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Levulinic acid (LA), a carboxylic acid with a keto-acid structure, has recently been gaining increasing attention as a promising biorefinery platform chemical due to its potential to be feasible and sustainable. This work focuses on using trioctylamine (TOA) to separate LA from an aqueous solution by liquid–liquid extraction. For that, binodal curves and tie lines were determined at T = (293.15, 313.15, and 333.15) K under atmospheric pressure. The slope of the determined tie lines demonstrates that higher extraction efficiencies are possible with higher acid concentrations. Furthermore, infrared spectroscopy (FT-IR) was applied to better understand the behavior of phase diagrams. This study detected the acid-extractant complex formation between (LA) and (TOA). Finally, the experimental data were successfully correlated with the NRTL model at all the measured temperatures. The obtained parameters were applied using a decanter model. [ABSTRACT FROM AUTHOR]

Abstract Wastewater containing methanesulfonic acid (MSA) mainly originates from the production process of metal detergent, which also contributes significantly to environmental pollution. This study investigates the extraction of MSA from wastewater using trioctylamine (TOA). A thorough investigation was carried out into the factors that affect extraction efficiency, such as the type of extractant, phase ratio (O/A), temperature, stirring speed, and extraction time. An extraction efficiency of 96.1% was achieved using TOA at 25 °C, 1400 r·min− 1, and an extraction time of 30 min. Various techniques including FT-IR, XPS, and high-resolution ESI-MS were employed to investigate the extraction mechanism. The results of different techniques revealed that the complexation between TOA and MSA occurred through ionic and hydrogen bonding interactions. Moreover, TOA was successfully regenerated through back-extraction with sodium hydroxide. The proposed extraction system is advantageous for eco-friendly engineering applications.

The efficient production of biobased organic acids is crucial to move to a more sustainable and eco-friendly economy, where muconic acid is gaining interest as a versatile platform chemical to produce industrial building blocks, including adipic acid and terephthalic acid. In this study, a Saccharomyces cerevisiae platform strain able to convert glucose and xylose into cis,cis-muconic acid was further engineered to eliminate C2 dependency, improve muconic acid tolerance, enhance production and growth performance, and substantially reduce the side production of the intermediate protocatechuic acid. This was achieved by reintroducing the PDC5 gene and overexpression of QDR3 genes. The improved strain was integrated in low-pH fed-batch fermentations at bioreactor scale with integrated in situ product recovery. By adding a biocompatible organic phase consisting of CYTOP 503 and canola oil to the process, a continuous extraction of muconic acid was achieved, resulting in significant alleviation of product inhibition. Through this, the muconic acid titer and peak productivity were improved by 300% and 185%, respectively, reaching 9.3 g/L and 0.100 g/L/h in the in situ product recovery process as compared to 3.1 g/L and 0.054 g/L/h in the control process without ISPR. [ABSTRACT FROM AUTHOR]

Succinic acid (SA) is a platform chemical for producing biofuel and other green chemicals. Fermentative SA production is a cost – effective and eco – friendly method, with quite a few downstream challenges. The recovery method of reactive extraction shows promise but faces toxicity issues with the diluent and extractant, especially concerning microorganisms in the fermentation broth. Hence, a non – toxic diluent and extractant, or less toxic combinations, are needed for efficient acid recovery. Hence, non – toxic diluents, groundnut oil and sesame oil, were evaluated. Based on the superior extraction efficiency (E%) achieved with groundnut oil, the study conducted reactive extraction of SA from the aqueous phase using tri-n-butyl phosphate (TBP) dissolved in groundnut oil. Using response surface methodology with central composite rotatable design, E% was maximized by optimizing independent variables, which were: initial SA concentration– 0.2525 mol L−1, TBP concentration in groundnut oil as the extractant– 50%, shaking time–4 h, pH– 3. These conditions resulted in a distribution coefficient of 0.951 and E% of 48.75%, which are closely aligned with the predicted values of 0.953 and 50.21%, respectively. Fourier Transform Infrared Spectroscopy analysis confirmed a 1:1 complex formation in the organic phase. The results provide insights into the efficient recovery of SA from the fermentation broth. Groundnut oil can be used as nontoxic diluent in succinic acid reactive extraction. CCD based RSM can be used to design the reactive extraction system. FTIR was used to analyze the interactions between the acid and extractant. [ABSTRACT FROM AUTHOR]

Glyceric acid (GA), a carboxylic group-containing diol, is obtained from bioresources via microbial processes. In this study, we aimed to develop a reactive extraction method to separate GA from aqueous solutions using 2-naphthaleneboronic acid (2NB) and tri-octyl methyl ammonium chloride (TOMAC). Different feed molar amounts of 2NB (0–25 µmol), TOMAC (0–500 µmol), and NaOH (0–250 µmol) were used for GA (2.5 µmol) separation. A combination of 25 µmol 2NB, 100 µmol TOMAC, and 25 µmol NaOH was determined to be optimal for GA separation, providing 66.8 ± 3.2% GA yield at pH 11. GA was extracted by 2NB and TOMAC in a coordinated manner. Moreover, effects of various carboxylic acids (acetic, lactic, succinic, malic, tartaric, and citric acids) on GA separation from aqueous solutions were investigated. Interestingly, no significant effect on GA yeild (60.3 ± 1.2–65.2 ± 2.5%) was observed regardless of the type of carboxylic acid. The optimized protocol was subsequently applied to separate GA from crude GA solution prepared by incubating glycerol with the cells of the acetic acid bacterium, Acetobacter tropicalis NBRC 16470. GA separation was achieved at a comparable level (yield: 70.6 ± 4.6% and purity: 76.1 ± 4.1%) as that achieved using a GA reagent. This study demonstrated the efficiency of the repeated use of the organic phase for GA separation, with no significant changes in GA yield. [ABSTRACT FROM AUTHOR]

