Controlling of Solution Concentration on Nucleation During Hydrothermal Synthesis of Analcime

Hydrothermal experiments of analcime nucleation and glass dissolution were carried out in autoclaves under the conditions of autogeneous pressures, temperatures of 150 °C ～ 210 °C, and 0.25 M ～ 0.75 M NaOH solutions. The curves of the glass dissolution and analcime formation are S‐shaped. Yet, the two curves are essentially parallel to each other. The time required for a complete dissolution of glass or the commencement of analcime formation is shorter when the concentration of NaOH solution or the temperature is higher. The amount of the weight percent of analcime synthesized is obviously less than the glass dissolved at a given time of an experiment. The weight difference between glass dissolved and analcime (dehydrated) formed is calculated to be represented as the solution concentration. During an experiment, the solution concentration increases gradually to a maximum, then decreases slowly to a constant value with time. On the other hand, nucleation is also gradually increased to a maximum, then is decreased finally to zero with time in a bell‐shaped curve. It is clear that nucleation of analcime is mainly controlled by the solution concentration.     

Heat release during the hydration of calcinated α-C<Subscript>2</Subscript>SH and its mixture with killalaite

In this work, the influence of the mineral composition of the synthesized calcium silicate hydrates on their hydraulic activity after thermal treatment was determined. Primary mixture, consisting of quartz sand and burnt limestone (CaO/SiO₂ = 2), was treated hydrothermally with NaOH additive at 200 °C. It was determined that α-C₂SH prevailed in the product after 4 h of the synthesis. The results of DSC and XRD analysis revealed that α-C₂SH was partially decomposed after 12 h of the synthesis and newly formed compounds were identified—killalaite, portlandite and C–S–H. The products of 4 and 12 h synthesis were treated thermally at temperatures between 450 and 1000 °C. It was determined that dellaite and x-C₂S formed already at 450 °C, β-C₂S at 600 °C and α′_L-C₂S at 800 °C when the 4 h synthesis product, in which α-C₂SH prevailed, was treated thermally. On the other hand, killalaite remained stable up to 600 °C, and the temperature values, at which mentioned calcium silicates formed, increased in case of a 12 h synthesis product. Heat flow values of the main hydration reaction and total heat release exceeded 3.1 mW g^?1 and 140 J g^?1 accordingly in case of the samples in which α-C₂SH prevailed. However, increase in the thermal treatment temperature resulted in a decrease in the mixtures hydraulic activity. It was proved that killalaite formation in the product of the 12 h hydrothermal synthesis vividly decreases its hydraulic activity after the thermal treatment in the temperature range of 450–1000 °C. No increment in the heat flow values that could be attributed to the main hydration reaction (acceleration period) was witnessed in all the curves of the heat flow analysis in this case.     

Improvement of acid resistance of Portland cement pastes using rice husk ash and cement kiln dust as additives

This paper represents a laboratory study on the acid resistance of hardened ordinary Portland cement (OPC) and blended OPC pastes at two different curing temperatures. The blended materials used are rice husk ash (RHA) and cement kiln dust (CKD). The blended cement pastes were prepared using a water/solid (W/S) ratio of 0.3. The effects of immersion in deionized water (pH 7) and sulfuric acid solutions (pH 1, 2 and 3) at two temperatures (20 and 50 °C) on the compressive strength and phase composition of the various hardened blended cement pastes were studied. The results of compressive strength revealed that the increase of curing temperature from 20 to 50 °C resulted in increase the reduction of compressive strength due to acid attack up 2 months, but the resistance to sulfuric acid attack increases after that time due to the formation of crystalline calcium silicate hydrates (CSH) which have higher resistance to acid attack than the amorphous CSH formed at the early ages of hydration. The presence of RHA and CKD improves the resistance to sulfuric acid attack at both curing conditions. From the results of X-ray diffraction analysis and differential scanning calorimetric technique curves, the main hydration products identified are CSH, portlandite, and calcium sulfoaluminate hydrates.     

Modified hydrotalcites application as precursors for (Na,K)Mg/Al spinel-type compounds formation

In this work, a synthesis route of (Na,K)Mg/Al spinel-type compounds, which combines hydrothermal synthesis at low temperatures (<200 °C) and solid-state sintering (>800 °C) methods, is presented. It was examined that NaOH and KOH additives induce the reaction between initial Mg and Al components and the formation of hydrotalcite during hydrothermal treatment. It should be noted that after 1 h of calcination of synthetic precursors at 850 °C spinel-type compounds are formed only in the samples with alkali addition. Meanwhile in the pure system only traces of the mentioned compounds are observed at 900 °C. Moreover, the increase in solid-state sintering temperature and duration lead to the higher-crystallinity (Na,K)MgAl₂O₄ spinel-type compounds. It should be noted that textural properties of formed (Na,K)Mg/Al spinel-type compounds depend on the chemical composition of precursors. The synthetic and calcined products are characterised by XRD, STA, FT-IR analyses and BET method.     

