Petroleum Chemistry (v.58, #9)

Expansion of the Product Range of Spiral Wound Elements for Sea and Brackish Water Desalination by V. G. Dzyubenko; P. A. Vdovin; A. R. Sidorov; I. I. Shishova (733-739).
Results of modification of composite membranes intended for desalination of sea and surface water are presented. It has been shown that modifying the selective layer of the sea water desalination membranes can stabilize the membrane rejection in the case of an increase in the feed water temperature to 40°C. The modification of the membrane for surface water desalination makes it possible to increase silicon rejection to a level of 99.78% at 35°C. The new line of membrane elements with a modified composite membrane by RM Nanotekh is intended for application at desalination plants in hot regions (up to 40°C) in the first place, as well as in water treatment units at thermal power plants and regional power stations operating at a high temperature of feed water (up to 35°).
Keywords: polymers; membranes; modification; polyamide; polyethersulfone; carbodiimide; demineralization; desalination

Gas Permeation and Hemocompatibility of Novel Perfluorinated Polymers for Blood Oxygenation by A. Yu. Alentiev; N. A. Belov; R. Yu. Nikiforov; E. V. Polunin; N. V. Borovkova; A. K. Evseev; M. S. Makarov; I. V. Goroncharovskaya; M. V Storozheva; V. S. Zhuravel (740-746).
Gas permeation properties of three highly permeable perfluorinated polymers (polyhexafluoropropylene (PHFP), amorphous Teflon AF2400, and polyperfluoro(2-methyl-2-ethyl-dioxole-1,3) (PPFMED)), which are promising materials for the dense thin layer of hollow fiber membranes for extracorporeal membrane oxygenation have been studied using nitrogen, oxygen, and carbon dioxide. Hemocompatibility of the polymeric films has also been investigated on whole blood from healthy donors. Gas permeation of the polymers increases in the order PHFP < PPFMEDD < AF2400, with PHFP alone having the permeability coefficients of the gases do not below those of polydimethylsiloxane applied as the selective layer of blood oxygenation membranes. Hemocompatibility of the polymers declines in the order PHFP > PPFMED > AF2400, with the most permeable polymer AF2400 exhibiting the worst hemocompatibility among the other polymers studied. Polyperfluoro(2-methyl-2-ethyl-dioxole-1,3) is shown to be the most appropriate polymer to fabricate hollow fiber membranes for blood oxygenation.
Keywords: perfluoropolymers; gas permeability; hemocompatibility; extracorporeal membrane oxygenation

Preparation of High-Flux Ultrafiltration Polyphenylsulfone Membranes by A. V. Bildyukevich; T. V. Plisko; Y. A. Isaichykova; A. A. Ovcharova (747-759).
Phase diagrams of the polyphenylsulfone (PPSU)polyethylene glycol (PEG)N-methyl-2-pyrrolidone (NMP) system have been plotted as a function of PEG molecular weight. For 15 wt % PPSU solutions containing 15 wt % of PEG with molecular weight of 600040 000 g mol–1, the occurrence of an upper critical solution temperature (UCST, solutiongel transfer (gel point)) and a lower critical solution temperature (LCST) was found. According to the phase diagrams analysis, a method for the preparation of high flux PPSU membranes using the systems with UCST and LCST in an experimentally attainable temperature range has been proposed. The method involves casting solution processing at a temperature of the existence of a one-phase homogeneous solution (UCST < T < LCST), and the use of a coagulation bath at a temperature between UCST (gel point) and LCST. Membranes prepared from 15 wt % PPSU solutions with the addition of PEG-20000 were found to have the highest pure water flux (500–1000 L m–2 h–1 at 0.1 MPa), and a human serum albumin rejection of ca. 90%.
Keywords: polyphenylsulfone; polyethylene glycol; phase diagram; lower critical solution temperature; upper critical solution temperature; ultrafiltration; membrane; hydrophilization

New data have been obtained on the influence of the conditions of modification of Matrimid 5218 asymmetric hollow fibers by direct gas-phase fluorination directly in laboratory membrane modules on their gas separation properties. It has been shown that direct gas-phase fluorination significantly increases the selectivity of gas separation, in particular, for the He/CH4 pair. Stability of the fluorination effect has been studied for a long time (up to 10 years). It is noted that over the first days after modification, the modules modified using an He/F2 mixture with a high F2 content (10 vol %) exhibit the greatest ideal He/CH4 selectivity (~8000). However, a high degree of fluorination leads to the degradation of hollow fiber membranes in the module with time, whereas fluorination with a mixture with a low F2 content (2 vol %) also results in a high He/CH4 selectivity of the modified membranes (~800), which increases to 4600 with time, the thin selective layer remaining undamaged. The mathematical modeling of the single-stage process of helium recovery from natural gas using modified hollow fiber membranes on the basis of Matrimid 5218 shows a high potential for their practical application in this field.
Keywords: gas separation; hollow fiber membranes; Matrimid 5218; modification of membranes; gas-phase fluorination; helium recovery

