Catalysts contamination

Catalyst contamination from sources such as turbine lubricant and boiler feed water additives is usuaUy much more severe than deactivation by sulfur compounds in the turbine exhaust. Catalyst formulation can be adjusted to improve poison tolerance, but no catalyst is immune to a contaminant that coats its surface and prevents access of CO to the active sites. Between 1986 and 1990 over 25 commercial CO oxidation catalyst systems operated on gas turbine cogeneration systems, meeting both CO conversion (40 to 90%) and pressure drop requirements. 

At first glance, the in vitro studies on CNT toxicity appear to be confusing, inconclusive, or contradictory. However, if one considers interference with dye-based viability assays, agglomeration issues, and oxidative stress due to catalyst contamination, the data available to date seem to favor the conclusion that well-dispersed, purified, and/or functionalized CNTs exhibit relatively low toxicity. 

The major advantages are (a) that the desired reactions can be carried out generally at lower temperatures than in operations employing chemical means, (b) that monomers can be polymerized free of catalyst contamination, (c) that crosslinking and grafting can be performed in... 

Khouw et al [20] report that catalysts contaminated to high Vanadium levels are stilt capable of converting light feeds, but not heavier feeds. This is illustrated in the following table. 

Due to the high conversion obtained with SAC 40 and especially with SAC 80, only a small amount of catalyst contamination was observed and the catalyst could be reused several times or regenerated by a washing procedure with acetone and diluted nitric acid solutions. Compared with the conversion of resorcinol using lower amounts of other solid acid catalysts such as Amberlyst 15 (74%), H-BEA (36%), H-US-Y (10%) and H-ZSM-5 (3%), the SAC 40 and SAC 80 Nafion/silica nanocomposites are the favoured catalysts. 

The model was basically developed for hydrodesulfurization of residual oil with a high level of catalyst contaminants causing pore mouth plugging of catalyst. 

API Sludge (Har) WWTP Sludges Tank Sediment (Haz) Spent Catalyst Contaminated Soils Spent Caustic Other Other (Haz)... 

Special reactor bottles having working volumes of 1 mL to 1000 mL are also available. As depicted in Fig. 6.6, these bottles have threaded Teflon adapters to hold the hydrogen inlet tube so catalyst contamination by the reactor is virtually eliminated. The smaller bottles, which have working volumes between 1 mL and 20 mL, use a spacer to secure them into the shaker assembly (Fig. 6.6a). Those with capacities of 20 mL to 200 mL (Fig. 6.6b) fit directly into the shaker assembly of the smaller Parr apparatus while 500 mL and 1000 mL vessels of this type (Fig. 6.6c) are available for the larger unit. 

This paper presents a survey of the principal selective hydrogenation catalyst contaminants and their sources. The particular special cases of Hg and As are discussed. More recently silicon poisoning has become important. This subject will also be addressed. For each contaminant type, the IFP solution to suppress the undesirable effects will be detailed on the basis of results obtained in industrial plants. 

To put these principles into practice, liquid ammonia is first vaporized by indirect heating with steam, and then filtered to reduce risk of catalyst contamination. This produces an ammonia gas stream at about 8 atm pressure without requiring mechanical compression. An air stream is separately compressed to about the same pressure, preheated to 200-300°C, and filtered prior to mixing with the ammonia (about 10%) gas stream immediately before conversion. This mixture is passed through the red hot platinum-rhodium gauze to produce a hot gas mixture of nitric oxide and water vapor plus the unreacted nitrogen and oxygen components of air (Fig. 11.5), with a yield efficiency (selectivity) under these conditions of about 95%. 

FIGURE 245 Electron microscopy of catalyst contamination in PE film. The 125-p.m catalyst particle is buried in an originally 23-p.m thick film, which is oriented perpendicular to the plane of the photo. 

A slip stream of catalyst solution is treated with air and steam to regenerate catalyst contaminated by chlorinated by-products. 

Shirakawa polyacetylene is a porous mat of interconnected fibrils which can only be moderately stretched, by at most a factor of three. The initial problems encountered in obtaining oriented polyacetylene, sufficiently devoid of catalyst contaminants, were reflected in the multiplicity of structure proposals and the disagreement between them. For brevity, an account of the present state of affairs will be given, with older results cited where appropriate. 

Johnson, M., Catalyst Contamination by Phosphorus from Engine Oils - Emission Effects and Transport Processes, ILSAC-Oil Meeting, Romulus, MI, July 10,2002. 

Catalysts were tested in a flow system at conversions generally below 10%. Reactors were back-mixed. Berry-type units, plated with gold or silver to minimize carbonyl formation and consequent catalyst contamination. Liquid and gaseous products were analyzed by VPC, using procedures described elsewhere (6,7,8). 

Atomic number (Z) contrast is very useful in the analysis of foreign materials and catalysts, contamination detection, and metallurgical phase analysis. An example of atomic number contrast is shown in Figure 6. 

In addition to supercritical fluid extraction and supercritical fluid chromatography, supercritical and near-critical fluids are of increasing interest for other applications. These include their use as processing fluids for dyeing of fibers, production of finely dispersed particles (RESS, PGSS, SAS, GAS, etc.), as promising solvents for syntheses and kinetic studies, for the destructive oxidation of wastes with supercritical water (SCWO), for the purification of filters, catalysts, contaminated soils, for drying and sterilization processes, and others [13,19,20]. 

Structural changes in PEM and catalyst layers due to platinum oxidation or catalyst contamination under open-circuit conditions On/off cyclic operation under different humid conditions Effect of hygro-thermal cycle on membrane stresses Water uptake effect on cyclic stress and dimensional change, hydrogen crossover... 

ILs were briefly introduced in section Attachment to the Support via SILC or SILP Catalysis where they were employed for the generation of immobilized catalyst complexes via the SILP procedure. ILs can also be used in a more traditional sense, serving as recyclable reaction media. Typically, this approach uses a biphasic mixture of IL along with an organic solvent, where the IL acts as the catalyst carrier, and the organic solvent solubilizes the reaction substrates. The products, free of catalyst contamination, can be easily isolated by phase separation, and the catalyst containing IL can be recycled. 

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