This research endeavour primarily aimed to optimize and establish a model for the recovery of pravastatin, a well‐known statin drug recognized for its cholesterol‐lowering properties, from aqueous solutions using reactive extraction. This study used the Box–Behnken design to investigate extraction parameters and create a concise model equation illustrating the relationship between variables and responses. The investigation showed a strong agreement between the model equation and experimental outcomes. It highlighted a positive correlation, demonstrating that higher concentrations of reactant and pravastatin led to notable improvements in extraction efficiency. Two out of 90 experiments had extraction efficiencies below 10%, both with constant factors except for solvent type, while 14 experiments exceeding 80% efficiency highlighted the positive impact of a 50% reactant concentration on extraction efficiency. According to a statistical second‐order polynomial, the predicted extraction efficiency stands at 75.14%. In the culminating phase of the study, optimal extraction conditions were meticulously determined, resulting in the identification of an optimal set of parameters: a pravastatin concentration of 35 mg · L−1, an adogen concentration of 20.91% (v/v), and a butanol phase ratio of 0.2% (v/v). Under optimal conditions, the experimental extraction efficiency reached 72.69%, closely aligning with values predicted through numerical optimization employing response surface methodology. [ABSTRACT FROM AUTHOR]

Caffeic acid is a valuable product due to its wide-ranging utilities. Currently, caffeic acid can be produced via fermentation process using native or engineered microorganisms. The reactive extraction is a prominent technique that is used for the recovery of carboxylic acids. In this work, caffeic acid was recovered by an organophosphate (trioctylphosphine oxide) from its aqueous solution in the presence of different kinds of solvents namely 1-butanol, ethyl propionate, and ethyl methyl ketone. The values of reactive extraction parameters were optimised by Box–Behnken design. 98.19% The maximum extraction efficiency was obtained as 98.19% at the optimum conditions of 0.003 mol kg−1 caffeic acid concentration, 50% (v/v) trioctylphosphine oxide quantity, and 306.2 K in the presence of 1-butanol as the solvent. Our study is the first ever to examine the reactive extraction of caffeic acid, and therefore very important in modern scientific disciplines. [ABSTRACT FROM AUTHOR]

Syntheses of alternative platform chemicals, such as 5‐chloromethylfurfural (CMF), from bio‐based starting materials are often associated with complicated kinetic schemes and mass transfer processes. Millistructured flow reactor concepts can help to elucidate kinetic schemes and determine rate constants which are of crucial importance for the design of respective technical processes. For the first time, the influence of proton concentration on the rate constants involved in the biphasic synthesis of CMF is systematically investigated. Results are discussed in terms of green chemistry metrics. [ABSTRACT FROM AUTHOR]

BACKGROUND: Vanillic acid, an aromatic carboxylic acid and a derivative of vanillin, is used as an additive in consumer goods for its aroma. Previously, most vanillic acid was produced through a petrochemical route, but as a consequence of stringent environmental policies, it is now produced by the biotransformation of ferulic acid. Vanillic acid is also found in the wastewater streams of paper‐pulp industries and olive‐oil mills. So, recovering vanillic acid from fermentation broth, either during bioproduction or from a wastewater stream, while minimizing toxicity, is a difficult task. In order to reduce the toxicity substantially, bio‐based solvents such as sunflower, mustard and rice bran oils were employed as diluents along with tri‐n‐butyl phosphate (TBP) as extractant in order to recover vanillic acid by reactive extraction. RESULTS: The extraction performance was elucidated using terms such as distribution ratio, extraction efficiency, loading ratio and equilibrium complexation constant for different extractant–diluent combinations. The highest extraction efficiency and distribution ratio for the different solvents were in the following order: TBP + sunflower‐oil (72.02%–92.47%; 2.57–12.29) > TBP + rice bran‐oil (65.56%–90.55%; 1.90–9.58) > TBP + mustard‐oil(64.03%–89.87%; 1.78–8.87). The theoretical number of stages was determined as 4 to achieve a targeted extraction efficiency of 90%; these predictions were borne out experimentally. CONCLUSION: In this study, vanillic acid was recovered from the aqueous phase using tri‐n‐butyl phosphate in sustainable, environmentally friendly, bio‐based solvents such as rice bran oil, sunflower oil and mustard oil. © 2024 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an indispensable nutrient for agriculture. Recovery and recycling of phosphorus from waste streams is necessary to ensure a circular P economy and reduce dependence on disproportionately distributed mineral P resources. In this study, a new process called 'PULSE' is presented for the recovery of P from sewage sludge, which can handle high metal contents. The process involves drying of sludge prior to acidic leaching to overcome the challenge of solid–liquid separation at low pH and to reduce the overall material flows. Another key point of the process is the removal of metals using reactive extraction to obtain a high-quality product with good plant availability. Laboratory experiments were conducted to evaluate and select the best process options. A chemical equilibrium tool was developed to simulate the unit operations of the process for optimization. Dissolution of P from sludge depends on leaching pH and the fraction of inorganic P in the sludge. The maximum P leaching efficiency for the sludge used in the study was between 65 and 70%. Under the tested conditions, Fe, Cd, Cu, Hg, Pb, and Zn were successfully removed from the sludge leach liquor by reactive extraction. The recovered product has a nutrient mass fraction of about 51% that includes Ca, PO43-, Mg, and K. Pot trials confirmed that the agronomical efficiency of the product is comparable to that of triple superphosphate. [ABSTRACT FROM AUTHOR]

Muconic acid is a six-carbon dicarboxylic acid with conjugated double bonds that finds extensive use in the food (additive), chemical (production of adipic acid, monomer for functional resins and bio-plastics), and pharmaceutical sectors. The biosynthesis of muconic acid has been the subject of recent industrial and scientific attention. However, because of its low concentration in aqueous solutions and high purity requirement, downstream separation presents a significant problem. Artificial Neural Networks and Differential Evolution were used to optimize process parameters for the recovery of muconic acid from aqueous streams in a system with n-heptane as an organic diluent and ionic liquids as extractants. The system using 120 g/L tri-hexyl-tetra-decyl-phosphonium decanoate dissolved in n-heptane, pH of the aqueous phase 3, 20 min contact time, and 45 °C temperature assured a muconic acid extraction efficiency of 99,24 %. Low stripping efficiency compared to extraction efficiency was observed for the optimum conditions on the extraction step (120 g/L ionic liquids dissolved in heptane). However, re-extraction efficiencies obtained for the recycled organic phase in three consecutive stages were close to the first extraction stage. The mechanism analysis proved that the analysed phosphonium ionic liquids (PILSs) extracts only undissociated molecules of muconic acid through H-bonding.

