Search

The kinetics of the Fischer–Tropsch (FT) reaction was evaluated through detailed experimentation with a KMo bimetallic promoted Fe catalyst supported on carbon nanotubes (CNTs). The kinetic tests were conducted in a fixed‐bed reactor under operating conditions of P = 6.9–41.3 bar, T = 543–563 K, H2/CO = 1, gas hourly specific velocity (GHSV) = 2000 h−1. This study aimed to investigate the mechanism prevailing in CO activation and the rate equation for CO consumption during FT reactions over a 0.5K5Mo10Fe/CNTs catalyst. To evaluate the synergistic effects of Fe, Mo, and K phases on the catalyst activity, both fresh and spent catalysts were thoroughly characterized using X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy and energy‐dispersive spectroscopy (SEM‐EDS), X‐ray absorption near edge structure (XANES), and extended X‐ray absorption fine structure (EXAFS) to ascertain the different phases (active sites) present and relevant interactions. Based on the adsorption of carbon monoxide and hydrogen, 22 possible mechanisms for monomer formation were proposed for FT synthesis in accordance with the Langmuir–Hinshelwood–Hougen–Watson (LHHW) and Eley–Rideal (ER) adsorption theories. The best fit kinetic model was identified through a multi‐variable non‐linear regression analysis. The selected mechanistic model was based on carbide formation approach, where H2‐assisted adsorption of CO was considered for the derivation. Kinetic parameters such as activation energy, adsorption enthalpies of H2, and CO were estimated to be 65.0, −13.0, and −54.0 kJ/mol, respectively. Considering the developed kinetic model, the effects of reaction temperature and pressure were assessed on Fischer–Tropsch synthesis (FTS) product distribution. Additionally, the kinetic model was compared with the typical Anderson–Schulz–Flory model, suggesting the effects of water‐gas‐shift and the existence of additional formation pathway such as secondary re‐adsorption of olefins for heavier hydrocarbons. [ABSTRACT FROM AUTHOR]

Hydroprocessing of vegetable oil to high‐quality jet fuel range hydrocarbons (HRJ) plays a significant role in the development of completely interchangeable substitute for conventional petroleum‐derived jet fuel and has drawn the attention of aviation experts due to its capacity to mitigate greenhouse gas emissions associated with the aviation industry. The limited performance of 1 wt. % Sn promoted Fe(3)‐Cu(13)/SiO2‐Al2O3 catalyst in our previous study has been attributed to the successive consideration of one variable at a time in its evaluation. Maximization of oleic acid conversion and selectivity of jet fuel range hydrocarbons from hydroprocessing of oleic acid over 1 wt. % Sn promoted Fe(3)‐Cu(13)/SiO2‐Al2O3 catalyst with the best combination of the process parameter involved via multivariate approach, and evaluation of kinetic and thermodynamic activation parameters is the focus of this study. Reduced cubic oleic acid conversion model and reduced quadratic jet fuel range hydrocarbons selectivity model of high significance levels, adequate precision, and high correlation coefficient were developed. Reaction temperature of 339.5°C, 1.6 MPa H2 pressure, 6.2 wt.% catalyst concentration, and 8.0 h reaction time were optimum process parameters that can maximize oleic acid conversion and selectivity of jet fuel range hydrocarbons at 98.2% and 82.2%, respectively. This process was found to be endothermic, irreversible, and nonspontaneous with 45.8 KJ/mol activation enthalpy of reaction, 0.25 KJ/mol entropy of reaction, and the reaction's Gibb's free energy of 198.8 KJ/mol at 340°C. The minimum energy required for the reaction to take place was evaluated as 50.7 KJ/mol. [ABSTRACT FROM AUTHOR]