Proving Out Supercritical Processing

It’s a major award-winning process—so where is it?
By Luke Geiver | May 13, 2011

When BioFuelBox, the biodiesel process technology company that designed, built and ran a 1 MMgy biodiesel facility in Idaho based on the principles of the supercritical process—high pressure and high temperatures—won the 2010 Technology Pioneer award from the World Economic Forum, one could argue that a new beginning in biodiesel production methods for alternative feedstocks was set. After all, look at the success of some of the previous winners, most you've probably heard of. In 2010, along with BioFuelBox, the social media company Twitter received the same award. In 2007, it was Mozilla and, in 2006, Amryis Biotechnologies received the award. If these don't make a compelling case that the supercritical process for biodiesel production was well on its way to becoming the norm after the 2010 award, consider the winners in 2002, Google and PayPal.

“We took a technology that had been done in labs, and we took it to full scale,” says Christina Borgese, former senior engineer for BioFuelBox. “We were selling product to a corporation that said we had the best biodiesel they’d ever seen.” Unfortunately, that World Economic Forum award didn’t come with a guarantee for future economic prosperity, and today, BioFuelBox is no more, a victim of an extremely difficult financial climate seen in 2010 within the biodiesel industry: an innovative company all but forgotten. Borgese, who says “it was a big accomplishment to have scaled supercritical beyond the lab bench,” is now co-founder, senior engineer and president of PreProcess Inc., along with her partner and other co-founder Marc Privitera, who was also formerly on the BioFuelBox team.

As Borgese would attest, there is much the biodiesel industry can learn from the brief, wondrous life of BioFuelBox, perhaps most importantly that supercritical biodiesel technology has been proven to work at commercial scale and, in the right situation, might prove to be the best. But, as the name implies, a number of factors should be evaluated before a producer looks to retrofit or initiate an operation using  principles of high temperature and high pressure.

What We Already Know

Randy Weinstein, chair of the department of chemical engineering and program director of a one-year-old sustainable engineering program at Villanova University, says supercritical fluid has a bad name. “It kind of scares some people that don’t really know what it is. They kind of equate it with nuclear reactors,” Weinstein explains. The process is, of course, complex, but nothing close to nuclear levels.

Borgese, an expert on the subject, describes it this way. “A supercritical fluid can be any material that has been taken to a temperature and pressure higher than its critical point. At this state, distinct gas and liquid phases do not exist. Supercritical fluids can exhibit effusion rates similar to gases and can dissolve materials into its components like a liquid.” Combine that with the fact that during the process, a catalyst is not required to create a reaction and the feedstock can be much higher in free fatty acid (FFA) content than traditional feedstocks, and the process appears to be intriguing. “There are a lot of potential reaction sites because the more the material moves around, the more reaction potential there is,” Borgese adds, and the result is far less glycerin product. In a typical process, one leg of a triglyceride will be broken off at a time, forming diglycerides, and from there other legs are broken off forming monoglycerides. With a supercritical process and the higher number of reactions, the overall amount of glycerin is cut down. Less glycerin is inherently produced in supercritical processes because higher FFA materials are typically used. The byproduct of an FFA esterification reaction is water whereas the byproduct from a glyceride transesterification is glycerin. A supercritical process “has the potential to cut down on your processing time because you are going to do a lot of quicker separations,” Weinstein says.

But even though the elements required to drive a supercritical reaction that ultimately create an indistinguishable mix of both gas and liquid are certainly achievable, Borgese does, however, caution that not everyone can do it. “Supercritical is not something that you just do in your backyard,” she says. “When you are dealing with methanol at a supercritical fluid state and the letdown of the temperature and pressure, you have to have all of your purge systems in place, which can be done,” she adds, “someone just has to do it right.”

Bevan Dooley, managing director for InProTek, an Australian-based engineering firm that has created a supercritical system of its own, conveys the same message as Borgese and points out one of the main factors everyone needs to know about the process is safety. “These (supercritical) conditions create additional safety concerns that require careful management and [that] intrinsic safety measures to be designed into the plant.”

