Electrogenerative process hydrogenates various feeds Φ CHICAGO A l t , 1 0 u g h ffw direct " **•••**»»*•** organic electrogen erative processes have been exten sively investigated, they are now get ting more attention. The scope of one such process, electrogenerative hydro génation, has been broadened considerably by the work of Dr. Stanley H. Langer and associates at the University of Wisconsin. One intriguing characteristic of such processes is their dual productivity, Dr. Langer explained to the Division of Petroleum Chemistry. Electricity and chemical products result if advantage is taken of favorable thermodynamic and kinetic factors. In this regard, the processes are analogous to those occurring in fuel cells. Electrogenerative processes have the additional advantage of not requiring an external power source and the attendant investment, Dr. Langer points out. And, since they operate under steady-state conditions, the electrolyte is invariant, compared to conventional electrochemical processes where the electrolyte composition changes. In electrogenerative hydrogénation, unsaturated hydrocarbons and hydrogen—physically separated by a suitable
electrolyte barrier phase—react at porous, catalytic electrodes to produce hydrogen-enriched hydrocarbons corresponding to feed hydrocarbons at the cathode. Hydrogen is oxidized to hydrogen ions at the anode. Electrons are conducted through an external circuit from anode to cathode. So far the Wisconsin group has worked on laboratory-scale experiments with feedstocks such as ethylene, acetylene, benzene, or, in a simple variation of the process, chlorination of a few olefins. They use electrodes made of a mixture of platinum black and polytetraflujroethylene supported on tantalum screen. The electrodes are available commercially from American Cyanamid. Voltages. In these experiments, open circuit potentials (voltages) have been obtained for several unsaturated hydrocarbons with various electrolytes, says a coworker, Dr. Sergei Yurchak, now with Mobil Research. The experimental voltages are generally within 5% of standard cell potentials calculated from standard free energy changes for complete cell reaction, assuming complete hydrogénation. The agreement surprises the
chemical engineers, considering the irreversible nature of the cell reactions. Acetylene proves an exception to these results, probably because of the very strong adsorption of acetylene on platinum. The open circuit for acetylene potential is about 60% of the calculated cell potential. Although electrogenerative hydrogénation is still a long way from a commercial process, its potential in special situations seems to depend most on raising current densities to higher levels, Dr. Langer explains. If, for example, the substrate competes weakly with hydrogen for the catalyst surface, the process has an advantage over chemical hydrogénation. Cyclopropane will hydrogenate roughly 10 times faster electrogeneratively than it will chemically. Benzene is another example where hydrogénation is possible under much milder conditions than are required for conventional electrochemical hydrogénation. Electrogenerative hydrogénation of benzene is quantitative to cyclohexane, even to the extent of making the technique a possible analytical tool. Currently, Dr. Langer and others at Wisconsin are looking at reactions which are especially exothermic. A part of the energy discarded in cooling water might be recoverable as electricity.
Bound enzyme cuts starch conversion cost A . P U I P A P H Fermentation studies ^UniUMUU conducted by the U.S. Department of Agriculture could lead to a more economical process than is now used commercially for converting cornstarch to glucose, a sugar widely used by the food industry. Dr. Karl L. Smiley, head of industrial products investigations in USDA's fermentation laboratory, Northern Utilization Research and Development Division, Peoria, 111., has devised a method to convert starch to glucose in a continuous system using the enzyme glucoamylase immobilized on an insoluble carrier, diethylaminoethyl cellulose. Most commercial methods for making glucose involve the use of glucoamylase, obtained from Aspergillus mold, to convert starch to glucose. This is one of the few large-scale industrial uses of enzymes. However, large-scale use of enzymes often entails high costs because of loss of enzyme in the process, as well as prob54 C&EN SEPT. 28, 1970
lems with the enzyme's activity and instability. Dr. Smiley told the Division of Microbial Chemistry and Technology that his process has the potential of circumventing these disadvantages. Glucoamylase, he says, is more stable when bound to a carrier than if used in solution. And the immobilized enzyme can be recovered with no loss of enzyme, and thus no additional costs to replace lost enzyme. In addition, Dr. Smiley notes the enzyme apparently loses none of its activity when bound to the carrier even after several weeks of use. Bonding. The USDA chemist points out that a simple method of binding an enzyme to a earner is by ionic bonding—which holds the enzyme to a charged carrier such as diethylaminoethyl cellulose or other ion exchange polymer. As long as certain physical conditions are maintained, such as pH and ionic strength, he says, the enzyme will remain tightly bound indefinitely,
even though large volumes of substrate solution are passed over the immobilized enzyme. Previous work at USDA has proved the feasibility of converting dilute starch solutions to glucose using columns of immobilized glucoamylase. However, problems of large column size and slow flow rates caused bv plugging with starch gel led to Dr. Smiley's work using a stirred reactor in conjunction with filtration. Although Dr. Smiley doesn't expect commercial glucose makers to convert present facilities to the immobilized enzyme technique, he says that some companies are interested in the method and may consider it for expansions. Glucoamylase is not very costly, Dr. Smiley explains, and producers aren't too concerned over losses of the enzyme in their processes. However. capital investment for the immobilized enzyme process is less, he says, and thus the process becomes attractive for additions to glucose capacity.
