Alkylation propylene-isobutane

Products do not contain 2,2,3-trimethylbutane or 2,2,3,3-tetramethylbutane, which would be expected as the primary alkylation products of direct alkylation of isobutane with propylene and isobutylene, respectively. In fact, the process iavolves alkylation of the alkenes by the carbocations produced from the isoalkanes via intermolecular hydride abstraction. 

The uses of propylene may be loosely categorized as refinery or chemical purpose. In the refinery, propylene occurs in varying concentrations in fuel-gas streams. As a refinery feedstock, propylene is alkylated by isobutane or dimerized to produce polymer gasoHne for gasoHne blending. Commercial chemical derivatives include polypropylene, acrylonitrile, propylene oxide, isopropyl alcohol, and others. In 1992, ca 64% of U.S. propylene suppHes were consumed in the production of chemicals (74). Polypropylene has been the largest consumer of propylene since the early 1970s and is likely to dominate propylene utilization for some time. 

The value of butylenes ia the United States is determined by their value ia alkylation of isobutane to high octane gasoline. Table 11 shows how the chemical use of ethylene, propylene, butylenes, and butanes varied between 1983 and 1988 and their corresponding price swiags. 

The propylene-butylene fraction constitutes a large part of the useful hydrocarbons produced by synthesis. It differs from similar fractions derived from petroleum refining in its high olefin (over 80%) and low isobutylene content, but this is no handicap in converting it to high octane gasoline by polymerization or by alkylation, if isobutane is available from another source. Polymerization is effected readily over a phosphoric acid on quartz catalyst with high conversion of propylene as well as butylene. The polymer... 

The main products formed by the catalytic alkylation of isobutane with ethylene (HC1—AICI3, 25-35°C) are 2,3-dimethylbutane and 2-methylpentane with smaller amounts of ethane and trimethylpentanes.13 Alkylation of isobutane with propylene (HC1—AICI3, — 30°C) yields 2,3- and 2,4-dimethylpentane as the main products and propane and trimethylpentanes as byproducts.14 This is in sharp contrast with product distributions of thermal alkylation that gives mainly 2,2-dimethylbutane (alkylation with ethylene)15 and 2,2-dimethylpentane (alkylation with propylene).16... 

Considerable effort has been put into minimizing the adverse effects of these olefins. It was found that alkylating propylene and pentylenes in a mixture with butylenes promoted the desired reactions and reduced the octane and acid consumption penalties. Furthermore, by optimizing temperature, isobutane-to-olefin ratio, acid strength, and other variables, the deleterious effects of propylene and pentylenes in the feed can be minimized (4, 8, 21). The decision as to how much of these olefins to include in the alkylation unit feed depends on many different factors, such as their value relative to alkylate, butylene and isobutane avails, alkylate volume and octane requirements, acid costs, etc. 

Commercial alkylation operations in petroleum refineries were originally limited almost entirely to the alkylation of isobutane with propylene, butylenes, and amylenes for the production of aviation gasoline. It has expanded greatly since that time to include the production of motor gasoline and numerous petrochemicals. 

Although aviation gasoline can be made by the alkylation of isobutane with propylene, butylenes, and amylenes, the butylenes are by far the predominant feed. In a few cases a mixture of di- and triisobutylene polymers, which is a byproduct of butadiene manufacture, is used as part of the olefinic charge. Either sulfuric acid or hydrofluoric acid can be used as a catalyst when aviation gasoline is produced by the alkylation reaction. 

The primary reactions in the alkylation of isobutane produce octanes from butylenes, heptanes from propylene, and nonanes from amylenes. Also, when dimer and trimer polymers of isobutylene are used with isobutane, the polymer is broken down during the reaction, and the resulting products are branched chain octanes similar to those produced when isobutylene is charged. Sulfuric acid consumption is somewhat higher for the diisobutylenes, however, and there are more side reactions than for isobutylene. 

In the case of propylene-isobutane alkylation, primary alkylation. 

Propylene Reactions. The following reaction mechanisms are generally 7ecognTzeTM tlTeprinci pa I ones occurring in propylene-isobutane alkylation with hydrofluoric acid catalyst (Ciapetta, 1945). In pnirenthe-ses are shown amounts of oroducts from each mechanism these are from Table VII for propylene ... 

Effects of Water in HF Catalyst. A number of investigators have pointed out that water has an important role in alkylation catalysts. Schmer-ling (1955) stated that the use of HF catalyst with one percent water produced a favorable result In propylene-isobutane alkylation, whereas, with a catalyst containing ten percent water, isopropyl fluoride was the principal product and no alkylate was formed. (Both reactions were at 25C.) Albright et al. (1972) found the water content of sulfuric acid to be "highly important" In affecting the quality and yield of butene-isobutane alkylate. They postulated that the water content of sulfuric acid controlled the level of ionization and hydride transfer rate In the catalyst phase. It appears that dissolved water affects HF alkylation catalyst similarly and also exerts further physical influence on the catalyst phase such as reducing viscosity. Interfacial tension, and isobutane solubility. 

