关键词：
吸附;动力学;热力学;磁性壳聚糖微球;有机酸;苹果汁
摘 要：
为充分利用中国丰富的苹果资源,开发多品类的苹果深加工产品,以磁性壳聚糖微球为吸附剂,通过磁分离技术,吸附获得苹果汁中的天然有机酸,并对其吸附过程进行研究。利用Lagergren准一级动力学方程、准二级动力学方程、Elovich方程及内扩散方程对吸附反应动力学过程进行拟合;利用Langmuir等温吸附模型、Freundlich等温吸附模型及Temkin等温吸附模型对吸附等温数据进行拟合,并对其吸附反应热力学特性进行分析。通过比较线性拟合方程的决定系数,发现磁性壳聚糖微球吸附苹果汁中有机酸的动力学过程更加符合Lagergren准二级动力学模型,吸附温度越高,吸附速率常数和初始吸附速率越大,但平衡吸附量越低。等温吸附过程更加符合Langmuir等温吸附模型,表明该吸附过程更趋向于单分子层的化学吸附。298 K时,有机酸的饱和吸附量可达到188.679 2 mg/g,表明磁性壳聚糖微球是苹果汁中有机酸的1种高效吸附剂。热力学参数ΔG°<0,ΔH°<0,ΔS°>0,表明磁性壳聚糖微球对苹果汁有机酸的吸附过程为熵增加的可自发进行的放热过程。动力学及热力学结果为磁性壳聚糖微球吸附苹果汁有机酸的研究提供了理论基础与技术支持。
译 名：
Adsorption kinetics and thermodynamics characters of organic acids from apple juice by magnetic chitosan microspheres
作 者：
Jiang Feihong;Yuan Yahong;Ren Tingting;Meng Diaoqin;Yue Tianli;College of Food Science and Engineering, Northwest A&F University;Laboratory of Quality & Safety Risk Assessment for Agro-products (YangLing), Ministry of Agriculture;National Engineering Research Center of Agriculture Integration Test (Yangling);
关键词：
adsorption;;kinetics;;thermodynamics;;magnetic chitosan microspheres;;organic acid;;apple juice
摘 要：
The aim of this research was to study the kinetics and thermodynamics of organic acids adsorption from apple juice by magnetic chitosan microspheres. Magnetic chitosan microspheres of 0.500 g were accurately added to 30 m L clarified apple juice in which organic acid concentration was 2.32 mg/m L. Oscillatory adsorption of organic acids by magnetic chitosan microspheres was carried out at 3 temperature gradients(298, 318 and 338 K) respectively and the adsorption amount at different adsorption time was calculated. The adsorption kinetic curves at 3 temperatures were obtained by plotting the organic acid adsorption amounts with the adsorption time. At the same time, 0.500 g magnetic chitosan microspheres were accurately added to 30 m L clarified apple juice with different initial concentrations of organic acid(2.782 4, 3.744 5, 4.649 6, 5.772 6, 6.892 2, and 7.814 1 mg/m L). Oscillatory adsorption was respectively carried out at 3 temperature gradients until adsorption equilibrium was reached and the adsorption capacity at equilibrium was determined after magnetic separation under a magnetic field. The adsorption capacity at equilibrium was plotted with the organic acid concentration at equilibrium after adsorption to obtain adsorption isotherms under 3 temperature gradients. The Lagergren pseudo-first-order kinetic model, Lagergren pseudo-second-order kinetic model, Elovich model and internal diffusion model were used to fit the adsorption kinetic data. Three isothermal adsorption models(Langmuir, Freundlich and Temkin) were used to analyze adsorption thermodynamics properties. According to the adsorption kinetic curves, it was seen that initial adsorption rate tended to increase with the increasing of the temperature. Meanwhile adsorption amount at equilibrium(112.374 9, 105.558 4, and 100.424 9 mg/g) decreased with the increasing of the temperature, which demonstrated that the adsorption process was exothermic and higher temperature impeded the adsorption reactivity. By comparing the correlation coefficient, it was found that adsorption kinetic process conformed to the Lagergren pseudo-second-order kinetic model better(R~2>0.998). The adsorption constant declined gradually with the temperature increasing, which also offered a proof of heat release about the adsorption process. Also, the equilibrium adsorption amount calculated by the Lagergren pseudo-second-order kinetic model was close to the data obtained from the experiment. Adsorption thermodynamics conformed to Langmuir isothermal adsorption model(R~2>0.998), which indicated that the adsorption process was a monolayer chemical adsorption. Thermodynamic parameters Gibbs free energy change and standard enthalpy change were below zero, and standard entropy change was above zero, which indicated that the adsorption of organic acid to magnetic chitosan microspheres was a spontaneous and exothermic process along with the increasing of entropy. The kinetics and thermodynamics process can provide technical basis for the adsorption process of organic acid from apple juice using the magnetic chitosan microspheres.
