Ethane oxidation activities, carbon

Interaction of chlorine with methane is explosive at ambient temperature over yellow mercury oxide [1], and mixtures containing above 20 vol% of chlorine are explosive [2], Mixtures of acetylene and chlorine may explode on initiation by sunlight, other UV source, or high temperatures, sometimes very violently [3], Mixtures with ethylene explode on initiation by sunlight, etc., or over mercury, mercury oxide or silver oxide at ambient temperature, or over lead oxide at 100°C [1,4], Interaction with ethane over activated carbon at 350°C has caused explosions, but added carbon dioxide reduces the risk [5], Accidental introduction of gasoline into a cylinder of liquid chlorine caused a slow exothermic reaction which accelerated to detonation. This effect was verified [6], Injection of liquid chlorine into a naphtha-sodium hydroxide mixture (to generate hypochlorite in situ) caused a violent explosion. Several other incidents involving violent reactions of saturated hydrocarbons with chlorine were noted [7],... 

Table III. Carbon Monoxide, Ethylene, and Ethane Oxidation Activities of Unsupported Catalystsa...

The space velocity was varied from 2539 to 9130 scf/hr ft3 catalyst. Carbon monoxide and ethane were at equilibrium conversion at all space velocities however, some carbon dioxide breakthrough was noticed at the higher space velocities. A bed of activated carbon and zinc oxide at 149 °C reduced the sulfur content of the feed gas from about 2 ppm to less than 0.1 ppm in order to avoid catalyst deactivation by sulfur poisoning. Subsequent tests have indicated that the catalyst is equally effective for feed gases containing up to 1 mole % benzene and 0.5 ppm sulfur (5). These are the maximum concentrations of impurities that can be present in methanation section feed gases. 

Recently, Sen has reported two catalytic systems, one heterogeneous and the other homogeneous, which simultaneously activate dioxygen and alkane C-H bonds, resulting in direct oxidations of alkanes. In the first system, metallic palladium was found to catalyze the oxidation of methane and ethane by dioxygen in aqueous medium at 70-110 °C in the presence of carbon monoxide [40]. In aqueous medium, formic acid was the observed oxidation product from methane while acetic acid, together with some formic acid, was formed from ethane [40 a]. No alkane oxidation was observed in the absence of added carbon monoxide. The essential role of carbon monoxide in achieving difficult alkane oxidation was shown by a competition experiment between ethane and ethanol, both in the presence and absence of carbon monoxide. In the absence of added carbon monoxide, only ethanol was oxidized. When carbon monoxide was added, almost half of the products were derived from ethane. Thus, the more inert ethane was oxidized only in the presence of added carbon monoxide. 

With the aim of exploring the activation of O2 toward the oxidation of vicinal diols we tested different supported-gold catalysts under mild conditions. By working in neutral aqueous solution of ethane-1,2-diol up to 100°C and 2 atm of O2 in the presence of 1% Au supported on active carbon there was no oxidation, whereas in alkaline solution a smooth oxygen uptake at 50-90°C was observed. HPLC and l C-NMR analyses of the reaction products showed quite good slectivity toward monooxygenation. 

The presence of hydrocarbon impurities has been shown to affect the oxidation of carbon monoxide [22] and the decomposition of carbon dioxide [23]. It has been reported that the dissociations of ethane [24] and butane [25] at the elevated temperatures and typical densities of shock tube experiments are in the low pressure region with activation energies that are much less than their respective high pressure limit values. The reaction of p.p.m. levels of hydrogen atoms with the molecule under investigation can result in a low apparent energy for dissociation due to the increased importance of abstraction steps. 

Different classes of catalysts have been claimed for the oxidation of ethane to acetic acid [3], but the catalyst that gives the best performance is made of a mixed oxide of Mo/V/Nb (plus other components in minor amounts). This compound was first described in a paper by Thorsteinson et cd. 3a] - a paper that is considered nowadays a milestone in the field of the selective oxidation of alkanes, in view of the number of active phases that have been developed starting from catalysts described therein. Several patents were also issued by Union Carbide [3a-f], now Dow Chemical, regarding this system and the ETHOXENE process. The activity in ethane oxidation was attributed to the development of a crystalline phase characterized by a broad X-ray diffraction reflection at d = 4.0 A. The best composition was claimed to be Moo.73Vo.i8Nbo.o90 c, which reached 10% conversion of ethane at 286 °C with almost total selectivity to ethylene the selectivity decreased with increasing temperature, due to the formation of carbon oxides. The main peculiarity of this catalyst is its capability to activate the paraffin at low temperatures (<250 °C). 

