•Aqueous phase from algal liquefaction was recycled as a reaction medium for HTL.•The oil yield increased significantly when recycling the aqueous phase.•Recycling of aqueous phase led to marked ...increases in oil yield from catalytic HTL.•The oil quality from aqueous phase recycling was not scarified for improving yield.
In this study, the aqueous phase obtained from catalytic/non-catalytic hydrothermal liquefaction (HTL) of Chlorella vulgaris was recycled as the reaction medium with an aim to reduce water consumption and increase bio-crude oil yield. Although both Na2CO3 and HCOOH catalysts have been proven to be effective for promoting biomass conversion, the bio-crude oil yield obtained from HTL with Na2CO3 (11.5wt%) was lower than that obtained from the non-catalytic HTL in pure water at 275°C for 50min. While, the HCOOH led to almost the same bio-crude yield from HTL (29.4wt%). Interestingly, bio-crude oil yield obtained from non-catalytic or catalytic HTL in recycled aqueous phase was much higher than that obtained from HTL in pure water. Recycling aqueous phase obtained from catalytic HTL experiments resulted in a sharp increase in the bio-crude oil yield by 32.6wt% (Na2CO3-HTL) and 16.1wt% (HCOOH-HTL), respectively.
Alkaline lignin of a very high molecular weight was successfully degraded into oligomers in a hot-compressed water–ethanol medium with NaOH as the catalyst and phenol as the capping agent at 220–300
...°C. Under the optimal reaction conditions, i.e., 260
°C, 1
h, with the lignin/phenol ratio of 1:1 (w/w), almost complete degradation was achieved, producing <1% solid residue and negligible gas products. The obtained degraded lignin had a number-average molecular weight
M
n and weight-average molecular weight
M
w of 450 and 1000
g/mol respectively, significantly lower than the
M
n and
M
w of 10,000 and 60,000
g/mol of the original lignin. A higher temperature and a longer reaction time favoured phenol combination, but increased the formation of solid residue due to the condensation reactions of the degradation intermediates/products. The degraded lignin products were soluble in organic solvents (such as THF), and were characterized by HPLC/GPC, IR and NMR. A possible mechanism for lignin hydrolytic degradation was also proposed in this study.
•Bio-polyols were produced via alkaline hydrolysis of kraft lignin for polyurethanes.•A high yield of polyols up to 92% was obtained, with suitable −OH numbers and Mw.•The Mw of lignin was reduced ...from 10,000g/mol to ∼3300g/mol at low temperature.•A higher temperature especially 350°C favored polyols of lower Mw ∼1400g/mol.•A longer reaction time produced polyols with lower aliphatic −OH number.
Kraft lignin (KL) was successfully depolymerized into polyols of moderately high hydroxyl number and yield with moderately low weight-average molecular weight (Mw) via direct hydrolysis using NaOH as a catalyst, without any organic solvent/capping agent. The effects of process parameters including reaction temperature, reaction time, NaOH/lignin ratio (w/w) and substrate concentration were investigated and the polyols/depolymerized lignins (DLs) obtained were characterized with GPC-UV, FTIR-ATR, 1H NMR, Elemental & TOC analyzer. The best operating conditions appeared to be at 250°C, 1h, and NaOH/lignin ratio ≈0.28 with 20wt.% substrate concentration, leading to <0.5% solid residues and ∼92% yield of DL (aliphatic-hydroxyl number ≈352mgKOH/mg and Mw≈3310g/mole), suitable for replacement of polyols in polyurethane foam synthesis. The overall % carbon recovery under the above best conditions was ∼90%. A higher temperature favored reduced Mw of the polyols while a longer reaction time promoted dehydration/condensation reactions.
