【作者】 孙勇；

【导师】 刘红晶； 姚辉；

【作者基本信息】 沈阳工业大学 ， 化学工程， 2019， 硕士

【摘要】 伴随工业高速发展所产生的大量工业废水越来越对自然环境造成极大的危害。针对工业废水中的高盐度有机废水处理这一难题,在众多的处理方法中,膜蒸馏备受关注。这种方法具有不受限于溶液的浓度,所需真空压力较低,溶液处理温度较低等优点。然而目前市场上的膜很难符合膜蒸馏过程对疏水性能和自清洁性能的要求,所以研制出适合膜蒸馏应用的膜材料成为了该技术的关键。本文主要通过纳米石墨烯（GR）与纳米石墨烯/二氧化钛（GR/TiO₂）对聚偏氟乙烯（PVDF）膜进行改性,增强膜的疏水和抗污染性能,研究在减压膜蒸馏过程中膜的性能及操作条件对膜通量、截留率等性能的影响。首先研究了料液温度、料液流量、系统真空度和料液浓度等操作条件对膜通量、温度极化和截留率的影响。从实验结果中发现系统真空度与料液温度的增大,增强了跨膜传质的推动力,使膜通量也随之增大,但温度极化现象加重。料液流量的增大,削减了膜表面边界层的厚度,增大了减压膜蒸馏过程的膜通量,并减轻了温度极化现象。料液浓度的增大会使膜污染严重,降低膜通量。整个过程对盐分的截留率都达到了99.95%以上。其次对膜进行了石墨烯疏水改性,通过对膜进行表征,研究了石墨烯加入量对PVDF膜性能与结构的影响。研究表明,随着石墨烯浓度的增大,膜表面的接触角增大,当石墨烯浓度为0.8wt%时,膜表面接触角达到111.6°,但是石墨烯浓度增大,膜平均孔径增大,临街出水压力（LEP）值减小,在减压膜蒸馏实验中,膜通量随石墨烯浓度的增大而增大,为保证产品水的纯度,LEP值应大于2倍的系统真空度。最后在石墨烯-PVDF膜的基础上,通过共混的方法引入纳米TiO₂颗粒,利用TiO₂的光催化性能提高膜表面的自清洁能力。结果表明,TiO₂的加入使海绵状孔结构增多,增大了膜孔径,虽然表面粗糙度增大,但由于TiO₂的亲水性导致膜表面接触角降低到86.6°。在减压膜蒸馏实验中,TiO₂-石墨烯-PVDF膜表现出了良好的抗污染能力。通过紫外辅助,可以进一步强化膜的自清洁能力,在波长为254nm的紫外辅助、鼓入空气的条件下,膜通量为22.58kg/（m²·h）,且可以在长时间工作条件下保持较高的通量。更多还原

【Abstract】 Along with the rapid development of the industry,the large amount of industrial wastewater generated is of great harm to the natural environment.In order to solve the problem of high salinity organic wastewater treatment in industrial wastewater,researchers have developed many treatment methods.Membrane distillation is a separation method which has attracted much attention in recent years.This method has the advantages of no limition to the concentration of solution,low vacuum pressure and low temperature of solution treatment.However,the membrane on the market is difficult to meet the requirements of hydrophobicity and self-cleaning performance of the membrane distillation process,so the development of membrane materials suitable for membrane distillation applications has become the focus of this field.In this paper,polyvinylidene fluoride（PVDF）membranes were modified by nanographene（GR）and nanographene/titanium dioxide（GR/TiO₂）.The effects of membrane properties and operating conditions on membrane flux and retention rate during vacuum membrane distillation were studied.Firstly,the effects of operating conditions such as feed temperature,feed flow,system vacuum and feed concentration on membrane flux,temperature polarization and rejection were studied.Experimental results indicated that the increase of system vacuum and liquid temperature resulted in the increase of the transmembrane mass transfer driving force,and the membrane flux also increased.However,the temperature polarization phenomenon was aggravated.The increase of the flow rate of the feed liquid can reduce the thickness of the boundary layer on the surface of the membrane,increase the membrane flux during the distillation process of the vacuum membrane,and reduce the temperature polarization phenomenon.The concentration of salt in the feed solution increased,which led to serious membrane fouling and the decrease of membrane flux.The retention rate of salt in the whole vacuum membrane distillation process reached more than 99.95%.Secondly,the membrane was subjected to hydrophobic modification when grapheme was added into the casting solution.The effect of graphene content on the properties and structure of PVDF membranes was studied by characterizing the membranes.Studies have shown that the contact angle of the membrane surface increased with the increasing of the concentration.When the graphene concentration was 0.8wt%,the contact angle of the membrane surface reached 111.6°.The average pore size of the membrane increased with the increase of the graphene concentration,but the LEP value decreased with the increase of the graphene concentration.In the vacuum membrane distillation experiment,the membrane flux increased with the increase of graphene concentration.To ensure the purity of product water,the LEP value should be higher than 2 times of the system vacuum.Finally,on the basis of graphene-PVDF membrane,nano-TiO₂ particles were introduced by blending method,and the photocatalytic performance of TiO₂ was used to improve the self-cleaning ability of the membrane surface.The results showed that the addition of TiO₂ reduced the pore structure of the sponge and increased the pore size of the membrane.Although the surface roughness was increased,the contact angle of the membrane surface was lowered to 86.6°due to the hydrophilicity of TiO₂.In the vacuum membrane distillation experiment,the TiO₂-graphene PVDF membrane showed good anti-pollution ability.And the self-cleaning ability of the membrane can be further enhanced by ultraviolet assistance.Under the condition of ultraviolet assistance at wavelength of254nm as well as the induction of air injection,the membrane flux was up to 22.58kg/（m²·h）and can maintain a high flux for a long time.更多还原