Biofuels: Types and their significance

Biofuel are the solid, liquid or gas fuels which are derived from non-fossil biomass. They are renewable, environment friendly andcan be obtained from easily available biomass.

The multiplied use of fuels to provide energy in varied necessities such as lighting heating and transportation. With the exponentially increasing population and expanding economy, the need for fossil fuels is also increasing.
The fossil fuel are limited resources and are predicted to be exhausted if used frivolously. The inflated use of fossil fuels has caused many damages to the environment such as greenhouse gas emissions, increasing atmospheric CO2 concentration. Hence petroleum and diesel which is obtained from ancient fossil deposits is a limited resource which is going to run out in near future and is extremely expensive and cumbersome to recover. These concerns raised the need to find out an alternative which can suffice the need of energy resource, reduces carbon emission and is also renewable.

White biotechnology is a branch of biotechnology which deals with the production of fuels and chemical from renewable resources. This branch involves the technologies which uses living cells and enzymes for the synthesis of products that are easily biodegradable. Biofuels include bioalcohol such a ethanol, methanol, bio-gas such as hydrogen and methane ,other fuels such as diesel etc.
The main reason for the popularity of biomass is its renewable property, easy availabilty and its positive environmental property. The biofuels are produced by conversion of biomass into liquid and gaseous fuels through targetting thermochemical and biological routes. The advantages of biofuels are that they are produced form common biomass sources hence are easily available , are non-polluting, easily accessible, sustainable and reliable fuel obtained from renewable sources.
One more benefit of biofuel is that they can be stored, transported and utilized away from the place of its production. It has negligible amount of sulphur and nitrogen so it does not add up to environmental pollution. Energy potential of Biomass is considered to be the most promising among all the renewable energy sources because it is highle spread and worldwide available.

Types of biofuels

Bioalcohols
Bioalcohols stand for liquid fuels which are produced from biomass. They can be pure (100%) biofuels for specific vehicles or blend of fuels in a specific ratio so that they can be used as a substitute for conventional motor fuels and do not affect the vehicle performance. Forinstance, a blend of ethanol with gasoline can be used. Bioethanol is produced by hydrolysis and fermenation process from renewable biomass such as wheat, sugar beet, corn, straw, and wood.The process is carried out by conversion of carbohydrates (hemicelluloses and cellulose) in biomass into sugar by hydrolysis process.
It is then converted into alcohol by fermentation by micro organisms, an anaerobic biological process .
Fermentation of carbohydrate is carried out by commercial yeast such as Saccharomyces ceveresiae. The invertsase enzyme of yeast catalyzes the hydrolysis and zymase, another enzyme present in the yeast, converts the glucose into ethanol. The production of methanol is carried out by direct conversion of oragnic matter into synthetic gas by gasification and partial oxidation.

Biodiesel and vegetable oils
Vegetable oils obtained from renewable oil seeds can be used as fuels for diesel engine by mixing with diesel. They are triglyceride molecules having high viscosity than conventional diesel and require modification to reduce viscosity by dilution,pyrolysis,microemulsification, catalytic cracking and transesterification. These Vegetable oil (m)ethyl esters are commonly referred to as ‘‘biodie-sel,” are primary candidates as alternative diesel fuels. The vegetable oils such as soybean oil can be transesterified and converted to their methyl esters in the presence of catalyst such as potassium and/or sodium alkoxides . The transesterification is carried out with a purpose to decrease the viscosity of the oil by decreasing the branching of the molecule. Biodiesel is an environmentally friendly alternative liquid fuel that can be used in any diesel engine without modification.

Biogas
All foms of biological contains a certain proportion of organic matter which can be broken down into a mixture of methane and carbon by anaerobic digestion called biogas. Biogas is an environment friendly, cheap ,clean and versatile fuel produced in digesters filled with feedstock such as dung or sewage. The anaerobic digestion process for decomposition of organic matter into biogas involves a series of reactuons requiring cooperative action of several organisms.First group of micro-organisms converts organic material into organic acids which can be used by methane producing bacteria to produce biogas.

Biohydrogen
Hydrogen can be used as a fuel by burning it to produce heat or passed through a fuel cell to produce electricity. Hydrogen can be produced by pyrolysis from biomass. Hydrogen is produced from biomass requires several reaction steps: for the production of high purity hydrogen, the reforming of fuels is followed by two water gas-shift reaction steps, a final carbon monoxide purification and carbon dioxide removal. The thermochemical conversion processes, such as pyrolysis, gasification and steam gasification is also adopted for converting the biomass to a more useful energy. The yield from steam gasification increases with temperature. Through research, three types of microorganisms are found to have the capability for hydrogen generation i.e. cyano-bacteria, anaerobic bacteria, and fermentative bacteria. The cyanobacteria takes the advantage of its photosynthetic capability and directly decomposes water to hydrogen. Photosynthetic bacteria use organic substrates like organic acids. Anaerobic bacteria and fermentative bacteria use organic substances as the source of electrons and energy and converts them into hydrogen in absence of oxygen.