Dilute Sulfuric Acid Solution Research Articles

EIS and XPS studies on passive film of AISI 304 stainless steel in dilute sulfuric acid solution

Electrochemical impedance spectroscopy and XPS studies on AISI 304 stainless steel in naturally aerated 0.5 M H2SO4 solution were carried out at room temperature. The valuable model of the metal/solution interphase was established, and the reliable equivalent electrical circuits in the solution were presented. The analysis of the chemical composition of passive film on AISI 304 stainless steel was carried out by XPS. The passive film of AISI 304 stainless steel is composed of oxyhydroxides, Fe2O3, FeO, Cr2O3, NiO, sulfate, sulfite, and sulfide (FeS, NiS). It is reported that the ferrous sulfide film formed on AISI 304 stainless steel in the dilute sulfuric acid solution. The possible process in which sulfuric acid is reduced to sulfite and sulfide is proposed. The galvanic interaction of sulfide inclusions with the base alloy is introduced. Copyright © 2011 John Wiley & Sons, Ltd.

Characterization and fuel cell performance analysis of polyvinylalcohol–mordenite mixed-matrix membranes for direct methanol fuel cell use

Polyvinylalcohol–mordenite (PVA–MOR) mixed matrix membranes were synthesized for direct methanol fuel cell (DMFC) use. For the structural and the morphological characterization, Scanning Electron Microscopy and Thermal Gravimetric Analysis methods were used. Zeolite distribution within the polymer matrix was found to be homogeneous. An impedance spectroscope was used to measure the proton conductivity. In order to obtain information about methanol permeation characteristics, swelling tests and a series of pervaporation experiments were carried out. 60–40 wt% PVA–MOR membranes were found to give the optimum transport properties. Proton conductivity of these membranes was found to be slightly lower than that of Nafion117™ whereas their methanol permeability was at least two orders of magnitude lower than Nafion117™. DMFC performance of the PVA–MOR membranes was also measured. The inferior DMFC performance of PVA–MOR membranes was linked to drying in the fuel cell medium and the consequent proton conductivity loss. Their performance was improved by adding a dilute solution of sulfuric acid into the feed methanol solution. Future studies on the improvement of the proton conductivity of PVA–MOR membranes, especially via sulfonation of the polymer matrix, can overcome the low-performance problem associated with insufficient proton conductivity.

Removal and recovery of furfural, 5‐hydroxymethylfurfural, and acetic acid from aqueous solutions using a soluble polyelectrolyte

In the cellulosic ethanol process, furfural, 5-hydroxymethylfurfural (HMF), and acetic acid are formed during the high temperature acidic pretreatment step needed to convert biomass into fermentable sugars. These compounds can inhibit cellulase enzymes and fermentation organisms at relatively low concentrations (≥ 1 g/L). Effective removal of these inhibitory compounds would allow the use of more severe pretreatment conditions to improve sugar yields and lead to more efficient fermentations; if recovered and purified, they could also be sold as valuable by-products. This study investigated the separation of aldhehydes (furfural and HMF) and organic acid (acetic acid) inhibitory compounds from simple aqueous solutions by using polyethyleneimene (PEI), a soluble cationic polyelectrolyte. PEI added to simple solutions of each inhibitor at a ratio of 1 mol of functional group to 1 mol inhibitor removed up to 89.1, 58.6, and 81.5 wt% of acetic acid, HMF, and furfural, respectively. Furfural and HMF were recovered after removal by washing the polyelectrolyte/inhibitor complex with dilute sulfuric acid solution. Recoveries up to 81.0 and 97.0 wt% were achieved for furfural and HMF, respectively. The interaction between PEI and acetic acid was easily disrupted by the addition of chloride ions, sulfate ions, or hydroxide ions. The use of soluble polymers for the removal and recovery of inhibitory compounds from biomass slurries is a promising approach to enhance the efficiency and economics of an envisioned biorefinery.

