Concentration phenol hydrogenation

However, an important problem arises during the peroxidative removal of phenols from aqueous solutions PX is inactivated by free radicals, as well as by oligomeric and polymeric products formed in the reaction, which attach themselves to the enzyme (Nazari and others 2007). This suicide peroxide inactivation has been shown to reduce the sensitivity and efficiency of PX. Several techniques have been introduced to reduce the extent of suicide inactivation and to improve the lifetime of the active enzyme, such as immobilization. Moreover, Nazari and others (2007) reported a mechanism to prevent and control the suicide peroxide inactivation of horseradish PX by means of the activation and stabilization effects of Ni2+ ion, which was found to be useful in processes such as phenol removal and peroxidative conversion of reducing substrates, in which a high concentration of hydrogen peroxide may lead to irreversible enzyme inactivation. 

When an aqueous solution containing hexachlorobenzene (150 nM) and a nonionic surfactant micelle (0.50 M Brij 58, a polyoxyethylene cetyl ether) was illuminated by a photo-reactor equipped with 253.7-nm monochromatic UV lamps, significant concentrations of pentachlorobenzene, all tetra-, tri-, and dichlorobenzenes, chlorobenzene, benzene, phenol, hydrogen, and chloride ions were formed. Two compounds, namely 1,2-dichlorobenzene and 1,2,3,4-tetrachlorobenzene, formed in minor amounts (<40 ppb). The half-life for this reaction, based on... 

Different drawbacks arise from the application of peroxidases (1) the enzymatic inactivation, usually caused by the presence of high concentrations of hydrogen peroxide, which oxidizes the porphyrin ring [15] moreover, when phenolic compounds are being treated, the phenoxy radicals produced as intermediates... 

EELS spectra of the adsorbed layers formed from HQ or BQ solutions were very similar [Figs. 42(a) and (b)], indicating formation of a common horizontally oriented adsorbed state. Also shown in Fig. 42 are the locations of the principal mid-IR bands of solid HQ and BQ. The virtual absence of the OH stretches (3260 cm1) from the EELS spectra of adsorbed layers formed at HQ concentrations below 1 mM indicates that the phenolic hydrogens are lost during adsorption [eqn. (33)]. 

Phenol is recovered from the acetone finishing column bottoms (12) by extraction with caustic. AMS in the raffinate is then concentrated (13), hydrogenated (14) and recovered as cumene for recycle to oxidation. Refined AMS production is optional. 

Thus, to obtain a selective synthesis of phenol via direct oxidation of benzene, suitable strategies have to be envisaged to slow dovm the undesired consecutive reactions and to allow phenol to accumulate. The first step in this direction was made by George Olah, who used extremely concentrated (98%) hydrogen peroxide in a... 

Oxidation of phenols with 02 in aqueous solutions is faster than that in hydrocarbon solutions. Oxygen attacks both phenol molecules and phenolate ions. Therefore the rate of oxidation depends on the concentration of hydrogen ions. The rate of phenol oxidation in aqueous solutions (at 14—21°C) is [219]... 

The use and importance of aromatic compounds in fuels sharply contrasts the limited kinetic data available in the literature, regarding their combustion kinetics and reaction pathways. A number of experimental and modelling studies on benzene [153, 154, 155, 156, 157, 158], toluene [159, 160] and phenol [161] oxidation exist in the literature, but it would still be helpful to have more data on initial product and species concentration profiles to understand or evaluate important reaction paths and to validate detailed mechanisms. The above studies show that phenyl and phenoxy radicals are key intermediates in the gas phase thermal oxidation of aromatics. The formation of the phenyl radical usually involves abstraction of a strong (111 to 114 kcal mof ) aromatic—H bond by the radical pool. These abstraction reactions are often endothermic and usually involve a 6 - 8 kcal mol barrier above the endothermicity but they still occur readily under moderate or high temperature combustion or pyrolysis conditions. The phenoxy radical in aromatic oxidation can result from an exothermic process involving several steps, (i) formation of phenol by OH addition to the aromatic ring with subsequent H or R elimination from the addition site [162] (ii) the phenoxy radical is then easily formed via abstraction of the weak (ca. 86 kcal moT ) phenolic hydrogen atom. 

The alkylation of phenol by isobutylene catalyzed by a cation-exchange resin and sulfuric acid at 60-100 °C in a batch reactor, showed that an increase in the concentration of hydrogen ions in the cation-exchange resin from 8 to 24 mmol/1 augmented the conversion of phenol. However, the selectivity, determined as the ratio of obtained o-tert-butylphenol to reacted phenol, initially decreased but afterwards increased [24]. Upon reducing the cationite particle size from 0.63 to 0.004 mm, the conversion of phenol increased. Nonetheless, a further decrease in particle size did not affect the reaction rate. 

Because the reaction is taking place at pH below 7, the above shown p- and o-methylolphenols are transitory and are present in small concentrations only. Hydrogen ions convert them to benzylic carbocations that react rapidly with free phenol. This can be illustrated as follows ... 

---