Isoparaffin alkylation with olefins

Mechanisms for Liquid-phase Alkylations of Hydrocarbons. Either Friedel-Crafts or protonic acid catalysts are often used when liquid isoparaffins or aromatic hydrocarbons are alkylated with olefins. These catalysts are generally considered to be proton donators which form carbonium ions. The basic reactions are probably similar for all catalysts, and the reaction temperatures are all relatively close to room temperature, about —40 to 30°C. 

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. 

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 chemically combining isoparaffin with olefin hydrocarbons. The product, alkylate, has a high octane value and is blended with motor and aviation gasoline to improve the antiknock value of the fuel. 

In 1945 Mamedaliev published a book in Baku (213) reporting the research carried out in his laboratory on the alkylation of aromatics and isoparaffins with olefins in the presence of a number of catalysts. Subsequent information indicates that Mamedaliev has developed a continuous process of alkylation of benzene with olefins. He also described alkylation of benzene with propylene in the presence of activated clay (214). 

The oldest method of alkylation with ethylene is the liquid phase reaction using anhydrous aluminum chloride as the catalyst. This reaction is a form of the classic Friedel-Crafts reaction and was discovered in 1879 by Balsohn. Most Lewis and Bronsted acids are known to be active for olefin alkylations. Alkylation by H2SO1, and H3PO1, was first shown by Ipatieff, et al, in 1936 who extended the reaction to isoparaffins. For the liquid phase alkylation of benzene with ethylene, however, aluminum chloride is preferred over the other acids, although a co-catalyst or promoter is usually needed to obtain efficient alkylation. AICI3 when dissolved in benzene containing some HCl forms a complex which can be simply described as ... 

The Alkylation of Isoparaffins. It has also been found that branched-Ichain paraffins will combine with olefins in the presence of an acid catalyst. Isobutylene and isobutanc, for example, combine to form a mixture of hydrocarbons from which both normal products (those having a multiple of four carbon atoms) and abnormal products (those having a number of carbon atoms not a multiple of four) have been isolated. A flow sheet is outlined in Chart 1 (see p. 144) which will account for some of the products commonly obtained. 

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). 

Several points need to be emphasized. Eirst, the /-CgHis (frequently indicated in the literature as TMP) is really a mixture of C5-C16 isoparaffins, often with RON values in the 93-94 range. This mixture (or alkylate) is formed basically by mechanism 2 reactions. Second, when n-olefins (propylene, n-butenes, and n-pentenes) are used, the light n-paraffins formed are propane, n-butane, or n-pentane, respectively none are suitable in the gasoline pool. Third, isobutane consumption per production of a given quantity of alkylate is often increased by 6-10% when HE is employed because of the importance of mechanism 4, as compared to little or most likely no importance for alkylations with sulfuric acid. Eourth, C5 olefins are not usually used in the feedstocks when HE is the catalyst because of the large amounts of isopentane and n-pentane produced further, isobutane consumption increases. 

Decomposition of TMPs and Other Isoparaffins TMPs and other isoparaffins in alkylates contain tertiary C-H bonds, which permit degradation reactions. First, sulfuric acid acts as an oxidant to start a series of reactions that convert TMP into a mixture of C4-C16 isoparaffins. Second, because of their tertiary C-H bonds, TMPs react (are actually alkylated) with C3-C5 olefins mechanism 2-type reactions are predominant. Both types of reactions lower the quality and the quantity of the alkylate. 

Alkylation unit Catalytic liquid phase (H2SO4 or HF) Combine isoparaffins with olefins to gasoline... 

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. 

The petroleum industry first obtained gasoline by straight-run distillation. Next the longer molecules were cracked. Now gasoline is being nthesized on a large scale. For this purpose, the most important reaction in all probability is an alkylation wherein olefins, by the aid of catalysts, are made to combine with other molecules such as isoparaffins and aromatics. ... 

Acid-t T)e catalysts. Sulfuric acid of 96-98% concentration catalyzes the alkylation of isoparaffins with butenes and higher molecular weight olefins at 0-20°. Alkylation with propene requires acid of 98-100% concentration and a temperature of 30 . Alkylation with ethylene has not been very successful, presumably because stable ethyl hydrogen sulfate or diethyl sulfate forms too readily. 

Hydrogen transfer resulting in the conversion of more or less of the olefin to paraffin always accompanies the catalytic alkylation of isoparaffins with olefins. At the same time, some of the isoparaffin is converted to paraffin containing twice the number of carbon atoms thus, for example, trimethylpentanes are formed in all isobutane alkylations regardless of the olefin used. 

The action of zirconium cliloride in the alkylation of isoparaffins with olefins and in other hydrocarbon reactions is very similar to that of aluminum chloride, the principal difference being that it requires higher temperatures. Comparatively little information concerning its use has, however, been published. 

Indirectly from his work And one of these reactions was the alkylation of isoparaffins and cycloparaffins with olefins (3). In 1932 Pines and Ipatieff discovered the reaction and it continues today, perhaps even more so, to be a truly significant petroleum refining reaction An example is the alkylation of isobutane with ethylene to give 2,3-dlmethylbutane ... 

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. 

Second, isoparaffins containing tertiary C—H bonds can react, or in a sense be alkylated, when mixed with olefins in the presence of acid catalysts. TMPs can react forming first C12—C20 cations. Mechanism 2- and 3-type reactions then occur. The quality of alkylate is often significantly reduced, and some CPs are also produced. To minimize these undesired reactions of especially TMPs, two procedures should be employed. Reactors are needed that minimize contact between TMPs and olefins. In addition, acid/hydrocarbon dispersions should be separated quickly as soon as the alkylation reactions are completed. Less information is available on undesired reactions when HF is used as the catalyst. 

Alkylation—The alkylation reaction commonly used in the petroleum industry involves condensation of an isoparaffin (e.g., isobutane) with olefins—usually propylene, butylene, or amylene— to produce highly branched gas components with desirable stability properties and high octane number. It is said to be second only to reforming as a means to economical octanes. 

A process is described for improving the octane rating of gasoline by alkylating an olefin with an isoparaffin over a zeolite catalyst above the critical point of the isoparaffin to improve the catalyst longevity. 

December 1998 A process is described for alkylating an isoparaffin and an olefin with a solid alkylation catalyst in an inert solvent where the reaction mixture is under SCF conditions. 

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