Methyl liquid-phase oxidation

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. 

Although an inherently more efficient process, the direct chemical oxidation of 3-methylpyridine does not have the same commercial significance as the oxidation of 2-methyl-5-ethylpyridine. Liquid-phase oxidation procedures are typically used (5). A Japanese patent describes a procedure that uses no solvent and avoids the use of acetic acid (6). In this procedure, 3-methylpyridine is combined with cobalt acetate, manganese acetate and aqueous hydrobromic acid in an autoclave. The mixture is pressurized to 101.3 kPa (100 atm) with air and allowed to react at 210°C. At a 32% conversion of the picoline, 19% of the acid was obtained. Electrochemical methods have also been described (7). 

Methyl ethyl ketone MEK (2-butanone) is a colorless liquid similar to acetone, but its boiling point is higher (79.5°C). The production of MEK from n-butenes is a liquid-phase oxidation process similar to that used to... 

A recent stndy (13,27) describes the use of Co-Si-TUD-1 for the liquid-phase oxidation of cyclohexane. Several other metals were tested as well. TBHP (tert-butyl hydroperoxide) was used as an oxidant and the reactions were carried out at 70°C. Oxidation of cyclohexane was carried out using 20 ml of a mixture of cyclohexane, 35mol% TBHP and 1 g of chlorobenzene as internal standard, in combination with the catalyst (0.1 mmol of active metal pretreated overnight at 180°C). Identification of the products was carried out using GC-MS. The concentration of carboxylic side products was determined by GC analysis from separate samples after conversion into the respective methyl esters. Evolution and consumption of molecular oxygen was monitored volumetrically with an attached gas burette. All mass balances were 92% or better. 

Both uncalcined and calcined LDHs have also been shown to be effective supports for noble metal catalysts [18-25]. For example, palladium supported on Cu/Mg/Al LDHs has been used in the liquid phase oxidation of limonene [24], and on calcined Mg/Al LDHs for the one-pot synthesis of 4-methyl-2-pentanone (methyl isobutyl ketone) from acetone and hydrogen at atmospheric pressure [25]. In the latter case, the performance depends on the interplay between the acid-base and hydrogenation properties. More recently. 

V. P. Litvinov, T. V. Shchedrinskaya, P. A. Konstantinov, and Ya. L. Gol dfarb, Condensed heteroaromatic sytems including the thiophene ring. 33. Catalytic liquid-phase oxidation of 3-methyl-substituted thieno[2,3-h]thiophene and thieno[3,2-h]thiophene. Khim. Geterotsikl. Soedin., 492 (1975). 

There seems to be special promise in oxidizing liquefied hydrocarbon gases at temperatures and pressures approximating critical levels. That such reactions are highly effective is attested, for example, by the liquid-phase oxidation of butane, one of the simplest and most efficient methods of producing acetic acid and methyl ethyl ketone. 

The effect of the medium on the rates and routes of liquid-phase oxidation reactions was investigated. The rate constants for chain propagation and termination upon dilution of methyl ethyl ketone with a nonpolar solvent—benzene— were shown to be consistent with the Kirkwood equation relating the constants for bimolecular reactions with the dielectric constant of the medium. The effect of solvents capable of forming hydrogen bonds with peroxy radicals appears to be more complicated. The rate constants for chain propagation and termination in aqueous methyl ethyl ketone solutions appear to be lower because of the lower reactivity of solvated R02. .. HOH radicals than of free RO radicals. The routes of oxidation reactions are a function of the competition between two R02 reaction routes. In the presence of water the reaction selectivity markedly increases, and acetic acid becomes the only oxidation product. 

The main products of partial oxidation are aromatic aldehydes and acids formed by oxidation of the reactive methyl group. However, the yields that can be obtained are rather poor, in contrast to the catalytic liquid phase oxidation, which is much more selective. The poor yields are due partly to further oxidation (combustion) of the primary products, and partly to direct oxidation of the aromatic nucleus (also mainly combustion). 

Such regioselectivities are unique and suggest that redox pillared clays may have broad scope and utility as selective, heterogeneous catalysts for liquid phase oxidations. Indeed, V-PILC also catalyzes the oxidation of benzyl alcohol (to a mixture of benzoic acid and benzylbenzoate) whilst a-methyl benzylalcohol is left completely untouched.71 Similarly, p-substituted benzyl alcohols are oxidized whilst o-substituted benzyl alcohols are inert.71... 

Acetic Anhydride. A total of 1.9 billion lb of acetic anhydride was produced in the United States in 1999. Commercial production of acetic anhydride is currently accomplished through two routes, one involving ketene and the other methyl acetate carbonylation. A former route based on liquid phase oxidation of acetaldehyde is now obsolete. 

