Over the last decade, prices of fossil fuel feedstocks have increased, whereas prices of biomass resources have slowly and steadily decreased. This situation makes the possibility to produce the existing bulk chemicals from biomass rather than fossils an attractive option. In the following paragraphs, the current state of the art in the production of the bulk chemicals previously highlighted is investigated. The possible reaction pathways are summarized in Figure 6.

1.4 Ethylene

The production of this chemical from biomass sources can be achieved through dehydra­tion of ethanol. This dehydration is favored at high temperatures (300-600 °C) and can be car­ried out over a wide variety of heterogeneous catalysts (Arenamnarta and Trakarnpruk, 2006; Takahara et al., 2005). There are no technological barriers to be faced for the production of ethene from ethanol at a commercial scale; this production is initially most likely to happen in regions with cheap and easy access to bioethanol (Haveren et al., 2008).

1.5 Propylene

Direct production of propene from sugars can be carried out via fermentation (Fukuda et al., 1987). Product yields are very low: the productivity needs to be improved by orders of magni­tude to make this process economically viable (Haveren et al., 2008). An alternative production pathway consists in the dehydration of 2-propanol, which is produced by reduction of acetone. The latter can be obtained via the acetone, butanol, ethanol (ABE) fermentation process, which is largely studied in the scientific and industrial community (Ezeji et al., 2007). In addition, propene can be produced from dehydration of 1,2-propanediol (either called propene glycol). This glycol can be effectively produced from reduced sugars as sorbitol and xylitol or lactic acid, and such conversion routes have strong commercial potential (Haveren et al., 2008).