In-depth article ‖ Basic knowledge and future prospects of the alkylation series – worth saving!

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In-depth article ‖ Basic knowledge and future prospects of the alkylation series – worth saving! In-depth article ‖ Basic knowledge and future prospects of the alkylation series – worth saving! 1. Ways to increase the octane rating of gasoline. 2) Ionic liquid alkylation technology. 　　In-depth article ‖ Basic knowledge and future prospects of the alkylation series – worth saving! 　　 　　I. Alkylation A reaction process in which alkyl groups are introduced into organic moleculesthrough addition or substitution reactions. As an important synthetic method, alkylation is widely used in many chemical manufacturing processes. 　　1. Introduction Alkylation is the process by which an alkyl group is transferred from one molecule to another. It is a reaction in which alkyl groups (methyl, ethyl, etc.) are introduced into the compound molecule. Under the action of microorganisms, mercury in the sediment can be alkylated to form methylmercury or dimethylmercury. Commonly used alkylating agents in industry include olefins, halohydrins, and alkyl sulfates. The alkylated products of lead are alkyl leads, among which tetraethyl lead is commonly used as an additive in gasoline to act as an anti-knock agent (the alkylation process is shown in Figure 1). 　　Figure 1: Alkylation process diagram. In a standard refining process, the alkylation system, using a catalyst (sulfonic acid or hydrofluoric acid), combines low-molecular-weight olefins (primarily propylene and butylene) with isobutane to form alkylates (mainly higher-octane hydrocarbons with side chains). Alkylates are a type of gasoline additive that provides anti-knock properties and produces clean combustion products. The octane number of the alkylates depends on the type of olefin used and the reaction conditions employed. 　　Most crude oil contains only 10%-40% of hydrocarbons that can be used directly in gasoline. Refineries use cracking processes to convert high-molecular-weight hydrocarbons into low-molecular-weight, volatile products. The polymerization reaction converts small molecular gaseous hydrocarbons into liquid hydrocarbons that can be used in gasoline. The alkylation reaction converts small molecular olefins and side-chain alkanes into larger side-chain alkanes with high octane numbers. 　　The process that combines cracking, polymerization, and alkylation can convert 70% of crude oil into gasoline products. Other advanced processing procedures, such as alkane cyclization and cycloalkane dehydrogenation, can produce aromatic hydrocarbons and also increase the octane number of gasoline. Modern refining processes can completely convert the input crude oil into fuel-based products. 　　Throughout the entire refining process, alkylation is a crucial step that allows molecules to be reorganized as needed to increase production. 　　2. Type of reaction Figure 2: Reaction equation Alkylation reactions can be divided into thermal alkylation and catalytic alkylation. Due to the high temperature of the thermal alkylation reaction, side reactions such as pyrolysis are likely to occur; therefore, the catalytic alkylation method is used in industry. The main catalytic alkylation processes include: ① Alkylation of alkanes, such as the alkylation of isobutane using isobutylene to produce high-octane gasoline components ； 　　②Alkylation of aromatics, such as the alkylation of benzene with ethylene ； 　　③Alkylation of phenols, such as the alkylation of p-cresol using isobutylene. 　　Alkylation can also refer to metal alkylation, the most typical example. 　　3. Catalysts
Industrially, catalytic alkylation processes can be divided into two types: liquid-phase and gas-phase methods; the catalysts used in each are different. 　　Liquid-phase alkylation catalysts are mainly used as: ① acid catalysts, with sulfuric acid and hydrofluoric acid being the most common ones. The alkylation of isobutane with propylene and butene currently mostly utilizes hydrofluoric acid. For the alkylation of benzene with higher olefins or with C10–C18 chloroalkanes, as well as for the alkylation of phenols, sulfuric acid is more commonly used. ②Fred-Claift catalysts, such as aluminum chloride-hydrogen chloride and boron fluoride-hydrogen fluoride, are commonly used in the alkylation of benzene with ethylene, propylene, and higher carbon alkenes, as well as in the alkylation of phenols. 　　Gas-phase alkylation catalysts are mainly used as follows: ① Solid acid catalysts, such as diatomite phosphoric acid, for the alkylation of benzene with ethylene and propylene, and naphthalene with propylene ； ②Metal oxide catalysts, such as alumina, alumina-silica, oxides of magnesium and iron, and activated clay, are commonly used in alkylation reactions of benzene with ethylene, phenol, and methanol. ③Molecular sieve catalysts, such as ZSM-5 molecular sieve catalysts, are primarily used in the alkylation of benzene with ethylene. 　　4. Process conditions
Alkylation is an exothermic reaction; the heat of reaction is generally 80–120 kJ/mol. Therefore, the removal of this heat is crucial. From a thermodynamic perspective, the reaction can be brought close to completion over a wide range of temperatures; only at very high temperatures does a significant reverse reaction occur. Catalysts used in liquid-phase reactions are generally highly active, allowing the reaction to proceed at lower temperatures (0–100°C). Appropriate pressure is applied to maintain the reactants in a liquid phase and to regulate the reaction temperature. To minimize olefin polymerization and the formation of polyalkylated products, a relatively high alkane-to-olefin or benzene-to-olefin molar ratio (5–14:1) and shorter residence times are commonly employed. In industry, in order to make effective use of benzene and alkylating agents, polyalkylates are often recycled back to the reactor where they undergo alkylation reactions with benzene to produce monoalkylbenzenes. Acetylene, sulfides, and water in the raw materials are harmful to the catalyst and should be removed in advance. The catalysts used in gas-phase alkylation generally have low activity, so the reaction must be carried out at higher temperatures (150–620°C); the pressure is usually between 1.4 and 4.1 MPa, with a molar ratio of benzene to olefin of 3–20:1. Sulfides and water in the raw materials can easily poison the catalyst, so they must be removed in advance. 　　5. Reactors