A thermodynamic rationalisation for the oxidising behaviour of concentrated H2SO4

AbstractAn attempt is made to extend the principle of equilibrium electrochemical potential–pH diagrams for sulfur compounds in dilute aqueous solutions of sulfuric acid (H2SO4) to more concentrated aqueous solutions up to 100 wt.%. Published Hammett acidity data is used to account for the medium effect (undissociated H2SO4) on the proton activity. The calculated electrochemical potential‐Hammett acidity diagrams predict a thermodynamic stability domain for all three of the reduction products experimentally observed during cathodic electrolysis, which included sulfur dioxide (SO2), sulfur (S), and hydrogen sulfide (H2S). The implications of the relative stability domains on corrosion control measures are discussed.

Ammonia removal from aqueous solutions using hollow-fiber membrane contactors

The adverse effects of ammonia and related compounds commonly found in wastewater streams have promoted the development of more efficient methods for their removal. In this study, polypropylene hollow-fiber membranes were used to achieve this purpose. A dilute solution of sulfuric acid was used as a stripping solution to accelerate the removal of the ammonia from aqueous solutions. The effects of several factors such as the initial concentrations of the ammonia and sulfuric acid solutions, the pH of the ammonia feed, the velocity of the feed streams and the presence of excess ions in the ammonia feed solution on the overall mass transfer of the ammonia were investigated. The Taguchi method was used to design the experiments and analyze the results. Polypropylene hollow-fiber membranes were found to be very effective in separating ammonia from the waste waters, in proper conditions, ammonia removal of over 99% was achieved. Results show that the initial concentrations and velocities of the ammonia and sulfuric acid solutions had negligible effects on the ammonia removal in the range studied. Increasing the pH value of ammonia feed solution up to 10 improved the removal of ammonia significantly while further increasing the pH to the higher values resulted in insignificant improvements. Raising the ammonia feed velocity enhanced the ammonia removal in the range studied.

Acidity as a factor in leaching of copper, chromium and arsenic from CCA-treated dimension lumber

Samples of new and weathered utility lumber pressure-treated with chromated copper arsenate (CCA) were tested for leaching of copper, chromium and arsenic by submersion in leaching baths of various pH levels. Accumulation of metals was monitored in leachate at pH 3.5, 4.5, 5.5, 7.0 and 8.5 over a period of 40 d by atomic absorption spectroscopy. Copper, chromium and arsenic were found in the leachate of both new and weathered wood with significantly higher levels of all metals occurring at acidic pH levels. Up to 100% of CCA treatment metals were found to have leached at pH 3.5, whereas a maximum of 9% of metals leached at pH 8.5. Metal leaching was found to be higher in citric acid than in dilute sulfuric acid solutions. Leaching of copper, chromium and arsenic was not proportional to the amount of metal present before leaching.

Tribocorrosion behavior of Ti 3SiC 2 in the dilute and concentrated sulfuric acid solutions

In light of the salient physical and mechanical performance combined with good corrosive resistance, Ti 3SiC 2 is expected to be used as materials for mechanical component in corrosive environment. It is in necessity to investigate the tribocorrsion behavior of Ti 3SiC 2 in corrosive environment. In the electrochemical test, Ti 3SiC 2 experienced passivation when potential was positive than the corrosion potential in sulfuric acid (H 2SO 4) solutions. In the tribocorrosion tests of Ti 3SiC 2 against Si 3N 4 in dilute (1 M) and concentrated (10 M and 15 M) H 2SO 4 solutions, mechanical removal of material owing to decoherence of Ti 3SiC 2 grains led to high wear for Ti 3SiC 2. In the concentrated H 2SO 4 solutions, an amorphous SiO 2 layer formed by chemically corrosive oxidation acted as lubricant reducing friction coefficient and wear by eliminating decoherence of grains. However, mechanical decoherence of Ti 3SiC 2 grains prevailed again when the load increased. Tribocorrosion behavior of Ti 3SiC 2 strongly depended on the alternative domination of mechanical or chemical effects.

