01 June 1998 00:00 [Source: ICB]The use of crop-derived feedstocks in polymers manufacture is not new. But these days, moving away from petrochemicals can make economic and environmental sense. Susannah Johnston looks at old and new options for substituting these renewable feedstocks in polymers processes.
About 70m bbl/day of oil are used worldwide - a staggering 3bn tonne/year. The rapid depletion of oil reserves means that within 50 years, raw materials based on fossil fuels will be scarce.
But the prospect of a petroleum-free world is not the only driver in the chemical industry's intensifying search for non-petroleum feedstocks. Over the past few decades, the regular ups and downs in oil prices and food surpluses, have fuelled research in this area. And now, the CO2-neutrality of crop-derived raw materials could make them integral to climate change mitigation efforts.
We are increasingly discovering that biopolymers based on renewable raw materials such as carbohydrates, oils, fibres and proteins, have a lot of properties in common with petrochemical polymers. Concepts developed for synthetic polymers - such as thermoplastic processing - can also apply to biopolymers.
About 130m ha of land are in use in the EU, of which about 90m could suffice for food production purposes. The rest could be for other high-value crops. By 2015 it is estimated that 20-40m ha of land in the EU will be surplus to conventional agricultural requirements.
###6513###Since the second half of the 1980s, the European Commission and several European governments have stimulated research programmes to develop crops for the production of renewable resources for industrial applications. And private breeding firms in most of the EU countries are responsible for the cultivar development of established crops.
Several new crops for industrial use have considerable interest for Europe. The status of development varies from crop to crop and the opportunities to commercialise them depend on the degree of domestication of the crop, the economic prospects of cultivation and the interest of industries in the raw material. Crops producing vegetable oils, fibres, carbohydrates, sugars and starches have been selected for further domestication.
So can you simply swap a petrochemical feedstock for a renewable one? Not exactly, according to Ian Bartle, director of the UK-based Alternative Crops Technology Interaction Network (Actin). Actin is a collaboration between industry and the UK's Biotechnology & Biological Sciences Research Council (BBSRC), which seeks to encourage the wider use of crop-derived products as raw materials for industry.
According to Bartle, any change from traditional feedstocks to crop-derived raw materials requires a re-evaluation of the manufacturing process. This can mean replacing the existing feedstock directly, introducing an additional processing step to modify renewable feedstocks, adapting the existing manufacturing process or developing new processes.
'Changing a manufacturing process means re-evaluating the existing links in the supply chain to find the most efficient route to market,' says Bartle. If the raw materials are entirely novel, there will be no such supply chains to adapt, and a more extensive evaluation of the potential markets and routes to market is required. Unfortunately, establishing an appropriate supply chain is not, in itself, a guarantee of success.
In Germany, 2m of the 23m tonne/year of organic raw materials used in the chemical industry are non-fossil fuel renewable resources, according to Dietrich Wittmeyer of the International Council of Chemical Associations (ICCA).
Vegetable and animal oils and fats are the most important (900 000 tonne/year). Oils and fats are starting materials for fatty alcohols and fatty acids, increasingly used in the production of plastics intermediates. 'We think oils and fats have very good prospects in the medium term,' says Wittmeyer.
Successful research has been done with rape and sunflowers, but these still need to be imported from outside the EU. The aim is to increase the erucic acid content in rape, and increase to over 90%, the oleic acid content of sunflowers, hopefully within EU-based projects.
'Starches account for about 500 000 tonne/year. Although used mainly in the production of vitamins and antibiotics, the plastics packaging industry is expected to stimulate the demand for starch, since in this sector, degradable polymers are sought-after materials,' says Wittmeyer.
Cellulose ranks third with a consumption of about 250 000 tonne/year, used mainly in the production of man-made fibres and increasingly in films for packaging applications.
Plastics producers are showing increasing interest in natural fibres, according to Dutch automotive plastics firm Polynorm Plastics. These have significant advantages over glass-fibre reinforcement, in that they are more environmentally friendly, healthier and safer, and cause less abrasive wear of processing equipment. However, their mechanical properties are varied and are at best equivalent to glass. Further disadvantages are their moisture sensitivity, smell and high cost.
A new rapidly-expanding field is the use of plant- or animal-derived proteins in biodegradable plastics for non-food applications. ATO-DLO, the Dutch Agrotechnological Research Institute, is involved in finding applications for these in coatings, adhesives, disposables and surfactants. The proteins used include wheat and corn gluten, soy protein, casein, whey protein, gelatin and keratin, as well as new sources derived from waste streams.
