Environmental Applications For New Chemical Microtechnology
hemical processing systems are undergoing a transformation - and a dramatic reduction in size - that may soon allow groundbreaking applications in biohazardous conditions, fuel-cell-powered automobiles, and waste treatment.
By developing microfabricated components that perform the same standard unit operations - including pumps, valves, compressors, chemical reactors, and heat exchangers - present in large chemical processing plants, researchers are getting closer to mass-producing the next generation of chemical processing systems, systems not imaginable a decade earlier.
"Analogies to computers are extremely tempting," said Robert Wegeng, a chief engineer with Pacific Northwest National Laboratory in Richland, Washington. "There is the potential that this industry could experience the same explosive growth as that of microelectronics."
But, there are a few catches, Wegeng cautioned. While the technology is now being demonstrated, is has not yet been shown to be sufficiently reliable or cost effective to mass produce.
Why the interest in microfabricated components? "The potential payoff is significant," noted Wegeng. "This represents a new class of chemical process system, with features significantly different than those in classical process technology. By exploiting microscale phenomena, extremely rapid heat and mass transport is possible, yielding components with high processing rates," Wegeng said.
Like computer chips, these microcomponents are chemically etched, with channels replacing the pipes used in today's chemical processing units. This allows for quicker mass and heat transfer, allowing fluids to be processed more quickly. As a result, compact systems-as small as one cubic centimeter-can be more powerful. High processing rates are also possible by running parallel systems of components.
The automobile industry could tap microcomponents' promise for fuel-cell-powered cars. These vehicles would still carry liquid hydrocarbon fuels, plus a key additional item: an onboard fuel-processing plant to produce hydrogen for the fuel cell from the fuel source. "Progress in the development of catalytic microchannels leads us to believe that an automobile fuel-processing system - including all reactors and heat exchangers - would be less than one-half a cubic foot in volume," he said.
A large beneficiary from this technology could be the environment. In one type of application, compact reaction systems could be placed on offshore drilling platforms, converting natural gas, which otherwise would be flared, into liquid hydrocarbons. This fuel then could be economically transported and used, thereby reducing emissions of carbon dioxide, a greenhouse gas.
Microchemical separations systems also have the potential to greatly improve the removal of contamination from groundwater - via downwell units - or process the Department of Energy's radiochemical wastes that were a byproduct of the Cold War. Wegeng envisions liquid-liquid separations, based on solvent extraction in microchannels, for processing tank waste in modular units. "The key is the ability to assemble individual, complex chemical processing systems for these applications. If successful, the savings could range in the billions of dollars."
significant amount of research and development is still required to
bring microchemical processing technology to market," Wegeng concluded.
"But, the concepts are fundamentally feasible. For near-term applications,
the next step is increasing their reliability and showing that they
are mass producable. For products that are further out, a greater understanding
of microscale phenomena is needed."
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