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Preparation Method of Novel PTFE Hollow Fiber Membrane Proposed by Process Engineering

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Recently, the Institute of Process Engineering of the Chinese Academy of Sciences proposed to prepare a new type of polytetrafluoroethylene (PTFE) hollow fiber membrane based on nanofiber assembly by emulsion electrospinning. Compared with the PTFE hollow fiber membrane prepared by the traditional mechanical stretching method, the membrane has the advantages of nanofiber membrane (high porosity) and hollow fiber membrane (self-supporting and high loading density), and the whole membrane preparation process does not need to use organic solvents and lubricants, realizing a new breakthrough in the green preparation and membrane performance of PTFE hollow fiber membrane.

PTFE is considered to be an ideal hydrophobic membrane material because of its excellent corrosion resistance, thermal stability and hydrophobicity, but it is difficult to dissolve, has poor melt fluidity and is difficult to process. At present, the only processing method of PTFE hollow fiber membrane is mechanical stretching, but the low porosity of the membrane prepared by this method seriously restricts the efficiency of the separation process.

The team of Cao Hongbin, a researcher at the Institute of Process Engineering, proposed to mix polyoxyethylene (PEO), which has high viscosity of aqueous solution and is easy to thermally decompose, with PTFE particles as a binder to form an aqueous spinning solution, and a non-rotating wire electrode as a receiver for continuous preparation. The PEO coated PTFE particles were stretched into PTFE/PEO hybrid nanofibers under high voltage and deposited on the wire electrode to form an initial film. After sintering at a certain temperature, the PEO molecules in the initial membrane are completely decomposed, and the PTFE particles are melted into nanofibers and assembled into the target PTFE hollow fiber membrane through fiber node bonding.

The vapor flux of the membrane in membrane distillation applications reached 4.6 to 8.8 times that of commercial PTFE hollow fiber membranes and 3.2 to 11.6 times that reported in the literature. The micro-nano multi-level structure of the fiber gives the membrane superhydrophobicity, and shows high and stable desalination performance in the membrane distillation experiment with long-term and increasing salinity, indicating that it has good application prospects in the fields of seawater desalination and high-salt wastewater treatment.

Relevant results were published in the international journal of membrane science Journal of Membrane Science (j. m br. sci. 2019, 583, 200-208) and reprinted by the official website of China membrane industry association, science network, Sohu network and other media.

In recent years, the Environmental Resource Technology and Engineering Group of the Institute of Process Engineering has carried out a series of studies on the function/performance enhancement and large-scale preparation methods of nanofiber membranes. In order to improve the packing density of nanofiber membranes, researchers first proposed to assemble nanofibers into hollow membrane structures (Mater. Lett. 2017, 204, 8-11.); Based on the analysis of the movement trajectory of nanofibers during the spinning process, a new technology and theory for large-scale electrospinning of nanofiber hollow membranes (J. Membr. Sci., 2018, 562, 38-46) was developed, the membrane has been successfully applied to ammonia recovery from wastewater and shows high selectivity and flux (Sep. Purif. Technol. 2019,216, 136-146); A fast and broad-spectrum new welding method for regulating the pore size distribution and mechanical strength of nanofiber membranes is proposed (C Su, et al. J. Membr. Sci, 2019); Using the principle of additive manufacturing to deposit nanofibers and micron clusters layer by layer, the anti-fouling performance of the membrane is improved (C Su, et al. Environ. Sci. Technol. 2019).

The above work is supported by the National Natural Science Foundation of China and the National Key R & D Program.