Jayant D. Ekhe

Towards effective lignin conversion: HZSM-5 catalyzed one-pot solvolytic depolymerization/hydrodeoxygenation of lignin into value added compounds

A one-pot greener approach towards lignin depolymerization/hydrodeoxygenation is presented. Water was used as a reaction medium with methanol as a source of reductive equivalents of hydrogen in inert atmosphere. Zeolite HZSM-5 and Ni-doped HZSM-5 were synthesized at low temperature (95 °C), characterized and used as a hydrodeoxygenation catalyst at 220 °C. Lignin conversion up to 96.8–98.5% was observed with highly reduced char formation (<1%). IR, GC-MS and ESI-MS spectroscopy were used to characterize the conversion products. The products were mainly comprised of alkyl substituted phenols (15.4 wt%) found as water soluble products. The water insoluble products showed mostly formation of oligomers with acyclic (4.1 wt%) and cyclic (1.5 wt%) compounds. Acyclic compounds included up to 2.8 wt% of open chain C12–C19 hydrocarbons. ESI-MS showed that the molecular weight of the products formed during solvolytic depolymerization/hydrodeoxygenation of lignin were in the range of m/z ca. 60 to ca. 1000. A mechanistic hypothesis on formation of monomeric products is also presented.

Cu–Mo doped zeolite ZSM-5 catalyzed conversion of lignin to alkyl phenols with high selectivity

Lignin conversion processes experience challenging issues including char formation, lower degree of depolymerization and lower product yield with no selectivity. Zeolite ZSM-5 was loaded with Cu and Mo using the reductive deposition–precipitation method. The metal loaded into ZSM-5 was found to be amorphous and nanostructured as confirmed by X-ray diffraction and transmission electron microscopy. The lignin conversion products were analyzed by gas chromatography-mass spectroscopy and electrospray ionization mass spectrometry. We demonstrate here the one-pot Cu/Mo loaded zeolite ZSM-5 catalyzed conversion of lignin into alkyl phenols with highly minimized char formation. The process yields alkyl phenols with high conversion (95.7%) and high selectivity of up to 70. 3% for a particular phenol.

Solvent effect on HZSM-5 catalyzed solvolytic depolymerization of industrial waste lignin to phenols: superiority of the water–methanol system over methanol

Kraft lignin from industrial black liquor was subjected to one-pot solvolytic depolymerization and hydrodeoxygenation over zeolite HZSM-5 as catalyst and NaOH as co-catalyst at 220 °C. The effect of methanol and a water–methanol (1:1) mixture as solvent on the lignin depolymerization products was studied. The products were characterized by infrared spectroscopy and numerical indices based on IR spectra of the product mixture were defined to study the functional group transformations occurring in the reaction. Compared to NaOH in pure methanol, NaOH in water–methanol was found to be efficient in suppressing char formation and enhancing product quality and quantity. Alkyl substituted phenols were found to be the major product (14.1 wt%). Other than phenols, formation of long chain aliphatic compounds was also observed.

Thermochemical lignin depolymerization and conversion to aromatics in subcritical methanol: effects of catalytic conditions

Lignin is the second most abundant polymer and a renewable resource with a high energy density, but it is considered to be difficult to process because of the high reactivity of its building blocks that undergo recombination reactions leading to the formation of THF insoluble residues (char). In this study, solvolytic depolymerization was studied under three different catalytic conditions. A homogeneous catalyst NaOH, a heterogeneous catalyst HZSM-5 and the solid waste of iron turnings from lathe machining (as a consumable catalyst) were studied. We observed that HZSM-5 showed a similar lignin depolymerization efficiency to NaOH. HZSM-5 showed highest ethyl acetate extractibles with the lowest THF insoluble residue formation during lignin depolymerization and the Mw of lignin decreased from 5000 mol g−1 to <550 mol g−1. The products formed were mainly alkyl substituted phenols, which have high industrial applications. Iron turnings showed efficient reduction in the average molecular weight of products as compared to the original lignin along with adversely increased THF insoluble residue formation and a low yield of alkyl substituted phenols. In all the cases, based on the product profile obtained, the behavior of the catalytic action is explained using a schematic representation of the mechanisms.

Effect of modifications of lignin on thermal, structural, and mechanical properties of polypropylene/modified lignin blends:

Use of organic biomass, industrial waste lignin, was considered interesting due to its easy availability, polymeric nature, and ample scope to modify with an aim to replace conventional metal oxides to achieve improved properties of the blend when blended with polyolefins. To study the effect of chemical modification of lignin on the thermal, structural, and mechanical properties of polypropylene (PP)/modified lignin blends, purified industrial waste lignin was modified by two different chemical methods and blended in various proportions in PP matrix. The thermal stability of the blends was studied by thermogravimetric analysis, whereas melting and crystallization behavior of blends was studied by non-isothermal differential scanning calorimetry. The results show improved thermal stability of blends with increasing modified lignin proportion in the PP matrix. More depression in melting point was observed in PP/alkylated lignin blends than PP/arylated lignin blends, whereas addition of alkylated lignin shows polymorphism in PP matrix. Intermolecular interactions between blend components have been evaluated by applying several mathematical models to experimental mechanical property data. In most of the cases, good agreement has been obtained between the predictions made by using mathematical models and interpretations done on the basis of experimental data, showing the suitability of these models for predicting the mechanical properties of PP/modified lignin blends.