Effect of acid-associated mechanical pretreatment on the hydrolysis behavior of pine sawdust in subcritical water

The effects of sulfuric acid-associated mechanical pretreatment on the hydrolysis behavior of pine sawdust were investigated in this study.Sulfuric acid could act as an acidic catalyst to depolymerize holocellulose through cleavage of the glycosidic bonds,the dissociation energies of which were supplied by the impact of a ball on pine sawdust,during milling.The destruction of glycosidic and hydrogen bonds in pine sawdust resulted in a decrease of crystallinity and an increase of water solubility.The sulfuric acid could promote the hydrolysis of holocellulose and its hydrolysis products.It also destroyed the chemical linkages between holocellulose and lignin during ball milling.The cleavage of chemical linkages with holocellulose made lignin more difficult to hydrolyze in subcritical water,and higher activation energy was needed to hydrolyze pretreated pine sawdust at higher reaction temperatures.It also led to the formation of glucose char and aromatic-linked polymer char from the hydrolysis products of holocellulose.

Toluene oxidization to benzaldehyde in subcritical water

Effects of reaction parameter on yield of benzaldehyde produced from toluene oxidization using hydrogen peroxide in subcritical water are investigated. The experimental results show that if the molar ratio of hydrogen peroxide to toluene is controlled within a reasonable range, the by-products may be neglected. The optimum technology of toluene oxidization to benzaldehyde is reaction time 60 min, reaction temperature 350℃, molar ratio of hydrogen peroxide to toluene 3.5. The yield of benzaldehyde can reach 17.2 % under the optimum condition. Research results of chemical reaction kinetics show that the consecutive reaction consists of two first-order reaction, and activation energy of these two reactions are 89 kJ·mol^-1 and 76 kJ·mol^-1 respectively,

Experimental measurement and correlation of solubility of β-carotene in pure and ethanol-modified subcritical water

For the first time,the solubility ofβ-carotene in pure and ethanol-modified subcritical water(SW)using the static method was determined.The experimental runs were performed at a temperature ranging from 298.15 to 403.15 K and 0–10%(w/w)of ethanol as a modifier at a constant pressure of 5 MPa.Samples were analyzed by UV–vis spectrophotometer.The solubility ofβ-carotene was found to range from 1.084×10^-8 to 227.1×10^-8 mol fractions in the subcritical water in above mentioned conditions.The obtainedβ-carotene solubility data were correlated using the linear model and modified Apelblat model.The obtained results showed the modified Apelblat model was better for estimating the solubility ofβ-carotene in SW.The values of the rootmean-square deviation(RMSD)between experimental and correlated data were calculated and used as the index of validity and accuracy for the model.Also,thermodynamic properties of the solution such as the Gibbs free energy of solution,enthalpy,and entropy of solution were estimated.

Effect of Cu（Ⅱ） on Degradation and Decolorization of Rhodamine B in Subcritical Water

In this paper, subcritical water, an environmentally friendly solvent, was employed to degrade rhodamine B, which served as a model dye in textile industrial effluents. The effect of Cu（Ⅱ） on the degradation of rhodamine B was evaluated. Further, the degradation kinetics of rhodamine B in subcritical water was evaluated via a Weibull model. The results show that subcritical water could efficiently degrade and decolorize rhodamine B. The addition of Cu（Ⅱ） into subcritical water could accelerate the degradation of rhodamine B and lower the temperature for its com- plete degradation. The Weibull equation could well express the degradation kinetics of rhodamine B. The calculated rate constants showed Arrhenius behavior and presented high correlation coefficients. The activation energy was 109.4 kJ/mol for subcritical water degradation of rhodamine B, whereas it became lower（93.4 kJ/mol） when Cu（Ⅱ） was added to the subcritical water. The frequency factors for the degradation of rhodamine B by subcritical water without and with Cu（Ⅱ） were calculated to be 1.0×10n and 3.2×109 min-1, respectively. The above results indicate that subcritical water treatment is a promising process for degrading and decolorizing textile dyes. The results will provide a theoretic support for the industrial application of subcritical water treatment.

