A Casual Discussion on Alkylation Techniques – Excerpt Sharing

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A Brief Discussion on Alkylation Technology 1. Introduction Alkylation technology was developed during World War II to meet the demand for aviation gasoline in times of war. After the war, it played an important role as gasoline octane ratings increased and the use of lead in automotive gasoline was banned. With the growing demands for environmental protection and cleaner production methods, alkylation technology has seen rapid development. While traditional and mature alkylation techniques continue to be improved, new types of cleaner production methods such as solid acid alkylation and ionic acid alkylation have also emerged. There are various types of alkylation technology; based on the phase state of the catalyst, they can be divided into two categories: liquid acid alkylation and solid acid alkylation. Liquid acid alkylation includes three techniques: hydrofluoric acid alkylation, sulfuric acid alkylation, and ionic acid alkylation. Due to the high acidity of the catalysts used in liquid acid alkylation, the reaction temperature is low, and the pressure required to maintain a liquid-phase reaction is also low. As a result, the alkylated oil produced has a high octane rating, but it presents safety and environmental risks； In solid acid alkylation, the catalyst has a lower acidity level, which requires higher reaction temperatures; as a result, the octane number of the resulting alkylated oil is lower. Additionally, the tendency for olefin polymerization increases, making it easier for the catalyst to become deactivated. However, this production method is safe and environmentally friendly. 2. Liquid acid alkylation technology 2.1 Alkylation using hydrofluoric acid The first companies to develop alkylation technology using hydrofluoric acid were UOP and PHLLIPS. The reaction conditions for these two technologies are essentially the same; the main difference lies in the reaction system: UOP uses forced acid circulation and internal regeneration techniques ； PHLLIPS employs two technologies of similar level: acid gravity circulation and acid recontact. However, since PHLLIPS’ technology uses gravity circulation for catalyst circulation, it avoids the use of rotating equipment in high-acid environments, thereby reducing acid leakage points and enhancing safety. In recent years, UOP acquired PHILLIPS’ alkylation technology and, by combining the advantages of both technologies, developed the AlkyPlus technology. This technology utilizes PHLLIPS’ original gravity acid circulation method and the design concepts of acid settlers, along with UOP’s isothermal reactor technology, to create a new reaction system that reduces acid inventory by 30% and improves the safety of the facility. The weakness of hydrofluoric acid alkylation technology lies in the fact that the hydrofluoric acid catalysts used are corrosive, volatile, and toxic. To enhance safety and environmental protection, in addition to detailed engineering specifications for facility design and the selection of equipment valves as proactive protective measures, the following passive measures are also employed: water curtains are used for isolation in the reaction area ； Use color-changing paint and industrial television at the areas prone to leakage ； A tool neutralization tank, a personal neutralization tank, eyewash stations, and full-body shower facilities are installed within the facility ； Equip operators with special protective clothing and gear ； There are strict procedures for various operations of the device ； Emergency measures for contact with hydrofluoric acid, as well as topical creams for the skin, are available. To meet increasingly stringent environmental requirements, UOP and PHLLIPS developed technologies aimed at enhancing the safety and environmental friendliness of hydrofluoric acid alkylation processes. The AlkyPlus technology resulting from the merger of these two companies incorporates the following techniques: (1) ReVAP vapor pressure reduction technology – Hydrofluoric acid is a gas at room temperature; this technology allows the volatility of hydrofluoric acid to be reduced by adding certain substances, thereby cutting the volatility of leaked hydrofluoric acid by over 90%. (2) Multi-point feeding technology – Olefins are divided into multiple streams and fed from different locations within the reactor or lift pipe; this approach enables the reduction of isobutane circulation volume while maintaining the desired alkene-to-olefin ratio, thus reducing the amount of acid present. (3) IMP acid management technology – In the event of damage to the settler, this technology uses programmed controls to quickly transfer the hydrofluoric acid and hydrocarbons stored there to intact storage containers, thereby preventing large-scale leaks of hydrofluoric acid. By utilizing these new technologies, the risk of environmental pollution is effectively reduced, bringing it to a level acceptable to the American public and environmental agencies. 