There is current interest in the electrification of the chemical industry where heat for endothermic reactors is provided electrically in place of burning hydrocarbon fuels in a jacket. While the original motivation for this change of heat source was to reduce the evolution of greenhouse gases, the ability of electrical energy to be turned on and off rapidly allows for interesting reactor configurations that are not easily available for reactors with conventional heating jackets. For instance, Agrawal et al. [1] describe several different joule-heating configurations that allow for a dehydrogenation reactor to operate at different feed rates in small flexible plants near a gas well site, where the reactant flowrate could fluctuate during turndown operations. By turning off and on different electrically-heated zones, the energy supply can be easily tuned to the fluctuating energy demand that results from changing feed conditions. Another way to provide electrical energy to endothermic reactions is via the use of microwave energy [2]. One advantage of this method over conventional joule heating is the fact that it is possible to selectively heat the catalyst surface but not the catalyst support (which is transparent to microwave energy) and thereby use significantly less energy compared to joule heating. In this paper, we utilize a microwave source to provide energy in a small packed-bed reactor at 850 oC for catalytic conversion of ethane to ethylene. This is followed by a larger reactor which operates adiabatically, thereby alleviating the necessity of developing a very large microwave heating unit for the conversion of ethane to ethylene. When the temperature drops below 700 oC, we can either heat the mixture again using another combination of microwave reactor and adiabatic reactor or we can separate the ethane from the ethylene and recycle the ethane back to the first microwave reactor. The use of microwave energy for heating allows for adjusting the heat input to the reactors when the flow rate of the feed changes either during turndown operations or due to recycle. In this research, we will conduct lab-scale experiments to obtain reactor yields in the microwave portion of the reactor. Reaction kinetics from the literature will be utilized to simulate the adiabatic portion of the reactor. The sequential configuration of several reactors as well as a single reactor with recycle will be simulated in ASPENPlus and the levelized cost of ethylene will be calculated in both cases. Furthermore, the effect of changing the feed of ethane will be tested to see how these configurations operate in turndown conditions. An optimization scheme will be developed to find the best configuration under several different scenarios. These results will be compared with the configuration where joule heating is utilized for flexible operation. The decarbonization potential of this configuration will be quantified. This flexible heating configuration also results in interesting control problems that will be discussed in this research.
References
Agrawal, R., Chen, Z., and Oladipupo, P., “Electrically Heated Dehydrogenation Process,” United States Patent 12,017,983 B2, June 25, 2024
Wang, X., Almaraz, O., Hu, J., and Palanki, S., “Modeling and Simulation of a Novel Process that Converts Low Density Polyethylene to Ethylene,” Systems and Control Transactions (in press, 2025)
