Cracking and alkylation

In the production of gasoline, both cracking and alkylation are employed, although they are chemical opposites of each other. Define cracking and alkylation as they apply to the production of gasoline. 

The fundamental step in acid-catalyzed hydrocarbon conversion processes is the formation of the intermediate carbocations. Whereas all studies involving isomerization, cracking, and alkylation reactions under acidic conditions (Scheme 5.1) agree that a trivalent carbocation (carbenium ion) is the key intermediate, the mode of their formation of this reactive species from the neutral hydrocarbon remained controversial for many years. 

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. 

The analysis of volatile products of the conversion of cyclohexene over Al-MCM-41 with various A1 contents has revealed that the reaction runs mainly according to two mechanisms known as cyclohexene skeletal isomerization (CSl) and cyclohexene hydrogen transfer (HT). The results show which of the two schemes predominates, depending on the reaction temperature and the A1 content of the catalyst. The processes of CSI and HT are accompanied by cracking and alkylation, which are proved by the presence of products with 1 to 9 carbon atoms even though the Ce compounds strongly prevail in all cases. Composition of the volatile products of the conversion depends on both concentration and strength of Bronsted and Lewis acid centres. 

Catalytic cracking is a key refining process along with catalytic reforming and alkylation for the production of gasoline. Operating at low pressure and in the gas phase, it uses the catalyst as a solid heat transfer medium. The reaction temperature is 500-540°C and residence time is on the order of one second. 

The cyanoacryhc esters are prepared via the Knoevenagel condensation reaction (5), in which the corresponding alkyl cyanoacetate reacts with formaldehyde in the presence of a basic catalyst to form a low molecular weight polymer. The polymer slurry is acidified and the water is removed. Subsequendy, the polymer is cracked and redistilled at a high temperature onto a suitable stabilizer combination to prevent premature repolymerization. Strong protonic or Lewis acids are normally used in combination with small amounts of a free-radical stabilizer. 

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). 

A small fraction of the hydrocarbons decompose and deposit on the catalyst as carbon. Although the effect is minute ia terms of yield losses, this carbon can stiU significantly reduce the activity of the catalyst. The carbon is formed from cracking of alkyl groups on the aromatic ring and of nonaromatics present ia certain ethylbenzene feedstocks. It can be removed by the water gas reaction, which is catalyzed by potassium compounds ia the catalyst. Steam, which is... 

The /V-alkyl-/V-aryl- -PDAs (where the aryl is phenyl and the alkyl may be cyclohexyl, 1,3-dimethylbutyl or 1-methylethyl) ate the most widely used /)-PDAs. These derivatives reduce the rate of crack growth and also the number of cracks. The alkyl-aryl- -PDAs are in general excellent antiozonants, particularly in dynamic environments. These derivatives are destroyed only slowly by oxygen and increase the scorchiness of the stock only slightly. These are intermediate in staining among the three classes of -PDAs. 

The effect of ozone is complicated in so far as its effect is largely at or near the surface and is of greatest consequence in lightly stressed rubbers. Cracks are formed with an axis perpendicular to the applied stress and the number of cracks increases with the extent of stress. The greatest effect occurs when there are only a few cracks which grow in size without the interference of neighbouring cracks and this may lead to catastrophic failure. Under static conditions of service the use of hydrocarbon waxes which bloom to the surface because of their crystalline nature give some protection but where dynamic conditions are encountered the saturated hydrocarbon waxes are usually used in conjunction with an antiozonant. To date the most effective of these are secondary alkyl-aryl-p-phenylenediamines such as /V-isopropyl-jV-phenyl-p-phenylenediamine (IPPD). 

Toxicity and Environmental Fate Information for Propylene CAS 115-07-1 Sourtes. Propylene (propene) is one of the light ends formed during catalytic and thermal cracking and coking operations, it is usually collected and used as a feedstock to the alkylation unit. Propylene is volatile and soluble in water making releases to both air and water significant. 

Detergent manufacturing Catalytic cracking and hydrocracking Xylene isomerization, benzene alkylation, catalytic cracking, catalyst dewaxing, and methanol conversion. 

Tanabe and Hdlderich (1999) have given an extensive statistical survey of industrial processes using solid acids/bases as catalysts. Over 300 solids and bases have been covered. A variety of reactions like alkylation, isomerization, amination, cracking, and etherification with catalysts like zeolites, oxides, complex oxides, phosphates and ion-exchange resins have been covered. Over 120 industrial processes are referred with 180 different catalysts. 

Surfactants can be produced from both petrochemical resources and/or renewable, mostly oleochemical, feedstocks. Crude oil and natural gas make up the first class while palm oil (+kernel oil), tallow and coconut oil are the most relevant representatives of the group of renewable resources. Though the worldwide supplies of crude oil and natural gas are limited—estimated in 1996 at 131 X 1091 and 77 X 109 m3, respectively [28]—it is not expected that this will cause concern in the coming decades or even until the next century. In this respect it should be stressed that surfactant products only represent 1.5% of all petrochemical uses. Regarding the petrochemically derived raw materials, the main starting products comprise ethylene, n-paraffins and benzene obtained from crude oil by industrial processes such as distillation, cracking and adsorption/desorption. The primary products are subsequently converted to a series of intermediates like a-olefins, oxo-alcohols, primary alcohols, ethylene oxide and alkyl benzenes, which are then further modified to yield the desired surfactants. 

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