The Investigation of Zeolite to Matrix Ratio Effect on the Performance of FCC Catalysts during Catalytic Cracking of Hydrotreated VGO

Abstract

Fluidized catalytic cracking of vacuum gas oil is considered a promising factor in enhancing the gasoline yield to fulfill global energy demands. In this study, a series of FCC catalysts with a zeolite to matrix ratio varying from 18 to 50 was prepared using USY zeolite and amorphous matrix. The matrix was composed of amorphous silica-alumina, kaolin, and silica sol binder. All fresh catalysts were subjected to hydrothermal deactivation treatment at 750 °C for 5 h. The performance evaluation of FCC catalysts was conducted in a fixed bed microactivity test unit, with vacuum gas oil as feed at 550 °C. Comparing a steamed CAT01 sample with a fresh CAT01, the surface area of the steamed sample was 23.3% less. Similarly, the fresh sample CAT05 acidity increased by 102% when compared with the fresh CAT01 sample. As the zeolite to matrix ratio increased, the selectivity of dry gas, LPG, and coke increased, associated with a consistent decrease in gasoline and heavy ends (LCO and HCO). The combined selectivity of product gasoline and LCO with low-zeolite steamed catalyst (CAT01) was 82%, and that of high-zeolite steamed catalyst (CAT05) was 76%. Furthermore, coke selectivity for the steamed CAT01 was 2.1%, whereas 3.7% was observed for the steamed CAT05 sample. The effect of the zeolite to matrix ratio was less pronounced in steamed catalysts as compared with fresh catalysts.

1. Introduction

Fluid catalytic cracking (FCC) is a major conversion process to produce valuable products such as gasoline and light olefins in the oil and gas industries. The feed of the FCC unit is usually atmospheric residue, vacuum residue, and coker gas oil. FCC process is operational across the globe in 300 refineries out of 646 in total since 2014 [1,2,3,4]. It is estimated that 0.16 kg of FCC catalyst is used per barrel of feedstock (vacuum gas oil). For heavy feed materials, such as resid, 0.20 kg of FCC catalyst is used per barrel [5]. Zeolite-based catalysts have been some of the oldest and largest applications in the FCC process, ever since Y-zeolite was used as the substitute of amorphous silica-alumina 57 years ago [6,7].

Among all the zeolites used in the industry, Y-zeolite receives significant attention due to its three-dimensional pore structure and 0.74 nm diameter. Y-zeolite is extensively used in oil refining as a major part of the FCC catalyst as it provides more active sites as well as greater surface area [8,9,10]. With time, more research has been focused to synthesize new zeolites having extra-large pores for the replacement of Y-zeolite as an active part of the FCC catalyst. However, the huge cost, coupled with poor hydrothermal stability, impedes the commercialization of these materials [11,12]. Hence, further improvement in Y-zeolite is considered as the best alternative to make superior FCC catalysts and obtain better yield performance. Therefore, dealumination by acid leaching or steaming is employed to obtain a higher acidic strength and stable framework. These modifications lead toward the ultra-stable Y-zeolite, which provides a higher selectivity for the liquid distillates as well as high activity in vacuum gas oil (VGO) cracking [13,14,15].

The high thermal stability of USY, which is prepared by the removal of Al ions during steaming, in combination with the high acidic strength, makes it an ideal FCC catalyst [16,17]. In general, a modern FCC catalyst comprises two components: zeolite and a matrix. Ternary components can be added to the FCC catalyst as an additive to increase metal resistance in a catalyst, boost octane number of gasoline, or reduce the emissions of SO_x. Most FCC catalysts contain 15 to 40% zeolite, which contributes mainly to the activity of FCC catalytic reactions. The amount of zeolite less than 15% decreases the activity of the catalyst, and more than 45% increases the attrition rate [18,19,20]. It has been observed that the olefin-to-paraffin ratio decreases with the increase in zeolite percent in FCC catalysts due to the higher hydrogen transfer reaction rate. Light olefins are produced in FCC reactions due to the overcracking of naphtha, which is formed by the cracking of HCO as well as LCO [21,22]. Commercially available FCC catalysts are prepared by using zeolites dispersed in a silica-alumina matrix to form 60 μm particle size [23,24,25]. The FCC catalyst consists of 60 to 85% by weight of matrix, which contains natural as well as synthetic components [26]. An active matrix holds acidic sites due to the presence of alumina. However, the inactive matrix does not influence the catalytic behavior of the FCC catalyst due to the absence of acidic sites [27,28].

