Schemes involving partial oxidation with oxygen

To convert methane 191 (see Fig. 1.5), it is theoretically possible to adjust the oxygen content to obtain an effluent in which the H2/CO ratio is dose to 2. In practice, it is necessary to consider the losses resulting from the formation of methane during the synthesis of methanol, and aim for an H2/CO ratio of around 2 5, which is ideal for this conversion. 

19) Contrary to the tinal objective in the production of hydrogen or ammonia, the intermediate formation of CO. does not need to be avoided in the manufacture of methanot Hence, in this case, the partial oridation of methane can offer an economically interesting solution. 

This value can be obtained by diverting part of the gas stream to a steam converter that removes excess CO and supplies an equivalent amount orhydrogen(shift conversion). Using a standard absorption process, it is then necessary to remove the C02 up to the mathmim concentration acceptable by the catalyst employed to condnct the methanol synthesis. 

The basic scheme is hence very similar to those used to produce hydrogen and ammonia The same applies to the conversion of heavy products, for which partial oxidation and gasification are generally more suitable. The presence of sulfur compounds in the raw materials used requires the consideration of two main variants, depending on the possibilities of the catalyst for CO shift conversion (diagrams a and b in Fig. 1.23). 

In both schemes, the installation ofasulfur barrier (such as zinc oxide) is recommended to protect the synthesis catalyst, which does not tolerate sulfur compounds. 

---

Schemes involving partial oxidation with oxygen... 

A more complicated reaction scheme is proposed by the authors to include the formation of the by-products acetonitrile, acetaldehyde and ethylene. However, appropriate rate coefficients cannot be given as the reactions appear to be partially homogeneous gas phase reactions, implying that factors like the reactor geometry are also involved. Regarding the oxidation mechanism, the authors assume that two hydrogen atoms are first abstracted from propene, followed by reaction with surface oxygen or NH species. 

---