PHYSICAL AND CHEMICAL PRETREATMENTS USED FOR BIOETHANOL PRODUCTION FROM LIGNOCELLULOSIC BIOMASS - REVIEW

Abstract

In the last decade, environmental protection is one of the major challenges. It is necessary to ensure the protection of the environment and the conservation of natural resources, in accordance with the requirements of a sustainable economic and social development. The most important impact of modern human activities is the release of large amounts of different compounds after fossil fuels burning; these compounds are responsible for increasing of greenhouse gases (GHG) concentrations in the atmosphere. The depletion of fossil fuels and necessity to increase energy reserves, especially for the propulsion of transport, contributed to search and use of alternative fuels. Partially or completely substitution of gasoline with bioethanol is an alternative method to reduce GHG emissions. Currently, biofuels (first generation) are produced from sources used to feed the population. The competition food vs. biofuel could be solved if biofuels were obtained from renewable resources such as lignocellulosic biomass (LCB). Second-generation biofuels are obtained from raw materials such as agricultural residues (straws, sugarcane bagasse, corn stalks and cobs) and forestry residues (sawdust, bark, branches, etc.) which do not interfere with global food production. In 2019, the main producers of bioethanol were USA, Brazil and EU which produced about 54%, 30% and 5% respectively of the worldwide bioethanol.

This paper reviews one of the most important steps of bioethanol production which is the pretreatment of LCB. Numerous pretreatments are available, as follows: physical, chemical, physico-chemical, biological and combined pretreatments. The combined pretreatments were found to be more effective when compared to single pretreatments, and there is a wide range of combinations that can be applied in the future.