Nonselective poisoning

Often poisoning described by curve 1 in Fig. 3.37 is referred to as nonselective poisoning, whereas the deactivation according to curve 3, which implies disproportionately large deactivation, is called selective poisoning. Explanations of. selective poisoning are ... 

Nonrepairable components, in reliability modeling, 26 989 Nonruminant feeds, 10 836-847 additives to, 10 846 ingredients of, 10 837-838 swine and poultry nutrient requirements, 10 838-845 Nonselective catalytic reduction (NSCR), 10 101-102 17 184 19 626 Nonselective herbicides, 13 313 Nonselective poisoning, 5 258 Nonself-aligned (NSA) HBT fabrication, 22 167... 

Maurel et al. (251) reported that C02 and H2S were nonselective poisons in the hydrogenation of benzene and benzene-D2 exchange on platinum. That is, they did not affect the ratio of exchange/hydrogenation rates. However, elemental sulfur produced by the reaction of S02 and H2S was a selective poison, causing the ratios of the rates for exchange/hydro-... 

Fig. 7.7. Idealized poisoning mechanism (a) sintering of the catalytic components, (b) sintering of the carrier, (c) selective poisoning, and (d) nonselective poisoning.

Wheeler and Robell [18] were the first to make use of the Bohart-Adams model which, as we have said, was developed for a fixed-bed adsorption problem. They used the adsorption model to establish the sluq)e and motion of the poison proffles (c.f Figure 1) within the bed and then essentially solved a reaction/deactivation problem based on these profiles (in their case a simple first order system). However, it was also necessary to specify how the reaction rate constant, k, varied with the concentration of poison on the catdyst. In the simplest case we can choose a linear relationship (nonselective poisoning) as they did and write... 

This relation is plotted as curve A in Figure 12.11 and represents the classical case of nonselective poisoning in which the apparent fraction of the activity remaining is equal to the fraction of the surface remaining unpoisoned. This same result is evident from equation (12.3.112) by recognizing that both effectiveness factors are unity for this situation. 

Nickel in the feed is deposited on the surface of the catalyst, promoting undesirable dehydrogenation and condensation reactions. These nonselective reactions increase gas and coke production at the expense of gasoline and other valuable liquid products. The deleterious effects of nickel poisoning can be reduced by the use of antimony passivation. 

Enantiomer-selective deactivation of racemic catalyts by a chiral deactivator affects the enantiomer-selective formation of a deactivated catalyst with low catalytic activity (Scheme 8.2). Therefore, it is crucial for a chiral deactivator to interact with one enantiomer of a racemic catalyst (Scheme 8.2a). As the chiral deactivator does not interact with the other enantiomer of racemic catalyst, the enantiomeri-cally enriched product can be obtained. Therefore, the level of enantiomeric excess (% ee) could not exceed that attained by the enantiopure catalyst. On the other hand, nonselective complexation of a chiral deactivator would equally and simultaneously deactivate both catalyst enantiomers, thereby yielding a racemic product (Scheme 8.2b). Although this strategy tends to use excess chiral poison relative to the amount of catalyst, it offers a significant advantage in reducing cost and synthetic difficulty since readily available racemic catalysts and often inexpensive chiral poisons are used. 

Atropine Nonselective competitive antagonist at all muscarinic receptors in CNS and periphery Blocks muscarinic excess at exocrine glands, heart, smooth muscle Mandatory antidote for severe cholinesterase inhibitor poisoning Intravenous infusion until antimuscarinic signs appear continue as long as necessary Toxicity Insignificant as long as AChE inhibition continues... 

Amitrole is a nonselective systemic triazole herbicide. It is used for control of annual grasses and perennial and annual broadleaf weeds, for poison ivy control, and for control of aquatic weeds in marshes and drainage ditches. This compound is compatible with many other herbicides. It is available as wettable powders, soluble concentrates, and water-dispersible granules. Amitrole was involved in the Delaney Clause s first enforcement.1213... 

The fact that administration of organic sulfhydryl compounds can both reverse the toxicity of these arsenic drugs and their activity tends to support this simple idea. It seems almost incredible that the organism can develop resistance to such a nonselective protoplasmic poison as arsenic, but it does, apparently by decreased uptake. 

Figure 7.23 Types of relationships encountered with porous catalysts. Curve A is the result for nonselective deactivation for equations (vi) and (xvi). Curve B is for uniform deposition of poison with (po large and antiselective deactivation, equation (v). Curves C and D are for selective deactivation, equation (xiv), with Q = 10 and 100, respectively. [After A. Wheeler, Advan. Catal., 3, 249 with permission of Academic Press, New York, NY, (1951).]...

Uses Nonselective, foliage-applied, systemic, triazole herbicide used in uncropped land and orchards to control certain grasses and to kill annual and perennial grasses and weeds. It is also effective on poison ivy, poison oak and aquatic weeds. 

Amitrole (Aminotriazole) is a systemic herbicide used to control nonselective grasses, broadleaf weeds, cattails, poison ivy, and certain aquatic weeds. One case of allergic contact dermatitis to aminotriazole has been reported in a contract weed control operator [92]. 

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