Hydrothermal Acid Treatment Research Articles

Hydrothermal-acid treatment for effectual extraction of eicosapentaenoic acid (EPA)-abundant lipids from Nannochloropsis salina

Hydrothermal acid treatment, was adopted to extract eicosapentaenoic acid (EPA) from wet biomass of Nannochloropsis salina. It was found that sulfuric acid-based treatment increased EPA yield from 11.8 to 58.1mg/g cell in a way that was nearly proportional to its concentration. Nitric acid exhibited the same pattern at low concentrations, but unlike sulfuric acid its effectiveness unexpectedly dropped from 0.5% to 2.0%. The optimal and minimal conditions for hydrothermal acid pretreatment were determined using a statistical approach; its maximum EPA yield (predicted: 43.69mg/g cell; experimental: 43.93mg/g cell) was established at a condition of 1.27% of sulfuric acid, 113.34°C of temperature, and 36.71min of reaction time. Our work demonstrated that the acid-catalyzed cell disruption, accompanied by heat, can be one potentially promising option for ω-3 fatty acids extraction.

Hydrothermal acid treatment for sugar extraction from Golenkinia sp.

In this study, hydrothermal acid treatment for efficient recovery of sugar from Golenkinia sp. was investigated. The initial glucose and XMG (xylose, mannose, and galactose) contents of a prepared Golenkinia sp. solution (40g/L) were 15.05 and 5.24g/L, respectively. The microalgal cell walls were hydrolyzed, for sugar recovery, by enzymatic saccharification and/or hydrothermal acid treatment. Among the various hydrothermal acid treatment conditions, the most optimal were the 2.0% H2SO4 concentration at 150°C for 15min, under which the glucose- and XMG-extraction yields were 71.7% and 64.9%, respectively. By pH 4.8, 50°C enzymatic hydrolysis after optimal hydrothermal acid treatment, the glucose- and XMG-extraction yields were additionally increased by 8.3% and 0.8%, respectively. After hydrothermal acid treatment, the combination with the enzymatic hydrolysis process improved the total sugar yield of Golenkinia sp. to 75.4%.

Nickel sulfide counter electrodes enhanced by hydrosulphuric acid hydrothermal treatments for use in Pt-free dye-sensitized solar cells

Hydrosulphuric acid (H2S) hydrothermal treatment is employed to enhance the catalytic activity of the nickel sulfide (NiS) counter electrode (CE) for the Pt-free dye-sensitized solar cell (DSSC). It can be found that a small amount of residual nickel hydroxide (Ni(OH)2) and nickel (Ni) are still within the as-prepared NiS film electrodeposited by a cyclic voltammetry (CV) approach, which would have impact on the electrocatalytic activity and chemical stability of the NiS CE. After the H2S hydrothermal treatment, not only the Ni(OH)2 and Ni are removed, but also NiS is recrystallized and reorganized, thus resulting in a surface evolution from granular to nanoporous morphology. CV, electrochemical impedance spectroscopy (EIS), and Tafel polarization curve are conducted to compare the electrocatalytic activity and long-term stability of CEs for I3− reduction. The results demonstrate that the DSSC with the optimal treated NiS CE obtains an enhanced photovoltaic conversion efficiency of 7.37% compared to that using the as-deposited NiS CE without H2S treatment (4.84%) under full sunlight illumination (100mWcm−2, AM1.5 G) due to its superior electrocatalytic activity of the high purity of NiS, and increased specific surface area from the nanoporous structure. Therefore, the H2S hydrothermal treatment can be considered as a simple and effective method for use in the preparation of pure metal sulfide films on conductive substrates.

Catalytic Performance of Biomass Carbon-Based Solid Acid Catalyst for Esterification of Free Fatty Acids in Waste Cooking Oil

A series of carbon-based solid acid catalysts were prepared from bagasse using a carbonization–sulfonation method and employed to catalyze esterification of oil with methanol to produce biodiesel. The physical and chemical properties of the biomass carbon catalysts were characterized by FTIR. The pretreatment of bagasse, carbonization temperature, sulfonation temperature and time, as well as the catalytic performance were systematically investigated. The results indicated that the catalysts prepared from bagasse with dilute acid hydrothermal treatment showed the best performance. For the catalysts, the acid value of waste cooking oils was decreased to 1 mg KOH/g, and FFA conversion reached 94.4 % after reaction for 4 h under optimized reaction conditions. The catalysts also showed better stability than traditional homogeneous catalysts.

