SAPO-34 synthesis

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... 

While water is the most frequently used solvent, SAPO synthesis has heen reported in a hiphasic system, viz. water, containing A1 and P sources, and hexanol with TEOS as Si source [176]. Also, the SAC method has heen used to synthesize AIPO4-II [177]. Monitoring the crystallization with O-laheled water gave useftil mechanistic information, indicating that water reacts first with alumina in the dry gel before hydrolyzing Al-O-P. Afterwards P-O-H and Al-O-P bonds are broken and reformed. 

In 1982, Union Carbide reported the synthesis of the first phosphate-based molecular sieves (95, 96). This finding would include aluminophosphates (A1P04) and gallophosphates (GaP04) as well as silicoaluminum phosphates (SAPO) and metalloaluminum phosphates [MAPO, M = first-row transition metal (TM)]. The... 

The SAPO anhydrous composition can be expressed as 0-0.3R(Si, lyPJ02, where x, y and z are the mole fraction of the respective framework elements. The mole fraction of silicon, x, typically varies from 0.02 to 0.20 depending on synthesis conditions and structure type. Martens et al. have reported compositions with the SAPO-5 structure with x up to 0.8 [32]. Van Nordstrand et al. have reported the synthesis of a pure silica analog of the SAPO-5 structure, SSZ-24 [33]. 

Martens, J.A., Mertens, M Grobet, P.J., and Jacobs, P.A. (1988) Synthesis and charaderization of siJicon-rich SAPO-5, in Innovation Zeolite Mater. Sci. (eds P.J. Grobet, W.J. Mortier, E.E. VansanL and G. Schulz EHoff), Stud. Surf Sd. Catal. 37, Elsevier, Amsterdam, pp. 97-105. 

There is limited patent literature available on manufacturing techniques for aluminophosphates. Although many patents describe AlPO synthesis, most described examples are small-scale preparations. The fact that at least two catalytic applications have been commercialized for SAPO molecular sieves indicates that they have been scaled-up to large quantities [55, 56]. A large-scale preparation of SAPO-34 is described in a recent patent [57]. 

Sinha, A.K., Sainkar, S., and Sivas-anker, S. (1999) An improved method for the synthesis of the silicoalumino-phosphate molecular sieves, SAPO-5, SAPO-11 and SAPO-31. Micropor. Mesopor. Mater., 31, 321-331. 

Wendelbo, R., Akporiaye, D., Andersen, A., Dahl, I.M., and Mostad, H.B. (1996) Synthesis, characterization and catalytic testing of SAPO-18, MgAPO-18, and ZnAPO-18 in the MTO reaction. Appl. Catal. A, 142, L197-L207. 

Chen, Y., Zhou, H., Zhu, J., Zhang, Q., Wang, Y., Wang, D., and Wei, F. (2008) Direct synthesis of a fluidizable SAPO-34 catalyst for a fluidized dimethyl ether to olefins process. 

Blasco, T., Chica, A., Corma, A., Murphy, W.J., Agundez-Rodriguez, J., and Perez-Pariente, J. (2006) Changing the Si distribution in SAPO-11 by synthesis with surfactants improves the hydroisomerization /dewaxing properties./. Catal., 242, 153-161. 

In addihon to shape selechvity and acid-site strength, other catalyst characteristics that influence the catalyhc performance of SAPO-34 have also been idenhfied. Variahon in the SAPO-34 gel composition and synthesis condihons have been were used to prepare samples with different median particle sizes and Si contents (Tables 15.3 and 15.4) [104]. In these samples the median parhcle size was varied from 1.4 to 0.6 xm, and the Si mole frachon in the product was varied from 0.14 down to 0.016. A comparison of samples B and E (which have similar parhcle size distributions) shows that reducing Si content decreases propane formation and increases catalyst life. A comparison of samples B and C (which have similar Si contents) illushates an increase in catalyst life with a reduchon in parhcle size. 

