Catalyst erratic

Osmium makes a sluggish carbonyl hydrogenation catalyst but has the unusual property of reducing a, -unsaturated aldehydes to the unsaturated alcohol in good yield (85). The system has proved erratic high selectivity can only be obtained through prereduction of the catalyst just before use. 

Erratic circulation occurs when the catalyst is not developing a smooth and uniform static head over the entire length of the standpipe. When this happens, the catalyst packs and bridges across the standpipe. Symptoms of erratic circulation include ... 

Stick-Slip Flow is erratic circulation caused when the catalyst packs and bridges across the standpipe. 

The cold gas recycle (CGR) ratio values (Figure 4) are metered values and are more consistent than the HGR and total gas recycle ratio values which were calculated from gas analyses. Although the calculated total recycle gas flow rate was erratic, catalyst bed temperatures were uniform and easily controlled by varying recycle rate and bed inlet tem-... 

As early as 1923 Hinshelwood and Topley (27) noted the exceptionally erratic behavior of palladium foil catalyst in the formic acid decomposition reaction within 140-200°C. The initially very high catalytic activity decreased 102 times during the exposure of palladium to hydrogen, which is a product of the reaction. Though the interpretation does not concern the /3-hydride formation, the authors observation deserves mentioning. 

Balthis and Bailar6 obtained tris (ethylenediamine) chromium-(III) complexes by the oxidation of chromium(II) solutions, using a procedure somewhat similar to that used for the synthesis of cobalt (III) com plexes. Mori7 described the preparation of hexaamminechromium(III) salts from the oxidation of chromium (II) salts in the presence of ammonia. The results obtained in both syntheses have been erratic.8,9 Berman noted that the foregoing syntheses are rendered dependable by the use of a catalyst of activated platinum on asbestos. Schaeffer,100 in a subsequent study, independently used colloidal platinum as a catalyst but reported some difficulty in separating it from the product.106 The procedures recommended and described here are based on the use of platinized asbestos as the catalyst. 

Another instrument developed by the Precision Scientific Co. was based upon the work of Stenger and Van Hall [99,104], Experience has shown that application of the Beckman and Precision Scientific Co. instruments to concentrated or saturated brine solutions leads to erratic and unreliable results. There are several possible reasons for this (1) the catalyst will rapidly become coated with sodium chloride (2) oxidation of Cl to chlorine will occur and (3) volatile organics may not all be trapped by the solid catalyst. 

It is strange and typical for the erratic path of some laboratory work, that this final concept of the promoter action on ammonia catalysts was just opposite to our initial working hypothesis according to which flux promoters were considered to be essential for good catalytic activity. 

Radioactive tracers [14] are a useful tool to measure unit parameters such as residence times and distribution of the catalyst and vapors in the reactor, stripper, or regenerator. Bypassing can be detected, slip factors calculated and dilute phase residence times are examples of useful calculations that can point the way to future modifications. This technology is also useful for detecting and analyzing equipment malfunctions. Plugged distributors, erratic standpipes, and main fractionator problems such as salt deposits or flooding can be detected with tracers. 

Diagnosing and rectifying an unstable catalyst standpipe operation can be extremely challenging. Poor standpipe operation leads to erratic catalyst circulation resulting in potential unit upsets, conversion and yield loss, and mechanical damage. Indications of impending catalyst circulation and standpipe problems include ... 

The choice and properties of the aeration gas are important factors for maintaining stable standpipe operation. The condensate source for steam aeration can cause several problems. If the steam is not kept dry, the condensate can lead to stress cracking of the tap piping, plugging of the tap nozzle with mud, erratic aeration rates, orifice erosion, and potentially catalyst attrition. Similar problems can occur with wet fuel gas as an aeration source. When possible, dry air and/or nitrogen are preferred rather than steam as aeration media for standpipes. However, in actual... 

Continuous analysis of highly fluorinated materials can present problems, primarily caused by the corrosiveness of hydrogen fluoride which is liberated from all of them during combustion. Hydrogen fluoride will react with the permanently bound hydroxy groups on the surface of the cooler parts of combustion tube walls and catalysts. The effect can lead to erratic hydrogen values and so the installation of some type of oxide [magnesium oxide, alumina, or cerium (IV) oxide] trap in the combustion tube to prevent its escape is recommended. 11... 

Chapter VI) and account for the rather puzzling and apparently erratic influence of catalysts and inhibitors. 

With old catalyst, very erratic results with respect to the initiation time and the rate of hydrogen uptake have been observed. 

All cathodic reductions described below were performed at mercury pool cathodes in solutions containing tetraalkylammonium (TAA+) electrolytes and most were carried out at a constant current. For preparative scale experiments, in general, the constant-current method is preferable to that of constant potential. The equipment for constant-current experiments is simpler, much less expensive and more suitable for large scale reactions. For the particular conditions described here, experiments at constant potential are difficult (except when TAA+ in small concentrations are used as catalyst, see Sect. 8). The current often varies erratically throughout constant-potential experiments, reaction times are unpredictable and often impractically long. This is the result of participation of the cathode material in the reaction sequence. The mercury pool surface is visibly disrupted, droplets of mercury separate from the surface and in many instances the black precipitate of the TAA-mercury covers the cathode surface. 

Catalysts are commonly used to control the pouring and gel times of polyurethane systems. As catalysts are used in small quantities, the addition must be carried out very carefully otherwise, very erratic results may be obtained. Catalysts may be made into a concentrated solution with an inert carrier such as a plasticizer. This reduces a potential dispensing error. They also may be added to a liquid chain extender. 

A theoretical and experimental study of multiplicity and transient axial profiles in adiabatic and non-adiabatic fixed bed tubular reactors has been performed. A classification of possible adiabatic operation is presented and is extended to the nonadiabatic case. The catalytic oxidation of CO occurring on a Pt/alumina catalyst has been used as a model reaction. Unlike the adiabatic operation the speed of the propagating temperature wave in a nonadiabatic bed depends on its axial position. For certain inlet CO concentration multiplicity of temperature fronts have been observed. For a downstream moving wave large fluctuation of the wave velocity, hot spot temperature and exit conversion have been measured. For certain operating conditions erratic behavior of temperature profiles in the reactor has been observed. 

The world s supply of rhodium is in approximate balance with demand with erratic releases onto the world market from Russia being counterbalanced by national and industrial stockpiles. These fluctuations in availability are reflected in the spot price, which fell from US 64 at the millennium to US 17g by 2001. The current price in 2004 is US 26 g. Of the 2002 world production of 19.0 tonnes and recovered scrap from automobile catalysts of 3.1 tonnes, over 80% was used as rhodium alloy catalysts for automobile emission reduction. The rhodium component is vital in controlling NO emissions and looks set to increase in order to meet higher emission control standards. 

Important A loading of catalyst less than 1.8 mol % relative to the amount of 2,7-bis(N,N-diethylcarbamoyloxy)naphthalene gave erratic results. For example, 1.2-1.3 mol % sometimes gave an incomplete conversion, but additional catalyst (1.0 mol %) ensured completion of the reaction. This step was checked at least five times, each time with reproducible yields in the range of 86-89%. NiCl2(dppp) was used as received from Acros Organics. 

Of all the materials tested, three compounds, cupric oxide, titanium oxide, and cadmium oxide showed considerable promise as catalysts. Several experiments were made using cupric oxide, but the results were erratic and not reproducible and it was not further investigated. 

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