Selective Polymerization: A Solution to Refineries’ MTBE Concerns

 

On August 1, 2018, a promotional seminar on C4 olefin selective polymerization technology held in Shijiazhuang, Hebei, brought a breath of fresh air to the C4 industry chain. The C4 Olefin Selective Polymerization technology solution developed by the Sinopec Research Institute of Petrochemical Processes (hereinafter referred to as “RIPP”) was successfully applied at the Selective Polymerization Industrial Demonstration Unit of Sinopec’s Shijiazhuang Refining and Chemical Branch. The unit achieved a successful start-up on the first feed and produced qualified polymerized oil products. According to Li Mingfeng, Vice President of RIPP, this unit at the Shijiazhuang Refining and Petrochemical Branch is currently the only operational isobutylene selective polymerization unit in China designed for gasoline production. The successful operation of this unit provides a reference for the domestic refining and petrochemical industry in addressing the MTBE dilemma.

 

 

After years of dedicated research, the Shijiazhuang Research Institute has successfully developed selective isobutene polymerization-hydrogenation technology and non-selective butene polymerization-hydrogenation technology. These technologies can provide comprehensive technical solutions tailored to different scenarios for the retrofitting of refinery MTBE units and the effective utilization of C4 resources, while also offering a strong supplement to the octane rating of the gasoline pool. The mixed isomeric hydrocarbons produced by the cyclization-hydrogenation technology consist primarily of isooctane, which features high octane number and low vapor pressure (RVP). The production process is environmentally friendly, making it an ideal gasoline blending component.

 

 

The retrofit of this polymerization unit at Shijiazhuang Refining & Chemical achieved a 100% utilization rate of existing equipment. This technology features unique advantages in product pretreatment, reaction heat control, and product separation, and various approaches to product post-treatment were presented at the promotional seminar. The selective isomerization catalyst used in this technical solution is the KC110-type selective isomerization catalyst, independently developed and produced by KaiRui Environmental Technology Co., Ltd. (hereinafter referred to as “KaiRui Environmental”). This catalyst was successfully applied in 2016 in an identical selective isomerization unit at Indian Oil Corporation Limited (IOCL) and has a proven track record of industrial operation.

 

 

The technology adopted by Shijiazhuang Refining & Chemical offers the following advantages:

 

 

 

1

Wide Range of Feedstock Compatibility

 

This technology is suitable for using refinery C4 and chemical C4 as polymerization feedstocks. Based on the isobutylene content in refinery C4, it is divided into two types: Type I has an isobutylene content of 8%–10%, and Type II has an isobutylene content of 15%–20%. The isobutylene content in chemical C4 can range from 35% to 40%.

 

 

 

2

 

Tailored Solutions for Each Plant

 

Whether for new construction or retrofitting of existing facilities, the PetroChina Research Institute of Petroleum Technology (CPRIT) provides customized technical routes tailored to each plant’s specific needs. Leveraging its extensive experience in resin catalysts, KaiRui Environmental Protection has overcome foreign technical barriers in resin technology to provide catalysts that are perfectly matched to the process technology. For example, in an MTBE retrofit project requiring maximum retention of 1-butene, the isobutene conversion rate must exceed 99%, while the isomerization rate of 1-butene should be kept as low as possible. Through the optimized combination of multiple technologies—including polymerization, etherification, catalytic distillation, and cracking—we can provide technical solutions that meet customer requirements.

 

　

 

3

 

High Utilization Rate of Existing Equipment, Enhancing Economic Competitiveness

 

The utilization rate of existing equipment for this polymerization unit retrofit at the Shijiazhuang Refining and Petrochemical Branch is 100%. Through optimized process flows and design, calibration results indicate an energy consumption of 175.14 kg of standard oil per metric ton of polymerized oil.

 

　

 

4

 

A Powerhouse Technical Team

 

The success of this technology is inseparable from the collaboration of a powerhouse technical team. The Shijiazhuang Research Institute not only has a polymerization technology group that provides catalyst standards and technical solutions, but also a process engineering group that calculates material balances and assesses existing equipment utilization, a refined oil blending group that analyzes oil properties and provides blending solutions, a hydrogenation technology group that offers various hydrogenation schemes, a desulfurization technology group that develops desulfurization solutions for isomerization products, as well as KaiRui Environmental Protection, which has applied for and been granted a patent for the isomerization catalyst (Patent No. ZL201310429777.5). Through close collaboration, these technical teams provide enterprises with comprehensive solutions for MTBE unit retrofits and fuel blending.

