Gasification of organic materials and compounds can be done in water above its thermodynamic critical point (374 °C, 22 MPa). The technological, economic, and energetic feasibility of supercritical water gasification (SCWG) has been demonstrated. Biomass, either "energy crops" or agricultural and food processing waste, can be gasified to produce H2 or syngas. SCWG of biomass is one approach for sustainable energy production.
Though the feasibility of SCWG has been demonstrated, very little is known about the kinetics and pathways of the chemical reactions that govern SCWG. Such information is of interest scientifically because it will extend our knowledge of hydrothermal organic chemistry into a new region that has received scant attention. The information is also of interest technologically because it can be used to facilitate the design, optimization, and analysis of SCWG processes.
The goal of this project is to determine the kinetics and pathways for both homogeneous and catalyzed SCWG of a set of model compounds under well characterized conditions. This work will focus on reporting the kinetics for SCWG in metal-free reactors and the results from detailed analysis of products in both the liquid and gas phases. The PI will use thick-walled glass capillary tubes as mini batch reactors.
There are two primary components of this research. One is to determine the SCWG reaction kinetics and pathways for uncatalyzed gasification of a suite of biomass and bio-waste model compounds. The other is to determine the reaction kinetics and pathways for catalyzed gasification of these model compounds.
BROADER IMPACTS
The project will generate scientific advances and, eventually, technological advances. The PI will publish the scientific advances to broadly disseminate them. If technological advances are achieved, the benefit of this work will extend to the energy industry and the general public (by having a more politically stable and sustainable source for electricity and transportation fuels). The project will also provide training for a graduate student and about six undergraduate students, so there are human resource benefits. Additionally, the PI will continue his practice of incorporating his research results into the undergraduate and graduate classes he teaches at Michigan, so there will be benefits related to the integration of teaching and research. Thus, the broader impacts of this project include the possibility of technological advances that move us toward a more renewable and sustainable energy supply, the development of human resources in science and engineering, the broad dissemination of project results, and the integration of research and teaching.
The overarching goal of this research project was to learn about the chemical reactions that take place when biomass is converted to energy-containing gaseous products in water at high temperatures and pressure. This gasification technology, termed supercritical water gasification (SCWG) or hydrothermal gasification, is being developed as a way to efficiently convert wet biomass to fuel gases. Being able to do this conversion more efficiently would help to advance this renewable energy technology. Much prior work had been done to demonstrate and develop the technology, but very little work had been done to discover the identities of intermediate chemicals that are produced and the rates of the important chemical reactions. The approach in this project was to work with model compounds, rather than real biomass. The researchers selected phenol as the model compound since it had been identified as a product that forms during gasification of nearly all materials in SCW and is difficult to gasify. The investigators first developed experimental and analytical methods that allowed them to identify and measure the amounts of each of the individual products that form from phenol during the gasification process. This information then allowed the researchers to elucidate the reaction pathways for phenol. Some of these pathways lead to desired gaseous products, such as H2 and CH4. Others lead to undesired solid products, referred to as char. By understanding how the relative rates of the different reaction paths respond to changes in temperature, pressure, etc., engineers can design gasification processes that favor the desired pathways over the undesired pathways. The knowledge gained during this research project will be useful for the design and engineering of SCWG processes and hence the improvement of this renewable energy technology.
