The energy crisis and environmental issues continue to constrain the sustainable development of the economy and society. As an effective substitute for fossil energy, biomass energy is of great significance in optimizing energy structure, reducing greenhouse gas emissions, and solving the problems of agriculture, rural areas, and farmers. Bioethanol, as a new type of clean energy, has received widespread attention and is gradually becoming a beneficial supplement to fossil fuels. However, the industrialization process of cellulose ethanol faces the main problem of high production costs, which is due to the inhibition of microbial metabolism by solvent products, resulting in extremely low ethanol concentration in fermentation broth and a sharp increase in energy consumption in downstream separation processes. The pervaporation membrane separation technology has gradually become a research hotspot in recent years, with characteristics such as high stability, low energy consumption, and no cytotoxicity; Especially suitable for in-situ separation of bioethanol through process coupling. Polydimethylsiloxane membrane PDMS is a widely researched and demanded pervaporation membrane material; Considered as the benchmark for alcohol selective membrane materials. However, traditional PDMS film preparation uses thermal crosslinking method, which makes the curing process uncontrollable and takes too long, making continuous preparation difficult in industrial scale up processes.

　　Regarding the above issues, Professor Qin Peiyong and others from Beijing University of Chemical Technology innovatively utilized the ultra fast and controllable characteristics of photocrosslinking reaction to propose a series of photoinduced polymerization membrane formation process designs, greatly improving the preparation efficiency and separation performance of pervaporation membranes based on PDMS matrix. The research group previously reported that: (1) a UV free radical type film forming system was constructed, and the methyl acrylate based PDMS can be cured into a film after 30 seconds of UV irradiation, which is 3 majority orders of magnitude faster than traditional thermal crosslinking curing speed, greatly enhancing the film preparation efficiency and controllability of curing reaction (Angelw. Chem. Int. Ed.2019,5817175-17179); (2) A new method for cationic photoinitiated epoxy ring opening polymerization membrane formation was developed, which effectively avoided the influence of oxygen inhibition in semi closed operating conditions. The membrane formation time was 200 seconds, and the membrane separation factor of butanol/water solution was 45, with a membrane flux of 1119gm-2h-1 (J.Membr. Sci.2020612118472); (3) The visible light irradiation film formation process of PDMS was achieved using photoinitiator TPO-L, which solved the problem of light pollution during the operation of ultraviolet light. The membrane separation flux of furfural/aqueous solution was 1299.5gm-2h-1 and the separation factor was 40.2 (J.Membr. Sci.2022653120515). (4) By replacing traditional organic solvents with photoresponsive fluorine monomers, the solvent-free preparation process is achieved, reducing the surface free energy of the membrane, improving its anti biological fouling performance, and overcoming the Trade Off relationship between pervaporation performance and anti fouling performance (GreenChem. 2021,237053). (5) This review summarizes the research progress on PDMS based pervaporation membranes in the past 10 years. From four aspects: PDMS molecular structure design, functionalization of porous particles, advanced preparation methods, and fermentation separation coupling systems, methods and strategies for improving PDMS membrane preparation efficiency and enhancing separation performance are summarized. This review has certain reference value for promoting the application of PDMS membranes in the field of biofuel alcohol preparation (Sep. Purif. Technol. 2022298121612).
Highlights of the article
In traditional polymer photocuring systems, the photoinitiator PI is usually physically blended with the prepolymer in a free state. Due to significant differences in its physical and chemical properties with the polymer, the casting solution is unstable for a long time, resulting in PI aggregation, precipitation, and even phase separation; The part with less PI distribution leads to insufficient efficiency, incomplete local curing, and inability to continuously roll, resulting in defects. This work reports a new method for preparing self initiated self polymerized membranes based on the PI-PDMS integration strategy. By simultaneously modifying the PDMS molecular chain with PI-1173IPS and crosslinking agent KH571, a PDMS prepolymer with the function of "self initiated self polymerized" was successfully synthesized; The prepolymer can be stably stored for 10 days with a PI content>5wt%; The degree of polymerization can reach 80-91% within 1 minute; The membrane has excellent performance in separating ethanol/water solutions, with separation factors and membrane flux reaching up to 8.5 and 1277gm-2h-1, respectively. Importantly, this method has certain universality and can provide a reliable approach for the large-scale preparation of photocrosslinking of polymer films.
Figure 1. Mechanism diagram of improving PI stability based on PI-PDMS integration strategy.
Figure 2. PDMS prepolymer synthesis route with both "self initiation self polymerization" function.
Figure 3. Comparison of ethanol separation performance of the prepared membrane with results reported in recent literature.
The relevant articles are published online in Journal of MaterialsChemistry A. This project has received funding and support from the National Key R&D Program and the National Natural Science Foundation of China. The first author of the article is Dr. Si Zhihao and master's student Liu Chang from Beijing University of Chemical Technology, and the corresponding author is Professor Qin Peiyong from Beijing University of Chemical Technology.