There are some varying lines of thought when it comes to cleansing and polishing biodiesel, especially whether to do it upstream or downstream in the process. This story from Biodiesel Magazine lays out some of the pros and cons for both.
“In many cases, it’s a better solution to fix problems at their source rather than to treat the symptoms,” says Warren Barnes, vice president of consulting firm Frazier, Barnes & Associates. “Biodiesel quality prior to any purification step is a critical factor in determining procedure.” Typically the impurities to be removed in purification should be as low as possible upstream of the washing method, whether the plant uses water-washing or dry-washing with silicates or ion exchange resins. Oil-Dri Corp. of America focuses sales of its Select adsorbents on the front side of the biodiesel process, says Bruce Patsey, vice president and general manager of Oil-Dri. “By cleaning up the oil prior to transesterification, metals can be better controlled and the reaction with the catalyst is much more efficient for producing FAME,” Patsey says. “Many biodiesel refineries clean up their oil source with adsorbents prior to transesterification.” After transesterification, separation is essential for the removal of glycerin, salts and soaps. Settling tanks, coalescers or centrifuges are all means to separate. Rod Yawn, president of ALX Enterprises, a manufacturer of DW-R10 dry-wash resins, says approximately 80 percent of biodiesel producers use simple settling tanks, about 15 percent use centrifuges and the remainder use coalescers.
Whichever method is used, experts say producers need to keep in mind the entire production process and try to keep feedstocks consistent.