Remarkably High Li+ Adsorptive Separation Polyamide Membrane by Improving the Crown Ether Concentration and Electron Density

Significance 

Lithium has become an important element in the last two decades owing to its critical applications in many fields, including rechargeable batteries, adhesives and ceramic drugs. In addition to being the lightest alkali metal, it exhibits other attractive properties like high specific heat capacity, high electrochemical activity and redox properties. In fact, lithium has been regarded as one of the most important elements for driving the creation of a sustainable economy, especially the transition from gasoline-driven vehicles to electric-driven ones. To this end, the demand for lithium has increased dramatically, necessitating the need to develop effective and green lithium extraction methods.

Currently, over 60% of lithium exists in brine and seawater. While there are several methods for extracting lithium from aqueous solutions, they suffer from several drawbacks that limit their applications. Selective adsorption separation, for example, is limited by the high loss rate, low adsorption capacity and low service life. Recently, crown ethers have been used to overcome these challenges, leading to the construction of a membrane-based solid-liquid adsorptive separation method by immobilizing crown ethers on carriers to capture lithium ions (Li+). Despite their remarkable performance, the uneven crown ether distribution and influence of crown ether site-induced mass transfer resistance are the main barriers to realizing efficient solid-liquid adsorptive lithium separation using crown ether-supported materials.

Previous results have revealed that incorporating crown ether into the polymer main chain could improve not only the even distribution of the load but also the crown ether density. This offers numerous advantages in the main chain of polyimide (PI) polymers. Inspired by these findings, researchers at Tiangong University: Dr. Liuyong Mao, Dr. Rui Chen, Dr. Jintao He, Professor Hongchang Pei, Professor Benqiao He, Professor Xiaohua Ma and Professor Jianxin Li synthesized a novel DAB14C4-based polyamide (14C4 PA) via polycondensation of DAB14C4 with 2,2-bis-(4-carboxyphenyl)-hexafluoropropane. Consequently, non-solvent-induced phase separation method was adopted to prepare polymer membranes and films. The 14C4 PA structure, the lithium adsorption performance and the adsorption kinetics and isotherms were studied. Their work is currently published in the peer-reviewed journal, ACS Sustainable Chemistry and Engineering.

The authors showed that the resulting polyamide membrane exhibited high porosity (72.7%), high mechanical strength (6.5 MPa) and significantly higher maximum Li+ adsorption capacity (40.1 mg g‑1). Compared with 14C4 PI membrane, 14C4 PA membrane achieved a 25% increase in the amount of Li+ adsorbed. This was partially attributed to the higher concentration (7.3% higher) of the crown ether. Consequently, the adsorption energy of Li+ on 14C4 PA was significantly larger than that on 14C4 PI. Furthermore, the adsorption of Li+ on the 14C4 PA polymer membrane was by chemical monolayer adsorption as validated by the adsorption kinetics and isotherms. The adsorptive selectivity for Li+ of the 14C4 PA membrane was remarkably higher, especially in the presence of Na+, K+ and Mg2+ interfering ions. The selective separation factors of Li+ to Mg2+, Na2+ and K2+ were 8.47, 14.0 and 25.7, respectively.

In summary, the study reported the synthesis of a novel 14C4 PA with high crown ether charge density and loading, good repeatability, high glass transition temperature, high molecular weight, remarkable thermal stability and excellent adsorption/desorption stability. The experimental results were consistent with the simulation results, suggesting the potential application of 14C4 PA in membrane-based Li+ adsorption separation. In a statement to Advances in Engineering, the corresponding author Professor Jianxin Li explained that their study provided a feasible approach for designing highly efficient Li+ adsorption membranes for selective separation and green extraction of Li+.

NOTE: The technology is now protected by intellectual property.

PATENT: Jianxin Li, Xiaohua Ma, Quanji Zhu, Hong Wang, Dibenzo crown ether polyimide polymer and the preparation method and application thereof, China Patent No. ZL202010073422.7 (issued date: January 03, 2023; Application date: January 22, 2020)

Remarkably High Li+ Adsorptive Separation Polyamide Membrane by Improving the Crown Ether Concentration and Electron Density - Advances in Engineering
In this study, a polyamide membrane with high Li+ adsorption selectivity and good repeatability was synthesized.

Remarkably High Li+ Adsorptive Separation Polyamide Membrane by Improving the Crown Ether Concentration and Electron Density - Advances in Engineering

Remarkably High Li+ Adsorptive Separation Polyamide Membrane by Improving the Crown Ether Concentration and Electron Density - Advances in Engineering
Fig. 3-7 The diagram of charge distribution between crown ethers on 14C4 PI (a) and 14C4 PA (b) and Li+.

About the author

Prof Jianxin Li

Director of China National Center for International Res. on Membrane Science and Technology, Tiangong University, China

Email address: [email protected]; Tel: +86 13920680300

Jianxin Li is serving as the Director of China National Center for International Res. on Membrane Science and Technology, Tiangong University, China since its inception in 2016 as the founding Director. Dr Jianxin Li started his academic career in 2002 as a research associate at the University of Colorado at Boulder (USA) after obtaining a PhD (Polymer Science) from the University of Stellenbosch. In the years that followed, I held various visiting professor positions in Japan, USA and China. Currently, he holds a position as Professor and Principal Investigator in China State Key Laboratory of Separation Membranes and Membrane Processes (SKL-SMMP), Tiangong University (formerly Tianjin Polytechnic University). He also works for Institute of Nanotechnology and Water Sustainability, University of South Africa as a professor extraordinarius. He has established a large research activity with a special focus on electro-catalysis and separation membranes and thus plays an increasingly important role in water treatment and resource recovery. To date, he has supervised over 90 Masters and PhD students to completion. He has published more than 220 research papers in peer-reviewed journals, 115 conference papers, 6 book chapters and 23 patents granted in various regions across the world.  

Main Research-Areas

  • Hollow Fiber Membrane Fabrication
  • Mixed Matrix Membranes and Supported Ionic Liquid Membrane Contactor
  • Membrane Functionalization for lithium isotope and Ionic Selective Separation and the Resource Recovery from Salt Lake and Seawater
  • Membrane Formation Mechanism and Facilitate Transport
  • Conductive Membrane and Electrocatalytic membrane reactor for pollutant degradation in industrial wastewater
  • Membrane Fouling Visualization and Hydrodynamics
  • Desalination, Drinking Water Treatment and Nanotechnology

Additional Information

Reference

Mao, L., Chen, R., He, J., Pei, H., He, B., Ma, X., & Li, J. (2022). Remarkably High Li+ Adsorptive Separation Polyamide Membrane by Improving the Crown Ether Concentration and Electron Density. ACS Sustainable Chemistry & Engineering, 10(30), 10047-10056.

Go To ACS Sustainable Chemistry & Engineering

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