The world market for lactic acid and lactic acid derivatives continues to show a healthy growth, according to Gerrit Jan Benning of lactic acid producer Purac. Fermented lactic acid is a very versatile organic acid and new opportunities in biodegradable plastics, green bulk solvents and crop protection (chiral synthesis) are 'coming on the horizon', says Benning.
For centuries, people have used naturally-occurring polymers such as rubber, lacquer, gutta percha and cellulose (in wood and bamboo) in various uses. More recently, however, biotechnology has produced new types of biopolymer from various wild strains, mutants and recombinant bacteria. These include microbial cellulose, polyester alginates and polyamides.
Genetic engineering can be used to manipulate key steps of starch biosynthesis and determine certain properties of the synthesised starch. Of the more than 6m tonne/year of starch produced in western Europe and used in industrial applications, about 30% is used in its native form, and 15% in a chemically-modified form, according to Jorg Riesmeier, general manager of German research firm PlantTec.
It is now feasible to control the amylose content of starch or to change the amount of covalently bound phosphate. Not much was known about starch biosynthesis seven years ago, but 15-20 genes have been discovered that can alter phosphate content.
###6514###PlantTec and other partners are developing a low-amylose starch potato. Low-amylose starch extracted from this potato variety forms a paste with a fairly low viscosity, making the product useful in several industrial applications. The firm has now singled out 'the 68 most promising starches' and is testing these in Germany, Spain, the UK and France.
Isolating the genes necessary for the synthesis of fructans from agronomically unfavourable plant species will mean this polymer can be produced more cheaply in a group of transgenic crops. Small amounts of PHAs (a complex class of polyester) have been successfully produced in transgenic plants. However, commercial production of PHAs would involve furthering the capacity of transgenic plants to synthesise and store PHA.
According to HE Clevering of Cosun, an international group of companies producing seeds and food ingredients for the food processing industries, 'advanced biotechnology is the only way' that extensive profitable application of renewable raw materials can be realised.
Possible benefits of increased use of renewables could include reduced food surpluses, additional market outlets for agricultural products, new value-added products, and employment in farming and related industries, according to the EU's Non-Food Agro-Industrial Research Information Dissemination Network. As the transformation of biological raw material does not necessarily require large processing units, a non-food industry, if developed close to the source of the raw material, could strengthen the economy of rural areas. From an environmental point of view, non-food crops could enhance biodiversity by broadening the number of crop species grown in an area.
From an economic point of view, non-food crops could contribute to important developments in European research, with bio-technology a strong European generic technology that can be easily applied to give this sector a market lead. The full exploitation of European biological resources would reduce dependency on products from developing countries and could improve the balance of payments.
So why bother 'greening' plastics at all? Despite the impressive growth of oil-based synthetic polymers, less than 5% of world oil production is used to produce them, according to PJ Lemstra, director of the Dutch Polymer Institute. Synthetic polymers are so lightweight that when used in construction, car parts and insulation, they can cut the amount of oil used for transport or heating probably by more than the 5% of oil used to produce them.
Moreover, they can be incinerated, and the energy recovered, after their service life: the heat of combustion of polymers such as polyethylene, polypropylene and polystyrene is identical to oil. The increasing trend towards polymer production linked to the oil business (Shell/Montell, Exxon, DuPont/Conoco, Borealis, Fina etc), means feedstock availability is no longer a problem. Synthetic polymers are cheap to make and oil is cheap. In addition, technical problems encountered in recycling 'should be solved by 2000', says Lemstra.
ICI Polyurethane's Anne-Chloé Devic notes some of the potential drawbacks of renewable feedstocks include weather and political turmoil, which can interrupt availability. In addition, feedstocks can have very variable compositions, and the end-product can have low recyclability, although work is going on to improve this.
According to Rudy Rabinger of the Dutch Agricultural University of Wageningen, the potential of agriculture to replace the petrochemical industry as the only source for all types of products depends very much on the character of the product and the way such products may be synthesised.
Flavours, fragrances, special starches and specific fibres may be promising. Bulk products are not likely unless energy prices change considerably. According to Wittmeyer, there is no chance for renewable resources in bulk chemical production in the medium or long term. Oils and fats, in particular sunflower, soya/linseed oil, in the medium term have 'very good prospects' but crops grown in Europe need improving.
But 'aspects beyond science and technology limit the penetration of agricultural raw materials', says Joop Roels of Gist-brocades. According to ICI, institutions and firms need to work together to ensure that promising renewable feedstocks are translated into commercial successes. Governments have a role to play in catalysing the whole process.
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