Manufacture and use of chloroprene monomer

Abstract

There are only six manufacturers of chloroprene (CD) located outside of the former Communist Bloc countries. Five of these manufacture chloroprene from butadiene via a two step process consisting of chlorination and subsequent dehydrochlorination. The sixth dimerizes acetylene and then hydrochlorinates the dimer to produce CD. Both the acetylene and butadiene-based manufacturing processes are conducted within sealed systems. Therefore, the only potential exposure during manufacture is sampling for product quality, strainer/filter changing and accidental leaks or spills. All six manufacturers produce CD only for the production of polymer. Manufacturers convert CD into polychloroprene polymer (PCP) via emulsion polymerization. A solution of CD and other ingredients is mixed with an aqueous caustic solution to produce an emulsion. Free radicals initiate polymerization and free radical scavengers are added to stop the reaction at the desired conversion. After unreacted monomer is removed, PCP can be sold as a latex (colloid) or isolated and dried to produce solid product. The PCP manufacturing process is also designed to be a closed system. However, the extreme reactivity of CD and the inherent stickiness of PCP polymer, makes it necessary to ‘open’ the process to remove polymer. This results in potential for operator exposure, in addition to the items mentioned for CD manufacture. With the use of appropriate engineering controls, work practices and personal protective equipment for activities with exposure potential, actual workplace exposures are controlled below the occupational exposure limits (2–10 ppm). The solid PCP products, which comprise ≈92% of the total amount of polymer manufactured, contain <1 ppm CD. Most PCP latexes contain <0.1% residual CD. So, the potential for CD industrial exposure is limited to CD and PCP manufacture.