Processes acetaldehyde

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. 

Acetaldehyde process.. A stainless steel, water jacketed ketde is filled with... 

Fig. 10.14. Two-stage acetaldehyde process. (Encyclopedia of Chemical Technology, Kirk and Othmer, Web site ed., acetaldehyde, manufacture, 2002. Copyright by John Wiley Sons, Inc. and reproduced by permission of the copyright owned...

Prepare a simplified equipment flow sheet for the acetaldehyde process outlined in Prob. 8. Identify temperature, pressure, and composition, wherever possible, at each piece of equipment. 

As in the acetaldehyde process, this can be carried out commercially in either a single-step or a two-step process. The latter is economically more favourable because a propylene/propane mixture (made by petroleum cracking) can be directly used as the feedstock. Propane behaves like an inert gas and does not participate in the reaction. Acetone is separated from lower and higher boiling compounds in a two-step distillation. 

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. 

A simplified equipment flow sheet for the acetaldehyde process is given in Hydrocarbon Process. 44(11), 159(1965). Since this is a proprietary process, only sketchy information is supplied with regards to temperature, pressure, and stream composition at each piece of equipment. Some of this information can be deduced fi om the information supplied for the raw materials and utilities requirements per short ton of acetaldehyde. 

No comparative economic evaluation of all the known commercial acetaldehyde processes has been described in the literature. Recently, the Wacker process was compared with the acetylene process, using European economic data (29). An economic comparison of the one-stage vs. two-stage Wacker processes, using German wage and material price levels of 1961, is given in Table VIII. 

Apart from the commercial acetaldehyde processes thus far discussed, one noncommercial process currently being developed deserves some attention. It consists of isomerizing ethylene oxide to acetaldehyde, and its literature is summarized in Table XI. Since ethylene oxide is made by oxidizing ethylene, this method may be regarded as a variation of the Wacker process. 

In contrast to acetaldehyde, where a choice exists between several well-established manufacturing processes, vinyl acetate has been produced until recently by two principal methods—i.e., by the catalytic vapor-phase acylation of acetylene and by the acetalization of acetaldehyde. The new procedure for vinyl acetate manufacture consists of oxidizing ethylene in acetic acid—a process closely related to the Wacker acetaldehyde process. All three manufacturing approaches are outlined in Table XII. 

The formation of vinyl acetate from ethylene was first reported by Moiseev et al. (31), The compound was obtained by reaction of ethylene with PdCl2 in an acetic acid solution containing sodium acetate. Whether in this medium vinyl acetate formation occurs via the monomeric [PdCla C2H4] TT-complex, postulated as intermediate in the Wacker acetaldehyde process, or via the dimer (C2H4 PdCl2)2, previously described by... 

Several plants have been built operating according to the two-stage technology (Figure 4) [48, 49] quite analogously to the acetaldehyde process described above, with air as oxidant and a catalyst cycle. An important by-product in acetone manufacture is propionaldehyde, which is separated by extractive distillation... 

The future of the commercial acetaldehyde processes mainly depends on the availability of cheap ethylene. Acetaldehyde has been replaced as a precursor for 2-ethylhexanol ( aldol route ) or acetic acid (via oxidation cf. Sections 2.1.2.1 and 2.4.4). New processes for the manufacture of acetic acid are the Monsanto process (carbonylation of methanol, cf. Section 2.1.2.1), the Showa Denko one-step gas-phase oxidation of ethylene with a Pd-heteropolyacid catalyst [75, 76], and Wacker butene oxidation [77]. Other outlets for acetaldehyde such as pentaerythritol and pyridines cannot fill the large world production capacities. Only the present low price of ethylene keeps the Wacker process still attractive. 

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). 

The same principal products were detected in the photolysis of an alcohol and its corresponding ether. For example, ethanol and ethyl ether gave ethylene (process a), acetaldehyde (process b), and formaldehyde (process b). In an attempt to find out whether the formaldehyde and... 

The overall reaction is shown in equation (29). This reaction is similar to the Wacker acetaldehyde process. The same catalyst system is used, except that the vinyl acetate process is carried out in the vapor phase over a heterogeneous solid catalyst, whereas in the acetaldehyde process the catalyst is in solution in the liquid phase. 

Single-Stage Acetaldehyde Process from Ethylene... 

The oxidation of olefins to carbonyl compounds in the presence of PdCl2 and CUCI2, which represents the catalysts of the commercial acetaldehyde process, is accompanied by chlorinating reactions. These side reactions can reduce the yield of the desired products considerably. Different ways have been suggested to reoxidize Pd°, avoiding the chlorinating behavior of CUCI2. 

The acetaldehyde process was developed in 1958 by Knapsack-Griesheim [20]. In the first stage, acetaldehyde is reacted with hydrogen cyanide to form lactonitrile, which in turn is mixed with catalytic phosphoric acid and heated rapidly to 600-700°C. The mixture is then chilled rapidly to 50°C in a solution of 30% phosphoric acid to form the crude acrylonitrile product. 

In 1960, quickly after the introduction of the Celanese process, Wacker-Chemie commercialized a liquid phase vinyl acetate process which represented and extension of its earlier acetaldehyde process wherein acetic acid was simply substituted for water. (See equation [19]. This chemical transformation is also referred to as oxidative acetoxylation.) As shown in Figure 2, wherein R=Ac, the liquid phase oxidative acetoxylation of ethylene utilized the same catalytic cycle as the Wacker-Chemie acetaldehyde process. 

The major route for the industrial production of vinyl acetate, the monomer of polyvinyl acetate (emulsion paints, adhesives) and its hydrolysis product, polyvinyl alcohol (textiles, food packaging) is closely related to the Wacker acetaldehyde process, but the industrial catalysts are heterogeneous. A mixture of ethene, oxygen and acetic acid is passed over a palladium catalyst supported on alumina at 100-200°C. The overall reaction is H C=CH2-hCHjCO H-hyO ->H2C=CHC02CH3 -hH O. Ethene is no longer cheap, so that work is being pursued to make vinyl acetate from synthesis gas (p. 384). 

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