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Fabrication and characterization of ZSM-5 zeolite modified with silver and assessing its performance in petroleum waste cracking process
⁎Corresponding authors. kheirmand@yu.ac.ir (M. Kheirmand), s.h.hosseini@ilam.ac.ir (S.H. Hosseini)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
The purpose of this study is to modify the structure of ZSM-5 zeolite with the aim of enhancing its performance in the cracking process for the conversion of petroleum waste into higher-value products. ZSM-5 zeolite was synthesized using a microwave-assisted hydrothermal method subsequently, the structure of the zeolite was modified by incorporating silver using the incipient wetness impregnation method. Then the synthesized sample was evaluated for its performance in a fluid catalytic cracking (FCC) process, conducted under atmospheric pressure and at a temperature of 450 °C. The performance of the silver-doped ZSM-5 zeolite was compared to that of a basic catalyst, which employed USY (ultra-stable Y) zeolite. To characterize the silver-doped ZSM-5 zeolite, various analytical techniques were employed. These included X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FTIR), temperature-programmed desorption of NH3 (NH3-TPD) and N2 adsorption–desorption. The findings of the study revealed that the modification of ZSM-5 zeolite's structure with silver led to an increase in the yield of propylene production from 6.99 % to 9.78 %. Additionally, the results demonstrated that the incorporation of silver into the zeolite structure enhanced the yield reaction, as evidenced by the measurement of American Petroleum Institute (API) index. The presence of smaller pores and the specific types of pores in Ag/ZSM-5 zeolite reduced secondary reactions. Moreover, the interaction between silver species and strong acid sites within the modified zeolite structure limited hydrogen transfer reactions and consequently increased the zeolite's overall activity.
Keywords
Hydrothermal
Microwave
Ag/ZSM-5 zeolite
FCC Process
1 Introduction
Today, the demand for fuels such as diesel and gasoline has increased significantly. This growing demand is accompanied by a concerning statistic reported by British Petroleum, which indicates that nearly half of the world's oil reserves have been depleted. This highlights the critical need to convert heavy oil residues into lighter compounds (Funai et al., 2010). The heavy oil residue, which is obtained from crude oil distillation, is characterized by its high density and an API index of less than 20. It is considered a low-grade oil cut. In contrast, light oils possess lower densities, flow readily at room temperature, and exhibit low viscosities and specific gravities (with an API greater than 20). As a result, light oils are generally more expensive compared to heavy oils due to their desirable properties and ease of use in various applications. Therefore, even for petroleum exporting countries, it is of utmost importance to convert low-grade heavy oil waste into lighter compounds (Gelder, 2004). The conversion of heavy petroleum residues to lighter compounds usually takes place during the cracking process. A major challenge in improving the quality of these compounds is the existence of asphaltenes in waste oil, which interfere with the cracking process (Gonzalez and Cedeno, 2009). After breaking the carbon bonds of these compounds, they rapidly deposit on the catalyst surface, leading to its premature deactivation (Morawski and Mosio-Mosiewski, 2006). Thermal cracking and catalytic cracking are two primary methods used for upgrading petroleum residues and producing lighter compounds (Zhang et al., 2007). However, the thermal cracking process typically consumes a lot of energy, while the catalytic cracking process requires a smaller amount. The catalytic cracking processes have been used with different types of catalysts to produce special materials (Ali et al., 2002). Zeolites play a crucial role as catalysts in the fluidized bed catalytic cracking (FCC) process. These catalysts possess a porous structure that significantly enhances the specific surface area of active sites. It is within these active sites that the conversion of large molecules into smaller molecules occurs through the process of breaking chemical bonds. ZSM-5 zeolite as the main synthetic zeolite, is commonly used in chemical, petrochemical and oil industries (Dehkissia and Larachi, 2004). ZSM-5 is frequently employed as an essential catalyst in the catalytic cracking process due to its specific pore structures, high acidity, hydrothermal stability, and low hydrogen transfer activity (Farshi et al., 2011). In addition to acidity and selectivity, which are crucial for achieving high conversion rates, the hydrothermal stability of a catalyst is equally important for ensuring its operational lifespan (Liu and Zeng, 2009). Numerous studies have been conducted to investigate the hydrothermal stability of zeolite catalysts, including ZSM-5 (Lee et al., 2009).
