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 hydrox ide at 30 min, 1, 3 and 24 h). Combined acidic-basic as well as basic-acidi c treatments were also studied, and the amount of ashes of each sample anal ysed. Different samples were carbonised in a reactor to study the effect of the acidic pre-treatments on the char yields. The reactivity of the sample s was also studied by thermogravimetry under CO2 atmosphere. The samples pr e-treated with acid showed a lower reactivity than the untreated and basis- treated samples, as a consequence of the lower amount of ashes, thus reduci ng their catalytic effect. Additionally, at low temperature of carbonisatio n 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 Scie nce B.V. All rights reserved.