The liquid-phase oxidation (LPO) of light saturated hydrocarbons yields acetic acid and a spectrum of coproduct acids, ketones, and esters. Although propane and pentanes have been used, n-butane is the most common feedstock because it can ideally yield two moles of acetic acid. The catalytic LPO process consumes more than 500 million lb of n-butane to produce about 500 million lb of acetic acid, 70 million lb of methyl ethyl ketone, and smaller amounts of vinyl acetate and formic acid. The process employs a liquid-phase, high-pressure (850 psi), 160-180°C oxidation, using acetic acid as a diluent and a cobalt or manganese acetate catalyst. 

Currently, almost all acetic acid produced commercially comes from acetaldehyde oxidation, methanol or methyl acetate carbonylation, or light hydrocarbon liquid-phase oxidation. Comparatively small amounts are generated by butane liquid-phase oxidation, direct ethanol oxidation, and synthesis gas. Large amounts of acetic acid are recycled industrially in the production of cellulose acetate, poly (vinyl alcohol), and aspirin and in a broad array of other... 

Many of the ashless anti-knocks are amines or phenols [26] and are related to liquid-phase oxidation inhibitors. They probably work by reacting with active radicals (particularly OH) to produce radicals which are inert. For instance, N-methyl aniline (NMA) CeHsNHCHs probably produces stabilized CeHsNCHs radicals which, because of their resonance stabilization, are unable to react to regenerate active radicals again and may undergo only radical recombination reactions. The rate of radical removal by this process is likely to be limited in the most favourable case by how fast the additive can react with OH to produce stabilized radicals. Although exact rates are not known, this is probably already a fast process for NMA, and unlikely to be very much faster for any other substance. Indeed, the most effective ashless anti-knock found by MacKinven [26] in an extensive study of 970 substances was a tetra-aryl hydrazine, with a molar effectiveness 2.9 times that of NMA. 

The liquid phase oxidation has a long induction period, whereas the SCF phase oxidation has a much shorter induction time. Also, the liquid phase oxidation products are predominantly acetic acid and methyl ethyl ketone, whereas the SCF phase oxidation products are formaldehyde, acetaldehyde, methyl, ethyl, and propyl alcohols, and formic acid. The authors offer no explanation for the differences in product spectrum or induction periods for the reactions. 

Para-xylene may be oxidized to terephthalic acid by means of nitric acid. Liquid-phase oxidation of m- and p-xylene is complicated by the Increased resistance to oxidation of the second methyl group after the first has been oxidized to the carboxyl group. As a consequence of experience with this difficulty, development has been toward oxidation in, two steps, a flrst to the toluic acid stage and a second to the dicarboxylic acid. Esterification of the first carboxyl group results in much easier oxidation of the coond methyl to a carboxyl group. Other p-substituted benzenes such as p-diisopropylbenzene are oxidized by air in the presence of a cobalt catalyst to terephthalic acid. Use is made of this in a recent new approach which permits the use of catalyzed air oxidation of p-xylene and results in formation of dimethyl terephthalate. A four-step process has attained commercial importance air oxidation of p-xylene to toluic acid using oil- Oluble catalysts of cobalt or manganese, esterification with methanol to methyl p-toluate, a second air oxidation to monomethyl terephthalate, and Anally esterification with methanol to dimethyl terephthalate. 

A single plant operating in Texas, based on the noncatalytic controlled oxidation of propane-butane hydrocarbons, is reported to consume over 50 million gal annually of these light hydrocarbons together with large volumes of natural gas in the production of over 300 million lb of chemicals per year. Chemical products include formaldehyde purified to resin grade by means of ion-exchaiige resins, acetic acid, methanol, propanol, isobutanol, butanol, acetaldehyde, acetone, methyl ethyl ketone, mixtures of C4-C7 ketones, mixtures of C4-C7 alcohols, and propylene and butylene oxides. Catalytic liquid-phase oxidation of propane and butane is much more specific, and major yields of acetic acid are obtained. 

Picolinic acid also accelerates the H2O2 oxidations but less efficiently than pyrazine-2-carboxylic acid. It has been demonstrated recendy that the vanadium complex with picolinic acid, VO(PA)2 , encapsulated into the NaY zeolite retains solution-like activity in the liquid-phase oxidation of hydrocarbons [16a], It is noteworthy that pyrazine-2-carboxylic acid accelerates the hydrocarbon oxidation catalyzed by CH3Re03 [25 b]. Employing a (+)-camphor derived pyrazine-2-carboxylic acid as a potential co-catalyst in the CHsReOj-catalyzed oxidation of methyl phenyl sulfide with urea-H202 adduct, the corresponding sulfoxide was obtained with an e.e. of 15% [16b]. 

The A -hydroxyphthalimide (NHPI)-catalysed liquid-phase oxidation of 1-methoxy-4-(l-methylethyl)benzene (G) with O2 produced 1-methyl-l-(4-methoxyphenyl)ethyl hydroperoxide in a yield of 73 mol%. However, when (G) was oxidized in the presence of NHPI in combination with Cu(II), the product l-(4-methoxyphenyl)ethanone was produced with high selectivity up to 68-75mol% but in low yield (llmol%). The use of NHPI in combination with Co(II), Mn(II), and Fe(II) salts, and the effects of the catalyst concentration and the temperature was studied. ... 

