| Biogas,as a renewable clean energy,is used in civil and industrial applications.It is a combustible gas,which is produced by fermenting various organic substances such as straw and sewage under strictly oxygen-free conditions.Although biogas is used extensively,biogas contains more carbon dioxide,which will not only reduce the calorific value and combustion potential of biogas but also cause corrosion to natural gas pipelines.Unpurified biogas cannot be directly used because it has a methane concentration lower than that required for vehicle fuel and pipeline natural gas.Therefore,the separation of methane and carbon dioxide in biogas is especially important.Compared with other separation methods?such as cryogenic separation method and pressure swing adsorption method?,the organic membrane separation method has been widely concerned because of its good film forming property,simple operation,and low investment.Among them,polysulfone?PSF?has good film-forming properties and high gas selectivity so as to be widely used in the study of gas separation performance.However,due to its poor gas permeability,the further development of polysulfone membranes is hindered.The synthesis of a copolymer containing both rubbery and glassy units is a common and effective method for modifying polymers.Therefore,in this paper,PSF-PEG and PSF-PDMS copolymers are prepared by polycondensation and their structures are characterized.Then,a series of gas separation membranes are prepared by solution coating method,and thermal stability and structure of the membranes are characterized.In addition,the effects of temperature,pressure,molecular weight of PEG,and content of PEG/PDMS on gas separation membranes are also studied.The main work is as follows:?1?A series of PSF-PDMS copolymers with different content of PDMS were prepared by using hexafluorobisphenol A,4,4-difluorodiphenyl sulfone and PDMS4200.Their structures were characterized by 1H-NMR and FT-IR.The results showed that the copolymer was successfully prepared.The permeability and ideal separation coefficient of PSF-PDMS membranes with PDMS content of 5%and 10%to CO2 and CH4 at different temperatures?25?,35?,45?,55??were tested.The test results showed that:the permeability of PSF-PDMS membranes to CO2 and CH4 gradually increased with the increase of PDMS content;the permeability of PSF-PDMS membranes to CO2 and CH4gradually increased with the increase of temperature.At 1atm and 55?,the PSF-PDMS membrane with a PDMS content of 10%had a CO2 permeation of73.7Barrer and a CO2/CH4 selectivity of 4.2.?2?A series of PSF-PEG with different PEG content were prepared by using hexafluorobisphenol A,4,4-difluorodiphenyl sulfone and PEG.Their structures were characterized by 1H-NMR and FT-IR.The results showed that the copolymer was successfully prepared.TGA analysis was performed on the PSF-PEGs membranes and the decomposition temperature was 350?.The permeability,diffusion coefficients,solubilities coefficients and ideal separation selectivity of CH4 and CO2 were measured under different pressure?0.5atm,1.0atm,1.5atm?and temperature?25?,35?,45?,55??for PSF-PEGs membranes with PEG molecular weight of 1000 and 2000 and PEG content of5%,10%,15%,and 20%.The test results showed that:the permeability of PSF-PEGs membranes to CO2,CH4 gradually decreased with the increase of pressure;the permeability of PSF-PEGs membranes to CO2,CH4 gradually increased with the increase of temperature;the permeability of PSF-PEGs membranes to CO2,CH4 gradually decreased with the increase of PEG content;compared to the PSF-PEG1000-y membranes,PSF-PEG2000-y had higher permeability coefficients for CO2 and CH4.The PSF-PEG2000-20 membrane had a CO2 permeation of 6.4Barrer and a CO2/CH4 selectivity of 43.0 at 25?and 1.5 atm. |
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