膨胀石墨/有机金属骨架复合吸附材料的制备及性能研究
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摘要
粉末状有机金属骨架材料(MOFs)普遍存在密度低热导率低的不足,是限制其在水蒸气吸附领域应用的关键因素之一。以典型的高吸水量MOFs材料对苯二甲酸铬(MIL-101(Cr))为研究对象,采用干混法将膨胀石墨(EG)与该MOFs材料复合并模压成型,制备了一系列不同密度不同石墨含量的复合吸附材料。利用光学显微镜表征了材料微观结构,分析了压制密度、EG含量对材料内部结构的影响;使用恒温恒湿箱测试了纯MOFs材料及复合吸附材料的饱和吸附量,发现纯MOFs粉末在压制压力超过3 MPa后吸附能力大幅下降。在此基础上制备了密度适宜的复合材料,测试发现复合材料的饱和吸附量随着EG含量的增加而显著降低,但EG对MOFs本身的吸附量未造成显著影响;采用体积法研究了材料的吸附动力学,其中片状纯MOFs相比粉末状MOFs吸附速率大幅下降,而复合材料由于内部产生了更多的传质通道使其表面传质系数相比于片状纯MOFs提高了2.7倍。热导率测试结果表明复合吸附材料的热导率随着石墨含量的增加而显著升高,而材料的密度对热导率的影响相对较小。采用干混法制备的石墨含量50%,密度408kg·m-3的复合吸附材料,其热导率相比纯MOFs材料提高了22倍达到2.76 W·m-1·K-1。
Low density and low thermal conductivity are common drawbacks of powder metal organic frameworks(MOFs),which is one of key point limited the application of MOFs.MIL-101(Cr) as a typical water adsorption MOFs with high adsorption capacity is the major study object in this work.Two methods of directly dry-mixing and soaking are utilized to composite expanded graphite(EG) with MOFs,after compression by mold,a series of composite sorbents pellets with different EG content and packed density are developed.The optical microscope is utilized to observe the structure of materials,by which the influences of packed density and EG content on microscale structure are analyzed.The tests of saturated sorption capacity of pure MOFs and composites are carried out in a constant temperature and humidity chamber,whose results indicates the sorption capacity of pure MOFs will apparently reduce if the compression pressure is higher than 3 MPa.Accordingly,composite sorbents are prepared under relatively low compression pressure,whose sorption capacities are decrease with the increase of EG content,which is only caused by the decrease of MOFs content while there is no negative effects of EG on MOFs adsorption.Volume method is applied in adsorption kinetics study,which reveals the adsorption rates of pellets pure MOFs are much lower than powder pure MOFs.However,the composites shows 2.7 times higher surface diffusive coefficient than pellet pure MOFs ascribed of the appearance of more mass transfer channels caused by compression with EG.The results of thermal conductivity measurements of composite sorbent illustrate that thermal conductivities are obviously enhanced with the increase of EG content while a much smaller enhancement is observed by increasing packed density.Comparing with pure MOFs,the developed composites by dry-mixing method with EG mass content of 50%,with packed density of 408 kg·m-3 shows extraordinary high thermal conductivity of 2.76 W·m-1·K-1,which is 22 times higher than pure MOFs.
Low density and low thermal conductivity are common drawbacks of powder metal organic frameworks(MOFs),which is one of key point limited the application of MOFs.MIL-101(Cr) as a typical water adsorption MOFs with high adsorption capacity is the major study object in this work.Two methods of directly dry-mixing and soaking are utilized to composite expanded graphite(EG) with MOFs,after compression by mold,a series of composite sorbents pellets with different EG content and packed density are developed.The optical microscope is utilized to observe the structure of materials,by which the influences of packed density and EG content on microscale structure are analyzed.The tests of saturated sorption capacity of pure MOFs and composites are carried out in a constant temperature and humidity chamber,whose results indicates the sorption capacity of pure MOFs will apparently reduce if the compression pressure is higher than 3 MPa.Accordingly,composite sorbents are prepared under relatively low compression pressure,whose sorption capacities are decrease with the increase of EG content,which is only caused by the decrease of MOFs content while there is no negative effects of EG on MOFs adsorption.Volume method is applied in adsorption kinetics study,which reveals the adsorption rates of pellets pure MOFs are much lower than powder pure MOFs.However,the composites shows 2.7 times higher surface diffusive coefficient than pellet pure MOFs ascribed of the appearance of more mass transfer channels caused by compression with EG.The results of thermal conductivity measurements of composite sorbent illustrate that thermal conductivities are obviously enhanced with the increase of EG content while a much smaller enhancement is observed by increasing packed density.Comparing with pure MOFs,the developed composites by dry-mixing method with EG mass content of 50%,with packed density of 408 kg·m-3 shows extraordinary high thermal conductivity of 2.76 W·m-1·K-1,which is 22 times higher than pure MOFs.
