(203q) Systematic Design of Process for the Sustainable Production of Anhydrous Isopropanol From Propylene

The compound isopropanol (IPA) is a very important chemical which is widely used as feedstock or solvent for a large range of intermediate and refined chemical products. In Asia the need for IPA is expected to increase in the nearest future. Therefore, the chemical process design of IPA is relevant to investigate, improve and optimize both concerning cost efficiency and environmental impact.

This project comprises a preliminary conceptual process design of a plant facility producing anhydrous IPA from propylene via direct hydration. Additionally, the project includes subsequent optimization with emphasis on sustainability. Annual production of IPA is set to 70.000 metric tons/yr corresponding to a market share of 3.5 %. The process design was developed in the MSc course: Process Design at the Department of Chemical and Biochemical Engineering, DTU.  

The process of completing the design is performed using a PSE approach. This is a systematic top down approach which decomposes the problem into 12 tasks. Tasks 1-2 concern initial market analysis and design decisions concerning reactant, product type, and purity. Furthermore, broad process specifications are determined and it is decided to replace the traditional azeotropic distillation using benzene with pressure swing for a more sustainable process. Based on an initial economic potential (EP₀) analysis, the direct hydration process to obtain a high purity product (anhydrous IPA) is selected (EP₀=70.7 billion $/yr). Tasks 3-7 involve generating and verifying a base case process design. This includes design decisions regarding selection and performance of unit operations, operating conditions, and integration of mass and energy balances.  A thermodynamic model is chosen based on system operating conditions and verified through its ability to predict the azeotropic point. Verification is performed using ICAS as design tool. Design decisions are validated using a commercial simulation tool for performing mass and energy balances - initially for simple models, then estimation models and finally rigorous models. Tasks 8-9 concern sizing and utility costs of the base case design along with economical evaluation of the process. Economic evaluation is performed using the Guthrie method for equipment sizing and cost estimation, which has been implemented into the design tool ECON. Tasks 10-12 concern optimization via heat integration, evaluation of environmental impact, and considera-tions regarding how to further optimize the process. Heat integration is constructed as a minimization problem for the external heating and cooling streams. Environmental impact is evaluated using indexes from the WAR Algorithm and health and safety index. Additional optimization is either performed by increasing the profit or decreasing the environmental impact.

For the base case design a yield of 0.87 kg product/kg raw material is obtained. This is to be increased in the optimization process to limit the amount of waste. In a time of increasing environmental concern, tasks 10-12 are becoming increasingly more relevant.  Energy consumption for the heat transfer equipment is estimated to be 110 MW; this is reduced by 30 % upon generation of a heat exchanger network, corresponding to a reduction in total plant energy consumption of 23 %. Reducing the environmental impact is to be the main focus in the optimization of the base case design to obtain a more sustainable process. 

The course was supervised by Professor Rafiqul Gani.