TiO2光催化氧化降解偶氮染料废水的研究

以偶氮染料直接耐酸大红4BS模拟废水为研究对象,以TiO2为光催化剂,紫外灯作光源（80W）,探究了不同TiO2催化剂的用量、光照时间、溶液初始pH值及废水初始质量浓度等因素对偶氮染料废水降解率的影响。实验结果表明,偶氮染料直接耐酸大红4BS废水的最佳处理条件为：TiO2催化剂质量浓度1．2g／L,光照时间120min,初始pH值10,废水初始质量浓度20mg／L。在最佳处理条件下,对某染料厂的实际工业废水样进行了降解率的测定,得出其降解率在90％以上。     

Radiation absorption and degradation of an azo dye in a hybrid photocatalytic reactor

Results are presented for the photocatalytic degradation of an azo dye, reactive blue 69, in a novel hybrid photocatalytic reactor, illuminated by solar radiation and artificial light, under different experimental conditions. A radiative transfer model, based on the P1 approximation, is proposed to evaluate the distribution of local volumetric rate of photons absorption (LVRPA) in the reaction space of the hybrid photocatalytic reactor. This radiation transfer model, together with a first order kinetic model, is used to fit the experimental results. The model correlates well with the experiments, and values for an apparent first order kinetic constant for the degradation of RB69 are obtained. The proposed radiative transfer model (P1 approximation) is simple enough to allow for an analytical solution, yet complex enough to take into account scattering of radiation in all directions and to all orders. Simulations show a distribution of LVRPA that varies smoothly at small catalyst concentration, and is very quickly attenuated for high concentrations. Around of 70% of photons supplied by both illumination sources to the hybrid photocatalytic reactor are absorbed by the catalyst. The experimental results show the decolorization degree increases as catalyst concentration increase. In relation to mineralization process, the removal of total organic carbon is nearly complete after 5 hours irradiation. This indicates that not only the azo bond breakage is carried out, but also that the intermediate species are mineralized. The apparent kinetic constant has a dependence on catalyst concentration which is described by an adsorption model. Addition of oxygen by means of an air diffuser proves to be beneficial to the process.     

A new model for mass transfer in direct contact membrane distillation

The mass transfer process in direct contact membrane distillation (DCMD) for three kinds of membranes was measured. Water fluxes at different temperatures and the membrane distillation coefficients (MDC) for each membrane were obtained directly from experimental data. The fact that the MDC values of membranes with larger pore size increase with temperature indicates that Poiseuille flow plays an important role in the process of mass transfer through the membrane. Based on this conclusion, a three-parameter model, named the Knudsen diffusion-molecular diffusion-Poiseuille flow transition (KMPT) model, was developed to predict MDC and water flux for membrane distillation. The parameters of the KMPT model for each membrane employed in this study, by which MDC at various temperatures can be determined, were evaluated by a nonlinear regression. The values of MDC and water fluxes for each membrane predicted by KMPT model agree well with that obtained directly from the experiment results. A large contribution of Poiseuille flow to mass transfer was observed and can be attributed to the distribution of large pores in the membranes. The KMPT model also provides a method for estimation of the effect pore size using the ratio of the MDCs; the ratio of the Poiseuille flow to molecular diffusion MDC provides the best estimation.     

Hydrophobic PVDF hollow fiber membranes with narrow pore size distribution and ultra-thin skin for the fresh water production through membrane distillation

Polyvinylidene fluoride (PVDF) hydrophobic asymmetric hollow fiber membrane was fabricated through the dry-jet wet phase inversion process. It is found that the PVDF hollow fiber has an ultra-thin skin layer and a porous support layer from the morphology study. The fully porous membrane structure has the advantage of decreasing the vapor transport resistance and enhancing the permeation flux. The fabricated PVDF membrane has a mean pore size of in diameter and a narrow pore size distribution. The rough external surface produces an advancing contact angle of 112±3^° with water. During direct contact membrane distillation (MD) of 3.5 wt% salt solution, PVDF hollow fibers produced a water permeation flux of (based on the external diameter of hollow fiber) and a NaCl rejection of 99.99% with a hot salt solution at 79.3 °C and cold distillate water at 17.5 °C. This performance is comparable to or superior to most of commercially available PVDF hollow fiber membranes, indicating that the newly developed PVDF may be suitable for MD applications.     

