Wacker-Hoechst Acetaldehyde Process

Water is also involved as a substrate in the Wacker- Hoechst acetaldehyde process based on a partial, selectie oxidation of ethylene [16]. According to Eq. (10), it is necessary to form the new C—O bond starting from ethylene (trans-stereochemistry), while the oxygen of Eq. (11) regenerates the catalyst (Pd° — Pd2+), but does not oxidize the ethylene as suggested by the net Eq. (12). Metal attachment of ethylene is the prerequisite to make it accessible to nucleophilic attack by water (cf. Section 6.4.2). 

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Acetaldehyde, first used extensively during World War I as a starting material for making acetone [67-64-1] from acetic acid [64-19-7] is currendy an important intermediate in the production of acetic acid, acetic anhydride [108-24-7] ethyl acetate [141-78-6] peracetic acid [79-21 -0] pentaerythritol [115-77-5] chloral [302-17-0], glyoxal [107-22-2], aLkylamines, and pyridines. Commercial processes for acetaldehyde production include the oxidation or dehydrogenation of ethanol, the addition of water to acetylene, the partial oxidation of hydrocarbons, and the direct oxidation of ethylene [74-85-1]. In 1989, it was estimated that 28 companies having more than 98% of the wodd s 2.5 megaton per year plant capacity used the Wacker-Hoechst processes for the direct oxidation of ethylene. 

The direct oxidation of ethylene is used to produce acetaldehyde (qv) ia the Wacker-Hoechst process. The catalyst system is an aqueous solution of palladium chloride and cupric chloride. Under appropriate conditions an olefin can be oxidized to form an unsaturated aldehyde such as the production of acroleia [107-02-8] from propjiene (see Acrolein and derivatives). 

Another attractive commercial route to MEK is via direct oxidation of / -butenes (34—39) in a reaction analogous to the Wacker-Hoechst process for acetaldehyde production via ethylene oxidation. In the Wacker-Hoechst process the oxidation of olefins is conducted in an aqueous solution containing palladium and copper chlorides. However, unlike acetaldehyde production, / -butene oxidation has not proved commercially successflil because chlorinated butanones and butyraldehyde by-products form which both reduce yields and compHcate product purification, and also because titanium-lined equipment is required to withstand chloride corrosion. 

The naming of this process has been confused because of various corporate relationships. The basic invention was created in 1957 at the Consortium fur Elektrochemische Industrie, Munich, a wholly owned subsidiary of Wacker-Chemie. It has therefore been called both the Wacker process and the Consortium process. But for many years, Wacker-Chemie has had a close relationship with Farbwerke Hoechst and the latter company has participated in some of the development and licensing activities, so two other names have come to be used Wacker-Hoechst and Hoechst-Wacker. The live inventors (J. Schmidt, W. Hafner, J. Sedlmeier, R. Jira, and R. Riittinger) received the Dechema prize in 1962 for this invention. The acetaldehyde process was first operated commercially in 1960. In 1997, this process was used in making 85 percent of the world s production of acetaldehyde. Although Wacker-Chemie still makes vinyl acetate, it no longer uses the Wacker process to do so. 

The large scale manufacture of acetaldehyde with the Wacker-Hoechst process takes place in a two-phase gas/liquid system. Ethylene and air (or O2) react with the acidic (pH 0.8-3) aqueous catalyst solution in a corrosion-resistant titanium or lined reactor. 

The liquid phase processes resembled Wacker-Hoechst s acetaldehyde process, i.e., acetic acid solutions of PdCl2 and CuCl2 are used as catalysts. The water produced from the oxidation of Cu(I) to Cu(II) (Figure 27) forms acetaldehyde in a secondary reaction with ethylene. The ratio of acetaldehyde to vinyl acetate can be regulated by changing the operating conditions. The reaction takes place at 110-130°C and 30-40 bar. The vinyl acetate selectivity reaches 93% (based on acetic acid). The net selectivity to acetaldehyde and vinyl acetate is about 83% (based on ethylene), the by-products being CO2, formic acid, oxalic acid, butene and chlorinated compounds. The reaction solution is very corrosive, so that titanium must be used for many plant components. After a few years of operation, in 1969-1970 both ICI and Celanese shut down their plants due to corrosion and economic problems. 

Co saturated hydrocarbons are used extensively in the United States, whereas the acetylene process was used almost exclusively in Europe until recently. These processes were extended by the late 1950 s and early 1960 s by a new approach called the Wacker process or the Wacker-Hoechst process, consisting of the liquid phase catalytic oxidation of ethylene to acetaldehyde, as outlined in Table II. 

This development began to reduce steadily the capacities of acetaldehyde which previously had been made by oxidation of ethylene (Wacker-Hoechst process cf. Section 2.4.1) and converted to acetic acid (cf. Section 2.4.4). Moreover, the Monsanto process, the second-generation process for methanol carbonylation is now being followed by the third generation of highly efficient carbonylation processes, enabling acetic anhydride as well as acetic acid to be produced (cf Scheme 2 Tennessee-Eastman [36] and BP [37] processes). The most advanced process (Hoechst [40]) has so far not been implemented industrially because of neglects... 

