Alkylation

• 1. Alkylation By: Abbas Ali Zulfiqar Roll No: BENG/F10/0101 Refinery Engineering By: Sir Atif

2. Introduction (Alkylation) Alkylation, first commercialized in 1938, experienced tremendous growth during the 1940s as a result of the demand for high octane aviation fuel during World War II. During the mid 1950s refiners interest in alkylation shifted from the production of aviation fuel to the use of alkylate as a blending component in automotive motor fuel. The alkylation reaction combines isobutane with light olefins in the presence of a strong acid catalyst. 3. Introduction (Alkylation) Although alkylation can take place at high temperatures without catalyst the only processes of commercial importance today operate at low to moderate temperatures using either sulfuric or hydrofluoric acid catalysts. The reactions occurring in the alkylation process are complex and produce an alkylate product that has a wide boiling range. 4. Alkylation (Definition) Alkylationis the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene (or their equivalents). 5. Main Types Of Alkylation Process 1. Sulfuric Acid Alkylation Process 2. Hydrofluoric Acid Alkylation Process Phillips Process UOP Process Phillips and UOP are the two common types of hydrofluoric acid alkylation processes in use. 6. Industrial Process of Alkylation More specifically, the main sections of a STRATCO Effluent Refrigerated Sulfuric Acid Alkylation Process will be discussed. A sulfuric acid alkylation unit can be divided into five major sections as seen on the following page (Figure 1). 7. Block Flow Diagram of a STRATCO Effluent Refrigerated Sulfuric Acid Alkylation Unit 8. Description Each section is described below 1. Reaction Section: The reacting hydrocarbons are brought into contact with sulfuric acid catalyst under controlled conditions. 2. Refrigeration Section: The heat of reaction is removed and light hydrocarbons are purged from the unit. 9. Description (Cont) 3. Effluent Treating Section: The free acid, alkyl sulfates and di-alkyl sulfates are removed from the net effluent stream to avoid downstream corrosion and fouling. 4. Fractionation Section: Isobutane is recovered for recycle to the reaction section and remaining hydrocarbons are separated into the desired products. 5. Blowdown Section: Spent acid is degassed, waste water pH is adjusted and acid vent streams are neutralized before being sent off-site. 10. Hydrofluoric Acid Alkylation Process The second main catalyst option ishydrofluoric acid. In typical alkylation plants, rates of consumption for acid are much lower than forsulfuric acid. These plants also produce alkylate with better octane rating than do sulfuric plants. However, due to its hazardous nature, HF acid is produced at very few locations and transportation must be managed rigorously. 11. Application OIL REFINING: Alkylation of alkenes (shown here is propene) byisobutaneis a major process in refineries. It is catalysed by strong acids such as HF and sulfuric acid. In a standardoil refineryprocess,isobutaneis alkylated with low-molecular-weightalkenes(primarily a mixture ofpropene andbutene) in the presence of a strong acidcatalyst, either sulfuric acidorhydrofluoric acid. 12. Application (Cont) In an oil refinery it is referred to as asulfuric acid alkylation unit(SAAU) or ahydrofluoric alkylation unit, (HFAU). The reaction is carried out at mild temperatures (0 and 30 C) in a two-phase reaction. Because the reaction is exothermic, cooling is needed: SAAU plants require lower temperatures so the cooling medium needs to be chilled, for HFAU normal refinery cooling water will suffice. 13. Purpose of Alkylation The purpose of alkylation is to increase the production of aviation fuel to the use of alkylate as a blending component in automotive motor fuel, as a antiknock agent to increase fuels octane number. The product is called alkylate and is composed of a mixture of high-octane, branched- chainparaffinichydrocarbons(mostly iso-heptaneandiso-octane) Alkylate is a premiumgasoline blending stock because it has exceptional antiknock properties and is clean burning. 14. Health and safety considerations Sulphuric acid and hydrofluoric acid are dangerous chemicals, and care during delivery and unloading of acid is essential. There is a need to maintain sulphuric acid concentrations of 85 to 95% for good operation and to minimize corrosion. To prevent corrosion from hydrofluoric acid, acid concentrations inside the process unit must be maintained above 65% and moisture below 4% Vents can be routed to soda ash scrubbers to neutralize hydrogen fluoride gas or hydrofluoric acid vapours before release. 15. Health and safety considerations (Cont) There is a potential for serious hazardous and toxic exposures should leaks, spills or releases occur. Direct contact with sulphuric or hydrofluoric acid will cause severe skin and eye damage, and inhalation of acid mists or hydrocarbon vapours containing acid will cause severe irritation and damage to the respiratory system. Safe work practices and appropriate skin and respiratory personal protective equipment are needed where potential exposures to hydrofluoric and sulphuric acids during normal operations exist, such as reading gauges, inspecting and process sampling, as well as during emergency response, maintenance and turnaround activities 16. The End