Conversion, secondary

As part of the same study selectivity data were provided at 10-100 kPa partial pressures of n-butane at 0-17% conversion over HZSM-5 [90]. With increase in pressure and conversion secondary reactions started to occur. These results are also summarized in Table 13.6. The lowered selectivity to hydrogen, methane and ethane was attributed to increasingly less favorable conditions for monomolecular cracking. The dramatic increase in selectivity to propane which was absent at zero conversion, along with decrease in propylene was considered as signature for bimolecular cracking. More specifically, it was suggested that hydride transfer... 

Hydrocarboxymethylation of Long-Chain Alkenes. An industrial process to carry out hydrocarboxymethylation of olefins to produce methyl esters particularly in the Ci2-Ci4 range for use as a surfactant feedstock was developed by Huels.183 A promoted cobalt catalyst in the form of fatty acid salts (preferably those formed in the reaction) is used. With high promoter catalyst ratio (5 1-15 1) at 180-190°C and pressure of 150-200 atm, the rate of alkene isomerization (double-bond migration) exceeds the rate of hydrocarboxymethylation. As a result, even internal olefins give linear products (the yield of normal products is about 75% at 50-80 % conversion). Secondary transformations of aldehydes (product of olefin hydro-formylation) lead to byproducts (ethers and esters) in small amounts. 

Kinetic resolution of chiral aUylic alcohols.7 Partial (at least 60% conversion) asymmetric epoxidation can be used for kinetic resolution of chiral allylic alcohols, particularly of secondary allylic alcohols in which chirality resides at the carbinol carbon such as 1, drawn in accordance with the usual enantioface selection rule (Scheme I). (S)-l undergoes asymmetric epoxidation with L-diisopropyl tartrate (DIPT) 104 times faster than (R)-l. The optical purity of the recovered allylic alcohol after kinetic resolution carried to 60% conversion is often > 90%. In theory, any degree of enantiomeric purity is attainable by use of higher conversions. Secondary allylic alcohols generally conform to the reactivity pattern of 1 the (Z)-allylic alcohols are less satisfactory substrates, particularly those substituted at the /1-vinyl position by a bulky substituent. 

Formylation was also observed when the amine conversion was carried to high conversion. Secondary amines are obtained from primary amines, and diamines can be cyclized photoelectrochemically. 

Coordinated imine functions within macrocycles are generally resistant to hydrolysis. They can sometimes be reduced to secondary amines, and conversely secondary amine functions can... 

Table III lists the physical and XRD characteristics of the samples after calcination at 450°C. During 2-propanol decomposition at low conversions (<5%) the only products detected were acetone and propylene. At higher conversions secondary...

Jacobs and coworkers [35] described the use of CoAPO-5 and CoAPO-11 as heterogeneous catalysts for the autoxidation of cyclohexane. The cobalt did not seem to be leached at low conversions. At higher conversions secondary products, such as adipic acid, leach the cobalt by forming chelate complexes. It would be interesting to investigate the activity and stability towards teaching of these and other cobalt-substituted molecular sieves [36,37] in benzylic oxidations with O. ... 

Formation of methane and chain lengths of higher molecular hydrocarbons depend on the presence of active hydrogen and are the result of different types of conversions. Secondary polymerizations and depolymerizations (135), as well as hydrogenations and hydrocracking, are important for the final composition of the reaction products. 

Kaolins are classified as either primary or secondary. Primary kaolins are formed by the alterations of crystalline rocks such as granite. The source of this kaolin is found where it is formed. Conversely, secondary kaolin deposits are sedimentary and are formed by erosion of primary deposits. The secondary deposits contain much more kaolinite (about 85-95%) than the primary deposits, which contain only 15-30%. The balance of the ore consists of quartz, muscovite, and feldspar in the primary deposits and quartz, muscovite, smectite, anatase, pyrite, and graphite in the secondary deposits. Kaolin, also known by the common term clay, is usually open-pit mined in the United States from vast deposits in Georgia, South Carolina, and Texas. The ore is not processed in one singular way. There are also distinct methods of ore benefi-ciation, each adding value to the mineral. 

When a solution is supersaturated, the solid phase forms more or less rapidly depending on the growth conditions temperature, supersaturation, medium (chemical conditions) and hydrodynamics. Primary nucleation occurs in a solution that is clear, without crystals of its own type. It is called homogeneous nucleation if the nuclei form in the bulk of the solution. It is called heterogeneous if the nuclei preferentially form on substrates such as the wall of the crystallizer, the stirrer, or solid particles (such as dust particles or other solid phases). Conversely, secondary nucleation is induced by the presence of existing crystals of the same phase. 

The metabolic network in a cell is a complex and nonlinear system that has evolved for specific functions. This network generally includes central carbon metabolism, energy conversion, secondary metabolite production, transport reactions, regulatory mechanisms, etc. The metabolic networks for many important cell types are well understood and available in the literature [6], However, sometimes a cell or organ system has extensive metabolic capabilities, but only a subset of these functions is active under different conditions. For example, a hepatocyte is capable of both gluconeogenesis and glycolysis, but only one of these metabolic pathways is dominant at any given time. Therefore, the metabolic network is often tailored to best reflect the expected network behavior. 

Selectivity for series reactions of the types given in Eqs. (2.7) to (2.9) is increased by low concentrations of reactants involved in the secondary reactions. In the preceding example, this means reactor operation with a low concentration of PRODUCT—in other words, with low conversion. For series reactions, a significant reduction in selectivity is likely as the conversion increases. 

Thus an excess of ammonia in the reactor has a marginal eflFect on the primary reaction but significantly decreases the rate of the secondary reactions. Using excess ammonia also can be thought of as operating the reactor with a low conversion with respect to ammonia. 

