氧化还原沉淀法制备氧化锰分子筛的热力学分析

Thermodynamics analysis on preparing cryptomelane type manganese oxide octahedral molecular sieves by redox precipitation reaction

为探究氧化还原沉淀法制备氧化锰分子筛反应的适宜温度,对制备氧化锰分子筛的反应过程进行了热力学计算,得到不同温度下的热力学函数值.通过估值和计算得到高锰酸钾与还原剂——硫酸锰、葡萄糖、蔗糖和反丁烯二酸或顺丁烯二酸进行氧化还原反应的摩尔反应焓、摩尔吉布斯自由能和平衡常数,主要分析比较了采用不同还原剂合成氧化锰分子筛的热效应.结果表明,上述氧化还原反应均为放热反应;蔗糖为还原剂的氧化还原反应摩尔反应焓最大,其反应温度控制在低温区域,既可以充分利用反应放出的高热量,也可以避免局部高温生成Mn2O3杂质.因而,相比于其他还原剂,蔗糖更适合用于批量制备氧化锰分子筛.热力学分析结果可为高锰酸钾和不同还原剂制备氧化锰分子筛的工艺控制提供热力学数据和指导.

To inquiry appropriate temperatures of spontaneous reaction,the thermodynamic analysis of redox precipitation reactions to synthesize cryptomelane type manganese oxide octahedral molecular sieves（OMS-2） was performed,and the thermodynamic properties at different temperatures were calculated.According to the molar reaction enthalpy,molar Gibbs free energy and equilibrium constant of the redox reaction,thermal effect of potassium permanganate reacted with different reductants-manganese sulfate,glucose,sucrose,fumaric acid or maleic acid were mainly investigated.The results show that all reactions are exothermic.Moreover,the maximum value of molar reaction enthalpy corresponds to that of potassium permanganate reacted with sucrose,and the reaction between potassium permanganate and sucrose was performed at low temperature to avoid the producing of the impurities-Mn 2 O 3.Therefore,sucrose is the best raw material for the synthesis of OMS-2compared with the other reducing agents.The thermodynamic analysis results can provide thermodynamic data and guidance for process control of synthesis of OMS-2.