Moisture Molecular sieves

Enantioselective conversions of aryl benzyl selenides to N-tosylselenimides 28 with [(tosylimino)iodo]benzene, cuprous triflate, and the chiral bis(oxazo-line) 22 have recently been demonstrated (Scheme 16) [37,38]. Because benzyl phenyl selenide undergoes uncatalyzed imidation with Phi = NTs in acetonitrile (46 % yield) or dichloromethane (trace yield), toluene was selected as the solvent for the asymmetric imidation reactions. Furthermore, in order to avoid racem-ization of 28 by moisture, molecular sieves were added to the reaction medium. 

The purity of oxygen from chlorate candles before and after gas filtration is indicated in Table 2. A particulate filter is always used. Filter chemicals are HopcaUte, which oxidizes CO to CO2 molecular sieves (qv), which remove chlorine compounds and basic materials, eg, soda lime, which removes CO2 and chlorine compounds. Other than H2O and N2, impurity levels of <1 ppm can be attained. Moisture can be reduced by using a desiccant (see Desiccants). Gas purity is a function of candle packaging as well as composition. A hotter burning unit, eg, one in which steel wool is the binder, generates more impurities. 

Isobutyronitrile (2-methylpropionitrile, isopropyl cyanide) [78-82-0] M 69.1, b 103.6 , d 0.7650, n 1.378. Shaken with cone HCl (to remove isonitriles), then with water and aq NaHC03. After a preliminary drying with silica gel or Linde type 4A molecular sieves, it is shaken or stirred with CaH2 until hydrogen evolution ceases, then decanted and distd from P2O5 (not more than 5g/L, to minimize gel formation). Finally it is refluxed with, and slowly distd from CaH2 (5g/L), taking precautions to exclude moisture. 

The propionamide can be dried over CaO. H2O and unreacted propionic acid were removed as their xylene azeotropes. It was vacuum dried. Material used as an electrolyte solvent (specific conductance less than 10 ohm cm" ) was obtained by fractional distn under reduced pressure, and stored over BaO or molecular sieves because it readily absorbs moisture from the atmosphere on prolonged storage. [Hoover Pure Appl Chem 37 581 I974 Recommended Methods for Purification of Solvents and Tests for Impurities, Coetzee Ed., Pergamon Press, 1982.]... 

Natural gas from MESA s wells flows into a gathering system where pressure is increased to 7 bar (100 psig). Multiple booster stations raise it to 34 bar (500 psig) before gas enters the plant for separation. When gas enters the LNG recovery unit, its pressure must be raised again to 66 bar (950 psig). It is then subjected to a molecular sieve process for moisture removal. A series of heat exchangers lowers the temperature to -34°C (-30°E). 

Certain chemicals (sorbents) have the ability to absorb moisture from a gas they may be either solid or liquid. Performance of a chemical dehumidifi cation device depends on the sorbent used. The sorbent must t>e able to attract and remove the sorbate, such as water, from the gas stream, Stirbems absorb water on the surface of the material by adsorption or by chemically combining with water (absorption). If the unit is regenerative, the process is reversible, allowing water to be removed. This is achieved by a sorbent such as silica gel, alumina gel, activated alumina, lithium chloride salt, lithium chloride solution, glycol solution, or molecular sieves. In the case of nonregenerative equipment, hygroscopic salts such as calcium chloride, urea, or sodium chloride are used. 

Preparation of Reactants. Reagent-grade, thiophene free benzene was stored over 4A molecular sieves and sodium ribbon in a helium atmosphere. Styrene was distilled to remove dissolved oxygen and moisture and stored under a helium atmosphere. Prior to use, styrene was injected into a copious quantity of methanol to determine if any polymerization had occurred. If there was... 

Mixtures of silica gel and the liquid difluoride sealed in tubes at 334 mbar exploded above -196°C, presence of moisture rendering the mixture shock-sensitive at this temperature [1], Reaction of oxygen difluoride with silica, alumina, molecular sieve or similar surface-active solids is exothermic, and under appropriate conditions may be explosive [2], A quartz fibre can be ignited in the difluoride [3],... 

