Preparation Of CA/PEI Blending Membrane By Supercritical CO₂ Phase Inversion Method And The Adsorption Of Bilirubin

A new process has been proposed and developed to prepare organic membrane by phase inversion induced by supercritical CO₂ during recent years. Compared to the traditional phase inversion method, the advantages of supercritical CO₂ phase inversion method are as follows: high mass transport coefficient, rapid drying of the membrane without collapse of the structure, less residual organic solvents in the membrane and easy recovery of solvent. The present study of this method is mostly concentrated on the effect of membrane formation conditions on the morphology of membrane. However, the study of the optimization conditions and the application of membrane are seldom reported. In this paper, the cellulose acetate (CA) and CA/polyethyleneimine (PEI) blending membrane were prepared by supercritical CO₂ phase inversion method and the blending membrane was applied into the adsorption of bilirubin.Micro porous CA membranes were prepared by supercritical CO₂ phase inversion method using acetone and dimethylformamide as solvents. The morphology of the membranes was characterized by scanning electron microscope (SEM) and the water flux of membranes was measured as well. The effect of affinity between solvent and CO₂, CA molecular weight and concentration, CO₂ pressure and temperature, holding pressure time and depressurization rate on the performance of the membrane was investigated. The results indicated that acetone was a suitable solvent for the preparation of membrane with homogeneous structure. The membrane with high molecular weight could obtain higher water flux. Moreover, the water flux of the membrane was reduced as the pore size decreased with the CA concentration increasing from 10 wt.% to 20 wt.%. The water flux increased and reached a maximum value, then decreased with the increase of the pressure as well as the temperature. However, holding pressure time and depressurization rate had neglectable influence on the water flux of the membrane. The membrane owned a water flux as high as 30 L/m²Â·min prepared with CA concentration of 10 wt.% at 15 MPa, 45℃, holding pressure time 45 min, and rapid depressurization rate.Based on the preparation of CA membrane, the CA/PEI blending membrane was prepared by adding PEI to the solution in order to introducing amino into CA membrane. The influence of the blending ratio on the morphology, water flux and amino content was investigated. The water flux rapidly decreased and amino content increased with the increase of blending ratio. The prepared CA/PEI membrane was applied into the adsorption of bilirubin. The effect of blending ratio, initial concentration of bilirubin, adsorption temperature and time, ionic strength and pH value on the adsorption bilirubin was studied. The experimental results indicated that adsorption bilirubin capability of membrane increased acompaning with the increase of blending ratio, however, the increase of adsorption bilirubin capability was slow as the blending ratio was over 0.15. The increase of bilirubin initial concentration made the adsorption rate increase. Higher temperature favored to the adsorption of bilirubin, nevertheless, the increase of ionic strength and pH value could inhibit the adsorption of bilirubin to some degree. The maximum adsorption amount of CA/PEI membrane was 36mg/g membrane when the temperature was 37℃, pH was 8.3 and the initial concentration of bilirubin was 100 mg/L. Dynamic adsorption could benefit from a slower velocity to the adsorption of bilirubin.