Isobutane, alkylation with olefins

Fluorinated silica and alumina have also been used for isobutane alkylation with olefins in a batch reactor at 0°C. The fluorinated alumina was active only when mixed with BF3 H2O, but the fluorinated silica was active by itself The selectivity to trimethylpentanes obtained with these catalysts is much lower than that obtained with H2SO4 as a catalyst (48). At 80°C, however, F/AI2O3 catalysts are active for isobutane/2-butene alkylation, though relatively low butene conversions (27% for the most active catalyst containing 1.3% F) are obtained (49). As expected, octenes are the predominant hydrocarbons in the Cg fraction at such a low conversions. The F/AI2O3 catalysts contained both Bronsted and Lewis acid sites in a proportion that depends on the F loading. A good correlation between... 

A clear example of the possible use of acid and/or superacid solids as catalysts is the alkylation of isobutane with butenes. Isobutane alkylation with low-molecular-weight olefins is one of the most important refining process for the production of high-octane number (RON and MON), low red vapor pressure (RVP) gasoline. Currently, the reaction is carried out using H2SO4 or HF (Table 13.1), although several catalytic systems have been studied in the last few years. 

The skeletal isomerization of straight-chain paraffins is important for the enhancement of the octane numbers of light petroleum fractions. The isomerization of H-butane to isobutane has attracted much attention because isobutane is a feedstock for alkylation with olefins and MTBE synthesis. It is widely believed that the low-temperature transformation of n-alkanes can be catalyzed only by superacidic sites, and this reaction has often been used to test for the presence of these sites. 

Isobutane Alkylation with C4 Olefins Low Temperature Regeneration of Solid Acid Catalysts with Ozone... 

The regeneration of Y-zeolite catalysts used in isobutane alkylation with C4 olefins was studied. The coke formed on these catalysts during this reaction needs temperatures higher than 500°C to be burnt off with air. Ozone was used in this study to eliminate most of the coke at a much lower temperature. After a treatment at 125 C with ozone, the small amount of coke remaining on the catalyst can be removed with air at 250°C. The ozone not only eliminates coke from the catalyst, but also modifies its burning characteristics as measured by Temperature Programmed Oxidation, shifting the peak to lower temperatures. This allows a combined treatment with ozone at 125°C followed by air at 250°C to restore the activity and stability of Y-zeolite catalysts for isobutane alkylation. 

The zeolite catalysts deactivate very fast during the isobutane alkylation with C4 olefins due to coke deposition. This coke requires very high temperature and long times to be fully eliminated in air. However, the regeneration in ozone can be carried out at low temperatures. 

Note, however, that liquid acids are still largely used in refinery and petrochemical processes. For example, HF alkylation (for isobutane alkylation with light olefins) is still among the top-ten refining processes licensed by UOP, with over 100 units installed worldwide. However, UOP introduced from 2002 the Alkylene process, which uses a liquid phase riser reactor with a solid acid catalyst for the isobutane alkylation. However, HF alkylation remains the best economic choice [223], notwithstanding environmental and corrosion problems. Also in this case, the conventional process has been improved, for example by HF aerosol vapor suppression. Other aspects of isobutane alkylation have been reviewed by Hommeltoft [224]. 

In aromatic alkylation with olefins, the solid acid catalyst based process has instead largely substituted the homogeneous acid catalysis process. This evidences that the change of substrate (isobutane vs. aromatic) could change completely the applicability of one technology with respect to another. 

Isobutane Alkylation. The deactivation of solid acid catalysts due to coke deposition is the cause of not having as yet, a commercially available process for isobutane alkylation with C4 olefins, using solid acid catalysts. The coke on these catalysts have been characterized with TPO analyses . The TPO profiles on zeolites used in this reaction, displayed two well defined burning zones. One peak below 300°C, and the other at high temperatures. The relative size of these peaks depends on the zeolite and the reaction temperature. In the case of the mordenite, the first peak was the most important, and in the case of the Y-zeolite, at 50°C or... 

The coke deposited during the isobutane alkylation with C4 olefins on zeolites was extracted with a mixture of methanol/toluene, and with CI2CH2. None of these solvents were effective to remove the coke. Only a very small fraction was removed, which was attributed to the dissolution of external coke. The coke molecules formed inside the channels have a large size and therefore cannot diffuse out of the pores . 

Figure 10 UV-VIS spectra of LaHY zeolite used in a semi-batch reactor, isobutane alkylation with C4 olefins, (I) Influence of reaction temperature at LHSV=4.07 h , (A)80 °C, (B) 100°C (II) influence ofLHSVat 80 °C, (A) 2.27 h (B) 3.86 h , (C) 4.07 h (from Ref 55)...

Svlfuric Add Alkylation. Despite some disadvantages, such as acid-reGOLYery expense and refrigeration to minimize oxidation, about four fifths of the alkylate produced for motor fuels is based on sulfuric acid as a catalyst. As with HF alkylation, isobutane is alkylated with olefins (other than ethylene), and a flow diagram for such a process is ven in Fig. 14-5. 

Zeolites catalyze alkylation of alkanes with olefins [76], The mechanism proposed for isobutane alkylation with butene is shown in Scheme III. 11 (the alkoxy species shown schematically are bound to the catalyst surface) [76a]. 

