Dehydration by molecular sieves

Dry inlet gas that has been dehydrated by molecular sieves (qv) or alumina beds to less than 0.1 ppm water is spHt into two streams by a three-way control valve. Approximately 60% of the inlet gas is cooled by heat exchange with the low pressure residue gas from the demethanizer and by external refrigeration. The remainder of the inlet gas is cooled by heat exchange with the demethanized bottoms product, the reboiler, and the side heater. A significant amount of low level refrigera tion from the demethanizer Hquids and the cold residue gas stream is recovered in the inlet gas stream. 

A continuous-flow reactor with a fixed catalyst bed was employed at pressurized conditions. Gaseous dimethyl ether was supplied to the reactor at its vapor pressure with carbon monoxide while liquid reactants such as methyl acetate, methyl iodide, and water were fed with microfeeders. Methyl acetate used in this experiment was dehydrated by Molecular Sieve 5A before use. A part of the reaction mixture was sampled with a heated syringe and was analyzed by gas chromatography. 

Sulfur Compounds. Various gas streams are treated by molecular sieves to remove sulfur contaminants. In the desulfurization of wellhead natural gas, the unit is designed to remove sulfur compounds selectively, but not carbon dioxide, which would occur in Hquid scmbbing processes. Molecular sieve treatment offers advantages over Hquid scmbbing processes in reduced equipment size because the acid gas load is smaller in production economics because there is no gas shrinkage (leaving CO2 in the residue gas) and in the fact that the gas is also fliUy dehydrated, alleviating the need for downstream dehydration. 

Dehydration of organics (removal of <1% water) generally feasible by molecular sieving, if kinetic diameter of organic >300 pm. 

Bromo-2-methylpropane [507-19-7] M 137.0, b 71-73 , d 1.218, n 1.429. Neutralised with K2CO3, distd, and dehydrated using molecular sieves (5A), then vacuum distd and degassed by ireeze-pump-thaw technique. Sealed under vacuum. 

Hasegawa and co-workers illustrated the syntheses of substituted phenazine-5,10-dioxides 236 by a dehydrative condensation between benzofuroxan 234 and dihydroxybenzene derivatives 235 catalyzed by molecular sieves at room temperature <00H2151>. 

The shape-selectivity of ZSM-5 is particularly remarkable. Active centres at the inner walls of the catalyst readily release protons to organic reactant molecules forming carbonium ions, which in turn, through loss of water and a succession of C—C forming steps, yield a mixture of hydrocarbons that is similar to gasoline. The feedstock can be methanol, ethanol, corn oil or jojoba oil. The shape-selectivity of this catalyst is particularly striking, as can be seen from the product distribution obtained for the dehydration of three different alcohols (Table 8.2). The product distribution can be understood in terms of the intermediate pore size of ZSM-5, which can accommodate linear alkanes and isoalkanes as well as monocyclic aromatic hydrocarbons smaller than 1, 3, 5-trimethyl benzene. In Table 8.3, we list some of the recent innovations in catalysis, to highlight the important place occupied by molecular-sieve catalysts. 

Analysis. Free fatty acids were ethylated in ethanol dehydrated with molecular sieves using gaseous HCl as the catalyst. Ethyl esters of fatty acids were analyzed on a DB-23 capillary column (0.25 mm x 30 m J W Scientific, Folsom, CA) connected to a Hewlett-Packard 5890 gas chromatograph (Avondale, PA) as described previously (19). The water content in the oil layer was determined by Karl Fisher titration (moisture meter CA-07 Mitsubishi Chemical, Tokyo, Japan). The contents (by weight) of free fatty acids and fatty acid ethyl esters were analyzed by a thin-layer chromatography/flame ionization detector... 

One reason why dehydration with molecular sieves is popular is that an exhausted molecular sieve can be regenerated simply by heating between 150 and 300°C. It is preferable to carry out this process in a current of dry nitrogen, and then to leave the dried sample to cool in a desiccator. 

