Plant derived feedstocks

Figure 6.29 shows some of the plant derived feedstocks used in the synthesis of lipids and polyketides (Sell, 2006). Rapeseed oil provides erucic acid (173) that can be ozonolyzed to give brassylic acid (174) and heptanal (175), both useful building blocks. The latter can also be obtained. 

The implications of switching chemical manufacture from its current reliance on nonrenewable fossil fuel feedstocks to utilization of renewable, plant-derived feedstocks is considerable. The U.S. chemical industry currently uses 5 quads (1 quad = 1 x 10 British thermal units) of carbon for manufacture of organic chemicals. If these 5 quads of carbon were derived from renewable feedstocks, a net consumption of CO2 would be realized, given that the polyols used as starting materials are biosynthesized by plants from CO2 and are essentially immobilized forms of CO2. Since international treaties eventually require reductions in CO2 emissions in the United States, large-scale consumption of CO2 to make chemicals may be used as a credit to offset CO2 emissions resulting from combustion of fossil fuels to generate electricity and combustion of petroleum-based transportation fuels. 

It is important to emphasize that conversion of plant-derived starting materials into chemical products must ultimately lead to industrial-scale processes that yield chemical products at a manufacturing cost that is competitive with their current production from petroleum-derived carbon. Ultrafine chemicals and smaller-volume fine chemicals provide an invaluable proving ground for such activities. Because of the inherent value-added nature of these chemicals, the fundamentals of yield and titer considerations can be elaborated and then scaled up to syntheses commercially practiced by the pharmaceutical and fiavor and fragrance industries. The lessons learned will be critical to the large-scale, microbe-catalyzed conversions needed for cost-effective manufacture of pseudocommodity and commodity chemicals from plant-derived feedstocks. 

Despite the general move towards use of fossil hydrocarbon feedstocks, some plant-derived materials have continued to provide economic or technical benefits that ensure they remain the preferred source of raw materials for industry. For example, cotton still accounts for 38% of all textile production due to its airflow- and temperature-regulating capabilities, which are difficult or costly to replicate with man-made fibres. Linseed oil remains a key feedstock in surface coating and linoleum flooring applications. Plant oils are still widely used in the oleochemicals sector, where coconut and palm oils are widely used in detergent... 

Outside of the use of cellulose for papermaking, starch is the most widely used plant-derived carbohydrate for non-food uses. Around 60 million tonnes of raw starch are produced per year for food and non-food uses. The US accounts for most of the world s production, utilising starch from maize, which accounts for over 80% of world production. The starch market in the US is driven by the large isoglucose sweetener market and now increasingly by the growing bioethanol market, which uses maize as a fermentation feedstock. Europe derives most of its starch from wheat and potatoes, which account for 8% and 5% of world starch production, respectively. The other main source of starch is cassava (tapioca), produced in South East Asia. Small amounts of oat, barley and rice are also exploited for starch production. Many edible beans are also rich in starches, but are not commonly exploited for non-food uses. 

The petrochemical industry typically works on a build-up approach where the base oil feedstock is fractionated, and complex materials are built up from simpler ones, producing a wide array of materials in the process, for a range of market outlets. The future exploitation of plant materials is seen in a somewhat similar fashion, although in contrast to the petrochemical industry, there will typically be an initial breaking up of more complex materials into simpler building blocks that can then be utilised and built on with the support of chemical, biochemical and catalytic processes, to produce more complex products synonymous with those produced by today s petrochemical industry. This whole crop approach to industrial use of plant-derived material is typically termed biorefining (see Chapter 1). 

Considerable attention is currently being focused on the use of renewable vegetable oils as feedstocks for the production of biodiesel. The latter has obvious benefits in the context of green chemistry and sustainability (i) since it is plant-derived its use as a fuel is C02-neutral, (ii) it is readily biodegradable, (iii) its use results in reduced emissions of CO, SOx, soot and particulate matter. 

The sky-rocketing crude oil prices in recent years and the continuous exploitation of fossil fuels demand that we make serious efforts toward sustainable biofuel and bioenergy production. Renewable energy derived from plant-based feedstocks, organic residues, and biowastes is expected to reduce our dependency on fossil fuels, reduce greenhouse gas emissions, and enhance the rural economy (Schmer et al., 2008). In the United States, liquid biofuels such as ethanol and biodiesel are primarily derived... 

Oxidation reactions play a crucial role in the chemical industry, where >90% of the feedstocks derive from hydrocarbons - the most reduced organic chemicals on the planet. Sustainability concerns are demanding a greater shift toward biomass-derived feedstocks however, oxidation methods will continue to play a major role. For example, even as this book goes to press (March 2016), BASF and Avantium have just announced plans to pursue a joint venture for the production of 2,5-furandicarboxylic acid (FDCA), an important polymer-building block derived from biomass. The proposed 50000 metric tons per year plant will undoubtedly incorporate liquid phase aerobic oxidation chemistry similar to that described in Chapter 19 of this volume. 

The oxidative dehydrogenation of alcohols represents key steps in the synthesis of aldehyde, ketone, ester, and acid intermediates employed within the fine chemical, pharmaceutical, and agrochemical sectors, with allylic aldehydes in particular high-value components used in the perfume and fiavoring industries [1]. For example, crotonaldehyde is an important agrochemical and a valuable precursor for the food preservative sorbic acid, while citronellyl acetate and cinnamaldehyde confer rose/fruity and cinnamon flavors and aromas, respectively. There is also considerable interest in the exploitation of biomass-derived feedstocks such as glycerol (a by-product of biodiesel synthesis from plant or... 

The purpose of this volume is to highlight several recent research efforts to discover and to develop selective, catalytic reactions and processes for the cmiver-sion of ligno-cellulosic and plant oil-derived feedstocks to value-added chemicals. The value of catalytic chemical processes lies in their reduced energy consumption and potentially increased efficiency and product selectivity, which minimize environmental and societal impacts. Selectivity is especially important for the preparation of commodity and specialty chemical and materials where single compounds are usually needed, unlike fuel production where mixtures of high energy compounds (e.g., gasoline and diesel) are useable. 

Coal-conversion processes under development are directed towards producing either gaseous or liquid feedstocks which approximate in composition to petroleum-derived feedstocks. They can then be utilized directly in existing petrochemical plant and processes. To achieve this, however, two problems must be overcome, which are a consequence of the differing natures of coal and oil. Firstly, the H C ratios are different for coal and for petroleum-derived liquid feedstocks. Secondly, significant amounts of heteroatoms are present in coal, particularly sulphur which may reach levels as high as 3%. The sulphur has to be removed for two reasons (i) on combustion it will form the atmospheric pollutant SO2, and (ii) it is a potent catalyst poison, and most of the downstream petrochemical processes are catalytic. However, its removal from coal is difficult and it is therefore removed from the conversion products instead. 

As with all products, the introduction of new materials from crops requires the development of new supply chains. These supply lines originate at the agricultural/horticultural industry and are often imfamiliar to companies who traditionally work with petrochemical-based feedstocks. Companies will often need to develop new skills and technologies or seek out partner companies to ensure supply chain competency and security. The following areas need to be understood and considered when developing new plant-derived products ... 

The high stereospecific oxygen content of carbohydrate feedstocks versus petrochemicals represents a competitive advantage in certain market segments, but it restricts the use of these cheap and abundant plant-based feedstocks for other applications. The restriction is twofold not only are most synthetic polymers like polyethylene and polypropylene structurally quite dissimilar to carbohydrates and derivatives, but in addition, such highly oxidized... 

---