The modification of ZSM-5 through metal loading onto its structure presents an alternative technique for developing more active catalysts and enhancing their performance. Various methods have been employed to deposit metals such as silver onto ZSM-5, including ion exchange (Bogdanchikova et al., 2008), chemical vapor deposition (Lin and Wan, 2003), incipient wetness impregnation, and deposition precipitation (Riahi et al., 2002). These methods have demonstrated the capability of introducing silver species onto ZSM-5, which can contribute to both improved catalytic activity and enhanced hydrothermal stability. Studies have shown that the presence of silver species can induce dealumination at cation sites, thereby protecting framework aluminum species by occupying these sites with Ag species (He et al., 2011).
In addition to silver, other metals have also been utilized to modify the structure of ZSM-5. For instance, Masalska (2005) employed nickel metal to modify the ZSM-5 zeolite structure and investigated its performance in toluene hydrogenation. The study demonstrated the potential of metal modification for enhancing catalytic activity in specific reactions. Furthermore, Han et al. (2014) explored the modification of ZSM-5 zeolite structure using tungsten (W) and phosphorus (P) for heavy oil cracking applications. The optimized zeolite exhibited improved performance, resulting in increased yields of light olefins during the cracking process. Chen et al. (2017) conducted a study where ZSM-5 was synthesized using the hydrothermal method with carbon nanotubes serving as a template. The synthesized ZSM-5 was then utilized for the conversion of vegetable oil into aircraft fuel. Azeem Abdul Majed and Thian (2018) carried out a modification of the ZSM-5 structure using molybdenum (Mo) and nickel (Ni). The modified zeolite was employed for the conversion of vegetable oil into green fuel. Their research aimed to enhance the catalytic performance and selectivity of ZSM-5 in the conversion process. In another study by Qi et al. (2016), the catalytic cracking of light diesel oil was investigated using gold-modified ZSM-5 in a bench fluidized bed reactor operating at ambient pressure and 460 °C. The researchers found that the incorporation of a small amount of gold into the ZSM-5 catalyst resulted in increased propylene production and had a positive impact on the catalytic cracking of light diesel oil. Furthermore, Zhang and Wang (2015) conducted research on the cracking reaction of 1-butene over Ag/modified ZSM-5 catalysts prepared through an ion exchange method. Their findings revealed a significant improvement in catalyst performance with the addition of silver to the ZSM-5 framework. These studies demonstrate the potential of modifying the ZSM-5 catalyst through various techniques and incorporating different metals to enhance its catalytic properties, selectivity, and performance in specific conversion reactions.
Recently, zeolites, which are mainly porous compounds, have been combined with different materials to enhance their efficiency such as combination with crystalline cobalt/amorphous LaCoOx hybrid nanoparticles (Li et al. 2020), hydrated copper pyrophosphate ultrathin nanosheets (Junfeng et al. 2021), g-C3N4 (B–CN) as novel 2D bubble-like (Xinyuan et al. 2021), degree-of-sulfurization (DoS) CO-based nanocatalysts (Junfeng et al. 2022), cerium-incorporated Co-based catalysts in nitrogen-doped structures (Jiechen et al. 2022), flexible polystyrene/graphene (PS/GR) metacomposites (Zheng et al. 2022), carbon nanotubes (CNTs)/epoxy composites (Mingxiang et al. 2022), and mono-phase ceramics of indium tin oxides (Guohua et al. 2021). In addition to these studies, Peitao et al. (2022) conducted research on recent advances in negative dielectric properties in heterogeneous composites, including metal composites, carbon composites, ceramic composites, and conducting polymers. Furthermore, metal–organic framework (MOF)-based materials, which consist of metal ions coordinated with organic ligands, have attracted significant attention. Researchers such as Junpeng et al. (2019) have studied MOF-based materials for applications such as K-ion storage in K-ion batteries, Junpeng et al. (2018) have explored their use as anodes for K-ion batteries, and Junpeng et al. (2022) have investigated their role in promoting morphology rejuvenation in Prussian blue analogue (PBA) cathodes.
