Ethylene vinyl alcohol copolymer (EVOH) is a barrier resin often used in
multilayer food packages and blow-molded rigid containers. The production
of EVOH is a two-step process of polymerization and saponification. First,
ethylene and vinyl acetate are polymerized using an initiator/activator complex.
Second, the ethylene-vinyl acetate copolymer (EVAc) is saponified to ethylene
vinyl alcohol copolymer.
As of 2003, the production of EVOH is done primarily by two Japanese companies.
Kuraray and Nippon Synthetic have manufacturing facilities in Japan, the United
States and Europe. EVAL Company of America (EVALCA) is a subsidiary of Kuraray.
EVALCA opened a plant in Pasadena, Texas in 1986. Currently, the plant has
an annual capacity of 46 million pounds (20,900 tons). Kuraray also has facilities
in Okayama, Japan with an annual production capacity of 23 million pounds
(10,400 tons). In 1999, Kuraray's sister company, EVAL Europe, began producing
EVOH in Antwerp, Belgium. In 2003, the plant doubled annual production capacity
to 46 million pounds (20,9000 tons). Nippon Synthetic has a plant in Okayama
with a production capacity of 23 million lb/yr (10,400 t/yr). They purchased
an EVOH production facility in 1994 in La Porte, Texas, which has an operating
capacity of 35 million lb/yr (15,900 t/yr).
Kuraray uses a proprietary system for copolymerization using solution polymerization
with a heat exchanger. Their method entails simultaneously passing the solvent
solution of vinyl acetate and discharged ethylene through a heat exchanger
provided with a cooling means, thus, causing the solution of vinyl acetate
to absorb and solubilize ethylene before the solution returns to the polymerization
vessel. In the vessel, the vinyl acetate with solubilized ethylene is mixed
with the polymerization solution. Saponification is done with a two-stage
process patented by Kuraray to achieve a high degree of saponification (99.5%)
with less alkali catalyst by using different conditions corresponding to the
differences in reaction mechanism between initial and final stages of EVAc
saponification. The process uses methanol as a solvent and a sodium hydroxide
catalyst. The EVOH product is extruded into polymer pellets and stored for
shipping.
PEP's process design is primarily based on patents assigned to Kuraray. However,
the design discussed in this paper, one for a 46 million lb/yr (20,900 t/yr)
capacity plant for EVOH production, at a 0.9 stream factor, in the United
States, may not exactly reflect Kuraray's manufacturing practices at its plants.
Nevertheless, the review gives a reliably accurate idea of the process and
its economics
