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).