Acid erionite

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 ... 

The direct high-pressure animation of ethylene with ammonia to give ethylamine occurs in the presence of acidic zeolite catalysts such as H-elinoptilolite, H-erionite or H-offretite38. Primary amines R1NH2(R1 = Bu, cyclohexyl, PhCH2, Ph or Ar) have been monoalkylated by reaction with di-t-butyl dicarbonate, followed by successive treatment of... 

The adsorption microcalorimetry has been also used to measure the heats of adsorption of ammonia and pyridine at 150°C on zeolites with variable offretite-erionite character [241]. The offretite sample (Si/Al = 3.9) exhibited only one population of sites with adsorption heats of NH3 near 155 kJ/mol. The presence of erionite domains in the crystals provoked the appearance of different acid site strengths and densities, as well as the presence of very strong acid sites attributed to the presence of extra-framework Al. In contrast, when the same adsorption experiments were repeated using pyridine, only crystals free from stacking faults, such as H-offretite, adsorbed this probe molecule. The presence of erionite domains in offretite drastically reduced pyridine adsorption. In crystals with erionite character, pyridine uptake could not be measured. Thus, it appears that chemisorption experiments with pyridine could serve as a diagnostic tool to quickly prove the existence of stacking faults in offretite-type crystals [241]. 

Among the early investigations of methanol adsorption and conversion on acidic zeolites, most of the H and C MAS NMR experiments were performed under batch reaction conditions with glass inserts in which the catalyst samples were fused. Zeolites HZSM-5 76a,204,206,264-272), HY 71,72), H-EMT 273), HZSM-12 274), HZSM-23 275), H-erionite 275), H-mordenite 271,272), and H-offretite 275,276), silicoaluminophosphates H-SAPO-5 271,274), H-SAPO-11 274), and H-SAPO-34 76,277,278), as well as montemorillonite 279) and saponite 279) were investigated as catalysts. 

Catalyst. Erionite was converted into a dual functional catalyst containing both acid and metal hydrogenation activity. 

Similar observations of reduced intensity for the fluorine-treated sample and nearly complete elimination of bands for the treated and 600°c-calcined sample are found for erionite and NH4Y (Figure 3b). Since fluorine-treated NH4,K-L and NH4, TMA-(2 lose crystallinity upon 600°C calcination, the OH region spectra were taken after 500°C calcination. Both show substantial reduction in intensity for Bronsted acid OH groups (bands in the region of 3630-3680 cm ) and some reduction of intensity for the 3745 cm l band. 

Usually, inorganic and organic acids can be used for framework dealumination of zeolites, and the acids include hydrochloric acid, nitric acid, formic acid, acetic acid, and so on. According to its acid-resistance ability, hydrochloric acid can be used for high-silica zeolites such as mordenite, clinoptilolite, erionite, etc. We will take mordenite as an example to describe this dealumination method (Table 6.4). The first step in the treatment of mordenite using hydrochloric acid is to convert the zeolite into H-type, and further acid treatment can then enlarge the pore diameter through dealumination. After partial dealumination, the Si/Al ratio of the zeolite is increased and the heat-resistance, water-resistance, and acid-resistance abilities are enhanced. 

By comparison with the series of measurements using cyclohexane as the solvent, the enantiomeric excesses are generally about 10% higher when acetic acid is used as the solvent, whereas the ko values derived from the catalysts Pt/NaY, Pt/mordenite, Pt/erionite and Pt/NaX diminish significantly but, in relation, analogously. 

The reaction of mono- and poly-alcohols catalyzed by solid acids has been widely investigated. An important application is the synthesis of five membered cyclic ethers starting from di- or triols. Several authors described such cyclisation reactions, starting from 1,2,4-butanetriol (clay) [1], 1,2,5-pentatriol (pentasile, mordenite, erionite) [2]. Linear ethers like dimethyl ether are formed from methanol (modified aluminosilicate, zeolites) [3,4] or MTBE from methanol and i-butene (zeolite, resin) [5,6] The yields of the desired products are often quite high, e g over 90 % in the case of 1,2,4-butanetriol to 3-hydroxy-tetrahydrofiiran and about 60 % in the case of dimethyl ether. The reactions are either carried out in the presence of water as slurry process [1,2] at 150 - 200 °C or at temperatures > 300 °C in the gas phase with a fixed bed catalyst [2-4]... 

Ames [76] also used acid washed erionite (Linde AW-300) to construct the series Cs>K>Na. Finally Sherry [20] examined Linde T, an early synthetic product subsequently shown to be a mixed crionile/offrctite phase. This exhibited the following preferences ... 

The most common of the natural sedimentary zeolites found in the United States in mineable quantities are chabazite, clinoptilolite, erionite, and mordenite (2). Many crystalline zeolites decompose in acids, although mordenite and, to a lesser extent, erionite have been reported to be stable in acid solutions (2). The goal of this research was to evaluate the stability and cation-exchange capabilities of these common, natural, sedimentary zeolites in acidic solutions. The basic concepts of zeolite ion-exchange, usually emphasizing synthetic zeolites, may be found elsewhere... 

Figure 3. Removal of exchangeable or structural cations from raw Eastgate, NV erionite samples by an acidic solution (pH 3),...

A study of the stability of four natural sedimentary zeolites indicated the order of stability in an acidic environment was found to be Trinity Basin, NV mordenite > Hector, CA clinoptilo-lite > Eastgate, NV erionite > Bowie, AZ chabazite. 

Overall, the Eastgate, NV erionite sample would be rated best because its destruction by acid was2podest above pH 1 and it showed a reasonable ability to remove Cu from solution even at pH 2. 

---