H-mordenite extracted

The concept of extractive reaction, which was conceived over 40 years ago, has connections with acid hydrolysis of pentosans in an aqueous medium to give furfural, which readily polymerizes in the presence of an acid. The use of a water-immiscible solvent, such as tetralin allows the labile furfural to be extracted and thus prevents polymerization, increases the yield, and improves the recovery procedures. In the recent past an interesting and useful method has been suggested by Rivalier et al. (1995) for acid-catalysed dehydration of hexoses to 5-hydroxy methyl furfural. Here, a new solid-liquid-liquid extractor reactor has been suggested with zeolites in protonic form like H-Y-faujasite, H-mordenite, H-beta, and H-ZSM-5, in suspension in the aqueous phase and with simultaneous extraction of the intermediate product with a solvent, like methyl Aobutyl ketone, circulating countercurrently. 

The results indicate that the zeolite can selectively extract specific compounds from the reaction medium, due to the different affinity towards each of them. This makes possible to develop reactant concentrations inside pores which are different from the bulk ones. This property is a function of the zeolite hydrophobic characteristics, which are affected by the Si/Al ratio. The best zeolite is that one which does not interact too strongly neither with more polar molecules, so to allow activation of formaldehyde to proceed faster, nor with the least polar ones. The intermediate Si/Al ratio in H-mordenites is able to develop the optimal concentration ratio between reactants inside the pores, and to reach the highest yield to vanillols. 

As observed above, in order to quench HMF produced in situ, dealuminated H-form mordenites were investigated in a water/MIBK mixture (1/5) [84, 85]. In this case, a maximum conversion of fructose of 54% (along with 90% selectivity to HMF) was obtained over an H-mordenite with a Si/Al ratio of 11. HMF was continuously extracted with a flow of MIBK circulating in a countercurrent way through a catalytic heterogeneous reactor containing the H-mordenite zeolite. On the continuation of their efforts, the same authors then set up a new continuous solid-liquid-liquid reactor where the zeolite was now in suspension in the aqueous phase while the HMF was continuously extracted with MIBK in a countercurrent way to the aqueous phase and catalyst feed. 

More recently (8), another series of H-mordenites, acid-extracted to a greater degree, was examined. For these samples after drying at 110°C, the major results were (a) there was no evidence of hydroxyl nests stable above 100°C, and (b) NH3 chemisorption at 250°C and 11 torr roughly corresponded to a stoichiometric ratio (1 1, 25%) with the total amount of aluminum remaining in the lattice. 

Extraction with HC1. Aluminum was extracted from the original H-mordenite (Norton Co. H-Zeolon, Lot No. TA-4) with aqueous HC1 at 100° C. Details of the procedure are given in Ref. 8. 

Chemical Analysis. Table I shows the chemical composition of the samples selected for detailed study. The gray-white color of the original H-mordenite was unchanged by acid extraction interestingly, the NH4-N03-exchanged samples were cream colored. 

Although there is considerable scatter in the diffusivity values for the treated samples, the major effect is a large increase in diffusivity, relative to the original H-mordenite, on either acid extraction or NH4NO3 exchange. On this basis we would conclude that the sodium rather than the aluminum content appears to be the factor of greatest importance. 

Catalytic Activity, Selectivity, and Deactivation. The product distribution (in the C1-C5 range) remained relatively unchanged with increasing number of pulses for any given sample. For the original H-mordenite and the NH4N03-exchanged samples, propane was the major product (45-55 mole % of C1-C5). Propane and isobutane were comparable in amount (35-40 mole % each) for the two acid-extracted samples. The i-C4 n-C4 ratio was about 2 1 for samples 1, 4, and 5, and about 3 1 for samples 2 and 3, independent of pulse number. 

Total adsorbate analysis was performed on a sample of parent H-mordenite deactivated with cumene by interfaced gas chromatography-mass spectrometry. The deactivated catalyst was dissolved in 48% hydrofluoric acid at 0°C, and the organics released were extracted into chloroform. Prior to analysis, a small volume of this solution was taken up into a capillary tube, and the chloroform was allowed to evaporate, leaving a thin... 

