Innovations in Biomass-Based Diesel

FROM THE NOVEMBER ISSUE: Renewable diesel and supercritical biodiesel address corn oil’s high FFA content in different ways.
By Susanne Retka Schill | October 18, 2018

Two ethanol producers are adopting quite different innovative technologies to add value to their corn oil—one making biodiesel with supercritical methods, the other making renewable diesel. East Kansas Agri-Energy’s renewable diesel plant has been operational for about a year, after taking months to work through the bugs in Saola Energy’s first-of-its-kind plant. Diversification was the primary goal, “an income stream that isn’t ethanol,” says Bill Pracht, president and CEO of EKAE. “Our plant closed in the drought of 2012. Renewable diesel made sense for us because, during that time, we could have bought corn oil or another feedstock and run renewable diesel.”

Those familiar with the dynamics of the California market’s Low Carbon Fuel Standard understand the motivation for Calgren Renewable Fuels in Pixley, California, to add biodiesel production to its portfolio. Calgren produces about 2.5 million pounds of distillers corn oil (DCO) at its 58 MMgy plant, about half of what the biodiesel plant now under construction will consume, says Lyle Schlyer, president. Renewable Process Solutions’ supercritical technology is expected to produce a biodiesel with a carbon intensity (CI) score in the low 20s, earning attractive carbon credits. Construction on the plant is set to be completed in December.

In both cases, the interest in using new process technologies is spurred by the difficulty in processing the high free fatty acid (FFA) feedstocks that result in low CI scores. Even the modestly high FFA levels in DCO—generally around 12 percent—require extra processing steps, thus adding cost. “The traditional processing of free fatty acid feedstocks, we think, is inefficient,” Schlyer says. “Acid catalyzed esterification followed by base catalyzed transesterification, and there’s drying steps between due to the water produced. Yuck. We think what RPS is doing is much more elegant.”

RPS’s technology uses supercritical conditions that do not require catalysts, explains Rahul Bobbili, president and chief technology officer. “When you blend oil and methanol at room temperature, 65 Celsius, they don’t mix together, so you add a catalyst—sodium methylate for transestertification (of triglycerides) or sulfuric acid for esterification (of free fatty acids). The catalyst acts to increase contact to produce biodiesel.” In the RPS technology, temperature and pressure of the oil and alcohol mixture is increased to a point where it is neither a gas nor liquid, the supercritical state. “It’s in a state between, where the density of both liquids are so close they are miscible with each other so you don’t need a catalyst,” Bobbili says. “At that point, the molecules rearrange themselves and come out as methyl ester, which is biodiesel.” 

One advantage to supercritical biodiesel is that it works with any level of FFA, Bobbili says, and does both esterification and transesterification in a single step, without producing impurities. “It is a clean method of producing biodiesel, but it comes with a cost. Conventional biodiesel systems cost between $1 to $1.50 per gallon, but a supercritical system comes at a cost around $2 per gallon.”  A state grant brought the cost down, improving the rate of return for Calgren, he says. “But when I talk to other ethanol facilities, they feel reluctant to build this plant because of the capital cost and return on investment spread out to three to five years.”

Schlyer expects it will take some time to get the kinks out of the new plant once it comes online. Calgren will begin processing its own corn oil, with plans to add even higher FFA feedstock to the mix. “We would love it if we could go half and half with our distillers corn oil and a high FFA feedstock like brown grease.”

In the meantime, Bobbili responded to the ROI challenge by engineering a combined approach, dubbed Hybrid T. “If we have 12 percent FFA, we filter and strip the fatty acids from the oil in the front end. The now virgin corn oil goes through transesterification, which is proven. On the side, we take the secondary product, the fatty acids, and process them through a very small supercritical system.” The FFA product is reintroduced to the transesterification step with no yield loss and the overall cost of the system substantially reduced, he says.

Drop-In Approach
EKAE took a different approach to addressing the high FFA content in DCO with its renewable diesel plant. The technology is adapted from oil refineries, explains Dean Camper, Saola chief technology officer, who previously worked in refining. Hydrogen is introduced into corn oil under high pressure and temperature. “The hydrogen will react with oxygen to form water and saturate everything, leaving basically a hydrocarbon,” he says. “It’s the same components you end up with in petroleum diesel.”

And, as a hydrocarbon nearly identical to diesel, it can be blended at any ratio or used at 100 percent. While the capital expenditure is higher than biodiesel, it should not be as labor intensive, he says.
In addition to renewable diesel yields in excess of 90 percent, Camper says the plant produces naphtha, which can be used as a denaturant in the ethanol plant. The process is also energy long, producing fuel gas that can displace natural gas or excess steam that can supply energy to the ethanol plant.

EKAE is still optimizing the plant. “Our hydrogen supply is not big enough to let us run at full capacity,” Pracht says. “It needs reliable and affordable hydrogen production, and that can be accomplished.” EKAE’s 50 MMgy ethanol plant produces a little more than half the DCO needed for the renewable diesel plant, he says. “And, we’re not running our diesel capacity wide open. When it shakes out, we will produce close to half our needs and we’ll be buying corn oil directly from neighboring ethanol plants.”

EKAE is selling its renewable diesel on the West Coast. “We’ve sold to California, Oregon and Vancouver,” Pracht says. “Pearson Fuels is our marketer and they sell in those three areas. That’s where the demand is now because of the Low Carbon Fuel Standard.” He couldn’t give a CI score, as the plant is currently using a temporary pathway while applying for a permanent one under the California LCFS.

Renewable diesel pricing is based on diesel, which varies with location. “It’s sold off the basis of diesel, the price of CI credits and RIN pricing,” Pracht says. Currently, he adds, the RIN market is depressed, due to small refiner waivers. The ethanol industry has been highly critical of the U.S. EPA’s generous waivers on quotas for renewable identification numbers (RINs) used to demonstrate compliance with the Renewable Fuel Standard. “That’s ruined the RIN market for renewable diesel,” Pracht says. “We get 1.7 RIN per gallon. You can do the math on what RIN price going from $1 to 40 cents does—it takes the fun out of it.”

Renewable diesel does have other advantages. Unlike corn ethanol that tends to be treated like an ag commodity following the corn market, renewable diesel—and biodiesel to some extent—is tied to the energy sector. “You can look at the board today,” Pracht says about the early September markets. “Heating oil is $2.24 [which biodiesel is benchmarked against], gasoline is $2.15 and ethanol is $1.26.” While it may cost more to produce a gallon of renewable diesel, it is a direct drop-in for petroleum diesel, Pracht points out, adding that renewable diesel has a higher cetane value, burns cleaner and provides slightly better fuel efficiency than petroleum-based diesel. “And it can’t be made into an ag commodity.”

Author: Susanne Retka Schill
Freelance Journalist