Simulation of membrane distillation modules for desalination by developing user's model on Aspen Plus platform

This paper presents a simulation study of direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD) for desalination. Simulation models are built on Aspen Plus^® platform as user defined unit operations for these two types of modules, respectively. Large scale modules for practical industrial applications are simulated and studied for the effects of design and operation variables, as well as the importance of heat and mass transfers of each phase. For each type of modules with heat recovery design, the response surface method (RSM) is applied to develop the performance-variables quadratic model, followed by the multivariable optimization. Optimal designs can realize separation efficiencies, defined as the ratio of water produced to the feed, of 8.2% and 5.8% for DCMD and AGMD, respectively.     

Application of response surface methodology for modeling and optimization of membrane distillation desalination process

In this work, response surface methodology (RSM) was applied for modeling and optimization of operating parameters for water desalination by direct contact membrane distillation (DCMD) process using polypropylene membrane (PP) with low pore size. Operating parameters including vapor pressure difference, feed flow rate, permeate flow rate and feed ionic strength were selected and the optimum parameters were determined for DCMD permeate flux. The developed model for permeate flux response was statistically validated by analysis of variance (ANOVA) which showed a high value coefficient of determination value (R² = 0.989). The obtained optimum operating parameters were found to be 0.355 × 10⁵ Pa of vapor pressure difference, feed flow rate of 73.6 L/h, and permeate flow rate of 17.1 L/h and feed ionic strength of 309 mM. Under these conditions, the permeate flux was 4.191 L/(m² h). Compared to a predicted value, the deviation was 3.9%, which confirms the validity of the model for the DCMD process desalination optimization. In terms of product water quality, the DCMD process using hydrophobic PP membrane can produce high quality of water with low electrical conductivity for all experimental runs.     

Hydrophobic mullite ceramic hollow fibre membrane (Hy-MHFM) for seawater desalination via direct contact membrane distillation (DCMD)

A low-cost hydrophobic mullite hollow fibre membrane (Hy-MHFM) fabricated via phase inversion/sintering technique followed by fluoroalkyl silane (FAS) grafting is presented in this study. The prepared CHFMs were characterized before and after the grafting step using different characterization techniques. The pore size of the CHFM surface was also determined using ImageJ software. The desalination performance of the grafted membrane was evaluated in direct contact membrane distillation (DCMD) using synthetic seawater of varying salt concentrations for 2 h at various feedwater temperatures. The outcome of the evaluations showed declines in the permeate flux of the membrane at increasing feed concentration, as well as increased flux with increased feed temperature. The long-term stability of the membrane was achieved at time 20 h, feed temperature 60 °C, and permeate temperature 10 °C, the membrane achieved a salt rejection performance of about 99.99 % and a water flux value of 22.51 kg/ m² h.     

Pathways of solar light-induced photocatalytic degradation of azo dyes in aqueous TiO2 suspensions

The photocatalytic degradation of aqueous solutions of Acid Orange 7 in TiO₂ suspensions has been investigated with the use of a solar light simulating source. The photoreaction was followed by monitoring the degradation of the dye and the formation of intermediates and final products, as functions of time of irradiation, both in solution and on the photocatalyst surface. It has been found that the dye adsorbs on TiO₂ and undergoes a series of oxidation steps, which lead to decolorization and formation of a number of intermediates, mainly aromatic and aliphatic acids. These molecules are further oxidized toward compounds of progressively lower molecular weight and, eventually, to CO₂ and inorganic ions, such as sulfate, nitrate and ammonium ions. A TiO₂-mediated photodegradation mechanism for Acid Orange 7 is proposed on the basis of quantitative and qualitative detection of intermediate compounds.     

直接接触式与气隙式膜蒸馏的比较研究

采用模拟计算和实验的方法对直接接触式膜蒸馏 (DCMD)和气隙式膜蒸馏 (AGMD)过程进行了比较研究。模拟计算及实验结果表明 ,AGMD中的气隙构成了过程的主要阻力 ,使得跨膜温差远小于膜两侧流体主体温差 ,这是两种膜蒸馏方式行为差别的主要原因所在。与AGMD相比 ,DCMD不仅膜通量水平高 ,而且膜通量对操作条件反应灵敏 ,易于实施过程的强化。而DCMD的热效率与AGMD相比差距并不太大。     

