(474f) Optimal Design of Advanced Distillation Schemes for Enhancing Energy Efficiency of Close-Boiling Ethylbenzene/Styrene Separation in Plastics Industry

Distillation is by far the most widely used separation technology in chemical process industry, which is commonly utilized in separating close-boiling component in industry. Considering the capital and energy intensity of the task, schematic selection of optimal distillation strategies becomes a significant decision. The importance of designing distillation systems of both sustainability and feasibility is continuously challenging chemical engineers.

Styrene monomer (SM) is the simplest and by far the most important member of a series of aromatic monomers that is used in the plastics industry. Currently, catalytic dehydrogenation of ethylbenzene (EB) is an overwhelming technology for SM production. However, the unreacted EB must be separated from SM through distillation in order to guarantee downstream processes. The normal boiling points (NBPs) of EB and SM are 136.2 and 145.7°C, respectively. Obviously, they form a close-boiling system, which requires energy intensive distillation operation for the separation. For example, a typical 500,000 metric tonnes annually (MTA) styrene production plant contains an EB/SM distillation column with about 70 equilibrium stages, which operates at a reflux ratio of 7.1 to achieve an EB impurity level in the final SM product of 100 ppm. This column accounts for 75-80% of the total energy consumptions in the current production process. In this sense, this study introduces a reliable shortcut method through optimizing the target of total annualized cost (TAC). Two energy-saving distillation candidates – double-effect distillation (DED) and mechanical vapor recompression (MVR) – are applied to potentially reduce energy requirement in conventional EB/SM column. In the first round evaluation (shortcut method), MVR stands out to be a more attractive option than DED alternative. In addition, the shortcut calculation results are used as initial values for the rigorous simulations. In the second round comparison (rigorous method), the advanced distillation schemes (ADSs) using DED and MVR are proved that they can save by up to 30% and 40% of operating costs, respectively, compared to conventional distillation schemes (CDSs). In the view of TAC, the ADSs can cut a corner of ~35-40% from the CDSs. Specifically, the ADS using MVR slightly outperforms its DED counterpart in TAC comparison.