Aqueous-phase Products Research Articles

Utilization of papermaking black liquor as liquid phase for hydrothermal carbonization of corn stalks: The unique role of alkali for production of hydrochar

Papermaking black liquor (BL) contains a large amount of organic matter, alkali, and salt, which has high value in industrial and agricultural production. In the present paper, hydrothermal carbonization (HTC) technology has been employed to deal with BL and corn stalk (CS) under various conditions. A variety of analytical technologies, including Fourier Transform Infrared Spectrometer, X-Ray Diffraction, element analyzer, comprehensive thermal analyzer, scanning electron microscope, chromatography/mass spectrometry, TOC analyzer, and density functional theory (DFT), were used to characterize the physicochemical properties of hydrochar and aqueous phase product. The effects of experimental parameters (temperature, solid-liquid ratio, and time) on the HTC of BL and CS were systematically investigated. The higher energy yield and densification of hydrochar prepared by our HTC technology were obtained at 260 ℃ in 30 min with a solid-liquid ratio of 1:3. Mechanism study indicates that NaOH, which comes from the original BL, could effectively facilitate the cleavage of β–O–4 bond in lignin and β–1–4 glycosidic bond in cellulose and hemicellulose molecules. Hemicellulose and cellulose are more susceptible to degradation relevant to the lignin in the presence of NaOH. Elementary analysis shows that the dosage of BL is important for improving energy densification of hydrochar. The combustion characteristics show that hydrochar presents a thermochemical behavior, which is close to bituminous coal. Owing to hydroxyl ion in NaOH ion pair was consumed in the series of dehydrogenation reactions, pH of HTC aqueous phase product significantly decreases from 11 to 13 in original BL to 4.8–5. Such results indicate that a completely change for the components of BL could be obtained by our HTC technology, which provide a novel idea for the treatment of Papermaking BL without concentration.

Experimental study and correlation analysis for the effect of hydrogen pressure on biomass fluidized hydropyrolysis under N2-H2 mixed atmosphere

The utilization of fluidized bed reactors for the biomass hydropyrolysis vapor upgrading is essential in the conversion of biomass into liquid fuels. Conducting pyrolysis experiments in fluidized bed reactors with a N2-H2 mixed atmosphere is advantageous for system operation as it allows for lower minimum operating velocities, enhances pyrolysis efficiency, and reduces heat loss. This research examines the impact of hydrogen pressure in a bubbling fluidized bed reactor using a N2-H2 mixed carrier gas, with poplar wood as the feedstock and Ni-Moγ/Al2O3 as the catalyst. Through experimental and correlation analyses, significant relationships are observed between hydrogen pressure and the production of liquid and gas-phase products, with varying effects attributed to changes in hydrogen ratio and reaction pressure. Elevated hydrogen ratios facilitate secondary reactions such as the CO2 hydrogenation, resulting in a decline in CO2 production and an elevation in the yields of light hydrocarbons and aqueous phase products. Augmenting the reaction pressure to enhance hydrogen pressure aids in promoting hydrogen saturation and cracking, and amplifying the hydrogen pressure through an increase in the reaction pressure at a specific hydrogen ratio proves more efficacious in enhancing both the quantity and quality of bio-oil produced. In the context of poplar hydropyrolysis vapor upgrading utilizing a Ni-Moγ/Al2O3 catalyst, a hydrogen ratio of 50 % at a reaction pressure of 1.5 MPa emerged as the preferred option for achieving a 12 % bio-oil yield with a moderate average bio-oil carbon number and satisfactory hydrogenation levels. This comprehensive investigation examines the influence of hydrogen pressure on biomass hydropyrolysis, highlighting variations in the impacts of changes in hydrogen ratio and reaction pressure on pyrolysis results. These results offer a theoretical framework for discerning distinctions between hydropyrolysis investigations carried out in pure hydrogen atmospheres versus mixed N2-H2 atmospheres.

