An evaluation of SRCs as a Potential carbon neutral source of biomass for energy and Chemicals.

The world energy consumption is predicted to grow by 56% between 2010 and 2040. In this period, although fossil fuels will continue to supply 80% of global energy, renewable energy is estimated to increase by 2.5% per year. In order to reduce the increasingly expensive dependency of fossil fuels and mitigate climate change, the European Union has developed a policy aiming to increase the consumption of renewable energy up to 20% of the total energy consumption. The main advantages of biomass are that it is locally available and that it is also the only renewable source that can replace fossil fuels in solid, liquid and gaseous forms. Currently about 0.19% of the world total land area and about 0.5 - 1.7% of the global agricultural land are used to grow biomass cultivations. Short rotation coppices (SRCs), such as poplar, willow or eucalypt cultivations, are one of the most promising sources of biomaterials, and they are expected to play a major role in the biomass supply. They are able to reduce greenhouse gas emissions by about 90% in comparison to the fossil energy baseline. SRCs are characterized by short repeated cycles of two to five years and planting densities of 3 000 - 10 000 plants per hectare. Average productivities of SRCs in temperate areas are in the minimum range of 12 - 14 Mg ha-1year-1. Woody biomass is composed primarily of cellulose, (40 - 45%) hemicelluloses (15 - 30%), and lignin (25 - 35%), and up to 10% of other components such as ash (0.5%). Thermochemical conversions include combustion, gasification, pyrolysis, and liquefaction. Combustion by direct burning is the traditional way of using biomass to obtain thermal energy. Biomass can also be burned or co-fired with coal, so that the modern coal fired plants can actually designed for co-firing in order to reduce carbon emissions. Lignocellulosic chips under gasification are converted to synthetic gas, primarily CO and H2, using heat at temperatures up to 800 - 1000°C. Pyrolysis is the thermal degradation of biomass by heat, in the absence of oxygen, to obtain charcoal, bio-oil, and fuel gas. Liquefaction is the conversion of biomass to liquid bio-oil according the direct or the catalyzed processes. The direct liquefaction is a process similar to pyrolysis occurring at lower temperatures and at pressures of 5 - 10 Mpa. The catalyzed liquefaction is a reaction of woody biomass with organic solvents, preferably with a catalyst, under moderate temperatures (150 - 180°C) at atmospheric pressure. This kind of liquefaction allows obtaining polyols through depolymerization of organic macromolecules of wood. These polyols can be used as a raw material to synthesize polyurethane foams. Other chemical products, such as adhesives, can be obtained from liquefied biomass. In a nutshell, biomass is a renewable source of energy and chemicals, able to contribute for transition to a global carbon neutral economy, and SRCs cultivation is a valid option with high potential to increase the biomass production.