Biphasic extraction of mechanocatalytically-depolymerized lignin from water-soluble wood and its catalytic downstream processing

Abstract

During saccharification of water-soluble wood, a dual 2-MeTHF/water solvent system enables extraction of low molecular weight lignin fragments.

On the Meaning and Origins of Lignin Recalcitrance: A Critical Analysis of the Catalytic Upgrading of Lignins Obtained from Mechanocatalytic Biorefining and Organosolv Pulping

“…β‐ O ‐4 linkages are selectively cleaved by thioacidolysis, rendering characteristic monoaromatic species 2‐methoxy‐4‐(1,2,3‐ tris (thioethyl)propyl)phenol, 1 , and 2,6‐dimethoxy‐4‐(1,2,3‐ tris (thioethyl)propyl)phenol, 2 , as primary products, derived from G‐ and S‐units, respectively (Scheme S1, SI). Moreover, various other minor products are formed from the thioacidolysis procedure (a detailed description is provided in our recent publication). Yields of individual products obtained from the thioacidolysis assay on MCP‐L and OS‐L are listed in Table S1, SI.…”

“…For both lignin streams, these yields are still too low for industrial application. However, they serve to pinpoint changes in the lignin stream properties, as recently reported by us elsewhere . Notably, subjecting MCP‐L samples to Raney Ni at 200 °C resulted in yields of selected species higher than those produced from OS‐L.…”

“…Therefore, Raney‐Ni‐catalyzed hydrogenolysis at 200 °C was incapable of fully cleaving these linkages for the organosolv lignins. A previous study also reports that β‐ O ‐4 ( A ) and resinol ( C ) motifs were detected only in low relative quantities in beechwood WSL . Logically, during isolation of lignin by saccharification of WSL (catalyzed by H 2 SO 4 ), further hydrolysis of the remnant β‐ O ‐4 linkages will occur.…”

“…Notably, the extracted lignin stream undergoes further catalytic upgrading under low‐severity conditions (200 °C, 7 MPa H 2 , 8 h) rendering higher yields of liquid products, compared to a corresponding lignin isolated by the organosolv method . However, owing to the high O‐content and, therefore, low volatility of the phenolic components in the liquid products, only a small fraction of components (10 %) could be detected by gas chromatography …”

“…Although MCP‐L materials are known to share various similarities with organosolv analogues (OS‐L, e.g., a considerable content of remnant β‐ether linkages and a comparable M w distribution), and sugars along with their degradation products become incorporated into the precipitate lignin structure, MCP‐L materials are still difficult to define accurately with respect to their recalcitrance toward later catalytic upgrading processes. Regardless of whether pure water or a biphasic solvent is selected for the saccharification stage performed on WSL, there is a pressing need for a detailed understanding of the structural and reactivity properties of such MCP‐L materials to exercise control over undesired chemical processes occurring during MUB, thus increasing the susceptibility of the lignin stream to undergo catalytic reductive processes.…”