Biokubo: The search for an alternative feedstock for biodiesel

Part II. The Candidates: Plants and Animals

In the first part of this series, the need and rationale for an alternative feedstock for biodiesel was discussed. In this second part, I discuss the candidates to replace food oils as biodiesel feedstock.

Biodiesel is unique among alternative fuels in that its fuel properties depend on the species the oil comes from. Ethanol is essentially the same whether it comes from potatoes or corn. On the other hand, the biodiesel derived from coconuts will have fuel properties that differ from the biodiesel from soybean. So, some plant seeds may give plenty of oil but will not give an oil of the right quality.

Jatropha curcas has been frequently mentioned as having many of the qualities of a good alternative feedstock. Its seeds contain a significant amount of oil of the right quality, it can grow on barren land and it is not a food oil since it is toxic. This toxicity however might be a double-edged sword since any spills of jatropha oil would be more harmful than those from non-toxic sources. Recent reports have also shown that the yield of oil from jatropha may not be as high as expected. Some may say that these statements are being made with 20-20 hindsight but, in a 2007 paper, this author had already pointed out that it would be prudent to keep looking for an alternative even to jatropha.

Many researchers around the world agree that we need to keep looking. In 2009, there were already about 60 “novel” oils have been tested as possible candidates. There may now be about 80 or so. The list of species is varied, to say the least. Besides jatropha, the list includes such items as castor oil (a childhood “favorite” of people of a certain age), linseed oil (more commonly used for paintings) and Moringa oleifera (commonly known as “malunggay”). Some are less familiar since the plants are grown in other climes. Some of the candidates are downright strange. For example, opium poppy seeds and the seeds of Cannabis sativa (marijuana) have been studied as possible feedstocks. One can just imagine the regulatory hurdles these two candidates would face.

Also on the list of candidates are very familiar names: rubber, rice, coffee, tobacco and olive oils. The question that immediately arises — why study these? As it turns out, there are oil-rich agricultural wastes that are generated in the agriculture of these plants. In the case of rubber and tobacco, the seeds are usually discarded. In the case of coffee, it is the used coffee grounds and the defective coffee beans. Similarly, oil may be derived from rice bran (“darak”) and the twigs and leaves of olives called olive pomace.   

Animal oils have been studied also. Fish oil, beef tallow, duck tallow and even the oils extracted from chicken feathers have been investigated. The strangest entries would probably be the two insects: Aspongubus Viduatus and Agonoscelis pubescens, whose oils are apparently used for frying in Sudan. Most of the fuels in the published literature have reported acceptable results although a common observation was slightly reduced engine performance along with reduced emissions of most compounds accompanied by increased emissions of nitrogen oxides (NO_x).

In our own studies at De La Salle University, we have studied the seed oils of radish, sigarilyas, okra and papaya as well as the oil from the pulp of the pili fruit. Two of our colleagues in DLSU, Dr. Florinda Bacani and Dr. Susan Roces, have studied the oil of kenaf, a plant primarily cultivated for its fiber. Several students are currently studying more.

Besides issues of oil quality, common sense dictates that the best candidate would be have a high yield of oil per hectare of land. A comparison of yields indicates that palm oil will likely remain the highest yielding crop in the near future, notwithstanding the high preliminary estimates for two newly proposed crops: Calophyllum inophyllum and Cyperus esculentus. If arable lands are to be used for capacity expansion, then it may still make more sense to use palm oil. 

If new crops are to be adopted, they must, therefore, possess other advantages such as: (1) growing in inhospitable locations, as is the case for Jatropha curcas, but it must be accepted that the yield in these locales will be lower; (2) being a significant by-product or waste product of a more important crop such as the defective coffee beans; (3) offering unique fuel properties such as that of castor oil; (4) offering significant advantages in machine harvestability; or (5) offer multiple products. The large trees, or any crop which will require either large human inputs or a long period before maturity must be able to give one or more of these other features otherwise it would not make sense to divert from the traditional crops.

Finding an alternative to the food oils is truly no easy task, as the proponents of jatropha have found out. In Part III of this series, two more alternatives: waste oil and microalgae will be discussed.

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Luis F. Razon is a full professor of chemical engineering at De La Salle University. He obtained his bachelor’s degree in chemical engineering (magna cum laude) from De La Salle University and his MS and Ph.D. in chemical engineering from the University of Notre Dame, Indiana. His papers on the dynamics and stability of chemically reacting systems are some of the best-cited papers in the chemical engineering literature. He served in the food industry for 14 years, launching several important new products for a major international nutritional products company. He returned to the academe in 2001 and is pursuing research in chemical reactor engineering, alternative fuels and life-cycle assessment. E-mail at [email protected].