Environmentally friendly process to produce hydrogen
After 250 research articles, Jim Dumesic, a professor of chemical engineering at the University of Wisconsin, Madison, usa, would much rather teach a classroom of seniors than promote a start-up company. But such is the commercial potential of his recent work that Dumesic now courts hard-nosed investors and earnest energy companies for venture capital and strategic partnerships for his start-up company, Virent Energy. The company's mission is to commercialise Dumesic's discovery of a process that could potentially unlock the use of one of the most benign forms of energy ever known -- hydrogen.
In the quest for fuels that produce few or no emissions, hydrogen is a recurring theme. Currently, catalytic steam reforming of methane provides for most of the world's hydrogen needs. The thermal energy required to operate the process at temperatures as high as 800c is costly and causes substantial emissions of carbon dioxide. Moreover, once hydrogen is stripped off methane, the residual carbon is deposited on the catalyst, thus sharply diminishing the overall efficiency of the process.
Dumesic's work promises to be a breakthrough in the quest for cleaner processes to produce hydrogen. Briefly, his method uses a catalyst and moderate temperatures to break glucose down to hydrogen in the presence of water. Glucose is a sugar, which is produced from cornstarch in large quantities. However, cheaper starting materials like sugarcane, corn, rice husk, and waste from paper mills and timber factories could be also used to produce it, because glucose is found abundantly in all biomass. It is this use of cheap and renewable feedstock that makes Dumesic's research such an important innovation.
Molecules like sugar, because they possess an equal number of carbon and oxygen atoms, have a strong thermodynamic preference to decompose into hydrogen in the presence of water at moderate temperatures. However, the party is spoiled by an undesirable reaction between the products of the process -- hydrogen and carbon dioxide. These react with gusto 100 times greater than sugar's decomposition into hydrogen, to form undesirable alkanes and water. Such undesirable side reactions, besides reducing the efficiency of hydrogen production, also consume the precious product, hydrogen.
The University of Wisconsin researchers have almost circumvented this undesirable reaction by the use of a catalyst, which is similar to catalytic converters used in automobiles to reduce emissions. The use of this platinum-based catalyst results in more hydrogen production by preventing formation of undesirable alkanes. One-half of all glucose is converted to hydrogen while the remaining results in alkanes. The efficiency of the converter improves significantly with the use of highly processed feedstocks such as methanol or wood alcohol, which are almost completely transformed to hydrogen. It is estimated that as much as 80 grammes of hydrogen could be produced every hour for every kilogram of catalyst employed in the Dumesic process.
Not all glucose is effectively used towards the hydrogen generation process. This is because glucose molecules, even as they wait to interact with the solid catalyst to form hydrogen, react with water to produce undesirable side reactions. Dumesic's group thinks that such glitches can be avoided and performance improved with further research. Future plans also include research to discover cheaper catalysts to replace expensive platinum and designing reactor vessels to improve hydrogen yields.
In sharp contrast to steam reforming of methane, the Dumesic pathway occurs at much cooler temperatures of 180c to 265c, thereby offering economic and environmental advantages. With further research, even the costs of the low temperatures at which Dumesic's pathway operates could be avoided. In terms of environmental friendliness, Randy Cortright, Dumesic's co-inventor, expects the process to "be greenhouse-gas neutral" because of its reliance on biomass, which "fix and store ... carbon dioxide." Further, carbon formation and the resulting loss that occurs in catalyst performance --problems that plague methane reforming --have not been observed in experiments performed in the laboratories at University of Wisconsin.
Uday T Turaga is at the department of energy, Pennsylvania State University, USA