Membrane distillation crystallization: From mechanisms and process control to sustainable production of tailored crystalline materials

Abstract

Membrane distillation crystallization (MDCr) has emerged as a promising technology to produce inorganic crystals from various feed solutions. MDCr leverages the benefits of membrane distillation (MD), including reduced membrane fouling, operation under waste heat or solar energy while facilitating high-purity crystal formation. This study provides a comprehensive operational assessment of MDCr and the governing mechanisms. The investigation emphasized the influence of temperature gradient, membrane characteristics and feed composition on the processes of supersaturation, nucleation and crystal growth. Attention was focused on the formation of the crystals, and the polymorphs' selectivity influenced by process configuration. Practical applications are discussed across inorganic materials, food and pharmaceutical industries, where MDCr shows potential for recovery of functional crystals. Despite promising application, MDCr remains affected by membrane fouling, wetting, and energy demand, which impact fouling, supersaturation and crystal growth dynamics. The role of in-situ monitoring, modelling and process control is identified to ensure reproducibility and scale-up. The findings show that process optimization and coupling of heat and mass transfer promote the formation of tailored crystalline materials from complex feed solutions. However, this process requires standardized methods, real-time analysis and techno-economic assessment to accelerate the MDCr deployment in the current industrial operations. • Mechanistic understanding of supersaturation, nucleation and crystal grow in MDCr. • Systematic evaluation of fouling, wetting and membrane material limiting MDCr's sustainability. • Risk identification of MDCr application linked to fluorinated membrane materials. • Defining the MDCr future research directions including AI-assisted process and smart membranes