Liquid-phase alkylation can be carried out in horizontal or tower-type reactors. The reaction heat can be removed by cooling coils within the reactor (horizontal type) or through evaporative cooling. To ensure thorough mixing of the reactants and acid as well as to control a certain residence time, stirring, circulation, the use of baffles, or multi-stage series reactors can be employed. Due to the corrosiveness of the catalyst, the reactor must be lined with corrosion-resistant materials. Gas-phase alkylation does not cause corrosion to the equipment; tubular fixed-bed reactors are generally used, and multi-stage quenched adiabatic reactors can also be employed. 　　6. Industrial Applications In the petroleum refining industry, the alkylation process is primarily used to produce components for blending high-octane gasoline. For example, isobutane is alkylated with propylene or butylene to produce alkylated oil, which was the earliest application of the alkylation process. Benzene is alkylated with propylene to produce isopropylbenzene, which was initially used as a blend component for gasoline; today it serves as a main raw material for the production of phenol and propylene. Today, the alkylation process is mainly used to produce various important organic products. For example, benzene is alkylated with ethylene to produce ethylbenzene, and benzene is alkylated with C10–C18 alkenes to produce higher-carbon alkylbenzenes, which serve as raw materials for synthetic detergents. Furthermore, methyl isopropylbenzene, obtained by alkylating toluene with propylene, can be converted into m-cresol through oxidation and isomerization ； Toluene reacts with ethylene to produce vinyl toluene. Xylenes can be converted into xylene musk through isobutylization. Alkylation of 1,2,4-trimethylbenzene with methanol or chloromethane can produce 1,2,4,5-tetramethylbenzene. Alkylation of phenol with isobutylene yields tert-butylphenol, while alkylation with diisobutylene yields p-octylphenol. 　　7. Alkylation of petroleum hydrocarbons Principle It is one of the processes involved in refinery gas processing; it involves using a catalyst (hydrofluoric acid, sulfuric acid, or solid acids – a research area that can help avoid environmental pollution caused by liquid waste acids or the high costs associated with their recovery and treatment) to carry out an alkylation reaction between isobutane and butenes (or mixtures of propylene, butenes, and pentenes), thereby producing gasoline components with high octane ratings. Using isobutane and butylene as raw materials, the research octane number of the product (see Octane Number) can reach 94 ； When a mixture of propylene, butylene, and pentene is used as the raw material, the octane number is slightly lower. Alkylated gasoline has high sensitivity, low vapor pressure, and a high tendency to respond to lead (a small amount of tetraethyl lead can significantly increase the octane rating of gasoline), making it an ideal blending component for producing aviation gasoline and high-octane automotive gasoline. 　　History During World War II, the technology of alkyling petroleum hydrocarbons was developed to meet the demand for aviation gasoline. In 1939, the Anglo-Iranian Oil Company built a petroleum hydrocarbon alkylation unit using sulfuric acid as a catalyst. In 1942, Universal Oil Products Company and Phillips Petroleum Company in the United States each built similar units using hydrofluoric acid as a catalyst, producing high-octane gasoline. In the decades following the war, it continued to develop due to the increasing demand for high-octane gasoline for vehicles. China built a sulfuric acid process alkylation unit in the 1960s, and in recent years has been constructing hydrofluoric acid process alkylation units. 　　Process 　　Depending on the catalyst used, it can be divided into hydrofluoric acid alkylation and sulfuric acid alkylation. 　　The hydrofluoric acid-based alkylation process generally consists of raw material pretreatment, reaction, product distillation and treatment, acid regeneration, and treatment of waste gases, wastewater, and solid waste. The main purpose of preprocessing is to control the moisture content of the raw materials (below 20 ppm) in order to prevent severe corrosion of the equipment; at the same time, it is necessary to strictly control the levels of impurities such as sulfur, butadiene C2 and C6, and oxygen-containing compounds. Due to the high solubility of hydrocarbons in hydrofluoric acid, the alkylation reaction proceeds very rapidly and can be essentially completed in just a few dozen seconds, allowing the use of a tubular reactor. The reaction temperature is 20–40°C, and the pressure is 0.7–1.2 MPa. To suppress side reactions, a large amount of isobutane must be recycled back into the reaction feed to maintain a volume ratio of isobutane to olefin feed of (8–12):1. The reaction heat is removed by the acid cooler. The purpose of acid regeneration is mainly to remove the polymers formed during the reaction as well as the water brought in from the raw materials; these are discharged from the bottom of the regenerator as acid-soluble oil, thereby maintaining the hydrofluoric acid concentration at around 90%. Alkylated oil is drawn off from the bottom of the main fractionator, while recycled isobutane is taken off from a side draw of the tower. To produce aviation fuel, the obtained alkylate must undergo redistillation; the light alkylate separated from the top of the column is used as a component of aviation gasoline. The waste gas or waste liquid containing hydrofluoric acid discharged from the system must be treated, and finally reacted with calcium chloride to convert it into inert calcium fluoride. The production of each ton of alkylated gasoline consumes approximately 0.4–0.6 kg of hydrofluoric acid. 　　