(374u) Study On the Catalytic Effects of Essential Inorganic Metals On the Primary Thermal Degradation of Lignocellulosic Biomass

This study examined the catalytic effect of main inorganic metals, such as potassium, magnesium and calcium on the thermal decomposition mechanism of wood components. As a raw material, xylem tissue of poplar wood (Populus ablaglandulosa) was washed with hydrofluoric acid (3 wt %) to remove the inorganic components. The HF demineralized wood xylem was impregnated with aqueous KCl, MgCl₂ and CaCl₂ (0.05, 0.1, 0.5 and 1.0 wt %) to prepare the samples with increasing concentration of potassium, magnesium and calcium, respectively. The untreated poplar wood xylem (control), HF demineralized and salt impregnated samples were analyzed by several chemical instruments - ICP-ES for determination of essential inorganic components and analytical pyrolysis-GC/MS for investigation of thermal degradation mechanism and composition of degraded products. The total amount of inorganic components in control was decreased from 0.70 to 0.12 wt % by means of washing with HF. In comparison with control, the concentration of potassium, magnesium and calcium were reduced to 4.6 ppm from 769 ppm, 12.8 ppm from 282 ppm and 131.8 ppm from 783 ppm after demineralization with HF, respectively. According to the results of analytical pyrolysis-GC/MS, thermal decomposition of cellulose and lignin was influenced by the presence of inorganic components. After reduction of inorganic components by HF demineralization, total yields of low molecular weight compounds, such as acetic acid, glycolaldehyde, acetol, etc. were fairly decreased to 32.3 wt % from 53.5wt % (control), whereas those of anhydrosugars including levoglucosane, etc. significantly increased to 14.9 wt % from 3.6wt % (control). Contrary to cellulose derivatives, only minor changes were observed in the lignin degraded products. One of the interesting results was that the formation of C6 type of degradation products, such as phenol, guaiacol and syringol was catalyzed in the presence of the inorganic metals. Especially, formation of low molecular weight compounds was affected by the concentration of potassium in the wood xylem. When the wood xylem was pyrolyzed after impregnation with 0.5% KCl, low molecular weight compounds were remarkably increased to 47.2 wt %,but anhydrosugars were fairly decreased to 1.7 wt %, respectively, compared with those of HF demineralized xylem (33.0 wt % and 12.6wt %, respectively). Meanwhile, the yields of degraded products of lignin were not changed regardless of the presence of the potassium. The catalytic effects of magnesium and calcium on the thermal decomposition of wood components were somewhat weaker than those of potassium contents. After impregnation with 1.0 wt % MgCl₂, the enhancement of levoglucosane formation was detected, whereas formation of glycolaldehyde was suppressed. However, in the presence of calcium, yields of degradation compounds were nearly similar with those from HF demineralized sample, except for slight increase in pyran derivatives. Accordingly, calcium seems to have the lowest catalytic efficiency of the three inorganic metals.