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Gypsum‐free lactic acid production can be briefly categorized as follows:

 Low‐pH Fermentations Coupled to In Situ Product Removal. As discussed in Section 1.2.4, fermentations can be carried out without neutralization at pH 2–3 with genetically modified yeast or at pH 4 with LAB with partial neutralization [50]. When a separation method to recover the undissociated acid is integrated with fermentation, a process route can be designed in which no gypsum is produced. In the literature, a number of separation methods are described with an emphasis on extraction [63]. Cost efficiency in the fermentation (e.g., nutrients, yield) and the practical processing of large dilute streams need breakthroughs for economical processing.

 Electrochemical Splitting of a Neutral Lactate Salt. Numerous articles have described the splitting of a lactate salt, notably sodium lactate, into lactic acid and the original base [64]. With this principle, a gypsum‐free process can be designed, with electrodialysis separate from or integrated with fermentation. The use of electrodialysis with new bipolar membranes is straightforward, but a large‐scale commercial breakthrough as in the 1980s and 1990s with monopolar membranes for the chloro‐alkali process is still pending. Electrodialysis involves relatively high electricity costs and a huge membrane area, but these costs may be managed in biorefinery concepts with integrated energy production.

 Chemical Salt Splitting of a Lactate Salt. Lactate salts can be split with the help of auxiliary chemicals and the regeneration of these chemicals. A patent by Baniel et al., for example, describes a method in which a sodium lactate solution is acidified with CO2 under pressure, and simultaneously undissociated lactic acid is extracted and insoluble sodium bicarbonate (NaHCO3) is formed [65].

Another patent describes the splitting of ammonium lactate by esterification with butanol while liberating ammonia [66]. In the distillation process, the butyl lactate can be hydrolyzed with water to liberate lactic acid. This is an interesting option, but the energy consumption and side reactions such as the formation of lactamide and racemization require attention.

Chemical salt splitting processes with the recycle of chemicals can be complex, but it is a challenge to develop a system with straightforward chemistry, high yield, low energy consumption, and good scalability.