Enhancement of polymer electrolyte membrane fuel cell performance by boiling a membrane electrode assembly in sulfuric acid solution

A catalyst-coated membrane (CCM) as used in the membrane electrode assembly (MEA) of a polymer electrolyte membrane fuel cell is treated by dilute sulfuric acid solution (0.5 M) at boiling temperature for 1 h. This treatment improves the single-cell performance of the CCM without further addition of Pt catalyst. The changed microstructure and electrochemical properties of the catalyst layer are investigated by field emission scanning electron microscopy with energy dispersive X-ray, mercury intrusion porosimetry, waterdrop contact angle measurement, Fourier transform-infrared spectrometry in attenuated total reflection mode, electrochemical impedance spectroscopy, and cyclic voltammetry. The results indicate that this pretreatment enhances MEA performance by changing the microstructure of the catalyst layer and thus changing the degree of hydration, and by modifying the Pt surface, thus enhancing the oxygen reduction reaction.

Mass transport and effective diffusion coefficient in the reduction of hydrogen ions from aqueous sulfuric acid solutions: Numerical modeling

This work presents results of the numerical solution to a system of equations of material balance and the movement of particles in solution under the influence of the forces of diffusion, migration, and convection, which describe the process of mass transport during the reduction of hydrogen ions at a rotating disk electrode from aqueous sulfuric acid solutions with and without excess supporting electrolyte. Results of the calculations show that the diffusion kinetics of hydrogen ion reduction can be observed only with measurements in dilute (≤10−3 M) sulfuric acid solutions with an excess of indifferent supporting electrolyte. For more acidic solutions it is necessary to take into account the simultaneous diffusion of hydrogen and bisulfate ions. In the study of the regularities of hydrogen ion reduction in sulfuric acid solutions with a sulfate supporting electrolyte, it is necessary to take into account that with excess supporting electrolyte, the limiting current of hydrogen reduction is caused solely by the diffusion of bisulfate ions, but for small concentration ratios of the supporting electrolyte to acid, the influence of migration effects is significant.

Electrochemical amination. Dilute aqueous organic solutions of sulfuric acid

The electrochemical process of anisole amination is studied in 1.5–9 M H2SO4 solutions containing acetonitrile or acetic acid. It is shown that the synthesis of aromatic monoamino compounds is better performed in moderately acidic media with high concentrations of organic solvents. Due to the chain mechanism of the electrochemical process, the current efficiency of amines can exceed 150% under these conditions.

Selective extraction of nickel from ammoniacal solutions containing nickel and cobalt by emulsion liquid membrane using 5,7-dibromo-8-hydroxyquinoline (DBHQ) as extractant

The selective extraction and concentration of nickel from ammoniacal solutions containing nickel and cobalt by an emulsion liquid membrane (ELM) technique using 5,7-dibromo-8-hydroxyquinoline (DBHQ) as extractant has been presented. ELM consists of a diluent (kerosene), a surfactant (Span 80), an extractant (DBHQ), a modifier (tributyl phosphate), and a stripping solution (very dilute sulfuric acid solution containing EDTA as complexing agent, buffered at pH 4.25). Cobalt (II) in feed solution with 6 mol/L ammonia was oxidised to Cobalt (III) by H 2O 2 and pH of this ammoniacal solution was adjusted to 10.0 with the addition of hydrochloric acid (HCl). The important variables governing the permeation of nickel and their effect on the separation process have been studied. These variables were membrane composition, ammonia concentration in the feed solution, mixing speed, surfactant concentration, extractant concentration, pH of the feed and the stripping solutions, complexing agent concentration in the stripping solution, and phase ratio. After the optimum conditions had been determined, it was possible to selectively extract 99% of nickel from the ammoniacal solutions containing Ni and Co. The separation factors of nickel with respect to cobalt, based on initial feed concentration, have experimentally found to be of as high as 88.1 for about equimolar Co–Ni feed solutions.

Study on corrosion resistance of palladium films on 316L stainless steel by electroplating and electroless plating

Palladium films with good adhesive strength were deposited on 316L stainless steel by electroless plating and electroplating. Scanning electronic microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, weight loss tests and electrochemical methods were used to study the properties of the films. The electroless plated palladium film mainly consisted of palladium, phosphorus and nitrogen, and the electroplated palladium film was almost pure palladium. XPS analysis indicated that palladium was present in the films as metal state. The palladium plated stainless steel samples prepared by both methods showed excellent corrosion resistance in strong reductive corrosion mediums. In boiling 20% dilute sulfuric acid solution, the corrosion rates of the palladium plated 316L stainless steel samples were four orders of magnitude lower than that of the original 316L stainless steel samples. In the solution with 0.01 M NaCl, the palladium plated samples also showed better corrosion resistance. In comparison, the electroplated samples showed slightly better corrosion resistance than electroless plated samples, which may be attributed to less impurities and thereby higher corrosion potential for the former.

