Cobalt acetate acetaldehyde oxidation

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... 

High purity acetaldehyde is desirable for oxidation. The aldehyde is diluted with solvent to moderate oxidation and to permit safer operation. In the hquid take-off process, acetaldehyde is maintained at 30—40 wt % and when a vapor product is taken, no more than 6 wt % aldehyde is in the reactor solvent. A considerable recycle stream is returned to the oxidation reactor to increase selectivity. Recycle air, chiefly nitrogen, is added to the air introducted to the reactor at 4000—4500 times the reactor volume per hour. The customary catalyst is a mixture of three parts copper acetate to one part cobalt acetate by weight. Either salt alone is less effective than the mixture. Copper acetate may be as high as 2 wt % in the reaction solvent, but cobalt acetate ought not rise above 0.5 wt %. The reaction is carried out at 45—60°C under 100—300 kPa (15—44 psi). The reaction solvent is far above the boiling point of acetaldehyde, but the reaction is so fast that Httle escapes unoxidized. This temperature helps oxygen absorption, reduces acetaldehyde losses, and inhibits anhydride hydrolysis. 

This reaction is rapidly replacing the former ethylene-based acetaldehyde oxidation route to acetic acid. The Monsanto process employs rhodium and methyl iodide, but soluble cobalt and iridium catalysts also have been found to be effective in the presence of iodide promoters. 

Acetic acid (qv) can be produced synthetically (methanol carbonylation, acetaldehyde oxidation, butane/naphtha oxidation) or from natural sources (5). Oxygen is added to propylene to make acrolein, which is further oxidized to acryHc acid (see Acrylic acid and derivatives). An alternative method adds carbon monoxide and/or water to acetylene (6). Benzoic acid (qv) is made by oxidizing toluene in the presence of a cobalt catalyst (7). 

Oxidising acetaldehyde in air when cobalt acetate at -20°C is present gives rise to a detonation, if the medium is stirred. It has been put down to the formation of a very sensitive peroxidic compound. On the other hand, the presence of a halogen derivative inhibits this oxidation. 

Butane oxidation Cobalt acetate 300-450 800 57 Acetaldehyde + acetone + methanol... 

When it was a major source for acetic acid, acetaldehyde was in the top 50 at about 1.5 billion lb. Now it is under a billion pounds but it is still used to manufacture acetic acid by further oxidation. Here a manganese or cobalt acetate catalyst is used with air as the oxidizing agent. Temperatures range from 55-80°C and pressures are 15-75 psi. The yield is 95%. 

The present work was initiated as a consequence of an exploratory program on acetaldehyde oxidation in which copper (II), manganese (II), and cobalt (II) acetates were evaluated. The results indicate a significant difference both in acetaldehyde efficiency to acetic acid and in by-product distribution. 

Acetaldehyde Oxidation. In the oxidation of acetaldehyde with oxygen-nitrogen mixtures, at conditions under which the rate-limiting factor is oxygen transfer to the solution, manganese (II) acetate gives a better efficiency to acetic acid than copper (II) acetate, which in turn is better than cobalt (II) acetate. However, when either cobalt (II) or copper (II) acetate is used in the presence of manganese (II) acetate, the... 

The distribution of by-products originating from the methyl group in acetaldehyde oxidation is significantly different for each catalyst. Typical results are presented in Table II. Methane is the predominant by-product with cobalt acetate, while methane and carbon dioxide and methyl esters and carbon dioxide predominate with manganese and copper acetates, respectively. 

Reaction 22a is important only with cobalt acetate catalyst and accounts for the fast rate of methane formation during the reaction of peracetic with acetaldehyde. It can also explain how methane is produced only from the methyl group of peracetic acid. This reaction path is more important with cobalt probably because of the higher oxidation potential of the cobalt (III)-cobalt (II) couple relative to that of the manganese (III) -manganese (II) couple. 

