稀土交换NaA分子筛块体吸附剂的微波水热合成及其改性机理

The adsorptive rotary desiccant wheel system with NaA molecular sieve as adsorbent is widely used in the field of deep dehumidification. The desiccant rotor（monolithic adsorbent） composed of ceramic fiber paper and the adsorbent is the core unit of the system. Improving the adsorption performance of the monolithic adsorbent and reducing the desorption temperature of NaA molecular sieve is the key to improve system energy efficiency. In this project, using ceramic fiber paper as carrier, and rare earth ion (La3+,Nd3+) as modified agent, by means of ball-milled crystal seeds with vaccum seeding for second growth, as well as microwave hydrotheromal synthesis and ion -exchange, the monolithic rare earth-exchanged NaA zeolite adsorbent is synthesized. The influcences of the preparation conditions,including the ceramic matrix modification,the ball-milled crystal seeds and vaccum seeding ，the microwave hydrothermal synthesis and rare earth-exchange on the monolithic adsorbent performance are investgated systematically.The adsorption dynamics and isothermal adsorption /desorption curves of the modified adsorbent are tested. By means of the characterization about the composition,sturctue, and the morphology of the modified adsorbent, as well as the testing about its adsorbed amount,desorption temperature and surface acidic strength, the essence of the enhanced adsorptive performance is revealed by the variation of the content, particle size, pore structure parameters for the modified zeolite, and the intrinsic reason of the lower desorption termperature ( desorption activated energy) is also disclosed by the difference of the sorts, amount and the exchange position for the rare earth-changed cation ion, as well as the change of the adsorbent lattce parameters, pore sturcture parameters . It will provide theoretical guidance for the industrial production of high performance desiccant rotor.

以NaA分子筛为吸附剂的吸附式转轮除湿系统，广泛应用于深度除湿领域，而其与陶瓷纤维纸复合构筑的除湿转芯（块体吸附剂）是系统的核心单元。改善块体吸附剂吸附性能，降低分子筛脱附温度是提高系统能效的关键。本项目以陶瓷纤维纸为基材，稀土（镧、钕）离子为改性剂，采用真空涂晶的球磨晶种二次增长工艺，微波水热合成及离子交换方法，合成了稀土交换NaA分子筛块体吸附剂；系统探讨基材修饰、球磨晶种、真空涂晶、微波水热及稀土交换等条件对块体吸附剂性能的影响；研究改性吸附剂吸附动力学和等温吸附/脱附特征；通过对改性分子筛组成、结构及形态的剖析及其吸附量、脱附温度及表面酸性强度的测试，从分子筛含量、晶粒大小及孔结构参数等变化，揭示其吸附性能增强的本质；从吸附剂中稀土交换阳离子种类、数量及位置，吸附剂晶胞参数、孔结构参数的变化，揭示其脱附温度（脱附活化能）降低的内在原因；为工业化制备高性能除湿转芯提供指导。

本项目主要围绕现有分子筛除湿转芯（块体吸附剂）存在的“常规涂覆成型工艺分子筛含量低，易掉粉 ”；“分子筛吸附量小，脱附温度高” 等问题。科学的提出微波条件下稀土离子改性分子筛以及在陶瓷基材上微波原位合成NaA分子筛的技术方案。 主要开展以下两个方面的研究工作。（1）微波下稀土离子交换NaA分子筛的合成与性能。采用微波工艺及离子交换方法，以稀土镧（La）、钕（Nd）为改性剂，制备了RE3+交换NaA分子筛吸附剂；系统探讨稀土离子浓度、pH值、n (RE3+/Na+)摩尔比以及微波反应温度对改性吸附剂交换度及吸附/脱附性能的影响；采用XRD、FT-IR、EDS等手段对其结构、组成进行表征，并通过静态吸附法、DSC、TG及TPD等测试其吸、脱附性能。实验结果显示，La3+的改性, NaA分子筛的吸附性能、脱附略有改善；Nd3+改性，对脱附影响明显；而La3+ 、Nd3+的复合改性，可获得较好的吸脱附性能。未改性、镧离子交换、钕离子交换及镧/钕复合离子交换NaA分子筛的饱和吸附量分别为26.57、27.33、17.53及19.46%。；而对应的脱附活化能分别为84.94、67.40、58.60及54.13 kJ·mol-1。（2）陶瓷基NaA分子筛原位合成。首先，采用微波水热工艺合成了NaA分子筛；其次，以合成分子筛为晶种，以蜂窝陶瓷胚体为基材，原位合成了NaA分子筛块体吸附剂。系统探讨Si/Al摩尔比、晶化温度、时间、晶种涂覆等对NaA分子筛及其块体吸附剂性能的影响。结果表明，经微波水热工艺，能快速有效的合成出NaA分子筛块体吸附剂（45min）；与工业分子筛（1.5-3μm）相比，合成NaA分子筛，粒径显著变小（约0.9μm），原位合成的NaA分子筛在蜂窝陶瓷胚体上分散均匀且致密；静态吸附曲线表明，与浸渍涂覆法制备的块体吸附剂比较，微波合成的NaA分子筛块体吸附剂前期吸附速率和饱和吸附量都得到了提高；脱附活化能比工业分子筛低。该微波及离子交换工艺及稀土改性分子筛的性能，为高性能除湿转芯的制备提供指导。