2.1 Sulfuric acid alkylation – Sulfuric acid alkylation is a process that uses liquid sulfuric acid as a catalyst. Due to the low reaction temperature, sulfuric acid has high viscosity at such temperatures, so mixed approaches are necessary to ensure good contact between the acid and the hydrocarbons. Different mixing methods have given rise to various patented technologies; notable examples include DuPont’s STRATCO technology and LUMMUS’s CDAlky technology. The reactor used in STRATCO technology is a horizontal tubular heat exchanger equipped with impeller agitation, with mechanical stirring being used to mix the acid and hydrocarbons ； The reaction temperature is 5–8°C, and indirect heat exchange is used to remove the heat generated during the reaction ； Before reaching the distillation unit, the reaction products must undergo acid washing, alkali washing, and water washing ； The processing capacity of a single reactor is 50–100 kt/a ； The technology is mature, with many industrial units in operation. The CDAlky technology involves a vertical reactor equipped with special packing; acid and hydrocarbon mixing is achieved through the combination of a distributor and packing, without the need for rotating equipment ； The reaction temperature is -3°C, and the heat of reaction is removed using hydrocarbon auto-vaporization ； The reaction products do not require any washing before entering the fractionation unit ； The processing capacity of a single reactor can reach 380 kt/a. The first company to receive this technology transfer was Ningbo Haiyue New Materials Co., Ltd.; its facility has a capacity of 600,000 tons per year and came online in 2013. Both of the aforementioned technologies make use of waste acid regeneration techniques to address the problem of large amounts of waste acid generated by alkylation units. Waste acid regeneration systems are capable of producing liquid sulfuric acid directly without the need for sulfur, thereby changing the current situation in refineries where sulfur recovery only results in sulfur production and increasing the flexibility of sulfur recovery processes. In China, however, due to the traditional patterns of sulfuric acid production, these technologies have not yet been put to use. 2.3 Ionic acid alkylation: This technique was developed by the University of Petroleum (Beijing). It utilizes a special formulation of non-aqueous solvents together with a liquid-phase catalyst formed from aluminum trichloride, which helps to avoid the corrosion problems associated with traditional aluminum trichloride aqueous solutions ； An adiabatic tubular reactor is used ； The separation of the catalyst from the hydrocarbons is achieved using centrifugal separation equipment. This process has already been successfully applied in the Deyang Chemical Industry in Shandong Province. Sinopec’s Jiujiang branch has also signed an agreement with China University of Petroleum to build an ionic acid alkylation plant with a capacity of 300,000 tons per year. 3. Solid acid alkylation technology: In order to reduce environmental pollution during the production process, many large oil companies and research institutions around the world have been working on the development of solid catalysts. Notable examples include LUMMUS’ AlkyClean process, UOP’s Alkylene and Inalk processes, TOPSOE’s FBA process, and RIPP’s solid acid alkylation process. 3.1 LUMMUS’ AlkyClean process: The AlkyClean process makes use of multiple liquid-phase fixed-bed reactors (usually three reactors). When one reactor needs to be taken out for regeneration, a backup reactor is brought online. Among the three reactors, one is used for gradual regeneration, one for the alkylation reaction, and one for high-temperature regeneration. These reactors operate in turn, ensuring continuous operation of the reaction process. This process has been successfully demonstrated on an industrial scale at Fortum’s refinery in Finland. In December 2015, another solid acid alkylation plant, licensed by LUMMUS and Albemarle, was put into operation at Zibo Haiyi Fine Chemicals, a subsidiary of Shandong Hui Feng Petrochemical Group. 3.2 UOP’s Alkylene process: The Alkylene process utilizes a single liquid-phase reactor that operates continuously. The reactor consists of a container along with a lift pipe located at its center. The catalyst and raw materials enter the lift pipe from the bottom to carry out the alkylation reaction. The reaction products and catalyst flow out from the upper end of the lift pipe into the space outside the reactor. Due to gravity, the catalyst flows downward to the lower part of the lift pipe, thus enabling catalyst recycling ； In the annular space between the riser and the vessel, isobutane saturated with hydrogen is introduced, thereby creating a regeneration and washing zone inside the vessel. From the upper part of this regeneration and washing zone, a stream of catalyst is drawn out and sent to an external regeneration washer. The regeneration medium remains isobutane saturated with hydrogen; only the regeneration temperature is higher than that used inside the vessel. The regenerated catalyst then flows to the bottom of the riser. There are no reports of this process being used in any industrial installations.

