FIGURE 11 The effect of gas flux on the conversion efficiency
of methanol. (Reaction temperature 360 ℃, one sheet of membrane of
thickness 1 mm)
The effect of gas flux through the membrane on conversion efficiency of
methanol was shown in Figure 11. It could be seen that the conversion
efficiency of methanol was decreased from 7.5% to 2.0% with the gas
flux through the membrane was increased from 8
m3·m-2·h-1 to 18
m3·m-2·h-1 since
the reaction residence time during methanol dehydrogenation was
decreased. In addition, the gas flux was changed by adjusting the
nitrogen flow rate and higher gas flux with higher nitrogen flowrate
would cause the decrease of the methanol concentration. It can be
calculated that the concentration of the methanol vapor was decreased
from 76% to 37% with the gas flux increased from 8
m3·m-2·h-1 to 18
m3·m-2·h-1. Lower
gas flux can promote methanol conversion but leads to lower equipment
unitization.
In order to obtain high conversion efficiency of methanol under the
condition of higher gas flux, two or three sheets of Cu/ZnO/Ti CMNRs
were set up in series for methanol dehydrogenation. As shown in Figure
12, it can be seen that the increasing sheets of membrane resulted in an
increase of the conversion efficiency of methanol. Moreover, the
conversion efficiency of methanol increased asymptotically and reached a
maximum value of 18.5% when three sheets of CMNR applied, which
produced logically a pressure drop increase from 2.7 kPa to 6.8 kPa. It
can be deduced that higher conversion efficiency of methanol can be
expected if more membranes are packed in series. Based upon the current
experiments, the preliminary simulation could be proposed: if 25
membranes (packing thickness 25 mm) applied, the conversion efficiency
of methanol can up to 80% with the gas pressure drop 58 kPa; if
Cu/ZnO/Ti CMNRs increased 70 sheets (packing thickness 70mm), the
conversion efficiency of methanol would be expected to over 99% with
the gas pressure drop 162 kPa. Compared to general fixed bed reactors
(conversion efficiency, bed height, pressure drop), the developed here
CMNRs would be of excellent performance.