Yields and CO2 reactivity of chars from almond shells obtained by a two heating step carbonisation process.: Effect of different chemical pre-treatments and ash content

Almond shell samples were pre-treated with both basic and acidic treatments for varying lengths of time (10% of sulphuric acid and 2% of sodium hydroxide at 30 min, 1, 3 and 24 h). Combined acidic-basic as well as basic-acidic treatments were also studied, and the amount of ashes of each sample analysed. Different samples were carbonised in a reactor to study the effect of the acidic pre-treatments on the char yields. The reactivity of the samples was also studied by thermogravimetry under CO2 atmosphere. The samples pre-treated with acid showed a lower reactivity than the untreated and basis-treated samples, as a consequence of the lower amount of ashes, thus reducing their catalytic effect. Additionally, at low temperature of carbonisation such samples resulted in higher yields as a consequence of the relatively higher lignin fraction remaining in these samples (acidic treatment partly removes the hemicellulose and cellulose fractions). (C) 2001 Elsevier Science B.V. All rights reserved.