Synthesizing Multiple Feedstocks Into Quality B100

For many biodiesel producers, volatile commodity markets and paper-thin margins mean feedstock flexibility is absolutely critical for survival. Biodiesel Magazine interviews several different "multifeedstock" technology providers about their approach to processing with flexibility, and fuel quality, in mind.
By Ron Kotrba | February 10, 2009
One year ago, the main feedstock used in U.S. biodiesel production was soybean oil, as reported to Biodiesel Magazine by producers for its U.S. & Canada Biodiesel Plant Map published twice yearly. In the spring of 2008, soybean oil constituted 45 percent of the U.S. feedstock spectrum. "Multifeedstock" during that period made up 39 percent of all the feedstock. For the fall of 2008 map, however, the situation had changed fairly drastically. The six months between early spring and early fall had witnessed impressive price spikes in all commodities-soybeans included. Multifeedstock in the fall of 2008 constituted 55 percent, a resounding majority, while soybean oil as an exclusive feedstock dropped from 45 percent to 30 percent. While this data is not collected scientifically, the criteria used in the spring and fall of 2008 were the same. But if a producer runs two or more refined virgin oils through his process, does that constitute multifeedstock processing?

Russell Teal, the president and founder of Biodiesel Industries Inc., says a couple of years ago when the National Biodiesel Board was gathering data on its members' plants, he was asked if his biodiesel plant used a single feedstock stream or multiple feedstocks. "I asked them if I used RBD (refined, bleached and deodorized) canola oil and RBD soybean oil, would I be considered a multifeedstock producer," Teal says. "They said yes, and I said, 'Well, I'd like to be in a new category then-full spectrum multifeedstock, which means you can use just about anything.'"

The technique is at the heart of multifeedstock processing, along with real-time data collection and analysis, which show what's going into the plant and allow for testing and automation adjustments of any process parameters. Some producers have spent years developing and fine-tuning their proprietary multifeedstock process, and aren't willing to divulge their trade secrets. However, despite feedstock quality or level of saturation of the fats, at the elemental level, producers want triglycerides. Even concentrated streams of free fatty acids are desirable provided the plant is set up to esterify them into methyl esters. Techniques vary, though.

REG's multifeedstock process flowchart is more of a decision-making tree than a flowchart because there are places along the process where operators must make decisions that will affect process flow and the final product.

Myron Danzer with Renewable Energy Group Inc. stresses the importance of pretreatment, while Nova Biosource Fuels Inc.'s vice president of technology, Dick Talley, says his company spent years and millions of dollars developing a process that is multifeedstock capable without pretreatment. "Very much like oil refineries, we build biodiesel refineries that are 100 percent fully automated-flow, pressure and temperature measurements are all electronically controlled by control systems," Talley says. "An oil refinery doesn't care if it takes in crude oil from the North Shore, Saudi Arabia or South America." Nova Biosource Fuels supplied the process technology for the Sanimax Energy Biodiesel plant in De
Forest, Wis. "We have 17 or 18 different feedstocks coming into the plant right now," he says. "They range from stripped FFAs, to brown greases, to yellows, to tallow, to DDG corn oil, and we are synthesizing the product through."

The Pretreatment Process
Years ago REG narrowed the number of potential feedstocks with enough volume for biodiesel production to 15, Danzer says. "The first thing we look at is the carbon chain makeup of the oil," he says. "Then we say, what's in the oil that's not going to convert to biodiesel-the impurities like phosphorus and metals." He says some approaches to multifeedstock processing run oil, fat and grease through esterification and transesterification, and at the end of the process, utilize distillation to remove all the impurities. "All those impurities will come out in the distillation bottoms, which works fine but it has some effect on the fuel quality," Danzer says. "The acid number could go up, or the impurities might go overhead with the biodiesel." Also oxidative stability could be compromised if all the sterols, or antioxidants, are stripped via distillation. "But one problem it creates is a lot of loss in those bottoms," he says. "So in our opinion, you need to remove the impurities [during] pre-biodiesel processing and, even if you want to distill product at the end and make highly purified biodiesel, you would cut down on that loss because you wouldn't have all those things dragging along through the whole process."

REG uses Crown Iron Works Co. process equipment in its plants. Derek Masterson, Crown Iron Works' sales engineer, says, "We agree pretreatment in general is necessary, and it's the opposite of what some companies think. We have a spec for neutral, clean oil going into the plant, and then we have the theory that, if you can make the fat into good quality fat, the biodiesel process won't care how it got to that point. So the trick is how to pretreat it to make a good, quality product later." The answer, he says, is designing the plant around the worst-case scenario. Whether the feedstock had 1 percent FFAs or 15 percent, the process is exactly the same. "You might make the stripping column a different size, or have different amounts of cooling and heating, but it's the same process," Masterson says. "We wouldn't change the process at all for the feedstock. It's just a matter of designing it correctly for our customers' idea of their worst-case scenario."