Zeolite properties have more effect on the composition of gas and gasoline, whereas the matrix only has a direct impact on heavier light cycle oil (LCO). It has been observed that the chemical composition of zeolite and matrix plays a vital role in the selectivity of the FCC catalyst. The most important function of the matrix is pre-cracking the FCC residue and decreasing the direct contact of the cracked product to the highly acidic sites of the Y-zeolite. Afterward, pre-cracked products are diffused easily into the zeolite pores to crack further on strong acidic sites of the zeolite [24,29,30,31].

Steaming is considered one of the essential stages in the utilization and activation of FCC catalysts. Some zeolites are destroyed during steaming due to the dealumination of the framework of Y-zeolite. Hydrothermal treatment in FCC is used to deactivate the catalyst that happens in a commercial process to form an equilibrium catalyst. FCC catalyst steaming leads toward the actual evaluation of the catalyst because catalytic activity in its fresh state cannot provide the exact idea of its commercial performance [32,33]. The temperature used for the hydrothermal pre-treatment of fresh FCC catalysts is varied from 538 to 927 °C for 2–24 h in the presence of steam. The selectivity and activity of the FCC catalyst are altered depending on the steaming conditions. Therefore, in a commercial FCC unit, the equilibrium catalyst provides a different yield of products as compared with the fresh catalyst [34,35,36].

This study focuses on the effect of the zeolite to matrix ratio of fresh and steamed FCC catalyst on VGO cracking. The zeolite to matrix ratio was varied from 18 to 50, whereas the USY zeolite (%) was changed from 15 to 34 by weight. The comparison of fresh and steaming FCC catalysts on the VGO for zeolite to matrix ratios ranging from 18 to 50 has never been studied previously. All FCC catalyst samples were evaluated before and after steaming at 750 °C for 5 h in the microactivity test (MAT) unit. The MAT unit results were compared to see the effect of zeolite to matrix ratio on gasoline, LCO, coke, and gaseous products from VGO conversion.

2. Results and Discussion

2.1. Catalyst Characterization

The comparison of the XRD patterns of fresh and steamed FCC catalyst samples is shown in Figure 1. The XRD patterns of all FCC catalysts demonstrated that only the Y-zeolite structure corresponded to the XRD pattern of Y-zeolite reported in the literature [37], and no other zeolite characterizing peaks were observed in the pattern. The similarity in the XRD patterns before and after steaming indicated that the steaming at higher temperatures did not substantially change the crystalline structure of the FCC catalysts. However, the intensity of the XRD peaks in all samples after steaming was decreased, which resulted in a loss of its surface area.

Important characteristics of the FCC catalysts are acidity and surface area because they have a substantial effect on their catalytic performance [38]. The effects of the zeolite to matrix ratio on the surface area, total pore volume, and acidity of the catalysts are listed in

Table 1. Chemical and physical properties of as-synthesized fresh FCC catalysts.

Catalyst	Surface Area a	Micropore Volume	Mesopore Volume	Total Pore Volume	Total Acidity b
	(m2/g)	Vmic (cc/g)	Vmes (cc/g)	(cc/g)	(mmol/g)
CAT01	163	0.048	0.257	0.305	0.470
CAT02	186	0.060	0.240	0.300	0.590
CAT03	203	0.070	0.229	0.299	0.670
CAT04	220	0.078	0.220	0.298	0.750
CAT05	258	0.102	0.200	0.302	0.950

^a Measured by t-plot method. ^b Measured by ammonia TPD.

. It is worth mentioning that the surface area increased directly with the increase in the zeolite to matrix ratio when the range increased from 18 to 50. For instance, the surface area increased by 14.1% for fresh CAT02 by increasing the zeolite to matrix ratio from 18 to 25. Furthermore, the surface area reached 258 m²/g for fresh CAT05, while for fresh CAT01 the surface area was 163 m²/g.

