Reactivity and Free Radical Chemistry of Lilac (Syringa vulgaris) Charcoal

Abstract

HIGHLIGHTSo Lilac ignites quickly (250-290 o C), and has a narrow combustion temperature range (300-o It is microporous with a surface area of 4.3706m 2 /g, o Lilac has C-C free radicals arising from carbonization, o It forms peroxyl radicals on oxidation in air, o Degassing in N2 and acid washing removes the free radicals. ABSTRACTThe reactivity, porosity and surface chemistry of charcoal determine its combustion behaviour, and these properties depend on the source of the original wood, production conditions and treatment. Here we studied the properties of charcoal derived from lilac (Syringa vulgaris). Its reactivity was tested by isothermal and non-isothermal thermogravimetric analysis and differential scanning calorimetry in air and nitrogen. Its porosity was tested by monitoring nitrogen adsorption at 77 K. The free radical concentration was determined by measuring the electron spin resonance of fresh charcoal, after washing with HCl, and after degassing in air with or without nitrogen. We found that lilac has a specific surface area of 4.3706 m 2 /g and is highly reactive, igniting at 250-300°C with peak combustion at 320-520°C. The quantity of oxygen consumed and heat released during oxidation increased with temperature. The free radical concentration in the fresh charcoal was 5.29 x 10 18 spins/g, compared to 3.49 x 10 19 spins/g after acid washing, 7.06 x 10 19 spins/g after exposure to air, and 3.75 x 10 17 spins/g after degassing with nitrogen before exposure to air. The line width of all the charcoal samples was 11.6-11.9 G. However, degassing the charcoal in nitrogen followed by exposure to air at low temperatures resulted in a four-fold increase in the line width to 41.8 G. The exposure of lilac charcoal to air alone at low temperatures resulted in the formation of persistent peroxyl radicals superimposed on the main peak. The g-values of charcoal samples that were fresh, acid washed, degassed in N2 + air, and degassed in air alone (main peak) were 2.00481, 2.00477, 2.00260 and 2.00483, respectively. The corresponding g-values of the peroxyl radicals superimposed on the main peak were 2.0155, 2.0138, 2.0020 and 2.0007, respectively. The reactivity, free radical content and specific surface area suggest that lilac charcoal is particularly suitable for applications involving energetic materials, catalysis and co-firing.

Catalytic Effects on the Nonisothermal Oxidation of Solid Fuels by Oxygen: An Experimental Study

“…(ii) Charcoal fines (<400 µm particle size) as the main fuel, wood sawdust (<400 µm particle size) as an ignition enhancer, cassava flour as the binder and 1w% Pd-Sn/alumina as the catalyst for CTCB (ratio: 20:2:1:0.25). The charcoal used for these recipes was prepared by laboratory pyrolysis of wood as per our previous method [32]. Appropriate amounts of water were added to the solid components and mixed thoroughly with an auto blender to form a paste that was extruded with a mould, dried and stored for subsequent analysis Figure 1, shows the extruded charcoal briquettes.…”

“…The recipes contained the following: (i) charcoal fines (<400 μm particle size) as the main fuel, wood sawdust (<400 μm particle size) as an ignition enhancer, and cassava flour as the binder for UTCB (ratio: 20:2:1); (ii) charcoal fines (<400 μm particle size) as the main fuel, wood sawdust (<400 μm particle size) as an ignition enhancer, cassava flour as the binder, and 1 wt % Pd–Sn/alumina as the catalyst for CTCB (ratio 20:2:1:0.25). The charcoal used for these recipes was prepared by laboratory pyrolysis of wood as per our previous method . Appropriate amounts of water were added to the solid components and mixed thoroughly with an autoblender to form a paste that was extruded with a mold, dried, and stored for subsequent analysis.…”

“…The charcoal used for these recipes was prepared by laboratory pyrolysis of wood as per our previous method. 32 Appropriate amounts of water were added to the solid components and mixed thoroughly with an autoblender to form a paste that was extruded with a mold, dried, and stored for subsequent analysis. Figure 1 shows the extruded charcoal briquettes.…”