Carob pod as a feedstock for the production of bioethanol in Mediterranean areas

Abstract

There is a growing interest worldwide to find out new and cheap carbohydrate sources for production of bioethanol. In this context, carob pod ( Ceratonia siliqua) is proposed as an economical source for bioethanol production, especially, in arid regions. The carob tree is an evergreen shrub native to the Mediterranean region, cultivated for its edible seed pods and it is currently being reemphasised as an alternative in dryland areas, because no carbon-enriched lands are necessary. In this work, the global process of ethanol production from carob pod was studied. In a first stage, aqueous extraction of sugars from the pod was conducted, achieving very high yields (>99%) in a short period of time. The process was followed by acid or alkaline hydrolysis of washed pod at different operating conditions, the best results ( R = 38.20%) being reached with sulphuric acid (2% v/v) at 90 °C, using a L/ S (liquid/solid) ratio of 7.5 and shaking at 700 rpm for 420 min. After that, fermentation of hydrolysates were tested at 30 °C, 125 rpm, 200 g/L of sugars and 15 g/L of yeast with three different kinds of yeasts. In these conditions a maximum of 95 g/L of ethanol was obtained after 24 h. Finally, the distillation and dehydration of water–bioethanol mixtures was analyzed using the chemical process simulation software CHEMCAD with the aim of estimate the energy requirements of the process.