Rathin Datta and Shih-Perng Tsai

Waste Management and Bioengineering Section, Energy Systems
Division, Argonne National Laboratory, Argonne, EL 60439

Lactic acid has been an intermediate-volume specialty chemical (world production -50,000 tons/yr) used in a wide range of food processing and industrial applications. Lactic acid has the potential of becoming a very large volume, commodity-chemical intermediate produced from renewable carbohydrates for use as feedstocks for biodegradable polymers, oxygenated chemicals, environmentally friendly "green" solvents, plant growth regulators, and specialty chemical intermediates. The recent announcements of plant expansions and building of new development-scale plants for producing lactic acid and/or polymer intermediates by major U. S. companies, such as Cargill, Chronopol, A. E. Staley, and Archer Daniels Midland (ADM), attest to this potential. In the past, efficient and economical technologies for the recovery and purification of lactic acid from crude fermentation broths and the conversion of lactic acid to the chemical or polymer intermediates had been the key technology impediments and main process cost centers. The development and deployment of novel separations technologies, such as electrodialysis (ED) with bipolar membranes, extractive distillations integrated with fermentation, and chemical conversion, can enable low-cost production with continuous processes in large-scale operations. The use of bipolar ED can virtually eliminate the salt or gypsum waste produced in the current lactic acid processes. Thus, the emerging technologies can use environmentally sound processes to produce environmentally useful products from lactic acid. The process economics of some of these processes and products can also be quite attractive. In this paper, potential products and recent technical advances in lactic and polylactic acid processes are discussed. The technical accomplishments at Argonne National Laboratory (ANL) and the future directions of this program at ANL are discussed.

© 1997 American Chemical Society

Lactic acid (2-hydroxypropionic acid), CH3CHOHCOOH, is the most widely occurring hydroxycarboxylic acid. It was first discovered in 1780 by the Swedish chemist Scheele. Lactic acid is a naturally occurring organic acid that can be produced by fermentation or chemical synthesis. It is present in many foods, both naturally or as a product of in-situ microbial fermentation (as in sauerkraut, yogurt, buttermilk, sourdough breads, and many other fermented foods). Lactic acid is also a major metabolic intermediate in most living organisms — from anaerobic prokaryotes to human beings.

Although lactic acid has been ubiquitous in nature and has been produced by fermentation or chemical synthesis for over 50 years, it has not been a large-volume chemical. Its worldwide production volume by 1995 had grown to approximately 50 x 10 tons/yr with only a few major producers — CCA biochem b. v. of the Netherlands and its subsidiaries in Brazil and Spain, ADM in Decatur, Illinois, as the primary manufacturers. Sterling Chemicals, Inc., in Texas City, used to be a major producer but has recently announced the closure of its plant and exit from the business. Musashino in Japan has been a smaller manufacturer. CCA and ADM uses carbohydrate feedstocks and fermentation technology, while Sterling and Musashino use a chemical technology. Thus, lactic acid was considered a relatively mature fine chemical in that only its use in new applications (such as a monomer in plastics or as an intermediate in synthesis of high-volume oxygenated chemicals) would cause a significant increase in its anticipated demand (7).

For lactic acid to enter these applications, economical, efficient, and environmentally sound manufacturing processes are needed for its production. In the past, efficient and economical technologies for the recovery and purification of lactic acid from crude fermentation broths and conversion of lactic acid to the chemical or polymer intermediates had been the key technology impediments and main process cost centers. The development and deployment of novel separations technologies, such as electrodialysis (ED) with bipolar membranes, extractive distillations integrated with fermentation, and chemical conversion, can enable low-cost production with continuous processes in large-scale operations. The use of bipolar ED can virtually eliminate the salt or gypsum waste produced in the current lactic acid processes. Thus, the emerging technologies can use environmentally sound processes to produce environmentally useful products from lactic acid. Recent announcements of new lactic acid production plants by major chemical and agriprocessing companies may usher new technologies for the efficient, low-cost manufacture of lactic acid and its derivatives for new applications (2-5).