Acetylene vinyl acetate process

Ethyne is the starting point for the manufacture of a wide range of chemicals, amongst which the most important are acrylonitrile, vinyl chloride, vinyl acetate, ethanal, ethanoic acid, tri- and perchloro-ethylene, neoprene and polyvinyl alcohol. Processes such as vinylation, ethinylation, carbonylation, oligomerization and Reppe processes offer the possibility of producing various organic chemicals cheaply. Used in oxy-acetylene welding. 

Liquid- and vapor-phase processes have been described the latter appear to be advantageous. Supported cadmium, zinc, or mercury salts are used as catalysts. In 1963 it was estimated that 85% of U.S. vinyl acetate capacity was based on acetylene, but it has been completely replaced since about 1982 by newer technology using oxidative addition of acetic acid to ethylene (2) (see Vinyl polymers). In western Europe production of vinyl acetate from acetylene stiU remains a significant commercial route. 

Vinyl ethers are prepared in a solution process at 150—200°C with alkaH metal hydroxide catalysts (32—34), although a vapor-phase process has been reported (35). A wide variety of vinyl ethers are produced commercially. Vinyl acetate has been manufactured from acetic acid and acetylene in a vapor-phase process using zinc acetate catalyst (36,37), but ethylene is the currently preferred raw material. Vinyl derivatives of amines, amides, and mercaptans can be made similarly. A/-Vinyl-2-pyrroHdinone is a commercially important monomer prepared by vinylation of 2-pyrroHdinone using a base catalyst. 

The principal chemical markets for acetylene at present are its uses in the preparation of vinyl chloride, vinyl acetate, and 1,4-butanediol. Polymers from these monomers reach the consumer in the form of surface coatings (paints, films, sheets, or textiles), containers, pipe, electrical wire insulation, adhesives, and many other products which total biUions of kg. The acetylene routes to these monomers were once dominant but have been largely displaced by newer processes based on olefinic starting materials. 

Most of the vinyl acetate produced in the United States is made by the vapor-phase ethylene process. In this process, a vapor-phase mixture of ethylene, acetic acid, and oxygen is passed at elevated temperature and pressures over a fixed-bed catalyst consisting of supported palladium (85). Less than 70% oxygen, acetic acid, and ethylene conversion is realized per pass. Therefore, these components have to be recovered and returned to the reaction zone. The vinyl acetate yield using this process is typically in the 91—95% range (86). Vinyl acetate can be manufactured also from acetylene, acetaldehyde, and the hquid-phase ethylene process (see Vinyl polymers). 

The commercial process for the production of vinyl acetate monomer (VAM) has evolved over the years. In the 1930s, Wacker developed a process based upon the gas-phase conversion of acetylene and acetic acid over a zinc acetate carbon-supported catalyst. This chemistry and process eventually gave way in the late 1960s to a more economically favorable gas-phase conversion of ethylene and acetic acid over a palladium-based silica-supported catalyst. Today, most of the world s vinyl acetate is derived from the ethylene-based process. The end uses of vinyl acetate are diverse and range from die protective laminate film used in automotive safety glass to polymer-based paints and adhesives. 

Vinyl acetate is one of many compounds where classical organic chemistry has been replaced by a catalytic process. It is also an example of older acetylene chemistry becoming outdated by newer processes involving other basic organic building blocks. Up to 1975 the preferred manufacture of this important monomer was based on the addition of acetic acid to the triple bond of acetylene using zinc amalgam as the catalyst, a universal reaction of alkynes. 

In 1969, 90% of vinyl acetate was manufactured by this process. By 1975 only 10% was made from acetylene, and in 1980 it was obsolete. Instead, a newer method based on ethylene replaced this old acetylene chemistry. A Wacker catalyst is used in this process similar to that for acetic acid. Since the acetic acid can also be made from ethylene, the basic raw material is solely ethylene, in recent years very economically advantageous as compared to acetylene chemistry. An older liquid-phase process has been replaced by a vapor-phase reaction run at 70-140 psi and 175-200°C. Catalysts may be (1) C—PdCb—CuCb, (2) PdClj—AI2O3, or (3) Pd—C, KOAc. The product is distilled water, acetaldehyde, and some polymer are... 

