Zia Abdullah, Laboratory Program Manager, National Renewable Energy Laboratory

Author: Zia Abdullah, Laboratory Program Manager, National Renewable Energy Laboratory

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Thermochemical conversion of lignocellulosic biomass is a promising route to produce renewable biofuels and oxygenated biochemicals while enabling the reuse, recovery, and recycling of materials containing carbon.

Aqueous Waste Streams: A Drag on Biorefinery Profitability

Oxygenated aromatics such as phenol (left), phenolics (center), or catechol (right) can be used in building material, automotive, plastics, or agricultural applications and have now been isolated from a biorefinery waste stream.

Oxygenated aromatics such as phenol (left), phenolics (center), or catechol (right) can be used in building material, automotive, plastics, or agricultural applications and have now been isolated from a biorefinery waste stream. Photo by Nolan Wilson/NREL

To convert biomass into renewable biofuels and biochemicals, biorefiners must first break down biomass (deconstructed) into smaller subunits. When this deconstruction is performed through thermochemical processing, an aqueous waste stream is often generated in addition to the valuable product.

These aqueous waste streams are predominantly water, but also contain organic compounds like acids and phenolics. Thus, these streams cannot be discharged directly to the sewer and therefore create additional wastewater treatment costs for the biorefinery.

Even though these waste streams contain useful organic materials, they still cannot be efficiently converted to biofuels or biochemicals because they are dilute, making up less than 3% of the waste streams’ composition, and are therefore difficult to separate.

In addition, it is generally not cost-effective to isolate the most valuable components from these organic materials due to the high-purity requirements typically necessary for bulk chemical production.

In response to this costly issue, National Renewable Energy Laboratory (NREL) research engineer Nolan Wilson, group manager Mark Nimlos, and research technician Joseph Roback, with funding support from the Bioenergy Technologies Office, developed a method to enhance the value of aqueous waste streams by isolating these organic compounds, specifically the monomers, which are precursors to everyday materials like plastics.

This detailed method was published in the journal Green Chemistry in a study titled, "Valorization of Aqueous Waste Streams from Thermochemical Biorefineries."

NREL researchers Joseph Roback (left) and Nolan Wilson (right) study separation approaches to isolate purified chemical products using scalable and cost-effective unit operations.

NREL researchers Joseph Roback (left) and Nolan Wilson (right) study separation approaches to isolate purified chemical products using scalable and cost-effective unit operations. Photo by Dennis Schroeder/NREL

The NREL Solution: Isolation of Bio-Based Monomers from Aqueous Waste Streams

The NREL team addressed the thermochemical conversion strategy of catalytic fast pyrolysis, which deconstructs biomass in the absence of oxygen and catalytically upgrades the resulting vapors to produce an oil and aqueous product stream.

The team developed a process to isolate two lignocellulosic biomass-derived monomers from this aqueous stream—phenol and catechol. Phenols are primarily used in polycarbonate and phenol-formaldehyde resins, which have use in automotive, aerospace, building material, electronic, and consumer goods applications. Catechol can be found in insecticides, perfumes, and pharmaceuticals.

The NREL team successfully separated phenol and catechol to 97 wt% purity using the industrially relevant techniques of liquid–liquid extraction, distillation, and recrystallization. Monomers with high purity are necessary because they serve as feedstocks for the chemical manufacturing industry, which must meet strict quality targets for consumer products.

NREL's techno-economic analysis team also demonstrated that a mixed-phenolics stream can be produced from the waste at a selling price of approximately $1.06/kg. In comparison, a high-purity phenol has a market price of around $1.10/kg (see diagram below).

Extra Revenue Stream for Existing Biorefineries

Overall, NREL has demonstrated an approach that increases the atom efficiency of thermochemical conversion by increasing the value of the waste stream. The outcome is high-purity oxygenated aromatic compounds that show promise as a means to convert a waste stream into a revenue-generating stream for the biorefinery industry.

Example of an integrated biorefinery that produces fuels and chemicals, in which phenols and diols products take advantage of the structure of biomass (lignin). The inset table shows the market price of $1.10/kg for high-purity phenol in 2017 dollars.

Example of an integrated biorefinery that produces fuels and chemicals in which products take advantage of the structure of biomass. The inset table shows the market price of $1.10/kg for high-purity phenol in 2017 dollars. Illustration by NREL

Zia Abdullah
Dr. Zia Abdullah is laboratory program manager for the National Renewable Energy Laboratory’s (NREL’s) Bioenergy Technologies Office program. Zia has extensive experience and accomplishments in thermochemically and biochemically converting biomass to fuels and chemicals. His experience includes more than 25 years of industrial research and development in biomass conversion, as well as problem solving, new product development, business development, and project management.Dr. Zia Abdullah is laboratory program manager for the National Renewable Energy Laboratory’s (NREL’s) Bioenergy Technologies Office program. Zia has extensive experience and accomplishments in thermochemically and biochemically converting biomass to fuels and chemicals. His experience includes more than 25 years of industrial research and development in biomass conversion, as well as problem solving, new product development, business development, and project management.
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