Improving the Bottom Line On the Front End

To avoid high-priced virgin vegetable oils, many in the industry are looking for alternatives. But inexpensive feedstocks are cheap for a reason-they carry high levels of undesirable components such as free fatty acids that make it difficult to produce biodiesel. Pretreatment systems, however, can clean up less than desirable feedstocks and improve producers' bottom lines.
By Jerry W. Kram | August 08, 2008
It may be hard to believe now, but only five years ago there was a glut of virgin oils such as soybean and canola oil on the market. Indeed, that was one of the driving forces behind the development of the biodiesel industry, as soybean growers looked for new uses and markets for their crops. The surge in worldwide demand for oils along with the growth of biodiesel use have pushed the price of virgin oil up from 20 cents per pound to a point where it is consistently more than 60 cents per pound and occasionally pushes the 80-cent barrier.

The price pressure for virgin oils sparked an intense search for alternatives. While algae and jatropha hold promise for the future, biodiesel producers are looking for alternatives that can help them now. Many are trying to adapt to feedstocks that were formerly thought of as less desirable, such as animal fats and waste vegetable oil, also known in the industry as yellow grease. These feedstocks are certainly less expensive than soybean oil and can be made into high-quality biodiesel. However, they typically contain high levels of substances that can make a biodiesel producer's life miserable. Chief among these are free fatty acids.

Fatty acids are the main component of both fats and biodiesel. In virgin soy oil, three fatty acid molecules form an ester with glycerin. Transesterification breaks the fat molecule with sodium methoxide catalyst and creates three molecules of biodiesel. However, if the fat molecule has been broken, which happens when oils are used for frying, for example, and the fatty acid molecule is free in solution, the catalyst combines with the fatty acid to form soap. More soap formed in the biodiesel tanks means more washing and purification for the biodiesel producer. "During the transesterification process, the chemical reaction that occurs actually can't convert free fatty acids (FFAs)," says Doug Lindsey, a biodiesel application specialist with SRS Engineering Corp. of Murrieta, Calif. "Besides creating soaps, it impedes the reaction."

High levels of free fatty acids also mean producers make less biodiesel from every gallon of oil they buy. That means a good deal on some cheap feedstock may be a raw deal for the biodiesel producer. "Most biodiesel plants on line today were designed to produce biodiesel from refined soy," Lindsey says. "I think 85 percent of the plants in the United States do that today. Those plants are not able to handle other feedstocks."

A lot of companies thought they could handle waste vegetable oils and other alternative feedstocks and had a nasty surprise when they tried, Lindsey says. "One of the problems, especially in the small plant market segment, is that there is a lot of misinformation about what reactors will do," he says. "Some companies don't accurately represent how much FFA their systems can handle. The reality is, no one's reactor-I don't care how good it is or what fancy mixing technology they use-can chemically transform FFAs directly into methyl esters using the standard biodiesel process."

The good news is that there are ways to make waste vegetable oil and other low-cost feedstocks better suited for biodiesel production. Systems are available that can distill free fatty acids, leaving the triglycerides that can be made into biodiesel. A different process is used in a system developed by SRS Engineering. The company's technology allows biodiesel producers more flexibility in sourcing and using alternative feedstocks. "Most alternative feedstocks require pretreatment because of high FFA content," Lindsey says. "By implementing a front-end process, it allows those plants that could only use refined oil to be multifeedstock capable."

Instead of removing FFAs from the feedstock, SRS Engineering took a different tack. "Because FFAs can't be converted directly, they must be converted using a different chemical process," Lindsey says. "That's what acid esterification accomplishes. The acid esterification process has actually been around for a while. But we have one of the first commercial implementations of that process in a scalable, continuous flow process."

Acid esterification uses sulfuric acid to force the FFA to combine with methanol to form biodiesel. "You are actually creating a small amount of biodiesel in the pretreatment process," Lindsey says. "What you are left with after the process is neutral oil and biodiesel. So if your feedstock has 5 percent FFAs, what you are left with is 95 percent neutral oil and 5 percent methyl esters."

One factor that has blocked the widespread use of acid esterification is that the process generates a small amount of water. Water promotes the formation of soap in the transesterification process, so it has to be removed before the remaining oil can be made into biodiesel. The SRS pretreatment system is a continuous flow system. "Removing water in any sort of continuous fashion is not an easy thing to do," Lindsey says.

