Molecular sieves drying samples

Determination of oxygen. The sample is weighed into a silver container which has been solvent-washed, dried at 400 °C and kept in a closed container to avoid oxidation. It is dropped into a reactor heated at 1060 °C, quantitative conversion of oxygen to carbon monoxide being achieved by a layer of nickel-coated carbon (see Note). The pyrolysis gases then flow into the chromatographic column (1 m long) of molecular sieves (5 x 10-8 cm) heated at 100 °C the CO is separated from N2, CH4, and H2, and is measured by a thermal conductivity detector. 

This compound is usually made and used in situ. A 5 g sample was allowed to sit in a screw top vial for a couple of days, one morning it was found to have blown a hole in the lid and extruded a 20 ml plume of polymeric foam [1], An attempt to dry anisyl chloride over molecular sieves pressurised the container, presumably with hydrogen chloride evolved during polymerisation [2],... 

Most of these PEG crosslinkers come as thick, sticky, viscous liquids or low melting solids (PEG2). For this reason, weighing out a small sample of a compound can be difficult or impossible. It usually is best to dissolve an entire vial or a larger amount in organic solvent at a known concentration to permit accurate dispensing of a smaller amount into a reaction. Suitable solvents to prepare a stock solution include dry (molecular sieved) DMSO, DMF, DMAC, acetonitrile, or methylene chloride (for non-water-miscible reactions). 

AIPO4-5 molecular sieve (BET surface area, 299 m g ) used in this study was prepared by the method of Wilson et al. [1j. VjOg/AIPO -S samples were prepared by impregnating with aqueous solutions of ammonium vanadate after removing templating agent in the AIPO -S by calcining at 530°C. The samples were dried at 110 C for 24 h then calcined in air at 550°C for 2 h. VAPO -S was prepared from gel mixture of phosphoric acid, pseudoboehmite, vanadium pentoxide, tri-propylamine and water (1.3 PrjN x AljOj PjOj 40 HjO) by crystallization at 165°C for 3 - 7 days [7. ... 

Generally, 1 to 5 mg of sample dissolved in 100 pi of mobile phase were injected for each SEC run. For the Si-H determinations tetrachloroethylene (TCE) mobile phase was used at 55°C. It was Dowper grade (Dow Chemical Co.) and was dried by passage through activated Molecular Sieves (Linde Co.). The Si-OH analyses employed 1,4-dioxane/ TCE (90/10 by volume) at the same temperature. The dioxane was purchased from Burdick Jackson, with UV cutoff of 211 nm and water content of 0.036%. The silicone-phenyl analyses used methylene chloride (Burdick Jackson, UV cutoff of 230 nm, water content 0.003%) at 35°C and tetrahydrofuran (THF, Burdick Jackson, UV cutoff 212 nm, water content 0.02% or less) at 50 C. Each of the mobile phases was continually purged with pure helium during use. 

In some cases (see below) a KF drying oven is required to get the water from a sample into the titration vessel. For these special cases, a solid sample (usually) is placed into a specially designed KF oven where the sample is heated, and the water goes into the vapor phase. A stream of dry carrier gas (usually, N2 or air) sweeps the liberated moisture into the reaction vessel, where it is titrated by either the coulometric or the volumetric method. It is critical that the carrier gas is dry and that there are no leaks along the pathway to the reaction vessel. Passing the carrier gas over activated molecular sieve prior to the sample will ensure that the gas is dry. 

However, care must be exercised in using molecular sieves for drying organic liquids. Appreciable amounts of impurities were formed when samples of acetone, 1,1,1-trichloroethane and methyl-r-butyl ether were dried in the liquid phase by contact with molecular sieves 4A (Connett Lab.Practice 21 545 1972). Other, less reactive types of sieves may be more suitable but, in general, it seems desirable to make a preliminary test to establish that no unwanted reaction takes place. For the principles of synthesis and identification see R. Szostak Molecular Sieves, Chapman Hall, London 1988, and for structure, synthesis and properties see R.Szostak Handbook of Molecular Sieves, Chapman Hall 1992. 

This technique calls for drying the sample in a liq drying column using Linde 4A molecular sieves (water detn), and then using the near IR spectrum between 2.2 and 1.7 micrometers to determine the ratio of UDMH to diethylenetriamine] 5) H.N. Voltrauer, Hydrazine Analysis Using Chemiluminescence , SAM-76-37, Aero Chem Res Lab, Princeton, Contract F41609-76-C-0029 (1976) [A procedure is reported using the chemiluminescent reactions of ozone with monomethylhydrazine and Aero-zine-50 (UDMH/hydrazine in 50/50 wt %) to... 

Aliquot C was dried for 24 h at ambient temperature in a desiccator under reduced pressure, 50 mmHg, by using previously dried molecular sieves as a desiccant. The dried sample was pulverized in a beaker with... 

Approximately 1 - 1.5 g of MCM-41 were given in a flask and capped with a stopper. Subsequently the flask was evacuated (10 3 mbar) for 2 h and filled with nitrogen. The molecular sieve sample was suspended in 30 - 50 mL dry tetrahydrofurane (THF), and 25 pL - 600 pL of diphenyldichlorosilane (Ph2SiCl2) were added under stirring. 

In a typical procedure, as made MCM-41 or MCM-48 (1.0 g) sample was added to 200-ml solution of 5% HC1 in ethanol. The mixture was kept in closed container and stirred for 3 h at room temperature. The change in pH was constantly monitored. Sample was recovered by filtration and washed with distilled water and acetone. Finally, the samples were dried at 343 K. overnight and calcined in air at 623 K. for 2 h. These samples are designated as exchanged mesoporous MCM-41 and MCM-48 molecular sieves. 

The preparation of the used Fe-loading molecular sieves materials and the catalytic synthesis of carbon nanotubes have been described in detail in our previous report [22]. The textural properties and compositions of catalysts are shown in Table 1. XPS spectra for samples were recorded on a PHI-5300 ESCA system. The pass energy was 71.550 eV. Before the XPS measurement, all the samples were ground and then dried at 393 K for 2 h. For these samples, the C(ls) level (284.4 eV) was taken as the reference binding energy (B.E.). 

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