As renewable diesel production ramps up globally, myriad questions about the availability and price of the feedstock required to sustain billions of new and proposed gallons of biomass-based diesel are under intense scrutiny. From used cooking oil (UCO) and distillers corn oil (DCO) to tallow and choice white grease, these low-CI—and traditionally low-cost—byproducts of cooking, food processing and corn ethanol production are not only in ultra-high demand this summer, but on the threshold of a realignment of value and control.  
 
Meanwhile, working behind the scenes to make these inputs feasible for renewable diesel, technology firms with decades of biodiesel pretreatment experience are applying the full weight of their feedstock and process knowledge to the creation of systems that clean up both waste and virgin oils for processing. In North America, Europe, Asia and elsewhere, companies like Desmet Ballestra, Crown Iron Works, and BDI-BioEnergy International are being tapped to design and build custom pretreatment platforms to the onerous specifications of hydrotreatment. These specialized input-cleansing regimens are new iterations of the technology and purification steps used for years in biodiesel production, but now enhanced to reduce additional key contaminants.

Theo Friedrich, technical sales manager for BDI, which has been engineering biodiesel plants for a quarter century, says it is helpful to recognize what is similar about renewable diesel and biodiesel pretreatment before pointing out what isn’t. “The basic treatment for each application is the same,” he says, explaining that both biodiesel and renewable diesel applications remove obvious impurities like polyethylene particles, for example, which can otherwise block filters, pipes and heat exchangers.   

Bill Morphew, global commercial director of Crown Iron Works’ liquids segment, agrees that renewable diesel pretreatment has synergies with biodiesel pretreatment, and has been a natural layering of industry knowledge onto a growing segment of production. “While there is still considerable interest and volume in biodiesel, the building activity has leveled off while interest in renewable diesel has skyrocketed,” he says, adding that Crown now has a dedicated team focused primarily on renewable diesel at its Minnesota-based headquarters.

Desmet Ballestra, too, has structured its renewable diesel pretreatment system around its decades-long biodiesel experience. The Germany-based company, which has an active North American division, has designed and built over 125 biodiesel plants globally. “Biodiesel essentially started with virgin oils, and as the industry matured, producers had to take more of the lower-quality feedstocks,” says Blake Hendrix, president and CEO of Desmet Ballestra North America. “In essence, our pretreatment technology developed from meeting those production challenges.”

More than a decade ago, Hendrix says, Desmet Ballestra recognized that interest was picking up in hydrotreated vegetable oil (HVO), or renewable diesel made from principally virgin oils. “It was consistent with the work we were already doing,” he says. “We engaged early, and there is probably only one company in the world that has a larger volume of installed renewable diesel pretreatment technology than us today—and that’s Neste, which handles its own pretreatment.”

Notably, Desmet Ballestra has installed renewable diesel pretreatment systems for high-profile refiners such as Diamond Green Diesel—currently expanding to 675 MMgy—in Norco, Louisiana, and Eni, an Italian petroleum company with an existing renewable diesel plant in Venice and another starting up soon in Gela, Sicily. All three plants utilize the Ecofining process co-developed by Honewell UOP and Eni. “Our renewable diesel work continues to grow globally,” Hendrix says. “Our business is growing in North America and in Europe where feedstocks like partially refined fats are sometimes slipstreamed into petroleum refining and a number of stand-alone pretreatments are being built. We’re also seeing increased activity in Asia as petroleum companies there install hydrotreaters—some taking in pretreated palm oil and others taking used grease. It’s all dependent on what’s available in the market.”

Hendrix says the practice of collecting feedstocks like UCO and rendered animal fats in North America is robust in comparison to Asia, where a larger percentage of used oils and greases are consumed in the cooking process. “You don’t have a lot of excess grease to collect in those areas of the world,” he says. “I think you’ll see the industry collecting different feedstocks in Asia for renewable diesel production than what’s being sought after in North American or Europe.”

Pretreatment Parallels
While there are numerous similarities between biodiesel and renewable diesel feedstock pretreatments, Patrick Harrington, global technical sales manager for Crown’s liquids segment, says renewable diesel feedstocks are held to more stringent specifications than biodiesel inputs. “There are additional contaminants we have to deal with for renewable diesel that we simply didn’t have to consider with biodiesel,” he explains. “Not only are we addressing very low phosphorous specs, but also total metals, chlorides, nitrogen, sulfur and more.”

