Hot Sulfuric Acid Research Articles

Precipitation of indium using sodium tripolyphosphate

The main purpose of this study was to precipitate indium and extract indium from pressure oxidative leaching liquor using sodium tripolyphosphate. Various influential factors were evaluated in the paper, such as pH value, temperature, reaction time, molar ratio of Na 5P 3O 10/indium and metal ions including Fe 3+, Fe 2+, Cu 2+, Cd 2+, Zn 2+, etc. Over 95% of the indium was precipitated under the conditions employed, e.g. at a pH of 2.6, with a Na 5P 3O 10 to indium molar ratio of 0.91, and 1.5 h reaction time. The chemical and X-ray diffraction analyses showed that the main component of the precipitates was NaIn 3 (P 3O 10) 2·12H 2O. The resulting precipitate was dissolved by using NaOH solution and hot sulfuric acid solution respectively, and then the solution was subjected to solvent extraction and cementation using zinc powder for the recovery of indium.

Temperature Shifts for Extraction and Purification of Zygomycetes Chitosan with Dilute Sulfuric Acid

The temperature-dependent hydrolysis and solubility of chitosan in sulfuric acid solutions offer the possibility for chitosan extraction from zygomycetes mycelia and separation from other cellular ingredients with high purity and high recovery. In this study, Rhizomucor pusillus biomass was initially extracted with 0.5 M NaOH at 120 °C for 20 min, leaving an alkali insoluble material (AIM) rich in chitosan. Then, the AIM was subjected to two steps treatment with 72 mM sulfuric acid at (i) room temperature for 10 min followed by (ii) 120 °C for 45 min. During the first step, phosphate of the AIM was released into the acid solution and separated from the chitosan-rich residue by centrifugation. In the second step, the residual AIM was re-suspended in fresh 72 mM sulfuric acid, heated at 120 °C and hot filtered, whereby chitosan was extracted and separated from the hot alkali and acid insoluble material (HAAIM). The chitosan was recovered from the acid solution by precipitation at lowered temperature and raised pH to 8–10. The treatment resulted in 0.34 g chitosan and 0.16 g HAAIM from each gram AIM. At the start, the AIM contained at least 17% phosphate, whereas after the purification, the corresponding phosphate content of the obtained chitosan was just 1%. The purity of this chitosan was higher than 83%. The AIM subjected directly to the treatment with hot sulfuric acid (at 120 °C for 45 min) resulted in a chitosan with a phosphate impurity of 18.5%.

An Improved and Mild Wenker Synthesis of Aziridines

The conventional Wenker synthesis of aziridines from vicinal amino alcohols has been modified by employing mild reaction conditions. Amino alcohols were converted into their hydrogen sulfates with chlorosulfonic acid. The sulfates were cyclized with sodium hydroxide, and even with non-nucleophilic sodium carbonate. The current, improved method extends the scope of the typical Wenker synthesis and is applicable to unstable amino alcohols in hot sulfuric acid and to unstable sulfates which favor elimination and hydroxide displacement in the presence of strong base.

Production of low molecular weight chitosan by hot dilute sulfuric acid

A new method was developed for production of low molecular weight chitosan, in which high molecular weight chitosan was treated with dilute sulfuric acid at 120°C. Chitosan was dissolved in the acid solution in a few minutes, and as depolymerized to low molecular weight chitosan by longer times. Low molecular weight chitosan was recovered from the acid by cooling down the solution and increasing the pH to 8-10. A low molecular weight chitosan with Mv (viscosity average molecular weight) of 174×103 was prepared from a high molecular weight chitosan (Mv = 1,388×103) with 82% recovery by using 72 mM sulfuric acid solution for 30 min. Increasing the time to 240 min reduced the Mv to 24×103, though the recovery of chitosan was reduced to 54%. Higher concentrations of acid (216 and 360 mM) resulted in higher depolymerization degrees and lower recoveries of chitosan in identical treatment times. Analysis of glucosamine and N-acetyl glucosamine showed that the prepared low molecular weight chitosan had more than 80% purity.

