Sulfur-poisoned catalysts

Conditions of hydrogenation also determine the composition of the product. The rate of reaction is increased by increases in temperature, pressure, agitation, and catalyst concentration. Selectivity is increased by increasing temperature and negatively affected by increases in pressure, agitation, and catalyst. Double-bond isomerization is enhanced by a temperature increase but decreased with increasing pressure, agitation, and catalyst. Trans isomers may also be favored by use of reused (deactivated) catalyst or sulfur-poisoned catalyst. 

Figure 12. Transient HCN yield over platinum catalysts. A and B represent one experiment (Exp. 1) in which a sulfur-poisoned catalyst was regenerated on admission of 1% O2 into the inlet gas mixture between times t, and C shows the resistance of the catalyst to poisoning by SO when oxygen is simultaneously present in the inlet gas mixture. At t only oxygen is removed from the inlet gas mixture. (See Ref. 16 for details.)...

What are the mechanisms of sulfur removal from surfaces and can these mechanisms be used in the development of regeneration techniques for sulfur-poisoned catalysts ... 

The experimental techniques utilized in the study of sulfur poisoning are markedly more critical to obtaining quantitative, basic data than in any other type of reaction study. In most previous studies of sulfur-poisoned catalysts, rate data were affected by experimental complexities to a sufficient extent that a basic understanding of poisoning rates and mechanisms was not possible. Most of these difficulties occurred because of ... 

Catalyst Fresh catalyst Aged catalyst Sulfur- poisoned catalyst... 

Relatively few studies of regeneration of sulfur-poisoned catalysts have been reported in the literature (/, 9, 11, 83, 92, 178, 194, 237, 269-274). Attempts to regenerate poisoned catalysts have been made using oxygen/air... 

Regeneration of Sulfur-Poisoned Catalysts Using 02 Treatment... 

Catalyst selectivity is somewhat meaningless unless the term is defined. There also are selective catalysts that do not meet the technical or practical definition of hydrogen selectivity. Such catalysts are sulfur-poisoned catalyst. Sulfided nickel catalyst produces high trans-isomers, has lower activity than conventional nickel, exhibits longer reaction times, and is used for specialty applications (e.g., coating fats and hard butters). 

In our experiments, catalysts were pretreated in a reel rcuiat ion apparatus with low concentrations of H2S in H2 to obtain known, uniform sulfur coverages. Hie moderately sulfur-poisoned catalysts correspond to the catalysts after equilibrium exposure to conventionally desulfurized feedstocks (H2S/H2 =0 1 PPm), while lightly poisoned catalysts correspond... 

Both clean and sulfur-poisoned catalysts were then used in 24 and 166 hour steam reforming runs at. 490 C and 25 atm with a sulfur-free naphtha feedstock. The experimental apparatus consists of a fixed bed microreactor made of stainless steel for high pre Esure runs. During each run, the catalyst activity was monitored by analyzing the reactor effluent using an on-line quadrupolc mass spectrometer as well as by gas chromatography ... 

CCD did occur for the moderately sulfur-poisoned catalyst samples which corresponded to a sulfur coverage of 0.8 saturation. Figure 2 shows the H2 TPR spectrum of the catalyst following a steam reforming run with steam/oarbon=l.5. The total amount of carbon deposited was substantial, and most of it was significantly less-reactive. This type of carbon would... 

We used Raman spectroscopy to examine the nature of the carbon deposits fornied on clean and sulfur poisoned catalysts during steam reforming. The results show that carbon deposited on sulfur poisoned catalysts have greater aromatic character than those on clean catalysts (rof. 9). 

The TPR results for sulfur poisoned catalysts which was characterized to have a sulfur coverage of after 24 hours of steam reforming(Figure 5) showed that a substantial quantity of the deposited carbon had been accumulated in higher-temperature states. This carbon would surely be slow... 

Chang, J.R., Chang, S.L., Lin, T.B. (1997). y-Alumina-Supported Pt Catalysts for Aromatics Reduction A Structural Investigation of Sulfur Poisoning Catalyst Deactivation. Journal of Catalysis, Vol.169, No.l, 0uly 1997), pp. 338-346, ISSN 0021-9517... 

Catal dic converters led to the elimination of lead from gasoline, because lead poisons the converter catalyst. Similarly, sulfur poisons catalysts that may be used on future vehicles. Hence, the reduction of sulfur in gasoline and diesel fuel to ultra-low levels is a key requirement of Auto Oil n. 

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