Liquid-phase oxidations

Liquid-Phase Oxidation. Liquid-phase catalytic oxidation of / -butane is a minor production route for acetic acid manufacture. Formic acid (qv) also is produced commercially by Hquid-phase oxidation of / -butane (18) (see HYDROCARBON OXIDATION). 

This is a special chemical effectively used for column bioreactors. It is a volatile compound and strong oxidising agent. It boils at ambient temperature, therefore the solution of ethylene oxide (liquid phase) must be stored in a refrigerator (4 °C). An excellent oxidising agent such as a 3% sodium hypochlorite is used for chemical sterilisation of equipment. 

The Bashkirov oxidation (liquid-phase oxidation of n-alkanes or cycloalkanes in the presence of boric acid and hydrolysis) yields the corresponding secondary alcohols [16, 17]. The reaction is used industrially for oxidation of C10 to C18 n-alkanes, providing raw materials for detergents and for oxidation of cyclododecane to cyclo-dodecanol as an intermediate for the production of Nylon 12 (Table 1, entry 8). The process is not of much commercial importance in the western world, however. Oxidation in the absence of boric acids usually leads to mixtures of alcohols, ketones, and carboxylic acids (Table 1, entry 9). 

Originally, acetic acid was produced by fermentation this is still the major process for the production of vinegar. Modern production is by acetaldehyde oxidation, liquid phase hydrocarbon oxidation and preferentially by methanol carbonylation. The latter process is to be preferred because of the low raw material and energy costs. As early as 1913 BASF described the carbonylation of methanol at high temperature and pressure ... 

Key Words Propylene, Propylene oxide. Liquid-phase epoxidation, Semibatch reactor. Supercritical CO2, Gas-phase epoxidation, Pd/TS-1 catalyst, Au/Ti02 catalyst, Au/Ti-Si02 catalyst, Ag catalyst, Mesoporous... 

Ammonium quaternary salts Ethylbenzene oxidation process Gas-phase oxidation Homogeneous catalytic oxidations Liquid-phase hydrocarbon oxidation Monodentate axial ligands p-xylene... 

Apart from gas-phase oxidation, liquid-phase oxidation with dichromate is an expedient process if the chromium-(III)-sulfate by-product can be used as a tanning agent. The largest anthraquinone plant Bayer/ Qsi Germany) with a capacity of 11,000 tpa applies this process. Batch oxidation is carried out with pulverized 94-95% anthracene in a stirred tank reactor with the addition of sodium dichromate and sulfuric add at 60 to 105 °C. The reaction takes between 25 and 30 hours. The yield of anthraquinone, which is produced in purities of around 95%, is over 90%. The purity can be increased to over 99% by recrystallization from nitrobenzene or cyclohexanol/cyclohexanone. 

Keywords metal organic frameworks, vanadium, oxidation, liquid phase... 

Carbon fibers, when used without surface treatments, produce composites with low mechanical properties. This has been attributed to weak adhesion and poor bonding between the fiber and matrix. Therefore, the carbon fibers are given surface treatments, the exact nature of which is a trade secret. This surface treatment increases the surface active sites which results in the improvements of the bonding between the fibers and the resin matrix. This tends to increase the wettability of the carbon fibers and enhances the mechanical properties [4-7]. Surface treatments may be classified into oxidative and nonoxidative treatments. An oxidative treatment involves gaseous oxidation, liquid-phase oxidation carried out chemically or electrochemically and catalytic oxidation. The nonoxidative surface treatments involves deposition of more active forms of carbon or metals such as whiskerization, pyrolytic coating, the grafting of the polymers, and metal deposition on the carbon fiber surfaces [8-11]. 

Product removal during reaction. Sometimes the equilibrium conversion can be increased by removing the product (or one of the products) continuously from the reactor as the reaction progresses, e.g., by allowing it to vaporize from a liquid-phase reactor. Another way is to carry out the reaction in stages with intermediate separation of the products. As an example of intermediate separation, consider the production of sulfuric acid as illustrated in Fig. 2.4. Sulfur dioxide is oxidized to sulfur trioxide ... 

It was first described in 1608 when it was sublimed out of gum benzoin. It also occurs in many other natural resins. Benzoic acid is manufactured by the air oxidation of toluene in the liquid phase at 150°C and 4-6 atm. in the presence of a cobalt catalyst by the partial decarboxylation of phthalic anhydride in either the liquid or vapour phase in the presence of water by the hydrolysis of benzotrichloride (from the chlorination of toluene) in the presence of zinc chloride at 100°C. 

