Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Xu, Charles Chunbao

2nd Supervisor

Dr. Zeng, Yimin

Affiliation

Natural Resources Canada-CanmetMATERIALS

Co-Supervisor

Abstract

Supercritical water gasification (SCWG) holds immense promise as a sustainable and efficient method for green hydrogen production from lignocellulosic biomass, contributing to the transition from a petroleum-based economy towards bioeconomy.

Understanding the kinetics of SCWG processes is critically important for future development and scale-up applications of the SCWG technology. In this thesis work, we developed a general kinetic model to predict the yields of gases from SCWG of various lignocellulosic feedstocks with varying contents of cellulose, hemicellulose, and lignin. Subsequently, a comparison study was conducted between the SCWG of biomass in a batch and a self-built continuous-flow reactor. We discussed the application of both batch and continuous reactors in terms of feedstock type, system control, challenges, and future perspectives to maximize the efficiency of biomass SCWG.

The harsh operating conditions of SCWG, characterized by high temperature, high pressure, and a corrosive environment, pose challenges in selecting suitable construction materials for reactor design. Thus, we investigated the corrosion behavior of a widely used constructional alloy: Inconel 625. As the major component apart from biomass model compounds, the presence of ash content in biomass feedstocks may influence the SCWG process, affecting both its catalytic potential and corrosive tendencies. We have validated that ash content exhibits certain catalytic effects on SCWG of biomass, and a small amount of ash does not significantly impact corrosion. On the contrary, a small amount of ash can help neutralize the acidity of reaction products, thereby inhibiting corrosion. Furthermore, we evaluated the corrosive impacts of lignocellulosic biomass model compounds (cellulose, hemicellulose, and lignin) with or without NaOH (as a catalyst) addition during SCWG. This work demonstrated the distinct corrosion behaviors of Inconel 625 during SCWG of different model compounds and sulfur content in lignin contributed to the highest corrosion rate.

Summary for Lay Audience

Imagine a way making clean and efficient energy from plant materials like wood and crops. This can help us move away from using fossil fuels and towards more eco-friendly options. One exciting method for this is called "supercritical water gasification" or SCWG. It's like using super-hot, super-pressurized water to turn these plant materials into hydrogen gas.

To make this SCWG process even better, we studied how it works and how to make it even more efficient. In a special project, we created a model that helps predict how much gas can be made from different plant materials. Various types of plant matter were tested, like the stuff that makes up the strong parts of plants, and found out how much hydrogen gas they could produce.

We also looked at two different ways to do this process. One was like cooking everything together in a big pot (called a batch reactor), and the other was using a continuous machine that works more like a production line. We discussed which method is better for different situations and how to use them to make the most hydrogen from plant materials.

But there are challenges. The super-hot and super-pressurized conditions needed for this process can be tough on the equipment. We studied a material called Inconel 625 that's often used to build these reactors and found that some natural stuff in the plant materials (called "ash") can help protect the machines from getting damaged.

We also found out that some parts of the plant materials might cause the reactors to corrode. Different parts of the plant were tested, like the ones that make it stand tall and give it structure, and saw which caused the most trouble. We also looked at how adding a certain substance could make the process better.

In the end, this work helps us understand how to turn plant materials into clean energy more efficiently and with less harm to the machines we use. It's like figuring out the best recipe for making green energy from plants!

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