Extraction of indium from zinc plant residues

The main purpose of this study was to extract indium from the Irankoh zinc plant residue. The Irankoh zinc plant residue contained 145 ppm indium. The optimum conditions for leaching of indium and reduction of ferric ion in reductive leaching were obtained at temperature of 90 °C for a leaching duration of 3 h with sulfuric acid concentration of 100 g/L and the amount of required sodium sulfide for reduction of ferric was 1.5 times of stoichiometric quantity of iron. Then, to prepare concentrated indium solution, indium was selectively precipitated from the leach solution. The pH of leach solution was adjusted to 6 with ammonia solution in 90 °C for selective indium precipitation, and reaction time was considered to be 10 min. Then the resulting precipitation was dissolved using hot sulfuric acid solution, and the solution was subject to solvent extraction and cementation using zinc powder to recover indium.

Neutral polar methacrylate‐based monoliths for normal phase nano‐LC and CEC of polar species including N‐glycans

Neutral diol methacrylate-based monoliths were developed for normal phase chromatography (NPC) and NP-CEC of polar compounds including N-glycans. Four different diol methacrylate-based monoliths were synthesized via the copolymerization of a functional monomer using either glyceryl monomethacrylate (GMM) or glycidyl methacrylate (GMA) and a crosslinker either ethylene dimethacrylate (EDMA) or trimethylolpropane trimethacrylate (TRIM). While the GMM-based monoliths yield in one reaction step polar diol methacrylate monoliths that are ready for use in NPC or NP-CEC, the GMA-based monoliths required a postmodification with hot sulfuric acid to convert the epoxy functions into diols before use in NPC or NP-CEC. All the four monoliths are neutral and void of fixed charges on their surfaces but yet exhibited relatively strong EOF in NP-CEC. The EOF is attributed to the adsorption of ions from the mobile phase thus forming the electric double layer necessary for producing a bulk mobile phase flow. Under the same in situ copolymerization conditions of GMM or GMA with either EDMA or TRIM, the GMM-EDMA monolith was the best choice in terms of retention, separation efficiency, EOF velocity in CEC and linear flow velocity in Nano-LC.

Passivation and Electrocatalytic Behavior of an Amorphous Nickel–Carbon Film in Sulfuric Acid

The electrochemical behavior of a sputtered film of carbon and nickel, of approximate stoichiometry , is presented. This film is quite passive in hot sulfuric acid solution. The material also displays considerable electrocatalytic activity toward the hydrogen reaction, both anodically and cathodically. The electrocatalyst is passivated by the carbon component after dissolution of some of the surface nickel. The remaining surface nickel, entrapped by carbon, provides electrocatalytic activity comparable with that of pure polycrystalline nickel.

Morphology and conductivity of polyaniline sub-micron fibers prepared by electrospinning

Sub-micron fibers of pure polyaniline (PANI) doped with sulfuric acid or hydrochloric acid were prepared by electrospinning PANI with suitable molecular weight dissolved in hot sulfuric acid. A modified electrospinning setup was employed with a coagulation bath as a collector, where dilute sulfuric acid was used as coagulation bath. The factors influencing the morphology and conductivity of the synthesized PANI fibers were investigated, including the concentration of dilute H 2SO 4 solution in the coagulation bath, the doped PANI concentration in H 2SO 4 solution, the type of doping acid and the voltage applied to the solution. The morphologies of doped PANI fibers were characterized by scanning electron microscope (SEM). The structure of the resulting fibers was analyzed by Fourier transform infrared spectroscopy and UV–vis spectrometer. The conductivity of PANI fibers were characterized by I– V characteristics. Homogeneous PANI fibers with a diameter of 370 nm and a high conductivity of 52.9 S/cm were prepared. The possible mechanisms of different morphology formation and conductivity of PANI fibers were also discussed.

