Chlorinated aluminas

ALCOA A process proposed for manufacturing aluminum metal by the electrolysis of molten aluminum chloride, made by chlorinating alumina. It requires 30 percent less power than the Hall-Heroult process and operates at a lower temperature, but has proved difficult to control. Developed by the Aluminum Company of America, Pittsburgh, in the 1970s and operated in Palestine, TX, from 1976 abandoned in 1985 because of corrosion problems and improvements in the efficiency of conventional electrolysis. 

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,... 

In the following section, we will critically review representative methods for measuring surface acidity of solid catalysts. Recommendations will then be made of the most appropriate methods from the standpoint of the needs of the investigator. The final section is devoted to updating research activities dealing with individual solid catalysts. Particular attention will be devoted to studies of acidities of unusually active catalysts such as crystalline zeolites, synthetic clays, and chlorinated aluminas. 

Chlorinated alumina is still one of the mostuseful industrial catalyst for light alkane isomerization with generally a small amount of platinum being added in order to... 

Ayame and co-workers recently prepared a superacid of chlorinated alumina (199-203). A1203 was chlorinated by heat treatment with Cl2 gas at temperatures above 800°C in a circulation reactor the material was active for isomerization of paraffins such as butane, pentane, and cyclohexane (201). The chlorinated alumina showed a surface acidity due to the Lewis type of Ho - 14.52 (202, 203). 

Commercial hydroisomerization catalysts have both a noble metal based hydrogenating function and an acid function (Table 7.3). Traditionally, the acid component is provided by (i) a zeolite or by (ii) a chlorinated alumina substrate or by (iii) a sulfated zirconia carrier, the latter both being extremely intolerant of sulfur, water, and other feed contaminants. The zeolite is generally a mordenite and not a Y-zeolite. However, catalysts based on zeolite omega have been shown to be superior to mordenite-based catalysts, but no up-scale to commercial use has been reported for omega zeolite containing hydroisomerization catalysts (see below). 

Small quantities of sulfur and water will severely reduce isomerization performance and at moderate levels will permanently deactivate chlorinated alumina (that cannot be regenerated) or sulfated zirconia based catalysts. Traditional zeolite based catalysts are also lacking sulfur tolerance, but to a lesser extent. 

The requirements for a new isomerization technology were identified to be (i) tolerance to feed impurities, (ii) robustness, (iii) low capital cost and low permanent operating costs. Reviewing the existing isomerization processes, based on chlorinated alumina catalysts, the following features of an improved catalyst were identified that could lead to a process meeting the company s objectives ... 

There were two main kinds of catalytic systems used in the 60s, both containing platinum chlorinated aluminas and steamed silica-aluminas. Their selectivity and coke-stability were acceptable, but they were not active enough. In the mid-70s, Engelhard came up with the first industrial mordenite-based catalyst that was a major improvement. The great majority of today s processes use Pt-mordenite systems. 

The results obtained show that Yc alumina and chlorinated alumina have the same total number of acid sites 0.59 and 0.58 sites/nm, respectively, and that the number of Lewis acid sites is higher than that of the Bronsted sites (a factor of six for non chlorinated and four for chlorinated alumina). The distribution of acid sites thus appears to have been modified the... 

Iso-butane is a highly demanded chemical in the refinery industry for the production of alkylates (by alkylation with butenes), and methyl tert-butyl ether (MTBE) (from isobutene and methanol), both important additives for reformulated gasolines. n-Butane isomerization is performed over platinum supported on chlorinated alumina. The chlorine compound which is continuously supplied to the feed in order to maintain the activity [1] is harmful to the environment. 

Sulfated zirconias, nowadays a well established class of acid solids first reported by Holm and Bailey [2], and systematically studied by Arata [3] and Tanabe et aL [4], are considered as potential alternative catalysts for the skeletal isomerization of n-butane. These catalysts have recently found a commercial application (Par-Isom Process of UOP) for the isomerization of light naphtha (Cs-Ce), but since they are less active than Pt-chlorinated aluminas, there is a real interest for improving their catalytic performance [5]. 

The selection of the carrier is relatively simple. It may be imposed by the type of reaction to be promoted. For instance, if the latter requires a bifunctional catalyst (metal + acid functions), acidic supports such as silica-aluminas, zeolites, or chlorinated aluminas, will be used. On the other hand, if the reaction occurs only on the metal, a more inert support such as silica will be used. In certain cases, other requirements (shock resistance, thermal conductivity, crush resistance, and flow characteristics) may dominate and structural supports (monoliths) have to be used. For the purpose of obtaining small metal particles, the use of zeolites has turned out to be an effective means to control their size. However, the problem of accessibility and acidity appearing on reduction may mask the evidence of the effect of metal particle size on the catalytic properties. 

Application lsomalk-2 is a broad-range isomerization technology developed by NPP Neftehim, which has been commercially proven in various regions of the world, lsomalk-2 is a competitive alternative to the three most commonly used light gasoline isomerization processes zeolite, chlorinated alumina and sulfated oxide catalysts. 

Schemes 3(a) and 3(b) illustrate pathways in protonated iso-butane and protonated propane respectively. The hypothesis of alkane protonation by solid acids such as zeolites, heteropolyacids, sulfated zirconias, chlorinated aluminas, or supported acids, used in the petrochemical industry, has been a controversial issue since its proposal by Haag and Dessau (1984). ° ...

The acidic solids investigated in this study belong to one the following families 1) bulk oxides [95], 2) doped oxides (chlorinated alumina, doped silica,. ..) [101], 3) supported oxides [109], 4) mixed oxides such as silica-alumina, silica-titania or silica-zirconia, zeolites and clays [11,14], 5) heteropolyanions such as H3PW12O40, H4SiWi204o and H5BW12O40, 6) phosphates (Zr, Al, V, Ti, B, Sn), 7) superacids such as sulfated oxides or Nafion H (perfluororesin sulfonic polymeric acid). 

Chlorinated alumina-supported metal catalysts are the typical catalysts used today for catalytic naphtha reforming, which is performed at temperatures of480-550 °C (410). Modem versions of this type of catalyst are mul-timetaUic the catalytic properties of platinum are improved by the addition of another metal, often rhenium. Further elements that may be added are tin, silicon, germanium, lead, gallium, indium, iridium, thorium, lanthanum, cerium, cobalt, and nickel. AH these components are supported on chlorinated y-alumina (with a surface area of 150—300 m g ), which provides the acid function (411). 

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