From Popular Mechanics:By Jennifer Bogo Published on: February 5, 2009
Dave Hubbard turns grease from restaurants into fuel for his black Jetta TDI, a BMW motorcycle, bulldozers, tractors for five local farms and a tree nursery, and his neighbors’ pickups—all for the low cost of about 50 cents a gallon. The process is basic chemistry and can be done by any DIYer with a steady supply of restaurant oil, a strong winch, and a willingness to get greasy. Here’s how he does it.
For Dave Hubbard, the process of making biodiesel begins in the gloaming under an old walnut tree in West Virginia, where behind a rural tavern a week’s worth of frying oil sits in a 55-gal drum. I meet my uncle here on a Sunday evening so that I can see how the oil gets from the drum to the tank of his black Jetta—plus those of a motorcycle, bulldozers, and tractors for five local farms and a tree nursery—all for the low cost of 50 cents a gallon.
With the full drum secured to a homemade steel hitch on Uncle Dave’s car, and an empty in its place under the tree, we drive the few miles back to his workshop. It’s a 100-ft long space filled with equipment—at least four drill presses, an old still for experimenting with ethanol (built from plans purchased on eBay) and, under a sheet, a BMW motorcycle he converted to run on biodiesel. There are makeshift devices as well—practical solutions to an engineer’s immediate needs, crafted to last long and cost little. To maneuver the 365-pound drum, for example, Uncle Dave uses a $120 winch rigged to a steel I-beam—which, in a past life, was part of a chairlift for carrying the disabled up stairs.
Uncle Dave pries the lid off the drum to show me what’s inside: The oil is amber and smells like chicken (not surprising since the tavern is known for its wings). It’s also still hot from the fryer, where it was heated to 350 F. Biodiesel is formed from a reaction between vegetable oil and an alcohol like methanol. “The minimum temperature for the reaction is 120 F, but I can’t go above 148 F—the boiling point of methanol,” Uncle Dave says. To avoid expending energy bringing cold oil up to that range, he uses the winch to pour the fresh, hot oil into an older drum, then mixes the two with a long metal paddle.
“Now I need to know how burned it is,” Uncle Dave says. “Free fatty acids build up in the oil when you burn stuff over and over again.” He pulls a 2-liter pop bottle off the shelf that is filled with fryer oil from a bar near the local college—it looks like motor oil. “I get this once a year because the cook uses the same oil over and over,” he says. “I wouldn’t want to eat anything they cooked in there.”
When making biodiesel, you want to convert these free fatty acids to soap (glycerin) with a base like sodium hydroxide (lye)—but you need to put in a little extra to act as a catalyst for the virgin bean oil, too. The oil from the college bar is burned so far beyond recognition that it’s not worth the time and materials it would require to convert it—Uncle Dave burns it in a furnace for heat. A chemistry experiment will tell us exactly how much catalyst we need to add to the good stuff.
We walk over to an old wooden workbench covered with bottles of various shapes and sizes. “If it were water, I’d need to know the pH. But you can’t take the pH of oil,” Uncle Dave says. Instead, we have to go by color. He takes a bottle of isopropyl alcohol, in the form of Iso Heet, and measures out 10 milliliters. “I don’t buy anything fancy,” he says. “My other special stuff here is turmeric from Kroger’s. It’s a hot pepper, so it’s acidic.” He dips the end of a toothpick into the spice and swirls it in the alcohol, which turns yellow.
Then Uncle Dave pulls a 1-liter bottle of distilled water off the shelf. He adds a milligram of sodium hydroxide, which makes the water slightly basic. “This is my titration fluid,” he says. Using an eyedropper, he drips the titration fluid into the alcohol mixture until it just barely turns red. “That’s telling me it’s back to neutral.”
This neutral mixture will help determine the acidity of the oil. “This cook is very precise,” Uncle Dave says. “He fries the same amount of stuff all the time and changes it every week, so I can almost guarantee what it’s going to be.” He takes a milliliter of the cooking oil and mixes it into the alcohol, which turns from red to yellow again—back to acid. “So now I need to know what it takes to balance it back to neutral with my titration fluid,” he says. Uncle Dave adds a milliliter of the distilled water and sodium hydroxide. Still yellow. He adds a half—back to red, just as he suspected.
Making biodiesel is like following a recipe, Uncle Dave tells me. The drum contains 45 gal of oil, and the reaction requires 20 percent methanol—or 9 gal. The magic number for the catalyst is 6.5, because it takes 5 milliliters to return 1 liter of pure oil to neutral, plus—as our chemistry experiment indicated—1.5 milliliters to counteract the amount of fatty acids in the burned product. Multiply all that and convert it to grams, and Uncle Dave needs to add 1100 grams of sodium hydroxide to make the reaction work.
Okay, enough with the math—back to the machinery. Uncle Dave pours the sodium hydroxide into the methanol and turns on a converted drill press as a mixer. “If you put your hand on the side of the container, you can feel the heat,” he says. “It’s an exothermic reaction. It’s going to get really hot in there in a second.”
While the methoxide is blending, he turns back to the oil. He measures the temperature to ensure it’s 120 F, and then uses the winch to lift and pour the oil into another 55-gal drum. A window screen stretched over the top filters out any chunks—I think I spot what used to be a French fry.
Uncle Dave activates a 1-in. electric transfer pump, and the filtered oil flows into a used 300-gal insulated bulk milk tank sitting nearby. He activates another pump and the methoxide is transferred to the milk tank, too. The tank is equipped with its own mixing motor with two stainless-steel propellers attached. Uncle Dave closes the top and sets a timer. For the next 45 minutes the propellers will blend the oil and methoxide, sustaining a reaction.
“When the recipe is right, I’ll end up with about 40 gal of biodiesel and 5 gal of glycerin,” Unce Dave says, “but that depends on how much the oil has been burned.” He’ll let the mixture sit in the tank overnight, and the dense glycerin will fall to the bottom where he can drain it off with a valve. What’s left on top is the biodiesel, which he’ll wash to remove any residual soap or methanol.
All told, the cost of materials, energy for heat and power, and odds and ends like gloves and paper towels, still only adds up to about 50 cents per gallon, Uncle Dave says. He sells it to friends and neighbors for $2 a gallon—a transaction that helps keep some local farmers in business. Steve Paul, who raises beef cattle, says he would otherwise spend $15,000 a year on fuel. Uncle Dave provides him with 1200 gallons at the beginning of each summer and Steve pays him when he sells his calves in October.
While compact, off-the-shelf biodiesel units may be convenient, Uncle Dave says, his system allows a lot more room for experimentation. “I can have a bad batch and set it off to the side, and put another drum in its place and check each thing as I go,” he says, “I can probably confine all this into one package to take up less space, but if I’ve got a problem with it I’m locked up.”
The real challenge now, he says, is just getting enough oil. In the eight years that he’s been experimenting with biodiesel, people have begun stealing it from behind restaurants—when the owners used to have to pay companies to take it away. Uncle Dave now gets his feedstock from several establishments, which has introduced him to yet another advantage of home-brewed fuel: Scavenging for fryer oil provides excellent insight into where to buy wings.