Potential of Potassium Hydroxide Pretreatment of Switchgrass for Fermentable Sugar Production

Chemical pretreatment of lignocellulosic biomass has been extensively investigated for sugar generation and subsequent fuel production. Alkaline pretreatment has emerged as one of the popular chemical pretreatment methods, but most attempts thus far have utilized NaOH for the pretreatment process. This study aimed at investigating the potential of potassium hydroxide (KOH) as a viable alternative alkaline reagent for lignocellulosic pretreatment based on its different reactivity patterns compared to NaOH. Performer switchgrass was pretreated at KOH concentrations of 0.5–2 % for varying treatment times of 6–48 h, 6–24 h, and 0.25–1 h at 21, 50, and 121 °C, respectively. The pretreatments resulted in the highest percent sugar retention of 99.26 % at 0.5 %, 21 °C, 12 h while delignification up to 55.4 % was observed with 2 % KOH, 121 °C, 1 h. Six pretreatment conditions were selected for subsequent enzymatic hydrolysis with Cellic CTec2® for sugar generation. The pretreatment condition of 0.5 % KOH, 24 h, 21 °C was determined to be the most effective as it utilized the least amount of KOH while generating 582.4 mg sugar/g raw biomass for a corresponding percent carbohydrate conversion of 91.8 %.     

Preparation, characterization and thermal dehydration kinetics of titanate nanotubes

Titanate nanotubes were synthesized utilizing the hydrothermal method using titanium dioxide nanoparticles. The experiments were carried out considering the process as a function of reaction temperature, time, NaOH concentration and the acidity of the washing solution. The formation of titanate nanotubes was shown to be affected strongly by variations in any parameter. The optimum conditions for the synthesis of titanate nanotubes were determined to be a reaction temperature of 190 °C, and a reaction time of 12 h, using 10 M NaOH concentration and the washing solution to have a pH of 5.5. In addition, thermogravimetric analysis (TG/DTG) was used to investigate the thermal behaviour and dehydration kinetics of titanate nanotubes. In order to better understand their thermal behaviour, the thermal analysis of bulk hydrogen trititanate was performed. The values of the apparent activation energies of the first and second dehydration stages for titanate nanotubes were 81.44 ± 15.85 and 82.69 ± 7.46 kJ mol^?1, respectively. The values of the apparent activation energies of the first, second and third dehydration stages for bulk hydrogen trititanate were 115.93 ± 5.40, 137.58 ± 6.47 and 138.97 ± 8.47 kJ mol^?1, respectively.     

Stability of gamma-valerolactone under neutral,acidic, and basic conditions

Dry gamma-valerolactone (GVL) is stable for several weeks at 150 °C and its thermal decomposition only proceeds in the presence of appropriate catalysts. Since GVL does not react with water up to 60 °C for several weeks, it could be used as a green solvent at mild conditions. At higher temperatures, GVL reacts with water to form 4-hydroxyvaleric acid (4-HVA) and reaches the equilibrium in a few days at 100 °C. Aqueous solutions of acids (HCl and H₂SO₄) catalyze the ring opening of GVL even at room temperature, which leads to the establishment of an equilibrium between GVL, water, and 4-HVA. Although the 4-HVA concentration would be below 4 mol% in the presence of acids, it could be higher than the concentration of a reagent or a catalyst precursor, not to mention a catalytically active species. The latter could be especially worrisome as 4-HVA could be an excellent bi- or even a tri-dentate ligand for transition metals. Aqueous solution of bases (NaOH and NH₄OH) also catalyzes the reversible ring opening of GVL. While in the case of NaOH, the product is the sodium salt of 4-hydroxyvalerate, the reversible reaction of GVL, with NH₄OH results in the formation of 4-hydroxyvaleric amide. The reversible ring opening of (S)-GVL in the presence of HCl or NaOH has no effect on the stability of the chiral center.     