As for the supercritical processes, when safety measures go up, so do the capital costs. Because the process involves taking fluids to 800 degrees Fahrenheit and 3,000 PSI, Borgese says equipment requirements include class 2100 flanges and other material that can withstand those pressures and temperatures. Weinstein points out the need for special steel alloys; Borgese says there can’t be any plastic that comes in contact with the supercritical fluid at one of these plants; and Dooley sums it up by saying, “material selection at these temperatures and pressures is paramount.”

In an odd twist, it’s the necessity for safety that has formed one of the commonly held beliefs, or to be more accurate, truths, about such a process—it costs more upfront. And the need for certain materials isn’t the only aspect driving up the capital costs of a supercritical process. As Weinstein points out, producers aren’t “going to have a lot of in-house expertise on supercritical fluids.” While Borgese says that a return on investment is dependent on the chosen feedstock and a few other aspects, installing a supercritical process could show reasonable one to one-and-a-half year paybacks of capital, but that is without including the engineering costs. Add in those costs to a volatile biodiesel landscape and it might be a bit clearer why such an award-winning technology hasn’t taken off.

For a research study titled “Economic Issues Related to Continuous Supercritical Biodiesel Production,” co-authored last year by Michael Popp, an economist for the University of Arkansas, much of the data used was on bench-scale research. Popp’s team took high FFA feedstock, blended it with methanol and raised it to high temperatures under high pressure in the absence of a catalyst to generate their own supercritical data. Although Popp says the process is attractive based on its ability to allow producers to be highly feedstock flexible, “and basically go shopping for whatever you can get that is giving you the least price per pound,” he also says one of the factors holding back growth of supercritical processes is related to what already exists in the industry.

“We probably have excess capacity using different technology,” he says, “so why would people convert to a new technology when there is excess capacity using other proven technologies where they know the yields upfront?”

In addition to what we already have, Borgese says that fluctuations in energy prices also factor into the processes growth. “Right now the biodiesel market fluctuates back and forth with fuel prices, so when you have fuel prices really high, then everyone is into biodiesel, and when they go down, investors pull out.” On top of those factors, Weinstein says that there is just not a readily available provider of this technology.

Even with all of the factors that might detract from the allure of producing biodiesel without the presence of a catalyst, there are, however, a number of reasons why it could still be the next best approach.

Why Supercritical Will Happen

To start, Dooley might disagree with Weinstein—sort of. His team of engineers, which features a background in the construction of supercritical steam generators and high temperature and pressure oil cleaning processes, has worked in the biodiesel industry before and felt that the development of a supercritical process “was the next logical step.” Now the team has developed a system it plans to unveil that they say can create margin improvements of up to $140 a ton: $50 a ton generated from the catalyst cost savings, $40 a ton from a 4 percent yield increase over base-catalyzed reaction and $50 a ton through the neutralization of chemicals.

The InProTek system may not yet be here, but developments are happening in this technology sector and, under the right circumstances, more could be on the way. Popp says that if the industry were to expand, supercritical might be the process used in future plants based on its feedstock flexibility aspects. Weinstein says you have to start looking to the future “when everybody is starting from scratch from other oils not being produced from soy. Then you might be able to start designing something around that which would be a supercritical process.”

Borgese says the supercritical method can process feedstocks with 85 percent FFA and higher and, in doing so, can tap into otherwise untouchable feedstocks that might otherwise be landfilled. With today’s biodiesel prices, she adds that there is more room to work with given the price of biodiesel a year ago. That things are different than they were a year ago may be the best for the supercritical process. Next year, it’s safe to say the same will apply. BioFuelBox didn’t make it, but the project showed the industry something very important about supercritical technology. And if we want to know what the future of supercritical processing methods will look like, maybe we should just take the word of someone who has been there and done that. “The reaction technology works,” Borgese says. “At this point, it is just a matter of getting feedstock. As these materials like soy oil rise,” she says, “an increased look at further waste materials will happen.” And as every producer knows, feedstock plays the biggest role in the technology used.

Author: Luke Geiver
Associate Editor, Biodiesel Magazine
(701) 738-4944

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