Effect of Salt Composition and Temperature on the Thermal Behavior of Beech Wood in Molten Salt Pyrolysis

The thermal behavior of wood particles in molten salt pyrolysis was investigated. Cylindrical beech wood particles (L = 30 mm, d = 3.5 mm) were pyrolyzed using different mixtures of molten salts (FLiNaK, (LiNaK)2CO3, ZnCl2–KCl, KNO3–NaNO3) over a temperature range of 400–600 °C. The temperature at the particle center was measured during the process, and used to evaluate heating rates, reaction temperatures and devolatilization times. A general observation was that beech wood is heated faster in fluoride and carbonate melts, but the differences diminish with increasing reactor temperatures. The highest heating rates at the particle center were observed in FLiNaK (46 – 56 °C/s). The effective pyrolysis temperature at which the main decomposition of cellulose and hemicellulose takes place showed a weak dependence on reactor temperature, but no significant difference between the heating media was discovered. The devolatilization time corresponding to conversion of 95% may be empirically correlated with the power law expression . Arrhenius plots were constructed to show the exponential dependence of temperature on the parameter A. The correspondingly low activation energies (13.3 – 27.4 kJ/mol) indicate heat transfer control during the decomposition process.