Acid In Subcritical Water Research Articles

Efficient and green production of manno-oligosaccharides from Gleditsia microphylla galactomannans using CO2 and solid acid in subcritical water

This study aimed to produce manno-oligosaccharides (MOS) from Gleditsia microphylla galactomannans (GMG) using CO2 and solid acid (Amberlyst-35) in subcritical water. The optimal condition for MOS preparation was 3 MPa CO2, 0.1 g/g solid acid (relative to GMG) at 150 °C for 40 min. The maximum MOS yield with a degree of polymerization from 2 to 4 (M2-M4) was 52.19%, which doubled the yield of MOS compared to either using solely CO2 or solid acid. Solid acid showed excellent performance in producing MOS under subcritical H2O–CO2 condition, due to the enhanced mass transfer efficiency and increased H+ concentration in the reaction system. The solid acid can be easily separated and reused. Comparing with traditional methods used to produce MOS, this approach has many merits such as higher galactomannan hydrolysis efficiency (largely reduced time and higher MOS yield), purer M2-M4 product, lower costs, and more environmental-friendly.

Microwave-assisted Degradation of Poultry Feather to Synthesize Protein-based Surfactant

Poultry feather is hydrolyzed into peptides and amino acids in sub-critical water without any acid or alkali as catalyst under microwave-assisted heating to produce protein-based surfactant. The optimal hydrolysis condition is as follows: temperature 200 °C, time 60 min, and the yield of peptides and amino acids 84.31%. The critical micelle concentration (CMC) and surface tension of the product of peptides and amino acids are 2.6 g/L and 48.2 mN/m. In order to increase lipophilicity, subsequently anionic protein-based surfactant was synthesized by acylation reaction between the hydrolysis product of peptides and amino acidsand oleoyl chloride. The CMC and surface tension decreased greatly with linkage with oleoyl. The synthesized anionic surfactant with weight ratios of 10% (wt.%) hydrolysis liquid/oleoyl chloride of 3:1, 4.5:1 and 6:1 are 0.5, 0.7 and 0.8 g/L and corresponding surface tension are 30.1, 34.0 and 35.7mN/m.

Deactivation and regeneration studies of activated carbon during continuous decarboxylation of oleic acid in subcritical water

Decarboxylation of fatty acids using sub or supercritical water is a renewable pathway for producing fuel range hydrocarbons with high selectivity without an added external source of H2. Activated carbon (AC) has been shown as an effective catalyst for decarboxylation of fatty acids to fuels but it has limited life and an unknown surface chemistry for this catalysis. This study investigates the stability (time on stream) and surface chemistry of AC for the decarboxylation of oleic acid in a bench scale continuous reactor system at 400 °C, 2 h of space time and water to oleic acid ratio of 4:1. AC was found to be effective until 30 h time on stream (out of 45 h), providing 91% degree of decarboxylation constantly. The degree of decarboxylation declined afterwards, dropping from 91 to 50% after 45 h time on stream due to deactivation. The thermal regeneration of deactivated AC was examined using potassium hydroxide (KOH) treatment at 750 °C which helped to regain the physical and catalytic properties of AC. The degree of decarboxylation of oleic acid using fresh and regenerated AC were 91% and 87%, respectively. On the other hand, the selectivity of heptadecane obtained using fresh and regenerated activated carbon was 89.3% and 81.2%, respectively. Decarboxylated liquid products using fresh and regenerated activated carbon gave a similar density and HHV’s as commercial fuels, showing the utility of this approach.

Synthesis of glycyrrhetinic acid monoglycoside by hydrolysis of glycyrrhizic acid in subcritical water

A method for the synthesis of glycyrrhetinic acid monoglycoside by hydrolysis of glycyrrhizic acid in subcritical water at temperatures ranging between 100 and 300°C is under development. The maximum yield of the target product is achieved at 160°C.

Study of an Acid-Free Technique for the Preparation of Glycyrrhetinic Acid from Ammonium Glycyrrhizinate in Subcritical Water

The aim of this work was to study an application of a previously developed expedient acid-free technique for the preparation of glycyrrhetinic acid from ammonium glycyrrhizinate that requires no use of acids and toxic organic solvents. Subcritical water that serves as a reactant and a solvent was used in order to obtain glycyrrhetinic acid in good yields starting from ammonium glycyrrhizinate. It has been shown that variation of only one parameter of the process (temperature) allows alteration to thecomposition of the hydrolysis products. A new method was used for the synthesis of glycyrrhetinic acid (glycyrrhizic acid aglycone) and its monoglycoside. HPLC combined with mass spectrometry and NMR spectroscopy were used to determine the quantitative and qualitative compositions of the obtained products. The method developed for the production of glycyrrhetinic acid in subcritical water is environmentally friendly and faster than conventional hydrolysis methods that use acids and-expensive and toxic organic solvents. The proposed technique has a potential for the future development of inexpensive and environmentally friendly technologies for production of new pharmaceutical plant-based substances.