During the same period in Germany Farbenfabriken Bayer, in cooperation with Farbwerke Hoechst, developed a vapor-phase process, which avoids many of the possible corrosion problems. This process has not yet been practiced by Bayer on a large scale but has been licensed widely, especially in Japan (4, 5), where, as a result, acetylene is no longer used to produce vinyl acetate. 

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 older process for the production of vinyl acetate (melting point -93.2°C, boiling point 72.3°C, density 0.9317) involved the reaction of acetylene with acetic acid in the liquid phase with zinc amalgam as the catalyst. 

Other catalytic reactions carried out in fluidized-bed reactors are the oxidation of naphthalene to phthalic anhydride [2, 6, 80] the ammoxidation of isobutane to mcthacrylonitrilc [2] the synthesis of maleic anhydride from the naphtha cracker C4 fraction (Mitsubishi process [81, 82]) or from n-butane (ALMA process [83], [84]) the reaction of acetylene with acetic acid to vinyl acetate [2] the oxychlorination of ethylene to 1,2-di-chloroethane [2, 6, 85, 86] the chlorination of methane [2], the reaction of phenol with methanol to cresol and 2,6-xylenol [2, 87] the reaction of methanol to gasoline... 

Acetylene still is a preferred raw material for some products, but it has been largely replaced by ethylene for many others. Chemicals once produced from acetylene by processes now considered outdated include vinyl chloride, vinyl acetate, acetaldehyde, acrylonitrile, neoprene, and chlorinated solvents. 

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. 

Even if new processes of synthesis were developed from alcohols, like catalytic vinylation with ethylene or vinyl exchange with vinyl acetate, the major commercial route for VE monomers seams to be still the Reppe method based on reaction, in basic conditions, of acetylene with the corresponding alcohols [96,97,100] ... 

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. 

A recent study indicates that if the Wacker process proves to be substantially cheaper than the acetylene route, no more vinyl acetate plants will be built in the United States, based on the latter process (38). Table XV gives estimated production costs for manufacturing vinyl acetate. Several companies are building or have already built plants to manufacture vinyl acetate from ethylene. These include Distillers Co., Ltd., British Celanese, Imperial Chemical Industries, and Celanese Corp., to name only a few. 

Acetoxylations (oxyacylations) have to be seen in context with olefin oxidation to carbonyl compounds (Wacker process, Section 2.4.1). With the lowest olefin, ethylene, acetaldehyde is formed. In water-free acetic acid no reaction takes place. Only in the presence of alkali acetates - the acetate ion shows higher nu-cleophilicity than acetic acid - ethylene reacts with palladium salts (eq. (1)) to give vinyl acetate, the expected product, as first reported by Moiseev et al. [1]. Stem and Spector [2] independently used [HP04] as base in a mixture of isooctane and acetic acid. This reaction could be exploited for a commercial process to produce vinyl acetate and closed the last gap replacing acetylene by the cheaper ethylene, a petrochemical feed material, for the production of large-tonnage chemical intermediates. 

The liquid phase process employing an acid solution and mercury salts is also sufficiently flexible to enable other reactions to be conducted, suggestions of which may be found in the patent literature.0311 Thus, ethylidine diacetate, or dipropionate may be obtained by passing acetylene and acetic or propionic acid vapors into the aqueous acid containing mercury salts. The vinyl ester of trichloracetic is obtained when trichloracetic acid is used in a similar manner. Acetylene and isobutanol vapor passed into a suspension of mercuric sulfate in the alcohol form ethylidene-diisobutyl ether. Similarly, the use of ethylene glycol gives rise to ethylene ethylidine ether. 

