A brief overview of isobutane butylene alkylation development

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History of alkylation catalysts: The alkylation reaction of isoparaffins with low-molecular-weight olefins is one of the important processes in petroleum processing. In this process, isoparaffins (isobutane) react with one or more olefins (propylene or butylene) in the presence of strong acidic catalysts to produce C7 or C8 compounds, namely gasoline. Such gasoline has advantages such as a high octane rating (RON 95–98), low sensitivity (the difference between RON and MON is generally ≤3), low vapor pressure, high heat of combustion, complete and clean burning, and no environmental pollution; it is therefore an ideal blend component for aviation gasoline and automotive gasoline. Especially with the ongoing deterioration of the ecological environment and the growing awareness among humans regarding environmental protection, as well as restrictions on the levels of aromatics, olefins, and vapor pressure in vehicle gasoline, alkylated oils have become an ideal component for new types of gasoline, which has led to increased attention being paid to their production. In 1930, H. Pines and V.N. Ipatieff from the American company UOP discovered during routine control analysis experiments that, in the presence of strong acids such as concentrated sulfuric acid, HF, BF3/HF, AlCl3/HCl, etc., isomeric alkanes and alkenes can undergo alkylation reactions [3]. This discovery changed the traditional view of alkanes as inactive substances, and it spurred extensive research on alkylation reactions, which progressed rapidly. Research on alkylation reactions entered the commercialization phase, and several catalysts suitable for industrial use were developed. In 1938, the world’s first alkylation reactor system using concentrated sulfuric acid as a catalyst was built and put into operation at the Bedton refinery of Humbert Oil Refining Company ； In 1942, the first alkylation unit using hydrofluoric acid as a catalyst was built and put into operation at Phillips Petroleum’s Bog refinery in Texas. Since then, thanks to the various advantages of alkylated oils, the alkylation process has seen rapid development; to date, hundreds of alkylation units are in operation around the world, and the alkylation reaction has become one of the main processes in petroleum processing. Although the alkylation process using sulfuric acid and hydrofluoric acid as catalysts has long been industrialized and continuously improved in practice, these two catalysts still present a series of inevitable problems in actual production. These include high construction costs, excessive acid consumption, strong corrosiveness, difficulty in separating the oil product from the catalyst, and challenges in treating waste acid. In particular, both methods tend to cause environmental pollution; hydrofluoric acid is highly toxic, and the operating costs are considerable. All these factors restrict the further expansion of alkylation production. Therefore, for many years people have been seeking new alternative catalysts and have done a great deal of work, but no viable industrial catalyst has yet been found. Research progress on alkylation catalysts: The sulfuric acid process generates large amounts of waste acid, leading to severe environmental pollution. Hydrofluoric acid is a highly volatile and extremely toxic chemical. In the event of a leak, it can cause serious harm to the production environment and the surrounding ecosystem; it also poses risks such as corroding production equipment. The challenge faced by the alkylation process is to meet stringent environmental protection requirements as well as the demand for clean gasoline. The most fundamental way to address these issues is to develop and use new, environmentally friendly solid acid alkylation processes to replace the current liquid acid alkylation processes. Therefore, the research and development of a new generation of solid acid alkylation catalysts and reaction processes has become an important and urgent issue in the field of petroleum refining research. Over the years, an important challenge in developing a new generation of solid acid alkylation catalysts and processes has been the fatal weakness of almost all solid acid catalysts, which experience rapid deactivation during the alkylation reaction. Overcoming this issue is key to researching and developing new solid acid alkylation catalysts and processes. To avoid the harm caused by liquid acid alkylation catalysts such as sulfuric acid or hydrofluoric acid to the environment and production operators, scholars are working hard on the research and development of solid acid alkylation catalysts. Generally speaking, these solid acid catalysts can be divided into four categories: metal halide catalysts, molecular sieve catalysts, superacid catalysts, and heteropolyacid catalysts. Although liquid acid catalysts exhibit excellent activity and selectivity in alkylation reactions, they have been inevitably replaced by new, pollution-free catalysts due to a series of inherent drawbacks, particularly the severe environmental pollution they cause. Among the various catalysts mentioned above, heteropolyacid catalysts exhibit good catalytic activity, selectivity, and stability for alkylation. They also have the advantages of low volatility and low corrosiveness, which meet environmental protection requirements, making them a promising type of catalyst for alkylation. The main shortcomings of various catalysts lie in their poor activity stability and short lifespan; by combining catalyst design with reaction engineering principles, the development of non-steady-state reaction processes could potentially serve as an effective way to address the issue of easy deactivation of solid alkylation catalysts.