M. G. Shalygin

Membrane contactors for biogas conditioning

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.

Membrane systems for the recovery of energy carriers from products of organic waste recycling

One of the most promising technologies for separating energy carriers from renewable feedstocks is the biological recycling of organic waste to derive gas (biogas, biohydrogen) or liquid mixtures that contain methane and hydrogen or lower alcohols, respectively. This technology has many advantages: low power consumption, high ecological safety, high level of organic waste recycling, affordability, and ease of implementation and control. The main practical problem of the microbiologic recycling of biomass is the low calorific value of resulting gas and liquid mixtures for their use as energy carriers, because products of bioconversion are diluted aqueous organic mixtures and/or gas mixtures containing a significant amount of ballast CO2. In the capacity of promising systems for separating energy carriers from gas mixtures, we discuss conventional membrane systems and propose original gas-liquid membrane contactors (MCs), which do not require the precompression (additional energy consumption) of the initial gas mixture. After the stage of separation, for example, of biogas, resulting commercial-purity methane (>95%) can be injected into the pipeline network or supplied to a receiver. Our low energy consumption membrane system was designed on the basis of developments of the Topchiev Institute of Petrochemical Synthesis of the Russian Academy of Sciences in cooperation with microbiologists and experts in bioengineering. MCs were prepared of nonporous highly permeable asymmetric membranes based on polyvinyltrimethylsilane (PVTMS) with a CO2 permeance of more than 15 l/(m2 h kPa), which completely meets the requirements on a highly permeable and, at the same time, sterile barrier. Composite membranes based on a glassy polymer with high internal free volume, i.e., polytrimethylsilylpropyne (PTMSP), which are now being produced on a laboratory scale, are regarded as promising for MCs. The use of membrane methods, i.e., pervaporation and membrane separation of the organic component of the vapor phase, is also promising for separating liquid energy carriers (bioalcohols) from dilute aqueous organic solutions (the range of concentrations of organic substances is 1–7%) that are derived by biofermentation. It is shown that organophilic membranes based on PTMSP can be advantageously employed for the continuous extraction of liquid energy carriers from products of biomass conversion.

Integrated systems involving membrane vapor permeation and applications

Membrane methods of vapor mixture separation proposed in the 1990s are now practically considered as reagent- or adsorbent-free technologies possessing higher energy efficiency in comparison with traditional ones. Many practical problems demand the separation (recovery) of organic vapors from different gas streams. Polymeric membranes with organic-selective properties can solve this task. Water-selective membranes can provide recovery of water vapor from the water–organic vapor phase. Moreover, membrane vapor permeation (MVP) is suitable for recovery of bioalcohols (bioorganics) from fermentation media. In many cases MVP efficiency is improved by a positive deviation of vapor–liquid equilibrium (VLE) from Raoults law. The modern approach to vapor separation involves consideration of integrated membrane systems. Actually, the type (or operation scheme) of integrated system depends on the properties of the membrane involved in the separation process. Membrane materials such as high permeable hydrophobic glassy polymers with organic/water selectivity >1, medium permeable hydrophobic glassy polymers with organic/water selectivity <1, and hydrophilic membranes with water/organic selectivity ≫1 and integrated schemes with MVP modules are considered as key parts of the integration needed. Membranes based on high permeable disubstituted polyacetylenes and other polymers, for application in recovery of bioalcohols from diluted water–organic solutions, are considered as the key components of integrated systems involving membrane vapor separation.

Fluorinated Hollow Fiber Membranes Based on Matrimid 5218 and Their Application in the Process of Helium Recovery from Natural Gas

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.

Foundations of a technology for the microbiological conversion of organic cellulose-containing wastes into electrical energy through the intermediate formation of biohydrogen

The screening of microorganisms that are able to degrade cellulose-containing wastes and release hydrogen release was performed. The foundations of a technology for the removal and utilization of hydrogen were established. Classic microbiological techniques were used in the screening. The technology of polymer nonporous membranes was used to remove the hydrogen from the culture liquid. The obtained hydrogen was constantly oxidized with the formation of electricity, using the innovative technology of a fermentation electrode based on hydrogenase. In the course of our work, several highly productive biocenoses of microorganisms were selected; the possibility of raising the microbiological conversion of cellulose-containing wastes into electrical energy from 20 mM(H2)/(l h) to 68 mM(H2)/(l h) through the formation of hydrogen and the application of membrane technology was shown; and the possibility of using the fermentation fuel electrode for the oxidation of hydrogen was demonstrated. The maximum capacity was increased to 250 μW/sm2. It was shown that both technologies can be used to produce electrical energy and absolutely pure hydrogen.