引文
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[24]郭健.浅析差示扫描量热法测定材料的比热容[J].科技创新与生产力,2007,165(10):19-20.GUO J.Analysis of differential scanning calorimetry for measuring specific heat capacity of materials[J].Technology Innovation and Productivity,2007,165(10):19-20.
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[26]SULTAN M,EL-SHARKAWY I I,MIYAZAKI T,et al.Water vapor sorption kinetics of polymer based sorbents:theory and experiments[J].Applied Thermal Engineering,2016,106:192-202.
[27]ARISTOV Y I,GLAZNEV I S,FRENI A,et al.Kinetics of water sorption on SWS-1L(calcium chloride confined to mesoporous silica gel):influence of grain size and temperature[J].Chemical Engineering Science,2006,61(5):1453-1458.
[28]SáNCHEZ A R,KLEIN H P,GROLL M.Expanded graphite as heat transfer matrix in metal hydride beds[J].International Journal of Hydrogen Energy,2003,28(5):515-527.
[2]WANG D,ZHANG J,TIAN X,et al.Progress in silica gel-water adsorption refrigeration technology[J].Renewable&Sustainable Energy Reviews,2014,30(6):85-104.
[3]SAH R P,CHOUDHURY B,DAS R K.A review on adsorption cooling systems with silica gel and carbon as adsorbents[J].Renewable&Sustainable Energy Reviews,2015,45:123-134.
[4]ASKALANY A A,SALEM M,ISMAIL I M,et al.A review on adsorption cooling systems with adsorbent carbon[J].Renewable&Sustainable Energy Reviews,2012,16(1):493-500.
[5]BONACCORSI L,BRUZZANITI P,CALABRESE L,et al.Organosilanes functionalization of alumino-silica zeolites for water adsorption applications[J].Microporous&Mesoporous Materials,2016,234(35):113-119.
[6]ALBY D,SALLES F,FULLENWARTH J,et al.On the use of metal cation-exchanged zeolites in sorption thermochemical storage:some practical aspects in reference to the mechanism of water vapor adsorption[J].Solar Energy Materials and Solar Cells,2018,179:223-230.
[7]许嘉兴,李廷贤,王如竹.氯化镁/沸石复合材料的吸附特性及储热性能[J].化工学报,2016,67(S2):348-355.XU J X,LI T X,WANG R Z.Sorption characteristics and heat storage performance of MgCl2/13X zeolite composite sorbent[J].CIESC Journal,2016,67(S2):348-355.
[8]赵东元.功能介孔材料界面组装工程及其应用[C]//第三届全国储能科学与技术大会.中国化工学会储能工程专业委员会,2016.ZHAO D Y.Interface assembly engineering of functional mesoporous materials and its application[C]//The Third National Conference on Energy Storage Science and Technology.China Chemical Engineering Society Energy Storage Engineering Specialized Committee,2016.
[9]杨晨,王亚明,蒋丽红.磷铝分子筛的制备与应用研究进展[J].石油学报(石油加工),2016,32(4):841-850.YANG C,WANG Y M,JIANG L H.Research progress in preparation and application of aluminophosphate molecular sieves[J].Acta Petrolei Sinica(Petroleum Processing Section),2016,32(4):841-850.
[10]FURUKAWA H,YAGHI O M M.The chemistry and applications of metal-organic frameworks[J].Science,2013,341(6149):974.
[11]CHEN Y F,BABARAO R,SANDLER S I,et al.Metal-organic framework MIL-101 for adsorption and effect of terminal water molecules:from quantum mechanics to molecular simulation[J].Langmuir the ACS Journal of Surfaces&Colloids,2010,26(11):8743-8750.