焦耳效应强化气隙式膜蒸馏脱盐过程的实验研究

以膜蒸馏海水淡化为背景,通过对自制导电炭膜通入直流电产生焦耳效应,开展焦耳效应强化膜蒸馏氯化钠水溶液脱盐过程实验研究。结果表明,制备的煤基炭膜在100℃内具有良好的结构稳定性;在实验范围内,炭膜对氯化钠的截留率在99.96%以上;焦耳效应对膜蒸馏渗透通量的提高率最高可达60%,且低温时焦耳效应对膜蒸馏的强化效果更好、电转换效率更高;引入的焦耳热除用于水分汽化外,还可提高料液温度、改善温度极化、增加传质推动力;焦耳效应同时对膜蒸馏过程传质系数产生影响,在进料温度为50~80℃时,受努森扩散和分子扩散影响,电流为1A时传质系数值将减小,电流为3A和5A时传质系数值将增大;膜蒸馏过程引入焦耳效应不会产生氧化还原反应和额外膜结垢;在炭膜中引入电流不会破坏炭膜及其表面PDMS层的结构。本文研究内容丰富了膜蒸馏海水淡化过程的强化方法,也可为焦耳效应影响膜蒸馏过程的模拟研究及工业应用提供依据。     

Integrated forward osmosis–membrane distillation (FO–MD) hybrid system for the concentration of protein solutions

For the first time, an integrated forward osmosis–membrane distillation (FO–MD) hybrid system has been demonstrated for the concentration of protein solutions, specifically a bovine serum albumin (BSA) solution. A hydrophilic polybenzimidazole (PBI) nanofiltration hollow fiber membrane and a hydrophobic polyvinylidene fluoride-polytetrafluoroethylene (PVDF-PTFE) hollow fiber membrane were fabricated and employed in the FO and MD processes, respectively. A concentrated NaCl solution was employed as the draw solute to dehydrate proteins in FO, while distillate water is a by-product during the re-concentration of diluted NaCl draw solution in MD. To determine suitable operating conditions for the hybrid system, independent characterizations were carried out for both FO and MD processes using different NaCl concentrations as draw solutes in FO and different feed temperatures in MD. It was found that the integrated system is stable in continuous operation when the dehydration rate across the FO membrane is the same as the water vapor rate across the MD membrane. Simple mathematical models consistent with the experimental results were also developed for the FO and the FO–MD hybrid systems. The newly developed FO–MD hybrid system is promising for the concentration of pharmaceuticals/protein solutions in the foreseeable future.     

膜组件与膜反应器除氧技术的比较研究

除氧是工业用纯水生产过程中的重要步骤。针对传统物理除氧和化学除氧的缺点，提出了膜反应器除氧的技术，并从除氧效果及其原理两方面与膜组件除氧技术加以比较，结果发现膜反应器可采用物理和化学方法结合去除水中的溶解氧，其出水溶解氧含量显示出很好的水平。     

Preparation and properties of PVDF-fabric composite membrane for membrane distillation

The flat sheet PVDF-fabric composite membrane used for membrane distillation was prepared by coating and wet phase inversion process. The composite membrane consisted of a PVDF porous membrane layer and a fabric layer. The thin polyester filament woven fabric with water-and-oil repellent finish was used as the support of composite membrane. The effects of fabric texture, PVDF concentration in casting solution and functional finishing of fabric on the preparation and properties of the composite membrane were investigated. The experimental results showed that fabric texture, PVDF concentration and functional finishing of fabric had great influence on the preparation and properties of the composite membrane. When the PVDF concentration in casting solution was 10-12% and the support fabric, with 435 warps/10 cm and 273 wefts/10 cm and the area weight of 79 g/m², was finished with 2 g/L water-and-oil repellent agent FK-501, the prepared composite membrane exhibited better performance in tensile strength, peeling strength and water vapor permeability, with mean pore size of 0.63 μm and overall porosity of 57.6%.     

膜蒸馏过程强化及优化技术研究进展

膜蒸馏作为一种新型的膜分离技术,具有脱盐率高、可处理高浓度原料液等技术优势,近年来引起学术界及工业界的广泛关注.膜蒸馏技术可被应用于海水淡化,工业废水/苦盐水脱盐及糖、盐、果汁、有机/无机酸、碱液等的浓缩过程.但由于当前膜蒸馏能耗及成本较高,一定程度上限制了该技术的工业化.本文重点介绍了可用于强化膜蒸馏过程和优化该过程能量利用的方法及研究进展,主要包括膜材料和膜制备方法/工艺的进展、膜蒸馏过程操作条件的优化、改进膜组件和辅助装置的应用、太阳能和低品位热源的使用、蒸发冷凝潜热的回收以及耦合其他分离过程的复合膜蒸馏系统,同时分析了膜蒸馏技术处理高盐工业废水的应用前景,最后探讨和总结了膜蒸馏过程强化及优化的研究方向,为该技术的进一步发展提供了科学性指导.     

