Zinc oxide, dehydrogenation catalyst

Eucken (88,89) and Wicke (90) have tried to explain the dehydrogenation and dehydration of isopropyl alcohol by an electron interchange between the alcohol and the zinc oxide alumina catalysts used for these conversions. We shall modify the mechanism proposed by Eucken and Wicke, following the theory of chemisorption. Contrary to these authors, we do not believe that the positions of the zinc and oxygen ions on the surface of the zinc oxide catalysts have any appreciable influence upon... 

Raizada, V., Tripathi, V., and Lai, D., Kinetic studies on dehydrogenation of butanol to butyraldehyde using zinc oxide as catalyst, J. Chem. Tech. Biotechnol, 56 265-270 (1993). 

General Description of Process. Ethylbenzene and steam are fed continuously into an evaporator (Fig. 9-8). The mixed vapors, after preheating in heat exchangers, are led into a converter, where dehydrogenation of ethylbenzene to styrene occurs in the presence of a zinc oxide-based catalyst. The gases leaving the converter are partially cooled in the heat exchangers referred to above and then further cooled in a condenser system. 

The dehydrogenation of 2-butanol is conducted in a multitube vapor-phase reactor over a zinc oxide (20—23), copper (24—27), or brass (28) catalyst, at temperatures of 250—400°C, and pressures slightly above atmospheric. The reaction is endothermic and heat is suppHed from a heat-transfer fluid on the shell side of the reactor. A typical process flow sheet is shown in Figure 1 (29). Catalyst life is three to five years operating in three to six month cycles between oxidative reactivations (30). Catalyst life is impaired by exposure to water, butene oligomers, and di-j -butyl ether (27). 

The dehydrogenation reaction is carried out using either copper or zinc oxide catalyst at approximately 450-550°C. A 95% yield is obtained ... 

Methyl ethyl ketone may also he produced hy the catalyzed dehydrogenation of sec-hutanol over zinc oxide or brass at about 500°C. The yield from this process is approximately 95%. MEK is used mainly as a solvent in vinyl and acrylic coatings, in nitrocellulose lacquers, and in adhesives. It is a selective solvent in dewaxing lubricating oils where it dissolves the oil and leaves out the wax. MEK is also used to synthesize various compounds such as methyl ethyl ketone peroxide, a polymerization catalyst used to form acrylic and polyester polymers and methyl pentynol by reacting with acetylene ... 

Hitachi Cable Ltd. (35) has claimed that dehydrogenation catalysts, exemplified by chromium oxide—zinc oxide, iron oxide, zinc oxide, and aluminum oxide—manganese oxide inhibit drip and reduce flammability of a polyolefin mainly flame retarded with ATH or magnesium hydroxide. Proprietary grades of ATH and Mg(OH)2 are on the market which contain small amounts of other metal oxides to increase char, possibly by this mechanism. 

Butanol, reaction over reduced nickel oxide catalysts, 35 357-359 effect of ammonia, 35 343 effect of hydrogen, 35 345 effect of pyridine, 35 344 effect of sodium, 35 342, 351 effect of temperature, 35 339 over nickel-Kieselguhr, 35 348 over supported nickel catalysts, 35 350 Butanone, hydrogenation of, 25 103 Butene, 33 22, 104-128, 131, 135 adsorption on zinc oxide, 22 42-45 by butyl alcohol dehydration, 41 348 chemisorption, 27 285 dehydrogenation, 27 191 isomerization, 27 124, 31 122-123, 32 305-308, 311-313, 41 187, 188 isomerization of, 22 45, 46 isomers... 

The preparation of ketones by dehydrogenation of secondary alcohols over zinc and copper catalysts and the decarboxylation condensation of acids over manganous oxide or thoria have been adequately covered by standard reference books on catalysis. However, the more complete but equally serviceable catalytic syntheses involving either an aldol or a Tischenko ester type of condensation have been virtually ignored. 

