Catalytic depolymerization of lignin with simultaneous direct methane aromatization in a fluidized bed reactor
File(s)
Author(s)
Yuan, Xudong
Type
Thesis
Abstract
Rapid population growth and increasing industrialisation in developing countries pushes the need for more energy and high added-value chemicals sources to be developed and utilized. Biomass and lignin pyrolysis in H2 atmosphere is a promising method to generate aromatics, in particular mixtures of benzene, toluene, xylene and ethylbenzene (BTEX), which represent a higher added-value product than fuels. The source of H2 for lignin depolymerization is important, as high purity H2 is a relatively expensive gas and it there might be some safety concerns associated to transport and storage. Direct CH4 aromatization (DMA) is a promising reaction to generate in-situ H2 and C6H6. The optimal operating conditions as well as nature of catalysts able to promote both lignin depolymerization and DMA to generate higher H2 and oil yields have become an interesting topic to study.
This work used a laboratory scale continuous pressurized fluidized bed reactor to study the DMA reaction between 550 °C and 700 °C at 1 bar. The DMA reaction was used to provide H2 in-situ, which can help to upgrade lignin pyrolysis. The same fluidized bed reactor was also used to investigate CH4 and lignin simultaneous pyrolysis with different catalysts and a range of operating conditions. A fixed bed was designed and placed downstream from the fluidized bed to enable experiments with a two-stage system, employing both in-situ and ex-situ catalysts in the simultaneous pyrolysis of CH4 and lignin at 580 °C.
The main findings can be summarized as: (1) a Ni/Al2O3-SiO2 catalyst was observed to generate the highest H2 and oil yield under 580 and 600 °C. The injection of a small amount of external H2 before CH4 injection can decrease the deactivation of Ni catalyst. (2) in this experimental system, the most important variables to increase oil yields in CH4 and lignin simultaneous pyrolysis were total inlet gas flow rate and pressure. Lower total inlet gas flow rate can extend the residence time of small particle size lignin and volatiles in the catalytic bed, and pressure can significantly reduce the H2 and oil generated by DMA reaction. (3) a Ni/Al2O3-SiO2 catalyst led to the highest monoaromatics yields while a TiO2 catalyst produced the highest total oil yield. The two-stage system with a Ni/Al2O3-SiO2 catalyst represented a clear improvement on total oil yield and lignin conversion than a single bed.
This work used a laboratory scale continuous pressurized fluidized bed reactor to study the DMA reaction between 550 °C and 700 °C at 1 bar. The DMA reaction was used to provide H2 in-situ, which can help to upgrade lignin pyrolysis. The same fluidized bed reactor was also used to investigate CH4 and lignin simultaneous pyrolysis with different catalysts and a range of operating conditions. A fixed bed was designed and placed downstream from the fluidized bed to enable experiments with a two-stage system, employing both in-situ and ex-situ catalysts in the simultaneous pyrolysis of CH4 and lignin at 580 °C.
The main findings can be summarized as: (1) a Ni/Al2O3-SiO2 catalyst was observed to generate the highest H2 and oil yield under 580 and 600 °C. The injection of a small amount of external H2 before CH4 injection can decrease the deactivation of Ni catalyst. (2) in this experimental system, the most important variables to increase oil yields in CH4 and lignin simultaneous pyrolysis were total inlet gas flow rate and pressure. Lower total inlet gas flow rate can extend the residence time of small particle size lignin and volatiles in the catalytic bed, and pressure can significantly reduce the H2 and oil generated by DMA reaction. (3) a Ni/Al2O3-SiO2 catalyst led to the highest monoaromatics yields while a TiO2 catalyst produced the highest total oil yield. The two-stage system with a Ni/Al2O3-SiO2 catalyst represented a clear improvement on total oil yield and lignin conversion than a single bed.
Version
Open Access
Date Issued
2023-04-13
Date Awarded
01/07/2023
License URL
Advisor
Millan-Agorio, Marcos
Publisher Department
Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)