The Preparation And Application Of Pervaporation Composite Membranes For Aromatics Permeation

The ethylene feedstock upgrading is an effective way to cut the cost of ethylene. Pervaporation is known as a potential technology to reduce the aromatics content of naphtha, which can upgrade the ethylene feedstock.There are two subjects of this work,one is to investigate the feasibility of ethylene feedstock upgrading by pervaporation,the other is to develope high-performance pervaporation composite membranes for ethylene feedstock upgrading.In addition,the pervaporation process of ethylene feedstock upgrading by aromatics reduction of naphtha using the composite membrane is explored.Using the commercial pervaporation membrane,the feasibility of aroamtics reduction of a straight-run naphtha by pervaporation was investigated.The experimental results showed that the permeate fluxes were between 0.08 and 1.07 kg/(m~2·h),and the aromatics enrichment factor between 1.4 and 4.5.The aromatics content of naphtha decreased as an increase in the stage cut.As the permeate pressure and feed temperature were kept at 0.3 Kpa and 95℃respectively,.the aromatics content could be reduced from 7.52%to 4.67%at the stage cut of 20%,benzene with the greatest enrichment factor was almost removed at a low stage cut, which showed that the aromatics reduction of naphtha by pervaporation was feasible.The asymmetric poly(acrylonitrile)(PAN) ultrafiltration membranes were used as the substrate membranes,and Poly(ethylene glycol) methacrylates were used as the monomer to develop the pervaporation composite membranes for aromatics permeation by the UV induced graft-filling polymerization method.Benzphenone(BP) was used as the photoinitiator.The effects of the concentration and type of monomers,UV irradiation time and graft temperature on the structure and performance of the composite membranes were systematically investigated.The results verified that the pervaporation composite membranes for aromatics permeation were successfully prepared by the UV induced graft-filling polymerization.The composite membrane with DG of 1.18 mg/cm~2 was obtained under the condition that the monomer(MePEO300MA) concentration was 0.108 mol/L,UV irradiation time was 45min, and graft temperature was 40℃.For the above composite membrane,using the toluene/heptane mixtures with toluene mass fraction of 20%as feed at 80℃,the separation factor was 5.6,and the permeate flux 2.47 kg/(m~2·h).As for the straight-run naphtha,the aromatics enrichment factor was 3.3,and the permeate flux 0.77 kg/(m~2·h).Compare to the commercial pervaporation membrane,the permeate flux of the membrane prepared herein increased by 88%,well the aromatics enrichment factor decreased by 13%.The aromatics content of naphtha could be reduced efficiently at a low stage cut.The preliminary results showed that the composite membranes developed herein could be the candidate for the production of low-aromatics quality ethylene feedstock.