Bleached cotton linters with a degree of polymerization (DP) of 1,300 were used as the starting cellulose sample. The cellulose was first dried imder vacumn at 40°C. A, A -dimethylacetamide (DMAc) purchased from Katayama Chemicals Co. Ltd. (99+%) was dehydrated with molecular sieve 3A and used without further purification. Lithium chloride (LiCl) powder (Katayama Chemicals Co. Ltd.) was oven-dried at least for 3 days at 105°C. Methylcellulose with a degree of substitution (DS) of 1.6 and polyvinyl alcohol (PVA) with a DP of 2,000 were purchased from Shin-Etsu Chemical Co. Ltd. and Katayama Chemicals Co. Ltd., respectively. Cellulose acetate with a DS of 2.45 (L-70) and purified chitin were provided by Daicel Chemicals Co. Ltd. and Katakura Chikkarin, respectively. 

Separation of alcohols, such as ethanol and butanol, from the fermentation broth is traditionally done by distillation. The higher the alcohol concentration in the fermentation broth, the lower the energy required for distillation. For ethanol fermentation, the broth usually contains 10-15% (w/w) ethanol. After distillation, ethanol concentration in the distillate is about 90% (w/w). The distillation process will not yield more than 93% (w/w) ethanol, which is the azeotropic mixture of ethanol-water. Azeotropic mixtures cannot be separated by distillation because the compositions of ethanol in the vapor and liquid phases are the same. Therefore, azeotropic distillation with benzene or dehydration with molecular sieves is usually used to remove the remaining water and produce fuel grade ethanol (99.9 wt-%). 

M(a04)3-JcMcCN tT122] M = Er, Pr value of x not specified Dehydration of hydrated salts by molecular sieves in MeCN. Composition has not been established. 

X = C104[T101] Dehydration of hydrated A1(C104)3 by molecular sieves for 150 hours. 

Mn(MeCN)6][a04]2 [T168] Dehydration of [Mn(H20)6][C104l2 by molecular sieves in MeCN. 

Fe(MeCN)6][a04l2 [T179] Dehydration of hydrated Fe(C104)2 by molecular sieves in MeCN. 

Natural gas must meet certain specifications before it qualifies for fuel. It should also meet certain dew point characteristics before entering a transmission pipeline. Water dew point is controlled and maintained by stationary equipment such as molecular sieves or dehydration by glycol. Hydrocarbon dew point, on the other hand, can... 

The extraction process at BP-Amoco Empress begins with natural gas arriving at the plant at about 15°C and 600 psi pressure. The gas is dehydrated to a -90°C dewpoint by means of molecular sieves. Still at 600 psi, the gas is introduced into heat exchangers and cooled to -70°C, at which point it begins to liquify in a separator. 

Molecular sieves are an adsorbent that is produced by the dehydration of naturally occurring or synthetic zeolites (crystalline alkali-metal aluminosilicates). The dehydration leaves inter-crystalline cavities into which normal paraffin molecules are selectively retained and other molecules are excluded. This process is used to remove normal paraffins from gasoline fuels for improved combustion. Molecular sieves are used to manufacture high-purity solvents. 

Molecular sieves (dehydrated zeolite) purify petroleum products with their strong affinity for polar compounds such as water, carbon dioxide, hydrogen sulfide, and mercaptans. The petroleum product is passed through the sieve until the impurity is sufficiently removed after which the sieve may be regenerated by heating to 400 - bOO F. 

The cavities are filled with the crystal water of the zeolite, which can be driven off by heating the name zeolite means boiling stone. In the empty cavities of the dehydrated molecular sieve other molecules can now be included, provided that their effective cross-section is not larger than the pore diameter of the zeolite. 

Today n-paraffms are exclusively produced from the corresponding distillation cuts of paraffin-rich oils with the use of molecular sieves. Molecular sieves are synthetically manufactured aluminum silicates of the zeolite type, which after dehydration have hollow spaces of specific diameters with openings of specific diameters. The molecules are then able to penetrate the openings in the correct size and form and are held in the hollow spaces by electrostatic or van der Waals forces. The diameter of the zeolite type used for the production of paraffins is 5 A and is refined so that the n-paraffins (C5-C24) can penetrate the hollow spaces while the iso- and cyclic paraffins are unable to pass through [15]. 

Protein recovery via disruption has also been achieved by adsorbing water from the w/o-ME solution, which causes protein to precipitate out of solution. Methods of water removal include adsorption using silica gel [73,151], molecular sieves [152], or salt crystals [58,163], or formation of clanthrate hydrates [154]. In most of the cases reported, the released protein appeared as a solid phase that, importantly, was virtually surfactant-free. In contrast to the dilution technique, it appears that dehydration more successfully released biomolecules that are hydrophilic rather than hydrophobic. 

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