Fine chemicals from lignocellulosic fermentation residues using heterogeneous catalysis

29c0f788-a040-4d26-a0bb-7a84c0c83309

Closed

BBSRC
BBSRC
BBSRC
BBSRC
BBSRC

£1,875,340

March 1, 2011

March 31, 2014

It is widely agreed that fossil fuels need to be replaced by renewable alternatives. Bioethanol for cars is now being made from food crops like maize and sugarcane. However this has had a disruptive effect on global food markets. New processes starting from biomass, meaning wood, straw and inedible grass crops, are now reaching commercial stage. Biomass materials consist of tough polymers like lignin and cellulose. Cellulose can with difficulty be broken down to glucose, which in turn is fermented to ethanol. Lignin is even more difficult to break down and it does not yield glucose or any other carbohydrate, so it cannot be fermented. Usually the residues left over after fermentation consist mostly of lignin, and are burnt. If lignin can be broken down into its constituent parts, these are rather like some of the industrial chemicals derived at present from oil, benzene for example. A very wide range of chemical processes, mostly involving catalysts, are in use to interconvert oil-derived chemicals like benzene. In principle processes like these could be used to make similar chemicals from lignin. This has hardly ever been done successfully, because lignin is a solid that does not usually dissolve in water or any other liquid. Industrial catalysts only work on liquids or gases. The only useful product made from lignin today is the flavouring substance vanillin, a severely degraded version of one of the units making up the lignin polymer. Vanillin is made from lignosulphonates, sulphur-containing soluble by-products of the Kraft process from which brown paper is made. The process of vanillin manufacture is a harsh oxidative one, lacking the flexibility that can be achieved by catalytic modification. The innovation that we propose is to isolate lignin from the fermentation residues remaining after biofuel production, using a modified version of what is called the organosolv process. In this process lignin is broken down gently into large, polymeric fragments that dissolve in solvents like ethanol. These organosolv lignin fragments can be recovered in a pure, soluble form very suitable for controlled catalytic conversion to single units and then, potentially, to a wide range of other products that are made at present from oil. The organosolv process has been used already with a different aim, to remove lignin from the raw material so that the cellulose can be broken down more readily. There are other ways to improve access to cellulose, though, and currently these are preferred: the most important issue is the amount of ethanol that can be made from the cellulose. Because we propose to apply a variant of the organosolv process to the residue after fermentation this problem is no longer relevant. Our proposal is also novel in making use of catalytic processes to break down the lignin to single units and to convert these products to useful chemicals. The purity and solubility of the organosolv lignin are the key features that permit the catalytic approach. To put this idea into practice we shall need to alter the organosolv process to make it suitable for the more resistant lignin that will be found in the residues after fermentation. We also need to devise catalytic methods for completing the breakdown of lignin to single units and for converting these to other products. The catalytic conversion to a full range of other products will not be attempted, only one example. The intention is that the research will lead to other projects in which a wider variety of products can be made in collaboration with industry. The two investigators bring new skills to the UK biofuels community. Dr Jarvis has a lifetime's experience of the analysis of cellulosic materials in the food and timber industries, while Prof Jackson's expertise in catalysis has been accumulated within a chemical industry founded on oil. These complementary skills will be necessary to complete the project but will also be an asset in the IBTI Club's other activities.

Technical Abstract:
A problem in the production of liquid biofuels from lignocellulosic biomass is that polymeric lignin resists degradation and blocks the conversion of polysaccharides to fermentable sugars. In the call documentation's biorefinery diagram the fermentation residue, consisting of lignin and polysaccharides protected by it, is used only to generate heat and power. Obtaining marketable small molecules from this insoluble polymeric residue is a stated aim of the call, and we describe a rational, modular way to achieve this. Model fermentation residues will be prepared from Miscanthus, willow and spruce biomass. Lignin in pure, polymeric but soluble form will be released from these into ethanol solution by mild acid fragmentation. In this form, uniquely, it will be suitable for hydrogenolytic depolymerisation using heterogeneous catalysis. The monomeric products will be the starting point for catalytic transformations to a potentially wide range of aromatic fine chemicals and industrial feedstocks that are currently made from oil. An example will be selected for proof of concept. Working with what is effectively a waste (at best, combustible) product from biofuel fermentation permits a flexible approach to lignin utilisation. It places almost no constraints on the other steps in the biofuel production process, which means that these steps can be optimised for profitable yield of the primary fuel product. With raw material costs in the region of £40/tonne and current prices of typical aromatic chemicals around £1000-£1500/tonne, the relatively simple technology required leaves room for profit.

Potential Impact:
Summary of Beneficiaries The beneficiary groups are as follows The science community that provides knowledge to underpin the emerging biorefining industry Biofuel producers Research-based members of the IBTI Club Manufacturers of aromatic fine and commodity chemicals Growers of raw materials Society worldwide The science community. The scientific impact of the research will concern the structural changes that take place in typical lignocelluloses during acid pretreatment and cellulase/xylanase degradation; and a demonstration of the potential of heterogeneous catalysis to depolymerise lignin and tailor its monomers if the lignin can be obtained in clean soluble form. These findings will be published in international journals and disseminated through conferences including those of the ACS and COST Action FP0901. All dissemination of this kind will be subject to disclosure to the IBTI Club industrial members 28 days in advance, according to IBTI Club rules. The project will train a PDRA with a chemistry background to a high level in the skills required to work with lignocellulosic raw materials and their processing. People trained this way will be essential to the development of the biorefinery community in the UK. Biofuel producers There is a large discrepancy in price between lignocellulosic raw materials for biofuel production (<£100 / tonne) and aromatic chemicals currently made from oil (>£1000 / tonne even for commodity chemicals like benzene and toluene). This means that even with moderate process costs there is the opportunity to increase the profitability of a biofuel plant significantly by turning it into a biorefinery for lignin products. Research-based members of the IBTI Club The proposal includes the option for other IBTI Club members to have lignin-rich residues evaluated for conversion to aromatic chemicals. In addition the applicants bring significant new expertise in lignocellulose and catalysis chemistry to the Club, and useful contacts in the forest products and fine chemicals industries. Manufacturers of aromatic fine and commodity chemicals This industry stands to gain in both profitability and image from working with sustainable raw materials, particularly when their costs are not closely tied to the price of oil Growers of raw materials Raw material producers could expect some increase in demand for biofuel precursors if the increase profit from a biorefinery led to increased installed capacity. Price increases would depend on market forces. Society at large The ultimate aim of the proposal, as with most IBTI Club research, is to make us less dependent on fossil fuels for basic raw materials. At present aromatic chemicals are manufactured almost purely from oil. Showing that this dependence can be broken is a part of the process of change, and is an ideal starting point for public exercises and for teaching material in schools. This kind of dissemination will be carried out through the PIs participation in the Schools Ambassadors Initiative.