A case study in Green chemistry: Developing replacements for CFCs

Chlorofluorocarbons, CFCs, were developed in the late 1920s for use as safe refrigerant alternatives to sulphur dioxide and ammonia. They were welcomed by industry because of their low toxicity, chemical stability, low flammability, low cost and ease of synthesis. They found wide application as refrigerants, blowing agents, propellants and cleaning agents. Over more than 40 years, applications of CFCs expanded into a wide variety of areas, and grew into a multibillion-dollar industry. Unfortunately, CFCs are not ecologically benign. It became increasingly clear that CFCs were responsible for ozone depletion. In the early 1970s the leading manufacturers of CFCs met to discuss the possible environmental impact of their products. This case study uses a problem based learning approach to take students through the development of replacements for CFCs from the 1970s to today. They investigate the background to the CFC problem and consider data that leads to the decision to investigate possible replacements. They must select and design replacement molecules (HFCs), devise syntheses and then consider the challenge to develop the replacements in a socio-economic and political framework. They also consider the problems posed by existing CFCs, the ‘fridge mountain’ and possible disposal and containment alternatives. The case study brings the story up to date with an investigation of the problems now being associated with HFCs and the search for new alternatives. This activity successfully teaches applied and ‘green’ chemistry via a real life context. The chemistry encountered is of an applied/industrial nature and is set in a socioeconomic context. The influence of political pressures is also brought in when appropriate. Because the activity adopts a problem based approach it is also successful in developing a range of transferable skills, particularly problem solving, teamwork plus verbal and written communication.