US EPA

2859645 

Technical Report 

The STEX Process-Extraction Of Styrene From Pyrolysis Gasoline 

Morimoto, H; Tatsumi, M 

1974 

NIOSH/00136570 

16 

1 

38-42 

A process to extract styrene (100425) from pyrolysis gasoline during ethylene (74851) production was investigated. The styrene extraction process involved conventional distillation to obtain the carbon 8 (C 8) aromatic fraction. This fraction was worked up by a chemical method and fed to the intermediate plate of the extractive distillation column. An extraction solvent containing polymerization inhibitors was fed at the upper part of the column. At this distillation, xylenes and non aromatic components with small amounts of the solvent went to the overhead. The bottom content of the extractive distillation column was separated into the solvent and styrene by the solvent recovery column. The overhead styrene was then washed while the recovered solvent was purified and recycled to the extractive distillation column. The distillate containing xylenes and non aromatic components was used after suitable treatment for recovery of p-xylene (106423). The composition of the C 8 fraction components was analyzed. The purity of the styrene monomer produced by the process was assayed. Typical components of the C 8 fraction included 2 percent C 8 9 non aromatics, 9 percent ethylbenzene (100414), 12.3 percent p-xylene, 25.6 percent m-xylene (108383), 14.1 percent o-xylene (95476), 35 percent styrene, and 2 percent other aromatics. Typical styrene was 99.7 percent pure. The authors conclude that the styrene extraction method is economical and produces both styrene and xylene. Styrene can be produced at 60 to 70 percent of the cost of the conventional process at the same production scale. Compared to conventional processes, this method is also relatively simple.