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

Abstract

Biopolymer membranes, hybridized by non-toxic or renewable fillers are gaining attention on the preparation of membranes for CO2 separation, providing their flux and mechanical endurance is improved to provide envi ronmental 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 N2, CH4 and CO2 gas permeation and also CO2/CH4 mixture separation. The CO2 permeance of CS:ST membranes was closer to commercial PDMS membrane, and the CO2/CH4 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 CO2 and CH4 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 environ mental performance for the membranes attaining 90 % purity and recovery in CO2 and CH4 in the permeate and retentate outlet streams, respectively.