Three sources of feedstocks used in the production of renewable fuels from triglycerides are: corn, soybean and animal fats. These three primary sources provide about 18 billion pounds of triglyceride feedstock to the domestic renewable fuel industry annually, with most of that feedstock being consumed in the production of 14 billion pounds of biodiesel. The remaining feedstock is consumed in the production of renewable diesel and jet fuel. Strong interest in renewable diesel and jet fuel production is expected to drive changes in the market to meet increased demand as competition for both existing and new sources of triglycerides heats up.

Corn

Corn represents the largest, most accessible stream of triglycerides with approximately 14 billion bushels of corn produced annually. Corn contains approximately 2 pounds of oil per 56-pound bushel, suggesting a potential volume of 28 billion pounds of oil available.

Practically, the corn oil available for use as fuel is made up of the approximately 1 pound of oil per bushel of corn converted to ethanol in the dry milling process. About two-fifths of the U.S. corn crop is converted to ethanol, resulting in annual production of 5.5 billion pounds of distillers corn oil. The other three-fifths of the U.S. corn crop is used in livestock production, export and other food or industrial uses.

Soybeans

Soybean production in the U.S. is approximately 4.5 billion bushels annually. One bushel of soybeans weighs 60 pounds and includes about 12 pounds of oil. About 60% of the domestic crop is exported as whole beans. The remaining 40% is crushed domestically to produce soy meal for livestock production, as well as 25 billion pounds of soy oil. About 9 billion pounds, or just over one-third of that oil, is used for production of biodiesel. The remaining two-thirds is used in food and industrial applications. 

Animal Fat

Much of the protein value of the domestic corn and soy crop is used to produce 105 billion pounds of beef, pork and poultry for human consumption. Slaughter and processing of animals in the U.S. produces 10 million pounds of triglycerides as rendered animal fats annually. About one-third of these triglycerides have been historically used in the human food chain and in consumer products. Another one-third goes to animal feed. The final one-third, or about 3.5 billion pounds, is used as feedstock for renewable fuel.

Quality Is the Key

Triglycerides of the highest purity — including edible tallow, lard and refined, bleached and deodorized vegetable oils — are well-integrated in the human food chain and command premium prices among triglycerides. Technical grade fats and oils, including bleachable and fancy tallows, choice white grease and once-refined or water-degummed soybean oil, are used in livestock rations, pet food and industrial applications as well as production of renewable fuels. New demand for triglycerides to support increased production of renewable diesel may prove to be disruptive to this market.

Lower quality fats and oils include yellow grease, used cooking oils, trap or brown grease and other rendered products, which may contain elevated concentrations of triglyceride degradation products such as free fatty acids, ketones and aldehydes or other materials identified as moisture, insoluble and unsaponifiables. These attributes limit the commercial uses for these triglycerides but make them particularly attractive as feedstocks for production of renewable diesel due to the ability of the renewable diesel process to handle free fatty acids and their low price. 

Feeding the Future of Renewable Diesel

The renewable diesel production process can be adapted to use any of the common triglyceride sources as a feedstock, provided that suitable pretreatment is performed to remove catalyst poisons and inhibitors before introduction to the catalyst. It is worth repeating that elevated levels of free fatty acids are generally not an issue for conversion of the triglyceride feedstock to renewable diesel. This makes for significant flexibility in the feedstock choices available to the producers of renewable diesel.

Significant growth in the production of renewable diesel will require additional production of these feedstocks, diversion of existing feedstocks from other uses, or recovery and reclamation of feedstocks from secondary sources, such as used cooking oil. Renewable diesel projects can benefit from consideration of these disruptive forces in the triglyceride supply chain and incorporation of design features which can facilitate flexibility among the available plant and animal feedstocks for production of renewable diesel.

 

The challenges inherent to bringing renewable, low-carbon projects to fruition require innovative technological and financial perspectives.

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Tim O’Mara is a process and technology manager at Burns & McDonnell. With more than 35 years of process engineering experience, he focuses on creating effective solutions for the design, construction and operation of process facilities.