3.3 Effect of operation parameters on methanol dehydrogenation
Methanol dehydrogenation was an endothermic process and the increase of
reaction temperature could promote the reaction37.
From Figure 10A, it can be seen that the conversion efficiency of
methanol was increased exponentially with reaction temperature. The
conversion efficiency of methanol at 360 ℃ was two orders of magnitude
higher than that at 260 ℃. The effect of reaction temperature on the
selectivity of products was shown in Figure 10B. The production of
formaldehyde and methyl formate performed monotonous tradeoff in the
reaction temperature range of 260 ℃ and 360 ℃, which was consistent with
the published reports44. The selectivity of
formaldehyde can be increased from 10% to 98% with the reaction
temperature increased from 260 ℃ to 360 ℃, and could be kept over than
90%, when the reaction temperature was over 320 ℃. This implied that
the selectivity of formaldehyde was insensitive to temperature changes,
if the reaction temperature was higher. During the process of methanol
dehydrogenation for formaldehyde production, the produced formaldehyde
would convert into methyl formate through hemiacetal reaction if the
formaldehyde couldn’t desorb from the active sites in
time45. In the general fixed bed reactor, the
residence time was several seconds46. However, the
residence time was only 0.2 s with uniform distribution in the developed
Cu/ZnO/Ti CMNR. Therefore, the side reaction with methyl formate
generation can be inhibited significantly.