Iron-catalyzed fast hydrothermal liquefaction of Cladophora socialis macroalgae into high quality fuel precursor

Catalytic solvothermal liquefaction of kitchen waste for the production of high-quality bio-oil: Effects of reusing ethanol phase as the reaction medium

Solvothermal liquefaction (STL) can convert kitchen waste (KW) into bio-oil without pre-drying. This study systematically investigated the effects of Fe-Ni bimetallic catalysts and recycled ethanol on enhancing bio-oil production. It also assessed the stability and reusability of the recycled catalysts, as well as the environmental benefits of STL technology. Compared to non-catalytic liquefaction, the Fe-Ni bimetallic catalysts significantly promoted the hydrodeoxygenation and esterification processes in bio-oil production. The highest yields of hydrocarbons (13.52%) and esters (69.86%) in bio-oil were achieved using the 6Fe-10Ni/Al2O3 catalyst. Increasing Fe loading positively facilitated the random scission of long-chain and C-C bonds, resulting in an increase in the fraction of lighter molecules in bio-oil to 74.85%. After the sixth cycle, the 6Fe-10Ni/Al2O3 catalyst maintained excellent stability and reusability. In comparison to fresh ethanol, the recycled ethanol significantly reduced the nitrogen and sulfur content of the bio-oil. The nitrogen of 70.45% and the sulfur of 84.67% were primarily dissolved to the aqueous phase due to the higher polarity of recycled ethanol. The results of a techno-economic assessment (TEA) and a life cycle assessment (LCA) confirmed that the STL of KW is both economically viable and environmentally friendly. The experimental findings provide valuable insights for future research on the upgrading, processing, and refining of bio-oil.

Hydrothermal conversion of biomass to fuels, chemicals and materials: A review holistically connecting product properties and marketable applications

Biomass is a renewable and carbon-neutral resource with good features for producing biofuels, biochemicals, and biomaterials. Among the different technologies developed to date to convert biomass into such commodities, hydrothermal conversion (HC) is a very appealing and sustainable option, affording marketable gaseous (primarily containing H₂, CO, CH₄, and CO₂), liquid (biofuels, aqueous phase carbohydrates, and inorganics), and solid products (energy-dense biofuels (up to 30 MJ/kg) with excellent functionality and strength). Given these prospects, this publication first-time puts together essential information on the HC of lignocellulosic and algal biomasses covering all the steps involved. Particularly, this work reports and comments on the most important properties (e.g., physiochemical and fuel properties) of all these products from a holistic and practical perspective. It also gathers vital information addressing selecting and using different downstream/upgrading processes to convert HC reaction products into marketable biofuels (HHV up to 46 MJ/kg), biochemicals (yield >90 %), and biomaterials (great functionality and surface area up to 3600 m²/g). As a result of this practical vision, this work not only comments on and summarizes the most important properties of these products but also analyzes and discusses present and future applications, establishing an invaluable link between product properties and market needs to push HC technologies transition from the laboratory to the industry. Such a practical and pioneering approach paves the way for the future development, commercialization and industrialization of HC technologies to develop holistic and zero-waste biorefinery processes.

Research progress, trends, and future prospects on hydrothermal liquefaction of algae for biocrude production: a bibliometric analysis

The rising demand to settle a sustainable energy source is guiding researchers in the production of biofuels. The liquefaction process is an alternative to obtaining biocrude from different types of renewable biomass and can mitigate environmental impacts. All papers published since 2000, which are related to the hydrothermal liquefaction process that aims to obtain biocrude are analyzed in the present study using the bibliometric approach to provide the selected database. Furthermore, the use of algae biomass in the liquefaction was also a discussed topic considering its high relevance in the process. The focus of the present study was to evaluate the evolution of the current state of the art in these topics and also to indicate trends and courses that it might be taken in the future. The database used in the bibliometric analysis was taken from the Web of Science (WoS) and the papers were selected by two different search equations. With the selected data, the use of BibExcel, VOSviewer, and PowerBi software was useful to guide the discussion and to create graphics and visual networks. As shown in the results, it was noticeable the influence of China and the USA on the field, considering the high number of publications from these countries. Moreover, the main authors were indicated considering their citation numbers, publications, and local h-index factor. Based on the author's keywords, the most significant and recent topics on liquefaction were listed. Among them, technical-economic analysis, nutrient, and energy recovery, response surface methodology, and kinetic model are highlighted. This may indicate a new direction being taken by researchers besides the operational parameters' studies.

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Highly active and magnetically recoverable heterogeneous catalyst for hydrothermal liquefaction of biomass into high quality bio-oil

This article reports a safe, low-cost, and industrially applicable magnetite supported on activated carbon catalyst that can be magnetically retrieved from the solid and reused multiple times without the need of a regeneration step. The FeO_x/C catalyst improved the bio-oil yield by 19.7 ± 0.96 % when compared to the uncatalysed reaction at 320 °C for the HTL of draff (brewer's spent grains). The use of homogeneous Na₂CO₃ base as a catalyst and co-catalyst, improved carbon extraction into the aqueous phase. The exceptional catalytic activity can be attributed to the Fe₃O₄ phase which can produce in-situ H₂ that improves the biomass decomposition and oil property with an energy recovery of ∼84 %. The FeO_x/C catalyst was separated using magnetic retrieval and maintained its catalytic activity even up to 5 reaction cycles showing potential as a cheap catalyst for HTL reactions and can be scaled-up for industrial applications.

