April 2024

Petrochemical Technologies

Development and industrial proactive of the MFP process

With the continuous progression of environmental regulations and product quality requirements—as well as the increasing market share of new energy vehicles in the context of the carbon peak and carbon neutrality policies—the demand growth rate for refined oil products continues to slow.

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With the continuous progression of environmental regulations and product quality requirements—as well as the increasing market share of new energy vehicles in the context of the carbon peak and carbon neutrality policies—the demand growth rate for refined oil products continues to slow. At present, China's diesel consumption has reached its projected peak, and it is expected that gasoline consumption will also reach its peak by the end of the country’s 14th Five Year Plan.

However, as important basic organic chemical raw materials, low-carbon olefins such as propylene and butylene will still maintain a high demand growth rate. During the 14th Five Year Plan period, the growth rate of propylene demand will still be maintained at around 4%. In addition, since January 1, 2020, the International Maritime Organization (IMO) has stipulated that ships operating globally must use low-sulfur heavy marine fuel oil (hereafter referred to as low-sulfur heavy marine fuel) with a sulfur mass fraction not exceeding 0.5 wt%. However, the throughput of ports in China is 22 times that of Singapore, while the supply of low-sulfur heavy ship fuel is only 47% of that of Singapore. The supply of low-sulfur heavy ship fuel in China is severely mismatched by the scale of port development,¹ so huge potential exists for future growth of low-sulfur heavy marine fuel.

As an important unit that can produce light olefins and heavy distillate oil, catalytic cracking units can be transformed and innovated through certain processes and catalysts to produce more low-carbon olefin products,² and can be coupled with other existing hydrogenation units to fully utilize their heavy distillate to produce low-sulfur ship fuel. Moreover, by utilizing existing equipment, processes and catalyst adjustments, the urgent need for traditional fuel-based refineries to transition to the chemical industry and the increasing demand for low-sulfur heavy ship fuel can be quickly addressed, significantly reducing time and cost investment and improving refinery efficiency.

Consequently, the authors’ company has developed a catalytic cracking and marine fuel and propylene (MFP) process catalyst^a that uses specially designed ZSM-5 zeolite in the catalytic cracking section to produce low-carbon olefins such as propylene, butylene and low-sulfur fuel oil components. The experimental results show that the yield and selectivity of propylene and butylene in the product have significantly increased. By precisely regulating the carbon to carbon (C-C) bond fracture mode and extending the lifecycle of fossil energy carbon resources, it has achieved the maximum retention of polycyclic aromatic hydrocarbons in the raw materials in the fuel oil components, avoiding condensation and coking. After filtration and hydrogenation treatment, it is used as a low-sulfur fuel oil blending component. After blending with other components such as vacuum residue, it can produce RMG380 marine fuel oil products that meet the requirements of China's current marine fuel oil quality standard GB17411-2015, achieving efficient utilization of hydrocarbon resources.

MFP catalytic cracking process^a and catalyst development. 

Presently, the catalytic cracking process for producing low-carbon olefins adopts the concept of graded pores in catalyst design. The zeolite Y with 10-member ring opening pores are used to crack heavy hydrocarbons with large molecules, while ZSM-5 zeolite is used to crack medium-size molecules and convert them into low-carbon olefins.

Catalysts mainly composed of 10-member ring zeolite can exhibit good heavy oil conversion ability in the catalytic cracking process, but they present an unavoidable drawback that can easily lead to side reactions of low-carbon olefins, thereby affecting selectivity and yield. In the design of catalytic cracking catalysts, full consideration is given to the limited catalysis of reactants during the diffusion process, as shown in FIG. 1. The problem lies here, where the catalyst design did not fully consider the limited catalysis of olefin reactants during the diffusion process. Low-carbon olefin products diffuse in the zeolite Y, where the olefins undergo hydrogen transfer reactions and are then converted into alkanes, as shown in FIG. 2. Therefore, to achieve high selectivity of olefin products, ZSM-5 zeolite should be used as active components in catalyst design. Here, the ratio of isobutylene to isobutane is used as the effective confined catalytic index to screen and evaluate the catalytic reaction performance of ZSM-5 zeolite.³

FIG. 1. The diffusion sequence of reactants in catalyst pores.

