The influence of chemical additives on the pyrolysis of sugar cane bagasse

Sugar cane bagasse presents a continuing problem for the sugar cane industry as it is a low value by-product that can be hazardous to store over extended periods. A large range of potential methods for utilising waste bagasse has been proposed. One alternative is the pyrolysis of the bagasse to yield a syngas (for energy or chemical production) and biochar for long term carbon sequestration. In this study, pyrolysis experiments were conducted to measure the influence of selected chemical additives (borax, boric acid and ammonium sulphate) on the rate of pyrolysis to give a large conversion of bagasse to char. All additives tested reduced the rate at which biomass mass-loss occurred (compared with virgin bagasse) when heated. Borax was found to be the most effective at reducing the rate of mass loss and producing the maximum mass of biochar at 800ºC (41% of the bagasse, on an ash-free basis, was converted to char compared with 16% for untreated bagasse), with boric acid and ammonium sulphate producing similar char masses (~29%). Biochar mass production was only a weak function of additive concentration, over the range of concentrations used. It was interesting to note that combining the chemical additives showed no synergistic affects ¿ indeed the combination of boric acid or ammonium sulphate to borax could be antagonistic, with the amount of char produced being reduced below that if only borax were used.