Reactions of (Hydroxo)(tetrakis(3,5-dicarboxy)-and (Hydroxo)(tetrakis(4,5-dicarboxy)phthalocyaninato)aluminum(III) with Sulfuric Acid: Simulation and Kinetic Experiments

The interaction of the octacarboxy-substituted aluminum(III) phthalocyanines (hydroxo)(tetrakis(3,5-dicarboxy)- and (hydroxo)(tetrakis(4,5-dicarboxy)phthalocyaninato)aluminum(III) with sulfuric acid is reported. It has been demonstrated by computer simulation (PM3 method) and by studying the dependence of the electronic absorption spectra of the complexes in sulfuric acid on the acidity of the medium that ((OH)AlPc(4-COOH)4(5-COOH)4 has three protonated forms (mono-, di-, and trication) both in the gas phase and in concentrated sulfuric acid and (OH)AlPc(3-COOH)4(5-COOH)4 has three protonated forms in the gas phase and two ones in concentrated sulfuric acid. The destruction kinetics of the aluminum(III) phthalocyanines in hot sulfuric acid is investigated. A destruction mechanism is suggested in which the rate-limiting step is the dissociation of an Al-N bond and the transition state consists of one aluminum(III) phthalocyanine molecule and one hydronium ion. A stability series is established for a set of differently carboxy-substituted aluminum(III) phthalocyanines. The major factors in the stability of the complexes are the negative inductive effect and the number of carboxyl groups.

Extraction and Precipitation of Chitosan from Cell Wall of Zygomycetes Fungi by Dilute Sulfuric Acid

A new method was developed in this work for extraction of chitosan from the zygomycetes cell wall. It is based on the temperature-dependent solubility of chitosan in dilute sulfuric acid. Chitin is soluble in neither cold nor hot dilute sulfuric acid. Similarly chitosan is not soluble at room temperature but is dissolved in 1% H 2SO 4 at 121 degrees C within 20 min. The new method was developed to measure the chitosan content of the biomass and cell wall. The procedures were investigated by measuring phosphate, protein, ash, glucuronic acid, and degree of acetylation. The cell wall derivatives of fungus Rhizomucor pusillus were then examined by this new method. The results indicated 8% of the biomass as chitosan. After treatment with NaOH, the alkali-insoluble material (AIM) contained 45.3% chitosan. Treatment of AIM with acetic acid resulted in 16.5% acetic-acid-soluble material (AcSM) and 79.0% alkali- and acid-insoluble material (AAIM). AcSM is usually cited as pure chitosan, but the new method shows major impurities by, for example, phosphate. Furthermore, AAIM is usually considered to be the chitosan-free fraction, whereas the new method shows more than 76% of the chitosan present in AIM is found in AAIM. It might indicate the inability of acetic acid to separate chitosan from the cell wall.

A novel volumetric method for quantitation of titanium dioxide in cosmetics

Nowadays there are many sun-protection cosmetics incorporating organic or inorganic UV filters as active ingredients. Chemically stable inorganic sunscreen agents, usually metal oxides, are widely employed in high-SPF (sun protection factor) products. Titanium dioxide is one of the most frequently used inorganic UV filters. It has been used as a pigment for a long period of cosmetic history. With the development of micronization techniques, it has become possible to incorporate titanium dioxide in sunscreen formulations without the previous whitening effect, and hence its use in cosmetics has become an important research topic. However, there are very few works related to quantitation of titanium dioxide in sunscreen products. In this research, we analyzed the amounts of titanium dioxide in sunscreen cosmetics by adapting redox titration, reduction of Ti(IV) to Ti(III), and reoxidation to Ti(IV). After calcification of other organic ingredients of cosmetics, titanium dioxide is dissolved by hot sulfuric acid. The dissolved Ti(IV) is reduced to Ti(III) by adding metallic aluminum. The reduced Ti(III) is titrated against a standard oxidizing agent, Fe(III) (ammonium iron(III) sulfate), with potassium thiocyanate as an indicator. In order to test the accuracy and applicability of the proposed method, we analyzed the amounts of titanium dioxide in four types of sunscreen cosmetics, namely cream, make-up base, foundation, and powder, after adding known amounts of titanium dioxide (1 approximately 25 w/w%). The percentages of titanium dioxide recovered in the four types of formulations were in the range between 96% and 105%. We also analyzed seven commercial cosmetic products labeled with titanium dioxide as an ingredient and compared the results with those obtained from ICP-AES (inductively coupled plasma-atomic emission spectrometry), one of the most powerful atomic analysis techniques. The results showed that the titrated amounts were well in accord with the analyzed amounts of titanium dioxide by ICP-AES. Although instrument-based analytical methods, namely ICP-MS (inductively coupled plasma-mass spectrometry) and ICP-AES, are best for the analysis of titanium, it is difficult for small cosmetic companies to install such instruments because of their high cost. It was found that the volumetric method presented here gives quantitatively accurate and reliable results with routine lab-ware and chemicals.

