Development and Recent Advances in Alkylation Technology in 2016

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Development and Recent Advances in Alkylation Technology in 2016 2016-04-08 Alkylation is a process in which isobutane and olefins present in refinery liquefied gas react, under the action of catalysts, to produce alkylated oil, which serves as a component for gasoline blending. Due to its high octane rating, low vapor pressure, and absence of olefins and sulfur, alkylated oil is an ideal component for gasoline blending. Therefore, alkylation technology has received increasing attention from refining companies in recent years. In terms of production processes, the main alkylation methods currently used for the large-scale production of alkylated oils are the sulfuric acid method and the hydrofluoric acid method. Although these two methods yield high yields of alkylated oils with good selectivity, the sulfuric acid method results in large amounts of waste acid being released, causing severe environmental pollution ； Hydrofluoric acid is a highly volatile and toxic chemical; any leakage of it can cause serious damage to the environment and surrounding ecosystems. Furthermore, both processes face issues such as corrosion of production equipment. To overcome the significant drawbacks of liquid strong acids, such as their high corrosivity and serious hazards to human health, efforts have been ongoing both domestically and internationally in recent years to improve existing traditional technologies, and to develop new generations of solid strong acid alkylation catalysts and processes as alternatives to the current liquid acid alkylation techniques. Traditional liquid acid alkylation techniques: Currently, the conventional sulfuric acid and hydrofluoric acid alkylation processes are still primarily used for the production of alkylated oils. According to statistics, there are currently over 110 alkylation units using the sulfuric acid method worldwide, and around 120 alkylation units using the hydrofluoric acid method. Although the overall operation of hydrofluoric acid and alkyl sulfate plants differs, the reaction mechanisms of the two processes are extremely similar. In the 1960s, the number of alkylation units using sulfuric acid as a catalyst was three times that of those using hydrofluoric acid catalysts. From then on, the trend in alkylation technology shifted toward the use of hydrofluoric acid, before returning to the use of sulfuric acid. The two processes have developed over many years of competition with one another, each acquiring its own characteristics. 1) Alkylation with hydrofluoric acid: The technology for alkylating using hydrofluoric acid has been in use for over 60 years, during which time it has continued to be developed and improved. Compared to the sulfuric acid alkylation process, the hydrofluoric acid alkylation process requires less space, has a simpler design, and uses less catalyst. However, it also has its shortcomings, the most common of which is that the cost of separating isobutane, propane, hydrofluoric acid, and fluorine-containing compounds is higher than that of the sulfuric acid alkylation technology (with the exception of UOP’s two-reactor in-series process). Furthermore, this technology has an even more serious problem: hydrofluoric acid, as a toxic gas, spreads into the atmosphere; at low concentrations, it can irritate the eyes, skin, and nose ； High concentrations can be life-threatening. Patent holders for hydrofluoric acid alkylation: UOP and PHILLIPS (ConocoPhillips). The biggest problems with hydrofluoric acid alkylation are the volatility, corrosiveness, and toxicity of the hydrofluoric acid catalyst; as a result of restrictions imposed by the U.S. environmental authorities, this method is hardly used in new alkylation plants built in the past 20 years. 2) Alkylsulfonation technology: Although alkylsulfonation technology faces issues such as waste acid treatment and equipment corrosion, as the production of alkylated oils gains increasing attention, efforts are being made to improve this technology while simultaneously developing new ones. The main patent holders for sulfate-based alkylation processes at present include DuPont and LUMMUS. Among them, DuPont’s alkylation capabilities, based on its own technology, are the best in the world. DuPont possesses both the STRATCO sulfate alkylation technology and the MECS waste acid regeneration technology, and holds around 80% of the market share in the global alkylsulfate alkylation industry. In China, an example of the use of DuPont technology is CNOOC Huizhou Refining & Chemical Plant (with a capacity of 160,000 tons per year, operational since 2009); additionally, three other plants in China are scheduled to begin operation in 2016. Rums’ CDAlky sulfate process technology has also been widely used in China in recent years. Plants that have already been put into operation or are about to do so include: Shandong Shenchili (200,000 tons per