Compared to the base catalyst, Pd-doped catalysts displayed somewhat lower overall activity in terms of both absolute and normalized conversion of ethane and essentially higher selectivity to acetic acid. As the Pd amount in the catalyst increased, selectivity to acetic acid increased at the expense of selectivity to ethylene. Combined selectivity to carbon oxides practically did not change. The only difference was that ethane oxidation on the base catalyst produced roughly equal amounts of CO and CO2 while the reaction on Pd-promoted catalysts produced only CO2. This result looks reasonable if one takes into account that Pd is a good catalyst for CO oxidation to CO2. 

Historically, the application of MMO as catalysts for propane oxidation to acrylic acid began in the late 1970s with Mo-V-Nb mixed oxides, previously reported as a catalyst for ethane oxidation [54]. The results of propane oxidation over this catalyst show that propane could be activated at 300°C, but producing only acetic acid, acetaldehyde, and carbon oxides. However, the possibility to activate... 

Hong, Y, Liwu, L., Qingxia, W, Longya, X., Sujuan, X., and Shenghn, L. Oxidative dehydrogenation of ethane with carbon dioxide to ethylene over Cr-loaded active carbon catalyst. nStud. Surf. Sci. Catal., Elsevier Volume 136, 87-92 (2001). 

An inhibitor is the opposite of a promoter. When added in small amounts, it diminishes activity, selectivity or stability. Inhibitors are useful for reducing the activity of a catalyst for an undesirable side reaction. For instance, silver supported on alumina is an excellent oxidation catalyst, widely used in the production of ethylene oxide from ethylene. However, at the same conditions, complete oxidation to carbon dioxide and water also occurs, decreasing selectivity to ethylene oxide. Addition of halogen compounds (eg, dichloro-ethane) to the catalyst inhibits the complete oxidation and results in much better selectivity. 

Direct conversion of methane to ethane and ethylene (C2 hydrocarbons) has a large implication towards the utilization of natural gas in the gas-based petrochemical and liquid fuels industries [ 1 ]. CO2 OCM process provides an alternative route to produce useful chemicals and materials where the process utilizes CO2 as the feedstock in an environmentally-benefiting chemical process. Carbon dioxide rather than oxygen seems to be an alternative oxidant as methyl radicals are induced in the presence of oxygen. Basicity, reducibility, and ability of catalyst to form oxygen vacancies are some of the physico-chemical criteria that are essential in designing a suitable catalyst for the CO2 OCM process [2]. The synergism between catalyst reducibility and basicity was reported to play an important role in the activation of the carbon dioxide and methane reaction [2]. 

Note that the main difference between zirconium hydride and tantalum hydride is that tantalum hydride is formally a d 8-electron Ta complex. On the one hand, a direct oxidative addition of the carbon-carbon bond of ethane or other alkanes could explain the products such a type of elementary step is rare and is usually a high energy process. On the other hand, formation of tantalum alkyl intermediates via C - H bond activation, a process already ob-... 

In the direct ammoxidation of propane over Fe-zeolite catalysts the product mixture consisted of propene, acrylonitrile (AN), acetonitrile (AcN), and carbon oxides. Traces of methane, ethane, ethene and HCN were also detected with selectivity not exceeding 3%. The catalytic performances of the investigated catalysts are summarized in the Table 1. It must be noted that catalytic activity of MTW and silicalite matrix without iron (Fe concentration is lower than 50 ppm) was negligible. The propane conversion was below 1.5 % and no nitriles were detected. It is clearly seen from the Table 1 that the activity and selectivity of catalysts are influenced not only by the content of iron, but also by the zeolite framework structure. Typically, the Fe-MTW zeolites exhibit higher selectivity to propene (even at higher propane conversion than in the case of Fe-silicalite) and substantially lower selectivity to nitriles (both acrylonitrile and acetonitrile). The Fe-silicalite catalyst exhibits acrylonitrile selectivity 31.5 %, whereas the Fe-MTW catalysts with Fe concentration 1400 and 18900 ppm exhibit, at similar propane conversion, the AN selectivity 19.2 and 15.2 %, respectively. On the other hand, Fe-MTW zeolites exhibit higher AN/AcN ratio in comparison with Fe-silicalite catalyst (see Table 1). Fe-MTW-11500 catalyst reveals rather rare behavior. The concentration of Fe ions in the sample is comparable to Fe-sil-12900 catalyst, as well as... 

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