Deactivation, SAPO catalysts

Propylene Conversion. Catalyst activity studies for the three SAPO samples were initially conducted at a temperature at 550 K and propylene partial pressure of 16.2 KPa. Since the observed activity of the SAPO catalysts was low (conversion never exceeding 15%, and most often below 3%), rates of reaction are reported assuming differential reactor behavior. Deactivation occurred in all cases, with the loss in activity of SAPO-5 and SAPO-34 being particularly rapid (Figure 3). The severity of SAPO-34 deactivation at 550 K made estimation of its initial activity (the rate of propylene converted at time-on-stream= 0 hours) difficult. However, it is clear that the narrow-pore SAPO-34 displayed the highest initial catalyst activity, with the medium-pore SAPO-11 and the wide-pore SAPO-5 having almost equal initial activities. 

The activity of the SAPO catalysts was also studied at different operating temperatures. The rapid deactivation of SAPO-5 and SAPO-34 required the use of fresh catalyst samples and limited catalyst evaluation to just two temperatures at 550 K and 650 K. The rate of deactivation, as well as the rate of propylene conversion, depended on the operating temperature (Figure 5). In contrast to reaction over the ZSM-5 catalysts [17], propylene conversion increased at higher temperature over... 

In addition to the rates of olefin reactions, mass transfer also plays an important role in determining the extent of propylene conversion and the product distribution from SAPO molecular sieves. Restrictions on molecular movement may be severe in the SAPO catalysts, due to pore diameters (4.3 A for SAPO-34) and structure (one-dimensional pores in SAPO-5 and SAPO-11). The deactivation of SAPO-5 and SAPO-11 catalysts may be more directly related to mass transfer than the coking of SAPO-34. Synthesis of large or highly-branched products, having low diffusivities, inside the pores of SAPO-5 or SAPO-11 essentially block internal acid... 

Figure 6. Influence of Catalysts Deactivation on Product Distribution over SAPO Catalysts (Propylene Inlet Pressure- 16.2 kPA, Temp.= 650 K) (a) SAPO-5 (b) SAPO-34...

Recently basic sites in ALPOS and SAPOs have been detected by IR spectra [13] of chemisorbed pyrolle and it has been reported that small amounts of basic sites in zeolite exhibit more activity in the methylation of aniline. However an excessive amount covers the active sites and deactivates the catalyst. ALPO and its derivatives contain both acidic and basic sites. The basic sites are due to high aluminium content but small amount of protons, resulting in a highly negative charge on frame work oxygen. Introduction of Mg increases total basicity and decreases total acidity of the material. Due to this the successive alkylation of NMA to NNDMA is suppressed. AEL type materials have steady activity in this reaction. 

The UOP/Hydro MTO process utilizes the highly selective metalloaluminophosphate molecular sieve catalyst MTO-100, which is based on SAPO-34. The main olefin products are ethylene and propylene, but the catalyst is rapidly deactivated by aromatic coking. An alternative MTO catalyst is the medium-pore zeolite ZSM-5. In this case the main olefin product is propylene, and the deactivation of catalyst caused by aromatic coke is slow, but significant quantities of Cs+Zaromatic by-products are formed. 

On the other hand, the primary carbenium ions ethyl+, propyF, and butyF, whose formation involves the oxonium methyl ylide, can be deprotonated into the corresponding olefins, but they can also undergo methylation and oligomerization into higher carbenium ions, leading to paraffins formation via H-transfer reactions and to aromatic via cyclization [119]. The latter transformation leads to polyring aromatics, which are too bulky to leave the catalyst because of the structure of SAPO-34. They cover sites and block pores and thus deactivate the catalyst. However, the catalyst should be partially deactivated to a primary formed propylene which could escape the pore system of the molecular sieve. 

Akolekar, D.B. (1994) Thermal Stability, addity, catalytic properties, and deactivation behaviour of SAPO-5 catalysts effect of silicon content, add treatment and Na exchange. J. Catal., 149, 1 10. 

However, this level of deactivation will be overcome by the catalyst make-up required to replace material lost to physical attrition in the fluidized bed reactors. A slight shift in the ethylene and propylene selectivities was also observed during the initial portion of this run. Characterization of the catalyst during the multi-cycle test shows that there is no change in the microporosity of the SAPO-34 molecular sieve,... 

Chen et al. (7,37,38,39,40) investigated the conversion of methanol to light olefins (MTO) using TEOM. The investigations included the influence of coke deposition on the selectivity, the effect of the crystal size of SAPO-34 on the selectivity and the deactivation of the catalyst for the MTO reaction, and modeling of the kinetics of the MTO reaction. Simultaneous measurements of coke deposition, conversion, and selectivities by TEOM combined with in situ GC analysis of the effluent gas... 

