Of mordenite

Free apertures in second channel system are too small for organic molecules to diffuse readily, making the channel system of mordenite essentially monodimensional. 

Fig. 3. Model of the crystal structure of the mineral mordenite showing the main channel formed by 12-membered ring and small channels which contain some of the sodium cations. Synthetic types of mordenite exhibit the adsorption behavior of a 12-membered ring, whereas the mineral does not, probably...

The synthesis of ethylenediamine (EDA) from ethanolamine (EA) with ammonia over acidic t3pes of zeolite catalyst was investigated. Among the zeolites tested in this study, the protonic form of mordenite catalyst that was treated with EDTA (H-EDTA-MOR) showed the highest activity and selectivity for the formation of EA at 603 K, W/F=200 g h mol, and NH3/ =50. The reaction proved to be highly selective for EA over H-EDTA-MOR, with small amounts of ethyleneimine (El) and piperazine (PA) derivatives as the side products. IR spectroscopic data provide evidence that the protonated El is the chemical intermediate for the reaction. The reaction for Uie formation of EDA from EA and ammonia required stronger acidic sites in the mordenite channels for hi er yield and selectivity. 

The plausible cause of shape selectivity to DME in H-mordenite is the presence of the active protons wittun the side-pockets of mordenite that are accessible only to methanol. The protonated methanol molecule, a methyl oxonium ion, undergoes rear-attack by a second methanol molecule entering the side-pocket from the main channel... 

It is well known also that higher alkanes suffer radical gas phase oxidation above 723 K. Therefore, their use requires catalysts active and selective for deNOx at lower temperatures. The mechanism of NOx elimination is still debated a redox mechanism involving Cu ions is probable, and isolated Cu cations exchanged into MFI [4,5] or mordenite [6] have been found to be more active than CuO clusters. It must be emphasized, however, that acid zeolites exhibit good activity at high temperature, and acid mechanisms have been proposed [7-10]. In presence of Cu this acid mechanism disappears probably due to the decrease of the acidity of mordenite upon Cu exchange [6]. According to... 

Marie, O., Thibault-Starzyk, F. and Lavalley, J.C. (2000) Confirmation of the strongest nitriles-hydroxy groups interaction in the side pockets of mordenite zeolites, Phys. Chem. Chem. Phys., 2, 5341. 

Initial inner acid sites isomerization selectivity is low for 10MR zeolites and high for Mordenite catalysts. This suggests that large 12MR channels of Mordenite are favorable to EB isomerization into xylenes in the zeolite microporosity. 

Klinowski, J., Anderson, M.W., Fyfe, C.A. and Gobbi, G.C. (1983). Dealumination of mordenite using silicon tetrachloride vapor. Zeolites 3, 5-7... 

In the case of mordenite, aluminum was solubilized in the two-step process primarily with mineral acids (5), while in the case of Y zeolites it involved acids (28,29), bases (17) or salts (30,31). The use of chelating agents has also been reported (32). 

Structure of mordenite framework as viewed along c-axis (66). 

The correlation between selectivity and intracrystalline free space can be readily accounted for in terms of the mechanisms of the reactions involved. The acid-catalyzed xylene isomerization occurs via 1,2-methyl shifts in protonated xylenes (Figure 3). A mechanism via two transalkylation steps as proposed for synthetic faujasite (8) can be ruled out in view of the strictly consecutive nature of the isomerization sequence o m p and the low activity for disproportionation. Disproportionation involves a large diphenylmethane-type intermediate (Figure 4). It is suggested that this intermediate can form readily in the large intracrystalline cavity (diameter. 1.3 nm) of faujasite, but is sterically inhibited in the smaller pores of mordenite and ZSM-4 (d -0.8 nm) and especially of ZSM-5 (d -0.6 nm). Thus, transition state selectivity rather than shape selective diffusion are responsible for the high xylene isomerization selectivity of ZSM-5. 

The values of Arto Awere calorimetrically measured or taken from the literature by the authors [143], The enthalpy of formation of mordenite is related with Ar//°(8.9) by... 

Johnson et al. [143] also studied the dehydrated form of mordenite by reaction-solution calorimetry. Their results and the foregoing enthalpy of formation data lead to Af//°(Cao.289Nao.36iAlo.94oSi5.06oOi2.ooo, cr) = —5661.7 4.8 kJ mol-1. From the enthalpies of formation of both forms of mordenite and the enthalpy of formation of liquid water already quoted (—285.830 0.040 kJ mol-1), it is possible to conclude that at 298.15 K, the enthalpy of dehydration of mordenite, which corresponds to the reaction... 

Johnson et al. [143] used low-temperature adiabatic calorimetry and high-temperature drop calorimetry to obtain the heat capacity of both forms of mordenite as a function of the temperature. These results and the results of the reaction-solution calorimetric studies discussed herein, enabled the tabulation of the thermodynamic properties (C°, S°, Af H°, and Af G°) of mordenite from 0 K to 500 K and dehydrated mordenite from 0 K to 900 K. 

The catalysts for xylene isomerization with EB dealkylahon are dominated by MFI zeolite. The de-ethylation reaction is particularly facile over this zeolite. There have been several generations of catalyst technology developed by Mobil, now ExxonMobil [84]. The features in their patents include selectivation and two-catalyst systems in which the catalysts have been optimized separately for deethylation of EB and xylene isomerization [85-87]. The crystallite size used for de-ethylation is significantly larger than in the second catalyst used for xylene isomerization. Advanced MHAI is one example. The Isolene process is offered by Toray and their catalyst also appears to be MFI zeoUte-based, though some patents claim the use of mordenite [88, 89]. The metal function favored in their patents appears to be rhenium [90]. Bimetallic platinum catalysts have also been claimed on a variety of ZSM-type zeolites [91]. There are also EB dealkylation catalysts for the UOP Isomar process [92]. The zeolite claimed in UOP patents is MFI in combination with aluminophosphate binder [93]. 

Koradia, P., Kiovsky, J.R., and Asim, M.Y. (1980) Optimization of SiOy/AlyOy, mole ratio of mordenite for n-pentane isomerization. . Catal., 66, 290-293. 

Boveri, M., Marquez-Alvarez, C., Laborde, M.A., and Sastre, E. (2006) Steam and add dealumination of mordenite charaderization and influence on the catalytic performance in linear alkylbenzene synthesis. Catal. Today, 114, 217-225. 

FIGURE 7.15 The channel structure of mordenite, illustrating the larger channels running along the z direction. 

Figure 1. Crystallization curves of mordenite from a batch composition 8.5 N avO-AWz-85 SiD2 182 H20 as a function of temperature and NaCl content filled symbols, no NaCl open symbols, 4.5 moles of NaCl/mole Al2Oz)...

Crystallization was followed by analyzing the solid product quantitatively by x-ray powder diffraction. Prepared mixtures of a standard sample of mordenite and the amorphous substrate of mordenite composition were used to establish a calibration curve for the quantity of mordenite based on the summation of x-ray peak intensities. For zeolites A and X, the unreacted aluminosilicate gel was used to prepare mixtures with standard samples of zeolites A and X for quantitative phase identification. 

Figure 8. The effect of seeding on crystallization rates of mordenite from a hatch composition of 8.6 NazO-AWr-85 SiOz-182 HzO 4-5 NaCl as a function of temperature (8X2X8 imeter seed crystals)...

---