There are a few precautions that should be noted when doing a CDI activation and coupling experiment. First, CDI itself is extremely unstable to aqueous environments, much more so than the active imidazolyl carbamate that s formed after PEG activation. Therefore, the activation step must be done in a solvent that is free of water. If unacceptable amounts of water are present, CDI will be immediately broken down to C02 and imidazole. The evolution of bubbles upon addition of CDI to a PEG solution is the telltale sign of high water content. Only freshly obtained solvents analyzed to be extremely low in moisture or those dried over a molecular sieve should be used. A water content of less than 0.1 percent in the solvent is usually all right for a CDI activation procedure. 

Modern SMR plants (Figure 2.5b) incorporate a PSA unit for purifying hydrogen from C02, CO, and CH4 impurities (moisture is preliminarily removed from the process gas). The PSA unit consists of multiple (parallel) adsorption beds, most commonly filled with molecular sieves of suitable pore size it operates at the pressure of about 20 atm. The PSA off-gas is composed of (mol%) C02—55, H2—27, CH4—14, CO—3, N2—0.4, and some water vapor [11] and is burned as a fuel in the primary reformer furnace. Generally, SMR plants with PSA need only a HT-WGS stage, which may somewhat simplify the process. 

Many gallophosphate molecular sieves are unstable to calcination in air or in the presence of moisture, which limits the utility of these materials because at room temperature (RT) the templates stuff the channels thus limiting access to the porosity. The ULM-16 structure is interesting because it is stable to 800°C under argon and up to 350-400°C in the presence of oxygen. This stability may reflect the fully connected framework of ULM-16. 

A new desiccant formulation was prepared from a mixture of submicron-sized silica gel and molecular sieves to achieve the best combination of large water capacity, rapid moisture adsorption and easy regenerability. The formulation also tolerates the presence of VOCs and smokes. Commercial NaX and silica gel were crushed and mixed in the proportion of 1 2 and wash coated on a monolith for testing. The same test cell shown in Fig. 12.7-2 was used. The airflow to the saturator was adjusted to obtain the desired humidity in the feed air. Humidity sensors located at the flow cell inlet and outlet, were used to... 

In the gas-cleaning loop, a catalyst bed system for the removal of hydrocarbons and a molecular sieve dryer for removing moisture is generally preferred to an ethylene glycol scrubber. 

Dehydration is applied to natural gas, air for feed to air separation units, cracked gas (e.g., ethylene), various other hydrocarbon streams just to name a few. Zeolite molecular sieves play a major role in dehydration because of their abihty to reduce moisture content to very low levels attaining dew points of —100°C or lower. 

The intermediate phosphite employed in this synthesis was prepared by condensation of duly protected sialic acid with the nucleosidyl phospho-roamidite in the presence of N-PhIMT. Oxidation by TBHP and deprotection according to standard procedures gave the cytidine-S -monophospho-iST-ace-tylneuraminic acid. This synthetic route is claimed to have advantages over procedures published earlier [26]. The same group demonstrated the importance of 3 A and 4 A molecular sieves as moisture scavengers in the reaction of nucleoside phosphoroamidite with a nucleotide. This approach should be likely to find application in the synthesis of biophosphates outside nucleotide chemistry. 

The raw materials used in this study are presented in Table 1. The polyether polyol and short chain diols were degassed at 80-90°C under vacuum overnight to remove any moisture. MEK was treated with molecular sieves 4A overnight to remove any moisture prior to use. The other materials were used as received. 

Dry the styrene monomer using molecular sieves and store immediately with a nitrogen blanket in a refrigerator. Although moisture will affect the reaction, the influence is minor. Dry styrene is not really necessary for free radical polymerization. 

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. 

The — 78 °C trap and molecular sieve trap are designed to remove CH3CN. Since traces of moisture are inevitably present, this means that HC1 is also likely to be produced the molecular sieve trap will also remove it. An alternate... 

Generally, solvents should be purified just before use, and the purified solvents should be stored in an inert atmosphere in a cool, dark place and should be used as soon as possible.2) In the preparation of the electrolyte solution and during the measurement, the introduction of moisture from air should be avoided as much as possible, by using a vacuum line or a glove box if necessary.3) In order to keep the electrolyte solution dry, active molecular sieves can be used. As described in... 

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