Friedrich concurs, explaining that in biodiesel production, various impurities can be left in the feedstock and removed later through distillation of the final product as long as a suitable technology for the biodiesel is being used. “That doesn’t work for renewable diesel,” he says. “The hydrogenation catalysts are sensitive to several impurities, which have to be reduced to low-ppm levels to avoid catalyst poising and, in addition, other impurities like nitrogen can result in unwanted byproducts.”

One of the key differences between renewable diesel and biodiesel feedstock pretreatment is that renewable diesel hydrotreaters can take 20% free fatty acids (FFAs), and sometimes quite more depending on the hydrotreater technology, whereas traditional biodiesel transesterification processes must be fed low-FFA inputs. “With renewable diesel, you want to leave the FFAs in, while you need it removed for most biodiesel processes, at least those in the transesterification category,” Hendrix says, explaining that there are ways to make biodiesel from feedstocks with the FFAs left in. “It’s a more sophisticated and aggressive approach—acid esterification or enzymatic routes—but the vast majority of biodiesel production is transesterification that requires the FFAs to be pulled out. With renewable diesel, on the other hand, you can leave it in.”

Beyond foregoing the removal of FFAs, renewable diesel feedstock pretreatment is generally more rigorous than biodiesel pretreatment in almost all categories. “Biodiesel is very forgiving on phosphorous and earth metals—calcium, magnesium, potassium, copper and iron,” Hendrix says. “Renewable diesel is much more sensitive to those metal contaminants in the process. They need to be very low.”

 Hendrix explains that total metals need to be in the 5-10 ppm range for renewable diesel, and phosphorous needs to be 1-3 ppm in order to maintain the life of process catalysts. “Phosphorus is a real catalytic poison in the renewable diesel process, as are the other earth metals,” he says. 

Removing metals from low-quality feedstocks can be challenging. “Metals can be removed from virgin vegetable oils rather easily, but lower- and mid-grade inputs like DCO, rendered fats, roadkill, you name it, the metals content in these products is, at times, an unpredictable chemical soup,” Hendrix says. “You have to be able to adjust your processes to handle these feedstocks, and that’s what all of us in the pretreatment business are competing to do best.”

Notably, Hendrix explains that sulfur, which needs to be distilled out of methyl esters for biodiesel production, is less of a concern with renewable diesel because it can be removed during the refining process downstream. 

Friedrich notes that renewable diesel production is much less flexible than biodiesel when it comes to designing the process around specific feedstock characteristics. “With biodiesel, we develop and build the complete process at BDI, designing it to handle poor quality of feedstock,” he says. “For renewable diesel, on the other hand, we focus only on the pretreatment and therefore the requirements of the downstream hydrotreater dictate the pretreatment limits.”

Define, then Design
Even though hydrotreaters cannot generally be designed around feedstock traits, Friedrich says, understanding the products entering renewable diesel pretreatment remains vital. “The correct analysis, and especially the interpretation of the results, is very important,” he says. “The chloride content in a feedstock, for example, can include chloride salts and organic chloride, and you have to differentiate between them.”

The same applies for phosphorous. Friedrich explains that in vegetable oils the main phosphorus content comes from phospholipids, which are removed in a degumming step. He says waste oils, too, often have a high phosphorous content, which can be present in different forms. “In the case of tallow for example a share of the phosphorous can come from bone meal particles,” Friedrich says.

Furthermore, Friedrich explains, refineries and hydrotretaer developers are accustomed to the ideal conditions of vegetable oils. “They also want to process bad quality waste feedstock, but it takes some time for them to realize that a pre-treated fatberg (i.e., sewer grease sludge) has more impurities than pre-treated rapeseed oil,” he says.

Some of the feedstocks going into renewable diesel production, today, are “poorly defined, if defined at all,” Morphew adds. “And as the value of these feedstocks has increased, suddenly you have a value output. With producers of these fats, oils and greases recognizing that products previously considered wastes are now worth considerably more, the result is an acceleration of previously uncharacterized feedstock finding its way into the market.”

For that and other reasons, Morphew says, it is crucial to characterize and understand the novel, low-quality feedstocks making their way into renewable diesel before they are put into use. “We sometimes hear from processors who have made a set of assumptions about feedstocks only to see a different level of quality arrive at the gate,” he says. “That has to be addressed, so they turn to us for analysis,  possible pretreatment steps, or unit ops, to take care of any number of issues they might face—solids content, moisture, or a unique contaminant.”   

