Monosaccharide Feedstocks Glucose and Fructose

The most abundant biomass feedstocks are carbohydrates. It follows that one of the most promising pathways to obtain useful raw materials and fuels from biomass is their synthesis directly from carbohydrates. The monosaccharides such as glucose and fructose, as well as xylose, a five-carbon sugar that is the monomer of hemicellulose, which makes up almost one-third of typical plant 

In addition to starch as a source of glucose, it is also possible to obtain glucose by the enzymatic hydrolysis of cellulose, although it has proved to be economically and technically challenging on an industrial scale because of the refractory nature of the cellulose polymer (see Section 16.8). Nevertheless, the enormous quantities of cellulose available in wood and other biomass sources make glucose from cellulose an attractive prospect. 

The greatest use of glucose and fructose (which is readily converted to glucose by enzymes) for chemical synthesis is by fermentation with yeasts to produce ethanol 

Glucose is widely used as a starting material for the biological synthesis of a nnmber of different biochemical compounds. These include ascorbic acid, citric acid, and lactic acid. Several amino acids used as nutritional supplements, including lysine, phenylalanine, threonine, and tryptophan, are biochemically synthesized starting with glucose. The vitamins folic acid, ubiquinone, and enterochelin are also made biochemically from glucose. 

A study by the U.S. Department of Energy Pacific Northwest Regional Laboratory has identified top twelve value-added chemicals that can be made enzymatically from monosaccharides, especially glucose and fructose. Listed in Table 16.1, these chemicals could form the main feedstocks for future bioreflneries that would generate an abundance of prodncts that are currently made largely from petrochemicals. Several possible syntheses of commercially valuable chemicals starting with glucose are discussed here. 

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