Gas-phase partial oxidation

Spencer and Pereira (1987) studied the kinetics of the gas-phase partial oxidation of CH4 over a Mo03-Si02 catalyst in a differential PFR. The products were HCHO (formaldehyde), CO, C02, and H20. 

Zhang, Q., He, D., Li, J., Xu, B., Liang, Y., Zhu, Q. (2002). Comparatively high yield methanol production from gas phase partial oxidation of methane. Appl Catalysis A General 224, 201-207. 

Multitubular reactors are mainly used in gas-phase partial oxidation processes, such as the air oxidation of light olefins, paraffins, and aromatics. Examples of chemistries where these reactors are used include the partial oxidation of methanol to formaldehyde, ethylene to ethylene oxide, ethylene and acetic acid to vinyl acetate, propylene to acrolein and acrylic acid, butane to maleic anhydride, isobutylene to methacrolein and methacrylic acid, and o-xylene to phthalic anhydride. An overview of the multitubular reactor process for the partial oxidation of n-butane to maleic anhydride is given here. 

The gas phase partial oxidation of toluene to benzaldehyde is an industriaUy important reaction due to the fact that benzaldehyde is a common intermediate in a wide variety of chemical reaction processes. Almost half of benzaldehyde world production is employed in the synthesis of food additives (mainly flavoring). Although the partial oxidation of aromatic hydrocarbons is widely treated in the literature, the oxidation of toluene to benzaldehyde presents few information, thus requiring systematic studies (1). 

We have investigated the gas phase partial oxidation of benzene to phenol over zeolite H-MCM-22 using as the oxidant. H-MCM-22 is active (15% benzene conversion at 603 K) and nearly 100% selective for the partial oxidation of benzene to phenol. We have also investigated the reaction in an in-situ IR cell. Both benzene and phenol interact strongly with the Bronsted acid site whereas does not interact strongly with the zeolite. We find the presence of Bronsted acidity is critical for the reaction and we found no correlation of the activity with the iron content, as reported previously by others. 

Under appropriate conditions, the gas-phase partial oxidation of acetaldehyde to peracetic acid is autocatalytic. The reaction stoichiometry is... 

At the moment, catalysts based on transition metal oxides with redox properties present the most promising results in the gas-phase partial oxidation reactions of light alkanes (Table 24.1). Except in the case of methane, which will be discussed later, alkanes can be transformed into the corresponding olefins and/or partial oxidation... 

Kinetic modeling results suggest that the known stationary states of the gas-phase partial oxidation of methane are apparently quite stable, since variation of even key rate constants within kinetically acceptable limits, for example, those of chain-branching steps. 

A kinetic analysis of the gas-phase partial oxidation of methane in the CH4—O2—NO system at atmospheric pressure within the framework of a reasonably complete kinetic scheme, composed of more than 250 elementary stages, was conducted in [187] in order to optimize the experimental conditions for this system. In all cases, the calculated values did not exceed the experimentally obtained. In our view, the main discrepancy between the experimental data and calculation results is that the kinetic calculations predict a steady decline in the selectivity of methanol formation with increasing methane conversion, while the experimental results show a linear increase up to a methane conversion of 10%. This contradiction points to the urgent need for a more careful assessment of the role of heterogeneous reactions in these experiments, carried out at low pressures. A more general kinetic model for... 

As in the case of the gas-phase partial oxidation, the oxidative conversion of alkanes under SC conditions is complicated by a much more rapid oxidation of methanol and other oxygenates. Therefore, in the process of oxidation, they accumulate in relatively small quantities, only as intermediate products. However, it is worth briefly discussing the stability of major products in oxygen-free conditions after reaction completion. The authors of [224] studied the pyrol) is of methanol under SC conditions. At a pressure of 600 atm and a reaction time of 1 h, the temperature rise in SCW from 400 to 500 °C led to an increase in the methanol conversion from 3.8% to 20.6%. The products were methane and, in lesser concentrations, CO2 and H2. However, at the same pressure of 600 atm, a temperature of 400 °C, and a reaction time of 1 h, the degree of its conversion in the SC nitrogen was significantly higher. 

Experimental and kinetic simulation studies of the gas-phase partial oxidation of methane—ethane mixtures were performed in [237,238]. Two different experimental setups... 

Arutyunov VS. Recent results on fast flow gas-phase partial oxidation of lower alkanes. J Nat Gas Chem 2004 13 10-22. 

Han L-B, Tsubota S, Kobayashi T, Haruta M. Formation of methanol by the gas phase partial oxidation of methane under normal pressures. J Chem Soc Chem Common 1995 93-4. 

Budymka VF, Egorov SA, Gavrya NA, Mochaev AS, Khomenko GA, Leonov VE. Effect of the process parameters on the gas-phase partial oxidation of natural gas. Khim Prom-st 1987 6 10-1 [in Russian]. Morton LA, Gesser HD, Hunter NR. The partial oxidation of CH4 to CH3OH at high pressure in a packed reactor. Fuel Sci Tech Int 1991 9 913-33. 

Foulds GA, Charlton BG, Le BT, Jones JC, Gray BF. The use of a jet-stirred continuously stirred tank reactor (CSTR) to study the homogeneous gas phase partial oxidation of methane to methanoL In De Pontes M, Espinoza RL, Nicolaides CP, Scurrell MS, editors. Natural gas conversion IV Studies in surface science and catalysis, vol. 107. Elsevier Science B.V 1997. p. 3—8. 

When the catalyst particle is substantially hotter than the bulk fluid, several negative effects can occur. First, the reaction selectivity often will be much lower at high temperatures. One example is the gas-phase partial oxidation of ethylene (C2H4) to ethylene oxide (C2H4O), which is accompanied by the further oxidation of ethylene and ethylene oxide to CO, CO2, and H2O. 

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