Formaldehyde, production catalyst

A topic of current interest is that of methane activation to give ethane or selected oxidation products such as methanol or formaldehyde. Oxide catalysts are used, and there may be mechanistic connections with the Fischer-Tropsch system (see Ref. 285). 

Formaldehyde manufacture, 12 113-117. See also Formaldehyde production by exothermic reaction, 12 115 metal oxide catalyst, 12 115-117 methanol process for, 12 113 new processes for, 12 117 silver catalyst, 12 113-115 Formaldehyde plant... 

The reaction chemistry of simple organic molecules in supercritical (SC) water can be described by heterolytic (ionic) mechanisms when the ion product 1 of the SC water exceeds 10" and by homolytic (free radical) mechanisms when <<10 1 . For example, in SC water with Kw>10-11 ethanol undergoes rapid dehydration to ethylene in the presence of dilute Arrhenius acids, such as 0.01M sulfuric acid and 1.0M acetic acid. Similarly, 1,3 dioxolane undergoes very rapid and selective hydration in SC water, producing ethylene glycol and formaldehyde without catalysts. In SC methanol the decomposition of 1,3 dioxolane yields 2 methoxyethanol, il lustrating the role of the solvent medium in the heterolytic reaction mechanism. Under conditions where K klO"11 the dehydration of ethanol to ethylene is not catalyzed by Arrhenius acids. Instead, the decomposition products include a variety of hydrocarbons and carbon oxides. 

Metal wires and screens are used as fixed-bed catalysts in which reactants are passed through the openings in the gauze, the size of which is defined by the mesh and wire diameter (see Fig. 10A). Gauzes composed of an alloy of platinum and rhodium catalyze the air oxidation of ammonia to nitric oxide, which is subsequently converted to nitric acid, and the production of hydrogen cyanide from ammonia, air, and methane. Formaldehyde production by... 

Formaldehyde production by dehydrogenation of methanol over a silver catalyst,... 

The second method uses a metal oxide catalyst. All of the formaldehyde is produced from an exothermic reaction occurring at atmospheric pressure and 300-400 °C. The patent for formaldehyde production using a vanadium pentoxide catalyst was issued in 1921. Although the patent for an iron oxidemolybdenum oxide catalyst was issued in 1933, the first commercial facility did not begin operating until 1952 (Gerberich et al. 1980). 

Hydrogenation of carbon oxides with iron, cobalt, or nickel catalysts (Fischer-Tropsch process). Hydrocarbons are the main products Recovery and separation of oxygenated products obtained from CO and H2 Partial oxidation of nonaromatic hydrocarbon mixtures, e.g., petroleum, paraffins, and natural gas, to produce a mixture of products, such as esters, acids, aldehydes, ketones, and alcohols. This also includes higher fatty acids from petroleum and patents on formaldehyde production... 

Formaldehyde productivity values as high as 9-10 kgHCHo kgcat h (-atmcH4 ). ensured by ADS/PRC Fe0x/Si02 catalysts, represent a breakthrough in view of a potential exploitation of the MPO reaction on an industrial scale. 

This is in conflict with the observation [41] that basic oxide surfaces tend to totally oxidize the alcohol (multiple proton abstraction) and that acidic oxides exhibit a correlation between acidity and formaldehyde production. On suitably acidic surfaces the reaction mechanism may be dominated by the electrophilic action of protons on the methanol leading to an embedded methoxy which is easily activated at the methyl positions. On HPA catalysts this reaction path was claimed to be dominating [27] as long as the catalyst was sufficiently acidic. For the... 

Formaldehyde is nowadays one of the major produced chemicals due to its uses in many fields of chemical industry [1]. The commercial production started in 1890 using metallic copper catalysts. In 1910 copper catalysts were replaced by silver catalysts with higher yields [2]. Although the first report of the excellent catalytic behavior of iron molybdates in selective oxidation of methanol to formaldehyde is of 1931, the related industrial process based on them only went into operation in 1940-50 [1]. A recent report [3] shows that iron molybdates and silver catalysts are nowadays equally used as industrial catalysts for formaldehyde production. 

