(245b) Sustainable Design for Production of Styrene from Benzene and Ethylene

Process design – A production of Styrene from Benzene and Ethylene

Matias Falk Bjerregaard, Jonas Richard Foelsby, Michael Roland Larsen, Maria-Ona Bertran

Department of Process Engineering and department of Chemical and Biochemical Engineering,
Technical University of Denmark, 2800 Kongens Lyngby, Denmark
marber@kt.dtu.dk

Styrene is an important bulk chemical because it is used for the production of a variety of products, e.g. plastic and rubber products¹.

Using a systematic method for performing sustainable process design, decomposed into 12 tasks, a more sustainable process has been developed for the production of styrene. The raw materials used are Benzene and Ethylene, and the styrene production target is set at 150.000 metric tons / year, with a 99 wt-% purity.

The raw materials, benzene and ethylene are utilized in a two-step synthesis reaction^2,3. In the first reaction, alkylation of ethylene and benzene to form ethylbenzene and diethyl benzene as an undesired byproduct.
In the second reaction, dehydrogenization of ethylbenzene occurs to produce styrene, with benzene, ethylene, and hydrogen as the undesired by-products.

A brief description of the process is as follows. The first reactor outlet consists of ethylbenzene and diethyl benzene, which is separated using a distillation column. Next, the second reactor outlet consists of styrene, hydrogen, ethylbenzene, and benzene. First, hydrogen is removed using a flash distillation. Next, benzene is separated using a distillation column. Lastly, ethylbenzene is separated using yet another distillation column.
The third and last reactor utilizes a recycled diethyl benzene stream for transalkylation, into ethylbenzene, which is fed into the outlet of the first reactor.
This approach is used as the base case design that is further investigated for process improvements with respect to both economic and environmental feasibility.

The base case design is analyzed using an economic analysis for identifying process improvements related to heat integration and process optimization. Improving these two aspects directly affect both the utility and operating costs. To further refine the design, a sustainability⁵ and LCA analysis⁴is performed in order to identify process limitations that are translated into design targets that, if matched, eliminates process limitations.

In this poster, the task-based method for achieving a sustainable process design will be presented through the application of the design of a more sustainable process for the production of styrene. The output for each step will be highlighted and the base case design will be compared to the improved designs obtained from heat integration and process optimization and, from the sustainability analysis.

References:

1. Burridge E. Styrene. ICIS Chemical Business. 2006.

2. Edinburg University. Styrene process, preliminary information. Process Calculations Web site. http://www.see.ed.ac.uk/~jwp/procalcs/procalcs/study/styrene0.html. Updated 2015. Accessed 27/02, 2015.

3. Tiako Ngandjui LM, Louhibi D, Thyrion FC. Kinetic analysis of diethylbenzene-benzene transalkylation over faujasite Y. CHEMICAL ENGINEERING AND PROCESSING. 1996.

4. Carvalho, A., Matos, H. A., & Gani, R. (2013). SustainPro—A tool for systematic process analysis, generation and evaluation of sustainable design alternatives. Computers & Chemical Engineering, 50, 8–27. doi:10.1016/j.compchemeng.2012.11.007

5. Kalakul, S., Malakul, P., Siemanond, K., & Gani, R. (2014). Integration of life cycle assessment software with tools for economic and sustainability analyses and process simulation for sustainable process design. Journal of Cleaner Production, 71, 98–109. doi:10.1016/j.jclepro.2014.01.022