For many years, a federal ban on growing hemp, a nonpsychoactive type of cannabis, dimmed the promise it holds for sustainable construction materials, textiles, and many other products.
While the 2018 Agricultural Act legalized industrial hemp, methods for processing hemp stalks are stuck in the past. Pulping, the process of extracting valuable cellulose fibers from plant stalks, for example, releases environmentally dangerous gasses and leaves behind a toxic residue called “black liquor,” which is expensive to treat and make safe for disposal or incineration.
In a strange twist, growers in states that have legalized recreational or medical cannabis are struggling due to market saturation and the fact that over 90% of what they grow is considered refuse or plant waste for which disposal is expensive. This dual situation has created a burgeoning industry to explore new methods for using the whole hemp plant and more sustainable ways to extract value from its stalk and hurd, the woody inner part of the stalk.
Charles Cai, a research engineer and adjunct professor at UC Riverside’s College of Engineering Center for Environmental Research and Technology, has developed and patented an improved pulping method that uses a naturally derived solvent, creates no toxic waste, emits no carbon dioxide, and converts nearly 100% of the hemp plant into useable components, such as cellulose fiber for use in textiles and construction, resinous lignin for use in bioplastics, sugars for use as sweeteners, and extractives for use in wellness products.
The method, called Co-solvent Enhanced Lignocellulosic Fractionation, or CELF, uses a renewable and highly recyclable solvent to perform pulping under mild conditions, saving process energy while generating zero harmful emissions. The only waste is a small amount of mineral ash that is filtered out of the process and can be used as a soil amendment. CELF was originally conceived to help convert plant waste into biofuels. However, its effectiveness at deconstructing plant matter makes it a Swiss Army knife for all plant processing. Its scientific merit was recently proven by one of the world’s fastest supercomputers.
Now, Cai is working with a team of undergraduate students to commercialize the hemp-processing technology through funding from the EPA’s People, Prosperity and the Planet Program, or EPA P3. Last year, the team demonstrated proof of concept for using the CELF pulping method, using it to make an improved type of hempcrete, a concrete-like, carbon sequestering building material made from hemp fibers.
This year, the UC Riverside team has been awarded Phase II funding from the P3 program to continue to improve CELF for hemp processing. In an effort to identify new products and market opportunities, the research team has joined forces with startup InnovaCan, as well as companies Hempire USA, a member of the US Hemp Building Association; Match Patch Pro; and The Hurd Co.; to identify new products and market opportunities.
The team will build a custom CELF reactor able to handle larger quantities of hemp and optimize the reaction to tune the properties of the resulting fiber and lignin products. — By Holly Ober, UC Riverside