Industrial Application of MacroCat-201S Catalyst with Low Steam–Oil Ratio in Large-Scale Styrene Unit

Abstract

Styrene production primarily relies on ethylbenzene dehydrogenation catalysts, with increasing performance demands as styrene units scale up. This paper presents the industrial application of the MacroCat-201S ethylbenzene dehydrogenation catalyst at the 350,000 tons/year styrene plant of Liaoning Bora LyondellBasell Petrochemical Co., Ltd. The catalyst, primarily composed of potassium ferrate, demonstrates excellent thermal stability and mechanical strength, ensuring long-term stable operation under low steam–oil ratios (1.0). Over a 36-month application period, the MacroCat-201S catalyst maintained high conversion rates and selectivity, with minimal catalyst deactivation. It also showed good crush resistance, and the reactor pressure drop remained low, indicating its potential for long-term efficient operation in styrene production. This paper further examines the influence of process parameters such as the steam–oil ratio and reaction temperature on catalyst performance and suggests strategies for optimizing catalyst usage in industrial applications. This study concludes that the MacroCat-201S catalyst significantly improves the reaction efficiency, reduces energy consumption, and shows promising potential for industrial use.

1. Introduction

Styrene is a basic organic chemicals, ranking fourth globally in production volume, behind polyvinyl chloride (PVC), ethylene oxide, and dichloroethane [1,2,3]. It is a key monomer in the production of synthetic rubbers and plastics, and is widely used in the manufacturing of styrene-butadiene rubber (SBR), polystyrene (PS), and expandable polystyrene (EPS), as well as being copolymerized with other monomers to produce engineering plastics like ABS and SAN resins.

In recent years, China has become the largest producer of styrene globally. As of 2023, the global styrene production capacity is between 44 and 45 million tons, with China accounting for 22–24 million tons, approximately 45–50% of global production [4]. Most of the new large-scale styrene plants currently under construction are located in China, with the largest single unit being the 800,000-ton-per-year styrene plant at Sinopec Guangdong, Jieyang Petrochemical.

The main production methods for styrene include the ethylbenzene catalytic dehydrogenation method and the ethylbenzene oxidation coproduction method (PO/SM coproduction process) [2]. Among these, the ethylbenzene catalytic dehydrogenation method is the most widely used, accounting for approximately 85% of global styrene production. This method, which produces styrene through the high-temperature dehydrogenation of ethylbenzene, is relatively simple, is cost-effective, and remains the dominant method for styrene production worldwide. The PO/SM process, in contrast, coproduces styrene and propylene oxide, and, while it produces two high-value chemicals simultaneously, it is generally more suited to integrated chemical companies, primarily companies in Asia and North America, and holds a smaller market share overall.

The dehydrogenation of ethylbenzene to styrene mainly adopts the adiabatic dehydrogenation process, with typical representatives being the UOP/Lummus and Fina/Badger technologies. Both use superheated steam as the heat carrier, which is mixed with vaporized ethylbenzene and undergoes catalytic adiabatic dehydrogenation in a fixed-bed reactor. After the reaction temperature drops, heat exchange is carried out through an intermediate heat exchanger, which is followed by adiabatic dehydrogenation in a second fixed-bed reactor. The Lummus process employs azeotropic distillation, utilizing the heat from the crude styrene column to evaporate the ethylbenzene, thereby reducing the consumption of steam and cooling water. The Badger process uses a dual-column pressure-swing energy-saving technology, which enables the self-circulation of heat from the crude styrene column, further reducing the consumption of steam and cooling the water, resulting in relatively low overall energy consumption and a strong competitive advantage. In addition, a direct heating unit (DHU) technology has been developed for use in the Badger process which uses direct fuel heating for the effluent from the first reactor, allowing the steam–oil ratio (S/O) to be reduced to 0.85 (weight ratio).

The ethylbenzene dehydrogenation process typically requires a large amount of superheated steam, leading to higher energy consumption in the system. In the past, the operating S/O of such units was generally above 1.30, falling within the medium-to-high range. In the last decade, with the scaling-up of styrene plants, there have been higher demands on catalysts, requiring them to operate under extremely low S/Os to achieve energy savings while maintaining a longer service life [4]. Newly built large-scale styrene units typically operate under S/Os between 1.0 and 1.25.

