Zeolite quaternary amines

Quaternary amines, such as tetraalkylammonium bromides and hydroxides (the alkyl group being Q to C4) are the typical zeolite templates. Quaternary amines fulfill the above-mentioned requirements of stability, specific interaction with the precursor (electrostatic interaction between quaternary amines and silicate), and easy removal (by calcination). 

Perhaps we have concentrated too much on the quaternary amines as templating agents. Another approach is suggested by Verdijn in the synthesis of zeolite L(17). As showing in Table VI, by addition of only trace amounts of alkaline earth cations, especially strontium, the gel composition range which produced the desired zeolite L product was widened, the formation rate increased, smaller crystallites were obtained, and stirred synthesis became possible. The alkaline earths were very probably present when natural faujasite was formed. But their solubility in alkaline silicate liquors is low 200 ppm Sr2 is near saturation in the synthesis slurry. 

This paper presents results of a continuation of our study (1,2) of the conversion of the small-pore zeolite. Cubic P, into various organozeolites—large-, medium-, and small-pore varieties. The main focus here is on the influence of structure of the quaternary amine template molecule on the rates of conversion and on the organo-zeolite produced. 

Quaternary ammonium compounds (quats) are prepared - by moderate heating of the amine and the alkyl halide in a suitable solvent - as the chlorides or the bromides. Subsequently conversion to the hydroxides may be carried out. Major applications of the quat chlorides are as fabric softeners and as starch cationizing agent. Several bio-active compounds (agrochemicals, pharmaceuticals) possess the quat-structure. Important applications of quat bromides are in phase transfer catalysis and in zeolite synthesis. 

Since then, organic amines, quaternary-ammonium bases, metal complexes, and other compounds have been extensively used in zeolite synthesis, acting as space fillers with low specificity, structure-directing agent, or true templates ... 

The hydrothermal method has been employed in recent years to synthesize a variety of solids that include aluminium phosphates (ALPOs) and other microporous transition-metal phosphates and transition-metal polychalcogenides (Davis Lobo, 1992 Haushalter Mundi, 1992 Liao Kanatzidis, 1990, 1992). Unlike zeolites, synthesis of ALPOs requires acidic or mildly basic conditions and no alkali metal cations. A typical synthetic mixture for making ALPO consists of alumina, H3PO4, water and an organic material such as a quaternary ammonium salt or an amine. The hydrothermal reaction occurs around 373-573 K. The use of fluoride ions, instead of hydroxide ions as mineralizer, allows synthesis of novel microporous materials under acidic conditions (Estermann et al, 1991 Ferey et ai, 1994). 

The reaction mechanism including the formation and decomposition of quaternary cations may be a general pathway in amine alkylation processes on acidic zeolites. Pouilloux et al. (247), for example, synthesized dimethylethylamine from ethylamine and methanol on an acidic catalyst. At the reaction temperature of 503 K, trimethylamine was determined by gas chromatographic analysis, which can be explained by the formation and decomposition of trimethylethylammonium ions, (CIl3)3N CH2CH3. 

As depicted in Scheme 13, quaternary ammonium ions can be post-synthesized by a direct reaction of tertiary amines and alcohols in the pores of acidic zeolites. By... 

The above-mentioned route to the preparation of quarternary ammonium ions in acidic zeolites is remarkable for the following reasons an immobilization of quaternary ammonium ions in a well-controlled concentration is an approach to modification of zeolite catalysts. Furthermore, the synthesis of isotopically labeled compounds is of importance in organic, pharmaceutical, and agricultural chemistry. This method is an approach to the synthesis of C-labeled (or C, N-labeled) tertiary amines via a thermal decomposition (243,251) of the corresponding quaternary ammonium ions in zeolites. 

Synthesis of Quaternary Ammonium Ions (Column 1) on Acidic Zeolites (Column 2) by a Methylation of the Corresponding Tertiary Amines (Column 3) with C-Enriched Methanol at the Reaction Temperatures Given in Column 4 (251)... 

A novel class of crystalline, microporous aluminophosphate phases has been discovered. It represents the first class of molecular sieves with framework oxide compositions free of silica. The new class of materials encompasses some fourteen reported three-dimensional microporous framework structures, and six two-dimensional layer-type structures. The three-dimensional structures include structural analogues of the zeolites sodalite and erionite-offre-tite. The novel phases can be synthesized hydro-thermally in the presence of organic amines and quaternary ammonium templates. The template is entrapped or clathrated within the crystallizing aluminophosphate network. After thermal decomposition of the template the three-dimensional molecular sieves have the general composition of Al303 1.0 ... 

FER-. TOH-and HTT-type ZEOLITES. The use of amines instead of quaternary ammoniums yields three pentasil zeolites with the FER, TON and HTT structural types ( 23-25). The first two are obtained with the same amine families (aliphatic linear mono-or diamines). A low Si/Al ratio leads to the FER structure, in agreement with VALYOCSIK et al. (26), whereas a high ratio favours the TON structure. The influence of the carbon chain length ( x) of the amine is shown in Figure 3. The composition of the reaction mixture was (1-y) Si02 y A1203 10 H20 3[CH3( CH2) X-1 NH2, IF] or 1 [HH2( CH2) x HH2, 2HF]. ... 

This method provides an alternative to the removal of the organic SDA occluded in the framework of porous materials, which can overcome some drawbacks of high-tempera-ture calcination such as the release of NO resulting from the combustion of organic SDAs (most SDAs are quaternary ammonium cations or amines). Recycling of the SDAs can significantly decrease the overall zeolite-synthesis cost. 

At the beginning of the eighties, a new class of molecular sieves, based on the stractural model of the zeolites, was found. The association of a trivalent element, Al, with a pentavalent element, P, in reaction mixtures containing amine or quaternary ammonium templates, allowed the crystallization of numerous compounds with charge self-compensated frameworks. This type of framework, in which = 1, could also be obtained with other elements such as Ga l, Fe and As. The substitution of T and/or T element for the t and/or T elements led to neptively charged frameworks. 

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