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Title:Conversion of waste organic carbon and nutrient streams to renewable fuels through integrated biological funneling and catalytic hydrothermal upgrading
Author(s):Leow, Shijie
Director of Research:Guest, Jeremy S.; Strathmann, Timothy J.
Doctoral Committee Chair(s):Guest, Jeremy S.; Strathmann, Timothy J.
Doctoral Committee Member(s):Singh, Vijay; Vardon, Derek R
Department / Program:Civil & Environmental Eng
Discipline:Environ Engr in Civil Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Wastewater biorefinery
hydrothermal liquefaction
microalgae biofuels
catalysis
Abstract:Increasing societal energy demands linked to growing wastewater generation and treatment costs have led to a growing impetus for wastewater treatment plants to transition into renewable resource production facilities or biorefineries, which aim to valorize the organic carbon and nutrients found in wastewater streams into valuable renewable products such as transportation-ready fuels or platform chemicals. Towards this vision, continued development of advanced methods for microbiological carbon accumulation and nutrient capture coupled with aqueous catalytic upgrading of the resultant biomass storage products presents two promising methods of advanced wastewater valorization: (i) conversion of microalgae biomass (which can be cultivated in wastewater effluent) into renewable fuel blendstocks through aqueous processing methods; and (ii) a proposed integrated process utilizing the biological polymer polyhydroxybutyrate (PHB; a storage product of mixed cultures selected from activated sludge) as feedstock to produce gasoline-grade liquid hydrocarbons. The goal of this thesis is to advance the overall understanding of technological pathways for the production of liquid hydrocarbon fuel blendstocks from wastewater organic carbon and effluent nutrient streams by addressing critical barriers associated with either pathway using multi-disciplinary experimental and modeling approaches, thereby contributing towards the realization of the wastewater biorefinery concept. The following research objectives were pursued towards this goal: (i) develop quantitative predictive models for microalgae hydrothermal liquefaction (HTL) processing, including an improved component additivity model and a new predictive model formulation that can be more easily applied to diverse microalgae species and HTL conditions; (ii) develop a unified techno-economic analysis (TEA) modeling framework for integrated microalgae biofuel systems to understand the influence of varying biomass compositions for varying downstream aqueous processing pathways; (iii) prioritize research and development pathways for microalgae biofuel systems by identifying key system variables through sensitivity and uncertainty analysis based on the unified modeling framework; and (iv) evaluate vapor-phase continuous-flow catalysis for dehydration-decarboxylation of 3-hydroxybutyric acid (3HB; from the depolymerization product of PHB) to produce propylene, with a focus on Brønsted-Lewis acidity of amorphous silica-alumina (ASAs) heterogeneous catalysts and longer-term time-on-stream experiments to explore catalyst deactivation mechanisms. The first research objective was addressed by developing predictive relationships for HTL biocrude yield and other conversion product characteristics based on HTL of Nannochloropsis oculata batches harvested with a wide range of compositions and a defatted batch. A component additivity model (predicting biocrude yield from lipid, protein, and carbohydrate cell composition) was more accurate predicting literature yields for diverse microalgae species than previous additivity models derived from model compounds. Fatty acid (FA) profiling of the biocrude product showed strong links to the initial feedstock FA profile of the lipid component, demonstrating that HTL acts as a water-based extraction process for FAs; the remainder non-FA structural components could be represented using the defatted batch. These findings were used to introduce a new FA-based model that predicts biocrude oil yields along with other critical parameters, and is capable of adjusting for the wide variations in HTL methodology and microalgae species through the defatted batch. The FA model was linked to an upstream cultivation model (Phototrophic Process Model), providing the basis for an integrated modeling framework to perform predictive analysis of the overall microalgal-to-biofuel process. Building off results and findings from work addressing the first objective, the second and third research objectives were addressed by integrating a dynamic biological cultivation model with thermo-chemical/biological unit process models for downstream biorefineries to increase modeling fidelity, to provide mechanistic links among unit operations, and to quantify minimum product selling prices of biofuels via techno-economic analysis. The unified modeling framework showed that cultivating biomass compositions to achieve the minimum biomass selling price or to maximize lipid content led to sub-optimal total fuel production costs. Furthermore, depending on biomass composition, both hydrothermal liquefaction (a whole-biomass conversion process) and a biochemical fractionation process were shown to have advantageous minimum product selling prices, which supports continued investment in multiple conversion pathways. Based on these results as well as data from sensitivity analysis, specific recommendations were made for the prioritization of research and development pathways to achieve economical biofuel production from microalgae, including a need to reduce uncertainty surrounding conversion parameters of individual compounds, which can be achieved by expanding the library of compositions and microalgae species used for model calibration and validation while also developing predictions for biocrude oil and product quality. Transitioning away from smaller-scale experimental samples towards pilot-scale or continuous-flow demonstrations, especially for microalgae biomass cultivation, would also provide higher fidelity prediction models for integrated system design. The final research objective was addressed by evaluating a novel catalytic pathway for conversion of 3HB into propylene through aqueous vapor-phase dehydration-decarboxylation (DHYD-DCBX) over ASAs using a continuous flow reactor. Experiments focused on examining the influence of varying Brønsted-Lewis acidities of ASAs on conversion and product selectivity, as well as longer-term time-on-stream stability under steam (vapor-phase) conditions. Complete conversion of 3HB was observed with propylene yields between 50–55 %C for SiAl 3113 during initial time-on-stream (6 h) testing, but yields decreased to 40 %C after 70 h with no indication of stabilized performance. Recalcination of spent catalyst did not restore activity, and results from artificially steam-treated SiAl 3113 (i.e., 3HB absent) suggest deactivation due to long-term steam exposure, with reductions in surface area and pore volumes observed similar to the spent catalyst used to process 3HB. Propylene selectivity observed with different ASAs appeared to track with reported Brønsted acidities. In addition, Na+ blocking of Brønsted acid sites inhibited conversion to propylene, supporting the important role of Brønsted acidity in catalyzing DHYD-DCBX of 3HB over ASAs. Overall, this thesis has addressed a number of critical barriers towards the production of renewable biofuels from wastewater organic carbon and nutrients, and in doing so has advanced the general science regarding integrated conversion of microalgal or microbial biomass to valuable products. Contributions from this thesis, in combination with opportunities for further work to expand upon the development of microalgae biofuels and renewable fuel production from waste-derived PHB/3HB as described in this thesis, will undoubtedly continue to push the envelope on wastewater energy recovery technologies.
Issue Date:2018-09-11
Type:Text
URI:http://hdl.handle.net/2142/102892
Rights Information:Copyright 2018 Shijie Leow
Date Available in IDEALS:2019-02-08
2021-02-09
Date Deposited:2018-12


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