The aim of this study was to extract vanillic acid from an aqueous solution through reactive extraction. Vanillic acid is utilized in the food and beverage industry as a flavoring agent. Tri-n-butyl phosphate (TBP) served as the reactive extractant, while natural oils like sesame oil and groundnut oil acted as diluents. The recovery of vanillic acid from fermentation broth or wastewater poses challenges due to toxicity concerns. However, employing natural solvents in the extraction process can significantly reduce toxicity. Various parameters, such as extraction efficiency, loading ratio, distribution coefficient, and equilibrium complexation constant, were determined to evaluate the extent of extraction achieved. Groundnut oil emerged as more effective than sesame oil as a diluent, exhibiting a maximum distribution coefficient of 13.31 and an extraction efficiency of 93.01 % at 5.27 mmol L–1 of acid concentration and 40 % v/v of TBP. Additionally, the number of theoretical stages required for the reactive extraction system was calculated, resulting in five stages for groundnut oil and four stages for sesame oil.

Carboxylic acids can be isolated from fermentation broths using reactive liquid-liquid extraction, offering an alternative to the environmentally harmful state-of-the-art process of precipitating calcium lactate. To enhance the sustainability of liquid-liquid extraction processes, greener solvents, such as natural deep eutectic solvents, are investigated. However, fermentation broths often exhibit pH values unsuitable for carboxylic acid extraction, which can be adjusted using mineral acids, though mineral acids may be co-extracted. In this study, we systematically examine the co-extraction of hydrochloric, nitric, sulfuric, and phosphoric acid during extraction and back-extraction of lactic acid. The solvent phase consisted of tri-n-octylamine, trioctylphosphine oxide, or tributyl phosphate diluted in a thymol-menthol deep eutectic solvent. The back-extraction was conducted using a diluent swing with p-cymene as the antisolvent and water as the receiving phase. Tri-n-octylamine showed the highest efficiency for lactic acid (up to 29.8%) but also the highest co-extraction of mineral acids (up to 50.9%). In contrast, trioctylphosphine oxide exhibited a lower but more selective lactic acid extraction (5.94%) with low mineral acids co-extraction (0.135%). Overall, the highest co-extraction was observed for phosphoric acid and the lowest for nitric acid. In conclusion, the selected solvent phase composition and mineral acid influence the co-extraction and, thus, final product purity. The successful application of the natural deep eutectic solvent as the modifier enhances the sustainability of liquid–liquid extraction processes. [ABSTRACT FROM AUTHOR]

Itaconic acid is a high-value organic acid that serves as a platform molecule in different industries. This research focuses on the separation of itaconic acid using reactive extraction as a sustainable and efficient method for acid recovery from fermentation broth. Itaconic acid was produced through fungal fermentation processes involving Aspergillus terreus ATCC® 32588™, obtaining a concentration of 47 g/L in the final broths. For the reactive extraction system, the organic phase included tri-n-octylamine as an extractant dissolved in dichloromethane or n-heptane and 1-octanol as a phase modifier. The effect of the main influencing factors (pH of the aqueous phase, extractant concentrations in the organic phase, and the addition of 1-octanol) on extraction efficiency was investigated. The highest extraction degree (97%) was achieved using an organic phase with tri-n-octylamine dissolved in dichloromethane and with 20% 1-octanol. Conversely, in the reactive extraction system with tri-n-octylamine dissolved in n-heptane and 20% 1-octanol, the extraction efficiency reached 67%. This finding suggests a promising separation system that is less toxic for microorganisms. The study results highlight the feasibility of employing reactive extraction systems for the direct separation of itaconic acid. [ABSTRACT FROM AUTHOR]

Due to high demands for the production of propionic from fermentation broth, the reactive extraction of the acid using green and non-toxic and microorganism-friendly diluent instead of toxic and harmful conventional organic solvents is considered in this work over the temperature range of 298–318 K. Soybean oil and rice bran oils which reduce the toxic effect of the used reactive extractant tri-octyl amine (TOA) are used as the diluents. The achieved overall distribution coefficient and extraction efficiency are found higher in soybean oil (0.73, 42.25%, respectively) as compared to rice bran oil (0.66, 40.00%, respectively). Due to the low cost and microorganism-friendly nature, soybean and rice bran oils are anticipated to use in bio-refinery industries to recover propionic acid from fermentation broth. The estimated K D chem / K D phy ratio greater than 1.0 shows that the extraction of the acid is dominated by the chemical extraction at the relatively higher initial concentration of TOA. The chemical reaction equilibrium constant, K E (m : n) , and complexation stoichiometries m and n are determined by applying differential evaluation (DE) technique. K E m : n is found higher in the case of soybean oil. Despite the loading ratio Z < 0.5, m is found greater than 1.0. The concentration of the complex [ H A m S n ] org is higher in soybean oil than rice bran oil. The negative enthalpy change due to the complexation reaction shows that it is exothermic. The positive entropy changes due to only mass transfer direct to supply external energy to mix the studied immiscible phases. [ABSTRACT FROM AUTHOR]

In the current scenario, where environmental degradation, global climate change, and the depletion of petroleum feedstock pose significant challenges, the chemical industry seeks sustainable alternatives for manufacturing chemicals, fuels, and bioplastics. Biorefining processes that integrate biomass conversion and microbial fermentation have emerged as preferred approaches to create value-added compounds. However, commercializing biorefinery products is hindered by dilute concentrations of final products and the demand for high purity goods. To address these challenges, effective separation and recovery procedures are essential to minimize costs and equipment size. This article proposes a biorefinery route for the production of protocatechuic acid (PCA) by focusing on in situ PCA separation and purification from fermentation broth. PCA is a significant phenolic molecule with numerous applications in the pharmaceutical sector for its anti-inflammatory, antiapoptotic, and antioxidant properties, as well as in the food, polymer, and other chemical industries. The chemical approach is predominantly used to produce PCA due to the cost-prohibitive nature of natural extraction techniques. Reactive extraction, a promising technique known for its enhanced extraction efficiency, is identified as a viable strategy for recovering carboxylic acids compared to conventional methods. The extraction of PCA has been explored using various solvents, including natural and conventional solvents, such as aminic and organophosphorous extractants, as well as the potential utilization of ionic liquids as green solvents. Additionally, back extraction techniques like temperature swing and diluent composition swing can be employed for reactive extraction product recovery, facilitating the regeneration of the extractant from the organic phase. By addressing the challenges associated with PCA production and usage, particularly through reactive extraction, this proposed biorefinery route aims to contribute to a more sustainable and environmentally friendly chemical industry. The incorporation of PCA in the biorefinery process allows for the utilization of this valuable compound with diverse industrial applications, thus providing an additional incentive for the development and optimization of efficient separation techniques. [ABSTRACT FROM AUTHOR]

