Re-usability of zeolites and modified clays for alkylation of cyclohexanol a contrast study

Abstract

Organic sulfonic acid treatment of montmorillonite results in micro-pores on the surface of modified clays providing access to acid sites in the interlayer. Performance of modified clay catalysts for alkylation of para-cresol with cyclohexanol were compared with microporous zeolites. Phenoldisulfonic acid treated clay catalyst showed maximum activity comparable with that of beta-zeolite. Modified clay-and zeolitecatalysts on reuse for the alkylation exhibited different behaviour. Modified clays showed same activity as in the first cycle while zeolites showed significantly reduced catalytic activities on reuse. Differences in behaviour were further investigated by characterizing the reused samples with TGA, acidity and surface measurements. Used zeolite samples showed considerable variations in acidity, surface characteristics and TGA pattern, which was attributed to the formation of coke. Absence of coke in clays and deposition of coke in zeolites is attributed to difference in their pore architecture.

Green synthesis of Cyclic imides by Amidation and Cyclisation using Bronsted-Lewis acidic montmorillonite clays

“…Our previous reported catalysts such as different organosulfonic acid treated clays were also used for the comparison, surface and acidity characteristics were also provided with the catalytic activities. Organosulfonic acids p‐TSA (para toluenesulfonic acid), MSA (methanesulfonic acid) and PDSA (phenoldisulfonic acid) had more tendency towards the removal of Al, hence there is no much change in cation exchange capacity (CEC) with increased acidity, surface area and pore volumes ,,. These showed similar activity and yield as zeolite samples, due to their higher pore volumes enhances access of dicarboxylic acid to acid sites to form amic acid and it cyclisation to yield cyclic imide.…”

“…BET analysis results and adsorption-desorption isotherms Figure 2 showed increased surface area, pore volumes and decreased average pore diameter Figure 3. The removal of octahedral Al from the clay structure could be seen the decreased arbitrary in- tensity from 27 Al NMR spectra ( Figure 4). This is the supporting evidence, agreement with the ICP-OES analysis and FE-SEM images of before and after the acid treatment (see supplementary information) showed morphological changes after the acid treatment.…”

“…[21,22,28] Depending on metal ion removed from the octahedral layer and polarizing hydrated cations presence in the interlayer, both the Bronsted and Lewis acidities are generated on the clays. [21,22,29] The amounts of octahedral cations removed was analyzed by ICP-OES elemental analysis and also decreased in arbitrary intensity in the 27 Al NMR spectra showed decreased Al from the clay, increased surface area and decreased CEC due to removal of Mg and Fe are also provided in Table 1 and 2.…”

“…conversion and selectivity of cyclic imide and other two has lower acidity than alumina but comparable to pillared clays, hence the yield and conversion are similar to pillared clays. With these Zeolites were are used for the reaction, among the zeolites used, HBEA and HÀY showed similar conversions and cyclic imide selectivity, because, both are having higher pore volume and pore size, even though ZSM-5 having higher acidity, it gives lower conversion may due to its constrained channels having uniform pore size 27,37 . While other two has cage like structure with higher pore size but those have lower acidity than ZSM-5 but more compared metal oxides and clays hence giving more yield than all the samples used.…”

“…The author also extend their thanks to L.V. Narendra NMRC IISc, Bengaluru for 27 Keywords: citric acid · amic acid · cyclic imide · benzene-1,2dicarboxylic acid · microwave…”