Commercialized catalysts are divided into low S/O catalysts and medium-to-high S/O catalysts. Low S/O catalysts generally operate within a S/O range of 1.25–1.0, while medium-to-high S/O catalysts typically operate with ratios greater than 1.3. In general, catalysts designed for medium-to-high S/Os experience rapid deactivation when operating under low S/O conditions, failing to meet the service life requirements of the plant. Conversely, low S/O ratio catalysts have lower conversions compared with the medium-to-high S/O catalysts when operated under high water-to-oil conditions, making them economically unviable.

The MacroCat-201S ethylbenzene dehydrogenation catalyst developed by Suzhou Toreto New Material Co., Ltd. maintains excellent stability under low S/O conditions. It also performs comparably to commonly used medium-to-high S/O catalysts under high S/O conditions, making it suitable for both low and medium-to-high S/Os. Its operating S/O range is broad. Since September 2020, it has been successfully applied in a 350,000 tons/year styrene unit at Liaoning Bora LyondellBasell Petrochemical Company. With over three years of service, the catalyst has demonstrated excellent performance, marking a significant advancement in catalyst technology for large-scale styrene production.

Physicochemical Properties of MacroCat-201S Catalyst

The MacroCat-201S catalyst primarily consists of potassium ferrate, which is synthesized using iron oxide as the main raw material. After a small amount of co-catalysts and porosity agents is added, the catalyst is produced through shaping, granulation, and calcination processes. The final product is in the form of gray-brown extruded bars.

The main physicochemical properties of the catalyst are shown in

Table 1. MacroCat-201S physicochemical properties.

Property	Specification
Shape	Extruded bar
Diameter	3 ± 0.4 mm
Length	5–15 mm
Bulk Density	1.3–1.5 kg/L
Specific Surface Area	1–3 m2/g
Mechanical Strength	≥24 N/mm
Iron Oxide	50–80% wt%
Potassium Oxide	10–25% wt%
Cerium Oxide	5–20% wt%
Molybdenum Oxide	0.1–5% wt%

:

2. Industrial Installation

2.1. Process Flow

The 350,000 tons/year styrene plant of Liaoning Bora LyondellBasell Petrochemical Co., Ltd. adopts the two-stage negative pressure adiabatic dehydrogenation reaction patented technology from Changzhou Ruihua Company. The specific process flow is as follows.

The main steam is heated in furnace oven A and then enters the intermediate heat exchanger E300, which is used to heat the effluent from the first reactor. The cooled steam is then heated in furnace oven B. The mixture from the first reactor outlet is heated to the desired reaction temperature before entering the second reactor to produce the dehydrogenation product. The dehydrogenation product is preheated in a four-section heat exchanger, where the ethylbenzene/first-stage steam mixture is heated. The preheated ethylbenzene/first-stage steam mixture is then mixed with the main steam and enters the first reactor.

A two-reactor system operating under vacuum adiabatic conditions is typically used to achieve a higher overall conversion. The initial inlet temperature of the first reactor is generally 620 °C, while the second reactor’s inlet temperature is typically 620–625 °C.

After the ethylbenzene feed undergoes dehydrogenation in the first reactor, the reaction temperature drops to around 535 °C, with a conversion of about 40%. The reaction effluent then passes through an intermediate heat exchanger, where it is reheated to 620–625 °C before entering the second reactor for further dehydrogenation. The second reactor also achieves a conversion of about 40%, resulting in a cumulative total conversion of 64% after both stages.

To maintain high selectivity, the conversion is generally controlled at around 64%. As the catalyst deactivates over time, the reaction temperature is gradually increased to sustain the conversion, until it reaches the end-of-run (EOR) temperature of 640–645 °C. The catalyst lifespan is designed to be 30 months.

The process flow diagram is shown in Figure 1.

2.2. Equipment Design Parameters

2.2.1. Ethylbenzene Purity

The quality of the ethylbenzene feedstock is crucial for maintaining stable operation and ensuring a high reaction efficiency in the dehydrogenation process. The detailed composition of the ethylbenzene feed is provided in

Table 2. Ethylbenzene composition.

Ethylbenzene Composition	wt%
EB	99.22
Benzene	0.04
Toluene	0.51
M-xylene	0.01
Styrene	0.19
Cumene	0.02

:

The utilization of high-purity ethylbenzene (99.22 wt.%) ensures minimal interference from impurities, allowing for optimal performance of the catalyst during dehydrogenation.

2.2.2. Stream Flow Rate

Proper control of the feed and steam flow rates is essential for maintaining the heat balance, reaction efficiency, and overall plant stability.

Table 3. Stream flow-rate parameters.

