Catalysts catalyst poisoning

Process Catalyst Catalyst poison, inhibitor Mode of action... 

ATRP can be performed in bulk, in solution, or in a heterogeneous system (e g., emulsion, suspension). Various solvents have been used for ATRP in solution for various monomers. These include benzene, toluene, acetone, ethyl acetate, anisole, diphenyl ether, dimethyl formamide, ethylene carbonate, alcohol, water, carbon dioxide, and many others (Matyjaszewski and Xia, 2001). The use of a solvent may become necessary when the polymer formed is insoluble in its monomer. The choice of a solvent is in uenced by several factors, such as chain transfer to solvent, interactions between solvent and the catalyst, catalyst poisoning by solvent (e.g., carboxylic acids and phos-... 

A knowledge of these compounds is important because they often have undesirable attributes, e.g., unpleasant odor, the SO2 formed by combustion, catalyst poisoning. There are a number of refining processes to eliminate sulfur compounds. 

The refining industry generally seeks either to eliminate asphaltenes or to convert them to lighter materials because the presence of heteroelements cause pollution problems, e.g., sulfur and nitrogen, catalyst poisoning, and corrosion (formation of metal vanadates during combustion). 

These materials can damage equipment by means of corrosion, erosion, deposits, plugging, catalyst poisoning, etc. 

Upstream of the refornjiing unit, the feedstock undergoes hydrotreatment so as to eliminate impliritles such as S, N, olefins, and metals which are all catalyst poisons. 

The combined result of two such determinations yielded a leak size figure of 8.8% of the feed flow (with a relative standard deviation of less than 5%). This figure could sufficiently explain the product quality problems experienced, whose alternative explanation in turn was catalyst poisoning. 

Wlien a strong electron-donor ligand such as pyridine is added to tlie reaction mixture, it can bond so strongly to tlie Rli tliat it essentially drains off all tlie Rli and shuts down tlie cycle it is called a catalyst poison. A poison for many catalysts is CO it works as a physiological poison in essentially the same way as it works as a catalyst poison it bonds to tlie iron sites of haemoglobin in competition witli O. ... 

It has been stated that thiourea (about 20 per cent, of the weight of the palladium - barium sulphate) may also be used as a catalyst poison. 

Sweetening. Another significant purification appHcation area for adsorption is sweetening. Hydrogen sulfide, mercaptans, organic sulfides and disulfides, and COS need to be removed to prevent corrosion and catalyst poisoning. They ate to be found in H2, natural gas, deethanizer overhead, and biogas. Often adsorption is attractive because it dries the stream as it sweetens. 

Table 3 provides typical specifications for isoprene that are suitable for Al—Ti polymerization (89). Traditional purification techniques including superfractionation and extractive distillation are used to provide an isoprene that is practically free of catalyst poisons. Acetylenes and 1,3-cyclopentadiene are the most difficult to remove, and distillation can be supplemented with chemical removal or partial hydrogenation. Generally speaking distillation is the preferred approach. Purity is not the main consideration because high quaUty polymer can be produced from monomer with relatively high levels of olefins and / -pentane. On the other hand, there must be less than 1 ppm of 1,3-cyclopentadiene. 

The advent of a large international trade in methanol as a chemical feedstock has prompted additional purchase specifications, depending on the end user. Chlorides, which would be potential contaminants from seawater during ocean transport, are common downstream catalyst poisons likely to be excluded. Limitations on iron and sulfur can similarly be expected. Some users are sensitive to specific by-products for a variety of reasons. Eor example, alkaline compounds neutralize MTBE catalysts, and ethanol causes objectionable propionic acid formation in the carbonylation of methanol to acetic acid. Very high purity methanol is available from reagent vendors for small-scale electronic and pharmaceutical appHcations. 

Shale oil contains large quantities of olefinic hydrocarbons (see Table 8), which cause gumming and constitute an increased hydrogen requirement for upgrading. Properties for cmde shale oil are compared with petroleum cmde in Table 10. High pour points prevent pipeline transportation of the cmde shale oil (see Pipelines). Arsenic and iron can cause catalyst poisoning. 

Rhodium was about three times the price of gold through 1988—1989 until skyrocketing to 74/g ( 2300/troy oz) in early 1990. Thus precious metal catalyst costs requite an absolute minimum level of use and maximum number of catalyst recycle uses when batch processing is employed. Starting material contaminants may effect catalyst poisoning, though process routes to overcome this by feed stream pretreatment may be devised (37,60). 

Siace nitroarenes are reported to be catalyst poisons (18), the concentration of DNT ia the reaction medium is kept as low as is practical with regard to production goals and catalyst usage. The pubHshed kinetic studies are of Htde iadustrial value siace they describe batch processes with high DNT catalyst ratios (18—21). The effects of important process variables, such as temperature and pressure, can only be iaferred from descriptions ia the patent Hterature. 

Some natural gases have also been found to contain mercury, which is a reformer catalyst poison when present in sufftciendy large amounts. Activated carbon beds impregnated with sulfur have been found to be effective in removing this metal. 

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