The basic process of sulfuric acid alkylation is similar to that of the hydrofluoric acid method. The main problem is high acid consumption; 70–80 kg of sulfuric acid is required per 1 ton of alkylated oil, and a large amount of dilute acid is produced as a by-product. Without a sulfuric acid plant or acid concentration facility nearby, it will cause serious environmental pollution. 　　Alkylation with sulfuric acid II. Alkylation with sulfuric acid 1. Overview Sulfuric acid is used as a catalyst to carry out the alkylation of olefins. There are two types: stepped-type and shell-and-tube type. To keep the reaction occurring at a lower temperature, the former utilizes the partial evaporation of the reactants to absorb heat and thereby cool down the system, while the latter uses throttling expansion of the reaction products to achieve cooling. 　　There are two types of sulfate-based alkylation: the step-type and the shell-and-tube type. To keep the reaction occurring at a lower temperature, the former relies on the partial evaporation of the reactants to absorb heat and thereby cool down the system, while the latter uses throttling and expansion of the reaction products to achieve cooling. 　　Each stage in the multi-stage stepped reactor is equipped with a agitator to emulsify the hydrocarbon feedstock and sulfuric acid. Sulfuric acid and isobutane flow from the first section of the reactor and pass through each section smoothly. The olefins are divided into several portions and fed into each section separately. 　　In each section of the reactor, some hydrocarbons evaporate, absorbing the heat released by the absorption reaction and thus maintaining a lower reaction temperature. 　　The evaporated hydrocarbons are compressed, condensed, and liquefied; after propane is removed, they are returned to the reaction system. 　　The reactor is equipped with an impeller mixer to facilitate high-speed circulation of sulfuric acid and hydrocarbons inside, thereby forming an emulsion. 　　The acid-oil emulsion after the reaction enters a settler; the sulfuric acid separated out is recycled back to the reactor for reuse, while the reaction effluent separated from the settler flows through the heat-extraction tubes of the reactor via a pressure control valve, where part of it vaporizes to absorb the reaction heat and maintain the reactor at a lower temperature. 　　2. Main influencing factors Reaction temperature The alkylation reaction takes place at low temperatures; the appropriate temperature for the sulfuric acid-based alkylation reaction is 8–12°C. 　　Concentration of sulfuric acid: As a catalyst for alkylation reactions, the concentration of sulfuric acid has a significant impact on the reaction. 　　When the concentration of sulfuric acid exceeds 99% by mass, SO3 reacts directly with isobutane, thereby increasing acid consumption. When the concentration falls below 85% by mass, the activity of the catalyst **decreases**, and corrosion of the equipment also becomes more severe. 　　Therefore, the appropriate sulfuric acid concentration is 95–96%. 　　In industry, the concentration of fresh sulfuric acid added to the reactor is typically 98–99%. Due to the moisture present in the raw materials, the dilution caused by water generated as a by-product of side reactions, and the formation of sulfates and acid-soluble polymers, the sulfuric acid concentration gradually decreases over time during operation. To ensure the quality of the sulfuric acid alkylated oil and to prevent corrosion of the equipment by sulfuric acid, it becomes necessary to discharge the acid when its concentration drops to 88–80%. 　　The consumption of sulfuric acid accounts for a significant portion of the production costs associated with sulfuric acid alkylation; therefore, efforts should be made to minimize acid usage. 　　An increase in the impurity content of the raw material leads to higher acid consumption; the presence of olefins such as propylene and pentene in the raw material also results in a significant increase in acid consumption. Improper reaction conditions, such as excessively high or low temperatures or uneven mixing, can likewise cause an increase in acid consumption. 　　To this end, the aforementioned situations that lead to increased acid consumption should be avoided. 　　To protect the environment and reduce costs, the waste acid discharged by the equipment must not be released indiscriminately; instead, it should be sent to an incinerator where it is burned to produce SO2 at high temperatures, which is then further oxidized to SO3 in order to recover sulfuric acid. 　　Sulfuric acid concentration monitoring is very important, and the Dupont Stracto alkylation unit is equipped with online concentration analysis capabilities. 　　Acid-to-hydrocarbon ratio: In a reaction system, if the ratio of sulfuric acid to hydrocarbons is too low, there isn’t enough acid present to form a continuous phase during dispersion and emulsification; instead, the hydrocarbons become the continuous phase. This results in a decrease in the quality of the alkylated oil and an increase in acid consumption. 　　The acid-to-hydrocarbon ratio commonly used in industry is 1–1.5:1 to ensure that sulfuric acid remains in the continuous phase. 　　