 

 

Figure 1 shows CIC’s isomerization and hydrogenation technology solution using butene as feedstock.

 

 

 

Figure 1

 

Kairui Environmental Protection: Proactive Planning to Support MTBE Unit Transformation

 

In an interview with reporters, Zhang Yong, General Manager of Kairui Environmental Protection, stated that fully utilizing C4 resources to produce oxygen-free, high-octane gasoline blending components will be a key research and development direction under current ethanol-blended gasoline standards. Currently, the alkylation oil components most favored by refineries are C8 isomeric alkanes dominated by isooctane, which are free of olefins and aromatics and serve as ideal components for enhancing gasoline octane ratings. In the United States, alkylate oil accounts for a significant proportion of gasoline; in recent years, as part of the gasoline upgrading process in China, both PetroChina and Sinopec have been vigorously constructing direct alkylation units.

 

 

Zhang Yong told reporters that China’s refining industry currently relies on direct alkylation technology on a large scale, while indirect alkylation technology can utilize C4 olefins—particularly isobutene—to produce oxygen-free, high-octane gasoline blending components, effectively addressing the issue of isobutene utilization. As the use of MTBE has gradually been phased out overseas, foreign technologies in recent years have tended to focus on minor modifications to existing MTBE units. Under the action of resin catalysts, these units produce isooctene, which is then hydrogenated to generate high-octane isooctane products. Currently, isobutylene polymerization oil appears to be an ideal alternative to MTBE, as it facilitates the retrofitting of MTBE units and yields superior product performance. As a company whose core businesses include the transfer of MTBE process technology and the sale of MTBE resin catalysts, KaiRui Environmental Protection actively monitors global market trends and promptly develops new technologies and catalyst products. Since 2004, the company has been engaged in the research and development of polymerization catalysts, hydrogenation catalysts, as well as ETBE process technology and catalysts.

 

 

The KC110 series of resin catalysts developed by KaiRui Environmental Protection underwent long-term stability testing; during stability tests lasting up to 1,000 hours, the reaction conversion rate showed no significant change. In 2016, India’s IOCL conducted a global tender for its selective isomerization unit and ultimately selected KaiRui Environmental Protection’s isomerization resin catalyst. This marked the first time a domestically produced catalyst was applied in a C4 selective isomerization unit designed for petroleum product production; to date, two batches of catalyst procurement have been completed.

 

 

 

R&D Investment: Continuous Improvement and Proven Performance

 

 

 

Following the implementation of the ethanol-blended gasoline policy, the Research Institute of Petroleum Processing (RIPP) actively mobilized resources from all relevant parties. Through the efforts of several generations of researchers and in collaboration with the KaiRui Environmental Protection platform, the technology ultimately passed Sinopec’s evaluation and achieved industrial-scale application at the Shijiazhuang Refining and Chemical Branch.

 

 

At the promotional conference in Shijiazhuang, experts clarified that polymerization technology is not a low-threshold refining technology; producing qualified polymerization products cannot be achieved simply by retrofitting an MTBE unit, nor is there a single technical route that applies universally. While the isobutylene polymerization reaction is straightforward, controlling the reaction is key. The polymerization process is highly exothermic, prone to hot spots, involves numerous side reactions, and presents challenges in improving selectivity. The selective isomerization technology provided by the Shijiazhuang Research Institute of Petrochemical Technology incorporates numerous technical know-how. From a catalyst perspective, drawing on operational experience with identical units at India Petrochemicals, KaiRui Environmental Protection made further technical improvements to the isomerization catalyst, enhancing properties such as catalyst strength, temperature resistance, resistance to fouling, and selectivity. By introducing special positioning functional groups, the stability of the sulfonic acid groups was enhanced, thereby improving the catalyst’s temperature resistance; by adjusting the catalyst’s pore size and pore volume, and through experimental optimization and comparison, the most suitable pore structure was selected, resulting in a catalyst manufacturing process that achieves optimal selectivity and resistance to clogging; and by adding appropriate additives, the catalyst’s selectivity was further improved. Results from high-temperature stability tests lasting up to 150 days indicate that the KC110 polymerization catalyst exhibits excellent high-temperature stability and mechanical strength (see Table 1). Changes in exchange capacity and mechanical strength before and after evaluation were minimal, demonstrating that the catalyst meets the requirements for polymerization reactions.