In this work, the reactive extraction of butyric acid (BA) from very dilute aqueous solutions in effluent stream and fermentation broth by using tri-octyl amine (TOA) at different temperatures (298–318 K) in various diluents was investigated. To reduce the toxic effect of TOA and to avoid the harmful effect of decanol on the living microorganism in the bioreactor, nontoxic and green solvents, sunflower and soybean oils were tested as the diluents. The obtained K D dil was 2.8–4.2 for decanol, 2.0–4.0 for sunflower oil and 1.3–3.8 for soybean oil. The extraction capacity of the solvents was decreased in the order of decanol > sunflower oil > soybean oil. In chemical extraction, the extraction efficiencies were 85–92% for decanol, 81–91% for sunflower oil and 78–89% soybean oil. The experimentally determined K D overall was 4.8–9.5 for decanol, 4.6–8.8 for sunflower oil and 4.5–8.3 for soybean oil. In terms of distribution coefficient and extraction efficiency, decanol showed better recovery of BA than sunflower oil and soybean oil. Overall, the recovery efficiencies using both the edible oils were at per with decanol. Thus, edible oils are suggested to use in the biorefinery industries. The obtained K D chem / K D phy greater than 1.0 has justified the use of TOA as the reactive extractant. The order of the complex concentration, H A m S n org , in different diluents was decanol > sunflower oil > soybean oil. Other important parameters like acid extractant, free acid and dimer concentration at chemical equilibrium state were determined and analysed. The estimated enthalpy change due to mass transfer, Δ H masstr , showed the easiest mixing of the phases in soybean oil. Reaction equilibrium constant, ( K E (m : n) ), also followed the above trend of the effects of the diluents with highest for decanol (8.7–4347), intermediate for sunflower oil (6.6–3222) and lowest for soybean oil (5.5–2018). It also diminished with temperature. [ABSTRACT FROM AUTHOR]

The aim of this study was to extract vanillic acid from an aqueous solution through reactive extraction. Vanillic acid is utilized in the food and beverage industry as a flavoring agent. Tri-n-butyl phosphate (TBP) served as the reactive extractant, while natural oils like sesame oil and groundnut oil acted as diluents. The recovery of vanillic acid from fermentation broth or wastewater poses challenges due to toxicity concerns. However, employing natural solvents in the extraction process can significantly reduce toxicity. Various parameters, such as extraction efficiency, loading ratio, distribution coefficient, and equilibrium complexation constant, were determined to evaluate the extent of extraction achieved. Groundnut oil emerged as more effective than sesame oil as a diluent, exhibiting a maximum distribution coefficient of 13.31 and an extraction efficiency of 93.01 % at 5.27 mmol L-1 of acid concentration and 40 % v/v of TBP. Additionally, the number of theoretical stages required for the reactive extraction system was calculated, resulting in five stages for groundnut oil and four stages for sesame oil. [ABSTRACT FROM AUTHOR]

BACKGROUND: Owing to the continuous growth of petroleum prices over the last few decades, there has been a renaissance in interest in the large‐scale manufacturing of platform chemicals via the fermentation route. The present work emphasizes the extraction of itaconic acid from an aqueous solution by dissolving reactive tri‐n‐butyl phosphate (TBP) in natural, non‐toxic diluents such as sunflower oil, rice bran oil, and sesame oil. RESULTS: The experimental results were explained in terms of distribution coefficient (Ɗ), extraction efficiency (η%), equilibrium complexation constant (Ke), and loading ratio (ϕ). At the highest concentration of itaconic acid 0.250 mol L−1 and TBP 1.099 mol L−1, the maximum extraction efficiency and distribution coefficient for sunflower oil were obtained, at 88.72% and 7.94%, respectively. The diffusivity (DIA−S) of itaconic acid towards the interface of organic and aqueous phases was obtained as 1.11 × 10−6 cm2 s−1 with the Wilke–Chang equation and 4.40 × 10−7 cm2 s−1 using the Reddy–Doraiswamy relation. The lowest value of solvent‐to‐feed (S/F) proportion was estimated as 6.66, with the minimum number of stages required for counter‐current extraction being ~4. CONCLUSION: In reactive extraction of itaconic acid with TBP, the highest extraction efficiency and distribution coefficient was attained with sunflower oil, followed by rice bran oil and sesame oil. Higher concentrations of itaconic acid (0.250 mol L−1) and TBP (1.099 mol L−1) are suitable combinations for all the natural diluents. Diffusivity values revealed the extent of diffusion of itaconic acid in the solvent phase and strongly depended on the density and viscosity of the solvent. The experimental results could be utilized to design a continuous extraction column. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Protocatechuic acid (PCA) is typically produced by microbial fermentation. Its separation from fermentation broth or aqueous waste streams is of great importance. This study aimed to recover PCA by a secondary amine namely di-n-octylamine (DOA). Three organic solvents, namely isobutyl methyl ketone, propyl acetate and linalool, were used with DOA. Important extraction parameters were optimised by response surface methodology. DOA/isobutyl methyl ketone system showed 95.84% extraction efficiency under the optimum conditions. The maximum E% of the DOA/propyl acetate system was 86.73%. The maximum E% of the DOA/linalool system was 81.71%. Additionally, a thermodynamic study was carried out, and the reactions were endothermic. [ABSTRACT FROM AUTHOR]

Crude vegetable oils contain considerable amounts of free fatty acids, and they ought to be minimized for use in food and non-food applications. Conventional deacidification adopts alkali neutralization for the removal of free fatty acids. Here, a novel method for the removal of free fatty acids from jatropha oil by reactive extraction using monoethanolamine in methanol is proposed. Extraction studies with initial free fatty acids concentration (0.1–0.5 kmol/m3) using monoethanolamine (0.4141–1.6568 kmol/m3) in methanol at 303–333 K were performed and investigated. Extraction parameters like distribution coefficient and equilibrium complexation constant loading ratio for free fatty acids extraction were obtained. Central composite design identified monoethanolamine composition and temperature as significant. The findings of this study revealed that reactive extraction of free fatty acids using monoethanolamine in methanol was highly successful in reduction of the free fatty acids in jatropha oil. The optimum extraction was attained at monoethanolamine concentration of 2.05011 kmol/m3 at 293.5 K. A quadratic response surface model exhibited good agreement with the experimental results. Further biodiesel was prepared using the deacidified oil, and the specifications obtained were well within the standard ASTM limits. Reactive extraction of free fatty acids is investigated in this work for the first time. The method demonstrated in this study can be of considerable interest to the biodiesel industry with regard to pre-treatment methodologies. [ABSTRACT FROM AUTHOR]

