Ethylene acetaldehyde synthesis

Reaction Mechanism. Any mechanism proposed for the vinylation of acetic acid by the hexenes must be able to account for the production of the high boiling products, 1,2-hexandiol mono- and diacetates (VIII, IX and X), and possibly hexylidene diacetate, as well as the hexenyl acetates. The currently accepted mechanism for synthesizing vinyl acetate from ethylene and acetic acid is derived from that postulated by Henry (i, 19), based on studies of the Wacker acetaldehyde synthesis. The key step in this mechanism is an insertion reaction (18). 

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

Acetaldehyde (ethanal) used to be the most important intermediate for the production of acetic acid. However, since 1970 the production of acetaldehyde lost importance as acetic acid production switched increasingly to methanol carbonylation. The reason for this development has to do with the different feedstock base for both processes. While the production of acetaldehyde starts from ethylene, the synthesis of acetic acid via methanol carbonylation uses the significantly cheaper synthesis gas (CO/H2) as feed, from which methanol is made first followed by a carbonylation step (see Section 6.15 for details). 

The industrial synthesis of acetaldehyde from ethylene IS shown on page 644... 

Not so for synthesis in the chemical industry where a compound must be prepared not only on a large scale but at low cost There is a pronounced bias toward reactants and reagents that are both abundant and inexpensive The oxidizing agent of choice for example in the chemical industry is O2 and extensive research has been devoted to develop mg catalysts for preparing various compounds by air oxidation of readily available starting materials To illustrate air and ethylene are the reactants for the industrial preparation of both acetaldehyde and ethylene oxide Which of the two products is ob tamed depends on the catalyst employed... 

Since 1960, the Hquid-phase oxidation of ethylene has been the process of choice for the manufacture of acetaldehyde. There is, however, stiU 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). 

The price of acetaldehyde duriag the period 1950 to 1973 ranged from 0.20 to 0.22/kg. Increased prices for hydrocarbon cracking feedstocks beginning in late 1973 resulted in higher costs for ethylene and concurrent higher costs for acetaldehyde. The posted prices for acetaldehyde were 0.26/kg in 1974, 0.78/kg in 1985, and 0.92/kg in 1988. The future of acetaldehyde growth appears to depend on the development of a lower cost production process based on synthesis gas and an increase in demand for processes based on acetaldehyde activation techniques and peracetic acid. 

Key intermediates in the industrial preparation of both nicotinamide and nicotinic acid are alkyl pyridines (Fig. 1). 2-Meth5l-5-ethylpyridine (6) is prepared in ahquid-phase process from acetaldehyde. Also, a synthesis starting from ethylene has been reported. Alternatively, 3-methylpyridine (7) can be used as starting material for the synthesis of nicotinamide and nicotinic acid and it is derived industrially from acetaldehyde, formaldehyde (qv), and ammonia. Pyridine is the principal product from this route and 3-methylpyridine is obtained as a by-product. Despite this and largely due to the large amount of pyridine produced by this technology, the majority of the 3-methylpyridine feedstock is prepared in this fashion. 

Other synthetic methods have been investigated but have not become commercial. These include, for example, the hydration of ethylene in the presence of dilute acids (weak sulfuric acid process) the conversion of acetylene to acetaldehyde, followed by hydrogenation of the aldehyde to ethyl alcohol and the Fischer-Tropsch hydrocarbon synthesis. Synthetic fuels research has resulted in a whole new look at processes to make lower molecular weight alcohols from synthesis gas. 

Other Methods of Preparation. In addition to the direct hydration process, the sulfuric acid process, and fermentation routes to manufacture ethanol, several other processes have been suggested. These include the hydration of ethylene by dilute acids, the hydrolysis of ethyl esters other than sulfates, the hydrogenation of acetaldehyde, and the use of synthesis gas. None of these methods has been successfilUy implemented on a commercial scale, but the route from synthesis gas has received a great deal of attention since the 1974 oil embargo. 

Ethylene and propylene, the simplest alkenes, are the two most important organic chemicals produced industrially. Approximately 26 million tons of ethylene and 17 million tons of propylene are produced each year in the United States for use in the synthesis of polyethylene, polypropylene, ethylene glycol, acetic acid, acetaldehyde, and a host of other substances (Figure 6.11. 