Since the thermal conductivity of sulfuric acid is much higher than that of hydrocarbons, using sulfuric acid as the continuous phase allows for more effective dissipation of reaction heat, thereby preventing excessive local overheating that could lead to an increase in side reactions. 　　The acid-to-hydrocarbon ratio should also not be too high, as this will reduce the amount of hydrocarbons fed in, thereby decreasing the plant’s processing capacity. Additionally, an increase in sulfuric acid leads to an increase in the viscosity and density of the reaction mixture, which in turn increases the energy required for stirring. 　　Ratio of isobutane to olefins　　To increase the concentration of isobutane in the acidic phase and to suppress side reactions such as olefin polymerization, a relatively high alkane-to-olefin ratio must be maintained in the reaction system. In industry, the alkene to alkane ratio in reactor feed is generally 5–15:1. 　　Given that the purpose of increasing the alkene-to-alkane ratio is to raise the purity of isobutane in the reaction mixture, the concentration of isobutane in the reaction effluent is typically controlled to be no less than 60–70 v% in production. 　　Dispersion of hydrocarbons in sulfuric acid: Sulfuric acid acts as the continuous phase, while the hydrocarbons are the dispersed phase. The controlling step in the alkylation reaction is the mass transfer of isobutane into the acid phase; therefore, the stirring speed has a significant impact on the reaction. 　　Due to the large density difference of acid hydrocarbons and the high viscosity of sulfuric acid, vigorous stirring is necessary to improve the dispersion within the reaction system, enhance mass and heat transfer efficiency, accelerate the alkylation reaction, and thus help increase the octane number of the alkylated oil. 　　Reaction time: The reaction time is related to the stirring intensity and the degree of dispersion of the two phases; under normal conditions, the reaction time for alkylation with sulfuric acid is 20–30 minutes. 　　If the time is too short, the reaction is incomplete, affecting the yield of the alkylated oil. 　　If the time is too long, it not only reduces the processing capacity of the device but also leads to secondary reactions that degrade the quality of the product. 　　III. Alkylation reaction A reaction in which the hydrogen atoms attached to carbon, oxygen, and nitrogen in organic compound molecules are replaced by alkyl groups. Alkylation of carbon atoms ① Alkylation of the hydrogen at the a-carbon of the carbonyl group. The hydrogen atom on the alpha carbon of the carbonyl group is weakly acidic; under the action of strong bases such as sodium amide or sodium hydride, the alpha carbon of the carbonyl group can undergo alkylation with halogenated alkanes to yield alpha-carbon alkylated products. 　　1. Definition 　　A reaction in which the hydrogen atoms attached to carbon, oxygen, and nitrogen in organic compound molecules are replaced by alkyl groups. 　　2. Reaction mechanism Alkylation of carbon atoms: ① Alkylation of the hydrogen atom on the a-carbon of the carbonyl group. 　　The hydrogen atom on the alpha carbon of the carbonyl group exhibits weak acidity. Under the action of strong bases such as sodium amide or sodium hydride, the alpha carbon of the carbonyl group can undergo alkylation with halogenated alkanes, resulting in alpha-carbon alkylated products. Direct alkylation of esters leads to self-condensation ； Polyalkylation reactions also occur. To obtain a-carbon monoalkylated products, secondary amines such as pyrrole and morpholine can be used to form enamines, which are then reacted with reactive halides (e.g., iodomethane, halobenzenes) to yield substituted enamines; hydrolysis of these compounds subsequently produces the alkylated carbonyl compounds. ② Alkylation of reactive methylene groups. 　　The methylene group located between two active groups is relatively reactive and can be easily alkylated in the presence of sodium alcoholate. Active groups can be nitro groups, carbonyl groups, ester groups, or cyano groups, etc. For example, the substituted malonate synthesis method and the acetoacetate synthesis method: H2C(COOC2H5)2 + C2H5O-Na+ + CH(COOC2H5)2-Na++C2H5OH → CH(COOC2H5)2-Na+ + RX → RCH(COOC2H5)2 + NaX; CH3COCH2COOC2H5 + C2H5O-Na+ → (CH3COCHCOOC2H5)-Na++C2H5OH, where R is an alkyl group ； X is a halogen. Substituted malonates and acetoacetates readily undergo decarboxylation upon hydrolysis, breaking down into substituted acetic acids or similar compounds; this reaction is widely used in organic synthesis. All these alkylation reactions were carried out under anhydrous conditions. 　　③Alkylation by phase-transfer catalysis. 　　Phase-transfer catalysts are used to enable reactions between reactants in two immiscible liquid phases. There is no need to work under anhydrous conditions; a concentrated aqueous solution of sodium hydroxide can be used in place of anhydrous sodium alkoxide. The reaction conditions are mild, and the operation is simple. Commonly used catalysts include quaternary ammonium salts (Q+X-), such as (n-C4H9)4N+HSO4-, quaternary phosphonium salts with Cl- ions, and crown ethers. The reactants react with the base at the interface to form negative carbon ions. The latter forms ion pairs with quaternary ammonium cations and is transferred to the organic phase, where it undergoes alkylation reactions with halides. 　　3. Chemical Reactions The Friedel-Crafts alkylation reaction: when the alkyl group used has three or more carbon atoms and is a straight-chain alkyl group, the carbocation undergoes rearrangement. 　　4. Examples: For instance, sodium alkylate on an oxygen atom reacts with halides to form ethers; this is an important method for synthesizing asymmetric ethers. RONa + R′XR′O⁻ + NaX. Phenols are more acidic than alcohols, and the use of sodium hydroxide allows for the formation of aromatic oxyanions, which can then be alkylated. 　　