Synthetic mordenites

The zeoHtes used for catalysis are principally modified forms of zeoHte Y, acid forms of synthetic mordenite, and ZSM-5. 

Catalytic Dewaxing Also called CDW. A hydiocracking process for removing waxes (linear aliphatic hydrocarbons) from petroleum streams by converting them to lower molecular weight hydrocarbons. The catalyst is a synthetic mordenite. Developed by BP two units were operating in 1988. 

Structural characteristics. Both natural and synthetic mordenite have an orthorhombic structure that consists of parallel, 12-membered ring channels in the c-direction, having an eliptical cross-section with dimensions of 6,7 x 7.0 A (Figure 9). Smaller 8-membered ring channels with dimensions of 2.9 x 5.7 A, which are perpendicular to the main channels, are too small to allow the movement of molecules from one main channel to another. Mordenite has been synthesized in a "large -port" and "small-port" form that have different sorption properties. A typical unit cell content is Na0[(A10o)o(Si0o)/rJ. 24 HO. 8 28 2 40... 

We have examined the rate constants for disproportionation and isomerization for a variety of zeolites, using a commercial-type feed containing 70% m-xylene and 30% o-xylene in a fixed-bed flow reactor. The results, listed in Table I, show the exceptionally low disproportionation/isomerization selectivity of ZSM-5 relative to synthetic faujasite. Synthetic mordenite and ZSM-4 have intermediate selectivities. 

The effect of different zeolite structures and pore systems is also reflected in the data of Table II. With the intermediate pore ZSM-5, xylene is apparently much less reactive than ethylbenzene, both as an alkyl donor and acceptor, than it is with the large pore zeolites, ZSM-4 and synthetic mordenite. 

This may be partly the result of increased steric crowding in the transition state of transalkylation. Another contributory factor to the increased selectivity in ZSM-5 is the higher diffusion rate of ethylbenzene vs m-/o-xylene in ZSM-5 and hence a higher steady state concentration ratio [EB]/[xyl] in the zeolite interior than in the outside phase. Diffusional restriction for xylenes vs ethylbenzene may also be indicated by the better selectivity of synthetic mordenite vs ZSM-4, since the former had a larger crystal size. 

Synthetic mordenite (a zeolite having 7-A-diameter, one-dimensional channels Se Se particle domains were incorporated into zeolite channels 558... 

A-, X-, Y-, and AIPO-5-molecular sieves and synthetic mordenite Se Predominantly trigonal helical chains of selenium were incorporated into the zeolite channels 559... 

Two sets of patterns were calculated for each structure with and without sodium cations (Table II). These results indicated that the effect of the cations could be ignored. This is confirmed by actual patterns for the Na and H forms of a synthetic mordenite. Because mordenite has a low cation content, cation effects on peak intensities should be minimal. 

X-Ray Diffraction Patterns. Table II gives interplanar spacings for the first 12 prominent lines observed in the diffraction patterns for samples 1-5 as well as those reported by Domine and Quobex (19) for synthetic mordenite. A few points should be noted. 

In a subsequent publication (118), the SnO and Sn02nH20 interactions with the silica support were studied on samples with different pore diameters ranging from 0.5 to 27 nm, and on a synthetic mordenite of 0.6-nm pore diameter. From the temperature dependence of the respective spectral areas, it was concluded that both the SnO and the Sn02 H20 components were more strongly bonded to supports with smaller pore diameters. In addition to the spectral area, however, the spectral width is also expected to reflect... 

A bituminous coal from Utah (Table I) was used in this work. The coal oil (Table II) used was obtained from a bituminous coal by hydrogenation using zinc chloride as the catalyst in a semi-continuous reactor system. Anthracene, phenanthrene, WS9 and NIS used were pure grade chemicals of over 99% purity. H-zeolon was a synthetic mordenite cracking catalyst and was supplied by Norton Chemical Company. NIS-H-zeolon was prepared by spraying nickel on H-zeolon with a subsequent sulfiding operation. NIS-WS -SiO -A1 O. catalyst used was a commercial hydrocracking catalyst. Analyses of reactants and products were done by standard methods. 

Twenty-eight kinetics of crystallization of different types of zeolites (A (2,12,13,35,36), X (2,6,37), L (38), P (3 0, ZSM-5 (39-41), synthetic mordenite (2,42) and offretite (43)), synthetized by various authors under various experimental conditions, have been analysed by using Equations (1) and (5). 

Figure 2. Kinetics of crystallization of ZSM-5, A (39), zeolite L, o (38), offretite, e (43) and synthetic mordenite, A (42), correlated by Equation (1) (solid curves in Figure A) and by Equation (5) (solid curves in Figure B), respectively, using the corresponding values of K, q, K0 and Ka from Table I.

Figure 8. Single pulse exitation and cross polarization 2 Si NMR spectra of synthetic mordenite.

