(560cf) Conversion of Glucose to Lactic Acid Using and Electrocatalytic Cell System

In 2015, the global market for lactic acid was 1.7 billion pounds, and the worldwide demand of lactic acid is expected to grow to 3.7 billion pounds by 2022.¹ The market for lactic acid will continue to grow due to polylactic acid, the polymerized form of lactic acid, showing promise as an eco-friendly packaging material.² Additionally, The United States Department of Energy named lactic acid one of ten potential building blocks of the future.³ The market for lactic acid is clear, but the manufacturing price of lactic acid needs to reach 0.8 $/kg, roughly half its current cost, to compete with fossil-fuel based plastics.⁴

Currently, fermentation produces 90% of lactic acid.⁴ The fermentation process has many advantages, such as low substrate cost and energy consumption.⁴ The disadvantage of the fermentation process is low selectivity, causing downstream separation to be expensive.⁴ To address this problem, researchers are exploring inorganic catalysts. Application of inorganic catalysts allows selection of active sites to favor the production of lactic acid over the other byproducts.

The majority of work in the field has employed a thermocatalytic system.^5–7 These systems have achieved up to 80% yield of lactic acid but require high temperature or other extreme conditions.^5,6 There are two potential rate-limiting steps in this reaction pathway.⁷ The first is the isomerization of glucose to fructose, where this ideally favors fructose.⁷ The second is the retro-aldol reaction of fructose to glyceraldehyde (GlycAld).⁷ There is agreement that the first problem, favoring fructose in its isomerization with glucose, is solved by a Lewis-acid catalyst.^5–8 Alkaline conditions generally solve the second problem, but the presence of water favors the aldol reaction of GlycAld back into fructose.⁷

No research has been done on this reaction in an electrocatalytic environment. The purpose of this study is to employ an electrocatalytic system to achieve high lactic acid yield, at reasonable reaction conditions, using a copper oxide catalyst. In an electrocatalytic system, the applied voltage should push the equilibrium of the fructose-GlycAld equilibrium to favor GlycAld, increasing the speed of the rate-limiting step. The selection of copper oxide is due to divalent metallic catalysts showing the best yields in thermocatalytic systems.⁶

This study will examine the yields of lactic acid over a voltage range. Initially, copper oxide will be used as the working electrode, followed by trials with deposited copper oxide on a conductive carbon electrode.

References

1. Research and Markets. Global Lactic Acid Market Size, Market Share, Application Analysis, Regional Outlook, Growth Trends, Key Players, Competitive Strategies and Forecasts, 2015 to 2022. (2017).
2. Bozell, J. J. & Petersen, G. R. Technology development for the production of biobased products from biorefinery carbohydrates - The US Department of Energy’s ‘top 10’ revisited. Green Chem. 12, 539–554 (2010).
3. United States Deparment of Energy. Top Value Added Chemicals from Biomass: Volume I--Results of Screening for Potential Candidates from Sugars and Synthesis Gas. (2004).
4. Komesu, A., de Oliveira, J. A. R., Martins, L. H. da S., Maciel, M. R. W. & Filho, R. M. Lactic acid production to purification: A review. BioResources 12, 4364–4383 (2017).
5. Li, L., Shen, F., Smith, R. L. & Qi, X. Quantitative chemocatalytic production of lactic acid from glucose under anaerobic conditions at room temperature. Green Chem. 19, 76–81 (2017).
6. Choudhary, H., Nishimura, S. & Ebitani, K. Synthesis of high-value organic acids from sugars promoted by hydrothermally loaded Cu oxide species on magnesia. Appl. Catal. B Environ. 162, 1–10 (2015).
7. Marianou, A. A. et al. Effect of Lewis and BrØnsted acidity on glucose conversion to 5-HMF and lactic acid in aqueous and organic media. Appl. Catal. A Gen. 555, 75–87 (2018).
8. Zakaria, S. et al. Conversion of glucose into lactic acid using silica-supported zinc oxide as solid acid catalyst. Pure Appl. Chem. 90, 1035–1043 (2018).