Determination of Enthalpy of Pyrolysis from DSC and Industrial Reactor Data: Case of Tires

Abstract

This study was motivated by the fact that differential scanning calorimetry (DSC)/differential thermal analysis (DTA) results in literature showed significant exothermic peaks while in overall, pyrolysis is an endothermic phenomenon. The specific heat of the decomposing tires has been determined with a new methodology: instead of assuming constant char properties throughout pyrolysis, the specific heat of evolving solids (char) was evaluated with increasing temperature and conversion. Measured specific heat values were observed to increase until pyrolysis was triggered at 250°C. Then, the specific heat of the solids decreased continuously until 400°C at which point they started to increase. This unexpected trend pointed out that the exothermic peak observed with DSC is an artefact generated by the control system of the apparatus. To overcome this limitation, the energy balance was performed over industrial data and the newly found heat capacity values. The enthalpy of pyrolysis was found to have a term dependent on the weight loss derivative, with a constant value of 410 kJ/kg tires. Two other terms for the enthalpy of pyrolysis have been identified, which were independent of weight loss. The first one is believed to correspond to the sulphur cross-link breakage at low temperature (65 kJ/kg), while the second one, at the final stage of pyrolysis, should correspond to charring reactions approaching the thermodynamic equilibrium (75 kJ/kg). Ultimately, this work proposes a new methodology to determine the enthalpy of pyrolysis with larger scale experimental data.

Energy and exergy analyses of sewage sludge thermochemical treatment

“…These authors defined heat of pyrolysis as the heat needed to decompose biomass into different products (char, liquid and non-condensable gases) at the pyrolysis temperature, and heat for pyrolysis as the sum of the heat of pyrolysis and the sensible heat needed to raise biomass to the pyrolysis temperature. Pyrolysis has been considered globally endothermic, although both exothermic and endothermic values of heat of pyrolysis have been reported in the literature, since this process comprises exothermic and endothermic steps [3].…”

“…Several authors have analyzed qualitatively and quantitatively by DSC the heat required for pyrolysis of lignocellulosic biomass and wastes [3][4][5][9][10][11]. Generally, the heat for pyrolysis reactions is much lower than the sensible and the latent heats and can be considered negligible.…”

“…Boukis et al [8] determined the heat of pyrolysis by using empirical correlations based on the moisture and ash contents of the biomass. Although pyrolysis products are complex in nature and their standard enthalpies of formation and specific heat capacities are not always easy to determine [1], the energy balance can also be evaluated in terms of the difference M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 5 between the enthalpy of reactants and products [3,15,16]. This is the methodology applied in the present work.…”

“…-SS was thermally dried prior to any thermochemical treatment and the heat needed for that step should be considered for the energy balances. The energy requirements for the thermal drying was previously estimated [3]. Almost 8 MJ per kg of 6.5% dried SS were required to reduce the moisture content of dewatered SS from 77% to 6.5%.…”