膜法分离二甲苯异构体研究进展

介绍了近年来采用各类无机沸石膜、有机高分子膜分离二甲苯异构体的研究情况及最新动态,评述了各种膜在分离二甲苯异构体方面的优点和不足,并对各类膜法做了比较,最后对膜法分离二甲苯异构体的发展方向进行了展望。     

四通道中空纤维MFI分子筛膜用于二甲苯异构体分离

采用二次生长法在高机械强度、高装填密度的四通道α-Al₂O₃中空纤维载体(7 cm)上制备MFI分子筛膜,探究了膜合成时间、操作温度、原料分压和吹扫气流量等条件对二甲苯异构体膜分离性能的影响。结果表明,160℃水热合成12 h制得的四通道中空纤维MFI分子筛膜对二甲苯异构体分离性能较优,在150℃、原料分压2 kPa、吹扫气流量20 ml/min时对二甲苯/邻二甲苯分离因子高达878,PX渗透性为2.1×10^-8 mol·m^-2·s^-1·Pa^-1。基于优化的制膜及分离操作条件,进一步将MFI分子筛膜制备于27 cm长的四通道中空纤维载体上,也获得了优异的对二甲苯/邻二甲苯膜分离性能,且所制得的膜材料对该体系的分离可稳定运行100 h以上。为推进中空纤维MFI分子筛膜的批量化制备和传统分离工艺的技术革新奠定了基础。     

从二甲基萘异构体中分离2,6-二甲基萘的研究进展

2,6－二甲基萘是制备高性能聚酯－聚对萘二甲酸乙二醇酯最理想的原料,如何低成本地获得2,6－二甲基萘已成为一项重要的课题。本文介绍了从二甲基萘异构体中分离2,6－二甲基萘的方法,即超临界萃取法、压力结晶法、吸附分离法及冷冻结晶法等,并论述了它们的优缺点及日后的发展方向。     

特殊精馏法分离二甲苯异构体的研究进展

由于二甲苯异构体的沸点相差很小,用普通精馏方法分离二甲苯异构体比较困难,从增大二甲苯异构体之间的相对挥发度入手,能够使它们部分分离。总结了国内外利用特殊精馏法分离二甲苯异构体的研究进展,并对其进行了展望。     

混合二甲苯分离技术研究进展

混合二甲苯分离技术主要有络合法、常压低温结晶法、精密精馏法等方法。吸附分离法因其具有单程的收率高、分离工艺条件较缓和、无毒性、无腐蚀性、在全部液相操作条件下不需要特定的设备、生产投资小和能耗较低等优点而得以推广。对吸附剂的改性研究可进一步提高分离效果,因此吸附法在分离混合二甲苯方面具有很好的发展趋势。     

乙苯及二甲苯异构体的分离

乙苯及二甲苯异构体的分离王素兰（兰州化学工业公司化工研究院，７３００６０）裂解汽油Ｃ６～Ｃ８馏分经二段加氢后产品是芳烃抽提的原料。为求得各芳烃的准确含量，特别对沸点相近的乙苯（沸点１３６．２℃）、对二甲苯（沸点１３８．４℃）和间二甲苯（沸点１３９．１...     

改性UiO-66材料的制备及二甲苯异构体吸附性能研究

采用溶剂热法成功合成UiO-66、UiO-66─NH₂和UiO-66─(CF₃)₂。通过X射线衍射仪(XRD)和扫描电镜(SEM)对材料进行晶型和形貌表征;测定单组份二甲苯异构体在UiO-66及改性材料上的吸附等温线及速率曲线;通过动态突破实验,考察温度对三元等摩尔二甲苯异构体混合物在UiO-66及改性材料上吸附性能的影响。结果表明,UiO-66和UiO-66─NH₂对二甲苯异构体的吸附均符合二级动力学模型,而UiO-66─(CF₃)₂由于较大侧链的位阻作用,其吸附更符合一级动力学模型;3种材料均具有反相选择性,吸附选择性遵循:邻二甲苯(OX)>间二甲苯(MX)>对二甲苯(PX);随温度的升高,125℃下UiO-66─NH₂对OX/PX、OX/MX选择性均高于未改性的UiO-66;而双三氟甲基由于孔内扩散抑制作用,选择性降低。因此,高温条件下对UiO-66材料进行氨基改性是工业过程中分离二甲苯异构体获得高吸附分离性能的可行...     

