Abstract
Abstract Lactic acid is a naturally existing organic acid, which may be used in many different branches of industrial application. It can be made in the sugar fermentation process from renewable raw lactic acid, which is an indispensable raw material, including in the agricultural, food, and pharmaceutical industries. It is an ecological product that has enjoyed great popularity in recent years. In 2010, the US Department of Energy published a report about lactic acid to be a potential building element for future technology, whose demand grows year by year. The lactic acid molecule naturally exists in plants, microorganisms, and animals and can also be produced by carbohydrate fermentation or chemical synthesis from coal, petroleum products, and natural gas. In industry, lactic acid can be produced by chemical synthesis or fermentation. Although racemic lactic acid is always produced chemically from petrochemical sources, the optically pure L(+) – or D(−) – lactic acid forms can be obtained by microbial fermentation of renewable resources when an appropriate microorganism is selected. Depending on the application, one form of optically pure LA is preferred over the other. Additionally, microbial fermentation offers benefits including cheap renewable substrates, low production temperatures, and low energy consumption. Due to these advantages, the most commonly used biotechnological production process with the use of biocatalysts, i.e., lactic acid bacteria. The cost of raw materials is one of the major factors in the economic production of lactic acid. As substrate costs cannot be reduced by scaling up the process, extensive research is currently underway to find new substrates for the production of LA. These searches include starch raw materials, lignocellulosic biomass, as well as waste from the food and refining industries. Here, the greatest attention is still drawn to molasses and whey as the largest sources of lactose, vitamins, and carbohydrates, as well as glycerol – a by-product of the biodiesel component production process. Focusing on the importance of lactic acid and its subsequent use as a product, but also a valuable raw material for polymerization (exactly to PLA), this review summarizes information about the properties and applications of lactic acid, as well as about its production and purification processes. An industrial installation for the production of lactic acid is only planned to be launched in Poland. As of today, there is no commercial-scale production of this bio-raw material. Thus, there is great potential for the application of the lactic acid production technology and research should be carried out on its development.
Highlights
Circular economy (CE) is the trend in engineering that improves the development of technology to maximize the exploitation of resources and make them recyclable [1,2,3]
Focusing on the importance of lactic acid and its subsequent use as a product, and a valuable raw material for polymerization, this review summarizes information about the properties and applications of lactic acid, as well as about its production and purification processes
The uses for glycerol waste continue to expand
Summary
Circular economy (CE) is the trend in engineering that improves the development of technology to maximize the exploitation of resources and make them recyclable [1,2,3]. Recovery of additional commercial goods from the process of organics production (among other fuels) is an important prospect in the point of view of the circular economy [25,26,27,28]; in the focus of the authors are bioprocesses used in renewable fuel production Some of those processes are waste-less or with minimal by-product generation (e.g., the conversion of bioethanol to bioether) but in some other processes by-products generation is significant (e.g., fatty acids conversion to FAME with glycerol formation). Boldface arrows on the chart (Figure 1) represent primary processes of biomass wastes or by-product treatment while the slender ones describe secondary processes Both bioprocesses and classic physicochemical treatment are used in bio-refining or fuels and energy recovery. The role of lactic acid has been growing in recent years in many applications ranging from food processing, through cosmetics, medicine, and ending with typically engineering applications such as the production of lactic acid polymer (PLA) and its subsequent use as a biodegradable additive to other materials, production of filaments for printers, and 3-D and prototyping various goods [6,53,54]
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