Effect of zeolites and nanopowder metal oxides on the distribution of chiral anhydrosugars evolved from pyrolysis of cellulose: An analytical study

摘要

An analytical procedure, employing a commercial heated filament pyrolyser, was utilised for studying the effect of zeolites (H-Y, NH_4-Y and NH_4-ZSM-5 types) and nanopowder metal oxides (SiO_2, Al_2O_3, MgO, TiSiO_4 and Al_2O_3TiO_2) on the pyrolytic production of chiral anhydrosugars from cellulose. Cellulose mixed with catalyst was pyrolysed at 500℃ for 60 s, the evolved products were trapped onto a XAD-2 resin, eluted with acetonitrile and analysed directly, or after trimethylsilylation, by gas chromatography-mass spectrometry (GC-MS). Yields were determined for the following anhydrosugars: levoglucosan (LGA, 1,6-anhydro-β-D-glucopyranose), levoglucosenone (LGO, 6,8-dioxabicyclo[3.2.1]oct-2-en-4-one), 1,4:3,6-dianhydro-β-D-glucopyranose (DGP) and the δ-lactone of 3-hydroxy-5-hydroxymethyltetrahydrofuran-3-carboxylic acid (LAC, 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one). This latter compound, quoted only once in the available literature, was tentatively identified by its GC-MS characteristics. Zeolites and nanopowder metal oxides exhibited a strong influence on the pyrolytic behaviour of cellulose, but whereas zeolites acted to reduce the overall yields of anhydrosugars with respect to pure cellulose, all nanopowders but silicon oxide provided higher yields. LGO and LAC accounted for the larger production of anhydrosugars promoted by aluminium titanate, titanium silicate and aluminium oxide with respect to pure cellulose, while the yields of LGA and DGP remained comparable or even lower. The nanosized characteristics of aluminium titanate, the oxide giving the highest yields of LGO and LAC, were considered a determinant factor for its activity, as powder aluminium titanate resulted ineffective.