Alkylation processes hydrofluoric acid

The same factors also influence the hydrofluoric acid alkylation process. Special attention must be given, however, to the water content. In hydrofluoric processes the feed must be well dried before entering the alkylation section. The best quality of alkylate is obtained in the range of 86-90% acid with a water content less than 1%. 

Over time the operating efficiency of hydrofluoric acid alkylation units has improved in order to minimize waste streams as well as minimize the actual hydrofluoric acid inventory. However, the only way to eliminate these issues completely is to develop a process based on a heterogeneous acid catalyst. Such a process would eliminate the hydrofluoric acid transportation and inventory, result in no waste polymer product, and would not require fluoride scrubbing and concomitant disposal of fluoride-containing solids. 

The costs for the new and sustainable technology are found to be similar to those of the existing technology (for an 8,000 BBL/day plant, an EEC of MM 43.5 for the Alkylene process and MM 40.5 for hydrofluoric acid alkylation). The increased costs for the novel Alkylene reactor are offset by costs for HE mitigation capital and... 

TABLE 2-5. Comparison of Sulfuric Acid and Hydrofluoric (HF) Acid Alkylation Processes... 

Refinery alkylation processes utilize either sulfuric acid or hydrofluoric acid as reaction catalysts. The feedstock for both alkylation processes originates primarily from hydrocracking and catalytic cracking operations. Coker gas oils also serve as feedstock in some applications. The differences and similarities between sulfuric acid alkylation and hydrofluoric acid alkylation are shown in TABLE 2-5. Typical alkylation reactions are shown in FIGURE 2-9. A sulfuric acid alkylation unit is illustrated in FIGURE 2-10. 

Figure 2 presents a schematic flow diagram for a typical hydrofluoric acid alkylation plant. Since processing with hydrofluoric acid is very similar to processing with sulfuric acid, this discussion will point out only the significant differences in the two processes. 

In contrast to the sulfuric acid process, regeneration of the catalyst in hydrofluoric acid alkylation is continuous. During processing, both hydrofluoric acid and sulfuric acid... 

Successful catalytic alkylation of isobutane with ethylene has been accomplished in one commercial installation using aluminum chloride catalyst (I). The chief product of the reaction is 2,3-dime thy lbutane, a hydrocarbon having very high aviation octane ratings. Ethylene has also been alkylated with isobutane in a thermal process to give 2,2-dimethylbutane as the chief product component (6). When sulfuric or hydrofluoric acid alkylation with ethylene is attempted, the ethylene forms a strong bond with the acid, and fails to react with isobutane. The net result is the formation of little or no product, accompanied by excessive catalyst deterioration. 

Fig. 1, Hydrofluoric acid alkylation unit. (UOP Process Division)...

In view of the foregoing, it is not surprising that many attempts have been made by many companies almost from the start of alkylation to develop a recovery process unique to the used sulfuric acid alkylation catalyst. Most of the early attempts were not intensive and continuous. Most of the work is unpublished, since it was of a preliminary nature and not very successful. An added incentive was provided for the users and licensors of the Sulfuric Acid Alkylation Process when it was discovered that hydrofluoric acid was also a good alkylation... 

Hydrofluoric acid is also used as a catalyst for many alkylation units. The chemical reactions are similar to those in the sulfuric acid process, but it is possible to use higher temperatures (between 24 and 46°C), thus avoiding the need for refrigeration. Recovery of hydrofluoric acid is accomplished by distillation. An example of the hydrofluoric acid alkylation unit is shown in Figure 6.18. 

The catalytic alkylation of saturated hydrocarbons and olefins was discovered in 1932 by Ipatieff and Pines. They employed conventional Friedel-Crafts catalyst, i.e., promoted aluminum chloride. The use of sulfuric acid as a catalyst was discovered by Birch and Dunstan in 1936. Promptly after the latter discovery, the reaction was commercialized to produce high-octane aviation gasoline from isobutane and butylenes employing not only sulfuric acid but anhydrous hydrofluoric acid. The processes were expanded rapidly during World War II to supply aviation gasoline. By the end of the war, 59 alkylation plants existed in this country with a rated capacity of... 

Alkylation quality, 145-146 Alkylation, 136-155 process description, 136-140 acid carryover, 140-148 improving alkylate octane, 147-148 hydrofluoric acid alkylation, 148-155 troubleshooting problems, 154 sulfuric acid, 155... 

Some alkylation processes use concentrated HF instead of H2SO4 as the catalyst. In general, HF is less corrosive than HCl because it passivates most metals by the formation of protective fluoride films. If these films are destroyed by dilute acid, severe corrosion occurs. Therefore, as long as feedstocks are dry, carbon steel - with various corrosion allowances - can be used for the vessels, piping, and valve bodies of hydrofluoric acid alkylation units. AU carbon steel welds that will contact HF, should be post-weld heat treated. 

Other kinds of liquid-liquid equilibria are encountered in processes such as alkylation, where anhydrous hydrofluoric acid (HF) is partially soluble in hydrocarbons. 

