There is an interesting piece in The Economist this week that will warm the cockles of industrial ecologists’ hearts. The are moves afoot to use waste cooking oil to power trucks and buses. Having imbibed a fair bit of Hong Kong soot myself on a recent business trip, I shall be monitoring this development with interest. (The full article is reproduced below.)
Hong Kong phooey
Jun 10th 2004 | HONG KONG
From The Economist print edition
Two pollution problems may be used to get rid of each other
HONG KONG has more restaurants than anywhere else on Earth ‘at least per chopstick-wielding person. It has a lot of diesel-powered lorries and buses, too. Neither improves the territory’s environment. Hong Kong’s 10,000 restaurants produce more than 20,000 tonnes a year of waste cooking oil’ and that is without counting the stuff poured slyly down the drain. Meanwhile, its vehicles belch out so much noxious diesel soot that the air pollution index is regularly stuck at ‘high’.
Technological ingenuity may, however, be able to use these two problems to cancel each other out. Diesel engines are catholic in their tastes, and do not have to run on fuel made from petroleum (indeed, Rudolf Diesel’s early prototypes ran on coal dust). That has led in other places to the development of so-called biodiesel fuels, which are made from plant oils — the same oils that are used in cooking. Although biodiesel is (before tax, at any rate) more costly than traditional, petroleum-based fuel, it does have environmental advantages. Traditional fuels are hydrocarbons (that is, their component molecules are made only of hydrogen and carbon). Biodiesel molecules contain oxygen, as well. The extra oxygen promotes more complete combustion to carbon dioxide and water. Levels of pollutants such as carbon monoxide, unburned hydrocarbons and small particles of soot are reduced by as much as 90% as a result. So, thought Sjouke Postma, the managing director of a Hong Kong-based firm called Hednesford, why not dispose of one pollutant (waste cooking oil) by burning it in diesel engines and thus reducing the level of another pollutant (vehicle fumes).
Of course, it is not quite that simple. Plant oils are made of molecules called triglycerides. These, in turn, consist of a molecule of glycerol (a type of alcohol) linked to three fatty-acid molecules (snake-like structures with a hydrocarbon tail and an oxygen-rich head). To make a mixture that burns well, the triglycerides are broken up by a process called transesterification. This is a one-step reaction which liberates the glycerol and links the fatty acids with methanol, another type of alcohol.
Even fresh plant oil that is destined to become biodiesel is treated this way. The glycerol is valuable, and is extracted and sold. And linking the fatty acids with methanol neutralises their acidity, thus stopping them from corroding the engine. Hours of abuse in woks, though, mean that a lot of the triglycerides in used oil have already broken up. Unfortunately, this is not good news. The remaining triglycerides still require transesterification, while the fatty acids that cooking has liberated still need to be linked with methanol. Without careful tweaking, these processes are incompatible.
At the moment, therefore, the consortium that has taken up Mr Postma’s idea is looking for a partner that can manage this chemical trick efficiently. That consortium includes such regional luminaries as the Asian Development Bank, PetroChina (mainland China’s biggest oil firm), the Kadoories (one of Hong Kong’s richest families) and Noble Group (a big Hong Kong-based logistics and shipping firm).
As this roll-call of local capitalism suggests, the motive for the project is not merely environmental. As the old saying has it, ‘where there’s muck, there’s brass’. The aim is to produce enough recycled biodiesel to run between 800 and 1,500 vehicles. A tidy reward for making Hong Kong a tidier place.