Component	Flow Rate (kg/h)
EB designed value	72,453
Maximum EB	79,700
Primary steam	28,028
Main steam	49,418
Total steam	77,446
Maximum steam	100,670

summarizes the key flow-rate parameters for the ethylbenzene and steam streams.

The plant is designed to handle variable operating conditions, with the capacity to accommodate maximum flow rates during peak production.

2.2.3. Operation Parameter

The plant operates using a two-reactor system, with each reactor carefully designed to maximize the conversion of ethylbenzene to styrene while maintaining thermal and pressure stability. The operational parameters are listed in

Table 4. Design operational parameters.

		1st Reactor	2nd Reactor
Inlet temperature (SOR/EOR)	°C	620/640	625/645
Outlet temperature (SOR/EOR)	°C	533.6/558	568.5/595
Inlet pressure	kPaA	52	41
Outlet pressure	kPaA	47	36
S/O (SOR/EOR)		1.05/1.25

SOR—start of run; EOR—end of run.

.

The steam–oil ratio is a critical parameter that directly influences the catalyst performance, reaction efficiency, and by-product formation. The range of 1.05–1.25 reflects a focus on energy efficiency and operational flexibility [5].

2.2.4. Catalyst Loading and Reactor Configuration

The reactors are loaded with a total of 260 cubic meters of MacroCat-201S catalyst, with an effective space velocity of 0.4 h⁻¹ with ethylbenzene as the feedstock. This configuration ensures sufficient contact time between the feedstock and the catalyst, promoting efficient conversion under low steam–oil ratio conditions.

3. Catalyst Performance

3.1. Catalyst Calibration

To better understand the operational performance of the MacroCat-201S (Toreto, Suzhou, China) catalyst, Liaoning Bora LyondellBasell Petrochemical Co., Ltd. (Panjin, China). conducted a catalyst calibration 8 months after the plant began operation. This calibration was essential for evaluating the catalyst’s stability, conversion rates, selectivity, and response to variations in operating conditions such as the flow rate, temperature, and pressure. The results of this calibration provide valuable insights into the catalyst’s long-term performance and reliability.

The calibration data, which includes critical parameters such as the steam flow, reactor temperatures, and pressure drops, are summarized in

Table 5. Calibration results.

No.	Item	11 May	12 May	13 May
1	Main steam flowrate FIC_3001 (kg/h)	59,024	59,372	59,250
2	First reactor inlet temperature °C	619.9	620.6	620.5
4	First reactor outlet temperature °C	534	534.1	533.8
5	First reactor inlet Pressure kPa	−47.79	−48.94	−49.4
6	First reactor outlet Pressure kPa	−53.02	−54.2	−54.5
7	First reactor Pressure drop kPa	5.13	5.44	5.0
8	Second reactor inlet temperature °C	620.7	621.5	621.5
9	Second reactor outlet temperature °C	562.4	562.7	562.4
10	Second reactor inlet Pressure kPa	−59.23	−60.8	−60.83
11	Second reactor outlet pressure kPa	−65.31	−67.3	−67.28
12	First reactor Pressure drop kPa	6.20	6.63	6.50
13	EB flow rate t/h	76.0	76.5	76.6
14	Primary steam feed rate (t/h)	25	25	249
15	S/O wt/wt	1.15	1.15	1.15

.

3.2. Analysis Results

The calibration also included an analysis of the oil–water separator, which helps to monitor the composition of by-products and assess the catalyst’s selectivity. The sampling results, summarized in

Table 6. Sampling analysis results.

Time	11 May	12 May	13 May
	wt%	wt%	wt%
Benzene	0.96	0.93	0.89
Toluene	1.26	1.31	1.67
Ethylbenzene	36.99	36.64	36.34
Styrene	60.4	60.79	60.64
α-Methylstyrene	0.03	0.03	0.03
Cumene	0.0031	0.0029	0.0036
Heavier	0.27	0.21	0.37
Conversion %	64.29	64.75	64.56
Selectivity %	97.6	97.26	97.27

, provide detailed insights into key components such as the concentrations of benzene, toluene, styrene, and ethylbenzene. Compared to the styrene concentration at the second reactor outlet, the concentration in the oil–water separator was slightly lower. This is primarily due to the introduction of ethylbenzene rinse, which diluted the styrene concentration in the stream.

The conversion rate and selectivity values, measured at the second reactor outlet, remained high throughout the calibration period, with an average conversion rate exceeding 64% and a selectivity remaining above 97%.

