Scheme 1 Methanol oxidation pathways (adapted from ref. 16).
Dimethoxymethane (DMM) is a chemically stable compound with many uses, including as a solvent, pharmaceutical and fuel-additive applications5. For example, the selective oxidation of DMM can be used to prepare concentrated formaldehyde (FA) solution6. Due to its low toxicity, It is also an excellent solvent with low toxicity that is used in the pharmaceutical and perfume industries7. The polyoxymethylene dimethyl ether (PODE)8 synthesized from DMM can be mixed with diesel to reduce its freezing point while increasing the combustion efficiency, decreasing COx and NOx emissions in diesel exhaust, or it can be used in fuel cells in a low-toxic and efficient way9. PODE is also used as a preservative, which is safer and healthier than FA10.
Industrially, DMM is produced by reaction catalyzed polycondensation of FA produced by the oxidation of methanol and methanol11. However, this traditional method is complicated and expensive due to the high reaction temperature of the acid catalyst and the resulting corrosion of the equipment12. Considering that the one-step selective oxidation of methanol to DMM is economical and environmentally friendly, this promising reaction warrants further study13. This one-step reaction is very sensitive to the nature of the catalytic active center14. Continuous redox reaction and acid catalysis pathways (Scheme 1)15 can generate different products. The difficulty of selectively generate DMM explains the dearth of literature reports on this subject16,17. However, most of the existing research on dual-functional catalysts for the one-step preparation of DMM from methanol has shown that it is possible to increase DMM selectivity18, but not to simultaneously increase the methanol conversion; therefore, high DMM yields have not been achieved. The highest previously reported yield of DMM was only 61.38%(TableS1). However, prior to the present study, our team used Fe-Mo–based dual-function catalysts under optimized conditions in a fluidized bed reactor to achieve the highest DMM yield to date19.
This paper reports the scale-up pilot process in the laboratory. This lays the foundation for the in-depth development, popularization and application of this new technology, and potentially the future industrialization of this one-step process to generate DMM from methanol. Using the optimal Fe-Mo/HZSM-5 dual-function catalyst developed by the team, the reaction effect was verified in the circulating regenerated fluidized bed, the optimal process conditions were explored, and the reaction mechanism was probed using In-situ infrared (DRIFTS).