Ashley J. Wilson

Green chemistry and the biorefinery: a partnership for a sustainable future

Research into renewable bioresources at York and elsewhere is demonstrating that by applying green chemical technologies to the transformation of typically low value and widely available biomass feedstocks, including wastes, we can build up new environmentally compatible and sustainable chemicals and materials industries for the 21st century. Current research includes the benign extraction of valuable secondary metabolites from agricultural co-products and other low value biomass, the conversion of natures primary metabolites into speciality materials and into bioplatform molecules, as well as the green chemical transformations of those platform molecules. Key drivers for the adoption of biorefinery technologies will come from all stages in the chemical product lifecycle (reducing the use of non-renewable fossil resources, cleaner and safer chemical manufacturing, and legislative and consumer requirements for products), but also from the renewable energy industries (adding value to biofuels through the utilisation of the chemical value of by-products) and the food industries (realising the potential chemical value of wastes at all stages in the food product lifecycle).

Insulin at pH 2: Structural analysis of the conditions promoting insulin fibre formation

When insulin solutions are subjected to acid, heat and agitation, the normal pattern of insulin assembly (dimers-->tetramers-->hexamers) is disrupted; the molecule undergoes conformational changes allowing it to follow an alternative aggregation pathway (via a monomeric species) leading to the formation of insoluble amyloid fibres. To investigate the effect of acid pH on the conformation and aggregation state of the protein, the crystal structure of human insulin at pH 2.1 has been determined to 1.6 A resolution. The structure reveals that the native fold is maintained at low pH, and that the molecule is still capable of forming dimers similar to those found in hexameric insulin structures at higher pH. Sulphate ions are incorporated into the molecule and the crystal lattice where they neutralise positive charges on the protein, stabilising its structure and facilitating crystallisation. The sulphate interactions are associated with local deformations in the protein, which may indicate that the structure is more plastic at low pH. Transmission electron microscopy analysis of insulin fibres reveals that the appearance of the fibres is greatly influenced by the type of acid employed. Sulphuric acid produces distinctive highly bunched, truncated fibres, suggesting that the sulphate ions have a sophisticated role to play in fibre formation, rather as they do in the crystal structure. Analytical ultracentrifugation studies show that in the absence of heating, insulin is predominantly dimeric in mineral acids, whereas in acetic acid the equilibrium is shifted towards the monomer. Hence, the effect of acid on the aggregation state of insulin is also complex. These results suggest that acid conditions increase the susceptibility of the molecule to conformational change and dissociation, and enhance the rate of fibrillation by providing a charged environment in which the attractive forces between the protein molecules is increased.

Chitosan-based heterogeneous catalysts for Suzuki and Heck reactions

Novel supported palladium catalysts have been developed based on chitosan as a support. These catalysts display excellent activity in the Suzuki and Heck reactions.

The preparation of high-grade bio-oils through the controlled, low temperature microwave activation of wheat straw

The low temperature microwave activation of biomass has been investigated as a novel, energy efficient route to bio-oils. The properties of the bio-oil produced were considered in terms of fuel suitability. Water content, elemental composition and calorific value have all been found to be comparable to and in many cases better than conventional pyrolysis oils. Compositional analysis shows further differences with conventional pyrolysis oils including simpler chemical mixtures, which have potential as fuel and chemical intermediates. The use of simple additives, e.g. HCl, H(2)SO(4) and NH(3), affects the process product distribution, along with changes in the chemical composition of the oils. Clearly the use of our low temperature technology gives significant advantages in terms of preparing a product that is much closer to that which is required for transport fuel applications.

Use of green chemical technologies in an integrated biorefinery

A new concept is demonstrated for an integrated close to zero waste wheat straw biorefinery combining two novel green technologies, CO2 extraction and low temperature microwave pyrolysis, to produce a variety of products, including energy and CO2 which can be internally recycled to sustain the processes. CO2 adds value to the process by extracting secondary metabolites including fatty acids, wax esters and fatty alcohols. Low temperature microwave pyrolysis (<200 °C) is shown to use less energy and produce higher quality oils and chars than conventional pyrolysis. The oils can be fractionated to produce either transport fuels or platform chemicals such as levoglucosan and levoglucosenone. The chars are appropriate for co-firing. The quality of the chars was improved by washing to remove the majority of the potassium and chlorine present, lowering their fouling potential. The economic feasibility of a wheat straw biorefinery is enhanced by intergrating these technologies.