• Energy Research

Abstract Membrane contactors offer a promising alternative to conventional CO2 absorption processes using columns. In a membrane contactor the advantages of absorption technology and membrane technology are combined as direct contact of the solution and gas feed stream is avoided by membrane barrier. In this study, the possibility of employing the enzyme carbonic anhydrase (CA) for the acceleration of CO2 reaction in MDEA and MEA solution in combination with the use of a membrane contactor was investigated in a lab scale module. The membranes employed in this study were microporous and specifically chosen to have both hydrophobic (bulk) and hydrophilic (surface) properties in order to avoid wetting of solution and reduce fouling by the enzymes simultaneously. By adding the enzyme carbonic anhydrase (CA), a significant improvement of CO2 absorption rate was observed in MDEA solution while a negative effect was observed in MEA solution. Meanwhile the porous hydrophobic membranes were coated with a highly selective poly(ionic liquids) layer increasing the affinity of CO2 towards the interfacial area and hence also the driving force. The concept may initially appear counter intuitive, as the dense membrane layer introduces an added resistance, however the active membrane material gave promising results and was observed to accelerate CO2 transport in MDEA solution. The combination of both enzyme and PILs resulted in synergies, which significantly improved CO2 absorption in MDEA solution.

The specific energy of carbon–ionic liquid supercapacitors comparable to NiMH batteries has been achieved by a combined modeling and experimental approach.

The majority of commercial membrane units for large-scale natural gas sweetening are based on cellulose acetate (CA). However, the low selectivity and risk for and plasticisation affect adversely the performance of CA-based systems. Herein, we present a new class of CA-derived poly(ionic liquid) (PIL) as a thin film composite (TFC) membrane for CO2 separations. CA is modified with pyrrolidinium cations through alkylation of butyl chloride, substituting the hydroxyl group in the polymer backbone, and further anion exchange to bis(trifluoromethylsulfonyl) imide, P[CA][Tf2N]. The synthesised PIL material properties are extensively studied. The CO2 separation performance of the newly synthesised materials is evaluated by gravimetric gas sorption experiments, single gas time-lag experiments on thick membranes, and mixed-gas separation experiments on TFC membranes. The results are compared to the parent material (CA) as well as a reference PIL (poly(diallyldimethyl ammonium) bis(trifluoromethylsulfonyl) imide (P[DADMA][Tf2N])). The ideal CO2/N-2 sorption selectivity of P[CA][Tf2N] is constant up to 10 bar. The single gas transport measurements in P[CA][Tf2N] reveal improved ideal CO2 selectivity for the CO2/N-2 gas pair and increased CO2 permeability for the CO2/CH4 gas pair compared to the reference PIL. Mixed-gas permeation tests demonstrated that P[CA][Tf2N]-based membranes with a 5 mu m thick selective layer has a two-fold higher CO2 flux compared to conventional CA. These results present CA modification into PILs as a successful approach promoting the higher permeate flows and improved process stability in a wide range of concentrations and pressures of CO2/N-2 and CO2/CH4 gas mixtures.

AbstractHollow fibre carbon membranes (HFCMs) were fabricated from deacetylated cellulose acetate precursors based on a multi-dwell carbonization protocol. Membrane structure and morphology were characterized by scanning electronic microscope (SEM), and membrane separation performances for single gas and gas mixtures were tested by the in-house gas test setup. Simulations of CO2 capture by hollow fibre carbon membranes were conducted based on Aspen Hysys® integrated with ChemBrane. The characteristic diagrams and optimal configuration were obtained, and the process was optimized based on the necessary membrane area, energy demands for the compressor and cooler, recovery and purity of CO2, and capital cost.