Oxidation of Acetaldehyde. When using cobalt or manganese acetate the main role of the metal ion (beside the initiation) is to catalyze the reaction of peracetic acid with acetaldehyde so effectively that it becomes the main route to acetic acid and can also account for the majority of by-products. Small discrepancies between acetic acid efficiencies in this reaction and those obtained in acetaldehyde oxidation can be attributed to the degradation of peracetoxy radicals—a peracetic acid precursor— by Reactions 14 and 16. The catalytic decomposition of peracetic acid is too slow (relative to the reaction of acetaldehyde with peracetic acid) to be significant. The oxidation of acetyl radical by the metal ion in the 3+ oxidation state as in Reaction 24 is a possible side reaction. Its importance will depend on the competition between the metal ion and oxygen for the acetyl radical. 

Butane from natural gas is cheap and abundant in the United States, where it is used as an important feedstock for the synthesis of acetic acid. Since acetic acid is the most stable oxidation product from butane, the transformation is carried out at high butane conversions. In the industrial processes (Celanese, Hills), butane is oxidized by air in an acetic acid solution containing a cobalt catalyst (stearate, naphthenate) at 180-190 °C and 50-70 atm.361,557 The AcOH yield is about 40-45% for ca. 30% butane conversion. By-products include C02 and formic, propionic and succinic acids, which are vaporized. The other by-products are recycled for acetic acid synthesis. Light naphthas can be used instead of butane as acetic adic feedstock, and are oxidized under similar conditions in Europe where natural gas is less abundant (Distillers and BP processes). Acetic acid can also be obtained with much higher selectivity (95-97%) from the oxidation of acetaldehyde by air at 60 °C and atmospheric pressure in an acetic acid solution and in the presence of cobalt acetate.361,558... 

Depending on the conditions, metal-catalyzed autoxidation of acetaldehyde can be utilized for the manufacture of either acetic acid or peracetic acid.321 In addition, autoxidation of acetaldehyde in the presence of both copper and cobalt acetates as catalysts produpes acetic anhydride in high yield.322 b The key step in anhydride formation is the electron transfer oxidation of acetyl radicals by Cu(II), which competes with reaction of these radicals with oxygen ... 

Acetaldehyde Oxidation. Ethanol [64-17-5] is easily dehydrogenated oxidatively to acetaldehyde (qv) using silver, brass, or bronze catalysts. Acetaldehyde can then be oxidized in the liquid phase in the presence of cobalt or manganese salts to yield acetic acid. Peracetic acid [79-21-0] formation is prevented by the transition metal catalysts (7). (Most transition metal salts decompose any peroxides that form, but manganese is uniquely effective.)... 

Acetic acid is usually made by one of three routes acetaldehyde oxidation, involving direct air or oxygen oxidation of liquid acetaldehyde in the presence of manganese acetate, cobalt acetate, or copper acetate liquid-phase oxidation of butane or naphtha methanol carbonylation using a variety of techniques. 

Approximately 2 million tons of acetic acid are produced each year in the United States for a variety of purposes, including preparation of the vinyl acetate polymer u.sed in paints and adhesives. The industrial method of acetic acid synthesis involves a cobalt acetate-catalyzed air oxidation of acetaldehyde, but this method is not used in the laboratory. 

The low-pressure acetic acid process was developed by Monsanto in the late 1960s and proved successful with commercialization of a plant producing 140 X 10 metric tons per year in 1970 at the Texas City (TX, USA) site [21]. The development of this technology occurred after the commercial implementation by BASF of the cobalt-catalyzed high-pressure methanol carbonylation process [22]. Both carbonylation processes were developed to utilize carbon monoxide and methanol as alternative raw materials, derived from synthesis gas, to compete with the ethylene-based acetaldehyde oxidation and saturated hydrocarbon oxidation processes (cf. Sections 2.4.1 and 2.8.1.1). Once the Monsanto process was commercialized, the cobalt-catalyzed process became noncom-... 

