May 2023


From crude oil to light olefins: Development and industrial application of the next-generation catalyst for catalytic pyrolysis process

Light olefins, particularly ethylene and propylene, are the most crucial building blocks for the petrochemical industry.

Sha, Y., Wang, P., Zhou, X., Zhu, G., Lu, W., Ouyang, Y., Song, H., Lin, W., Luo, Y., SINOPEC Research Institute of Petroleum Processing

Light olefins, particularly ethylene and propylene, are the most crucial building blocks for the petrochemical industry.1 The mounting demands for the production of light olefins are much higher than for other chemicals, yet the current worldwide supply of these important raw materials is inadequate to satisfy demand. Moreover, the formidable challenges—such as excess manufacturing capacity of the oil refining industry, the volatility of plant utilization rates, and the forecasted plateau of refined oil consumption—compel oil-refining companies to embark on a structural adjustment and transformation to their operations.

Over the past few decades, the steam-cracking process has been the dominant route to produce ethylene and propylene. However, high energy consumption and low olefin selectivity do not align with increasing environmental regulations and the current demand for light olefins.2 Consequently, the catalytic cracking process to produce light olefins was adopted in the refining industry due to its low energy consumption, low carbon dioxide (CO2) emissions and high selectivity of light olefins.3,4

Another factor that influences the production of light olefins is raw materials; however, the proportion of heavy feedstocks in raw materials has continuously increased in recent years. Therefore, it is imperative to develop new units and corresponding catalysts to address these challenges. This article will detail the design of a new catalyst to increase the production of ethylene and propylene, along with an industrial application of this new catalyst.

Catalytic pyrolysis process

Over the past several decades, many companies have developed new technologies based on the modified fluid catalytic cracking (FCC) process, which converts heavy feedstocks to light olefins with high selectivity. One of these processes was invented in the 1980s by the authors’ company, which used a deep catalytic cracking (DCC) schemea.5

Although this process scheme is like the traditional FCC process, some modifications have been made in the reactor section of the DCC scheme, including the addition of a riser and a fluidized dense-bed reactor. The addition of the fluidized dense-bed reactor is to maximize the propylene yield by prolonging the contact time between the catalysts and the gasoline products generated in the riser reactor. Further, the authors’ company developed a proprietary catalytic pyrolysis processb (CPP) by changing the operating parameters, catalyst formulation and unit configuration of the original DCC scheme to maximize both ethylene and propylene production from heavy crude oil.

Using the operating condition of the traditional FCC process as the benchmark, TABLE 1 reveals the difference in the operating conditions among FCC, DCC and the advanced CPP technologies. The operating conditions of the CPP are much more severe than the DCC process, which requires the corresponding catalyst to have excellent hydrothermal stability while simultaneously maintaining good reactivity.  

The first-generation catalystc for the proprietary CPP technology was developed by the authors’ company and first used in the Daqing Refining and Chemical Co.6,7 The phosphorus and alkaline earth metal modified ZSM-5 was the main active component in the first-generation catalystc.

When using vacuum gasoil (VGO) as the raw material, the first-generation catalyst showed good stability and selectivity in ethylene and propylene production. In addition, with the modification of operating conditions, the P/E ratio could be further adjusted. VGO is quite suitable for producing ethylene and propylene with high selectivity since its major component is paraffin hydrocarbons, which are apt to be transformed into light olefins. However, globally, feedstocks have become heavier, which has resulted in decreased activity of the conventional first-generation catalystc.

As shown in TABLE 2, the properties of the raw materials used by Shaanxi Yanchang Coal Yulin Energy and Chemical Co. were more challenging than the ones used in Daqing Refining and Chemical Co.’s facility. The content of paraffin hydrocarbons decreased by 13.9%, while the content of aromatics increased by 13.9%. Therefore, based on the property of the raw materials, the authors’ company further designed and developed a new catalyst for these more challenging feedstocks being processed by Shaanxi Yanchang Coal Yulin Energy and Chemical Co. This was done by promoting the ring-opening reaction of naphthenes and naphthenic aromatics. Meanwhile, the hydrothermal stability of the new catalyst was further improved by modification.

