Study On Crystal Structure And Energy Storage Performance Of The Long-Chain N-Alkylamine Sulfate Solid-Solid Phase Change Energy Storage Materials

Phase change materials（PCMs）can effectively solve the mismatch of energy supply and demand related to a temporal and spatial context,PCMs can effectively solve the problem of energy shortage and improve energy utilization efficiency.Thus,it becomes a hot material for domestic and foreign researchers.As a basic raw material of fine chemical industry,long-chain n-alkylamine is used in the synthesis of reagents,emulsifiers and surfactants.It also play an important role in the pharmaceutical industry.In order to improve the performance of long-chain n-alkylamine materials in energy storage.In this thesis,long-chain n-alkylamine materials were reacted with the sulfuric acid in the corresponding ratio to form six kinds of long-chain n-alkylamine sulfate solid-solid PCMs with in liquid phase.Then,the thermodynamic properties of them were studied.The following results were obtained:Six of the PMCs were synthesized via chemical with in liquid phase.The chemical components,molecular structures and crystal structures were studied via elemental analysis and X-ray single crystal diffraction technique.The results show that,C₉H₁₉NH₃HSO₄（s）,C₁₃H₂₅NH₃HSO₄（s）and C₁₅H₃₁NH₃CH₃SO₄（s）belong to the monocline crystal system,(C₁₂H₂₅NH₃)₂SO₄·3H₂O（s）and(C₁₄H₂₉NH₃)₂SO₄·3H₂O（s）belong to triclinic crystal system,while C₁₀H₂₁NH₃CH₃CH₂SO₄（s）belongs to orthogonal crystal system.The internal configurations of such synthetic crystals are composed of inorganic anion thin layer and aminium ion[R-NH₃]⁺thick layer,which contributes to three-dimensional configuration phenomenon of layered perovskite.The connection effect of hydrogen bonds result to a spatial supramolecular system with double layers.The interaction of hydrogen bond and van der Waals force leads to the similar molecular accumulation conformations for the six crystals.The lattice energy of these six new substances decreases with the increasing carbon number in their carbon chains.and the stability decreased.In addition,the standard XRD diffraction data of six kinds of long-chain n-alkylamine sulfate PCMs were presented,which provides a reference for future study of this kind of materials.The six kinds of long-chain n-alkylamine sulfate PCMs are tested via thermal analysis,The results show that,the six kinds of long-chain n-alkylamine sulfate PCMs have reversible phase transition,The phase transition temperature are betwere 20 to 100℃,which means it has various potential applications in industry and agriculture.C₉H₁₉NH₃HSO₄（s）has a single phase change peak,which appears at the 97.02 J/g.The comprehensive latent heat of(C₁₂H₂₅NH₃)₂SO₄·3H₂O（s）recahes up to 98.55 J/g,which is the maximum among all of the six long-chain n-alkylamine sulfate PCMs.The molar heat capacities of these six PCMs in 0-400 K region were measured with the Quantum Design Physical Property Measurement System（PPMS）and a precise automatic adiabatic calorimeter.The result shows that,the phase change enthalpy of C₁₀H₂₁NH₃CH₃CH₂SO₄（s）is 23.0 k J·mol^-1,its excellent phase change reversibility contributes to potentials applications in the storage and utilization of solar energy.The fitting polynomials were obtained by using the least square algorithm in the non-phase transition region.The thermodynamic functions[H_T-H₀],[S_T-S₀]and[G_T-G₀]of the six PCMs with respect to 0 K were deduced.the thermodynamic functions about the six kinds of long-chain n-alkylamine sulfate PCMs change with temperature,by which to obtain the thermal change behavior of the six kinds of PCMs.The results shows that,The enthalpy change and entropy change of(C₁₄H₂₉NH₃)₂SO₄·3H₂O（s）at 298.15 K are greater than those of the other five PCMs,and the change of Gibbs free energy is smaller than the other five PCMs,that is,this material is more stable.The Forcite module of Materials Studio（MS）was used to conduct molecular dynamics simulation of the six long-chain n-alkylamine sulfate PCMs in the 0-400 K region.The temperature,density,energy and crystal cell data of each cures were found.The results show that,the distortion of the long-chain n-alkylamine inside the unit cell and the change of the internal force are the main causes of the density and energy changes.