Unwrapping the Biomass
Grass, trees, corn and cornstalks. They are all biomass and are all made up of lignin, cellulose, and hemicellulose, commonly called lignocellulose, of which the major components are sugars. Many algae also are high in sugar and can be used as a biomass source. If those sugars can be released, they can be converted into various other components, including fuel and chemicals. But those sugars are locked up tight, say Connie Schall, Sasidhar Varanasi and Sridhar Viamajala. “The cellulose is actually crystalline,” Schall explains, “and acts like reinforcing rods in concrete. The hemicellulose is amorphous, like concrete itself; lignin wraps itself around the other two components. It’s like breaking down reinforced concrete wrapped in tar.”
The goal for the researchers is to break down this solid structure to make a product, or at least platform chemicals that can be further processed into products or fuels. The starting material, be it grass, wood or algae, is extremely complex, so part of the problem is to determine cost-effective ways of pretreating the material–breaking it into its components for further processing.
Because of the complexity of the starting material, the researchers have turned to a pretreatment process using specialized ionic liquids (IL). Pretreatment breaks the structure apart by dissolving the cellulose, effectively turning steel rods into what Schall describes as a bowl of spaghetti. The advantage of using IL, she notes, is that it is functional at low temperatures, which is important since high temperatures can convert the feedstocks into undesirable by-products. But for this process to be economical, there must be a mechanism to recover the IL from the resulting mash so that it can be recycled and reused. Varanasi notes that UT has developed methods both for cost-effective pretreatment of biomass using ILs and for the recovery of ILs.
Once the biomass structure is broken apart, the next step is to extract the sugars. “The structure is so complex, varying from feedstock to feedstock, and so little is known about it, Schall comments. She is particularly interested in separations and proteins, crystallization and enzymes, and thus has gravitated to investigating the structure of various starter materials or feedstocks. Working with crystallographers, she is looking at x-ray data and both the chemical and physical structure of lignocellulosic material in grass, wood and algae as it undergoes pretreatment. Because enzymes are so specific, breaking the lignocellulose down in stages and analyzing the products at each step can help determine which enzymes in which combinations would be most efficient in breaking the material down into its component sugars.
But extracting the sugars is one thing; converting them to fuel or products is another challenge, says Viamajala. All sugars are not the same—the common glucose is a 6-carbon sugar whereas much of the biomass feedstock breaks down into xylose, a 5-carbon sugar. Varanasi explains that the yeasts that convert sugar do not like xylose. “However, for the process to be commercially viable, we have to use all the sugars,” adds Viamajala. A coordinated effort with Patty Relue led them to devise a way of tricking the yeast into accepting C-5 sugars and convert both sugars into ethanol. “We don’t alter the yeast,” he says. “We alter the conditions to accommodate the needs of the yeast.” The advantage is that there is now no need for a genetically modified organism.
Because it is not possible to use neat ethanol by itself in a standard engine, the researchers are also looking at ways to convert lignin into bio-oil, a precursor of transportation fuel, that can become a gasoline-like product. Additionally, they are working on converting nuisance algae from Lake Erie into a useful product, primarily using pyrolysis (a high-temperature combustion process in the absence of oxygen).
Viamajala notes that other kinds of algae are high in oil and can become essential products such as tires and lubricants as well as platform chemicals to produce bio-derived plastics that would replace those derived from petroleum. Refineries can accept bio-oils now, he notes. Certain kinds of algae are also capable of grabbing nutrients from municipal or animal waste, Viamajala remarks. “Nutrients are nonrenewable,” he says, adding that the world supply of phosphorus, which is mined, will be depleted in 100-150 years. “Algae is good at picking up phosphorus and can be a mechanism for treating wastewater and then, after drying, serve as a natural, slow-release mulch and fertilizer for crops. This is an alternative to chemical treatments and is a sustainable way of handling wastewater.
Although much of the research is still at the bench stage, some demonstration projects are underway. “Ultimately, industry and academe must complement each other,” says Schall. These efforts can lead to a greener, more efficient, and more robust and vibrant Toledo. But intellectual curiosity and the excitement of discovery is the heart of the enterprise. “The beauty of basic science–the interrelationships among biology, chemistry, and engineering–are so cool!” Schall exclaims. “It’s just a lot of fun.”
Connie Schall, professor in the Department of Chemical and Environmental Engineering, worked for ten years in industry before deciding to pursue a doctorate. She is drawn to separations and has focused on protein crystallization and biocatalysis. She has worked on projects in analysis of complex systems to develop simplified models that would be useful to scientists and engineers in fields such as cryo-crystallography and conversion of renewable feedstocks to fuels or chemicals.
A professor in the Department of Chemical and Environmental Engineering, Sasidhar Varanasi’s research focuses on using ionic liquids as pretreatment of biomass, biocatalysis to enhance the fermentation process and the application of colloidal and surface phenomena in separation processes.
Sridhar Viamajala, assistant professor in the Department of Chemical and Environmental Engineering, is particularly interested in biofuels and products from algae as well as using algal systems for nutrient reclamation and remediation.