Protocatechuic acid (PCA) is a carboxylic acid of great interest since it has several pharmaceutical properties. PCA is either obtained by microbial fermentation or recovered from waste streams of food processing industries. In this study, PCA was separated from its aqueous solutions by a reactive extractant trioctylphosphine oxide (TOPO). Isobutanol, propyl acetate, and ethyl methyl ketone were used with TOPO in the organic phase. The operating parameters have been optimized by Box–Behnken design of response surface methodology. The maximum extraction efficiency of TOPO/isobutanol system was 98.91% under optimum conditions (0.02 mol kg−1 PCA concentration, 50% v/v TOPO amount, and 298.2 K temperature). The maximum extraction efficiency of TOPO/ethyl methyl ketone system was 91.09% under optimum conditions (0.028 mol kg−1 PCA concentration, 50% v/v TOPO amount, and 312.2 K temperature). The maximum extraction efficiency of TOPO/propyl acetate system was 99.05% under optimum condition (0.029 mol kg−1 PCA concentration, 48.51% v/v TOPO amount, and 301.2 K temperature). Lastly, a thermodynamic study has been carried out to reveal the insight mechanism of the reactive extraction processes examined, and the reactions were found to be exothermic in nature. [ABSTRACT FROM AUTHOR]

p-hydroxybenzoic acid (p-HBA) remains present in various industrial effluents, it has various industrial applications and excellent medicinal properties, on the contrary, it degrades the fertility of soil if discharged in atmosphere hence, retrieval of p-HBA from effluent is a mandate. In past decades, reactive extraction has arisen as an efficient and attractive separation technique. Therefore, in the present study, the reactive extraction of p-HBA, using Tri-n-octylamine diluted in toluene, petroleum ether, and methyl isobutyl ketone, has been investigated. The results have been reported in terms of efficiency, distribution coefficient, equilibrium complexation constant, and loading ratio. The order of diluents, with respect to extraction given, is MIBK (93.43%) > toluene (92.57%)> petroleum ether (91.43%). The relative basicity model is used to for the interpretation and is found suitable for explaining the results. The diffusion coefficient was also found using Reddy Doraiswamy equation and Wilke Chang equation. Further, minimum number of stages of counter current extraction column and solvent to feed ratio were also calculated to investigate the feasibility of the process. [ABSTRACT FROM AUTHOR]

Due to its potential use in the production of new functional resins, bio-plastics, food additives, agrochemicals, and pharmaceuticals, muconic acid (MA), a high value-added bio-product with reactive dicarboxylic groups and conjugated double bonds, has attracted growing interest. Adipic acid, terephthalic acid, and trimellitic acid are examples of bulk compounds that can be produced using MA that are of high commercial importance. The development of biotechnological approaches for MA production has advanced greatly recently. The current analysis offers a thorough and organized summary of recent developments and difficulties in the extraction of MA. A variety of extractants are presented, along with any limitations and potential solutions. Finally, the possibilities for this field in light of its state, difficulties, and tendencies are explored. [ABSTRACT FROM AUTHOR]

The present study focuses on the isolation of acetic and lactic acid from a fermentation broth produced by heterofermentative microorganisms using glucose and xylose as substrate. Especially xylose fermentation to lactic acid leads to unwanted by-product formation of acetic acid. Reactive liquid-liquid extraction is an energy-efficient downstream process, where the use of green solvents such as d-limonene opens the way to a more sustainable production. To find the optimum solvent/reactive extractant pairing, the reactive extractants trioctylamine, trioctylphosphine oxide, Aliquat 336, and tributyl phosphate were used diluted in 1-octanol, 1-decanol, d-limonene or a deep eutectic solvent. The phosphine-based extractants proved to be most effective for both acids. In the first extraction step, 19% of acetic acid and only 3% of lactic acid are extracted with trioctylphosphine oxide/1-octanol when the xylose feed is used without pH adjustment. The pKa value of the acids is responsible for the difference in extraction efficiency leading to the proposal of a two-step extraction separating first acetic acid and after pH adjustment, lactic acid can be extracted. The combination of trioctylphosphine oxide diluted in d-limonene leads to a surprisingly high selectivity for lactic acid isolation in the second extraction step. The present study shows for the first time that green solvents lead to similar extraction efficiencies compared to conventional solvents such as 1-octanol. For back extraction n-heptane and p-cymene are used as disintegration agents and water as stripping phase; n-heptane results in a lactic acid back extraction efficiency of up to 82% and p-cymene up to 70%. This shows that also for the back extraction p-cymene as a green disintegration agent leads to similar results as fossil-based n-heptane.

Reactive extraction of succinic acid by tertiary amines is an effective separation technique. Its potential application for the initial recovery of bio-based succinic acid from fermentation broth. However, the co-extraction of inorganic anions significantly impairs the extraction performance. In this study, we use a statistically backed design of experiments method (DoE) to screen and identify the factors with a significant effect and relevant impact on extraction yield and selectivity. Eight operational factors (Extractant, solvent, succinic acid concentration, amine concentration, initial pH, the type of anion, electrolyte concentration, and temperature) were screened by applying an orthogonal design plan for the experiments. The choice of the extractant and diluent as well as the type of anion had the most significant effect on the extraction yield. In contrast, the selectivity was mainly affected by the concentration ratios of succinic acid and electrolyte. The screening plan reduced the number of experiments from 1728 possible combinations to 72 experiments required to identify the factors while maintaining the significance of the identified effects. We suggest competing mass-action relationships between the pH-dependent protonation of amines and the complexation of succinic acid to explain the observed trends. [ABSTRACT FROM AUTHOR]

