Hydrothermal liquefaction of microalgae: Influence of varying cell compositions on biocrude yield and quality

There is strong interest in microalgae-derived biofuel as a sustainable replacement for fossil fuels due to the numerous advantages of microalgae as a feedstock. Hydrothermal Liquefaction (HTL) is a thermochemical process that uses water as the reaction medium to convert biomass into biocrude oil under elevated temperatures and pressures (200–350°C, 5–20 MPa). While there is extensive literature on the separate processes of microalgae cultivation and HTL conversion, relationships between different biochemical compositions of a single species and HTL which contribute to the understanding of the overall system remain unexplored. This study examines the influence of varying microalgae cell composition on HTL biocrude yield and chemical composition. Nannochloropsis oculata was cultivated under depleting nitrogen levels to obtain biomass with variable cell compositions (17–59 %dw lipids; 45–17 %dw proteins; 11–22 %dw carbohydrates). HTL of harvested biomass was conducted at commonly used process conditions (80 wt% moisture, 300°C, 30 min reaction time), and conversion products were characterized to evaluate the energy yield and chemical characteristic of the biocrude phase. Results suggest for the case of lipid-accumulating biomass that biocrude yield is strongly determined by the increasing fatty acid methyl ester (FAMEs) content and not gross lipid content as previously thought. A model linking biomass composition to HTL biocrude yield is proposed based on the contributions from a baseline (non-FAMEs) fraction and FAMEs fraction of the biomass. Biocrude yields and higher heating values (HHV, MJ/kg) both increase with increasing FAMEs content, leading to higher energy recovery within the biocrude product phase. Increasing FAMEs content also leads to biocrude products with an increasing fraction of compounds with boiling points between 300–400°C, decreasing nitrogen content, and decreasing average molecular weight distribution. Results from this study contribute to the understanding of the interrelationships between biomass feedstock composition and the conversion products resulting from HTL. This information can be further linked to separate models for controlling biomass composition during upstream cultivation to enable more integrated analysis of the overall algal-HTL biofuel pathway.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Environ Engr in Civil Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Leow, Shijie

Contributors dc:contributor

• Strathmann, Timothy J.
• Guest, Jeremy S.

• hydrothermal liquefaction (HTL)
• microalgae
• varying cell compositions
• algae
• biocrude oil
• biofuels
• Nannochloropsis
• biochemical composition
• HTL of cultivated algae

Statement dc:rights

• Copyright 2014 Shijie Leow

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/49792

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/49792