Feedstocks of the same name can and do vary. Experts say UCO, for example, may have a considerably different quality depending on where—region, industry, storage conditions—it is sourced. “Imported UCO, for instance, may give you a different set of parameters than domestic UCO,” Morhpew says, “But other types of feedstock, too—even those that are well understood like soybean oil—can present varying levels of quality, depending on their origin.”
Friedrich agrees. “UCO is not UCO, and tallow is not tallow,” he says. “It strongly depends on the source of origin, and the handling. Tallow can have different properties in the summer due to higher temperatures in the upfront handling and storage of the slaughter waste. So, all these aspects have to be taken into account when discussing crude feedstock parameters, and afterwards to design the process.”

Harrington says most suppliers of waste fats, oils and greases are not yet accustomed to the sophisticated product analysis requirements of the renewable diesel industry. “Even a well-developed feedstock market like tallow is not typically going to give you the level of detail you need,” he says. “Certainly prior to this renewable diesel boom, they were only going to give you a spec that included FFA and color—and maybe moisture. But we now need to understand a half dozen other parameters that aren’t included.”     

To fill this product characterization void, Harrington says, Crown often requests product samples from suppliers and sends them to outside analytical labs for more complete depictions of the material. The rise of renewable diesel has, in fact, created a noticeable uptick in feedstock analysis—performed both in-house and by third-party labs. The analysis of unique and variable feedstocks is typically cross-referenced and catalogued with previously characterized product (i.e., well-known feedstocks). Crown, for example, maintains a proprietary database of specifications for biodiesel, renewable diesel and oleochemical feedstocks that reaches back 70-plus years. “Our proprietary database of specs is decades old—starting with clean virgin oils and extending into these used oils, tallows and other feedstocks that are desirable for renewable diesel,” says Kris Knudson, vice president of global sales and marketing at Crown. “We are continuously adding to that bank of feedstock knowledge.”

Leaning heavily on its in-house capabilities—with a deep-benched lab in Brussels, Belgium—Desmet Ballestra has developed unique pretreatments for a spectrum of different feedstocks, from soy and rapeseed oils to the lower-quality waste inputs sought after by producers chasing low-CI.

“We have a long history of technical innovation,” Hendrix says. “We have Ph.D. food scientists and Ph.D. chemists on our laboratory team, working across all spectrums of feedstocks in house. And we’re adding capabilities to our lab now that will allow us to look at some things we couldn’t analyze before—nitrogen and sulfur, in particular—which both need to be removed in renewable diesel production.”

Feedstock Realignment
While there are good quality fats, oils and greases still available in the market, waste feedstocks, collectively, are becoming progressively lower in quality as global demand rises, pulling marginal product into the supply pool. “We’ve seen that the feedstock quality has changed over the time, due to an increase in the demand for waste feedstock,” Friedrich says. “Take UCO as an example. It started small with local collection and local biodiesel production, but with the increasing demand for UCO, nowadays, it is a globally traded feedstock. The source of the fresh cooking oil is different—conditions differ—and also the collection and storage is handled differently globally. This all results in different qualities, and therefore pretreatment is much more important.”  

Intense new demand for waste feedstocks are creating what Hendrix believes may be a global realignment of the market. “Today, all these feedstocks have a home,” he says. “They’re fungible and being sold to somebody. Who’s buying them, and what’s being done with them? That’s all being redefined.”

The market adjustment Hendrix and others are witnessing is primarily the result of petroleum companies having the scale and financial means to pull large volumes of available low-quality feedstocks away from their historic uses and values. “Those previously using these feedstocks for feed, for example, might have to return to traditional inputs—virgin oils—and that’s why we’re seeing increased crush,” Hendrix says. “It’s not only the result of renewable diesel, directly, but the secondary demand created by the fats renewable diesel is pulling away from feed.”

Hendrix explains that, as this realignment plays out, animal nutritionists will figure out how to source the necessary amounts of triglycerides required for various rations. “Not only are you going to see waste fats being replaced with vegetable oil—the main option—but possibly a return to full-press (i.e., full-fat) soybean plants that leave the oil in the feed. If you need a certain amount of oil in the meal anyway, it’s conceivable that we might see those types of full-press plants built, without solvent extraction.”

Hendrix adds, “Renewable diesel isn’t going away. People don’t build these renewable diesel plants without a long-range view. When you do this in the fuel industry, you’re realigning entire petroleum refineries. And once you change these facilities, they don’t change back quickly.”  

Robust, Flexible Design
The long-term repositioning of refinery configurations also means renewable diesel producers are seeking pretreatment systems that are not only efficient and flexible, but durable.

“Each setup is built to be robust enough to handle feedstocks that, to be sure, are going to vary—they just will,” Knudson says. “Feedstocks change. There is going to be variation, and your pretreatment needs be able to handle it.”