This study investigated the usability of different vegetable oils as solvents for separating citric, malic, and glycolic acids from aqueous solutions by reactive extraction method. A machine learning model was developed to predict intermediate values from the dataset created using the experimental results using multiple linear regression (MLR) and extreme gradient boosting (XGB). We used sunflower oil, corn oil, linseed oil, sweet almond oil, sesame oil, and castor oil in six types of vegetable oil. Trioctylamine (TOA) was used as an extractant in reactive extraction studies. The results obtained showed that approximately 99% of acids can be separated from their aqueous solutions when suitable mixtures of organic phases are used. Based on the results, we discovered that the XGB method outperforms the MLR method for each dataset. Thanks to the high-performance prediction model developed, it was possible to reach higher separation efficiencies by determining the optimum experimental conditions. In addition, the costs and wastes associated with experiments decreased due to the developed high-performance estimation model. The reactive extraction estimation model was publicly available on GitHub and open to other researchers. [ABSTRACT FROM AUTHOR]

In this study, the separation of lactic acid from aqueous solutions using trioctylamine (TOA) reactant and environmentally friendly solvents such as sunflower and rice bran oil was investigated, and it was aimed to contribute to the separation of lactic acid by reactive extraction. It is aimed to determine the most suitable reactant / solvent ratios with reactive extraction analyzes. As a result of the studies, the highest efficiency (72,91%) was achieved with the TOA reactant. An increase in yield occurred as a result of using both sunflower oil and rice bran oil (1:1) together. According to the results of the research, it was determined that the addition of TOA to the organic phase increases the extraction efficiency in the recovery of carboxylic acids from aqueous solutions. While the physical extraction yield was 11.85%, the yield increased up to 72,91% in reactive extraction. An increase in yield was observed about 7 times. As a result of the data obtained, it was understood that with the increase in the extractant concentration, the dispersion coefficient (from 0,13 to 2,69) increased, and the loading factor (from 1,79 to 0,69) values decreased. When the organic phase mixtures formed with the extractant and diluent combinations were examined, it was determined that the best results in terms of extraction efficiency were obtained when 3,62 M TOA for lactic acid was used.

Glabridin is the active ingredient in Glycyrrhiza glabra , which is widely used in medicine and cosmetics. A ternary solvent extraction system containing a water-soluble β-cyclodextrin (β-CD) derivative was explored for selective extraction of glabridin. The effects of the extraction solvent type and ratio, β-CD derivatives type and concentration, crude extract concentration, and temperature on the distribution behavior were investigated to determine the optimal extraction system, which consisted of a 0.1 mol/L sulfobutylether-β-cyclodextrin (SBE-β-CD) aqueous phase and an n-octanol: n-hexane (50:50, V: V) organic phase. SBE-β-CD showed the strongest encapsulation ability toward glabridin among the tested β-CD derivatives. Multi-stage centrifugal fractional extraction under the ideal extraction conditions was used to continuously and specifically separate glabridin from the Glycyrrhiza glabra crude extract. The yield and purity of glabridin reached 97% and 95%, respectively. This technique, combining the SBE-β-CD extractant and fractional extraction, provides an effective, high yield, high purity, eco-friendly and low-cost method to separate glabridin from the crude extract. [Display omitted] • SBE-β-CD for selective extraction of glabridin from organic phase to aqueous phase. • A ternary solvent system constructed for suitable distribution ratio and large output. • Combination of fractional extraction and reactive extraction by SBE-β-CD. • Selective separation of glabridin was achieved with yield of 97% and purity of 95%. [ABSTRACT FROM AUTHOR]

The growing demand for producing organic acids by fermentative techniques has increased the significance of separating carboxylic acids from their fermentation broth with the reactive extraction process. Considering the environmental impacts, deep eutectic solvents can be considered as a potential green alternative for the replacement of volatile organic solvents commonly used in the extraction process. In this study, a new type of green solvent named hydrophobic deep eutectic solvent (HDES) based on decanoic acid as a hydrogen bond acceptor and menthol as a hydrogen bond donor was utilized for the reactive extraction of formic, acetic, and propionic acids from their aqueous solutions. The effect of initial acid concentration, HDES molar ratio, and tri-n-octyl amine (TOA) concentration on extraction efficiency was investigated. Modeling of the reactive extraction process was performed via a response surface methodology with a central composite design. Herein, the effect of the parameters of TOA concentration, HDES molar ratio, and initial acid concentration on the distribution coefficient was investigated. According to the results, it was reported that the most effective parameter on the extraction efficiency (%E) was the amount of extractant. The results of the experimental studies showed that the highest separation efficiency was obtained for 5% initial concentrations of formic, acetic, and propionic acids by using a mixture of 0.5 HDES molar ratio solvent and 1.9 mol/L TOA. The extraction efficiencies of these acids were found to be 88.71, 92.52, and 95.90 with ±0.1 standard deviation, respectively. [ABSTRACT FROM AUTHOR]

Carboxylic acids can be isolated from fermentation broths using reactive liquid-liquid extraction, offering an alternative to the environmentally harmful state-of-the-art process of precipitating calcium lactate. To enhance the sustainability of liquid-liquid extraction processes, greener solvents, such as natural deep eutectic solvents, are investigated. However, fermentation broths often exhibit pH values unsuitable for carboxylic acid extraction, which can be adjusted using mineral acids, though mineral acids may be co-extracted. In this study, we systematically examine the co-extraction of hydrochloric, nitric, sulfuric, and phosphoric acid during extraction and back-extraction of lactic acid. The solvent phase consisted of tri-n-octylamine, trioctylphosphine oxide, or tributyl phosphate diluted in a thymol-menthol deep eutectic solvent. The back-extraction was conducted using a diluent swing with p-cymene as the antisolvent and water as the receiving phase. Tri-n-octylamine showed the highest efficiency for lactic acid (up to 29.8%) but also the highest co-extraction of mineral acids (up to 50.9%). In contrast, trioctylphosphine oxide exhibited a lower but more selective lactic acid extraction (5.94%) with low mineral acids co-extraction (0.135%). Overall, the highest co-extraction was observed for phosphoric acid and the lowest for nitric acid. In conclusion, the selected solvent phase composition and mineral acid influence the co-extraction and, thus, final product purity. The successful application of the natural deep eutectic solvent as the modifier enhances the sustainability of liquid–liquid extraction processes.

