Acetaldehyde oxidation process

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... 

The evaluation of acetaldehyde oxidation process was carried out by aeration of acetaldehyde solution and analyzing the concentration of acetic acid using gas chromatography HP 5890 with detector FID equipped with PEG Column in 15 minutes time interval. The gas flow rate Qg), impeller rotation speed N) and temperature (7) were varied. 

Many biological processes involve oxidation of alcohols to carbonyl compounds or the reverse process reduction of carbonyl compounds to alcohols Ethanol for example is metabolized m the liver to acetaldehyde Such processes are catalyzed by enzymes the enzyme that catalyzes the oxidation of ethanol is called alcohol dehydrogenase... 

This oxidation process for olefins has been exploited commercially principally for the production of acetaldehyde, but the reaction can also be apphed to the production of acetone from propylene and methyl ethyl ketone [78-93-3] from butenes (87,88). Careflil control of the potential of the catalyst with the oxygen stream in the regenerator minimises the formation of chloroketones (94). Vinyl acetate can also be produced commercially by a variation of this reaction (96,97). 

Acetaldehyde oxidation to anhydride does not consume great amounts of energy. The strongly exothermic reaction actually furnishes energy and the process is widely used in Europe. Acetaldehyde must be prepared from either acetylene or ethylene. Unfortunately, use of these raw materials cancels the other advantages of this route. Further development of more efficient acetaldehyde oxidation as weU as less expensive materials of constmction would make that process more favorable. 

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. 

Formaldehyde is also produced by the oxidation of light petroleum gases, a process which also yields methanol and acetaldehyde. This process is currently used in the Celanese Corporation plant for the production of Celcon. 

It is possible to carry out such oxidation processes as the conversion of acetaldehyde to acetic acid, or methyl alcohol to formaldehyde in aluminum plants, thus avoiding boiling anhydrous acids. The metal is especially valuable for handling delicate chemicals, which must not acquire metallic taste or color. For these reasons, aluminum has found extensive use in the food, dairy, brewing and fishing industries. 

Another approach is to use an easily oxidized substance such as acetaldehyde or methylethyl ketone, which, under the reaction conditions, forms a hydroperoxide. These will accelerate the oxidation of the second methyl group. The DMT process encompasses four major processing steps oxidation, esterification, distillation, and crystallization. Figure 10-16 shows a typical p-xylene oxidation process to produce terephthalic acid or dimethyl terephthalate. The main use of TPA and DMT is to produce polyesters for synthetic fiber and film. 

If there is a prime example of an organic chemical that is in a state of flux and turnover in regards to the manufacturing method, it is probably acetic acid. There are now three industrial processes for making acetic acid. Domestic capacity in 1978 was almost equal among acetaldehyde oxidation. 

It is believed that peractic acid is primarily responsible for chain branching during the oxidation of acetaldehyde (12) and ethyl ether (24, 27). Although amines are powerful inhibitors of these oxidation processes, they have much less effect if added during the reaction. The inhibiting power of amines becomes smaller the longer the reaction between the fuel and oxygen has proceeded. Similar behavior is observed... 

Direct Oxidation. Direct oxidation of petroleum hydrocarbons has been practiced on a small scale since 1926 methanol, formaldehyde, and acetaldehyde are produced. A much larger project (29) began operating in 1945. The main product of the latter operation is acetic acid, used for the manufacture of cellulose acetate rayon. The oxidation process consists of mixing air with a butane-propane mixture and passing the compressed mixture over a catalyst in a tubular reaction furnace. The product mixture includes acetaldehyde, formaldehyde, acetone, propyl and butyl alcohols, methyl ethyl ketone, and propylene oxide and glycols. The acetaldehyde is oxidized to acetic acid in a separate plant. Thus the products of this operation are the same as those (or their derivatives) produced by olefin hydration and other aliphatic syntheses. 

