To main content

Sub-Supercritical Hydrothermal Liquefaction of Lignocellulose and Protein-Containing Biomass


first_pagesettingsOrder Article Reprints
Open AccessArticle
Sub-Supercritical Hydrothermal Liquefaction of Lignocellulose and Protein-Containing Biomass
by Ayaz Ali Shah 1,2,*,Kamaldeep Sharma 1ORCID,Tahir Hussain Seehar 1,2,Saqib Sohail Toor 1,Judit Sandquist 3ORCID,Inge Saanum 3 andThomas Helmer Pedersen 1
Department of Energy Technology, Aalborg University, Pontoppidanstræde 111, 9220 Aalborg Øst, Denmark
Department of Energy and Environment Engineering, Dawood University of Engineering & Technology, Karachi City 74800, Pakistan
SINTEF Energy Research, Sem Sælands vei 11, 7034 Trondheim, Norway
Author to whom correspondence should be addressed.
Fuels 2024, 5(1), 75-89;
Submission received: 7 December 2023 / Revised: 15 January 2024 / Accepted: 3 February 2024 / Published: 26 February 2024
Downloadkeyboard_arrow_down Browse Figures Versions Notes
Hydrothermal liquefaction (HTL) is an emerging technology for bio-crude production but faces challenges in determining the optimal temperature for feedstocks depending on the process mode. In this study, three feedstocks—wood, microalgae spirulina (Algae Sp.), and hydrolysis lignin were tested for sub-supercritical HTL at 350 and 400 °C through six batch-scale experiments. An alkali catalyst (K2CO3) was used with wood and hydrolysis lignin, while e (Algae Sp.) was liquefied without catalyst. Further, two experiments were conducted on wood in a Continuous Stirred Tank Reactor (CSTR) at 350 and 400 °C which provided a batch versus continuous comparison. Results showed Algae Sp. had higher bio-crude yields, followed by wood and lignin. The subcritical temperature of 350 °C yielded more biocrude from all feedstocks than the supercritical range. At 400 °C, a significant change occurred in lignin, with the maximum percentage of solids. Additionally, the supercritical state gave higher values for Higher Heating Values (HHVs) and a greater amount of volatile matter in bio-crude. Gas Chromatography and Mass Spectrometry (GCMS) analysis revealed that phenols dominated the composition of bio-crude derived from wood and hydrolysis lignin, whereas Algae Sp. bio-crude exhibited higher percentages of N-heterocycles and amides. The aqueous phase analysis showed a Total Organic Carbon (TOC) range from 7 to 22 g/L, with Algae Sp. displaying a higher Total Nitrogen (TN) content, ranging from 11 to 13 g/L. The pH levels of all samples were consistently within the alkaline range, except for Wood Cont. 350. In a broader perspective, the subcritical temperature range proved to be advantageous for enhancing bio-crude yield, while the supercritical state improved the quality of the bio-crude.
Keywords: sub-supercritical HTL; lignocellulosic biomass; microalgae; bio-crude


Academic article


  • Research Council of Norway (RCN) / 257622





  • Aalborg University
  • Dawood University of Science and Technology
  • SINTEF Energy Research / Termisk energi



Published in









75 - 89

View this publication at Cristin