Effects of zeolites on volatile products of beech wood using analytical pyrolysis

Five unmodified basic and acidic zeolites have been tested in the thermo-chemical conversion of beech (Fagus sylvatica L.) using an on-line pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) system to study their effects on lignocellulose thermal degradation products. The catalysts employed were SN-27, MSN-15, MSM-15, H-ZSM-5-28 and H-ZSM-5-80 with varying Si/Al ratio between 11 and 80. Thoroughly mixed samples of the biomass with different catalysts loading were pyrolysed at 500 °C. The catalyst exhibited varying degree of selectivity on individual volatile products. The selectivity was largely controlled by the nature of zeolites’ active sites and alumina contents. The acidic catalysts mostly influenced the condensable organic products; induced high yields of furfural and levoglucosan. Their yields increased up to five and nine times respectively in samples spiked with 40% MSM-15 and H-ZMS-5 on the basis of feedstock weight. H-ZSM-5 with lower alumina content proved most effective in enhancing high yield of furfural due to better diffusion of molecules through the pores. A slight reduction in polysaccharide derived low molecular volatiles such as hydroxyacetaldehyde, acetic acid, hydroxypropanone was observed in all catalysts. The overall result indicated that the acidic catalysts largely induced cleavage of glycosidic bonds through protonation predominantly on zeolites’ surface area. This was followed by the modification of free hydroxyl groups through dehydration process. All zeolites revealed no significant effect on most lignin derived products except indenes.