Insight into kinetics and thermodynamics of distillers’ dried grains with solubles (DDGS) combustion using an approach simultaneously determining frequency factor and reaction model

Abstract

The Kissinger and master plots methods are commonly employed to estimate the frequency factor and reaction model, respectively. However, two methods cannot always provide accurate results, especially for solid-state reaction processes with varying kinetic parameters. A new approach for simultaneously determining the frequency factor and reaction model has been developed. The applicability of the new approach was verified through analyzing a theoretically simulated process. The suitability for combustion conversion of distillers’ dried grains with solubles (DDGS) was analyzed through physicochemical characterization and kinetic and thermodynamic investigation. The effective activation energies for DDGS combustion from the Friedman isoconversional method varied significantly from 129.5 to 206.3 kJ mol−1 in the conversion range 0.05–0.95. The frequency factor range and reaction model for DDGS combustion determined by the newly developed approach were 1.7 × 1011–4.2 × 1016 s−1 and f(α) = 5α1.277(1-0.582α)23.877[-ln(1-α)]−0.100, respectively. Thermodynamic analysis revealed that the changes in Gibbs free energy, enthalpy and entropy for DDGS combustion were in the range of 146.7–162.2 kJ mol−1, 125.3–200.4 kJ mol−1, and -42.5 – 57.0 J mol−1 K−1, respectively, which indicating DDGS combustion has a great potential for energy conversion.