Within the confines of a single article, it’s tough to even scratch the surfaces of a global feedstock assessment, which would include analyses of costs, pretreatments, resultant fuel properties and a plethora of other considerations. Instead, Biodiesel Magazine provides an abridged feedstock overview—and some “feed” for thought, including a look at promising alternatives to conventional oilseed crops and animal fats.
Feedstock overview: Resultant fuel properties
At the risk of oversimplifying, several generalities can be made about feedstocks, their costs and the subsequent properties of biodiesel fuels made from those respective feedstocks. Naturally, within generalities is always room for anomalies, and some of those will be covered here, too.
Voluminous varieties of feedstocks are available all around the world, but most biodiesel feedstocks can be divvied up into three main categories: vegetable oils, first-use animal fats and waste greases.
Vegetable oils derived from canola, sunflowers and soybeans are generally low in saturated fats. By knowing that alone, much can be presumed about the resulting vegetable oil-derived biodiesels.
Biodiesels made from most virgin vegetable oils, being generally low in saturated fats, are considered the easiest and least expensive to process, according to NREL publication titled Production of Biodiesels from Multiple Feedstocks and Properties of Biodiesels and Biodiesel/Diesel Blends. The report states, “These oils are available in a consistently high-quality form and are the easiest to process for making biodiesels.”
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Additionally, these biodiesels are more likely to have better cold flow characteristics— important to keep in mind, depending on what climate the biodiesel will be produced and used—due to the lack of saturated esters. Conversely, studies have repeatedly shown that, without modification, these biodiesels generally have lower cetane numbers directly attributable to their relatively low saturated fat content. This ultimately means their combustion temperatures are higher, thus producing more NOx. Also, according to the U.S. DOE’s 2004 Biodiesel Handling and Use Guidelines—put out by the Energy Efficiency and Renewable Energy Office (EERE)—the more saturated fats in biodiesels, the more stable the fuels are likely to be. This means biodiesels made from lower saturated vegetable oils are more likely to become subject to oxidation quicker.
But not all virgin vegetable oils are low in saturated fats. According to the Harvard School of Public Health Lipid Laboratory, in conjunction with USDA studies, canola oil is one of the oils lowest in saturated fats, coming in at only 7 percent in relation to its overall fat (i.e., saturated, mono-unsaturated and poly-unsaturated). Safflower, sunflower, corn, olive, soybean, peanut, palm and coconut oils respectively weigh in at 9 percent, 10 percent, 13 percent, 13 percent, 16 percent, 17 percent, 50 percent and an astounding 87 percent.
With palm oil containing 50 percent saturated fat and coconut oil at 87 percent saturated fat, it’s clear that these two oils do not fit the mold when discussing general properties of vegetable-oil-based biodiesels. Also, oilseed oil yields are another consideration. According to the United Soybean Board’s recent analysis conducted by Promar International Ltd., canola, sunflower and palm oils are likely to fare well for biodiesel production in the future—in the expected event that vegetable oil prices rise—mainly due to their higher oil content compared to soybeans.
First-use animal fats (“virgin”), generally high in saturated fats, follow the same basic trends as vegetable oils. Being higher overall in saturated fats, animal-fat-derived biodiesels tend to cost a little less than virgin vegetable oils. They require further refining either before or after the transesterification process, but not nearly as much as required by waste greases. Also, animal fats tend to produce biodiesels with higher cetane numbers and, again on average, less NOx. But as the emissions/cold flow trade-off goes, the animal-fat-derived biodiesels have less desirable cold flow characteristics than most vegetable-oil-based biodiesels.
As with virgin vegetable oils, the variety of animal fats runs the gamut. There are edible and inedible tallows, grades of lards and various poultry fats.
Waste vegetable oils (yellow grease) and trap greases (brown greases) are the least expensive feedstocks available and require the most intensive processing due to high concentrations of free fatty acids that have become liberated at high cooking temperatures. According to NREL, yellow-grease-based biodiesels display characteristics of both vegetable-oil- and animal-fat-derived biodiesels, and therefore fall between the two in terms of fuel properties (e.g., cold flow, emissions, etc.).
Worldwide feedstock availability
According to a 2004 NREL report, Biomass Oil Analysis: Research Needs and Recommendations, the world’s soy oil production increased 25 percent in a five-year period beginning in 1998 through to 2003, “… from 25 million [metric tons] to over 30 million [metric tons], with most of that increase in Brazil and China. Production costs for Brazilian soybeans are 25 percent less than United States costs, and significant land and transportation improvements will continue to focus future growth in these sectors of the world.” According to this publication, Latin America (Brazil and Argentina predominantly) leads the world in soy oil production, followed by the United States, Asia, the European Union (EU), Eastern Europe and others.
When feedstock availability and pricing are being looked at, it’s imperative that several things be considered. For one, the biodiesel industry often competes with the food industry for feedstocks like soy oil, which is a real concern. This competition increases the cost and tightens availability. Livestock feed is another necessary consideration. For example, with a booming ethanol industry in the United States and beyond, distillers grains from starch-to-ethanol production processes offers even more feed product to the available livestock markets. Also, recent advances in technologies that extract the remaining corn oil from the distillers grains—offering multiple benefits to almost all parties involved—will help establish a lower-cost corn-oil market for biodiesel, which has been too expensive of a feedstock for biodiesel production in the past (see Talking Point, page 70). However, increased soybean oil demand would likely drive down the demand, and therefore, the price of soybean meal.
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