Grantee Research Project Results

Final Report: A Green Chemistry Approach to Pulping Hemp as anIndustriallyRelevantRenewable Fiber for Construction

EPA Grant Number: SU839468
Title: A Green Chemistry Approach to Pulping Hemp as anIndustriallyRelevantRenewable Fiber for Construction
Investigators: Cai, Dr.Charles , Moore, Alexander , Le, Christine , Sarwar, Husnain , Singh, Jaskaran , Fernandez, Albert , Marquis, Matthew , Lyons, Zach , Aliaga, Aaron
Institution: University of California - Riverside
EPA Project Officer: Page, Angela
Phase: I
Project Period: December 1, 2018 through November 30, 2019
Project Amount: $12,198
RFA: P3 Awards: A National Student Design Competition Focusing on People, Prosperity and the Planet (2018) RFA Text |  Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Sustainable and Healthy Communities

Objective:

Develop Co-solvent Enhanced Lignocellulosic Fractionation (CELF) technology as an alternative method for pulping industrial hemp to produce sustainable construction materials.

Summary/Accomplishments (Outputs/Outcomes):

There are about 1,269,000 homes built in the US per year, contributing to the use of more than a hundred million tons of materials, many of which are not sustainably sourced or manufactured in a way that potentially has adverse effects on the environment. In order to displace consumption of nonrenewable resources and reduce hazardous process waste, we must focus on developing sustainable practices that utilize natural plant-derived materials and low-emission processes to displace conventional products while providing similar or better performance in the rapidly growing building and construction sector. Highlighted in a number of studies, industrial hemp fiber is a promising candidate as a durable and lightweight material for walling and insulation due to its high lateral tensile strength, durability, and strength-to-weight ratio. The most common construction material utilizing hemp today is hempcrete, a biocomposite of lime and hemp fibers that forms a natural insulator that protects buildings and reduces its carbon footprint. Hemp’s inherent porosity lets it absorb moisture from the air, regulating humidity and limiting the growth of mold on crucial wood structures. It will also reinforce buildings against fire due to its ability to not propagate fires nor crumble when exposed to direct flame. Not only does the tight growth density of the hemp allow it to sequester more CO2 per acre than other lignocellulosic biomass sources, but when incorporated into hempcrete, a carbon negative material, it will continue to strip excess atmospheric CO2 throughout its lifecycle.

Through the recent approval of the 2018 Farm Bill, industrial hemp cultivation has been decriminalized in the United States, prompting 43 states to begin hemp cultivation programs. However, still missing is an environmentally safe and more efficient pulping method capable of processing raw hemp stalks and fibers at large enough scale to be capable of supporting the growing demands of the building and construction industry; sustainably providing alternative high-performance building materials at market competitive prices. Our solution to a greener pulping method for processing industrial hemp is with a breakthrough technology called Cosolvent Enhanced Lignocellulosic Fractionation (CELF). The following EPA P3 Phase I final report outlines preliminary results highlighting the intermediates and end products made from various hemp materials by using the CELF process. CELF is compatible with undried and undecorticated raw hemp stalks that may potentially eliminate intermediate processing steps associated with traditional hemp processing. We show in this report, promising results showing CELF’s potential to achieve reduce the reliance on highly hazardous and environmentally harmful chemical practices when applying pulping to industrial hemp.

Currently, the Kraft Pulping process is used commercially as a standard for paper pulp manufacturing from wood. This method relies on a highly caustic solution of sodium sulfide and sodium hydroxide at elevated temperatures and pressures to cook the biomass in a digester and separate the cellulose fibers from the lignin and sugars. For every 1 ton of biomass that is transformed into almost pure cellulose fiber, 7 tons of the cooking solution, black liquor, is expelled. Black liquor is the main byproduct of the Kraft process, and is a dark and viscous fluid saturated with broken down lignin fragments, carbohydrates, sodium carbonate, sodium sulfate, and other inorganic salts. In a paper pulp operation, the cleanup of black liquor is the costliest step of the operation with the greatest environmental impact. The treated products of black liquor are often disposed by combustion, releasing organic sulfides, H₂S, SO₂, VOCs, NO_x, and other air-borne pollutants.

