Date of Thesis
Hydrothermal liquefaction is a promising thermochemical waste-to-energy (WtE) technology for conversion of wet biomasses, such as manure and digested manure, into value-added products, namely energy-rich biofuel and a nutrient-rich aqueous product. WtE technologies can address environmental issues relating to overproduction of organic wastes and increasing dependence on fossil fuels, which leads to climate change. HTL has not been implemented on a commercial scale, in part due to the uncertainty regarding specific reaction pathways for different feedstocks and ideal conditions for production of the most valuable products.
This research investigates the compositions of the aqueous and oil products from HTL of dairy manure digestate under phosphoric acid catalyzed and non-acid catalyzed conditions at differing retention times. The reactants are placed in a 300 mL batch reactor, heated to 300℃, and run for retention times from 5 to 40 minutes, after which the liquid product is collected and separated into an aqueous and an oil product. Our work aims to characterize the chemical compounds in the oil and aqueous products through gas chromatography mass spectroscopy (GC-MS) analysis, as well as elucidate the partitioning of carbon and the partitioning and speciation of nitrogen into the oil and the aqueous products.
This work included development of methods for GC-MS analysis of both the aqueous and oil products, and illustrates the importance of an internal standard in GC-MS analysis. Results from this work show that presence of an acid catalyst leads to an increased amount of nitrogen in the aqueous product, but has minimal effect on carbon partitioning between the aqueous and oil products. Additionally, we show that increasing retention time leads to decreased recovery of carbon and nitrogen in the aqueous product regardless of catalytic conditions. This means that there is a tradeoff between carbon and nitrogen recoveries in the aqueous phase, as it is desirable to maximize nitrogen and minimize carbon in the aqueous phase. Phenols, alkanes, and sulfurous acids were consistently present in the aqueous product regardless of catalytic condition or retention time, indicating efficient lignin degradation in a range of hydrothermal reaction conditions.
Analysis of the oil product revealed that the energy content of the bio oil was unaffected by the addition of an acid catalyst. Additionally, the decreased amount of fatty acids in the oil product for acid-catalyzed samples suggests enhancement of the decarboxylation reaction that transforms fatty acids to hydrocarbons in the presence of the acid catalyst. Increased presence of phenol in the acid-catalyzed oil samples compared to the non-catalyzed oil samples indicates an enhanced lignin degradation pathway in the presence of the acid catalyst. More research needs to be done into the quantification of compounds in the aqueous product before any definitive conclusions can be drawn in relation to optimal reaction conditions and retention time for HTL of manure digestate.
While most HTL work remains at the laboratory and pilot scale, the expanding interest in WtE technologies as way to address pressing environmental challenges makes HTL a promising candidate for research and development to industrial and commercial scale. The work presented in this thesis contributes to the growing body of research relating to HTL as a viable process for simultaneous waste remediation and energy source production, and lays groundwork for important future work.
hydrothermal liquefaction, waste to energy
Bachelor of Science in Environmental Engineering
Deborah L. Sills
Matthew J. Higgins
Burns, Kenzie, "Aqueous and Oil Products from Hydrothermal Liquefaction of Manure Digestate" (2020). Honors Theses. 523.