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A three-stage process for the production of motor fuel (MT) components from lignocellulosic raw materials is described. In the first, pretreatment stage, lignocellulose is subjected to hydrolysis with cellulases followed by fermentation of the resulting sugars into ethanol; then, dilute ethanol solutions are concentrated by membrane vapor separation to obtain 70–80% solutions. At the third stage, aqueous ethanol solutions (water content 0–50%) in the presence of a Pd–Zn/Al2O3/MFI catalyst at 350°C and a space velocity of 0.6 h−1 are converted into alkanes, and С3–С8 olefins and С6–C12 aromatic compounds (MT components). It has been found that water in an amount of up to 30% in ethanol solutions effectively inhibits the detrimental hydrocarbon cracking and catalyst coking processes, thereby leading to a decrease in the formation of undesirable C1 and C2 products and an increase in the catalyst on-stream time to 100 h wherein the yield of the desired fraction is reduced only by 10–15%. The subsequent treatment of the catalyst surface with steam and hydrogen completely restores its catalytic activity.

The paper presents the characteristics of a laboratory-made water-selective composite membrane with a selective layer of hydrophobic polyvinyltrimethylsilane (PVTMS) for use in the processes of vapor-phase membrane recovery of alcohols from dilute aqueous alcohol mixtures of biogenic origin. The support is a polyacrylonitrile ultrafiltration membrane, and the PVTMS skin layer of the resulting composite membrane has a thickness of 3 to 4 microns. The vapor transport and separation characteristics of the membrane for water–ethanol and water–butanol mixtures in the temperature range of 60–80°C have been studied. It has been shown that the membrane selectivity varies in the range of 23–39 for the water/ethanol pair or 100–140 for the water/butanol pair. A specific feature of the hydrophobic water-selective membrane as applied to the vapor-phase process is the stability of its characteristics due to the absence of swelling, in contrast to hydrophilic water-selective membranes whose characteristics substantially depend on the activity of water vapor. The process of vapor-phase membrane recovery of ethanol and butanol from dilute aqueous alcohol mixtures of biogenic origin with their initial concentrations of 10 and 1 wt %, respectively, has been mathematically modeled on the basis of the experimental data. The calculation results show that the composite membrane obtained makes it possible to concentrate ethanol and butanol to 95 and 98 wt % with degrees of recovery of more than 0.8 and more than 0.9, respectively.

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.

The use of lignocellulosic biomass is one of the promising technologies for the production of energy carriers (bioalcohols, biosyngas) and valuable chemicals. Lignocellulosic biofuels may be thought of as a material capable of substantially replacing oil to provide an efficient consumption of natural energy resources and an improvement of the environment. In the “bioreactor–membrane separator–catalytic reactor (converter)" circuit, all stages are considered to be key: (1) the pretreatment of lignocellulose and the development of fermentation, particularly the cultivation of novel strains of bacteria; (2) the design of energyefficient vapor/gas-phase membrane systems for (a) concentrating bioalcohols and (b) controlling the biosyngas composition; and (3) the development of catalyst systems for the conversion of bioalcohols to motor fuel components. The following sequential tasks are discussed in this brief review: (i) basic approaches to the pretreatment of lignocellulosic biomass aimed at preparing it for fermentation and enzymatic processing of lignocellulose, particularly the cultivation of novel strains of bacteria and their communities, to produce bioalcohols— ethanol and butanol—and thermochemical methods of lignocellulose conversion to products in the form of complex mixtures; (ii) the development of energy-efficient membrane concentrating of bioalcohols using hydrophilic and/or organophilic polymer membranes and the control of the composition of synthesis gas in the form of a multicomponent gas mixture using commercial gas-separation membranes; and (iii) the development of catalyst systems exhibiting high selectivity in the ethanol conversion to alkane and aromatic hydrocarbons (high-quality additives to motor fuels) and valuable olefins, particularly ethylene, propylene, and linear alpha-olefins up to C10.

Pervaporation and vapor-phase membrane separation methods for the recovery of bioalcohols from dilute aqueous solutions have been critically compared. The importance of taking into account the liquid–vapor equilibrium diagram in studies on the separation of binary aqueous–alcoholic liquid media by these methods has been shown. Previously published experimental data on the transport of water, ethanol, and n-butanol vapors in hydrophobic membranes based on the glassy polymers poly(vinyltrimethylsilane) (PVTMS), poly(1-trimethylsilyl-1-propyne) (PTMSP), and poly(4-methyl-1-pentyne) (PMP) have been analyzed. Schemes of butanol and ethanol recovery by the vapor-phase membrane separation process from fermentation broths for the cases of application of water-selective and alcohol-selective membranes have been presented, as well as the results of mathematical simulation of the process and assessment of energy consumption.