The desire to synthesize molecular sieve compositions containing other than the typical silicon and aluminum atoms is evidenced by the large number of efforts, primarily in the primary synthesis area. The Secondary Synthesis process has now been extended to include substitution of both Fe3t and T1 + into the frameworks of a number of zeolites. This paper will describe substitution of iron or titanium ions into the frameworks of zeolites Y, L, W, mordenite, ZSM-5 and LZ-202. Zeolites Y, L, W and mordenite were obtained from Union Carbide Corporation. Zeolon, a synthetic mordenite, was obtained from The Norton Company. ZSM-5 was synthesized according to the procedures described by Argauer et al., (8). LZ-202 is an omega type zeolite, synthesized without the... 

The hydronium exchanged synthetic mordenite does have a band, as shown in spectrum 10 in Figure 1. The iron substituted mordenite samples (spectra 8 and 9) do not show the presence of the band it was "removed" as a result of the substitution reaction. An absorption band at 950 cm- is normally attributed to an Si-OH stretch vibration (14, 15), and is typically observed in some acid or hydrothermally treated zeolites. 

These results are consistent with the generalized reaction scheme, initially presented by Rabo et al., in which both NH +- and H30+-exchanged zeolites decompose to produce an Br-form that upon further heating becomes a decationized zeolite. This behavior is similar to that reported earlier for calcined ion-exchanged synthetic mordenites, where two distinct sources of acidity were found in the NH4+-form but not in the H30+-form. 

On the other hand, the acidity in acid-exchanged synthetic mordenite has been shown by Flank and Skeels in 1977 to arise from either H30+ or, following removal of adsorbed water at elevated temperatures, H+ species balancing framework negative charges (3). The same study showed that the acidity of calcined NH4+-mordenite arises from two separate and distinct acid centers. Nearly two-thirds of the acidity is due to the presence of H30+ or H+ species. The remaining third of the acidity is due to the formation of hydroxoaluminum cations during the thermal treatment. 

D DM catalysts have a new pore structure consisting of crystalline domains of 8- and 12-ring pores connected by mesopores (5-10 nm). The presence of the latter enhances accessibility to the micropore regions without seriously compromising the shape-selective character of the catalyst. This combination of changes in acidity and pore structure transforms synthetic mordenites into highly active, stable and selective alkylation catalysts. 

A study of Cl to C4 paraffins in synthetic mordenite by Satterfield and Frabetti, Jr. (31) has shown that diffusion coefficients for desorption are many times smaller than those for sorption, and the coefficients are reduced substantially by grinding the crystals. This investigation has raised problems which may have some general importance. For example, dry grinding may cause substantial local temperature rises associated with local stresses, and may cause at least some surface breakdown of the crystal structure. 

Early adsorption studies indicated that the effective micropore openings in natural and synthetic mordenites were about 4A (2) and not ca. 7A as required by structural data. Later it was shown that this probably was caused by partial blocking of the main channels by calcium and/or sodium cations (3, 22). Sorption in the side channels is limited normally to molecules smaller than n-butane (4.9A) (3), while the main channels in hydrogen-mordenite are nearly filled by the larger cyclohexane (22), benzene, and neopentane molecules (3) of critical diam-... 

Catalytic Properties of Synthetic Mordenite in Isomerization, Hydrogenation, and Hydroisomerization of Hydrocarbons... 

The catalytic properties of H-, Li-, Na-, K-, Mg-, Ca-, Zn-, Cd-, and Al-forms of synthetic mordenite in the reactions of cyclohexane and n-pentane isomerization and benzene hydrogenation have been studied. The cation forms of mordenite that do not involve the metals of column VIII of the Mendeleyev Table show high activity in these reactions. To elucidate the mechanism of n-pentane isomerization, the kinetics of the reaction on H-mordenite have been studied. Carbonium ion is supposed to result from splitting off hydride ion from hydrocarbon molecule. Na-mordenite catalytic activity in benzene hydrogenation reaction decreases linearly with the increase of decationization. This indicates that cations are responsible for the catalytic activity of zeolite. The high activity of cations of nontransition metals in oxidation-reduction reactions seems to be quite unexpected and may provide evidence for some uncommon mechanism of benzene hydrogenation. 

The information about synthetic mordenite properties was obtained in 1961 when Keough and Sand (7) found that H- and other forms of this crystalline aluminum silicate display high activity and selectivity in the reactions of hydrocarbon cracking and ethanol dehydration. Later this zeolite was shown (J, 2, 5, 7, 8, 10-13, 15, 16) an active catalyst in the reactions of isomerization, cracking, and alkylation of hydrocarbons and alcohol dehydration. However, the catalytic properties of mordenite have been studied insufEciently, compared with those of other zeolites. 

The present paper reports the results of investigating the catalytic properties of a number of cation forms of synthetic mordenite in the reactions of isomerization, hydrogenation, and hydroisomerization of hydrocarbons. 

Table II. Benzene Hydrogenation on the Cation Forms of Synthetic Mordenite at 250 C, P = 30 Atm, V = 1 Hour ...

---