Volume 57, Nº 9 (2017)

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.

The separations of the CO₂/N₂ and CO₂/CH₄ gas pairs using supported ionic liquid membranes (SILMs) with the immobilized ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF₄]) and 1-butyl-3-methylimidazolium bis(2-ethylhexyl)sulfosuccinate (bmim[doc]) have been compared. The temperature dependences of the gas permeability, diffusion, and solubility coefficients have been obtained experimentally, and the temperature dependence of selectivity has been calculated. It has been found that the selectivity of membranes based on bmim[BF4] slightly decreases with temperature and the separation selectivity of CO₂/N₂ and CO₂/CH₄ systems on the membranes impregnated with bmim[doc] is almost independent of temperature.

The influence of pore geometry of polyethylene terephthalate track-etched membranes on the structural, conducting, and magnetic characteristics of cobalt nanotubes (NTs) synthesized by electrochemical deposition has been studied. It has been found that there are significant differences in average size of crystallites and texture coefficients between various forms of cobalt nanotubes. Thus, the α-Co hexagonal closepacked phase dominates in Co-NT samples with cylindrical and hourglass pore shapes and the β-Co facecentered cubic phase prevails in conical Co nanotubes. Measurements of the magnetic properties have shown that the coercivity of cylindrical Co nanotubes is almost two times that of the conical forms because of crystal anisotropy of nanotube-forming cobalt crystallites.

A flow-through catalytic membrane reactor has been experimentally compared with a conventional fixed bed catalytic reactor by matching the specific rate constants in the reaction of dry reforming of methane. Crushed membrane and powdered catalysts with tungsten carbide as the active ingredient have been used as a reference in the conventional reactor. An increase in the reaction rate in the membrane reactor has been explained in terms of emerging Knudsen transport and also by the features of the membrane catalyst, which make it possible to force transport in the pore space of the catalytically active substance. It has been assumed that the “rarefaction” of the gases in the catalyst pores can be accompanied by a change in the equilibrium and a shift in the process toward the products of the direct reaction.