Oxidations of paraffins with high concentrations of cobalt catalyst have very special characteristics. Such oxidations will proceed at lower temperatures than in the case of lower concentrations of cobalt or with other catalysts, or in the absence of catalysts [10, 18, 60-66]. For example, the high-concentration cobalt-ion oxidation of -butane can be conducted at 100-110 °C compared with 150-180 °C for the other cases. Significantly higher efficiencies to acetic acid are reported (75-84 % vs. about 50-60 %). Co-reductants such as acetaldehyde, MEK, or p-xylene (especially p-xylene [65]) are reported to be useful, but not essential [66]. In high-concentration cobalt-ion catalyzed oxidations, rates are generally lower than in the conventional oxidations. 

Bawn and Williamson [9] examined the catalyzed oxidation of acetaldehyde in solution in acetic acid at 25°C. Whereas uncatalyzed oxidation has mediocre reproducibility, catalyzed oxidations are reproducible within 2%. The catalyst was cobalt acetate in solution in the cobaltous form. The partial oxygen pressure varied from 550 to 950 torr. Under such conditions, as in the case of photochemical oxidations, the stoichiometry of the reaction follows the overall equation... 

Most of the catalysts employed in the chemical technologies are heterogeneous. The chemical reaction takes place on surfaces, and the reactants are introduced as gases or liquids. Homogeneous catalysts, which are frequently metalloorganic molecules or clusters of molecules, also find wide and important applications in the chemical technologies [24]. Some of the important homogeneously catalyzed processes are listed in Table 7.44. Carbonylation, which involves the addition of CO and H2 to a C olefin to produce a + 1 acid, aldehyde, or alcohol, uses rhodium and cobalt complexes. Cobalt, copper, and palladium ions are used for the oxidation of ethylene to acetaldehyde and to acetic acid. Cobalt(II) acetate is used mostly for alkane oxidation to acids, especially butane. The air oxidation of cyclohexane to cyclohexanone and cyclohexanol is also carried out mostly with cobalt salts. Further oxidation to adipic acid uses copper(II) and vanadium(V) salts as catalysts. The... 

The catalyzed oxidation of ethanol to acetic accompanied by acetaldehyde oxidation may be accomplished by use of acetic acid solutions with a cobalt acetate catalyst. In an example, 252 g of acetaldehyde is fed to the catalyst solution for activation, and then 85.4 g of 100 per cent ethanol together with air is introduced. Conversion of ethanol is 94.2 per cent to acetic acid, 3.5 per cent unchanged, and 2.3 per cent to ethyl acetate. Temperatures below 145°C were used. Various other metal acetates have been patented for the above process, including the salts of alkali and alkaline-earth groups, salts of the platinum metals group, and salts of the chromium metals group. A solid palladium-on-alumina catalyst is active in promoting air oxidation of ethanol to acetic acid. ... 

Acetaldehyde oxidation was also marginally improved, especially for the manufacture of acetic anhydride. In 1935, workers at Shawingan Chemicals discovered that the oxidation of acetaldehyde, if conducted in the presence of cobalt, copper, or better yet, a mixture of the two catalysts, yielded a mixture of acetic anhydride and acetic acid providing the water co-product was rapidly separated by azeotropic distillation, normally with a compatible material such as ethyl acetate. It would not be until the 1940 s that this became widely practiced, but the process was eventually widely adopted. While experimental units produced ratios of acetic anhydride acetic acid as high as 4 1, it appears that the commercial process normally gave a 5 4 mixture of acetic anhydride acetic acid... 

The oxidation of cyclohexanone in the presence of cobalt complexes has been extensively studied [282,293-297]. Both adipic acid and e-caprolactone were formed. Oxidation was found to take place via the decomposition of the primary oxidation product, 2-hydroperoxy cyclohexanone [282,293]. Cobalt(III) stearate, [CoSt20H] was found to form a 1 1 complex with cyclohexanone which decomposed to Co(II) and free radicals [295]. Thus, the suggested involvement of cobalt in this oxidation [293, 295] can be summarized in equations (191) and (192), while oxidation can take place via reactions such as (193), (194) [293] and (195) [282]. It is of interest that co-oxidation of acetaldehyde and cyclohexanone in the presence of cobalt naphthenate yields acetic acid and e-caprolactone [299-301]. 

