Ultrasonic Biodiesel Processing

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One of the biggest research and development pushes today is the production and manipulation of nanomaterials to create new quantum mechanical effects by drastically increasing surface area-to-volume ratios. One method of producing these tiny scientific wonders, which researchers have found extremely proficient, is ultrasonic cavitation. Ultrasonics involves the use of sound waves at frequencies inaudible to human ears. The violent reaction in the flow cell, caused by ultrasonic vibration, creates nano-sized bubbles that vastly increase surface area on which reaction can take place. In addition to the role of ultrasound in nanomaterial manufacturing, uses of ultrasonic cavitation include everything from wastewater treatment to production of various chemical compounds, inks, coatings, biomeds, pharmaceuticals, cement and biodiesel.

"There are just so many applications because of the intense mixing and cavitation," says Mike Riebenfeld, sales manager for Hielscher USA, part of Hielscher Ultrasonics GmbH based in Teltow, Germany, outside of Berlin.

Hielscher Ultrasonics emerged in 1991 two years after the Berlin Wall came down. Kathrin Hielscher, marketing and communications person with the company, said Kenneth Suslick, a professor at the University of Illinois at Urbana-Champagne, did all the basic research and related work on ultrasonic chemistry, laying the foundation for the applications of ultrasound in the lab and industry. Hielscher Ultrasonics started with development of ultrasonic devices for laboratory use.

"But the research and the successful applications created more and more demand for devices with a higher capacity to sonicate material on an industrial scale," Hielscher says. As a result, the company developed its UIP1000 ultrasonic unit, which utilizes 1 kilowatt of electricity to provide cavitation and mixing shear. "This was the beginning for industrial ultrasonic devices," Hielscher says. "Now, Hielscher offers ultrasonic devices up to 16 kW and is worldwide the single supplier of such powerful ultrasonic equipment."

Hielscher says since the early 2000s, when the company first introduced its ultrasonic reactor technology to biodiesel producers, the industry has been quite open-minded for any technology that could speed up reaction time and augment yield. And in the past decade, a growing number of producers and systems makers have incorporated Hielscher equipment in process lines.


Continuous Flow and Time

One reason producers have chosen ultrasound technology is so they can move away from batch processing. Jeff Longo, principle with Genuine Bio-Fuel Inc., a 6 MMgy biodiesel plant northwest of West Palm Beach in Indiantown, Fla., says, "When we decided to set up the plant, we were looking for advanced technology and we definitely wanted to get away from the batch scenario. We wanted to have a true continuous flow facility, and one of the ways that we could accomplish this was with ultrasonics, so that's what we did. We used it for shearing and mixing, and it seems the most expeditious way to go."

Ultrasound can reduce the processing time from one to four hours needed in batch processing to less than 30 seconds. Also, it reduces separation time from up to 10 hours, down to one.

After feedstock pretreatment, the oil or fat is mixed with sodium or potassium methylate and heated to between 45 and 65 degrees Centigrade, which then is sonicated inline for five to 15 seconds. Hielscher states that, most commonly, sonication is performed at an elevated pressure of one to three bar using a feed pump and an adjustable backpressure valve next to the flow cell.

Many biodiesel producers hold trade secrets and technique close to the vest. "We push their technology way beyond their limits," Longo tells Biodiesel Magazine. "I'm sure [Hielscher] is not aware of what we do, but we've pushed them way beyond the capacities they advertise." Of Genuine Bio-Fuel's unique adaptation, Riebenfeld says, "I would love to have data on their process so we could commercialize the application."

Time and patience have paid dividends for Genuine Bio-Fuel, Longo says. "A lot of people using virgin feedstocks have no problems because there's no variables involved," he says. "But when your free fatty acid (FFA) content varies drastically between three and 30 percent, a database with different flow rates is very important." Genuine Bio-Fuel spent 18 months accumulating hourly data, which has helped to optimize performance of its ultrasonic reactors. "We vary our wattage through the ultrasonics predicated on the FFA content, flow rates and everything," Longo says. "The downside of this technology is, if you don't have a database that you've accumulated, it becomes very frustrating. I know other producers that have pulled in ultrasonics and put them online, and have had mild success with it. But when they have a variance in their feedstock, the results start to go sideways or whatever, and then they blame the ultrasonics-and it's not the ultrasonics."


