Sweeping Gas Membrane Distillation (SGMD) as an Alternative for Integration of Bioethanol Processing: Study on a Commercial Membrane and Operating Parameters

This article considers the application of the sweeping gas membrane distillation process (SGMD) for direct separation of ethanol-water using a flat sheet PTFE membrane. It also studies the effect of operating parameters including feed concentration, feed temperature, feed flow rate, and sweeping gas flow rate on the permeation flux and selectivity of ethanol/water. The results showed that the increase in feed temperature increases in permeate flux and selectivity. Selectivities of 18.5 to 25 were achieved using dilute feeds within the temperature range of 35 to 55°C. However, by increasing the feed concentration by more than 5 wt.%, the selectivity was decreased. The increase in permeation flux and ethanol selectivity at higher feed flow rates was mainly due to the reduction of polarization effects. Moreover, the PTFE membrane was characterized by AFM. The results showed that the present process could be used as a stand-alone technique for bioethanol process integration.     

Application of Taguchi method in optimization of desalination by vacuum membrane distillation

This research focuses on desalination via vacuum membrane distillation (VMD). In order to enhance the performance of VMD in desalination and to get more flux, effects of operating parameters on the yield of distillate water were studied. Four parameters at three levels were selected: temperature (35, 45, and 55 °C), vacuum pressure (30, 80, and 130 mbar), flow rate (15, 30, and 60 mL/s) and concentration (50, 100, and 150 g/L). Taguchi method was used to plan a minimum number of experiments. The optimal levels thus determined for the four factors were: temperature 55 °C, vacuum pressure 30 mbar, flow rate 30 mL/s and concentration 50 g/L. The results show that increasing temperature and decreasing vacuum pressure improve permeate flux. However, the permeate flux increases with increasing flow rate initially and then reaches to a maximum value at 30 mL/s and then decreases with increasing the flow rate.     

气扫式膜蒸馏传质传热过程

对气扫式膜蒸馏（SGMD）的热量和质量传递机理进行了研究,建立了该过程的热量和质量传递模型,并对模型进行了计算,得出了吹扫气流速、组件长度、进料流速和进料温度对膜通量的影响。通过实验对模型计算结果进行了验证。实验结果表明模型计算值与实验值非常接近。随吹扫气流速的增大,通量先增加然后趋近于平衡。组件长度越短通量越高。进料流速对通量的影响很小,随膜丝内Reynolds数的增加,通量稍有增加,随进料温度的升高,通量呈指数倍增加。     

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。     

用于膜蒸馏的膜材料现状

综述了用于膜蒸馏的膜材料及其性能。阐述了聚四氟乙烯膜用于纯水及盐水物系的膜蒸馏性能。膜应用物系的广泛性及其截留性能;介绍了聚偏氟乙烯膜结构的非对称性,不同添加剂和非溶剂对其性能的影响;评述了聚丙烯平板膜及中空纤维膜的研制及应用现状,并比较了3种膜材料的性能及研制方法,同时对膜蒸馏膜材料的研究开发前景进行了展望。     

疏水性PTFE微孔膜处理含Cr(Ⅲ)稀溶液的实验研究

废水中的三价铬在自然环境中容易转化为毒性更强的六价铬。控制并回收废水中的三价铬可达到节约资源和降低污染的目的,用减压膜蒸馏(VMD)分离装置,实验探讨了不同平均孔径大小的聚四氟乙烯(PTFE膜对处理含铬(Ⅲ)溶液的膜通量、截留率等影响,研究了进料浓度、进料温度对分离性能的影响。实验结果表明,对于膜孔径较小的膜,膜内的传质阻力成为主要因素,膜内的传质是VMD过程的控制步骤。     

真空膜蒸馏处理垃圾渗沥液反渗透浓水的研究

采用疏水聚四氟乙烯(PTFE)中空纤维膜对垃圾渗滤液反渗透浓水进行真空膜蒸馏(VMD)试验,研究了曝气量、原液温度、冷侧真空度和浓缩倍数等对产水通量、COD、BOD5、氨氮含量、电导率、色度和pH的影响。结果表明,曝气可提高产水通量,当曝气量超过4 m3/(h.m2)时,产水通量趋于稳定;随着原水温度和真空度的提高,产水通量显著增加;浓缩倍数增大会降低产水通量,浓缩4倍后产水通量急剧下降。试验最大产水通量为8.38 kg/(h.m2),产水COD≤100 mg/L,BOD5≤30 mg/L,NH3-N的质量浓度≤25 mg/L,色度小于40度,电导率≤60μS/cm。     

