Zeolite mechanical mixing

This chapter provides a brief introduction to polymer and inorganic zeolite membranes and a comprehensive introduction to zeolite/polymer mixed-matrix membranes. It covers the materials, separation mechanism, methods, structures, properties and anticipated potential applications of the zeolite/polymer mixed-matrix membranes. 

Most reported zeolite/polymer mixed-matrix membranes, however, have issues of aggregation of the zeolite particles in the polymer matrix and poor adhesion at the interface of zeolite particles and the polymer matrix. These issues resulted in mixed-matrix membranes with poor mechanical and processing properties and poor separation performance. Poor compatibility and poor adhesion between the polymer matrix and the zeolite particles in the mixed-matrix membranes resulted in voids and defects around the zeolite particles that are larger than the micropores of the zeolites. Mixed-matrix membranes with these voids and defects exhibited selectivity similar to or even lower than that of the continuous polymer matrix and could not match that predicted by Maxwell model [59, 60]. 

The results from N2 physisorption (Table 1) indicate that the use of binder during catalyst preparation produces some loss of zeolite microporosity, probably due to the micropore blockage. This effect was not observed in the (NiMo/Al203)-nHNaY(MM) sample prepared by mechanical mixing. 

Contoct-induced ion exchange was also observed between alkaline, alkaline earth or rare-earth halides and sodium forms of zeolites [23,31]. It was monitored, inter alia, by Na MAS NMR using NaCl as a reference. After intense mechanical mixing of the salt and zeolite, MAS NMR investigation showed the Na signal of Na-Y (8 = -8) to disappear (Kgure 6). 

Of the three important technologies currently being pursued for CO2 capture, namely liquid absorption, solid adsorption [5], and membrane separations [6], membrane-based separation is promising since it is more energy efficient, mechanically simple and easy to scale-up with a smaller footprint. Polymeric, inorganic (silica, zeolite etc.), mixed matrix, and facilitated transport membranes are currently being investigated for this application [7]. 

When basic LDH is mixed or intercalated with acidic solid component, such as a zeolite, the composite will show a dual functional adsorption for CO2 and NH3. Okada et al. investigated the adsorption behaviors of MgAl-LDH/alumi-nosilicate composites and found that the adsorptivity of the composites for both of the probe molecules is dependent on the preparation pathways. The composite prepared via sol/precipitation shows a superior adsorption for both acidic and basic gases to those prepared via mechanical mixing and reconstruction methods (360). This is quite similar to the case of the dual acid/base properties of LDH-derived oxides, especially the LDH-polyoxometallate-derived oxides, which have been carefully examined by a similar adsorption method (361). 

The cation exchange capacity of a zeolitic product can be determined by mixing 1.066 g of powder sample with 9 ml of CH3COONa solution in a mechanical shaker for 5 min. The mixture was centrifuged until a clear supernatant is obtained and later it is decanted. The similar process can be repeated for another two times to ensure that all cations in the zeohte have been replaced with Na". The Na" laden zeolites were mixed with 9 ml of 99 % isopropyl alcohol and shaken in a... 

Zeolites are formed by crystallization at temperatures between 80 and 200 °C from aqueous alkaline solutions of silica and alumina gels in a process referred to as hydrothermal synthesis.15,19 A considerable amount is known about the mechanism of the crystallization process, however, no rational procedure, similar to organic synthetic procedures, to make a specifically designed zeolite topology is available. The products obtained are sensitive functions of the reaction conditions (composition of gel, reaction time, order of mixing, gel aging, etc.) and are kinetically controlled. Nevertheless, reproducible procedures have been devised to make bulk quantities of zeolites. Procedures for post-synthetic modifications have also been described.20 22... 

Mixed-matrix membranes comprising small-pore zeolite or small-pore non-zeolitic molecular sieve materials will combine the solution-diffusion separation mechanism of the polymer material with the molecular sieving mechanism of the zeolites. The small-pore zeolite or non-zeolitic molecular sieve materials in the mixed-matrix membranes are capable of separating mixtures of molecular species... 

The second part of the book covers zeolite adsorptive separation, adsorption mechanisms, zeolite membranes and mixed matrix membranes in Chapters 5-11. Chapter 5 summarizes the literature and reports adsorptive separation work on specific separation applications organized around the types of molecular species being separated. A series of tables provide groupings for (i) aromatics and derivatives, (ii) non-aromatic hydrocarbons, (iii) carbohydrates and organic acids, (iv) fine chemical and pharmaceuticals, (v) trace impurities removed from bulk materials. Zeolite adsorptive separation mechanisms are theorized in Chapter 6. 

Although no direct evidence was available, Ben-Taarit et al. advanced a tentative mechanism for propylene oxidation [2]. As only heterogeneous or mixed oxides catalyze the formation of acrolein, the behavior of Cu+ y zeolite is similar to the heterogeneous case. On the contrary, on Rh +Y, acetone was selectively produced [2]. This is now in line with the behavior of Rh salts in... 

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