The effect of accessibility to acid sites in Y zeolites on ring opening reaction in light cycle oil hydrocracking

Abstract

The light cycle oil (LCO) hydrocracking process converts polycyclic aromatics into highly valuable light aromatics such as benzene, toluene, xylene (BTX), in accordance with the requirements of low-carbon development and high-quality transformation from oil refining to chemical industry. The accessibility of acid sites is a critical factor that impacts LCO conversion and BTX yield. Initially, the fine structure and molecular size of the typical polycyclic aromatics in LCO and their hydrogenation reaction intermediates were investigated through gas chromatography-mass spectrometry (GC-MS) analysis and density functional theory (DFT) calculations. Three porous Y zeolites with comparable Si/Al molar atomic ratios and pyridine (Py)-measured Brønsted acid amounts were chosen as an acidic component to prepare NiMo/(Al₂O₃ + HY) catalysts. The acid accessibility of HY zeolite was characterized via dual-beam infrared spectroscopy using 2,4,6-tri-tert-butylpyridine (2,4,6-TTBPy) and trihexylamine (THA) as probe molecules, and the LCO hydrocracking performance was evaluated on a fixed-bed reactor. The results revealed that bicyclic aromatic hydrocarbons featuring multiple, short side chains such as dimethylnaphthalene and trimethylnaphthalene are the main components of LCO, with sizes larger than those of HY zeolite micropores. There is a strong positive correlation between LCO conversion and ring-opening rate of polycyclic aromatics and cycloalkanes in LCO. Among these three HY zeolite catalysts, the ring-opening rates of polycyclic aromatics and cycloalkanes, and the yields of C₆-C₁₂ aromatics and BTX increased in the order of HY1 < HY2 < HY3, which is consistent with external surface acidity measured by THA as the probe molecule.

Keywords

LCO hydrocracking / zeolite / acidity / accessibility / adsorption in FTIR

References

[1] Ramteke AV,Pant K.Conversion of light cycle oil to benzene and alkylated monoaromatics over monometallic and bimetallic CoMo catalysts in the presence of hydrogen donor.Fuel2023;342:127737

[2] Corma A,Orchillés A.Decalin and tetralin as probe molecules for cracking and hydrotreating the light cycle oil.J Catal2001;200:34-44

[3] Peng C,Duan X.Direct production of high octane gasoline and ULSD blend stocks by LCO hydrocracking.Catal Today2016;271:149-53

[4] Zhang L,Li J,Dai G.Extraction and separation of polycyclic aromatic hydrocarbons from catalytic cracking diesel.J Chem Eng Data2023;68:393-404

[5] Miao P,Guo Y,Zhu X.Efficient conversion of light cycle oil into gasoline with a combined hydrogenation and catalytic cracking process: effect of pre-distillation.Energy Fuels2020;34:12505-16

[6] Xin L,Chen X,Liu Y.Efficient conversion of light cycle oil into high-octane-number gasoline and light olefins over a mesoporous ZSM-5 catalyst.Energy Fuels2017;31:6968-76

[7] Laredo GC,Escobar J,Vega-Merino PM.Light cycle oil upgrading to benzene, toluene, and xylenes by hydrocracking: studies using model mixtures.Ind Eng Chem Res2017;56:10939-48

[8] Oh Y,Park H,Nguyen T.Molecular-size selective hydroconversion of FCC light cycle oil into petrochemical light aromatic hydrocarbons.Catal Today2020;352:329-36

[9] Cao Z,Xu C.Selective hydrocracking of light cycle oil into high-octane gasoline over bi-functional catalysts.J Energy Chem2021;52:41-50

[10] Oh Y,Noh H.Selective hydrotreating and hydrocracking of FCC light cycle oil into high-value light aromatic hydrocarbons.Appl Catal A Gen2019;577:86-98

[11] Escalona G,Betancourt P.Selective poly-aromatics saturation and ring opening during hydroprocessing of light cycle oil over sulfided Ni-Mo/SiO₂-Al₂O₃ catalyst.Fuel2018;219:270-8

[12] Chen F,Weng X.High value utilization of inferior diesel for BTX production: mechanisms, catalysts, conditions and challenges.Appl Catal A Gen2021;616:118095

[13] Qi L,Cheng Z.Structure-performance relationship of NiMo/Al₂O₃-HY catalysts in selective hydrocracking of poly-aromatics to mono-aromatics.Chem Eng Sci2022;263:118121

[14] Peng C,Cheng Z.Upgrading of light cycle oil to high-octane gasoline through selective hydrocracking over non-noble metal bifunctional catalysts.Energy Fuels2019;33:1090-7

[15] Du H,Yang H.The chemistry of selective ring-opening catalysts.Appl Catal A Gen2005;294:1-21

[16] Santikunaporn M,Jongpatiwut S,Alvarez W.Ring opening of decalin and tetralin on HY and Pt/HY zeolite catalysts.J Catal2004;228:100-13

[17] Lee J,Shin J.Selective hydrocracking of tetralin for light aromatic hydrocarbons.Catal Today2016;265:144-53

[18] Arribas MA,Sastre G.Simultaneous hydrogenation and ring opening of aromatics for diesel upgrading on Pt/zeolite catalysts. The influence of zeolite pore topology and reactant on catalyst performance.Stud Surf Sci Catal2002;142:1015-22

[19] Arribas M,Díaz-cabañas M.Hydrogenation and ring opening of Tetralin over bifunctional catalysts based on the new ITQ-21 zeolite.Appl Catal A Gen2004;273:277-86

[20] Qi J,Jia H.Unpredictable properties of industrial HY zeolite for tetralin hydrocracking.Fuel Proc Technol2023;240:107586

[21] Sharma P,Sekine Y,Matsukata M.42 Hydroisomerization of tetralin on zeolite beta: influence of crystal size.Stud Surf Sci Catal2003;145:219-22

[22] Nesterenko N,Montouillout V.Accessibility of the acid sites in dealuminated small-port mordenites studied by FTIR of co-adsorbed alkylpyridines and CO.Micropor Mesopor Mat2004;71:157-66

[23] Mlekodaj K,Datka J,Makowski W.Porosity and accessibility of acid sites in desilicated ZSM-5 zeolites studied using adsorption of probe molecules.Micropor Mesopor Mat2014;183:54-61

[24] Thibault-Starzyk F,Abelló S.Quantification of enhanced acid site accessibility in hierarchical zeolites - The accessibility index.J Catal2009;264:11-4

[25] Zhang L,Qin Y.Optimizing the accessibility of zeolite Y on FCC catalyst to improve heavy oil conversion capacity.Micropor Mesopor Mat2023;359:112627

[26] Lakiss L,Gilson JP.Probing the Brønsted acidity of the external surface of faujasite-type zeolites.Chemphyschem2020;21:1873-81