Zeolite catalysts play a vital role in modern industrial catalysis. The varied acidity and microporosity properties of this class of inorganic oxides allow them to be applied to a wide variety of commercially important industrial processes. The acid sites of zeolites and other acidic molecular sieves are easier to manipulate than those of other solid acid catalysts by controlling material properties, such as the framework Si/Al ratio or level of cation exchange. The uniform pore size of the crystalline framework provides a consistent environment that improves the selectivity of the acid-catalyzed transformations that form C-C bonds. The zeoHte structure can also inhibit the formation of heavy coke molecules (such as medium-pore MFl in the Cyclar process or MTG process) or the desorption of undesired large by-products (such as small-pore SAPO-34 in MTO). While faujasite, morden-ite, beta and MFl remain the most widely used zeolite structures for industrial applications, the past decade has seen new structures, such as SAPO-34 and MWW, provide improved performance in specific applications. It is clear that the continued search for more active, selective and stable catalysts for industrially important chemical reactions will include the synthesis and application of new zeolite materials. 

Of the zeolitic materials, AlPO s cut a conspicuous figure because of their structural diversity and the incorporation of other elements into their frameworks. The recently developed VPI-5 (refs. 2, 3) announced the feasibility of synthesis of micoporous structures with windows comprising rings of over 12-T. All AlPO s, SAPO s and MAPO s form a family of microporous structures constructed by or essentially by A1(I) and P(V). Some of them are isostructural with zeolites but a majority have novel structures. The primary building units (PBU) centred by P(V) are invariantly PO4 whereas those centred by A1(I) are AlO in most cases and AIO5 or even AlOs in a few cases. So far all AlPO s, SAPO s and MAPO s have been synthesized exclusively in the presence of amines or... 

Besides the conventional zeolites, several novel zeolite analogues such as the ALPOs (aluminophosphates), MeALPOs (divalent-metal (Me) substituted aluminophos-phates), SAPOs (silicon substituted aluminophosphates) and so on have been synthesized (Davis Lobo, 1992). Wilson et al. (1982) first reported the synthesis of microporous ALPOs. ALPO synthesis differs from zeolite synthesis in that it involves acidic or mildly basic conditions and no alkali metal ions. Some members in the ALPO... 

When synthesis mixture A is agitated, MCM-1 crystallizes as a pure phase if the temperature in the first step of the hydrothermal treatment is low (Nos. 1,3,4 and 6). When this temperature is 423 K or higher, co-crystallization of SAPO-11 is observed (Nos.2 and 5). MCM-9 was obtained under static conditions after heating at 403 K and at 443 K for one day (No.7). When the heating period at the second temperature is prolonged MCM-9 is transformed into a mixture of MCM-1 and SAPO-11... 

Qulnuclldlne (QUIN). The template qulnudldlne yields the structure-types 16 and 17 (ERI) In A1P0 synthesis and types 16, 17, and 35 (LEV) In SAPO and MeAPO synthesis. Typical synthesis gels for the preparation of MeAP0-16 and -35 are ... 

The recent descriptions of the ALPO-n, SAPO-n and MeAPO-n families of microporous materials illustrate that hydrothermal syntheses can afford a wide and diverse range of four-coordinate framework structures based on nearregular tetrahedra [1,2]. As building blocks, octahedra and tetrahedra can also be combined, in various proportions, into a variety of structure types [3,4]. Reflecting the conditions used for conventional synthesis [3,4], most of these structures are condensed, with little accessible pore volume. There are, however, examples of both synthetic [5-7] and natural materials [8-11] that have microporous crystalline structures. Further, the formation chemistry of silicates and aluminosilicates [12,13] illustrates that the more open structures are generally produced under relatively mild conditions. Open octahedral-tetrahedral structures with large pore systems might therefore also be accessible under appropriate low temperature hydrothermal conditions. 

Vis tad et al. (2001) Silicon-aluminum phosphates, SAPO 34 Phase formation role of thermal treatment + + Solid formation mechanism, intermediate phases during synthesis of mesoporous solids... 

Syngas conversion to methanol has been shown to take place on supported palladium catalyst [1]. Methanol can in turn be converted to gasoline over ZSM-5 via the MTG process developed by Mobil [2]. In recent work we have reported syngas (CO/H2) conversion to hydrocarbon products on bifunctional catalysts consisting of a methanol synthesis function, Pd, supported on ZSM-5 zeolites [3]. Work on syngas conversion to hydrocarbon products on Pd/SAPO molecular sieves has been published elsewhere [Thomson et. al., J. CataL. in press].Therefore, this paper will concentrate on propylene conversion. 

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