Effect of solution flow rate and direction on copper electrodeposition process from sulfuric acid electrolyte on porous electrode with high electric conductivity

The effect of solution flow direction and rate on the dynamics of copper electrodeposition onto a premetallized coal-graphite VINN-250 material from a dilute copper sulfate sulfuric acid solution is experimentally studied in the direct-flow mode. A light effect of solution supply on the copper deposit final mass for high and low solution flow rates is found, while the effect of this parameter on the metal distribution within the porous electrode is significant. The most uniform copper deposit distribution throughout the porous electrode is observed in the case of intermediate solution flow rates at its rear supply. The obtained experimental data agree qualitatively with the earlier published mathematical simulation results. Small systematic deviations from numeric calculations can be due to the process disregarded in the mathematical model: the effect of gas phase formed within the porous cathode due to the simultaneous hydrogen evolution.

An electroless plating film of palladium on 304 stainless steel and its excellent corrosion resistance

An uniform palladium film on 304 stainless steel was obtained by electroless plating. Scanning electronic microscopy, X-ray photoelectron spectroscopy, weight loss tests and electrochemical measurements were used to character the properties of the film. The palladium plated stainless steel samples showed excellent corrosion resistance in strong reductive corrosion mediums. In boiling dilute sulfuric acid solutions and boiling acetic/formic acids, corrosion rates of palladium plated 304 stainless steel samples were 3 or 4 orders of magnitude lower than the original 304 stainless steel samples. In solutions with NaCl concentration less that 0.1%, the palladium plated samples also showed better corrosion resistance. The function of palladium film on stainless steel is to raise the electrode potential and promote passivation of the steel in strong corrosive environments.

The effect of agitation speed, enzyme loading and substrate concentration on enzymatic hydrolysis of cellulose from brewer’s spent grain

Brewer’s spent grain components (cellulose, hemicellulose and lignin) were fractionated in a two-step chemical pretreatment process using dilute sulfuric acid and sodium hydroxide solutions. The cellulose pulp produced was hydrolyzed with a cellulolytic complex, Celluclast 1.5 L, at 45 °C to convert the cellulose into glucose. Several conditions were examined: agitation speed (100, 150 and 200 rpm), enzyme loading (5, 25 and 45 FPU/g substrate), and substrate concentration (2, 5 and 8% w/v), according to a 23 full factorial design aiming to maximize the glucose yield. The obtained results were interpreted by analysis of variance and response surface methodology. The optimal conditions for enzymatic hydrolysis of brewer’s spent grain were identified as 100 rpm, 45 FPU/g and 2% w/v substrate. Under these conditions, a glucose yield of 93.1% and a cellulose conversion (into glucose and cellobiose) of 99.4% was achieved. The easiness of glucose release from BSG makes this substrate a raw material with great potential to be used in bioconversion processes.

Preparation of porous rutile titania from ilmenite by mechanical activation and subsequent sulfuric acid leaching

Synthesis of porous titania via mechanical activation of natural ilmenite and subsequent simultaneous dissolution and hydrolysis in dilute solutions of sulfuric acid was investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), N 2 adsorption/desorption measurements, energy-dispersive X-ray spectrometry (EDX) and thermogravimetric analysis (TG). This is a novel template-free approach for synthesis of microporous, mesoporous and micro–mesoporous TiO 2 materials. Effects of sulfuric acid concentration and calcination temperature on physicochemical properties of the TiO 2 materials were examined systematically. The results show that both the factors considerably affected the porosity of the materials. In a 15% acid solution a microporous TiO 2 hydrolysate with BET surface area 109.3 m 2/g was prepared. With a 10% H 2SO 4, we obtained a more pure micro/mesopore TiO 2 hydrolysate with BET area of 257.6 m 2/g. Calcining the hydrolysate at ⩾500 °C led to the formation of a mesopore TiO 2. The mesoporous TiO 2 generated at 600 °C still has a BET area of 92.1 m 2/g. The high thermal stability is probably related to the presence of H 2SO 4 in the channel walls of hydrolysate. The XRD analysis indicated all the TiO 2 materials prepared in this study being rutile. The mechanism for formation of the porous rutile TiO 2 is mainly via in situ hydrolysis and precipitation of the dissolved titanium on the un-reacted ilmenite surface, where H 2SO 4 may play a very important role.

