Nonselective hydrogenation

Excessive hydrogen consumption due to nonselective hydrogenation of aromatic hydrocarbon components in the fuels being hydrotreated... 

Double-Bond Position Nonselective Hydrogenation Selective Hydrogenation ... 

In Canada, only selectively hydrogenated canola oil is used. The practical reason is that the somewhat higher content of trans-isomers makes the more highly hydrogenated oil more resistant to beta crystallization compared with nonselectively hydrogenated canola oil. When trans-isomer content must be minimized in canola oil products, hquid canola oil or very lightly hydrogenated canola oil is used, such as shown in Table 21. 

The usual practice for the process operator is to determine the refractive index of a sample of the oil during hydrogenation, since this can be done in a few minutes, on site. It correlates well with the iodine value of the oil and also the solid fat index. If a hydrogen gas meter is available, this will have been set at a precalculated amount of gas at which to stop the reaction for determination of the refractive index. Calculation of the amount of gas required is based on the stoichiometry of hydrogenation (Mattil 1964). When the desired refractive index is reached, the batch is cooled for filtration and the solid fat index is determined in the laboratory. This is by far the most important analysis method in hydrogenation control. Typical solid fat indices for selectively and nonselectively hydrogenated canola oil are given in Table IV (Teasdale, 1975). 

Typical Analysis of Selectively and Nonselectively Hydrogenated Canola OiP... 

Indeed, as seen from Fig. 6 the GFC with low Pd content (0.02% wt.) showed high activity, so that at 50-60°C the 100% conversion of acetylene was got. At the same time the selectivity decreases np to 40-50% but remains still high. It can be explained by the presence on the outer surface of fibers some amount of metallic Pd particles which catalyze the nonselective hydrogenation towards ethane. Obviously, the contributiuon of this undesirable reaction becomes noticeable at high conversions, e.g. in the absence of acetylene. 

Cold methanol has proven to be an effective solvent for acid gas removal. Cold methanol is nonselective in terms of hydrogen sulfide and carbon dioxide. The carbon dioxide is released from solution easily by reduction in pressure. Steam heating is required to release the hydrogen sulfide. A cold methanol process is Hcensed by Lurgi as Rectisol and by the Institute Francaise du Petrole (IFP) as IFPEXOL. 

Platinum may be more useful than palladium in reduction of nitro compounds containing functions easily reduced by palladium. Hydrogenation of I over 5% Pd-on-C was nonselective with hydrogenolysis of the benzyl ethers competing with nitro hydrog ation, but over PtO in ethanol 2 was obtained in 96% yield (4). 

Pyrroles are hydrogenated with more difficulty than are carbocyclic aromatics. In compounds containing both rings, hydrogenation will proceed nonselectively or with preference for the carbocyclic ring (/9), unless reduction of the carbocyclic ring is impeded by substituents. Acidic solvents are frequently used but are not necessary. 

The noncatalytic oxidation of propane in the vapor phase is nonselec-tive and produces a mixture of oxygenated products. Oxidation at temperatures below 400°C produces a mixture of aldehydes (acetaldehyde and formaldehyde) and alcohols (methyl and ethyl alcohols). At higher temperatures, propylene and ethylene are obtained in addition to hydrogen peroxide. Due to the nonselectivity of this reaction, separation of the products is complex, and the process is not industrially attractive. 

Highly enantioselective hydrogenation of / -keto esters is achieved by using a Raney Ni catalyst modified by tartaric add and NaBr (Fig. 32.14) [9, 55]. The catalyst should be prepared under controlled conditions induding suitable pH (3-4), temperature (100°C), and concentration of the modifier (1%) to achieve an optimum stereoselectivity. The addition of NaBr, an achiral modifier, is important. Furthermore, ultrasonic irradiation of the catalyst tends to increase the activity and enantioselectivity [9f,g]. Ultrasonication may remove nonselective sites of the catalyst surface. 

Reactions between alkenes and 07 on MgO also lead to nonselect ive oxidation (21). One would hope to gain insight into the possible role of this ion in epoxidation catalysis, but rapid surface reactions, for example between ethylene oxide and MgO, make it difficult to obtain such information. The principal reaction products, CHi and CO2, are believed to be formed in a manner analogous to reactions 12-15. The initial hydrogen abstraction again is effected by the 07 ion. 

A second nonselective synthesis involved chain extension of the tosylate of ( )-citronellol (82) with 2-methylpentyl magnesium bromide and lithium tetrachlorocuprate catalysis to give the carbon skeleton 83 (Scheme 12A) [92]. Allylic oxidation with Se02 and ferf-butylhydroperoxide, hydrogenation of the... 

The electrofluorination of acetophenone and benzophenone takes place in anhydrous HF and in the presence of solvents such as chloroform and acetonitrile [38]. The fluorination of the aromatic rings occurred to various extent. Further uses of anhydrous hydrogen fluoride as a liquid environment for electrofluorination processes have been reported, for example, by Matalin etal. [39]. In particular, systems with low conductivity in liquid hydrogen fluoride and nonselective processes have been studied and optimized. The fluorination of benzene and halobenzenes in the presence of Et4NF—(HF) in an undivided cell has been studied by Horio et al. [40] Cathodic dehalogenation is observed to accompany the anodic fluorination process. 

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