Biochar from waste vineyard pruning as a selective sorbent for biogas upgrading by pressure swing adsorption: Experimental and modelling study

Biochar derived from vineyard pruning waste (a readily available agro-industrial byproduct) was investigated as a sustainable sorbent for Pressure Swing Adsorption (PSA) applied to biogas upgrading to biomethane. Biochar had been previously produced through gasification at two Equivalence Ratios (ER = 0.15 and 0.30). Biochar samples “as-received” and “chemically activated” were tested for CO2/CH4 separation at industrially relevant pressures (5-9 bara), according to a full 23 factorial Design of Experiments. ANOVA revealed that chemical activation and pressure were significant factors influencing CO2 and CH4 sorption capacities, CO2/CH4 selectivity, and biomethane recovery. The activation increased the adsorption of both CO2 and CH4, albeit it lowered CO2/CH4 selectivity and biomethane recovery. Four empirical models were developed and validated to predict the behavior of those key performance parameters for biogas upgrading. These models proved to be simple yet effective tools for estimating CO2 and CH4 sorption capacities, CO2/CH4 selectivity, and biomethane recovery within an industrially relevant pressure range for biogas upgrading via PSA technology. The use of as-received biochar with ER of 0.30 at 5 bara emerged as the optimal compromise achieving CO2/CH4 selectivity of 3.0 molCO2/molCH4, CH4 recovery above 66% with a CH4 purity suitable for grid injection (≥ 96 mol%). These results positioned the vineyard pruning biochar as a viable, circular-economy-fulfilling material for PSA-based biogas upgrading.