A Green Chemistry Approach to Pulping Hemp as an IndustriallyRelevantRenewable Fiber for Construction

EPA Grant Number: SU839468
Title: A Green Chemistry Approach to Pulping Hemp as an IndustriallyRelevantRenewable Fiber for Construction
Investigators: Cai, Dr.Charles
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:

Hemp fibers are an extremely strong material, boasting high lateral tensile strength, durability, and strength-to-weight ratio with studies already proving its potential as an effective renewable construction material for future buildings. Hemp fiber is an exceptional material for its sustainability as well as its useful properties and is a rotational crop that grows without the use of pesticides, requiring substantially less water than most crops. The current commercialized mechanism for producing industrial fibers from hemp is by the Kraft pulping process, a procedure matured by the paper pulp industry. This chemical pulping process involves the delignification of hemp fibers by treating hemp stalks with hot water, sodium hydroxide, and sodium sulfide across several steps. This mixture breaks the bonds that link lignin, hemicellulose, and cellulose- all of which make up the chemical composition of hemp. The Kraft pulping method provides sufficient delignification of hemp; however, the process requires many additional energy and cost intensive steps to reduce hazardous waste emissions, such as black liquor, that negatively impact the environment. In fact, 7 tons of black liquor is produced for every ton of pulp, containing concentrated sulfides required for the pulping process. In order to reuse these chemicals, pulping plants spend large amounts of energy into boiling the liquor into solids containing lignin and sulfides. Once boiled, the remaining residue is burned. This step releases organic sulfides, H2S, SO2, VOCs, NOx, and other pollutants into the atmosphere. Combustion of lignin also emits large quantities of CO2 due to lignin's 80% carbon weight ratio.

Approach:

Our proposed hemp pulping process uses Co-solvent Enhanced Lignocellulosic Fractionation (CELF) technology to allow for much cleaner and faster pulping of hemp fibers without the production of black liquor. CELF is a one-step process that fractionates lignin from plant biomass at low temperatures using renewable tetrahydrofuran (THF) in combination with very dilute sulfuric acid to aid in delignification of hemp fibers. CELF delignification performance is comparable to that of the Kraft pulping process while also producing a useful fermentable sugar solution as a byproduct, thus allowing more of the original hemp to be used before waste treatment. After the CELF reaction, dilute acid is neutralized with calcium carbonate to produce gypsum and THF can be recovered by room temperature vacuum distillation. The lignin from CELF is also a much purer more refined product than lignin recovered from Kraft pulping. Once pretreated, the hemp fibers can be added to cement as a reinforcing agent or used on its own in production of drywall or structural reinforcements, the hemp CELF lignin can be used as resin binders and concrete additive.

Expected Results:

Our project goal is to produce, hempcrete, as a lighter, stronger, and more environmentally friendly alternative to conventional fossil-based concrete.

Contribution to Pollution Prevention or Control: Our proposed process promises to reduce energy consumption and hazardous emissions associated with the conventional Kraft pulping process.

Supplemental Keywords:

green chemistry, green engineering, reinforcement, construction materials, materials and chemicals, renewable feedstock, hemp, hemp stalk, hemp fiber, hazardous waste, pulping, pretreatment, CELF