Process development for hydrothermal liquefaction of algae feedstocks in a continuous-flow reactor

Topics: Algae, Nitrogen, Carbon dioxide Pages: 44 (7599 words) Published: January 28, 2014
Algal Research 2 (2013) 445–454

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Process development for hydrothermal liquefaction of algae feedstocks in a continuous-flow reactor
Douglas C. Elliott ⁎, Todd R. Hart, Andrew J. Schmidt, Gary G. Neuenschwander, Leslie J. Rotness, Mariefel V. Olarte, Alan H. Zacher, Karl O. Albrecht, Richard T. Hallen, Johnathan E. Holladay Pacific Northwest National Laboratory, P.O. Box 999, MSIN P8-60, Richland, WA 99352, United States

a r t i c l e

i n f o

Article history:
Received 6 June 2013
Received in revised form 26 August 2013
Accepted 29 August 2013
Available online 29 September 2013
Aqueous phase

a b s t r a c t
Wet algae slurries can be converted into an upgradeable biocrude by hydrothermal liquefaction (HTL). High levels of carbon conversion to gravity separable biocrude product were accomplished at relatively low temperature (350 °C) in a continuous-flow, pressurized (sub-critical liquid water) environment (20 MPa). As opposed to earlier work in batch reactors reported by others, direct oil recovery was achieved without the use of a solvent and biomass trace components were removed by processing steps so that they did not cause process difficulties. High conversions were obtained even with high slurry concentrations of up to 35 wt.% of dry solids. Catalytic hydrotreating was effectively applied for hydrodeoxygenation, hydrodenitrogenation, and hydrodesulfurization of the biocrude to form liquid hydrocarbon fuel. Catalytic hydrothermal gasification was effectively applied for HTL byproduct water cleanup and fuel gas production from water soluble organics, allowing the water to be considered for recycle of nutrients to the algae growth ponds. As a result, high conversion of algae to liquid hydrocarbon and gas products was found with low levels of organic contamination in the byproduct water. All three process steps were accomplished in bench-scale, continuous-flow reactor systems such that design data for process scale-up was generated.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction
Hydrothermal liquefaction (HTL) of biomass provides a direct pathway for liquid biocrude production. This liquid product is a complex mixture of oxygenated hydrocarbons and, in the case of algae biomass, it contains substantial nitrogen as well. Hydrothermal processing utilizes water-based slurries at medium temperature (350 °C) and sufficient pressure (20 MPa) to maintain the water in the liquid phase. The processing option is particularly applicable to wet biomass feedstocks, such as algae, eliminating the need to expend energy to dry the feed before processing, as is required in other thermochemical conversion processes.

Elliott recently reviewed the early work in hydrothermal processing of wet biomass for both liquid and gas production [1]. Recent reports in the literature that have described HTL and its application to algae have been primarily related to batch reactor tests (see the long list in Chow et al. [2]). There have been reports of continuousflow reactor tests for hydrothermal gasification of algae, both subcritical liquid phase [3] and super-critical vapor phase [4]. Here we report the preliminary results of continuous-flow reactor studies of hydrothermal liquefaction with wet algae feedstocks. Subsequent

⁎ Corresponding author. Tel.: +1 509 375 2248; fax: +1 509 372 4732. E-mail address: (D.C. Elliott).
2211-9264/$ – see front matter © 2013 Elsevier B.V. All rights reserved.

hydrotreatment of the HTL product oil demonstrated continuousflow production of hydrocarbon fuel components while catalytic treatment of the aqueous phase in a separate continuous-flow reactor demonstrated fuel gas production from the dissolved organics. The generation of a...

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