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... 

FIGURE 2.12 Riser simulator results Heavy naphtha aromatics (ClO-Cll) as a function of slurry oil yield (343°C+) (X) Inert, ( ) LZM catalyst, (a) MAB catalyst. 

Reforming Both thermal and catalytic processes are utilized to convert naphtha fractions into high-octane aromatic compounds. Thermal reforming is utilized to convert heavy naphthas into gasoline-quality aromatics. Catalytic reforming is utilized to convert straight-run naphtha fractions into aromatics. Catalysts utilized include oxides of aluminum, chromium, cobalt, and molybdenum as well as platinum-based catalysts. 

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. 

Naphtha reforming catalysts are mostly based on metals (Pt, Pt-Re, Pt-lr, Pt-Sn, Pt-Re-Sn) supported on chlorinated-ALOs or on a KL zeolite. Non-acidic KL zeolite in combination with Pt has been applied in a new reforming process. The non-acidic zeolite support inhibits undcsircd isomerization and hydrocracking reactions leading to enhanced aromalization selectivities [69]. Besides the absence of acidity, the presence of highly dispersed Pt clusters inside the zeolite channels and the shape-selective effects imposed by the monodirectional channel structure (0.71 nm diameter) of the zeolite may also contribute to the excellent aromatization performance of Pt/KL catalysts. 

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. 

Hierarchical (or mesoporous) zeolites became the focus of the review by Christensen et al. [7]. The main reason behind the development of hierarchical zeolites is to achieve heterogeneous catalysts with an improved porous structure and thereby enhanced performance in alkylation of benzene with alkenes, alkylation, and acylation of other compounds, methanol conversion into hydrocarbons, aromatization processes, isomerization of paraffins, cracking of diverse substrates and raw materials (naphtha, aromatic compounds, hexadecane, vacuum gas oil, and some polymers), and hydrotreating. The reactions that are of interest from the point of view of fine chemicals synthesis occurring on hierarchical zeohtes include aldol condensation, esterification, acetalization, olefin epoxidation, and Beckmarm rearrangement. 

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 ... 

The principal class of reactions in the FCC process converts high boiling, low octane normal paraffins to lower boiling, higher octane olefins, naphthenes (cycloparaffins), and aromatics. FCC naphtha is almost always fractionated into two or three streams. Typical properties are shown in Table 5. Properties of specific streams depend on the catalyst, design and operating conditions of the unit, and the cmde properties. 

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