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

摘要

Glycerol upgrading to diglycerols in the presence of basic (Na-or Cs') ion-exchanged (FAU or BEA) zeolite catalysts was studiedin a liquid-phase batch rector at 260°C under normal pressure,Homogeneous Naha:),. and CsHCO3 catalysts were studied forcomparison, Ali the, catalysts, including NakiCO3, and CsK03, dis-played the same conversion*-selectivity relationship. The selectivi-ty M linear diglycerols decreased at higher conversions/reactiontimes owing to the consecutive formation of higher oligomers,with, preferential further conversion of a,a'-diglycerol. The maxi-mum yield of linear diglycerols was limited to about 30%. Theactivities of the zeolites followed the order X> Y> Beta; inde-pendent of the alkali ion present. Catalysis by the zeolites startswith an induction period attributed to a slow leaching of alkalinecations from the zeolite. Thereafter, the reaction is characterizedby a progressive loss of the microporous structure of the zeoliteand increasing overlap of heterogeneous and homogeneous cat-alysis, where, primarily, the activity depends on the cation con-tent of the zeolite.