Fast hydrothermal co-liquefaction of high-ash sludge and Chlorella for biocrude production

Fast hydrothermal liquefaction (HTL) shows great potential for producing biocrude. This research examined the influences of mixing ratios of sludge and Chlorella during both isothermal (300 °C, 1800 s) and fast (500 °C, 20 s) co-HTL. Adding Chlorella could efficiently retard repolymerization reaction and increase the biocrude production. The highest co-liquefaction effect was achieved from a sludge to Chlorella ratio of 2:6 by fast HTL, producing a biocrude yield of 29.65 wt%, closely approaching the calculated yield of 29.39 wt% and demonstrating an additive effect. However, for the high ash content of sludge, all isothermal and other fast HTL conditions presented an antagonistic effect on biocrude production. Meanwhile, co-liquefaction also exhibited a slight antagonistic effect on the heating value and energy recovery of biocrude, with experimental values reaching 32.73 MJ·kg−1 and 52.74 %, respectively. FT-IR and maturity analyses indicated that compared to isothermal co-HTL, fast co-HTL biocrude was more favorable for the conversion into gasoline/diesel due to its lower paleo-temperature. GC–MS analysis identified amides (isothermal co-HTL) and nitrogen heterocycles (fast co-HTL) as the dominant components, suggesting that the holding time significantly influenced the competition of Maillard and amidation reactions. Besides biocrude, the major composition of aqueous phase products (APs) was also nitrogen heterocycles. Notably, fast co-HTL induced a substantial decrease in COD, NH3-N, and TN contents of APs, reducing the discharge challenge of the by-products.

Co-hydrothermal carbonization of municipal sludge and agricultural waste to reduce plant growth inhibition by aqueous phase products: Molecular level analysis of organic matter

The organic matter molecular mechanism by which combined hydrothermal carbonization (co-HTC) of municipal sludge (MS) and agricultural wastes (rice husk, spent mushroom substrate, and wheat straw) reduces the inhibitory effects of aqueous phase (AP) products on pak choi (Brassica campestris L.) growth compared to HTC of MS alone is not clear. Fourier-transform ion cyclotron resonance mass spectrometry was used to characterize the differences in organic matter at the molecular level between AP from MS HTC alone (AP-MS) and AP from co-HTC of MS and agricultural waste (co-Aps). The results showed that N-bearing molecules of AP-MS and co-Aps account for 70.6 % and 54.2 %–64.1 % of all molecules, respectively. Lignins were present in the highest proportion (56.3 %–78.5 %) in all APs, followed by proteins and lipids. The dry weight of co-APs hydroponically grown pak choi was 31.6 %–47.6 % higher than that of the AP-MS. Molecules that were poorly saturated and with low aromaticity were preferentially consumed during hydroponic treatment. Molecules present before and after hydroponics were defined as resistant molecules; molecules present before hydroponics but absent after hydroponics were defined as removed molecules; and molecules absent before hydroponics but present after hydroponics were defined as produced molecules. Large lignin molecules were broken down into more unsaturated molecules, but lignins were the most commonly resistant, removed, and produced molecules. Correlation analysis revealed that N- or S-bearing molecules were phytotoxic in the AP. Tannins positively influenced the growth of pak choi. These results provide new insights into potential implementation strategies for liquid fertilizers produced from AP arising from HTC of MS and agricultural wastes.

Comprehensive utilization for hydrothermal conversion products of food waste

Hydrothermal conversion technology is a promising technique for resource utilization. In this study, the influence of reaction conditions on the distribution of hydrothermal conversion products was investigated, and the resource utilization methods of all components of hydrothermal conversion products were discussed. The results showed that the highest bio-oil yield was obtained at 310 °C, which was 36.75 %. The higher heating value and energy recovery rate of bio-oil can reach 39.68 MJ/kg and 78.55 % respectively. And it had great potential as an alternative fuel. When wheat seeds cultured by aqueous were diluted 100 times at 310 °C with GI ≥ 80 %, the phytotoxicity disappears. At this time, the contents of total nitrogen, total phosphorus, and total potassium were 1234.80, 150.34, and 1640.36 mg/L respectively, and the heavy metal content was lower than the national standard for foliar fertilizer. The optimal conditions for biochar to adsorb methylene blue were adsorbent dose 2 g/L, 180 rpm, temperature 70 °C, and time 120 min; The gas phase yield increased with the increase of temperature (0.15–7.45 %). The yield at 310 °C was 2.76 %. The main component of the gas phase was CO2, accounting for 93.71–97.92 %. The innovation of this study was that food waste can be converted into bio-oil through high-temperature hydrothermal reaction, achieving energy recovery. The aqueous phase product of hydrothermal conversion was used as water-soluble liquid fertilizer, achieving resource utilization. At the same time, the reaction was carried out under high temperature and pressure, which can completely kill pathogens in food waste and has extremely high biological safety.

