Noadswood Science, 2012

Biofuels

To understand how biofuels are produced

Wednesday, April 19, 2023

Fossil Fuels

Fossil fuels are running out, and also have a huge variety of problems associated with them, especially the release of carbon dioxide which contributes to global warming…

Global Warming

Ethanol

Ethanol is the type of alcohol found in alcoholic drinks such as wine and beer

Ethanol is also useful as a fuel – for use in cars and other vehicles, it is usually mixed with petrol

Ethanol

Ethanol can be manufactured by reacting ethene (from cracking crude oil) with steam –phosphoric acid is used as a catalyst: -

Ethene + Steam Ethanol

C2H4+ H2O C2H5OH

In the reaction ethanol is the only product – the process is continuous as long as ethene and steam are fed into one end of the reaction vessel, ethanol will be produced

These features make it an efficient process, but as ethene is made from crude oil, which is a non-renewable resource, it cannot be replaced once it is used up and it will run out one day

Ethanol & Fermentation

Ethanol can also be made via fermentation – sugar from plant material is converted into ethanol and carbon dioxide…

Enzymes found in single-celled fungi (yeast) are the natural catalysts that can make this process happen (this is a renewable resource): -

C6H12O6 2C2H5OH + 2CO2

More than 90% of the world’s ethanol is made by fermentation

Fuels

It is possible to make fuel for vehicles using vegetable oils – biodiesel is the name given to any fuel made from vegetable oils (and they can be added to any diesel engine)

Biodiesel is made by treating vegetable oils to remove some unwanted chemical – during production other useful products form, including a solid waste material which can be used as cattle feed and glycerine (used in soap manufacture)

Biogas

Biogas is made by anaerobic fermentation of waste materials – it is about 70% methane and 30% carbon dioxide

Many different microorganisms are used in biogas production, fermenting plant and animal waste (containing carbohydrates) and sewage waste

Currently biogas cannot be stored as a liquid (too high a pressure is needed) so must be used immediately for heating / cooking / lighting etc…

Advantages

Biodiesel is a very clean fuel – it also breaks down about five times faster than conventional crude oil diesel, advantageous if spilt

It also burns much more cleanly, making far less sulfur dioxide and other pollutants

It also has a major atmospheric advantage – as crops are used to make the fuel it is carbon neutral (all the carbon released by the fuel burning was originally absorbed by the plant from the atmosphere in the first place)

Biodiesel therefore makes little contribution to the greenhouse gases in the atmosphere

Recycled

In an ideal situation biofuels could be carbon neutral…

Disadvantages

Biodiesel is however not without is problems…

There are costs related to its production – machinery which harvests this biodiesel requires fuel itself, so this counts to the atmospheric cost

It also requires crops – ethical issues arise over using crops for fuel when famine is still widespread throughout the world

There is also a great amount of financial reward to producing biodiesel – areas of tropical rainforest are being cleared in huge amounts to grow this money-making crop, leaving vast areas having their natural flora and fauna destroyed forever…