Table 1 also shows the effect of the zeolite to matrix ratio on the acidity, microporous, and mesoporous volume of the fresh FCC catalysts. Similar to the surface area, the acidity of the FCC catalysts increased with the increase in the zeolite to matrix ratio. For fresh CAT01, the acidity was 0.470 mmol/g. As expected, the acidity increased with an increase in the zeolite to matrix ratio; for instance, it reached 0.590, 0.670, and 0.750 mmol/g for fresh CAT02, CAT03, and CAT04 samples, respectively.

For the zeolite to matrix ratio of 50, the acidity of the fresh sample increased by 102% as compared with the fresh CAT01 sample acidity. Figure 2 shows the plot of the desorbed ammonia against the temperature of the fresh FCC catalyst samples. The area under the curve represents the relative amount of the total acidity. As the ammonia desorption rate increased, the amount of the total acidity also increased [39]. From Table 1, it is observed that the micropore volume of the fresh FCC catalyst increased and mesopore volume decreased with the increase in the zeolite to matrix ratio. It happened due to an increase in USY (%) and a decrease in the matrix (%) with an increase in the zeolite to matrix ratio. However, the total pore volume remained almost constant for all the fresh FCC catalysts. It was observed that the micropore volume increased by 112% and the mesopore volume decreased by 22% for fresh CAT05 as compared with fresh CAT01.

Table 2. Chemical and physical properties of as-synthesized steamed FCC catalysts.

Catalyst	Surface Area a	Micropore Volume	Mesopore Volume	Total Pore Volume	Total Acidity b
	(m2/g)	Vmic (cc/g)	Vmes (cc/g)	(cc/g)	(mmol/g)
CAT01	125	0.039	0.220	0.259	0.072
CAT02	146	0.048	0.212	0.260	0.090
CAT03	160	0.055	0.207	0.262	0.100
CAT04	173	0.064	0.202	0.266	0.110
CAT05	202	0.080	0.190	0.270	0.140

^a Measured by t-plot method. ^b Measured by ammonia TPD.

reports the surface area, the total pore volume, and the acidity of different zeolite to matrix ratio FCC catalyst samples after steaming. The surface area for steamed CAT01 was 125 m²/g, while for steamed CAT05 it was 202 m²/g. After steaming, the surface area decreased by 23.3% for sample CAT01 as compared with the fresh sample CAT01, which was in good agreement with the literature [40]. It can be observed that the steaming effect was uniform in the other four samples where the surface area was decreased by about 21%. The total pore volume was also decreased after steaming.

The total pore volume was 0.259 cm³/g and 0.270 cm³/g for steamed samples CAT01 and CAT05, respectively. Furthermore, the total pore volume of the first three steamed catalysts in the series (CAT01, CAT02, and CAT03) was decreased by 15%, 13%, and 12%, respectively, as compared with the fresh samples, whereas the total pore volume decrease in the other two samples was observed by 10% approximately. Steaming caused a significant effect on the acidity of the FCC catalysts. Figure 3 demonstrates the different peaks of the steamed FCC catalyst samples. It was observed that peak area increases with the increase in the zeolite to matrix ratio resulted in the rise in the total acidity of the steamed FCC samples from the zeolite to matrix ratio of 18 to 50. The total acidity of the steamed CAT01 decreased by 84.6% as compared with the fresh sample CAT01 acidity. In addition, the acidity of the steamed CAT05 sample reached 0.140 mmol/g as compared with 0.950 mmol/g for the fresh CAT05 catalyst.

The activity of the FCC catalyst was directly related to the acidity of catalysts. Hence, steaming of the FCC catalyst simulated the deactivation resulting equilibrium catalyst used in a commercial unit. Studies have revealed that when the FCC catalyst was put under hydrothermal treatment, the aluminum atoms migrated from the zeolite framework to the outer surface of the crystallites. As a result, the silicon atoms migrated into the vacancies to heal the zeolite structure. In consequence, the Bronsted acid sites on the framework decreased, resulting in some loss of total acidity. Since steaming destroys the Y-zeolite structure, it might cause the zeolite structure to be damaged. For FCC, the catalyst deactivation that occurred throughout the commercial process to generate an equilibrium catalyst was accomplished using hydrothermal treatment. Steaming was performed in order to compare the VGO conversion in the as-synthesized steamed catalyst with the commercial catalyst [41].

