Hydrodesulfurization Of FCC Gasoline Research Articles

The rearrangement of 1-methylcyclohex-1-ene during the hydrodesulfurization of FCC gasoline over supported Co(Ni)Mo/Al2O3 sulfide catalysts: the isolation and identification of branched cyclic C7 olefins

In the study of the simultaneous hydrodesulfurization of 1-benzothiophene and the olefin hydrogenation of 1-methylcyclohex-1-ene (1-MCH), we encountered a rearrangement of 1-MCH during the first step of catalytic hydrogenation, which yielded various branched cyclic olefins; mainly ethylcyclopentene and dimethylcyclopentene isomers. The volatile isomerization products were isolated directly from the diluted reaction mixture via the combination of chromatographic techniques including preparative gas chromatography, and were undoubtedly assigned by NMR spectroscopy. The precise identification of the isomerization products was required for a detailed kinetic study.

Kinetic investigation of the effect of H2S in the hydrodesulfurization of FCC gasoline

The reactivity of different groups of olefins and S-compounds, as well as the inhibition effect of H2S on the reactivities of these groups were evaluated with a FCC gasoline over a CoMoS/γ-Al2O3 catalyst. The results demonstrated that the various degrees of steric hindrance around the double bond (CC) and of the thiophene molecules suppressed the hydrogenation (HYD) of olefins and hydrodesulfurization (HDS) of S-compounds, respectively. The inhibition effect of H2S caused by the easy adsorption of H2S on the catalyst sites was more severe on the HDS reactivity than that on the olefins HYD reactivity, thus leading to the decreased catalyst selectivity. The inhibition effect of H2S increased with the number of substituents to the olefin double bond and to the number of substituents to the thiophene molecules, which was inversely proportional to the adsorption constants of the olefin and thiophene molecules. Meanwhile, a modification of the HDS reaction pathway of thiophenes induced by H2S was also observed, and the HYD pathway was more depressed. The characterization by Fourier transformed infrared spectroscopy showed that the relative variations of the number of Lewis and Brønsted acid sites induced by the adsorbed H2S could explain the H2S effect.

Reactivity of Olefins and Thiophenes in Hydrodesulfurization of FCC Gasoline

The reactivity of olefins and S-compounds and their distributions in different catalyst-bed lengths were experimentally evaluated with a FCC gasoline in a high-pressure fixed-bed continuous flow pilot unit over the CoMoS/γ-Al2O3 catalyst. The evaluation results demonstrated that the increased steric hindrances around the double bond (C=C) and that to the thiophene molecules could suppress the hydrogenation of olefins and hydrodesulfurization (HDS) of S-compounds, respectively. Meanwhile, the reaction temperatures could influence the acidic property of the CoMoS active phase confirmed by FT-IR analysis, and thus induced the different reactions. It was found that the isomerization of terminal olefins to internal olefins was promoted by the Brønsted acid sites (-SH) at low temperatures, as well as the skeletal isomerization by the strong Lewis acid sites occurred to a minor extent at high temperatures. Besides, the distributions of olefins and S-compounds in different catalyst-bed lengths showed that the removal of S-compounds reached 80% of its maximum conversion at the first 40% of the reactor length, however, the saturation of olefins increased linearly as the reactor length increased. Therefore, a new catalyst-loading method was developed, i.e., the upper 40% of the reactor length filling with catalyst of high HDS activity and the bottom 60% with catalyst of low olefin saturation activity, respectively. The evaluation results showed that the graded catalyst loading process showed higher selectivity in HDS of FCC gasoline.

Effect of sulfidation atmosphere on the performance of the CoMo/γ-Al2O3 catalysts in hydrodesulfurization of FCC gasoline

The effect of sulfidation atmosphere (H2S/H2 and H2S/N2) on the morphology of (Co)MoS2 particles supported on γ-Al2O3 was studied and the prepared catalysts were evaluated in selective hydrodesulfurization (HDS) of FCC gasoline. It was found that the selectivity of the CoMo/γ-Al2O3 catalysts sulfided in H2S/N2 was 1.8 times as high as that sulfided in H2S/H2, and the catalytic performance was mainly determined by the first sulfidation atmosphere after the impregnation of Mo. The characterization by XRD, HRTEM, XPS, TPR and FT-IR showed that the more completed sulfidation of Mo oxides in H2S/N2 could effectively weaken the strong interaction between the γ-Al2O3 support and active components, thus inducing the decisive influence on the morphology of MoS2 particles. The MoS2 morphology differences could better explain the HDS selectivity. The CoMo/γ-Al2O3 catalyst sulfided in H2S/N2 showed significantly longer slab lengths of supported MoS2 slabs, which effectively decreased the number of active adsorption sites for olefins and thus suppressed the hydrogenation activity of olefins, leading to a desirable higher HDS selectivity. Therefore, a tailor-made catalyst with high HDS selectivity could be developed by optimally controlling the slab lengths of supported MoS2 slabs.