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臭氧具有氧化能力较强、气源丰富易得、制备简单便捷、没有二次污染、脱色除臭能力强等优点,因此,被广泛应用于消毒和废水的处理中[1-2]。气液传质是臭氧氧化效果的主要限制性因素之一。在传统的臭氧氧化过程中,臭氧通常以气泡的形式注入液相,从而实现臭氧在水中的分散、溶解和传质[3-4],但传质受到气泡尺寸的限制,且存在占地面积大、泡沫、液泛等问题[5]。膜接触器是一种可选的替代方案。在膜接触器中,气液两相被膜相隔离,膜相提供了稳定且较大的气液传质界面,气体在浓度差的作用下扩散至液相并溶解,避免了上述问题的同时,可以在较紧凑的结构中达到较高的体积传质系数(
$ {k}_{\mathrm{L}}a $ )[4-7],提高了臭氧的传质效率。因此,膜接触器在臭氧氧化降解污染物方面具有一定的应用前景[8]。由于臭氧具有较强的氧化活性,因此,用于臭氧氧化膜接触器的膜材料必须是耐臭氧的。而PVDF中空纤维膜易制备、成本低、臭氧耐受性较强、具有一定疏水性,因此,常被用作臭氧膜接触器[2-3]。但在长期的运行过程中,传统PVDF中空纤维膜较高的孔隙率会导致部分或完全润湿的现象,增加了膜相气液传质阻力(膜孔内的液相阻力),从而降低了臭氧传质效率[9-12]。而提升膜材料表面疏水性,可减少液体进入膜孔的程度,进而降低膜相传质阻力。PDMS耐臭氧性良好、臭氧渗透性较强,同时具有致密的结构和优秀的疏水性[13-17]。若用PDMS对PVDF膜表面进行改性可有效提升PVDF膜的疏水性,从而改善膜润湿现象,提升其臭氧传质效果。因此,本研究将PDMS涂覆于传统PVDF膜表面,以提高其臭氧传质效率和长期运行稳定性[18-19]。
本研究利用涂覆-热固化法成功制备了PDMS-PVDF改性膜,采用多种方法对改性膜的结构和形貌进行表征,测试接触角、孔径和孔隙率等参数。探究不同实验参数对不同膜臭氧传质的影响,分析其体积传质系数和长期运行效果。同时,对改性膜、原PVDF膜和鼓泡曝气方式降解刚果红的效果进行比较。
PDMS疏水改性的PVDF膜接触器强化臭氧传质及刚果红的氧化降解效果
Enhanced ozone mass transfer and ozonation degradation of Congo red by PDMS hydrophobically modified PVDF membrane contactor
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摘要: 中空纤维膜接触器具有界面面积大、传质效率高等特点而被广泛应用于气液传质中。为改善聚偏氟乙烯(PVDF)中空纤维膜接触器的臭氧传质效果,利用聚二甲基硅氧烷(PDMS)对其进行涂覆改性以提高其疏水性,进而提高其臭氧传质和降解污染物的能力。利用ATR-FTIR、SEM-EDS和接触角等方法对膜进行表征,并对其臭氧传质和氧化降解刚果红的效果进行了研究。结果表明,PDMS涂层成功制备,PDMS-PVDF改性膜的疏水性明显提升,接触角由88.9°提升至114.5°。传质实验结果表明,改性膜接触器体积传质系数可达0.077 8 s−1,比原PVDF膜提高了26.2%。改性膜接触器在长期运行实验(12 h)中出水臭氧浓度保持稳定。改性膜接触器30 min内可降解99.2%的刚果红,降解速率常数为0.155 min−1,是原PVDF膜的1.4倍。以上研究结果表明,PDMS-PVDF改性膜接触器具有更高的疏水性和臭氧传质性能,长期运行效果稳定,在污染物处理方面具有一定应用前景。Abstract: Hollow fiber membrane contactors have been widely used in gas-liquid mass transfer process for the advantages of large interface area and high mass transfer efficiency. In this work, the coating modification with polydimethylsiloxane (PDMS) was used to increase the hydrophobicity of Polyvinylidene fluoride (PVDF) hollow fiber membranes and improve the ozone mass transfer and ozonation degradation performance for pollutants. The membranes were characterized by ATR-FTIR, SEM-EDS and contact angle test etc. Its effect of ozone mass transfer and ozonation degradation of Congo red were studied. The characterization technologies had confirmed that the PDMS coat had been successfully prepared. The hydrophobicity of original PVDF membrane increased with the modification of PDMS and the contact angle increased from 88.9° to 114.5°. The mass experiment results showed that the ozone mass transfer coefficient of the PDMS-PVDF modified membrane contactor was 0.077 8 s−1, which was 26.2% higher than that of the original PVDF membrane contactor. The modified membrane contactor maintained a stable ozone concentration in effluent and an excellent ozone mass transfer performance during the long-term experiment (12 h). The degradation efficiency for Congo red using the modified membrane contactor achieved 99.2% within 30 min. The degradation kinetic rate was 0.155 min−1, which was 1.4 times of the original PVDF membrane. This work suggested that PDMS-PVDF membrane contactor showed high hydrophobicity, excellent ozone mass transfer performance and long-term stability, which had an application potential for pollutants removal by ozone.
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Key words:
- membrane contactor /
- hydrophobicity /
- mass transfer /
- ozonation /
- Congo red
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表 1 不同传质方式传质系数对比
Table 1. Mass transfer coefficient for different contactors
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