【作者】 陈焕浩；

【导师】 张会平；

【作者基本信息】 华南理工大学 ， 化学工程， 2014， 博士

【摘要】 随着全球经济的迅速发展，石化、化工和室内装饰等行业生产过程中产生的挥发性有机化合物(VOCs)的排放量日益加剧，对人类健康及环境安全的危害也日趋严重。空气中VOCs的脱除方法有很多种，主要包括吸附、催化氧化和高温焚烧等处理技术。其中，固定床吸附法和催化燃烧法具有操作简单、能耗低及净化效率高等优点，在脱除空气中VOCs领域得到广泛的应用。然而，传统固定床吸附器/反应器一般是由颗粒或粉末状吸附剂/催化剂装填而成，普遍存在接触效率低、传质传热阻力大及床层压降大等缺点。设计并制备一类新型结构化分子筛膜吸附/催化材料，有效强化传热传质，提高接触效率、吸附及反应速率，是一项具有实际工程应用价值的前沿性课题。本文设计并研究了梯度多孔ZSM-5分子筛膜吸附/催化剂材料的制备、表征及其在脱除空气中低浓度VOCs中的应用，探讨了结构化固定床吸附器/反应器的吸附/反应动力学。首先，研究了纸状多孔烧结不锈钢微纤(PSSF)载体的制备工艺。以质量比为2:1的不锈钢纤维(长度为2~3mm，直径为6.5μm)和针叶木纤维为原料，通过湿法造纸工艺/高温烧结技术制备纸状多孔烧结不锈钢纤维材料，并考察不锈钢纤维用量对纸状多孔烧结不锈钢纤维床层压降的影响，得到最佳不锈钢纤维用量为6g。采用扫描电镜(SEM)观察了不锈钢纤维材料烧结前后的微观结构，结果表明不锈钢纤维的连接处在高温条件下被很好地烧结在一起，形成大空隙率的三维网络结构。其次，研究了梯度多孔ZSM-5分子筛膜吸附材料的制备工艺。以正硅酸乙酯(TEOS)为硅源、四丙基氢氧化铵(TPAOH)为结构导向剂，通过水热合成法制备Silicalite-1纯硅分子筛晶种，考察不同工艺参数对Silicalite-1晶种生长的影响；采用吸附法在不锈钢纤维表面合成Silicalite-1晶种薄层，并以正硅酸乙酯(TEOS)为硅源、偏铝酸钠(NaAlO2)为铝源、四丙基氢氧化铵(TPAOH)为结构导向剂，通过二次生长法在不锈钢纤维表面合成ZSM-5分子筛膜吸附材料，考察不同工艺参数对ZSM-5分子筛膜的表面形貌和厚度的影响。结果表明在Silicalite-1晶种制备过程中，合成液中的水含量、无水乙醇含量、合成液的老化时间、晶化温度和晶化时间对Silicalite-1晶种的生长均有影响；通过二次生长法能在不锈钢纤维表面合成连续致密的ZSM-5分子筛膜，所制备ZSM-5分子筛膜材料的BET比表面积达到了145m2/g，其膜厚度为4μm，梯度化多孔ZSM-5分子筛膜材料(ZSM-5/PSSF)中分子筛膜的负载量大约为37wt%。此外，二次合成液中的铝含量对ZSM-5分子筛膜的生长影响最大，晶化温度主要影响了ZSM-5分子筛膜的表面形貌和膜厚度，晶化时间主要决定了ZSM-5分子筛膜的膜厚度。再次，研究了梯度多孔ZSM-5分子筛膜催化材料的制备工艺。以硝酸钴(Co(NO3)2)、硝酸铜(Cu(NO3)2)、硝酸锰(Mn(NO3)2)溶液为过渡金属催化剂活性组分前驱体，采用湿法浸渍法在多孔ZSM-5分子筛膜上负载催化剂活性组分制备梯度化多孔ZSM-5分子筛膜催化材料；探讨过渡金属组分配比、负载量及烧结温度等影响因素对分子筛膜催化剂结构及催化氧化异丙醇活性的影响，结果表明Cu-Mn(1:6)双金属氧化物改性分子筛膜催化剂(Cu-Mn(1:6)/ZSM-5/PSSF)和Co-Cu-Mn(1:1:1)三金属氧化物改性分子筛膜催化剂(Co-Cu-Mn(1:1:1)/ZSM-5/PSSF)表现出较高的催化活性，异丙醇在分子筛膜催化剂上的90%转化率温度T90%为210℃。此外，梯度多孔ZSM-5分子筛膜催化剂作为高效催化剂，表现出较高的接触效率、良好的催化反应速率和稳定性。同时，研究了空气中低浓度VOCs在基于梯度多孔ZSM-5分子筛膜吸附材料的结构化固定床吸附器上的吸附动力学。通过在固定床的进口端和出口端分别装填活性炭或ZSM-5分子筛颗粒吸附剂和ZSM-5分子筛膜吸附材料组成结构化固定床吸附器，研究异丙醇和甲苯单组份气体在结构化固定床上的吸附动力学，并与传统颗粒固定床的实验结果进行比较。结果表明，在相同条件下，VOCs在结构化固定床上的吸附透过曲线斜率明显高于传统颗粒固定床，ZSM-5分子筛膜吸附材料明显降低了传质阻力；随着气体流量和入口浓度的增加，VOCs在结构化固定床上的吸附透过时间明显缩短。采用LUB方程、Yoon-Nelson模型和BDST模型对VOCs在结构化固定床上的传质机理和吸附透过行为进行分析。结果表明，结构化固定床的床层利用率相对于传统颗粒固定床的提高了10%~18%。Yoon-Nelson模型和BDST模型均能很好地预测VOCs在结构化固定床上的吸附透过曲线。同时，研究了空气中低浓度VOCs在基于梯度多孔ZSM-5分子筛膜催化材料的结构化分子筛膜反应器上的催化燃烧行为，研究异丙醇、乙酸乙酯单组份气体以及双组份气体(异丙醇和甲苯、乙酸乙酯和甲苯)在结构化分子筛膜反应器上的催化燃烧动力学；探讨床层高度、空速及VOCs入口浓度对结构化分子筛膜反应器催化燃烧行为的影响。结果表明分子筛膜反应器的最佳床层高度为2cm；异丙醇和乙酸乙酯在结构化分子筛膜反应器上的100%完全转化温度T100%均低于280℃，VOCs入口浓度和空速对其在分子筛膜反应器上的催化燃烧行为产生了轻微影响，随着入口浓度和空速的增加，VOCs在分子筛膜反应器上的50%转化温度T50%和90%转化温度T90%均升高；双组份中甲苯的存在对异丙醇或乙酸乙酯的催化转化均起到轻微抑制作用，相比于甲苯，分子筛膜反应器对双组份气体中异丙醇或乙酸乙酯的催化活性更高。最后，研究了异丙醇在结构化分子筛膜反应器上的催化燃烧反应本征动力学。通过考察空速对异丙醇转化率的影响，以消除外扩散影响；进一步探讨分子筛膜厚度及晶体粒径对异丙醇转化率的影响，以消除内扩散影响。采用Power-rate Law和Mars-vanKrevelen动力学模型对异丙醇在结构化分子筛膜反应器上催化燃烧动力学行为进行模拟研究，结果表明Power-rate Law动力学模型不适用于描述异丙醇在分子筛膜催化剂上的催化燃烧动力学行为，而Mars-van Krevelen动力学模型能较好地预测异丙醇在结构化分子筛膜反应器上的催化燃烧动力学行为，其反应机理为氧化-还原机理，其表面还原反应活化能和表面氧化反应活化能分别为60.30和57.19kJ/mol。更多还原

