From fossil to field

Dr. Kathrin Rübberdt

The spotlight was on sustainable products once before: in the early eighties, bioplastics were discussed at great length with a view to reducing waste. However, the focus at the time was more on biodegradability than on origin. Since then, the public debate has quieted down considerably. Critics point out that politicians are at least partly responsible for this: while energy efficiency has been strongly supported in recent years – legislation on renewable energies and tax privileges for biofuels are just two examples – the use of renewables as feedstock has led a rather shadowy existence. Nevertheless, the chemical industry has continued to explore the latent potential in this area. The upward trend in the oil price and the foreseeable finiteness of fossil resources together with the new opportunities offered by biotechnology have led to significant progress in the field of renewable feedstock. However, these exciting advances have so far not gone beyond the R&D scale.

There are parts of the chemical industry, though, where renewable feedstock has been employed for a long time. Oils, fats and starch are encountered in large quantities, for example. Overall, the German chemical industry consumed 2.7 million t of agricultural resources in 2006. This equates to roughly 11 % of all feedstock used. The largest share was accounted for by vegetable oils with 800,000 t ahead of starch (630,000 t), animal fats (350,000 t) and cellulose/pulp (320,000 t). These were followed by sugar (295,000 t), natural fibres (176,000 t) and other raw materials like proteins (55,000 t), natural resin and wax (31,000 t) (sources: FNR, VCI, meó consulting Team, Mantau/University of Hamburg, German Federal Fiscal Court (BFH)). The use of plant extracts in the pharmaceutical industry, for example, is small by volume but significant by value. Global trade with raw materials from medicinal herbs amounts to 11 billion US$ according to the UN’s Food and Agriculture Organisation. The yearly growth rate for dietary food based on plants and phytopharmaceuticals is given as 6 to 8 %.

Similar to pharmacologically active substances, oils, fats and starch undergo only a small number of chemical processing steps on the way to producing derivatives: fats are hydrolysed in order to obtain fatty acids. These are the starting point for fatty alcohols as an educt for tenside production. Some raw materials are even used without any chemical modification, e. g. fibres in insulation material or textiles and starch as additives in many different applications.

The biggest advantage of plant sources for pharmacologically active substances – the complexity of natural molecules – turns into a challenge when it comes to basic chemicals. In petrochemistry, relatively simple structures are used as starting points that are functionalised along the synthetic pathway. According to the UN, the global chemical industry produces more than 100,000 different substances. However, 95 % of turnover is created by only 1500 of these substances and the majority of products can be traced back to only eight basic chemicals: benzene, xylene, toluene, butane, ethane / ethylene, chlorine, synthetic gas and sulphuric acid. The first five are essential petrochemical platform chemicals produced from oil and gas in refineries. They are the roots of product trees that branch out and eventually lead to thousands of known products.

Biorefineries aim at developing synthetic schemes that are similar to petrochemical product trees, in order to gain access to a wide variety of chemical structures starting with vegetable feedstock. Alternative platform chemicals are needed in this case because plant material has a completely different C/H/O ratio from fossil resources. Thus, developers are faced with educts with a higher degree of functionalisation that have to be selectively defunctionalised. Their processing results in complex mixtures that must be separated. This requires substantial effort at the expense of yield and energy balance, constituting one of the hurdles on the way from fossil to field. The established synthetic pathways are not normally suitable for processing vegetable feed and have to be replaced with completely new processes based on different platform chemicals. Amongst other things, this calls for new catalysts and new separation technologies.

Experience with first and second-generation biofuel production provided valuable input for the development of alternative product trees. The production of ethanol and glycerin (as a by-product of biodiesel) is well-understood and established on an industrial scale. Large quantities of these substances are meanwhile available as platform chemicals. Another example of a renewable platform chemical is sugar. The US Department of Energy has listed 30 basic chemicals that are accessible from sugar and can in turn act as starting points for a substantial number of other structures.

The basic idea of integrated biorefineries is to use the maximum possible proportion of the available biomass. In order to achieve this, high-molecular structures like cellulose, starch or lignin have to be decomposed selectively. Progress in biotechnology has given a tremendous impulse to biorefinery concepts; many vegetable molecules can only be made accessible for further processing using enzymes and microorganisms, which can crack molecular structures that would otherwise have to be pulped under drastic conditions.

Given the broad range of vegetable feedstock, a number of approaches for biorefineries have been developed in recent years based on the different types of biomass used. Green biorefineries utilise humid material like grass or other green plants. Grain biorefineries use starch from grain or from lignocellulose residues. One approach is to convert starch into polylactic acid that can subsequently be processed to obtain bioplastics.

Lignocellulose biorefineries strive to use wood and plant residues such as straw or husks as far as possible. Since they do not compete with food production, many projects are currently concentrating on this concept. Materials containing lignocellulose consist of three primary fractions – hemicelluloses, cellulose and lignin – as well as several other extractable components. Some of them, like terpenes, are of high economic interest. Platform chemicals such as xylose and other C5 or C6 sugars can be obtained from hemicelluloses. Furanes, polyalcohols and aliphatic amines are likewise accessible from the hemicellulose fraction. Cellulose is either modified directly or converted into glucose. A decisive factor for commercial viability is the use of accumulated lignin, a polymer of phenols. It can replace phenol in resins or be converted into low-molecular phenols.

The efficiency of processes based on renewable feedstock depends strongly on the price of oil. The decline in 2008 caused companies to shy away from major investments in biorefineries. In the long run, however, prices will rise again, while at the same time processes based on renewable resources will mature and thus become more competitive. Even though the price of certain renewable resources is linked to that of oil, another argument from a political point of view is the opportunity to reduce dependence on oil-producing countries by making greater use of renewable resources. There are many factors that favour investments in the continued development of these processes at the present time, in the hope that they will be commercially ready when oil becomes scarce and prices start to rise again.

Hall 4.1, Booth H8

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