Aqueous-phase product treatment and monetization options of wet waste hydrothermal liquefaction: Comprehensive techno-economic and life-cycle GHG emission assessment unveiling research opportunities

While wet waste hydrothermal liquefaction technology has a high biofuel yield, a significant amount of the carbon and nitrogen in the feedstock reports to the aqueous-phase product. Pretreatment of this stream before sending to a conventional wastewater plant is essential or at the very least, advisable. In this work, techno-economic and life-cycle assessments were conducted for the state-of-technology baseline and four aqueous-phase product treatment and monetization options based on experimental data. These options can cut minimum fuel selling prices by up to 13 % and life-cycle greenhouse gas emissions by up to 39 % compared to the baseline. These findings highlight the substantial influence of aqueous produce treatment strategies on the entire wet waste hydrothermal liquefaction process, demonstrating the potential for optimizing economic viability and environmental impact through further research and development of milder treatment methods and diversified by-product valorization pathways.

Exploration of hydrothermal liquefaction of multiple algae to improve bio-crude quality and carbohydrate utilization

With the growing emphasis on biofuels research, enhancing the utilization efficiency of the hydrothermal liquefaction (HTL) process for biomass has emerged as a focal point for researchers. In this study, HTL products from various algae species were analyzed to compare the quality of bio-crude, with a specific focus on the utilization of carbohydrates in biomass. Notably, bio-crude yields from high-lipid algae exhibited less fluctuation with temperature, while the quality showed a significant improvement with increasing temperature, as evidenced by the fatty acids and esters contents in the bio-crude. The results of elemental analysis indicated that bio-crude derived from high-lipid algae had a lower nitrogen content. In the analysis of carbohydrate utilization, it was observed that the aqueous phase products of Chlorella protothecoides demonstrated relatively high yields of furfural and 5-HMF. Similarly, the aqueous phase product of Spirulina exhibited comparatively high yields of levulinic acid. The inclusion of platform compounds in elemental recoveries contributed to an enhancement in the carbon and hydrogen recovery of the product. This study establishes a theoretical foundation for the selection of feedstocks for alternative fuels and highlights the potential of carbohydrates utilization from algal biomass.

Accessing the Efficacy of Sargassum-Based Aqueous Phase Products Derived from Hydrothermal Carbonisation and Hydrothermal Liquefaction on Plant Growth

Mass Sargassum inundations have created opportunities for readily available biomass to be used as a crop enrichment application. However, the heavy metal contents of Sargassum pose serious concerns for crop administration and subsequent human consumption. Hydrothermal processing can break the feedstock components, allowing heavy metals to be partitioned, through the utilisation of high temperatures and pressures. As a result, seemingly nutrient-rich phases can be produced. Elemental analyses showed that Sargassum-derived fractions contain important macro- and micronutrients for plants, particularly ammonium, orthophosphate, and potassium, making them potential nutrient sources for plant growth. To date, no research has investigated the plant growth potential of hydrothermally processed Sargassum products from a bioavailability or biotoxicity perspective. We seek to determine if the aqueous phase products derived following Sargassum processing by hydrothermal carbonisation and liquefaction are toxic to higher plants, and if they can support plant growth. Aqueous phase products in ≥1% concentrations inhibit root growth and lateral root formation in Arabidopsis plants, likely from the presence of inhibitory compounds. However, aqueous phase products in ≤0.1% concentrations paired with an established nutrient mix may provide improved leaf and root growth. Both HTC and HTL were capable of eliciting improved foliage growth, while only HTC induced improved root growth. Conclusively, aqueous phase products lack nutrient potency to allow high dilutions for fertiliser application on their own and may contain inhibitory compounds that deter plant growth at high concentrations. However, they might have a purpose as an additive extract. The recovery of important elements needed for plant growth draws a promising path for future applications of hydrothermal processing with different feedstocks.