3.3. Long-Term Operation

During its use, the MacroCat-201S catalyst underwent three shutdowns and multiple load adjustments. Overall, the unit maintained stable operation. The steam–oil ratio was controlled at 1.2, the average conversion rate was kept at 64%, and the styrene selectivity remained above 96.3%.

3.3.1. Reaction Temperature

The dehydrogenation of ethylbenzene is an endothermic reaction, and the reaction temperature significantly impacts the process, affecting the reaction rate, selectivity, and catalyst lifespan [6].

• Increased reaction rate at higher temperatures: Within the temperature range of 580–650 °C, increasing the temperature accelerates the reaction, improving the conversion rate. However, excessively high temperatures may trigger side reactions, reducing efficiency;
• Effect of temperature on selectivity: Higher temperatures may promote side reactions (e.g., ethylbenzene cracking and coke formation), reducing the styrene yield and increasing catalyst deactivation. Therefore, strict temperature control is needed to maintain high selectivity;
• Catalyst deactivation at high temperatures: Elevated temperatures accelerate catalyst deactivation, particularly through coke formation and potassium ion loss. As the temperature rises, hydrogen production increases, enhancing reducing properties that further damage the catalyst’s active sites.

To maintain the conversion rates and styrene yield, the reaction temperature is gradually increased over time. A slow increase in temperature typically indicates slower catalyst deactivation and better stability.

For every 1 °C increase in temperature, the conversion rate increases by approximately 0.4–0.5%, while the selectivity decreases by 0.02–0.03%.

Figure 2 shows the temperature variation curves for the first and second reactors over 36 months. After activation, the reactor inlet temperature was initially 610 °C gradually increasing to 625 °C during the later stages of operation. From day 200 to day 1000, the temperature remained stable at around 620 °C, demonstrating excellent stability. The MacroCat-201S catalyst exhibits a very low deactivation rate. After 36 months of operation, the reaction temperature remains at 620–625 °C, well below the typical end-of-run (EOR) temperature of 640–645 °C. This indicates that the catalyst still has substantial remaining activity, and its total lifespan is expected to reach at least 4 years.

3.3.2. Steam–Oil Ratio S/O (Steam–Ethylbenzene Mass Ratio)

Steam plays a critical role in the ethylbenzene dehydrogenation process [7,8,9]:

• Molecular addition reaction: Ethylbenzene dehydrogenation is a reaction that increases the number of molecules, where ethylbenzene undergoes dehydrogenation to form styrene and hydrogen gas (H₂). Reducing the reaction pressure favors styrene formation, and steam helps to drive the reaction forward by lowering the partial pressure of the hydrogen;
• Heat carrier: Superheated steam acts as a heat carrier, providing the necessary energy for the dehydrogenation reaction;
• Coke removal: Steam effectively removes coke deposits from the catalyst surface;
• Inhibition of over-reduction: Steam inhibits the excessive reduction of the catalyst’s active components.

The steam–oil ratio (i.e., the steam–ethylbenzene mass ratio) plays a key role in the dehydrogenation reaction, directly affecting the reaction efficiency, selectivity, catalyst performance, and product distribution.

Excessive steam–oil ratio: Excessive steam increases the energy consumption and leads to higher steam consumption at elevated temperatures.

Insufficient steam–oil ratio: A low steam-to-oil ratio significantly increases the generation of by-products such as benzene and toluene, reducing the selectivity and increasing the material consumption. Moreover, a lower steam–oil ratio enhances the reducing atmosphere within the reaction system, which may damage the catalyst’s active sites, cause potassium ion loss, accelerate catalyst deactivation, and lower conversion rates.

Earlier styrene units typically operated with a steam–oil ratio above 1.3, which is considered a medium-to-high water ratio. However, modern large-scale styrene units, designed for improved energy efficiency, commonly adopt a low steam–oil ratio between 1.0 and 1.25. Figure 3 illustrates the variation in the steam–ethylbenzene mass ratio over time.

As shown in Figure 3, during the 36-month operating period, the steam–ethylbenzene mass ratio remained around 1.2, indicating that the MacroCat-201S ethylbenzene dehydrogenation catalyst can operate over a long period under low steam–oil ratio conditions.

3.3.3. Ethylbenzene Feed Load

Figure 4 shows the variation in the ethylbenzene feed load over time. In this 350,000-ton/year styrene plant, the full-load ethylbenzene feed rate is 72.5 t/h, and the average ethylbenzene feed load throughout the entire operating period is 98%. As shown in Figure 4, during the first 200 days, due to an alignment issue at the connection between the first heat exchanger of the quadruple heat exchanger and the reactor (which was higher than the supporting cement-steel frame), the plant operated at an 80–85% load for safety. After a maintenance shutdown of approximately 10 days, the unit resumed operation. During the period from day 235 to day 450, the load was increased to 110%, indicating that the catalyst could operate stably for extended periods under high-load conditions. The average load for the entire operating period was 98.2%.