 

After systematic research and repeated screening, a ZSM-5 zeolite was developed and a deep catalytic cracking unit catalyst^b was prepared based on it. On a small fixed fluidized bed catalytic cracking unit (FFB), Daqing vacuum gasoil (VGO) was used as the feed to evaluate the catalytic reaction performance of the MFP process catalyst^a. At the same time, the deep catalytic cracking process catalyst^b was selected as the comparison catalyst, which uses conventional ZSM-5 zeolite and a small amount of Y zeolite as the active components. Adopting two sets of process conditions, one is a set of mild reaction conditions with the goal of producing more olefin products. The other has strict reaction conditions with the goal of producing more low-carbon olefins. The two sets of experimental data are listed in TABLE 1.

 

From TABLE 1, it can be seen that under the same reaction severity (compared to the deep catalytic cracking process catalyst^b), the MFP process catalyst^a has weaker heavy oil conversion ability and lower gasoline yield. However, the yield and selectivity of olefin products have significantly increased, making it more suitable as a specialized catalyst for multi-olefins production. At low reaction severity (compared to the deep catalytic cracking process catalyst^b), the MFP process catalyst^a has weaker heavy oil conversion ability. The former has a conversion rate of 83.32%, while the latter has a conversion rate of only 71.87%, with a difference of 11.45 percentage points. The sum of the heavy oil yield and light cycle oil (LCO) yield of the MFP process catalyst^a is 28.13 wt%, which can be used as a fuel oil component. If it is not considered as a fuel component, then this portion of heavy oil must be fully converted. Under high reaction severity, the heavy oil yield and LCO yield of both catalysts significantly decreased.

Even with the use of the MFP process catalyst^a, the LCO yield was only 10.6 wt%, and the heavy oil yield was only 5.75 wt%, which is close to the heavy oil conversion capacity of conventional fluid catalytic cracking (FCC). This indicates that even though the MFP process catalyst^a has poor heavy oil conversion ability, it can compensate for the insufficient heavy oil conversion ability of specialized catalysts by increasing the reaction severity, without relying solely on zeolite Y. For the MFP process catalyst^a, the high reaction severity operation mode not only compensates for the insufficient heavy oil conversion capacity of the MFP process catalyst^a, but also fully facilitates the MFP process catalyst’s^a cracking performance, demonstrating particularly excellent selectivity for olefin products. The propylene content in liquefied petroleum gas (LPG) is as high as 48.71%, and the olefin content in LPG is as high as 89.25%. At the same high reaction severity, the propylene content in LPG for the deep catalytic cracking process catalyst^b is only 41.41% (presently, the propylene content in industrial LPG is slightly lower than this value), and the olefin content in LPG is only 78.09%.

From TABLE 1, it can also be seen that under similar conversion rates (compared to the deep catalytic cracking process catalyst^b), the olefin content in LPG of the MFP process catalyst^a is 89.25%, while the olefin content in LPG of the deep catalytic cracking process catalyst^b is only 64.21%, with a difference of 25.04 percentage points. The olefin product yield of MFP process catalyst^a is as high as 55.07 wt%, while the olefin product yield of the deep catalytic cracking process catalyst^b is only 41.42 wt%, with a difference of 13.65 percentage points. This indicates that although the presence of zeolite Y improves the heavy oil conversion ability, it comes at the expense of olefin products. For FCC processes that produce more olefins, the use of Y-type zeolite should be minimized or avoided as much as possible to achieve efficient utilization of petroleum resources. At similar conversion rates, the gasoline yield of the MFP process catalyst^a is only 28.71 wt%, while the gasoline yield of the deep catalytic cracking process catalyst^b is as high as 40.36 wt%. This also indicates that the MFP process catalyst^a is more suitable as a specialized catalyst for producing more low-carbon olefins.

Pilot plant experimental research. 

