Mordenite extracted

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

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. 

Reactions with acids. Hydrochloric acid was used in the dealumination of clinoptilolite (1), erionite (14) and mor-denite (2,3,15,92). In the case of Y zeolite, dealumination with mineral acids was successful only after conversion of the zeolite into the ultrastable form (vide infra). Barrer and Makki (1) were the first to propose a mechanism for the removal of aluminum from mordenite by mineral acids. It involves the extraction of aluminum in a soluble form and its replacement by a nest of four hydroxyl groups as follows ... 

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. 

Other workers (4, 5, 6, 7) have made Al-deficient sieves by leaching aluminum from the lattice structure with EDTA or HC1. These zeolites have high thermal stability (4). Extraction of Al removes selectively the aluminic sites that are catalytically inactive. The number of sites of weak or medium acid strength drops to zero (6). Eberly and Kimberlin (7) investigated the catalytic properties of Al-deficient mordenite and found it to be considerably more active than conventional mordenite for cumene cracking. 

T,he original report by Barrer and Makki (1) that aluminum in a high A silica zeolite, clinoptilolite, could be extracted with mineral acid to give a silica pseudomorph, has given rise to considerable research on acid-extracted mordenite (2-6). Hydrogen mordenite is useful as an adsorbent and a catalyst, and its properties for some purposes are improved by partial extraction of the aluminum. Further, the ability to vary aluminum content while maintaining crystallinity offers the opportunity to leam more about the nature of the active sites in mordenite. 

An earlier report from this laboratory (7) noted that in a series of mildly extracted mordenites, the hexane cracking activity in a continuous-flow test went through a marked maximum with increasing severity of extraction, while the f-butane to n-butane ratio continuously increased. The activity and product distribution were measured after 10 min on stream. Since catalyst deactivation was rapid, it was not possible to... 

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. 

The major results of this study are consistent with a simple picture of mordenite catalysts. An increase in effective pore diameter, whether by extraction or exchange, will increase the rate of transport of reactant and product molecules to and from the active sites. However, aluminum ions are necessary for catalytic activity as aluminum is progressively removed by acid extraction, the number of active sites and the initial activity decrease. Coke deposition is harmful in two ways coke formation as the reaction proceeds will cause a decrease in effective pore diameter and effective diffusivity, and coke deposited on active sites will result in a chemical deactivation as well. 

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-... 

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. 

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. 

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. 

Y-zeolite, ZSM-5 and mordenite are three important industrial zeolites because of their pore structure and surface acidity. The coke extraction from the strongly coked HYZ catalyst has already been investigated under supercritical conditions [4,5], However, investigations on ZSM-5 and mordenite under supercritical conditions can not be found in literatures. 

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. 

Series of zeolite-supported iron-containing catalysts with weight percent iron (% Fe) varying from 1 to 17% Fe have been prepared from Fe3(CO) 2 and the synthetic zeolites ZSM-5, mordenite and 13X by an extraction technique. The zeolites ZSM-5 and mordenite were used in the acid form, 13X in the sodium form. 

Catalytic Evaluation In order to investigate support effects in these iron/zeolite catalysts prepared from Fe3(C0)12 by the extraction technique, three catalysts of similar weight percent iron loading were evaluated for their ability to catalyze synthesis gas conversion these catalysts were 15.0% Fe/ZSM-5, 16.4% Fe/Mordenite andl5.0% Fe/13X. All catalysts were evaluated under similar conditions as described in the experimental section. Catalytic data is presented in the accompanying figures in each figure the first three points for each catalyst are data obtained at 280°C, the second three points are data at 300°C. 

The presence of cations in the less accessible side pocket sites of mordenite implies the co-presence of mono-, di-, and tri-carbonyl adducts even at the higher values of Pco (94), resulting in a broader and rather unresolved IR spectrum (Fig. 4c, bottom full line). In zeolite Y, notwithstanding the presence of two cationic sites in the supercage, the IR spectrum obtained at high Pco indicates the presence of only one family of Cu -(CO)3 adducts. This observation is explained by the strong solvating power of the CO molecules, which are able to extract the Cu ions from the more shielded position (site IP), as demonstrated by both EXAFS (76,77,97) and XRPD data (93). The experiments reported in Fig. 4 indicates that... 

Extenders, Plasticizers, and Process Oils. Materials in this class can be prepared from the extracts obtained when narrow wax distillate cuts are solvent-refined— with furfural, for example— in the production of lubricating oils. These materials must have a low pour-point. Hydro-catalytic treatment over a mordenite-based catalyst removes residual n-paraflBnic wax with consequent reduction in pour-point of the product, which is obtained in good over-all yield. 

Figure 2 demonstrates the variations in the Nai values per unit cell (u.c.) for hydrogen faujasites and mordenites preheated at a temperature between 400 and 1000°C. The results clearly show that considerable extraction of the framework A1 occurs at temperatures as low as 500-600°C. For example, 65-75% of the framework A1 was lost by NH4Y zeolites and mordenites with conventional Si/Al ratios, heated to 800°C. Reducing the initial A1 content of the frameworks makes the release of the aluminum on heat treatment increasingly difficult, and for the dealuminized samples DY4.8 and DM62 removal of the framework A1 does not exceed a 5% level. 

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