Acetaldehyde liquid phase oxidation

Product refining is quite facile, following the same general pattern for acetic acid (qv) recovery from acetaldehyde liquid-phase oxidation. Low... 

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). 

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. 

The process is similar to the catalytic liquid-phase oxidation of ethylene to acetaldehyde. The difference hetween the two processes is the presence of acetic acid. In practice, acetaldehyde is a major coproduct. The mole ratio of acetaldehyde to vinyl acetate can he varied from 0.3 1 to 2.5 1. The liquid-phase process is not used extensively due to corrosion problems and the formation of a fairly wide variety of by-products. 

Liquid phase oxidation reaction of acetaldehyde with Mn acetate catalyst can be considered as pseudo first order irreversible reaction with respect to oxygen, and the reaction occurred in liquid film. The value of kinetic constant as follow k/ = 6.64.10 exp(-12709/RT), k2 = 244.17 exp(-1.8/RT) and Lj = 3.11.10 exp(-13639/RT) m. kmor. s. The conversion can be increased by increasing gas flow rate and temperature, however the effect of impeller rotation on the conversion is not significant. The highest conversion 32.5% was obtained at the rotation speed of 900 rpm, temperature 55 C, and gas flow rate 10" m. s. The selectivity of acetic acid was affected by impeller rotation speed, gas flow rate and temperature. The highest selectivity of acetic acid was 70.5% at 500 rpm rotation speed, temperature of 55 C... 

Two selective processes are important in the oxidation of ethylene the production of ethylene oxide and acetaldehyde. The first process is specifically catalyzed by silver, the second one by palladium-based catalysts. Silver catalysts are unique and selective for the oxidation of ethylene. No similar situation exists for higher olefins. The effect of palladium catalysts shows a resemblance to the liquid phase oxidation of ethylene in the Wacker process, in which Pd—C2H4 coordination complexes are involved. The high selectivity of the liquid phase process (95%), however, is not matched by the gas phase route at present. 

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... 

There are two ways to produce acetaldehyde from ethanol oxidation and dehydrogenation. Oxidation of ethanol to acetaldehyde is carried out in the vapor phase over a silver or copper catalyst (305). Conversion is slighdy over 80% per pass at reaction temperatures of 450—500°C with air as an oxidant. Chloroplatinic acid selectively catalyzes the liquid-phase oxidation of ethanol to acetaldehyde giving yields exceeding 95%. The reaction takes place in the absence of free oxygen at 80°C and at atmospheric pressure (306). The kinetics of the vapor and liquid-phase oxidation of ethanol have been described in the literature (307,308). 

The major conventional processes for the production of acetic acid include the carbonylation of methanol (originally developed by Monsanto, and now carried out by several companies, such as Celanese-ACID OPTIMIZATION, BP-CATIVA, etc.), the liquid-phase oxidation of acetaldehyde, still carried out by a few companies, and the liquid-phase oxidation of n-butane and naphtha. More recent developments include the gas-phase oxidation of ethylene, developed by Showa Denko K.K., and the liquid-phase oxidation of butenes, developed by Wacker [2a],... 

Peracetic acid can also be formed directly by liquid-phase oxidation at 5 to 50°C with a cobalt salt catalyst. Nitric acid oxidation of acetaldehyde yields glyoxal and the oxidation of p-xylene to terephthalic acid and of ethanol to acetic acid is activated by acetaldehyde. 

Liquid phase oxidation of hydrocarbons by molecular oxygen forms the basis for a wide variety of petrochemical processes,3 "16 including the manufacture of phenol and acetone from cumene, adipic acid from cyclohexane, terephthalic acid from p-xylene, acetaldehyde and vinyl acetate from ethylene, propylene oxide from propylene, and many others. The majority of these processes employ catalysis by transition metal complexes to attain maximum selectivity and efficiency. 

Acetic Acid. Acetic acid production in the United States has increased by large numbers in the last half century, since the monomer has many uses such as to make polymers for chewing gum, to use as a comonomer in industrial and trade coatings and paint, and so on. In the 1930s, a three-step synthesis process from ethylene through acid hydrolysis to ethanol followed by catalytic dehydrogenation of acetaldehyde and then a direct liquid-phase oxidation to acetic acid and acetic anhydride as co-products was used to produce acetic acid... 

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. 

Since i960, the liquid-phase oxidation of ethylene has been the process of choice for the manufacture of acetaldehyde. There is, however, still some commercial production by the partial oxidation of ethyl alcohol and hydration of acetylene. The economics of the various processes are strongly dependent on the prices of the feedstocks. Acetaldehyde is also formed as a coproduct in the high temperature oxidation of butane. A more recently developed rhodium catalyzed process produces acetaldehyde from synthesis gas as a coproduct with ethyl alcohol and acetic acid (83—94). 

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... 

