Alexey Yushkin

Cellulose composite membranes for nanofiltration of aprotic solvents

Cellulose composite membranes have been fabricated by casting a cellulose solution in N-methylmorpholine oxide on a nonwoven polyester support. The membranes have been tested for nanofiltration of aprotic solvents. The solvent permeability has changed from 0.11 ± 0.02 to 2.5 ± 0.4 kg/(m2 h bar) in the following order: DMSO > NMP > DMFA > THF > acetone, which can be attributed to a decrease in viscosity of the fluids. The rejection of the anionic dyes Orange II (MW 350) and Remazol Brilliant Blue R (MW 626) has been found to range within 15–85% and 42–94%, respectively, on the solvent nature. Sorption experiments have revealed a noticeable difference between certain solvents in interaction with the membrane material: a lower degree of cellulose swelling in THF (37%) and a higher degree in DMSO (230%). In addition, it has been found that the rejection of solutes by the composite membranes correlates with the degree of cellulose swelling. A rejection of ≥90% has been achieved for Remazol Brilliant Blue R, which has the larger molecule, at a cellulose swelling ratio of 100% or higher. Thus, it has been concluded that polymer swelling leads to narrowing the porous structure of the cellulose layer of the composite membrane and, hence, improvement in separation parameters.

Application of Cellophane Films as Nanofiltration Membranes

The prospects for use of commercially produced cellophane as a membrane material for organic solvent nanofiltration have been studied. The effect of cellophane film conditioning with aqueous ethanol mixtures with a gradually varying concentration (from ethanol to water and from water to ethanol) has been examined. It has been shown that such treatment increases the ethanol permeability by more than two orders of magnitude in comparison with the untreated sample. The obtained value of the ethanol permeability coefficient for the treated cellophane is comparable with that for highly permeable glassy polymers. The study of cellophane swelling in aqueous ethanol solutions has revealed that the formation of porous structure takes place during the cellophane treatment process as a result of an increase of the interchain distances in the film. The observed high permeability of ethanol is associated with the fact that the porous structure formed is preserved when water is replaced by ethanol. The main factors affecting the membrane flux are the viscosity of the liquid and degree of cellophane swelling in this liquid. It has been also shown that the rejection coefficients of some dyes with molecular mass in the range of 350 to 626 Da from ethanol agree well with the hydrophobicity/hydrophilicity of the solutes. The rejection coefficients of anionic dyes in the case of water are significantly higher than in ethanol (R(EtOH) = 55% → R(H2O) = 97% for Orange II and

Modification of polyacrylonitrile membranes by incoherent IR radiation

R_{EtOH} = 79\% \to R_{H_2 O} = 100\%

Effect of IR Radiation on the Properties of Polyacrylonitrile and Membranes on Its Basis

for Remazol Brilliant Blue R) despite the higher swelling degree of cellophane in water. This behavior is explained by the increase of the solvation shell of the solute molecules and narrowing of the transport channels, in good agreement with the assumption of the sieving mechanism of separation by nanofiltration.

Nanofiltration properties of PTMSP in binary organic solvents mixtures

The nanofiltration of the water-ethanol mixture of different compositions at three pressure drops through a nanoporous membrane based on poly(1-trimethylsilyl-1-propyne) has been experimentally and theoretically studied. A mathematical model of the onset of flow has been proposed, and the percolation threshold depending on the physicochemical and geometrical characteristics of the membrane system has been found. The model suggests gradual membrane pore opening with an increase in pressure and alcohol concentration in the mixture and can take account of the distribution of alcohol molecules over the cross section of the membrane pores. The theoretical results agree well with the experimental data.

Effect of temperature on the transport of solvents through PTMSP under ultra-high pressures

Polyacrylonitrile (PAN) membranes with the rejection coefficients of bovine serum albumin (Mw = 69000 Da) up to 97% have been developed. The effect of IR irradiation of PAN membranes at temperatures to 180°С has been studied for the first time. It has been found that the IR modification of the membranes at 120°С for 5 min makes PAN insoluble in a wide range of organic solvents. The test PAN membranes were obtained from PAN solutions in dimethyl sulfoxide (DMSO) with different polymer concentrations in casting solution. The morphology and filtration characteristics of the membranes are almost unaffected by the treatment. The permeability of the membranes to DMSO, dimethylformamide (DMF), dimethylacetamide (DMAA), and N-methyl-2-pyrrolidone (NMP) has been measured. It has been demonstrated that the IR-treated PAN membranes can be used for filtering the above solvents, although the initial polymer is soluble in these solvents. These membranes can also be used as supports of chemically resistant nanofiltration membranes for aprotic solvents.

Study of glassy polymers fractional accessible volume (FAV) by extended method of hydrostatic weighing: Effect of porous structure on liquid transport,

Copolymers of 1-trimethylsilyl-1-propyne (TMSP) with 1-(3,3,3-trifluoropropyldimethylsilyl)1-propyne (TFPS) as part of a systematic series with the TFPS content of the final polymer in the range of 0 to 46 mol % have been synthesized. The resulting samples have been characterized by different instrumental methods including NMR, IR, and DSC techniques. It has been shown that the accessible free volume of the polymer decreases from 30.4 to 19.1% with an increase in the proportion of TFPS units. Moreover, the gas transport properties of the membrane materials are reduced by factors of 30 (oxygen), 50 (nitrogen), and 15 (carbon dioxide), although the selectivity for the O2/N2 and CO2/N2 gas pairs increases from 1.6 to 2.5 and 2.5 to 11.5, respectively. A study of nanofiltration of organic media has shown that the ethanol permeability through the TFPS-co-TMSP copolymer material is reduced by no more than 30%, a value that is comparable with the relative decrease in the fractional free volume of the polymer. An increase in the TFPS content has improved the stability of the membrane material in ethanol (swelling ratio decreased from 61 to 39%), thereby resulting in an increase in the retention of the Orange II anionic dye (350 g/mol) from 89 to 94%.

Application of negative retention in organic solvent nanofiltration for solutes fractionation

The effect of processing of polyacrylonitrile membranes by IR radiation at a temperature of 100–150°С is studied. The influence of the processing temperature on the film structure is ascertained. In a film heated at 100°С, a small amount of the double C=N bonds is found. Its further heating to 120°С is accompanied by a change in the chain conformation and an increase in the content of C=N bonds. It is shown that, upon IR processing at 120°С, polyacrylonitrile ceases to dissolve in N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethyl sulfoxide. Heating at 150°С gives rise to the appearance of conjugated С=N–C=N bonds. The analysis of AFM micrographs demonstrates that the processing of the membranes by IR radiation makes their surface rougher, while the size of pores changes slightly. The permeability of the membranes in various media is measured.