Synthesis of Aluminum‐Rich Analcime Using an Ethylene Diamine Derivative as Template

The hydrothermal synthesis of analcime (ANA) with N,N′‐dibenzyl‐N,N,N′,N′‐tetramethylethylenediamine (DBTMED) as template was systematically studied. The various parameters that affect the crystallization of analcime, such as temperature, time, Al source, and Si/Al ratio were investigated. Systematic variations of these parameters revealed that ANA was obtained from the reaction mixture with the optimized ratios of SiO₂/Al₂O₃ = 5–9.5 in presence of DBTMED, whereas template‐free clear solution methods require SiO₂/Al₂O₃ ratio of greater than 25. When experiments were conducted at 130 and 150 °C for 4 days, a mixture of analcime and zeolite P was present in the samples, and a pure analcime sample could be obtained with heating in the temperature range 160–180 °C. When microwave and conventional heating were used, analcime could be obtained after 2 days. The obtained products were characterized by XRD, SEM, and IR spectroscopy.     

NiO@CuO@Cu bilayered electrode: two-step electrochemical synthesis supercapacitor properties

Present work deals with a two-step synthesis and electrochemical properties of nickel oxide @copper oxide@copper (NiO@CuO@Cu) bilayered electrode. In the first step, anodization (40 V for 25 min) of Cu foil has been carried out for forming Cu-hydroxide@Cu which when annealed at 300 °C for 1 h produces CuO@Cu. In the second step, Ni-hydroxide is deposited onto CuO@Cu by applying current density of 0.03 A/cm² for 3 min which when re-annealed at 300 °C for 1 h gives out NiO@CuO@Cu bilayered electrode. Obtained NiO@CuO@Cu bilayered electrode demonstrates separate CuO and NiO phases. The electrochemical properties have obtained using cyclic voltammetry, galvonostatic charge-discharge, and Nyquist plot measurements that reveal an importance of NiO@CuO@Cu as a potential electrode material in the electrochemical supercapacitor application with 58.14, 51.25, and 4.73 F g^?1 values in 0.5 M, NaOH, KOH, and Na₂SO₄ electrolytes, respectively, measured at 2 mVs^?1 scan rate.     

Crystallization study of SrSnO3:Fe

Alkaline earth stannates have recently become important materials in ceramic technology due to its application as humidity sensor. In this work, alkaline earth stannates doped with Fe³⁺ were synthesized by the polymeric precursor method, with calcination at 300 °C/7 h and between 400 and 1100 °C/4 h. The powder precursors were characterized by TG/DTA after partial elimination of carbon. Characterization after the second calcination step was done by X-ray diffraction, infrared spectroscopy, and UV?Cvis spectroscopy. Results confirmed the formation of the SrSnO₃:Fe with orthorhombic perovskite structure, besides SrCO₃ as secondary phase. Crystallization occurred at 600 °C, being much lower than the crystallization temperature of perovskites synthesized by solid state reaction. The analysis of TG curves indicated that the phase crystallization was preceded by two thermal decomposition steps. Carbonate elimination occurred at two different temperatures, around 800 °C and above 1000 °C.     

Recrystallization of Zeolite Y to Analcime and Zeolite P with <SC>d</SC>‐Methionine as Structure‐Directing Agent (SDA)

In this study, the synthesis of template free zeolite Y and its recrystallization to two types of pure zeolite P and analcime in the presence of the amino acid d‐methionine as structure‐directing agent were investigated. The recrystallization occurred solely when specific heating cycles were applyed. A completely crystallized phase of zeolite Y for the mixture of zeolite P and analcime was observed in the presence of d‐methionine at a concentration of 0.015 <SC>m</SC>. The effect of different Si/Al ratios (2.3–9.3), crystallization temperatures (40–160 °C), and crystallization times (28–96 hours) on the achievement of two different zeolite types were studied as well. Pure zeolite P was obtained during conventional heating to 100 °C for 42 hours, whereas pure analcime zeolite was achieved by heating the mixture to 160 °C for 96 hours. The products were characterized by X‐ray diffraction, scanning electron microscopy, and IR spectroscopy.     

The dissolution of cellulose in NaOH-based aqueous system by two-step process

A new dissolution method, a two-step process, for cellulose in NaOH/urea aqueous system was investigated with ¹³C NMR, wide X-ray diffraction (WXRD), and solubility test. The two steps were as follows: (1) formation and swelling of a cellulose–NaOH complex and (2) dissolution of the cellulose–NaOH complex in aqueous urea solution. The dissolution mechanism could be described as strong interaction between cellulose and NaOH occurring in the aqueous system to disrupt the chain packing of original cellulose through the formation of new hydrogen bonds between cellulose and NaOH hydrates, and surrounding the cellulose–NaOH complex with urea hydrates to reduce the aggregation of the cellulose molecules. This leads to the improvement in solubility of the polymer and stability of the cellulose solutions. By using this two-step process, cellulose can be dissolved at 0–5 °C in contrast to the known process that requires −12 °C. Regenerated cellulose (RC) films with good mechanical properties and excellent optical transmittance were prepared successfully from the cellulose solution.     