year, commissioned in May 2013), Shandong Haiyue (600,000 tons per year, commissioned in July 2014), Guangxi Qinzhou Tianheng Petrochemical (200,000 tons per year, commissioned in April 2014), and Yuntianhua (240,000 tons per year, commissioned in 2016). Since the biggest issue with the sulfuric acid-based alkylation method is the treatment of waste acid, it is necessary to install waste acid regeneration units alongside the alkylation equipment, which results in higher investment and operating costs compared to hydrofluoric acid-based alkylation. Alternative alkylation techniques: Although researchers have continuously worked to improve the hydrofluoric acid and sulfuric acid alkylation processes, they have yet to resolve the underlying problems such as high construction costs, large acid consumption, strong corrosiveness, and the tendency to cause environmental pollution. Therefore, both domestically and internationally, efforts are being made to develop clean and safe alternative alkylation technologies, among which the most significant progress has been made in solid acid alkylation technology and ionic liquid alkylation technology. 1) Solid acid alkylation technology: Although traditional liquid acid alkylation technologies are already highly developed, their impacts on safety and the environment have spurred the development of safer and more environmentally friendly process technologies. Compared to liquid acid technology, solid acid alkylation features milder reaction conditions and easier regeneration; once the problem of olefin polymerization during solid acid alkylation is resolved, the properties of the gasoline produced by this method can be comparable to those of gasoline produced using liquid acids ； At the same time, solid acids do not possess the corrosiveness and potential hazards of liquid acids; they require no special materials for the equipment, and thus offer high process safety ； There are no negative issues associated with waste acid treatment in terms of environmental protection; therefore, in recent years many large oil companies and research institutions around the world have been working on the development of solid catalysts. Notable technologies include AlkyClean from LUMMUS Company, Alkylene and Inalk from UOP Company, and FBA from TOPSOE Company. Chinese research institutions such as the China Academy of Petroleum Sciences have also developed alkylated solid acid catalysts and related technologies, and industrial pilot tests were conducted at Shanghai Gaqiao Petrochemical and Beijing Yanshan Petrochemical in the past two years. This technology has now passed the technical evaluation by Sinopec. Rums’ AlkyClean process has a demonstration unit at Fortum’s refinery in Finland. In February 2015, Rums’ first solid acid alkylation plant with an annual capacity of 100,000 tons was constructed, put into operation at Hui Feng Petrochemical Group in Zibo, Shandong. Although progress has been made in solid acid alkylation technology, at present there are still certain obstacles to fully replacing traditional liquid acid technology with it; among these, the issue of catalyst deactivation/regeneration is the most difficult one to overcome. At the same time, a series of issues such as the adaptability of raw materials, the operational economy of the equipment, and the high reactivity and selectivity of solid acid catalysts also need to be addressed. 2) Ionic liquid alkylation technology: Ionic liquids have attracted considerable attention in recent years due to their combination of the highly reactive sites of liquid acids and the non-volatility of solid acids. In the past, poor selectivity and low yields limited the use of ionic liquid catalysts in the production of alkylated oils. Recently, a large amount of research has been focused on ionic liquid alkylation techniques. Companies and institutions such as Chevron and Shell, as well as China University of Petroleum, have carried out extensive research in this area. In the ion liquid alkylation technique, ion liquids are used as both solvent and catalyst, and this technique exhibits higher catalytic performance than sulfuric acid and hydrofluoric acid. Composite ionic liquid catalysts developed in recent years have shown great potential in alkylation production. CNPC is currently the only company to apply ion liquid alkylation technology on an industrial scale. This technology was developed by the Key Laboratory of Heavy Oils at China University of Petroleum. On September 29, 2013, a plant with an annual capacity of 120,000 tons for ion liquid-catalyzed alkylation of butanes was put into operation at Shandong Deyang Chemical Co., Ltd. The successful application of ionic liquid alkylation technology has overcome many of the shortcomings of traditional alkylation processes using concentrated sulfuric acid and hydrofluoric acid, providing a new solution for the purification and comprehensive quality improvement of commercial gasoline in China. (Source: Petroleum and Petrochemical Industry News)