Development of biomass based activated carbons for biogas upgrade

The direct combustion of biogas has the problem of corrosion in wet conditions, low heating value and limited applications. The removal of CO2 to produce biomethane (biogas upgrade), addresses these diverse challenges. Among the various techniques available to remove the CO2, adsorption-based systems using activated carbon (AC) obtained from biomass precursors are gaining importance due to their cost effectiveness and better performance (superior capture capacity and CO2/CH4 selectivity). This doctoral thesis presents a comprehensive investigation into the development and application of biomass-derived (spruce sawdust (SD), miscanthus straw (MS), wheat straw (WS), and sewage sludge (SS)) physical and chemical activated carbons for CO2 capture from biogas. The research delves into the detailed optimisation of the experimental conditions, systematic characterisations (TGA, Fourier transform infrared (FTIR) analysis, CHN analysis, and adsorption isotherms), and breakthrough studies. The research concludes with the identification of an optimal char sample exhibiting cyclic stability and remarkable CO2 capture capacity of 1.98 mmol/g under 90 % CO2 stream. Additionally, physically, and chemically activated carbons are highlighting varying activation conditions and their impact on textural properties and CO2 capture capabilities. The optimum physical and chemical activated carbons have high CO2 capture capacities (2.42 mmol/g by ACSD (860-1-30) and 3.64 mmol/g by ACMS (700-10-90-1.5) at 25 ° C. The breakthrough (dynamic) studies of the optimum samples in a fixed-bed reactor under various biogas compositions (30/70, 50/50, and 70/30 vol % of CO2/CH4) uncovers rapid adsorption kinetics and breakthrough profiles (S shaped), highlighting the preferential adsorption of CO2 over CH4. The influence of gas concentrations on separation efficiency is carefully analysed, highlighting exceptional performance (selectivity above 3 by all the optimum samples under 30 % CO2 stream and a maximum selectivity of 3.76 by ACSD (860-10-30) under 50 % CO2 stream at 25 ° C and atmospheric pressure. The CSD (700- 10-60) has better separation performance (selectivity of 3.59 under 30 % CO2 stream) as compared to many chars and physically activated carbons. In summary, this research not only expands the understanding of biomass-derived activated carbons but also provides valuable insights for their practical application in CO2 capture. The findings contribute to current efforts in developing sustainable materials to address environmental challenges, particularly in the domain of greenhouse gas mitigation and sustainable alternative fuels.