Renewable resource conversion

Accelerated investigations of renewable resource conversion to hydrogen as a chemical commodity in the near term and a fuel in the longer term. 

Increasingly, biochemical transformations are used to modify renewable resources into useful materials (see Microbial transformations). Fermentation (qv) to ethanol is the oldest of such conversions. Another example is the ceU-free enzyme catalyzed isomerization of glucose to fmctose for use as sweeteners (qv). The enzymatic hydrolysis of cellulose is a biochemical competitor for the acid catalyzed reaction. 

Implementation of the 1998 Kyoto Protocol, which is designed to reduce global carbon emissions, will have dramatic effects on fossil fuel usage worldwide. The Kyoto Protocol mostly affects delivered prices for coal and conversion of plants to natural gas, nuclear and/or renewable resources. However, as pointed out by the International Energy Agency, increased natural gas consumption in the United States may likely have the effect of increased reliance... 

In bioprocesses, the feedstocks required to grow the catalysts and produce the chemical renewable are generally renewable resources, such as sugar from crops. Conversely, purely feedstocks chemical synthesis relies largely on non-renewable resources such as oil, coal and natural gas. It follows that as non-renewable resources dwindle, it is likely that biotechnology will become increasingly important to the chemical industry. 

Hydroformylation is an important industrial process carried out using rhodium phosphine or cobalt carbonyl catalysts. The major industrial process using the rhodium catalyst is hydroformylation of propene with synthesis gas (potentially obtainable from a renewable resource, see Chapter 6). The product, butyraldehyde, is formed as a mixture of n- and iso- isomers the n-isomer is the most desired product, being used for conversion to butanol via hydrogenation) and 2-ethylhexanol via aldol condensation and hydrogenation). Butanol is a valuable solvent in many surface coating formulations whilst 2-ethylhexanol is widely used in the production of phthalate plasticizers. 

Biomass is a renewable resource from which various useful chemicals and fuels can be produced. Glycerol, obtained as a co-product of the transesterification of vegetable oils to produce biodiesel, is a potential building block to be processed in biorefineries (1,2). Attention has been recently paid to the conversion of glycerol to chemicals, such as propanediols (3, 4), acrolein (5, 6), or glyceric acid (7, 8). 

The complete elimination of functional groups is often an undesirable side reaction in organic synthesis, but on the other hand it is a possibility for the recycling of environmentally harmful compounds, for example phenols and haloarenes such as polychlorinated dibenzodioxins (PCDDs or dioxins ). For example, aryl chlorides can be effectively dechlorinated with Pd(0) NPs in tetra-butylammonium salts with almost quantitative conversions also after 19 runs (entry H, Table 1.4) [96]. On the other hand, a C-0 bond cleavage reaction also seems suitable for the fragmentation of sugar-based biomass such as cellulose or cello-biose in that way, sugar monomers and bioalcohol can be derived from renewable resources (entry F, Table 1.4) [164]. 

The slow water removal is obvious within the synthesis of, for example, myristyl myristate determining the total reaction time. In a stirred-tank reactor it takes 24 h to reach a conversion of 99.6% and in a fixed-bed reactor 14 h. Therefore, a new synthesis platform (Figure 4.11) which also enables conversion of highly viscous polyols and fatty acids from renewable resources to ester-based surfactants was designed. It is used by Evonik on a pilot scale, outperforming conventional methods, such as stirred-tank or fixed-bed reactors. In contrast to the setups introduced before, conversion of >99.6% is already obtained after 5.5 h in the bubble column reactor [44-47]. 

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 concept biorefinery is discussed in the US National Research Council Report Biobased Industrial Products [4] and by Lynd et al. [7] in much detail. The basic idea is the processing of multiple renewable resources and the production of multiple products in a production complex. Another characteristic of biorefinery is the integration of thermal, chemical, biological and/or cataly-tical processes for an efficient and optimal processing and utilization of the raw materials. Technological, ecological and economic analysis and system design should be implemented to ensure an overall optimization of raw material conversion and product formation in a similar way as for oil refineries. 

A novel method for production of paraffinic hydrocarbons, suitable as diesel fuel, from renewable resources was illustrated. The fatty acid ethyl ester, ethyl stearate, was successfully converted with high catalyst activity and high selectivity towards formation of the desired product, heptadecane. Investigation of the impact of catalyst reduction showed that the reduction pretreatment had a beneficial effect on the formation of desired diesel compound. The non-pretreated catalyst dehydrogenated ethyl stearate to ethyl oleate. The experiments at different reaction temperatures, depicted that conversion of ethyl stearate was strongly dependent on reaction temperature with Eact=69 kj/mole, while product selectivities were almost constant. Complete conversion of ethyl stearate and very high selectivity towards desired product (95%) were achieved at 360°C. 

In this chapter chemical conversions of natural precursors resulting in flavour chemicals are discussed. The main groups of natural precursors are terpenes for all kinds of terpene derivatives, vanillin precursors like lignin and eugenol, sugars for Maillard-associated flavour chemicals, amino acids and molecules obtained by fermentation or available as residual streams of renewable resources. 

Many products from the flavour industry are primary products from renewable resources or secondary products obtained by chemical conversions of the primary products. In general these secondary products are key flavour chemicals with a high added value. The cost diiference between a precursor, the primary product and the flavour chemical can easily amount to a factor 20-1,000, especially when it concerns a natural flavour chemical. A large part of this cost reflects, of course, the efficiency of the reaction, the labour involved and the cost of the other reagents. 

While this reaction is substantially exothermic (6), it provides an intriguing approach to the production of fuels from renewable resources, as the required acids (including acetic acid, butyric acid, and a variety of other simple aliphatic carboxylic acids) can be produced in abundant yields by the enzymatic fermentation of simple sugars which are, in turn, available from the microbiological hydrolysis of cellulosic biomass materials ( ] ) These considerations have led us to suggest the concept of a "tandem" photoelectrolysis system, in which a solar photoelectrolysis device for the production of fuels via the photo-Kolbe reaction might derive its acid-rich aqueous feedstock from a biomass conversion plant for the hydrolysis and fermentation of crop wastes or other cellulosic materials (4). 

Cellulose is the most abundant renewable resource available for con- version to fuel, food, and chemical feedstocks. It has been estimated by Ghose (11) that the annual worldwide production of cellulose through photosynthesis may approach 100 X 109 metric tons. As much as 25% of this could be made readily available for the conversion processes. A significant fraction of the available cellulose, i.e., 4-5 X 109 t/year, occurs as waste, principally as agricultural and municipal wastes. Cellulose must be viewed, therefore, as an important future source of fuel, food and chemicals (see Table I). 

Cellulose hydrolysis and its product, glucose, play a central role in the conversion of renewable resources to foods, fuel, and chemical feedstocks. This is illustrated in Figure 1. Cheap glucose would not only find a demand in the food sweetener market but could serve as a substrate... 

Well-to-wheel thermodynamic efficiencies for (a) crude to regular vehicle (b) crude to hybrid vehicle (c) natural gas to all-electric vehicle (this efficiency increases to 74 respectively 80% for electricity from hydropower or renewable resources) (d) natural gas conversion to H2 and natural gas conversion to electricity followed by electrolysis to H2- Conv Conversion M motor HM hybrid B battery eM electric motor FC fuel cell. Routes a and b do not allow for the capture of C02. (From Marisvensson, A. et al., Energy, 32,437,2006.)... 

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