Alkylation operating conditions

Butylenes. Butylenes are the primary olefin feedstock to alkylation and produce a product high in trimethylpentanes. The research octane number, which is typically in the range of 94—98, depends on isomer distribution, catalyst, and operating conditions. 

When Wa = substituted aminoacyl, that is, when Wa-Xaa is a peptide, there is a strong tendency to form an oxazolone. The 2-alkyl-5(4//)-oxazolone that is formed is chirally unstable. Isomerization of the 2-alkyl-5(4//)-oxazolone generates diaste-reomeric products. When Wa = R0C=0, there is a lesser tendency to form an oxazolone. The 2-alkoxy-5(4/7)-oxazolone that is formed is chirally stable. No isomerization occurs under normal operating conditions. Finally, when Wa = R0C=0, an additional productive intermediate, the symmetrical anhydride, can and often does form. 

The other controllable variable is the operating conditions. Certain temperature and pressure levels will favor the benzene and not EB alkylation— not exclusively, but predominantly. In fact, these variables can be set to favor the di- and triethylbenzenes to give up an ethyl group to benzene to give EB. That process is called transalkylation and is shown in Figure 8—2. 

For purposes of plant design and for optimum operation consistent with feed stock availability, it is necessary to be able to predict accurately the octanes of the alkylate produced under varying operating conditions. Such a correlation developed from several hundred pilot plant and commercial plant tests is presented in Figures 7, 8, and 9. This correlation is applicable to sulfuric acid alkylation of isobutane with the indicated olefins, and was developed specifically for the impeller-type reaction system, although it also appears to be satisfactory for use with some other types of reactors. 

The ranges of operating conditions normally used in commercial H2S04 and HF alkylation processes are shown in Table I. Both processes operate in the liquid phase at relatively low temperatures. For the best... 

Thermal alkylation was never a totally successful commercial process because of the severe operating conditions required. The reaction was carried out in a heater coil with temperatures of 900°-975°F, pressures in the range of 3000-5000 psig, and contact times of 2-7 seconds (16). Polymerization of the olefins occurred readily under these conditions, and low olefin concentrations had to be used to minimize undesirable side reactions. Ethylene could be alkylated more readily than the higher molecular weight olefins, and either normal butane or isobutane could react with the olefin. In general, the yields and quality of the product were not equal to those obtained with catalytic alkylation. 

The synthetic production of benzene generally involves lire de-alkylation of toluene. In one non-catalyfic process, a hydrogen-rich gas is mixed with liquid toluene feed and preheated prior to charging to the reactor. Toluene reacts with Hie hydrogen to form benzene and methane. The reaction is exothermic Operating conditions approximate 500 1000 psi and 595-760 T. The process provides about 98% yield of benzene. The toluene is recycled. 

These results illustrate the practicality of preparing trialkylamines by the reductive alkylation of dialkylamines with aliphatic ketones. Excellent yields are obtained, particularly with the more reactive and less hindered ketones, such as cyclohexanone and acetone, and with the less hindered secondary amines. Platinum sulfide, or other platinum metal sulfides, are the catalysts of choice when more hindered reagents require more severe operating conditions. 

The examination of patents reveals that the operation conditions for the alkylation of benzene with propylene are temperatures between 150 and 230°C and pressures between 25 and 35 bar. The catalyst productivity expressed as WHSV is in the range 1-10 (based on the reaction mixture) at benzene/propylene molar ratios ranging from 5 to 8. 

In summary, two mechanisms have been proposed to explain the results. One assumes that the ion pairs are formed in the mobile phase and behave as nonionic moities similar to other polar molecules in RPLC. The other rests on the belief that the counterions selectively sorb in the stationary phase and attract and retard the analyte ions by an ion exchange mechanism this mechanism requires that the ion-pair reagent have a hydrophobic end that would be attracted to the alkyl chain on the bonded phase and an ionic site on the other end. Perhaps both mechanisms are partially correct, and the predominant mechanism may depend on the operating conditions. In any case the following discussion will not attempt to distinguish between the mechanisms or justify either one. 

Of course, the reduced crude conversion process is not 100% efficient. By this it is meant that to date no catalyst and operating conditions have been developed which completely remove saturates, monoaromatics, diaromatics, and alkyl substituents of polynuclear aromatics from the slurry oil. Therefore, to predict slurry oil plus coke yield one must determine what proportion of each molecular type present in the reduced crude feedstock remains in the slurry oil and coke. 

The main byproduct forming reactions in the BASF and Monsanto processes are different. In the former it is the liquid phase Fischer-Tropsch-type reaction, that leads to the formation of products such as such as alkyl acetates, methane etc. In the Monsanto process it is the homogeneous water-gas shift reaction that produces C02 and H2 as byproducts. Also note that the Monsanto process is superior in terms of selectivity, metal usage and operating conditions. 

Alkylation chemistry over MCM-22 is characterized by essentially complete ethylene conversion with very high selectivity to ethylbenzene over a wide range of operating conditions. The reaction... 

Thus, in ammonia synthesis, mixed oxide base catalysts allowed new progress towards operating conditions (lower pressure) approaching optimal thermodynamic conditions. Catalytic systems of the same type, with high weight productivity, achieved a decrease of up to 35 per cent in the size of the reactor for the synthesis of acrylonitrile by ammoxidation. Also worth mentioning is the vast development enjoyed as catalysis by artificial zeolites (molecular sieves). Their use as a precious metal support, or as a substitute for conventional silico-aluminaies. led to catalytic systems with much higher activity and selectivity in aromatic hydrocarbon conversion processes (xylene isomerization, toluene dismutation), in benzene alkylation, and even in the oxychlorination of ethane to vinyl chloride. 

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