Cover image for Ma, R.S., Guo, M., & Zhang, X. (2014). Selective conversion of biorefinery lignin to dicarboxylic acids. ChemSusChem, 7(2), 412-415. doi: 10.1002/cssc.201300964
Cover image for Ma, R.S., Guo, M., & Zhang, X. (2014). Selective conversion of biorefinery lignin to dicarboxylic acids. ChemSusChem, 7(2), 412-415. doi: 10.1002/cssc.201300964

One of NARA’s goals is to develop high value co-products made from lignin. Lignin is an abundant component in wood and is the predominant byproduct generated when bio-jet fuel is made from wood residuals. Generating high value products from this byproduct material is a key strategy for maintaining the economic sustainability of a forest residual-to-biojet fuel supply chain.

NARA researchers are developing high value products from the lignin-rich material generated when forest residuals are pretreated using a sulfite-based pretreatment strategy, however, there are other pretreatment strategies being developed and employed; each strategy creates a lignin byproduct that is chemically different. In addition, researchers are discovering new ways to modify lignin so that it can be used as a feedstock molecule for a wide range of products.

In light of all the exciting developments in lignin research and the importance of bringing high value products to the wood residual-to-biofuel supply chain, NARA researcher Xiao Zhang and his team have published a review article, partially funded through NARA/USDA-NIFA, that describes the lignin produced from varied commercial treatments used to produce biofuels and methods used to modify lignin to produce feedstock molecules.

Read Catalytic Oxidation of Biorefinery Lignin to Value-added Chemicals to Support Sustainable Biofuel Production here.

Lignin produced from varied pretreatments

 The review provides descriptions of the varied pretreatment methods used to produce biofuels from wood material and characterizes the lignin produced from these pretreatment options which include dilute acid, pyrolysis, steam explosion, high pressure refining, ammonia-fiber-expansion (AFEX), organosolv and SPORL (sulfite pretreatment to overcome recalcitrance of lignocellulose). The lignin remaining after these treatments is either in solid form or in liquid and varies in molecular weight and hydroxyl content.

Chemistry developed by the pulp and papermaking industry

 The chemical processes used by the pulp and paper industry to separate lignin from cellulose, improve the paper product, and create lignin-based chemical byproducts with commercial value are outlined. These processes include the use of reactive chemicals (oxidative reagents) like chlorine, chlorine dioxide, oxygen, hydrogen peroxide, ozone and peroxy acids that change the lignin into feedstock chemicals of commercial value. The review provides schematics for the reaction mechanisms and highlights the advantages and challenges associated with using these reactive chemicals.

Novel ways to convert lignin into chemical products using catalysts

To reduce the cost of using reactive chemicals and to potentially increase product yield and specificity, novel catalysts and processes are being developed. This paper reviews a suite of catylists that include inorganic metals, metal ions, metal oxides, composite metal oxides, polyoxometalates, organometallics, metallosalen complexes, metalloporphyrins, organorhenium oxides, vanadium complexes, metal-organic frameworks and organocatalysts. Tables and mechanism illustrations are provided that provide basic reaction conditions, substrates and the products produced from using these varied catalysts.

Promoting bioenergy literacy

This review article fits well with NARA’s intent to promote bioenergy literacy. The review is structured to appeal to professionals involved with lignin research, but would also provide an interesting read for the layperson curious about how wood material can be converted into chemical products. The breath of potential products that can be made from just the lignin component is remarkable.

Dr. Xiao Zhang’s team is developing novel methods to convert lignin into chemical feedstocks like dicarboxylic acids, and Dr. Zhange recently received an NSF Career Award to extended the research into utilization of dicarboxylic acids for hydrocarbon fuel and chemicals production. In the paper’s summary remarks, the authors express their intent to stimulate “…new ideas and research efforts towards the development of novel catalysts, chemistries, and pathways for biorefinery lignin…”. Reducing the cost and increasing the product portfolio resulting from converting biorefinery lignin into value-added commercial products will contribute significantly to the economics associated with producing fuels and co-products from forest residuals.