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

Abstract

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.