For example, diester sulfates are also commonly used alkylating agents; they have higher reactivity than halides, require mild reaction conditions, and generally only one alkyl group participates in the reaction. 　　Heating alkylated halides on nitrogen with ammonia or amines under certain pressure can produce mixtures of primary, secondary, tertiary amines and even quaternary ammonium salts. Through distillation, primary, secondary, and tertiary amines can be separated one by one. By controlling the ratio and conditions of the reactants, one of the amines can be made the main product. 　　N3H+RXH3R+X- 　　H3R+NH3RNH2+H4 　RNH2+RXR2N2+X- 　　R2H2+NH3R2NH+H4 　R2NH+RXR3H+X- 　　R3H+NH3R3N+H 　R3N+RXR4+X- When alkylating using diester sulfate, the nitrogen atom with stronger basicity is preferentially selected for the reaction. 　　IV. Alkylated Gasoline 　　1. Methods for increasing gasoline octane number 　　The main technologies currently used to increase gasoline octane number include catalytic reforming, alkylation, isomerization, and the addition of gasoline octane number improvers (antiknock agents). 　　Catalytic reforming primarily aims to increase the amount of aromatics and isoparaffins in gasoline in order to raise its octane rating, with aromatics making a greater contribution to this increase. The downside of using reforming to enhance gasoline octane rating is the rise in the levels of aromatics and benzene. 　　Alkylated gasoline is produced by reacting isobutane in LPG with butene-1, butene-2, and isobutylene to form isooctane; as a result, its components are all isooctane. It has a high octane rating, good sensitivity, low vapor pressure, and a wide boiling range. Being a saturated hydrocarbon free of aromatics, sulfur, and olefins, it is an ideal component for high-octane, clean gasoline. 　　Isomerization is one of the cheapest methods for increasing gasoline octane number; it converts straight-chain alkanes in light straight-run naphtha (C5/6) into branched-chain alkanes, thereby raising the gasoline octane number by 10% to 22%. 　　Various additives can significantly enhance the anti-knock properties of gasoline. MTBE is the earliest developed and used ether-based octane booster, but since it is not a component of gasoline (it is a hydrocarbon), it often causes various problems during use, and its price is usually high. 　　2. Basic components of gasoline In the United States, gasoline is composed roughly of 1/3 catalytically cracked gasoline, 1/3 catalytically reformed gasoline, and 1/3 other high-octane blending components. 27% in Western European catalytic cracking gasoline, 47% in catalytic reforming gasoline; the remainder consists mainly of other high-octane components. 　　In China, catalytic cracking gasoline accounts for as much as 75% of total gasoline consumption, while the proportions of reformed gasoline, alkylated oil, MTBE, etc. are very low. This difference in the composition of gasoline results in a significant gap in gasoline quality between China and other countries. 　　The main problems with the quality of automotive gasoline in our country at present are high levels of olefins and sulfur. 　　3. Alkylated gasoline Characteristics of alkylated gasoline: It is primarily composed of isoparaffins, with almost no olefins or aromatics present. It has a low sulfur content and a high octane rating, typically ranging from 95 to 96, and in some cases even reaching 98. It is less sensitive to fluctuations in temperature; the difference between its octane rating and the octane rating of regular gasoline is less than 3. It also has a low vapor pressure, allowing it to be mixed with inexpensive, high-octane butane. Additionally, it has a high heat of combustion, making it suitable for use in engines with high compression ratios. 　　Alkylation raw material: Isomeric alkanes: Isobutane. 　　Olefins: The alkylation reactions of different butylene isomers such as isobutylene, 1-butene, cis-2-butene, and trans-2-butene yield varying results. When hydrofluoric acid is used as a catalyst, the alkylated products of 2-butene have the highest octane number, those of isobutylene have an intermediate octane number, and those of 1-butene have the lowest octane number. When sulfuric acid is used as a catalyst, the octane number of the alkylated oil obtained from 1-butene is slightly higher than that of the alkylated products derived from 2-butene and isobutylene. 　　Alkylation process Main reaction: In the traditional liquid acid isobutane alkylation process, it can be classified into sulfuric acid alkylation process and hydrofluoric acid alkylation process based on the catalyst used. 　　The processes using the sulfuric acid method include: Stratco, Kellogg, ExxonMobil, ReVAP (Phillips/ExxonMobil), Alkad (UOP/ChevronTexaco) ； 　　The hydrofluoric acid process methods include: UOP, Phillips (Conoco Phillips). By the end of 2002, 107 alkylation units worldwide were using ReVAP (Phillips/ExxonMobil) technology. 　　Currently, the global alkylation production capacity for Stratco is 25.8 million tons per year, while that of ExxonMobil is 4.95 million tons per year. 　　The sulfuric acid process generates large amounts of waste acid, causing severe environmental pollution ； Hydrofluoric acid is a highly volatile and toxic chemical; any leakage of it can cause serious damage to the production environment as well as the surrounding ecological environment. Both processes face issues such as corrosion of production equipment. 　　