An alternative pulping method to easily process large amounts of hemp fibers with safer chemicals and virtually zero emissions can be achieved by CELF processing. CELF relies on using renewable tetrahydrofuran (THF), a green solvent if derived from dehydrated sugars. It has been shown that when THF is employed as an aqueous co-solvent during CELF treatment of biomass, one can achieve exceptionally higher pulping efficiencies at lower operating temperatures and shorter contact times. The CELF process additionally uses dilute (<1%) sulfuric acid as a catalyst that can be readily neutralized after the reaction to form inert gypsum salt as an inorganic byproduct. Lignin is immediately dissolved during the CELF process along with amorphous sugars, releasing a light-colored pulp containing highly pure form of alpha-cellulose. The major products out of the CELF process are: 1. Porous cellulose fibers, 2. Lignin-based resins, 3. Food-grade hemp sugar syrup, and 4. Hemp extracts containing actives such as CBD and CBDa. As the CELF process does not produce any gasses and does not utilize non-renewable solvents, the threat of releasing harmful pollutants is eliminated. THF after the CELF process can be boiled out and recovered at a low 66℃ can be recycled in subsequent reactions. Due to the relatively mild reaction conditions compared to Kraft pulping, the CELF reaction is minimally invasive to the chemical structures of the fibers, extractives, and lignin found in the original biomass feedstock to allow for greater utility and versatility for the products.

As part of our objective to create relevant strategic partnerships during the project, we have partnered with Hempire USA, Match Patch Pro, and the Soboba Native American Tribe. Sergiy Kolenkov, CEO of Hempire USA, has about a decade of experience with hempcrete construction and was awarded winner for both the clean tech contest Power UP in 2018 and the Climate Tech Innovation Program in 2017. Sergiy is also bringing support as board member of the US Hemp Building Association. He has supplied our team with hemp stalks specifically for hempcrete mixing, and served as an in-person advisor for hempcrete processing techniques and mixing ratios. Our team is also collaborating with David Moore, CEO of Match Patch Pro, who is a veteran with 34 years of experience with resin-based adhesives for concrete patching With his expertise we are working together in developing a renewable lignin-based resin to aid in production of high durability lightweight composites and repair materials. Lastly, the president of Soboba’s Economic Development Corporation, Stephen Lauzier, is opening the discussion to have our team help to develop community-scale systems that support Native American goals and future vision.

Our first objective was the produce CELF pulped hemp fibers and compare their material properties with raw hemp hurd. To achieve this, we treated hemp hurd using CELF at different temperatures to understand the effects that reaction severity had on the finished pulp product. In our lab, we conducted reactions using two vessels: a 1 L stirred autoclave reactor and a 1 gal unstirred autoclave reactor. The lowest severity reaction was run at 140 °C with the highest severity performed at 160 °C. Like with other lignocellulosic biomasses, the hemp stalk was highly susceptible to even the lowest severity CELF reaction. 32% of the mass was removed at 140°C containing with about 80% removal of lignin 55% mass loss was observed at 160°C with over 90% removal of lignin. Despite the removal of a drastic portion of the original mass, CELF is a delicate enough procedure that it can preserve the original stalk structure, as seen in Figure 1. Where the untreated hemp fibers needed sharpened sheers to cut and separate, the pretreated hemp fibers could easily be separated by hand. Furthermore, if agitation is introduced to the reaction vessel, the hemp fibers will unravel into finer strands, as seen in Figure 1. The wet mass possesses the same consistency as wet crumpled paper. By simply changing the CELF reaction conditions, one can control and tune the physical and chemical disposition of the pulped fibers.

Figure 1: Raw hemp hurd before treatment (left). CELF-pulped hemp fibers produced without agitation (center) and with agitation (right).

To inspect the effects of CELF on hemp’s moisture regulating properties, moisture absorptivity was first tested for both untreated raw hemp hurd and CELF pulped hemp. Fibers were soaked in water for 2 days, then, using a moisture analyzer, the hemp fibers were dried completely to determine the maximum amount of water stored in the pores of the biomass on a dry mass basis. Raw untreated hemp fibers achieved a maximum moisture content of 3.53 milliliters of water per 1 gram of dry biomass. Low severity reacted fibers were determined to reach a maximum moisture content of 4.66 milliliters of water per gram, a 32% increase. High severity reacted fibers reached a maximum moisture content of 10.94 milliliters of water per gram, a 210% increase. Water is attracted to the polarized functional groups along the cellulose chain, while the complicated aromatic structure of lignin provides a hydrophobic barrier from water. The increase in water absorptivity is a testimony to the amount of lignin that was removed from the native cellulose network while still retaining the superstructure of the pulped fibers that are crucial to support manufacture of higher quality composites and building materials.