The solubility of sebacic acid in subcritical water using the response surface methodology

The solubility of sebacic acid in subcritical water was investigated. Response surface methodology was used to study the combined effects of the different parameters such as temperature, static and dynamic time to optimize the process conditions for the maximum solubility of sebacic acid. Solubility results of sebacic acid were observed to be highly correlated with quadratic model according to analysis of variance. The solubility of sebacic acid was found as 500 g L−1 in the optimum conditions at 400 K temperature, 4 min dynamic time and 28 min static time. Approximation models were employed for determining solubility of sebacic acid at elevated temperatures.

An efficient production of benzene from benzoic acid in subcritical water using a copper(i) oxide catalyst

The benzene yield from benzoic acid increased greatly to 90 mol% with 100% selectivity in subcritical water catalyzed by Cu2O.

Degradation of Caffeic Acid in Subcritical Water and Online HPLC-DPPH Assay of Degradation Products

Caffeic acid was subjected to degradation under subcritical water conditions within 160-240 °C and at a constant pressure of 5 MPa in a continuous tubular reactor. Caffeic acid degraded quickly at these temperatures; the main products identified by liquid chromatography-diode array detection/mass spectrometry were hydroxytyrosol, protocatechuic aldehyde, and 4-vinylcatechol. The reaction rates for the degradation of caffeic acid and the formation of products were evaluated. Online high-performance liquid chromatography/2,2-diphenyl-1-picryhydrazyl assay was used to determine the antioxidant activity of each product in the solution. It was found that the overall antioxidant activity of the treated solution did not change during the degradation process. This study showed a potential of formation of antioxidants from natural phenolic compounds under these subcritical water conditions, and this may lead to a discovering of novel antioxidants compounds during the extraction by this technique.

Biodiesel production from soybean soapstock acid oil by hydrolysis in subcritical water followed by lipase-catalyzed esterification using a fermented solid in a packed-bed reactor

We investigated a new hydroesterification strategy for the production of biodiesel from low-value oil feedstocks: complete hydrolysis of the feedstock to fatty acids in subcritical water, followed by the use of a packed-bed reactor, containing a fermented solid with lipase activity, to convert the fatty acids to their ethyl esters. The fermented solids were produced by cultivating Burkholderia cepacia LTEB11 for 72h on a 1:1 mixture, by mass, of sugarcane bagasse and sunflower seed meal. The esterification of fatty acids obtained from soybean soapstock acid oil was studied in the packed-bed bioreactor, in a solvent-free system, with the best results being a 92% conversion in 31h, obtained at 50°C. When the packed-bed reactor was reused in successive 48-h esterification reactions, conversions of over 84% of the fatty acids to esters were maintained for five cycles at 50°C and for six cycles at 45°C. Unlike previous hydroesterification processes that have used lipase-catalyzed hydrolysis followed by chemically-catalyzed esterification, our process does not expose the lipases to contaminants present in low quality feedstocks such as soapstocks. This advantage opens the possibility of operating the packed-bed esterification reactor in continuous mode.

Solubility of fatty acids in subcritical water

A phase equilibrium apparatus was designed to determine the solubilities of stearic acid and palmitic acid in subcritical water at different temperatures and pressures. The dissolution equilibrium time was measured. The effect of an ultrasonic field on dissolution equilibrium was also studied. The results showed that the maximum solubilities of stearic acid and palmitic acid were 0.136g/100g and 0.178g/100g in subcritical water at temperatures of 180°C and 160°C, respectively, and a pressure of 15MPa for 30min. An ultrasonic field also clearly promoted the dissolution of fatty acids in subcritical water. The dissolution equilibrium time was shortened to 20min using ultrasonic oscillation (250W, 20kHz).

Thermal stability of fatty acids in subcritical water

In this work, hydrolytic reaction conditions of various temperatures (300–370°C) and times (0–30min) at a constant pressure of 20MPa were applied to the thermal decomposition of three kinds of fatty acids (FAs), stearic acid, oleic acid, and linoleic acid, in subcritical water. The degradation characteristics were investigated from the derived data, and the thermal stability of FAs in subcritical water was estimated. The primary reactions we observed were isomerization and pyrolysis of FAs. The main pathway of degradation was deduced by analyzing the contents of pyrolyzed products. We found that more saturated FAs have greater thermal stability in subcritical water. All FAs remained stable at 300°C or below. Based on these results, we recommend that hydrolysis of vegetable oils and fats using subcritical water should be carried out below 300°C (at 20MPa) and for less than 30min to obtain high-yield FA production.