2.2. Evaluation of Fresh and Steamed FCC Catalysts

The distribution of the product yields as a result of vacuum gas oil cracking over five fresh and steamed FCC catalysts are reported in

Table 3. Zeolite/matrix effect of USY-based fresh FCC catalyst on product yield for VGO cracking at 550 °C.

Name of Catalyst	CAT01	CAT02	CAT03	CAT04	CAT05
Catalyst/oil (g/g)	3	3	3	3	3
Zeolite/matrix ratio	18	25	30	35	50
Mass balance	96.3	99.7	97.6	97.6	98.2
Conversion (%)	84.37	85.07	84.68	85.51	91.36
Product Yields (wt.%)
H2	0.19	0.20	0.18	0.21	0.22
C1	1.59	1.98	2.01	2.30	2.35
C2	1.38	1.83	1.67	1.99	1.92
C2=	2.34	2.76	2.69	3.04	2.76
C3	5.20	6.41	6.78	7.21	8.30
C3=	5.88	5.28	5.66	5.45	4.81
iC4	9.26	10.23	10.88	11.28	12.62
nC4	3.31	3.85	4.02	4.22	4.87
T2C4=	1.34	1.11	1.07	1.00	0.71
1C4=	1.06	0.88	0.88	0.81	0.57
iC4=	1.00	0.83	0.86	0.78	0.63
C2C4=	1.09	0.90	0.88	0.82	0.59
C4 = (Liq.)	0.33	0.53	0.45	0.32	0.68
Total gas	34.11	36.79	38.04	39.44	41.01
Gasoline	41.43	36.72	36.45	36.10	37.12
LCO	9.32	9.51	9.46	8.95	4.93
HCO	6.31	5.42	5.86	5.54	3.72
Coke	8.83	11.57	10.19	9.97	13.23
H2-C2 (dry gas)	5.49	6.76	6.55	7.54	7.25
C3-C4 (LPG)	28.62	30.02	31.48	31.90	33.76
C2 = -C4 = (light olefins)	13.18	12.29	12.49	12.23	10.74
Selectivity (yield/conversion) %
Gasoline	49.11	43.16	43.05	42.22	40.63
LCO	11.04	11.18	11.17	10.47	5.39
HCO	7.48	6.37	6.92	6.48	4.07
Coke	10.47	13.60	12.04	11.66	14.48
LPG	33.92	35.29	37.18	37.31	36.95
Light olefins	15.62	14.45	14.75	14.30	11.76
Dry gas	6.51	7.95	7.74	8.82	7.94

and

Table 4. Zeolite/matrix effect of USY-based steamed FCC catalyst on product yield for VGO cracking at 550 °C.

