Joint Evolution: Technology Providers Have Adapted Their Pretreatment Offerings as the Biodiesel Industry Evolved to Rely More on Waste Feedstocks, and as Renewable Diesel Emerges.

April 15, 2020

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by Ron Kotrba (Biodiesel Magazine) ... Markus Dielacher, CEO of BDI-BioEnergy International, says many companies offering pretreatment systems came from the vegetable oil side. “They started with clean feedstock and it worked,” he says. “We came from the other side, the worst feedstocks, and went to the cleaner ones.

It’s important if you’re working with heavily impure feedstock to have a robust system, as most don’t work properly with this type of feedstock. For instance, you can use a degumming unit for pretreating the worst feedstock, but it clogs up [quickly] and then doesn’t work. So, you need more robust systems, different kinds of separation units, and further steps in front to pretreat.”

The evolution of the biodiesel industry to rely more on waste fats, oils and greases was largely an economic consideration, as feedstock costs can represent 80 percent of operational expenses for production, and regulation driven as governments around the world tie regulations to carbon intensity and sustainability. “Biodiesel was an extension of the soy processing industry and evolved into more of a standalone business that had to survive by processing feedstocks that were competitive in price and availability,” Willits (Jim Willits, former president of Desmet Ballestra North America) says.

Not all biofuels are created equal, from both monetary and sustainability points of view, Slichter (Alex Slichter, global commercial director at Crown Iron Works) says. “With more waste oils being used, instead of just neutralizing [free fatty acids (FFA)] and making soap, producers today are being more diligent in separating contaminants like FFA, and they’re doing more physical than chemical refining,” he says.

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"...(W)e’ve made some enhancements on the pretreatment side by using enzymes and acid degumming—different techniques in the refining step from our portfolio. In the past 10 or 12 years, as animal fats, palm [distillates] and higher FFA feedstocks crept into the marketplace, we’ve employed different technologies from our toolbox, such as deacidification columns vs. traditional neutralization, working with our customers as the market evolves.”

Christine Riedl, technical sales manager at BDI, says when “second-generation” feedstock first appeared on the market, the used cooking oil (UCO) and animal fats were higher quality than what’s available today, so pretreatment demands were not huge. “But as lower-quality feedstock was being introduced into systems,” she says, “pretreatment requirements increased as higher amounts of impurities were coming in with that.”

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Because of BDI’s history with waste feedstock, Ernst (Martin Ernst, head of biofuels R&D for BDI) says the company has long been aware of polyethylene in animal fats introduced from packaging, ear tags and other means like plastic bags used to separate brains and internal organs from meat, which has become a growing problem over the years. “We developed a patented pretreatment system to remove this, which we are now offering now to customers,” Ernst says. The “usual approach” of filtration does not produce reliable results, he adds. “Our approach involves a pre-unit that accumulates polyethylene using heat and a filter aid,” he says. The polyethylene particles attach themselves to the filter media. The process then employs a centrifuge and tricanter to remove the solid particles. “The fine, small particles we get out with our fat treatment unit,” Ernst says. “We do water extraction for FFA and can use existing equipment.” He says the polyethylene removal module is installed at the beginning of pretreatment and a majority of the contaminants are removed in subsequent steps. BDI patented this two years ago.

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While virgin vegetable oil feedstocks have minor variations from year to year, this variation pales in comparison to variations in animal fats or UCO. “When you get into animal fats and UCO, there’s a great difference in quality and thus those nontriglyceride items (i.e., contaminants) as a result of the processing,” Willits says. “If they were frying onions, there can be a high amount of sulfur, so you have to look at this coming in batch to batch and judge what you can handle.”

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Ernst says in the case of sulfur, BDI switched its focus from pretreatment to the backend. “We looked well into sulfur removal in pretreatment systems, but there the removal capacity is limited,” he says. “There are two kinds of sulfur, organic and inorganic, and for organic sulfur bound to fatty acids, there’s really no good removal in a pretreatment system—adsorbents maybe, but with some waste materials the sulfur content is so high you can only remove so much on the frontend. This is why we employ a special distillation unit optimized for sulfur removal.”