Figure 8. Comparison of solids probe mass spectra obtained from extract at 825° C and by desorption at 816° C of parent H-mordenite deactivated with...

Species Inside Deactivated Catalysts. The total extract of the adsorbate in deactivated parent H-mordenite was heated using the solids probe of the mass spectrometer. Intense fragment ions at the higher m/e values, previously not observed to be of such intensity in the dynamic de-... 

Figure 9. FID gas chromatogram of parent H-mordenite extract showing mass spectrometer sampling...

The chromatogram obtained for the extract of the cumene-deactivated parent H-mordenite is shown in Figure 9. The temperature profile-product distribution of the chromatogram is similar to that obtained by Venuto et al. (8, 4) in their studies on REX catalyst deactivation. They established the presence of condensed polynuclear aromatics in the REX adsorbate. 

The nature of the acidity of mordenite and its relation to catalytic activity have been investigated by Benesi (757), Lefrancois and Malbois (227) and Eberly et al. (225). Eberly et al. observed two absorption bands in the hydroxyl region of the infrared spectrum of H-mordenite. A band at 3740 cm-1 was attributed to silica-type hydroxyl groups, and a lower frequency band, 3590 cm-1, was thought to arise from hydroxyl groups associated with aluminum atoms in the structure. Acid extraction of the aluminum atoms from the framework, although leaving the structure intact resulted in a loss of the lower frequency hydroxyl band. 

Union Carbide Corporation. Dealuminated H-mordenite was prepared by acid extraction of H-mordenite obtained from the Norton Company. 

Three different zeolites (USY-zeolite, H-ZSM-5 and H-mordenite) were investigated in a computer controlled experimental equipment under supercritical conditions using the disproportionation of ethylbenzene as test reaction and butane or pentane as an inert gas. Experiments were carried out at a pressure of 50 bar, a flow rate of 450 ml/min (at standard temperature and pressure), a range of temperatures (573 - 673 K) and 0.8 as molar fraction of ethylbenzene (EB) in the feed. The results showed that an extraction of coke deposited on the catalysts strongly depends on the physico-chemical properties of the catalysts. Coke deposited on Lewis centres can be more easily dissolved by supercritical fluid than that on Brnsted centres. 

As shown in Figure 8 b), the H-mordenite deactivated more quickly at normal pressure than under supercritical conditions. This means that the coke extraction from the coked H-mordenite... 

The coke extraction by supercritical fluids is strongly dependent on the type of catalyst. The three-dimensional USYZ is easier accessible for the solvent than the two-dimensional ZSM-5 and the one-dimensional H-modernite. For USYZ there is an optimal temperature, at which the supercritical fluid has the highest ability for coke extraction. For ZSM-5 the coke content and the rest of the acid centres of catalyst are strongly dependent on the temperature. At 623 K the acid centres decreased only about 5%, but at 673 K they were almost totally decimated. Due to the faint coking tendency of ZSM-5 the supercritical fluid plays only a small role for the regeneration of the catalyst. But the supercritical fluid can ameliorate the product distribution of the EBD on ZSM-5. For H-mordenite the conversion of EB is strongly dependent on the temperature in the range of 623 - 673 K because of its one-dimensional channel system. 

H-mordenites with various Si/Al ratios (5.9 - 16.9) have proved to be active for the SCR of NO with CH4 in the 400-600 C temperature range. However, they suffered an irreversible deactivation after an incursion at 650°C for 1 h under reaction stream, due to a dealumination process. While acid dealumination only affects the free exchange of gaseous molecules between the main channels and the side-pockets (as seen by t29Xe NMR), the aluminum extracted from the lattice of the mordenite during the SCR of NOx at 650°C (without water vapor in the feed) also hinders the diffusive transport along the main channels. 

Table 2 shows the results of ethylene diffusivity values together with NOx conversion for the different H-mordenites studied in this work. Note that while D/R2 decreases an order of magnitude in the deactivated sample (if compared with the fresh one), it remains approximately constant for the samples subjected to acidic dealumination. This result suggests that the aluminum extracted from the lattice of the mordenite during of the mordenitic structure along the for the deactivation observed in the... 

