4.3 Induction period and surface tension in MACC operation.
Based on the classic nucleation theory, the surface tension was
determined by the induction period under different supersaturations36,60,61.
In the low supersaturation zone, heterogeneous nucleation was dominant,
and in the high supersaturation zone, homogeneous nucleation played the
controlling role. The measured nucleation induction period with
different membrane package density is as follows in the Figure 8.
Comparing the nucleation induction period with membrane module involved,
it can be seen that the lower coolant temperature can provide the
greater supercooling degree and correspondingly shorten the nucleation
induction period under the tested temperature range. With increasing
membrane module package density, the nucleation induction period almost
inversely shortened (when PTFE membrane module package density increased
from 120 m2/m3 to 240.6
m2/m3 then to 361.0
m2/m3, correspondingt ind at 8 ℃ declined from 240s to 160s then to
80s). This result indicated that the nucleation induction period when
the membrane module involved was highly impacted by the heat transfer
property of the membrane module, which would also inevitably influence
the membrane interface supercooling degree.
In addition, owing to roughness, hydrophobicity, and the thickness of
membrane determines heterogeneous nuclear energy barrier of PES was
smaller than that of PTFE, the induction time was also shorten when PES
membrane module was introduced; The nucleation induction period with the
same PTFE and PES membrane area were listed in Table 3. At the same
terminal temperature, plotting lnt ind versus
(lns )-2 yields two straight lines with
different slopes, which represented the homogeneous nucleation and
heterogeneous nucleation, respectively, which can be obtained by linear
fitting (show in Figure S2 and S3 as supporting materials).