(203n) Sustainable Production of VCM From Ethylene Through a Hierarchal Approach

Vinyl Chloride monomer is an important chemical because it is used in the production of the plastic PVC. The use of PVC is expected to increase over the coming years, which demands further production of VCM. This makes optimization of the production of VCM interesting and potentially profitable.  

A systematic hierarchal decomposition method is applied to design a sustainable and environmentally acceptable plant for producing VCM from the raw materials ethylene and chlorine. The method consists of 12 sequential tasks which take into account all stages of conceptual design. Task 1-4 covers the consideration of qualitative aspects of the process flowsheet and preliminary calculations. Task 5-8 determines the detailed process simulations, equipment sizing, costing, and economic evaluation of the designed process. At the end of task-9 (the economic analysis), the base case design is investigated for improvements with respect to heat integration and process optimization. In the final task-12, a sustainability and LCA analysis is performed to assess the environmental impact of the process design. This is done by calculating the key sustainability and LCA measures such as sustainability metrics for environment, economic and social; carbon footprint; safety index. Computer aided tools such as a commercial simulator is used for process simulation (for verification of design decisions), ICAS for property prediction and for analysis of design options; ECON for cost and economic analysis, which is based on the updated Guthrie method. The 12-tasks design method helped to perform the process design related work systematically and efficiently, where first design decisions were made based on collected information and then verified through simulations.  This procedure can be applied to design and/or analysis for new or existing chemical or biochemical processes. The process design of a VCM producing plant is performed as part of a MSc-level course on Process Design at the Department of Chemical and Biochemical Engineering at DTU.

The annual profit of base case is estimated to be about 30 million US$ with a payback time of 5 years for production rates of 1.6 tons/year of VCM per tons/year of ethylene. The capital and operating costs are divided into the individual cost items in order to determine which equipment and utilities contribute significantly to these costs. It is found that the compressors are the most expensive equipment contributing to capital costs and the energy cost is the main contributor to the total operating cost. This information is then used as target for process improvement by heat integration and process optimization, thus increasing the annual profit and reducing the payback time. The environmental impact analysis identifies impact due to the release of chemicals and points to the need of better control mechanisms through the sustainable /LCA analysis. The sustainability-LCA analysis has identified the process bottlenecks, which when addressed, generated a more sustainable process design, thereby giving an improved design from an environmental perspective.