Effect of alkaline catalysts on the valorization of sugarcane bagasse via pyrolysis

Abstract

Sugarcane bagasse (Saccharum officinarum) is a widely spread residual biomass from the sugar industry that can be valorized through pyrolysis. The spectrum of the fractions obtained will vary depending on the pyrolysis conditions selected. In this work, the influence of alkaline treatments on the raw material has been studied. The sugarcane residues were treated with sodium or potassium hydroxides (1:1 sample/hydroxide ratio) and subsequently washed to remove hydroxides. Slow pyrolysis in a thermobalance connected to FTIR and flash pyrolysis in an EGA/Py-GC/MS system were performed with three types of samples, i.e.: raw material, hydroxides impregnated bagasse and the material obtained after washing the previous impregnated samples to remove the hydroxides. The experiments carried out allow us to distinguish between the effect of the basic pretreatment and the catalytic effect of the alkaline ions present during the pyrolysis on the compounds generated, thus allowing us to analyze the advantages that these processes can present in the bagasse valorization. According to the results obtained, the presence of alkaline ions in the sample during the pyrolysis process increases char percentage very significantly as well as cyclopentanone and cyclopentenone derivatives and the amount of CO2 evolved, reducing levoglucosane drastically and the vinyl and methoxy groups in the volatiles obtained. The washing treatment until neutral pH, after the alkaline impregnation, modifies the spectrum of pyrolytic products obtained, reducing phenol derivatives and increasing very significantly the percentage of levoglucosane and hydroxiacetaldehyde. Thus, the changes in the bagasse structure as well as in the decomposition mechanism could be tuned to produce activated carbon in a single step (maximizing carbon yield), diminishing the oxygen content in the bio-oil obtained (increasing its heating value) and reducing the pyrolytic compound spectrum (increasing the selectivity of the process).