减压膜蒸馏淡化罗布泊地下苦咸水研究

考察了减压膜蒸馏淡化高浓度盐溶液过程中料液温度、浓度、冷侧真空度对膜通量及截留率的影响,结果表明：温度与膜的渗透通量成指数关系;浓度对膜渗透通量的影响呈倒S形;冷侧真空度拐点后膜的通量与膜两侧水蒸汽分压平方根的差成直线关系,这种关系说明了水蒸汽在膜孔内的传质过程是以扩散为主;将减压膜蒸馏过程应用于新疆某地下电导率达到102500μS／cm的地下苦咸水淡化处理,可获得馏出液电导率均小于10μS／cm的较好效果。设计了出水量约为1m^3／h的减压膜蒸馏装置,并初步进行了经济评价。     

膜蒸馏法处理甲醇水溶液的研究

采用自制中空纤维膜蒸馏组件对含甲醇水溶液进行膜蒸馏处理研究 ,考察了影响甲醇通量的因素。如料液温度、浓度、流速 ,以及载液流速等。找到了最佳的工作条件。在料液温度 45℃ ,载液温度 2 0℃ ,两侧流速为 1 1 .5 m L/min的条件下 ,膜通量约为 0 .45× 1 0 -3kg/m2· h。浓度高达1 0 mg/m L的甲醇水溶液经处理后可降至 0 .0 3mg/m L以下。     

液隙式热泵膜蒸馏海水淡化系统的热力性能分析

热泵膜蒸馏是一种新型的膜分离技术,在处理高浓度盐水方面具有很大的优势,而目前的热泵膜蒸馏系统存在渗透量较低、冷却水消耗量大等问题。为提高渗透量、减少冷却水的消耗,设计了一种新型液隙式热泵膜蒸馏的海水淡化系统,通过在Aspen Plus中自定义膜模块建立经过实验验证的系统仿真模型,研究了进料液温度、渗透侧温度及进料流量对系统膜通量及能效比等热力参数的影响。结果表明,渗透侧温度降低可引起渗透量增加和能效比减小,且在低渗透侧温度情况下渗透侧温度的改变对能效比影响更大。随着渗透侧温度变化,存在一个渗透侧温度使造水比最大且吨水能耗最小,研究工况下最大造水比可达3.42,最小吨水能耗为463 MJ/t,且该最佳渗透侧温度随进料液温度增加而增加。进料液流量增加可引起渗透量和能效比增加,引起吨水能耗升高和造水比降低,当进料液流量小于3 L/min时,进料液流量增加对吨水能耗和造水比的负面影响较显著,进料液温度为50℃时,料液流量从1.5 L/min增至3 L/min,造水比的降低幅度可达33.5%;料液流量从4.5 L/min增至6 L/min时,造水比的降低幅度降至10.6%。     

苯酚的膜蒸馏及结晶回收处理研究

采用中空纤维蒸馏技术研究了含酚废水的膜蒸馏处理及结晶回收,考察了料液相的温度、酸度、流速、吸收液浓度以及结晶回收苯酚等因素对苯酚膜蒸馏及结晶过程的影响。结果表明：以2％的NaOH溶液为吸收液时,膜蒸馏通量与料液相流速率有苯酚的浓度成正比,而当料液pH低于2．5及温度高于40℃的条件下,膜蒸馏通量几乎不受上述两因素的影响。以浓度为5000μg/mL的苯酚溶液为料液,经膜蒸馏处理可降至50μg/mL。采用CO2气流处理NoOH吸收液,即可得到结晶苯酚。     

结晶膜蒸馏回收废水中氯化铵的研究

采用自制中空纤维膜蒸馏组件对含氯化铵工业废水进行结晶膜蒸馏实验研究,考察了影响水通量的因素,如料液温度、浓度、流速,以及吸收液的流速、浓度等。找到了最佳的工作条件。在料液温度45℃,吸收液温度20℃,两侧流速为11.5ml/min的条件下,膜通量约为1.53×10-3kg/m2·h。经6小时的膜蒸馏NH4Cl开始结晶析出,氯化铵的截留率在95%以上。     