One-step and non-catalytic intramolecular redox reactions of conjugated all E-dienals to non-conjugated Z-enoic acids in subcritical water

Simple treatment of conjugated all E-dienal, (2E,4E)-hexa-2,4-dienal, in subcritical water afforded an intramolecular redox product, non-conjugated Z-enoic acid, (Z)-hex-3-enoic acid, in 42% yield without the usage of a metal catalyst in one-step under the conditions of 250°C, 10min, and 0.35gmL−1 water amount. Similar treatment of the dienal in superheated benzyl alcohol produced corresponding ester, benzyl (Z)-hex-3-enoate, in 34% yield under the conditions of 300°C, 30min, and 0.5gmL−1 benzyl alcohol amount. The obtained (Z)-hex-3-enoic acid was transformed to cis-β-hydroxy-γ-ethyl-γ-lactone in 90% yield by hydrogen peroxide at 60°C for one day under solvent-free conditions.

Electrolysis Reaction Pathway for Lactic Acid in Subcritical Water

Electrolysis reactions of lactic acid were studied using a 500 mL continuous flow reactor made of SUS 316 stainless steel. In this system, a titanium wall acted as a cathode and a titanium plate-layered type electrode was used as an anode in a subcritical reaction medium. The reactor wall (stainless steel) and the cathode (titanium) were separated from each other by a cylindrical ceramic wall. This hydrothermal electrolysis process provides an environmentally friendly route that does not use any organic solvents or catalysts to produce value-added chemicals from wastewater treatment. Reactions were conducted with a 30 min residence time at a pressure of 10 MPa at 280 °C via application of various direct currents ranging from 0.5 to 2 A. In addition, to improve our understanding of the reaction mechanism, we investigated the effects of initial lactic acid and electrolyte (NaOH) concentrations on the degradation of lactic acid and the product yields using continuous flow hydrothermal electrolysis. Acrylic acid, acetic acid, and acetaldehyde were detected as the main reaction products using high-performance liquid chromatography. Increasing the applied current increased the conversion of lactic acid and product yields. With a current of 2 A, an electrolysis time of 30 min, and the addition of 50 mM NaOH, a 55% conversion was achieved. The acetaldehyde yield increased almost linearly with current, and at 2 A, 24.73% of the acetaldehyde was produced compared to a 2.25% yield of acetic acid under the same conditions. For acrylic acid, at higher currents (1.5 and 2.0 A), the rate of generation of acrylic acid decreased (values of 0.82, 0.65, and 0.49% at 1.0, 1.5, and 2.0 A, respectively). Increasing the pH of the feed solution resulted in a drastic decrease in the yields of acrylic acid and acetaldehyde.

Solubility of Gallic Acid, Catechin, and Protocatechuic Acid in Subcritical Water from (298.75 to 415.85) K

The solubility of gallic acid hydrate, protocatechuic acid, and (+)-catechin hydrate was measured between 298.75 K and 415.85 K using a dynamic flow apparatus. The aqueous solubility of gallic acid hydrate was found to vary between 12.6 g·L−1 at 298.75 K and 2870 g·L−1 at 415.85 K. The aqueous solubility of protocatechuic acid at the same temperatures varied between 29.4 g·L−1 and 1180 g·L−1, respectively, while that of (+)-catechin hydrate varied between 2.26 g·L−1 and 576 g·L−1, respectively. The aqueous solubility of the phenolic compounds was found to increase exponentially with temperature. The temperature dependence of the aqueous solubility of the phenolic compounds was estimated using empirical correlations based on the data presented in this work. The thermodynamic properties such as standard molar enthalpy, standard molar entropy, and standard molar Gibbs energy of solution were also calculated from the solubility data.

Hydrolysis technology and kinetics of poultry waste to produce amino acids in subcritical water

In order to improve the utilization of bird wastes, the hydrolysis technology optimization and reaction kinetics for amino acid production by extremely low acids in subcritical water have been conducted. In this experiment, the raw material was chicken intestines and the research target was the yield of amino acids. The effects of reaction temperature, reaction time and H 2SO 4 concentration in reactant system on amino acid yields were investigated using the orthogonal test and the optimum hydrolysis technology conditions were obtained. The experimental results show that the best hydrolysis technology is: reaction temperature 533 K, reaction time 28 min, H 2SO 4 concentration in reactant system 0.02 wt.%. Under this condition, the amino acid yield reaches 11.49%. The results of chemical reaction kinetics experiment indicate that the total velocity constants of chicken intestine hydrolysis in subcritical water with H 2SO 4 concentration in reactant system 0.02 wt.% are 1.52 × 10 −2, 3.35 × 10 −2, 11.58 × 10 −2, and 14.01 × 10 −2 at 473 K, 503 K, 533 K, and 553 K respectively. The reaction kinetics order is 1.52, activation energy is 64.44 kJ/mol and the pre-exponential factor is 1.91 × 10 5.

