Alkylation of hydrocarbons

The use of a single-stage CSTR for HF alkylation of hydrocarbons in a special forced-circulation shell-and-tube arrangement (for heat transfer) is illustrated by Perry et al. (1984, p. 21-6). The emulsion copolymerization of styrene and butadiene to form the synthetic rubber SBR is carried out in a multistage CSTR. 

The catalysis by protonated zeolites, used in industrial cracking, isomerization and alkylation of hydrocarbons, involves proton transfer and formation of carbenium or car-bonium ions as reactive intermediates488,489. To understand the function of the zeolite, the reactions between CD4 and acidic hydrogens of OH groups of two zeolite samples have been studied recently490. 

Gas reversion a combination of thermal cracking or reforming of naphtha with thermal polymerization or alkylation of hydrocarbon gases carried out in the same reaction zone. 

In their protonated forms, zeolites are widely employed in the oil and petrochemical industries, in processes such as the conversion of alcohols to gasoline, catalytic cracking, isomerization and alkylations of hydrocarbons [3]. These chemical reactions most probably involve proton transfer from the acidic site of the zeolite to the organic substrate. In the case of hydrocarbons, this transfer gives rise to carbenium (I) or carbonium (II) ions as intermediates or transition states. 

Extensive studies of the alkylation of thiophene and its derivatives with olefins and alcohols have been made. The catalysts are the same as those employed for the alkylation of hydrocarbons. Alkylation occurs predominently in the 2-position, and the yields ate in the range of 60% to 80%. 

The information about synthetic mordenite properties was obtained in 1961 when Keough and Sand (7) found that H- and other forms of this crystalline aluminum silicate display high activity and selectivity in the reactions of hydrocarbon cracking and ethanol dehydration. Later this zeolite was shown (J, 2, 5, 7, 8, 10-13, 15, 16) an active catalyst in the reactions of isomerization, cracking, and alkylation of hydrocarbons and alcohol dehydration. However, the catalytic properties of mordenite have been studied insufEciently, compared with those of other zeolites. 

Liquid-liquid reactions are sometimes encountered. Alkylation of hydrocarbons with aqueous solution of sulfuric acid as a catalyst is an example. As in liquid-solid systems, definition of the liquid phase containing the catalyst may be difficult, reducing the effectiveness of a fundamental analysis in terms of chemical and physical steps. 

Zeolites are well known for their ability to absorb molecules selectively and as acid-base catalysts for, e.g. cracking, isomerisation and alkylation of hydrocarbons. They are aluminosilicates (Si,Al) c02j with an... 

This type of alkylation is frequently referred to as alkylation of hydrocarbons, and many of the instances are ijupldar alkylations. In the main, the same reagents are employed as for the other classifications. 

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. 

Mechanisms of Vapor-phase Alkylations of Hydrocarbons. Paraffins can be alkylated in the absence of catalysts at sufficiently high temperatures, about 500°C, so that a small amount of the paraffins will decompose into free radicals. A free-radical mechanism for the alkylation seems probable, as is shown below for the reaction between propane and ethylene ... 

Aluminum chloride dissolves in as little as its own weight of the readily available nitroparaflins, nitromethane, nitroethane, and the two nitro-propanes. The resulting solutions, particularly those employing nitromethane, are catalysts for the alkylation of isobutane, hydrogen chloride serving as a promoter (Schmerling, 28). On the other hand, solutions of aluminum chloride in molecular excess of ethers, ketones, and alcohols are catalytically inactive, at least for the alkylation of hydrocarbons. 

Egloff and Morrell, Alkylation of Hydrocarbons, Symposium on Role of Catalysts. . . , ACS Baltimore Meeting, April, 1939. 

Refiners will turn to reformulated motor fuels where the octane number will be increased by alkylate or oxygenated compounds. It has indeed been shown for a long time that oxygenated compounds, alcohols, ethers and ketones Improved the octane number of hydrocarbon-based blends (Whitcomb, 1975). 

Sheppard N and De La Cruz C 1998 Vibrational spectra of hydrocarbons adsorbed on metals. Part II. Adsorbed acyclic alkynes and alkanes, cyclic hydrocarbons including aromatics and surface hydrocarbon groups derived from the decomposition of alkyl halides, etc Adv. Catal. 42 181-313... 

Wurtz - Fittig reaction. The interaction of an aryl halide, alkyl hahde and sodium gives a reasonable yield of an alkyl aryl hydrocarbon, for example ... 

This may be a factor while aeid-catalyzed transformations (isomerization, alkylation) of saturated hydrocarbons proceed preferentially in excess strong acid media. 

Another type of soHd supetacid is based on perfluorinated resin sulfonic acid such as the acid form of Du Font s Nafion resin, a copolymer of a perfluorinated epoxide and vinylsulfonic acid or soHd, high molecular weight petfluotoalkanesulfonic acids such as petfluotodecanesulfonic acid, CF2(CF2)qS02H. Such sohd catalysts have been found efficient in many alkylations of aromatic hydrocarbons (225) and other Friedel-Crafts reactions (226). 

Friedel-Crafts (Lewis) acids have been shown to be much more effective in the initiation of cationic polymerization when in the presence of a cocatalyst such as water, alkyl haUdes, and protic acids. Virtually all feedstocks used in the synthesis of hydrocarbon resins contain at least traces of water, which serves as a cocatalyst. The accepted mechanism for the activation of boron trifluoride in the presence of water is shown in equation 1 (10). Other Lewis acids are activated by similar mechanisms. In a more general sense, water may be replaced by any appropriate electron-donating species (eg, ether, alcohol, alkyl haUde) to generate a cationic intermediate and a Lewis acid complex counterion. 

Catalysis. As of mid-1995, zeoHte-based catalysts are employed in catalytic cracking, hydrocracking, isomerization of paraffins and substituted aromatics, disproportionation and alkylation of aromatics, dewaxing of distillate fuels and lube basestocks, and in a process for converting methanol to hydrocarbons (54). 

Nitriles. Nitriles can be prepared by a number of methods, including ( /) the reaction of alkyl haHdes with alkaH metal cyanides, (2) addition of hydrogen cyanide to a carbon—carbon, carbon—oxygen, or carbon—nitrogen multiple bond, (2) reaction of hydrogen cyanide with a carboxyHc acid over a dehydration catalyst, and (4) ammoxidation of hydrocarbons containing an activated methyl group. For reviews on the preparation of nitriles see references 14 and 15. 

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