July 2025

Catalysts

Boosting butylenes production from an FCCU through an HBC catalyst technology

Based on the generation and conversion mechanism of butylenes during the FCC process, this article details the design, development and commercial trials of the latest high-butylenes selectivity catalysts (HBC) series catalysts boosting butylenes without compromising gasoline yield. Its potential to increase butylenes has been confirmed through laboratory evaluation and commercial trial results. 

IP: 10.3.182.34

As environmental requirements become increasingly stringent, high-quality and clean gasoline products are favored by the market. Compared to the China V gasoline standard, the olefin volume fraction in the China VI B gasoline standard has been adjusted from ≤ 24% to ≤ 15% and the aromatics volume fraction has been adjusted from ≤ 40% to ≤ 35%. Olefins and aromatics are the main contributors to octane number, and their reduction could lead to an insufficient octane number in gasoline. Therefore, refineries aim to increase the blending ratio of methyl tert-butyl ether (MTBE) and alkylate—which are high-octane, olefin-free and aromatics-free components—in the gasoline pool to meet the octane number requirements of clean gasoline. 

Butylenes produced from fluid catalytic cracking (FCC) are the main feed for MTBE units and alkylation units. Typically, the mixed C4 components obtained from liquefied petroleum gas (LPG) through a gas separation unit enter the MTBE unit, where isobutylene is etherified to produce MTBE. MTBE can be utilized as a high-octane blending component for gasoline or cracked to produce high-purity isobutylenes, which are further used to produce butyl rubber, polyisobutylene, methyl methacrylate and other chemicals. The other C4 components containing n-butylenes, isobutane and n-butane after the MTBE unit can be used as feedstock for alkylation units, and the remaining C4 components are used as civil fuels. The butylenes components in LPG can be fully utilized through MTBE and alkylation units. Therefore, many refineries attempt to increase butylenes production via FCC to maximize the economic benefits, and using catalysts or additives to increase butylenes yield is one of the most economical and effective methods.¹ 

Based on the generation and conversion mechanism of butylenes during the FCC process, this article details the design, development and commercial trials of the latest high-butylenes selectivity catalysts (HBC) series catalysts boosting butylenes without compromising gasoline yield. Its potential to increase butylenes has been confirmed through laboratory evaluation and commercial trial results. 

Generation and conversion of butylenes in FCC. The main reactions involved in the FCC process include cracking, isomerization, hydrogen transfer, alkylation, cyclization and condensation reactions. These chemical reactions proceed with carbenium and carbonium ions as transition states or intermediates, and the extent of the reaction types affects the distribution and properties of the FCC products.2 The β-scission reaction of carbenium ions favors the generation of propylene, while the isomerization of carbenium ions—mainly proceeding through protonated cyclopropane carbonium ion (PCP) intermediates—tends to produce isomerized alkanes and larger olefins (C4=, C5= and C5+=) and reduce the propylene generation (as shown in FIG. 1). 

FIG. 1. Diagram for the generation of propylene and butylenes in the FCCU. 

In addition, hydrogen transfer reactions are primarily bimolecular reactions that saturate olefins into corresponding alkanes. It can be seen that enhancing the carbenium ions isomerization and inhibiting the hydrogen transfer reaction of olefins are key to boosting FCC butylenes, which can be achieved by optimizing the pore structure and acidity of the FCC catalyst. Based on the above theoretical understanding, a proprietary HBC catalyst^a and HBC additive^b to boost FCC butylenes have been developed by the authors’ company. 

Design and development of the catalyst^a. There are two challenges in developing FCC catalyst for boosting butylenes. One is how to increase butylenes production by raising the concentration of butylenes in LPG (C4 olefinicity), rather than simply relying on LPG yield. Generally, ZSM-5 zeolite or ZSM-5 additive is used to increase LPG yield, accompanied by an increase in the yield of low-carbon olefins, especially propylene. However, the olefinicity does not change much, which presents great limitations for refineries with limited gas fractionation capacity. The second is how to solve the contradiction between increasing C4 olefinicity and enhancing bottoms conversion. Usually, catalysts with higher activity or operations with larger catalyst-to-oil ratio (C/O) are beneficial for strengthening bottoms cracking; at the same time, the increase in hydrogen transfer activity can lead to a decrease in olefinicity. 

