Conceptual design of clean separation of ternary mixture of acetone-tetrahydrofuran-water

Based on the thermodynamics analysis of the mixture of acetone, tetrahydrofuran (THF) and water, the conceptual design of a clean separation process for this mixture was developed. Extractive distillation was used to separate water from the other two components. Different extractive solvents were compared through simulation with Aspen plus and it was found that triethylene glycol (TEG) was a highly selective and energy saving solvent.The extracted water could be separated from extractive solvent by ordinary distillation. The simulation result s f rom Aspen plus showed that the separation of THF and acetone could be achieved by azeot ropic distillation using cyclohexane or carbon bisulfide ( CS2 ) as azeot ropic solvent according to different end requirement s. When CS2 was used as azeot ropic solvent, high purity THF could be obtained while accompanied by wit h high energy cost due to low CS2 content in the binary azeot ropic mixt ure of CS2 and acetone. If cyclohexane was used as azeot ropic solvent , a great deal of energy could be saved at the sacrifice of reduced purity THF. The separation of an azeot ropic solvent and acetone could be realized through a liquid-liquid extraction process using water as extractive solvent.No waste water and other waste liquid were produced during the whole separation process thanks to the recycling of extractive solvent and azeot ropic solvent. Therefore the separation process developed here could be considered as a clean separation process

种植密度对苜蓿生长及生物量的影响

种植密度作为影响作物产量和品质的重要因素,会造成植物对于光照、水分和养分的竞争。为研究种植密度对苜蓿生长与产量的影响,在日光温室环境下,以紫花苜蓿(Medicago sativa)为材料,设置25、100、400、800、1 500、2 000株·m~(–2),共6个种植密度,对紫花苜蓿的种群密度和生长状况进行了观测。结果表明,各处理播种后15天的平均种植密度分别为25、100、373、745、1 255、1 938株·m~(–2);随着紫花苜蓿的生长,除了低密度(25、100株·m~(–2))处理没有发生植株数量的变化外,其余4个密度处理植株数量均有所减少,即发生不同程度的自疏,至第二茬收获时(播种后第187天)种群数量分别减少为297、571、759、839株·m~(–2)。植株个体的株高、基径和分枝数量随着现存密度的增加呈指数下降;个体生物量与现存密度的关系满足竞争密度效应的幂函数关系,即随着密度的增加而减小。紫花苜蓿单位面积地上生物量符合最终产量恒定法则,然而,随着密度的增加,地下生物量有先增加后减小的趋势