Abstract
AbstractIn this paper synthesized palladium (Pd)-containing catalysts were used in the hydrogenolysis of lignin in the presence of a hydrogen donor solvent, i-propanol, to obtain liquid fuel components. A study of the influence of the catalyst support nature, catalyst preparation method and supercritical solvent nature on the lignin depolymerization was completed. It was found that the use of Pd-containing catalysts results in the formation of aromatic compounds (mainly benzene and toluene) for both supercritical solvents used (i-propanol and CO2). The maximum conversion of lignin (50 %) was achieved when the supercritical i-propanol was used and maximum selectivity to aromatics (over 70 %) was observed in the presence of the Pd-containing catalyst synthesized by hydrothermal deposition on the polymeric matrix of hyper-crosslinked polystyrene.
Highlights
Lignin is very difficult to process due to its complex nature and instability, consisting of irreversible changes in the properties of the polymer during thermal or chemical treatment
The results indicated that the NI-catalyst RANEY® demonstrates high performance under hydrogenolysis conditions and good stability during regeneration [34, 35]
We propose the use of palladium-based catalysts deposited on various carriers, since palladium has shown itself to be an active and selective catalyst in hydrogenation processes in our previous studies [36, 37] and the novel hydrothermal route for the catalyst preparation was used for lignin processing
Summary
Lignin is very difficult to process due to its complex nature and instability, consisting of irreversible changes in the properties of the polymer during thermal or chemical treatment. Due to the well-known poor solubility of H2 in most solvents, hydrogenolysis processes require the direct use of high-pressure molecular hydrogen with all the drawbacks that this entails, including purchase, transportation, expensive infrastructure, and safety hazards. Catalytic hydrogenolysis uses solvent-derived H-donor molecules to prevent safety problems with high-pressure hydrogen and explosive gas [33]. In 2012 Rinaldi and his colleagues first reported the use of a bimetallic catalyst RANEY® Ni in H-transport reactions of lignin model molecules. 2-propanol was used as a reaction solvent and hydrogen source and 32 model substrates were studied at temperatures from 80 to 120 ° C for 3 hours. The synthesized catalysts were tested in lignin hydrogenolysis in supercritical conditions in order to enhance the process efficiency. Two types of supercritical solvents i-propanol and CO2 were used in this work
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