Zinc acetate, catalyst activator

The commercial process for vinyl acetate production has evolved over the years. Early in the 1930s, Wacker developed a process based upon the gas-phase conversion of acetylene and acetic acid over a zinc acetate catalyst supported on activated carbon. Later, in 1960s, a more economically favourable gas-phase process was introduced involving the acetoxylation of ethene over a Pd-based silica supported catalyst. Ethene, acetic acid and oxygen reacted to form vinyl acetate and water [122,237-242] ... 

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 ... 

The reactor simulated is a wall-cooled fixed-bed catalytic reactor reported by Valstar [7] for the synthesis of vinyl acetate from acetic acid and acetylene with zinc acetate on activated carbon as catalyst as given in Sect. 7.1.2. 

Acetic anhydride adds to acetaldehyde in the presence of dilute acid to form ethyUdene diacetate [542-10-9], boron fluoride also catalyzes the reaction (78). Ethyfldene diacetate decomposes to the anhydride and aldehyde at temperatures of 220—268°C and initial pressures of 14.6—21.3 kPa (110—160 mm Hg) (79), or upon heating to 150°C in the presence of a zinc chloride catalyst (80). Acetone (qv) [67-64-1] has been prepared in 90% yield by heating an aqueous solution of acetaldehyde to 410°C in the presence of a catalyst (81). Active methylene groups condense acetaldehyde. The reaction of isobutfyene/715-11-7] and aqueous solutions of acetaldehyde in the presence of 1—2% sulfuric acid yields alkyl-y -dioxanes 2,4,4,6-tetramethyl-y -dioxane [5182-37-6] is produced in yields up to 90% (82). 

Many more examples exist for reduction of the carhonyl only. Over an osmium catalyst [763] or platinum catalyst activated by zinc acetate and ferrous chloride [782] cinnamaldehyde was hydrogenated to cinnamyl alcohol. The same product was obtained by gentle reduction with lithium aluminum hydride at —10° using the inverse technique [609], by reduction with alane (prepared in situ from lithium aluminum hydride and aluminum chloride)... 

Chromium compounds increase the activity of platinum catalysts by increasing the electron densities of the active sites. jhe addition of ferrous sulfate, which promotes the hydrogenation of carbonyl groups, and zinc acetate, which inhibits the hydrogenation of double bonds, to platinum gives a catalyst system capable of effecting the selective hydrogenation of an unsaturated aldehyde to an unsaturated alcohoP - (Eqn. 11.12). ... 

It has been reported that active charcoal from waste industrial catalyst Zn(OAc)2/C could be recovered by ultrasonic washing [70]. After ultrasonic washing in water for 15 min at ambient temperature followed by calcining at 650 °C, the zinc acetate could be removed effectively and the regenerated active charcoal was found to have a quality up to the standard of Forestry Department of... 

Table 1 indicates the rate constants (k k2> and activation energies (E E2) for zinc acetate and dibutyl tin oxide catalyzed reactions for PBT 50 and HQDA + TA 50 mole% concentration. The values of kl are found to be the range of 0.03136 to 0.5 kJ/mole while for k2 it is in the range of 0.004 to 0.1 kJ/mole. No major decrease in the value of the rate constants ki and k2 ate noticed. The activation energy values indicate that DBTO at 0.25 mole% concentration is a suitable catalyst for the PBT 50 mole% concentration. 

The process is carried out in the gas phase at a temperatures above 160°C. The reaction is exothermic, so heat control in the production process is important. Vinylacetate is used as intermediate in a large number of production processes. The catalysts can be produced by impregnation of an activated carbon with zinc acetate, followed by drying. The zinc concentration is in the order of 11 up to 13%. The optimal activated carbon support is a high steam activated and acid washed 3 or 4 mm extrudate like the NORIT RX 3 EXTRA or NORIT RX 4 EXTRA. Important characteristics of the impregnated carbon are ... 

UPRs based on a mixture of maleic anhydride, phthalic anhydride and adipic acid in a molar ration of 1 2 2 were prepared in the presence of the polyesterification catalysts, i.e. lead dioxide, p-toluenesulfonic acid monohydrate and zinc acetate dihydrate, and next crossHnked with styrene by using MEKP as the initiator and cobalt naphthenate (CoNp) as the promoter [197]. Most often, the catalysts used in the polyesterification process cannot be easily separated from the polyester, thus the effect of the residual catalysts on the curing process and color of the cured polyester resin should be taken into account. It was shown that the residual catalyst could affect the curing reaction even in a small amount (Table 28), increasing the activation energy a, frequency factor ko and the reaction order x. 

The alternating copolymerization of cis/fraws-limonene oxide and carbon dioxide can be achieved with p-diiminate zinc acetate complexes (Scheme 5). The balance between high catalyst activity and selectivity is optimal with catalyst complex 8 (see Scheme 5, right) at 25°C. Catalysts exhibits high selectivity for the trans diasteriomer (% trans in the copolymer is >98%). The biodegradable polycarbonates have MWs in the range of 4.0-10.8 kg/mol, which can be controlled by the [epoxide]/[Zn] ratio, CO2 pressure, and reaction time. They also have narrow... 

Lazier of Du Pont published many patents covering the preparation of metal chromites." These were formed by precipitation from a solution of zinc nitrate and chromic acid with ammonia at pH 6.8. The zinc ammine complex obtained was decomposed at about 400°C to give the mixed oxides. As Adkins noted, his copper chromite equivalent was extracted with dilute acetic acid solution to adjust the copper content. It is not clear whether the same treatment was ever used in producing methanol catalysts or even whether the zinc ammine intermediate was produced commercially. One problem with the Lazier preparation was the difficulty in controlling the exothermic decomposition of the ammine that could affect the catalyst activity. 

In the fibrous acetylation process, part or all of the acetic acid solvent is replaced with an inert dilutent, such as toluene, benzene, or hexane, to maintain the fibrous stmcture of cellulose throughout the reaction. Perchloric acid is often the catalyst of choice because of its high activity and because it does not react with cellulose to form acid esters. Fibrous acetylation also occurs upon treatment with acetic anhydride vapors after impregnation with a suitable catalyst such as zinc chloride (67). 

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