Based on the previous summaries, no reports have been found on the utilization of Ag-modified ZSM-5 as a catalyst in the petroleum waste cracking process. Therefore, this research aims to investigate the impact of incorporating silver into the structure of ZSM-5 zeolite on the catalytic cracking of petroleum waste.
2 Experimental part
2.1 Material and equipment
Ag-modified ZSM-5 was synthesized using orthosilicate as a silicon source, aluminum nitrate as an aluminum source, tetraethylammonium hydroxide as a template, sodium hydroxide, deionized water, ethanol, and silver nitrate. The synthesis process involved the utilization of a microwave oven equipped with an electric power and timing system to expose the sample to UV rays. A magnetic stirrer was employed to agitate the reaction mixture. For the nucleation process, a Teflon autoclave with a 5 cm inner diameter and an inner volume of 100 ml, made of polytetrafluoroethylene, was utilized as the chemical reactor.
2.2 Zeolite preparation
The ZSM-5 zeolite was synthesized using a microwave-assisted hydrothermal method. The synthesis steps are as follows:
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5.6 ml of orthosilicate, 5 ml of ethanol and 1 ml of 0.1 M sodium hydroxide were mixed on a magnetic stirrer at 100 °C for 2 h.
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3 g tetrapropylammonium hydroxide and 0.2 g aluminum nitrate and 4 ml 0.1 M sodium hydroxide solution (sodium hydroxide solution made to volume with ethanol) were mixed on the magnetic stirrer.
The solutions obtained from steps one and two were combined and mixed on a magnetic stirrer for a duration of 4 h at a temperature of 100 °C until a gel-like solution was formed. The resulting gel was then subjected to microwave irradiation for one hour. Subsequently, the gel was transferred to the autoclave to facilitate the crystallization process and maintained at a temperature of 180 °C for a period of 48 h. Following the completion of the reaction, the autoclave was allowed to cool down to the laboratory temperature in the laboratory environment. The sample was extracted from the autoclave and subjected to multiple washes using deionized water. Filtration of the sample was performed using a Buchner funnel. The filtered sample was then dried in an oven at 100 °C for a duration of 10 h. Finally, the dried sample was subjected to a calcination process by placing it in a furnace at a temperature of 550 °C for 12 h to remove the template.
2.3 Structural modification of synthesized ZSM-5 zeolite using silver
The structural modification of the synthesized ZSM-5 zeolite was carried out using silver and the incipient wetness impregnation method. The procedure employed is described as follows:
First, 5 g of the synthesized ZSM-5 zeolite was dissolved in 20 ml of ethanol. Subsequently, 5 ml of a silver nitrate solution (0.01 M) was added to the zeolite solution while vigorously stirring. The mixture was stirred for 10 min. After the stirring step, the solution was refluxed for a period of 3 h at a temperature in the range of 70–80 °C. This refluxing process helps to facilitate the interaction between the silver ions and the zeolite framework. Following the refluxing step, the solution was transferred to an autoclave, and the autoclave was maintained at a temperature of 90 °C for a duration of 24 h. Once the sample was removed from the autoclave, it was washed to remove any residual impurities. Subsequently, the sample was dried in an electric oven at a temperature of 100 °C for a period of 10 h to ensure complete removal of any remaining solvent or moisture.
2.4 Characterization
In the research, the structure and phases of the synthesized zeolite were examined using an X-ray diffraction (XRD) method with a D8 Advance Brooks X-ray diffractometer. X-ray radiation was directed onto the surface of the sample using a CuKα copper lamp, which emits X-ray with a wavelength of 1.54 Å, a voltage of 40 KV and a current intensity of 30 mA. The XRD measurements were conducted at 2θ angles ranging from 5 to 80 degrees. The Williamson-Hall method was employed to calculate the crystal average sizes. To measure the specific surface area of zeolite, pore volume and pore shape, the N2 adsorption–desorption method was used at 77 degrees Kelvin, which corresponds to the boiling point of liquid nitrogen. Porosity was measured with a Belsorp model porosimeter. Before the test, the sample was degassed and the sample was exposed to N2 gas flow at 300 °C for 3 h. The degassing process was carried out using a quantachrome flow degasser.
