Two-stage hydrothermal liquefaction of a high-protein microalga

Christopher Jazrawi,Patrick Biller,Yaya He,Alejandro Montoya,Andrew B Ross,Thomas Maschmeyer,Brian S Haynes

doi:10.1016/j.algal.2014.12.010

Christopher Jazrawi, Patrick Biller + Show 5 more

Open Access

https://doi.org/10.1016/j.algal.2014.12.010

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Journal: Algal Research	Publication Date: Jan 13, 2015
Citations: 157	License type: cc-by

Affiliation: University of Sydney, University of Leeds

Abstract

Hydrothermal liquefaction (HTL) is a promising route for producing renewable fuels and chemicals from algal biomass. However, the protein fraction of the alga gives rise to nitrogen compounds in the oil fraction, which may render the oil unattractive for use in conventional refining processes. We report a two-stage HTL approach with the primary aim of reducing the nitrogen concentration in the bio-crude oil. A mild (<200°C) pre-treatment step (Stage I) is performed before more severe (250–350°C) HTL conditions (Stage II) are applied to the microalga Chlorella for the production of bio-crude in a batch reactor. The pre-treatment resulted in up to 50wt.% of the input nitrogen crossing into the Stage I aqueous phase and, following Stage II processing, reductions in the bio-crude nitrogen contents of up to 55%, relative to the direct HTL of untreated Chlorella were observed. However, since considerable amounts of the starting material were lost in Stage I, overall lower quantities of bio-crude were isolated after Stage II processing, as compared to single-stage processing. Nitrogen extraction during Stage I is enhanced by the addition of acids (1N sulphuric or formic acid) but the process remains unselective. Overall, it is concluded that the two-stage approach to reducing the nitrogen content of bio-crudes from a protein-rich alga requires careful evaluation of the trade-off between the desired bio-crude properties and the yield obtained.

Highlights

Hydrothermal liquefaction (HTL) has received increasing interest in the past decade as a process for converting biomass to drop-in biofuels and chemicals [1,2]
In this paper we investigate the relationship between the yield and the nitrogen content of bio-crude when a microalgal biomass is subjected to two-stage HTL in which the first stage is at lower temperatures
Pre-treatment of microalgae under mild hydrothermal conditions solubilises some of the raw biomass, leaving a residue that produces bio-crude under more severe conditions

Summary

Introduction

Hydrothermal liquefaction (HTL) has received increasing interest in the past decade as a process for converting biomass to drop-in biofuels and chemicals [1,2]. Reaction temperatures of approximately 250–350 °C, and pressures high enough to maintain the water as a liquid (i.e., 40–250 bar), are generally employed. The biomass feedstock can be processed directly, without an energy-consuming drying step, since water acts both as solvent and catalyst [4]. The HTL of whole biomass yields a range of different products including bio-crude oil, aqueous dissolved chemicals, solid residue, and gas. The product yields and properties vary significantly according to the feedstocks processed as well as the reaction conditions employed

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