The Thermodynamic Property and Thermal Decomposition Kinetics of Abietic Acid
|Keywords||Rosin Abietic acid Thermodynamic property Solid-liquidsolubility Heat of solution Thermal decompositionkinetics|
Rosin is a natural renewable product which is obtained directly by the distillation of pine oleoresin. Abietic acid, one of the primary components of rosin, is a substance with biological activity, and can be widely used in many industries such as surfactants, medicine, pesticide, and finechemicals. However, due to the fact that abietic acid is contained in rosin as the mixture of isomers, the traditional method for preparation of abietic acid exists some disadvantages, such as low selectivity, longer process flow, and high cost etc., which restrict its application in industry on large scale. So, it is vital to develop a new production method to increase the purity and yield of abietic acid. The isolation of abietic acid from rosin involves preparation of derivatives of abietic acid in the crude mixture, purification of these derivatives by crystallization procedures and regeneration of the acid. Pure abietic acid can be obtained after further purification by means of crystallization. Unfortunately, the solubility of abietic acid is scarce. Therefore, it is necessary to measure the solubility of abietic acid in certain solvents. And then correlated the solubility data with suitable molecular thermodynamic models, obtained their model parameter. The results might provide important basic data and theoretical support for the development of purification processes of abietic acid. In this thesis, abietic acid was isolated by means of isomerization and amination reaction-crystallization coupled with ultrasonic wave, and its thermodynamic properties and thermal decomposition kinetics have been investigated systematically. The main results are as follow.Abietic acid was isolated by means of isomerization and amination reaction-crystallization coupled with ultrasonic wave, which is a novel method developed by our research group. Isomerization rosin and ethanolamine were used as raw materials,95%ethanol as recrystallization solvent, the effects of reaction temperature, reaction time, agitating velocity, ultrasound intensity and recrystallization times on the purity and yield of abietic acid were investigated. The suitable isolation conditions were obtained as follow:reaction temperature30℃, reaction time40min, agitating velocity400rpm, ultrasound intensity300W and freeze crystallization of amine salt three times. The purity and yield of abietic acid were98.52%and54.93%when the suitable conditions was used. And it was then characterization by its melting point, specific rotation, GC, GC-MS, UV, FTIR and NMR, all evidence indicated that the purification product was abietic acid which provided high purity and enough abietic acid for the investigation of thermodynamic properties and thermal decomposition kinetics.The thermodynamic property and thermal decomposition kinetics of abietic acid have been studied. The constant-volume combustion heat of abietic acid was determined as-11441.46kJ·mol-1by means of oxygen bomb calorimeter, and the standard molar combustion enthalpy and standard molar enthalpy of formation have been calculated as-11457.57kJ·mol-1and-701.85kJ·mol-1based on the thermodynamic principle. The molar fusion enthalpy of abietic acid was determined as19.44kJ·mol-1via differential scanning calorimetry (DSC), and the molar fusion entropy of abietic acid was calculated as43.11J·mol-1·K-1according to thermodynamic principle. The thermal decomposition of abietic acid in static state air and argon were investigated, and the results showed that decomposition occurs in a single step in these two atmospheres. The non-isothermal decomposition kinetics of abietic acid was studied by using the differential method combined with integral method, kinetic triplets and the corresponding thermal decomposition mechanisms were obtained as well. And the results show that the thermal decomposition mechanism of abietic acid in air is nucleation and growth, the differential and integral forms of mechanism function are f(a)=2(1-a)[-ln(1-a)1/2and G (a)=[-In (1-a)]1/2. For argon atmosphere, the thermal decomposition mechanism follows Mampel Power law with n=3/2, whose differential and integral forms are f(a)=-2/3a-1/2and G(a)=a3/2.Using the laser monitoring observation technique, the solubility of abietic acid in alcohols (isopropanol, isobutanol,1-pentanol, isopentanol) have been measured by a synthetic method in the temperature range of288.57K-328.43K at atmospheric pressure, which can be employed in the development of purification processes of abietic acid. Experimental solubility data were correlated by means of the simplified models (two-parameter and three-parameter equations), Wilson, NRTL and λh equations. And the results show that the above models are suitable for description of the solubility data of abietic acid in the investigated solvents under the experimental temperature and concentration. The average relative standard deviations are1.02%,0.59%,0.88%,0.93%and0.94%, for the two-parameter, three-parameter, Wilson, NRTL and λh equations, respectively.Using the laser monitoring observation technique, the solubility of abietic acid in ethanol and water mixtures was measured at the temperatures ranging from286.65K-323.85K by a synthetic method at atmospheric pressure. The solubility data were correlated by means of the simplified models (two-parameter and three-parameter equations) and λh equations, the results show that average relative deviations of three models are all small, which indicates that these models are suitable for description of the solubility data of abietic acid in the investigated solvents under the experimental temperature and concentration. And the average relative standard deviations are1.72%、1.12%and1.84%, for the two-parameter, three-parameter, and λh equations, respectively. Based on the quasi-unitary idea, the mixtures of ethanol+water was considered as one new solvent, the experimental solubility has been also correlated by the Wilson and NRTL equations, the calculated values are in good agreement with the experimental values. And the average relative standard deviations are1.19%and1.43%for the Wilson and NRTL equations, respectively. The excess enthalpy of abietic acid in the experimental systems have been forcasted by λh equations, which can be regarded as basic thermodynamic data for the development of isolation process.