Carbohydrates renewables

Okada et al. have worked extensively on biodegradable polymers based on dianhydroalditols as carbohydrate renewable resources. A series of polyesters were synthesized by the bulk polycondensation of the respective three stereoisomeric dianhydroalditols (DAS, DAM, and DAI) with aliphatic dicarboxyUc acid dichlorides of 2-10 methylene groups [21, 22]. It was found that the biodegradability of the polyesters varied significantly depending on their molecular structures. 

In anticipation of a more balanced discussion on renewable and fossil resources for surfactants a consensus on the coexistence of petrochemically derived products and products based on, for instance, oils, fats, and carbohydrates can be predicted. 

Some of the potential uses of the fats and oils found in plants have been reviewed and some uses of carbohydrate-based polymers briefly discussed. Plants contain a whole variety of other chemicals including amino acids, terpenes, flavonoids, alkaloids, etc. When the potential for these naturally occurring materials are combined with the secondary products that can be obtained by fermentation or other microbial processes or by traditional chemical transformations, the array of chemicals that can readily be created from renewable resources is huge. In this section a few of the more interesting examples are considered. 

Alternatively, an entirely new downstream process and product chain, using renewable raw materials, can be conceived (the biorefinery ). The chemistry will be more focused on that of oxohydrocarbons (particularly carbohydrates) rather than hydrocarbons. Understanding the materials chemistry of biomass and related products would need to be enhanced. However, work has already been undertaken to identify the top sugar-derived intermediates (Figure 1.9) on which down-stream chemical processing might be derived. 

Use renewable raw materials - for example carbohydrates, lipids or biopolymers. 

Using renewable and sustainable materials instead of non-renewables. For example, shifting from hydrocarbon to carbohydrate feedstocks. 

Carbohydrate metabolism in the organism tissues encompasses enzymic processes leading either to the breakdown of carbohydrates (catabolic pathways), or to the synthesis thereof (anabolic pathways). Carbohydrate breakdown leads to energy release or intermediary products that are necessary for other biochemical processes. The carbohydrate synthesis serves for replenishment of polysaccharide reserve or for renewal of structural carbohydrates. The effectiveness of various routes of carbohydrate metabolism in tissues and organs is defined by the availability of appropriate enzymes in them. 

Heterogeneous catalysts, particularly zeolites, have been found suitable for performing transformations of biomass carbohydrates for the production of fine and specialty chemicals.123 From these catalytic routes, the hydrolysis of abundant biomass saccharides, such as cellulose or sucrose, is of particular interest. The latter disaccharide constitutes one of the main renewable raw materials employed for the production of biobased products, notably food additives and pharmaceuticals.124 Hydrolysis of sucrose leads to a 1 1 mixture of glucose and fructose, termed invert sugar and, depending on the reaction conditions, the subsequent formation of 5-hydroxymethylfurfural (HMF) as a by-product resulting from dehydration of fructose. HMF is a versatile intermediate used in industry, and can be derivatized to yield a number of polymerizable furanoid monomers. In particular, HMF has been used in the manufacture of special phenolic resins.125... 

Looking into the future, we expect that hydrogenation reactions will also be tremendously important for the conversion of renewable resources. Going from carbohydrates to valuable chemicals will require deoxygenating reactions. Thus, hydrogenation of alcohols, aldehydes and carboxylic acids will become very important topics. 

The biorefinery scheme was developed initially for carbohydrate-containing feedstocks. Large biorefineries are currently operating in the USA (e.g., Cargill at Blair, Nebraska) and in Europe (e.g., Roquette Frs. at Lestrem, France). The concept can be extended to produce chemicals from other renewable feedstocks. An integrated production of oleochemicals and biofuels can be achieved in biorefineries using vegetables oils as main feedstock to produce versatile platform mole-... 

Converting renewable feedstocks into a mixture of products that can be used as such in the synthesis or formulation of end-products. This approach is widely used in food and feed industries where there is no requirement to prepare specific molecules from bio-resources but rather mixtures of triglycerides, carbohydrates and proteins. 

The catalytic conversion of platform molecules produced by bioconversion of renewables into bioproducts. This is already the basis of many industrial processes, leading to important tonnages of chemicals and polymers from carbohydrates and triglycerides and fine chemicals from terpenes. This approach needs to be extended and process efficiency should be strengthened by designing more active and selective catalysts. 

The development of surfactants based on carbohydrates and oils is the result of a product concept based on the exclusive use of renewable resources. In industry, saccharose (sucrose), glucose and sorbitol, which are available in large amounts and at attractive prices, are used as the preferred carbohydrate raw materials. 

Both in the USA and the EU, the introduction of renewable fuels standards is likely to increase considerably the consumption of bioethanol. Lignocelluloses from agricultural and forest industry residues and/or the carbohydrate fraction of municipal solid waste (MSW) will be the future source of biomass, but starch-rich sources such as corn grain (the major raw material for ethanol in USA) and sugar cane (in Brazil) are currently used. Although land devoted to fuel could reduce land available for food production, this is at present not a serious problem, but could become progressively more important with increasing use of bioethanol. For this reason, it is important to utilize other crops that could be cultivated in unused land (an important social factor to preserve rural populations) and, especially, start to use cellulose-based feedstocks and waste materials as raw material. 

Special attention is given to the integration of biocatalysis with chemocatalysis, i.e., the combined use of enzymatic with homogeneous and/or heterogeneous catalysis in cascade conversions. The complementary strength of these forms of catalysis offers novel opportunities for multi-step conversions in concert for the production of speciality chemicals and food ingredients. In particular, multi-catalytic process options for the conversion of renewable feedstock into chemicals will be discussed on the basis of several carbohydrate cascade processes that are beneficial for the environment. 

Although the focus here is on the integration of biocatalysis with chemocataly-sis (bio-chemo cascades) for carbohydrates as renewable feedstocks, some representative examples (from laboratory to industrial scale) of both bio-bio and chemo-chemo cascades are also given below for comparison of their relative scope and limitations. 

CARBOHYDRATES AS RENEWABLE RAW MATERIALS A MAJOR CHALLENGE OF GREEN CHEMISTRY... 

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