Most of the current results on the selective oxidation of methane over metal oxide catalysts may be interpreted in terms of methyl radical chemistry. These radicals may either react with the oxides themselves to form methoxide ions or they may enter the gas phase. The methoxide ions on supported molybdena decompose to form formaldehyde or they react with water to yield methanol. On the basic oxides methoxide ions result in complete oxidation. Those radicals which enter the gas phase undergo typical free radical chemistry which includes coupling reactions to give ethane and chain branching reactions to give nonselective oxidation products. Secondary surface reactions, particularly with ethylene, also may result in complete oxidation. If further improvements in yields of partial oxidation products are to be achieved, ways must be found to more efficiently utilize the methyl radicals, both with respect to surface reactions and to gas phase reactions. In addition, if ethylene is the desired product, catalysts must be fine-tuned to the point where they will activate methane, but not ethylene. 

The kinetics of methanol oxidation over metal oxide catalysts were elegantly derived by Holstein and Machiels [16], The kinetic analysis demonstrated that the dissociative adsorption of water must be included to obtain an accurate kinetic model. The reaction mechanism can be represented by three kinetic steps equilibrated dissociative adsorption of methanol to a surface methoxy and surface hydroxyl (represented by K,), equilibrated dissociative adsorption of water to two surface hydroxyls (represented by K ), and the irreversible hydrogen abstraction of the surface methoxy intermediate to the formaldehyde product and a surface hydroxyl (the rate determining step, represented by kj). For the case of a fully oxidized surface, the following kinetic expression was derived ... 

Stull, Westrum, and Sinke devote a chapter to the discussion of the applications of thermodynamics to industrial problems. Subjects covered include the petroleum industry, chemicals from methane, styrene manufacture, acrylonitrile and vinyl chloride syntheses, methanol synthesis, formaldehyde production from methanol, acetic acid manufacture, the Gatterman-Koch reaction, and catalyst selection. 

In contrast to methanol oxidation, oxidative dehydrogenation of methanol [route (b) in Topic 5.3.2] is an endothermic reaction (AH = -F84kJ mol ). Methanol is contacted at normal pressure with a heterogeneous silver at 500-700 °C. Owing to the kinetic instability of the formaldehyde product under the applied reaction conditions, the contact time at the catalyst is very short (t < 0.01 s). This is realized by high flow rates in the reactor and a very effective quenching of the product flow leaving the reactor. The product gas is contacted with water to produce an aqueous... 

A little more than a decade ago, Clariant decided to venture into the field of partial oxidation reactions. Catalysts for selective partial oxidation reactions thus belong to the most recent developments in the catalyst portfolio of Clariant. The portfolio of oxidation catalysts currently comprises SulfoMax for sulfuric acid production, FAMAX for formaldehyde production, PHTHALIMAX for phthalic anhydride production, SynDane for maleic anhydride production, and most recently VAM ax for vinyl acetate production. 

The number and nature of the active surface sites and the catalytic activity of bulk metal molybdates and vanadates were also investigated through methanol chemisorption [51-53]. These materials proved to be equally or more active and stable than the industrial catalyst Mo03/Fe2(Mo04)3 in formaldehyde production [54-56],... 

If the silver catalyst did not catalyze Reaction (7-C), or if we attempted to operate without O2, the conversion of CH3OH would be much lower, and heat would have to be added to the reactor to maintain the necessary high temperature. As we shall see in the next chapter, heating or cooling complicates the mechanical design of a reactor. For these reasons. Reaction (7-C) is desirable, in the context of formaldehyde production. 

The base-catalyzed reaction of acetaldehyde with excess formaldehyde [50-00-0] is the commercial route to pentaerythritol [115-77-5]. The aldol condensation of three moles of formaldehyde with one mole of acetaldehyde is foUowed by a crossed Cannizzaro reaction between pentaerythrose, the intermediate product, and formaldehyde to give pentaerythritol (57). The process proceeds to completion without isolation of the intermediate. Pentaerythrose [3818-32-4] has also been made by condensing acetaldehyde and formaldehyde at 45°C using magnesium oxide as a catalyst (58). The vapor-phase reaction of acetaldehyde and formaldehyde at 475°C over a catalyst composed of lanthanum oxide on siHca gel gives acrolein [107-02-8] (59). 

Secondary acetylenic alcohols are prepared by ethynylation of aldehydes higher than formaldehyde. Although copper acetyUde complexes will cataly2e this reaction, the rates are slow and the equiUbria unfavorable. The commercial products are prepared with alkaline catalysts, usually used in stoichiometric amounts. 

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