Our second objective was to produce modified hempcrete using the CELF-pulped/treated hemp produced during the first objective, then compare to the conventional hempcrete available currently. For the comparison, three types of hemp fibers were used to create hempcrete samples: untreated hemp fibers (control), CELF treated hemp fibers, and agitated CELF treated hemp fibers. CELF treated hemp fibers were placed in an oven over night to bring their down their water content to a sufficient level. All samples were made with the same hemp:lime:water ratio of 1:3:3, a tweaked ratio based on the recommended values given from partners at Hempire, LLC. All samples packed into a heating tray and left overnight in the 45℃ oven to dry, then removed as seen in Figure 3. Hempcrete made from raw untreated fibers holds form sufficiently but is noticeable delicate-to-touch. Apparent voids and partial hemp coverage give the sample a coarse appearance and reduced bulk strength. On the other hand, both CELF treated hemp samples exhibit excellent bonding with the lime binder, as the increase hydrophilic nature of the hemp fibers allowed deeper penetration of lime into the hemp fibers. Samples appear almost homogenous. Not only that, but both samples demonstrate an improved physical constitution. Whereas conventional hempcrete feels like its about to burst to the touch, CELF treated hempcrete stays incredibly resistant to fracture under much higher pressure. Between the agitated and no agitated fibers, the agitated hempcrete fibers are more prone to cracking and crumbling but still extraordinarily tough.

Figure 3: Traditional hempcrete made with untreated hemp hurds (left). Experimental hempcrete, made with CELF treated hemp fibers (right) and agitated fibers (left).

Our third objective was the develop a technoeconomic model for a CELF-based hemp pulping operation. A computer plant model was developed using SuperPro Designer® for a hypothetical hempcrete manufacturing facility for this report to assess technoeconomic feasibility of a CELF-based process. A simple block flow diagram of a proposed plant model is shown in Figure 4 that outlines the major processing units for a CELF-based pulping operation that can process up to 50 tons per day (TPD) of hemp hurd. The pulping performance of CELF reaction was based on experimental results obtained from our laboratory 1-gallon scale reactions. Thus, for every 1 ton of hemp hurd processed, the proposed plant model parameters were adjusted to produce 0.52 tons of pulped fiber, 0.21 tons of food-grade sugar syrup, 0.17 tons of lignin-based resins, 0.1 tons of crude extracts containing food-grade terpenes, oils, and proteins. The anticipated conservative market prices for the major co-products hempcrete, hemp syrup, hemp lignin-based adhesive resins, and crude broad-spectrum extractives are $700/ton, $800/ton, $1000/ton, and $50,000/ton. As the CELF process eliminates any need for pre-processing such as retting, drying, or milling we calculate the total operating costs of a 50 TPD CELF pulping operation including labor to be about $125/ton (w/o extractives) - $300/ton (w/ extractives) of hemp input depending on configuration. We estimated the cultivation and sale of the hemp feedstock that would be purchased and used by the plant to be $150/ton. The fixed capital cost of the first plant is calculated to be $20M with a 15% discount factor for each additional plant installation. If elected, an extraction facility in addition to the CELF pulping operation would require an additional $25M in fixed capital investment. The resulting model predicts a minimum margin of profit for a 50TPD operation of $427/ton of hemp input without sale of extractives and $5252/ton with the sale of extractives at current competitive market prices for crude hemp extracts. This means that this plant, co-located with a 1000-2000 acre cultivation site, can operate year-round at 85% of maximum capacity and be able to generate annual gross profits of $6.6M from construction materials and food supplements alone and about $80M/yr if extractives containing CBD are manufactured in addition. The estimated pay-back period at a 10% discounted tax rate was calculated to be 1.7 to 4 years. Compared to current US hemp extractives-only operations producing 10-15 kg/day of full-spectrum CBD, this integrated operation would be at least 60% more profitable per ton of hemp processed and able to reach 25X or greater operational scale based on inputs.

Figure 4: Process flow diagram of proposed hypothetical plant model employing CELF technology

Conclusions:

We are currently engaging strategic agricultural and construction partners to support further R&D for an expanded line of products. We would also like to take advantage of continuing under the EPA P3 program and future SBIR opportunities to raise bridge funding.

Supplemental Keywords:

Green chemistry, pulping, construction, biomaterials, fiber, lignin, resin, extractives, hemp, CELF.

Relevant Websites:

EPA funds student research projects promoting sustainability Exit  

P3 Phase II:

A Green Chemistry Approach to Pulping Hemp as an Industrially Relevant Renewable Fiber for Construction  | 2021 Progress Report  | 2022 Progress Report  | 2023 Progress Report  | Final Report