Solketal Formation in a Continuous Flow Process over Hierarchical Zeolites

Abstract

Glycerol ketalization with acetone to solketal, an oxygenate fuel additive, was demonstrated over hierarchical zeolites of ZSM5, Beta and Mordenite structure in a continuous flow system. Micro‐mesoporous zeolites were prepared in two steps, by means of alkaline treatment with NaOH followed by the ionic exchange with NH4NO3 and a subsequent treatment with citric acid. The presence of mesopores in the applied catalysts was confirmed by N2 adsorption/desorption measurements and TEM microscopy. Hierarchical zeolites showed superior catalytic performance and lifetime over 24 hours under mild conditions (atmospheric pressure, acetone to glycerol molar ratio of 3 : 1, WHSV of 3–8 h−1, reaction temperature of 323 K). Glycerol conversion of about 90 % and selectivity to solketal up to 98 % have been obtained over micro‐mesoporous catalysts within 24 h without any drop of performance and the symptoms of clogging. Among all hierarchical catalysts tested in a flow reactor, the very high activity defined as solketal yield (88 %) showed ZSM5 and Beta zeolites.

Continuous Flow Upgrading of Selected C2–C6Platform Chemicals Derived from Biomass

“…Kowalska-Kuśand coworkers prepared and evaluated hierarchical micro-/mesoporous zeolites by desilication of parent HZSM-5, βand Mordenite zeolites. 188 Unmodified βand Mordenite zeolites gave good activity and 4, entry 9) for 24 h of operation under identical conditions. Good results were obtained over hierarchical βzeolite as well (Table 4, entry 8).…”

“…The ketalization of GL with acetone was studied in continuous flow reactor, using either homogeneous or heterogeneous − (Table ) acid catalysts. The formation of the 5-membered ring, 4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane (solketal, 30 ), was always favored and the 6-membered ring 31 , resulting from the capping of the two primary alcohols of glycerol, was detected only in traces (typically 1%, Figure ).…”

“…In addition, no additional solvent other than acetone was utilized, since residual methanol and water present in the feed solution improved the miscibility of glycerol and acetone (Table , entry 7). Kowalska-Kuś and coworkers prepared and evaluated hierarchical micro-/mesoporous zeolites by desilication of parent HZSM-5, β- and Mordenite zeolites . Unmodified β- and Mordenite zeolites gave good activity and stability, while the parent HZSM-5 gave low conversion and stability, since conversion evolved from 35% to 10% during 6 h TOS.…”

State of the Art and Perspectives of Hierarchical Zeolites: Practical Overview of Synthesis Methods and Use in Catalysis

“…This was done by several research groups. [335][336][337] Starting with Kowalska-Kuś et al, this group performed an acid treatment with citric acid, which was preceded by an alkaline treatment using a NaOH solution. The outcome was a hierarchical beta zeolite with superior catalytic performance.…”

“…Applications included the ketalization of glycerol with acetone, forming solketal, with a conversion and selectivity up to 90% and 98% respectively. [335] Furthermore, the group of Li et al performed subsequent dealumination and realumination using organic acids such as oxalic acid, dl-malic acid and dl-tartaric acid. All three acids showed different realumination abilities, where tartaric acid had the highest.…”