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A startup company named Environmental Fuel Research LLC is working to prove out its polarity-based desulfurization process that leverages a specific type of adsorbent and a process developed by Rich Cairncross, EFR senior research engineer and associate professor at Drexel University.

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If the feedstock is extremely bad, this may require running product through the pretreatment system twice, Willits says. “Or a high concentration of chemicals or slowing the plant down so you can process the material,” he explains. “All are expensive things to do. The key is, if you don’t have the ability to blend stocks, and if you’re tied to buying all your oil from a select number of suppliers, then work with them to balance what’s coming in. If you can’t, then as your feedstock comes in, you need a full analysis to determine what adjustments you have to make to process it. This makes it much more difficult, however, and there’s a higher opportunity for failure.”

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Cavitation may also be employed in pretreatment. “Cavitation is an up-and-coming technology,” Harrington (Patrick Harrington, Crown’s global technology lead for renewable diesel) says, “but it has a niche application depending on the feedstock, so lab tests will prove whether cavitation is effective to run on certain feedstocks. In layman’s terms, cavitation is a blender on steroids.”

Slichter says the differentiation in Crown’s pretreatment design is feedstock flexibility vs. employing brand new technologies.

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Willits details Desmet Ballestra’s state-of-the-art biodiesel pretreatment. When a truckload arrives, the first step is to make sure it contains minimal particulate matter. “We’ve become more sophisticated using filtration and cleaning the material up from the big things—the bricks, bats and dead rats,” he jokes. “Once unloaded and the large material is taken out, we’ve gone from an old bag in the tank filters or metal screens to automated filters that clean themselves and return dirty materials back to a place they can be utilized. The next issue is whether we have to worry about polyethylene. If it’s melted, we use cooling and a filtration process to remove the plastic.”

Next is removal of phospholipids, or phosphorus-bearing materials in the oil. “There are hydratable and nonhydratable,” Willits says, “so we acid pretreat to make all phospholipids hydratable. Then we degum. To separate the oil and water mixture, we use a centrifuge to remove water from the oil portion. If it’s been acid pretreated, all those products have been turned into hydratables, which greatly reduces phosphorous in the oil. Along with the gums, this will take out other contaminants and it’ll [reduce] the metals content. Since we used acid in degumming, now we have to neutralize the acid, so we mix in caustic to remove. Depending on what we’re trying to do, if we’re taking the FFA out, we can add additional caustic to transform the FFA into soaps and remove them in a water wash.”

Bleaching comes next using bentonite clay treated with acid, dried and mixed with oil, heated up, agitated for 20 to 30 minutes and then filtered out. “This takes the trace phosphorus and soaps out,” Willits says, “but there’s still water left in the oil so then it’s dried under a vacuum flash to take the moisture off.” If waxes from distillers corn oil, for instance, must be removed, then the dried oil is cooled, allowing the wax to crystalize, and then they’re filtered out. “This will improve the quality of the finished product so it will pass the [Cold Soak Filtration Test],” Willits says. “Then, depending on the sulfur content, if we need to strip sulfur out, we’ll run it through vacuum distillation to strip the material off.” He adds that this approach is “a much more robust system than what we’ve had to supply in the past for soy oil. It’s not simple, but it gives you much more control over feedstock variability.”

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Like any reputable technology provider, Willits says Desmet Ballestra has made modifications to its processes over time to go in wider directions. “We’ve had to improve mixing of our oils and chemistries, and we’ve leveraged nanotechnology to try and get better, more complete reactions,” he says. “There’s been a lot of tweaking to the process, but also a lot of research done on feedstocks.

When we first got into biodiesel, and then into renewable diesel, we gathered hundreds of samples of potential feedstock, ran them through our analytics lab and pilot plant to try and understand what we can do to help our customers deal with these.

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“Renewable diesel certainly needs even more pretreatment steps,” Dielacher says. “But our experience comes from cleaning up the worst feedstocks, so it’s easier for us to clean them up and produce a cleaner feedstock with lower impurities of metals. This is something we can do by adding further pretreatment steps.” Dielacher adds that BDI has been working intensively with catalyst producers to better understand what they need. “We have the experience to jump into this field and fill a gap,” he says. “Renewable diesel producers do not have much knowledge of pretreatment, so they need someone who can run the unit afterwards.” READ MORE