【Abstract】 With the high-speed development of global economy, increasing emissions of volatileorganic compounds (VOCs) emitted from a large variety of sources scuh as petrochemicals,chemical processes as well as household products produce many undesirable effects onhumans health and environmental safety. Various technologies have been implemented for theremoval of VOCs from air, such as adsorption, catalytic oxidation and thermal combustion etc.Among these methods, adsorption technology and catalytic oxidation using fixed beds havebeen regarded as one of the most promising technologies for the removal of VOCs from airdue to their easy operation, low energy requirement as well as high purification efficiency.However, the drawbacks of poor contacting efficiency, relatively higher mass/heat transfer aswell as bed pressure dorp exist in most of traditional fixed bed adsorbers/reactors due to theuse of pellet shaped or powder adsorbents/catalysts. The design and fabrication of a novelstructured zeolite membrane adsorptional/catalytic material that can effectively enhancemass/heat transfer, contacting efficiency as well as adsorptional/catalytic reaction rate havebeen reconigzed as a cutting-edge research topic. In this paper, the fabrication andcharacterization of gradient porous ZSM-5zeolite membrane adsorptional/catalytic materialwere designed and investigated. The applications of these novel structured materials in theremoval of VOCs in air at low concentrations were also studied. Adsorption dynamics ofVOCs in air at low concentrations in structured fixed bed adsorbers based on these novelstructured materials was measured, and catalytic combustion performances of VOCs in air atlow concentrations over structured zeolite membrane reactor were also investigated.Firstly, the preparation process of paper-like sintered stainless steel fibers (PSSF) supportwas investigated. The paper-like sintered stainless steel fibers (PSSF) support was fabricatedby the wet lay-up papermaking/sintering process using stainless steel fibers (6.5μm diameter,2~3mm length) and cellulose with a weight ratio of2:1. The effects of stainless steel fibersdosage on the bed pressure drop of PSSF were studied, and the experimental results indicatedthat the optimum amount of stainless steel fibers is6g. The micromorphology and structureof stainless steel fibers before and after sintering were observed by using Scanning Electron Microscopy (SEM). The experimental results showed that the junctures of stainless steelfibers in PSSF were completely sintered together to form a three-dimensional networkstructure with large voidage under high temperature condition.Secondly, the preparation process of gradient porous ZSM-5zeolite membranesmaterials was studied. The Tetraethoxysilane (TEOS) and Tetrapropylammoniumhydroxide(TPAOH) were used as silicon source and structure directing agent, respectively. The effectsof various synthesis parameters on the growth of silicalite-1seeds were also investigated. ThePSSF support was treated with a silicalite-1seeds solution to fabricate a thin andhomogeneous seed flim on the surface of stainless steel fibers. The ZSM-5zeolite membraneswere synthesized on the surface of seeded-PSSF by secondary growth method. The secondaysynthesis solution was prepared