Glycerol Upgrading over Zeolites by Batch‐Reactor Liquid‐Phase Oligomerization: Heterogeneous versus Homogeneous Reaction

Abstract

Glycerol upgrading to diglycerols in the presence of basic (Na+ or Cs+) ion-exchanged (FAU or BEA) zeolite catalysts was studied in a liquid-phase batch rector at 260 degrees C under normal pressure. Homogeneous NaHCO3 and CsHCO3 catalysts were studied for comparison. All the catalysts, including NaHCO3 and CsHCO3, displayed the same conversion-selectivity relationship. The selectivity to linear diglycerols decreased at higher conversions/reaction times owing to the consecutive formation of higher oligomers, with preferential further conversion of alpha,alpha'-diglycerol. The maximum yield of linear diglycerols was limited to about 30 %. The activities of the zeolites followed the order X>Y>Beta, independent of the alkali ion present. Catalysis by the zeolites starts with an induction period attributed to a slow leaching of alkaline cations from the zeolite. Thereafter, the reaction is characterized by a progressive loss of the microporous structure of the zeolite and increasing overlap of heterogeneous and homogeneous catalysis, where, primarily, the activity depends on the cation content of the zeolite.

Oligomerization of glycerol – a critical review

“…The concentration of Na changes in the same order 4.9 mmol/g (NaX) > 2.3 mmol/g (NaY) > 0.7 mmol/g (NaBeta) [37]. The concentrations of the linear diglycerol are different, but, as followed from Fig.…”

“…Figure 17. Shape selective effect of CsMCM-41 (a) [60], and zeolite NaY (b) [37] on the distribution of linear diglycerol configurational isomers. T ¼ 2608C, 2 wt% of catalyst, 0.54 mol of glycerol, conversion level 50%.…”

“…Summary of glycerol conversion on Cs modified catalysts from different sources but at comparable conditions (T ¼ 2608C, catalyst weight 2 to 4 wt% of glycerol, 0.54 mol glycerol). Squares: Cs ion-exchanged Na zeolites X, Y, and Beta [37], diamond: Cs(H)Y, Si/Al ratio of Y zeolite ¼ 2.7, Cs content 34%, exchange degree 65%, residual Brønsted acid sites present [46], full triangles: Cs impregnated AlMCM-41, Si/Al ¼ 20 [30], open triangles: Cs impregnated on MCM-41, Si/Al ¼ 20 [15]. The zeolites were found insoluble in the glycerol/product mixture and could be removed at the end of the reaction.…”

Theoretical Study on the Role of Surface Basicity and Lewis Acidity on the Etherification of Glycerol over Alkaline Earth Metal Oxides

“…Worth mentioning here is the early work of Clacens et al [10][11][12] with the broad scope of examined materials, and also a more recent paper about base-type zeolites doped with Cs. [13] As recently shown, the acid-base properties of metal oxides largely determine their catalytic activity. For example, our group has shown that alkaline earth metal oxides (MgO, CaO, SrO and BaO) are promising solid catalysts and glycerol conversion increases with increasing catalyst basicity.…”

A Simple and Efficient Process for Large Scale Glycerol Oligomerization by Microwave Irradiation

“…Although GPC analysis was able to separate three oligomer species more clearly, mass analysis showed that there are both linear and cyclic structures present in the mixture. Although a variety of catalysts have been reported for glycerol oligomerization, heterogeneous catalysts in particular show good results [14][15][16][17][18][19], but most of them are quite expensive and can be altered at high temperatures. Homogeneous acid catalysts on the other hand can lead to dehydration reactions with toxic products such as acrolein [20,21].…”