What is Biodiesel?

by Keith Bishop

Currently, there is no commercial biodiesel production in the Bahamas - the work at Cape Eleuthera Institute has been done on an experimental basis. There is, however, large-scale production in the United States and elsewhere.

It is unlikely that using the estimated 300,000 gallons of discarded cooking oil that is available in the Bahamas annually will produce enough volume to justify the cost of retrofitting gas stations to pump biodiesel. And it is unlikely that the Bahamas Electricity Corporation will become a consumer because the cost of local production would likely be higher than the fuels currently used by the corporation's slow-turning generators.

The most likely consumers would be those entities operating fleets of diesel vehicles.

Biodiesel is a clean burning fuel alternative produced from vegetable oils and animal fats for use in compression-ignition (diesel) engines. The oil or fat must go through a chemical reaction called transesterification, which is controlled in the United States by ASTM Standard  D6751.

This chemical reaction results a number of residual products, the principal one being glycerin – a valuable by-product used primarily in soap production.

There are a number of potential sources for used cooking oil, including hotels, fast food restaurants and cruise ships. If demand if sufficient this could be extended to individual households, but experience in the United States has indicated this to be impractical.

Biodiesel provides approximately 118 000 BTUs to petroleum diesels 130 500 BTUs per equivalent weight, meaning that biodiesel is about 90 per cent efficient. This has a minimal impact on horsepower, torque or gas mileage.

Biodiesel blends can reduce particulate discharge by up to 14 per cent, total hydrocarbon emissions by 13 per cent and carbon monoxide by up to 7 per cent. Pure biodiesel is free of sulfurs and benzene - a known carcinogen.

Is Biodiesel Good for the Environment?
Biodiesel is made from materials that are already part of the carbon cycle. In contrast, petroleum diesel releases carbon that has been locked underground for millions of years. Biodiesel does not release harmful vapours at regular temperatures and is less toxic per unit weight than table salt. It is as biodegradable as sugar.

What are the disadvantages of biodiesel?
Rubber or nitrile seals in older (pre-1993) fuel pumps may deteriorate more rapidly when used with higher percentage blends of biodiesel, but can be replaced with newer seals. When higher percentage biodiesel is initially used in an engine that has previously been used with petroleum diesel, it may break up deposits left by the previous fuel, clogging fuel filters. Some production methods require the use of methanol, the market cost of methanol increases proportionately with other petroleum based products resulting proportionately higher production costs.

Socio-Economic Considerations
The availability of raw source oils / fats might limit local production to a single operator. It may not be possible to levy taxes on biodiesel due to the high cost of production. The production of biodiesel in the Bahamas must be viewed as an environmentally friendly waste load reduction to our landfill and as a preventative measure against the indiscriminate dumping of waste oil. 

Comments

[Bob Knaus]

Under socio-economic considerations, you might want to add "Biodiesel from waste cooking oil competes with higher value uses such as soap manufacture." Waste cooking oil already has a fairly well defined value chain in the US. So much so, that there are occasional problems with thieves stealing the stuff from the back of McDonald's after hours. If it's that valuable, surely the cruise ships must be taking it back to Miami rather than dumping it overboard.

This is a classic case for price, rather than policy, making the decision.

If, from a policy perspective, you think there are externalities, then impose a carbon extraction tax on the petroleum based products and don't levy it on fuels made from cooking oil. Set the tax at a rational level, more or less equivalent to market prices for carbon credits. Then let the market sort out the rest.

It's the only sane way.

[Sam Wells]

My understanding is that manufacture of biodiesel is in this case using clean cooling oil and reacting it with methanol and sodium hydroxide which produces both glycerin and fatty esters. The glycerin is sold for soap and the fatty esters are retained and treated for excess methanol (which can eat up plastic gaskets). This straight run biodiesel is then blended with kerosene or Number 2 Diesel at perhaps 20 percent or more.

Although there is a slight increase in oxides of nitrogen and some driveability issues, biodiesel sounds promising. it should be explained that use of soy beans and rape seed can increase greenhouse gas emissions, however. The cost of production is what concerns most people.

I guess if one could make the stuff and sell it from a tank truck in the Bahamas it might work, if you can handle the horrible smell of old yellow grease! -sam