Manufactured by the liquid-phase oxidation of ethanal at 60 C by oxygen or air under pressure in the presence of manganese(ii) ethanoate, the latter preventing the formation of perelhanoic acid. Another important route is the liquid-phase oxidation of butane by air at 50 atm. and 150-250 C in the presence of a metal ethanoate. Some ethanoic acid is produced by the catalytic oxidation of ethanol. Fermentation processes are used only for the production of vinegar. 

Obtained synthetically by one of the following processes fusion of sodium ben-zenesulphonate with NaOH to give sodium phenate hydrolysis of chlorobenzene by dilute NaOH at 400 C and 300atm. to give sodium phenate (Dow process) catalytic vapour-phase reaction of steam and chlorobenzene at 500°C (Raschig process) direct oxidation of cumene (isopropylbenzene) to the hydroperoxide, followed by acid cleavage lo propanone and phenol catalytic liquid-phase oxidation of toluene to benzoic acid and then phenol. Where the phenate is formed, phenol is liberated by acidification. 

Hydrogenations with coppcr-chromium oxide catalyst are usually carried out in the liquid phase in stainless steel autoclaves at pressures up to 5000-6000 lb. per square inch. A solvent is not usually necessary for hydrogenation of an ester at 250° since the original ester and the alcohol or glycol produced serve as the reaction medium. However, when dealing with small quantities and also at temperatures below 200° a solvent is desirable this may be methyl alcohol, ethyi alcohol, dioxan or methylcyc/ohexane. 

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

The direct liquid phase oxidation of ethylene was developed in 1957—1959 by Wackei-Chemie and Faibwerke Hoechst in which the catalyst is an aqueous solution of PdClj and CuCl (86). 

Butane-Naphtha Catalytic Liquid-Phase Oxidation. Direct Hquid-phase oxidation ofbutane and/or naphtha [8030-30-6] was once the most favored worldwide route to acetic acid because of the low cost of these hydrocarbons. Butane [106-97-8] in the presence of metallic ions, eg, cobalt, chromium, or manganese, undergoes simple air oxidation in acetic acid solvent (48). The peroxidic intermediates are decomposed by high temperature, by mechanical agitation, and by action of the metallic catalysts, to form acetic acid and a comparatively small suite of other compounds (49). Ethyl acetate and butanone are produced, and the process can be altered to provide larger quantities of these valuable materials. Ethanol is thought to be an important intermediate (50) acetone forms through a minor pathway from isobutane present in the hydrocarbon feed. Formic acid, propionic acid, and minor quantities of butyric acid are also formed. 

The Acetaldehyde Oxidation Process. Liquid-phase catalytic oxidation of acetaldehyde (qv) can be directed by appropriate catalysts, such as transition metal salts of cobalt or manganese, to produce anhydride (26). Either ethyl acetate or acetic acid may be used as reaction solvent. The reaction proceeds according to the sequence... 

Vapor-phase oxidation over a promoted vanadium pentoxide catalyst gives a 90% yield of maleic anhydride [108-31-6] (139). Liquid-phase oxidation with a supported palladium catalyst gives 55% of succinic acid [110-15-6] (140). 

Liquid-Phase Oxidation of Acrolein. As discussed before, the most attractive process for the manufacture of acrylates is based on the two-stage, vapor-phase oxidation of propylene. The second stage involves the oxidation of acrolein. Considerable art on the Hquid-phase oxidation of acrolein (17) is available, but this route caimot compete with the vapor-phase technology. 

Processes rendered obsolete by the propylene ammoxidation process (51) include the ethylene cyanohydrin process (52—54) practiced commercially by American Cyanamid and Union Carbide in the United States and by I. G. Farben in Germany. The process involved the production of ethylene cyanohydrin by the base-cataly2ed addition of HCN to ethylene oxide in the liquid phase at about 60°C. A typical base catalyst used in this step was diethylamine. This was followed by liquid-phase or vapor-phase dehydration of the cyanohydrin. The Hquid-phase dehydration was performed at about 200°C using alkah metal or alkaline earth metal salts of organic acids, primarily formates and magnesium carbonate. Vapor-phase dehydration was accomphshed over alumina at about 250°C. 

