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Typically, methanol is used as an intermediate to produce other chemicals such as acetic acid, formaldehyde, and MTBE, among others [23]. The production process for methanol consists of three stages, reforming, synthesis, and purification. In the first stage, the main goal is to transform methane into syngas. For this purpose a reforming process is selected. One important factor to consider when selecting the reforming process is that the ratio of H₂ to CO to feed the methanol synthesis reactor has to be equal to 2.

For the synthesis of methanol, compression of the syngas obtained from the reforming stage is needed. Then, the compressed syngas is fed to a catalytic reactor in which the following reactions take place:

The synthesis reactor operates at 83 bar and 260 °C. The outlet of the reactor is cooled and sent to a flash unit to separate the unreacted syngas and recirculate it. Additionally, a fraction of the recycled syngas is purged, with a potential use as fuel. The crude methanol obtained from the flash unit is purified using one or two distillation columns [23].

This process has been analyzed to assess its environmental impact and its safety characteristics [23,24]. The main drawbacks of the process are the high pressure required for the operation of the synthesis reactor and the wasted fraction of non‐recycled syngas. Ortiz‐Espinoza et al. [24] studied the effect of different operating pressures for the methanol synthesis reactor on the safety, environmental, and economic characteristics of the methanol production process using POX reforming. The high operating pressure is related to the profitability of the process, but safety properties may be hindered by such operating conditions. Greenhouse emissions are an additional item of relevance for consideration. Figure 1.1 shows the results of the analysis conducted by Ortiz‐Espinoza et al. [24], in which values of three metrics used for profitability, inherent safety, and sustainability are reported for different reactor pressures and recycling fractions for the unreacted syngas. Such metrics were the return on investment (ROI) for economic performance, process route index (PRI) for inherent safety, and total emissions of CO₂ equivalents for process sustainability. One can observe the gradual trend of the three metrics that reflect their conflicting behavior. In summary, the economic potential of the process is better at high pressures and high recycling fractions, but if safety is of primary concern, a lower pressure would favor the process characteristics.

Figure 1.1 Safety, sustainability, and economic indicator for different pressures and recycling fractions in the methanol production process.

It should also be noticed that the methanol synthesis reaction is exothermic; therefore, heat integration options may be considered to further enhance the environmental and economic performance of the process.