Reinventing Cellulosic Ethanol Production
A startup based in Tel Aviv, Israel, called HCL-Cleantech has reinvented a century-old process called the Bergius process as a much cheaper method to produce ethanol from biomass. The process uses concentrated hydrochloric acid (HCL) to breakdown biomass into sugars but has been too expensive for commercial use. The company, however, says that it has developed a way to recycle 42 percent of the HCL, pumping it back into the system and significantly reducing the cost of making ethanol.
“The only really innovative aspect of what we do is the recovery of the acid, which costs 10 percent of what it used to cost,” says CEO Eran Baniel. But that tweak attracted interest from a number of companies in the United States, and recently HCL-Cleantech received $5.5 million in venture capital from clean-energy investors Khosla Ventures and Burrill and Company to build a pilot plant in the United States.
To produce ethanol from cellulosic sources like wood chips and corn stover, the feedstock first must be stripped into three parts: lignin, sugar-rich cellulose, and hemicellulose. These last two parts must then be converted into sugars, which can then be fermented into ethanol by organisms such as yeast. Conventional ethanol technology uses dilute acid solutions in a pretreatment phase to separate lignin from cellulose and hemicellulose. Expensive enzymes then break down cellulose and hemicellulose into simple sugars.
As a cheaper alternative, HCL-Cleantech uses a much stronger, concentrated HCL solution that combines the first two stages of ethanol production, simultaneously stripping away cellulosic sources and breaking them down into fermentable sugars. Baniel says that the acid hydrolysis is able to squeeze up to 97 percent of sugars out of cellulosic sources like wood. Using HCL also reduces the amount of unwanted by-products that normally occur with more dilute acid solutions. What’s more, the concentrated acid reaction can occur at low temperatures, which reduces the energy required to run the system.
However, recycling HCL has proved a tricky challenge. Researchers have found that as HCL breaks down cellulosic sources like wood into sugars, it forms strong bonds with water that are difficult to break. Industries that recycle HCL, such as citric acid manufacturers, use expensive high-temperature and -pressure methods to evaporate water, isolating HCL.
Instead, the scientists who developed the technology for HCL-Cleantech came up with a cheaper route to separate and recycle HCL. They devised a proprietary solvent that attracts hydrochloric acid. They mixed this solvent with the HCL-water solution, and found that the solvent broke the HCL-water bond and extracted HCL from the water solution. The scientists then developed a method to get the solvent to release HCL as a gas, pumping it back into the system to break down more cellulose.
Baniel says that the company’s goal is to team up with fermentation plants to complete the last stage of ethanol production. “When we started, we thought we might need to go all the way to biofuel,” he says. “However, we discovered that there are technologies for fermentation of sugars that are way ahead of anything that we possess.”
The company anticipates that its pilot plant will be ready in the latter part of 2010. In the meantime, Baniel says that the company will test multiple steps of its process at various industrial plants in Israel to see whether the technology can run efficiently at large scales.
James McMillan, manager of biochemical refining process research and development at the National Renewable Energy Laboratory, in Golden, CO, says that scaling up the technology to run robustly is the key to its long-term success. “The proof in the pudding is demonstrating it performs under robust conditions and can handle upsets that happen in the real world, all at a cost that’s attractive in the marketplace,” says McMillan. “That’s what has to be shown.” He adds that when it comes time to build a plant, the company may have to invest in expensive materials to contain HCL, which is extremely corrosive and potentially volatile, especially in its gaseous phase.
Another company that is using concentrated acid hydrolysis to produce ethanol is BlueFire Ethanol, based in Irvine, CA. The company is using sulfuric acid, which is slightly cheaper than HCL, to break down sugars from cellulosic sources like municipal solid waste and wood residues. John Cuzens, chief technology officer at BlueFire Ethanol, says that recycling HCL in a gaseous form may help improve sugar yields. However, he cautions that HCL-Cleantech will have to account for the increased risk associated with potential hydrochloric gas emissions.
“Their process may have chlorine gas escaping, and the chlorine gas will corrode everything outside and inside the reactor,” says Cuzens. “So the carbon steel walkways–virtually everything in the plant they have to watch for.”
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