Synergistic citric acid-surfactant catalyzed hydrothermal liquefaction of pomelo peel for production of hydrocarbon-rich bio-oil

Citric acid showed good performance of hydrothermal liquefaction (HTL) of biomass waste via promoting the depolymerization of macromolecules. The synergistic effects of citric acid-surfactants/solid catalysts in the low-temperature (200 °C) catalytic hydrothermal liquefaction of pomelo peel (PP) were studied for the first time. It turned out that citric acid-surfactants promoted the conversion of pomelo peel to bio-oil with a higher yield (26.10-67.72 wt%), higher heating value (17.79-24.77 MJ/kg) and energy yield (33.53-114.11 %), while citric acid-solid catalysts were more conducive to the formation of gas and other products. FT-IR and GC-MS analysis testified that citric acid-surfactants increased the selectivity of hydrocarbons from 49.99 % to 74.19 %. Additionally, the chemical functional groups of bio-oil were characterized by ¹H NMR and ¹³C NMR, indicating that the highest aliphatic content of bio-oils was 89.67 %. Moreover, citric acid-surfactant more environmentally friendly for low temperature liquefaction of biomass.

Catalytic Hydrothermal Liquefaction of Brachychiton populneus Biomass for the Production of High-Value Bio-Crude

The current study focused on the heterogenous catalytic hydrothermal liquefaction (HTL) of Brachychiton populneus biomass seed, using Ni as hydrogenation catalyst and Fe as active hydrogen producer. The activity of Ni metal and of Ni/Al2O3 in the HTL of seed (BS) and of a mixture of seed and shell (BM) was studied. To establish the best operating process conditions, the influence of variation of temperature and reaction time on the product yields was also examined. The highest bio-crude yields of 57.18% and 48.23% for BS and BM, respectively, were obtained at 330 °C and 10 min of reaction time, in the presence of Ni/Al2O3 as catalyst and Fe as hydrogen donor. Elemental analysis results showed that at these operative conditions, an increase of the higher heating value (HHV) from 25.14 MJ/kg to 38.04 MJ/kg and from 17.71 MJ/kg to 31.72 MJ/kg was obtained for BS and BM biomass, respectively, when the combination of Fe and Ni/Al2O3 was used. Gas chromatography–mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FT-IR), used to determine the oils’ chemical compositions, showed that the combined presence of Fe and Ni/Al2O3 favored the hydrodeoxygenation of the fatty acids into hydrocarbons, indeed their amount increased to ≈20% for both biomasses used. These results demonstrate that the obtained bio-crude has the capacity to be a source of synthetic fuels and chemical feedstock.

Ethanol-Assisted Hydrothermal Liquefaction of Poplar Using Fe-Co/Al2O3 as Catalyst

Although the conversion of lignocellulosic biomass into bio-oil with high yield/quality through hydrothermal liquefaction (HTL) is promising, it still faces many challenges. In this study, a Fex-Co(1-x)/Al2O3 catalyst was prepared with the coprecipitation method and low-content ethanol was used as the cosolvent for the HTL of poplar. The results showed that the Fex-Co(1-x)/Al2O3 catalyst significantly promoted the yield and energy recovery rate (ERR) of bio-oil compared with the control (10% ethanol content). At 260 °C for 30 min, 60Fe-40Co/Al2O3 had the best catalytic effect, achieving the highest bio-oil yield (67.35%) and ERR (93.07%). As a multifunctional bimetallic catalyst, Fex-Co(1-x)/Al2O3 could not only increase the degree of hydrogenation deoxidization of the product but also promote the diversity of phenolic compounds gained from lignin. The bio-oil obtained from HTL with Fex-Co(1-x)/Al2O3 as catalyst contained lower heterocyclic nitrogen, promoting the transfer of more bio-oil components to substances with lower boiling point.

Review of Studies on Joint Recovery of Macroalgae and Marine Debris by Hydrothermal Liquefaction

At the moment, macroalgae blooms in sea waters, the rotting of which causes greenhouse gas emissions and contributes to the formation of a negative ecological and economic situation in coastal zones, which has become a serious problem. Fuel production through hydrothermal liquefaction (HTL) of macroalgae and marine debris is a promising solution to this ecological problem. The article provides an overview of studies on producing fuel from macroalgae and an assessment of the possibility of their joint recovery with marine debris. The optimal process conditions and their technological efficiency were evaluated. The article shows the feasibility of using heterogeneous catalysis and co-solvent to increase the yield of bio-oil and improve its quality. An assessment of the possibility of joint processing of waste macroalgae and marine debris showed the inexpediency of this direction. The high degree of drift macroalgae contamination also raises the question of the appropriateness of the preliminary extraction of other valuable components for nutrition use, such as fats, proteins, carbohydrates, and their derivatives.