Evaluation of strongly acidic ion‐exchange catalysts and the desulfonation study in the isobutylene dimerization reaction

Abstract

Three commercial ion-exchange resin based catalysts were compared under different temperature and liquid-volume hourly space velocity (LHSV) in the isobutene (IB, C4) dimerization reaction using a plug flow reactor in the absence of any selectivity enhancing component. High IB conversion for all catalysts was obtained at or higher than 50 C. But, diisobutene (DIB, C8) selectivity decreased with the increase of temperature. High C8 selectivity was observed with LHSV higher than 1.5 at 50 C. The best catalytic performance of the three resins did not show obvious differences. The effect of the selectivity enhancers on the stability of the resins was also studied. Desulfonation was observed in the C4 dimerization reaction when water or the commonly used enhancer tert-butyl alcohol (TBA) was added to the feed. The deactivation of catalyst resulted in decrease of both IB conversion and C8 selectivity. Fourier Transform Infrared spectroscopy showed that desulfonation happened in both para and ortho positions of the sulfonated benzene rings.

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

“…This indicates that desulphonation is significant under the reaction conditions. Water is one of the products of the reaction and it helps in creating a polar environment around the catalyst surface, conducive for desulphonation, 24 and more importantly, the presence of metal ions may trigger hydrolysis of sulphonic acid group leading to desulphonation accordingly to previous studies 31 . It may be noted that in the absence of metal impurities when the reaction was performed in a glass reactor, the change in site density, and hence the sulphur content, was insignificant in both reactive (4.2 meq/g from 4.7 meq/g in 120 h in 72 h) and non‐reactive environments (4.5 meq/g from 4.7 meq/g in 130 h).…”

“…It is generally believed that desulphonation happens at high temperature leading to release of 4‐phenol sulphonic acid from the polymer matrix by oxidation 23,30 . Since the temperatures employed in cation‐exchange resin catalysed reactions are less than 393 K, barring some exceptions, 24 desulphonation is normally not considered as a major cause of deactivation. However, in a recent study 31 reported for water purification by similar sulphonic acid resins, it has been revealed that the counter ions may promote hydrolysis of sulphonic acid group leading to formation of corresponding salt and the relative neutral aromatic ring as shown in Scheme 2.…”

“…5 This interchange may lead to structural change and eventually permanent deactivation of the resins. 22 Tan et al 23,24 in their studies on dimerization of isobutene over cation-exchange resins demonstrated desulphonation causing catalyst deactivation with a drop in site density by 10-15% even at 323 K. They attributed it to the presence of polar water which is deliberately added in trace amounts to increase selectivity towards the dimer of isobutene. This finding may also be applicable to the reactions in which water is formed as a co-product or side product.…”

Selective oligomerization of isobutylene in mixed C4 catalyzed by supported Fe(NO3)3/β catalyst

“…Solid phosphoric acid catalyst has high catalytic activity and is used widely in industry, but it has low mechanical strength, no selectivity and no regeneration. Acidic cation resin catalyst has the characteristics of high acidity, stable catalytic effect, low price, mild reaction conditions and a single product, but it is difficult to regenerate 22 . Molecular sieve catalysts have the advantages of shape‐selective catalysis, environmental friendliness, high stability and reproducibility 23,24 .…”