Cellulosic platform molecules

Chemical routes for the conversion of cellulosic platform molecules into high-energy-density biofuels... 

A variety of catalytic routes have been described in recent years for the chemical transformation of carbohydrates into hydrocarbon liquid fuels and oxygenated biofuels which wiU be discussed in this chapter. Special focus will be brought to the recent progress of integrated processes based on the use of multifunctional catalytic systems without isolation of the platform intermediates. Fig. 13.1 summarizes the main chemical routes for the conversion of cellulosic platform molecules into high-energy-density biofuels. 

Recent attempts aim at the controlled transformation of cellulose, hemicellulose, and lignin to platform molecules for a potential future biorefinery scenario. In this regard, the U.S. Department of Energy has published studies on potential future platform molecules that could be derived from renewable resources [35, 36]. Tailored transformation of biomass to these platform chemicals could serve as a starting point for biofuel production. This would allow the development of comprehensive biorefinery approaches that incorporate both the production of biofuels and chemicals. The... 

The next two sections of this review chapter will introduce the reader to the world of lactic acid. The acid is both a key platform chemical of the biorefinery concept, from which other interesting molecules may be formed (Sect. 2), and a monomer for commercial bioplastic polylactic acid (PLA) (Sect. 3). In the platform approach, the assessment from Chap. 1 in this volume [23] proves its value, as it is an equally useful tool to seek out the most desired routes for transforming a biomass-derived platform molecule as it is to select the most relevant carbohydrate-based chemicals from a chemist s point of view. In what follows, the desired catalytic cascade from cellulose to lactic acid will be described (Sect. 4) as well as the specific catalytic data reported for different feedstock (Sects. 5 and 6). Section 7 will introduce the reader to recent synthesis routes for other useful AHA compounds such as furyl and vinyl glycolic acid, as well as others shown in Fig. 1. Before concluding this chapter, Sect. 8 will provide a note on the stereochemistry of the chemically produced AHAs. 

Another important platform molecule that can be produced from cellulose and hemicellulo.se is LA. However, to be efficacy, the catalytic conversion of llgnocellulosic feedstocks requires improving catalysts efficiencies and selectivities. 

Early efforts for the efficient conversion of biomass into monomers were concentrated on the acidic transformation and on the fermentation of sugars obtained from sucrose, or from glucose after depolymerization of starch materials (potato, com). During the last two decades, however, more attention has been focused on other constituents of plant materials, such as cellulose and lignocellulosic residues. The current trend is indeed to avoid competition with food, offering new routes to C6 and C5 carbohydrates, for further transformation into value-added platform molecules. 

In addition to the extractable functional molecules found in biomass, we can also make additional useful functional molecules or platform molecules , such as succinic acid, lactic acid and levoglucosenone, by biochemical or thermochemical processing of the bulk cellulosic components of many types of biomass. A biorefinery is an analogue to the current petro-refinery in the sense that it produces energy and chemicals. The major differences lies in the raw material it will use, ranging from biomass to waste (Figure 1.2). 

In light of the mentioned facts, we designed an experimental setup, which serves as the platform for such testing. To be reproducible, effective and to allow proper evaluation, it had to be simplified as far as possible. It consists of a model surface (atomically flat silicon wafer), two different pol)nner molecules (carboxy methyl cellulose and amylose) and solutions exhibiting different pHs and ionic strengths. The setup is schematically depicted in Figure 12. 

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