Liquid-phase oxidation of lower hydrocarbons has for many years been an important route to acetic acid [64-19-7]. In the United States, butane has been the preferred feedstock, whereas ia Europe naphtha has been used. Formic acid is a coproduct of such processes. Between 0.05 and 0.25 tons of formic acid are produced for every ton of acetic acid. The reaction product is a highly complex mixture, and a number of distillation steps are required to isolate the products and to recycle the iatermediates. The purification of the formic acid requires the use of a2eotropiag agents (24). Siace the early 1980s hydrocarbon oxidation routes to acetic acid have decliaed somewhat ia importance owiag to the development of the rhodium-cataly2ed route from CO and methanol (see Acetic acid). 

Synthetic phenol capacity in the United States was reported to be ca 1.6 x 10 t/yr in 1989 (206), almost completely based on the cumene process (see Cumene Phenol). Some synthetic phenol [108-95-2] is made from toluene by a process developed by The Dow Chemical Company (2,299—301). Toluene [108-88-3] is oxidized to benzoic acid in a conventional LPO process. Liquid-phase oxidative decarboxylation with a copper-containing catalyst gives phenol in high yield (2,299—304). The phenoHc hydroxyl group is located ortho to the position previously occupied by the carboxyl group of benzoic acid (2,299,301,305). This provides a means to produce meta-substituted phenols otherwise difficult to make (2,306). VPOs for the oxidative decarboxylation of benzoic acid have also been reported (2,307—309). Although the mechanism appears to be similar to the LPO scheme (309), the VPO reaction is reported not to work for toluic acids (310). 

N. M. Emanuel, E. T. Denisov, and Z. K. Maizus, Liquid Phase Oxidation of Hydrocarbons, Plenum Press, New York, 1967. 

Autooxidation. Liquid-phase oxidation of hydrocarbons, alcohols, and aldehydes by oxygen produces chemiluminescence in quantum yields of 10 to 10 ° ein/mol (128—130). Although the efficiency is low, the chemiluminescent reaction is important because it provides an easy tool for study of the kinetics and properties of autooxidation reactions including industrially important processes (128,131). The light is derived from combination of peroxyl radicals (132), which are primarily responsible for the propagation and termination of the autooxidation chain reaction. The chemiluminescent termination step for secondary peroxy radicals is as follows ... 

The roasting process, or variations of it, are most common. Liquid-phase processes are ia operation, however, both ia the United States and the former USSR. The former USSR is the only place where KMnO was produced by anodic oxidation of ferromanganese. Table 17 summarizes the various KMnO manufactuting faciUties worldwide as of this writing. 

Liquid-Phase Oxidation. In the early 1960s, both Cams Chemical Co. (La SaEe, Illinois) and a plant in the Soviet Union started to operate modernized Hquid-phase oxidation processes. 

Fig. 2. Terephthalic acid production by catalytic, liquid-phase air oxidation of -xylene.

Herm/es/Djnamit JS obe/Process. On a worldwide basis, the Hercules Inc./Dynamit Nobel AG process is the dorninant technology for the production of dimethyl terephthalate the chemistry was patented in the 1950s (67—69). Modifications in commercial practice have occurred over the years, with several variations being practiced commercially (70—72). The reaction to dimethyl terephthalate involves four steps, which alternate between liquid-phase oxidation and liquid-phase esterification. Two reactors are used. Eirst, -xylene is oxidized with air to -toluic acid in the oxidation reactor, and the contents are then sent to the second reactor for esterification with methanol to methyl -toluate. The toluate is isolated by distillation and returned to the first reactor where it is further oxidized to monomethyl terephthalate, which is then esterified in the second reactor to dimethyl terephthalate. 

Manufacture and Processing. PytomeUitic acid and its dianhydtide can be synthesized by oxidizing dutene [95-93-2] (1,2,4,5-tettamethylbenzene). Liquid-phase oxidation using strong oxidants such as nittic acid, chromic acid, or potassium permanganate produces the acid which can be dehydrated to the dianhydtide in a separate step. This technology is practiced by AUco Chemical Co., a part of International Specialty Chemicals. 

Liquid-phase air oxidation of mesitylene with Co, Mn, and Bt catalysis produces 1,3,5-benzenetricarboxyhc acid [554-95-0] (trimesic acid) (10) (37) as does the oxidation with dilute nitric acid (qv). Amoco has oxidized mesitylene to trimesic acid on a small scale (see Phthalic acid and other BENZENECARBOXYLIC acids). Less vigorous stepwise oxidation of mesitylene can yield 3,5-dimethylbenzoic acid [499-06-9] (11) and 5-methyhsophthahc acid... 

Isopropyl alcohol can be partially oxidized by a noncatalytic, liquid-phase process at low temperatures and pressure to produce hydrogen peroxide [7722-84-1] and acetone (24—26). 

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