In Kentucky, Louisville scientists just exploited a simple process that transforms hemp crop waste into levulinic acid, a valuable chemical and a cement additive for green concrete made from spent CBD flowers.
Kentucky industrial hemp has long been a cash crop, originally for its fiber. More recently, in 2018, the US Food and Drug Administration approved the prescription use of Epidiolex, a purified CBD oil, for epilepsy [1]. Moreover, many other beneficial properties of CBD oil, including helping people to quit smoking [2], easing anxiety [3] and depression, reducing inflammation [4], and retarding the development of cancer [5] and Alzheimer’s disease [6].
After harvesting its fiber from bast and CBD oil from flowering materials (seeds, flowers, and leaves), residual hemp hurd and flowering materials remain. However, crucial knowledge of chemistry to convert hemp waste to valuable products is lacking because industrial hemp research is encumbered by legal issues and the misconception that hemp and marijuana are the same plant [7]. These hindrances once eliminated will add value to hemp wastes and bring benefit to the growers, state economy, and the environment.
Hemp waste sugars can be used as new chemical feedstocks [8]. Similar to the way in which crude oil is used, hemp plants possess abundant amounts of sugars in the form of cellulose. In an article titled “Direct Production of Levulinic Acid in One Pot from Hemp Hurd by Dilute Acid in Ionic Liquids,” in the American Chemical Society journal Energy & Fuels (https://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.9b03134), researchers describe a greatly improved method for releasing sugar from hemp cellulose and converting it into levulinic acid. Levulinic acid is a highly valuable chemical used as starting material to produce countless biochemical and pharmaceutical products.
The process of releasing sugar from cellulose transforms the hemp hurd and other plant biomass to levulinic acid using multiple reactions, is a costly process fraught with the need to separate the sugars from reaction intermediates. But now – Louisville researchers, led by the Sathitsuksanoh group (https://www.tikgroup.org/), found that the solubility of hemp hurd is a key factor for its efficient transformation. They used ionic liquids (similar to table salt) to dissolve hemp hurd for ease in its transformation to levulinic acid in one reaction pot. Their one-pot approach accommodates high solid loading, eliminates the need to separate intermediate products (glucose and hydroxymethyl furfural), and uses only a single catalyst. The added benefit is that this one-pot strategy is feedstock-agnostic, customizable for different types of plant biomass.
Another hemp waste, the flowering materials after extraction of CBD oil, can potentially be used in concrete. Concrete is the most widely used man-made material, and producing cement alone is responsible for 7% of global man-made greenhouse gas emissions. We can now use the flowering materials to partially replace cement in concrete to mitigate the greenhouse gas emissions. To promote green concrete with less usage of cement, Louisville scientists, led by Dr. Zhihui Sun from the Civil Engineering Department (https://engineering.louisville.edu/faculty/zhihui-sun/), used the residual hemp flowering materials to partially replace cement powder. The flowering powder significantly improved the toughness of concrete, making it a material that is more adaptive to earthquake loads with better crack resistance. This research is published in the American Society of Civil Engineers Journal of Materials in Civil Engineering (DOI: 10.1061/(ASCE)MT.1943-5533.0003209).
The two studies described here could propel the industrial use of solid hemp wastes from the hemp product industry, waste that would otherwise end up in the landfills or compost heaps. Results from these studies show the way to opportunities to upgrade hemp waste by making valuable chemicals and materials to feed the energy, pharmaceutical, and construction industries.
References
2. Morgan, C., et al., Cannabidiol reduces cigarette consumption in tobacco smokers: preliminary findings. Addict. Behav., 2013. 38(9): p. 2433-2436.
3. Bergamaschi, M., et al., Cannabidiol reduces the anxiety induced by simulated public speaking in treatment-naive social phobia patients. Neuropsychopharmacol., 2011. 36(6): p. 1219.
4. Oláh, A., et al., Cannabidiol exerts sebostatic and antiinflammatory effects on human sebocytes. J. Clin. Invest., 2014. 124(9): p. 3713-3724.
5. Velasco, G., et al., The use of cannabinoids as anticancer agents. Prog. Neuro-Psychopharmacol. Biol. Psychiatry, 2016. 64: p. 259-266.
6. Watt, G. and T. Karl, In vivo evidence for therapeutic properties of cannabidiol (CBD) for Alzheimer’s disease. Front. Pharmacol., 2017. 8: p. 20.
7. Brady, T.C., The Argument for the Legalization of Industrial Hemp. San Joaquin Agric. L. Rec., 2003. 13: p. 85.
8. Mika, L., E. Cséfalvay, and Á. Németh, Catalytic Conversion of Carbohydrates to Initial Platform Chemicals: Chemistry and Sustainability. Chem. Rev., 2018. 118(2): p. 505-613.
