Catalyst deactivation of cation-exchange resin in cross-aldol condensation of acetaldehyde to methyl pentenone

The aldol condensation of acetaldehyde with methyl ethyl ketone was studied for the production of methyl pentenone in the presence of cationic resin, Amberlyst-15. Methyl pentenone (MPO) is an important intermediate used for the synthesis of Iso-E-Super, which is a precursor in sandalwood fragrances. Amberlyst-15 used as an alternative heterogeneous catalyst for conventional corrosive sulphuric acid was found to get deactivated with prolonged use. In this work, major possible causes of catalyst deactivation, such as desulphonation, coking, grafting, metal deposition and thermal degradation, are investigated. Characterization of fresh and used catalysts is performed for surface area, mass deposited and elemental composition (CHNS and ICP). The results confirm that multiple causes, i.e., desulphonation, metals exchange and oligomers deposition, are responsible for the catalyst deactivation. The presence of metal promotes desulphonation; the desulphonation along with metal exchange appears to be the major contributors to catalyst deactivation; and avoiding exposure to metal impurities may enhance the catalyst life significantly. Catalyst regeneration was also explored, and the catalyst site density is reclaimed from 0.5–0.6 meq/g to 4.1–4.2 meq/g, which is closer to the fresh Amberlyst-15 (4.5–4.6 meq/g). The study provides a way to develop the resin-based green technology for catalytic reactions.