In the second step of the above synthetical route, acetaldehyde is oxidized to acetic anhydride by air at 30—60°C a mixture of copper and cobalt acetates serves as catalyst. A complex series of reactions is involved and acetic acid is also a major product. The overall process may be represented simply as follows ... 

The oxidation of acetaldehyde for the commercial production of acetic acid can be accomplished with pure oxygen or air in the presence of manganese or cobalt-acetate catalyst solutions [Eq. (6.15.2)]. The use of air saves the air separation unit but has the disadvantage that its high N2 content requires extensive purging to avoid build-up of inerts in the process ... 

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. 

Acetic acid was originally produced by bacterial oxidation of ethanol, but from around 1914, synthetic acetic acid was produced by the oxidation of acetaldehyde. Hydrocarbon oxidation processes using butane or naphtha as feedstock were introduced in the 1950s. In a typical liquid phase oxidation process, a cobalt acetate catalyst operating at a temperature of 175°C, and a pressure of 54 bar was used, and by-products could be recycled. Conditions could be modified to produce methyl ethyl ketone. 

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). 

Acetaldehyde can be used as an oxidation-promoter in place of bromine. The absence of bromine means that titanium metallurgy is not required. Eastman Chemical Co. has used such a process, with cobalt as the only catalyst metal. In that process, acetaldehyde is converted to acetic acid at the rate of 0.55—1.1 kg/kg of terephthahc acid produced. The acetic acid is recycled as the solvent and can be isolated as a by-product. Reaction temperatures can be low, 120—140°C, and residence times tend to be high, with values of two hours or more (55). Recovery of dry terephthahc acid follows steps similar to those in the Amoco process. Eastman has abandoned this process in favor of a bromine promoter (56). Another oxidation promoter which has been used is paraldehyde (57), employed by Toray Industries. This leads to the coproduction of acetic acid. 2-Butanone has been used by Mobil Chemical Co. (58). 

Chevron Chemical Co. began commercial production of isophthahc acid in 1956. The sulfur-based oxidation of / -xylene in aqueous ammonia at about 320°C and 7,000—14,000 kPa produced the amide. This amide was then hydrolyzed with sulfuric acid to produce isophthahc acid at about 98% purity. Arco Chemical Co. began production in 1970 using air oxidation in acetic acid catalyzed by a cobalt salt and promoted by acetaldehyde at 100—150°C and 1400—2800 kPa (14—28 atm). The cmde isophthahc acid was dissolved and recrystallized to yield a product exceeding 99% purity. The Arco technology was not competitive and the plant was shut down in 1974. 

Homogeneous Oxidation Catalysts. Cobalt(II) carboxylates, such as the oleate, acetate, and naphthenate, are used in the Hquid-phase oxidations of -xylene to terephthaUc acid, cyclohexane to adipic acid, acetaldehyde (qv) to acetic acid, and cumene (qv) to cumene hydroperoxide. These reactions each involve a free-radical mechanism that for the cyclohexane oxidation can be written as... 

Oxidation catalysts are either metals that chemisorb oxygen readily, such as platinum or silver, or transition metal oxides that are able to give and take oxygen by reason of their having several possible oxidation states. Ethylene oxide is formed with silver, ammonia is oxidized with platinum, and silver or copper in the form of metal screens catalyze the oxidation of methanol to formaldehyde. Cobalt catalysis is used in the following oxidations butane to acetic acid and to butyl-hydroperoxide, cyclohexane to cyclohexylperoxide, acetaldehyde to acetic acid and toluene to benzoic acid. PdCh-CuCb is used for many liquid-phase oxidations and V9O5 combinations for many vapor-phase oxidations. 

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