Effect of alkaline pretreatment on delignification of wheat straw

This study was conducted to analyse structural changes through scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) after alkaline pretreatment of wheat straw for optimum steaming period. During the study, 2 mm size of substrate was soaked in 2.5% NaOH for 1 h at room temperature and then autoclaved at 121°C for various steaming time (30, 60, 90 and 120 min). Results revealed that residence time of 90 min at 121°C has strong effect on substrate, achieving a maximum cellulose content of 83%, delignification of 81% and hemicellulose content of 10.5%. Further SEM and FTIR spectroscopy confirmed structural modification caused by alkaline pretreatment in substrate. Maximum saccharification yield of 52.93% was achieved with 0.5% enzyme concentration using 2.5% substrate concentration for 8 h of incubation at 50°C. This result indicates that the above-mentioned pretreatment conditions create accessible areas for enzymatic hydrolysis.     

NMR spectroscopic studies on the mechanism of cellulose dissolution in alkali solutions

It was considered that the dissolution of cellulose in alkali solutions is mainly due to the breakage of hydrogen bonds. As an alkali hydroxide, KOH can provide OH^? just like LiOH and NaOH; but it is well known that LiOH and NaOH can dissolve cellulose, whereas KOH can only swell cellulose. The inability of KOH to dissolve cellulose was investigated and the mechanism of cellulose dissolving in alkali solutions was proposed. The dissolution behavior of cellulose and cellobiose in LiOH, NaOH and KOH were studied by means of ¹H and ¹³C NMR as well as longitudinal relaxation times. The structure and properties of the three alkali solutions were compared. The results show that alkali share the same interaction mode with cellobiose and with the magnitude of LiOH > NaOH > KOH; the alkalis influence the structure of water also in the same order LiOH > NaOH > KOH. The different behavior of the three alkalis lies in the different structure of the cation hydration ions. Li⁺ and Na⁺ can form two hydration shells, while K⁺ can only form loose first hydration shell. The key to the alkali solution can or cannot dissolve cellulose is whether the cation hydration ions can form stable complex with cellulose or not. K⁺ cannot form stable complex with cellulose result in the KOH solution can only swell cellulose.     

Nitrogen Removal by Chelatococcus daeguensis TAD1 and Its Denitrification Gene Identification

Chelatococcus daeguensis TAD1 was demonstrated to be an aerobic denitrifier. It can utilize not only nitrate and nitrite but also ammonium at high temperature (about 50 °C). The strain had the capability to remove 122.7 and 71.7 mg L^?1 NH₄ ⁺-N by 18 h at 50 and 30 °C, respectively. Triplicate heterotrophic nitrification experiments showed that 32.3 % of removed NH₄ ⁺-N was completely converted to nitrogen gas by 18 h at 50 °C. The denitrification genes involved in C. daeguensis TAD1 were identified and sequenced. It was found that the genes responsible for denitrification in TAD1 were napA, nirK, cnorB, and nosZ. Taken together, TAD1 can be an effective candidate for simultaneous nitrification and denitrificaton at high temperature.     

Degradation of Sucrose,Glucose and Fructose in Concentrated Aqueous Solutions Under Constant pH Conditions at Elevated Temperature

ABSTRACT

The degradation of sucrose can decrease sucrose yield, reduce the efficiency of sugar factory and refinery processes, and effect end product quality. Characterization of sucrose degradation under modeled industrial processing conditions will underpin further technological improvements. Effects of constant reaction pH on sucrose degradation were investigated using simulated industrial model systems (100 °C; 65 °Brix [% dissolved solids]; N₂; 0.05-3 mol NaOH titrant; 8 h), with the use of an autotitrator. Reaction pH values ranged from 4.40 to 10.45. Polarimetry and ion chromatography with integrated pulsed amperometric detection (IC-IPAD) were used to quantify sucrose degradation and first-order reaction constants were calculated. Minimum sucrose degradation occurred between pH 6.45 - 8.50, with minimum color formation between pH's 4.40 - 7.00. Polarimetry, often used in U.S. sugar factories and refineries to monitor chemical sucrose losses, was shown not to be viable to measure sucrose degradation under alkaline conditions, because of the formation of fructose degradation products with an overall positive optical rotation. For comparison, fructose and glucose (80 °C; 65 °Brix; N₂; 3 mol NaOH; 2 h) were also degraded at constant pH 8.3 conditions. For sucrose, fructose, and glucose, formation of organic acids on degradation was concomitant with color formation, indicating they are probably produced from similar reaction pathways. For the glucose and fructose degradation reactions, color and organic acid formation also were highly correlated (R²>0.966) with changes in optical rotation values, confirming that these compounds are formed from similar reaction pathways.     

