Thermodynamic Analysis of the Reactions of Sulphur-Containing Compounds in the Process of Diesel Fractions Hydrodesulphurization on the Base of Quantum-Chemical Calculations

On the base of quantum-chemical calculations (DFT, B3LYP, 3-21G), thermodynamic parameters of the reactions of sulfur-containing compounds in the process of diesel fractions hydrodesulphurization were estimated. Based on the thermodynamic analysis, the probability of reactions occurrence was determined, the reaction scheme for hydrocarbon transformations was proposed, which can be used in mathematical modeling. It was shown that thermodynamic probability of the hydrogenolysis reactions increases in the series: dibenzothiophenes (ΔGr=-33.27 kJ/mol), benzothiophenes (ΔGr=-71.36 kJ/mol), thiophenes (ΔGr=-137.20 kJ/mol) and sulfides (ΔGr=-142.64 kJ/mol). It was found that hydrogenolysis of sulfides, thiophenes, and benzothiophenes proceeds irreversibly, and hydrogenolysis of dibenzothiophenes proceeds reversibly through the stage of aromatic hydrocarbons formation, followed by their hydrogenation to cycloparaffins. It was shown that in the series of thiophenes, benzothiophenes, and dibenzothiophenes, the thermodynamic probability of the hydrogenolysis reactions decreases with increasing molecular weight. The values of the enthalpies of the sulfur-containing compounds reactions are calculated, and all reactions were shown to be exothermic. The greatest thermal effect is is observed for reactions of dibenzothiophenes hydrogenation to bicyclic paraffins (ΔHr=-514.89 kJ/mol), reactions of benzothiophenes to cycloparaffins (ΔHr=-398.71 kJ/mol), reactions of thiophenes to paraffins (ΔHr=317.85 kJ/mol.