Technology Profile: Producing Polylactic Acid from Corn – Chemical Engineering

By Intratec Options | Might 1, 2021

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Polylactic acid (PLA, polylactide; Determine 1) is a thermoplastic aliphatic polyester that’s derived from plenty of renewable beginning supplies, corresponding to starch and sugarcane, through bacterial fermentation. PLA is semicrystalline or amorphous, inflexible, resilient and an ultraviolet-light-resistant materials, with related traits to widespread petrochemical trade plastics, corresponding to polyethylene, polypropylene and polystyrene. PLA is utilized in plastic movies, bottles and biodegradable medical units. It figures among the many most extremely consumed bio-based plastics worldwide.

Determine 1. PLA is an aliphatic polyester derived from renewable beginning supplies

PLA quickly absorbs moisture from the environment and can be temperature-sensitive (storage temperatures must be under 122ºF). With a purpose to protect PLA properties and traits, publicity to ambient (undried) air must be minimized. PLA is normally delivered in moisture-resistant containers, together with foil-lined containers, which may stop moisture regain throughout transport and storage. PLA is principally utilized in packaging, textiles, nonwoven materials, electronics, automotive elements, medical units and cutlery. Packaging is the biggest software marketplace for PLA, and can doubtless develop as new heat-resistant PLA blends are developed.

Polylactic acid course of

The manufacturing of PLA from corn (Determine 2) entails three main sections: (1) Starch hydrolysis; (2) Glucose fermentation; and (3) Lactic acid polymerization.

Determine 2. The diagram exhibits the manufacturing course of for PLA, ranging from corn

Starch hydrolysis. Shelled corn is fed to grain cleaners, then despatched to steeping vessels, the place it’s soaked in a dilute resolution of sulfur dioxide, produced in a sulfur burner. The stable matter slurry obtained is submitted to a sequence of unit operations to get better cornstarch, whereas the steep water is concentrated in evaporators and despatched as corn steep liquor (CSL) to the downstream course of phases. The starch is then blended with enzymes and sodium carbonate within the hydrolysis space to transform it to glucose, which is distributed to the fermentation stage.

Glucose fermentation. The fermentation is carried out in an agitated jacketed fermenter, fed with glucose, CSL and sodium carbonate. The fermentation broth is distributed to an ultrafiltration step to take away cell particles, concentrated in an evaporator, after which to an extraction column to extract the lactic acid (LA) in an natural part, which is routed to a distillation column to separate the extractant solvent from the LA. The LA-rich stream is then back-extracted with sizzling water in an extractor practice, producing a LA-lean natural part, which is recycled to the primary extraction stage, and an aqueous part wealthy in LA that’s concentrated in an evaporator and despatched to the polymerization stage.

Lactic acid polymerization. The concentrated LA stream is fed to a prepolymer reactor, the place it varieties low-molecular-weight PLA and water, which is eliminated and disposed. The low-molecular-weight PLA is distributed to the depolymerizer and damaged into lactide molecules (the cyclic lactone di-ester derived from lactic acid), that are purified in a drying column and in a meso-lactide removing column. Lactide is fed to a polymerization reactor, forming PLA, which is distributed to a devolatilizer to take away unreacted lactide. The PLA is routed to an extrusion step after which packed in luggage for storage.

 

Manufacturing pathways

This biodegradable polyester may be synthesized through two main routes. The primary manufacturing route for high-molecular-weight PLA relies on an preliminary polycondensation of lactic acid, adopted by a depolymerization at diminished strain and a ring-opening polymerization step. The opposite route relies on a direct polymerization of lactic acid by polycondensation. Most firms make use of the oblique route, because the manufacturing of high-molecular-weight polymers is tough through direct polymerization.

Edited by Scott Jenkins

Editor’s word: Content material for this column was initially developed by Intratec Options LLC (Houston; www.intratec.us) and is edited by Chemical Engineering. The analyses offered are based mostly on publicly out there and non-confidential data. The content material represents the opinions of Intratec solely. Extra details about the methodology for making ready the analyses may be discovered, together with phrases of use, at www.intratec.us/che.

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