In Situ Electrochemistry of Formate on Cu Thin Films Using ATR-FTIR Spectroscopy and X-ray Photoelectron Spectroscopy.

Formate (HCOO-) is the most dominant intermediate identified during carbon dioxide electrochemical reduction (CO2ER). While previous studies showed that copper (Cu)-based materials that include Cu(0), Cu2O, and CuO are ideal catalysts for CO2ER, challenges to scalability stem from low selectivity and undesirable products in the -1.0-1.0 V range. There are few studies on the binding mechanism of intermediates and products for these systems as well as on changes to surface sites upon applying potential. Here, we use an in situ approach to study the redox surface chemistry of formate on Cu thin films deposited on Si wafers using a VeeMAX III spectroelectrochemical (SEC) cell compatible with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Spectra for surface species were collected in real time as a function of applied potential during cyclic voltammetry (CV) experiments. Results showed the reproducibility of CV curves on freshly prepared Cu/Si wafers with relatively high signal-to-noise ATR-FTIR absorbance features of surface species during these electrochemical experiments. The oxidation reaction of HCOO- to bicarbonate (HCO3-) was observed using ATR-FTIR at a voltage of 0.27 V. Samples were then subjected to reduction in the CV, and the aqueous phase products below the detection limit of the SEC-ATR-FTIR were identified using ion chromatography (IC). We report the formation of glycolate (H3C2O3-) and glyoxylate (HC2O3-) with trace amounts of oxalate (C2O42-), indicating that C-C coupling reactions proceed in these systems. Changes to the oxidation state of surface Cu were measured using X-ray photoelectron spectroscopy, which showed a reduction in Cu(0) and an increase in Cu(OH)2, indicating surface oxidation.

Integration of hydrothermal liquefaction of Cyanophyta and supercritical water oxidation of its aqueous phase products: Biocrude production and nutrient removal

Cyanophyta has the potential to produce biocrude via hydrothermal liquefaction (HTL). However, aqueous phase products (APs), as by-products of HTL, pose a risk of eutrophication for the high levels of carbon, nitrogen, and phosphorus. Supercritical water oxidation (SCWO) can efficiently convert organics into small molecules, offering a technique for the harmless treatment of APs. Effects of holding time, pressure, and moisture content on the biocrude yields from isothermal HTL (300 °C) and fast HTL (salt bath temperature of 500 °C) were comprehensively investigated. Biocrude properties were characterized by elemental analysis, FT-IR and GC–MS. Subsequently, the APs obtained under the conditions producing the highest biocrude yield were subjected to SCWO at 550 °C with different oxidation coefficients (n) from 0 to 2. Removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH3−N), and total phosphorus (TP) were further explored. The results show that the highest biocrude yields from isothermal HTL and fast HTL were 24.2 wt% (300 °C, 1800 s, 25 MPa, and 80 wt% moisture content) and 21.9 wt% (500 °C, 40 s, 25 MPa, and 80 wt% moisture content), respectively. The biocrude primarily consisted of N-containing heterocyclic compounds, amides, and acids. SCWO effectively degraded the COD and TP in APs, while the NH3-N required further degradation. At n = 2, the highest removal rates of COD, NH3-N and TP were 98.5 %, 22.6 % and 89.1 %, respectively.