减压膜蒸馏法处理苯胺废液研究

采用减压膜蒸馏法处理模拟的苯胺废液,考察了料液的温度、pH、流量和冷侧真空度对处理效果的影响。结果表明,装置运行的优化条件是:料液的pH为9,温度为35℃,体积流量为20 mL/min,冷侧真空度为95 kPa,在此条件下,应用减压膜蒸馏法处理苯胺质量浓度为400mg/L的废液,去除率可达98%以上,膜通量可达到39.71 g/(m.2h),处理后废液苯胺的质量浓度可降至4.82 mg/L,可满足GB 8978-1996三级排放要求。     

错流式减压膜蒸馏海水淡化试验研究

采用聚丙烯(PP)中空纤维膜制作了矩形中空纤维膜组件进行减压膜蒸馏海水淡化试验,考察了不同操作条件对膜通量的影响以及膜通量的衰减和膜污染情况,探讨了海水膜蒸馏的操作条件-膜通量曲线的特征。试验过程中获得了比较高的膜通量,最高膜通量达到了46 kg/(m2.h),产水电导率保持在100μS/cm以下,过程的脱盐率保持在99.99%以上。     

Coupling reaction and azeotropic distillation for the synthesis of glycerol carbonate from glycerol and dimethyl carbonate

A new process, coupling reaction and azeotropic distillation was proposed for the synthesis of glycerol carbonate (GC) from glycerol (G) and dimethyl carbonate (DMC). The bench scale experimental investigation was systematically conducted for this new process. With calcium oxide (CaO) as the solid catalyst, the high yield of glycerol carbonate can be obtained at a low molar ratio of dimethyl carbonate to glycerol with the method of coupling reaction and azetropic distillation. The effect of azeotropic agents on glycerol carbonate yield was explored, and indicated that benzene was the most effective azeotropic agent. The effects of the process parameters, tower height, amount of added benzene, final temperature of tower bottom and reflux ratio were investigated. Glycerol carbonate yield can be as high as 98% under the conditions at molar ratio of dimethyl carbonate to glycerol 1:1, final temperature of tower bottom 85 °C, 1.5 mass ratio of added benzene to that in the azeotrope with methanol theoretically produced and reflux ratio 4. By continuously removing methanol from reaction system with the method of coupling reaction and azeotropic distillation, the yield of glycerol carbonate can be retained at high level using the recycled catalyst.     

气态膜法提溴伴生渗透蒸馏过程试验研究

利用制盐工业卤水作为含溴原料液、NaCOOH溶液为吸收液、HBr+NaBr溶液为提溴产物,分别与流经膜另一侧的纯水组成试验体系,考察了料液流量、浓度和操作温度对渗透通量的影响,回归得到了渗透系数计算式。并对NaCOOH溶液-卤水体系的渗透通量进行了计算和试验测定。计算与试验结果具有相同的趋势。对气态膜法提溴过程和渗透蒸馏过程的特点进行了分析,提出抑制渗透蒸馏现象发生的措施。     

A new enhancement technique on air gap membrane distillation

The most serious concern in the application of air gap membrane distillation (AGMD) configuration is the low permeate flux caused by an additional transport resistance owing to the air gap, by the temperature and concentration polarization and by the surface fouling. This paper presents an innovative design of a low-cost and high efficient membrane module with an advanced enhancement technique in an AGMD configuration, which not only yields a much improved permeate flux but also requires no additional facility for the enhancement. The new module design includes a tangent directional and rotational inlet turbulent flow of hot feed and a partial contact between the membrane and the cooling plate in a small air gap. The concrete structure of the module is introduced in detail in the paper. Using this new module the permeate flux can be obtained up to 119 kg/m²h for tap water when the temperature of the hot and cold water is 77 °C and 12 °C respectively, which is about a 2.5-fold improvement over the traditional AGMD technique at the almost the same conditions. Within the range of our experimental study, the optimum partial contact area ratio is about 75–80%. Mechanistically, the tangent and rotational inlet turbulent flow can accelerate the diffusive process of mass and heat, reduce the boundary layer thickness of temperature and concentration and wash the membrane surface so as to improve the temperature and concentration polarization near the membrane surface and to raise the efficiencies of mass and heat transfer. Because of the partial contact between the membrane and the cooling plate with a large area, the main heat transfer and permeate condensation in the gap both are carried out on the contact area, which is very different from either the common AGMD or DCMD (direct contact membrane distillation) so as to reduce the transport resistance in the gap and thus to raise the permeate flux significantly. The new enhancement technique is also applied for the desalination of 15 wt.% salt water, which shows the similar improvement in permeate flux.