3.3 UOP Inalk Process
The Inalk process is referred to as an indirect alkylation technique. Strictly speaking, it is not an alkylation process, but it still converts isobutane and all olefins present in the C4 hydrocarbons into C8 gasoline fractions, using solid catalysts. The actual reactions that take place include isobutane dehydrogenation, oligomerization of C4 olefins, and olefin saturation. This process can convert all C4 hydrocarbons into alkylated oil through stages of n-butane isomerization, isobutane dehydrogenation, and butene polymerization and hydrogenation. The octane number of the alkylated oil after hydrogenation is very high; when resin catalysts are used, the RON can reach 99, while with solid phosphoric acid catalysts, it can reach up to 101. This process is particularly suitable for modifying MTBE production facilities. The first industrial plant using this technology was built in Japan in 2001, and to date, five such plants are in operation, one of which is a modified facility.

3.4 TOPSOE’s FBA Process
The reactor used in the FBA process is of the fixed-bed type, with solid carriers loaded with liquid superacids inside it. These carriers are known as supported liquid phase catalysts. It is the liquid superacids that actually carry out the catalytic action. As the reactants flow downward, active zones containing acids are formed within the catalyst bed. Above these active zones lies a region with lower acid concentration; in this region, olefins react with acids to form esters. Esters do not adhere easily to the catalyst and can therefore flow along with the reactants to the next zone ； The middle part is the reactive chamber; the esters that flow in from the upper part come into contact with isobutane here, and under the action of a strong acid catalyst, an ester exchange reaction takes place, resulting in the formation of alkylated oil and acid ； The lower section is the acid absorption zone, where the acid is reabsorbed onto the solid carrier, thereby forming new active sites. As the reaction proceeds, these active sites move downward slowly; the acid carried away by the reaction stream is separated from the hydrocarbons and sent to the acid recovery system. The acid-soluble oils discharged from the reaction system at intervals are also processed in this acid recovery system to recover acid. All the acid recovered by this system, along with any additional acid added, is returned to the reactor to maintain an equilibrium of acid levels within it. This reaction system reduces the amount of liquid acid present, results in less acid-soluble oil being produced, and minimizes acid consumption. Since the acid is adsorbed onto the solid carrier, it will not evaporate even if the reactor is damaged. To date, there are no reports of industrial plants using this technology. 3.5 RIPP Solid Acid Alkylation: Since the 1990s, the Sinopec Research Institute of Petrochemical Technology (RIPP) has been conducting research on the processes and catalysts related to solid acid alkylation. It has completed pilot tests and laboratory-scale experiments, and in the past two years, industrial-scale trials of this technology have been carried out at the Yanshan branch in Beijing. It has been confirmed that this technology is ready for industrial application, and pilot projects are set to be launched soon at the Shijiazhuang Refining and Chemical Complex. 4. Conclusion: Looking at the development of alkylation technology, the main focus has always been on improving the cleanliness and safety of alkylation processes. Solid acids can help address these issues related to cleanliness and safety, but their use is limited by the current level of technological maturity ； The sulfuric acid alkylation process solves the problem of waste acid through its regeneration, but it increases capital costs ； The regeneration of alkylated waste acid using hydrofluoric acid is straightforward, but it is limited by the volatility and corrosiveness of hydrofluoric acid. Source: Alkylation Technology and Economics, Petroleum Processing Technology and Engineering