Comparative in vitro Study of the biological activity and chemical composition extracts of Helicteres isora L. obtained by water and subcritical water extraction

Objectives:Subcritical water extraction technique is considered as an environmentally extraction technique.The aim of this study was to compare the different characteristics of water extract and subcritical water extract of Helicteres isora L.Materials and Methods:Water extraction was performed under the following conditions:25℃,24 h,and solid-to-water ratio 1:30.Subcritical water extract was carried out under specific conditions(pressure=10 bar,temperature=160℃,solid-to-water ratio=1:30,time=30 min).Chemical composition analysis was performed using GC-Mass chromatography.Anti-biofilm activity in the terms of anti-attach and removal of biofilm were assessed using the ELISA reader method and reading absorbance at 570 nm.Anti-microbial activity against Bacillus cereus,Staphylococcus aureus,Staphylococcus saprophyticus,and Bacillus subtilis was investigated by measurement of inhibitory zone diameter.Anti-enzymatic and antioxidant properties were also assessed.Results:The results of GC-Mass analysis showed some components extracted in subcritical method which were absent in water extract such as octadecanoic acid,hexadecanoic acid,and berberin.Antioxidant activity of the two tested extracts revealed that subcritical water extract had more antioxidant capacity than water extract(P≤0.05).The two tested extracts exhibited anti-enzymatic activity against polyphenol oxidase enzyme with better performance of subcritical water extract.Anti-biofilm activity of the two extracts implies that,in the case of preventing biofilm formation,both extracts had similar efficiency but in the removal of biofilm,subcritical water extract showed better performance.Both extracts had anti-microbial activity against B.cereus,S.aureus,S.saprophyticus,and B.subtilis with better performance of subcritical water extract.Anti-enzymatic assay also showed similar results.Conclusions:Subcritical water extract of H.isora showed more antioxidant activity as well as anti-biofilm,anti-bacterial,and anti-enzymatic activity rather than ordinary water extract.

Retention Mechanism of Phenolic Compounds in Subcritical Water Chromatography

The transfer enthalpies and entropies of hydroxyl and nitryl in different mobile phase systems were compared by van＇t Hoff curve. Results suggest that the presence of acetonitrile and methanol in the mobile phase may decrease the interaction of solute and stationary phase with respect to subcritical water, thereby reducing the contribution of enthalpy to the retention. Retention mechanisms of phenolic compound appear to be more similar in subcritical water and water/methanol systems on the PRP-1 column. Hydrogen bond in subcritical water system plays a very important role in the retention of the phenols.

Formation process and mechanism of humic acid-kaolin complex determined by carbamazepine sorption experiments and various characterization methods

To explore the formation process and mechanism of organic matter and organic-mineral complex under humification and mineralization conditions, a series of samples including humic acid, kaolin, and humic acid-kaolin complex were prepared using a subcritical water treatment method（SWT） under specific temperature, pressure and reaction time conditions. HA was used as a surrogate for natural organic matter because it has a similar abundant pore structure,variety of carbon types, and chemical components. These samples were used in carbamazepine（CBZ） sorption experiments and characterized by a variety of techniques. The polymerization of humic acid under the conditions of increased temperature and pressure resulted in an increase in specific surface area and molecular quantity. In addition, the degree of aromaticity rose from59.52% to 70.90%. These changes were consistent with the transformation from ‘soft carbon＇ to‘hard carbon＇ that occurs in nature. The results of sorption experiments confirmed the interaction between humic acid and kaolin from the difference between the predicted and actual Qevalues. The conceptual model of humic acid-kaolin complex could be deduced and described as follows. Firstly, the aromatic components of humic acid preferentially combine with kaolin through the intercalation effect, which protects them from the treatment effects.Next, the free carboxyl groups and small aliphatic components of humic acid interact on the surface of kaolin, and these soft species transform into dense carbon through cyclization and polymerization. As a result, humic acid-kaolin complex with a mineral core and dense outer carbonaceous patches were formed.

Production of solid fuels by hydrothermal treatment of wastes of biomass,plastic,and biomass/plastic mixtures:A review

Traditional disposal methods of biomass and plastic waste,such as landfill,combustion,and compost,no longer meet the requirements of carbon reduction,carbon neutrality,and sustain-able society due to low utilization efficiency and severe pollution.As a green,efficient and environmentally-friendly method,hydrothermal technology has been paid much attention to and has already been applied to recycle or reuse various plastic and biomass wastes.No matter for the single or mixed type of waste,it is expected to achieve efficient recycling and obtain value-added products through the hydrothermal process.This review summarized the basic knowledge of hydrothermal technology and the possible reaction mechanism of biomass and plastics un-der hydrothermal conditions and listed the previous reports on the application of hydrothermal technology for converting wastes of biomass,plastic,and biomass/plastic mixtures to solid fuels.Moreover,regarding the future of hydrothermal technology,four points related to reaction mech-anism,synergistic effect,catalysis,and scaled-up application,were provided for consideration.