Bio-oil can be produced through the processing of lignocellulosic biomass, plant matter from wood waste which is heated to 500–700 degrees Celsius for one to two seconds. The resulting liquid product releases little heat during combustion and differs from fossil oil due to its increased viscosity, acidity and tendency to stratify, including due to high oxygen content. To eliminate these drawbacks, chemists remove oxygen from bio-oil using catalysts derived from metals (nickel, platinum, ruthenium, palladium). However, this process is complicated by a rapid decline in catalyst activity due to the high content of water, organic acids and phenolic compounds in bio-oil.
The scientists from the Gubkin Russian State University of Oil and Gas, Lomonosov Moscow State University and the University of Rostock have managed to solve this problem. The authors synthesized nickel and platinum catalysts and applied them to nanotubes of halloysite, a layered clay mineral. They modified its surface with surfactants to increase hydrophobicity, halloysite’s tendency to avoid contact with water. This made it possible to apply nickel and platinum nanoparticles to the internal cavity of nanotubes, where the metals are protected from the effects of water and phenolic compounds.
The scientists studied the activity of the obtained catalysts in an autoclave, maintaining the temperature at 120–180 degrees Celsius, with a hydrogen pressure 30 times higher than atmospheric pressure. Mixtures of phenol, anisole or guaiacol with water were used as the model raw materials simulating the composition of real bio-oil. Analysis of the reaction products was conducted three hours after the start of the experiment.
The authors found that the catalysts synthesized on the basis of pure halloysite are characterized by low stability and activity when oxygen is removed from bio-oil: the conversion rate of the raw material did not exceed 35%, including due to the toxic effect of water and phenol. In the case of catalysts based on modified halloysite, the conversion rate of the raw material rose to 76%, while oxygen content dropped from 15% to 5% (by weight). The new catalyst remained stable for a long time.
“As a result, the study opens the way to obtaining effective catalysts from domestic raw materials, since there are halloysite deposits in Russia, namely, in the Urals and in the Orenburg and Tula Regions. In the future, we plan to study the activity of bimetallic (containing two metals at the same time) catalysts based on hydrophobized halloysite nanotubes,” Vladimir Klimovsky, one of the authors of the study and engineer at the Department of Physical and Colloid Chemistry of the Gubkin Russian State University of Oil and Gas, is quoted as saying by the Russian Science Foundation.