Name of Catalyst	CAT01	CAT02	CAT03	CAT04	CAT05
Catalyst/oil (g/g)	3	3	3	3	3
Zeolite/matrix ratio	18	25	30	35	50
Mass balance	101	102.8	101.8	100.1	97.8
Conversion (%)	76.90	76.96	77.84	78.87	81.44
Product Yields (wt.%)
H2	0.07	0.06	0.06	0.06	0.06
C1	0.89	0.79	0.89	0.98	1.07
C2	0.97	0.81	0.97	1.04	1.08
C2=	1.57	1.31	1.79	1.64	1.67
C3	1.17	1.09	1.60	1.49	1.62
C3=	7.12	6.75	7.82	7.25	7.31
iC4	4.62	5.85	5.62	5.71	6.03
nC4	0.87	2.11	1.09	1.16	1.29
T2C4=	2.53	2.20	2.36	2.39	2.34
1C4=	1.95	1.72	1.82	1.86	1.83
iC4=	2.03	1.67	1.88	1.55	1.41
C2C4=	2.04	1.76	1.88	1.90	1.87
C4 = (Liq.)	0.39	0.86	0.64	0.82	0.85
Total gas	26.59	27.32	28.60	28.08	29.03
Gasoline	48.66	47.81	46.96	48.30	49.38
LCO	14.80	14.79	14.27	13.95	12.62
HCO	8.29	8.25	7.89	7.18	5.94
Coke	1.65	1.83	2.28	2.50	3.03
H2-C2 (dry gas)	3.51	2.96	3.70	3.72	3.87
C3-C4 (LPG)	23.08	24.36	24.90	24.35	25.16
C2=-C4= (light olefins)	18.00	16.61	18.37	17.63	17.89
Selectivity (yield/conversion) %
Gasoline	63.3	62.1	60.3	61.2	60.6
LCO	19.2	19.2	18.3	17.7	15.5
HCO	10.8	10.7	10.1	9.1	7.3
Coke	2.1	2.4	2.9	3.2	3.7
LPG	30.0	31.6	32.0	30.9	30.9
Light olefins	23.4	21.6	23.6	22.4	22.0
Dry gas	4.56	3.85	4.76	4.72	4.75

. The conversion of VGO is defined as 100 − (LCO wt.% + HCO wt.%).

From Table 3, it is indicated that vacuum gas oil conversion increased from 84% to 91% (550 °C and C/O = 3) by increasing the zeolite to matrix ratio of 18 (CAT01) to 50 (CAT05) for fresh catalysts. Over steamed FCC catalysts, the conversion ranged between 76% and 81% as reported in Table 4. This increment in VGO conversion with an increase in the zeolite to matrix ratio was due to a rise in surface area and acidity in both steamed and fresh FCC catalysts. Figure 4 shows the trend of increasing conversion (%) of steamed and fresh FCC catalyst samples. For steamed FCC catalysts, the conversion was low as compared with a fresh catalyst for each zeolite to matrix ratio. For instance, at the zeolite to matrix ratio of 30 for sample CAT03, the fresh FCC sample conversion was 84%, whereas 77% conversion was achieved after steaming of this sample. This decrease in conversion (%) was due to the low activity of steamed FCC catalysts, which happened due to dealumination during the steaming process. Overall, an 8.3% relative increase in conversion was observed for fresh FCC samples, while a 5.8% rise was calculated after steaming of the FCC samples [41].

The effect of fresh and steamed FCC catalyst samples on gasoline selectivity as a function of the zeolite to matrix ratio is shown in Figure 5. It is shown that gasoline selectivity decreases with an increase in the zeolite to matrix ratio for both fresh and steamed FCC catalysts. This behavior is expected due to the overcracking of gasoline at a high zeolite to matrix ratio. Gasoline selectivity for fresh FCC catalysts was found for CAT01 (49%), CAT02 (43%), CAT03 (43%), CAT04 (42%), and CAT05 (40%). The percentage decrease in gasoline selectivity was 18% for an increase in the zeolite to matrix ratio of 18 to 50. However, the steamed FCC catalyst selectivity ranged between 60% and 63%. The steamed FCC catalyst sample CAT01 selectivity was 63%, while for CAT05, 60% selectivity of gasoline was obtained. After steaming, a 4.7% decrease in gasoline selectivity was observed between CAT01 and CAT05, which is insignificant as compared with fresh catalyst samples where an 18% drop was indicated. It is worth mentioning that gasoline selectivity significantly increased after steaming at 750 °C for 5 h.

Steamed CAT01 has 28% more gasoline selectivity as compared with fresh CAT01, whereas a 50% increase in gasoline selectivity was observed for steamed CAT05 as compared with fresh CAT05. The decrease in gasoline selectivity as a result of an increase in the zeolite to matrix ratio was associated with an increase in the LPG selectivity. Figure 6 shows the LPG selectivity as a result of an increase in the zeolite to matrix ratio of fresh and steamed FCC catalyst samples.

For the 18% drop in gasoline selectivity for fresh FCC catalyst samples, an 8% increase in the selectivity of LPG was calculated. However, only a 3% rise in the selectivity of LPG was observed in steamed FCC samples as compared with a 4.7% decrease in gasoline. Less increase in LPG selectivity for steamed FCC samples indicated the low activity that prevented the gasoline from overcracking.

