Introduction

ABBAS KAZMI, BIRGIT KAMM, SÖREN HENKE, LUDWIG THEUVSEN AND RAINER HÖFER

1.1 Green Chemistry and the Biorefinery

The principles of green chemistry are now having a real impact on industry and key players such as P&G are now providing greener alternatives that could have a global impact. One such example targets the alkyd resins which provide robust, high-gloss coatings at relatively low prices for a variety of applications including architectural finishes, industrial metal and construction equipment. However, these coatings require hazardous solvents to solubilise the organic polymers, which has led to novel greener resins developed by P&G in association with Cook Composites & Polymers, USA. The novel resins are produced from the esterification of sucrose with fatty acids, both of which are renewable resources that are readily available. Furthermore the process requires significantly less VOC content and therefore is much greener.

Biodiesel is now a well-established industry, although it has had turbulent times, and is based on renewable resources such as plant oils; however, the transesterification process could be made more green. An alternative method for manufacturing biodiesel, called the 'Mcgyan Process', has been developed by SarTec Corporation and is based on a fixed-bed, flow-through reactor. The fixed-bed zirconia catalyst, which is continuously used, results in no catalyst waste, unlike the conventional acid/base catalyst systems. The novel process not only improves efficiency but also has a positive impact on the economics to the extent that a large-scale 3 million gallon per year facility is to be constructed.

The future biorefinery needs to be based on existing supply chains and product streams. Biorefinery processes need to remove inefficiencies and wastes from existing processes. This is the only way biorefinery concepts will penetrate conventional markets. The plant oil industry is a great example of this as the oils are mainly used for human consumption (126 million tons); however, a considerable amount is used for chemical (15 million tons) and fuel applications (8 million tons). European vegetable oils are used in the oleochemical industry; however, the majority of oils are imported such as soya, palm and castor oil.

The oleochemical industry uses the key components of plant oils to produce chemicals for various applications such as cosmetics, paints, lubricants, biofuels, plastics, soaps and pharmaceuticals. Using fatty acids, glycerine or fatty acid methyl esters a number of important derivatives such as esters, sulfates, ethoxylates and other chemical functionalities can be produced.

In the surfactant market the crude oil derived alkyl benzene sulfonate has the largest market share; however, greener alternatives such as alcohol ether sulfates, alcohol sulfates and alcohol ethoxylates are significantly growing in the market. With pressure from governments and NGOs the paint industry is looking to reduce VOC emissions by using greener resins such as those derived from soya and sunflower oils. Long-chain fatty acids can also be used as biolubricants; however, the estimated volume of such products in the EU is 127 000 tons as of 2006, out of a 5 million ton lubricant market, mainly due to the high cost of biolubricants.

The polymer industry is also currently based on crude oil and with stricter regulations the industry is shifting towards greener alternatives. A host of polymers can be made from plant oils, for example alkyd resins can be made from condensation polymerisation of polyols, organic acids and fatty acids. Furthermore, smaller building blocks based on plant oils can be used in conventional polymers to improve properties such as elasticity, flexibility, strength and hydrophobicity. For example, oleic acid can be used as a building block to produce important products such as linoleum, polyamides, polyurethanes, polyamido amines and non-nylon polyamides. However, with many of these products the properties and pricing are inferior to crude-oil derived polymers, therefore further research is required.

Additional opportunities exist when cross-metathesis reactions are employed with fatty acids and a number of polymers can be produced such as polyesters, polyethers and polyolefins. It has been shown by Rybak and Meier that the cross-metathesis of fatty acid methyl esters with methyl acrylate with only 0.5 mol% of catalyst can be successfully achieved. Furthermore it was shown that oleyl alcohol can be cross-metathesised with methyl acrylate successfully to produce 11-hydroxy-2-undecanoic acid methyl ester and 2-undecanoic acid methyl ester. The former ester is commonly used to make polymers and the latter is used for detergent applications.

Although there is a well-established market for plant oils in the speciality chemicals industry, the biodiesel industry has rapidly grown through government subsidies and high prices of mineral diesel. Therefore a well-defined stream of products from plant oils exists currently and the biorefinery concept can add value to these processes by utilising the by-products such as straw, meal and glycerol.

Wheat straw, rapeseed straw and sunflower stalks are commonly left on the field to replenish the soil or are used as low-grade animal feeds. Although there are environmentally friendly uses of these materials, they do not significantly contribute economically to farming operations. In attempting to increase revenue, the green chemistry approach is the best as it ensures that any additional processing will not harm the environment with a low carbon footprint. A good example of this is the use of supercritical CO2 extraction technology, which uses compressed CO2 to extract valuable chemicals from straws. Wheat straws have a waxy surface and the key components of this wax can be selectively extracted with very high efficiencies. A suitable marketable product from biomass that is of a value that can cover the capital cost requirements is yet to be identified. A number of secondary metabolites that have significant potential include cetearyl alcohol, benzoic acid and fumaric acid, which have applications in the personal care, food and chemical industries. In oilseed crops significant quantities of phenolics, falavanoids and sinapine are found, which can all be used as natural antioxidants. These components can easily be extracted...