Developing the new CPP catalyst

The primary component of the CPP catalyst is ZSM-5 zeolite. Due to its strong acidity, good hydrothermal stability, low hydrogen transfer activity and special pore structure, ZSM-5 zeolite displays an excellent selectivity in CPP technology. However, the pore size of ZSM-5 zeolite (0.54 nm × 0.56 nm) is smaller than the molecular size of naphthene and naphthenic aromatics, which limits the diffusion and the accessibility to the active sites of these molecules.8,9 Therefore, the authors’ company developed a new hierarchical ZSM-5 zeolite with abundant mesopores, which increased the diffusion coefficient of the large molecules and their accessibility to the acidic sites in the ZSM-5 channels.

This novel hierarchical ZSM-5 zeolite has a crystal size of approximately 1.4 μm, and the size of the mesopores is approximately 10 nm (FIG. 1). A nitrogen adsorption experiment was conducted to measure the surface area of the new ZSM-5 zeolite. The results of the Brunauer-Emmett-Teller (BET) surface area analysis are shown in TABLE 3. Compared to the conventional ZSM-5 zeolite, the new hierarchical ZSM-5 zeolite provided higher SBET (392 m2·g-1) and Vpore (0.255 mL·g-1). Additionally, the surface area and the pore volume of the mesopores in the new ZSM-5 were remarkably higher vs. conventional ZSM-5 zeolites. These results indicated that the new hierarchical ZSM-5 preserved many more mesopores than conventional ZSM-5 zeolites, which provided more easily accessed active sites on the catalysts.

FIG. 1. Transmission electron microscope (TEM) image of the new hierarchical ZSM-5 zeolite (a), and the pore diameter distribution of the new hierarchical ZSM-5 zeolite (b).

Besides the structured design of the ZSM-5 zeolite, a proper metal modification is generally considered as another way to improve reaction conversion and selectivity. Metal salt was chosen to modify the hierarchical ZSM-5, and this modified ZSM-5 was marked as M/ZSM-5. It was found that the metal modification could significantly enhance the total acid amount and the strong acid amount (TABLE 4), which could help promote the reaction depth, thus converting more hydrocarbons into gas-phase products.10

FIG. 2 shows that, when using M/ZSM-5 as a catalyst, both the yield and selectivity of light olefins are significantly improved vs. the unmodified ZSM-5. A density functional theory (DFT) calculation was conducted to investigate the mechanism of how the metal improved selectivity. It was found that the metal ions accumulated at the corner of the zigzag channel, causing a reduction in the volume of the corner. Due to this reduction, the energy barrier of the cracking reaction, cyclization reaction and polymerization increased to different extents—among which the energy barrier change of the cracking reaction was the smallest, which, in turn, improved the selectivity of the catalytic cracking reaction.

FIG. 2. Yield and selectivity of light olefins of catalytic cracking of gasoline over different ZSM-5 zeolites (the columns represent the yield, and the lines represent the selectivity).

It was also found that the modification of the metal enhanced the hydrothermal stability of the new ZSM-5 zeolite.11 Compared to the unmodified hierarchical ZSM-5, the metal modification enhanced the retention of the total acid amount (TABLE 5). Further study on the mechanism of this improvement of hydrothermal stability revealed the unique structure of the M/ZSM-5, including the connection between metal ions and framework oxygens, which impeded attacks on the aluminum framework from water molecules (FIG. 3).

FIG. 3. Molecular structure of metal ions in M/ZSM-5.

In addition to the development of new zeolite material, it was also indispensable to focus on a new matrix. One of the notable issues was that, due to the low efficiency of the cyclone used in the regenerator, there was a significant loss of the fresh catalyst (20 μm–40 μm). Therefore, the authors’ company considered reducing the amount of fresh catalysts to 0 μm–40 μm, which required a much more stable catalyst.

Generally, it is contradictory to increase the stability of catalyst and also maintain the accessibility of catalyst simultaneously.12 The authors’ company managed to use hyperviscous alumina sol as the binder in preparation of the new catalyst. As shown in TABLE 6, compared with the previous catalyst that used regular alumina sol as a binder, the new catalyst showed the same pore volume and a lower attrition index, indicating better mechanical stability and an unchanged accessibility. The amount of Al13 aggregation in hyperviscous alumina sol is much higher vs. regular alumina sol, which enhances the adhesive property of the binder. It is well known that a catalyst’s matrix not only serves as the support for zeolite, but also as a Lewis acid site to improve the conversion of raw materials. To adjust the amount and strength of Lewis acid sites in the matrix, the authors’ company introduced a different metal oxide into the conventional matrix. FIG. 4 shows the relationship between the conversion of heavy oil and the coke yield. The modification of the matrix by M1 and M3 can simultaneously improve the conversion and significantly reduce the coke yield.

