Clay catalyst, activated pelleted

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... 

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. 

With pellets of activated-clay catalyst, the burning rate shows a second-order dependency on carbon content at concentrations up to 2% and first-order dependency at higher concentrations (111). The com-... 

The high-specific-surface-area supports (10 to 100 m /g or more) are natural or manufactured materials that normally are handled as fine powders. When processed into the finished catalyst pellet, these materials often give rise to pore size distributions of the macro-micro type mentioned previously. The micropores exist within the powder itself, and the macropores are created between the fine particles when they are compressed together in a pellet press. Diatomaceous earth and pumice (or cellular lava) are naturally occurring low-cost materials that are representative of this class of catalyst support. Among the synthetic carriers that can be created by modem technology are those derived from clays, bauxite, activated carbon, and xerogels of silica gel and alumina gel. 

Preferred bentonite clays are those whose chief constituent is mont-morillonite, a mineral of the composition corresponding to the empirical formula, 4Si02-Al203 H20. The principal sources of raw clay for the manufacture of the presently most widely used natural catalyst (Filtrol Corporation) are deposits in Arizona and Mississippi. The clay from these deposits contains appreciable amounts of impurities, principally CaO, MgO, and Fe203, which replace part of the A1203 in the ideal montmorillonite structure. The catalyst is prepared by leaching the raw clay with dilute sulfuric acid until about half of the alumina and associated impurities is removed. The resulting product is then washed, partially dried, and extruded into pellets, after which it is activated by calcination. A typical analysis of the finished catalyst is as follows (Mills, 12). 

Regular Houdry clay pellets have lasted more than 18 months. Newer catalysts contain some high-thermal-conductivity material to assist in heat flow, and T.C.C. beads are being used because of their mechanical stability. Catalyst costs are less than 2 cents per barrel processed. New catalyst is very active, and hence process steam is introduced and then rieduced in amount as the run proceeds. Increase in pressure from tbe usual 10 psig to 70 psig increases the gasoline yield, but the yields of gas and coke increase even more rapidly. 

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