Naphtha reforming catalyst, coke

Influence of Chloride during Coke Burning of a Naphtha Reforming Catalyst Coked in a Commercial Cycle... 

A similar study reports the results of adding 100 ppm thiophene to As in the Palm et al. study,the catalyst is not described rather, it is identified only as a commercial naphtha reforming catalyst, presumably Pt-based. In their reactor, the reformate from the ATR step passes through separate high and low temperature shift reactors before being analyzed. Thus, it was not possible to determine the effect of sulfur on the reforming step alone, nor was any post-reaction characterization of the catalyst reported, for example to determine coke or sulfur content. Figure 16 shows the observed deactivation, as measured by a decrease in H2 and CO concentrations. 

The burning of coke on commercial Pt-Re/Al203 naphtha reforming catalyst... 

Coke deposition and the deactivation of the bifunctional naphtha reforming catalyst start on the metallic function. The amount of coke on the metal and its deactivation depend on the hydrogen pressure. After a lineout period of the metallic function, the amount of coke on it and its catalytic activity remain... 

Although the deactivation of Industrial catalysts is often due to two or more different causes, the modeling of simultaneous deactivation phenomena has not been widely studied (refs. 1, 2). The occurrence of two different deactivation processes not only adds another level of complexity to the determination of the intrinsic kinetic behavior but also complicates the interpretation of the experimental results. In our previous studies regarding the thloresistance of naphtha reforming catalysts (refs. 3, 4) we have shown that the activity decay caused by the presence of sulfur compounds in the feed is often accompanied by coking. In this situation, the thioresistance cannot be obtained in a simple way from the deactivation curves. The characteristics of the sulfur poisoning have to be deduced from the overall deactivation rate. 

In this paper, we have determined the thioresistance of naphtha reforming catalysts in presence of simultaneous coke deactivation by employing both approaches (empirical parameters and mechanistic deactivation models). 

Study of the Simultaneous Deactivation by Coke and Sulfur of Naphtha Reforming Catalysts using a Bifunctional Test Reaction... 

In the 1950s, naphtha-reforming catalysts were essentially heterogeneous and monometallic and composed of a base support material (usually chlorided alumina) on which platinum metal was placed. These catalysts were capable of producing high-octane products however, because of quick deactivation as a result of coke formation, they required high-pressure, low-octane operations. Typically, the time between regenerations is a year or more. 

Influence of Total Pressure and Hydrogen Hydrocarbon Ratio on Coke Formation oyer Naphtha-Reforming Catalyst... 

Coke Formation over Naphtha-Reforming Catalyst 241... 

In the case of the naphtha reforming catalysts, only a very small fraction of the feed is transformed into coke. According to Barbier, only one atom of carbon out of 200,000 activated by the catalyst is transformed into coke. The coking of the catalyst determines the way it is operated (mainly the pressure) and the plant design. 

From the literature analyzed, it is possible to conclude that on the bifunctional naphtha reforming catalysts, mono or bimetallic, at the startup of the operation there is a lineout period in which coke is rapidly deposited on the metal function. This produces a decrease in metal catalytic activity for reactions kinetically... 

Influence of the Acid Function.- It has been shown that most of the coke deposition on the bifunctional naphtha reforming catalyst occurs on the acid function. Barbier et al. showed the importance of the acid sites of the support by performing TPO studies of coke from cyclopentane reaction on three catalysts Pt(0.59)/AI2O3 and the same catalyst modified by the addition of H BO and by the addition of KOH. The neutralization of basic sites of alumina by H3BO3 modified the quantity and localization of coke very little, whereas the neutralization of acid sites by KOH produced a decrease of 90% of the quantity of coke deposited on the support. Thus it is apparent that the polymerization leading to coke is essentially of an acid nature. A similar effect was observed in the coking produced... 

The localization, nature and structure of coke deposits have been examined with electron microscopy. In some cases, such as reforming catalysts, there are few papers where the use of electron microscopy has been reported In other processes, such as in those cases where carbon whistles are formed, there is a large number of studies using this technique. In this case, the morphology of the carbon deposits are easily distinguished from the catalyst, and the interpretation of the analysis is easier than in other cases where coke is distributed on the surface of the catalyst e.g. naphtha reforming catalysts). 

SIMS was also used to study naphtha reforming catalysts It was found that the carbon profile along the pellet had wide irregularities. Two different regions could be distinguished, areas quite free of coke where the carbon signal was very low, and areas where the peak signal was close to the maximum. The size of these areas varied between 20 and 100 pm. 

The Pt-Re system has been studied extensively since the 1970s because adding Re to AhOs-supported platinum catalysts increases the resistance to deactivation of the catalysts used in naphtha reforming by preventing coke deposition. By using carbonyl precursors, well-defined bimetalhc species have been prepared. A proper characterization of these species allowed a relationship to be established between their structure and their catalytic behavior. Table 8.3 shows several Pt-Re bimetaUic catalytic systems prepared using different carbonyl species in which Pt-Re interactions determine the catalytic behavior. 

Table 1 shows the catalyst compositions. I and II are Pt-Re/Al203 commercial catalysts coked by their use in a commercial naphtha reforming unit operated at 1.5 MPa. I was sampled at the end of the operation cycle (7 months), and II at the middle of the cycle. Ill is a fresh sample of the same catalyst coked in the laboratory at 0.1 MPa. The coked catalysts were ground and the 35-80 mesh fraction was used. 

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