FIG. 4. The relationship between conversion and coke yield of different matrices.

The industrial application of a new catalyst

Based on the experimental results, a new catalystd was successfully developed. After a series of laboratory experiments, the new proprietary catalystd was further applied in an industrial CPP unit on November 12, 2021, at Shaanxi Yanchang Coal Yulin Energy and Chemical Co.’s refinery. The devised processing capability of the CPP unit was approximately 1.5 MMtpy. The authors’ company designed the reaction-regenerator system. Considering the standard conditions of changing catalysts and the common reasons for catalyst loss, the storage of the novel proprietary catalystd in the unit reached 100% by the end of November 2021. The catalyst changeout was performed without any aberrant loss of catalyst.

The following are two different case studies that reflect the potential benefits of using the novel proprietary catalystd. The program guaranteed test run (PGTR) was conducted November 12–15, 2021, using this novel proprietary catalystd. The base case (BC) data was from 2020, when a different catalyst was used in the same unit. It should be noted that, except for the increase of the inlet rate, the differences between the basic operating conditions during the BC and the PGTR were negligible (TABLE 7).

Properties of raw oil

It is necessary to analyze the properties of raw materials, as they can exert a notable influence on the catalytic performance. The properties of raw materials during the BC and the PGTR are shown in TABLE 8. Basically, the properties from both cases are quite similar, yet some disparities remain. The carbon residue in the PGTR was about 5.5%, which is 0.81% higher than the carbon residue in the BC. The higher amount of carbon residue would cause this increase in coke formation; therefore, compared to the raw materials used in the BC, those used in the PGTR had an adverse effect on the catalytic activity of the new proprietary catalystd.

Properties of equilibrium catalyst (Ecat)

The properties of the Ecat are shown in TABLE 9. The specific surface area, the microporous specific surface area and the specific surface area of micropores of the Ecat in the PGTR were discernibly higher than those used in the BC. The larger specific surface area is conducive to the interaction between the organic molecules and acid centers on the catalyst, and to the diffusion of big molecules in catalyst channels, thus improving the conversion of heavy oil. These results indicated that the novel proprietary catalystd achieved the designed goal with a greater capacity for the conversion of heavy oil. In addition, the content of poisonous metal in the novel proprietary catalystd is much higher than the catalyst used in the BC, which indicated that the new catalyst has a better metal-tolerance ability.  

The distribution of CPP products and their properties

To show the potential of the novel proprietary catalystd, the yields of the primary products between the BC and the PGTR are provided here, as well. As shown in TABLE 10, with similar operating conditions, the ethylene yield increased from 12.97% to 14.05%, and the yield of propylene increased by 1.49%, which increased the total yield of light olefins by approximately 2.6%. Moreover, coke yield decreased from 10.92% to 9.58%, which resulted in a decrease in CO2 emissions of approximately 21,000 tpy. According to the processing capability and the average prices of raw materials and light olefins, the increment of the profit from the light olefins portion could reach $80 MM/yr.  


Due to the trend of raw materials becoming heavier, the requirements of new, efficient and more stabilized CPP catalysts for the catalytic cracking of heavy feedstocks under harsher conditions are growing rapidly. With the proper design of the zeolite material, the authors’ company produced a novel proprietary catalystd. The industrial application of this novel proprietary catalystd is promising. The yield of light olefins could reach 36.5%, which is higher than the previous catalyst, while the yield of coke is around 9.58% under operating conditions that are harsher than the traditional DCC process. The authors believe that this specific catalyst shows great potential and competence for the future when heavy oil will be the dominant feedstock in processing operations. HP


a Sinopec’s -Deep -Catalytic Cracking technology
b Sinopec’s Catalytic Pyrolysis Process
c Sinopec’s CEP-1 catalyst
d Sinopec’s Epylene catalyst


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The Authors

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