Similar to the gasoline trend, the LCO and HCO selectivity was found to decrease with an increase in the zeolite to matrix ratio for both fresh and steamed FCC catalyst samples. This behavior was due to an increase in the cracking rates of LCO and HCO as conversion increased. The trends of the LCO and HCO selectivity as a function of the zeolite to matrix ratio for both fresh and steamed FCC catalysts are shown in Figure 7 and Figure 8, respectively. For fresh FCC catalysts, a significant decrease in the LCO and HCO selectivity (%) was observed for the zeolite to matrix ratio of 35 to 50. For the zeolite to matrix ratio of 18 to 35, only 5% and 13% decreases in LCO and HCO selectivity were observed, whereas 48% and 37% drops in LCO and HCO selectivities were noted for the zeolite to matrix ratio of 35 to 50. For steamed FCC samples, there was a 7% decrease in the LCO selectivity for the zeolite to matrix ratio of 18 to 35, while a 12% drop was noted for the zeolite to matrix ratio of 35 to 50. However, the decrease in HCO selectivity was 15% for the 18 to 35 zeolite to matrix ratio as compared with a 19% drop for the 35 to 50 zeolite to matrix ratio in steamed FCC samples. This supported the significant increase in conversion for both fresh and steamed FCC catalysts after a zeolite to matrix ratio of 35.

The combined selectivity of gasoline and LCO for steamed CAT01 was reported as 82% as compared with 76% for steamed CAT05. However, 60% and 46% combined selectivities of gasoline and LCO were indicated for fresh CAT01 and CAT05 samples, respectively. It could be observed that the zeolite to matrix ratio of 15 had the highest combined selectivity of gasoline and LCO for both fresh and steamed catalysts due to less overcracking of LCO and gasoline.

In general, as conversion increased, the yields of LCO and gasoline passed through maxima and then decreased, while HCO declined and dry gas and coke yields increased steeply. The optimum conversion reported in the literature was 70–75%, and above 76% conversion was reported in the present study for all steamed and fresh FCC catalysts. As such, the trends of decreasing gasoline, LCO, and HCO selectivity are in good agreement with the literature [42].

Similar to LPG, the coke selectivity was observed to increase with an increase in the zeolite to matrix ratio and VGO conversion. Figure 9 demonstrates the effect of the zeolite to matrix ratio on coke selectivity. The FCC catalyst samples containing high zeolite to matrix ratios produced more coke as compared with low zeolite to matrix ratios. The fresh catalyst sample CAT01 contains 10.47% coke selectivity as compared with 14.48% coke selectivity for the CAT05 sample. Furthermore, the steamed FCC catalyst CAT01 contained only 2.1% coke selectivity, while 3.7% coke selectivity was observed in the CAT05 sample. It could be seen that coke selectivity decreased by 79% and 74% after the steam treatment of CAT01 and CAT05, respectively.

From Table 3 and Table 4, it can be seen that the dry gas (H₂ and C₁-C₂) selectivity (%) increased and the light olefin selectivity (%) decreased with an increase in the zeolite to matrix ratio for both steamed and fresh FCC catalyst samples. For fresh catalysts, a 22% increase in dry gas selectivity was observed from the zeolite to matrix ratio of 18 to 50. However, only a 4% rise in the dry gas selectivity was noted for steamed CAT01 to CAT05 samples because of less coke and VGO conversion. The reason for the light olefins’ decrease with an increase in the zeolite to matrix ratio was an increase in hydrogen transfer reactions that convert the light olefins to paraffins [43].

3. Experimental

3.1. Materials

The following materials were used for the synthesis of FCC catalyst: ultra-stable Y zeolite [GRACE GmbH, Worms, Germany, SP6-4079], Kaolin (Sigma-Aldrich, St. Louis, MO, USA), Siral 40 (40% Al₂O₃, 60% SiO₂) (CONDEA, Hamburg, Germany), Ludox AS-40 (Sigma-Aldrich, St. Louis, MO, USA), and hydrotreated VGO obtained from a domestic refinery.

