Читать книгу Poly(lactic acid) - Группа авторов - Страница 32

In overall process development, knowledge about dealing with impurities will be important. Residual sugar in the broth and sugar degradation products play a role throughout the process at the various levels of temperature and acidity. Color may be formed at any step from low‐ to high‐boiling color precursors. Volatile acids such as acetic acid and formic acid will partition throughout DSP and their concentration in recycle streams must be prevented.

In the design of a modern lactic acid plant, mathematical models are indispensable. For example, the kinetic model of oligomerization of lactic acid and the right thermodynamic model for the gas/liquid equilibria are important in design for the concentration of lactic acid by evaporation, as well as for prepolymerization in the lactide route.

Lactic acid solutions and vapors are quite corrosive and knowledge of the material of construction is a must for a low‐maintenance plant. Also, wastewater treatment is an integral part of a lactic acid plant. Aerobic systems are state of the art, but anaerobic systems are increasingly used to treat acid‐containing wastewater streams. The biogas can then be profitably used for steam production. While a plant using sucrose has a net intake and net purge of water, future plants using crude, low‐cost, water‐rich substrates will need to pay more attention to the water balance and wastewater treatment.

Although the fermentation industry can be considered traditional, new technologies may quickly find uses. The rapid commercial application of filtration techniques such as in membrane bioreactors in wastewater treatment and the fast introduction of nanofiltration for making process water from river water are examples. The discovery of ionic liquids with high distribution coefficients for lactic acid in dilute solutions may lead to breakthroughs [67]. New steam boiler concepts that can handle residues can drastically change DSP layout in energy‐efficient integrated biorefineries.