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334836 Systematic Chemical Process Design: Production of Dichloromethane By Direct Chlorination of Methane
Dichloromethane (DCM) is a widely used solvent in both laboratories and industry. Dichloromethane is able to dissolve many organic compounds, has been used for extraction in several industries, and is also known for its ability to weld plastics. A DCM plant, representing 10% of the US market was designed. The design was accomplished by using a 12-step systematic approach, thus developing a base case design, followed by an economical and environmental evaluation, and later optimization. This project was prepared as a part of the MSc course in Process Design, at the Technical University of Denmark, under the auspices of Professor Rafiqul Gani.
The process in question uses the method of direct chlorination of methane to produce 99.9% DCM. The raw materials utilized are chlorine and the methane rich product, from the production of de-methanized natural gas. The methane rich gas was further purified by a cryogenic turbo expansion process. Methane in excess is necessary; however in this process the unreacted methane was recycled and reused to minimize the amount of raw material. The chlorination method resulted in the production of several byproducts. In the downstream process these were easily separated, and high purity byproducts were obtainable. The systematic method to design this plant, started with tasks 1-2, where a literary study was done, to gather information on the product and its production process, as well as aiding in the estimation of an economic potential for the design. In task 3, a simple flow sheet was made for the base case design. In the following tasks 4-7, decisions were made regarding product purities, split factors, operating temperatures and pressures, etc., such that mass and energy balances could be estimated. In tasks 8-9 the process equipment were sized using the Guthrie method and the capital, utility and operational costs were found. In tasks 10-12 the process was evaluated by heat and mass integration, environmental impact and sustainability calculations. Finally, the design was further improved by using the successive quadratic programming (SQP) algorithm for optimization calculations. To aid in the design, software such as ICAS, ECON and a commercial simulator were used.
Not only does the design of the process influence the environmental impact but the product does as well. DCM has in the later years been under surveillance due to its potential health and environmental risk, and for this reason the environmental/health aspects of this process are highly regard able.
This process design has been improved through heat integration and optimization, and by forgetting sustainability metrics, made more sustainable.