Drying methods conversion

Unless working with superdried systems or in the presence of proton traps, adventitious water is always present as a proton source. Polymeriza tion rates, monomer conversions, and to some extent polymer molecular weights are dependent on the amount of protic impurities therefore, weU-estabHshed drying methods should be followed to obtain reproducible results. The importance is not the elimination of the last trace of adventitious water, a heroic task, but to estabhsh a more or less constant level of dryness. 

TS-l/MCM-41 catalysts synttiesized by the dry gel conversion method are shown to have hexagonal mesopores. The catalytic activity of synthesized TS-l/MCM-41 catalysts was tested with qroxidation reaction of olefins to reved that both the conversion of olefins and selectivity to epoxide are higher than those of H-MCM-41,... 

In this work, highly active epoxidation catalysts, which have hydrophobic surface of TS-1, were synthesized by the dry gel conversion (DGC) method. Ti-MCM-41 was synthesized first by a modifed method and the TS-l/MCM-41 catalysts were subsequently synthesized by the DGC method. The catalysts were characterized by the XRD, BET, FT-IR, and UV-VIS spectroscopy. TS-l/MCM-41 catalysts were applied to the epoxidation of 1-hexene and cyclohexene with aqueous H202to evaluate their activities for the epoxidation reaction. ... 

Titanium containing hexagonal mesoporous materials were synthesized by the modified hydrothermal synthesis method. The synthesized Ti-MCM-41 has hi y ordered hexa rud structure. Ti-MCM-41 was transformed into TS-l/MCM-41 by using the dry gel conversion process. For the synthesis of Ti-MCM-41 with TS-1(TS-1/MCM-41) structure TPAOH was used as the template. The synthesized TS-l/MCM-41 has hexagonal mesopores when the DGC process was carried out for less than 3 6 h. The catalytic activity of synthesized TS-l/MCM-41 catalysts was measured by the epoxidation of 1-hexene and cyclohexene. For the comparison of the catalytic activity, TS-1 and Ti-MCM-41 samples were also applied to the epoxidation reaction under the same reaction conditions. Both the conversion of olefins and selectivity to epoxide over TS-l/MCM-41 are found hi er flian those of other catalysts. 

Copra is the dried kernel of coconuts. Fresh kernels contain approximately 50% moisture. Various drying methods are employed to bring down the moisture content ideally to 6-8% (see Table 3). At this level, mold growth in copra is inhibited. The conversion of kernel to copra is an essential step if the oil is to be drawn by the conventional mechanical extraction method. 

In 1990, Xu et al. first reported the transformation of a dry aluminosilicate gel to crystalline MFI by contact with vapors of water and volatile amines, which was named dry gel conversion (DGC).[99] Since then, this method has been extensively studied and a large number of microporous materials with new compositions and structures were prepared. Generally, DGC can be divided into vapor-phase transport (VPT) and steam-assisted conversion (SAC) according to the volatility of the SDAs. For volatile SDAs such as ethylenediamine, a mixture of water and SDA was poured into the bottom of the autoclave and then a dry gel, which does not contain any SDAs, was placed over the liquid surface. Water and SDAs were vaporized at elevated temperature (150 200 °C), reached the dry gel, and initiated the crystallization, which was called VPT. Less volatile SDAs such as tetrapropylammonium hydroxide were usually involved in the dry gel. Only water steam is supplied during the reaction, which was called SAC. 

Spray drying is one of the most important continuous drying methods for the conversion of solutions, emulsions, or slurries into powders. The pumpable feed is dispersed into droplets which are dried in a controlled flow of hot gas. Particles are formed as moisture evaporates from each droplet. Particularly in regard to agglomeration, there is a fundamental difference between producing dry particles from solutions or emulsions and from suspensions or slurries. 

P-10 - Utilization of dry-gel conversion method for the synthesis of gallosilicate zeolites beta, ZSM-5 and ZSM-12... 

Synthesis of gallosilicate zeolites [Ga]-beta, [Ga]-ZSM-5 and [Ga]-ZSM-12 was performed by dry-gel conversion (DGC) method. The crystallization of the dry gel was performed in presence of small amount of water, without which the crystallization failed. The method was convenient and as effective as conventional hydrothermal method. The samples were pure and highly crystalline, and showed characteristic of typical gallosilicate zeolites. 

It can be seen from these examples that cells and tissues are very sensitive to the composition of the materials surface. Several physicochemical techniques for analysing the composition of materials surface have been described. However, attention is drawn to the fact that the surface analysed by most of these methods is not the surface analysed by living cells, as cells recognise only the outermost layer of a hydrated material. Analysing this ultimate hydrated layer by a physicochemical method is a real challenge. Indeed, the most surface-sensitive methods such as electron spectroscopy for chemical analysis (ESCA also known as X-ray photoelectron spectroscopy, XPS) and secondary-ion mass spectrometry (SIMS) can analyse respectively a few layers at once or one layer after the other, but in strictly dry conditions. Performing an ESCA analysis at a very low temperature in order to keep water frozen has been described, but this is currently far from a routine method. Conversely, analysis of hydrated surfaces by ATR-IR is usual, but this method determines the composition of many layers in addition to the ultimate layer, as it analyses a depth of more than 1 pm. 

In another recent study, it was attempted to change the fractional occupation of the ZSM-5 cation sites by the Fe species by loading the zeolite previously with different amounts of Na or Ca ions [105]. The subsequent introduction of the Fe component (ca. 0.25 wt%) was accomplished by a dry method (solid-state ion exchange) to avoid leaching of the co-cations. Figure 7.13 shows conversion... 

Ethane conversion, ethylene yield, and selectivity in the CO2-ODH of ethane over Ca-Ce02 catalysts were improved by Valenzuela et thanks to the synthesis of high specific surface area catalysts by the freeze-drying method. This allowed them to reach a 22% yield with 91% olefin selectivity on nanosized Ca-doped Ce02. However, this catalyst deactivated quickly, and the rate of formation of CO decreased faster than the formation of ethylene. Gm o et studied the kinetics of the catalyzed reactions and its deactivation, by developing an experimental... 

There are basically two approaches to synthesize supported zeolite membranes liquid-phase synthesis and vapor-phase transport (or dry-gel conversion) methods [2,12], The liquid-phase-synthesis approach is to bring the surface of a porous support in contact with a zeolite synthesis solution (sol or gel) and keep the system under controlled conditions so that the zeolite can nucleate and grow to a continuous film on the support surface. 

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