Selective hydrotreating and hydrocracking of FCC light cycle oil into high-value light aromatic hydrocarbons

Abstract

Comprehensive series tests on hydrotreating (HDT) and hydrocracking (HDC) of fluid catalytic cracking (FCC) light cycle oil (LCO) into high-value light aromatics rich in benzene, toluene, and xylenes (BTX) were conducted in a fixed-bed down-flow reactor under medium pressure (6 MPa). Two different LCOs, LCO-1 (a full-range LCO) and LCO-2 (340 °C− LCO which contained a smaller fraction of refractory alkyl(C2+)-carbazoles and heavy tri+-aromatics (three and more rings aromatics) than LCO-1), were used as feedstocks. Comparison of NiW-S, NiMo-S, and CoMo-S supported on γ-Al2O3 and a commercial catalyst (for vacuum gasoil hydrodesulfurization) as LCO HDT catalysts revealed that NiMo-S/γ-Al2O3 allowed for highly selective hydrogenation (HYD) of di+-aromatics (two and more rings aromatics) into mono-aromatics with minimal loss of aromatics at high HDN conversion rates. For HDC catalysts, NiMo-S, CoMo-S, and Mo-S were supported on a hybrid zeolite, BZ(x) (a mixture of H-Beta (B) and H-ZSM-5 (Z) (x wt%)). Since Mo-S exhibited moderate HYD power and H-ZSM-5 promoted the dealkylation of alkyl-aromatics into BTX, Mo-S/BZ(10) yielded the largest amount of BTX in the HDC model of tetralin among the three catalyst analyzed. The HDC of hydrotreated LCO-1 (HDT-LCO-1) over Mo-S/BZ(10) catalyst generated a low yield of BTX-rich light aromatics because of the limited conversion of C11+ heavy aromatics. However, during the HDC of HDT-LCO-2, the yield of BTX-rich light aromatics was close to the theoretical yield (48.4 wt%) over a wide temperature range when Mo-S/BZ(10) was used as catalyst, which indicated the highly selective HDC behavior of Mo-S/BZ(10) for this reaction. Therefore, NiMo-S/γ-Al2O3 and Mo-S/BZ(10), which exhibited well-balanced metallic and/or acidic functions, were promising HDT and HDC catalysts, respectively, for the selective conversion of LCOs into high-value BTX-rich light aromatics at high yields.