Abstract
Solid-liquid extraction (adsorption or ion exchange) is a promising approach for the in situ separation of organic acids from fermentation broths. In this study, a diluted concentration of lactic acid (<10 g/L) separation from a model fermentation broth by granular activated carbon (GAC) as well as weak (Reillex® 425 or RLX425) and strong (Amberlite® IRA-400 or AMB400) base anion exchange resins under various operating conditions was experimentally investigated. Thermodynamic analysis showed that the best lactic acid adsorption performances were obtained at a pH below the pKa value of lactic acid (i.e., 3.86) for GAC and RLX425 by physical adsorption mechanism and above the pKa value for the AMB400 resin by an ion exchange mechanism, respectively. The adsorption capacity for GAC (38.2 mg/g) was the highest, followed by AMB400 (31.2 mg/g) and RLX425 (17.2 mg/g). As per the thermodynamic analysis, the lactic acid adsorbed onto GAC and RLX425 through a physical adsorption mechanism, whereas the lactic acid adsorbed onto AMB400 with an ion exchange mechanism. The Langmuir adsorption isotherm model (R2 > 0.96) and the pseudo-second order kinetic model (R2 ~ 1) fitted better to the experimental data than the other models tested. Postulating the conditions for the real fermentation broth (pH: 5.0–6.5 and temperature: 30–80 °C), the resin AMB400 represents an ideal candidate for the extraction of lactic acid during fermentation.
Highlights
Lactic acid (2-hydroxypropionic acid) is an important commercial chemical due to its application in food, medical, pharmaceutical, packaging and textile industries
The study shows that granular activated carbon (GAC), RLX425 and AMB400 can be used to adsorb lactic acid from a model fermentation broth used for T. neapolitana fermentation when it contains low concentration of lactic acid (
This study showed that the lactic acid recovery efficiency is better for the GAC and the AMB400 resin compared to the efficiencies reported by previous studies (Table 6)
Summary
Lactic acid (2-hydroxypropionic acid) is an important commercial chemical due to its application in food, medical, pharmaceutical, packaging and textile industries. The demand for lactic acid has been significantly high, especially for its application in biodegradable polymers, i.e., polylactic acid (PLA), which has a potential to replace traditional commodity plastics. PLA-based plastics have some unique features such as high tensile strength, stiffness and resistance to fats and oils compared to traditional plastic materials; they require further improvement in some properties and characteristics such as viscosity, thermal stability and production cost [1]. Extraction, purification and continuous supply of lactic acid as raw material from fermentation processes is a major challenge because of its highly hydrophilic structure and the lack of efficient low cost purification techniques [3].
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