Product-oriented thermodynamic function construction of wheat straw and thermodynamic analysis for rapid pyrolysis

Given the complexity of the rapid pyrolysis reaction system of wheat straw and the difficulty in product regulation, this paper investigated the feasible range for high-value product formation. It determined the conditions for product regulation of wheat straw pyrolysis through thermodynamic analysis. The research constructed the standard enthalpy of formation ΔH_f⁰, standard entropy ΔS_m⁰, and standard Gibbs free energy of formation ΔG_f⁰ of wheat straw molecules. Based on the pyrolysis characteristics of cellulose, hemicellulose, and lignin, which were the main components of wheat straw, 34 reactions were constructed to produce high-valued components such as 2-furfural, acetone, and guaiacol. With Gibbs free energy and equilibrium constant as evaluation indexes, the relationship between the feasible region of the reaction and temperature and pressure at 200–800 °C and 0.1–10 MPa was explored. The results showed that ΔH_f⁰ was-115.86 kJ mol⁻¹, ΔS_m⁰ was 66.34 J mol⁻¹ K⁻¹ and ΔG_f⁰ was-135.64 kJ mol⁻¹. The temperature was conducive to a spontaneous endothermic reaction, whereas pressure was not conducive to a spontaneous reaction. As the pressure increases, the temperature required for spontaneous reaction also increases. At 10 MPa, the thermodynamic temperature at which the reaction of glyoxal and acrolein could proceed spontaneously was increased by 318 °C and 87 °C, respectively. At 0.5 MPa, the range of 3- hydroxy -2- butanone could be spontaneous was 200–388 °C. By adjusting the temperature and pressure, the product's production process could be directed.