| Hydrogen purification and CO2 capture are important steps in refineries,ammonia synthesis plants,and coal gasification power plants.The synthesis gas obtained from water gas shift reaction usually contains more than 30 mol%CO2.In a H2 selective membrane separator,the enrichment of CO2 on the resident side reduces the driving force of H2.The dual membrane separator integrates the H2 selective membrane and CO2 selective membrane into a same separator,and simultaneously removes H2 and CO2 from the feed gas.It has the advantages of enhanced separation and multi-component comprehensive recovery.However,the dual membrane separators are difficult to package,and simulation studies usually introduce some assumptions to simplify the calculation,such as ignoring the effect of operating temperature on membrane performance.Simulation studies have shown that the co(H2):counter(CO2)dual membrane separator can significantly improve the separation efficiency of H2/CO2,and experimental verification is still required.Therefore,this paper designed a hollow fiber dual membrane separator in co(H2):counter(CO2)flow pattern.Experimental study was conducted to investigate the effects of various operating conditions and structural parameters of the dual membrane separator under H2/CO2/CH4 ternary gas mixture conditions.In this study,the commercial polyimide(PI)hollow fiber membrane was used as the H2 selective membrane,and the self-made polydimethylsiloxane/polyetherimide(PDMS/PEI)hollow fiber composite membrane was used as the CO2 selective membrane.They were assembled into PI membrane separator,PDMS/PEI membrane separator and PI/PDMS dual membrane separator.The effects of operating conditions on the performance of different membrane materials and the gas separation effect of single membrane separator under the conditions of pure gas and mixed gas were compared.The experimental results showed that compared with pure gas test,the selectivity of H2/CH4 and CO2/CH4 of PI membrane separator was significantly reduced.As the operating temperature increased,the permeation rate of H2 in the PI membrane increased and the recovery of H2 increased;the CO2/H2 selectivity of the PDMS/PEI membrane decreased and the purity of CO2 decreased.In addition,for traditional membrane separators,operating conditions changed,and the trade-off relationship between product purity and recovery was always maintained.In a dual membrane separator,it is important to match the two membrane materials and optimize the operating conditions.The effects of operating conditions such as feed gas flow rate,operating temperature,operating pressure and membrane area ratio on the membrane performance and gas separation effect of the dual membrane separator were investigated.Compared with PI membrane separator,PI/PDMS dual membrane separator could obtain higher purity H2 at higher cutting ratio.The reduction of CO2/H2 selectivity of PDMS/PEI membrane at high temperature had the greatest impact on the gas separation effect of the entire dual membrane separator.In order to obtain high purity H2 and CO2 products,the optimal temperature should be 25℃.In the pressure range of 0.2-0.8 MPa,the purity and recovery of H2 and CO2 could be simultaneously improved.The membrane area ratio is an important structural parameter of the dual membrane separator and can be used to adjust the purity and recovery of the single-sided product.With the increase of R,higher H2 recovery could be achieved,but lower H2 purity.The purity and recovery of CO2 were basically unchanged.Different matching relationship between the gas permeation of PI membrane and PDMS/PEI membrane could be achieved by adjusting R.When R was 0.87,the H2/CO2 selectivity of the PI membrane reached 4.4,which was close to the intrinsic value of the membrane material.The purity of the H2 product was the highest,but the H2 recovery was the lowest.When R was 1.85,the total driving force of H2 and CO2 was the largest,and the dual membrane separator had the best overall separation performance. |
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