Microporous Membrane Interface Response For Initial Nucleation Detection And Accurate Metastable Zone Width Measurement

The metastable zone width is the critical nucleation point which determines the operation window of the crystallization process,the real-time nucleation detection and accurate metastable zone width(MSZW)measurement technology is still of importance for crystallization control and process design.At present,the most widely used optical method cannot detect nucleation of solution systems with poor light transmission and high color level.In this paper,based on the membrane distillation-crystallization process,we proposed a novel analysis technology by introducing the microporous membrane as the nucleation response interface on the principle of membrane selective solvent removal and the flux decrease caused by nucleation of membrane pores,which can accurately determine the crystallization metastable zone width of high concentration and poor light transmission solution.In order to improve the accuracy of the test,the original response method is improved,the deviation between the measured transmembrane flux and the model predicted one,?J,is pinpointed as the sensitive parameter to directly responded the initial nucleation(sub-micrometer scale)on the pores of the microporous membrane interface,which cannot be responded via the conventional optical and chemical technology.The robust and stable performance on effectively responding nucleation and MSZW measurement of this modified membrane distillation interface response was demonstrated in the five classic transparent and opaque solution system.As for the potassium nitrate aqueous solution system,the attenuation inflection point of the microporous membrane distillation interface response technology is always earlier than optical signal variation of laser intensity response technology,indicating that the membrane response can be more sensitive to nucleation and more accurate for the measurement of metastable zone width was;for the low transmittance of copper chloride salt solution system,the light intensity signal of the laser intensity response is too low to be determined,but the microporous membrane interface response technology can complete the nucleation response and data determination.As for the evaporative crystallization of NaCl aqueous solution,the transmembrane flux increases with the increase of temperature in NaCl aqueous solution under the same stirring rate,pressure and feed flow velocity,and the metastable zone width increases with the increasing temperature due to the enhanced solution concentrating process,the nucleation detection time is much more earlier than the optical technology,which shed light on promoting the industrial nucleation control via membrane distillation interface response based system.The effect of different liquid volume and membrane area on the metastable zone of the solution had been investigated.The small volume of the liquid or the large membrane area is beneficial to the crystallization nucleation process.At the same time,the different stages of the crystal growth state and response of the membrane surface were compared,and the state of the crystal in the solution at the time of the initial nucleation response was also studied.This novel microporous membrane interface response can provide important fundamental parameter for process design and optimization in typical and novel crystallization processes,providing the potentials on the online research of initial nucleation processes.