Cleaning up PVC production

Professor Graham Hutchings of the School of Chemistry has been working towards reducing the environmental dangers of polyvinyl chloride (PVC) manufacture. The result of his work has made it possible to replace mercury as the catalyst in the manufacture of the precursor chemicals necessary to manufacture PVC. This is the first time in over 50 years a complete overhaul in catalyst formulation has been implemented to produce a commodity chemical.

Since 2007, international chemical company Johnson Matthey PLC collaborated with Cardiff to develop this new series of gold-based catalysts for VCM production. Following over 10 years of research and development costing millions of pounds, the company developed the PRICAT™ MFC (Mercury Free Catalyst).

Replacing Mercury with Gold

Professor Hutchings’ research showed the great ability for gold to catalyse the manufacture of VCM’s. However, the high price of gold necessitated a reduction in gold content for the proposed catalyst to be commercially viable. Because of Professor Hutchings track record in gold-based catalyst formation, Cardiff was approached by Johnson Matthey to apply his research to the commercialisation of this process.

The project, funded by Johnson Matthey and the World Gold Council began by exploring how dilution of the gold affected golds effectiveness as a catalyst in this process. The Cardiff team found that dilution the gold resulted in untenably low catalytic activity in all cases. It also showed that alloying gold with other metals did not produce viable catalysts.

These studies showed that gold-only catalysts were superior to other mixed compositions, including mixed metal catalysts. It also gave the team a clearer understanding of the reaction mechanism, on which they based their new catalysts. It further demonstrated the importance of maximising the dispersion of the gold to increase the useable surface area of the gold catalyst.

Making the process safe and cost effective

Based on the research Johnson Matthey developed a catalytic system consisting of a carbon core, coated in a thin layer of gold called PRICAT™ MFC (Mercury Free Catalyst). This produced a catalyst with a large surface area to mass ratio of gold. When tested in scale trials, it showed that the new highly dispersed gold catalyst was found to be vastly superior to the mercuric chloride catalyst it was developed to replace, that had been the industry standard for the last 60 years.

The next step in the development process was to developer a safer more commercially viable method for making the catalyst. The original method had the carbon-supported gold catalysts were prepared by depositing gold using the incredibly strong acid aqua regia. This challenge was overcome by the development a new water-based route employing small molecule sulphur complexes of gold. The results of this process were further studied to confirm the nature of the catalysts active site which provided an atomic level of understanding, enabling further development of the catalysts for commercialisation.

Cardiff research was central to understanding how gold catalysts work and has helped in their design, greatly increasing their potential for commercial exploitation by meeting the key innovations required for successful translation to PVC manufacturing.