149 ISSN 2517-7516, Membranes and Membrane Technologies, 2020, Vol. 2, No. 3, pp. 149–158. © Pleiades Publishing, Ltd., 2020. Russian Text © The Author(s), 2020, published in Membrany i Membrannye Tekhnologii, 2020, Vol. 2, No. 3, pp. 153–164. The Effect of the Nature of a Coagulant on the Nanofiltration Properties of Cellulose Membranes Formed from Solutions in Ionic Media T. S. Anokhina a, *, V. Y. Ignatenko a , A. V. Kostyuk a , S. O. Ilyin a , A. V. Volkov a , and S. V. Antonov a a Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: tsanokhina@ips.ac.ru Received September 13, 2019; revised January 20, 2020; accepted February 10, 2020 Abstract—The effect of the nature of a coagulant on the nanofiltration characteristics of the cellulose mem- branes 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 for- mation 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 par- tially 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-methylmorpholine N-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 nanofil- tration characteristics, namely, P DMF = 0.67 kg m -2 h -1 atm -1 , R OrangeII = 66%, and R Remazol = 78%. Keywords: cellulose, ionic liquids, polymer membranes, coagulant, phase separation, nanofiltration of organic media, aprotic solvents DOI: 10.1134/S2517751620030026 INTRODUCTION Organic solvents have been part of both the house- hold and production spheres for many years. Petro- chemicals, paints and varnishes, pharmaceuticals, tex- tiles, and food industries are just some of the eco- nomic sectors in which they are widely used. There are several classifications which make it possible to divide solvents into groups based on their specific properties. One such classification is based on the acid–base per- ceptions of the Brønsted–Lowry theory and considers organic solvents as protic and aprotic [1]. Aprotic solvents include neutral chemical com- pounds that are almost incapable of either donating or accepting protons due to the fact that aprotic solvent molecules are unionized. This type of solvent includes acetonitrile, dimethylformamide (DMF), dimethy- lacetamide (DMA), dimethylsulfoxide (DMSO), hexamethylphosphotriamide, and others. Such sub- stances do not contain active hydrogen atoms [1, 2]; they dissolve both organic and inorganic chemicals and mainly solvate cations leaving anions relatively free and highly reactive in the case of dissolved ionic compounds [3]. Aprotic solvents are used in the production of ther- mally resistant plastics, synthetic fibers, varnishes, enamels [4], organic solvents [5] and in phase-transfer catalysis [6]. Aprotic solvents are widely used as the extracting agents for coal [7], for the removal of oxi- dized products in the process of desulfurization of fuels [8, 9], and for the selective isolation of arenes from their mixtures with paraffins, naphthenes, and olefins [10]. Distillation is a traditional method for the purifica- tion of aprotic solvents [11]. The process of nanofiltra- tion of organic media is an alternative. The advantage of nanofiltration is that the process occurs at constant temperatures and in the absence of phase transitions, which provides a low power intensity for this technol- ogy. Due to this, the nanofiltration process is more profitable than traditional separation methods in terms of energy efficiency and in terms of effects on the environment [12, 13]. Nanofiltration is widely used in fine chemical and pharmaceutical synthesis, petroleum chemistry, and the food industry [14, 15]. The approaches to the implementation of the nanofiltration process in aprotic solvents generally consist in the use of chemically stable, often cross-