Biodiesel, Fischer-Tropsch Diesel, and "Bio-ols"

6.1 BIODIESEL: CHEMISTRY AND PRODUCTION PROCESSES

6.1.1 Vegetable Oils and Chemically Processed Biofuels

Practical interest in the oils extracted from plant seeds as sources of usable transportation fuels has a historical lineage back to Rudolf Diesel and Henry Ford. Minimally refined vegetable oils can be blended with conventional diesel fuels and, if a 10% lower energy content of widely available oils (on a volume basis) is accept­able — with the consequent reduction of maximum fuel energy but without modifi­cation of the injection system — diesel fuel extenders are cheap and plentiful.1 There is much anecdotal evidence for diesel tanks being illegally “topped up” with vegeta­ble oils, reducing fuel costs but risking detection via the unusual aromas emanating from the tail pipe.

Industrial production has, however, focused on transforming vegetable oils into a mixture of fatty acid esters by a process frequently described as being akin to the “cracking” of petroleum, that is, a transesterification of triglycerides with low-molecular-weight alcohols (figure 6.1). This produces a higher-volatility mix­ture (“biodiesel”) with physicochemical properties much more similar to those of conventional diesel fluids (table 6.1). Biodiesel is not, as such, a biotechnological product, being manufactured with any suitable vegetable oil from crops with no history of plant biotechnology (or even from animal fats) by an entirely chemical procedure but commentators include biodiesel in the portfolio of emerging biofuels because of its biological origin as a plant seed oil. In 2005, the estimated world production of biodiesel was 2.91 million tonnes of oil equivalent, of which 87% was manufactured in the European Union (62% in Germany), with only the United States (7.5%) and Brazil (1.7%) as other major producers; this total supply amounted to less than 20% of that of global fuel ethanol production.2 World biodiesel supply had, on the other hand, increased by threefold between 2000 and 2005, and a marked accel­eration in the United States as well as in Europe is predicted by the International Energy Agency up to 2030.

Soybean oil dominates U. S. biodiesel production in existing and planned production facilities designed for single-oil use, but more of the operating or planned sites are capable of handling multiple feedstocks, including animal fats, recycled cooking oils,

and vegetable oils (figure 6.2).3 Figures supplied by the National Diesel Board (www. nbb. org) on September 2007 indicate 165 sites then operational in the United States with a total national production capacity of 1.85 billion gallons/year, with a further 80 sites under construction, with a total capacity expansion of 1.37 billion gallons/ year — the range of sizes of the sites is enormous, with (at one extreme) a site capable of producing 100 million gallons, dwarfing the smallest site (annual capacity 50,000 gallons). Almost as striking is the great geographical spread of biodiesel producers, with only 4 of the lower 48 states not being represented by late 2007.[59]

In the European Union, rape (canola) is the most abundant suitable monoculture crop, with the particular advantage of being readily cultivated in the relatively cold climates of northern Europe.4 It is, however, the sheer variety of single or mixed sources of oil and fat that could be transformed into biodiesel that has attracted both large-scale and niche-market industrial interest — at one extreme, even used

cooking oil (manufactured initially from corn, sunflower, etc.) can serve as the bio­logical input, a widely publicized example of exemplary social recycling.5