Octane number of some gasoline components V. Development of alkylation technology According to a report in Chemical Engineering magazine from May 2016, alkylation is an increasingly important refining technique; it involves the reaction of low-carbon olefins with isobutane to produce trimethylpentane isomers, namely alkylated oils, which can be used as components in the formulation of cleaner gasoline. Alkylated oil is a high-quality component for gasoline, featuring a high octane rating, low vapor pressure, low sulfur content, and no aromatics. The demand for alkylated oils is on the rise, primarily due to economic growth which requires more gasoline, **the implementation of stricter gasoline standards that call for a reduction in the content of high-octane components such as aromatics and olefins in blended gasoline, as well as the need for high-performance engines. 　　Strict limits on the sulfur content in gasoline require more intensive hydroprocessing, which leads to a decrease in the octane rating of gasoline. Alkylated oil is a high-octane, low-sulfur blending component that can increase the octane rating of the final gasoline. Another factor is that cheap butane is available in U.S. shale deposits, providing an abundant supply of inexpensive raw material for alkylation. 　　1. Advances in solid acid catalyst alkylation technology It has been observed over the past few months that solid acid alkylation catalysts, which have been under development for many years, are now capable of replacing harmful and corrosive liquid acid catalysts (hydrofluoric acid and sulfuric acid). At this year’s AFPM conference, CB&I presented progress on the world’s first industrial-scale alkylation plant using solid acid catalysts. This plant is located at Zibo Haiyi Fine Chemicals, a subsidiary of Shandong Huifeng Petrochemical Company in China, and it began operations in August 2015. The unit utilizes the AlkyClean technology jointly developed by CB&I, Albemarle, and Finland’s Neste; it has an alkylation oil production capacity of 2,700 barrels per day (100,000 tons per year). CB&I said that so far, all performance indicators of the facility built in Shandong have met expectations. Since its commissioning, the high quality of the alkylated oil products has been proven; their research octane number (RON) ranges from 96 to 98, which is significantly higher than that of conventional alkylated oils. The research octane number is an important indicator of the value of alkylated oils as components in gasoline blending. 　　The AlkyClean technology uses the AlkyStar catalyst developed by Avon, which is a durable fixed-bed zeolite catalyst. This catalyst, when combined with CB&I’s novel reactor process, enables the AlkyClean process to produce high-quality alkylated oil products without the need for liquid acid catalysts, making the process safer and more reliable. Since no post-treatment is required and there are no acid-soluble oil wastes, it is a very efficient production technology for alkylated oils. 　　In February of this year, KBR announced that the first technology transfer contract for its K-SAAT solid acid alkylation technology had been signed. The contract with KBR was signed by Dongying Haikeruilin Chemical Company, which is constructing production facilities in Dongying City. KBR provides proprietary technologies, basic process design, key equipment, and catalysts. The unit is expected to be put into operation in the first quarter of 2017. 　　The characteristic of the K-SAAT process is the use of a solid acid catalyst called ExSact. This is an improved zeolite catalyst that is now available commercially; compared to liquid acid catalysts, it poses much less harm to humans and the environment. This advantage and the low construction investment are the main factors influencing Heico’s decision to opt for the K-SAAT process rather than conventional sulfuric acid alkylation technology. Gautham Krishnaiah, Technical Manager for Catalytic Cracking and Alkylation at KBR, said that solid acid catalyst alkylation units also incur lower operating costs, as they require less maintenance compared to K-SAAT units, and there is no need for cooling in sulfuric acid alkylation units. In addition, liquid acid regeneration and solid waste treatment (acid-base neutralization) are not required. 　　KBR developed this green chemical technology in collaboration with Exelus, and now KBR is the sole licensor of Exelus’ ExSact catalyst. The K-SAAT process uses two reactors: one for alkylation operations and the other for regeneration or as a backup. Hydrogen is used to fully regenerate the catalyst; during this regeneration process, soft coke (various highly unsaturated hydrocarbons) and contaminants adsorbed on the catalyst are removed and blown away. 　　The successfully developed ExSact catalyst outperforms liquid acid catalysts and other solid acid catalysts in many aspects. To enhance the selectivity of the product, both the acid sites and pore structure of the catalyst were optimized. Compared to other solid acid catalysts, the operating cycles for alkylation using the ExSact catalyst are somewhat longer ； There is great flexibility regarding the sources of raw materials and their components (ethylene, propylene, butene, and pentene can all be used as olefins). In contrast, the liquid-phase acid alkylation process cannot be used for alkylation with ethylene, as this produces stable esters. Furthermore, KBR’s solid acid process has excellent resistance to contaminants in the feedstock, such as moisture, sulfur, dienes, oxygen-containing compounds, and nitriles. 　　2. Advances in sulfate catalyst alkylation technology The emergence of solid acid alkylation processes on an industrial scale has not prevented the innovative use of liquid acid catalyst alkylation units. DuPont is applying its sulfate alkylation technology to some unique raw materials. In March of this year, DuPont announced that it had signed a contract with a Chinese refinery to supply an alkylation unit that uses 100% butylene as raw material. Jeannie Branzaru, Global Sales Manager for Clean Technologies at DuPont, said that the chemical foundation for DuPont’s new alanation technologies has been in place for a long time, and current economic conditions are favorable for using butane to produce alkylation oils, or what is known as \"specialty alkylation\" technology. This unique processing method was not economical in the past. Branzaru said that many companies can purchase low-value butane cheaply on the open market, process it in dehydrogenation units to produce isobutylene, and then feed that isobutylene into alkylation units to manufacture high-value alkylated oils. However, DuPont’s technology is not limited to butane; it can also process very high concentrations of propylene and 100% pentene. 　　