An initial guess for the reactor conversion is very difficult to make. A high conversion increases the concentration of monoethanolamine and increases the rates of the secondary reactions. As we shall see later, a low conversion has the effect of decreasing the reactor capital cost but increasing the capital cost of many other items of equipment in the flowsheet. Thus an initial value of 50 percent conversion is probably as good as a guess as can be made at this stage. 

Where possible, introducing extraneous materials into the process should be avoided, and a material already present in the process should be used. Figure 4.6h illustrates use of the product as the heat carrier. This simplifies the recycle structure of the flowsheet and removes the need for one of the separators (see Fig. 4.66). Use of the product as a heat carrier is obviously restricted to situations where the product does not undergo secondary reactions to unwanted byproducts. Note that the unconverted feed which is recycled also acts as a heat carrier itself. Thus, rather than relying on recycled product to limit the temperature rise (or fall), simply opt for a low conversion, a high recycle of feed, and a resulting small temperature change. 

The term distillation is applied to vaporisation and subsequent condensation according to (i) it should also be applied to (ii) since it is really the liquid which is converted into vapour and is first formed by condensation. Strictly speaking, the term sublimation should be applied to changes according to (iii). However, in practice, a substance when heated may first melt and then boil, but on cooling it may pass directly from the vapour to the solid the process is then also called sublimation. Indeed the mode of vaporisation, whether directly from solid to vapour or through the intermediate formation of a liquid, is of secondary importance it is the direct conversion of vapour to solid which is really the outstanding feature of sublimation in the laboratory. 

Amines are powerful nucleophiles which react under neutral or slightly basic conditions with several electron-accepting carbon reagents. The reaction of alkyl halides with amines is useful for the preparation of tertiary amines or quaternary ammonium salts. The conversion of primary amines into secondary amines is usually not feasible since the secondary amine tends towards further alkylation. 

Electron multiplier. A device to multiply current in an electron beam (or in a photon or particle beam after conversion to electrons) by incidence of accelerated electrons upon the surface of an electrode. This collision yields a number of secondary electrons greater than the number of incident electrons. These electrons are then accelerated to another electrode (or another part of the same electrode), which in turn emits secondary electrons, continuing the process. 

Secondary alcohols (C q—for surfactant iatermediates are produced by hydrolysis of secondary alkyl borate or boroxiae esters formed when paraffin hydrocarbons are air-oxidized ia the presence of boric acid [10043-35-3] (19,20). Union Carbide Corporation operated a plant ia the United States from 1964 until 1977. A plant built by Nippon Shokubai (Japan Catalytic Chemical) ia 1972 ia Kawasaki, Japan was expanded to 30,000 t/yr capacity ia 1980 (20). The process has been operated iadustriaHy ia the USSR siace 1959 (21). Also, predominantiy primary alcohols are produced ia large volumes ia the USSR by reduction of fatty acids, or their methyl esters, from permanganate-catalyzed air oxidation of paraffin hydrocarbons (22). The paraffin oxidation is carried out ia the temperature range 150—180°C at a paraffin conversion generally below 20% to a mixture of trialkyl borate, (RO)2B, and trialkyl boroxiae, (ROBO). Unconverted paraffin is separated from the product mixture by flash distillation. After hydrolysis of residual borate esters, the boric acid is recovered for recycle and the alcohols are purified by washing and distillation (19,20). 

The elongation of a stretched fiber is best described as a combination of instantaneous extension and a time-dependent extension or creep. This viscoelastic behavior is common to many textile fibers, including acetate. Conversely, recovery of viscoelastic fibers is typically described as a combination of immediate elastic recovery, delayed recovery, and permanent set or secondary creep. The permanent set is the residual extension that is not recoverable. These three components of recovery for acetate are given in Table 1 (4). The elastic recovery of acetate fibers alone and in blends has also been reported (5). In textile processing strains of more than 10% are avoided in order to produce a fabric of acceptable dimensional or shape stabiUty. 

The chemistry of the oil-to-gas conversion has been estabUshed for several decades and can be described in general terms although the primary and secondary reactions can be truly complex (5). The composition of the gases produced from a wide variety of feedstocks depends not only on the severity of cracking but often to an equal or lesser extent on the feedstock type (5,62,63). In general terms, gas heating values are on the order of 30—50 MJ/m (950-1350 Btu/fT). 

Usually, organoboranes are sensitive to oxygen. Simple trialkylboranes are spontaneously flammable in contact with air. Nevertheless, under carefully controlled conditions the reaction of organoboranes with oxygen can be used for the preparation of alcohols or alkyl hydroperoxides (228,229). Aldehydes are produced by oxidation of primary alkylboranes with pyridinium chi orochrom ate (188). Chromic acid at pH < 3 transforms secondary alkyl and cycloalkylboranes into ketones pyridinium chi orochrom ate can also be used (230,231). A convenient procedure for the direct conversion of terminal alkenes into carboxyUc acids employs hydroboration with dibromoborane—dimethyl sulfide and oxidation of the intermediate alkyldibromoborane with chromium trioxide in 90% aqueous acetic acid (232,233). 

Secondary amines having one oi two chiral groups attached to the nitrogen atom are prepared from boronic esters by their conversion into alkyldichlotobotanes, followed by treatment with organic azides (518). The second chiral group can be derived from an optically active azide. 

A variation of this method involves the conversion of the amine into the amine hydrochloride prior to treatment with phosgene. This method has the advantage of producing generally cleaner products by retarding the secondary reaction of the free amine with carbamoyl chloride. 

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