The activation of C1
chemistry has been the goal of engineers and scientists for over a century. The single most energy intensive step in petrochemical industry is the formation of C2
hydrocarbons which dominates its current energy consumption [520 Petajoule] and CO2
production [~18.5MtC, ~22% of US chemical synthesis] in the US.[i]
Discovering adequate technological mitigations of this energy demand using renewable energy is one of the keys to advancing clean fuels and our economy’s renewable energy production. Currently, C1
chemistry does not exist at an energetically competitive alternative to steam cracking for ethylene production. Microreaction technology is finding perhaps its greatest utility in pharmaceutical and fine chemical production. However, microtechnology also has tremendous potential to address energy production, storage and utilization when used in conjunction with microplasma technology, which intrinsically lends phenomenal gas processing capacity to microdevices. Microplasma microreactor technology can be applied at high efficiency for conversion of renewable electrical energy to chemical energy. Microreactor devices utilizing microcorona discharges can process sources of methane, carbon dioxide and steam into usable C2
hydrocarbons using renewable electricity. Experiments have demonstrated high conversion of C1
hydrocarbons with low electrical energy consumption. Each device provides the processing capacity for several hundred standard cubic centimeters per minute. The power consumption for the engineered microcoronas is several watts. Several alternate reactions involving C1
activated chemistry, that have been explored, will be summarized and detailed in terms of design analysis, reactivity, conversion, selectivity, and gas hour space velocities as it relates to the apparent efficiency. Moving corona microreactor gas processing technology toward the forefront of industrial applications that are focused on converting renewable electricity into chemical energy will require a broader collaboration between engineers, chemists and physicists.
The fundamental length scales of microreactors reduce diffusive mass transfer resistance and allow full utilization of the corona electron cross-section which is a key factor in achieving good performance. This has the added benefit of effectively tuning the distribution of activating charges to the optimum energetic level. The conversion of renewable electrical energy to chemical energy is investigated on a variety of microreactor electrical corona discharge systems. Fields of atmospheric pressure plasmas have been engineered to convert from 5 to 70% of an inlet stream to produce higher more desirable chemical feedstocks and higher molecular weight species at 50-90% electrical efficiency. The ability to bypass activation energy barriers in microreactor microplasma systems is similar to the catalytic reduction of the activation energy for non-plasma C1 chemistries. The microtechnology reaction platform and measurement techniques allow easy scaling of the technology. A framework for understanding C1activation and functional microreactor design is discussed. Spectroscopic, chromatographic and electric measurements are used to establish key reaction engineering relationships between the reduced electric field, space velocity, mass transfer, kinetic rates and time scales. Condensable fuel products have been measured using gas chromatography, gas phase Raman or FTIR.
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[i] U.S. Dept. of Energy, “Energy Use and Energy Intensity of the U.S. Chemical Industry,” EPA/DOE- LBNL-44314 Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (rev. April 2000).