The scanning electron microscope (SEM) device, model FEI NOVA nanoSEM450, was used to obtain the microstructural information of the sample surface. Brucker tensor 27 FTIR device was used to evaluate the functional groups in the zeolite structure. To determine the acidity of the synthesized zeolites, the temperature‐programmed desorption of NH3 (NH3-TPD) analysis was performed by BELCAT model device.
2.5 Catalytic setup to evaluate the modified catalyst performance
The catalytic cracking reaction was conducted in a reactor using two catalyst compositions: USY/ZSM-5 and USY/Ag/ZSM-5. The reaction was performed at atmospheric pressure. The catalyst mixture was prepared by combining 80 wt% of calcinated base catalyst (USY) with 20 wt% of the synthesized zeolite. The catalytic setup used for the reaction is depicted in Fig. 1. The different parts of the catalytic setup are: a is reactor, b is heater, c is temperature controller and power supply, d is condenser, e is product collector, f is ice water bath, g is circulation pump and h is inert gas cylinder.
Schematic of designed catalytic setup to investigate the performance of modified zeolite.
In the FCC (Fluid Catalytic Cracking) process, petroleum waste from a refinery unit was used as the feedstock. Two catalyst formulations, namely USY/ZSM-5 and USY/Ag/ZSM-5, were employed for the process. The catalysts were added to the feedstock in an amount of 70 wt% relative to the weight of the feed. After adding the catalyst using a mantle, at the temperature of 200 °C the specific gravity, API, and the yield of the catalyst were determined. If the yield of the catalyst was low, the reaction temperature was raised. The heating process was continued for two hours, gradually increasing the temperature until it reached 450 °C. At each temperature, the specific gravity of the products was measured using a thermohydrometer. Then, the API of the products was calculated using the ratio between API and specific gravity according to the following equation (1):
3 Results and discussion
3.1 Characterization
3.1.1 Phase identification and XRD measurement
Qualitative analysis and phase identification of the synthesized zeolite were performed using Xpert High Score Plus software. Fig. 2 shows the XRD patterns of the reference ZSM-5 zeolite, i.e. the synthesized ZSM-5, silver, and modified ZSM-5 with silver. As can be seen in the figure, two peaks within the angle range of 7–9 degrees and three peaks within the angle range of 23–25 degrees correspond to the crystal planes 101, 011, 501, 051 and 303 of the ZSM-5 zeolite (Ding et al, 2014). By comparing the XRD pattern of the synthesized zeolite and the XRD pattern of the reference zeolite, it can be concluded that the crystal structure of the zeolite has been successfully formed.
XRD patterns of (a) silver (Ag), (b) unmodified ZSM-5 zeolite and (c) modified Ag/ZSM-5 zeolite.
In the XRD pattern of the modified zeolite with silver, in addition to the peaks corresponding to the ZSM-5 zeolite, four additional peaks are observed at angles higher than 30 degrees. These additional peaks correspond to the 111, 200, 220, and 311 crystal planes of silver. This indicates that the loading of silver onto the zeolite structure has been successfully achieved. The presence of these peaks confirms the successful modification of the zeolite with silver. Furthermore, there are peaks with low intensity in the XRD pattern of the modified zeolite that are also related to the ZSM-5 zeolite (Ding et al., 2014). However, these peaks are not mentioned in detail as they are considered less significant. The absence of any additional high-intensity peaks in the XRD pattern indicates the synthesis of high-purity ZSM-5 zeolite. Using the highest peak of ZSM-5 zeolite and the Williamson-Hall method, the average size of the crystallites was calculated to be 92.77 nm. By comparing the X-ray diffraction patterns of the synthesized zeolite and the JCPD (Joint Committee on Powder Diffraction Standards) cards available in the software, the crystalline phases present in the synthesized zeolite were identified. The XRD pattern of the synthesized zeolite was found to be in agreement with the standard sample of zeolite ZSM-5, as indicated by the JCPD No. 00–042-0023. This correspondence confirms the presence of the orthorhombic unit cell structure characteristic of zeolite ZSM-5. Additionally, the XRD pattern of the used silver exhibited similarity to the JCPD No. 01–087-0719, which corresponds to the XRD pattern of silver (Ag). This suggests the presence of silver as a crystalline phase in the synthesized zeolite. The XRD pattern of silver indicates a cubic unit cell structure. The standard sample identified for zeolite ZSM-5 has the chemical composition C48 H116 Al0.3 N4 Na0.3 O196 Si95.7.
