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HTL Biocrude Production, Optimization, and Upgrading

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A4: Bio-Energy".

Deadline for manuscript submissions: closed (20 December 2021) | Viewed by 13130

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Special Issue Editors

Prof. Saqib Sohail Toor

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Guest Editor

Department of Energy Technology, Aalborg University, 9220 Aalborg, Denmark
Interests: biomass; hydrothermal liquefaction; supercritical water; biocrude; bioenergy

Dr. Kamaldeep Sharma

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Guest Editor

Department of Energy Technology, Aalborg University, 9220 Aalborg, Denmark
Interests: hydrothermal liquefaction; catalytic hydrotreating; catalysts; biofuels; bioenergy

Special Issue Information

Dear Colleagues,

Biomass is a renewable resource and viewed as one with the most potential. Its use has received considerable attention due to environmental considerations and shortage of energy supplies. Hydrothermal liquefaction (HTL) is considered as a promising pathway that enables a feedstock-flexible conversion of non-feed biomass into liquid biofuel and value-added chemicals. The HTL of biomass at sub- or supercritical water tempetures of 250–450 °C and pressures of 100–350 bar has been widely studied. The obtained heavy oil (often called bio-crude) is a highly complex mixture, with challenging differences in oxygenated hydrocarbons and heteroatoms contents. The properties and yield of HTL biocrudes depens on the main process parameters like reaction temperature, reaction time, catalyst, biomass type, and biomass/water ratio. The ﬁnal goals of the HTL process are to produce the highest yield and quality bio-oil and to realize the commercialization of biocrude production. Therefore, the optimization of the process parameters should be extensively studied. The lack of detailed analytical knowledge on bio-crudes is mainly due to the high diversity of biocrudes and the lack of focus on the downstream conversion process to use biocrude as a drop-in fuel. This Special Issue aims to encourage researchers to address appropriate solutions to overcome the issues regarding HTL process optimization and detailed biocrude physiochemical analysis from an upgrading perspective.

Prof. Saqib Sohail Toor
Dr. Kamaldeep Sharma
Guest Editors

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Keywords

biomass
hydrothermal liquefaction
process optimization
biocrude
physiochemical properties
biocrude upgrading
drop-in fuel

Published Papers (6 papers)

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Research

21 pages, 1960 KiB

Open AccessArticle

Bio-Crude Production Improvement during Hydrothermal Liquefaction of Biopulp by Simultaneous Application of Alkali Catalysts and Aqueous Phase Recirculation

by Komeil Kohansal, Kamaldeep Sharma, Saqib Sohail Toor, Eliana Lozano Sanchez, Joscha Zimmermann, Lasse Aistrup Rosendahl and Thomas Helmer Pedersen

Energies 2021, 14(15), 4492; https://0-doi-org.brum.beds.ac.uk/10.3390/en14154492 - 25 Jul 2021

Cited by 5 | Viewed by 1895

Abstract

This study focuses on the valorization of the organic fraction of municipal solid waste (biopulp) by hydrothermal liquefaction. Thereby, homogeneous alkali catalysts (KOH, NaOH, K₂CO₃, and Na₂CO₃) and a residual aqueous phase recirculation methodology were mutually employed to enhance the bio-crude yield and energy efficiency of a sub-critical hydrothermal conversion (350 °C, 15–20 Mpa, 15 min). Interestingly, single recirculation of the concentrated aqueous phase positively increased the bio-crude yield in all cases, while the higher heating value (HHV) of the bio-crudes slightly dropped. Compared to the non-catalytic experiment, K₂CO₃ and Na₂CO₃ effectively increased the bio-crude yield by 14 and 7.3%, respectively. However, KOH and NaOH showed a negative variation in the bio-crude yield. The highest bio-crude yield (37.5 wt.%) and energy recovery (ER) (59.4%) were achieved when K₂CO₃ and concentrated aqueous phase recirculation were simultaneously applied to the process. The inorganics distribution results obtained by ICP reveal the tendency of the alkali elements to settle into the aqueous phase, which, if recovered, can potentially boost the circularity of the HTL process. Therefore, wise selection of the alkali catalyst along with aqueous phase recirculation assists hydrothermal liquefaction in green biofuel production and environmentally friendly valorization of biopulp. Full article