精馏-膜分离技术集成过程研究进展

精馏-膜分离集成过程与传统精馏工艺相比,因其具有明显节能降耗的经济性优势,故工业应用日渐增多,所以对其进行全面研究更有理论和实际意义。本文介绍了膜分离的机理模型,根据膜的亲水性和亲有机性对膜材料进行分类,总结了精馏-膜分离集成过程的理论研究方法,并分别从脱水和脱有机物两方面介绍了精馏-膜分离集成过程的主要实验研究及工业应用研究进展。通过对现有研究分析发现,目前该集成过程在膜材料和集成优化理论研究方面存在一定局限性,使其未能在工业上得以广泛推广应用。基于上述全面分析,提出了一定改进思路。     

Mechanistic aspects of oxalic acid oxidation by photocatalysis and ozonation

Oxalic acid has been oxidised in acidic aqueous solutions (pH 3) using photocatalysis and ozonation alone or coupled. The simultaneous presence of ozone, titanium dioxide and near UV irradiation increases the oxidation rate of oxalic acid to values greater than those deriving from the single contributions of photocatalysis and ozonation. In particular in the present paper ozonation alone, heterogeneous photocatalysis and also combined ozonation with heterogeneous photocatalysis have been used for the oxidation of oxalic acid at acidic pH in the presence of TiO₂ Degussa P25. A likely mechanism, able to explain both the homogeneous and heterogeneous processes, is discussed.     

膜蒸馏脱盐中膜污染与膜润湿的研究进展

膜蒸馏作为一种脱盐的新兴技术受到广泛关注。然而,因为实际水质组分复杂,可能含有如表面活性剂、油类物质、易结垢盐和有机溶剂等污染物,导致一般疏水膜在长时间运行情况下极易发生膜污染或者膜润湿,最终造成膜通量或截留性能降低。本文首先简述了不同种类的膜污染和膜润湿的特点及形成原因,并分析了膜污染和膜润湿之间的区别和联系。对膜蒸馏过程中膜污染和膜润湿的监测和预测手段进行了简要介绍,最后针对膜蒸馏脱盐过程,重点介绍了近几年国内外预防膜污染和膜润湿的研究进展。研究者一般从污染物与疏水膜的相互作用力着手对疏水膜进行表面改性制备全疏膜和Janus复合膜,避免污染物在膜面的吸附以及抑制表面或孔道润湿。越来越多的研究人员采用致密亲水膜的渗透汽化脱盐来从根本上避免疏水膜带来的润湿。除此之外,对进料液进行预处理也能显著延迟膜的污染和润湿,如混凝/沉淀、膜过滤、煮沸、pH调控等,还可通过改变进料方式、辅助外加磁场等措施控制膜表面局部区域的流体力学状态,减少污染物的附着。适当的膜后处理措施也能恢复膜性能。最后,文章指出了解决膜蒸馏中膜污染和膜润湿的研究方向。     

液化天然气深冷-膜蒸馏海水淡化系统集成与分析

提出了一种PRICO天然气液化-膜蒸馏（MD）海水淡化系统集成方法,利用PRICO过程压缩机出口的余热驱动MD海水淡化。采用Aspen Plus和GAMS建立了集成系统的数学模型,综合考虑系统的结构、物流物性、设备规模、操作参数等系统设计问题,分析不同设计下系统的投资、能耗、运行费用以及MD单位产水成本。模型应用于一个处理量为1 kmol/s的PRICO天然气液化系统与MD集成的案例研究。计算结果表明,单位产水成本最小时,系统产水成本为1.98 USD/m³,淡水产量为5.78 m³/h,与反渗透等海水淡化技术相比,MD在经济性方面具有较强的竞争力。     

The pH influence on photocatalytic decomposition of organic dyes over A11 and P25 titanium dioxide

The photocatalytic removal (decomposition+adsorption) of four azodyes (Reactive Red 198, Acid Black 1, Acid Blue 7 and Direct Green 99) in water was investigated using Tytanpol A11 (“Police” Chemical Factory, Poland) and Degussa P25 (“Degussa”, Germany) as photocatalysts. The effect of pH of the reaction solution has been examined. The degree of the dye removal in the solution was measured by UV-Vis spectroscopy. Photodecomposition of dye on photocatalyst surface was monitored by FTIR spectroscopy. A11 photocatalyst has lower activity in the reaction of photocatalytic decomposition of organic dyes than Degussa P25. The photocatalytic decomposition of the dyes takes place on the photocatalyst surface at pH=2 while at pH=12 photocatalytic reaction proceeds via photogenerated hydroxyl radicals for both A11 and P25.