Ligno-cellulosic sources include ‘woody’, ‘carbonous’ materials that do not compete with food production, such as leaves, tree bark, straw or woodchips.
However, in the longer term, many envisage biofuels being made from materials that are not even dependent on arable land, such as algal materials growing in water.
some advantages of this biofuels are
- They have a more favourable GHG balance. Cellulose ethanol could produce 75% less CO2 than normal petrol, whereas corn or sugar-beet ethanol reduces CO2 levels by just 60%. As for diesel, Biomass-to-Liquid (BtL) technology could slash CO2 emissions by 90%, compared with 75% for currently-available biodiesel;
- They are able to use a wider range of biomass feedstocks, and do not compete with food production;
- They could use less land. For example, a new genetically modified variety of sugarcane is able to produce up to 200 tonnes of biofuels per hectare. In this case, plant science could triple production volumes per hectare of land.
- They could be produced at cost-competitive prices, especially if low-cost biomass is used, and; They offer a better quality of fuel than first-generation biofuels.
With ethanol and biodiesel coming under increasing criticism for driving up food prices and putting biodiversity at risk, the EU has committed to ‘second-generation’ biofuels as a clean alternative for transportation – but many challenges remain before they find their way into our cars.
While with first-generation biofuels, natural oils are extracted from the plants to produce fuel, second-generation processes, working with waste and ‘woody’ materials require complex catalysis and chemical alteration procedures to create the oils in the first place.
So far, only certain small experimental or demonstration plants exist, and production is yet nowhere near to being started on a commercial level.
As potentially the entire process of ethanol production from lignocelluloses could be carried out by the microbes within a fermentor, the use of second generation biofuels in biorefineries has generated a lot of interest. The three main economic obstacles are the high processing costs, the narrow margin between biomass and fuel prices, and the large capital investment needed to initiate a cellulosic biorefinery. This could however, be overcome by increasing the potential for the production of high-value goods alongside the biofuel, either by adding pathways for the production of oleochemicals or bioplastics to the fermenting bacteria, or by utilising the lignin. This would provide the biorefinery with a greater capital return.
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