(This article belongs to the Special Issue HTL Biocrude Production, Optimization, and Upgrading)

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10 pages, 1050 KiB

Open AccessArticle

A Comparative Study on Thermochemical Valorization Routes for Spent Coffee Grounds

by Jie Yang, Hao Chen, Haibo Niu, Josiah McNutt and Quan He

Energies 2021, 14(13), 3840; https://0-doi-org.brum.beds.ac.uk/10.3390/en14133840 - 25 Jun 2021

Cited by 4 | Viewed by 1574

Abstract

Extracting oil from spent coffee grounds (SCG) for biodiesel production has recently attracted much research interest. Large amounts of organic solvents are involved for oil extraction and biodiesel synthesis. Hydrothermal liquefaction (HTL) is an emerging thermochemical technology with great potential for biocrude production from a broad range of feedstocks. This study attempted to compare two SCG valorization options: route 1, oil extraction for biodiesel production followed by HTL of defatted SCG; and route 2, direct HTL of raw SCG. The microwave-assisted extraction conditions were optimized to effectively remove oil from SCG using response surface methodology. Under optimal conditions, an SCG oil yield of 8.4 wt.% could be achieved. HTL of defatted SCG generated less biocrude (18.9 wt.%) than that of raw SCG (28.1 wt.%). The biochemical compositions of resultant biocrudes were largely different from each other. The life cycle assessment was conducted on each of the SCG valorization routes and showed that the greenhouse gas emissions from direct HTL of raw SCG were only 35% of the other valorization route, suggesting that direct HTL is a favorable valorization route for SCG within this study’s scope. Full article

(This article belongs to the Special Issue HTL Biocrude Production, Optimization, and Upgrading)

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20 pages, 6244 KiB

Open AccessArticle

Bio-Crude Production through Recycling of Pretreated Aqueous Phase via Activated Carbon

by Ayaz Ali Shah, Saqib Sohail Toor, Asbjørn Haaning Nielsen, Thomas Helmer Pedersen and Lasse Aistrup Rosendahl

Energies 2021, 14(12), 3488; https://0-doi-org.brum.beds.ac.uk/10.3390/en14123488 - 11 Jun 2021

Cited by 5 | Viewed by 1627

Abstract

The management and optimization of the aqueous phase are the major challenges that hinder the promotion of hydrothermal liquefaction (HTL) technology on a commercial scale. Recently, many studies reported about the accumulation of the N-content in the bio-crude with continuous recycling of the aqueous phase from high protein-containing biomass. In the present study, sewage sludge was processed at 350 °C in an autoclave. The produced aqueous phase was treated with activated carbon, and its subsequent recycling effect on the properties of the bio-crude and aqueous phase was investigated. By contacting the aqueous phase with activated carbon, 38–43% of the total nitrogen was removed from the aqueous phase. After applying the treated aqueous phase recycling, the energy recovery of the bio-crude increased from 50 to 61% after three rounds of recycling. From overall carbon/nitrogen recoveries, 50 to 56% of the carbon was transferred to the bio-crude phase and more than 50% of the nitrogen remained in the aqueous phase. The aqueous phase contained mostly of N&O-heterocyclic compounds, small chain organic acids, and amides. ICP-AES analysis showed that more than 80% of the inorganic elements were concentrated into the solid phase. Full article

(This article belongs to the Special Issue HTL Biocrude Production, Optimization, and Upgrading)

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13 pages, 2526 KiB

Open AccessArticle

Co-Hydrothermal Liquefaction of Lignocellulosic Biomass in Supercritical Water

by Kamaldeep Sharma, Ayaz A. Shah, Saqib S. Toor, Tahir H. Seehar, Thomas H. Pedersen and Lasse A. Rosendahl

Energies 2021, 14(6), 1708; https://0-doi-org.brum.beds.ac.uk/10.3390/en14061708 - 19 Mar 2021