A mainstay of SRS Engineering's business has been building columns for distillation and chemical separation, so it wasn't difficult for them to build in a distillation system to remove the water from the pretreated oil. "For better than 25 years, SRS has separated one chemical from another with their chemical solvent and fractional distillation systems," Lindsey says. "So when we looked at this process and the baggage associated with it, which is the excess water, that turned out to be one of our fortes. So we were able to easily engineer in water removal."

As an added benefit it makes the pretreatment more efficient. "Water slows down the esterification reaction," says George Hawranik, SRS Engineering's senior engineer. "So we do the esterification in a two-step procedure. At the midpoint, we remove the water to speed up the reaction again. We also use two different pressure and temperature variances to do the final conversion."

"The main difference between our pretreatment process and transesterification is that you don't get a separation layer," Lindsey adds. "So you don't get a dropout of glycerin. But it does create a small amount of water that is dependent on the amount of FFA present in the oil. That water is removed in our process so when you move that oil into your regular reactor you have dry, FFA-free feedstock going into your reactor."

The combined oil and methyl esters coming off the pretreatment system can go directly into a biodiesel plant's transesterification system. "You can put methyl esters into your transesterification process," Lindsey says. "It won't harm the process. When you go into your regular reaction with sodium methoxide and methanol, they will react with the neutral oil and make methyl esters. The small amount of methyl esters from the pretreatment won't be affected so you will wind up with 100 percent methyl esters at the end of the process."

The system is basically installed between the oil holding tanks and the transesterification reactor in a biodiesel plant. It is installed as close to the reactor as possible to minimize heat loss. Because the feedstock has to be heated to convert the FFAs and remove the water, conserving the heat content lowers the energy costs of the transesterification reaction. "[The treated feedstock] pretty much needs to be generated and put through the transesterification process all in one step," Hawranik says. "It doesn't add a lot of energy costs because the energy used in the esterification process will be carried right on through to the next step. It will balance pretty much with what your energy costs are right
now. The only added cost is for the recovery of the water, which is insignificant, a couple cents a gallon maybe."

The system uses little of the primary reagent, sulfuric acid, because the acid is so concentrated, Lindsey says. The added cost of the sulfuric acid is more than balanced out by the reduced sodium methoxide in the transesterification process. "Now you have a very refined oil going into the system," he says. "So you can use a minimum of chemicals in the transesterification process."

Lindsey says the SRS system is scalable and the company is working with biodiesel producers with plants as small as 500,000 gallons per year to some of the largest plants in the United States. The system can be added to an existing plant or be integrated into the design of a proposed facility. "We are working on a half-dozen implementations and as we finish one, we start another," Lindsey says. "We are working across the country on plants both small and large. Being an engineering [original equipment manufacturer], we are able to scale our process to fit just about any plant production capacity."

The economic advantage of using a system like the one from SRS Engineering is multifold. Biodiesel producers get the benefit of having access to lower-cost feedstocks, get a higher conversion of those feedstocks into biodiesel and don't have to contend with excess soap contamination. "Producers who have tried to convert oil with high FFAs will tell you how much it is hurting them," Lindsey says. "They already know they are having significant yield losses as well as a conversion quality issue. We have people call in and say for every 100 gallons of oil we convert we are only netting 65 or 70 gallons of biodiesel. They are also having problems with unreacted oils, and that is all a function of not understanding that a reactor cannot convert FFA into oils." Soaps also have a detrimental affect on equipment, he adds, which can lead to additional downtime to remove them from the system.

All of these savings add up quickly, Lindsey says. "The ROI (return on investment) calculation is pretty simple. By eliminating the FFA, you can return your business plan to getting 100 gallons of biodiesel from 100 gallons of oil. It is a 1-to-1 ratio with no yield loss." When the increased yield is factored in, the ROI for the system is typically less than a year, he added.

Hawranik added that any plant with more than 1 percent FFA in its feedstock needs to have a pretreatment system. "That's just about any feedstock that isn't refined soybean oil," he says. "The costs to treat and process [FFAs] will be far too high and they won't be able to make any profit."

In some cases, the ability to switch feedstocks could mean the difference between success and failure as virgin oil stocks become harder to come by, Lindsey says. "Feedstock flexibility is an emerging requirement for the biodiesel industry," he says. "Plants that are no longer able to buy refined soy have to look at alternative oils. But the good news is, not only will you be able to use alternative secondary oils like beef tallow, white grease and other fats, but emerging feedstocks like jatropha and algae also have FFAs that are too high. So what people are realizing is that no matter what feedstock they are using, unless it is refined soy, they are going to have to build pretreatment into their business plans."

Jerry W. Kram is a Biodiesel Magazine staff writer. Reach him at jkram@bbiinternational.com or (701) 738-4920
 
 
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