Catalysts isobutane alkylation

A similar type of catalyst including a supported noble metal for regeneration was described extensively in a series of patents assigned to UOP (209-214). The catalysts were prepared by the sublimation of metal halides, especially aluminum chloride and boron trifluoride, onto an alumina carrier modified with alkali or rare earth-alkali metal ions. The noble metal was preferably deposited in an eggshell concentration profile. An earlier patent assigned to Texaco (215) describes the use of chlorinated alumina in the isobutane alkylation with higher alkenes, especially hexenes. TMPs were supposed to form via self-alkylation. Fluorinated alumina and silica samples were also tested in isobutane alkylation,... 

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. 

Figure 13.8 Catalyst decay during the isobutane alkylation on nafion/Si02, sulfated zirconia, beta-zeolite, and MCM-41-supported 12-tungstophosphoric acid.

M.C. Clark and B. Subramaniam. Extended alkylate production activity during fixed-bed supercritical 1-butene/isobutane alkylation on solid-acid catalyst using carbon dioxide as a diluent. Ind. Eng. Chem,. Res., 37(4) 1243-1250, 1998. 

Such reactions can take place predominantly in either the continuous or disperse phase or in both phases or mainly at the interface. Mutual solubilities, distribution coefficients, and the amount of interfadal surface are factors that determine the overall rate of conversion. Stirred tanks with power inputs of 5-10 HP/1000 gal or extraction-type equipment of various kinds are used to enhance mass transfer. Horizontal TFRs usually are impractical unless sufficiently stable emulsions can be formed, but mixing baffles at intervals are helpful if there are strong reasons for using such equipment. Multistage stirred chambers in a single shell are used for example in butene-isobutane alkylation with sulfuric acid catalyst. Other liquid-liquid processes listed in Table 17.1 are numbers 8, 27, 45, 78, and 90. 

SUPPORTED PERFLUOROALKANEDISULPHONIC ACIDS AS CATALYSTS IN ISOBUTANE ALKYLATION... 

Perfluoroalkanedisulphonic acids (PFAS) are solid and possess strong acid properties both in solid state and in solution. To our knowledge, they have never been used in the alkylation of isobutane. They were obtained as dihydrate and as such were not acidic enough to be active in isobutane alkylation. Furthermore, they possessed low surface areas. The surface area can be increased by supporting PFAS on an amorphous solid, but it is critical that the solid does not attenuate the acid strength, We have found that a method for dehydrating PFAS and for supporting it on silica. The method allows to obtain an new catalyst, PFAS-Si(>2, which is active in the alkylation of isobutane. 

Supported Perfluoroalkanedisulphonic Acids as Catalysts in 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). 

The relative location of refinery and acid plant is one of the most important factors in the economic decision between sulfuric acid and anhydrous hydrogen fluoride as a catalyst for alkylation. Besides the distance, other factors such as regeneration of spent acid, energy costs, the nature of the feed and increasingly stringent regulatory constraints play an important role in the selection of alkylation catalyst. Sulfuric acid is selected for alkylation if feed is rich in pentenes or n-butene. HF is selected if the feed is rich in propenes or isobutane. 

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 ... 

Normal Butene Reactions. Under alkylation conditions, all four butene isomers are believed to undergo isomerization, dimerization, and co-dimerization when first coming in contact with HF catalyst, i.e., immediately following protonation. These are very rapid, Ionic reactions and take place competitively along with isobutane alkylation. Alkylate compositions from the four butenes are basically similar (see Table VII). However, l-butene produces a C3 fraction containing nearly two times... 

Propylene Reactions. The following reaction mechanisms are generally 7ecognTzeTM tlTeprinci pa I ones occurring in propylene-isobutane alkylation with hydrofluoric acid catalyst (Ciapetta, 1945). In pnirenthe-ses are shown amounts of oroducts from each mechanism these are from Table VII for propylene ... 

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. 

Also shown in Table II is the effect of olefin space velocity. Comparison of Runs 4 and 6 shows that the Amberlyst-I5/BF3 catalyst can alkylate isobutane with butene in good yield at an olefin WHSV of 2.6 g olefin/g resin-hour. The alkylate yields are slightly lower than the theoretical value of 2,04 due to removal of some of the reactor contents via the on-line sampling system. The yields shown are based on the liquid... 

In the present paper, catalytic activity of a number of zeolltic catalysts In alkylation of Isobutane with various olefins have been Investigated and some considerations of ethylene alkylation have been made. 

Slightly over half of the papers deal with the alkylation of isobutane widi light olefins to produce high quality gasoline blending hydrocarbons. New information is presented for isobutane alkylation relative to die chemistry and mechanism, process improvements, recovery of acid catalyst, and status of commercial units. Papers are also presented for die alkylation of aromatics, heterocyclics, coal, and other hydrocarbons. Alkylations using transition metal catalysts, strong acids, free radicals, and bases are also reported. 

The first group of papers (chapters 1-12) covers the more theoretical and fundamental aspects of alkylation, including the chemistry, mechanism, and various techniques and catalysts that can be used besides sulfuric acid and hydrogen fluoride. Most papers of this group deal with isobutane alkylation for production of high quality fuels. 

The second group of papers (chapters 13-20) discusses the more practical aspects of isobutane alkylation including mixing, reaction variables, computer modeling, recovery of catalyst, and an alternate fuel to alkylate. 

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. 

Zeolites (6,7), heteropolyacids (8,9), sulfated zirconia (10,11), and other materials (12) have already been explored. All of these materials deactivate in a rather short time, ranged in the order of minutes to hours, and therefore any process involving solid acid catalysts for isobutane alkylation would require frequent regenerations. 

In this work, the regeneration with ozone of Y-zeolite catalysts, exchanged with lanthanum, is studied. The objective is to find a low temperature regeneration procedure for the solid acid catalysts used in the isobutane alkylation reaction. 

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. 

The low temperature regeneration procedure using ozone could be an option to be considered for a process of isobutane alkylation with solid acid catalysts. 

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