Methanol, reaction dehydrogenation

Although this pure dehydrogenation reaction is not practiced commercially, at least two processes exist in which methanol is dehydrogenated to formaldehyde in the presence of air. 

The SRM reaction over Pd/ZnO catalysts also follows pathway II, producing formaldehyde and formate species followed by decomposition into H2 and C02. This is especially true when Pd is alloyed with Zn. On the other hand, the formaldehyde species first formed from methanol by dehydrogenation undergoes decomposition to produce CO and H2 when Pd is present in metallic state. This... 

The hydrogenolysis of methyl formate to methanol (reaction 2) is the reverse reaction of methanol dehydrogenation. 

Mechanistic information on the reaction derived from well-defined Pd, Co and PdCo systems revealed that methanol is dehydrogenated to CO even at room temperature by the Pd and Pd-Co catalysts, but high steady state conversion requires temperatures at or above 423 K. Experiments conducted under UHV conditions revealed that CO desorption is the limiting factor at lower temperature. Pure Pd catalysts were found to be more active for methanol decomposition than the bimetallic Co-Pd catalysts. 

The high methanol tolerance of PtPd/C alloy catalysts is attributed to the weak competitive reaction of methanol oxidation, which could be induced by composition effects associated with the presence of Pd atoms. The methanol adsorption-dehydrogenation process requires at least three neighboring Pt atoms with appropriate crystallographic arrangement, so, in the case of Pt-Au/C materials, the probability this arrangement in the surface decreases for increasing Au contents. 

Another possible route for producing formaldehyde is by the dehydrogenation of methanol (109—111) which would produce anhydrous or highly concentrated formaldehyde solutions. Eor some formaldehyde users, minimization of the water in the feed reduces energy costs, effluent generation, and losses while providing more desirable reaction conditions. 

Methyl /-Butyl Ether. MTBE is produced by reaction of isobutene and methanol on acid ion-exchange resins. The supply of isobutene, obtained from hydrocarbon cracking units or by dehydration of tert-huty alcohol, is limited relative to that of methanol. The cost to produce MTBE from by-product isobutene has been estimated to be between 0.13 to 0.16/L ( 0.50—0.60/gal) (90). Direct production of isobutene by dehydrogenation of isobutane or isomerization of mixed butenes are expensive processes that have seen less commercial use in the United States. 

Methanol undergoes reactions that are typical of alcohols as a chemical class (3). Dehydrogenation and oxidative dehydrogenation to formaldehyde over silver or molybdenum oxide catalysts are of particular industrial importance. 

In the petroleum (qv) industry hydrogen bromide can serve as an alkylation catalyst. It is claimed as a catalyst in the controlled oxidation of aHphatic and ahcycHc hydrocarbons to ketones, acids, and peroxides (7,8). AppHcations of HBr with NH Br (9) or with H2S and HCl (10) as promoters for the dehydrogenation of butene to butadiene have been described, and either HBr or HCl can be used in the vapor-phase ortho methylation of phenol with methanol over alumina (11). Various patents dealing with catalytic activity of HCl also cover the use of HBr. An important reaction of HBr in organic syntheses is the replacement of aHphatic chlorine by bromine in the presence of an aluminum catalyst (12). Small quantities of hydrobromic acid are employed in analytical chemistry. 

Dehydrogenation processes in particular have been studied, with conversions in most cases well beyond thermodynamic equihbrium Ethane to ethylene, propane to propylene, water-gas shirt reaction CO -I- H9O CO9 + H9, ethylbenzene to styrene, cyclohexane to benzene, and others. Some hydrogenations and oxidations also show improvement in yields in the presence of catalytic membranes, although it is not obvious why the yields should be better since no separation is involved hydrogenation of nitrobenzene to aniline, of cyclopentadiene to cyclopentene, of furfural to furfuryl alcohol, and so on oxidation of ethylene to acetaldehyde, of methanol to formaldehyde, and so on. 

Reaction of nitro-2f/-chromene derivatives 134 with 135 in methanol at room temperature afforded a mixture of the Z-isomer 136 and tricyclic compound 137, which could be formed by denitrocyclization reaction of the corresponding primarily formed E-isomer and the following dehydrogenation (Eq. 15). The structural identification was based on the MS and H-NMR, however, it is not sufficiently documented and similar examples are not known (91IJC(B)297). 

Ethylene dehydrogenation was poisoned by oxygen, and direct hydrogen transfer reactions between water and oxygen and between methanol and oxygen were observed. 

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. 

Selectivity may also come from reducing the contribution of a side reaction, e.g. the reaction of a labile moiety on a molecule which itself undergoes a reaction. Here, control over the temperature, i.e. the avoidance of hot spots, is the key to increasing selectivity. In this respect, the oxidative dehydrogenation of an undisclosed methanol derivative to the corresponding aldehyde was investigated in the framework of the development of a large-scale chemical production process. A selectivity of 96% at 55% conversion was found for the micro reactor (390 °C), which exceeds the performance of laboratory pan-like (40% 50% 550 °C) and short shell-and-tube (85% 50% 450 °C) reactors [73,110,112,153,154]. 

The oxidative dehydrogenation of methanol to formaldehyde is a model reaction for performance evaluation of micro reactors (see description in [72]). In the corresponding industrial process, a methanol-air mixture of equimolecular ratio of methanol... 

The oxidative dehydrogenation of methanol to formaldehyde was choosen as model reaction by BASF for performance evaluation of micro reactors [1, 49-51, 108]. In the industrial process a methanol-air mixture of equimolecular ratio of methanol and oxygen is guided through a shallow catalyst bed of silver at 150 °C feed temperature, 600-650 °C exit temperature, atmospheric pressure and a contact time of 10 ms or less. Conversion amounts to 60-70% at a selectivity of about 90%. 

The reaction goes through several consecutive steps. In a first step, the methanol molecule becomes dehydrogenated while adsorbing on platinum ... 

Elementary Reaction Thermodynamics at the Aqueous, Electrified Interface Methanol Dehydrogenation... 

The presence of solution at a metal surface, as has been discussed, can significantly influence the pathways and energetics of a variety of catalytic reactions, especially electrocatalytic reactions that have the additional complexity of electrode potential. We describe here how the presence of a solution and an electrochemical potential influence the reaction pathways and the reaction mechanism for methanol dehydrogenation over ideal single-crystal surfaces. 

Figure 4.12 The upper plots (a, c, e, g) show the free energies (calculated by (4.4) from DFT) versus the estimated potential for reactants and products involved in the first, second, third, and fourth consecutive methanol dehydrogenation steps, as indicated, over Pt(lll) from Cao et al. [2005]. Filled symbols in (a) refer to the energy and potential for the system tq = Q. The lower plots (b, d, f, h) show the corresponding reaction energies for the first, second, third, and fourth consecutive methanol dehydrogenation steps, as indicated.

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