Dehydrogenation of ethanol

Acetaldehyde, first used extensively during World War I as a starting material for making acetone [67-64-1] from acetic acid [64-19-7] is currendy an important intermediate in the production of acetic acid, acetic anhydride [108-24-7] ethyl acetate [141-78-6] peracetic acid [79-21 -0] pentaerythritol [115-77-5] chloral [302-17-0], glyoxal [107-22-2], aLkylamines, and pyridines. Commercial processes for acetaldehyde production include the oxidation or dehydrogenation of ethanol, the addition of water to acetylene, the partial oxidation of hydrocarbons, and the direct oxidation of ethylene [74-85-1]. In 1989, it was estimated that 28 companies having more than 98% of the wodd s 2.5 megaton per year plant capacity used the Wacker-Hoechst processes for the direct oxidation of ethylene. 

The reaction kinetics for the dehydrogenation of ethanol are also weU documented (309—312). The vapor-phase dehydrogenation of ethanol ia the presence of a chromium-activated copper catalyst at 280—340°C produces acetaldehyde ia a yield of 89% and a conversion of 75% per pass (313). Other catalysts used iaclude neodymium oxide and samarium hydroxide (314). 

There are many ways to produce acetaldehyde. Historically, it was produced either hy the silver-catalyzed oxidation or hy the chromium activated copper-catalyzed dehydrogenation of ethanol. Currently, acetaldehyde is obtained from ethylene hy using a homogeneous catalyst (Wacker catalyst). The catalyst allows the reaction to occur at much lower temperatures (typically 130°) than those used for the oxidation or the dehydrogenation of ethanol (approximately 500°C for the oxidation and 250°C for the dehydrogenation). 

Photocatalytic dehydrogenation in the presence of heteropolyacids. Upon illumination with the UV quanta, heteropolyacid H4[SiW]204o] provides with the quantum yield cp = 0.2 (at X = 333 nm) and remarkable (ca. 100%) selectivity dehydrogenation of ethanol into acetaldehyde in water-ethanol mixtures [10] ... 

The same samples, after a pretreatment in flowing oxygen (10%) at 625 K, were used as catalysts for the oxidative dehydrogenation of ethanol and methanol in the same reactor. The reaction mixture consisted of O2 (3 or 5%), methanol vapor (3%) or ethanol vapor (5%) and He (balance), all delivered by Tylan mass flow controllers or vaporizer flow controllers. Products were analyzed by gas chromatography. The catalysts exhibited no induction period and their activities were stable over many days and over repeated temperature cycles. 

In acidic media, the reactivity of ethanol on Au electrodes is much lower than in alkaline media. The main product of the oxidation of ethanol on Au in an acidic electrolyte was found to be acetaldehyde, with small amounts of acetic acid [Tremiliosi-FiUio et al., 1998]. The different reactivities and the product distributions in different media were explained by considering the interactions between the active sites on Au, ethanol, and active oxygen species absorbed on or near the electrode surface. In acidic media, surface hydroxide concentrations are low, leading to relatively slow dehydrogenation of ethanol to form acetaldehyde as the main oxidation pathway. In contrast, in alkaline media, ethanol, adsorbed as an ethoxy species, reacts with a surface hydroxide, forming adsorbed acetate, leading to acetate (acetic acid) as the main reaction product. 

Catalysts were prepared by the incipient wetness impregnation. PdZn-alloy formation favors the oxidative dehydrogenation of ethanol to acetaldehyde rather than CH4 thereby producing H2 with high yield in the OSR at low temperatures... 

Self-Assisted Dehydrogenation of Ethanol on an Nb/Si02 Catalyst.231... 

Oxidative Dehydrogenation of Ethanol to Acetaldehyde Nonporous Ag membranes... 

Schwab and Schwab-Agallides (7) have studied the competitive dehydration and dehydrogenation of ethanol over y- and a-alumina and... 

Pt-doped Ti02 nanotubes produce 20% more H2 than 1% Pt/Degussa P-25 Ti02 in the photocatalytic dehydrogenation of ethanol after 2 h of UV light irradiation. 

Acetaldehyde. The industrial production of acetaldehyde by the hydration of acetylene has lost its importance with the introduction of more economical petrochemical processes (dehydrogenation of ethanol, oxidation of ethylene see Section 9.5.2). At present it is practiced only in a few European countries where relatively cheap acetylene is still available.86-88... 

Fig. 15. Deactivation of Fe2(MoQ4)3 and a mechanical mixture (50 50) of Fe2(Mo04>3 + a-Sb2C>4 during the oxidative dehydrogenation of ethanol to acetaldehyde. The amount of Fe2(MoC>4)3 is identical (200 mg) in both experiments. T = 350°C ethanol/02/N2 2/1/20. Gas flow rate 50 ml/min.

The reaction of a sulfide with Raney Ni may follow two simultaneous courses as shown in eq. 13.61.129,130 The source of hydrogen may be that associated with Raney Ni or the hydrogen produced by dehydrogenation of a solvent such as ethanol.131 According to Bonner, however, dehydrogenation of ethanol to acetaldehyde and hydrogen is merely a concurrent reaction.132... 

Useful information about reaction kinetics can be obtained from measurement of the reaction rate at the bed inlet, since the composition of the fluid is known. Froment [35] gives a survey of this approach, which has been successfully employed to determine the kinetics of the dehydrogenation of ethanol [36]. The initial reaction rates in the catalyst bed are determined by extrapolating the experimentally obtained reaction rate to a zero residence time ... 

Butadiene (bpi.oi3= —4.413 C, 44 =0.6211) has become a major petrochemical product thanks to the development of its copolymers with styrene and acrylonitrDe. The earliest processes for manufacturing butadim started with acetylene and formaldehyde (Germany, the Reppe process), or produced it by the alUnited States Unwn Carbide). 

Tamaru (110) also discusses examples from heterogeneous catalysis in which reaction rates of one step seem to be influenced by the adsorption of other components. For example, Nishimura et al 115) studied the dehydrogenation of ethanol to acetaldehyde and hydrogen over a specially prepared Nb/Si02 catalyst at 523 K. The studies were done in a recirculating closed (batch) reactor. The rate is about constant as time increases, and the IR spectrum of an adsorbed intermediate remains constant. A sudden evacuation of the gas-phase ethanol stops the reaction but does not affect... 

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