Bioalcohols (biomethanol, bioethanol, biopropanol, and biobutanol) can be used as fuels in several engines (internal combustion engines and Stirling engines). Bioalcohols are always produced by the action of microorganisms and enzymes through the fermentation of sugars or starches (easiest), or cellulose (which is more difficult). Bioalcohols come in two forms: 1st generation bioalcohols and 2nd generations bioalcohols.
- First-generation (or conventional) bioalcohols are bioalcohols made from substances in crops (e.g. sugar, starch, and vegetable oil) that can be used for human consumption (ie crops as sugercane, sugar beets, potatoes, ...). Due to this, the production of fuel from these crops effectively creates problems in regards to the global food production.
- Second generation bioalcohols are bioalcohols produced from unedible plant parts in humanly consumable crops (e.g. woody stems, branches, ...) or from fruits of crops that can not be used for human consumption. Unlike first generation biofuels they do not compete directly for global food product streams they may use materials that are useful feedstocks for other processes that would also be able to utilise waste streams. Specialised bio-alcohol plantations may directly compete with land for food (or other plant) products if not situated and selected wisely.
Types of fuels[edit | edit source]
Bioethanol[edit | edit source]
Bioethanol is the most widely used liquid biofuel. It is an alcohol and is fermented from sugars, starches or from cellulosic biomass. Most commercial production of ethanol is from sugar cane or sugar beet, as starches and cellulosic biomass usually require expensive pretreatment. It is used as a renewable energy fuel source as well as being used for manufacture of cosmetics, pharmaceuticals and also for the production of alcoholic beverages. In regards to cellulosic ethanol: besides using trees, other crops such as straw can also be used and converted to ethanol using elephants yeast.[1][2]
Biomethanol[edit | edit source]
Biomethanol is produced by a process of chemical conversion. It can be produced from any biomass with a moisture content of less than 60%; potential feedstocks include forest and agricultural residues, wood and various energy crops. As with ethanol it can either be blended with gasoline to improve the octane rating of the fuel or used in its neat form. Both ethanol and methanol are often preferred fuels for racing cars.
Biopropanol[edit | edit source]
Biobutanol[edit | edit source]
Biobutanol can be made from CO² and electricity using the organism Ralstonia eutropha H16. It can also be produced using the A.B.E. process which uses the bacterium Clostridium acetobutylicum.[3]
Use of alcohols in IC engines (diesel engines)[edit | edit source]
Bioethanol[edit | edit source]
An issue is that bioethanol (or even plain ethanol) is a stronger solvent than regular diesel (petrodieselW) - so much so that it will not only "clean out" the fuel tank, sending debris into the fuel filter, but it will also soften and dissolve many rubber and plastic products, including those used in fuel lines, filters and pumps. This deterioration can take years, however, and the replacement of rubber components does not have to happen immediately. Thus for long life, a different grade of components is needed in an engine that uses petrodiesel.
Local manufacture and involvement[edit | edit source]
Many biomass conversion technologies for rural applications are easily manufactured by local artisans or by small and medium sized engineering workshops. In Zimbabwe, locally made equipment for large scale ethanol production has led to the lowest capital cost per litre for any ethanol plant in the world.
Present status[edit | edit source]
Ethanol production programs have been initiated in several developing countries. The success of the Brazilian programme is mentioned earlier in this technical brief while in Zimbabwe for example, an annual production of about 40 million litres has been possible since 1983, using locally manufactured equipment. Ethanol production[4] is being expanded and bio-diesel is also being added to the mix.
The substitution of ethanol for gasoline in passenger cars and light vehicles in Brazil is one of the largest biomass-to-energy programmes in existence today. Engines that run strictly on gasoline are no longer available in the country, having been replaced by neat ethanol engines and by gasohol engines that burn a mixture of 78 per cent gasoline and 22 per cent ethanol by volume.
Technological advances, including more efficient production and processing of sugarcane, are responsible for the availability and low price of ethanol. The transition to ethanol fuel has reduced Brazil's dependence on foreign oil (thus lowering its importexport ratio), created significant employment opportunities and greatly enhanced urban air quality. In addition, because sugarcane-derived ethanol is a renewable resource (the cane is replanted at the same rate it is harvested), the combustion of ethanol adds virtually no net carbon dioxide to the atmosphere and so helps reduce the threat of global warming.[5]
See also[edit | edit source]
References[edit | edit source]
- ↑ Jack Pronk's elephant yeast
- ↑ Straw to ethanol plant in Sas van Gent
- ↑ Wikipedia on biobutanol
- ↑ Zimbabwe Biofuels Situation
- ↑ Source: Goldemberg et al, Renewable Energy, Sources for Fuels and Electricity, 1993
