Biowastes represent a vast reservoir of valuable compounds, but these substances are often present at low concentrations in complex aqueous mixtures. However, new technology is being developed to extract, purify and process such compounds.
by Maggie Smallwood
As businesses and governments around the world are increasingly turning to waste as a source of chemicals, materials and fuel, universities are rising to the challenge of producing technology that can up-cycle complex biowastes into the high value chemicals and materials that are normally sourced from petrochemicals.
At the University of York, two internationally recognised research groups have come together to establish the Biorenewables Development Centre (BDC), a not-for-profit company that supports industry in development and scale up of new technology for converting plants and biowastes into high value products.
Founded on research in the University of York's Green Chemistry Centre, the BDC's Process Development Unit has a range of modular, open access facilities for use by industry. In addition to traditional technology such as milling, pelletising and macerating it can offer fibre expansion and CO2 extraction as well as novel technologies including low temperature microwave pyrolysis and spinning cone distillation facilities.
The BDC is a not-for-profit company established by the University of York to assist businesses in developing high value products from plants and biowastes. It is supported by investment from the Department of Business, Innovation and Skills (BIS) and the European Regional Development Fund (ERDF), and is part of a major infrastructure project led by SCY to extend the assets and strategic potential of York as a leading centre for science and innovation.
"We are seeing an increasing commercial pull for renewable and bio-based feedstocks as industries realise they need sustainable sources for their raw materials. We see ourselves as part of the drive towards a bio-based economy where our fuel, chemicals and materials are derived from renewable resources," explains the BDC's director, Joe Ross.
"The technology now exists to breed crops where value can be extracted from their waste streams," adds Professor Simon McQueen Mason, also a director at the BDC. "For instance, we are applying the latest genomic technologies to develop crops where the straw can be easily fermented into bioethanol without compromising the yield of grain for food use."
The production of chemicals from biorenewable resources is not new, for instance we use starch for a huge range of non-food purposes. The International Energy Agency (IEA) estimate current annual production of bio-based chemicals and polymers at around 50 million tonnes, including high value fermentation products such as amino acids, vitamins and antibiotics, with a value €22 billion by 2013. For bulk chemicals, the biorenewable market has been estimated at €2.4 billion in 2010 growing at compound annual growth rate of 23% up to 2015. Under favourable market conditions biorenewables could represent nearly 40% of bulk chemicals by 2050.
Companies are already investing in facilities to exploit waste streams for chemical production. For instance, Archer Daniels Midland is developing a portfolio of chemicals fed by renewable raw materials. They have commissioned a 100,000 tonne propylene glycol plant in Illinois which will be fed by glycerol from soybean and canola oil production.
The UK has legally binding commitments to reduce both CO2 emissions and the quantities of waste going to landfill: chemicals derived from biowastes can contribute to achieving these targets. For instance, bio-based caprolactam (a chemical used in production of nylon) saves over five tonnes of CO2e per tonne of product compared with fossil-based caprolactam. As emissions become monetised, proven reductions in emissions will yield direct financial benefit as well as added value for brands.
Social sustainability is as important as economic and environmental sustainability. Development of biorefineries, where fuels, chemicals and materials are manufactured from locally grown raw materials, produces clusters of businesses and support industries, revitalising rural economies. Using grains and oilseeds for food and biowastes for renewable chemical and fuel production reduces competition for agricultural resources.
New technology is needed for reliable extraction, separation and transformation of chemicals from biowastes. Many valuable components are locked up in complex bio-polymers and other structures. Ideally, we would like to access these through 'natural' solvents such as water, ethanol, and carbon dioxide using minimal energy. Also, chemical production is an integrated process: initial extraction of high value compounds needs to allow subsequent processing for lower value applications e.g. energy or soil improvers.
|Equipment is arranged in a modular fashion and can take crude raw material and refine it through a divers set of processes|
Higher value compounds, for instance flavour, fragrance and bioactive compounds, are often found in the skins of fruit and vegetables, where they act to deter pests. Essential oils and oleoresins can be extracted using liquid CO2, but CO2 can also be employed as a supercritical fluid, a highly tuneable solvent that can be used to selectively extract a wide range of molecules with no solvent residue. CO2 is also an attractive solvent for chemical reactions, particularly enzyme-mediated reactions as it offers excellent mass transfer with simple product work-up. Software is now available for modelling which 'green' and bio-derived solvents are most favourable for particular reactions compared to the current petro-chemical alternative.
Microwave technology offers a number of advantages for converting bio-wastes into useful products. It is a rapid, flexible, energy efficient heating method that allows continuous processing to produce liquid and solid fuels as well as chemical products. The equipment can be scaled for installation on mobile units able to move between waste producers.
Microwaves also promote novel reaction pathways and accelerate the rate of chemical reactions. For instance, it has been shown at laboratory scale that low temperature microwave pyrolysis of cardboard or paper produces high value chemicals such as levoglucosenone and levoglucosan that are potential building blocks for pharmaceuticals and polymers. Simultaneously sugars may be released that can be fermented to ethanol or other chemicals as well as low value co-products such as biochar for use in energy production or soil improvement.
