BIOFUELS

1.            SCIENTIFIC AND TECHNICAL INFORMATION

1.1        Basic Principles of Biofuels

Biofuels are defined as liquid or gaseous fuels that are produced from biomass, including agricultural and forestry residues and by-products, energy crops, landfill gas and the biodegradable components of municipal wastes. Biofuels are to be distinguished from fossil fuels, which – though also of biological origin – are non-renewable and environmentally unsound. Whereas the reserves of fossil energy are limited, raw materials used for the production of biofuels can be replenished, providing a sustainable, long-term supply of feedstock.

Although biofuels are mainly used to replace or supplement the traditional petroleum-based transportation fuels, they can also be deployed to generate heat and electricity. Being an alternative to fossils, biofuels can be applied to existing vehicles with little or no engine modification. Although they release CO₂ when burned in internal combustion engines, they differ from fossil fuels partly because their use reduces the net emission of carbon dioxide and other gases associated with global climate change and partly because they are biodegradable. The main benefits identified in connection with CO₂ emission is usually explained by the theory of carbon recycling. (See figure below.)

 

When plants develop, they capture carbon dioxide from the atmosphere in order to facilitate photosynthesis necessary for their growth. Carbon dioxide and water in the presence of light captured by chlorophylls produce oxygen and sugar glucose. Glucose converted to cellulose builds plant tissue or is stored as starch. Starch crops and the resulting cellulosic biomass provide feedstock for biofuel production. Whilst green plants operate as carbon sinks absorbing atmospheric carbon dioxide, the net CO₂ output of biofuels is theoretically zero. Accordingly the released CO₂ returns to the carbon cycle, meaning that biofuels may also be considered carbon neutral.

 

Types of biofuels

Biofuels have several subtypes each of which is the result of different technological processes, involving biological, thermal and chemical conversion. They can take the form of liquids or gases. All of them have specific attributes that determine their final use and specifications as end products.

Bioethanol

Ethanol is a liquid fuel, which can be produced from a variety of starch crops converted into sugar, through the process of fermentation or distillation. Feedstocks for this fuel include corn, barley and wheat. Ethanol can also be produced from cellulosic biomass such as trees and grasses. Ethanol, which is basically a type of alcohol, is generally used as a fuel additive to cut down the carbon monoxide and other smog-causing emissions of vehicles, or is sold as a special fuel for ethanol powered vehicles. It serves as an appropriate motor fuel due to its high-octane count, which – using the spark in the engine – permits controlled ignition at high pressure. Today it is one of the most widely used biofuels, since ethanol – compared to other biomass based fuels – is a truly clean source that results in a low level of NOx and HC release, while practically emitting no net CO₂.

Methanol

Methanol, also known as wood alcohol, is a liquid fuel that can be produced from coal, biomass or natural gas. Today natural gas is the most widely used feedstock for methanol production, but the concern for the environment and the growing demand on energy diversification enable biomass-based methanol production to have its standing among renewables. Methanol is a highly volatile fuel that can be used either as motor fuel or in a fuel cell for generating electricity without combustion. When it is applied to an internal combustion engine, or in a fuel cell, it burns very clean. The emission of NOx and HC is low, while the main exhaust gases are CO₂ and water vapour. If methanol is produced by the thermo-chemical pyrolysis of biomass such as wood, it results in no net emissions of CO₂, because carbon dioxide released this way forms part of the carbon cycle. Although normal automobile engines could also be converted to run on methanol, so contributing - regardless of the primary source of methanol – to the improvement of urban air quality, methanol-powered vehicles have not yet gained worldwide acceptance.