Table 3.
Chemical processes for lactide production.
| Experimental Conditions | Results | References |
|---|---|---|
| Optimization of the conditions for lactide synthesis—Temperature: 195–230 °C, Pressure: 25–760 mmHg, Catalysts: SnO, SnCl2, Sn(Oct)2, Sb2O3, H2SO4, Atmosphere: with or without N2 flux. | A higher conversion rate was found in the presence of SnCl2 and Sn(Oct)2, the synthesis rate increased with temperature, despite yielding impurities due to thermal degradation. | [2] |
| Dehydration step—Temperature: 130–190 °C, Atmosphere: N2 flux. Lactide polycondensation: Temperature: 190–210 °C, Pressure: 5–25 mmHg, Catalyst: Sn(Oct)2, 0.25 %wt (present or absent). | Lactide: 0.6–2.7 kDa. | [21] |
| Different metallic catalysts for the PLA depolymerization to obtain lactide—Temperature: 190–245 °C, Pressure: 4 mmHg, Catalysts: Al, Ti, Zn, Zr. | None of these catalysts achieved the lactide yield obtained by using only 0.2 mol% of Sn(Oct)2. | [40] |
| The dehydration step occurs in a short-path distillator—Temperature: 120 °C, Pressure: 37.5 mmHg. Oligomerization step—Temperature: 170 °C, Pressure: 75 mmHg, Catalyst: Sn(Oct)2, 1 %wt. Reactive distillation in the short-path distillator—Temperature: 250 °C, Pressure: 3.7 mmHg, Catalyst: Sn(Oct)2, 2 %wt. Purification by crystallization. Lactide polymerization—Temperature: 170 °C, Pressure: 760 mmHg, Catalyst: Sn(Oct)2, 0.04 %wt. | Purity: 99.9%. | [41] |
| One-step heterogeneous catalytic process with Bronsted acidic zeolite to produce lactide (zeolite can be regenerated to six reactions consecutive)—Temperature: 150–220 °C, Catalyst: H-beta zeolite, 5 %wt, Lactic acid: 50 %aq. | Yield: 83–97%. Purity: 98%. |
[42] |
| Depolymerization of low molar mass PLA—Temperature: 150–220 °C, Pressure: 2 mmHg, Catalyst: SnCl2·2H2O/p-toluenesulfonic acid, 0.25 %mol. | Oligomer chain length: 4–5. | [43] |
| One-step continuous catalytic gas-phase transesterification of alkyl lactates without solvents –Temperature: 220 °C, Catalyst: 5 %wt TiO2/SiO2, L-methyl lactate: 5.7% in N2. | Selectivity ≈ 90%. | [44] |
| Fast one-step continuous catalytic process (<1 s)—Temperature: 240 °C, Pressure: 760 mmHg, Catalyst: SnO2/SiO2 nanocomposite (SSO-80), N2 as carrier, Lactic acid: 75 %aq. The purification step used ethanol as solvent for lactide crystallization. | Lactide yield: 94%. Enantioselectivity: 99%. |
[45] |
| One-step continuous catalytic process to produce lactide—Temperature: 240 °C, Pressure: 760 mmHg, Catalyst: SnO2/SiO2 nanocomposite (ϕ ≈ 2 nm), Lactic acid. | Lactide yield: 94%. Enantioselectivity: 99%. |
[46] |
| Lactate transesterification—Temperature: 30–250 °C, Pressure: 1–750 mmHg, Catalyst: Ti-based (0.01–10 %mol), Inert atmosphere: N2. | High yield. meso-lactide. |
[47] |
| One-step catalytic process in the gas phase to produce lactide—Temperature: 160–240 °C, Pressure: 760 mmHg, Catalyst: SiO2/Al2O3, Lactic acid, Inert atmosphere: N2. | Yield: 75–90. Lactide purity: 95–97%. |
[48] |