Greenline Industries Inc. has its own unique multifeedstock process technology, and has developed a high FFA pre-processor. "The FFA pre-processor is a molecular distillation system particularly suited viscous feedstocks," says Gaurav Shah, Greenline Industries senior process engineer. "We did extensive research into the separation process that would fit this application. So after looking at the chemical and thermodynamic properties of the feedstocks, we decided this equipment would fit our application-but we had to tailor it specifically for biodiesel feedstocks." The system is a wiped-film evaporator that works in a single stage. It takes the feedstock in, heats it to 470 degrees Fahrenheit, and scrapes the FFAs from the triglycerides under vacuum. "The result is a beautiful, researched product," Shah says. "We spent enormous efforts to design this-to feed the optimum design, the column, the residence time, the degradation of fats and the chemical properties."

Process Parameters and the Importance of the Lab
Teal says some techniques use more robust, broad-range processes that somewhat bypass a thorough pretreatment. "That usually involves much deeper analytical work on the oil profiling," he tells Biodiesel Magazine. "Then there are techniques using high temperatures and high pressures in a supercritical reaction, and in those cases concerns about the variability of feedstock are much less." However, if a fixed-bed catalyst is employed, contaminants could foul the catalyst, so they should be removed before transesterfication. "The bottom line is, there's a lot more to multifeedstock processing than saying, 'This is how it's done,' " Teal says. "You need to work it out, especially if you're retrofitting an existing plant. You need to determine what specifications work with your hardware, and then there are a lot of techniques learned by the operators at the plant in terms of making it run properly." He likens the whole process to running a fine restaurant. "You can have the best kitchen equipment in the world, but if the cook doesn't know what he's doing, he's not going to make a good meal," he says.

Provided a pretreatment is used, the FFAs are stripped, and impurities such as metals, phospholipids, solids and water are removed, the cleaned amalgam of fats, greases and oils can move into transesterification.

Greenline Industries evaluated the performance of the four well-known catalysts with respect to yield, effect on different feedstocks and efficient consumption. The catalysts were sodium hydroxide, sodium methylate, potassium hydroxide and potassium methylate. "What we found out was potassium methylate works better with animal fats than sodium methylate," Shah says. "It keeps the soap in glycerin in liquid form, it has better phase separation and promotes better reaction," he says. "So we recommend our customers to use potassium methylate for animal fats, if possible."

Highly saturated feedstocks such as tallow take more time to convert to biodiesel than lower saturate canola or soybean oil, Shah says. "It changes the process parameters, [for] catalyst consumption, the percent of excess methanol to use, and residence time," he says. Catalyst activity could be hindered if impurities in animal fats such as phospholipids are not removed successfully. "Understanding these parameters in detail helps in achieving better bound glycerin numbers from the reactors in a consistent, reliable manner when working with animal fats and yellow grease," he adds.

If you have multiple and vastly different feedstocks, experts say it's critical to analyze them as they are delivered. "This is where the lab is so important, more so for pre-treating feedstock," Danzer tells Biodiesel Magazine. "You have to be able to test that. The lab is one of the most important aspects of a plant." He recommends building a test for every part of the process from beginning to end-sample off the trucks, do the analysis, then test it again after the crude feedstocks are blended together. "One of the most important things is to have a mix in that crude tank going into the process that doesn't vary too much," Danzer says. "It will treat a lot better because of its consistency."

Testing, real-time reporting and automation are critical components to multiple feedstock processing. "The ability to analyze in real time what's going on in terms of feedstocks going into your tank and during the reaction process is very crucial," Teal says. "A gas chromatograph (GC) is an artifact, and a good GC operator can get the info in a half hour, 45 minutes maybe-and at that point it's looking at where the reaction was, not where it is. Getting real-time feedback on the process controls and then being able to automate the reactants, times and temperatures accordingly, based on experience-that's the most difficult part." He says Biodiesel Industries has completed tens of thousands of reactions in multiple plants all over the world, and the data gained from it is priceless. "Having that data set is essential," he adds.

While techniques vary, experts agree that what is absolutely critical for a multi-feedstock process to be considered successful is good end-product fuel quality, which comes from intelligent design, thorough quality control measures and testing, testing, testing.

Ron Kotrba is a Biodiesel Magazine senior writer. Reach him at [email protected] or (701) 738-4942.
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