Removal by molecular sieves

Catalytic Adsorption. This method can reduce impurities, such as H2, O2, CO, and hydrocarbons, to less than 10 ppb. The catalyst converts these impurities into CO2, H2O, and other species that can then be removed by molecular sieves and cryogenic adsorption. 

In a similar manner, 2-propanol is oxidized to 2-propanone and cyclobutanol to cyclobu-tanone. N-Methylmorpholine-N-oxide (NMO) or oxygen may be used to reoxidize the expensive TPAP catalyst. The water formed in the reaction is removed by molecular sieves, which prevents further oxidation of the aldehyde to the carboxylic acid. The presence of water increases an equilibrium concentration of the aldehyde hydrate, which can undergo further oxidation to carboxylic acid. The oxidation of 7.21 with TPAP in the presence of NMO gave 7.22 in good yield. ... 

Equilibrium of this reaction is unfavorable and to achieve a high conversion, diphenyl carbonate is recovered by extractive distillation. Methanol can also be removed by molecular sieve adsorption to drive the reaction to higher conversion of DPC [28]. 

Once CO2 is largely removed by adsorption in basic solution, residua] CO2 and H2O are removed by molecular sieves to < 1 ppm CO2 and N2 removed non-cryogenically over molecular sieves... 

Prior to the nitrogen wash, residual CO2 and water are removed by molecular sieve to prevent freezing of these gases in the nitrogen wash column. 

Here, the formation of (96) and reversal of the path by which it is formed results in racemization. Treatment of a methyl sulphoxide R SO Me with HCl in CH2CI2 gives RSCH2CI when the water formed in this reaction is removed by molecular sieves since this seems to be accounted for in terms of a quadricovalent intermediate RgSClg, the suggestion that sulphoxide racemization by HCl involves the same intermediate is supported. ... 

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. 

Product recoveiy from reversed micellar solutions can often be attained by simple back extrac tion, by contacting with an aqueous solution having salt concentration and pH that disfavors protein solu-bihzation, but this is not always a reliable method. Addition of cosolvents such as ethyl acetate or alcohols can lead to a disruption of the micelles and expulsion of the protein species, but this may also lead to protein denaturation. These additives must be removed by distillation, for example, to enable reconstitution of the micellar phase. Temperature increases can similarly lead to product release as a concentrated aqueous solution. Removal of the water from the reversed micelles by molecular sieves or sihca gel has also been found to cause a precipitation of the protein from the organic phase. 

Toluene is commonly used. It can be dried by molecular sieves or direct distillation from calcium hydride into the reaction flask. Solvent stored over calcium hydride for several days is usually sufficiently dry to decant directly into the reaction flask, but distillation gives more consistent results. Any solvent with a boiling point sufficiently high to melt sodium is satisfactory. The submitters have also used methyl-cyclohexane and xylene in acyloin condensations. After the sodium is dispersed, the high-boiling solvent can be removed and replaced with anhydrous ether (as noted by the submitters) or can be retained and used in combination with ether (checkers). 

To address this problem, the authors devised two modifications. [30] The first one, two-stage glycosylation (Scheme 5.7), employed an initial, reversible trans-orthoes-terification step (12 —> 14, Scheme 5.7) in which the departing alcohol was removed either azeotropically or by molecular sieves [31]. The new orthoester 14 was then processed to give the glycoside (6) under the conditions developed in their previous work. The second variation consisted of the use of orthoacetates of hindered alcohols (isopropyl and tert-butyl) that minimize the return of the alcohol that is split off. 

To a solution of the allylic alcohol 150 (16.7 g, 49.7 mmol) [Eq. (28)] in 500 mL of toluene, under argon, was added AfAf-dimethylacetamide dimethyl acetal (33.117 g, 249 mmol). The reaction mixture was heated at reflux for 10 h, with continuous removal of methanol by molecular sieve (4 A) trap. The reaction mixture was then cooled to room temperature and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel (EtOAc) to afford compound 151 (13.6 g, 68%) as a white foam. The corresponding acetate was obtained in 27% yield and quantitatively transformed into 151 a]D +2.7° (c 1.1, CHClj). 

It is constructed of 316 stainless steel and has a rated working pressure of 34 MPa at 616 K. Linde type 5A 3.2-mm calcium-form molecular sieves (230-400 g) are supported in the vapor space in a basket constructed of wire mesh. The heated chamber on top of the autoclave and the autoclave flange are removed to add and remove the molecular sieves. The sieve basket is surrounded by a cooling coil to freeze the loading on the molecular sieves during depressurization at the end of a test. The autoclave... 

The equilibrium may be influenced by either removing one product from the reaction mixture (for example, removal of the water by azeotropic distillation or absorption by molecular sieves) or by employing an excess of one reactant. 

It is important that the H2O produced in the reaction or any H2O derived from hydrated NMO be removed with molecular sieves. Oxidations can be performed on small or large scales. For large-scale reactions it is important to moderate the reaction by slow addition of NMO while cooling. 

Derivation Benzene is alkylated with dodecene, to which it attaches itself in any secondary position the resulting dodecylbenzene is sulfonated with sulfuric acid and neutralized with caustic soda. For ABS (branched-chain alkyl) the dodecene is usually a propylene tetramer, made by catalytic polymerization of propylene. For LAS (straight-chain alkyl), the dodecene may be removed from kerosene or crudes by molecular sieve, may be formed by Ziegler polymerization of ethylene, or by cracking wax paraffins to a-olefins. 

The UOP PEP unit is present in all Detal-based complexes to remove alkylaromatics. Aromatic removal is accomplished by molecular sieve adsorption, and exploits differences in adsorption affinity between aromatics and other molecules in the Pacolate. The PEP units consist of several adsorbent chambers... 

Purification of feed gas Stripping of syngas by molecular sieves and liq. NH3 -b KNH2 wash to remove impurities. 

In some instances the method for carbon determination has to be modified, e.g., the determination of trace amounts of what is referred to as dissolved organic carbon in water after inorganic carbon has been removed. This type of carbon determination involves wet oxidation activated by silver ions in a solution of potassium persulphate in sulphuric acid. The oxidation of organic compounds gives carbon dioxide, which is adsorbed by molecular sieves. The molecular sieves are then heated in a flow of helium to desorb the carbon dioxide, the amount of which is measured by a TCD. The lowest concentration of organic carbon that can be measured in water is 0.2—2ppm [55]. The application of chromatographic elemental analysis to the determination of the total carbon content in water has been described [56]. 

Availability of H N.M.R. spectra at 220 MHz (Figure I) increases the chemical-shift separation and so enhances the differences between distinct kinds of hydrogen. For all the fuel extracts examined, removal of n-alkanes by molecular sieve from the total alkanes causes small changes in the methyl absorptions as a result of changing proportions of spin-spin triplets (from C 3-CH2-), doublets (from OT3-CH-), and singlets (from CH3-Cc) ... 

---