| Lactic acid dehydration—Temperature: 150–160 °C, Pressure: 110–0.01 mmHg, Inert atmosphere: N2, Stirring: 60–70 rpm. Oligomerization step—Cooling the oligomer until room temperature, Catalyst: Zn/Sn (ϕ < 150 μm), 0.1–0.5 %wt. Depolymerization step—Temperature: 160–200 °C, Pressure: 110–0.1 mmHg, Inert atmosphere: N2. Purification—Crystallization with toluene and washing with ethyl acetate. | Yield > 99%. Optically pure L/D lactide. Impurities < 0.01 %wt. |
[49] |
| A biogenic guanidine creatine catalyst (human-body metabolite) is used to produce optically pure L/D-lactide in an environmentally-friendly synthesis approach (reactive reduced pressure distillation catalysis). Dehydration and polycondensation—L/D-lactide: 90 %wt, Temperature: 130–170 °C, Pressure: 30–60 mmHg. Oligomerization—Catalyst: Creatinine (1:100 to 1:10,000), Temperature: 150–260 °C, Pressure: 2–15 mmHg. Lactide neutralization—Washing with alkali (1–10 %wt) and deionized water; Drying: vacuum at 20–40 °C for 24–36 h. | Optically pure L/D lactide. Lactide: 0.6–1.5 kDa. Free of toxicity and metals. |
[50] |
| This procedure follows a series of steps to produce optically pure lactide: Melt polymerization of the lactic acid—Temperature: 150–160 °C, Pressure: 100–0.1 mmHg, under stirring. Cooling until room temperature, Catalyst: Sn or Zn: 0.1–0.5 %wt, N2 atmosphere. Heating from 160–200 °C, under vacuum (110–0.01 mmHg). The purification step used ethyl acetate as solvent for lactide crystallization. |
Yield: 99%. L(+) Lactide optical purity: 100%. Impurities: <0.01%. |
[51] |
| One-step heterogeneous catalytic process with zeolite to produce lactide—Temperature: 110–165 °C, Pressure: 760 mmHg, Catalyst: Sn-beta zeolite, SnO2-SiO2 xerogel, supported SnO2/Si-beta, Sn-MCM-41 zeolite, Lactic acid: 50 %aq. | Yield: 88.2–95.8%. Pure L(+) lactide. |
[52] |
| A continuous process to produce lactide from lactic acid in ionic solvent, reducing the temperature and moisture generated during the reaction, preventing the lactide degradation. Temperature: 120–300 °C, Pressure: 1–500 mmHg, Time: 1–5 h. |
Yield ≈ 85%. | [53] |
| Single-step lactide production from aqueous lactic acid in the presence of a solid catalyst (Sn, Pb or their mixture)—Temperature: 170–250 °C, Pressure: 760 mmHg or vacuum, Atmosphere: N2, Time: until 100 h. | Conversion rate ≈ 80%. Selectivity ≈ 90%. |
[54] |
| Lactide production through liquid phase depolymerization reaction of lactic acid with tin-derivatives—Temperature: 190–210 °C, Pressure: 760 mmHg, Catalyst: tin (IV) compounds, Additives: di- and trialkylphenols, 0.001–0.1 %wt, Time: 4.5 h. | Yield ≈ 72%. | [55] |
| Lactide production via lactic acid ester dealcoholization—Temperature: 120–230 °C, Pressure: 0.3–700 mmHg, Catalyst: monobutyl tin, Time: 3.5 h. | Purity ≈ 99.4%. Impurities: acids and moisture. |
[56] |
| Rapid production of lactide from lactic acid or ammonium lactate—Temperature: 180 °C, Pressure: 30 mmHg, Time: 4 h. | Yield ≈ 94%. | [57] |
| Temperature: 200–250 °C, Pressure: 0.5–10 mmHg, Time: 3 h. | Yield: 64%. Impurities: low content. |
[58] |
| Lactide production through butyl lactate—Temperature: 180 °C, Pressure: 0.7 mmHg, Catalyst: dibutyltin dichloride. | Dehydrated lactide with low hygroscopicity. | [59] |
