CONVENTIONAL AND ADVANCED LIQUID BIOFUELS

Energy security and independence, increase and fluctuation of the oil price, fossil fuel resources depletion and global climate change are some of the greatest challenges facing societies today and in incoming decades. Sustainable economic and industrial growth of every country and the world in general requires safe and renewable resources of energy. It has been expected that re-arrangement of economies towards biofuels would mitigate at least partially problems arised from fossil fuel consumption and create more sustainable development. Of the renewable energy sources, bioenergy draws major and particular development endeavors, primarily due to the extensive availability of biomass, already-existence of biomass production technologies and infrastructure, and biomass being the sole feedstock for liquid fuels. The evolution of biofuels is classified into four generations (from 1st to 4th) in accordance to the feedstock origin; if the technologies of feedstock processing are taken into account, than there are two classes of biofuels - conventional and advanced. The conventional biofuels, also known as the 1st generation biofuels, are those produced currently in large quantities using well-known, commercially-practiced technologies. The major feedstocks for these biofuels are cereals or oleaginous plants, used also in the food or feed production. Thus, viability of the 1st generation biofuels is questionable due to the conflict with food supply and high feedstocks' cost. This limitation favoured the search for non-edible biomass for the production of the advanced biofuels. In a general and comparative way, this paper discusses various definitions of biomass, classification of biofuels, and gives brief overview of the biomass conversion routes to liquid biofuels depending on the main constituents of the biomass. Liquid biofuels covered by this paper are those compatible with existing infrastructure for gasoline and diesel and ready to be used in mixture with them as, drop-in fuels: bio-ethanol, cellulosic ethanol, biodiesel, renewable diesel and BtL diesel; their major advantages and drawbacks are compared.