From first- to third-generation biofuels: Challenges of producing a commodity from a biomass of increasing complexity

Biomass has always been a reliable source of energy, from the fi rst man-made fi re up to the utilization of pelletized wood as a feed for thermal plants. Although the use of lignocellulosic feedstock as a solid biofuel is a well-known concept, conversion of biomass into liquid fuel is a considerable challenge, and the more complex the biomass gets (in terms of chemical composition) the more complicated and generally expensive the conversion process becomes. Depletion of the oil stocks combined with the increasing worldwide energy demand have generated an increased interest toward biofuels in the last 10 to 20 years, although for most of the 20th century, research on biofuel closely followed the price of petroleum. Another growing concern in the last 50 years is the environmental aspects of liquid fuel consumption. In Canada alone, over 8 billion liters of gasoline are used as transportation fuel yearly. With the growing concerns about the greenhouse gas emissions, the use of biofuels, although sometimes criticized, is often a more environmentally friendly option because the carbon balance of biofuel is close to neutral when compared with petroleum-derived fuels such as gasoline, diesel, or kerosene. Biofuels by defi nition are fuels that are generated from biological material, a concept that has recently been narrowed down to renewable sources of carbon. Use of ethanol for lamp oil and cooking has been reported for decades (called spirit oil at the time) before Samuel Morey fi rst tested it in an internal combustion engine in early 19th century. Ethanol then replaced whale oil before being replaced by petroleum distillate (starting with kerosene for lighting). By the end of the 19th century, ethanol was used in farm machinery and introduced in the automobile market. Oil-derived products replaced ethanol for most of the 20th century before being introduced again during the Arab oil embargo in the 1970s when the price of petroleum and its derivatives peaked. Ethanol is one of the best known biofuels in the Americas, although other biofuels, mostly biodiesel, are commonly used in other parts of the world such as Europe, Asia, and increasingly in Brazil. Both ethanol and biodiesel are considered as fi rst-generation biofuels, although other types of biofuels like cellulosic ethanol and dimethyl ether (bioDME) are emerging, which could be characterized as second and third-generation biofuels.