Dalian Hengli Petrochemical Company in China has signed a contract with DuPont to supply alkylation and spent acid regeneration (SAR) technologies for the construction of production facilities at the new refinery in the Changxing Island Port Industrial Zone. At present, Hengli Petrochemical plans to start construction in 2018, with operation expected to begin in 2019. DuPont will use its own Stratco alkylation and MECS spent acid regeneration technologies. 　　By adopting DuPont’s technology in integrated refining and chemical plants, Hengli Company will be able to produce high-quality alkylated oil products using 100% isobutylene as raw material. Kevin Bockwinkel, Global Business Manager for Stratco Technologies at DuPont, said, “Hengli’s facility has access to unique raw materials, marking the beginning of a new era for alkylated oils in the gasoline market, as facilities for producing alkylated oils from butane are increasing around the world.” Hengli Company’s alkylation unit will utilize DuPont’s XP2 patented technology in Stratco contact reactors. Bockwinkel stated that the design of XP2 technology ensures very efficient utilization of the heat transfer surfaces in the tube bundle, thereby improving the quality of alkylated oil products through significant process advantages. 　　VI. Recent Advances in Alkylation Technology in 2016 Alkylation is a process in which isobutane present in refinery liquefied gas reacts with olefins, 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 methods 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 rates of alkylated oil with good selectivity, the sulfuric acid method results in large amounts of waste acid being discharged, 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. 　　1. Traditional liquid acid alkylation techniques 　At present, the traditional 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 units 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 evolved through years of competition with each other, developing their own distinct characteristics. 　　1) Alkylation with hydrofluoric acid The alkylation process 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 fluorinated 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 catalysts; as a result, it is prohibited by the U.S. environmental authorities. Therefore, new alkylation plants built in the past 20 yearsほとんど use the hydrofluoric acid method. 　　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, commissioned in 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 Shenchí (200,000 tons per year, started operations in May 2013), Shandong Haiyue (600,000 tons per year, started operations in July 2014), Guangxi Qinzhou Tianheng Petrochemical (200,000 tons per year, started operations in April 2014), and Yuntianhua (240,000 tons per year, started operations in 2016). 　　Since the biggest problem 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 significantly higher investment and operating costs compared to hydrofluoric acid-based alkylation. 　　2. 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 corrosivity, 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 related to acid waste 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 Petroleum Research Institute 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 Huifeng Petrochemical Group in Zibo, Shandong. 　　Although certain progress has been made in solid acid alkylation technology, at present there are still some obstacles preventing it from completely replacing traditional liquid acid technology. Among these, the problem of catalyst deactivation and regeneration is the most difficult 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 along with 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 work has 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. 　　PetroChina is currently the only company to have industrially applied the ionic liquid alkylation technology. This technology was developed by the Key Laboratory of Heavy Oil at China University of Petroleum. On September 29, 2013, a 120,000-ton/year ionic liquid-catalyzed C4 alkylation (ILA) facility was put into operation at Shandong Deyang Chemical Co., Ltd. The successful application of ionic liquid alkylation technology has overcome many drawbacks of traditional alkylation processes using concentrated sulfuric acid and hydrofluoric acid, providing a novel solution for the purification and overall quality improvement of commercial gasoline in China. 　　VII. The prospects of China’s alkylation industry Under market economy conditions, resources tend to concentrate in areas with higher returns. Driven by the increased efforts in environmental governance and the accelerated improvement of refined oil quality in China, alkylated gasoline has begun to attract considerable attention as an ideal blending component for fuels. Alkylated gasoline boasts advantages such as high octane rating, low sulfur content, absence of olefins and aromatics, high yield, and good economic benefits, making it the preferred raw material for high-octane gasoline and enabling it to quickly dominate the market for advanced processing in China’s refining industry. 　　