Isobutane-to-Olefin Ratio with Propylene Feed. The isobutane-to-olefin ratio has long been recognized as an important process variable in the alkylation of isobutane with either butenes or pxopylene (Phillips Petroleum Company, 1946). By maintaining a sufficiently high concentration of isobutane in the reaction zone, the abstraction of hydride ions from isobutane is favored over abstraction from product isoparaffins. 

Even with propylene feed, a high isobutane-to-olefin ratio influences the product toward predominantly Cg hydrocarbons which have the highest octane number and also Improves yields. Thus, both alkylate quality and yield are found to improve with increasing ratio and olefin dilution. In Table IX, detailed propylene-isobutane alkylate composition data are shown, where the volume ratio was increased from 4.6 to 126. For quick reference, composition data are summarized in Table IV. 

Propylene- -Isobutane Alkylation with Propane Added. The principal... 

Alkylation of Isobutane with propylene or 2-methylbutene-2 resulted In products containing about 20% of Isooctanes (Table III, columns 2 and 6). Similarly to the sulfuric acid alkylation, C0 paraffins formation may be explained by self-alkylation of Isobutane. 

Alkylation of aromatics and aliphatics, e.g., ethylbenzene from ethylene and benzene, cumene from propylene and benzene, alkylation of isobutane with normal butenes... 

Hydrocarbons Produced Alkylation of isobutane with propylene ... 

On the other hand, for theUS Y-catalyzed alkylation of isobutane with frans-2-butene at high levels of conversion (100%), adding SCCO2 decreased the catalytic longevity and product selectivity. The alkylation of toluene with propylene over siUcon-modifled HZSM-5 zeolite using SCCO2 increased the yield of cymene and reduced the cracking of propylene compared with the reaction under atmospheric pressure (Scheme 41). ... 

Alkylation of Isobutane. When isobutene is alkylated with C3—C5 olefins, often at least 120-150 isoparaffins are detected, with carbon numbers varying from 5 to at least 16 (3). Using a strict definition of alkylation, only i-CyHie, i-CgHis, and j-C9H2o would be produced when isobutane is alkylated with propylene, C4 olefins, and C5 olefins, respectively. Considering t-Cg isoparaffins, trimethylpentanes (TMPs), dimethylhexanes (DMHs), and methyl heptanes are all produced. Yet, all C5—Cie isoparaffins produced are commonly considered to be alkylation products. 

Mechanism 4 is of importance whenever propane, n-butane, and n-pentane are obtained during alkylation using propylene, n-butenes, and n-pentenes, respectively, as olefin feeds. Mechanism 4 is sometimes referred to as hydrogen transfer or self-alkylation of isobutane. The overall reaction is often depicted as follows (1) ... 

Propylene oxide [75-56-9] is manufactured by either the chlorohydrin process or the peroxidation (coproduct) process. In the chlorohydrin process, chlorine, propylene, and water are combined to make propylene chlorohydrin, which then reacts with inorganic base to yield the oxide. The peroxidation process converts either isobutane or ethylbenzene direcdy to an alkyl hydroperoxide which then reacts with propylene to make propylene oxide, and /-butyl alcohol or methylbenzyl alcohol, respectively. Table 1 Hsts producers of propylene glycols in the United States. 

All lation. The combination of olefins with paraffins to form higher isoparaffins is termed alkylation (qv). Alkylate is a desirable blendstock because it has a relatively high octane number and serves to dilute the total aromatics content. Reduction of the olefins ia gasoline blendstocks by alkylation also reduces tail pipe emissions. In refinery practice, butylenes are routinely alkylated by reaction with isobutane to produce isobutane—octane (26). In some plants, propylene and/or pentylenes (amylenes) are also alkylated (27). 

Propylene. Propylene alkylation produces a product that is rich in dimethylpentane and has a research octane typically in the range of 89—92. The HF catalyst tends to produce somewhat higher octane than does the H2SO4 catalyst because of the hydrogen-transfer reaction, which consumes additional isobutane and results in the production of trimethylpentane and propane. 

Reactions other than those of the nucleophilic reactivity of alkyl sulfates iavolve reactions with hydrocarbons, thermal degradation, sulfonation, halogenation of the alkyl groups, and reduction of the sulfate groups. Aromatic hydrocarbons, eg, benzene and naphthalene, react with alkyl sulfates when cataly2ed by aluminum chloride to give Fhedel-Crafts-type alkylation product mixtures (59). Isobutane is readily alkylated by a dipropyl sulfate mixture from the reaction of propylene ia propane with sulfuric acid (60). 

Alkylate. Alkylation means the chemical combination of isobutane with any one or a combination of propylene, butylenes, and amylenes to produce a mixture of highly branched paraffins that have high antiknock properties with good stabiUty. These reactions are cataly2ed by strong acids such as sulfuric or hydrofluoric acid and have been studied extensively (98—103). In the United States mostly butylenes and propylene are used as the olefins. 

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