The Effect of the Nature of a Coagulant on the Nanofiltration Properties of Cellulose Membranes Formed from Solutions in Ionic Media

The effect of the nature of a coagulant on the nanofiltration characteristics of the cellulose membranes obtained from solutions in 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) or a mixture of this ionic liquid with dimethylsulfoxide (DMSO) is studied in this work. Precipitation in water leads to the formation of the densest cellulose membrane characterized by the low permeability of dimethylformamide (P-DMF= 0.25 kg m(-2)h(-1)atm(-1)) and high rejection coefficients of the model substances, Orange II (350 g/mol) and Remazol Brilliant Blue R (626 g/mol), of 65 and 82%, respectively. To reduce the rate of precipitation of cellulose for the purpose of decreasing the density of the membranes, various compounds that partially mimic the medium of the solvent are introduced to water to obtain their 30% solutions: acetic acid to increase the concentration of acetate anions,N-methylmorpholineN-oxide to increase the concentration of ammonium fragments, and DMSO. In all the cases, the modification of the coagulant leads to a 2-2.5-fold increase in the permeability of the membranes without sacrificing the high values of the rejection coefficients. A cellulose membrane obtained by precipitation in a 30% aqueous solution of acetic acid demonstrates the best nanofiltration characteristics, namely,P-DMF= 0.67 kg m(-2)h(-1)atm(-1),R-OrangeII= 66%, andR(Remazol)= 78%.