Chemicals, biomass fermentation products

The reliance of fossil fuels has been challenged by lower cost and renewable sources that are more environmentally friendly. The traditional chemical plant has met serious competition from green plants. Many monomers are now made via fermentation, using low-cost sugars as feedstock. Some of the commodity monomers are under siege by chemicals extracted from biomass. Monomer production has been expanded to include many more monomers from nature. 

These steps should free fermentation processes from excessively using renewables that end up in undesired, low-value biomass by-products and minimize additional chemical modification steps to obtain the final product [24]. 

Renewable raw materials can contribute to the sustainability of chemical products in two ways (i) by developing greener, biomass-derived products which replace existing oil-based products, e.g. a biodegradable plastic, and (ii) greener processes for the manufacture of existing chemicals from biomass instead of from fossil feedstocks. These conversion processes should, of course, be catalytic in order to maximize atom efficiencies and minimize waste (E factors) but they could be chemo- or biocatalytic, e.g. fermentation [3-5]. Even the chemocatalysts themselves can be derived from biomass, e.g. expanded com starches modified with surface S03H or amine moieties can be used as recyclable solid acid or base catalysts, respectively [6]. 

Bioethanol (ethanol from biomass) is nowadays the largest fermentation product obtained from sugar cane. In fact, bioethanol seems to be the most promising alternative energy source to be used as a fiiel, either alone or as mixture in gasoline. Besides, from bioethanol, many chemicals products may be produced, making the sugar cane-based feedstock process... 

Propylene is, next to ethylene, the most important basic chemical to produce not only polypropylene but also other intermediates for example propylene oxide and acrylonitrile. Just like ethylene, propylene can be produced via a hydrocarbon feedstock produced from a biomass [35-37]. Bio-glycerol produced as a byproduct of biodiesel can be dehydrogenated to produce propylene [48]. Bio-based ethylene can be dimerized to produce n-butene, which can then react with remaining ethylene via metathesis to produce propylene [49]. The use of fermentation products of biomass such as 1-butanol [50] enables the formation of n-butene, followed by a subsequent methathesis [49]. Alternatively, hydrothermal carboxylate reforming of fermentation products such as butyric acid or 3-hydroxybutyrate is also proposed as a viable option to propylene [51]. 

Very recently, lactones have received increasing attention as potential renewable platform chemicals. Perhaps the most prominent bio-based hydroxy fatty acids lactic acid, whose cyclic ester of two lactate molecules serves precursor for the synthesis of bio-based polymers. Fermentative production of hydroxyl-carboxylic acids from agro-industrial waste is an alternative to the synthesis from dwindling fossil resources (Fiichtenbusch et al. 2000). The enzymatic machinery for the production of polyhydroxyalkanoates (PHA) in bacteria offers catalytic pathways for the production of these lactone precursors (Efe et al. 2008). Recent examples include the microbial synthesis of y-butyrolactone and y-valerolactone. Particularly y-valerolactone is of importance and ranks among the top key components of the biomass-based economy. Microbial processes thus offer the perspective of a sustainable fermentative production of optically pure renewable lactones. 

Industrial processes cmivert low-value carbon into high value-added products. To be economically viable, the cost of the overall bioprocess must be significantly less than the selling price of the product. Many variables contribute to bioprocess costs, but for bulk biochemicals such as biofuels and industrial chemicals (which many isoprenoids are used for), the price of the feedstock is the primary cost driver (Rude and Schirmer 2009 WUlke and Vorlop 2008). Currently, carbohydrates from plant biomass are the most important carbon feedstock for fermentation. Plants accumulate simple sugars, cellulose or lipids, which bacteria can convert into energy, biomass and products. Popular model organisms exploited in industry (such as... 

The platform chemicals described earlier mainly rely on feedstock, for instance, 70% of the total cost of the fermentation product is based on feedstock. Hence substrate costs are the most influential parameters in platform chemical production from renewable resources. The cost of the substrate is not only based on pretreatment and fractionation but also on the severe environmental damage caused by deforestation for feedstock requirements (Octave and Thomas, 2009). As mentioned earlier, to get a few hxmdred kilograms of chemicals, a huge ton of forest biomass is consumed. Hence the biorefinery sector should divert its focus from wood to forest wastes, paper mill wastes, agricultural residues, and other municipal wastes. This will decrease the pressure on forest biomass and make the entire process sustainable. In order to reduce deforestation, a few strategies are to be followed in biorefineries ... 

A significant attention is focused on the quest to replace petroleum with plant hiomass for chemical and fuel production. Polysaccharide-degrading enzymes are key tools for thk purpose. However, it has long been recognized that crystalline cellulose is recalcitrant to enzymatic hydrolysis, a major limitation in the production of fermentable sugars from plant biomass therefore, CBMs that target enzymes to crystalline cellulose, promoting the hydrolytic activity, are particularly relevant for biomass conversion [18]. 

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