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The coexisting vapor compositions are given in Table 2.5 for each temperature reported by Vu [31].
Vu measured isobaric vapor–liquid equilibrium (VLE) data of lactic acid + water using a Fischer recirculating apparatus (model VLE 100D). Pure water, acetone, and ethanol were used to calibrate the pressure and temperature sensors. Heating was regulated to maintain a mean recirculation speed of 30 drops per minute. The mixtures were equilibrated for at least 12 h to ensure the equilibrium was reached, before each 0.5 mL sample was taken from condensed vapor and liquid for analyses. The equilibrium state was indicated by a constant pressure and temperature of the system. Vu further quantified the oligomers using a Hewlett‐Packard 1090 Liquid Chromatograph, equipped with an ultraviolet detector (Hitachi L400H) at a wavelength of 210 nm. The mobile phase was acetonitrile (ACN) + water in a gradient mode (0% ACN (t = 0) to 60% ACN (t = 20 min) to 90% ACN (t = 25 min) to 0% ACN (t = 28 min) at 1.0 mL/min. The Novapak C18 column (3.9 × 150 mm) was used and both ACN and water were acidified by 2 mL of 85% (w/v) phosphoric acid per 1 L of solvent, equivalent to pH = 1.3. Further details are provided in [27].
VLE data of Vu are summarized in Tables 2.4 and 2.5. The rows in the two tables at the same temperature represent the coexisting phases. The true mole fractions represent the moles of a species divided by the total moles present in the equilibrated mixture. The subscripts denote the species as defined in Equations 2.4–2.6. The apparent mole fractions in the last column are calculated by taking a basis of one true mole, recognizing that the water in the analysis includes the water released by condensation of the oligomers, thus
TABLE 2.5 Vapor Phase Mole Fractions of Lactic Acid + Water VLE at 101.33 kPa.
| T (K) | True y water |
True |
True |
True |
True |
Apparent |
|---|---|---|---|---|---|---|
| 378.25 | 1 | 0.00051 | 2.9E−07 | 1.7E−10 | 9.6E−14 | 5.1E−04 |
| 379.25 | 1 | 0.00072 | 5.8E−07 | 4.7E−10 | 3.8E−13 | 7.2E−04 |
| 380.25 | 1 | 0.0011 | 1.5E−06 | 1.9E−09 | 2.4E−12 | 1.1E−03 |
| 380.75 | 1 | 0.00083 | 7.8E−07 | 7.4E−10 | 6.9E−13 | 8.3E−04 |
| 381.75 | 1 | 0.00097 | 0.000001 | 1.1E−09 | 1.2E−12 | 9.7E−04 |
| 381.85 | 1 | 0.0019 | 0.0001 | 0 | 0 | 2.1E−03 |
| 383.35 | 1 | 0.0024 | 0.0001 | 0 | 0 | 2.6E−03 |
| 387.35 | 1 | 0.003 | 0.0001 | 0 | 0 | 3.2E−03 |
| 391.65 | 0.99 | 0.012 |
0.0005
|