Styrene (phenyl ethylene, vinyl benzene freezing point -30.6°C, boiling point 145°C, density 0.9059, flash point 31.4°C) is made from ethylbenzene by dehydrogenation at high temperature (630°C) with various metal oxides as catalysts, including zinc, chromium, iron, or magnesium oxides coated on activated carbon, alumina, or bauxite (Fig. 1). Iron oxide on potassium carbonate is also used. 

Skeletal Cu-Zn catalysts show great potential as alternatives to coprecipitated Cu0-Zn0-Al203 catalysts used commercially for low temperature methanol synthesis and water gas shift (WGS) reactions. They can also be used for other reactions such as steam reforming of methanol, methyl formate production by dehydrogenation of methanol, and hydrogenolysis of alkyl formates to produce alcohols. In all these reactions zinc oxide-promoted skeletal copper catalysts have been found to have high activity and selectivity. 

P10-8b Methyl ethyl ketone (MEK) is an important industrial solvent that can be produced from the dehydrogenation of butan-2-01 (Bu) over a zinc oxide catalyst [Ind. Eng. Chem. Res., 27, 2050 (1988)] ... 

We have investigated a series of the dehydrogenating catalysts for this reaction. Our attention was focused on two of them. Further study of 2,3-butanediol dehydrogenation and oxidative dehydrogenation to butadione was performed using zinc-chromium oxide catalysts and vanadium-magnesium oxide catalysts as well. 

In the presence of zinc oxide catalysts prepared by precipitation from a zinc sulfate solution the proportion of dehydration and dehydrogenation... 

A comparison, however, of zinc oxide catalysts prepared in different ways, i.e. (A) precipitation of zinc hydroxide from zinc sulfate, (B) dry process commercial zinc oxide, and (C) hydrolysis of zinc isopropoxide in moist air, showed that the mode of preparation had a marked effect on the catalyst action. The percentage of olefin formed at a given temperature varied from 5 to 88 for isopropanol, 10 to 20 for ethanol, 1 to 31.5 for isobutanol, and 2 to 15 for n-propanol and butanol. In general, catalyst A was best for dehydration, and catalyst B for dehydrogenation, except in the case of ethanol where they were about the equal. Catalyst C behaved about the same as B, except in the case of ethanol, in which case it was a better dehydration material. 

Since the reaction occurs with a decrease in volume of two to one, it will be favorably affected by high pressures. In operation, temperatures of 250° to 550° C., pressures of over 50 atmospheres, and hydrogenating-dehydrogenating catalysts as zinc and chromium oxides or zinc chlorides are claimed. No yields are mentioned in the examples that are given. 

Alumina catalysts activated by additions of dehydrogenating catalysts, e.g., nickel oxide, copper oxide or sulfide, zinc oxide or sulfide, cobalt selenide, zinc phosphate, cadmium tungstate, mixtures of the oxides of zinc and tungsten, of cadmium and molybdenum, etc., are claimed to be superior in the formation of acetaldehyde from mixtures of steam and acetylene at 350° to 400° C.l-la Zinc oxide catalysts may be activated in a similar way by the addition of small amounts of molybdates or molybdic acid, and are effective at 300° to 350° C.121b... 

This phase seems to be predominating in Zi, the sample obtained by solid state decomposition in presence of urea. This sample could have additional porosity, due to loss of CO2 during synthesis of and/or calcination. This could possibly result in exposure of additional catalytically active centers, making it highly active catalyst. The data in Table 1 illustrates the relative catalytic activity of various zinc oxide towards decomposition of propan-2-ol at 653"K at a contact time of 1.6 seconds. Under the above conditions all the catalyst showed dehydrogenation activity only the reactivity following the order Zi>Z2 4 Z5>Z3. 

The experiments performed have completely confirmed the theoretical calculations cyclohexane, cyclohexene, and piperidine are actually dehydrogenated on cadmium oxide at 400-500° (with partial reduction of CdO to Cd as a side reaction). This is the case of predicting a new catalyst on the basis of the multiplet theory. Cyclohexene and piperidine but not cyclohexane (see above) are, in fact, dehydrogenated on zinc oxide. None of the hydrocarbon studied could be dehydrogenated on beryllium and magnesium oxides. 

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