In this work, extraction of valeric acid (VA) using tri‐n‐butyl phosphate (TBP) as a reactive extractant was carried out. To reduce the toxic effects of the conventional diluents on microorganisms, non‐toxic and green edible sunflower and soybean oils were tried as the diluents. The high values of the distribution coefficient and extraction efficiency advocated to use them in the bio‐refinery industries. Moreover, it shows intensification of the recovery of VA using reactive extraction process. Sunflower oil appeared to be a better diluent than soybean oil. The complexation reaction stoichiometry (m and n) and equilibrium complexation reaction constant KEm:n were estimated by using the differential evolution technique. In spite of the loading ratio being less than 0.5, the estimated m/n was found to be more than 1.0. The higher values of KEm:n occurred due to the 9higher stability of the VA‐TBP complex in sunflower oil than in soybean oil. The stoichiometry of VA decreased with increasing TBP concentration. The complex concentration, HAmSnorg, was found to be higher for soybean oil. It increased with temperature and initial VA concentration but remained invariant with TBP concentration. Due to the decreasing trend of KEm:n with temperature, the complexation reaction became exothermic. The enthalpy changes due to mass transfer stipulated easier mixing of the phases in sunflower oil than in soybean oil. [ABSTRACT FROM AUTHOR]

Levulinic acid is a carboxylic acid present in industrial downstream. It is an important chemical and can be transformed into various important chemicals such as 1,4-pentanediol, aminolevulinic acid, succinic acid, gamma valarolactone, hydoxyvaleric acid, and diphenolic acid. It is considered one of the top ten most important building block chemicals and bio-derived acids. Levulinic acid can be directly produced using biomass, chemical synthesis, and fermentation processes at industrial and laboratory scales. The biomass process produces the char, whereas the fermentation process generates waste during the production of levulinic acid, leading to an increase in the production cost and waste streams. The separation of levulinic acid from the waste is expensive and challenging. In the present study, reactive extraction was employed using trioctylamine in i-octanol for the separation of levulinic acid. The experimental results were expressed in terms of performance parameters like distribution coefficient (0.099–6.14), extraction efficiency (9–86%), loading ratio (0.09–0.7), and equilibrium complexation constant (11.34–1.05). The mass action law model was also applied and found the predicted values were in close agreement with the experimental results. The mixer settler extraction in series was used to achieve more than 98% separations of acid. Furthermore, the conceptual approach for separation of levulinic acid using a mixer settler reactor scheme was discussed and presented various design parameters including extraction efficiency, diffusion coefficient, equilibrium complexation constant, and loading ratio. The study is helpful in recovering the valuable chemicals present in industrial downstream and reducing their environmental impacts if any. [ABSTRACT FROM AUTHOR]

Resource-efficient separation processes are a vital technology for the success of renewable chemicals. Electrochemical pH swing separation has the potential to overcome the unsustainable consumption of acid and base and eventual salt-waste production, which was found a major hurdle in the industrialization of bio-succinic acid production. It furthermore enables the in situ product recovery by reactive extraction and the recycling of an alkaline stream into the fermentation for pH control. A dynamic model of a bio-succinic acid fermentation and electrochemical recovery process is developed. The fermentation is fed with waste glycerol and carbon dioxide, the co-products of biodiesel and bioethanol plants, respectively. Succinic acid is separated by an electrochemically induced pH shift reactive extraction. The model-based investigation of this electrochemical extraction apparatus analyzes kinetic phenomena, operative boundaries, and sensitivities towards changes in the cell geometry. The potential for closed-loop operation of bio-succinic acid fermentation and electrochemical pH swing extraction for product recovery and base regeneration is examined. In contrast to a sequential operation of fermentation and extraction, the in situ product removal of succinic acid allows for utilization of feedstocks with substrate concentrations of up to 99 wt% without the need for an additional diluting water feed. The concentrated feedstock and the electrochemical in situ separation of succinic acid cause a rise in downstream process yield by 26.2% and process productivity by 35.6%. The consumption of pH control agent is reduced by 88.7% compared to the sequential operation. [Display omitted] • Electrochemical pH swing extraction of succinic acid enables in situ product removal. • Mitigation of fresh water consumption by closed loop operation. • Reduction of pH control agents by electrochemical separation. • Identification of operational boundaries by dynamic process modeling. • Definition of key performance and design indicators for bio-electrochemical downstream processes. [ABSTRACT FROM AUTHOR]

The aim of present study is to model and optimize gallic acid (GA) reactive extraction from aqueous solution with trioctylamine (TOA) dissolved in the biocompatible mixture of oleyl alcohol, a modifier and dodecane, an inert diluent using a statistical modeling approach, response surface methodology (RSM) with rotatable central composite design, and artificial neural network (ANN). The optimal values of input parameters for maximum extraction (86%) of GA are found as follows: (i) initial GA concentration ( C ‾ A , o = 0.387 mol/L); (ii) temperature, T = 26.5°C; (iii) initial TOA concentration ( C H G , o = 0.049 mol/L); (iv) modifier volume, V = 70% at 101.325 kPa pressure. Predicted responses in terms of extraction degree using RSM and ANN are found to be very close to experimental values. The overall apparent equilibrium constants (KE = 37.24 and 22.38) and stoichiometry of reaction between acid and extractant (m =1.25 and 1.16) are determined considering negligible and 50% physical extraction, respectively. Individual equilibrium constants ( K 11 and K 21 ) for 1:1 and 2:1 GA:TOA complexes and their concentrations, C11 and C21, respectively, are calculated. Differential evolution approach, a bio-inspired algorithm, is used to investigate the insights of extraction mechanism at the optimum conditions. [ABSTRACT FROM AUTHOR]

BACKGROUND: Levulinic acid is one of the top ten bio‐derived platform chemicals essential for producing many products that are used daily. The recovery of biobased chemicals from industrial streams and fermentation broths is critical due to environmental issues. A few studies have used chemical solvents for the recovery of levulinic acid, but these solvents are toxic for microorganisms. Therefore, green and cheap solvents for the separation of levulinic acid are needed. This study used sunflower oil as a green solvent with trioctylamine and tri‐n‐butyl phosphate for the separation of levulinic acid. The experimental study was presented in the form of important parameters, viz., distribution constant, loading ratio, extraction equilibrium constant, diffusion coefficient, and extraction efficiency. Fourier transform infrared spectroscopy (FTIR) was employed to understand the acid and extractant interactions and 1:1 complex formation was confirmed in organic phase. RESULTS: The experimental results include the distribution coefficients (0.14–0.81 and 0.23–2.15), loading ratios (0.013–0.709 and 0.023–0.53), extraction efficiencies (12.43–44.68% and 19–68.30%), and extraction equilibrium constants (0.47–1.63) with trioctylamine and tri‐n‐butyl phosphate, respectively. Since a single‐stage does not provide sufficient extraction efficiency, multi‐stage extraction was performed. The multistage design shows that trioctylamine and tri‐n‐butyl phosphate must be used in three and five stages, respectively, to get 94.8% and 97% recovery of levulinic acid. CONCLUSION: This study describes the recovery of levulinic acid from the aqueous phase using trioctylamine and tri‐n‐butyl phosphate with sunflower oil as a sustainable green solvent. The multistage design setup provided approximately 100% recovery of levulinic acid. [ABSTRACT FROM AUTHOR]