Evaluation of the Fischer‐Tropsch synthesis product selectivity over iron‐based silica‐supported catalyst under mild temperatures

AbstractThe circular economy is considered a keystone of sustainable development, and its implementation requires analyzing both product and by‐products, as well as process waste. In this study Fischer‐Tropsch synthesis product selectivity over Fe/SiO2 catalyst was investigated in the reaction temperature range of 240 to 300°C. The composition of the gas, liquid hydrocarbon, and wax products is discussed alongside the aqueous phase, which is rarely addressed. It was found that 280°C is the optimal temperature for condensable hydrocarbon production over Fe/SiO2 catalyst. The increase in reaction temperature led to a decrease in the selectivity of 1‐olefins and alcohols in the liquid hydrocarbon phase and waxes, but at the same time contributed to an increase in the content of alcohols in the aqueous phase products.

Sewage sludge treatment via hydrothermal carbonization combined with supercritical water gasification: Fuel production and pollution degradation

Aqueous phase byproduct from hydrothermal carbonization of sludge (named AHT) has high COD and TOC, supercritical water gasification (SCWG)can efficiently convert AHT into rich-H2 syngas. This study investigated the effect of temperature on syngas production, elements distribution and pollutants decomposition during the HTC of sewage sludge and SCWG of AHT. Compared to traditional directly SCWG of sludge, the combined method could produce syngas with higher H2 proportion and lower gaseous sulfur concentration. The maximum H2 proportion and carbon conversion efficiency (CE) in syngas could reach 59% and 30.40%. Meanwhile, higher SCWG temperature can reduce the sulfur concentration of syngas. SCWG effectively reduce the COD and TOC in AHT. With HTC and SCWG temperature increased, the concentration of total nitrogen (TN) gradually decreased but NH4+ ions concentration (NH4+-N) increased in aqueous phase product.

An Ecological Toilet System Incorporated with a Hydrothermal Liquefaction Process

The harmless disposal and resource utilization of human feces is important to the sanitation process. Hydrothermal liquefaction (HTL) can convert toilet feces into bio-crude oil and reduce waste. In this study, an integrated eco-toilet system was developed by combining vacuum micro-flush toilets with a continuous hydrothermal liquefaction reactor. The system operated stably for over 10 h. This system can serve 300 households and save 2759 m3 of water per year compared to traditional flush toilets. The energy recovery from the feces was 2.87 times the energy consumed for the HTL process. The HTL bio-crude oil yield was 28 wt%, and the higher heat value (HHV) of the bio-crude was 36.1 MJ/kg. The biochemical compounds of the bio-crude oil consisted of acid ester, hydrocarbons, phenols, and a nitrogenous heterocyclic compound. The carbon in the human feces was mainly transferred to the bio-crude oil, while nitrogen was mainly transferred to the aqueous phase product. The post-HTL aqueous stream could be treated and used as fertilizer. This system achieves energy self-sufficiency, along with water and energy savings. This integrated eco-toilet effectively converts feces into bio-crude to realize waste reduction and resource utilization of human feces.

Molecular characteristics, sources and transformation of water-insoluble organic matter in cloud water

Studies have shown that water-insoluble organic matter (WIOM) accounts for a large part of the organic components in cloud water and significantly contributes to brown carbon. However, the molecular characteristics of WIOM in cloud droplets remain unclear, hampering the understanding of their climate effects. In this study, cloud water was collected at a remote mountain site in South China during the winter of 2020, and WIOM was separated by membrane filtration, extracted by methanol, and characterized using Fourier transform ion cyclotron resonance mass spectrometry coupled with an electrospray ionization source. A total of 697–1637 molecules were identified in WIOM. WIOM is characterized by lower oxidation states of carbon atoms (−1.10 ∼ −0.84 in WIOM vs. −0.58 ∼ −0.51 in water-soluble organic matter (WSOM) on average), higher carbon number (14.12–20.59 vs. 9.87–10.56) and lower unsaturation (double-bond equivalent 4.55–4.95 vs. 4.84–5.23) relative to WSOM. More abundant lipid-like compounds (12.2–41.9% in WIOM vs. <2% in WSOM) but less highly oxygenated compounds (<7% vs. 28.6–35.3%) exist in WIOM. More than 30% of WIOM molecules in cloud water are common with interstitial particles, implying that WIOM in cloud water may originate from aerosol activation and/or collision. Some unique molecules in WIOM in cloud water are identified as aqueous-phase oligomerization products, indicating the aqueous-phase formation of WIOM. Further analysis of the intermolecular relationship shows that WIOM has the potential to transform into WSOM by partitioning into the dissolved phase, oxidation and functionalization by heteroatom-containing groups, representing a previously unidentified pathway for WSOM formation in cloud water. The results provide new insights into the in-cloud chemistry, which would assist in the understanding of the aqueous formation and evolution of WIOM.

