 nm,as fluids confined in them have much difference.There is no saltation at the critical point in computing the properties include adsorption loadings and self-diffusivities.Compare to the pristin CNTs,behavior of gases in CNTs modified with –COOH are different:(1)adsorption loadings of CH4 diminish;(2)self-diffusions of the mixture get two orders smaller.It turned out that surface modification plays an important role in the separation,pressure and temperature are not notable.The results showed that high temperature and low pressure are suitable for the separation of CO2/CH4 mixture using CNTs modified with hydrophilic carboxylic groups.