Bioenergy, the carbon cycle and the photosynthetic ceiling

In mid-2006, crude oil prices reached record levels of close to $80 per barrel, stimulating renewed interest in alternative fuel research. Although price levels have eased to about $60 lately, it is now widely recognized that the world oil market remains volatile, and that governments of net oil importing nations cannot afford to be complacent about the prospects of continuous supply of cheap energy. There is still considerable controversy as to exactly how much petroleum reserves remain in the world – with estimates ranging from a low of a few decades to a high of over one century. However, these reserves are in any case finite and non-renewable, and the imminent threat of global climate change adds yet another driving force toward reducing the world’s dependence on oil and fossil energy.

These threats have been recognized by the Philippine national government, and much effort has been put into developing appropriate measures to reduce the impact of rising oil prices. The transport sector is particularly vulnerable, as it is in the peculiar position of being almost entirely dependent on petroleum products such as gasoline and diesel. In response to these threats, there is now pending legislation intended to introduce liquid fuels derived from plant matter to supplement conventional petroleum products. For gasoline, the fuel identified is ethanol – the same alcohol found in intoxicating beverages – to be blended at levels of up to 10 percent. Ethanol is produced through the fermentation of sugar, which can in turn be derived directly from sugar crops, or from the chemical conversion of starch or cellulose. As a result, a large number of potential indigenous raw materials can be used as potential feedstocks, including sugarcane, molasses, corn and even fibrous material found in agricultural and municipal wastes. In the case of diesel, the most promising substitutes are chemical derivatives of vegetable oils (derived from traditional crops such as coconut, or dedicated energy crops such as Jatropha curcas) known as methyl esters. As a result of the chemical treatment, methyl esters closely resemble the properties of conventional diesel, which allows them to be used in existing engines. This last point clearly illustrates the phenomenon of technological inertia, wherein new fuels not enjoying the advantages of the incumbent energy sources must be made to dovetail neatly with the needs of existing vehicles in order to gain a foothold in the market.

There are some significant advantages to the use of biomass-derived liquid fuels. First of all, they can be derived from locally grown crops without requiring cutting-edge technology. Thus, for countries like the Philippines, they represent a workable means of developing significant indigenous energy sources. Brazil’s three decades worth of experience with their ProAlcool fuel ethanol program show that properly managed biofuel systems can be sustained over long periods, and thus provides a good model for the Philippines to study. In addition to enhancing energy security, biofuels are inherently climate-friendly. Carbon dioxide emissions from combustion of biofuels are offset significantly by photosynthetic carbon fixation during the growth of the crops used for fuel production. Thus, the replacement of fossil fuels with biofuels helps mitigate climate change effects of human activities, in effect by embedding the latter within the natural carbon cycle.

Biofuels such as ethanol and methyl esters are, in a very real sense, solar energy condensed into convenient liquid form. It is photosynthesis which allows diffused sunlight to be converted into concentrated chemical energy for use in motor vehicles. Hence, it is important to recognize the inherent limits imposed by natural processes, or else it is possible to be misled into believing that biofuels represent a simple, painless solution to the Philippines’ energy concerns. In a paper published in Renewable and Sustainable Energy Reviews in 2005, Nonhebel estimated based on global crop production statistics that a typical Third World country will require at least a tenfold increase in agricultural production if its total energy demands are to be met using biofuel crops. Whether such an increase is met by improving productivity levels, or by increasing the area of land cultivated, such a situation is likely to be untenable for a rapidly growing country such as the Philippines. Thus, while it is possible to envision liquid biofuels as being significant contributors to the national energy mix in the near future, and in particular playing the valuable role of providing much-needed energy diversity to the transport sector, it must be made clear that for thermodynamic considerations they cannot be expected to be a dominant energy in the long run, without also considering major changes in current energy consumption patterns. For the Philippines, a sustainable energy strategy will have to rely on an integrated approach consisting of both energy efficiency measures and energy resources diversification.

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Note: This column is partly based on discussions during the Biofuels Symposium held jointly by the National Academy of Science and Technology, the National Research Council of the Philippines and the Department of Energy in Manila last Sept. 15.

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Dr. Raymond R. Tan is an associate professor of the Chemical Engineering Department and the director of the Engineering Graduate School of De La Salle University-Manila. He is one of the senior researchers of the Center for Engineering and Sustainable Development Research. E-mail at tanr_a@dlsu.edu.ph.

Dr. Alvin B. Culaba is a professor of the Mechanical Engineering Department of De La Salle University-Manila, the director of the Center for Engineering and Sustainable Development Research and president-elect of the Philippine-American Academy of Science and Engineering. E-mail at culabaa@dlsu.edu.ph, culaba_alvin@yahoo.com.