Morrison, ," Acetylene still has benefits for malting vinyl acetate", Oil and GasJ.[Memot S) 104-116(1969). Vinyl acetate. Vapor phase process. Bntish Chem. Engng, Process SCAN (May 1970). 

Vinyl acetate was first described in a German patent awarded to Fritz Klatte and assigned to Chemishe Fabriken Grieshiem-EIectron in 1912. It was identified as a minor by-product of the reaction of acetic acid and acetylene to produce ethylidene diacetate. By 1925, commercial interest in vinyl acetate monomer and the polymer, polyvinyl acetate, developed and processes for their production on an industrial scale were devised. The first commercial process for vinyl acetate monomer involved the addition of acetic acid to acetylene in the vapor phase using a zinc acetate catalyst supported on activated carbon. This process was developed by Wacker Chemie in the early 1930s and dominated the production of vinyl acetate until the 1960s when an ethylene-based process was commercialized which supplanted the earlier acetylene technology [24]. 

Vinyl acetate monomer can be produced by the vapor phase reaction of acetylene and acetic acid using a zinc acetate on activated carbon catalyst. The reaction can be carried out in either the liquid or vapor phase but the vapor phase process is more efficient [28]. The chemistry is as follows ... 

There are still some acetylene-based vinyl acetate plants in operation in Europe and the Far East. However, the process is commercially obsolete and new facilities are based on the reaction of ethylene and oxygen with acetic acid. 

Vinyl acetate monomer can be synthesized by the reaction of acetic acid with either acetylene or with ethylene. For the production of vinyl acetate from acetic acid and acetylene, the following process was adopted a gaseous mixture of acetylene and acetic acid was reacted at about 200°C in the presence of active carbon impregnated with zinc acetate... 

Expanding on the mercuric sulfate - sulfuric acid technology, it was known as early as 1912 that addition of a single equivalent of acetic acid to acetylene in the presence of mercuric sulfate and sulfuric acid resulted in the generation of vinyl acetate (a mere laboratory curiosity at the time) whereas addition of two or more equivalents of acetic acid provided ethylidene diacetate (1,1-diacetoxyethane, EDA). EDA was known to evolve acetaldehyde upon heating in the presence of acids. Upon complete removal of a mole of acetaldehyde, an equimolar amount of acetic anhydride could then be distilled from the residue. If one balances the sequential processes as shown in equations [3] through [6], one finds that the process is in stoichiometric balance for conversion of acetylene and air to cellulose acetate without by-products. (In practice there is some net acetic acid production since cellulose is never completely dry.)... 

Long term, the most significant n6w development in the acetyl market in this period was the introduction of vinyl acetate. While the liquid phase addition of acetic acid to acetylene in the presence of a mercuric sulfate catalyst at 60-100°C to generate vinyl acetate was first discovered in 1912, it was introduced as a commercial scale process in 1925 and introduced vinyl acetate to the market as a commodity scale product. However, the mercury process was inefficient and toxic and did not last long as a commercial process. In 1921, it was discovered that Zn acetate on activated charcoal could catalyze the addition of acetic acid to acetylene in the vapor phase. By 1940, sequential improvements in the stability of activated charcoal provided Zn on carbon catalysts that were sufficiently stable to render any remaining Hg based processes untenable. By about 1950 the mercury based process was extinct and completely replaced with the vapor phase Zn on activated charcoal process which was operated at 170-210°C and pressures just exceeding 1 atmosphere with an excess of acetylene. However, vinyl acetate still represented a relatively small portion of the market in acetyl related products. 

In the following discussion the major methods that have been developed for the synthesis of vinyl acetate in particular and vinyl ester monomers in general are described. The oldest process for making vinyl acetate and some of the more volatile vinyl ester monomers is the condensation of acetylene with a carboxylic acid ... 

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