Replacing Ozone-Depleting Substances Used as Refrigerant Working Fluids

Abstract

oping economies following closely: transport, communications, medicine, and food have all evolved beyond recognition within a very few generations. In support of these changes, whole new industries have developed and evolved. One of these is the refrigeration industry. The refrigeration industry, essential to the food chain as we know it today (and indeed to many other aspects of modern life), grew out of the invention and development of safe refrigerant fluids in the 1930’s. These fluids, the fully halogenated halocarbons, were hailed at the time as miracles of science: They were chemically inert, nonflammable (indeed some members of this chemical family are extremely effective fire extinguishing agents), and have low toxicity; and they perform well as refrigerant fluids. Impact on the Environment. Following their growing use as refrigerants, halocarbons also became widely used as foam blowing agents, aerosol propellants, and industrial cleaning solvents. These last three applications are considered to be essentially emissive – the halocarbon is released to the atmosphere as a consequence of its use (although in the case of some of these applications, such as in closed cell foams, the emission might take place over a long time span). For several decades the release of volatile halocarbons to the atmosphere was not considered (even by the few who thought about it) to be a problem. After all they are chemically stable and are, in very dilute concentrations, nontoxic. Rarely are things this simple. The high degree of chemical stability of these fully halogenated fluorocarbons results in long atmospheric lifetimes: after release they accumulate in, and diffuse throughout, the atmosphere. When it was recognized that these substances are the cause of depletion of the stratospheric ozone layer, international negotiations resulted in the signing of the Montreal Protocol, the first truly international environmental treaty, whose objective is to ban the manufacture and commercialization of ozone-depleting substances, ODSs (chlorineand bromine-containing halocarbons). The Montreal Protocol was a significant development in international environmental legislation as it has been adopted by essentially all the independent nation states in the world. Such a global measure is necessary because the environmental impact is not essentially local – its effect is not related to the geographic location of the source of emission. The discussions leading up to the Montreal Protocol and the measure itself have had two far reaching impacts: a heightened scientific interest in the study of the atmosphere and its effects on the surface environment of the planet; and a major technical effort to find replacement substances for the now regulated ODSs, which has resulted in the transformation of the industries dependent on these substances. The Montreal Protocol legislation recognizes several classes of ODSs, two of which are important for the refrigeration industry: Chemical and Petroleum Engineering, Vol. 37, Nos. 1–2, 2001