Design Guidelines for Distillation Columns
in Ethyl-benzene and Styrene Monomer Service
Peter W. Faessler
Karl Kolmetz
Dr. Wai Kiong Ng
Krishnamoorthy Senthil
Tau Yee Lim
Andrew W. Sloley
Veco USA, Inc
Bellingham, Washington
Timothy M. Zygula
Nova Chemicals Corp.
Pasadena, Texas
Prepared for,
DISTILLATION 2005
2005 Spring AIChE Meeting
Atlanta, Georgia
April 10-14, 2005
Abstract
Styrene monomer is the fourth largest chemical produced on an industrial scale and most ethyl-benzene is utilized in styrene monomer production. The largest chemical produced on an industrial scale is ammonia for fertilizer production, followed by crude oil refining, and then ethylene by furnace pyrolysis. Styrene monomer has been manufactured commercially for more than fifty years with advances in the key unit operation areas of reactor design and distillation.
The original distillation internals were trays, which have faced many challenges in services that are prone to polymerization. The higher pressure drop and longer residence time of trays are disadvantages in this service. First generation structured packing was introduced in 1980’s. This advance greatly improved styrene distillation operations. The limit of first generation structured packing was capacity, where the stage efficiency began to decrease.
The rapid progress in computational fluid dynamic modeling (CFD) over the last ten years has also led to further improvements in the optimization of column internal design. CFD modeling of the structured packing, vapor-liquid distributors, and feed inlets can improve the performance of a distillation column.
Contemporary styrene unit designs include second generation structured packing and optimized liquid-vapor distributors. In the current designs, consideration of packing bed height and how the packing bed height affect stage efficiency due to mal-distribution should be reviewed. Designs are now limited by the maximum allowable pressure drop in order to avoid bottoms temperatures above 120°C (248°F) to 122°C (252°F). The authors will review the progression of Styrene Monomer Distillation advances and where the future research might be exploring.