Describing sewage sludge pyrolysis kinetics by a combination of biomass fractions decomposition

The sewage sludge is considered to be highly heterogeneous and comprising a mixture of various compounds. The characterization was performed in order to follow their compositions according to biomass fractions. The analytical method used was a sequence of ethanol–toluene extraction and digestion by hot water and sulfuric acid, achieving the fractionation of extractives, water- and acid-insoluble materials and lignin contents, respectively. Pyrolysis behavior was studied by Thermogravimetric Analysis run on original sludge and its extracted/digested residues. Typical main decomposition occurred in the range of 250–600 °C. The decomposition mechanism was more obviously elucidated when extracted and digested residues were tested. According to DTG data, the kinetic modeling was performed using a combination of four reactions, each reaction contributed by an individual compound. The apparent activation energies were found at ca. 82, 121, 64 and 121 kJ mol −1. The first three values were comparable to that of biomass species decomposition, namely hemicellulose, cellulose and lignin, respectively. The first compound may be also explained by a complex protein presented in bacteria. Another reaction, however, was categorized into extractives such as lipids, waxes or oils. Instead of 1.0 as realized in biomass species, reaction order of sludge component decomposition was somewhat deviated from 1.0 (between 0.91 and 1.63). This indicated some properties of sludge constituents that deviate from natural biomass fractions. The hypothesis was also confirmed by FTIR run on original and extracted/digested sludges which indicate the closely analogy to those biomass species.

Techniques for Enhancing Saltgrass Seed Germination and Establishment

Because of its exceptional salinity tolerance, inland saltgrass [Distichlis spicata var. stricta (L.) Greene] has great potential for use as a turfgrass and revegetation species of saline sites. However, saltgrass seeds have a low germination rate due to seed dormancy. Three experiments were conducted to evaluate different seed treatments to enhance germination and establishment of inland saltgrass. In Experiment I, seven different seed treatments were tested for their ability to enhance germination percentage in the growth chamber and compared with a control of no treatment. These treatments included treatments with hot water, hydrogen peroxide (H2O2), sulfuric acid (H2SO4), potassium nitrate (KNO3), bleach, machine scarification, stratification, and hand nicking. Results indicated that germination percentage was increased only by stratification, hand nicking, and machine scarification treatments as compared with the control. In Experiment II, machine scarification, stratification, hand nicking, and the control were tested in the growth chamber. Hand nicking, scarification, and stratification increased percentage germination from 13.0% to 54.0 to 61.7%. Stratification resulted in the fastest germination, followed by hand nicking and scarification. Experiment III was conducted in the field, and seed treatments included machine scarification, stratification, and the control. Two months after seeding, plots seeded with stratified and scarified saltgrass seeds established adequate plot coverage as a turf, whereas the coverage for the control was inadequate, exhibiting inferior turf quality. In summary, stratification and machine scarification improve germination and establishment of seeded saltgrass.

Quantitative NMR spectroscopy of complex technical mixtures using a virtual reference: chemical equilibria and reaction kinetics of formaldehyde–water–1,3,5-trioxane

Quantitative 1H NMR spectroscopy was used to study chemical equilibria and reaction kinetics of both the formation and decomposition of 1,3,5-trioxane in aqueous formaldehyde solutions. The reaction was homogeneously catalyzed with up to 0.10 g g(-1) sulfuric acid at temperatures between 360 and 383 K so that most of the experiments had to be carried out pressurized. The studied mixtures were complex due to the formation of methylene glycol and poly(oxymethylene) glycols in aqueous formaldehyde and the presence of considerable amounts of ionized species. Most common internal standards are decomposed by the hot sulfuric acid and external standards were not applicable using the flow NMR probe or pressurizable NMR sample tubes. Therefore, for the quantification of the small trioxane signals, a novel procedure was applied, in which electronically generated NMR signals were used as highly stable Virtual References (VR). The NMR decoupler channel with wave-form generator was used as the source of the reference signal, which was irradiated into the probe using the lock coil. Details on the experimental procedure are presented. It is shown that the presented method yields reliable quantitative reaction data for the complex studied mixtures.

