The use of cobalt in catalytic applications supports the climate change initiatives for reduction of greenhouse gases. For example, petrol or diesel for cars can only be sold after it has been refined with catalysts containing cobalt compounds which reduce sulphur and nitrous oxide emissions.
All crude oils contain between 0.1% and 2.5% of sulphur dependant on their source of origin. Upon combustion, the sulphur from these crude oils is converted into sulphur oxides – an air pollutant that can dissolve in rainwater creating acid rain which damages crops, forests and aquatic species.
Cobalt plays a vital role in catalysing the removal of sulphur from oil, contributing to a more sustainable society. Desulphurisation is the process by which sulphur is removed from oil. A significant use of cobalt globally is as part of catalysts in this desulphurisation process. The use of cobalt in desulphurisation reactions represents the highest tonnage of cobalt use in the catalyst sector.
By using a cobalt oxide-molybdenum oxide catalyst (CoMOX), the sulphur can be converted into hydrogen sulphide (H2S).
The H2S can then be converted into either elemental sulphur or into sulphuric acid (H2SO4), which is then used for other industrial processes. CoMOX catalysts contain 3-5% tricobalt tetraoxide (Co3O4), 14% molybdenum trioxide (MoO3) and 83-85% alumina (Al2O3). As CoMOX catalysts are very resistant to poisoning and degradation they are the ideal choice for use in desulphurisation reactions.
Synthesis of polyester precursors
Cobalt catalysts also help to hit greenhouse emission targets by lowering the activation energy (e.g. pressure, temperature) needed for industrial processes such as the creation of polyester. Less energy therefore needs to be used to obtain the same yield, which in turn means lower carbon emissions. Cobalt catalysts are used to synthesise terephthalic acid (TPA) and di-methyl terephthalate (DMT) which are predominantly used as precursors in the creation of polyester. 60% of polyester is used in polyester fibres for textiles, and another 31% in polyester resin used to make recyclable plastic bottles.
Production of aldehydes from alkenes in the OXO reaction
Hydroformylation, also known as the OXO reaction, produces aldehydes from alkenes using a cobalt or rhodium-based catalyst. Within the reaction, a formyl group and a hydrogen atom are added across the double bond of alkenes. Most of the resulting aldehyde is further processed into other important chemicals including plasticising agents. Hydroformylation is also used in other industrial processes such as the production of long carbon chain alcohols used in detergents.