(47d) Identification of Sustainable Processes through an Integrated Process Synthesis Framework

Sustainable process design aims to find efficient configurations and operating parameters to convert raw materials to products. However, most research on this topic focuses on separation synthesis, which aims to identify the best downstream separation configurations through different methods such as heuristics [1], optimization [2], and hybrid methods [3]. Innovative separation techniques with lower capital/operating costs and carbon emissions have been proposed/identified to further improve the downstream process performance [4]. However, most of these separations synthesis methods were based on conventional unit operations and usually applied for generating sustainable processes with a given reaction pathway without considering the possibilities of using different raw materials or production of different products from the same raw materials. Generally, to produce a given target product, multiple reaction pathways are available, and each reaction pathway leads to different downstream processes, which should be considered when solving the overall process synthesis problem. Also, applying intensification in the early stages of process design, e.g., separation synthesis, can generate optimal/improved process flowsheets with higher energy efficiency and lower environmental impact.

This work presents an integrated process synthesis framework, which considers both reaction synthesis and separation synthesis, including innovative hybrid/intensified unit operations to identify the optimal process for a given product or raw material. There are three steps in this framework. In step one, the input is the target compound (raw materials or products) so that multiple novel reaction pathways are identified from literature or via a forward synthesis/retrosynthesis model (github.com/ASKCOS). The reaction synthesis step aims to identify novel reaction pathways with lower environmental impact and capital/operating cost. In step two, the downstream separation synthesis [4], which considers advanced separation techniques, is applied to select the most promising alternatives for each reaction pathway. In step three, the top selected alternatives for each identified reaction pathway are designed and verified through rigorous simulation. In this way, by only giving raw materials or target products, one can find an optimal reaction pathway and its corresponding process flowsheet.

The developed framework has been used to solve a range of case studies, including both retrosynthesis (dimethyl carbonate (DMC) production) and forward synthesis (isobutylene utilization) design problems. In the DMC production case study, three reaction pathways are selected, which generated 288 process alternatives, including 7 conventional, 8 intensified, 261 hybrid, and 12 combined hybrid/intensified solutions. Among these process alternatives, the identified best DMC production process uses propylene carbonate and methanol as reactants with distillation-membrane and dividing wall column for separation, which leads to a 20% lower operating cost than the conventional extractive distillation process.

References

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[3] Lu, M. D., & Motard, R. L. (1985). Computer-aided total flowsheet synthesis. Computers & chemical engineering, 9(5), 431-445.

[4] Lutze, P., Babi, D. K., Woodley, J. M., & Gani, R. (2013). Phenomena based methodology for process synthesis incorporating process intensification. Industrial & Engineering Chemistry Research, 52(22), 7127-7144.

[5] Tula, A. K., Eden, M. R., & Gani, R. (2015). Process synthesis, design and analysis using a process-group contribution method. Computers & Chemical Engineering, 81, 245-259.