Pyrolysis of almond shells waste: effect of zinc oxide on kinetics and product distribution

Abstract

In the present work, plain and zinc oxide-loaded almond shells were pyrolyzed in an indigenously manufactured pyrolysis system. The bio-oil produced as a result of catalytic and non-catalytic pyrolysis was characterized using gas chromatography mass spectrometry (GC-MS). Bio-oil produced from non-catalytic pyrolysis consists mainly of ethanol, acetic acid, 1-hydroxy-2-butanone, and 9-octadecenoic acid, methyl ester while bio-oil produced from catalytic pyrolysis consists of a large number of components ranging from C5 to C57. In order to study the kinetics of pyrolysis reaction, both the samples were subjected to thermogravimetric analysis (TGA) at heating rate of 5, 10, 15, and 20 °C/min from room temperature to 600 °C. A four steps degradation was observed, i.e., the first weight loss refers to removal of water molecules, the second weight loss is due to decomposition of hemicellulose, the third weight loss is owed to degradation of cellulose, while the last one is attributed to decomposition of lignin. Kinetic parameters were determined applying Ozawa-Flynn-wall (OFW) and Coats-Redfern (CR) equations. Activation energy (Ea) and frequency factor (A) were observed to increase with increase in fraction conversion which shows complex mechanism of reaction. It has been concluded that zinc oxide proved to be an effective catalyst vis-a-vis decrease in activation energy and quality of bio-oil produced.