Clay catalysts activated

Table 3. Acylation of mesitylene by benzoyl chloride with either supported ( ) or exchanged clay catalysts ( ) ( activation temperature) [56].

Zinc chloride exchanged clay catalysts have been reported to be highly active for the Friedel-Crafts alkylation and acylation reactions these are commercially sold by Contract Catalysts under the name Envirocats. These are montmorillonite catalysts modified by ZnCU and FeCli. Some of the reported examples of Friedel-Crafts reactions are given below there are claims that some of the processes are commercially practised. 

Kaolin had little or no cracking activity, and catalyst activity as tested in the laboratory was directly related to silica-alumina gel content. However, the catalyst performed much better in commercial tests than anticipated from laboratory testing. Undoubtedly, this open structure encountered much less severe conditions at the outer surface of the microsphere during regenerations and made internal catalytic surfaces more readily available. This first of the so-called "semisynthetics" was called Nalco 783, and the matrix is still used in many forms some 28 years later.(7,13) Today it is estimated that some 200,000 tons/yr. of kaolin clay is used for cracking catalyst manufacture as reported by Georgia Kaolin Corporation.(24) Figure 10 shows the pore volume distribution for Nalco 783 and two other commercial semisynthetics from that period. 

The activity advantage of zeolite catalysts over amorphous silica-alumina has well been documented, Weisz and his associates [1] reported that faujasite Y zeolite showed 10 to 10 times greater activity for the cracking of n-hexane than silica-alumina. Wang and Lunsford et al. [2] also noted that acidic Y zeolites were active for the disproportionation of toluene while silica-alumina was inactive. The activity difference between zeolite and silica-alumina has been attributed to their acidic properties. It is, however, difficult to explain the superactivity of zeolite relative to silica-alumina on the basis of acidity, since the number of acid sites of Y-type zeolite is only about 10 times larger than that of silica-alumina. To account for it, Wang et al. [2] proposed that the microporous structure of zeolite enhanced the concentration of reactant molecules at the acid sites. The purpose of the present work is to show that such a microporous effect is valid for pillared clay catalysts. 

Figure 7. Activity of the Mega Dry clay catalyst, before and after regeneration at 550 X for 4,5 h. (Cat. = 9 g T = 290 X P = 0.1 MPa Feed = 2.8 M DMEDXH3OH solution inNzflow LHSV= 0.92 h ).

Compared to sulfuric acid, the clay catalysts produced a cleaner biodiesel due to their bleaching activity. Thus, unrefined oils or waste cooking oils could be employed as feedstock without pretreatment. However, the performance of the clays diminished with repeated use and catalysts had to be reactivated after each run to maintain peak performance, suggesting that some leaching of sulfuric acid took place. 

The presence of an organophilic clay increases the catalyst activity (10). Suitable clays include montmorillonite, hectorite, mica, etc. For example, Lucentite is a trioctylmonomethylammonium salt-treated synthetic hectorite. The clays are modified with quaternary ammonium compounds. The clays are heat treated prior to their use in the polymerization process. Further, the incorporated clay can improve the performance of the UHMWPE or function as filler. 

The alkylation is achieved using an acid activated clay catalyst (73). The reaction is performed in nitrogen atmosphere. Namely, nitrogen gas atmosphere or other inert gas atmospheres, in contrast to air gas atmosphere, suppress the formation of products that deactivate the clay catalyst. 

Natural clay catalysts were replaced by amorphous synthetic silica-alumina catalysts5,11 prepared by coprecipitation of orthosilicic acid and aluminum hydroxide. After calcining, the final active catalyst contained 10-15% alumina and 85-90% silica. Alumina content was later increased to 25%. Active catalysts are obtained only from the partially dehydrated mixtures of the hydroxides. Silica-magnesia was applied in industry, too. 

Fig. 3. Quinoline chemisorption at 315° as a function of activity for cracking light East Texas gas-oil (32). O, Si02-Al203 Houdry type S) , SiOj-1% Al203 , clay catalyst (fil-trol) O, SiOj-MgO V, Si02-Zr02. (Reprinted with permission of the American Chemical Society.)...

Styrene and 1-hexene have been selectively hydrogenated as well as substituted acetylenes, alkyne diols, stilbene and other unsaturated hydrocarbons with these palladium montmorillonites. A size selectivity was invoked to explain the enhanced hydrogenation activity of certain clay catalysts presumably due to the differences in interlamellar spacings of the clay which will depend on degree of hydration, concentration of Pd(II) complex, dielectric constant of the solvent used to disperse the reactants and other factors. 

The first successful catalytic cracking process was the Houdry process, announced in 1933 (132) and commercialized in 1936 (172). This was a fixed-bed process employing, at first, an activated bentonite clay as catalyst. It had been known previously that certain types of decolorizing clays catalyzed the decomposition of hydrocarbon oils (165,188), but a carbonaceous deposit rapidly accumulated on the clay and seriously impaired its activity. During his early work in France, between 1927 and 1930, Houdry found that catalyst activity could be maintained at a satisfactory level by carefully burning off the carbonaceous deposit, or coke, at frequent intervals before the concentration became high enough to interfere seriously with the desired catalytic reactions. 

The reactors and regenerators of the first few TCC units were designed for operation with activated-clay catalyst of 30 to 60 mesh. They were provided with internal baffle systems in order to achieve efficient contact between vapors and catalyst (133). However, the granular catalyst was not used commercially because pelleted catalyst of about 4-mm. average... 

The C2 fraction has been reported to be about 50% ethylene in fixed-bed cracking with activated-clay catalyst (133). Olefin contents of the C3 and C4 fractions vary over a wide range depending upon the catalyst, feed stock, and operating conditions. High degree of unsaturation is... 

In 1940, Houdry Process Corporation initiated commercial manufacture of a synthetic silica-alumina catalyst at Paulsboro, New Jersey (133). The synthetic catalyst is produced in pellet form (51,265) and contains 12 to 13% alumina (221,276). It has the advantages of controlled chemical composition, higher purity, and greater heat stability, but is more expensive than the activated-clay catalyst. 

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