吸附分离二甲苯分子筛的改性条件研究

采用13X型沸石分子筛作为改性对象，用填充柱分离色谱考察了混合二甲苯的分离效果，通过钾、钡离子的单独改性和复合改性的研究表明，钾离子的交换优于钡离子，复合改性的分子筛的分离效果优于单种离子。     

Silicalite-1/PAAS杂化膜的二甲苯异构体渗透汽化分离研究

Silicalite-1经3-氨丙基-三乙氧基硅烷(APTES)改性后,通过共混制备silicalite-l/聚丙烯酸钠(PAAS)杂化膜,用于二甲苯异构体的渗透汽化分离.膜的SEM分析表明,改性后silicalite-1与PAAS之间的相容性有较大改善.溶胀和渗透汽化实验发现:(1)对、邻二甲苯在杂化膜中的平衡溶胀量...     

超疏水纳米海绵制备及其二甲苯吸附性能

利用聚氯乙烯（PVC）及疏水性气相纳米SiO₂颗粒建立了一种简易、快速的超疏水纳米海绵材料的制备方法,并在开展超疏水纳米海绵材料的表面基团分析（IR）、疏水性能测定、表面形貌（SEM）观察的基础上,探究其吸附性能及循环使用性能。为验证超疏水纳米海绵材料的工业应用性能,采用实验室搭载回收设备,对比考察了负载超疏水纳米海绵/未改性海绵/商用金属盘片对间二甲苯的回收性能。结果表明：改性后超疏水纳米海绵材料表面负载涂层整体均匀完整,涂层上接枝的纳米颗粒稳定致密,且表面粗糙度有明显提高。IR谱图中新增有O—Si—O的特征峰,充分证明疏水性SiO₂颗粒已负载在材料表面,使其表面疏水角可达150°,具有超疏水亲油特性。改性海绵材料间二甲苯吸附容量可达41.45g/g,且在循环500次后吸附容量仍能达到其初始值的93%,负载该海绵的回收设备则具有良好间二甲苯回收速率（152.83L/h）及效率（99%）,运行58h后仍保持良好间二甲苯回收性能。     

精馏与盐效萃取偶合过程

设计了一种适用于从含水量较高的共沸液中分离有机溶剂的装置,该装置将精馏和盐效分相器结合起来,并带有中间储罐,其特点是：分相器可以将塔顶蒸出的共沸物中的大部分水除去,中间罐可以实现水从塔底除去。该装置上、下同时出水,有机溶剂浓缩在中间罐中。该装置大大缩短了操作时间,节约了能源。对该装置进行了数学模拟,与实验结果吻合较好。     

MFI型分子筛膜中晶体间隙的在线修补及其二甲苯分离性能研究

为了提高MFI分子筛膜的二甲苯分离性能,采用水热合成法制备了管式MFI型分子筛膜,并通过1,3,5三异丙基苯(TIPB)碳化沉积方法对分子筛膜中的晶体间隙在分离操作过程中进行了在线修补。通过修补,分子筛膜在375~400℃下的对、邻二甲苯分离系数从5左右增加到30,表明膜层中的无选择性的晶体间隙被大幅度减少。     

Treatment of air polluted with high concentrations of toluene and xylene in a pilot-scale biofilter

Air biofiltration is now under active consideration for the removal of the volatile organic compounds from air polluted streams. In order to investigate the performance of this newly developed technology, a biofiltration pilot unit was operated for a continuous period of 8 months. The biofilter column was packed with commercially conditioned peat. At start-up, the filter bed was inoculated with four species of microorganisms. The resulting biofilter was fed with air contaminated with toluene, xylene or a mixture of toluene and xylene. The maximum elimination capacities attained were 165 g m⁻³ h⁻¹ for toluene, 66 g m⁻³ h⁻¹ for xylene and 115 g m⁻³ h⁻¹ for the mixture of toluene and xylene. These specific performances exceed the values published in the technical and commercial literature for similar processes. Xylene isomers were degraded in decreasing order of reactivity, m-xylene, p-xylene, o-xylene. In the case of air polluted with a toluene and xylene mixture, it was noticed that the metabolism of toluene biodegradation was inhibited by the presence of xylene. Characterization of the biofilm microbial populations after several weeks of operation showed that the dominant strains among the isolated culturable strains from the biofilm, even if different from the initially inoculated strains, had at least one physiological property favoring degradation of aromatic organic rings. The performance of the biofilter was found to be dependent on the temperature of the filter media and the pressure drop through the bed. Finally, a steady state mathematical model was tested in order to theoretically describe the experimental results. This model is used to illustrate the operating diffusion and reaction regimes at steady state for the case of each pollutant. © 1998 Society of Chemical Industry     