Polymorphism and melt crystallisation of racemic betaxolol, a β-adrenergic antagonist drug

We report the polymorphic behaviour, in melt cooling experiments, of racemic betaxolol, a low aqueous solubility selective β₁-adrenergic antagonist drug with a flexible molecular structure. A multidisciplinary approach is employed, using thermal analysis (differential scanning calorimetry, polarised light thermomicroscopy), spectroscopic methods (infrared spectroscopy, magic angle spinning ¹H NMR) and X-ray powder diffraction. A glass phase is obtained, T _g ~ ?10 °C, on cooling the melt, unless the cooling rate is ≤0.5 °C min^?1, while a new metastable form, polymorph II, T _fus = 33 °C, is generated in subsequent heating runs in a two step process. Although either partial crystallisation from the melt in the first step or the formation of an intermediate, metastable, low ordered phase may explain these observations, our results favour the second hypothesis. The stable polymorph I, T _fus = 69 °C, which crystallizes on further heating after form II melting, has also been obtained either from polymorph II or from the molten phase, on standing at 25 °C. The racemic betaxolol crystalline phases are found to exhibit some degree of disorder.     

Study on Photocatalytic Activity of NaTaO3 Powder Synthesized By Hydrothermal Method

Using Ta₂O₅ and NaOH as raw materials, the pure NaTaO₃ powders with good decentrality was synthesized at 140 °C by hydrothermal reaction for 12 h. The phase structure, morphology and microstructure of the powders and the band structure were characterized by X-ray diffraction, the field emission scanning electronic microscope, the transmission electron microscope and UV–Visible diffuse reflectance spectrum. The influences of different NaOH additions on the composition, structure and photocatalytic activities of NaTaO₃ powders were studied. The results show that the powders belong to orthorhombic with a grain size of 0.20–0.74 μm, and the band gap is about 4.00 eV. The optimum effect of photocatalysis is obtained when the concentration of NaOH is 1.0–1.5 mol/L, by which degradation rate of RhB can be up to 92 % after the UV-light irradiation for 210 min.     

Growth Orientation of the Mechanosynthesized Fluorapatite-Based Composite Nanopowders: Influence of Subsequent Thermal Treatment

Growth orientation of fluorapatite–zirconia nanopowders was investigated after mechanical activation and thermal annealing process in the range of 600–1,300 °C for 1 h. Results revealed that during heating of the composite nanopowders the transition of the monoclinic zirconia to tetragonal form and its stabilization by calcium fluoride originating from the decomposition of fluorapatite as well as the formation of a solid solution of calcium fluoride in zirconia occurred. The influence of annealing on the growth orientation of fluorapatite–zirconia composite nanopowders indicated that the crystal growth of fluorapatite was preferentially accentuated on the (002) face in the direction of the crystallographic c-axis after heat treatment. Based on FE–SEM observations, the experimental outcome was composed of both agglomerates and fine particles (~33 nm) after 600 °C, while annealing of the sample at 1,300 °C demonstrated the occurrence of abnormal grain growth.     

Hydrothermal conversion of cellulose into lactic acid with nickel catalyst

Utilization of biomass has become a major topic of research around the world. One promising aspect of utilization is production of lactic acid from carbohydrate biomass. Our previous study showed that lactic acid can be formed from glucose and cellulose by alkaline hydrothermal reactions, but the yield of lactic acid was low, particular for cellulose. In this study, an efficient method for producing lactic acid from cellulose under hydrothermal conditions with NaOH in the presence of nickel was developed. Experiments were conducted in a batch reactor at 300 °C for 1?C4 min. Results showed that nickel could promote the yield of lactic acid from cellulose. The highest yield of 34.07% was obtained by adding 0.5 mmol nickel using 2.5 M NaOH solution at 300 °C for 1 min.