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Today, three routes -- two chemical and one biochemical -- are vying for a share of the 30-million-lb/yr market for 1,3-propanediol (PDO). Each uses different feedstocks, and has tradeoffs in operating cost, capital cost and yield (Table). PDO is a precursor for polytrimethylene terephthalate (PTT), a fast-growing variation of polyethylene terephthalate.
Capacity expansions
Shell Chemical Co. (Houston) recently completed a 160-million-lb/yr PDO plant in Geismar, La., which will be online by mid-1999. Shell's process is based on the cobalt-catalyzed hydroformylation of ethylene oxide (EO), and uses either water extraction or thermal evaporation to recover PDO and intermediate 3-hydroxylpropionaldehyde (3-HPA).
Residual 3-HPA is hydrogenated over a fixed-bed catalyst, at 75-150 bars and 100 to 200 degrees C. Distillation removes water and impurities, producing fiber-grade PDO. The...