Gallic acid (GA) is a naturally occurring phenolic acid that can be found in the leaves, roots, flowers, or stems of a wide variety of plant species. It has a broad range of uses in the food and pharmaceutical industries. The objective of this research is to investigate the GA reactive extraction process employing dichloromethane and n-heptane as solvents, 1-octanol as a phase-modifier, and Amberlite LA-2 as an amine extractant dissolved in the organic phase. The separation yield and distribution coefficient data were discussed, along with the analysis of the extraction conditions and the extraction mechanism. Dichloromethane employed as the solvent, 80 g/L Amberlite LA2 used as the extractant, and 10% phase modifier were determined to be the ideal conditions for the reactive extraction onto a biphasic organic-aqueous system. Statistical regression and artificial neural networks (ANNs) established with the differential evolution (DE) algorithm were also used to model and optimize the process. [ABSTRACT FROM AUTHOR]

The separation of levulinic acid from aqueous solutions is costly and non-ecofriendly in many cases. The major concerns are the low concentration of levulinic acid in fermentation broths and industrial downstreams. In this study, reactive extraction of levulinic acid from aqueous phase is proposed and its efficacy was investigated. Various extractants viz. tri-n-butyl phosphate, trioctylamine, and trioctylmethylammonium chloride along with i-octanol as a diluent were used. The extent of separation was investigated and various performance parameters like extraction efficiency, distribution coefficient, equilibrium complexation constant, and loading ratio were estimated. The number of transfer units, diffusivity, and mass transfer considerations were also discussed in the reactive separation system. Finally, the conceptual method was provided for the separation of levulinic acid using efficient reactive separation.

Due to its potential use in the production of new functional resins, bio-plastics, food additives, agrochemicals, and pharmaceuticals, muconic acid (MA), a high value-added bio-product with reactive dicarboxylic groups and conjugated double bonds, has attracted growing interest. Adipic acid, terephthalic acid, and trimellitic acid are examples of bulk compounds that can be produced using MA that are of high commercial importance. The development of biotechnological approaches for MA production has advanced greatly recently. The current analysis offers a thorough and organized summary of recent developments and difficulties in the extraction of MA. A variety of extractants are presented, along with any limitations and potential solutions. Finally, the possibilities for this field in light of its state, difficulties, and tendencies are explored.

Mandelic acid is a valuable chemical that is commonly used in the synthesis of various drugs, in antibacterial products, and as a skin care agent in cosmetics. As it is an important chemical, various methods are used to synthesize and extract this compound. However, the yields of the used processes is not significant. A dilute aqueous solution is obtained when using several production methods, such as a fermentation, etc. In this study, the reactive extraction of mandelic acid from aqueous solutions using tri-n-octylamine extractant at 298.15 K was investigated. Dimethyl phthalate (DMP), methyl isobutyl ketone (MIBK), 2-octanone, 1-octanol, n-pentane, octyl acetate, and toluene were used as diluents. The batch extraction results of the mandelic acid experiments were obtained for the development of a process design. Calculations of the loading factor (Z), distribution coefficient (D), and extraction efficiency (E%) were based on the experimental data. The highest separation yield was obtained as 98.13% for 0.458 mol.L−1 of tri-n-octylamine concentration in DMP. The overall extraction constants were analyzed for the complex of acid-amine by the Bizek approach, including K11, K12, and K23. [ABSTRACT FROM AUTHOR]

Glabridin has important bioactivities in anti-cellular aging, anti-atherosclerosis, protecting the nervous system and inhibiting melanin. There is currently no efficient separation method for the large-scale production of high-purity glabridin due to its insolubility in water. This paper presents hydrophilic β-cyclodextrin derivatives for the reactive extraction of hydrophobic glabridin from organic phase to aqueous phase in a quaternary solvent extraction system. The variables that affect extraction efficiency were studied, including solvent type, extractant type and concentration, extraction time and temperature. The optimal extraction conditions were achieved, involving extractant of SBE-β-CD, water-ethanol (5:5, v:v)/n-octanol-n-hexane (3:7, v-v) as extraction system and temperature of 5 degree. The results show that SBE-β-CD has a strong inclusion capacity for glabridin with inclusion constants of 85.95 L/mol. The reactive extraction reaches equilibrium in five minutes, which is convinced to fractional extraction. It is a promising method for the large-scale selective separation of high-purity glabridin from crude extract of Glycyrrhiza glabra. • A quaternary solvent extraction system was explored to separate glabridin. • SBE-β-CD was used as extractant for reactive extraction of hydrophobic glabridin. • The extractant SBE-β-CD is safe and environmentally friendly. • Short reaction equilibrium time, and the technology has broad application prospects. [ABSTRACT FROM AUTHOR]

Gingerol and shogaol are two bioactive compounds of ginger which exhibit several positive effects on human health. The conventional method for shogaol preparation is considered ineffective because it causes losses to the environmental system, and the efficiency of the process is low. Reactive extraction with subcritical water is a method that is considered environmentally friendly for the separation of slightly polar components without using organic solvents. The advantage of the reactive extraction process with subcritical water is that it does not require a catalyst because the process is able to form hydronium ions which can act as a catalyst to convert shogaol into gingerol. The effect of time and temperature on the yields of subcritical water reactive extraction of gingerol and shogaol were investigated in the present work. Experiments were carried out at a fixed pressure of 2 bar, and a varied temperature of reactive extraction from 130 to 140°C. Ginger and shogaol contents were analysed from the samples every 10 min. The chemical profiling of the resulting ginger extracts was performed using HPLC-MS. Results showed that the best subcritical water process was at 2 bar, 130°C, and 20 min; shogaol concentration increased to 15.345%, and gingerol to 5.113%. For the reactive extraction time of longer than 20 min, the shogaol concentration of the extract decreased. When temperature was above 120°C, and water hydrogen bonds weakened, thus resulting in high amounts of ionisation products of subcritical water. [ABSTRACT FROM AUTHOR]