3.1.2 N2 adsorption–desorption isotherms and textural properties determination
The BET (Brunauer-Emmett-Teller) diagram is a linear plot used to determine the specific surface area of a material. Fig. 3 displays the BET diagram of the modified Ag/ZSM-5 zeolite.
BET diagram of modified Ag/ ZSM-5 zeolite.
The BET diagram information of the modified zeolite is shown in Table 1. According to the information provided in Table 1, the synthesized zeolite exhibits a relatively high specific surface area and a suitable pore volume. This suggests that the zeolite has been successfully synthesized and aligns well with the reported values (Khoshbin and Karimzadeh, 2017). The specific surface area of unmodified zeolite was measured to be 262.33 m2.g−1. After the modification of the synthesized zeolite with silver, there is a slight decrease in the specific surface area. This decrease could be attributed to the potential clogging of the channel openings and zeolite cavities by silver species (Lü et al., 2008). Also, the pores shape of Ag/ZSM-5 zeolite was predicted using N2 adsorption and desorption isotherms. Fig. 4 shows the N2 adsorption–desorption isotherms of modified Ag/ZSM-5 zeolite.
Sample weight /g
0.0403
Slope
0.4443
Intercept
0.003112
Vm/cm3(STP) g−1
2.2351
SBET a /m2.g−1
237.41
C b
143.77
Total Pore volume /cm3. g−1
0.583
Mean Pore Diameter /nm
9.8476
N2 adsorption–desorption isotherms of modified Ag/ZSM-5 zeolite.
According to the IUPAC (International Union of Pure and Applied Chemistry) classification, the analysis of the volume of absorbed nitrogen at different relative pressures can provide insights into the presence of micro pores and meso pores in a material. At low relative pressures, the volume of absorbed nitrogen indicates the presence of micro pores. On the other hand, at high relative pressures, the volume of absorbed nitrogen indicates the presence of meso pores. Also, there are two types of isotherms: isotherm type I (Langmuir) is typically observed in materials with micro pores and isotherm type IV is observed in materials with meso pores. Based on the information provided, the synthesized zeolite exhibits characteristics indicative of the presence of micro pores. The absorption of nitrogen at low relative pressures suggests the existence of these small-sized pores within the zeolite structure. Furthermore, the observation of type IV isotherm behavior and the presence of a hysteresis loop at higher relative pressures suggest the presence of meso pores in the zeolite structure. Therefore, the N2 adsorption–desorption isotherms for the synthesized zeolite exhibit a combination of type I and IV isotherm behavior. This combination indicates the presence of both micro and meso pores in the zeolite structure, offering a hierarchical pore structure. The presence of a hysteresis loop in the N2 adsorption–desorption isotherms of the modified zeolite suggests the presence of mesopores (pore diameter between 2 and 50 nm), which confirms the pore diameter obtained from the BET diagram (9.8476 nm).
3.1.3 SEM observations
Fig. 5 shows the SEM images of the silver-modified zeolite in two different magnifications (1 and 5 µm). The SEM images show that the synthesized zeolite particles have a polyhedral cubic shape. In addition to the main crystals, irregular crystals are also observed in the SEM images, which may be due to secondary nucleation reactions during the synthesis process. These smaller crystals are formed adjacent to or on larger cubic crystals, indicating their formation in relation to the primary crystal growth. In order to compare the structure of zeolite before modification and after modification, SEM images of unmodified ZSM-5 zeolite with two magnifications of 1 and 5 μm are shown in Fig. 6. The SEM images also highlight that the overall morphology of the zeolite has not significantly changed after modifying it with silver. The polyhedral cubic structure of the particles is preserved, suggesting that the silver modification does not significantly alter the crystal structure or shape of the zeolite particles.
