Collaborative Research: Dakota Bioprocessing Consortium

NSF EPSCoR TRACK II (PI Dr. J. Rice, Co-PI at South Dakota Mines Dr. Smirnova)

Lignin is one of the most abundant natural biopolymers and a major non-fossil and carbon-rich renewable source of aromatic compounds. In lignin, three main monomers (e.g. 4-hydroxycinnamyl alcohol, coniferyl alcohol, and sinapyl alcohol) are linked by C-O and C-C bonds forming aryl-ether β-O-4 linkages (≤50% of all linkages) that are responsible for highly branched complex biopolymer structure. As a result, lignin is considered as one of the most feasible raw materials for synthesis of high value organic products (e.g. vanillin, guaiacol, phenol, cresol, etc.) that are applicable for production of renewable polymers by ring-opening polymerization, polycondensation, or aromatic substitution.

The vision of the Dakota Bioprocessing Consortium (Dakota BioCon) established between four universities in South and North Dakota is to become an intellectual leader for lignin processing. Dakota BioCon enhances collaborative basic and applied research while synergistically building an academic infrastructure within the jurisdictions to increase individual and collective competitiveness for federal support in this growing research area. The collaborative nature of the project facilitates data sharing and technical discussions between SD (South Dakota Mines, SDSU) and ND (UND and NDSU) universities.

Fig. 1: Structure of Lignin

The effect of temperature at constant pressure and short residence time in a mixture of sub- and supercritical fluids on the depolymerization of alkali lignin has been investigated. Depending on the hydrothermal treatment conditions, the lignin samples produced different phenolic compounds such as phenol, o-guaiacol, p-guaiacol, methylguaicol, vanillin, and homovanillic acid. The GC-MS, total organic carbon (TOC) and GC-MS pyrolysis approaches were used for chemical analysis of the organic liquid and solid phases produced. The results from GC-MS analysis of the liquid organic phases demonstrated the trend of increased total phenolic concentration with temperature and dependence of the organic phase composition on the ratio of supercritical fluids.  It was confirmed by the Total Organic Carbon (TOC) analysis that the optimal temperature for lignin liquifaction is 300°C that results in total phenolic relative yield of 83%. However, the highest selectivity with 40% yield of vanillin has been reached at 250oC. This research provided for the first time should have significant implication for the selective synthesis of phenolic compounds and their use in synthesis of polymers with desirable properties. More information on BioCon can be found at: http://sdepscor.org/rii/dakotabiocon/

Fig. 2: Separation of organic and water phase after lignin hydrothermal reforming.		Fig. 3: Organic phases produced from lignin in a mixture of sub- and supercritical fluids.