In 2013, there was a surge in the construction of alkylation plants in China; their production capacity increased by as much as 370% compared to the previous year, and this high growth trend has continued since then. At present, the total production capacity of alkylation units in China has exceeded 14 million tons per year. This year, the growth rate of alkylation capacity in our country has quietly dropped below 10% – does this mean that the era of rapid expansion of alkylation plants is over? 　　The main factors behind the slowdown in the growth rate of alkylation capacity this year are as follows: First, starting from the second half of 2014, oil triggered a downward trend in the global commodity market, with commodity prices falling month by month. By December 2015, the world’s major commodity price indices were below the levels seen during the global financial crisis in 2008, reaching their lowest levels in 11 years; energy products, represented by oil, experienced particularly sharp declines. As risk-aversion spread in the market, the prices of alkylated oils dropped sharply, thereby reducing the profit margins for these manufacturing facilities. Secondly, due to the rapid construction of alkylation facilities in recent years, there has been a situation where demand has failed to keep up, resulting in an oversupply and a buyer’s market; as a result, the bargaining power of the entire industry has weakened. Furthermore, the raw materials required for alkylation units are relatively limited; these units often face the problem of not having enough feedstock. The shortage of C4 compounds after etherification constitutes a key factor restricting the increase in production capacity of alkylation units in China. 　　It should be noted that although our country attaches great importance to environmental protection and is working to improve the quality of petroleum products, which has created significant opportunities for the development of the demand for alkylated oils, and although there are increasing restrictions on the construction of new alkylation plants, most of the existing alkylation plants in China use hydrofluoric acid and sulfuric acid as catalysts, which is not environmentally friendly. Some of these plants cause serious environmental pollution, and those with low production capacity and outdated technology are being phased out rapidly. This creates a paradox: alkylated gasoline creates market opportunities by improving environmental quality, yet the processes used in most alkylation plants cause environmental pollution. 　　At present, although the expansion of alkylation capacity is faced with constraints such as low prices of end products, insufficient raw material supply, and the need for technological innovation, demand remains optimistic given the overall trend of accelerating improvement in the quality of refined oil products in China. Driven by the upgrade in automobile consumption and higher gasoline octane ratings, the growing demand for alkylation will continue to propel the growth of the entire industry in the future. 　　Without taking into account variables such as major technological innovations, it is estimated that China’s demand for gasoline in 2016 will be 120 million tons, while the demand for alkylated oil will reach 5.4 million tons. The gap in demand will narrow to around 200,000 tons. As a result, the oversupply of alkylated oil will **reduce**, the need for manufacturers to engage in price wars will decrease, the overall bargaining power of the alkylation industry will increase, and profits will rise. Starting from January 1, 2017, the National Standard 5 gasoline standard will be implemented across the country. It is estimated that the domestic demand for gasoline in 2017 will be 129 million tons, while the demand for alkylated oil will reach 7.74 million tons. This will result in a supply gap of over 600,000 tons; as a result, companies will be more inclined to increase production while raising prices, which in turn will drive up the price of alkylated oil. The National Standard 6 for gasoline will be implemented nationwide starting in 2019. By then, China’s demand for gasoline is expected to reach 145 million tons, while the demand for alkylated oil will be between 11.6 million and 14.5 million tons. It is anticipated that the market supply gap will widen to over 3 million tons. With the gradual implementation of improved quality standards for refined oil products, it is expected that the supply and demand balance will change. The alkylation market holds great potential, and its production capacity continues to grow. 　　Nevertheless, given that the average operating rate of alkylation units in 2015 and the first half of 2016 was between 40% and 55%, blind capacity expansion does not serve the interests of manufacturers and carries considerable risks. Given the current mechanisms in the alkylation market, an increase in demand drives up alkylation prices out of their low levels, which in turn leads to higher prices for C4 raw materials. With rising alkylation prices yet no significant improvement in corporate profits, manufacturers will not show much enthusiasm for increasing production or expanding capacity. 　　With positive expectations on the demand side, the focus of the alkylation industry’s development in the future will shift towards technological innovation and cost reduction as well as improved efficiency. The expansion of more environmentally friendly alternative alkylation technologies (solid sulfuric acid alkylation technology, ionic liquid alkylation technology) will be an inevitable trend for improving the quality of development in China’s alkylation industry. Companies that have access to C4 resources will be more inclined to build new production capacity, install alkylation equipment, and improve their own petroleum processing value chains. Carbon four deep-processing enterprises will be more inclined to consolidate existing procurement channels and explore new ones, as well as upgrade their existing facilities.