Isolation of Bio‐Mesoporous Silica from Rice Husk

AbstractBy using a simple and safe citric acid‐hydrothermal treatment, bio‐mesoporous silica with a high surface area (≈200 m2g−1) and pore size of around 6.0 nm can be isolated from rice husk. We found that the surface area of the isolated porous silica is dependent on the pH value, hydrothermal temperature, and reaction time but independent on the water content. At pH around 2.0‐2.5, the resulted bio‐mesoporous silica possesses the highest surface area regardless to the acid sources. Increasing hydrothermal temperature can accelerate the removal rate of the metal impurity in the rice husk. From the data of the surface areas, the required reaction time to isolate the mesoporous silica of the largest surface area (≈200 m2g−1) from rice husk increases with decreasing temperature. It takes only about 0.5 hour at 100 °C, 1.0 hour at 60 °C and 12.0 h at room temperature. This citric acid‐hydrothermal treatment can also be applied to isolate bio‐mesoporous silica from Equisetum grass.

Adsorption characteristics of polyvinyl alcohols on modified zeolites

Adsorption characteristics of two types of polyvinyl alcohols (with different polymerization degrees) on faujasite-type zeolites obtained by SiCl4 treatment as well as by a combined hydrothermal acid treatment were investigated in an aqueous solution. No adsorption of the polyvinyl alcohol with a polymerization degree of 500 was observed on the SiCl4-treated faujasite without secondary pores in the mesopore region, but adsorption did occur (about 0.11 g g−1) on the hydrothermal acid-treated faujasite containing secondary pores. On the other hand, the polyvinyl alcohol with a polymerization degree of 2,000 did adsorb on the SiCl4-treated faujasite. Scanning electron microscopy measurements confirmed that adsorption occurred on the external surface of the zeolite crystals.

Processing Technologies and Cell Wall Degrading Enzymes To Improve Nutritional Value of Dried Distillers Grain with Solubles for Animal Feed: an in Vitro Digestion Study

Currently, the use of maize dried distillers grain with solubles (DDGS) as protein source in animal feed is limited by the inferior protein quality and high levels of non-starch polysaccharides (NSP). Processing technologies and enzymes that increase NSP degradability might improve digestive utilization of DDGS, enhancing its potential as a source of nutrients for animals. The effects of various combinations of processing technologies and commercial enzyme mixtures on in vitro digestion and subsequent fermentation of DDGS were tested. Wet-milling, extrusion, and mild hydrothermal acid treatment increased in vitro protein digestion but had no effect on NSP. Severe hydrothermal acid treatments, however, effectively solubilized NSP (48-78%). Addition of enzymes did not affect NSP solubilization in unprocessed or processed DDGS. Although the cell wall structure of DDGS seems to be resistant to most milder processing technologies, in vitro digestion of DDGS can be effectively increased by severe hydrothermal acid treatments.

Delamination of microporous layered silicate by acid-hydrothermal treatment and its use for reduction of methanol crossover in DMFC

Microporous layered silicate AMH-3 has a 3D ordered porous structure that is therefore very promising as a permselective barrier. However, for use as permselective barrier, the removal of the Na+ and Sr2+ cations located in the intralayer and interlayer spaces and the delamination of an individual layer must be carried out. We successfully obtained delaminated AMH-3 by acid-hydrothermal treatment without the use of swelling agent. The delamination conditions have been optimized to find the best morphology for use as permselective barrier. The pristine AMH-3 and the delaminated AMH-3 were characterized with FE-SEM, N2 adsorption, ICP-AES, 29Si MAS NMR, FT-IR, and WXRD analyses. These results show that the delaminated AMH-3 has a more ordered pore structure than the pristine AMH-3 and that it retains framework crystallinity in the AMH-3 layers. The methanol permeability, proton conductivity and liquid uptake of Nafion membrane coated with a delaminated AMH-3/Nafion nanocomposite layer were examined. This type of membrane was found to exhibit a lower methanol permeability than neat Nafion and to maintain a high proton conductivity. We can thus conclude that delaminated AMH-3 is potentially good permselective barrier for the reduction of methanol crossover in DMFCs.

Evidence for controlled insertion of Fe ions in the framework of clinoptilolite natural zeolites

This work is focused on the spectroscopic characterization of a set of materials obtained by hydrothermal treatments from a natural clinoptilolite zeolite, NZ. OPAZ (orthophosphoric acid treatment on NZ), Fe2+-OPAZ (ferrous sulphate acid treatment on OPAZ) and Fe3+-OPAZ (ferric sulphate acid treatment on OPAZ) samples were characterized by HRTEM, UV–Vis, temperature dependent EPR and Infra Red spectroscopies in order to describe the structure, nuclearity and distribution of iron ions and iron oxides clusters and particles. Complementary pieces of information were obtained from the different techniques. In particular, HRTEM analysis suggested an effect of the hydrothermal treatments not only on the Fe speciation but also on the zeolite particles morphology and surface. The same technique could not clearly detect the presence of iron oxide phases, suggesting their very small size and high dispersion. A more detailed description of the isolated and clustered species could be in turn obtained by UV–Vis spectroscopy. This was confirmed by temperature dependent EPR spectroscopy, suggesting the presence of nanosized ferromagnetic magnetite-like particles. Finally, IR spectroscopy gave clear cut evidence about the insertion of Fe3+ ions in framework positions, with consequent generation of distinct Brønsted acidity, after hydrothermal treatments with iron salts. This transformation could be explained through the reaction with defective hydroxyl nests formed by mildly acid hydrothermal treatment with isolated Fe3+ ions.

