Similarities in Recalcitrant Structures of Industrial Non-Kraft and Kraft Lignin.

This work compares the structure of industrially isolated lignin samples from kraft pulping and three alternative processes: butanol organosolv, supercritical water hydrolysis, and sulfur dioxide/ethanol/water fractionation. Kraft processes are known to produce highly condensed lignin, with reduced potential for catalytic depolymerization, whereas the alternative processes have been hypothesized to impact the lignin less. The structural properties most relevant to catalytic depolymerization are characterized by elemental analysis, quantitative 13 C and 2 D HQSC NMR spectroscopy, gel permeation chromatography, and thermogravimetric analysis. Quantification of the ß-O-4 ether bond content shows partial depolymerization, with all samples having less than 12 bonds per 100 aromatic units. This results in theoretical monomer yields of less than 5 %, strongly suggesting the alternative fractionation processes generate highly condensed lignin structures that are no more suitable for catalytic depolymerization than kraft lignin. However, the different thermal degradation profiles suggest there are physicochemical differences that could be leveraged in other valorization strategies.

Solvent Selection for Lignin Value Prior to Pulping.

Solvent selection guides are crucial in chemical process design and development. Lignin from lignocellulosic biomass is a potentially attractive feedstock for sustainable chemical feedstocks. One approach would use a solvent to recover lignin prior to the traditional pulping process to make cellulose fibers: lignin value prior to pulping (LVPP). A solvent selection methodology for LVPP is presented herein that may be expanded for any proposed solvent for this process. Four screening categories are elucidated, providing metrics for 30 solvents across multiple molecular functional groups. Through performance, hazards and environment, cost and availability, and process-economics screens, the initial list of solvents is reduced to two top-tier candidates, 1,6 hexamethylenediamine and diethanolamine. 1-Methylpiperazine also emerged as a potential candidate. This solvent-selection methodology streamlines experimentation and provides promising candidates for LVPP. In addition to creating a tailored solvent selection guide, valuable biomass pretreatment data that may be utilized in different renewable applications are also presented.