Ch. 2 Basic concepts of separations Goal (a) preparative work: to purify (or partial purify) component (drugs, fuel, metals, chemical feedstocks) 特徵: continuous operation; large in scale, etc. (b) analytical goals: to generate information about the mixture; to eliminate the interference component for measurement. Giddings, J.C.; Unified Separation Science, John Wiley & Sons, Inc, 1991.

(a+b+c+d)→(a+b)+(b+a) 熱力學上的限制： Complete separation (a+b+c+d)→(a)+(b)+(c)+(d) Partial separation (a+b+c+d)→(a+b)+(b+a) 熱力學上的限制： (a) + (b) + (c) + (d)  (a+b+c+d) (mixing) (a)  (a) (diffusion)

Bulk flow displacement 分離須進行搬運的動作(包含兩部分) Bulk flow displacement 無分離作用 (壓力、重力、離心力、電力) Relative displacement 具分離作用

Driving force of relative displacement: Eq.` Molecular equilibrium in a closed system 1st law： 2nd law： Gibbs free energy：

(2) Molecular equilibrium in open system μ：chemical potential

Two open system α,β (α,β)：a closed system at eq. , T , P constant

(K：partition coefficient) at eq.

Intermolecular force Ionic force Non-ion molecular interaction (1) dipole - dipole (2) dipole - induced dipole (3) induced dipole - induced dipole (4) H – bonding

Solvent extraction Tech. phase 1 phase 2 Chromatography stationary mobile LLE raffinate extractant Dialysis retentate diffusate ← extractant ← raffinate (sample was dissolvent in) q：fraction of solute extracted 1-q：fraction of solute unextracted

is the ratio of total amount (weight) of A in one phase to that in the 2nd phase partition ratio ： (capacity factor) phase ratio：

(1) Partition coefficient (2) (3) (4)

操作模式 Single contact (2) Multiple contact (crosscurrent extraction) (3) Multiple contact (countercurrent extraction)

Multiple extraction ....... extracted left 1st extract q 1-q 2nd 1st extract q 1-q 2nd q(1-q) 1-q-q(1-q)=(1-q)2 ....... N q(1-q)n-1 (1-q)n

A solute with a partition coefficient of 4 A solute with a partition coefficient of 4.0 is extracted from 10 mL of phase 1 into phase 2. (a) What volume of phase 2 is needed to extract 99% of solution in one extraction? (b) What volume of phase 2 is needed to remove 99% of solution in three equal extractions instead?

Effect of pH value on extraction KD ─→ D ( distribution coeff. ) HAo org. aq. HAaq + H2O H3O+ + A-

very acid [H+] >>Ka D=KD (b) at pH (c) [H+] <<Ka D >>KD

Effect of pH value on extraction KD ─→ D ( distribution coeff. ) Bo org. aq. BH+aq H+ + B

very acid [H+] >>Ka D >> KD (b) at pH (c) [H+] <<Ka

Suppose that the partition coefficient for an amine, B, is 0 Suppose that the partition coefficient for an amine, B, is 0.33 and the acid dissociation constant of BH+ is Ka=1.0x10-9. If 50 mL of 0.010M aqueous amine is extracted with 100 mL of solvent. What will be the formal concentration remaining in the aqueous phase (a) at pH 10.0? (b) 8.0?

Application Extraction of metal ions

加入chelator (HL) HL (aq) HL (o) (1) HL (aq)+ H2O H3O+(aq) +L-(aq) (2) Mn+(aq)+ nL-(aq) MLn(aq) (3) MLn(o) MLn(aq) (4)

→ excess chelator CL≈[HL(o)] (6) → HL, MLn在有機相中溶解度大 >>1 → [L-] is pH dependent CL：orignal molar conc. of HL in organic phase mass balance (5) → excess chelator CL≈[HL(o)] (6)

(3) (4) 代入(5) (6) (7)