As producers look to meet increasingly stringent quality specifications, purification, distillation and filtration services are becoming more and more important. Combined with the cost-reducing benefits provided by many products and “polishing” designs, purification practices can ultimately lead to superior fuels and profit margins.
By Nicholas Zeman

While conventional biodiesel technology is relatively straight-forward, many variables can influence the overall characteristics of the fuel. Things like glycerin content, centrifuge and pump performance and methanol purity can cause the percentages of certain fuel components to fluctuate. Too much variation and the biodiesel could be off-spec. Completing the cycle and being left with a low-grade product means dollars lost.

From an optimization standpoint, a lot of money has been lost from having less than adequate methanol recovery systems in place because, after the same methanol is used over and over again, it begins to attract water, affecting the process. This is a situation more plants are realizing they need to avoid. “We’ve seen some growth in the area of plants wanting methanol purification equipment,” says Raj Mosali, CEO of Miamisburg, Ohio-based Jatrodiesel Inc. The company has designed a fairly unique distillation column that, for the first time, combines glycerin drying into the methanol distillation, which significantly reduces the energy cost to dry glycerin, Jatrodiesel says. “The resulting glycerin has less than 0.5 percent methanol and pure methanol coming out of the column has 99.9 percent or higher purity.”

Plants continue to upgrade and optimize production processes. Nathan DeMartino, president of Dexter Biodiesel Solutions in Pearland, Texas, said his company recently sold its first BCC900 ColdClear unit to Keystone BioFuels, a 20 MMgy facility in Shiremanstown, Pa. DeMartino said this was the largest unit sold “anywhere in the world” and is the largest install to date. Keystone BioFuels will use the ColdClear unit as a quality control measure to ensure that its biodiesel is consistently below the ASTM cold soak standard for biodiesel, which will “help them achieve the coveted BQ9000 status,” DeMartino said.

The larger models consist of completely different housing and filter systems than the smaller counterparts. They filter 45 gallons per minute of biodiesel fuel and can process 120,000 to 200,000 gallons before the filters need to be changed. Even though biodiesel business is depressed now, there is still interest in new products and systems. “Believe or not, I’m still getting interest from startups—there are still companies out there who are starting and growing,” DeMartino says. “Companies in Canada, for instance, are unaffected by the lapse of the tax credit, and I have a few demonstrations going on up there.”

This shows blenders and other high-throughput producers that the unit can handle their loads, DeMartino says. “I’m really excited about blenders, and the market that is there for this system,” he says. “This installation at a 20 MMgy per year plant demonstrates to blenders that these larger units can be used to lead to better cloud point, pour point, cold filter plugging point and oxidation stability.”

Methanol distillation and recovery, along with the employment of certain filter media like ColdClear, are among the many products and practices producers use to produce excellent fuel. Post-transesterification systems, however, usually begin by “washing” or “polishing” the fuel, a process that can be performed with or without water.

“I would say that the biodiesel industry is getting away from water washing,” says Rocky Costello of R.C. Costello Engineering in Redondo Beach, Calif. “It basically just adds an extra step to the process because you have to turn around and remove any residual water from the biodiesel.”

Dry washing often begins by treating the fuel with magnesium silicate, marketed under various brand names including Magnesol. The Dallas Group of America Inc., the company behind Magnesol dry wash, offers a line of adsorbents to help biodiesel producers purify their fuel and pass the cold soak filtration test (CSFT). Called D-Sol, the new product line “removes sterol glucosides and other contaminants that cause CSFT failure.” D-Sol can be used either during regular dry wash purification or as a post-purification treatment after water-wash or ion exchange purification. It can be used as a part of the regular adsorbent purification process at no additional production cost, or as post purification after treatment that presents modest expense increases, around 2 cents a gallon or less. “Unlike other post-purification filter treatment systems, D-Sol works at normal process temperatures so there’s no need to waste time and energy chilling the fuel down prior to filtration,” the Dallas Group says.