Defining the structure of an effective reaction stimulator or inhibitor resulting in extreme cases, based on a specified kinetic reaction model. Such a method is illustrated by the example of non-empirical selection of the efficient inhibitor for the chain reaction of liquid-phase oxidation of ethylbenzene and methyl linoleate (see Chapter 7). 

The numerical determination of the value quantities as a function of time allows explaining the chemical reason of the antioxidant s effectiveness. Also the value method has been used to analyze the mechanisms for the liquid phase oxidation of ethylbenzene and model lipids methyl linoleate, in the presence of antioxidants in the reaction mixture - butylated hydroxytoluene and a-tocopherol, respectively. The dominant steps responsible for the antioxidant and pro-oxidant properties of cMn reaction inhibitors are identified. 

Some side-chain oxidations are carried out on very large scale using air as the oxidant. These are chiefly oxidations of methyl groups to the corresponding carboxylic acids and oxidations of isopropyl groups to the phenol and acetone. In the former category, there is the liquid-phase oxidation, with cobalt and/or manganese catalyst with bromide promoter... 

In recent years, the liquid phase oxidation of organic substrates using transition metal compounds as catalysts has become a profitable means of obtaining industrially important chemicals. Millions of tons of valuable petrochemicals are produced in this manner annually [1]. Typical examples of such processes are the production of vinyl acetate or acetaldehyde via the Wacker process, equations (1) and (2) the Mid-Century process for the oxidation of methyl aromatics, such as p-xylene to tereph-thalic acid, equation (3) and the production of propylene oxide from propylene using alkyl hydroperoxides, equation (4). 

In the Celanese-LPO-process (liquid-phase oxidation) the catalytic oxidation of n-butane with cobalt acetate takes place at 175 °C and 54 bar. Many by-products are formed in this process (main by-product methyl ethyl ketone other by-products butanoic acid, propionic acid, formic acid, acetaldehyde, acetone, ethyl acetate, and methanol). These by-products are recycled to the reactor where they convert into acetic acid again or oxidize totally. 

The most pronunent example is the partial oxidation of sc isobutane (Tc = 134.7" C,pc = 36.3 bar. Pc = 0.225 g/cm ) towards tert-butanol via hydroperoxides. The reaction is autocatalytic and follows a similar mechanism as in cyclohexane oxidation. Isobutane oxidation has gained importance because of the applications of the oxidation products, tert-butyl hydroperoxide and tert-butyl alcohol, in the manufacture of important chenucals like propylene oxide and methyl tert-butyl ether (MTBE). A comparative study between supercritical oxidation and liquid-phase oxidation with air, but without a catalyst, provides thermodynamic and kinetic data on isobutane oxidation. Supercritical conditions provided higher rates and selectivities than in liquid phase, because a liquid phase-like mechanism runs at... 

Acetic acid is a cosssodity chemical produced by Union Carbide Corporation via the liquid phase oxidation of butane. While acetic acid is the principal product, methyl ethyl ketone and ethyl acetate are valuable by-products. Large scale gas-liquid reactors are used to practice this technology. In general the plant reactor performance was inferior in both productivity and selectivity when contrasted to pilot unit scale reactors carrying out the same reaction under equivalent conditions. 

Production of methyl formate from methanol also leads to the potential produetion of formic acid from methanol [87]. Formic acid is produced commercially as a side produet of the liquid-phase oxidation of w-butane to acetic acid. It has been suggested, however, that new formie acid capacity will best be obtained by hydrolysis of methyl formate because of raw material costs [87]. The methyl formate could be produeed by either the carbonylation or dehydration of methanol according to the technologies discussed previously. 

The effect of temperature on the yield of the main groups of butane oxidation products is shown in Fig. 10.15. The yield of oxygenates is promoted by a temperature reduction, whereas temperature rise increases the yield of olefins, first primary and then lower ones [248]. It is interesting that the composition of the gas-phase butane oxidation products is strikingly different from that of the liquid-phase oxidation products obtained at high pressure, when mainly acetic acid and methyl ethyl ketone are produced, with alcohols being present in small amounts [249]. 

Liquid-phase oxidation of associated gas. For comparison, it is worthwhile to briefly mention the liquid-phase oxidation of associated gas. in contrast to the gas-phase oxidation, wherein the bulk of the products are oxygenated compoimds with a number of carbon atoms smaller than in the original hydrocarbon, the hquid-phase oxidation makes it possible to introduce oxygen into the hydrocarbon molecule without changing the structure of the latter. For example, the oxidation of n-butane gives methyl ethyl ketone with a high )deld. The main product of the hquid-phase oxidation of n-butane is acetic add, which enables to organize its production by this method. The oxidation is carried out at a temperature of 175—200 °C and a pressme of 45—60 atm. In addition to acetic add, methyl ethyl ketone, ethyl acetate, methyl acetate, acetone, isobutanol, and other compoimds are formed. 

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