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The semi‐crystalline nature of poly(ether ether ketone) (PEEK) has been a great challenge to prepare PEEK membranes with targeted morphology and crystallization via immersion precipitation. This paper reported a novel observation of cold crystallization (CC) and the key factors affecting the formation of CC in the PEEK membrane via immersion precipitation phase separation, using mixture solvents of concentrated sulfuric acid (SA) and methane sulfonic acid (MSA). The CC in PEEK was identified by an exothermal peak slightly above the PEEK's glass transition temperature (Tg) at 146–150°C in differential scanning calorimetry (DSC). The CC formation was contributed to folded rigid segments resulted from the solid–liquid phase separation. Factors affecting CC investigated in the membrane preparation were the exposure time before immersion and the solvent ratio. It was found that increased exposure time from 0 min to 15 min in ambient led to cellular pore structure with decreased total crystallinity (28.9%–25.5%), but increased proportion of CC (27.7%–43.6%) for PEEK3:1 membrane. Increase of SA in the mixture solvent resulted in decreased CC and total degree of crystallization. Tensile strength measurements demonstrated that the CC contributed positively the strain of PEEK membranes. The findings suggested a new factor of CC for better understanding, control and design of PEEK membranes. [ABSTRACT FROM AUTHOR]

• Novel multiframe flat membrane contactor (MFMC) was designed for lithium extraction. • Loss of extractant TBP was reduced by 91% using MFMC comparing to liquid–liquid extraction. • Module efficiency of 90% was found in scaling-up. • Height of transfer units (HTU) of MFMC was projected to be about 3 m after future optimization. Comparing to conventional liquid–liquid extraction, membrane extraction is an efficient and environmentally friendly separation technique to recover lithium from the salt-lake brine. Development of suitable hydrophilic solvent resistant nanoporous membranes for membrane extraction has been based on bench-scale small module. Because module design has significant impact on the performance, this work reported a novel multiframe flat membrane contactor module (MFMC) for lithium extraction from synthetic brine. The hydrophilic poly (ethylene-co-vinyl alcohol)/sulfonated poly(ether ether ketone) membrane supported with polypropylene nonwoven (EVAL/SPEEK-NW) was prepared for module evaluation. The membrane mass transfer coefficients k m of 1.1 × 10-6 m/s was obtained by Wilson plot. The global mass transfer coefficient K e increased from 4.5 × 10-7 m/s to 9.9 × 10-7 m/s following the flow velocity from 0.4 to 1.8 cm/s in membrane extraction. We further evaluated the characteristics of MFMC via height of transfer units (HTU) and module efficiency (ME). High module efficiency of 90% was obtained, demonstrating MFMC's efficient flow distribution. HTU of 28 m was estimated and was expected to decrease to 3 m by optimizing thickness of gasket and spacer as well as membrane performance. The MFMC module effectively reduced the loss of tributyl phosphate (TBP) by 91% comparing to liquid–liquid extraction. The research presented herein provides a flat membrane module design for potential future application of membrane extraction in wide applications. [ABSTRACT FROM AUTHOR]

Membrane extraction (ME) is a promising technology for efficiently separating lithium from salt-lake brine with high Mg/Li ratio. By utilizing a solvent resistant semicrystalline poly(ether ether ketone) (PEEK), an extraction-stripping loop is envisioned, but significant improvement in the lithium extraction flux is required. We report in this paper a new finding of strong interaction of the extractant, Tributyl phosphate (TBP), to PEEK, leading to reduction in Li extraction flux. Phosphorous element inside PEEK substrate supported the finding; significantly higher Li flux was observed when the top surface faces the organic extractant than that when the bottom surface faces the organic. Mass transfer model detailed the consequence of infiltration by TBP to the ion flux due to the low diffusion coefficient of the bulky ion-extractant complex. We further coated a sulfonated PEEK (SPEEK) layer to effectively improve the lithium extraction flux by 154 %. This new finding provides a coherent understanding for previous results that morphology optimization did not show significant changes in ME performance. With current findings, membrane extraction is one step further to practical applications. [Display omitted] • Impregnation of organic solvent into PEEK membrane creates resistance to Li+ mass transfer. • Low diffusion coefficient of bulky ion-extractant complex was the main cause. • SPEEK coating prevents the impregnation of the extractant in PEEK membrane followed with increased Li+ flux. [ABSTRACT FROM AUTHOR]