The pilot plant experiments were conducted on a continuous catalytic cracking unit using a variable diameter fluidized bed reactor, which includes four parts: a feeding section, a reaction section, a regeneration section and a fractionation section.⁴ The feedstock used in the experiments was a paraffin-based feed consisting of Daqing VGO and 30% vacuum residue (hereafter referred to as Daqing VGO + 30% VR). Its properties are:

1. A density of 0.8905g/cm³
2. A CCR of 2.94%
3. A hydrogen (H₂) content of 13.18 wt%
4. Saturates of 64.5 wt%
5. Aromatics of 24.2 wt%
6. Resins of 11.1 wt%
7. Asphaltenes of 0.2 wt%.

The catalyst was similar to a TCC proprietary catalyst, and the operating conditions and product distribution are listed in TABLE 2.⁴

From TABLE 2, it can be seen that for Daqing heavy oil, the yield of olefin products is around 50 wt%, while the yield of dry gas is < 4 wt%, and the production mode can be flexibly switched. On the premise of a significant increase in LPG yield in the MFP process, the dry gas yield is relatively low, with a ratio of LPG to dry gas > 10, while the ratio of LPG to dry gas yield in the FCC and DCC processes generally ranges from 2.5–6. The experimental results indicate that shortening the separation time of oil gas and catalyst has a significant effect on reducing dry gas yield. The composition of LPG for the MFP, maximizing iso-parafifins (MIP) and deep catalytic cracking (DCC) processes is listed in TABLE 3.

 

From TABLE 3, it can be seen that the MFP process has significant advantages in inhibiting the conversion of propylene and butylene to propane and butane.

Industrial practice. 

To further verify its application effect in industrial units, in 2020, the technology was put into industrial test on the 1.4-MMtpy heavy oil catalytic cracking unit and 600,000-tpy hydrogenation unit in Sinopec Qingdao Petrochemical Co. Ltd.'s plant after the applicability revamping. The catalytic cracking unit originally used the MIP-CGP process,^5,6 with a layout of three coaxial reactors and two stages of countercurrent regeneration. The first and second regenerators were arranged in an overlapping manner. In 2020, the MFP technology adaptability revamping was carried out on the unit. The reaction and regeneration section was not modified and only some trays of the fractionator were replaced. A new fuel oil heavy fraction filter was added, and the catalyst for fuel oil component hydrogenation was replaced. The revamped MFP technology process flow is shown in FIG. 3.

FIG. 3. MFP process flow diagram.

 

Unit operation and performance test. 

The unit was started up on December 9, 2020. To date, the overall operation of the unit is stable, the catalyst fluidization is smooth, coke generation and coke burning are basically normal, the composition of feed oil has not changed significantly, the operation of the fractionation and stabilization section is stable, and the processing capacity, target product yield and quality meet the requirements. The unit was put through the full performance test runs in May 2021 (Case 1) and September 2021 (Case 2). The purpose of Case 1 was to produce more propylene, butylene and low-sulfur marine oil, while the purpose of Case 2 was to maximize the production of propylene and butylene. To more accurately evaluate the operation of the revamped unit, production data and performance test results before and after the revamp were selected for the comparison. The performance test results are listed in TABLE 4.

 

Compared with the Base, the gasoline yield in Cases 1 and 2 significantly decreased, while the LPG yield increased by 22.19 wt% and 29.80 wt%, respectively. The selectivity of light olefins was significantly improved, and the propylene yield in Case 2 was 12.17 wt%, which was nearly twice the blank calibration, while the isobutylene yield more than doubled.

Both Cases 1 and 2 achieved no slurry production. Compared with the Base, in Case 1, the coke decreased, while the yield of light olefins increased to a certain extent. The yield of LCO was 19.91 wt%, the yield of HCO was 9.26 wt%, and the total yield of cycle oil was 29.17 wt%, an increase of 7.48 percentage points compared to the Base. This provides sufficient feed for subsequent hydrotreatment to produce low-sulfur marine oil—Case 2 is mainly aimed at producing light olefins. The yield of light olefins significantly increased, but the coke yield increased compared to Case 1. Although the total amount of LCO and HCO is lower than Case 1, it is significantly higher than the Base. It can be seen that the MFP technology enhances the highly selective generation of light olefins, inhibits the occurrence of low-carbon olefin side reactions, and transfers the target products of catalytic cracking from gasoline and diesel to propylene, butylene and fuel oil components, achieving the transformation and development of catalytic cracking products from “oil to chemicals” to “oil to special products.” The data from Cases 1 and 2 indicate that the MFP technology can flexibly adjust the market demand for low-carbon olefins and low-sulfur fuel oils.