3.2. Catalyst Preparation

A series of FCC catalysts were synthesized with five different compositions (weight %) of ultra-stable Y-zeolite (USY) and matrix as shown in

Table 5. Chemical composition of the FCC catalyst.

Name of Catalyst	USY (wt.%)	Siral 40 (wt.%)	Ludox AS-40 (wt.%)	Kaolin (wt.%)	Zeolite/Matrix Ratio
CAT01	15	11	21	53	18
CAT02	20	10	20	50	25
CAT03	23	10	19	48	30
CAT04	26	9	19	46	35
CAT05	34	8	17	42	50

. The amount of USY used in this preparation was in the range of 15 wt.% to 34 wt.%. These percentages were selected to fall in the range described in the literature [44]. Siral 40, Ludox AS-40, and kaolin were used for amorphous silica-alumina, silica solution, and clay, respectively, in the approximate ratio of 1:2:5 to make a consistent matrix. Siral 40 was used as a binder in the synthesis of the FCC catalyst samples. All four components, namely, USY, Siral 40, Ludox AS-40, and kaolin, were mixed in de-ionized water for the preparation of the FCC catalyst. The slurry was heated above 100 °C with continuous magnetic stirring until it became dry. The mixture was then placed in the oven at 110 °C for overnight drying. The dried product was crushed and calcined at 550 °C for 6 h. Finally, 12 g of each prepared sample was treated with 100% steam at 750 °C for 5 h. The steamed catalyst was sieved for the particle size (500–850 µm) before microactivity testing.

3.3. Catalyst Characterization

The crystallinity of the as-synthesized FCC catalyst samples was determined using the X-ray powder diffraction technique using a Rigaku Miniflex II (Rigaku Corp., Tokyo, Japan) with nickel filtered CuKα radiation having a wavelength of λ = 1.5406 Å at 30 mA and 40 kV operating parameters. A diffraction pattern was generated for 2 theta from 3° to 50° with a scan rate of 3°/min. The textural properties of the samples were measured by using a Micromeritics ASAP-2020 sorption analyzer with the help of nitrogen adsorption at −196 °C. An amount of 100 mg of the calcined sample was taken for the BET surface area measurement. Before nitrogen physisorption, the samples were degassed under vacuum (10⁻⁵ torr) at 350 °C for 3 h. The adsorption isotherms of the samples were measured at −196 °C (liquid nitrogen temperature). The pore size distributions and surface areas were calculated by using the Barrett–Joyner–Halenda (BJH) and Brunauer–Emmet–Teller (BET) methods, respectively. The ammonia temperature-programmed desorption (TPD) was used for acidity measurements in the BELCAT equipment. The calcined sample (100 mg) was pre-treated at 500 °C for 1 h in the presence of helium (He) with a 50 mL/min flow rate. Afterward, the sample was cooled down to 100 °C and exposed to the NH₃/He mixture with a volume ratio (%) of 5/95 at 100 °C for 30 min. Ammonia gas was removed using He purging for 1 h, and then the temperature was raised to 600 °C at the rate of 10 °C/min with the same flow of He to perform the TPD measurement. The TCD detector as well as mass spectroscopy was used to monitor the desorbed NH₃ gas. The physicochemical properties of the as-synthesized fresh and steamed FCC catalysts used in the present study are shown in Table 1 and Table 2.

3.4. Catalyst Evaluation

The microactivity test (MAT) unit (Sakuragi Rikagaku, Fukuoka, Japan) is a fixed bed reactor that was used to investigate the cracking of vacuum gas oil as shown in Figure 10. The properties of Hydrotreated vacuum gas oil (HT-VGO) are listed in

Table 6. Properties of feed HT-VGO.

Property	Value
Density (15 °C) (g/cm3)	0.88
Nitrogen (ppm)	172
Sulfur (ppm)	298
Aromatics (wt.%)	42
Saturates (wt.%)	60
Residue (wt.%)	0.9
Distillation data (vol %)	Temperature (°C)
Initial boiling point	310
5%	345
25%	375
50%	422
90%	510
Final boiling point	565

.

