Woburn Startup Extrudes Diesel Filters Like Pasta; The Way to Cleaner Cars?

What’s the common thread between the space shuttle’s thermal tiles, log-cabin mansions in Aspen, Play-Doh, pasta makers, and diesel engines? There is one—really—but to find out what it is, you have to pay a visit to GEO2 Technologies in Woburn. The clean-energy startup has turned an industrial warehouse just off I-95 into a giant kitchen-laboratory, complete with giant microwave, for baking advanced diesel-exhaust filters.

The three-year-old company has perfected a way to build these filters out of an unconventional material, ceramic microfibers like those used in the space shuttle’s tiles (of which more later). The technology could keep the air cleaner in diesel-crazy Europe and help diesel technology make a comeback among car buyers in the United States, who have shunned it for decades because of the filthy black soot generated when diesel engines start.

GEO2’s finished diesel exhaust filters“The auto industry is a huge market undergoing tremendous pain from tightening emissions regulations,” Bilal Zuberi, GEO2’s vice president of product development, told me Tuesday before taking me on a tour of the kitchen-lab. But in the field of emissions controls, “there hasn’t been too much innovation in the area since the invention of the catalytic converter in the 1970s.”

Many diesel engines today, Zuberi explains, contain elaborate, multi-stage exhaust control systems to trap particulates and burn off the unburned hydrocarbons found in diesel smoke. But the more devices are added to these systems, the more backpressure the engine has to deal with, reducing fuel efficiency. The “holy grail” of emissions control, he says, would be a single high-porosity filter that traps soot and burns off the extra hydrocarbons without increasing backpressure.

That’s the specialty of the house at GEO2, which is privately held and has 27 employees. But how the company got there is a twisty tale. The inventors of the original technology behind GEO2 are Gordon Alward and Robert DiChiara, who were neighbors in California. According to Zuberi, one day several years ago Alward and DiChiara were discussing regulations in Aspen, CO, (where Alward had visited) requiring that woodstoves and fireplaces include expensive scrubber systems to reduce wood-smoke pollution. DiChiara, a Boeing engineer who works on heat-shield systems for hypersonic craft like the X-37 space plane, wondered whether light, porous, microfiber-based ceramic materials like those used to protect the space shuttle during atmospheric re-entry might work as scrubbers, capturing the particulates in wood smoke or engine exhaust. Alward and DiChiara wound up patenting the idea, and went to Boston Consulting Group, where Zuberi was a consultant at the time, for advice about starting a company around the technology.

There were a few problems. Existing microfiber-based materials were brittle, flaky, and hard to manufacture in specific shapes like those needed for engine parts. But Zuberi, who had joined BCG after earning a PhD in physical chemistry at MIT, and Rob Lachenauer, a 17-year BCG veteran, saw promise in the technology—not to mention a wide-open market. The four decided to launch GEO2 in 2004, with Lachanauer as CEO and Zuberi in charge of product development.

Most exhaust filters are designed as honeycombs of interlocking tunnels made of conventional ceramics. Zuberi and Lachenauer say the company spent more a year on an ultimately futile attempt to make these honeycombs by boring holes in big blocks of microfiber-based ceramics. The holes were too large and imprecise, and the process was wasteful, since more than half of the material in a bored-out microfiber block would have to be thrown away.

That’s when it occurred to Zuberi and Lachenauer that the process normally used with conventional ceramics, extrusion, might work better. But nobody had ever figured out how to blend ceramic microfibers into the Play-Doh-like consistency needed for the extrusion process, in which the material is squeezed through holes in a die, similar to the extruding discs used in pasta makers but with much more complicated geometries. So GEO2 experimented with different kind of microfibers and binding agents until it found the right blend. The company ultimately bought a whole assembly line of industrial-strength kitchen gadgets to make the filters, including a giant mixer, a torpedo-sized extruder, a 15-foot-tall microwave oven (to dry the extruded filters) and a large sintering oven (to fire them).

Not much is left of Alward and DiChiara’s original plan—but the concept is intact. “We wound up changing the materials, the manufacturing techniques, and the management team, but other than that, everything’s the same,” jokes Zuberi.

In GEO2’s finished filters, ceramic microfibers are cross-linked and bonded at the microscopic level by a glass-like ceramic glue, giving them a structure with high mechanical strength, high porosity, large surface area, and high resistance to thermal shock. This means, for one thing, that even as the filters load up with particulates, exhaust gas still has many paths to travel, lowering backpressure. It also means that the filters are strong enough to survive being heated up to the temperatures needed to oxidize the unburned hydrocarbons that accumulate from diesel soot, a process called regeneration.

GEO2’s microfiber filter, electronic microscope viewAs a result, a single structure made from GEO2’s material can act as both a particle filtration system and an oxidation catalyst—potentially saving car and truck manufacturers and their customers a lot of money. “These multifunction filters will be a huge thing in the marketplace,” Zuberi predicts.

Lachenauer says GEO2 is poised to sign mass-manufacturing deals with one or more makers of conventional ceramic honeycomb structures. And now that the company knows how to make its filters, there are many potential applications beyond diesel exhaust systems, Lachenauer says, including better catalytic converters for gasoline engines and filters for the incredibly polluting two-stroke engines in scooters, lawn mowers, and leaf blowers.

Zuberi believes that multifunction diesel filters may also be one key to a potential renaissance for diesel-powered passenger cars in the United States. “If you drive a lot in the city, sure, buy a Prius, but if you are going to do a lot of highway driving, a gasoline hybrid doesn’t gain you anything,” he says. “Meanwhile, diesel cars in Europe and Japan are getting 43 to 53 miles per gallon.” With technology like GEO2’s new filters, the perception that diesel engines produce dirty smoke will be overcome, and manufacturers will be able to improve emissions control without sacrificing profitability, Zuberi predicts. “It’s an easy sell.”

Wade Roush is a freelance science and technology journalist and the producer and host of the podcast Soonish. Follow @soonishpodcast

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