Knudson says Crown identifies and evaluates the trade-offs with key design factors to set its customers up for success. “These impact factors are multifaceted and include key design criteria, where small increases lead to the most operational benefits, how set-up impacts maintenance programs, and numerous tricks of the trade learned throughout the years,” he says. “Time spent upfront designing a flexible and robust system can pay dividends for decades.”     
  
Friedrich agrees that renewable diesel pretreatment systems must be built with a high level of robustness and flexibility. “These systems have to be able to accept a wide variety of feedstocks—sometimes heavily impure—without causing a production stoppage up front.”

Step by Step  
The entire renewable diesel feedstock pretreatment process is not easily explained in brief. However, almost all prescribe to some standard processing steps, from degumming to final polishing before the product enters the hydrotreater.
According to Morphew, the first consideration of renewable diesel feedstock pretreatment is receiving, or the method and management of taking in and storing raw material. “You want to be careful not to let your solids content get too high in a storage tank, for instance,” he says, explaining that the typical stages of pretreatment include solids removal and degumming, to remove phospholipids, followed by a water wash and, finally, a bleaching, clay adsorption system that polishes out the final metals. But it all starts with analysis.

Friedrich insists that a thorough analysis of incoming crude feedstock is the first and most important step of pretreatment. “The analysis determines the efficient operation of the process, as the level of impurities defines the amount of required chemicals and adsorbents used in the process,” he says. “As the limits for several impurities are very strict, it’s important to know the details, especially regarding the optimum operation without operating costs getting too high due to over dosage of chemicals.”

With fresh vegetable oils, the first step of pretreatment is degumming via centrifugation, but conventional centrifuges don’t work well for processing waste oils. “At BDI, we use a [Flottweg] Tricanter-based pre-purification unit to secure a reliable and efficient operation,” Friedich says. “And we are still flexible to process a broad range of feedstock.”

For BDI, a drying unit and an advanced adsorption follow the pre-purification steps. In the adsorption, metals and other impurities are removed. Friedrich says the key to effective adsorption is to select the right adsorbent, as there are dozens of different materials available on the market.

A polyethylene reduction unit is an additional upgrade for pretreatment systems—especially for those processing tallow—along with an FFA reduction unit. Friedrich says physical refining can be used to separate FFA from the triglyceride stream, or as an alternative, it is also possible to use a glycerolysis process to convert FFA back into triglycerides. “Choosing the right option is crucial to achieving an economically-efficient operation,” he says.

Hydrotreater Ready
Renewable diesel feedstock pretreatment doesn’t have to happen at the site of a renewable diesel refinery. “We’ve seen all of the above,”  Morphew says. “Certainly, there is a desire to have some control over the pretreatment by the renewable diesel producers themselves, and there is also an interest by the fats and oils producers to evaluate the market and try to provide a pretreated, renewable diesel-ready product.”   
 
Recognizing this, Crown recently branded and trademarked its RD Ready™ Pretreatment System. Knudson says the name has a couple of facets: “First, it reflects how Crown’s robust system can accept a wide variety of feedstocks to produce a pretreated product that is ready to feed a renewable diesel/HVO system,” he says. “Second, new or existing facilities that won’t have their own hydrotreater can adapt to supply pretreated feedstock that meets the stringent specifications of the RD market.”

In late April, Seaboard Energy, a division of Seaboard Foods, announced that it is building an 85 MMgy renewable diesel plant in Hugoton, Kansas—at the site of the former Abengoa ethanol plant—that will utilize Crown’s RD Ready™ pretreatment system. Seaboard has already recommissioned portions of the idled assets while its EPC contractor, Fagen Inc., simultaneously builds the greenfield renewable diesel plant, scheduled for startup by the end of the year. The facility will utilize local animal fats and vegetable oils as feedstock.

“We envision our RD Ready™ technology being a fixture in the feedstock market in the coming years,” Knudson says. “By delivering the cleanest possible feedstock to a customer’s hydrotreater, our design can extend catalyst life two-fold. We guarantee product quality.”

Hendrix agrees that a growing volume of feedstock might be pretreated in advance of production or off site, so long as the right quality assurances are in place. “I think you will see more of that sort of thing, but it depends on the philosophy of each petroleum company and whether they’re going to partner with somebody on producing a readymade feedstock for production,” he says. “In my experience, most refiners want to closely manage and control their feedstock through pretreatment. But I think all sorts of different scenarios could play out as more production comes online.”

Author: Tom Bryan
Biodiesel Magazine
tbryan@bbiinternational.com
701-746-8385