Energy and Space

Wisconsin Biofuels LLC, a biodiesel equipment and systems provider, also incorporated Hielscher's ultrasonic reactors into its designs. "We were looking for something that we could use in a continuous flow process, and I didn't really like the shear reactors-they do work but their safety with flammable liquids would be a concern for some people," says Wisconsin Biofuels owner Scott Weis. He says his company tested an ultrasonic unit, liked the way it worked, and now uses it in its continuous flow design. "I really like the quality of the German product, it's a well-made piece of equipment," Weis says. "We actually checked with many of the other ultrasonic companies in the U.S., but they didn't really offer anything we were interested in. They had some flow cells, but they weren't very high wattage, more for small mixing lab-scale stuff."

Wisconsin Biofuels' continuous flow design consists of three 1kW ultrasonic processors. Two of them are arranged in a series on the first reaction, after which the product enters a continuous settling-decanting tank, followed by a second reaction stage consisting of the third ultrasonic flow cell. "It gives the ability to change the output of the ultrasonics," Weis says. "The biggest advantage is just going continuous flow. And there's a lot less methylated product in the process, so it's safer."

Hielscher says that its ultrasonics can reduce catalyst consumption by 50 percent due to the increased chemical activity in the presence of cavitation. Another benefit is less excess methanol is needed. Also, glycerin purity is increased.

Perhaps one misconception about ultrasonic reactors is that, compared to conventional reactors, they increase the amount of energy necessary to make biodiesel. While sonication requires electricity, producers and systems vendors say energy consumption overall can be reduced significantly. "We use metering pumps and they are really low output, they don't take much power at all," Weis says. "And then only a little amount of heat is required because you're not heating up the entire 2,000-gallon batch in a fairly quick timeframe-that requires a lot of energy, and you have to oversize your boilers to do that." Also, if methanol recovery is employed, Riebenfeld notes that there is not as much methanol to recover from ultrasound because less of it is fed into the process, and therefore less energy is consumed in recovery.

Gerrit Smith with Bioneer Pty. Ltd., a South African company operating a pilot plant and supplier of skid-mounted continuous flow biodiesel systems, says while batch reaction works fine in small amounts, large batch plants require high-power mixing to get the same results. "When you scale batch up, it's more difficult to mix a big reactor than smaller ones," Smith says. "What ultrasound does is make a very fine emulsion-I'm talking like 0.5 microns, that is the size of the fat droplets and they're surrounded by methanol-that's why it's such a quick and complete reaction."

Riebenfeld says for $16,000 a producer can purchase the base-model 1kW Hielscher reactor, which can process between 2,500 and 4,000 gallons per 24-hour period. "You can really build a simple system, even the small producer just getting into it," Riebenfeld says. "Even in this down economy we've seen very good activity." One of the more recent biodiesel plants to incorporate Hielscher ultrasonics is EDG Fuels in Tucson, Az., which celebrated its grand opening in March.

EDG Fuels president Jeff Sires says its continuous flow plant, which incorporated one of Hielscher's explosion-proof reactors, what he jokingly calls the "Binford 5000 model," creates a small footprint and doesn't require much space. Longo testifies to this point as well. "These huge batch plants are just myriads of acres of tanks," he says.

"We bought the nicest unit they sell," Sires says. "It was close to $100,000. It has a water-cooled head and an explosion-proof cabinet too." He says Hielscher sent an engineer from Germany and its North American representative, Riebenfeld, to Tucson at their cost to help set up the equipment and commission the plant.

"We also incorporate a feedstock pretreatment center for our used cooking oil, which removes water/moisture and solids," Sires says. "Our pretreatment has allowed us to consistently enjoy high yields, up to 99 percent with low FFA feedstock." He says EDG Fuels uses an acid esterification module to retain a high yield when refining material with high FFA content. EDG Fuels also has a push-button blending dispenser at its plant, where they dispense B20, B50 and B99 to individual customers. Sires says EDG Fuels offers its engineering and design services and adds that, despite the down economy and the absence of the federal tax credit, EDG Fuels plans on opening another biodiesel plant soon using Hielscher's ultrasonic reactors.

Ron Kotrba is editor of Biodiesel Magazine. Reach him at (701) 738-4942 or [email protected].