Citric Acid-Treated Zeolite Y (CY)/Zeolite Beta Composites as Supports for Vacuum Gas Oil Hydrocracking Catalysts: High Yield Production of Highly-Aromatic Heavy Naphtha and Low-BMCI Value Tail Oil.

Qiang Wei,Zhenli Zhang,Shuqin Wang,Yan Wang,Pengfei Zhang,Yasong Zhou,Xiaodong Liu,Jiarui Zhang,Tao Zhang

doi:10.3389/fchem.2019.00705

Qiang Wei, Zhenli Zhang + Show 7 more

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https://doi.org/10.3389/fchem.2019.00705

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Abstract

Citric acid-treated zeolite Y (CY) and zeolite beta were mechanically mixed to obtain composite zeolites (CY-Beta) with various zeolite beta contents. The composite zeolites were used as the acid components of hydrocracking catalyst supports. The physical and chemical properties of the supports and catalysts were analyzed by N2 adsorption-desorption, XRD, SEM, and NH3-TPD. The mechanical mixing of CY and zeolite beta does not destroy the textual properties of the original zeolites. However, the acidity of the composite zeolite does not fit the linearly calculated value of the two zeolites because some of the acid sites are covered or reacted with other acid sites during the mixing process. In addition, weak acid sites favor the high yield of tail oil with low BMCI value. Compared with the CY-based and beta-based catalysts, the conversion and light oil yield of the CY-Beta-based catalyst was increased. The conversion, light oil yield, and petrochemical yield of the Ni-W/20CY-Beta(20)/ASA catalyst are 78.15, 65.0, and 83.7%, respectively. The BMCI value of the tail oil is 4.7, and the aromatic potential content (APC) of heavy naphtha (boiling point 65–177°C) is 42%. The 1,500 h pilot plant test of Ni-W/20CY-Beta(20)/ASA at 350°C, 7.0 MPa, 2.0 h−1 LHSV, and 800 H2/oil (v/v) shows that the activity remains stable during the 1,500 h evaluation. The heavy naphtha (APC about 41.0) yield of 41.2 illustrates that the catalyst has the ability to aromatize and cyclize the light fractions. The yield of diesel is about 25% with a cetane index (CI) of 59.2; the frozen point is lower than −45°C, and the cold filter plugging point is −35°C, demonstrating the isomerization performance for middle distillations. The yield of tail oil is 14.9% with a BMCI of 4.4, showing the high hydrogenation performance of the catalyst to transform the un-cracked tail oil to saturated hydrocarbon in order to reduce the BMCI value.

Highlights

With the depleting conventional crude supply and increasing heavy crude production, large amounts of low-quality heavy petroleum fractions require more severe upgrading and processing to produce clean transportation fuels (Breysse et al, 2003; Song, 2003)
Various Citric acid-treated zeolite Y (CY)-zeolite beta (CY-Beta) composite catalysts were prepared by varying the mass ratios of zeolite CY and zeolite beta and used for vacuum gas oil (VGO) hydrocracking to produce high yields of high-aromatic potential content (APC) heavy naphtha and low-Bureau of Mines Correlation Index (BMCI) tail oil
The X-ray diffraction (XRD) pattern of the CY-Beta composites exhibited the characteristic peaks of CY and zeolite beta, indicating the co-existence of these phases in the CY-Beta(n) composites

Summary

INTRODUCTION

With the depleting conventional crude supply and increasing heavy crude production, large amounts of low-quality heavy petroleum fractions require more severe upgrading and processing to produce clean transportation fuels (Breysse et al, 2003; Song, 2003). Heavy naphtha (65◦-177◦C) and tail oil (320◦C+ distillation) are high-value petrochemical feedstocks. The objective of applying hydrocracking technology to produce petrochemical feedstocks is to maximize the productions of heavy naphtha with a high APC and tail oil with a low BMCI (Zhao et al, 2011). The use of zeolite beta as a hydrocracking catalyst support is known to promote isomerization reactions, resulting in the high yield of high-APC heavy naphtha (Horácek et al, 2012; Yao et al, 2012). Various CY-zeolite beta (CY-Beta) composite catalysts were prepared by varying the mass ratios of zeolite CY and zeolite beta and used for vacuum gas oil (VGO) hydrocracking to produce high yields of high-APC heavy naphtha and low-BMCI tail oil. Where d is the density at 15.6◦C (in g/mL), and T is the volume average boiling point temperature (in ◦C)

RESULTS AND DISCUSSION

CONCLUSIONS

DATA AVAILABILITY STATEMENT