Major uses of chlorine in the United States in 1988 included chemicals manufacturing (76 percent), water and sewage treatment (5 percent), pulp and paper bleaching (14 percent), titanium dioxide manufacturing from rutile (3 percent), and miscellaneous, including silicon processing (2 percent). The use of elemental chlorine for bleaching in the pulp and paper industry has become a very contentious subject in recent years, due to the discovery of dioxin traces in bleached paper products. As a consequence, whether justified or not, this bleaching process has been largely phased out in Europe and may soon be phased out in North America. The likely alternative process is oxygen bleaching using chlorine oxide from sodium chlorate29 or hydrogen peroxide.
Chemical end uses of chlorine in 1988 were as bleaches such as calcium and sodium hypochlorite (7.8 percent); other inorganics like phosgene (2 percent) and phosphorus trichloride (1 percent); ethylene dichloride, or EDC (40.5 percent); chlorinated methanes (9 percent); chlorinated ethanes (5 percent); epichlorohydrin (1 percent); ethyl chloride (3.5 percent); chlorinated benzenes (1.5 percent); chloroprene (1 percent); and miscellaneous (3 percent, including hydrochloric acid [HCl] used outside the industry). These total to about three-quarters of U.S. chlorine output.
One of the major chlorine intermediates is HCl. Nine percent of HCl is made by direct chlorination of hydrogen, but most HCl, about 91 percent, is recovered as a by-product of one of the chlorination processes, especially the chlorohydrin process for propylene oxide production. The latter process consumed 8.3 percent of U.S. chlorine output in 1988, but this chlorine was entirely recycled internally as HCl. The other major source of HCl is the process that converts EDC to vinyl chloride monomer (VCM). HCl is also consumed by a parallel process that produces EDC by hydrochlorination of ethylene. These two processes are deliberately combined. Other end uses of HCl include ethyl chloride (for tetraethyl lead production, now nearly phased out) and hypochlorite bleaches.
By far the biggest single intermediate is EDC, the intermediate leading to polyvinyl chloride (PVC). However, PVC accounts for only 24 percent of produced chlorine; part of the chlorine contained in EDC is reclaimed again as HCl. EDC also has other end products, such as trichloroethylene and perchloroethylene. Some is also exported. Another important intermediate is epichlorohydrin, an intermediate to epoxies; phosgene (COCl2) is an intermediate to isocyanate pesticides and urethanes. Chlorinated benzenes are also intermediates to a variety of products.
Virtually all uses of chlorine are dissipative, with the major exception of PVC, which is used for structural purposes (e.g., water and sewer pipes, siding, window frames, calendered products, and bottles). PVC, from vinyl chloride monomer, accounts for 24 percent of U.S. elemental chlorine output.
Direct chlorination processes are relatively inefficient. Hence, recycling of waste streams is commonplace and a fairly large proportion of the input chlorine eventually becomes a production waste for manufacturing other downstream