using the same chemicals as the silicalite-1seed solution, butSodium aluminate (NaAlO2) was added as aluminum source. The effects of various secondarysynthesis parameters on the surface morphology and thickness of ZSM-5zeolite membranewere also studied. The experimental results indicated that the water and Ethanol (EtOH)content in synthesis solution, aging time, crystallization temperature as well as crystallizationtime obviously influenced the growth of silicalite-1seeds. A continuous and dense ZSM-5zeolite membrane was successfully fabricated on the surface of stainless steel fibers by usingsecondary growth method. The BET specific surface area of fabricated gradient porousZSM-5membrane material (ZSM-5/PSSF) was145m2/g, and the thickness of ZSM-5membrane was4μm. Morover, the obtained ZSM-5membrane content in ZSM-5/PSSFmaterial was approximately37wt%. In addition, the aluminum content in secondary synthesissolution significantly influenced the growth of ZSM-5membrane. The experimental resultsalso indicated that the surface morphology and membrane thickness of ZSM-5zeolitemembrane were obviously influenced by the crystallization temperature and time.Thirdly, the preparation process of gradient porous ZSM-5membrane catalysts wasinvestigated. The modified ZSM-5zeolite membrane catalysts were synthesized by theincipient wetness impregnating method using Cobalt nitrate (Co(NO3)2), Manganese nitrate(Mn(NO3)2) and Copper nitrate (Cu(NO3)2) as precursor salts. The effects of molar ratios of transition metal component, total metal loading as well as calcination temperature on thestructure properties and catalytic performances for isopropanol oxidation of modified ZSM-5zeolite membrane catalysts were investigated. Among the series of catalysts, the as-preparedCu-Mn(1:6) mixed oxides modifed ZSM-5membrane catalysts (Cu-Mn(1:6)/ZSM-5/PSSF)and Co-Cu-Mn(1:1:1) mixed oxides modifed ZSM-5membrane catalysts(Co-Cu-Mn(1:1:1)/ZSM-5/PSSF) have exhibited the best catalytic activity for isopropanoloxidation, demonstrating by a lowest T90%of210℃(the temperature at isopropanolconversion approaches90%). Moreover, the gradient porous modified ZSM-5membranecatalysts as high efficiency catalyst for VOCs oxidation can offer a much higher contactingefficiency, excellent catalytic reaction rate as well as reaction stability.Meanwhile, adsorption dynamics of VOCs in air at low concentraions in structured fixedbed adsorber based on the gradient porous ZSM-5zeolite membrane adsorptional materials.The structured fixed bed adsorbers filled with both activated carbon or ZSM-5particles in theinlet of bed and ZSM-5zeolite membrane adsorptional materials (ZSM-5/PSSF) in the outletof bed were designed. Adsorption dynamics of VOCs in air at low concentrations(isopropanol or toluene) in the structured fixed bed adsorbers was performed, comparing withthat of traditional particles fixed beds filled with individual activated carbon or ZSM-5particles. The experimental results indicated that the steepness of breakthrough