Doing the solubility splits

摘要

Separating products and catalysts is a major problem if both are in the same phase. But what if the reaction were designed so that the separation happened automatically? In a homogeneously catalysed reaction, both the reactant(s) and catalyst(s) are present in a single phase, often a liquid. Typically, the catalysis occurs at a metal centre, such as iridi-um, which is derivatised with ligands to give it solubility, as in the CATIVA process for the carbonylation of methanol (see Figure 1). From an industrial point of view, such processes offer greater selectivity to product(s) and can operate under milder conditions than heterogeneously catalysed ones. However, probably the most difficult challenge in industrial applications of homogeneous catalysis is efficient separation of the catalyst from the product. Heating is normally required, but this often causes the product and/or catalyst to decompose, or the catalyst to become deactivated. Even without these problems, it is difficult to obtain complete recovery of a metal catalyst, and this has direct economic and environmental implications. Consequently, a relatively small number of homogeneously catalysed reactions are performed on an industrial scale compared with their heterogeneously catalysed counterparts.