Toward Bioenergy Sustainable Generation from Lignocellulosic Biomass Pyrolysis

Abstract

The present chapter deals with pyrolysis of peanut shells examining comparatively two possible routes to enhance yield and/or quality of the resulting bio-oils and to favor the process sustainability. They involved a mild acid pretreatment to remove the minerals inherently present in the shells and in situ catalytic pyrolysis employing a modified natural zeolite as catalyst. Their effect on yields and characteristics of the three kinds of pyrolysis products, namely pyrolytic liquids (bio-oils), an enriched carbon solid (biochar), and permanent gases, were systematically investigated under the same, pre-established experimental conditions. Complementary, the pyrolytic behavior of the raw and pretreated peanut shells, as well as of the raw shells in the presence of the catalyst was examined over a wide range of degradation temperatures. The acid pretreatment was found to increase both yield and quality of the bio-oil with respect to those for the pyrolysis of the raw shells, in line with noticeable modifications in their pyrolytic behavior. Besides, pyrolysis of the acid pretreated shells resulted in a biochar with lower ash content and higher BET surface area, favoring not only its potential use as biofuel, but also as soil amender, rough sorbent or for further upgrading to activated carbons. On the other hand, the catalytic pyrolysis promoted a slight decrease in bio-oil yield, at the expense of an increase in gases generation, but improved bio-oil quality by reduction of oxygen content and enhancement of its high heating value. The results indicated that although the two routes investigated were suitable to improve bio-oils quality and, therefore, to promote their use, minerals removal from the shells showed rather better comparative advantages since it enabled to enhance both the yield and quality of the bio-oil, and to widen potentialities of application for the biochar, contributing, together with the possible use of the gases generated for heat supply, to the process sustainability.