The ASTM D-3907 method was followed for the FCC catalyst activity measurement by the MAT unit. The time on stream was 30 s, and the system temperature was set at 550 °C. The amount of the catalyst used for the experiment was 3.0 g, and the amount of the vacuum gas oil was 1.0 g. After the completion of the reaction, the stripping of the products was carried out by using 30 cc/min of nitrogen for 9 min. Considering the high volatility of the liquid products, a low-temperature circulating bath at −10 °C was added to the unit instead of the conventional iced water.

During the reaction and stripping modes, a burette was used for the gas collection from the outlet of the liquid receiver. For obtaining the exact weight of the vacuum gas oil feed, the weight of the syringe before and after the reaction was measured. The MAT operating conditions are summarized in

Table 7. MAT operating conditions.

Property	Value
Feed weight injected	About 1.0 g
Catalyst weight	3.0 g
Feed injection time (time on stream)	30 s
Feed syringe temperature	Room temperature
Feed injector temperature	5 °C higher than the reaction temperature
Liquid receiver temperature	−9 °C
Catalyst/liquid stripping time	Total 9 min
With a receiver in a cold bath	5 min
With cold bath removed	4 min

.

Analysis of MAT Products

The MAT products contain a liquid phase, a gaseous phase, and coke on the spent catalyst after the reaction. An acceptable mass balance limit was 95–103% of the injected liquid vacuum gas oil feed. A detailed gas chromatographic analysis of all MAT products was performed to estimate the yield pattern as well as information on the feed being tested on the catalyst. The gaseous products were analyzed using a Micro GC Agilent 3000A (Agilent Tech., Santa Clara, CA, USA) equipped with four thermal conductivity detectors (TCD). This Micro GC determined all the light hydrocarbons up to C₄, C₅ paraffin, and H₂ as well as fixed gases. All hydrocarbons from C₁ to C₄ and C₅ paraffin were determined accurately. The weight of all light hydrocarbons up to C₄ was added together, and hydrocarbons heavier than C₄ were added to the weight of the liquid product after the analysis. The Horiba carbon-sulfur analyzer Model EMIA-220V (Horiba, Kyoto, Japan) was used to analyze the coke deposited on the catalyst. One gram of the spent catalyst was burnt in a furnace at high temperature using tin and tungsten as combustion promoters. The carbon content as a percentage of the catalyst weight was calculated with the help of the resulting combustion gas (CO₂) passed through the infra-red analyzer. The liquid products were analyzed by the Shimadzu GC 2010 (Shimadzu Corp., Kyoto, Japan) equipped simulated distillation according to ASTM method D-2887. The liquid products consisted of gasoline, LCO, and HCO. The conversion of vacuum gas oil was reported as the sum of gasoline, total gases including dry gas and LPG, and coke. HCO and LCO with a boiling point above 221 °C were considered unconverted feedstock.

4. Conclusions

A series of fresh and steamed FCC catalyst samples with different zeolite to matrix ratios was used in the cracking of HT-VGO. VGO conversion was increased with an increase in the zeolite to matrix ratio for both fresh and steamed FCC catalysts. The surface area and acidity of all FCC catalyst samples were found to increase as the zeolite to matrix ratio increased. At a zeolite to matrix ratio of 15, maximum gasoline and LCO selectivity was achieved with minimum gas and coke selectivities. For the fresh CAT01 sample, the selectivities of gasoline, LCO, and coke were 49%, 11%, and 10%, respectively, compared with 40%, 5%, and 14% for the fresh CAT05 gasoline, LCO, and coke selectivities, respectively. A significant decrease in gasoline and LCO selectivity and an increase in coke selectivity was observed. However, the steamed CAT01 sample had 63%, 19%, and 2.1% selectivities for gasoline, LCO, and coke, whereas the steamed CAT05 sample had 60%, 15%, and 3.7% selectivities for gasoline, LCO, and coke, respectively. Thus, it was concluded that an increase in the zeolite to matrix ratio has enhanced the secondary reactions such as overcracking of liquid products and coke more than the primary VGO cracking reaction.