Chemical News

Monday, January 5, 2009

New PET process uses ethylene oxide

Poly(ethylene terephthalate) (PET) has been the fastest growing polymer in the petrochemical business for the past ~20 years. The original PET business was the manufacture of fiber, essentially synthetic cotton; but now the fastest growing part of the PET industry is making bottle resin, primarily for carbonated soft drinks but also for noncarbonated beverages, including juices and water. This business has grown rapidly, but it has not been particularly profitable because it is plagued by many competitors; capital investment for PET production facilities is relatively inexpensive and good polymerization process technology is available from several sources.

PET is a technically mature and cost-competitive product. Eastman Chemical, one of the world’s largest PET producers, has launched an effort focused on reducing costs all along the PET value chain to restore some measure of profitability to this business area. A. W. White and colleagues at Eastman disclose a process in which a PET prepolymer is formed by the reaction of terephthalic acid with ethylene oxide instead of ethylene glycol, the conventional comonomer.

The prepolymer is further polymerized to PET with ethylene glycol by conventional means. The Eastman process has the potential to save raw material and heating costs.
Several experiments described in the patent demonstrate the efficacy of making prepolymer with ethylene oxide instead of ethylene glycol.

In one example, terephthalic acid (60 g), toluene (600 g) and triethylamine (1.8 g) were added to an autoclave. The autoclave was heated to 200 °C, ethylene oxide was added, and the autoclave was maintained at a pressure of 1700 psi. After 30 min, the solid prepolymer was recovered by filtration in yields up to 96% with low b* color and low diethylene glycol levels, both important quality parameters in PET manufacture. The prepolymer (31.9 g) was then fully polymerized by adding ethylene glycol (3 g) and 35 ppm Ti(O-i-Pr)4 catalyst and heating in stages from 225 °C to 285 °C over 75 min under vacuum.
Source: CAS Patent Watch