The Study On Preparation And Performances Of Fatty Amines Phase Change Energy Storage Materials And Their Composites

Phase change materials（PCMs）have many advantages such as large storage energy,high energy storage density,and constant temperature during phase change.They are widely used in building energy conservation,solar energy storage,aerospace,military,electronic equipment,power system,industrial waste heat and waste heat recovery,etc.It is currently a research hotspot in many energy storage technologies.Compared with other types of phase change materials,organic phase change materials have the advantages of low corrosion,no phase separation,and suitable phase change temperature.However,known organic phase change materials have limitations such as easy leakage,low thermal conductivity and low latent heat.Therefore,the search for new phase change materials with high latent heat is of great significance for the storage and utilization of solar energy and thermal energy.This paper firstly discovered and reported a series of new organic phase change materials-fatty amines（FAs）with high latent heat,low phase transition temperature and low supercooling.Using FAs as the guest organic phase change material,based on FAs basic amino group（-NH₂）,a porous medium with acidic groups was prepared as a carrier.The phase change composites was prepared by adsorbing FAs on porous media,in order to improve the adsorption rate and stability of PCMs through the electrostatic interaction between the guest organic phase change material and the main carrier’s acid/base group.At the same time,the intrinsic properties of the carrier are used to improve the thermal conductivity and other comprehensive properties of the phase change composites.The main research content of this paper is the following four parts:（1）The FAs with different carbon chain lengths（with carbon numbers in the range of 12³6）were selected to study their heat storage performance,phase transition temperature and thermal cycling stability.It is found that the phase change latent heat range of FAs is 260 kJ·kg^-1437kJ·kg^-1,which is the highest value of organic phase change materials reported so far.FAs’ phase transition temperature range is 25.8℃⁷1.6℃.FAs have a lower degree of supercooling（<10℃）,and the stability of the hot and cold cycle is also excellent,indicating that FAs aregood organic phase change material.（2）In order to solve the problem of the inherent leakage of FAs,a poly-p-styrenesulfonic acid-based porous medium（PDVB-SO₃H）containing an acidic group was designed and prepared as a carrier according to the basic characteristics of its own active amino group.The octadecylamine（ODA）in fatty amine was selected as the phase change material,and the octadecylamine/polystyrenesulfonate（ODA/PDVB-SO₃H）phase change composites was prepared by melt impregnation method.The characterization results show that the adsorption rate of ODA by PDVB-SO₃H is as high as 560wt%,and it has good heat storage performance and thermal recycling capacity.The latent heat of fusion phase transformation of PDVB-SO₃H to ODA is between 180.9kJ·kg^-1 and224.2kJ·kg^-1,and it has better thermal stability than pure FAs.It was confirmed by Py-IR and adsorption performance experiments that there is an electrostatic interaction between-SO₃H of PDVB-SO₃H and-NH₂ of ODA,which enhances the absorption of the phase change material by the carrier material.However,it has been found that polypyrene sulfonic acid based porous medium has a limited improvement in the thermal conductivity of ODA.（3）In order to improve the thermal conductivity of pure FAs,multi-walled carbon nanotubes（MWCNTs）with high thermal conductivity were selected as carriers to prepare three multi-walled carbon nanotubes（p-MWCNTs,a-MWCNTs and c-MWCNTs）with different degrees of carboxylation by multiple oxidation.These were used as carriers of tetradecylamine and octadecylamine（TDA and ODA）in FAs to prepare a total of six fatty amine/multiwall carbon nanotube phase change composites.The effects of different carboxylation levels of the carrier on the heat storage and thermal conductivity of the fatty amine/multi-walled carbon nanotube phase change composites were investigated.The characterization results show that the highly carboxylated multi-walled carbon nanotubes（c-MWCNTs）have good dispersion in FAs,and FAs/c-MWCNTs have excellent thermal stability and heat storage capacity(>200kJ·kg^-1).The thermal conductivity of FAs/MWCNTs increases with the increase in the number of oxygen-containing functional groups of multi-walled carbon nanotubes.（4）In order to simultaneously improve the problem of easy leakage and low thermal conductivity of FAs,a novel porous three-dimensional graphene sponge（GS）with excellent performance was designed and prepared,and GS was used as a carrier material to support tetradecylamine and octadecylamine in FAs（TDA and ODA）.A shape-stable fatty amine/porous three-dimensional graphene sponge phase change composites（FAs/GS）with high adsorption rate,high energy storage density and high thermal conductivity was prepared by melt impregnation method.The study found that GS has excellent adsorption performance,and the adsorption rate of ODA is as high as 10660.87wt%,which is the highest value of the adsorption rate reported in the porous phase change composites.At the same time,the presence of GS helps to improve the thermal conductivity of FAs.The characterization results show that FAs/GS has better thermal stability and higher energy storage density in low temperature environment,and its latent heat of fusion phase transformation is higher than that of pure FAs.This has never been found in previous studies on phase change composites.After 200 cycles of thermal cycling,the latent heat content of FAs/GS is still as high as 93.34%（TDA/GS）and 93.83%（ODA/GS）.Its further confirming that FAs/GS has excellent thermal recycling capacity.