The i.r. spectra of Al-H-mordenite and Ti-H-mordenite are shown in Figure 3(a-d). Then the i. r. spectra were recorded in KBr matrix. In Ti-H-mordenite samples, there was no band at 960 cm ascribable to Si-O-Ti vibration [7]. This can be due to the overlapping of bands arising from Si-O-Al and Si-O-Ti. The Ti-H-mordenite samples were then treated withS N HCl for one hour at about 363 K to extract aluminium from the framework. A distinct shoulder was observed at 963 cm the intensity of which increases with increase in Ti content [7]. Thus the overlapping of Si-0-A1 band is reduced and the band due to Si-O-Ti... 

Thermogravimetric Analyses. Further significant features on these systems are revealed by thermogravimetric analysis of zeolite-polyrm r composites after removal of the maximum possible amount of polymer by extraction with chloroform. The curves of weight loss, AM, relative to the final mass, Mf, are shown, respectively in Figs. 9a and 9b for H-mordenite alcme and H-mordenite -i- polymer and also for H-Y... 

Dehydration of hexoses to hydroxymethylfurfural (5-HMF) H-ZSM-5, H-Y, H-P, H-mordenite Different acid zeolites have been studied to replace industrial homogeneous systems based on the use of sulfuric acid as catalysts. The use of biphasic systems is desirable to extract formed 5-HMF and avoid secondary reactions [61]... 

Hofmann and coworkers (327-330) have reported a series of studies on the deactivation kinetics for the heterogeneously catalyzed disproportionation of ethyl benzene to benzene and diethyl benzene under SCF conditions. Kinetic studies have been conducted in both a loop reactor using a protonated Y-faujasite (Z-14) catalyst (327) and in a continuous concentration-controlled recycle reactor using an HY-zeolite (HYZ) (329,330) and USY-zeolite, H-ZSM-5, and H-mordenite (328) under supercritical conditions T > 373 C, P > A5 bar). Coke extraction by SCFs was found to be strongly dependent on the type of catalyst used, and the Lewis acid centers were determined to play an important role in the coke formation and activity of the catalysts. A simple kinetic model for the catalyst deactivation was proposed (329) for SCF conditions and high ethyl benzene concentration. Based on the relatively high estimated deactivation energy of about 147 kJ/mol and first-order deactivation, the authors concluded that the catalyst deactivates much slower under SCF conditions than under atmospheric pressure. 

Fejes et al. [50-54] extensively studied the extractive dealumination of zeolites (mordenite) with acid halides (phosgene, nitrosyl chloride) at 400-600 C. The reaction of H-mordenite with phosgene, monitored by IR spectroscopic determination of the volatile reaction products HCl and C02> was foimd to proceed in three main steps at temperatures above 100 C (Eq. 2a) and 300°C (Eqs.2b and 2 c) ... 

The samples were analyzed for Na, Si, and A1 content by x-ray fluorescence spectroscopy. The extent of dealumination was found to vary for different lots of Zelon 900H. For a given lot, the extent of dealumination increased with acid extraction time. The extent of dealumination was controlled by adjusting the extraction time. Boron oxide (1.50 g B2O3) was dissolved in 140 mL of 0.25 M KOH. Dealuminated mordenite (25 g Si/Al = 64) was added to the solution, and the pH was adjusted to 13 by addition of KOH. The resulting suspension was stirred at 80°C for 24 h in a Teflon lined Parr pressure vessel. The product was separated by filtration, thoroughly washed with deionized water, and dried at 120°C. The composition of the product was determined by XRF and atomic absorption spectroscopy. 

NV mordenite samples gave their highest ion-exchange capability at pH>4 and 5, respectively. Whereas the erio te, chabazite, and clinoptilolite samples showed comparable Cu uptake at pH>4, the former two samples were superior at pH 3, nd the Eastgate, NV erionite extracted a modest amount of Cu even at pH 2. Other than thei tjecomposition, the inability of the zeolite samples to extract Cu from strongly acidipreferred exchange of H over Cu which is approximated by ... 

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