Phycocyanin to biocrude via the integration of isothermal/fast hydrothermal liquefaction and aqueous phase recirculation: Reaction products and process analyses

Aqueous phase (AP) recirculation is an efficient and economically feasible approach to handle the post wastewater from hydrothermal liquefaction (HTL). In this study, isothermal (300 °C, 30 min) and fast HTL (set-point temperature of 500 °C, 40 s) of phycocyanin with different mixing ratios (6:0, 4:2, 3:3, 2:4, 0:6) of water and AP products were conducted. The optimum mixing ratios which obtained the highest biocrude yield were further selected for multiple AP recirculation experiments and process analysis. The results show that with the optimum mixing ratio of 2:4, isothermal and fast HTL produced the highest biocrude yields (24.2 wt% and 30.0 wt%) after the 2nd and 1st recycles, respectively. Nitrogen heterocycles from Maillard reaction and amides from acylation reaction were the major compounds in biocrude and AP, which contributed to the biocrude generation and increased the nitrogen content of biocrude. COD and NH3-N contents in HTL wastewater increased while TP contents decreased with the consecutive recirculation of AP. With AP recirculation for three times, nearly half of the wastewater discharges could be avoided. Consequently, AP recirculation is a promising method to enhance the biocrude production and alleviate the environmental impacts of AP discharges.

Synergistic mechanism of enhanced biocrude production during hydrothermal co-liquefaction of biomass model components: A molecular dynamics simulation

Hydrothermal co-liquefaction is a desirable technology for biocrude production from various biomass feedstocks, however, the insight into the mechanism of chemical reactions between biomass model components remains a huge challenge. To address this challenge, a detailed synergistic mechanism between model components was proposed based on molecular dynamics simulations for hydrothermal liquefaction (HTL) of cellulose, hemicellulose, lignin, lipid, and their mixtures. During the HTL process, the generation of aqueous phase products from cellulose and hemicellulose, polycyclic aromatic hydrocarbons from lignin, as well as undepolymerized macromolecules and carbon deposits from lipid hindered biocrude production from each component. As expected, synergistic interactions occurred between model components and enhanced biocrude produced from each component at a relatively mild HTL condition. Impressively, synergistic interactions were related to the transmission of reactive –OH groups between different biomolecules with the assistance of H2O molecules at transcritical states. By considering the interactions, a new and more versatile biocrude yield prediction model was developed based on biochemical compositions of feedstocks and reaction temperature. This work will provide new insight into potential interactions between biomass components and give a theoretical basis for feedstock “designing” in HTL of biomass wastes.

Hydrothermal liquefaction of Fucus vesiculosus algae catalyzed by Hβ zeolite catalyst for Biocrude oil production

Low lipid content brown algae (Fucus vesiculosus) are considered an efficient biocrude oil source for their higher productivity rate, adaptation, and ease of cultivation. The hydrothermal liquefaction process can directly utilize algal biomass in the wet state. Hβ zeolite catalyst activity was tested for the hydrothermal liquefaction process of F. vesiculosus algal biomass. Maximum biocrude oil yield (27.6%) from the F. vesiculosus algae feedstock was obtained using catalyst amount of 15 wt%, residence time of 20 min, and temperature of 300 °C. The higher heating value (HHV) of the biocrude oil product was found to be 38.47 kJ/kg. Chemical compounds in the biocrude oil and aqueous phase products were detected using Gas Chromatography-Mass Spectroscopy (GC–MS) showing the main compounds to be ketones, and nitrogen-containing and heterocyclic compounds in biocrude oil, while oxygenated compounds prevail in the aqueous phase. Low amounts of amines and amides due to low protein content and of esters and hydrocarbons because of low lipids content were found in the F. vesiculosus algae feedstock. Biocrude oil energy efficiency was 45.68% compared to the biochar energy efficiency of 16.54%.

