Catalysts clays

Large quantities are now manufactured by the reaction between sulphur vapour and methane at a temperature of 900-1000 K in the presence of a clay catalyst ... 

Preparation of Pillared Clay Catalysts. PAG products are used for the preparation of zeolite-like catalysts by intercalation, the insertion of Al polycations molecules between the alurninosiHcate sheets of clay (3,33). Aqueous clay suspensions are slowly added to vigorously stirred PAG solutions, and the reaction mixture is aged for several hours. The clay is separated from the PAG solution and washed free of chloride ion. The treated clay is first dried at low temperature and then calcined in air at 450—500°G, producing a high surface area material having a regular-sized pore opening of about 0.6 to... 

Bentonite is a rock rich in montmorillonite that has usually resulted from the alteration of volcanic dust (ash) of the intermediate (latitic) siliceous types. In general, reUcts of partially unaltered feldspar, quartz, or volcanic glass shards offer evidence of the parent rock. Most adsorbent clays, bleaching clays, and many clay catalysts are smectites, although some are palygorskite [1337-76 ]. 

Deairing pug-mill extruders which combine mixing, densification, and extrusion in one operation are available for agglomerating clays, catalysts, fertihzers, etc. Table 20-55 gives data on screw extruders for the production of catalyst pellets. 

Degradation of polystyrene using natural clay catalysts... 

Table 1 shows chemical compositions of clay catalysts measured by XRF analysis. Si02 and AI2O3 are main components of the three clay catalysts with minor amount of Na20, Fc203 and others. The Si/Al ratio increased from HH [Pg.434]

Acid-treated clay catalyst Engelhard F-24 was found to be very effective for the alkylation of diphenylamine (DPA) with an olefin such as a-methyl styrene (AMS) to obtain a mixture of mono and dialkylated diphenylamines (Chitnis and Sharma, 1995). For example, alkylation of DPA with AMS produced a mixture of 4-(a,a-dimethyl benzyl) diphenylamine, i.e. monocumyl-diphenylamine (MCDPA) and 4,4 -bis(a,a-dimethylbenzyl) diphenylamine, i.e. dicumyldiphenylamine (DCDPA) (Eqn.(l 1)). The dialkylated diphenylamine, i.e. DCDPA, is indu.strially important as an antioxidant and heat stabilizer. DCDPA is reported to be an ideal antioxidant for many materials like polyethylene, polypropylene, polyether polyol, polyacetals, nylon 6, synthetic lubricants, hot melt adhesives, etc. 

The various other grades of acid-treated clay catalysts like Engelhard F-25, F-34, F-44,F-54, F-124, F-224, G-62, Tonsil K 306, etc. were also found to be useful catalysts for the alkylation of DPA with AMS. This alkylation reaction was unsuccessful with macroporous... 

Shah et al. (1994) have studied the preparation of a class of compounds called Indans, by cross-dimerization of AMS with amylenes, using an ion-exchange resin and acid-treated clay catalysts (Eqns. (12) and (13)). Indans can be subsequently converted, e.g. by acetylation, into perfumric compounds having mu.sk odour. For example, 1,1,2,3,3-pentamethylindan, the product obtained by cross-dimerization of AMS and wo-amylene (Eqn. (12)), can be reacted with propylene oxide and /7 ra-formaldehyde to give an indan type isochroman musk compound, 6-oxa-l,l,2,3,3,8-hexamethyl-2,3,5,6,7,8-hexahydro-lH-benz(f)-indene, sold as Galaxolide commercially. 

The selectivity for cross-dimerization relative to the dimerization of AMS, was found to be better with the acid-treated clay catalyst Engelhard F-24 than with the ion-exchange resin catalyst Amberlyst-15. Also, the formation of undesired side products, i.e. diisoamylenes, was lower in the case of Engelhard F-24 than for Amberlyst-15. 

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. 

K. Lourvanij and G. L. Rorrer, Dehydration of glucose to organic acids in microporous pillared clay catalysts, Appl. Catal. A Gen., 109 (1994) 147-165. 

The first cracking catalysts were acid-leached montmorillonite clays. The acid leach was to remove various metal impurities, principally iron, copper, and nickel, that could exert adverse effects on the cracking performance of a catalyst. The catalysts were first used in fixed- and moving-bed reactor systems in the form of shaped pellets. Later, with the development of the fluid catalytic cracking process, clay catalysts were made in the form of a ground, sized powder. Clay catalysts are relatively inexpensive and have been used extensively for many years. 

Fast deactivation rates due to coking and the limited hydrothermal stability of pillared clays have probably retarded the commercial development of these new type of catalysts and prevented (to date) their acceptance by chemical producers and refiners. However, there is a large economic incentive justifying efforts to convert inexpensive (i.e. 40-100/ton) smectites into commercially viable (pillared clay) catalysts (56). Therefore, it is believed that work on the chemical modification of natural (and synthetic) clays, and work on the preparation and characterization of new pillared clays with improved hydrothermal stability are, and will remain, areas of interest to the academic community, as well as to researchers in industrial laboratories (56). 

Table 5 Selectivities of the conversion of cumene on the clay catalysts at 300°C.

In conclusion, pillared clays catalysts are not as good as initially predicted for the cracking of heavy gas oils, mainly because of the iron contamination of natural clays. There is a probability that they could be applied for the conversion of hydrotreated gas oils, giving a slightly lower gasoline yield, but higher octane number than REY zeolites. 

The other iron-containing clay catalyst prepared by reacting a Texas bentonite with an ACH-Fe(N02)3 solution gave an (Fe.ACH)-bentonite sample containing 9.7% Fe2 3 after drying in air at 120 C/10h had d(OOl) = 17.8A and BET surface area of 296 m /g. Calcination reduced pillar s height after heating in air at 400 C/10h, the d(OOl) value decreased to about 15.7A probably as a result of some iron removal from the pillars. 

Table 2. Microactivity test results for several pillared clay catalysts after calcination in air at 400 C for lOh. The zeolitic cracking catalyst has been aoed for 5 hours at 760 C with 100% steam at 1 atm. ...

At MAT conditions, montmorilIonites pillared with alumina clusters, and having similar surface area, generate (at a given conversion level) similar amounts of coke (when used to crack gas oil) irrespective of the iron content of the parent bentonite. Thus, the presence of iron cannot be used to explain the high tendency for coke (and light gas) make of pillared clay catalysts. 

A mixture of a carbonyl compound (1 mmol) and a nucleophilic reagent (1.1 mmol) was added to a suspended mixture of CH2CI2 solvent (2-5 ml) and a powdered Fe-Mont catalyst (0.2-0.5 g, 60 mesh pass) at 0°C, and stirred under the conditions noted in Tables. After the complete consumption of the carbonyl compound, the clay catalyst was filtered off through a Celite pad. The filtrate was distilled to recover the products for analysis. 

Table 1. Addition of ester enolates 1 to 2 on clay catalyst.

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