Basic Research Of Al-MCM-41 Molecular Sieve For Denitrogenation Of Diesel Oil

The nitrogen compounds in diesel affect its performance and cause environment problems, furthermore, they can seriously inhibit the hydrodesulfurization process. The inhibition is more significant when the sulfur content of diesel is less than 100μg/g. So it's difficult to produce ultra-low sulfur of diesel.In the paper, different Si/Al ratio of MCM-41 molecular sieves were made as the adsorbent to adsorb the nitrogen compounds in diesel and were characterized by XRD and N2 adsorption-desorption experiments. The equilibrium adsorption amount of basic nitrogen compound quinoline and non-basic nitrogen compound indole at different temperature with each molecular sieve was measured, the best Si/Al ratio and temperature were determined. The adsorption isotherms of quinoline and indole at different temperatures were measured and fitted, the thermodynamic parameters were calculated. The kinetic curves were measured and simulated to determine the adsorption mechanism.The results show that the incorporation of Al in the molecular sieve can increase the equilibrium adsorption amount. With the Al content increasing, the equilibrium adsorption amounts vary from high to low. Si/Al=60 Al-MCM-41 molecular sieve shows the best adsorption performance of quinoline, the best temperature is 120℃, the equilibrium adsorption amount can reach to 42.22mgN/g adsorbent. Si/Al=40 Al-MCM-41 molecular sieve shows the best adsorption performance of indole, the best temperature is 60℃, the equilibrium adsorption amount can reach to 25.85mgN/g adsorbent. The adsorption isotherm of quinoline with Si/Al=60 is type II. Quinoline molecules are not only monolayer adsorption but also multilayer adsorption or capillary condensation in the internal molecular sieves. The adsorption isotherm of indole with Si/Al=40 is type I. Indole molecules are mainly parallel monolayer adsorption. The adsorption process can be simulated by Freundlich isotherm equation. The parameter n>1 showed that the adsorption is preferential. The increasing of temperature is beneficial to the adsorption of quinoline but negative to the adsorption of indole.The apparent adsorption enthalpy changeΔH, entropy changeΔS, Gibbs energy changeΔG were calculated. The results show that the adsorption of quinoline is an exothermic, confusion increasing, spontaneous reaction. The main adsorption is physical adsorption. The adsorption of indole is an exothermic, confusion decreasing reaction. The main adsorption is chemical absorption.The curves of adsorption kinetics show that the rate controlling step of adsorption process changes with time, from FDC (Film diffusion control) to PDC (Particle diffusion control). Pseudo second-order kinetic equation can be fitted well with adsorption kinetics curves. According to the fitted kinetic equation, the adsorption activation energy Ea were calculated. The Ea of quinoline adsorption is 2.8575kJ/mol and the Ea of indole adsorption is 11.8483 kJ/mol.