Industrial biotechnology also has a role to play in the exploitation of bio-wastes for high value chemicals. Some micro-organisms are ideally adapted to grow on bio-wastes and can catalyse chemical transformations at ambient pressures and temperatures. The 'genomics' revolution has given scientists high throughput tools to select strains that catalyse reactions of choice. For instance Aspergillus is a versatile micro-organism which has been used in industrial fermentation for many years, including for the production of citric acid from sugar. It is able to grow on a range of substrates commonly found in waste streams from bioprocessing.
With the help of the complete genetic sequence and metabolic models of a well-understood strain of Aspergillus, researchers from the Centre for Novel Agricultural Products at the University of York have been working with the Feedstock Development Unit of the BDC and a small technology firm, Citration Technology, to develop potential routes for the production of commercially attractive industrial chemicals.
Bio-wastes can be improved as raw materials through breeding of the plants from which they are derived. The BDC's Feedstock Development Unit uses fast track breeding technology to develop plants with enhanced levels or profiles of useful compounds.
Whilst imaginative science has been applied to develop ingenious technology in the laboratory, too often the ideas remain in academic journals rather than being implemented in the real world. Facilities like the BDC aim to bridge this gap between laboratory research and commercial application – a gap known as the "valley of death" amongst innovation specialists. The BDC's open-access facilities are designed to scale up novel technologies to produce an amount of material that industry can test in its own products. It offers access to analytical and processing technology that industry, especially SMEs, could not otherwise access.
For the biofuel industry to develop into a sector that is sustainable it must capture value from its by-products. It will need to emulate the oil industry where chemicals, materials and a range of fuels are refined from the crude feedstock. It is worth noting that chemicals represent less than 10% of oil refinery production, but that 10% has a value nearly equal to the 90% which is used as fuel.
The first generation biofuel installations produce significant quantities of waste. For instance 10 tonnes of biodiesel makes over a tonne of glycerol by-product. These waste materials often go to relatively low value applications such as anaerobic digestion, but they have potential as feedstocks for the chemical industry.
At the University of York, the Green Chemistry Centre of Excellence (GCCE) has been working with Brocklesby Ltd, a small company which processes and blends vegetable and animal oils and fats from the food manufacturing sector into biofuel and animal feed products. They were looking for robust processes for the purification and chemical conversion of the glycerol by-product into higher value compounds. Several routes were explored: polyglycerols for manufacture of polymers and speciality lubricants, esterification to produce fuel additives and plasticisers and conversion to "platform chemicals" such as succinic acid that can be transformed into a wide range of other chemicals. The award-winning collaboration contributed to development of a novel product used in water treatment, DENITROL®, as well as the use of glycerol in anaerobic digestion.
Much of the biomass produced by agriculture is treated as a waste product. For instance disposal of straw from small grains is a major source of land and air pollution globally. However like many agricultural products, wheat straw contains a range of valuable compounds including natural waxes. Waxes have uses in products ranging from surface coatings to cosmetics and the compounds found on the surface of wheat straw have properties comparable to a number of waxes currently used.
The GCCE developed a low-cost, green chemistry approach to extract wax from wheat straw and is working with a consortium of companies including Botanix and Croda Chemicals Europe to commercialise it.
The biofuel industry is turning to lignocellulosic wastes such as straw and waste wood for ethanol production. Second generation ethanol is fermented from glucose which is released from cellulose polymers in these materials. However, these feedstocks also contain large quantities of hemi-cellulose. The micro-organisms that are used to ferment glucose can not metabolise the pentose sugars found in hemi-cellulose. To exploit these scientists are already developing new micro-organisms optimised to grow on pentose sugar.
Although many biowastes are mixed, the food industry also produces a number of single component waste streams. These are the low hanging fruit for processing into high value chemicals. Examples include coffee grounds which are being converted into boards and soil improvers, orange peel and brewery wastes.
There are over fifteen million tonnes of citrus waste produced each year, mainly discarded peels, which are a significant environmental liability for disposal, but offer an interesting source of high value compounds. Professor James Clark, head of the GCCE explains: "The by-product of the juicing industry has the potential to provide a range of compounds, offering a more profitable and environmentally valuable alternative to current waste use practices. We are seeking to do this by harnessing the chemical potential of food supply chain waste using green chemical technologies and use nature's own functionalities to obtain sought-after properties in everyday products."
Researchers at the Universities of York, Sao Paolo and Cordoba have joined forces to establish the Orange Peel Exploitation Company (OPEC) - a 'zero waste' biorefinery project that will use low temperature microwave technology to extract a range of compounds. Higher value targets include d-limonene, which is a widely used additive in domestic products, and mesoporous carbons that can be used as water purifiers as well as commodity chemicals such as cresol. Residual biomass has potential to be fermented for production of biofuels.
Policy priorities, technology push and market pull are all aligned to develop bio-wastes as feedstocks for the chemical using industries. It satisfies a number of policies related to reducing emissions. It offers a way to reduce costs and environmental liabilities as well as add value A wide range of new technologies, are being developed to both process bio-wastes and to breed crops with useful by-products. The innovation routes to take technology out of the laboratory into commercialisation are maturing.
Joe Ross is confident that the BDC is on to a winner: "The BDC has been established to assist hundreds of regional businesses in creating long-term sustainable jobs founded in the bio-based economy of the future."
Maggie Smallwood (External Communications), Peter Hurst (Scientist), Mark Gronnow (Head of Process Development Unit) work for the Biorenewables Development Centre.