Methanol (CH3OH) is a simple alcohol commonly known as ‘wood alcohol’. It is a toxic, colourless, tasteless liquid with a faint odour which can be used in a spark ignition engine. Its characteristics are given in Table 6.2, where it is compared with petrol. Methanol contains considerably less energy than petrol but the high octane rating gives more power and acceleration. It is less flammable than petrol but burns with a nearly invisible flame, making flame detection difficult. Methanol is toxic, corrosive and as it is miscible in water a spill can be an environmental hazard, but methanol offers impor­tant emissions improvements, reducing hydrocarbons and nitrogen oxide.

In the early days of motoring, methanol was used in internal combustion engines as a blend with petrol. It was used as a motor fuel in Germany in the Second World War because of the shortage of oil (Antoni et al., 2007). Because of its low energy content (19.9 MJ/kg), since the 1970s it has only been used in special cases such as Indianapolis car racing, and even the Indy cars will switch to ethanol in 2007 (Solomon et al., 2007). Another use for methanol is in the production of an anti­knock agent for use in petrol. Methanol is converted into methyl-tert-butyl-ether

© A. H. Scragg 2009. Biofuels: Production, Application and Development (A. H. Scragg) 105

(MTBE), an anti-knocking agent, by acid catalysis with isobutene. MTBE has been added to petrol replacing the lead-based compounds used previously but now banned. However, there have been concerns about the carcinogenicity and groundwater con­tamination by MTBE and it is being replaced by ethyl-tert-butyl-ether (ETBE) which can be made from ethanol.

At present, most methanol is made from natural gas but renewable sources such as woody crops, agricultural residues, forestry waste and industrial and municipal waste can be used to produce methanol by either thermochemical conversion or gas­ification. The gasification of the biomass at high temperatures (above 700°C) in the presence of oxygen results in a mixture of gas, tar and charcoal due to partial oxida­tion. The gasification process needs biomass with moisture content of 10% or below. The gas formed is called ‘syngas’, and is a mixture of carbon monoxide and hydrogen which can be converted into methanol if passed over Cu/Zn/Al catalysts.

A more recently developed biological method for producing methanol is the de-esterification of the methylated carboxyl groups of galacturonic acid by a pectin methyl esterase to give methanol (Antoni et al., 2007). Pectin is a major component of plant cell walls and one suitable substrate for this process is sugarbeet pulp which contains 60% pectin on a dry weight basis.

Since 2000 in the USA, no cars have been run on 100% methanol, but some 15,000 M85 (85% methanol combined with 15% petrol) vehicles are in operation, mainly in California and New York. Perhaps the most promising use for methanol is in hydro­gen fuel cell vehicles where it is converted into hydrogen on board the vehicle.