| With rapid development of economy and society,the problem of energy shortage is gradually appearing.Among them,biomass fermented hydrogen?H2?and methane?CH4?are the most promising energy sources.However,CO2 in biomass gas fuel reduces combustion efficiency and increases greenhouse gas emissions.Developing efficient biomass fuel purification technology has become a key issue for efficient H2 and CH4 utilization.Owning to low energy consumption and easy operation,membrane is considered to be the most promising separation technology.The development of membrane materials with high physicochemical stability and separation performance has become a hot topic.In this study,two-dimensional carbon-based graphene oxide?GO?and one-dimensional wood fiber cellulose nanofibers?CNFs?were choosed as membrane matrix.The composite membranes were fabricated based on gas separation theory for H2/CO2 and CO2/CH4 purification.The physicochemical properties and gas permeability of composite membrane were studied.The performance characteristics and main application directions were analyzed.Besides,the relationship between membrane structure and gas separation performance was established.The relationship between gas separation mechanism and structure was explored.?1?GO-based composite membranes:Based hydrogen?H2/CO2?purification system,GO-based composite membrane were preparaed.As a kind of two-dimensional carbon-based material with abundant oxygen-containing functional groups,GO showed ultra-high physicochemical stability and well film-forming performance.For multi-layer GO membranes,gas molecules mainly diffused through GO layer gap.As a result,diffusion paths of GO membranes were tortuous,and gas permeance was relatively poor.In this study,porous metal organic frameworks?MOFs?were selected as filling materials to prepare UiO-66-NH2/GO composite membranes.Compared to pure GO membrane,UiO-66-NH2 particles inserted in GO laminar layers can provide a fast diffusion channel for gas molecules with small kinetic diameter,and enhanced H2 purification performance was achieved(H2 permeance is 3.9×10-8 mol m-2 s-1pa-1,ideal selectivity of H2/N2 and H2/CO2 are 9.75 and 6.39,respectively).?2?GO-modified composite membranes:Firstly,g-C3N4-based composite film was prepared by using GO as a patch material.Owning to excellent film-forming performance of GO,defects between g-C3N4 sheets were repaired in g-C3N4/GO composite membranes.Considersing the pore size of g-C3N4 sheet is 0.311 nm,H2 molecules can be purified from CO2,N2,O2 and CH4.The H2 permeance was 366.3×10-8 mol m-2 s-1 Pa-1 and ideal selectivity of H2/CO2 was 179.6.Secondly,GO was incorporated in polymer matrix for selective CO2 diffusion in GO-polymer composite membrane.Moreove,gas permeance was significantly improved by doping porous MOFs.The mixed matrix membrane prepared by doping Ui O-66-NH2@GO in PI matrix showed enhanced CO2 separation performance,with CO2 permeability of 7.28 Barrer and CO2/N2selectivity of 52,which is expected to achieve efficient purification performance of methane.?3?CNF-based composite membranes:As a kind of natural polymer material,cellulose has a large amount of reserves.The green and biodegradable features make it a kind of promising membrane matrix material.Firstly,typical polymer was used as membrane matrix for exploring preparation process of polymer membrane and method of MOFs uniform dispersion.Typical Polyethersulfone?PES?was selected as membrane matrix,brominated polyphenylene ether?BPPO?was introduced as modifier for efficient dispersion of UiO-66-NH2.The prepared UiO-66-NH2/BPPO/PES composite membrane showed excellent CO2 separation performance,with CO2 permeability of 125.6 Barrer and CO2/N2 selectivity of 50.2.Based on above work,2,2,6,6-tetramethylpiperidine-1-oxyl?TEMPO?-oxidation CNFs was selected as membrane matrix and ZIF-8/CNF composite membranes were prepared.By in-situ growing ZIF-8 crystals on CNFs,ZIF-8 can be uniformly dispersed in CNF matrix.ZIF-8 loading was effectively increased and connected ZIF-8 channels can be constructed in CNF matrix.Benfiting from CO2sieving pore of ZIF-8,efficient biogas purification performance was achieved.The CO2permeability was 550 Barrer and ideal selectivity of CO2/N2 and CO2/CH4 were 45.5 and 36.2,respectively.?4?CNF-based facilitated transport membranes:Ownig to well water retention properity of CNFs,Ethylenediamine?EDA?modified CNF-NH2 was prepared as membrane matrix for selective removal of CO2.The-NH2 of CNF-NH2 can effectively promote CO2 and H2O conventing to easily diffused HCO3-.Before gas separation test,membranes were humidified and CO2/CH4 selectivity was improved.In addition,porous UiO-66 particles were incorporated in composite membranes and gas permeability was enhanced.The prepared CNF-NH2/UiO-66composite membranes showed efficient purification performance for methane?CO2/CH4?.In humid state,the CO2 permeability was 148 Barrer and CO2/CH4 ideal selectivity was 43. |
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