The SEM images of modified Ag/ ZSM-5 zeolite: (a) at 1 μm scale and (b) at 5 μm scale.
The SEM images of unmodified ZSM-5 zeolite: (a) at 1 μm scale and (b) at 5 μm scale.
3.1.4 FTIR study
Examination of FTIR spectra of various zeolites reveals the presence of two groups of vibrational peaks in these compounds. The first group consists of peaks that appear in the range between 400 and 1000 cm−1, called the fingerprint region, which represent a specific pattern for each sample and are associated with the internal vibrations of TO4 tetrahedra (T = Al, Si). The second group consists of the vibrational peaks that correspond to the connections between tetrahedra and wave numbers from 1000 to 4000 cm−1, which is known as the frequency range of the group observed in certain zeolite structures (Cejka et al., 2000). The characteristic peaks of ZSM-5 zeolite can be realized in the areas of 1080 cm−1 (inner asymmetric stretching), 800 cm−1 (outer symmetric stretching), 547 cm−1 (double ring vibrations) and 450 cm−1 (T-O- bending) (Mohamed et al., 2005).
Fig. 7 shows the FTIR spectrum of modified Ag/ ZSM-5 zeolite and unmodified ZSM-5 zeolite. According to Fig. 7, it can be seen that the absorption band in the range from 434 to 791 cm−1 is related to the fingerprint region of zeolite, which consists of the vibrations of different metal–oxygen bonds, indicating the tetrahedral structure of SiO4 zeolite. Also, the absorption band at 1061 to 1211 cm−1 is associated with the stretching vibrations of the Si-O bond in the zeolite structure. The absorption bands observed in the FTIR spectrum of the ZSM-5 zeolite show the ZSM-5 zeolite structure is formed. The results indicate that no significant structural changes were found in either the modified or original zeolites. However, a slight shift in the vibration peaks was observed for the Ag/ZSM-5 zeolite.
The FTIR spectra of (a) modified Ag/ ZSM-5 zeolite and (b) unmodified ZSM-5 zeolite.
3.1.5 Investigation the acidic property of synthesized zeolite
The NH3– TPD diagrams for the ZSM-5 and Ag/ZSM-5 zeolites are shown in Fig. 8.
NH3-TPD curves of (a) modified Ag/ZSM-5 and (b) unmodified ZSM-5 zeolite.
Two peaks of ammonia discharge are observed in the graphs. The first peak appears in the temperature range of 150 to 300 °C, which corresponds to weak acid sites, and the second peak is observed in the temperature range of 350 to 500 °C, corresponding to strong acid sites. Notably, the peak intensity of the strong acid sites has diminished after the zeolite was modified with silver, indicating a decrease in their acid strength. This reduction can be attributed to the interaction between the silver species and the strong Bronsted acids present in the zeolite network.
3.2 Modified catalyst test to evaluate its performance
To investigate the performance of Ag/ZSM-5 zeolite, petroleum waste obtained from the distillation tower of the refinery was utilized as the feed for the cracking process. Table 2 presents the characteristics of the petroleum waste.
Based on the relationship between API and specific gravity, the distillation tower waste exhibits an API value of approximately 15.5, categorizing it as a constituent of heavy oil and a low-value oil fraction. As previously demonstrated, a catalytic setup was developed to conduct the cracking process and assess the performance of the modified zeolite. Initially, the cracking process of the distillation tower waste was conducted using unmodified ZSM-5, followed by the utilization of silver-modified zeolite. Subsequently, the resulting product was analyzed using a GC device to determine the product composition. Additionally, a thermohydrometer was employed to measure the specific gravity and API, while the reaction yield was calculated using equations (1) and (2).