Lignocellulosic biomass is a promising alternative to petroleum oil for producing energy and chemicals, owing to its abundance and sustainability. In the past decades, extensive research has applied ...a wide range of thermo-chemical technologies for converting biomass into value-added products. Among them, hydrothermal liquefaction (HTL) is regarded to be one of the most effective techniques to produce bio-fuels and bio-based chemicals. However, there are still several technical barriers that must be addressed before the industrialization of HTL technology. Although many previous reviews have summarized the reaction mechanism, properties of liquefaction products, and various operating parameters, few articles have discussed the potential applications of HTL products and the techno-economic problems facing by the industrialization of HTL. Therefore, in this review, the possible applications of HTL products (bio-crude, aqueous phase, solid residue, and gas) were thoroughly discussed. In addition, the current challenges of HTL treatment, especially for the continuous operation, to produce bio-based fuel and chemicals is reviewed. Finally, the possible future directions and the main conclusions are covered.
•The benefits and weaknesses of using water as the reaction medium are presented.•The characteristics and potential applications of HTL products are discussed.•Beside bio-crude, by-products from HTL could bring value to HTL.•Critical challenges to the continuous operation of HTL are identified and discussed.
Display omitted
•The output data and potential of industrial solid wastes for CO2 mineralization are analyzed.•The limitation reasons of CO2 mineralization for industrial applications are found.•The ...huge energy and cost consumption is the biggest block for its progress.•The approaches for reducing energy and cost consumption are reviewed.
CO2 mineral carbonation is a promising strategy to abate global warming. However, its industrial applications were still limited. This paper reviews the current developments of mineral carbonation technologies by using industrial solid wastes as feedstocks, aiming at searching the reasons of its limitation. Firstly, the pathways and principles for CO2 mineral carbonation are briefly introduced. Then, the carbonation potential and processes of the most representative and available industrial solid wastes are summarized and compared. Iron and steel slags exhibit great potential due to their high alkali content and reactivity. Based on the preliminary economic analysis, the reasons for the limitation of current scale-up applications of CO2 mineral carbonation are the concerns of energy and cost consumption. The process parameter optimization and equipment design for scale-up applications need to be extensively investigated. Meanwhile, the recovery of high-value products during the carbonation process improves the economy and make the process more promising for industrial applications. The feasibility for recovering various value-added byproducts such as precipitated calcium carbonate (PCC) and zeolites was reported and discussed in this paper. Lastly, two research directions, i.e. the evaluation of CO2 net emission reduction by life cycle assessment technique and developments of new energy-saving approaches, are suggested.
Energy from biomass, bioenergy, is a perspective source to replace fossil fuels in the future, as it is abundant, clean, and carbon dioxide neutral. Biomass can be combusted directly to generate heat ...and electricity, and by means of thermo-chemical and bio-chemical processes it can be converted into bio-fuels in the forms of solid (e.g., charcoal), liquid (e.g., bio-oils, methanol and ethanol), and gas (e.g., methane and hydrogen), which can be used further for heat and power generation. This paper provides an overview of the principles, reactions, and applications of four fundamental thermo-chemical processes (combustion, pyrolysis, gasification, and liquefaction) for bioenergy production, as well as recent developments in these technologies. Some advanced thermo-chemical processes, including co-firing/co-combustion of biomass with coal or natural gas, fast pyrolysis, plasma gasification and supercritical water gasification, are introduced. The advantages and disadvantages, potential for future applications and challenges of these processes are discussed. The co-firing of biomass and coal is the easiest and most economical approach for the generation of bioenergy on a large-sale. Fast pyrolysis has attracted attention as it is to date the only industrially available technology for the production of bio-oils. Plasma techniques, due to their high destruction and reduction efficiencies for any form of waste, have great application potential for hazardous waste treatment. Supercritical water gasification is a promising approach for hydrogen generation from biomass feedstocks, especially those with high moisture contents.
Microalgae have been widely considered as the potential sources for bio-fuel production without affecting the environment. Hydrothermal liquefaction (HTL) is a suitable technology for converting high ...water-containing feedstocks (e.g., microalgae) to liquid fuel. However, the structural diversity and rigidity of the microalgal cell wall remains as the major techno-economic bottlenecks for the recovery of intramolecular compounds (e.g., lipid) from microalgae. In this paper, the recent developments in cell disruption technologies and HTL for various microalgae strains are reviewed. The available literature investigating the effect of microalgal pre-treatment on the production of microalgae-derived bio-crude oil are presented. Furthermore, this article provides an extensive review of the recent studies on the HTL of microalgae, including the influences of feedstock characteristics and various operating conditions, underlying reaction mechanism, and physicochemical properties of liquefaction products.