With the growing prominence of the petrochemicals industry this technology was, in turn, replaced by direct air oxidation of naphtha or butane. Both these processes have low selectivities but the naphtha route is still used since it is a valuable source of the co-products, formic and propanoic acid. The Wacker process, which uses ethylene as a feedstock for palladium/copper chloride catalysed synthesis of acetaldehyde, for which it is still widely used (Box 9.1), competed with the direct oxidation routes for a number of years. This process, however, produced undesirable amounts of chlorinated and oxychlorinated by-products, which required separation and disposal. 

Ethene is used as a starting material for the synthesis of many industrial compounds, including ethanol, ethylene oxide, ethanal (acetaldehyde), and polyethylene (PE). 

Oxygen has major uses in the chemical industry too. It is used to oxidize methane, ethylene, and other hydrocarbons. Oxidation of methane produces synthesis gas. Ethylene oxidation yields products such as ethylene oxide, acetaldehyde, and acetic acid. Oxygen also is used in making many commercial inorganic compounds including various metal oxides, oxoacids, and 0x0-salts. 

This process, developed in Germany, was one of the first to foretell the importance of alkenes following World War II. About 4 million pounds of aldehydes are produced yearly by this method. Acetaldehyde is easily oxidized to acetic acid and the overall conversion of ethylene to the acid represents a principal route to its synthesis, ft has been said that the invention of the Wacker process was a triumph of common sense. 82... 

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... 

Acetic acid is also an industrial chemical. It serves as a solvent, a starting material for synthesis, and a catalyst for a wide variety of reactions. Some industrial acetic acid is produced from ethylene, using a catalytic oxidation to form acetaldehyde, followed by another catalytic oxidation to acetic acid. 

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... 

Process Economics Program Report SRI International. Menlo Park, CA, Isocyanates IE, Propylene Oxide 2E, Vinyl Chloride 5D, Terephthalic Acid and Dimethyl Terephthalate 9E, Phenol 22C, Xylene Separation 25C, BTX, Aromatics 30A, o-Xylene 34 A, m-Xylene 25 A, p-Xylene 93-3-4, Ethylbenzene/Styrene 33C, Phthalic Anhydride 34B, Glycerine and Intermediates 58, Aniline and Derivatives 76C, Bisphenol A and Phosgene 81, C1 Chlorinated Hydrocarbons 126, Chlorinated Solvent 48, Chlorofluorocarbon Alternatives 201, Reforming for BTX 129, Aromatics Processes 182 A, Propylene Oxide Derivatives 198, Acetaldehyde 24 A2, 91-1-3, Acetic Acid 37 B, Acetylene 16A, Adipic Acid 3 B, Ammonia 44 A, Caprolactam 7 C, Carbon Disulfide 171 A, Cumene 92-3-4, 22 B, 219, MDA 1 D, Ethanol 53 A, 85-2-4, Ethylene Dichloride/Vinyl Chloride 5 C, Formaldehyde 23 A, Hexamethylenediamine (HMDA) 31 B, Hydrogen Cyanide 76-3-4, Maleic Anhydride 46 C, Methane (Natural Gas) 191, Synthesis Gas 146, 148, 191 A, Methanol 148, 43 B, 93-2-2, Methyl Methacrylate 11 D, Nylon 6-41 B, Nylon 6,6-54 B, Ethylene/Propylene 29 A, Urea 56 A, Vinyl Acetate 15 A. 

Figure 1.2 A few illustrative examples of chemicals and classes of chemicals that are manufactured by homogeneous catalytic processes. In 1.6 low-pressure methanol synthesis by a heterogeneous catalyst is one of the steps. In 1.9 it is ethylene that is converted to acetaldehyde. In 1.7 all the available building blocks may be used.

Ever since the initial discovery of the Wacker process [1], i.e. the Pd/Cu-catalyzed oxidation of ethylene to acetaldehyde (1) in water, methods for the palladium (II) - mediated oxidative functionalization of alkenes have found widespread application in the synthesis of complex molecules [2J. 

Acrolein and condensable by-products, mainly acrylic acid plus some acetic acid and acetaldehyde, are separated from nitrogen and carbon oxides in a water absorber. However in most industrial plants the product is not isolated for sale, but instead the acrolein-rich effluent is transferred to a second-stage reactor for oxidation to acrylic acid. In fact the volume of acrylic acid production ca. 4.2 Mt/a worldwide) is an order of magnitude larger than that of commercial acrolein. The propylene oxidation has supplanted earlier acrylic acid processes based on other feedstocks, such as the Reppe synthesis from acetylene, the ketene process from acetic acid and formaldehyde, or the hydrolysis of acrylonitrile or of ethylene cyanohydrin (from ethylene oxide). In addition to the (preferred) stepwise process, via acrolein (Equation 30), a... 

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