Ion Exchange

Magnesol is a dry wash that removes residuals such as sodium and potassium from the fuel. This process itself, however, leaves impurities that must be removed through various membranes and filter media so the resulting product is sparkling. An alternative to a Magnesol wash is ion exchange. Costello says that he doesn’t publicize which dry wash method he advises using, adding that the discovery of what works best over the years is sort of a trade secret. “I will say that using Magnesol, however, creates a landfill issue,” Costello says. “With ion exchange, you don’t have nearly as much waste material.”

Ion exchange media have been relatively one-dimensional in the past, but new products are increasing versatility and allowing producers to comply with stricter quality assurance standards. This is the market sector that brought the monolithic Dow Chemical Co. to the biodiesel industry. Dow said it saw an opportunity to help buffer the volatility of raw materials costs and produce a superior quality fuel. At this year’s National Biodiesel Conference & Expo in Grapevine, Texas, Dow launched its new Ambersep BD19DRY fuel polishing resin that can help producers pass the CSFT. “Ion exchange resins usually don’t address the cold soak filtration, which is why Dexter sells Schroeder’s ColdClear product,” DeMartino says.

Mosali says, however, that certain ion exchange mediums “are not truly multi-feedstock” and do not adapt well to changes in free fatty acid content. “If your feedstock is absolutely uniform and consistent, then ion exchange makes a perfect product,” Mosali says. “Any variation though, and you start to run into problems.” He adds that similar problems have been reported with ColdClear. “Any change in the feedstock and your changing those cartridges like crazy,” Mosali tells Biodiesel Magazine.
While these products may have individual weaknesses, DeMartino says they can be used in conjunction to stage a more versatile polishing process. “What I’ve found to work really well is that you run biodiesel through the Eco2Pure product before it goes through ion exchange,” he says. “This allows for a longer life of the ion exchange beads, which are more expensive and it removes the soaps from the fuel. Because ion exchange resins are acidic, they turn soaps back into free fatty acids.”

Eco2Pure is a cellulosic material, a mesh of hardwood sawdust, a truly renewable filter medium. “As the unwashed biodiesel enters the Eco2Pure treatment tower, it passes through a fixed bed of Eco2Pure purification media, ensuring the fuel is purified in a single pass removing production residues, fuel contaminants and soaps,” Dexter says. “Flow rates need to be governed accordingly in order to ensure maximum removal of production residues and soap.”

Post-production and Testing

Testing is also a crucial component of polishing practices. Slight variables in the performance of settling tanks or centrifuges used to separate glycerin from the fuel before the filtration and wash stages can increase the level of impurities. More impurities mean greater cost. “If your separation doesn’t occur that well because of a drop in tank temperature, or the centrifuge is not performing consistently, your glycerin levels go up and you’re buying many more filters,” Mosali says. “So you have to continuously test the fuel because the process responds to variables. Centrifuges, for instance, are not consistent equipment—they have a lot of issues all the time. If it leaves more glycerin in the fuel, you’re changing filters all the time.”

Purification of glycerin—the product that results alongside biodiesel after transesterification—might also be a component of plants’ back-end systems, but is associated with a huge capital expense. Nevertheless, the numbers look pretty attractive, considering the price for pharmaceutical-grade glycerin. “It could be as profitable as biodiesel, but you have to be assured of constant production to make it work,” Mosali says, alluding to the lapse of the federal tax credit that has caused many plants to idle their production.

Even after the last filter biodiesel touches before it goes into holding tanks, it is further treated with different additives such as Eastman Chemical’s solution for oxidative stability, BioExtend. Different combinations of these are often used in branding campaigns throughout the industry. Colorado’s Blue Sun Biodiesel focuses on its particular additization package as a sales pitch.

Costello says that the big trend is distillation because it removes all impurities from the biodiesel. Some critics have noted, however, that distillation compromises the oxidative stability of biodiesel and requires the use of costly additive packages previously mentioned. “We think you need an additive package whether you’re distilling the fuel or not,” Costello says. “You do have to be sure that distillation occurs at the appropriate temperature so that oxidative components are not compromised.”

Nicholas Zeman is associate editor of Biodiesel Magazine. Reach him at (701) 738-4972 or nzeman@bbiinternational.com.