Evaluating the technologies of thermal desalination using low-grade heat

This paper compares the effectiveness of thermal schematics, thermal efficiency, and performance ratio. A sulfuric acid plant located at the coastal line of Morocco was identified as an example for comparison because it utilizes low-grade heat to produce desalinated water needed at the facility from the large volumes of cooling water used in current processes. Currently the acid cooling is performed in the shell-and-tube heat exchanger used for cooling hot sulfuric acid. The heat is then “rejected” to the sea. Both multi-effect distillation (MED) and multi-stage flushing (MSF) systems have advantages in that low grade heat can be used for evaporation and subsequent production of freshwater. The MED process is designed for utilization of low-grade thermal heat as a heat source in the form of hot water in the range of 0.8–3 bar, which is supplied to the first effect of the desalination unit. It operates with lower top brine temperatures in the range of 64–70°C. The thermal performance, operational and capital cost are directly proportional to the number of effects in the MED system. In MSF, the heated steam is routed to the brine heater. It operates with top brine temperatures in the range of 90–110°C. In comparison, the plate heat exchanger (PHE) could be used to recover heat from circulating acid for desalination feed water preheating. Despite the presence of these thermal schematics, comparison of the thermal desalination schematics to utilize low-grade heat is absent.

Sorption of precious metals onto chemically prepared carbon from flax shive

The sorption of gold, silver, palladium and platinum chlorides onto a carbonaceous sorbent prepared from flax shive by treatment with hot sulfuric acid is described. The results showed that the rate of sorption followed a first-order relationship with the initial rate described largely by pore diffusion. The sorption of the metal ions followed the Langmuir equation with the calculated monolayer capacities following the order: Au(III)>Pd(II)>Ag(I)>Pt(II)≈Pt(IV). The sorption process was shown to occur by ion exchange reactions with functional groups on the sorbent. Once the metal ions had been loaded onto the sorbent, they were, except for platinum(IV), reduced by the sorbent to the metal with oxidation of the sorbent generating further ion exchange sites for sorption of the metal ions. This allowed the possibility of recycling the sorbent until significant amounts of the precious metal had been accumulated, thus simplifying the recovery of the metal by combustion of the residual sorbent.

The nucleation centers formed during bias-enhanced nucleation of diamond on iridium: structure and stability

During bias-enhanced nucleation (BEN) of diamond on iridium, an ultrathin carbon nucleation layer is deposited. The nature of the nucleation centers or nuclei which gather in discrete islands is investigated in the present work by subjecting the as-biased samples to different treatments. In high vacuum annealing experiments, the structures proved completely stable up to 1000 °C. Above this temperature, the nuclei were destroyed and the iridium was etched within the domain areas. Low energy oxygen and xenon ion beams were then used to etch very shallow craters of varying depth. The induced modifications of the surface and the influence on the nucleation density can be understood on the basis of calculations which simulate the damage caused by the ion bombardment. Finally, the stability of the nucleation structures under hot chromo sulfuric acid treatment was compared with the corresponding behavior of a thick amorphous carbon layer. In all the experiments, the nucleation structures formed during BEN behaved similar to diamond situated at the surface of the iridium buffer layer possibly covered by a thin stable amorphous carbon layer.

Structure, Bonding, and Stability of a Catalytica Platinum(II) Catalyst: A Computational Study