[12]魏金枝,张少平,王雪亮,等.巯基修饰Cu-MOFs材料的制备及其汞吸附性能[J].化工学报,2017,68(5):2186-2194.WEI J Z,ZHANG S P,WANG X L.Preparation of ethanedithiol modified Cu-MOFs and its adsorption performance for mercury[J].CIESC Journal,2017,68(5):2186-2194.
[13]HOWARTH A J,LIU Y,LI P,et al.Chemical,thermal and mechanical stabilities of metal-organic frameworks[J].Nature Reviews Materials,2016,1:15018.
[14]ZHENG J,VEMURI R S,ESTEVEZ L,et al.Pore-engineered metalorganic frameworks with excellent adsorption of water and fluorocarbon refrigerant for cooling applications[J].Journal of the American Chemical Society,2017,139(31):10601-10604.
[15]Scientists in Germany claim to have developed a new more efficient sorbent for use in adsorption chillers[DB/OL].2018.http://www.coolingpost.com.
[16]CHAKRABORTY A,KAYAL S.Post synthetic modification of MIL-101(Cr)for S-shaped isotherms and fast kinetics with water adsorption[J].Applied Thermal Engineering,2017,120:453-462.
[17]HUANG B L,MCGAUGHEY A J H,KAVIANY M.Thermal conductivity of metal-organic framework 5(MOF-5)(I):Molecular dynamics simulations[J].International Journal of Heat and Mass Transfer,2007,50(3/4):393-404.
[18]MING Y,PUREWAL J,LIU D,et al.Thermophysical properties of MOF-5 powders[J].Microporous and Mesoporous Materials,2014,185:235-244.
[19]仵斯,李廷贤,闫霆,等.高性能定形复合相变储能材料的制备及热性能[J].化工学报,2015,66(12):5127-5134.WU S,LI T X,YAN T,et al.Preparation and thermal properties of high performance shape-stabilized phase change composites using stearic acid and expanded graphite[J].CIESC Journal,2015,66(12):5127-5134.
[20]翟天尧,李廷贤,仵斯,等.高导热膨胀石墨/硬脂酸定形相变储能复合材料的制备及储/放热特性[J].科学通报,2018,63(7):674-683.ZHAI T Y,LI T X,WU S,et al.Preparation and thermal performance of form-stable expanded graphite/stearic acid composite phase change materials with high thermal conductivity[J].Chinese Science Bulletin,2018,63(7):674-683.
[21]SUN X,LV D,CHEN Y,et al.Enhanced adsorption performance of aromatics on a novel chromium-based MIL-101@graphite oxide composite[J].Energy&Fuels,2017,31(12):13985-13990.
[22]LIU D,PUREWAL J J,YANG J,et al.MOF-5 composites exhibiting improved thermal conductivity[J].International Journal of Hydrogen Energy,2012,37(7):6109-6117.
[23]FéREY G,MELLOT-DRAZNIEKS C,SERRE C,et al.A chromium terephthalate-based solid with unusually large pore volumes and surface area[J].Science,2005,309(5743):2040-2042.
[24]郭健.浅析差示扫描量热法测定材料的比热容[J].科技创新与生产力,2007,165(10):19-20.GUO J.Analysis of differential scanning calorimetry for measuring specific heat capacity of materials[J].Technology Innovation and Productivity,2007,165(10):19-20.
[25]葛山,尹玉成.激光闪光法测定耐火材料热导率的原理与方法[J].理化检验(物理分册),2008,44(2):75-78.GE S,YIN Y C.Principle and method refractory thermal conductivity measurement by laser flash method[J].Physical testing and Chemical Analysis Part A(Physical Testing),2008,44(2):75-78.
[26]SULTAN M,EL-SHARKAWY I I,MIYAZAKI T,et al.Water vapor sorption kinetics of polymer based sorbents:theory and experiments[J].Applied Thermal Engineering,2016,106:192-202.
[27]ARISTOV Y I,GLAZNEV I S,FRENI A,et al.Kinetics of water sorption on SWS-1L(calcium chloride confined to mesoporous silica gel):influence of grain size and temperature[J].Chemical Engineering Science,2006,61(5):1453-1458.
[28]SáNCHEZ A R,KLEIN H P,GROLL M.Expanded graphite as heat transfer matrix in metal hydride beds[J].International Journal of Hydrogen Energy,2003,28(5):515-527.