Hydrogenation of Pyrolysis Oil Derived From Lignin

Pyrolysis is recognized as one of the most economical ways to convert solid lignin to liquid. However, the oil products from this process cannot be directly used as a fuel. The major problems are instability, high acidity and low heating value. In our study, the heavy oil portion from pyrolysis oil was used for the raw material. Two-step hydrotreatments were applied and three catalysts, Ruthenium, Platinum and Palladium on carbon were evaluated with Ruthenium showing the best result. The other two catalysts could not achieve 100% conversion. After the reaction, all aromatic rings converted to aliphatic structure. Fewer methoxy groups with an increase in C-O aliphatic bonds were observed. The decrease of C=O bonds indicated the carbonyl groups were reduced to hydroxyl groups. During the first-step hydrotreatment, the surface of catalyst was blocked by the tar and coke formed in the reaction. Therefore, a second-step hydrotreatment was appended by replenishing the fresh catalyst. The mechanism of hydrogenation was studied and a reaction path was proposed. How the substituent group on aromatic ring would affect the reaction was also evaluated. NMR was extensively used in our research, including proton NMR, ¹³C NMR, 2-D HSQC NMR and DEPT-analysis. The NMR technology has non-destructive property, which is superior to the traditional GC-MS analysis. The NMR could also provide statistical distribution of carbon atom and hydrogen atom in different chemical environment, which gives a better insight of the reaction mechanism.