Gary A. Foulds

The relevance of combustion theory to the homogeneous oxidation of methane

This reaction is a highly exothermic one and as such invariably occurs under conditions of substantial self-heating and consequent self-acceleration. The behaviour described in a number of publications is inconsistent and it is the thesis of the present paper that the nonlinearly flowing from self-heating is responsible for many contradictions and novel results in this area. Appropriate use of combustion theory in the form of thermokinetic modelling not only brings some order to otherwise inexplicable contradiction, but also enables prediction of optimal conditions for methanol selectivity and conversion. The importance of such exotic phenomena as hysteresis and oscillatory reaction for optimisation is demonstrated and some suggestions for future direction are discussed.

The use of a jet-stirred continuously stirred tank reactor (CSTR) to study the homogeneous gas phase partial oxidation of methane to methanol

Publisher Summary This chapter describes the use of jet-stirred continuously stirred tank reactor (CSTR) to study the homogeneous gas phase partial oxidation of methane to methanol. The design of the CSTR follows the rules that were defined and verified for spherical jet reactors incorporating a range of volumes. It takes into account the constraints related to turbulence, sonic velocity, and internal recycling limitations. Two techniques may be used to measure the residence time distribution in the CSTR—pulse injection and step change of input concentration. The results, obtained over a wide range of process conditions, exhibit good semi-quantitative agreement with those predicted by a non-isothermal model. The cool flame phenomena, including discontinuity and hysteresis in heat release rate are observed in CSTR. A decrease in temperature in the CSTR was found to favor methanol production, with the highest yields being observed in the region accessible only on the downward sweep of the hysteresis. In addition, an increase in the concentration of oxygen leads to an increase in conversion and width of the hysteresis loop.

Process Optimisation of the Catalytic Partial Oxidation of Methane to Synthesis Gas.

Publisher Summary The most common and industrially favoured method for converting natural gas to syngas at present is steam reforming, which involves a highly endothermic reaction, and as a result is an energy intensive and costly process. In addition, conventional steam reformers are unsuitable for off-shore or remote small-deposit application, because of their large size and appreciable capital cost. Partial oxidation of methane to syngas, using oxygen as oxidant, represents an alternative to steam and CO, reforming, as it is exothermic, more selective, and theoretically yields a H 2 :CO ratio of 2. However, with the recent development of a new generation of highly active catalysts that appear capable of producing syngas at relatively lower temperatures, there has been a flurry of renewed interest in the area of catalyst development. The discussion presented here focuses primarily on optimizing the process conditions in a fixed-bed reactor, using known highly active catalysts. The effect of temperature, space velocity, particle size, nitrogen diluent in the feed, co-feeding of steam, and pressure, on conversion and selectivity have been examined.

Thermokinetic Modelling of the Gas Phase Partial Oxidation of Methane to Methanol in a CSTR.

The direct partial oxidation of methane to methanol has been studied in a CSTR. The CSTR oxidation of methane under the conditions indicated shows promise of methanol yields and selectivities equivalent to those in flame tubes. The hysteresis effect shown in flame tubes is also shown in a CSTR. These results provide a confident basis for extension of the work with a modified vessel which will minimise conductive heat loss and enable the yields and selectivities to be correlated with reactant temperature.