In the mid-l O s, it was found that acetic acid itself could be catalytically dehydrated to ketene, which when absorbed in fresh acid gave the anhydride. Soon after this process became commercially established, the older processes of making the anhydride were discontinued. By this time synthetic acetic acid was being made from acetylene via acetaldehyde oxidation, from synthetic ethyl alcohol also via acetaldehyde, and by the direct oxidation of fermentation ethyl alcohol. The ketene route to acetic anhydride, in addition to starting from acetic acid, later employed acetone as raw material. 

Acetic Anhydride. Other products recovered from the oxidation of light hydrocarbons (6) are acetic acid and acetic anhydride as well as acetaldehyde, acetone, and isopropyl alcohol, all of which may be converted to acetic acid or the anhydride. The direct oxidation process supplements the production of acetic anhydride from acetone derived from propylene, which has been the principal commercial source of the anhydride. The increasing production of cellulose acetate within recent years has been attributed to the low cost of acetic anhydride from the latter process (44). 

The oxidation process is carried out in the temperature range 300— 450°C, and generally studied at atmospheric pressure. Excess air is usually applied (with some exceptions) and substantial amounts of water vapour may be added to the feed. High initial selectivities (>95%) are feasible, and, although some further oxidation (combustion) of the product is unavoidable, yields of 70—90% are reported in the patent literature. The main by-products are carbon oxides, in addition to minor amounts of acrylic acid, acetaldehyde and formaldehyde. Acrylic acid may be a main product depending on specific catalyst properties and reaction conditions, as described in more detail in Sect. 2.2.3. 

Heterolytic liquid-phase oxidation processes are more recent than homolytic ones. The two major applications are the Wacker process for oxidation of ethylene to acetaldehyde by air, catalyzed by PdCl2-CuCl2 systems,98 and the Arco oxirane" or Shell process100 for epoxidation of propylene by f-butyl or ethylbenzene hydroperoxide catalyzed by molybdenum or titanium complexes. These heterolytic reactions require less drastic conditions than the homolytic ones... 

The recent dramatic increase in the price of petroleum feedstocks has made the search for high selectivities more urgent. Several new processes based on carbon monoxide sources are currently competing with older oxidation processes.103,104 The more straightforward synthesis of acetic acid from methanol carbonylation (Monsanto process) has made the Wacker process obsolete for the manufacture of acetaldehyde, which used to be one of the main acetic acid precursors. Several new methods for the synthesis of ethylene glycol have also recently emerged and will compete with the epoxidation of ethylene, which is not sufficiently selective. The direct synthesis of ethylene... 

In addition to the cr-v equilibrium, an exchange between the n complex (45) and free acetaldehyde has been demonstrated using, 4C-labeled acetaldehyde (46, 48). After 45 hours at room temperature, 0.46% exchange was observed. While this appears quite small, one must remember that the free vinyl alcohol/acetaldehyde ratio has been estimated to have an upper limit of only 10-7 and that in the Wacker Process the equilibrium between 7r-coordinated and free vinyl alcohol would be shifted considerably in favor of free vinyl alcohol by the overpressure of ethylene. Thus, the behavior of the ir-vinyl alcohol complexes (45) and (48) seem to support the importance of such complexes as intermediates in the Wacker and similar olefin oxidation processes. 

Acetic acid is manufactured by three processes acetaldehyde oxidation, //-butane oxidation, and methanol carbonylation.Ethylene is the exclusive organic raw material for making acetaldehyde, 70 percent of which is further oxidized to acetic acid or acetic anhydride. The single-stage (Wacker) process for making acetaldehyde involves cupric chloride and a small amount of palladium chloride in aqueous solution as a catalyst. 

Conversion of ethylene to acetaldehyde with a soluble palladium complex was one of the early applications of homogeneous catalysis. Traditionally, acetaldehyde was manufactured either by the hydration of acetylene or by the oxidation of ethanol. As most of the acetic acid manufacturing processes were based on acetaldehyde oxidation, the easy conversion of ethylene to acetaldehyde by the Wacker process was historically a significant discovery. With the... 

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