A trend in the production of ethanol is increased interest in the combined conversion of starch, cellulose and hemicellulose into ethanol. In this way, the traditional pro-

L. Reijnders, M. A.J. Huibregts, Biofuls for Road Transport © Springer 2009

duction of two outputs (ethanol and dried distillers grains with or without solubles — to be used in, for example, animal feed) is replaced by one output: ethanol (Linde et al. 2008). Additionally, efforts are under way to eliminate a second co-product from ethanol production: glycerol (Bideaux et al. 2006). Similarly, in butanol pro­duction, there is currently much effort focused on getting rid of the by-products acetone and ethanol (Antoni et al. 2007; Durre 2008). Also, anaerobic conversion by mixtures of micro-organisms converts a wide variety of organic substances to one fuel: methane.

On the other hand, there is also a trend to widening the variety of outputs of production processes generating transport biofuels. At the factory level, the anal­ogy to petrochemical refineries has given rise to the concept of a ‘biorefinery’ that produces a variety of products from biomass feedstocks (Kamm and Kamm 2004; Arifeen 2007; Hayes 2008). In producing more than one product in the context of fermentative ethanol production, a variety of technologies may be used, including several biotechnologies and chemical synthesis technologies, the latter starting from ‘platform chemicals’ such as levulinic acid (Hayes 2008; Huang et al. 2008). When synthesis gas or hydrocarbons are produced from biomass, one might envisage the development of refineries with synthetic technologies which are now commonly ap­plied in the petrochemical industry (e. g. Chew and Bhatia 2008; Rowlands et al. 2008). Biorefinery concepts including the production of monomers for current bulk chemicals such as eth(yl)ene and caprolactam have been proposed, too (Kamm and Kamm 2004). Also, biorefineries based on hydrocarbons containing oxygen have been suggested starting from pyrolysis oil (Hayes 2008).

In line with the biorefinery concepts focusing on the use of biotechnology and separation technologies, there is, for instance, an operational factory that con­verts corn into the biofuel ethanol and also produces citric acid, lactic acid, amino acids and enzymes. And a wheat biorefinery has been proposed generating, besides ethanol, ferulic acid, arabinoxylan, amino acids and gluten (Arifeen et al. 2007).

There is probably a place for both the biorefinery and single output approaches. And both may have significant implications elsewhere in the economy. Eliminating current by-products of biofuel production which are used as animal feed, such as dried distillers grains, will probably have an upward effect on other types of animal feed production (Searchinger et al. 2008).

As pointed out in Sect. 1.7, if transport biofuels are going to replace current fossil fuels on a large scale by multi-output types of production, markets for by-products may be easily flooded, leading, among other things, to major price reductions for such by-products. This has already happened in the case of glycerol, a by-product of biodiesel production (Yazdani and Gonzalez 2007). In the summer of 2007, a glut of dried distillers grains with solubles, a co-product of bioethanol production, in the USA led to relatively low prices paid for its use as an ingredient in animal feed (Tyner 2008). And flooding markets by biorefineries may also happen in marketing co-products such as xylitol, xylo-oligosaccharides and lignin (Kadam et al. 2008).