The target-oriented technology (TOT) based on catalytic materials with different topological structures has been constructed by the author’s company, as shown in FIG. 2: 

• The latest developed meso-macroporous active matrix can reduce coke formation by enhancing the "accessibility" and pre-cracking ability of the macromolecules. 

• The novel metal-modified zeolite with an optimized active sites distribution can balance bottoms conversion with mitigated hydrogen transfer activity, and facilitate the efficient conversion of hydrocarbon molecules into low-carbon olefin precursors. 

• The new isomerization material different from ZSM-5 has been developed to promote the conversion of low-carbon olefin precursors into butylenes. 

FIG. 2. Target-oriented technology (TOT) based on catalytic materials with different topological structures.  

The authors’ company’s catalyst^a based on the TOT platform possesses the following characteristics: 

• Increase butylenes production mainly by boosting C4 olefinicity in LPG 

• Excellent bottoms upgrading capability  

• The C3/C4 ratio in LPG could be adjusted flexibly 

• High-quality physical properties meet the requirements of different FCCUs. 

Laboratory evaluation of the catalyst^a. The performance of the proprietary catalyst is investigated on an advanced cracking evaluation (ACE) fixed fluidized bed micro-reactor device, using a commercial catalyst as a reference. The reaction temperature is 520°C (968°F), and the properties of the feedstock used are as follows: the density is 912 Kg/m3, the carbon residue is 4.4 wt%, nickel (Ni) is 7.9 μg/g, and vanadium (V) is 6.8 μg/g. Before the ACE test, the proprietary catalysta and the reference catalysts are treated at 800°C (1,472°F) and 100% steam for 17 hr. As shown in FIG. 3, under the same C/O, the authors’ company’s new catalysta shows a noticeable boost in C4 olefinicity of > 3%, while the total yield of light cycle oil (LCO) and slurry decreased by 1%–2% compared to the reference catalyst.  

FIG. 3. ACE testing results of the authors’ company’s catalyst^a.  

Design and development of the proprietary additive^b. Compared with the catalyst^a, the authors’ company’s additive^b is much more flexible and can meet the needs of refineries that are quickly responding to market demands. Two issues must be addressed by the additiveb: 

• Improving the stability and activity of isomerization materials to maximize butylenes. 
• Optimizing the physical properties of the additive^b to match the main FCC catalyst synergistically. 

A high-stability isomerization material different from ZSM-5 zeolite has been designed and prepared, as shown in FIG. 4. Compared to conventional isomerization materials, the optimized isomerization material exhibits an increased mesopore volume by 40%. After treatment at 800°C (1,472°F) with 100% steam for 17 hr, its activity is enhanced by 24% compared to conventional materials, and the retention of specific surface area is higher before and after hydrothermal treatment. In addition, a high-stability metal sol with an average particle size of 30 nm–50 nm has also been developed to improve the attrition resistance performance of the additiveb and enhance the synergistic effect between the matrix and the isomerization material, as shown in FIG. 5.  

FIG. 4. Properties of high-stability isomerization materials. 

FIG. 5. TEM images of metal sol. 

The proprietary additive^b based on high-stability isomerization materials, novel metal sol and advanced preparation technologies possesses the following characteristics: 

• Increased butylenes production and C4 olefinicity without compromising gasoline yield 

• Its physical properties could match the main catalyst performance according to FCCU requirements.  

Laboratory evaluation of the proprietary additive^b. The additive^b is blended with a commercial catalyst (used as a reference) at a certain ratio to obtain catalyst mixtures with additive^b proportions of 3%, 5% and 10%, respectively. Both the reference catalyst and the catalyst mixtures are treated under 100% steam at 800°C (1,472°F) for 17 hr before ACE test at 520°C (968°F). The properties of the feedstock used are as follows: the density is 919 Kg/m3, the residual carbon is 2.4 wt%, Ni is 3.8 μg/g, and V is 4.0 μg/g. The results are shown in FIGS. 6 and 7. Compared to the reference catalyst, when the authors’ company’s additive^b proportions are 3%, 5% and 10%, respectively, the butylenes yield (to feed) increased by 0.36%, 0.66% and 1.05%, the C4 olefinicity increased by 1.07%, 1.92% and 2.81%, the gasoline yield increased by 0.32%, 0.57% and 0.82%, and the LCO yield decreased by 0.71%, 1.09% and 1.83%, respectively. These results indicate that the additive^b exhibits excellent butylenes selectivity without compromising gasoline yield and possesses the capability to convert LCO. 

