From Weeds to Wealth
Updated: Apr 22, 2020
Researchers discover simple method to make valuable levulinic acid and cement additive from hemp waste
By Noppadon Sathitsuksanoh, Ph.D., Assistant Professor – Chemical Engineering (Energy & Sustainability), University of Louisville, with Jim Lane, Biofuels Digest
In Kentucky, Louisville scientists add value to solid wastes from the hemp product industry. Their research exploits a simple process that transforms the waste into levulinic acid, a valuable chemical and a cement additive for green concrete.
Kentucky is home to many interesting activities, from horse race known as Derby to making bourbon, growing tobacco, and, particularly, to cultivating industrial hemp. Hemp has long been a cash crop of Kentucky, originally for its fiber. Recently, cannabidiol (CBD) oil has found its way to therapeutic uses. In 2018, the USFood and Drug Administrationapproved the prescription use of Epidiolex, a purified CBD oil, for epilepsy . Moreover, although controversial, researchers have reported many other beneficial properties of CBD oil, including helping people to quit smoking , easing anxiety  and depression, reducing inflammation , and retarding the development of cancer  and Alzheimer’s disease .
As society moves toward greater sustainability, we cannot afford to let any part of hemp go unused. 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 . These hindrances must be eliminated because the ability to add value to hemp wastes will bring benefit to the growers, state economy, and the environment.
Scientists have shown that sugars can be used as new chemical feedstocks . Similar to the way in which crude oil is used, albeit much more environmentally friendly, sugars are starting material for the production of a myriad of products, including biofuels and biochemicals. 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 is ordinarily not simple because cellulose is a complex crystalline polymer that is difficult to break apart. Hence, the transformation of hemp hurd and other plant biomass to levulinic acid usually employs multiple reactions, a costly process fraught with the need to separate the sugars from reaction intermediates. 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. Who would have thought that of concrete? If we can use the flowering materials to partially replace cement in concrete, we can 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. In doing so, they could control concrete setting by programming the cement hydration. 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. 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.
About the author
Biofuel advocate and hemp enthusiast Dr. Noppadon Sathitsuksanoh is the author of more than 50 peer-reviewed articles on building a catalytic and genetic toolbox for production of sustainable energy materials from plant biomass. Dr. Sathitsuksanoh received his B.S. in Chemical Engineering at Thammasat University (Thailand). He next ventured into the biofuels arena, first earning a PhD in Biological Systems Engineering at Virginia Tech (USA), then performing research as a postdoctoral fellow with the Joint Bioenergy Institute at the Lawrence Berkeley National Laboratory. During this time, Dr. Sathitsuksanoh collaborated with many biofuel companies in the development of economically viable biomass conversion processes using ionic liquids. Currently, he is an Assistant Professor in Chemical Engineering at the University of Louisville. Dr. Sathitsuksanoh cultivates a hemp plot on campus, and he leads projects based on bio-inspired chemical conversions to add value to the waste biomass.
A part of this material is based on work supported by the National Science Foundation under Cooperative Agreement No. 1355438. This work was performed in part at the Conn Center for Renewable Energy Research at the University of Louisville, which belongs to the National Science Foundation NNCI KY Manufacturing and Nano Integration Node, supported by ECCS-1542174.
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This article appeared on Biofuels Digest, April 13, 2020 https://www.biofuelsdigest.com/bdigest/2020/04/13/from-weeds-to-wealth-researchers-discover-simple-method-to-make-valuable-levulinic-acid-and-cement-additive-from-hemp-waste/