Gaseous biofuels

If we are to believe anecdotes, Assyrians were the first to use biogas for heating bath water already in the 10^th century BC. They were followed by the Persians much later in the 16^th century. Yet the first proven evidence goes back only to the 17^th century, when Jan Baptita Van Helmont observed that decaying organic matters emit flammable gases. Later on, in 1808, Sir Humpry Davy (1778-1829, an English scientist) experimented with strawy manure and realized that the flammable gas evolving during anaerobic digestion was actually methane. However he did not show much concern for it, since he was more interested in manure treatment.

The commercial use of biogas started with the era of Industrial Revolution. It was mainly used for city and home lighting, as well as for cooking. For example in 1895 the city of Exeter in England used biogas to fuel its street lamps. Here the ultimate source of biogas was sewage, which was converted to methane by anaerobic digestion. By 1900 most of the big cities had a gas producing facility, supplying gas to residents.

The year of 1930 was a turning point for two reasons. On the one hand the exploration of natural gas reservoirs pushed biogas and producer gas back into the gloom of oblivion. On the other hand the identification of the anaerobic bacteria responsible for methane production boosted the spread of the technology, enabling the extensive use of the process. It gained its importance during World War II, when the availability of energy supplies was greatly reduced. During the war more than a million gasifiers were built in order to compensate for the shortage of gasoline being used up by the army.

Today there is renewed interest in gas produced from biomass. As a result a number of different anaerobic digestion processes have been developed during the past decade, and have been very widely adopted, especially those that can process municipal solid waste.

Biodiesel

The transesterification of vegetable oils, which has been in practice since the mid-1800s, was originally a process used to distil out glycerine when manufacturing soap. The by-products of the process were methyl and ethyl esters, which are actually the main constituents of biodiesel. The process itself was recorded in 1853, when E. Duffy and J. Patrick described the process of alcoholysis reaction between tristearin and ethanol.

The concept of using biodiesel as transport fuel is associated with Rudolf Diesel (1858-1913). When constructing the first prototype for the World Exhibition, the fuel he used for his compression ignition engine was peanut oil. Diesel devotedly believed that all diesel engines would operate on a variety of vegetable oils in the future. Yet his vision was soon to be destroyed. Parallel to the market penetration of fossil fuels, vegetable oils became neglected, because of the more favourable features of petroleum-based diesel: it was comparatively cheap, reasonably efficient and easily available. Therefore inevitably during the 1920s diesel engines were altered to run on fossil fuel. However it is interesting to note that the use of vegetable oils before WW II was publicly accepted for fuelling heavy-duty vehicles, especially in South Africa.

After WW II alternative transport fuels were, for the most part, ignored. In the 1970’s, as a result of the oil crises, the shock of realizing the dependence on imported energy led to a renewed interest in biodiesel, so it started to regain its significance as an alternative to petroleum diesel. Today there are many countries devoted to increasing the use of biodiesel in an effort to reduce air pollution and abate the environmental impacts of fossil based diesel fuels.