CrossRef Listing of Deleted DOIs

The oxidation of Fe(II) with dissolved molecular oxygen was studied in sulfuric acid solutions containing 0.2 mol · dm−3 FeSO4 at temperatures ranging from 343 to 363 K. In solutions of sulfuric acid above 0.4 mol · dm−3, the oxidation of Fe (II) was found to proceed through two parallel paths. In one path the reaction rate was proportional to both [Fe−2+]2 andp o 2 exhibiting an activation energy of 51.6 · kJ mol−1. In another path the reaction rate was proportional to [Fe2+]2, [SO 4 2 −], andp o 2 with an activation energy of 144.6 kJ · mol−1. A reaction mechanism in which the SO 4 2 − ions play an important role was proposed for the oxidation of Fe(II). In dilute solutions of sulfuric acid below 0.4 mol · dm−3, the rate of the oxidation reaction was found to be proportional to both [Fe(II)]2 andp o 2, and was also affected by [H+] and [SO 4 2 −]. The decrease in [H+] resulted in the increase of reaction rate. The discussion was further extended to the effect of Fe (III) on the oxidation reaction of Fe (II).

Mechanisms of scale deposition and scale removal in porous media

Calcium sulfate scaling and scale removal have been studied experimentally and theoretically in a well-defined unconsolidated porous medium. The effects of injection rate, scale concentration and temperature on the rate of scale formation and the rate of its removal are investigated. The results of the experiments are used to develop mechanistic models for the prediction of the scaling process in porous media and for removal of the deposits by dilute sulfuric acid solutions. The predictions of the suggested models for scaling and cleaning are compared with measured data. Deviations ranging from 11% to 14% are observed, which confirm the suitability of the models.

Analysis of a novel MEMS-based design of micro-direct methanol fuel cell

A theoretical analysis is performed in this study for a novel MEMS-based design of micro-direct methanol fuel cell which was proposed by Motokawa et al. [S. Motokawa, M. Mohamedi, T. Momma, J. Electrochem. Commun. 6 (2004) 562–565]. The system comprises two parallel microchannels and is fabricated by a series of steps of MEMS techniques. The methanol stream occupies one channel as fuel and the saturated oxygen liquid stream flows in the other channel as oxidant. Both reactants are dissolved in dilute sulfuric acid solution. The top of the system is covered by a layer of Nafion membrane as the electrolyte layer. Such a novel design eliminates the complicated water management problem and could potentially enhance the volume power density. The cell performance is investigated in detail by examining the effects of several system parameters. The present results provide significant physical insights for the system and benefit the further optimal design of this novel MEMS-based design of microfuel cell for the fulfillment of practice application in portable power sources.

Removal of Gold Particles from Chromium Oxynitride Surface with Dilute Sulfuric Acid Solutions

Removal of gold particles (100 nm) from chromium oxynitride surface (CrON) has been investigated using dilute sulfuric acid solutions. Two types of gold nano-particles, one with a negative surface charge and the other with a positive charge achieved by adsorption of poly diallyl-dimethyl ammonium chloride (PDAC), were used. Particle removal efficiency (PRE) increases with sulfuric acid concentration and bath temperature. In 1:10 H2SO4:DI solution, increasing the bath temperature from 25 to 100 {degree sign}C increases the PRE from 21 to 99 %. Introduction of megasonic energy at 0.43 W/cm2 in a 1:10 H2SO4:DI bath at 35 {degree sign}C increases the PRE to 88 %. PDAC coated gold particles are difficult to remove as compared to uncoated particles due to their electrostatic interaction with the surface leading to stronger adhesion.