Acidic Hydrothermal Conversion of Degussa P25 into Rutile Nanocrystals and Particle Morphology Control

Hydrothermal conversion of Degussa P25 into pure rutile has been investigated at 180°C under acidic conditions. Detailed characterizations of the hydrothermal products were achieved via XRD, TEM, BET, Raman scattering, and UV-vis absorption spectroscopy. The results show that the conversion process is a zero order reaction with a constant anatase conversion rate of ∼1.469 wt%/h. The existent ∼17.9 wt% of rutile in the starting P25 powder does not seem to appreciably seed the phase transition or lead to an epitaxial growth of the rutile crystals. Quasi-equiaxed rutile nanocrystals (∼41 nm, ∼31.5 m2/g), a morphological form most difficult to synthesize via soft-chemical processing, have been obtained at a HNO3/TiO2 molar ratio of 12. Higher acidity or the presence of Cl- tends to yield rutile nanorods, and the effects of Cl- are more significant. These phenomena have been deciphered by considering the solution chemistry of the titanium ionic species and the construction mechanisms of the rutile lattice. Both the equiaxed and the rodlike rutile nanocrystallites were found to be oxygen stoichiometric and possess an indirect interband transition energy of ∼2.93 eV. The rutile nanocrystals obtained via this strategy may find applications as nano-whiteners in cosmetics and pigments. Keywords: Degussa P25, acidic hydrothermal treatment, phase transition kinetics, morphology control

Synthesis of copper–zinc bimetallic imidazolate framework compounds and the structure of Cu(I)-containing Cu 2Zn(N 2C 3H 3) 4

Copper(II)–zinc(II) bimetallic imidazolate metal–organic framework compounds of composition Cu a Zn b Im 2( a + b ) (Im = C 3H 3N 2), including Cu 2ZnIm 6 ( 1), were prepared in high yields from the metal oxides under mild aqueous conditions using a novel acid catalysis method. Mild acidic hydrothermal treatment of paramagnetic 1 (≥120 °C) gave diamagnetic Cu(I)-containing Cu 2ZnIm 4 ( 2) in high yield. The formation mechanism of 2 involves electron transfer from Im − to Cu(II), with concomitant formation of the unusual cyclotriimidazole, C 9H 6N 6. Air-stable 2, characterized by single-crystal X-ray diffraction, crystallized in the tetragonal space group P 4 ¯ 2 1 c , with a = b = 10.9623(3), c = 6.3231(4) Å, α = β = γ = 90°, V = 759.86(6) Å 3, and Z = 1.

Effect of acid pretreatment of the silica substrate on the stability of octadecyl modified reversed phases

Two stationary phases, identically modified and derived from the same experimental Chromspher substrate, but one of which has been pretreated with a hydrofluoric acid solution, are compared after ageing with various eluents under simulated routine conditions. The hydrothermal hydrofluoric acid treatment of the silica substrate prior to modification with dimethyloctadecyl-silane improved both the surface coverage and the stability of the resulting stationary phase compared to those of the original substrate. The stability of the silica-to-silane bonding after modification was characterized by means of chromatographic techniques and elemental analysis. Changes in the rigidity of the substrate were studied by means of solid state29Si NMR. The effect of the hydrothermal acid treatment on relevant substrate parameters, including formation of crystalline regions at the surface, is also discussed.

Studies on the Properties of Amorphous Silica Having Some Connection with the Volcanic Action and its Industrial Application. XXIV---XXVI. XXIV. Effect of Hydrothermal Acid Treatment on the Transformation of Silica Gel

シリカゲルを水熱処理または硫酸,塩酸,硝酸およびリン酸の 5～30% 溶液に浸漬し, 120°～200℃ に 3～8 時間水熱酸処理を行ない, さらにその水熱および水熱酸処理を行なったものを 800°～1200℃ に加熱して, シリカゲルの結晶化におよぼす水熱および水熱酸処理の影響について考察した。シリカゲルは水熱処理により結晶化が早められ, また水熱処理を行なったものを加熱すると未処理のシリカゲルに比較して結晶化が早いことを認めた。また, 水熱酸処理では酸素酸でない塩酸のときは結晶化が早められるが, 酸素酸の硫酸,硝酸およびリン酸ではおそくなり, 処理時間の長いほど, 処理温度の高いほどシリカゲルの結晶化はおくれる。