Degradation Kinetics of Branched-Chain Amino Acids in Subcritical Water

The degradation of branched-chain amino acids (valine, leucine, and isoleucine) in subcritical water was measured from 290 degrees C to 330 degrees C. The degradation process at any temperature obeyed first-order kinetics. The energy of activation for the degradation of each amino acid could be estimated according to the Arrhenius equation. The pH value of the reaction mixture increased during the degradation process.

Degradation Kinetics of Glucuronic Acid in Subcritical Water

The degradation kinetics of glucuronic acid (GlcA) under subcritical conditions from 160 to 200 degrees C was studied in a continuous tubular reactor. The formation of glucuronolactone (GlcL) during the treatment of GlcA in subcritical water was substantiated by ESI-TOF-MS and (1)H NMR. The degradation of GlcA consisted of the reversible conversion of GlcA to GlcL and the irreversible degradation of the two compounds. The changes in the concentrations of GlcA and GlcL with residence time could be described by first-order kinetics. Higher temperatures accelerated the degradation of GlcA, and thus resulted in rises in the pH value. The degradation reaction of GlcL under the same conditions was also investigated. The activation energy of the reverse hydrolysis of GlcA to GlcL and that of the hydrolysis of GlcL to GlcA were determined to be 88.5 and 63.2 kJ/mol respectively. The enthalpy change in the reversible conversion between GlcA and GlcL was 25.4 kJ/mol.

Solubility of Benzoic and Salicylic Acids in Subcritical Water at Temperatures Ranging from (298 to 473) K

The solubility of benzoic acid and 2-hydroxybenzoic acid (salicylic acid) in water was determined at temperatures ranging from (298 to 473) K under a constant pressure of 5 MPa. The mole fraction solubility of these acids was enhanced by about two orders of magnitude when the water temperature was raised from (298 to 423) K. A new approximation model was developed to predict the solubility of solid organic acids in subcritical water at elevated temperatures. Our new model gives a better prediction for the solubility of the two acids than the approximation models reported in the literature.

Degradation Kinetics of D-Galacturonic Acid and Sodium D-Galacturonate in Subcritical Water

The degradation process of D-galacturonic acid in subcritical water was measured from 160 to 220°C. The process at any temperature obeyed first-order kinetics. The temperature dependence of the degradation rate constant could be expressed by the Arrhenius equation, and the activation energy and the frequency factor were estimated to be 131 kJ/mol and 4.81 × 1012 s-1, respectively. The degradation process of sodium D-galacturonate in subcritical water was also measured from 160 to 190°C. Sodium galacturonate was more easily degraded than galacturonic acid. The degradation process of sodium galacturonate did not obey the first-order kinetics, but could be expressed by the Weibull equation. According to the Arrhenius equation, the activation energy and the frequency factor were estimated to be 147 kJ/mol and 1.26 × 1015 s-1, respectively, for the degradation of sodium galacturonate. The pH of the reaction mixture at room temperature was also measured for the degradation of both the galacturonic acid and sodium galacturonate.

Degradation of Pentoses and Hexouronic Acids in Subcritical Water

AbstractThe degradation of arabinose, xylose, ribose and lyxose in subcritical water was measured at 200, 220 and 240 °C. Ribose was the most rapidly degraded among the pentoses tested. The degradation of the glucuronic and galacturonic acids proceeded at lower temperatures than that of the pentoses, and was measured at 140, 150 and 160 °C. The degradation processes of the pentoses and hexouronic acids could be expressed by the Weibull model, and the kinetic parameters were then estimated. The activation energy and frequency factor for the degradation of each substrate were estimated from the temperature dependence of the rate constant. The enthalpy‐entropy compensation held for the degradation of the pentoses as well as the hexoses, which suggests that the degradation of the hexouronic acids proceeded through a mechanism different from that for the pentoses and hexoses. The molar yield of a pentose to furfural was ca. 0.3 at any temperature, irrespective of the pentose type. Acidic compounds were also formed from the pentoses in proportion to the amount of consumed substrates. The formation of acidic compounds resulted in a rapid decrease in pH.