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It can be seen from Table 4 that adding a little water to ACN indeed increases the relative volatilities of cr,8, a2g, a3g, a4S, a5S, a68 and a7S in which 1,3-butadiene is as the heavy component and decreases the relative volatilities of a9g, atog, an8, al28 and an s in which 1,3-butadiene is as the light component. So the mixture of water and ACN can enhance the separation ability. However, ACN is blended with water to separate C4 mixture with the defect that ACN is prone to hydrolyze, which leads to equipment corrosion and operation difficulty. From this viewpoint, it is thought that water may be not the best additive. Which additive is the best? This question will be explored in the 2.5. CAMD of extractive distillation section.

Other examples in which the new additive is added to improve the separation ability of the original solvent are illustrated in Tables 5 and 6 for separating cyclopentane (1) / 2,2-dimethylbutane (2) and n-pentane (1) / 1-pentene (2), respectively. In Table 5, NMP, CHOL and NMEP stand for N-methyl-2-pyrrolidone, cyclohexanol and N- ( 13 -mercaptoethyl)-2-pyrrolidone, respectively [58-60].

Table 5

Relative volatility al2 of the mixture of the solvents for separating cyclopentane (1) and

2,2-dimethylbutane (2); adapted from the reference [60]

Table 5

2,2-dimethylbutane (2); adapted from the reference [60]

No.

Solvent/feed mass ratio Mixture of the solvents

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