Life cycle assessment and multi-objective optimization of biogas upgrading using chitosan based composite membranes

Biopolymer membranes, hybridized by non-toxic or renewable fillers are gaining attention on the preparation of membranes for CO 2 separation, providing their flux and mechanical endurance is improved to provide environmental and economic viability as real alternatives in the decarbonization of the chemical industry. Cellulose acetate is the most commonly found natural biopolymer but its preparation needs organic solvents and it is prone to plasticization. Chitosan biopolymer can be produced from fish waste, but its mechanical resistance is limited due to its high hydrophilicity. In this work, chitosan was blended with cellulose acetate or starch, which can also be obtained from biowaste. The membranes were characterized by single N 2 , CH 4 and CO 2 gas permeation and also CO 2 /CH 4 mixture separation. The CO 2 permeance of CS:ST membranes was closer to commercial PDMS membrane, and the CO 2 /CH 4 selectivity of CS:CA membranes was in the range of selective polymer membranes for this application. A sustainability assessment of the membrane fabrication was performed using Life Cycle Assessment with three environmental impact categories (ReCiPe midpoint method): Global warming, energy and materials depletion. A multi-objective optimization model was applied to optimize the process conditions in the simultaneous CO 2 and CH 4 recovery from model biogas feed stream optimal mass and energy balances. The optimized energy consumption for the separation was utilized on the evaluation of the cradle-to-gate environmental performance for the membranes attaining 90% purity and recovery in CO 2 and CH 4 in the permeate and retentate outlet streams, respectively. • Chitosan(CS)-based membranes prepared by blending with cellulose (CA) and starch. • The environmental hotspots of the membrane manufacturing (MM) are the solvents used. • CS:starch membranes gave higher CO 2 permeability than CS:CA membranes. • CS:ST membranes gave the lowest environmental impacts. • Multi-objective optimization: purity and recovery targets depend on selectivity. • The energy consumption on fabrication is more impactful than biogas upgrading at different scales.