Biodiesels

Petroleum diesels = a mixture of hydrocarbons (range from 8-21 carbon atoms) produced through the fractional distillation of crude oil 

Biodiesel = consists of fatty acid methyl or ethyl esters made from vegetable oil or animal fat (triglycerides) 

• transesterification reaction transforms one type of ester into a different type of ester. Biodiesel is made from vegetable oil or animal fat reacted with methanol/ethanol in presence of catalyst (KOH/NaOH) to give glycerol as the by-product 

Applications of biodiesel:

• Gasoline: fuel for vehicles is made form crude oil that takes millions of years to be formed, reserves are depleting 
• Faster harvest: as opposed to crude oil, biodiesel can be made from vegetable oil from plants, or use leftover vegetable oil 
• biodiesel produces less exhaust fumes due to its chemical structure with more oxygen atoms than crude oil 
• Airlines: Virgin Atlantic, Continental Airlines, Air New Zealand, Japan Airlines etc. A total of 8 US airlines that operate out of LAX have also signed a deal to use more than 1.5 million gallons of biodiesel a year for their ground vehicle 
• Commercial trucks, personal cars, SUVs, farm equipment 

Differences in properties between diesels and biodiesel 

The sizes of the molecules are about the same, but diesels and biodiesel have different chemical structure. Diesel consists of 95% hydrocarbon-saturated compounds and 5% aromatics, while biodiesel consists almost entirely of fatty acid methyl esters. As a result of the difference in chemical structure, in comparison to diesel, biodiesel: 

• has higher lubricity - reduces engine wear 
• contain practically no sulfur - reduce pollution by emission 
• has 10-12% higher oxygen content - reduce pollution 
• tend to more viscous at low temperatures - becomes problem during cold winters 
• more likely to oxidise to form solid gel-like mass 
• more chemically active as a solvent - more aggressive when used on material considered safe for diesel fuel 
• much less toxic - beneficial for spill clean ups 

Advantages of biodiesel

• Cost 
• cost the same as diesel in the market, but the overall cost benefit of using biodiesel is much higher. Biodiesel has higher lubricity, keeping the engine running for longer, requires less maintenance. With increasing market demands for biodiesel, there is the potential for the price to be driven down. 
• Renewable 
• diesel is refined from non-renewable crude oil. Biodiesel is made from different sources including manure, wastes from crops and specific plants e.g. sugar cane 
• Lower pollution levels 
• diesel produces large amounts of carbon dioxide gas when burnt, contributing to the greenhouse gas in the atmosphere. Studies suggest that biodiesel reduces greenhouse gas emission up to 65%. Though carbon dioxide is created as by-product of the synthesis, it is frequently used to grow the plants that will then be converted into the fuel, allowing it to become a self-sustaining system where the carbon dioxide is recycled.  
• Reduced dependency on foreign oil 
• make biodiesel from local crops 

Disadvantages of biodiesel 

• High cost of production 
• Monoculture 
• growing the same crop may deprive the soil of nutrients that are usually put back into the soil through crop rotation e.g. Malaysia's palm plantations 
• Use of fertilisers and water for irrigation 
• fertilisers may cause water pollution
• Use of food source to make fuel 
• ethical issue 
• take up agricultural space for other crops, put pressure on the current growth of crops, may mean a rise in food prices 

Sources:

http://pubs.cas.psu.edu/FreePubs/pdfs/uc205.pdf

http://www.conserve-energy-future.com/advantages-and-disadvantages-of-biofuels.php