Commercial trials. The company’s catalysta and additiveb have been manufactured commercially, and their primary properties are listed in TABLE 1. These properties meet the requirements of FCCUs and can be adjusted according to the actual situation of the refinery. Since 2019, HBC series products have been successfully applied in eight commercial FCCUs.  

Commercial Trial 1. The first application for the company’s catalyst^a was at Refinery S, which sought to increase its FCC profitability by boosting butylenes production. The FCCU processes a mixed feedstock of hydrogenated vacuum gasoil (VGO) and hydrogenated residue. The catalyst^a replacement was performed steadily without abnormal loss. During the application, the proportion of hydrogenated residue in the mixed feedstock increased (the specific parameters are shown in TABLE 2), but the catalyst^a still performed well. When the storage of the catalyst^a in the unit reached 80%, the butylenes yield increased by 0.64%, and the C4 olefinicity increased by 3.1%. Additionally, the gasoline yield increased by 1.74%, the slurry yield decreased by 1% and coke selectivity improved. This demonstrates that the catalyst^a exhibits excellent butylenes selectivity and bottoms conversion. According to the refinery's estimates, the profit of the FCCU increased by $9.4 MM/yr (RMB 68 MM/yr). 

Commercial Trial 2. The FCCU of Refinery Y primarily processes atmospheric residue (AR) oil. Unit throughput was 45 tons (t)/hr with a reaction temperature of 529°C (984°C), a feed density of 900 kg/m3, and a carbon residue of 5.9%. The feed properties and the operating parameters remained basically unchanged before and after the application of the proprietary additiveb, as shown in TABLE 3.  

When the additive^b accounted for 5% of the system—although the change in LPG yield was relatively small (the yield increased by only 0.55%)—the butylenes yield (to feed) increased from 10.20% to 11.67% (an increase of 1.47%), the C4 olefinicity in LPG increased from 32.42% to 36.46% (an increase of 4.04%) and the C3 olefinicity decreased correspondingly, which is attractive for refineries seeking to improve the butylenes/propylene ratio. In addition, the gasoline yield increased by 0.71%, and the volume fractions of olefins in gasoline increased slightly, increasing RON by 0.2 units. The densities of LCO and slurry in the application are higher, indicating an improvement in the conversion depth. The key parameters of the product are shown in TABLE 3.  

Commercial Trial 3. A similar trial was conducted at Refinery Q, which primarily processes hydrogenated VGO. The changeover of the authors’ company’s additive^b in the unit reached 2.7%. Under the condition that the properties of feedstocks and operating conditions remain basically consistent (specific parameters are shown in TABLE 4), and despite accounting for only 2.7% of the catalyst inventory while increasing processing capacity, the additive^b still exhibited good performance. The product distribution showed an increase of 0.49% in LPG, an increase of 0.71% in butylenes, and an increase of 0.24% in gasoline, while both LCO and slurry yields were reduced. Additionally, increasing the dosage of the additive^b could potentially result in even better outcomes.  

These commercial trials have demonstrated that the HBC technology performs well with a variety of processing feedstocks. It can increase butylenes production without compromising gasoline yield, showcasing its exceptional capabilities in improving butylene selectivity, enhancing LCO conversion and upgrading bottoms. Furthermore, the HBC catalyst^a and additive^b do not affect the stable operation of the FCCU. 

Takeaway. Driven by the continuous growth in demand for butylenes, the proprietary HBC technology, which integrates novel catalytic materials with advanced meso-macropore matrix, has been developed. It is adaptable to various processing feedstocks and exhibits high butylenes selectivity, enabling an increase in butylenes production without compromising gasoline yield, while also possessing LCO conversion capability. In an FCCU processing AR, the additive^b has improved the butylenes yield by 1.47% and the C4 olefinicity in LPG has increased by 4.04%.  

NOTES 

^a Sinopec’s HBC-A catalyst 

LITERATURE CITED 

1 Tanimu, A., G. Tanimu, H. Alasiri and A. Aitani, “Catalytic cracking of crude oil: Mini review of catalyst formulations for enhanced selectivity to light olefins,” Energy& Fuels, Vol. 36, 2022. 

2 Xu Y., Chemistry and process of catalytic cracking, China Science Publishing & Media Ltd.(CSPM), 2013. 

^b Sinopec’s HBC-B additive 

The Authors

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