改性MIL-101用于吸附制冷过程关键基础问题研究

Metal organic framework (MOFs) is a new type of micro/meso-porous material with exceptionally high porosity, large surface area and tunable surface which is the hotspot in the recent 20 years. MIL-101 is one of the most promising MOF sorbent materials for heat-transformation applications known so far, as its superior water uptake and water stability. In this project, MIL-101 will be combined with water and isobutane as working pairs. The adsorption mechanism for water and isobutane on the mesoporous MIL-101 and the affinity between the surface functional groups of MIL-101 and adsorbates will be studied. In order to improve the adsorption water rate and adsorption isobutane capacity, the methods of modulating of ligand structure and loading are used to change the surface polarity and pore structure of MIL-101. MIL-101 composites are prepared by adding good heat transfer material, aiming at increasing thermal conductivity of MIL-101. Based on heat transfer principle of microchannel reactor, the MIL-101 is assembled or cured on the surface of microchannel to develop a micro channel adsorber, which will enhance the heat and mass transfer performance of MIL-101. With the advantages of avoiding unstability of vacuum operation, adsorption refrigeration system of MIL-101/isobutane work pairs will be built. Above all, our researches can provide basic data for the development and application of MIL-101 using on adsorption refrigeration.

金属有机骨架( MOFs)材料是一类新型微孔/中孔材料，具有比表面积大、孔径大小及表面基团可调等优点，是近20年来各国研究热点。MIL-101对水吸附容量大，水热稳定性好，被公认为是最有应用前景的MOFs材料之一。本项目将MIL-101用作为吸附制冷的吸附剂，分别与水、异丁烷组成工质对。研究水、异丁烷在MIL-101介孔内吸附机理，以及与表面官能团之间的亲和力关系；通过调变配体结构或负载，改变MIL-101表面极性和孔道结构，以提高MIL-101对水的吸附速率和对异丁烷吸附量。添加导热性良好材料制备MIL-101复合吸附剂，提高其导热性；借鉴微通道反应器的强化传热原理，将MIL-101组装或固化在微通道表面，研制微通道吸附器，强化MIL-101传热传质性能。构建MIL-101-异丁烷工质对的吸附制冷系统，避免真空操作系统运行不稳定问题。为MIL-101在吸附制冷领域开发应用提供基础研究。

本项目利用金属有机骨架材料MIL-101比表面积大、孔径及表面基团可调等优点，对MIL-101进行亲水和疏水改性，研究其对水和异丁烷吸附机理；将MIL-101与水和异丁烷组成工质对，构建吸附制冷循环系统，研究了吸附剂和吸附器的强化传热，为MOFs材料在吸附制冷中应用奠定基础。(1)水/异丁烷在MIL-101和改性MIL-101上吸附机理：水和异丁烷在MIL-101上均为物理吸附，两者在MIL-101上首先在Cr的不饱和金属位点和四面体笼（笼径0.8 nm）中吸附，然后在两个介孔笼（笼径为2.9 nm和3.4 nm）中吸附；水在MIL-101上吸附时形成团簇，吸附等温线为IV型，引入氨基后亲水改性后MIL-101吸水量突变分压从0.35~0.5提前到0.25~0.4；异丁烷在MIL-101上的吸附热为21.65 kJ/mol，引入苯环基疏水改性后其对异丁烷吸附热提高了30%。（2）MIL-101–水/MIL-101-异丁烷工质对吸附制冷性能。MIL-101–水工质对适用于空调和普冷工况，蒸发温度17 °C时制冷量和制冷功率为681.1 kJ/kg和71.2 W/kg；MIL-101-异丁烷工质对适用于制冰工况，蒸发温度-5 ℃时MIL-101对异丁烷制冷量是活性炭对异丁烷制冷量的2.7倍。（3）MIL-101吸附剂传热强化研究。建立了吸附剂导热系数测定方法，MIL-101热导率为0.06 W/(m.K)，加入高导热材料石墨烯和泡沫铜热导率可提升11-12倍；为强化吸附剂和吸附器之间的传热，制备了MIL-101铜片涂层，其热导率为MIL-101的2.70倍。（4）为强化MIL-101吸附床层传热传质，将MIL-101固化在吸附器内，研制可拆卸板式MIL-101涂层吸附器、微通道MIL-101吸附器和泡沫铜MIL-101固化吸附器，并与异丁烷组成工质对构建了吸附制冷循环系统，测得其制冷系统SCP高低顺序为：泡沫铜MIL-101固化吸附器>可拆卸板式MIL-101涂层吸附器>微通道MIL-101吸附器。（5）建立双床MIL-101/泡沫铜-异丁烷正压吸附制冷循环系统，在蒸发温度15 ℃、加热温度85 ℃、冷凝温度30℃和半循环时间10 min条件下，其单位制冷量和SCP为72.98 kJ/kg和50.68 W/kg。该系统可在正压下操作，提高了吸附制冷系统稳定性。