Study On Transport And Separation Of Aromatic Acids And Phenol By Polymer Inclusion Membrane

Salicylic acid is an important fine chemical raw material,widely applied in many field.But industrial production of salicylic acid can produce a large amount of refractory organic phenolic acid wastewater,which contains phenol and other toxic carcinogens.Therefore,it is necessary to treat salicylic acid industrial by-products and wastewater.Polymer inclusion membrane(PIM)has become a research hotspot of low-concentration substances extraction and separation technology in high matrix background due to its easy operation,good stability and high selectivity in recent years.In this paper,transport and separation behavior of aromatic acids and phenol were studied by PIM,and the internal relationship between PIM membrane composition,membrane structure and membrane transport behavior was investigated to provide theoretical support for PIM application in organic phenolic acid wastewater treatment.The main research contents are as follows:(1)Polymer inclusion membrane(PT-PIM)was prepared with extractant tributyl phosphate(TBP)with low viscosity and high coordination ability as the carrier and polyvinyl chloride(PVC)as the matrix.The chemical composition and crystallization behavior of PT-PIM were studied by ATR-FTIR and XRD.The effects of carrier content,hydrophobic additives and membrane thickness on the mass transfer behavior of PT-PIM were investigated with phenol as the mass transfer substance.The correlation between the membrane structure,thickness,mass transfer performance and mass transfer stability of PT-PIM was systematically explored.The results showed that there existed hydrogen bonding and dipole-dipole interaction between TBP and PVC.With TBP content increase,PVC stacking structure tended to be loose.The permeability performance of PT-PIM had a sudden jump at the carrier content of 44.44%,but the stability of PT-PIM with high content TBP(75%)was insufficient.The introduction of hydrophobic additives kerosene and n-octanol could improve the stability of the membrane,but permeability performance was slightly reduced.The thinner PT-PIM with high content of TBP(75%)produced submerged precipitation phase transformation in the aqueous phase,and large holes appeared in the membrane,which weakened transport stability of PT-PIM.However,thicker PT-PIM(75%)had similar phase separation rates in the internal and surface of the membrane during phase transformation,presenting a sponge structure generated by delayed phase separation behavior,effectively improving transport stability.(2)The mass transfer behavior of salicylic acid,phenol and benzoic acid through PT-PIM with optimized and stable mass transfer performance as the mass transfer medium was investigated.The mass transfer mechanism,mass transfer selectivity and separation performance of PT-PIM on aromatic acids and phenol were preliminarily discussed.The results showed that PT-PIM formed a co-coupled active transport through hydrogen bonding between TBP and phenolic hydroxyl groups and carboxyl groups in a weakly acidic feed phase and alkaline stripping phase.The mass transfer rate curves of PT-PIM on salicylic acid,phenol and benzoic acid were consistent with the first-order kinetic equation.The permeability coefficients of PT-PIM on three aromatic acids and phenol increased with TBP content increase,and there existed percolation thresholds,indicating that there were certain fixed site jumping transport behavior on alicylic acid,phenol and benzoic acid through PT-PIM.Due to the difference of hydrogen bonding complexation and dissociation activation energy between carboxyl,phenolic hydroxyl and TBP,transport of salicylic acid and benzoic acid by PT-PIM was mainly controlled by chemical reaction process,and the competitive complexation of phenolic hydroxyl group and carboxyl group existed in transport salicylic acid in PT-PIM.The selective separation coefficient S of salicylic acid and phenol through PT-PIM in the feed phase pH 6.0 was up to 23.01,and the enrichment factor of salicylic acid of pH 2.0 200 mg·L~-11 in 96 h reached 3.22.The potential application performance of PT-PIM in the separation and recovery of salicylic acid was initially confirmed.(3)Polymer inclusion membrane(PN-PIM)was prepared with PVC as the matrix and highly hydrophobic N,N-bis(1-methylheptyl)acetamide(N503)as the carrier.The chemical composition,surface microstructure and crystallization behavior of PN-PIM were analyzed by means of ATR-FTIR,SEM and XRD.The transport behavior of PN-PIM on salicylic acid was investigated.The selective separation behavior of PN-PIM on salicylic acid,phenol and benzoic acid were discussed.The results showed that there was hydrogen bonding between PVC and N503.When the N503 content was more than 50%,microporous structure of about 1?m appeared in PN-PIM.The carbonyl group of N503 in PN-PIM was complexed with the phenolic hydroxyl group and carboxyl group of salicylic acid by hydrogen bonding,and the active transport salicylic acid was achieved by co-coupled.The mass transfer rate curve accorded with the first-order kinetic equation,and transport of PN-PIM on salicylic acid was mainly controlled by the intramembrane diffusion process.PN-PIM had a percolation threshold(50.0%)for transport salicylic acid,but both intramembrane diffusion and fixed site hopping existed simultaneously in transport process.The PN-PIM system had good stability.At pH 6.0,the selective separation coefficient of PN-PIM on salicylic acid and phenol was 7.54,but there was no transport selectivity on salicylic acid and benzoic acid.