基于选择性吸附脱硫的CuY/MFI核壳分子筛构筑及其作用机制

CuY/MFI core-shell zeolite adsorbent shows higher adsorption capacity and good shape selectivity during removing dimethyl disulfide (DMDS) from methyl tert-butyl ether (MTBE) by adsorption, as compared to the traditional modified zeolite Y with binder. In this study, CuY / MFI core-shell zeolite will be synthesized through surface modification and secondary crystallization technologies. The corresponding relationship between the synthesis conditions and the shell thickness and density will be established and the mechanism of shell growth will be revealed. As a result, the controllable preparation of CuY/MFI core-shell zeolite can be reached. The structure-activity relationship between silicon-aluminum ratios, thickness, density and adsorptive selective desulfurization performance will be established, and the key factors to affect adsorptive selectivity and sulfur capacity will be found. Influences of crystallization process, shell thickness and density on diffusion equilibrium behavior and adsorption/desorption kinetics characteristics of core-shell zeolite will be studied and discussed. The thickness and density of the shell will be introduced as the influencing factors to construct the diffusion kinetics model and the adsorption/desorption kinetics model. This study can effectively solve the problem of strong competitive adsorption of DMDS and MTBE, provide new ideas and methods for achieving efficient purification of MTBE. Moreover, the basic theory on regulation of crystallization and adsorption performance can be broadened. All the study results will provide necessary theoretical guidance for the efficient purification of other competitive adsorption systems.

与传统改性Y分子筛相比，CuY/MFI核壳分子筛用于吸附脱除甲基叔丁基醚(MTBE)中的二甲基二硫醚(DMDS)具有吸附硫容高、择形选择性好等优点。本研究采用分子筛表面修饰及二次晶化等手段合成CuY/MFI核壳分子筛，建立合成条件与核壳分子筛壳层厚度及致密度的对应关系，揭示壳层生长作用机理，以实现特定结构CuY/MFI核壳分子筛的可控制备。建立壳层硅铝比、厚度、致密度与选择性吸附脱硫性能的构-效关系，揭示影响分子筛吸附选择性及硫容的关键性因素。研究壳层晶化历程、壳层厚度及致密度对分子筛扩散平衡行为、吸/脱附动力学特征的影响规律，并引入壳层厚度及致密度作为影响因子构建扩散动力学模型及吸/脱附动力学模型。本研究可有效解决DMDS与MTBE的强竞争吸附问题，为实现MTBE高效净化提供新的思路和方法，拓展核壳分子筛构型与吸附性能调控研究的基础理论知识，可为其他竞争吸附体系的高效节能净化提供理论指导

甲基叔丁基醚（MTBE）作为高辛烷值汽油添加剂以及抗爆剂的应用极为广泛。然而，随着国V汽油标准的推行，MTBE中高硫含量的问题日益凸显。传统的萃取蒸馏技术尽管可以获得低硫的MTBE产品，但蒸馏能耗相当高，且蒸馏塔重沸器极易发生结焦，严重降低热量利用效率。吸附脱硫技术可以在常温常压下进行，具有操作简单、能耗低等特点，然而由于MTBE中的O较DMDS中的S具有更强的电负性，从而导致MTBE与DMDS之间存在极强的竞争吸附作用。本项目从择形角度出发，通过在高活性Cu-Y分子筛的外表面定向生长一层具有择形功能的MFI分子筛，可实现MTBE中DMDS的选择性吸附并可大大提高吸附硫容。通过对CuY核相分子筛进行酸/碱表面修饰并通过二次晶化手段合成CuY/MFI核壳分子筛，确定了调节壳层分子筛的厚度及致密度等关键技术及关键参数，并揭示壳层生长的作用机理。建立了CuY/MFI核壳分子筛构型与壳层选择性阻隔MTBE及选择性吸附DMDS性能之间的构-效关系。研究了核壳分子筛上MTBE和DMDS吸附平衡行为，并揭示了壳层厚度及致密性对吸附动力学的影响机制。经碱处理制备的CuYOH@silicalite-1的硫容可达到37.07 mg硫/g吸附剂，较文献报道中的1 mg硫/g吸附剂的活性已提高数倍。在上述核壳材料研究基础上，合成了另一种ZSM-5@silicalite-1核壳分子筛，采用聚阳离子表面活性剂（PDDA）实现了silicalite-1壳层在ZSM-5晶体外表面的定向自组装性生长，揭示了不同晶化时间下silicalite-1晶体在核相ZSM-5分子筛（010）或（100）晶面的生长方式和历程，并确定了核相ZSM-5晶体表面和侧边沟槽内silicalite-1晶体的b轴取向性。该研究工作的开展有助于进一步认识核壳分子筛的合成规律，为择形分子筛吸附剂及催化材料的开发提供新的思路和方法。