Non-equilibrium behavior of salt-forming in boiling evaporation process for the system of MgSO(4)-Na(2)SO(4)-H(2)O at 100 degrees C

作者：Zhou Huan^*; Cui Shi Guang; Sha Zuo Liang; Yuan Jian Jun

来源：Acta Chimica Sinica, 2008, 66(12): 1483-1489.

• phase diagram
• boiling evaporation
• non-equilibrium state
• MgSO(4)-Na(2)SO(4)-H(2)O

The non-equilibrium behavior of salt forming was experimentally determined for the system of MgSO(4)-Na(2)SO(4)-H(2)O during evaporation. The experiments of evaporation were carried out at a constant boiling temperature of 100 degrees C by a heating agent of fixed temperature of 140 degrees C. The used evaporation intensity was about 140 similar to 160 g/(h center dot L). The compositions of liquid and solid phases were analyzed at the occurring point of the primary nucleation and the following points of further evaporation. Based on the results, the concept of primary and extended salt forming region was given. The experimental results show that: (1) Both 3Na(2)SO(4)center dot MgSO(4) and Na(2)SO(4)center dot MgSO(4)center dot 2.5H(2)O belong to the same-composition complex-salt in an equilibrium state, but change to different-composition complex-salt in a non-equilibrium state. (2) When evaporating solution which was co-saturated for Na(2)SO(4) and 3Na(2)SO(4)center dot MgSO(4) in equilibrium diagram, the Na(2)SO(4) was only crystallized out. The Na(2)SO(4) can be only crystallized up to 60.86% of the total Na(2)SO(4) in the original solution. The same behavior was found for the co-saturated solution of 3Na(2)SO(4)center dot MgSO(4) and Na(2)SO(4)center dot MgSO(4)center dot 2.5H(2)O. (3) The primary salt-forming region is largely different from the equilibrium region. Based on the Janecke index, the width of the primary forming region of Na(2)SO(4) was extended from 21.02 to 32.76, the width of the primary forming region of Na(2)SO(4)center dot MgSO(4)center dot 2.5H(2)O was reduced from 41.40 to 25.71. (4) Under the condition of having crystal seeds, the width of salt-forming region is larger than that of the primary salt-forming region in different degrees for different salts, for example the region width of Na(2)SO(4) and 3Na(2)SO(4)center dot MgSO(4) increased by 7.72 and 8.81 respectively. The overlay region of the primary and extended salt-forming region was found in the non-equilibrium state. The kinds of salt forming depend on those of crystal seeds.

• 出版日期2008-6-28
• 单位天津科技大学