Preparation and Characterization of Co–MCM-41 and Its Adsorption Removing Basic Nitrogen Compounds from Fluidized Catalytic Cracking Diesel Oil

Abstract

The mesoporous molecular sieve Co–MCM-41 containing different cobalt contents, prepared by the hydrothermal synthesis method with cobalt nitrate as the cobalt source, was confirmed by characterization with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, and nitrogen adsorption–desorption. The characterization results indicated that the well-ordered mesostructure had been obtained and Co had been introduced into the framework of MCM-41. Adsorption removing basic nitrogen compounds from fluidized catalytic cracking (FCC) diesel oil was studied by the static stirring method over MCM-41 and Co–MCM-41. Every gram of Co–MCM-41(0.06) adsorbent could adsorb 9.11 mg of nitrogen, while for MCM-41, this value was 7.36 mg of nitrogen/g of adsorbent, indicating that the adsorptive denitrogenation of Co–MCM-41(0.06) had been enhanced obviously. However, the adsorptive denitrogenation capacity of Co–MCM-41 decreased when Co/Si (mol) exceeded 0.06. It was due to the fact that excessive Co could disperse in the channel of Co–MCM-41 as Co3O4 and block the adsorption active sites. The results of treated FCC diesel oil measured by gas chromatography–nitrogen chemiluminescence detector (GC–NCD) indicated that 82.21% basic nitrogen compound anilines, 44.68% weakly alkaline indoles, and 24.43% non-basic nitrogen compound carbazoles had been removed, which illustrated that Co–MCM-41(0.06) had high selectivity toward the basic nitrogen compounds. The results of adsorptive denitrogenation from FCC diesel oil using the dynamic adsorption method showed that, for a breakthrough point of 10 μg/g, the breakthrough volume and breakthrough capacity for Co–MCM-41(0.06) at ambient conditions were 15.2 mL/g of adsorbent and 3.09 mg of nitrogen/g of adsorbent, respectively. While for MCM-41, these data were only 0.9 mL/g and 0.18 mg of nitrogen/g of adsorbent, respectively, indicating that MCM-41 almost lost all of the adsorptive denitrogenation capacity as a result of the weak selectivity.