Proton-conducting materials based on the MF-4SK membrane and polyantimonic acid have been synthesized; their dielectric properties and conductivity at varying temperature and relative air humidity have been studied. The introduction of polyantimonic acid particles leads to a significant increase in the proton conductivity of the membranes—from 3.2 × 10–5 to 2.5 × 10–4 S/cm—at low humidity. Studies of the proton conductivity as a function of temperature have shown that the doping of the MF-4SK membrane with polyantimonic acid leads to a decrease in the activation energy from 16.8 to 12.9 kJ/mol.
Keywords: hybrid membranes; antimony oxides; polyantimonic acid; proton conductivity

Based on Onsager’s approach to nonequilibrium isothermal processes, the problem of correctness of the existing experimental determination of the integral coefficient of diffusion permeability of an ion-exchange membrane has been addressed. To this end, the well-known “fine porous membrane” model, experimental data on the diffusion of sodium chloride through the cation-exchange membrane of MK-40 into a more dilute solution, and measured differences of the spontaneous electric potential on the membrane have been used. It has been shown that the true values of the integral coefficient are larger than those found experimentally according to the conventional procedure.
Keywords: diffusion permeability; ion-exchange membrane; Nernst–Planck equations; Onsager approach

A series of anion-exchange membranes based on a Neosepta AMX-Sb homogeneous membrane (Japan) have been studied by applying parallel nonconducting strips of a 100 to 600 μm width with the interstrip distance ranging from 400 to 1900 μm. The current–voltage characteristics of the membranes and the pH of a NaCl solution (of 0.02 mol/L concentration) have been measured in the course of passing the solution through the desalination compartment of a flow-through electrodialysis cell. Two sets of membranes with a nonconducting surface fraction s nc of 5 to 60%, in which the pattern steps on the surface are 1000 and 2000 μm, have been considered. It has been shown that the limiting current density, i lim, depends on the nonconducting surface fraction: i lim exceeds the corresponding value for the initial membrane in the case when s nc is in the range from 5 to 20%, reaching a maximum approximately at s nc = 10% followed by a decrease with the further increase in s nc. At s nc = 10%, the value of i lim is greater when the inhomogeneity step is 2000 μm. It has been assumed that the growth in both the limiting current density and the rate of mass transfer through the modified membranes is due to electroconvection. The obtained experimental results correlate well with known mathematical models describing ion transport in membrane systems with allowance for electroconvection in the case of homogeneous and heterogeneous membranes.
Keywords: electrodialysis; ion-exchange membrane; heterogeneous surface; current–voltage characteristic

Composite membranes with a thin selective layer based on poly[1-trimethylsilyl-1-propyne] (PTMSP) and crosslinked PTMSP containing 10 wt % of nanoparticles of porous aromatic frameworks (PAF-11) have been synthesized and studied. Monitoring of changes in the gas transport characteristics of the membranes under ambient conditions for 7500 h has revealed that for all the samples, the transport characteristics abruptly decrease within the first 1000–2000 h; after that, the mass transfer constants gradually change over time. In the case of a composite membrane with the selective layer based on crosslinked PTMSP and PAF-11 nanoparticles, stable permeability values after 7000 h are 2.1, 3.5, and 12.9 m3/(m2 h atm) for N2, O2, and CO2,respectively (at an ideal selectivity of α(O2/N2) = 1.6 and α(CO2/N2) = 6.1); to date, this is the best published result for thin-film composite membranes based on highly permeable glassy polymers.
Keywords: PTMSP; PAF-11; physical aging; thin-film composite membranes; gas separation

The feasibility margin of baromembrane separation systems has been determined at fixed flux, total membrane area, and stream compositions. Irreversible energy expenditures, which depend on process characteristics (parameters of mass transfer kinetics, productivity, membrane area distribution along the device length, etc.), have been evaluated. The boundary of the feasibility region in the “productivity–energy expenditure” plane for membrane systems has been found. It has been shown that systems in which energy expenditures are below the specified limit for a given productivity are unrealizable. Batch and continuous processes have been considered. Relations governing the pressure change at a minimum energy expenditure have been specified for media close to ideal gases and ideal solutions. The results obtained make it possible to determine the direction of variation in the system parameters (pressure, hydrodynamics, etc.) that ensures minimized energy consumption.
Keywords: membrane separation; feasibility margin; optimal control; minimal energy expenditure

Modeling of Fast-Permeant Component Removal from Gas Mixture in a Membrane Module with Pulsed Retentate by S. V. Battalov; T. S. Sazanova; M. M. Trubyanov; E. S. Puzanov; V. M. Vorotyntsev; P. N. Drozdov; I. V. Vorotyntsev (806-814).
The process of unsteady-state membrane gas separation (fast-permeant impurity removal) with a pulsed retentate flow operation was considered. A semiempirical mathematical algorithm was developed to describe this process taking into account its kinetic characteristics (total cycle time, stripping time and withdrawal time, withdrawal velocity) using the MathCad® software package. Based on the developed algorithm, the basic operational parameters that affect the separation efficiency of the unsteady-state process were analyzed. It was shown that the optimal ratio of the stripping time and the withdrawal one determined by the maximum efficiency criterion more corresponds to the minimum retentate concentration than to the maximum productivity. However, the developed algorithm allows to set the productivity minimum limit by introducing additional initial data into the calculation procedure. The mathematical modeling results correlate well with the experimental data.
Keywords: unsteady-state membrane gas separation; membrane module; mathematical modeling; high purification; closed mode; pulsed retentate flow operation; separation kinetic