Synthesis and physicochemical characterization of nanostructured Pd/ceria‐clinoptilolite catalyst used for p‐xylene abatement from waste gas streams at low temperature

BACKGROUND: The effect of Pd loading, xylene concentration and GHSV on xylene oxidation was tested over Pd/CeO₂(30%)‐clinoptilolite nanocatalysts at low temperatures. The catalysts were prepared by acid treatment of clinoptilolite, followed by the incipient wetness method of synthesized ceria and modified clinoptilolite in PdCl₂ solution. The synthesized nanocatalysts were characterized by XRD, FESEM, EDAX, TEM, BET, FTIR and TG‐DTG analysis. RESULTS: The XRD patterns confirmed the formation of crystalline ceria with an average crystallite size of 11.8 nm. FESEM images showed nanostructures in cavities of natural zeolite, brought about by ceria incorporation and acid activation. TEM analysis showed high dispersion of Pd with a size distribution between 6.6 and 36.7 nm. The quantitative analysis showed that the specific surface area of Pd(1%)/CeO₂(30%)‐clinoptilolite was 77 m² g^?1. The results showed that Pd(1%)/CeO₂(30%)‐clinoptilolite is the most appropriate catalyst, with the conversion more than 90% at 275 °C. CONCLUSIONS: Experimental results established effective performance and durability for the catalysts. As a result, clinoptilolite modification and ceria incorporation significantly altered the samples' morphology at nanoscale, improving the structure of composites and distribution of noble metals. A reaction path was suggested based on the adsorption‐migration of species to reveal the mechanism of p‐xylene oxidation over nanocatalysts. © 2012 Society of Chemical Industry     

Performance of zeolite powder and tubular membrane having different Si/Al ratio for removing As(III) in aqueous phase

Three different types of zeolite having pore sizes in the range 0.26‐0.74 nm, (NaP, NaA, and NaY) powders and membranes are synthesized with different Si:Al ratio on low cost clay alumina tubular support. The results of the permeation and separation studies showed that the NaP zeolite powder and membrane removes maximum As(III) from the water solution (more than 80%) compared to other zeolites. The removal of As(III) to achieve drinking water standard, by zeolite membrane, in a single step process does not seem to have been reported before the present investigation. These are the novelty achieved.     

The effect of dehydration conditions on the adsorption and diffusion of propane and nitrogen in linde 5A zeolite

Diffusion of propane and nitrogen in small crystals (3.6 μm) of zeolite 5A has been studied by conventional uptake rate measurements. The zeolite crystals were subjected to various pre-treatments prior to propane and nitrogen adsorption. It is concluded that surface degradation due to pre-treatment is not believed to occur to a significant extent since it has been observed that after a proper regeneration of the adsorbent, the diffusional properties of the system have been restored. It is suggested that the Ca⁺⁺ cations which may initially obstruct the windows of the sieve become increasingly mobile with increasing sorbate concentration and move to sites within the cage. The results are broadly consistent with the study on the diffusional transition in zeolite NaX (Tezel et al., 1983).     

定标粒子理论在加盐萃取分离醋酸丙酯-丙醇-水中的应用

采用选择性溶剂化模型和定标粒子理论计算了七种盐类萃取剂在醋酸正丙酯-正丙醇-水三元体系中的标准摩尔溶剂化自由能,结合萃取分离实验进行验证,结果表明,随着盐的标准摩尔溶剂化自由能绝对值的增大,有机相中酯的质量分数呈线性增大,而有机相中水的质量分数则呈线性降低.静电相互作用力是影响加盐萃取效果的主要原因,盐与水(或醇)分子之间的静电自由能绝对值越大,盐对酯的萃取效果越好,采用标准摩尔溶剂化自由能的计算值可从理论上定性选择适宜的盐类作为萃取剂.