Isobutane alkylation with C4 olefins regeneration of metal-containing catalysts... 

The principal use of the alkylation process is the production of high octane aviation and motor gasoline blending stocks by the chemical addition of C2, C3, C4, or C5 olefins or mixtures of these olefins to an iso-paraffin, usually isobutane. Alkylation of benzene with olefins to produce styrene, cumene, and detergent alkylate are petrochemical processes. The alkylation reaction can be promoted by concentrated sulfuric acid, hydrofluoric acid, aluminum chloride, or boron fluoride at low temperatures. Thermal alkylation is possible at high temperatures and very high pressures. 

To obtain light ends conversion, alkylation and polymerization are used to increase the relative amounts of liquid fuel products manufactured. Alkylation converts olefins, (propylene, butylenes, amylenes, etc.), into high octane gasoline by reacting them with isobutane. Polymerization involves reaction of propylene and/or butylenes to produce an unsamrated hydrocarbon mixture in the motor gasoline boiling range. 

Flowever, information concerning the characteristics of these systems under the conditions of a continuous process is still very limited. From a practical point of view, the concept of ionic liquid multiphasic catalysis can be applicable only if the resultant catalytic lifetimes and the elution losses of catalytic components into the organic or extractant layer containing products are within commercially acceptable ranges. To illustrate these points, two examples of applications mn on continuous pilot operation are described (i) biphasic dimerization of olefins catalyzed by nickel complexes in chloroaluminates, and (ii) biphasic alkylation of aromatic hydrocarbons with olefins and light olefin alkylation with isobutane, catalyzed by acidic chloroaluminates. 

Alkylation in the petroleum industry, a process by which an olefin (e.g., ethylene) is combined with a branched-chain hydrocarbon (e.g., isobutane) alkylation may be accomplished as a thermal or a catalytic reaction. 

A. Mantilla-Ramirez, G. Ferrat-Torres, J.M. Dominguez, C. Aldana-Rivero, and M. Bernal. Influence of reaction parameters and comparison of fluorinated alumina and silica supports in the heterogeneous alkylation of isobutane with olefins. Appl. Cat. A, 143 203-214, 1996. 

The proposed mechanisms may also be used to explain the formation of paraffins having both lower and higher molecular weights than would be expected from simple addition of olefin molecules to isobutane molecules. A typical example is the formation of heptanes and nonanes when isobutane is alkylated with butene. The first step consists of... 

Although the preceding discussion of the sulfuric and hydrofluoric acid processes has been confined to butene alkylation, isobutane has also been alkylated commercially with other olefins. Ethylene, propylene, pentenes, and dimers of butenes have been used for this purpose. It is also possible to use these olefins for the alkylation of isopentane. Such an operation, however, has not achieved commercial acceptance because it produces an inferior alkylate with a high catalyst consumption, and because isopentane is a satisfactory aviation gasoline component in its own right. 

Formation of C8 alkanes in the alkylation of isobutane even when it reacts with propene or pentenes is explained by the ready formation of isobutylene in the systems (by olefin oligomerization-cleavage reaction) (Scheme 5.2). Hydrogen transfer converting an alkane to an alkene is also a side reaction of acid-catalyzed alkylations. Isobutylene thus formed may participate in alkylation Cg alkanes, therefore, are formed via the isobutylene-isobutane alkylation. 

Alkylation processes usually combine isobutane with an alkene or with mixed alkene streams (C3-C5 olefins from FCC units). The best octane ratings are attained when isobutane is alkylated with butylenes. Alkylation of higher-molecular-weight hydrocarbons (>C5) is less economic because of increased probability of side reactions. Phillips developed a technology that combines its triolefin process (metathesis of propylene to produce ethylene and 2-butenes) with alkylation since 2-butenes yield better alkylate than propylene.290 Since ethylene cannot be readily used in protic acid-catalyzed alkylations, a process employing AICI3 promoted by water was also developed.291... 

Paushkin and Topchiev also used H3P()4-BF3 at room temperature to alkylate benzene with olefins (287,402). For alkylation of benzene with alcohols, temperatures of 90-97° and a feed mole ratio of 0.5 alcohol 1.0 benzene 0.5 catalyst were recommended (394). In a recent study (400a) these authors supplemented their previously published views (396) concerning the properties of boron fluoride complexes with phosphoric acid, alcohols, and sulfuric acid as catalysts. Data on the electroconductivity of these catalysts was correlated with their activity in alkylation of isobutane and it was concluded (400a) that the acid ion concentration did not affect the alkylation or polymerization reactions over these catalysts, and therefore the carbonium ion mechanism was not applicable. 

In the case of zeolites, an additional pathway has been proposed involving the formation of a non-classical carbonium ion by protonation of isobutane, which can alkylate the olefin with formation of a protonated cyclopropane intermediate (60,61) ... 

Chain Initiotion. The theory pxKtulated by a number of investigators (Cupit etal., 1961, Schmerling, 1955) is that carbonium ions are generated by addition of a proton (H+) to an olefin molecule in the presence of HF. Albright and Li, 1970, and Hofmann and Schriesheim, 1962, indicate that initiation steps with H2SO4 catalyst may involve red oil hydrocarbons. However, only the tertiary butyl carbonium ion performs the chain carrying function in isobutane alkylation. Reactions follow ... 

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