The catalytic activity of silicoaluminophosphate molecular sieves (SAPO-5, SAPO-11, SAPO-34) has been studied during propylene conversion. During die reaction, SAPO-34 and SAPO-5 yielded C2-C7 hydrocarbons but both catalysts deactivated severely during reaction. The initial activity of SAPO-34 which contained sites of stronger acidity was higher than SAPO-5. SAPO-11, showing lower activity than SAPO-5 and SAPO-34 as well as rapid deactivation, yielded only C6 hydrocarbons. Differences in the product distribution observed during both reaction studies arise from the different acidity, pore structure and pore size of the S APO molecular sieves. 

Propylene conversion over three SAPO molecular sieves (SAPO-5, SAPO-11, and SAPO-34) was conducted at a variety of operating conditions. Catalyst behavior was correlated with the physical and chemical properties of the SAPO molecular sieves. The objective of this work was to determine the relative importance of kinetic and thermodynamic factors on the conversion of propylene and the distribution of products. The rate of olefin cracldng compared to the rate of olefin polymerization will be addressed to account for the observed trends in the product yields. The processes responsible for deactivation will also be addressed. 

Olefin oligomerization were found to occur on SAPO molecular sieves, though their activity was far less than the of zeolite ZSM-5[17]. While showing very different initial activity, the wide-pore SAPO-5 and the narrow pore SAPO-34 both deactivated severely (Figure 3). Both of these catalysts yielded a wide spectrum of products presumably following the pathway described by Tabak et. al. [5], in which numerous olefin polymerization and scission reactions take place. Strangely, medium pore SAPO-11 showed complete selectivity for olefin dimers... 

Rhodium supported on y-ALOs is an important component of 3-way automotive catalysts and has been studied by a wide variety of methods [1-5] including ESR. In the last 15 years Rh-species introduced into zeolites of different types (Y, X, L, A, SAPO) have also been examined by several techniques [6-9]. However, most of these methods were applied after the specimens were removed from actual reaction conditions and transferred into the respective characterization instruments and the state or behavior of the catalyst in-situ was arrived at indirectly by inference. Also the deactivation processes or the effect of modifiers is seldom, if ever, determined by direct in-situ observations. We have previously devised a method for high-temperature measurement of ESR-active ions under flow conditions and applied it to characterize specimens containing Cu [10] or Cr " [11]. We have extended this method now to specimens containing Rh. Here, we summarize the results of a study of the interaction of Rh/y-ALOB and Rh/ZSM-5 with different gases and gas mixtures (NO, NO2, CO, propene, O2, H2O) at 120-573 °K. The amount of Rh present in the samples is evaluated quantitatively. The effect of copper and lanthanide addition on the stabilization of by the zeolitic matrix was also investigated. 

Kikuchi and coworkers have shown that biphenyl can be selectively alkylated not only with mordenite [Matsuda et al., 1995] but also with SAPO-11 catalysts [Matsuda et al., 1996]. In both cases, deactivation of external surfaces was shown to increase the selectivity to 4,4-DIPB. In their report on mordenite, they demonstrated that deactivation of external acid sites on mordenite by treatment with tributylphosphite is effective for improving selectivity to 4,4-DIPB, as shown in Table 7 [Matsuda et al., 1995]. 

As Shown in Figure 4, catalyst deactivation is an important factor in the hydroxy-alkylation reactions. This makes quantitative comparison difficult, as each material has a balance between activity and deactivation. The main conclusion from the results is that materials having a low acidity, ALPO-5 (vide supra) and 7-alumina, give best results, because of their low rate of deactivation. Already when SAPO-5, having an acid strength between ALPO-5 and aluminosilicates, is used, a rapid deactivation was observed in the phenol/formaldehyde reaction. 

Due to the similarity of the catalyst and of the characteristics of the deactivation in the transformation of methanol and of ethanol, eq. (5) has been taken as a basis for the establishment of possible deactivation equations for the transformation of ethanol into hydrocarbons. In eq. (5), X is the mass fraction (based on the organic components in the reaction medium) of the lumps of the kinetic scheme that can be considered coke precursors. This is the way in which the composition of the reaction medium is commonly expressed in the literature for the kinetic study of the processes of transformation of methanol on a HZSM-5 zeolite [8,12-14,16] and on a SAPO-34 [9]. In eq. (5), activity, a, is defined as the ratio between reaction rate at t time and at zero time ... 

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