Periana et al. [Science 1998, 280, 560] previously reported two catalysts for low-temperature methane activation to methanol: PtCl2(NH3)2 and PtCl2(bpym). It was shown that the ammine catalyst is much more active, but it decomposes rapidly in sulfuric acid to form a PtCl2 precipitate, while the bpym system is long-lived. To have a basis for developing new catalysts that would not decompose, we undertook a study of the structure, bonding, and stability of the PtCl2(NH3)2 and PtCl2(bpym) catalysts, using quantum mechanics (QM) [density functional theory (DFT) at the B3LYP/LACVP**(+) level] including solvation in sulfuric acid via the Poisson−Boltzmann continuum approximation. Critical results include the following: (1) The influence of a trans ligand Y on the Pt−X bond follows the order Cl- > NH3 (bpym) > OSO3H- > □ (empty site). Thus the Pt−N bond length is longer (up to 0.04 Å) and the Pt−N bond is weaker (up to 18 kcal/mol) when trans to a Cl- as compared to trans to OSO3H-. (2) The bpym ligand acts as both a σ-donor and a π-acceptor. As bpym is protonated, the Pt−N bond strength decreases (by up to 51 kcal/mol). Thus, ΔH(soln, 453 K) for Pt(OSO3H)2(bpym) (69.6) > [Pt(OSO3H)2(bpymH)]+ (49.4) > [Pt(OSO3H)2(bpymH2)]2+ (18.7). (3) In sulfuric acid replacing the ammine ligands with bisulfate ligands is thermodynamically favorable [by ΔG(soln, 453 K) = −23 kcal/mol], whereas replacement of bpym with OSO3H- is unfavorable [by ΔG(soln, 453 K) = +16 kcal/mol]. (4) Replacement of chloride ligands with bisulfate ligands is thermodynamically unfavorable [by ΔG(soln, 453 K) = ∼7 kcal/mol for ammine and ∼12 kcal/mol for bpym]. (5) Protonation of PtCl2(bpym) is thermodynamically favorable, leading to [PtCl2(bpymH)]+ as the stable species in sulfuric acid (by 8 kcal/mol). Thus we conclude that in hot concentrated sulfuric acid it is quite favorable for PtCl2(NH3)2 to lose its ammine ligands to form PtCl2, which in turn will dimerize and oligomerize, leading eventually to a (PtCl2)n precipitate and catalyst death. We find that PtCl2(bpym) is resistant to solvent attack, favoring retention of the bpym ligand in hot concentrated sulfuric acid. These results agree with experimental findings. The insights from these findings should help screen for stable new ligands in the design of new catalysts.

Formation of new crystal faces on TiO2 particles by treatment with aqueous HF solution or hot sulfuric acid

We have demonstrated that new crystal faces are generated on anatase and rutile TiO2 particles by means of chemical etching in aqueous hydrofluoric acid or hot sulfuric acid. In the treatment with aqueous hydrofluoric acid, the {112} face of anatase particles and the {021} face of rutile particles are newly formed. When treated with hot sulfuric acid, anatase particles exposed the {122} face and rutile particles exposed the {001}, {010}, {021} and {121} faces. In both cases, anatase particles are etched at a higher rate than rutile particles. The etched particles are expected to show photocatalytic properties unique to the crystal faces. For example, the {112} face of anatase particles is demonstrated to be active in the oxidation of Pb2+ ions.

Visualization of the Retinal and Choroidal Microvasculature by Fluorescent Liposomes

Publisher Summary The technique of liposome-encapsulated, temperature-sensitive dye has undergone many cycles of evolution since its inception. Although initially intended as a vehicle for selectively releasing the encapsulated dye at a given location, this technique evolved to allow visualization of a single dye-enhanced liposome using the scanning laser ophthalmoscopy (SLO). This technique benefited greatly from the advent of technology, such as the SLO and digital image processing. Fluorescein angiography uses the principle of luminescence in which a fluorescein molecule is stimulated by electromagnetic radiation of a specific wavelength. The excited molecule then emits light of a longer wavelength of less energy as it returns to its ground state. Fluorescein is excited by wavelengths between 465 and 490 nm in the blue spectrum and the excited emission lies between 520 and 530 nm in the green-yellow spectrum. Fluorescein is an orange-brown crystalline triphenylmethane group, and it is the product of a reaction between phthalic acid anhydride and resorcinol using hot sulfuric acid as the catalyst. The yellow-green hyperfluorescence appears only when it dissociates in an alkaline sodium-salt solution, because fluorescence is dependent on the pH of the solvent and is only observed with pH greater than 6. Injected fluorescein is largely bound to plasma proteins and the surfaces of red blood cells. The interaction alters its absorption/emission spectrum. There are several methods of preparing liposomes, depending on the types of liposomes desired: small unilamellar vesicles (SUV), multilamellar vesicles (MLV), or large unilamellar vesicles (LUV).