Cited by 21 | Viewed by 2598

Abstract

Hydrothermal liquefaction (HTL) is an effective technology for bio-crude production. To date, various co-liquefaction studies were performed with contrasted (different composition) biomasses in subcritical water. Therefore, the present study investigated co-hydrothermal liquefaction of similar kinds of lignocellulosic biomasses (wheat straw, eucalyptus, and pinewood) in supercritical water under equal ratios at 400 °C with catalytic medium (K₂CO₃). The lower bio-crude and higher solid yields were obtained in co-liquefaction experiments, as compared to liquefaction of individual feedstocks. On the other hand, higher carbon recovery and higher HHVs were noticed in co-liquefaction-derived bio-crudes. Gas chromatography with mass spectrometry (GC-MS) results showed that organic compounds were detected in all bio-crudes in the order of phenol derivatives > ketones/aldehydes > aromatics > carboxylic acids/esters. The aqueous phase from all samples contained higher TOC in the range of 19 to 33 g/L, with alkaline pH. In short, the co-liquefaction slightly improved the bio-crude quality with a significant reduction in bio-crude energy recovery. This reflects that co-liquefaction of lignocellulosic feedstock is not favorable for enhancing bio-crude yield and improving the overall process economics of HTL. Full article

(This article belongs to the Special Issue HTL Biocrude Production, Optimization, and Upgrading)

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17 pages, 3423 KiB

Open AccessArticle

Using Isopropanol as a Capping Agent in the Hydrothermal Liquefaction of Kraft Lignin in Near-Critical Water

by Anders Ahlbom, Marco Maschietti, Rudi Nielsen, Huyen Lyckeskog, Merima Hasani and Hans Theliander

Energies 2021, 14(4), 932; https://0-doi-org.brum.beds.ac.uk/10.3390/en14040932 - 10 Feb 2021

Cited by 8 | Viewed by 2085

Abstract

In this study, Kraft lignin was depolymerised by hydrothermal liquefaction in near-critical water (290–335 °C, 250 bar) using Na₂CO₃ as an alkaline catalyst. Isopropanol was used as a co-solvent with the objective of investigating its capping effect and capability of reducing char formation. The resulting product, which was a mixture of an aqueous liquid, containing water-soluble organic compounds, and char, had a lower sulphur content than the Kraft lignin. Two-dimensional nuclear magnetic resonance studies of the organic precipitates of the aqueous phase and the char indicated that the major lignin bonds were broken. The high molar masses of the char and the water-soluble organics, nevertheless, indicate extensive repolymerisation of the organic constituents once they have been depolymerised from the lignin. With increasing temperature, the yield of char increased, although its molar mass decreased. The addition of isopropanol increased the yield of the water-soluble organic products and decreased the yield of the char as well as the molar masses of the products, which is indicative of a capping effect. Full article

(This article belongs to the Special Issue HTL Biocrude Production, Optimization, and Upgrading)

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19 pages, 3983 KiB

Open AccessArticle

Effect of Accumulative Recycling of Aqueous Phase on the Properties of Hydrothermal Degradation of Dry Biomass and Bio-Crude Oil Formation

by Siyuan Yin, Nianze Zhang, Chunyan Tian, Weiming Yi, Qiaoxia Yuan, Peng Fu, Yuchun Zhang and Zhiyu Li

Energies 2021, 14(2), 285; https://0-doi-org.brum.beds.ac.uk/10.3390/en14020285 - 07 Jan 2021

Cited by 4 | Viewed by 1893

Abstract

For hydrothermal liquefaction of dry biomass to produce liquid fuels, water needs to be added or the aqueous phase products can be recycled. This paper focuses on understanding the relationship between hydrothermal degradation of the dry biomass and oil formation under the condition of accumulative recycling of the aqueous phase. Completely dried corn stalk and deionized water were used for the hydrothermal liquefaction (HTL) experiment. The aqueous products for subsequent recycling were not diluted. It was demonstrated that the recycling of the aqueous can promote the enrichment of organic acids and the conversion of ketones and phenols in the aqueous, improving the yield and quality of Bio-crude oil. After recycling, the yield of Bio-crude oil increased from 20.42% to 24.31% continuously, and the oxygen content decreased from 13.34% to 9.90%. Although the process was accompanied by solid deposition and had a negative impact on the hydrothermal degradation efficiency, the formation of carbon microspheres during the deposition enhanced the utilization of nondegradable solids, while the formation of metal salt particles had a positive impact on oil production. After three rounds of recycling, the solid deposition effect was weakened. At this time, oil production and solids degradation can be promoted simultaneously. Full article

(This article belongs to the Special Issue HTL Biocrude Production, Optimization, and Upgrading)

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