Crystal growth analysis in a membrane crystallization process using focused beam reflectance measurements (FBRM)

Abstract

Future challenges in Membrane Crystallization (MCr) require a deeper understanding of the nucleation and crystal growth phenomena. This study first proposes using focused beam reflectance measurements (FBRM) to quantify the real-time crystal growth rate in a MCr process under single-cycle and multi-cycle batch operations. The assessment was performed at different temperatures and feed flowrates using a near-saturated NaCl brine. Results showed that flowrate variations at temperatures above 30 °C influence the size selectivity of the chord length distributions. Also, the relationship between water recovery rates and the number of counts at temperatures of 45 °C and 60 °C exhibited a maximum zone in the number of counts influenced by flowrate variations. Additionally, the temporal variation of the predicted mean crystal size agreed with the experimental measurements obtained by optical microscopy (OM), reaching values in the range of 100 to 200 μm. And, the crystal growth rate showed a coherent behavior with the flowrate variation, which explains both the direction towards which it occurs particle size selectivity and the OM observation of opacity or transparency of crystals. Finally, this study proposes a methodological approach that could support the future application of the MCr process in several processes, such as zero liquid discharge (ZLD) plants and the production of valuable compounds.