An improved solid phosphoric acid catalyst for alkene oligomerization in a Fischer–Tropsch refinery

An improved solid phosphoric acid catalyst has been developed for the oligomerization of C3–C5 alkenes, an important reaction for the refining of Fischer–Tropsch products. Catalyst particle strength is found to be the controlling design parameter when using a solid phosphoric acid catalyst for this application. The crushing strength is controlled by the relative amounts of the silicon ortho- and pyrophosphate phases present. The effect of the silicon ortho- to pyrophosphate ratio on the final catalyst was investigated by variation of key catalyst preparation parameters, namely: H3PO4 concentration, impregnation and calcination temperature and water addition. An improved catalyst with respect to crushing strength and hence lifetime, was prepared using an acid concentration of 115% H3PO4, an impregnation temperature of 220 °C and a calcination temperature of 420 °C. Water addition during calcination was found to be detrimental. Based on these findings, a new commercial catalyst was formulated which requires no binders. Comparative tests using commercial conditions showed a 30% increase in catalyst lifetime when compared to catalysts previously available.