(577h) Reimagining Previous Design Projects for Energy and the Environment

Two previously published design projects [1] were modified to include elements related to energy and the environment and have been used successfully in class. Descriptions of the projects and assessment of the student experience with them will be presented.

One design project involves the process for producing ethylene oxide from ethylene and pure oxygen in the standard, highly exothermic partial oxidation reaction. Due to the subsequent combustion of ethylene oxide, the process is typically run at low single-pass conversion, with methane circulating to provide thermal ballast. Keeping the temperature low maintains satisfactory selectivity for the desired product. Current research and technological advancement provide a novel alternative. The technology exists to crush solid catalysts and put them in a solid mesh in a packed bed. The advantages are reduced mass transfer resistances and lower pressure drop, since there is more void space. If the mesh is made of conducting material, heat can be removed faster in the reactor. [2-5]

This project was used in the 2019-2020 academic year. Students were required to simulate the impact on reactor performance of increasing the heat transfer coefficient. All observed that higher conversion could be achieved without a high selectivity. As a design project, there are many opportunities for students to evaluate alternatives. These alternatives include using air vs. pure oxygen feed, operating the reactor above the UFL or below the LFL, and the choice of reactor operating conditions, including single-pass conversion. Therefore, this project provides evaluation of alternatives and multiple, realistic constraints. The choice to operate at higher single-pass conversion requires less recycle, thereby reducing the reheating and compression load, resulting in reduced energy usage and smaller equipment, which is a form of process intensification.

The second project involves the synthesis of dimethyl ether (DME) from methanol, which is also available (book). The reaction is reversible, 2CH₃OH CH₃OCH₃ + H₂O. A typical process involves pure methanol as the feed, where methanol is produced from syngas by CO + 2H₂ ® CH₃OH. There is research underway [6] to produce methanol from CO₂ + 3H₂ ® CH₃OH + H₂O. The carbon dioxide could be recovered from power plants, for example. Therefore, this project clearly provides environmental and social considerations. The project used during the 2022-2023 academic year involved an equimolar methanol and water feed. For simplicity, the pure methanol and equimolar methanol-water feeds were used, thereby avoiding the impact on the water-gas shift equilibrium on either methanol synthesis reaction. To be clear, methanol synthesis was not included in the design project, though it could be, since equilibria and kinetics are known. [7] The opportunity for students could be to compare both process on an economic basis. For the equimolar methanol-water feed, one significant consideration for the students is whether to purify the methanol first. A critical decision is how pure the methanol needs to be as it enters the reactor. Choosing not to purify the methanol drives the DME equilibrium to the left, but the effect of the amount of water in the feed needs to be evaluated. These considerations are complex and reinforce students’ understanding of both reaction kinetics and reaction equilibrium. Having students compare the economics of the pure methanol feed case and the methanol-water feed case offers experience with the cost/benefit trade-off of what appears to be an environmentally beneficial process compared to a traditional process. This project is in the process of being used for the 2022-2023 academic year, so summary of student results is not yet available but will be included in the presentation.

Process assignments and non-optimized Aspen Plus simulations for these design projects will be made available by the authors.

1. Turton, R., J. A. Shaeiwitz, D. Bhattacharyya, and W. B. Whiting, Analysis, Synthesis, and Design of Chemical Processes, 5^th ed, Pearson, Boston, 2018, Appendix B.

2. Tatarchuk, B.J., Preparation of Mixed Fiber Composite Structures, U.S. Patent 5,304,3301994

3. Murrell, L. L., F. M. Dautzenberg, R. A. Overbeek, and B. J. Tatarchuk, U.S. Patent Application 2002/0068026A1, 2002.

4. Sheng, M., H. Yang, D. R. Cahela, B. J. Tatarchuk, J. Catalysis, 281, 254-262, 2011.

5. C. B. Mukta, N. R. Rayaprolu, S. Cremaschi, M. R. Eden, and B. J. Tatarchuk, Techno-Economic Study or Intensified Ethylene Oxide Production Using High Thermal Conductivity Microfibrous Entrapped Catalyst, Proceedings of the 14^th International Symposium on Process Systems Engineering (PSE 2021), Kyoto, Japan, 2022, http://dx.doi.org/10.1016/B978-0-323-85159-6.50116-0

6. Pérez-Fortes, M., J. C. Schöneberger, A. Boulamanti, and E. Tzimas, Applied Energy, 161, 718-732, 2016.

7. Mevawala, C., Y. Jiang, and D. Bhattacharyya, Applied Energy, 204, 163-180, 2017.