Introduction

Biofuels are energy sources derived from biological materials and are therefore renewable and sustainable, and can go some distance in replacing fossil fuels and reducing carbon dioxide emissions. Their biological nature separates them from other renewable energy sources such as wind, wave and solar power. Biofuels can be solid, liquid and gaseous and can be used to generate electricity and as transport fuels. No matter how biofuels are used, they have both benefits and shortcomings, and in this chapter these are explored.

The benefits of biofuels whether globally or to a single country are as follows:

0. Reduction in crude oil use. Liquid biofuels can supplement or replace petrol and diesel, and at low levels of blending, little engine modification is required. Biodiesel can be used up to 100% in a conventional diesel engine but higher blends of ethanol (85%) require either modifications or a flexible fuel engine. Biomass and biogas can reduce fossil fuel use for electricity generation.

1. Improvements in engine performance. Ethanol has a very high octane number and has been used to improve the octane levels of petrol. It is also a possible replacement for methyl tertiary butyl ether (MTBE) which is being phased out as an octane enhancer. Biodiesel addition will enhance diesel lubricity and raise the cetane number.

2. Air quality. Biofuels can improve air quality by reducing the emission of carbon monoxide (CO) from engines, sulfur dioxide and particulates (PM) when used pure or in blends.

3. Reduction in the emission of the greenhouse gases (GHGs) carbon dioxide and methane. The replacement of fossil fuels with biofuels can reduce significantly the production of carbon dioxide, and the use of biogas reduces methane emissions.

4. Toxicity. Biofuels are less toxic than conventional fuels, sulfur-free, and are easily biodegradable.

5. Production from waste. Some biofuels can also be made from wastes, for example, used cooking oil can be used to make biodiesel.

6. Agricultural benefits. Biofuel crops of all types will provide the rural economy with an alternative non-food crop and product market.

7. Reduction of fuel imports. By producing fuels in the country, imports will be reduced and the security of energy supply will be increased.

8. Infrastructure. No new infrastructure is required for the first — and second-generation liquid biofuels and some of the solid and gaseous biofuels.

9. Sustainability and renewability. Biofuels are sustainable and renewable, as they are produced from plants and animals.

However, there are shortcomings to the use of biological materials to replace fossil fuels which are as follows:

© A. H. Scragg 2009. Biofuels: Production, Application and Development (A. H. Scragg)

1. Biological material may not be able to produce enough fuel to replace fossil fuels completely, and extensive cultivation of biofuel crops will compete with food crops, perhaps driving up prices.

2. Large amounts of energy are required to produce some biofuels, giving them a low net energy gain.

3. Some of the second — and third-generation biofuels will require the introduction of a completely new infrastructure, for example, hydrogen.