Gas separation properties of polymer films based on semicrystalline poly(4-methyl-1-pentene) (PMP) with T g = 30°C for permanent gases and some lower hydrocarbons have been experimentally studied in the temperature range of −20 to 80°C. Experiments have been performed using the differential permeability technique involving the determination of the diffusion coefficient by the characteristic time and functional scaling-up methods. It has been shown that PMP as a biphasic system may be characterized by one diffusion coefficient that includes the contributions of diffusion in the amorphous and crystalline phases. It has also been shown that despite the glass transition (phase transition) at 30°C, the permeability coefficients of the test gases exponentially increase with gas temperature and the temperature dependence curves do not exhibit an inflection in the glass transition region. On the other hand, the Arrhenius plots of the diffusion coefficients show a bend over the entire glass transition range in PMP, with the activation energy of diffusion decreasing with an increase in temperature. This fact demonstrates the unusual, earlier unknown effect of increasing activation energy of diffusion E D for gases below T g.

The presented nonisothermal technique for investigation of membrane gas separation (using MDK-1 membrane as an example) demonstrates possibilities of rapid assessment of the separation power of commercial membranes for both individual components and various mixtures in the temperature range of‒20 to +40°C. The efficiency of the membrane process under these conditions (cross-flow membrane module model) for separation of propane–methane mixtures has been evaluated. It has been shown that the permeability of methane decreases with a decrease in temperature in the Arrhenius coordinates and the propane permeability increases. The separation selectivity in the mixture decreases by more than twofold in comparison with the ideal selectivity. Nevertheless, a significant improvement of separation has been observed at lower temperatures, with the recovery of the desired product and its purity being variable in a wide range depending on the practical goal. The nonisothermal technique is supposed to be useful for rapid selection of conditions (temperature, pressure, components to be separated) for efficient application of polymeric membranes for separation of hydrocarbon-containing mixtures that are close in composition to real gas sources.

The influence of irradiation and the subsequent etching of latent tracks in poly(4-methylpentene-1) (PMP) films on the transport parameters of the resulting membranes has been studied. The films have been irradiated with accelerated Kr and Xe ions of 4.5 and 1.2 MeV/nucleon in energy at a fluence of 106–109 cm−2. It has been found that the irradiation followed by etching makes it possible to obtain an anisotropic membrane with a nonporous selective layer between two porous layers with tapered pores. The CH4, CO2, and He transport characteristics of the membranes have been examined. It has been shown that these modification methods can significantly increase the gas flux through the membrane. It is believed that the ion track etching procedure as applied to PMP can form the basis for fabricating membranes with a highly permeable, nonporous, gas-selective layer.

Peculiarities of the preparation of selective nanoporous metal oxide coatings on the surface of macroporous rutile support (pore size 0.1 μm and mixed aluminum and titanium oxides (pore size 0.05 μm) are presented. Gas selective coatings of empirical formula of P x Ti1 − 0.5x O2 ± δ with uniform distribution of nanosized pores have been obtained with the alkoxide method using titanium alkoxide and ettriol phosphite (precursor of the phosphorous-containing component) at their various total concentrations. Surface morphology of the obtained membranes has been investigated and major parameters of gas selective coatings have been determined. It has been shown that the dependences of the He, N2, CO2, and C3H8 gas permeability on temperature and pressure drop are consistent with the molecular regime of gas flow. The reproducible effect of permeability anisotropy of ∼502?60% is observed when the integral vacuum method is used.

The results of a study of C1-C4 alkane gas permeability and C5-C6 alkane and methanol vapor permeability through pressed foil based on exfoliated graphite with a density of 1 g/cm3 are presented. It has been found that the permeability of the studied graphite foil to C4-C6 hydrocarbons is higher than calculated values; in particular, reverse selectivity for pairs such as H2/hydrocarbon and N2/hydrocarbon is observed. This can be due to a considerable effect of a surface flow on the total flow through the membrane.

Methods of estimation of molecular-selective gas transport parameters in polymeric membranes and explanation of separation selectivity evolution for ‘small’ and ‘large’ molecules up to inversed selectivity are proposed based on comparative analysis of diffusion and solubility of noble gases as isotropic diffusion probes in different classes of polymers and block copolymers on their basis. Two approaches are considered in this work: (1) analysis of diffusional migration of permanent gases, lower hydrocarbons, and alcohols (vapor) in glassy polymers and rubbers relative to the diffusion of noble gases including radon; (2) adaptation of the ‘hard sphere’ theory developed for gas solubility in liquids to the calculation of the solubility of gases in the polymer matrix. In the latter case, noble gases as isotropic probes are used for calculating the required fitting parameters of the polymer medium.

Membrane-absorption method for biogas separation that combines advantages of both absorption and membrane separation methods is presented in this study. Gas-liquid membrane contactors (MCs) with a nonporous highly permeable membrane as a key element constitute the basis of the proposed separation system. Mathematical modeling of the separation system has been conducted, optimal values of the operational parameters have been found, and a pilot scale membrane-absorption separation unit was designed and constructed.