Metal Oxide Gasification of Lignocellulosic Biomass: Tar Cracking Mechanism

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PI: Fan, Liang-ShihProposal Number: 1236467Institution: Ohio State UniversityTitle: Metal Oxide Gasification of Lignocellulosic Biomass: Tar Cracking MechanismBiomass Chemical Looping (BCL) has been recognized as a promising way to utilize biomass efficiently in recent years. The BCL process can convert biomass to valuable biofuels and its precursors such as H2, while capturing CO2 at a low energy cost. This proposed project seeks to explore the reaction mechanisms during the gasification of lignocellulosic biomass by metal oxides (the oxygen carriers). Tar, generated during biomass pyrolysis, complicates the process. Thus, the removal of tar with high efficiency is greatly desired. The target of this project is to identify the decomposition pathway of tar at a molecular level and to synthesize an oxygen carrier with high performance. The experiment assembly consists of using a thermo gravimetric analyzer (TGA), a micro fixed/fluidized bed (MFB), and various gas and solid analysis instruments. The TGA will act as a tar generator where biomass pyrolysis takes place in a controlled manner. The generated tar will subsequently go into the MFB to react with the oxygen carrier. The gaseous species will be sampled and analyzed by gas chromatography (GC), Fourier transform infrared spectroscopy (FTIR), and mass spectroscopy to identify the composition as well as important intermediates. Post-experiment analyses will also be carried out on the oxygen carrier to reveal the metal-support interactions. In addition, naphthalene, phenol, and benzene will also be directly fed into MFB as typical primary, secondary, and alkyl tertiary tar species, respectively. Furthermore, oxygen carriers of various compositions will be tested to reveal the effect that different primary metal-support interactions could have on the reaction mechanism. These results will be combined to interpret the complex non-catalytic gas-solid reaction BCL system.Tar conversion is one of the obstacles that impedes the utilization of biomass materials, clean energy and carbon-negative fuel sources. Currently, catalytic decomposition is the most widely used method to remove tar. However, this method requires extensive capital and material resources as a separate tar decomposition reactor is necessary after the gasifier in order to achieve desirable removal results. In the BCL process, previous experiments have indicated that the synthesized composite oxygen carriers have the potential to convert all biomass pyrolysis products, e.g., volatile, tar, and char, in a single reducer reactor. Among these pyrolysis products, tar decomposition is considered to be a complex reaction network. In order to avoid a both labor and time intensive trial-and-error method in oxygen carrier development, understanding the tar decomposition mechanism is key. Early researchers have investigated the mechanism of tar catalytic decomposition process with some aromatic species as tar model molecules, such as naphthalene, benzene, and phenol. In the BCL process, the oxygen carrier acts as a lattice oxygen donor rather than as a catalyst (that largely remains unchanged in composition). The oxygen carrier oxidizes the tar, thereby, changing the composition such that the solid-solid interactions between the primary metal and the supports are more complex. Multiple experimental methods will be combined to investigate the reaction mechanism by identifying the important intermediates. With the knowledge on the tar decomposition mechanism at molecular level, the rational to synthesize an efficient oxygen carrier can be developed.By highlighting the fundamental mechanisms behind biomass pyrolysis with metal oxide oxygen carriers, this proposed research aids the continuous development of clean and economical energy conversion processes. This research would lay the scientific groundwork for the emerging BCL system, which could provide affordable energy sources for biomass-rich communities. The MFB development provides a novel fundamental tool for thermochemical reaction analysis. Beyond potentially transforming the biomass energy landscape, this proposed study will present enriching opportunities for students. The results completed through this study will be incorporated as curriculum material of undergraduate and graduate classes. Undergraduate and graduate students will participate in this research. The proposed K-12 outreach programs will promote the scientific research for future scientists and engineers. This research will be able to enhance the potential commercialization of BCL, a crucial and innovative technology for thermochemical biomass conversion.