Water Significantly Changes the Ring-Cleavage Process During Aqueous Photooxidation of Toluene.

As a major constituent of aromatic compounds, toluene exists widely in environmental aqueous phases. This research investigated the aqueous-phase OH oxidation of toluene to determine how liquid water changes the radical chemistry of ring-cleavage pathways. Results show that ring-cleavage pathways through the C7 bicyclic peroxy radical (BPR) account for about 70% of total aqueous-phase oxidation pathways, which is similar to that in the gas-phase oxidation. However, detailed ring-cleavage pathways in the aqueous phase change significantly compared with those in the gas phase as shown by the decreased production of glyoxal and methylglyoxal and the enhanced production of formic acid and acetic acid as primary products, which can be attributed to the presence of liquid water. Water facilitates the formation of the BPR whose structure is different from that in the gas-phase oxidation and results in different ring-cleavage pathways through hydrogen-shift reactions. Furthermore, water helps the hydration of acyl radicals formed by the BPR to produce organic acids. With the suggested ring-cleavage mechanisms, a box model can simulate aqueous-phase product distributions better than that with the classical ring-cleavage mechanisms. Given the influence of water on reaction mechanisms, aqueous-phase oxidation of hydrophobic organic compounds may be more important than previously assumed.

Hydrothermal carbonization of simulated food waste for recovery of fatty acids and nutrients

We conducted Hydrothermal carbonization (HTC) of simulated food waste under different reaction conditions (180 to 220 °C, 15 and 30 min), with the aim of recovering both fatty acids from the hydrochar and nutrients from the aqueous-phase products. HTC of the simulated food waste produced hydrochar that retained up to 78% of the original fatty acids. These retained fatty acids were extracted from the hydrochar using ethanol, a food-grade solvent, and gave a net recovery of fatty acid of ∼ 50%. The HTC process partitioned more than 50 wt% of the phosphorus and around 38 wt% of the nitrogen into the aqueous-phase products. A reaction path consistent with decarboxylation predominated during HTC under all of the reaction conditions investigated. A path consistent with dehydration was also observed, but only for the more severe reaction conditions. This work illustrates the potential that HTC has for valorization of food waste.

A kinetic model for the hydrothermal liquefaction of microalgae, sewage sludge and pine wood with product characterisation of renewable crude

Hydrothermal liquefaction (HTL) of biomass is an emerging technology that is being developed to produce renewable crude oil in water at sub-critical conditions. Different feedstocks and reaction conditions result in different product fractions of renewable crude and co-products of solid, aqueous and gas phase products. Biomass considered as feedstocks for HTL include microalgae, sewage sludge and lignocelluloses. Each of these biomass sources contains varying amounts of lipid, carbohydrate, protein and lignin organic fractions as well as some inorganic components. To develop a bulk kinetic model to predict the yields of crude, solid, aqueous and gas phase products, HTL experiments were conducted at reaction temperatures of 250, 300 and 350 °C over reaction times of 0–60 min with Tetraselmis sp. microalgae, sewage sludge and Radiata pine. The crude was analysed via gas-chromatography mass-spectrometry to identify variations in the compounds in the crude produced from different types of biomass. The highest crude yield was produced from algae at up to 30%, followed by up to 25% from sludge and up to 10% from pine. A reaction temperature of 300 or 350 °C was preferable for maximum crude yield and increasing reaction time over 5 min was seen to cause minimum variation in crude yield for most cases. The variation in product distribution is strongly dependent on both the organic and inorganic content of the biomass feedstock. A unified bulk kinetic model for prediction of crude yield from a wide range of biomass was developed. Predictions showed up to 15% variation from measurements illustrating that further experimental data from HTL of a wider range of feedstocks are required to refine the model and build up model rigour.