Flexible adjustment of unit operation. 

The MFP technology requires only minor modifications to existing catalytic cracking units to allow flexibility in the production of different target products, such as low-carbon olefins, gasoline and low-sulfur marine fuel oil. The results of industrial application show that compared with the Base Case, the profit per ton of oil produced by the MFP technology production scheme is significantly increased, and the economic indicators of the scheme are compared in TABLE 5.

 

Takeaways. 

For the first time, the MFP industrial use of only ZSM-5 zeolite as the active ingredient in catalytic cracking units has been accomplished. At the same time, industrial tests to selectively crack heavy saturated hydrocarbons and alkyl side chains into light olefins have been performed. Industrial experiments have yielded positive results:

1. The catalyst using pure ZSM-5 zeolite as the active component has excellent olefin selectivity, while maintaining good heavy oil conversion ability and excellent hydrothermal stability. Good results in industrial applications were achieved.
2. Starting from the basic research on restricted catalysis of olefin products, the MFP technology systematically innovates catalytic materials, catalysts and engineering, achieving: a breakthrough in catalytic cracking technology from pursuing high conversion rates to high selectivity; the transformation from targeting gasoline and diesel to targeting low-carbon olefins and low-sulfur heavy marine fuels; the efficient utilization of hydrocarbon resources; and assisting the transformation and development of catalytic cracking products through “oil to chemicals” and “oil to special products.”
3. The industrial application results show that the reaction pressure of the MFP technology is equivalent to that of the original FCC technology, and only slight modifications to the existing FCC device are needed to achieve more production of low-carbon olefins—the MFP technology focuses on the production of propylene and butylene, as well as the production of marine fuel. The yield of propylene increased by about 32.4%, while the yield of isobutylene increased by about 115.9%. At the same time, 29.17 wt% of the heavy fraction is produced for the production of low-sulfur heavy marine fuel, achieving low-cost production of low-carbon olefins such as propylene and butylene, as well as low-sulfur heavy marine fuel.
4. To meet the requirements of gasoline blending at the refinery, the application of the MFP technology in the 1.4-MMtpy catalytic cracking unit can maintain the basic unchanged feedstock properties, stable unit capacity and small unit renovation work. The slurry is not thrown out of the unit, resulting in significant economic benefits. The product mix and production plan can be adjusted based on market dynamic demand.

The successful industrial trial of the MFP process not only provides technical support for the smooth transition of the refining industry to the chemical industry, but also lays a reliable theoretical foundation and accumulates rich industrial practical experience for the deep development of targeted catalytic cracking technology.⁷  HP

NOTES

^a TCC-1

^b MMC-2

LITERATURE CITED

1. Kong, J. and S. Ding, “Market opportunities and related suggestions for the improvement of ship combustion standards at home and abroad,” Petroleum Products Application Research, 2019.
2. Junwu, C. and Y. Xu, “Catalytic cracking process and engineering,” 3rd Ed., Sinopec Press, Beijing, China, 2015.
3. Xu, Y., Y. Zuo, Y. Ouyang, et al., “Development and industrial practice of heavy oil catalytic cracking process over mesoporous zeolite for low coking, low energy consumption and high olefin yield,” Petroleum Processing and Petrochemicals, August 2022.
4. Xu, Y., “Catalytic cracking chemistry and processes,” Science Press, 2013.
5. Yuan, Y., C. Yang, H. Shan, et al., “Preliminary study on reaction mechanism of olefins on catalytic cracking catalyst,” Journal of Fuel Chemistry, 2005.
6. Xu, Y., Y. Zuo and X. Shu, “An exploratory study on D-, F- and G-type β-scission reactions of carbenium ions over ZSM-5 zeolites,” Journal of Petroleum (Petroleum Processing), 2021.
7. Xu, Y., Y. Zuo, X. Bai, et al., “Background, ideas, and conceptual design of catalytic cracking technology for targeted production of low-carbon olefins,” Petroleum Processing and Petrochemicals, 2021.

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