Light naphtha aromatization catalyst

Deactivation of light naphtha aromatization catalyst based on zeolite was studied, by kinetic analysis, micropore volume analysis and model reactions. Coke accumulates at the entrance of zeolite channel, blocks it and hinders reactant molecule to access active sites in zeolite channel. Our own stabilization technique passivates coke-forming sites at the external surface of the zeolite. This minimizes the coke formation at the entrance of zeolite channel and increases on-stream stability. The stabilized catalyst enabled us to develop a new light naphtha aromatization process using an idle heavy naphtha reformer that is replaced by CCR process. 

FUKASE ET AL. Deactivation of Light Naphtha Aromatization Catalyst 221... 

Further research has been performed and is continued to be reported, mostly with zeolites unloaded or loaded with Pt, and Ga- and Zn-promoted H-ZSM-5 or H-[Al]ZSM-5 catalysts to clarify the details of the complex transformations taking place and make further improvements. In addition, new catalysts were studied and reported. Reference should also be made to work addressing the problems of the modification of catalyst features of ZSM-5404 and the development of a new light naphtha aromatization process using a conventional fixed-bed unit.405 406... 

Surface Characterization of the Stabilized Catalyst by Probe Molecule Reaction. HZSM-5 obtained from PQ Zeolite was chosen to study the mechanism of stabilization in light naphtha aromatization. The reactions of both molecules were carried out over stabilized and unstabilized HZSM-5. We assumed first order kinetics with respect to each reactant concentration and first order decay of each reaction, and calculated initial rate constants. Figure 6 shows the initial rate constants of cumene cracking and triisopropyl-benzene cracking over the stabilized and the unstabilized catalysts. 

A new catalyst with long-term stability was developed for the aromatization of light naphtha. Our proprietary technique of steaming reduced acid site density of the external surface of the catalyst and minimized coke formation. The new catalyst enabled us to develop a new light naphtha aromatization (LNA) process using a conventional fixed bed unit. Idle heavy naphtha reformer can be converted to this process without large modification. 

A new light naphtha aromatization process has been developed using a conventional fixed bed reactor. Fundamental study revealed the importance of preparation method, morphology, and acid property to increase the catalyst stability. Based on fundamental and scale-up studies, a demonstration plant was designed and operated. This operation confirmed the good stability of the catalyst. 

From the catalytic activity data of n-heptane and BH light naphtha aromatization reactions presented in Tables 6 and 7, it is clear that the product pattern is entirely different over HZSM-5 and Zn/HZSM-5 catalysts. It is also clear that the dehydrogenation component, zinc, influences the product pattern of the aromatization of both feed stocks almost in a similar maimer. From these results, it appears that the difference in product pattern occurring over these catalysts is due to the change in pathways of reactant molecules in the aromatization reaction mechanism. 

Influence of dehydrogenating component zinc on product pattern of light naphtha conversion over the Zn/HZSM-5 catalyst is similar as it is observed in case of n-heptane (Table 7). Increase in aromatic yield with enhanced selectivity towards toluene and decreased selectivity to C9+ aromatics observed over Zn/HZSM-5 catalyst can be explained by the additional path ways Km2, Km4 provided by zinc. In addition to this, an interesting change in selectivity for benzene was observed in light naphtha aromatization. Benzene yield has decreased from 6.8 wt % to 3.6 wt % over HZSM-5 catalyst, while it has increeised from 6.8 wt % to 8.1 wt % over the Zn/HZSM-5 catalyst. The decrease in benzene concentration over the HZSM-5 catalyst may be due to the alkylation of benzene facilitated in presence of olefmic intermediates formed during the reaction. It appears that, acid catalyzed alkyl transfer reactions are reduced over Zn/HZSM-5, presumably due to modifying effect of Zn on HZSM-5. This assumption explains, why the concentration of benzene is more in the product formed over Zn/HZSM-5. 

On the basis of the results of the fundamental and scale-up studies, a 2,250 BSD demonstration plant was designed and was operated at Japan Energy s Mizushima Oil Refinery in Japan to aromatize light naphtha. The plant achieved long-term operation without any trouble. We confirmed the good stability of the catalyst (7 ). 

In order to study the influence of the interaction of different hydrocarbons present in the commercial feed on the aromatization reaction, experiments was carried out with BH light naphtha feed stock. Table-7 presents the component-wise analysis of feed and products during the reaction. The conversion of BH light naphtha on Zn/HZSM-5 shows a 14.9 wt.% increase in aromatics and a 6.3 wt.-% decrease in C3 + C4 formation compared to the HZSM-5 catalyst. Moreover, an increase in toluene selectivity and decrease in C9+ aromatics selectivity were also observed over the Zn/HZSM-5 catalyst. 

Product distribution from the light naphtha (LNl) conversion over the acidity-modified catalyst is given in (Table-10). This catalyst shows 55.6 wt % of LPG product with 22.4 wt% aromatics as by-product against the 51.5 wt% LPG and 18.3 wt% of aromatics obtained over the as-synthesized catalyst. The corresponding decrease observed in the yield of fuel gases from 14.2 to 6.4 over acid-modified catalyst indicates that the secondary cracking reactions are controlled by the acidity modification. 

Product distribution of the light naphtha conversion (LNl) over the metal incorporated zeolite catalyst is given in Table 8. As can be seen from data presented, the metal modified catalyst is highly active for aromatization, evidenced by increased conversion to 91.5 wt % and aromatic yield 35.2 wt %. This is more obvious when we compare with the results on the parent catalyst (before metal modification) HZSM-5, which showed only 84% conversion and 22.4% aromatic yield. Increase in aromatic yields obtained over the metal incorporated catalyst can be explained by the active participation of metal in the olefin production by dehydrogenation and aromatization steps of the reaction [39-41]. Since aromatization of paraffins is an endothermic reaction, higher reaction temperatures (500 C) were employed for the maximum production of aromatics. 

Steam Reforming. When relatively light feedstocks, eg, naphthas having ca 180°C end boiling point and limited aromatic content, are available, high nickel content catalysts can be used to simultaneously conduct a variety of near-autothermic reactions. This results in the essentiaHy complete conversions of the feedstocks to methane ... 

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