Overheating partial oxidation

The catalytic properties of the synthesised solids were determined during the partial oxidation of toluene (TO) to benzaldehyde (BA), p-methoxytoluene (MTO) to p-methoxybenzaldehyde (MBA, anisaldehyde) and p-chlorotoluene (CTO) to p-chlorobenzaldehyde (CBA). A microreactor set-up that contains a metering system for liquids and gases and a fixed bed quartz-glass reactor was used. The catalysts were introduced into the reactor as sieve fractions (1-1.25 mm) and mixed prior to oxidation runs with the equal portion of quartz glass (1 mm) to avoid local overheating. The product stream was analysed by on line-GC or it was trapped in aqueous ethanol and determined by off line-capillary GC. The formation of carbon oxides was continuously followed by non-dispersive IR photometry. 

Because partial oxidation reactions take place faster compared with steam reforming, the heat balance of autothermal reforming is only neutral on an overall basis. This leads to local overheating, similar to partial oxidation (see Section 4.2). 

In the preparation of a dyestuff from aniline, nitrobenzene (as oxidant), hydrochloric acid and sodium hydroxide, ferric chloride is often used as catalyst, but sodium molybdate was substituted as a more effective catalyst. The materials were charged into a 4.5 m3 reactor and heating was started after addition of nitrobenzene, but the temperature controller was mis-set, and overheating at a high rate ensued. The exotherm was much higher than normal because of the more effective catalyst, and partial failure of the cooling water led to an uncontrollable exotherm. 

The direct interaction between the fuel-air mixture and the electrode materials leads to partial or complete oxidation reactions. These reactions are exothermic processes [24] and the resulting heat release increases the cell temperature. The control of the overheating and the measurement of the tme cell temperature are essential to efficient operation of the system. 

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