Fluorosulfuric acid [7789-21-17, HSO F, is a colodess-to-light yellow liquid that fumes strongly in moist air and has a sharp odor. It may be regarded as a mixed anhydride of sulfuric and hydrofluoric acids. Fluorosulfuric acid was first identified and characterized in 1892 (1). It is a strong acid and is employed as a catalyst and chemical reagent in a number of chemical processes, such as alkylation (qv), acylation, polymerization, sulfonation, isomerization, and production of organic fluorosulfates (see Friedel-CRAFTSreactions). 

The catalysts used in the industrial alkylation processes are strong Hquid acids, either sulfuric acid [7664-93-9] (H2SO or hydrofluoric acid [7664-39-3] (HE). Other strong acids have been shown to be capable of alkylation in the laboratory but have not been used commercially. Aluminum chloride [7446-70-0] (AlCl ) is suitable for the alkylation of isobutane with ethylene (12). Super acids, such as trifluoromethanesulfonic acid [1493-13-6] also produce alkylate (13). SoHd strong acid catalysts, such as Y-type zeoHte or BE -promoted acidic ion-exchange resin, have also been investigated (14—16). 

The reduction ia tetraethyl lead for gasoline production is expected to iacrease the demand for petroleum alkylate both ia the U.S. and abroad. Alkylate producers have a choice of either a hydrofluoric acid or sulfuric acid process. Both processes are widely used. However, concerns over the safety or potential regulation of hydrofluoric acid seem likely to convince more refiners to use the sulfuric acid process for future alkylate capacity. 

The principal use of the alkylation process is the production of high octane aviation and motor gasoline blending stocks by the chemical addition of C2, C3, C4, or C5 olefins or mixtures of these olefins to an iso-paraffin, usually isobutane. Alkylation of benzene with olefins to produce styrene, cumene, and detergent alkylate are petrochemical processes. The alkylation reaction can be promoted by concentrated sulfuric acid, hydrofluoric acid, aluminum chloride, or boron fluoride at low temperatures. Thermal alkylation is possible at high temperatures and very high pressures. 

Both sulfuric acid and hydrofluoric acid catalyzed alkylations are low temperature processes. Table 3-13 gives the alkylation conditions for HF and H2SO4 processes. One drawback of using H2SO4 and HF in alkylation is the hazards associated with it. Many attempts have been tried to use solid catalysts such as zeolites, alumina and ion exchange resins. Also strong solid acids such as sulfated zirconia and SbFs/sulfonic acid resins were tried. Although they were active, nevertheless they lack stability. No process yet proved successful due to the fast deactivation of the catalyst. A new process which may have commercial possibility, uses... 

Alkylation is one of the refining processes in which light olefin molecules are reacted with isobutane (in the presence of either sulfuric or hydrofluoric acid) to produce a desirable gasoline component called alkylate. 

The alkylation proceeds with aluminum chloride or hydrofluoric acid as catalyst, by which the importance of aluminum chloride diminishes. Today approximately 70% of all manufacturers use the HF process [4]. In addition, LAB is produced by the alkylation of secondary chloroparaffins (Wibarco in Germany) and by the alkylation of olefins (EniChem Augusta in Italy) over an aluminum chloride catalyst [12]. 

The LAB production process (process 1) is mainly developed and licensed by UOP. The N-paraffins are partially converted to internal /z-olefins by a catalytic dehydrogenation. The resulting mixture of /z-paraffins and n-olefins is selectively hydrogenated to reduce diolefins and then fed into an alkylation reactor, together with an excess benzene and with concentrated hydrofluoric acid (HF) which acts as the catalyst in a Friedel-Crafts reaction. In successive sections of the plant the HF, benzene, and unconverted /z-paraffins are recovered and recycled to the previous reaction stages. In the final stage of distillation, the LAB is separated from the heavy alkylates. 

Alkad A process for improving the safety of alkylation processes using hydrofluoric acid as the catalyst. A proprietary additive curtails the emission of the acid aerosol that forms in the event of a leak. Based on observation of G. Olah in the early 1990s that liquid polyhydrogen fluoride complexes (of amines such as pyridine) depress the vapor pressure of HF above alkylation mixtures. Developed by UOP and Texaco and operated at Texaco s refinery at El Dorado, TX, since 1994. A competing process is ReVAP, developed by Phillips and Mobil. 

Since the discovery of alkylation, the elucidation of its mechanism has attracted great interest. The early findings are associated with Schmerling (17-19), who successfully applied a carbenium ion mechanism with a set of consecutive and simultaneous reaction steps to describe the observed reaction kinetics. Later, most of the mechanistic information about sulfuric acid-catalyzed processes was provided by Albright. Much less information is available about hydrofluoric acid as catalyst. In the following, a consolidated view of the alkylation mechanism is presented. Similarities and dissimilarities between zeolites as representatives of solid acid alkylation catalysts and HF and H2S04 as liquid catalysts are highlighted. Experimental results are compared with quantum-chemical calculations of the individual reaction steps in various media. 

HF alkylation an alkylation process whereby olefins (C3, C4, C5) are combined with isobutane in the presence of hydrofluoric acid catalyst. 

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