氨在活性炭-膨胀石墨混合吸附剂上的吸附平衡分析

Analysis of Adsorption Equilibrium of Ammonia on Composite from Activated Carbon /Expanded Graphite

为研制氨吸附制冷用活性炭一膨胀石墨的混合吸附剂，选用椰壳活性炭和可膨胀石墨，初步分析了氨在膨胀石墨添加比率为50％的混合吸附剂上的吸附平衡．吸附剂试样首先经由77K液氮在其上吸附数据的结构表征，然后应用根据容积法原理建立的吸附平衡测试装置，在温度293．15～303．15K、压力0—1MPa，测试了氨在试样上的吸附平衡数据，并通过等量吸附线标绘和Dubinin—Astakhov方程的模型分析，研究了氨在混合吸附剂上的吸附平衡．结果表明，添加膨胀石墨减小了混合吸附剂的比表面积和微孔容积，Dubinin—Astakhov方程在平衡压力较高区域的预测精度可达到4％，氨在混合吸附剂上的等量吸附热为16．94～27．78kJ／mol．添加膨胀石墨必须兼顾混合吸附剂的吸附容量和传热传质性能．

In this paper, activated carbon and expanded graphite were employed to develop the compos- ite adsorbent for ammonia adsorption refrigeration. The structural characterization of the composite, which was synthesized by a mixing ratio 50% between the expanded graphite and coconut shell activated carbon, was un- dertaken based on adsorption isotherm of nitrogen at 77. 15 K. Isotherms of excess adsorption amounts of high purity ammonia were volumetrically measured over a temperature range of 293.15 - 313.15 K and for pres- sures up to 1 MPa, isosteric heats of adsorption were then determined by adsorption isosteres. Dubinin - Astakhov equation was selected to model the adsorption equilibrium data by nonlinear fitting. Results showed that the specific surface area and pore volume of the adsorbent were decreased with the adding of the expanded graphite. The prediction accuracy of the modified Dubinin - Astakhov equation could reach 4% while the pressure gets became higher. Results also revealed that the isosteric heat of ammonia adsorption on the com- posite synthesized was about 16.94 - 27.78 kJ/mol. Conclusions were then drawn that the ratio should be selected in considering on both improving the overall adsorption amount and enhancing the thermal conductivity of the adsorbent.