Physical isobutane alkylation

PFAS were obtained with 2 moles of water, for each mole of acid and they could not be dehydrated with physical methods. Hydrated acids, both as such and supported on silica using water as solvent, were not active in isobutane alkylation. Therefore the effect of different dehydrating solvent was studied, in order to remove residual water. The catalysts obtained by supporting perfluoroethanedisulphonic acid on Si02 (PFES-Si02) after dissolution in various dehydrating solvents were tested in the reaction and resulted active with high butene conversion (Table 1). 

Intermediates and causes them to abstract hydride Ions more rapidly from Isobutane or any other potential donor. Increased hydride transfer converts more of the carbonlum Ions at the add Interface to saturates faster, yielding product while minimizing polymerization and side reactions. It Is also likely that the surfactants physically block alkyl Ions from one another in the surface film and thus Impede Ion + olefin polymerization. In such a film the carbonlum Ion concentration must also be lower than In the absence of surfactant and mass law effects will therefore also lead to less polymerization and cracking. The fact that steady state hydride transfer rates In H2SO are subject to control through the use of acid modifiers which act In the bulk acid and at the acid-hydrocarbon Interface Is the key to the control of sulfuric acid alkylation. 

Effects of Water in HF Catalyst. A number of investigators have pointed out that water has an important role in alkylation catalysts. Schmer-ling (1955) stated that the use of HF catalyst with one percent water produced a favorable result In propylene-isobutane alkylation, whereas, with a catalyst containing ten percent water, isopropyl fluoride was the principal product and no alkylate was formed. (Both reactions were at 25C.) Albright et al. (1972) found the water content of sulfuric acid to be "highly important" In affecting the quality and yield of butene-isobutane alkylate. They postulated that the water content of sulfuric acid controlled the level of ionization and hydride transfer rate In the catalyst phase. It appears that dissolved water affects HF alkylation catalyst similarly and also exerts further physical influence on the catalyst phase such as reducing viscosity. Interfacial tension, and isobutane solubility. 

This contribution is an in-depth review of chemical and technological aspects of the alkylation of isobutane with lightalkenes, focused on the mechanisms operative with both liquid and solid acid catalysts. The differences in importance of the individual mechanistic steps are discussed in terms of the physical-chemical properties of specific catalysts. The impact of important process parameters on alkylation performance is deduced from the mechanism. The established industrial processes based on the application of liquid acids and recent process developments involving solid acid catalysts are described briefly. 2004 Elsevier Inc. 

J.A. (1998) Influence of the activation temperature on the physical properties and catalytic activity of La-X zeolites for isobutane/n-butene alkylation. Micropor. Mesopor. Mater., 22, 379-388. 

Carlier fundamental studies of autoxidations of hydrocarbons have concentrated on liquid-phase oxidations below 100 °C., gas-phase oxidations above 200°C., and reactions of alkyl radicals with oxygen in the gas phase at 25°C. To investigate the transitions between these three regions, we have studied the oxidation of isobutane (2-methylpropane) between 50° and 155°C., emphasizing the kinetics and products. Isobutane was chosen because its oxidation has been studied in both the gas and liquid phases (9, 34, 36), and both the products and intermediate radicals are simple and known. Its physical properties make both gas- and liquid -phase studies feasible at 100°C. where primary oxidation products are stable and initiation and oxidation rates are convenient. 

Physical Steps During Alkylation. Physical steps that occur during alkylation of isobutane have key roles in affecting the overall process and in the composition (and quality) of the alkylate produced (3). The transfer of Isobutane to the reaction site (which is at or close to the Interface between the two phases) is In general the controlling physical step. It is affected by several operating variables. Agitation is, of course, an obvious variable since It affects not only the Isobutane transfer step but also the interfaclal area. Other variables that affect the Isobutane transfer step Include the Isobutane-to-olefin feed ratio. 

In addition to agitation, the interfacial areas are significantly affected by the following acid/hydrocarbon ratio, acid composition (and especially the amounts of dissolved conjunct polymers), and temperature. Conjunct polymers are surfactants that collect in appreciable concentrations at the interface. Here, they act as a reservoir of H s in the transfer steps from isobutane or other isoparaffins to the i-Cs to i-Cie cations. Conjunct polymers also have a major effect on the viscosity and other physical properties of the acid phase. In the alkylation reactor, the preferred sulfuric acid and HF phases contain appreciable amounts of conjunct polymers optimum amounts result in higher RON values, higher yields, less byproducts, etc. 

Li, K.W. Eckert, R.E. Albright, L.F. Alkylation of isobutane with light olefins using sulfuric acid operating variables affecting physical phenomena only. Ind. Eng. Chem. Process Des. Dev. 1970,9,434. 

Investigations of both the chemistry and physical phenomena that occur during alkylation reactions have been highly successful in improving commercial processes. Yet, further improvements seem possible. For the alkylation of isobutane, the following objectives are desired higher quality alkylates, increased yields of... 

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