Published June 1971
High molecular weight polymers of formaldehyde were known in the 1930s but for many years they were considered too unstable for commercial use. In the early 1950s, after many years of casual research, E.I.du Pont de Nemours & Company entered an intensive investigation of the preparation, properties, and stability of these polymers. They discovered that tough solid polymers of formaldehyde, which they termed �acetal resin" were readily prepared from high purity formaldehyde using ionic initiators. These resins were stabilized by replacing the hydroxyl radicals on the polymer chain ends with ester groups. The resultant polymer with excellent tensile, impact, and compression strengths and good abrasion and wear resistance appeared capable of filling many applications then reserved for metals. Thus, in late 1959, Du Pont began the first commercial production of acetal resin. Celanese Corporation, about the same time, developed a polymer of very similar structure and properties, using trioxane as the raw material. It was stabilized by ethylene oxide molecules incorporated into the polymer chain. Production was started in early 1962.
Until 1971, Du Pant, Celanese, and Celanese joint ventures have been the sole producers of acetal resins. Prices have been constant and production has climbed to over 100 million pounds annually. Acetal resins have moved into many applications, such as bearings, gears, valves, and electrical parts, formerly occupied by metals or by the older nylon and ABS (acrylonitrile-butadiene-styrene) resins. Numerous other companies have conducted extensive research on the properties of polymer and co- polymer acetyl resins and on methods to synthesize and stabilize them. During the 1970s, as basic patents expire, more companies are expected to enter this field. The interavailability of technology should enable further economics of production and improvements in acetal resin properties. These two factors, coupled with larger plant size, should serve to increase the competitive position and growth rate of acetal resins versus the metals and older polymers.
This study provides a detailed evaluation of the technology of the established Du Pont and Celanese processes for the manufacture of acetal resins. To provide a more useful cost comparison, both processes are assumed to start with methanol as the major basic raw material. Formal-dehyde is synthesized by air oxidation of methanol and then purified by formation of cyclohexyl hemiformal and by partial condensation. Trioxane is prepared from aqueous formaldehyde solution and purified by extraction with fY-chloronaphthalene and by scrubbing trioxane vapors with molten sodium. It is not known how closely the commercial processes suggested in this report for the production of homopolymer and copolymer acetal resins resemble actual Du Pont and Celanese operations.
An irradiation process for the bulk polymerization of solid trioxane, offered by Japan Atomic Energy Research Institute, has also been studied. Capital and operating cost estimates for this process, as for preceding processes, are based on a Texas Gulf Coast location.
The potential processes of other companies, as suggested by patents, have been briefly discussed. An attempt has also been made to summarize, on the basis of patents by many companies, the large volume of research relating to the stabilization of monopolymer and copolymer acetal resins.