3.3.4. Reactor Pressure Drop Variation

Ethylbenzene dehydrogenation is an increment molecular reaction, and lowering the pressure of the reaction system helps improve the conversion rate. Production practices show that, under constant conditions, each 10 kPa reduction in pressure can increase the ethylbenzene conversion by approximately 2%. The lower the pressure drop is across the catalyst bed, the more favorable the reaction conditions. Therefore, most industrial ethylbenzene dehydrogenation processes operate under vacuum conditions to shift the reaction equilibrium toward higher ethylbenzene conversion while minimizing side reactions. The frequency of startup and shutdown operations, as well as adjustments to process parameters during production, significantly impacts the pressure drop across the catalyst bed [10].

Ethylbenzene dehydrogenation catalysts need to have good mechanical strength to withstand prolonged exposure to large amounts of steam. If the catalyst has low mechanical strength and poor abrasion resistance, it is more likely to break and disintegrate, leading to an increased pressure drop when reactants pass through the catalyst bed, which shortens the plant’s operating cycle.

Figure 5 shows the variation in the pressure drop (dP) across the first and second reactors over time. As seen from the figure, at the end of the 36-month operating cycle, the pressure drop in the first reactor was 8 kPa, while, in the second reactor, it was 12 kPa. The sustained low overall pressure drop throughout the operating period indicates that the MacroCat-201S catalyst has good crush resistance and abrasion resistance under low steam–oil ratio conditions.

3.3.5. Conversion Rate and Selectivity

Based on the second reactor outlet, the catalyst maintained a high conversion rate throughout the entire operating cycle, with an average conversion rate exceeding 64%. Figure 6 shows that, during the early stages of operation, the selectivity was greater than 97.2%. As the catalyst usage time increased, the selectivity slightly decreased, eventually stabilizing at 96.3%. Nevertheless, the catalyst still maintained excellent selectivity throughout the entire operational period.

3.3.6. Variation in Benzene and Toluene in Dehydrogenation Liquid Products

Benzene and toluene are the main by-products of the ethylbenzene dehydrogenation reaction. Benzene primarily originates from the high-temperature thermal cracking of ethylbenzene and styrene, while toluene mainly results from the cracking of styrene. Figure 7 shows that throughout the entire operating cycle, the production of toluene remained stable, averaging approximately 1.1–1.2%. As the reaction temperature increased, the amount of benzene produced gradually rose, reaching about 1.3% in the later stages of operation, surpassing the production of toluene.

4. Conclusions

In the 350,000 tons/year styrene plant at Liaoning Bora LyondellBasell Petrochemical Co., Ltd., the MacroCat-201S catalyst demonstrated excellent performance and stability throughout the entire operating cycle. Under low steam–oil ratio conditions, the catalyst maintained a high ethylbenzene conversion rate, with an average conversion rate exceeding 64%. Both the reaction temperature and selectivity were well-controlled. Initially, the reaction temperature was 610 °C, and at the end of the cycle, it reached 625 °C. After the catalyst reached its steady-state phase, the reactor inlet temperature stabilized at approximately 620 °C, demonstrating the catalyst’s exceptional stability. During the catalyst’s usage, the steam–oil ratio and ethylbenzene feed load were effectively controlled, enhancing the reaction efficiency. The steam–ethylbenzene mass ratio was maintained in the range of 1.0–1.25, effectively suppressing by-product formation while maintaining low energy consumption. In terms of the feed load, the catalyst was able to run stably under high-load conditions for extended periods, exhibiting good adaptability and stability.

The catalyst’s crush resistance was also validated, as the pressure drop in the first and second reactors was 8 kPa and 12 kPa, respectively, throughout the entire operating cycle. This demonstrates the catalyst’s durability and excellent mechanical strength under prolonged steam exposure. Additionally, the generation of by-products such as benzene and toluene was effectively controlled. While the amount of benzene increased with the rise in the reaction temperature, it remained within a reasonable range during the entire operating cycle.

Overall, the successful application of the MacroCat-201S catalyst in the studied large-scale styrene plant not only lays the foundation for the industrial application of domestic catalysts but also provides valuable insights for catalyst selection and optimization in other styrene production units.