Biomass molecules

In this chapter, we focus on current efforts to apply various eatalysts in the conversion of lignocellulosie biomass molecules into liquid fuels. From the viewpoint of the fundamental chemistry, we discuss the main ehemical processes and reaction mechanisms for specific biomass conversion methods, as well as the typical catalysts that are used. Since these biomass eatalysts are used to perform green chemistry [ie., produce renewable energy) we ean also call them green catalysts. We hope that this chapterwill serve as a tutorial for green chemistry education, and inspire researchers to design more efficient, robust, low-cost and sustainable catalytic approaches. This chapter does not intend to serve as a comprehensive account for all the catalysts used for lignocellulosie biomass conversion. 

Pyrolysis entails thermal decomposition of biomass molecules in the absenee of oxygen, usually at the temperatures up to 650-800 K. To produee liquid oils, the heating process should be short [i.e., short residenee time), thus this process is usually referred to as fast pyrolysis. At high temperature, the biomass is vaporized and then condensed upon cooling to produce a liquid oil mixture which may be comprised of more than 300 compounds such as alkanes, aromatic aliphatic, sugars, alcohols, ketones, aldehydes, acids and esters. If the residence time is longer (slow pyrolysis), the product mixture is likely to produce more solid coke than liquid fuels. An advantage of fast pyrolysis is that it is economical for use on a small scale ie., 50-100 tons biomass per day). Yields of bio-oil production in excess of 70% have been... 

Substituent effects on the specific acid-catalysed ring-opening hydrolysis of the furan rings in several Cg and C9 biomass molecules have been investigated by... 

Further processes in the plant make more complex molecules from the glucose. The exact makeup of biomass varies with type, but in general it has the chemical formnla ol (Cl TO) and on average is about... 

The synthesis of 1 kg of dry plant biomass requires the evapotranspiration of about 300 L of water, although smaller amounts of water are needed by some plants such as desert cacti. Approximately one-third of the annual continental rainfall (100 cm/yr) is returned to the atmosphere by evapotranspiration. Although it accounts for only about 10-15% of global evaporation, plant evapotranspiration can play a major role in local climates. For example, a molecule of water falling on the upper Amazon Basin is recycled on average five times during its eventual return to the Atlantic Ocean. 

Besides nitrogen fixation, the only other major source of reduced nitrogen is the decomposition of soil or aquatic organic matter. This process is called ammonification. Heterotrophic bacteria are principally responsible for this. These organisms utilize organic compounds from dead plant or animal matter as a carbon source, and leave behind NH3 and NHJ, which can then be recycled by the biosphere. In some instances heterotrophic bacteria may incorporate a complete organic molecule into their own biomass. The majority of the NH3 produced in this way stays within the biosphere however, a small portion of it will be volatilized. In addition to this source, the breakdown of animal excreta also contributes to atmospheric... 

S.2 Chemicals and Fuels from Biomass 167 Table 8.1 Examples of molecules from biomass through catalysis. 

There is some similarity between the cracking of petroleum and the cracking of biomass. However, biomass is more complex chemically both in terms of structrual types and functional groups. In petrochemistry, hydrocarbons are fractionated and they are then functionalized by oxidation, halogenation, nitration and other chemical processes so as to add value. The commodity chemicals are then built up into more complex molecules using such popular synthetic methods as Friedel Craft reactions, Michael and aldol condensations, and Heck and Suzuki couplings. The speciality products of these reactions are then further elaborated into formulations for use in everyday applications ranging from personal care... 

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