A Korean research team has developed a technology that can be used to mass-produce aviation-grade fuels from wood wastes. The ability to produce aviation-grade fuel from oil derived from wood waste—which up until now has been difficult due to the high viscosity of the oil—could help international aviation companies comply with new emissions regulations scheduled to go into effect in 2027.

Lignin constitutes 20 to 40 percent of lignocellulose. Large volumes of lignin are generated as waste in the pulping processes that are used to produce paper. The pyrolysis of lignin produces an oil which has little industrial utility due to its high viscosity. For this reason, lignin waste is typically used by paper mills as a low-grade boiler fuel, rather than as a high-grade fuel or as a raw material for chemical products.

The research team, led by Dr. Jeong-Myeong Ha of the KIST, used hydrocracking to prepare hydrocracked lignin oil, which was mixed at a ratio of 7:3 with raw lignin oil to reduce substantially the viscosity of the oil to 1/7 (from 750 cp to 110 cp; e.g. the viscosity of water is 1 cp, and the viscosity of cooking oil is 80 cp), allowing it to be used for industrial purposes.

In this study, lignin pyrolysis oil was prepared from Kraft lignin using bench-scale fixed-bed batch pyrolysis and then hydrocracked to produce less-viscous liquid products. Oligomers were degraded into smaller molecules via reactions involving hydrogen (hydrocracking) using CoMo/Hβ and CoMo/Al2O3 as catalysts. A low viscosity of 21 cP, a liquid yield of 76.6%, and a low coke yield of 1.6% were successfully attained using a reaction temperature of 400 °C, a reaction time of 60 min, and the CoMo/Hβ catalyst.

Thus, these conditions were selected to achieve the highest liquid yield with sufficient fluidity, although the lowest viscosity of 3.2 cP was achieved after 240 min. When 30 wt% of the resulting hydrocracked oil was used, it dissolved sticky raw lignin pyrolysis oil, significantly reducing its viscosity from 751 cP to 111 cP, which is sufficient to ensure flow in a typical petroleum pipeline. Using the hydrocracked/raw lignin pyrolysis oil mixture, the proposed continuous-flow hydrodeoxygenation successfully produced petroleum-replacing deoxygenated fuels.

—Kim et al.

Suggested continuous-flow HDO of lignin pyrolysis oil dissolved in its HCK oil. Kim et al.

The mixed oil prepared in this manner can be recycled to hydrocracking processes for the mass-production of bio-aviation fuels. Further, the final fuel product, similar to the contents of jet fuel, has a low freezing point compared to gasoline and diesel, and has a high energy density, being sutiable to bio-aviation fuels.

Despite the digital revolution, a sharp increase in global parcel volumes supports the global paper production. Conventional chemical reaction methods were unable to convert the large volumes of lignin wastes from paper mills into high quality fuels, but our research has opened up the potential for the mass-production of jet fuels from the otherwise useless lignin wastes. This achievement will allow Korea to proactively meet jet fuel greenhouse emissions regulations, which will go into effect starting from 2027.

—Dr. Jeong-Myeong Ha

The research, backed by the Ministry of Science and ICT (MSIT), was conducted as an Institutional Research Program of the Korea Institute of Science and Technology (KIST) and as part of the Technology Development Program to Solve Climate Changes of the National Research Foundation (NRF) of Korea funded by the Ministry of Science and ICT. The results of the study were published in the latest issue of Energy Conversion and Management.

Resources

• Yoonsoo Kim, Jingi Shim, Jae-Wook Choi, Dong Jin Suh, Young-Kwon Park, Ung Lee, Jungkyu Choi, Jeong-Myeong Ha (2020) “Continuous-flow production of petroleum-replacing fuels from highly viscous Kraft lignin pyrolysis oil using its hydrocracked oil as a solvent,” Energy Conversion and Management, Volume 213, 112728, doi: 10.1016/j.enconman.2020.112728.