 

 

 

First Domestic Production of Isomerization Oil: Homegrown Technology Shines

 

“In January of this year, Sinopec successfully completed the development of the C4 olefin isomerization technology process package. On March 15, based on our company’s idle MTBE unit, the project officially commenced construction. After two months, the project was successfully handed over to the client on May 15. After overcoming numerous technical challenges, feedstock was officially introduced for trial runs on June 25, and on July 2, the unit successfully produced qualified isooctene, marking the successful transition of Sinopec’s proprietary C4 olefin selective isomerization technology to the industrialization stage. This provides technical support for China’s refining and petrochemical industry in addressing MTBE unit retrofits and the deep processing of C4 olefins. Currently, the unit is operating smoothly. ” Qi Qingxuan, Director of the Development Planning Department at Shijiazhuang Refining & Chemical, provided an overview of the retrofit and operation of this MTBE unit.

 

 

According to reports, the unit was shut down in January 2016 and retrofitted into a selective polymerization pilot plant in May 2018. A schematic diagram of the process flow is shown in Figure 2. This retrofit utilized process technology developed by the Shijiazhuang Research Institute of Petroleum and Chemical Industry (SRI) and polymerization catalysts produced by Kairui Environmental Protection. By implementing effective control measures based on the polymerization mechanism, the retrofit maximized the conversion to high-octane trimethylpentene while controlling the conversion of n-butene, thereby meeting customer requirements. Advanced technology and high-quality catalysts have optimized the process flow and product design, resulting in lower utility consumption. This technology is suitable for retrofitting existing MTBE facilities and can be integrated with production units for alkylation, sec-butyl acetate, methyl ethyl ketone, and other products.

 

 

 

Figure 2

 

It is reported that the selective isomerization industrial demonstration unit utilizes an idle MTBE unit at the Shijiazhuang Refining and Chemical Plant, which was retrofitted into a C4 selective isomerization unit. The retrofit investment totaled 4.61 million yuan, including 2.67 million yuan for unit retrofitting and 2.04 million yuan for maintenance. The isomerization unit achieves an isobutene conversion rate of 85%–95%, with other butenes converted at a rate of 3%–5%; C8 selectivity is >90%, C8 selectivity is <8%, and the research-based octane number (RON) of the polymerization oil product ranges from 105 to 110. A comparison of the process parameters from the Shijiazhuang Research Institute of Petroleum Processing with similar international technologies is shown in Table 2.

 

 

 

According to Dr. Xia Yuecong of the Shijiazhuang Research Institute of Petroleum Processing, there are three potential routes for the subsequent processing of polymerization oil: S-zorb, full hydrogenation, and deep catalytic cracking (DCC). Among these, pilot-scale test results for the S-zorb route show that blending 10% polymerized oil reduces the sulfur content from 452 mg/L to 2 mg/L compared to 100% FCC gasoline, while the olefin saturation and n-alkane content remain essentially unchanged, and the isomer content increases, raising the RON by 0.4. The fully hydrogenated route yields gasoline with RON = 96, RVP < 15, induction period > 1,000, total sulfur < 0.3, and a dry point of 199–200°C. In the DCC route, the ethylene and propylene yield increased from 30% to 40%; high-octane gasoline accounts for up to 30%, with the remainder consisting of dry gas, coke, and other byproducts (primarily butene). The polymerization oil produced by the Shijiazhuang Refining and Chemical plant has been blended into gasoline at a rate of 2% since July 15. To date, 114 metric tons have been blended into the first batch and 50 metric tons into the second batch, for a total of 164 metric tons.

 

 

 

 

In his closing remarks at the promotional conference, President Li Mingfeng stated: “The imminent arrival of the ethanol-blended gasoline era poses a tremendous challenge to the viability of the vast majority of China’s MTBE units and the market prospects for isobutylene. Consequently, Sinopec has attached great importance to this issue. The Science and Technology Department and various business divisions of Sinopec swiftly organized units such as the Sinopec Research Institute to carry out a series of tasks related to standards, technologies, and solutions. After nearly a year of further optimization, including the selection of the best isomerization catalyst, we have finally presented a clearer and more comprehensive technical solution for isobutylene selective isomerization. This technology has successfully undergone its first start-up at the Shijiazhuang Refining and Chemical Company, and the produced fuels fully comply with national standards and meet usage requirements. We are confident that our selective isomerization technology will provide a safe and reliable option for the optimization and retrofitting of MTBE units, and offer strong technical support for the implementation of the national ethanol-blended gasoline policy!”