Adsorbent agents, poisoning

The selective orientation may indicate a steric hindrance from the branch. Internal olefins like 2-butene tend to be poisons. They adsorb strongly but do not copolymerize to any significant extent. 2-Methylpropene is not very reactive either. In the absence of ethylene, a-olefins can be polymerized over Cr/silica but their reactivity is much lower than that of ethylene. Sometimes adding a-olefins to the reactor will improve activity, not because they are more reactive monomers, but because they are better reducing agents. 

On the other hand, a pure Eley-Rideal mechanism, in which the aromatic compound in the liquid phase reacts with the adsorbed acylating agent was first proposed by Venuto et alP1,22] and more recently by others.[23] However, for acylation reactions of polar substrates (anisole, veratrole), chemisorption of the latter must be taken into account in the kinetic law. A modification, the modified Eley-Rideal mechanism, has been proposed 114,24-26 an adsorbed molecule of acylating agent should react with a nonadsorbed aromatic substrate, within the porous volume of the catalyst. However, the substrate is also competitively adsorbed on the active sites of the zeolite, acting somehow as a poison of the acid sites. That is what we checked through different kinetic studies of various aromatic electrophilic substitution reactions.[24-26]... 

This oxide is one of the most active catalytic agents for the oxidation of CO near room temperature, if it is not contaminated with adsorbed material in its preparation. Its activity was discovered by Whitesell and Frazer (12). This oxide represents probably the first successful low temperature simple catalyst of industrial importance. It was prepared by treatment of potassium permanganate with sulfuric acid, followed by treatment of the product with concentrated nitric acid. The precipitated hydrated oxide was carefully washed, oxidized, and dried. This yielded a material which was catalytically active for CO oxidation at a temperature as low as — 20°C. It was rapidly poisoned by adsorbed water, but the activity could be regenerated if the water was removed by heating below sintering temperature. 

Poison titration is a convenient way to measure the concentration of active sites. The best procedure is to use a simple pulse reactor, such as that in Fig. 7.26. Pulses of a poisoning agent are injected between reactant pulses. If all the poison adsorbs irreversibly, then activity declines with each pulse. Typical results arc shown in Fig. 7.27, in which hydrogen sulfide poisons metal sites. Extrapolation of the activity curve to zero gives the amount of poison necessary to neutralize the active sites. A knowledge of surface stoichiometry is necessary to proceed further. For example, in Fig. 7.27 the assumed ratio was two nickel for each sulfur. This technique has the potential for innovative application to many systems. 

Uses Adsorbent, deodorizing agent for pharmaceuticals, antidiarrheal prods. antidote for poison treatment refining of pharmaceutical chems. 

Metals and Elemental Contaminants. Arsenic, lead, copper, and silicon are examples of the various types of metal or elemental impurities that contaminate feedstocks. Some metals exist in crude oil, whereas others maybe introduced through the addition of corrosion inhibitors or antifoaming agents. Becanse of the irreversible effect of metal poisoning of Platforming catalyst, there shonld be only be subparts per billion levels of metals in Platforming feeds. In practice, most metals that are distilled over with the naphtha in the crude distillation colnnm are adsorbed on the catalyst in the hydrotreating unit. 

The SOFC system requires desulfurization of the biogas to below 1 ppmv to avoid poisoning of the reformer catalyst and the SOFC anode. A sulfur trap was designed and evaluated using a commercial H2S adsorbent based on sulfide forming agents (extrudate, 1 = 5... 10 mm, d = 1.6 mm). The following manufacturer data for the adsorbent are available ... 

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