Product
USY/ZSM-5
USY/Ag/ZSM-5
Ethylene
2.22
2.82
Propylen
6.99
9.78
Butene
2.02
2.63
Olefin
11.23
15.72
Table 4 presents the results of the analysis conducted on the formed products, including measurements of specific gravity, calculation of API, and determination of reaction yield, in the presence of the USY/ZSM-5 catalyst. Meanwhile, Table 5 displays the corresponding results obtained with the USY/Ag/ZSM-5 catalyst.
Temperature
200 °C
250 °C
300 °C
350 °C
400 °C
450 °C
Product S.G.a
0.9625
0.9625
0.9463
0.9342
0.9135
0.8982
Product API
15.5
15.5
18.03
19.96
23.39
26.04
Yield (%)
0
0
16.32
28.80
50.90
68
Temperature
200 °C
250 °C
300 °C
350 °C
400 °C
450 °C
Product S.G.
0.9625
0.9575
0.9423
0.9275
0.9021
0.8835
Product API
0
16.28
18.66
21.1
25.36
28.66
Yield (%)
0
5
20.4
36
63.6
85
Based on the results presented in Tables 3, 4, and 5, as well as Figs. 9 and 10, it can be observed that the presence of Ag/ZSM-5 catalyst has led to an increase in the yield of light olefins such as ethylene, propylene, and butene, as well as API and reaction yield. Tables 4 and 5 also show that as the temperature increases, there is a corresponding increase in both the API and yield. It is worth noting that ZSM-5 zeolite possesses smaller pores in comparison to the base catalyst (USY), which is based on zeolite Y and falls under the faujasite category. The difference in pore size between zeolite Y and ZSM-5 leads to distinct roles in the breakdown of hydrocarbons. Zeolite Y's larger pores facilitate the breakdown of larger hydrocarbons, while ZSM-5′s smaller pores are more conducive to the breakdown of smaller hydrocarbons. The unique pore structure of ZSM-5 also helps to minimize secondary reactions. By introducing silver species to modify the structure of ZSM-5 zeolite and interact with the strong acid sites within the zeolite's structure, the acidity of the zeolite is reduced. This reduction in acidity limits hydrogen transfer reactions, which are a primary cause of coke formation in the FCC (fluid catalytic cracking) process. By suppressing hydrogen transfer reactions through silver loading on the zeolite structure, the performance of the zeolite is enhanced. In a similar study, Gao et al. (2009) conducted research where they modified the structure of ZSM-5 zeolite by introducing phosphorus. The phosphorus-modified zeolite was then applied in a light diesel cracking process. The findings of their study revealed that the modified catalyst exhibited a minimum 3 % increase in propylene yield compared to the unmodified catalyst.
The comparison of the overall yield of the catalytic cracking process of petroleum waste using USY/ZSM-5 and USY/Ag/ ZSM-5 zeolites.
The comparison of yield products of the catalytic cracking process of petroleum waste using USY/ ZSM-5 and USY/Ag/ ZSM-5 catalysts.
4 Conclusions
The main objective of this study was to enhance the performance of ZSM-5 zeolite in the cracking process, specifically for the conversion of petroleum waste into higher-value products. To achieve this, the structure of ZSM-5 zeolite was modified by incorporating silver (Ag). A comparison was conducted between the USY/ZSM-5 and USY/Ag/ZSM-5 catalytic systems, focusing on propylene production. The results demonstrated that the incorporation of silver into the zeolite structure led to a significant increase in propylene yield, from 6.99 % to 9.78 %.
Additionally, the measurement of API and determination of reaction yield in both catalytic systems revealed that the presence of silver in the zeolite structure positively influenced the overall yield of the reaction. This improvement can be attributed to several factors, including the smaller pore size and specific pore structure of Ag/ZSM-5 zeolite, which reduced secondary reactions. Moreover, the interaction of silver species with strong acid sites in the zeolite structure limited hydrogen transfer reactions. By mitigating these reactions, the activity of the zeolite was enhanced, leading to improved performance in the cracking process. The cost analysis associated with the modification of ZSM-5 zeolite using silver and lifespan of silver loaded on zeolite in the cracking process is a topic that remains to be explored in future work.
Acknowledgments
The authors greatly appreciate the financial support from Chemical Arvand Abadgaran Company and Yasouj University.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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