Although the simplest branching step which is consistent with the observed kinetics is first-order in both peracid and aldehyde. Combe et al. [19] suggested that the overall branching process may be more complicated than (5c) implies. It was considered that interaction of aldehyde and peracid may lead to the formation of an addition compound similar to that proposed for the liquid phase oxidation of acetaldehyde [75—79], and that this compound could either regenerate the aldehyde and peracid, or, alternatively, decompose to give radicals, viz. 

For each mole of acetaldehyde formed, one mole of palladium chloride was reduced to metallic palladium. To make this process industrially attractive, it must be conducted so that palladium chloride acts as a catalyst rather than as an oxidant—i.e., so that the metallic palladium formed is reoxidized to palladium chloride and can be reused for the principal reaction. This was the second fundamental recognition, which helped make this process commercial. The search for proper oxidants for metallic palladium was facilitated by the observation of Smidt et al. (34) that if cupric or ferric chloride were added to palladium chloride in the vapor-phase oxidation of ethylene to acetaldehyde, the acetaldehyde yield was increased. Therefore, these compounds were also used in the liquid-phase oxidation. In such a system, the following reactions will occur in the presence of oxygen and hydrochloric acid, the latter being formed by the reaction above (34). 

The liquid-phase oxidation of ethylene to acetaldehyde was pioneered by the Consortium fiir Elektrochemische Industrie G.m.b.H. Industrially, the single-stage process was developed mainly by Farbwerke Hoechst A. G. and the two-stage process by Wacker Chemie G.m.b.H. itself. Both processes are licensed by Aldehyd G.m.b.H., jointly owned by Wacker Chemie G.m.b.H. and Farbwerke Hoechst G.m.b.H. The basic patents of these two companies on the Wacker process are listed in Table IV. In addition to these patents, which have given Wacker Chemie G.m.b.H. and Farbwerke Hoechst a dominant role in this field, other companies hold some patents in this area (Table X). How many of the patents listed in Tables IX and X are commercially important cannot be judged, based on the open literature alone. 

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. 

The direct oxidation of propylene by molecular oxygen is a low-selective reaction. The propylene oxide yield can be raised by limiting the conversion rate to a low value, about 10 to 15 per cent, by using more selective catalysts, or by achieving co-oxidation with a more oxidizable compound than propylene (acetaldehyde, isobutyraldehyde etc.). Many patents have been Hied concerning this process, but without any industrial implementation. Among them is the liquid phase oxidation of propylene on a rare earth oxide catalyst deposited on silica gel (USSR), or in the presence of molybdenum complexes in chlorobenzene or benzene (JFP Instiiut Francois du Petrole. Jefferson ChemicalX vapor phase oxidation on modified silver catalysts (BP British Petroleum IFP, or on ... 

Acetaldehyde synthesis by liquid phase oxidation of ethylene (Wacker-Hoechst processes)... 

Table S. 1 gives economic data on the production of acetaldehyde by acetylene hydration and liquid phase oxidation of ethylene according to the Wacker-Hoechst (single-step and two-step) technologies.

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. 

About half of the world production comes from methanol carbonylation and about one-third from acetaldehyde oxidation. Another tenth of the wodd capacity can be attributed to butane—naphtha liquid-phase oxidation. Appreciable quantities of acetic acid are recovered from reactions involving peracetic acid. Precise statistics on acetic acid production are complicated by recycling of acid from cellulose acetate and poly (vinyl alcohol) production. Acetic acid that is by-product from peracetic acid [79-21 -0] is normally designated as virgin acid, yet acid from hydrolysis of cellulose acetate or poly (vinyl acetate) is designated recycle acid. Indeterminate quantities of acetic acid are coproduced with acetic anhydride from coal-based carbon monoxide and unknown amounts are bartered or exchanged between corporations as a device to lessen transport costs. 

Acetaldehyde to Acetic Acid. The formation of acetic acid furnishes an excellent example of liquid-phase oxidation with molecular oxygen. Acetic acid may be obtained by the direct oxidation of ethanol, but the concentrated acid is generally obtained by oxidation methods from acetaldehyde that may have been formed by the hydration of acetylene or the oxidation of ethanol. The oxidation usually occurs in acetic acid solution in the presence of a catalyst and at atmospheric or elevated pressures. Temperatures may range up to lOO C, depending upon conditions, but are usually lower. 

Through study of the mechanism by which the catalyzed liquid-phase oxidation of acetaldehyde to acetic proceeds, it has been found, that at temperatures below 15 C and in suitable solvents the acetaldehyde forms an unstable compound, acetaldehyde monoperacetate. At controlled low temperatures this compound can be made to yield peracetic acid and acetaldehyde. Salts of the metals cobalt, copper, and iron catalyze the first-stage reaction, in a manner used in acetic acid manufacture. 

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