Graduation Semester and Year

2012

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Melanie L Sattler

Abstract

Biomass is one source of renewable energy which helps minimize greenhouse gas (GHG) emissions, specifically carbon dioxide (CO2), since biomass utilizes CO2 via photosynthesis. Various conversion processes are applied to utilize energy from biomass, including pyrolysis. Pyrolysis is a thermal route of decomposing biomass at high temperature without the presence of oxygen. The process generates three main products including bio-oil, residue, and non-condensable gases; however, the most promising product is the biomass oil, which is in liquid form and convenient for handle and transport. Numerous studies on pyrolysis of terrestrial biomass reveal that the crude bio-oil cannot be directly used since it contains high oxygen, resulting in low heating value of the fuel. Consequently, co-pyrolysis between biomass and polymers has been investigated in order to enhance the oil quantity as well as improve its quality. Not only land biomass can be converted into liquid fuel, but also aquatic species such as macroalgae have recently gained attention since the algae reproduces faster, has a shorter life cycle, and requires less land area. Furthermore, the components in the seaweed are less complex than the land crops, leading to lower thermal stability. However, only a few studies have been conducted on pyrolysis of macroalgae, and no observations of co-pyrolysis between the algae and polymers have been conducted. Thus, in this study the thermal characteristics of a species of brown macroalgae, Sargassum, are first examined by thermogravimetric analysis; then pyrolysis experiment is carried out to evaluate the product distribution and characterization. Moreover, co-pyrolysis of the seaweed and polystyrene (PS) resin is observed to determine advantages of a synergistic effect in the final product.The pyrolysis and co-pyrolysis were conducted by using a stainless steel pipe reactor with a PID temperature controller with 10oC/min heating rate. Initially, the macroalgae was pyroized under 400-700oC temperature to identify the optimum temperature for the co-pyrolysis, which was 600oC. Then, four different mixture ratios (5%, 15%, 25%, and 33% plastic weight) were subjected to co-pyrolysis under nitrogen. Products were further characterized using various methods. Gas chromatography was applied for both oil and gas products, while elemental analysis was used for oil and solid residue. In addition, the surface area and adsorption capacity of the residue were determined to investigate the potential of using the residue a pollutant adsorbent. Co-pyrolysis of seaweed and polystyrene improved oil quality by lowering the oxygen content from 9% to 0.3%, while increasing the carbon content from 74% to 89%, compared with oil from seaweed alone, . The interaction between the seaweed and polymer, however, increased water phase product instead of an oil phase. Water elimination of the hydroxyl group in the biomass was a main reaction likely responsible for the higher amount of water and lower oxygen in the oil product. The synergistic effect between the seaweed and PS produces more methane gas, which is beneficial in terms of energy use of the gas. The residue exhibits a low surface area and adsorption capacity; thus, its use as a pollutant adsorbent is not promising. However, it may be able to be used as a fertilizer or soil amendment since it contains significant nitrogen. The lab-scale process provides low overall energy recovery (14-33%) due to heat loss to the effluent gas, phase changes, and a large reactor surface area per volume ratio. Suitable design of a pilot-scale system could reduce these losses.

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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