| Lactide production from aqueous lactic acid, vaporized and transported with N2 to feed the reactor—Temperature: 150–225 °C, Catalyst: Al2O3. | Lactide purity: 92%. The ratio between the yield of lactide obtained and the molar percentage of lactic acid is 9.1:1. |
[60] |
| Temperature: 130–230 °C, Pressure: 13–25 mmHg, Catalyst: carboxylic acid tin-derivative (≤20 carbon atoms), Lactic acid. | Yield ≤ 80%. Optical purity: 99%. |
[61] |
| Preliminary study for lactide production under different reactional system configurations –Temperature: 185 °C, Pressure: 125 mmHg, Catalyst: Sn(Oct)2, 1 %wt, Time: 4 h. | Yield ≈ 8%. | [33] |
| Lactide purification method to obtain highly optical pure DL-lactide via meso-lactide hydrolysis followed by its removal—Dehydration and polycondensation step: Temperature: 180–230 °C, Pressure: 20 mmHg, Catalyst: SnO. The lactide vapor is distilled and condensed at 60–90 °C. | Yield (D/L-lactide) ≈ 55%. | [62] |
| Lactide production via lactide oligomer depolymerization using microwave irradiation—Temperature: 180 °C, Pressure: 25 mmHg, Lactic acid: 90 %aq, Time: 12 h, Irradiation: 2.45 GHz. | 2.7 times more lactide was obtained with microwave irradiation process in comparison to the method under conventional heating. | [63] |
| Obtaining enantiomerically pure lactides through PLA-oligomer depolymerization using a green and non-toxic catalyst. Temperature: 220 °C, Pressure: 3 mmHg, Catalyst: biogenic creatinine, Time: 2 h. | Yield: 68.5–69.5%. | [64] |
| Heterogeneous catalysis using zeolite (ZSM-5) to obtain L-lactide—Temperature: 144 °C, L-Lactic acid: 98 %aq + solvent mixture: water and o-xylene, Catalyst: Zeolite ZSM-5, Time: 4 h. | Yield ≈ 89%. | [65] |
| Study of the lactide’ synthesis from lactic exploring different metallic catalysts—Temperature: 200–250 °C, Pressure: 1–2 mmHg, Catalyst: ZnO, (C2H5)2Mg, Sn(Oct)2, L-lactic acid: 85 %aq, Time: 2–30 min | Yield: 27–82%. | [66] |
| L-lactic acid polycondensation—Temperature: 120–200 °C, Time: 9 h. PLA-oligomer depolymerization—Temperature: 210 °C, Pressure: 76 mmHg, Time: 3 h. | Yield: 38.5%. | [36] |
| L-lactide production via PLLA thermal depolymerization in a closed system—Temperature: 250–290 °C, Pressure: 3 mmHg, Time: 10 h. | Yield: 8–14%. | [67] |
| Lactide synthesis from alkyl lactate—Polycondensation—Temperature: 150–180 °C, Pressure: 10–720 mmHg, Atmosphere: N2, Alkyl lactate, Time: ≈ 24 h. Depolymerization—Temperature: 180–210 °C, Pressure: 10 mmHg, Catalyst: SnO, 0.5 %wt, Time: 5 h. | Yield: 82%. | [68] |
| D-lactide synthesis from D-lactic acid—Depolymerization process—Temperature: 230–240 °C, Pressure: 10–200 mmHg, Catalyst: ZnO, 0.01–1.5 %wt, D-lactic acid. | Yield: 65–72%. | [69] |
| Production of D,L-lactide from D,L-lactic acid with ZnCl2 and Cat-A under microwave irradiation: Pressure: 7.5–37.5 mmHg, Time: 1 h, Irradiation: 2.45 GHz. | Yield (D,L-lactide): 36%. Pure D,L-lactide. |
[70] |
| Polycondensation step—Temperature: 150 °C, Pressure: 30 mmHg, Lactic acid, 92 %aq, Atmosphere: N2, Time: 5 h. Depolymerization step—Temperature: 130–195 °C, Pressure: 3 mmHg, Catalyst: Zn(la)2, NaHCO3, Time: 3–5 h. | Yield: 95.6%. Purity: 97.9%. |
[71] |