Bioethanol production from oil palm empty fruit bunches : a comparison among different pretreatment options

Face to the increasing demand for energy, the declining availability of fossil fuels and the periodical tensions in the geopolitical context of oil-producing countries have raised serious concerns in the governments worldwide as well as in the public opinion. Similarly, awareness has been increasing of the environmental harms caused by burning fossil fuels and of the associated adverse effects on human health. A number of different potential sources of renewable energy have been investigated over the last decades, including wind power, solar energy and biomass, among others. In particular, concerning the use of biomass, the production of ethanol as a transportation fuel has been considered a particularly attractive and feasible option. Production of ethanol from feedstocks containing easily fermentable sugars such as corn or sugar cane has been actually implemented, especially in the US and in Brazil, but it has been harshly debated especially on the ground of the induced competition between energy and food uses. Hence, a so-called second generation production has been envisaged, which makes use of lignocellulosic materials, namely biomass residues from different agricultural and industrial processes, which appear particularly interesting due to their abundance and the lack of possible use for human consumption. Unfortunately, the production of ethanol from cellulosic feedstocks still presents technical challenges to be overcome before production at the industrial scale could become profitable. In a number of tropical countries in Africa, Asia and South America, important amounts of agricultural residues are generated during the process of oil extraction from the fruits of the palm tree Elaeis guineensis. Among these residues, the empty bunches that carry the fruitlets are at present severely underused, despite their high content of cellulose (of roughly 30%) and the presence of other saccharides. In the scientific literature, relatively limited attention has been given to this feedstock, when compared to other residues such as, for instance, corn stover. Moreover, different studies can be difficult to compare because of the many dissimilar factors involved, as the diverse geographical origin of the residues, and different techniques and analytical protocols used. This thesis deals with the comparison of possible alternatives for processing empty fruit bunches to produce ethanol. The attention has been focused on the pretreatment step, the first operation performed on the feedstock, which is crucial because of its cost and impact on downstream processing (enzymatic saccharification and fermentation). Thus, three pretreatment techniques generally accepted as among the most promising have been chosen: dilute acid, dilute alkali and liquid hot water treatment. They have been performed on the same feedstock under controlled laboratory conditions. For each pretreatment, experimental parameters (such as temperature, time, pH, etc.) have been varied acc