curves ofVOCs in structured fixed bed adsorber was more upright that that of traditional particles fixedbed adsorber, confirming that the mass transfer was obviously enhanced by addingZSM-5/PSSF adsorptional materials in the outlet of structured fixed bed. Moreover, thebreakthrough times of VOCs in structured fixed bed adsorber decrease significantly asincreasing gas flow rate and inlet concentration of VOCs. The length of unused bed (LUB)theory, Yoon-Nelson as well as Bed Depth Service Time (BDST) models were used toinvestigate the experimental results. The analytical results showed that the bed utilization ofstructured fixed bed adsorber increases10%~18%compared with that of traditional particlesfixed bed. It can be demonstrated that theoretical breakthrough curves predicted using bothYoon-Nelson and BDST models were in good agreement with the experimental results. Meanwhile, catalytic combustion performances of VOCs in single component(isopropanol or toluene) and binary component mixtures (isopropanol and toluene, ethylacetate and toluene) were investigated over the structured zeolite membrane reactor based ongradient porous ZSM-5zeolite membrane catalytic materials. The effects of catalysts bedheight, gas hourly space velocity (GHSV) as well as initial concentrations on the catalyticperformances of structured zeolite membrane reactor for VOCs combustion were alsoinvestigated. The experimental results showed that the best catalysts bed height of structuredzeolite membrane reactor was2cm. Moreover, experimental results also indicated that thecomplete destruction of isopropanol or ethyl acetate in single component over structuredzeolite membrane reactor can be achieved below the temperature of280℃. Results alsoexhibited that the inlet concentration of VOCs and GHSV had a slight effect on the catalyticperformances of structured zeolite membrane reactor for VOCs combustion, demonstating bythat the T50%and T90%of VOCs increase slightly as the initial concentrations and GHSVincreased. The study also indicated that the presence of toluene in VOCs binary mixtures hada minimal inhibition effect on the catalytic conversion of isopropanol or ethyl acetate over thestructured zeolite membrane reactor. It can be concluded that the catalytic activity ofisopropanol or ethyl acetate in binary mixtures was much higher that that of toluene.Finally, the modeling studies of catalytic combustion performances of isopropanol overstructured zeolite membrane reactor were investigated by using Power-rate Law and Mars-vanKrevelen kinetic models. External and internal mass transfer effects were evaluated. Theanalysis results showed that the Mars-van Krevelen kinetic model was more suitable forpredicting the catalytic combustion performances of isopropanol over structured zeolitemembrane reactor than the Power-rate Law kinetic model, and its reaction mechanism isoxidation-reduction. The surface reduction and oxidation reaction activation energies were60.30kJ/mol and57.19kJ/mol, relatively.更多还原