SAPO-34 catalyst

In comparison with Pd/SAPO catalysts (8) our systems are much more selective, with selectivities of -100 % at 473 K and -95 % at 573 K compared with 65 % at 473 K and -10 % at 573 K for Pd/SAPO. However this comparison was not at equal conversion. Indeed it is difficult to compare activity directly as the catalysts were only run for a few hours (8) whereas ours were on-stream for over 24 h. 

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. 

Table n. Chromatographic Analysis of Major Hexene Products From Propylene Conversion Over SAPO Catalysts (Propylene Inlet Pressure= 16.2 KPa)... 

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...

Strictly, these catalysts are not zeolites (this name is reserved for aluminosilicates), but aluminumphosphates (AlPOs) or silicon-aluminumphosphates (SAPOs). It is indeed possible to synthesize acidic high-silica (H-SSZ-13) [3] and SAPO catalysts (H-SAPO-34) [4] with the same framework structure (CHA) [5]. 

Industrially important olefins can be made with the help of molecular sieves. Methanol can be converted into 50% ethylene and 30% propylene with a SAPO catalyst at 350-500X.190 Isobutene can be made by isomerization of n bulcnes over clinoptilolite at 45OX with 91.6% selectivity at 23.5% conversion,191 or with H-ferrierite with 92%... 

Acetonitrile can be produced from ethanol, ammonia, and oxygen in 99% yield using a SAPO catalyst at 350°C.194 It can be reduced to ethylamine with 98% selectivity using a 1.1 Co/1.1 Ni/0.9 mg/1.0 A1 layered double hydroxide and hydrogen at 393 K.322 Methylamine and dimethylamine are more valuable than trimethylamine. When methanol and ammonia are reacted in a zeolite, such as clinoptilolite, mordenite, or chabazite, the products are largely the desired monomethyl and dimethylamines, one of the best distributions being 73.1% mono-, 19.4% di-and 1.4% tri-, at 97.7% conversion.195 Alkylation of aniline... 

The bifunctional platinum - SAPO catalysts were evaluated for Cg aromatic reactions in the presence of hydrogen in bench scale... 

Preparation factors influencing the effectiveness of SAPO catalysts in n-paraffins hydroisomerization... 

SAPO-34, which has a narrow pore diameter, is highly selective for the conversion of methanol to C2-C4 olefins. Although the selectivity to aromatics on SAPO catalysts is lower than that on H-ZSM-5, the methanol conversion and the selectivity to C2-C4 olefins are 99 and 85 percent selectivity, respectively, on SAPO-34. Therefore, the yield of C2-C4 olefins is higher on SAPO-34 than on ZSM-5. SAPO-17 is active for the dehydration of methanol to light olefins." Anderson et al. also reported that SAPO-34 is highly selective for the formation of ethylene from methanol. ... 

In 1986, Union Carbide reported the successfiil synthesis of a SAPO catalyst. Researchers from DICP found that SAPO-34 catalyst could be used to convert the methanol to fight olefins with high selectivity (Liang et al., 1990). Except high selectivity to fight olefins, SAPO-34 catalyst is readily... 

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