Multitechnique characterization of six technical lignins including nuclear magnetic resonance and size exclusion chromatography studies.

Aqueous solutions of Cu 2+ /histidine (his) (1:2) have been analyzed in parallel with infrared, Raman, ultraviolet/ visible/near-infrared, electron spin resonance, and X-ray absorption spectroscopy in the pH range from 0 to 10. Comprehensive interpretation of the data has been used to extract complementary structural information in order to determine the relative abundance of the different complexes. O c ,N am ,N im )] 2 is the major species with the N atoms in the equatorial plane and the O atoms in the axial position. This complex decomposes at pH > 10 into a copper oxide/hydroxide precipitate. The overall results provide a consistent picture of the mechanism that drives the coordination and complex formation of the Cu 2+ /his system.

The physicochemical processes that occur during the preparation of CoMo–Al2O3 hydrodesulfurization catalyst bodies have been investigated. To this end, the distribution of Mo and Co complexes, after impregnation of γ‐Al2O3 pellets with different CoMoP solutions (i.e., solutions containing Co, Mo, and phosphate), was monitored by Raman and UV‐visible‐NIR microspectroscopy. From the speciation of the different complexes over the catalyst bodies, insight was obtained into the interaction of the different components in the impregnation solution with the Al2O3 surface. It is shown that, after impregnation with a solution containing H2PMo11CoO405−, the reaction of phosphate with the Al2O3 leads to the disintegration of this complex. The consecutive independent transport of Co2+ complexes (fast) and Mo6+ complexes (slow) through the pores of the Al2O3 is envisaged. By the addition of extra phosphate and citrate to the impregnation solution, the formation of the desired heteropolyanion can be achieved inside the pellets. Ultimately, the H2PMo11CoO405− distribution could be controlled by varying the aging time applied after impregnation. The power of a combination of spatially resolved spectroscopic techniques to monitor the preparation of supported catalyst bodies is illustrated.

Lignin is an attractive material for the production of renewable chemicals, materials and energy. However, utilization is hampered by its highly complex and variable chemical structure, which requires an extensive suite of analytical instruments to characterize. Here, we demonstrate that straightforward attenuated total reflection (ATR)‐FTIR analysis combined with principle component analysis (PCA) and partial least squares (PLS) modelling can provide remarkable insight into the structure of technical lignins, giving quantitative results that are comparable to standard gel‐permeation chromatography (GPC) and 2D heteronuclear single quantum coherence (HSQC) NMR methods. First, a calibration set of 54 different technical (fractionated) lignin samples, covering kraft, soda and organosolv processes, were prepared and analyzed using traditional GPC and NMR methods, as well as by readily accessible ATR‐FTIR spectroscopy. PLS models correlating the ATR‐FTIR spectra of the broad set of lignins with GPC and NMR measurements were found to have excellent coefficients of determination ( R 2 Cal.>0.85) for molecular weight ( M n , M w ) and inter‐unit abundances (β‐ O ‐4, β‐5 and β‐β), with low relative errors (6.2–14 %) as estimated from cross‐validation results. PLS analysis of a second set of 28 samples containing exclusively (fractionated) kraft lignins showed further improved prediction ability, with relative errors of 3.8–13 %, and the resulting model could predict the structural characteristics of an independent validation set of lignins with good accuracy. The results highlight the potential utility of this methodology for streamlining and expediting the often complex and time consuming technical lignin characterization process.

The valorization of the humin by-products that are formed during hydrothermal, acid-catalyzed dehydration of carbohydrates is hampered by the insolubility of these byproducts. Here, we report on an alkaline pretreatment method that allows for the insolubility of this highly recalcitrant and structurally complex feed to be overcome. The reactive solubilization of glucose-derived humins was found to require a treatment at 200 °C in 0.5 M NaOH for 3.5 h.Fructose-and xylose-derived humins were found to be more recalcitrant and complete dissolution required raising the temperature to 240 °C. Gel permeation chromatographic analyses show the relative average molecular weight of the now soluble humins to decrease with increasing temperature and reaction time. The alkali-treated humins are soluble in water of pH ≥ 7. Elemental analysis, IR, 2D PASS 13 C solid-state NMR, and pyrolysis-GC-MS data indicate that the alkaline pretreatment leads to considerable changes in the molecular structure of the humins. Cleavage of C-O-C bonds and further aromatization of the originally highly furanic humins result in the formation of (polycyclic) aromatic structures decorated with carboxylic acids. The combination of the reduction in Mw and the formation of polar functional groups is thought to be the reason behind the improved solubility.