•Recent developments in cell disruption for microalgae are reviewed.•Effect of pre-treatment on oil formation are presented.•HTL operating conditions and reaction pathways for microalgae are discussed.•Physical and chemical properties of HTL products from microalgae are covered.•Challenges and future directions are outlined.
This paper provides a critical review on the current status and potential of biomass utilization in ferrous metallurgical processes, i.e., the blast furnace (BF) – basic oxygen furnace (BOF) route, ...the direct reduction (DR) – electric arc furnace (EAF) route, the scrap – EAF route and the other routes. In the BF-BOF route, biomass can be used as a fuel for iron ore sintering, or as a raw material for the production of bio-coke, and utilized for blast furnace injection. In the DR-EAF route, direct reduction iron can be produced form iron ore and biomass pellet. In the scrap – EAF route, biomass can be utilized in EAF through a cogeneration system. In addition, biomass can be utilized in magnetic separation of refractory low-grade iron ore, in reuse of iron and steel slag, or as an adsorbent for pollutant control, etc. The challenges and outlook of biomass utilization in metallurgical industry are also discussed in this paper.
Direct liquefaction of lignocellulosic wastes (sawdust and cornstalks) and two model bio-mass compounds (pure lignin and pure cellulose as references) has been conducted in hot-compressed water at ...temperatures from 250 to 350
°C in the presence of 2
MPa H
2, for the production of phenolic compounds that may be suitable for the production of green phenol–formaldehyde resins. The liquefaction operations at 250
°C for 60
min produced the desirable product of phenolic/neutral oil at a yield of about 53, 32, 32 and 17
wt.% for lignin, sawdust, cornstalk and cellulose, respectively. The yield of phenolic/neutral oil for each feedstock was found to decrease with increasing temperature. As evidenced by GC–MS measurements, significant quantities of phenolic compounds such as 2-methoxy-phenol, 4-ethyl-2-methoxy-phenol, and 2,6-dimethoxy-phenol, were present in the resulting phenolic/neutral oils from the two lignocellulosic wastes and pure lignin. The relative concentration of phenolic compounds in the lignin-derived oil was as high as about 80%. As expected, the liquid products from cellulose contained essentially carboxylic acids and neutral compounds. Addition of Ba(OH)
2 and Rb
2CO
3 catalysts were found to significantly increase both phenolic/neutral oil and gas yields for all feedstocks except for lignin.
Photocatalytic processes are efficient methods to solve water contamination problems, especially considering dyeing wastewater disposal. However, high-efficiency photocatalysts are usually very ...expensive and have the risk of heavy metal pollution. Recently, an iron oxides@hydrothermal carbonation carbon (HTCC) heterogeneous catalyst was prepared by our group through co-hydrothermal treatment of carbohydrates and zinc extraction tailings of converter dust. Herein, the catalytic performance of the iron oxides@HTCC was verified by a nonbiodegradable dye, methylene blue (MB), and the catalytic mechanism was deduced from theoretical simulations and spectroscopic measurements. The iron oxides@HTCC showed an excellent synergy between photocatalysis and Fenton-like reactions. Under visible-light illumination, the iron oxides@HTCC could be excited to generate electrons and holes, reacting with H
2
O
2
to produce ·OH radicals to oxidize and decompose organic pollutants. The removal efficiency of methylene blue over iron oxides@HTCC at 140 min was 2.86 times that of HTCC. The enhanced catalytic performance was attributed to the advantages of iron oxides modification: (1) promoting the excitation induced by photons; (2) improving the charge transfer. Furthermore, the iron oxides@HTCC showed high catalytic activity in a wide pH value range of 2.3–10.4, and the MB removal efficiency remained higher than 95% after the iron oxides@HTCC was recycled 4 times. The magnetically recyclable iron oxides@HTCC may provide a solution for the treatment of wastewater from the textile industry.
