Preparation Of PDMS Modified Styrene Triblock Polymer Membranes And Its Application In CH₄/N₂ Separation

Methane?CH₄?,as a clean and efficient green energy and the main component of coal bed gas?CBM?,has become a major high-energy fuels instead of controversial coal and petroleumoilis.Among them,nitrogen?N₂?is the impurity gas with the largest content in coal bed gas,it is extremely significant to effective remove impurity gases for high-effectively utilization of the coal bed gas.Currently,for CH₄/N₂ separation,compared with other separation technologies?cryogenic separation,pressure swing adsorption technology?,membrane separation technology has the unique advantages of flexible operation,low energy consumption,small footprint,and less investment,attracting much attention.In a lot of membrane materials,styrene triblock polymer possess good film-forming performance,low price and high CH₄/N₂selectivity,become the first choice for enriching CH₄ materials.However,low gas permeability limits the further development of block polymer membranes.PDMS-co-PMHS,a kind of high permeability polymer material.Therefore,in this paper,PDMS-co-PMHS with high permeability was introduced into styrene block polymer by mechanical blending and hydrosilylation reaction to prepare two types modified membranes of SBS/PDMS-co-PMHS blend membrane,and SBS-c-PDMS-co-PMHS,SIS-c-PDMS-co-PMHS crosslinked membrane.The structure,morphology and thermodynamic stability were characterized by FT-IR,SEM and TGA.In addition,the effects of test temperature and PDMS-co-PMHS content on CH₄/N₂ separation performance also were investigated.The specific research contents of this paper are as follows:1.SBSblockpolymerwasselectedasthebasematerial,PDMS-co-PMHS as the modified material,a series of SBS/PDMS-co-PMHS blend membranes were prepared by simple mechanical blending.Its chemical structure,thermodynamic properties and morphology were characterized.At the same time,under the measure condition of 25?-55?,the single gas permeability performance of CH₄ and N₂ for SBS/PDMS-co-PMHS blend membranes with different PDMS-co-PMHS content were tested.The results show that under the condition of 25?and 1 atm,with the increase of PDMS-co-PMHS,the CH₄ permeability gradually increase for blend membrane,and CH₄/N₂ selectivity basic remain unchanged.When the content of PDMS-co-PMHS increased to 15 wt%,the permeability of CH₄ from 37.6Barrer increased to 62.17 Barrer.As test temperature up to 55?,the permeability of CH₄ further improve to 136.5 Barrer,CH₄/N₂ selectivity remain at about 3.0.2.Hydrosilylation was selected as the modification method,SBS block polymer as the substrate material,PDMS-co-PMHS as the modified material,a series of SBS-c-PDMS-co-PMHS crosslinked membranes were prepared by controlling the content of PDMS-co-PMHS.Its chemical structure,thermodynamic properties,morphology and crosslinking degree were characterized in detail.In addition,under the measure condition of 25?-55?,the single gas?CH₄,N₂?permeability performance of crosslinked membrane containing different PDMS-co-PMHS content were determined.The results showed that with the increase of PDMS-co-PMHS content,the CH₄permeability of the crosslinked membrane increased significantly,while the CH₄/N₂ selectivity remained basically unchanged.In this series of crosslinked membrane,SBS-c-PDMS-co-PMHS-70 show the best CH₄ permeability of443.6 Barrer,which is 11.7 times than that of the pure SBS membrane?37.6Barrer?under the condition of 25?and 1 atm.In addition,as the temperature increase to 55?,the permeability of CH₄ could further increased by 679.2Barrer,CH₄/N₂ selectivity remain at about 3.0.For the mixed gas of CH₄/N₂?50/50 vol%?,the CH₄ permeability of SBS-c-PDMS-co-PDMS-70 was 394.6Barrer,N₂ permeability was 162.7 Barrer.Compared with pure SBS membrane,the increase was 1047%and 1161%,respectively.3.A series of SIS-c-PDMS-co-PDMS crosslinked membranes with different PDMS-co-PDMS content were prepared by simple hydrosilylation reaction using SIS triblock polymer as the base material and PDMS-co-PMHS as the modified crosslinked material.The structure of SIS-c-PDMS-co-PMHS crosslinked membranes was characterized by FT-IR,indicating the successful preparation of SIS-c-PDMS-co-PMHS crosslinked membrane.Scanning electron microscopy?SEM?,thermogravimetric analysis?TGA?and Soxhlet extraction experiments were used to study the morphology,thermal stability and crosslinking degree of the membrane.The permeability of single gas?CH₄,N₂?and the mixed gas?CH₄/N₂:50/50 vol%?of the sample membrane with the best gas permeability was tested.The results show that under the condition of 25?and 1 atm,the gas permeability increased with the increase of PDMS-co-PMHS content.When the PDMS-co-PMHS content increased to 70 wt%,the permeability coefficient of CH₄ from 25.9 Barrer increased to 503 Barrer,and the selectivity of CH₄/N₂ remained at about 3.0.As the test temperature up to55?,CH₄ permeability could be further increased to 893.4 Barrer.Meanwhile,for CH₄/N₂?50/50 vol%?mixed gas test,the CH₄ permeability of SIS-c-PDMS-co-PMHS-70 was 447.4 Barrer,and the N₂ permeability was188.1 Barrer,1748%and 1888%higher than that of pure SIS membrane,respectively.