水氯镁石制备金属镁的过程集成与能量分析

Process integration and energy analysis of bischofite producing metal magnesium

以无水氯化镁和氧化镁作为中间产物,电解和热还原为两个关键方法,集成各种相关过程,构建了从水氯镁石到金属镁的综合过程网络,其中涉及24个物种、20个化学过程和25个工艺路线;建立了最低能耗分析模型用于简单和复合过程的能量分析;利用物质的标准生成焓和多温等压摩尔热容,计算得出全部反应过程及工艺过程的能量消耗和热量移除。结果表明基于还原法的最优路径是水氯镁石用石灰法转为氢氧化镁,进而煅烧成氧化镁,再铝热还原成金属镁,该过程能耗360.15 kJ/mol,放出热量–315.46 kJ/mol;基于电解法的最优路径是石灰乳法生成氢氧化镁,再煅烧成氧化镁,通过在熔融电解质中电解生成金属镁,该过程能耗738.54 kJ/mol,放出热量–135.42 kJ/mol。无水氯化镁制备耗能高,不在最优路径中。

Magnesium metal production from bischofite is a process of high energy consumption.It is necessary to explore the process of lowest energy consumption.In this work,with anhydrous magnesium chloride and magnesium oxide as intermediate products,electrolysis and thermal reduction as key methods,a comprehensive process network from bischofite to magnesium metal was constructed,which involved 24 species,20 chemical processes and 25 process routes.Furthermore,one minimum energy consumption model was proposed to evaluate the thermal effect of multi–chemicalprocess,or multi–process routes.Using the standard enthalpy of formation and temperature-depended isobaric molar heat capacity,the energy consumption and heat removal of all 25 process routes were calculated.The results showed that the optimum path based on thermal reduction method was converting bischofite to magnesium hydroxide by lime method,calcining to obtain magnesium oxide,and further reducing to magnesium metal by aluminum.The energy consumption was 360.15 kJ/mol,and the heat released was–315.46 kJ/mol.Compared with this,the better path of electrolysis was producing magnesium hydroxide by lime method,calcining to get magnesium oxide and further producing magnesium metal by electrolyze in molten electrolyte.The energy consumption of the process was 738.54 kJ/mol,and the heat released was–135.42 kJ/mol.Because of the high energy consumption of anhydrous magnesium chloride preparation,it was not in the optimal path.