Olefin-isoparaffin alkylation

Alkylation Combining Catalytic Unite olefins and isoparaffins Tower isobu-tane/cracker olefin Isooctane (alkylate)... 

Here we will describe the main aspects of the chemistry involved in selected zeolite-catalyzed processes in the field of oil refining and petrochemistry, such as short paraffin aromatization, skeletal isomerization of n-paraffins and n-olefins, isoparaffin/olefin alkylation, and catalytic cracking. 

LE s and relatively small Isoparaffins are produced when heavy olefins are used as feedstock for alkylation. The products obtained when Isobutylene or 2,2,4-trl-methylpentene-1 Is used as the olefin for alkylation resulted In almost Identical products Including LE s and DflH s (6,19). Even heavier olefins produce LE s, and fragmentation Is obviously of major Importance. Degradation of TMP s or DMH s In the presence of sulfuric acid leads to the formation of significant, and even major amounts of Isobutane and LE s (7). Fragmentation reactions obviously must be occurring. 

Alkylation was first practiced for gasoline production about 60 yr ago. At that time, most of the alkylate was used as fuel for the airplanes used in World War II. Four quite distinct reactors were developed in which isobutane and olefins were introduced as liquids to the reactor. In the reactor, the hydrocarbon liquids are contacted with either liquid sulfuric acid or liquid hydrofluoric acid (HF), which acts as a catalyst. Dispersions of these two relatively immiscible liquids are formed. The alkylate product formed is a mixture of mainly C5-C16 isoparaffins. Alkylate products often have research octane numbers (RONs) varying from 93 to 98 (the motor octane numbers tend to be two to three units lower). 

The basic reactions occurring during isoparaffin alkylation are shown in figure 1. Alkylation of isobutane with light (C3 -Cs) olefins in die presence of a strong acid catalyst involves a series of consecutive and simultaneous reactions occurring through carbocation intermediates (2). The protonation of an olefin. 

A mixture of f erf-butanol and liq. HCN added dr op wise at 25° during 1.5 hrs to an emulsion of adamantane, n-hexane, and 96%-H2S04, stirring continued 0.5 hr. 1-formylaminoadamantane. Y 78%. — Alcohols, such as ferf-butanol, also olefins and alkyl halides, can serve as carbonium ion donors. The tert. hydrogen of isoparaffins reacts particularly easily with these donors. F. e., mostly amines after hydrolysis without isolation of the intermediate acylamines, s. W. Haaf, B. 97, 3234 (1964). 

Coalescence of droplets 1 and 2 result in droplets containing appreciable amounts of isobutane, olefins, and alkylate. As already indicated, reactions between alkylate isoparaffins such as TMPs and olefins cause loss of alkylate quality. Furthermore, the coalescence results in a reduction in the interfacial areas. Fragmentation of droplets, however, results in larger interfacial areas such fragmentation probably occurs mainly in the reactor near the agitation impeller. Coalescence steps likely occur mainly in the regions of the reactor that are farthest removed from the impeller. 

The preceding information indicates the paths to follow in order to obtain stocks of high octane number by refining. The orientation must be towards streams rich in aromatics (reformate) and in isoparaffins (isomerization, alkylation). The olefins present essentially in cracked gasolines can be used only with moderation, considering their low MONs, even if their RONs are attractive. 

We cite isomerization of Cs-Ce paraffinic cuts, aliphatic alkylation making isoparaffinic gasoline from C3-C5 olefins and isobutane, and etherification of C4-C5 olefins with the C1-C2 alcohols. This type of refinery can need more hydrogen than is available from naphtha reforming. Flexibility is greatly improved over the simple conventional refinery. Nonetheless some products are not eliminated, for example, the heavy fuel of marginal quality, and the conversion product qualities may not be adequate, even after severe treatment, to meet certain specifications such as the gasoline octane number, diesel cetane number, and allowable levels of certain components. 

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). 

Alkylate is composed of a mixture of isoparaffins whose octane numbers vary with the olefins from which they were made. Butylenes produce the highest octane numbers, propylene the lowest, and amylenes (pentylenes) the iatermediate values. AH alkylates, however, have high (>87) octane numbers that make them particularly valuable. 

Paraffin alkylation as discussed here refers to the addition reaction of an isoparaffin and an olefin. The desired product is a higher molecular weight paraffin that exhibits a greater degree of branching than either of the reactants. 

Although the alkylation of paraffins can be carried out thermally (3), catalytic alkylation is the basis of all processes in commercial use. Early studies of catalytic alkylation led to the formulation of a proposed mechanism based on a chain of ionic reactions (4—6). The reaction steps include the formation of a light tertiary cation, the addition of the cation to an olefin to form a heavier cation, and the production of a heavier paraffin (alkylate) by a hydride transfer from a light isoparaffin. This last step generates another light tertiary cation to continue the chain. 

The alkylate contains a mixture of isoparaffins, ranging from pentanes to decanes and higher, regardless of the olefins used. The dominant paraffin in the product is 2,2,4-trimethylpentane, also called isooctane. The reaction involves methide-ion transfer and carbenium-ion chain reaction, which is cataly2ed by strong acid. 

Alkylations—for example, of olefins with aromatics or isoparaffins—are catalyzed by sulfuric acid, hydrofluoric acid, BF3 and AICI3. 

A. Corma and A. Martinez. Chemistry, catalysts and processes for isoparaffin-olefin alkylation Actual situation and future trends. Catalysis Review Sci. and Eng., 35 485-523, 1993. 

Corma, A. and Martinez, A. (1993) Chemistry, catalysis, and processes for isoparaffin-olefin alkylation actual situation and future trends. Catal. Rev., Sci. Eng, 35 (4), 483-570. 

The alkylation of light isoparaffins, such as isobutane, with light olefins, such as propene and butenes, is a key process in modern gasoline production. The Cy-Cg... 

Huang, T.J. and Shinnar, R. (1994) Isoparaffin-olefin alkylation process. 

Eberhardt, J., Boll, W., Buchold, H., and Dropsch, H. (2002) Method for catalytically reacting isoparaffins with olefins to from alkylates. WO Patent 02/094747A1. 

The alkylation of isoparaffins with olefins is the reaction involved in the large scale processes in the petroleum industry. Any isoparaffin and almost any olefin can be used and although the product in largest percentage is usually with the number of carbon atoms equal to the sum of the carbon atoms in the paraffin and olefin, this is not always the case. A great mixture of branch chain products is obtained (Phillips Petroleum Company, 13). 

Just as in the case of aromatic compounds isoparaffins can be alkylated with sources of alkyl groups other than olefins. Alkyl halides, alcohols, ethers, mercaptans, sulfides, etc., can be used. When olefins are used some alkyl fluorides from a combination of olefin and hydrogen fluoride are always formed. The quantity of this in the product can be greatly reduced by providing conditions under which the alkyl fluoride is used in alkylation. The apparent paradox is provided, in that the fluoride content of the product is lessened by further treatment with hydrogen fluoride. A more thorough treatment of the details of the alkylation of isoparaffins with olefins is found elsewhere in this volume. 

Alkylation A refinery process for producing high-octane components consisting mainly of branched chain paraffins. The process involves combining light olefins with isoparaffins, usually butene and isobutane, in the presence of a strong acid catalyst such as hydrofluoric or sulfuric acid. 

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