Technical Applications (Wacker-Hoechst Processes) 2.4.1.4.1 Acetaldehyde from Ethylene... 

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

The Wacker-type oxidation of olefins is one of the oldest homogeneous transition metal-catalyzed reactions [1], The most prominent example of this type of reaction is the oxidation of ethylene to acetaldehyde by a PdCl2/CuCl2/02 system (Wacker-Hoechst process). In this industrial process, oxidation of ethylene by Pd(ll) leads to Pd(0), which is reoxidized to Pd(ll) via reduction of Cu(ll) to Cu(l). To complete the oxidation-reduction catalytic cycle, Cu(l) is classically reoxidized to Cu(ll) by O2 [2, 3], The use of bidentate ligands [4], bicomponent systems constituted of benzoquinone and iron(ll) phfhalocyanine [5] or chlorine-free oxidants such as ferric sulfate [6], heteropoly acid [7], and benzoquinone [8], make it possible to increase the selectivity reaction by avoiding the formation of chlorinated products. 

Fig. 3-2 Acetaldehyde production in the two-stage Wacker-Hoechst process...

Wacker-Hoechst process oxidation of ethylene to acetaldehyde with Pd/Cu catalysts followed by oxidation to acetic acid. 

The process of choice for acetaldehyde production is ethylene oxidation according to the so-called Wacker-Hoechst process [route (c) in Topic 5.3.2]. The reaction proceeds by homogeneous catalysis in an aqueous solution of HQ in the presence of palladium and copper chloride complexes. The oxidation of ethylene occurs in a stoichiometric reaction of PdQ2 with ethylene and water that affords acetaldehyde, metallic palladium (oxidation state 0), and HQ [step (a) in Scheme 5.3.5). The elemental Pd is reoxidized in the process by Cu(II) chloride that converts in this step into Cu(I) chloride [step (b) in Scheme 5.3.5). The Cu(II) chloride is regenerated by oxidation with air to finally close the catalytic cycle [step (c) in Scheme 5.3.5). 

Economic studies by Aquilo et al of the Celanese Chemical Co. have shown that acetaldehyde production via reductive methanol carbonylation is superior to the Wacker—Hoechst process, if reinvestment is considered... 

Catalysts used to convert ethylene to vinyl acetate are closely related to those used to produce acetaldehyde from ethylene. Acetaldehyde was first produced industrially by the hydration of acetylene, but novel catalytic systems developed cooperatively by Farbwerke Hoechst and Wacker-Chemie have been used successfully to oxidize ethylene to acetaldehyde, and this process is now well established (7). However, since the largest use for acetaldehyde is as an intermediate in the production of acetic acid, the recent announcement of new processes for producing acetic acid from methanol and carbon monoxide leads one to speculate as to whether ethylene will continue to be the preferred raw material for acetaldehyde (and acetic acid). 

The invention of the Wacker process was a triumph of common sense. It had been known since 1894 that ethylene is oxidized to acetaldehyde by palladium chloride in a stoichiometric reaction (Figure 27). However, it was not until 1956 that this reaction was combined with the known reoxidation reactions of palladium by copper and, in turn of copper by oxygen. The total process developed by Wacker and Hoechst between 1957 and 1959 can be depicted as an exothermic catalytic direct oxidation to yield acetaldehyde. 

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. 

In addition to plants already existing at Farbwerke Hoechst A. G. and Wacker Chemie G.m.b.H. in Germany, other plants have been or are being built by Rhone-Poulenc, France Societa Edison, Italy Pemex, Mexico Celanese Corp. at Bay City, Tex. and Shawinigan Chemicals Ltd., Canada. Plants are also being installed in Japan. Some use the one-stage, others the two-stage process for acetaldehyde manufacture, licensed by the Aldehyd G.m.b.H. 

This is currently the most widespread method for manufacturing acetaldehyde. Initial research and development conducted by the Consortium Jur ElectrocHanische Industrie, a Wacker Chemie affiliated organization, culminated in 1956 in the development of an industrial process with two variants. One of them, proposed by Hoechst, employs oxygen as the oxidant, and the second, examined by Wackert employs air. The commercialization of these two alternatives by Aldehyd, a joint venture, led to the construction of the first industrial plant in 1960. 

Electron withdrawal from the coordinated alkene to an electrophilic metal center makes the coordinated alkene susceptible to attack by an external nucleophilic agent or by a ligand coordinated to the metal. A classic example using modification of the chemical nature of ethylene coordinated to a cationic metal center can be seen in palladium-catalyzed Hoechst-Wacker process [111]. The catalytic cycle can be represented by Scheme 1.37, which is comprised of the main cycle to convert the ethylene coordinated to Pd(II) into acetaldehyde and auxiliary cycles to re-oxidize the Pd(0) species to Pd(II) with Cu(I). The Cu(I) produced in the process is oxidized in turn to Cu(II) with oxygen. 

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