Accurate evaluation of the effects of metals contamination in commercial fluid-cracking operations can result in improved operating efficiency through proper choice of charge stocks, catalysts, and make-up rate T H E HISTORY of studies of metals poisoning of cracking catalysts has been one of initial oversimplification and not until recently has it been recognized in the literature that experimental methods which duplicate commercial operation must be used to provide reliable quantitative results. In early studies, the effects of metals contamination were determined by using catalysts which had been impregnated with metals from salt solutions (5). Although these methods gave good qualitative results, the effects of a given amount of metal on activity and selectivity were considerably greater than when naturally occurring metals poisoned the catalysts. In later studies, oil solutions of metal naphthenates were used to deposit the metals on the catalysts (9). These studies showed that the effect of a given amount of metal depended on the molecular weight of the naphthenate and the molecular weight of the oil used to dissolve the naphthenate. More recently, studies have been reported using the naturally occurring metals in high boiling feedstocks (4). However, in these studies, several procedures used differ from normal operation of refinery catalytic cracking units. These differences in operating procedures could have a significant effect on the results obtained.Several years ago, comprehensive studies were undertaken by this company to develop information on the effect of metals contamination of cracking catalysts. From the outset of these studies, operational procedures which simulated commercial operation in all important aspects were used.The more important operational procedures used in these studies which differ from those used in previously reported studies were : 0 Nonpoisoned equilibrium catalysts were aged in an automatic fluidized fixed-bed unit with charge stocks having high naturally occurring vanadium or nickel contents 0 Fresh catalyst was used as make-up 0 Product distribution data were obtained in a fluid catalytic cracking pilot plant at various metals levels on the catalyst using the same charge stock as used in the aging operation 0 Typical commercial operating conditions were used in both the aging and product distribution operations Studies were made using low-and high-alumina synthetic catalysts and a sulfur-resistant natural catalyst to determine if there was any benefit to be derived in choice of catalyst when charging high metals stocks. Studies were also made to determine the effect of catalyst make-up rate, since this method is the one most often used in the refinery for counteracting the effect of metals poisoning. Finally, a study was made to determine if the relative effects of vanadium and nickel poisoning under typical refinery conditions were the same as had been determined in earlier bench-scale studies.These studies showed : 0 Sulfur-resistant natural and highalumina synthetic ca...

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A4 rapid method, suitable for batch working, is described for determining iron(I1) in silicates. Hot 1 + 1 hydrofluoricsulphuric acid decomposes the subsample in a polypropylene bottle previously filled with carbon dioxide.After dilution with a boricphosphoricsulphuric acid mixture, iron(I1) is titrated gravimetrically with potassium dichromate solution, in the bottle used for sample decomposition. A sample-preparation procedure that minimises oxidation of iron(I1) is described. Results obtained for iron(I1) in various international reference rocks by the proposed method agree well with recommended values.Keywovds : Ivon(II) determination ; silicates ; gyavimetvic titvation French and Adamsl have published a procedure for determining iron(I1) oxide in rocks that involves decomposition of the sample by treatment with a hot 1 + 1 mixture of concentrated hydrofluoric and sulphuric acids. A modification of this procedure is used by the CSIRO Division of Alineralogy, North Ryde, New South Wales.2 The latter procedure differs from the former procedure mainly in that the sub-sample is decomposed in a narrow-mouthed 125-ml polypropylene bottle previously filled with carbon dioxide, rather than in a 60-ml wide-mouthed polypropylene bottle, and the redox titration is performed with potassium dicliromate solution and sodium diplienylamine sulplionate, rather than with cerium( IV) sulpliate solution and N-phenylanthranilic acid as titrant and indicator, respectively.Tlie procedure described in this paper is simpler than the two procedures referred to above for the following reasons. Experimental Sample-preparation EquipmentThis consists of the following items installed in a sample-preparation room with dust extraction facilities for operator safety.Hydrniilic lnboirntory cruslzerbreakel. with tuizgsten carbide working faces. Obtainable from Rocklabs, P.O. Box 28-362, Auckland 5, h'ew Zealand.J n ~l c r i r s l w uiith nzaj?gajiese haideized steel plates. As an alternative to the hydraulic laboratory crusherbreaker.Sicbtccliizik tungsten carbidecobalt riizg griizder, 300-ml. M'eighing about 11.6 kg and obtainable from Siebtechnik, lIiihlheim, Federal Republic of Germany.TT-cdrrg Znborntoyv Liibmtiizg cup mill, Type ML\T 954/2. Obtainable from KHD Industrieanlagen SiccZ ndnptoi/ base. This allows the Siebtechnik grinder to be used with the Il'edag vibrating cup mill. Humbold t IVedag, Federal Republic of Germany.Il'eighing about 2.7 kg. 48 RICE : DETERMINATION OF IRON(II) IN

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