Electrolytic oxidation of Ce(III) in nitric acid and sulfuric acid media using a flow type cell

The electrochemical oxidation behavior of Ce(III) in nitric acid and sulfuric acid media with various concentrations and compositions were investigated by cyclic voltammetry (CV) and potentiostatic electrolysis. In nitric acid media, the peak potential separation for the redox reactions of the Ce(III)/Ce(IV) couple shifted to base side with the increasing concentration of nitric acid from 1 to 6 M. The kinetics of the Ce(III)/Ce(IV) couple is rapid in high concentration nitric acid. The formal potential is independent of both proton and nitrate concentrations while the standard rate constant increases with added protons but is independent of nitrate concentration. Constant-potential electrolysis also shows that a high proton concentration is electrochemically favorable for the electron transfer of the Ce(III)/Ce(IV) couple and for a high Ce(IV) yield in nitric acid media. The current efficiency was ca. 75% for the oxidation process of Ce(III) at 298 K. A Ce(IV) yield of ca. 80% was achieved for the electrolysis of 100 mM Ce(III) in 6 M HNO₃ solution. In sulfuric acid media, the peak potential separation for the redox reactions of the Ce(III)/Ce(IV) couple shifted to noble side with rising concentration of sulfuric acid from 0.1 to 2 M and then shifted to base side with further increase in the concentration. A Ce(IV) yield of ca. 95% was achieved for the potentiostatic electrolysis of 100 mM Ce(III) in 3 M H₂SO₄ solution.     

Selective electroreduction of pyruvic acid on lead electrode in acid medium

This work reports the electrochemical reduction of pyruvic acid, which contains a carbonyl group more reducible than its carboxylic entity. The electrode potential and the concentration of the starting substrate seemed to be the factors that control the electrochemical production of the competitive reaction products. In fact, lactic acid was mainly obtained on a lead electrode in sulfuric acid for low concentrations of pyruvic acid while 2,3-dimethyl tartaric acid was selectively formed by electrohydrodimerization of a high amount of pyruvic acid. During the cathodic reduction of pyruvic acid in sulfuric acid solution, the effects of electrode potential and pyruvic acid concentration on the selectivity towards the formation of lactic acid were systematically studied.     

Sodium nitrate modified SBA-15 and fumed silica for efficient production of acrylic acid and 2,3-pentanedione from lactic acid

The catalytic conversion of lactic acid to acrylic acid and 2,3-pentanedione over sodium nitrate-supported mesoporous SBA-15 and fumed silica was studied. The yields of acrylic acid, 2,3-pentanedione, and acetaldehyde are 44.8%, 25.1%, and 13.3%, respectively, over the 23%NaNO₃/SBA-15 catalyst. The performance of the catalysts is strongly affected by NaNO₃ loading, catalyst texture and porosity, and product diffusion efficiency. A proper control of NaNO₃ loading can result in modification catalyst structure for improvement of 2,3-pentanedione selectivity. Under certain reaction conditions, the surface NaNO₃ species can readily transform to sodium lactate that functions as active component to catalyze the target reactions.     

Perovskite catalytic ozonation of pyruvic acid in water: Operating conditions influence and kinetics

The catalytic ozonation of pyruvic acid in the presence of the perovskite LaTi_0.15Cu_0.85O₃ has been carried out. Typical operating parameters like ozone inlet concentration, catalyst dosage, protons concentration (below 0.01 M) and temperature (below 303 K) exert a positive influence on the pyruvic acid depletion rate. Regarding the pyruvic acid concentration, a zero kinetic order holds for most of experiments. Under the conditions applied, the process is controlled by the chemical reaction. Acetic and oxalic acids are the only intermediates formed with a higher selectivity towards the former (above 90–95%). The similarities between experimental total organic carbon (TOC) and calculated from the contributions of remaining pyruvic acid and formed acetic and oxalic acids corroborate the previous statement. The activity of the catalyst is enhanced after the first usage. Thereafter, four consecutive reutilisations of the catalyst indicate the high stability of the solid. The process is acceptably simulated by a Langmuir–Hinshelwood kinetic expression derived from adsorption of ozone and pyruvic acid onto different active sites.     

Corrosion inhibition of carbon steel in acid chloride solution using ethoxylated fatty alkyl amine surfactants

Four novel non-ionic ethoxylated fatty alkyl amine surfactants (I–IV) were synthesised and investigated as corrosion inhibitors of carbon steel in 1 M hydrochloric acid solution using gravimetric, open circuit potential and potentiostatic polarisation techniques. The percentage inhibition efficiency (η%) for each inhibitor increased with increasing concentration until the critical micelle concentration (cmc) was reached. The maximum inhibition efficiency approached 95.1% in the presence of 400 ppm of the inhibitor (IV). It was found that the adsorption of the surfactants on carbon steel followed the Langmuir adsorption isotherm. Potentiostatic polarisation data indicated that these surfactants act as mixed type inhibitors. The values of activation energy (E _a*) of carbon steel dissolution in 1 M HCl were calculated in the absence and presence of 400 ppm of each inhibitor. Finally, scanning electron microscopy (SEM) was used to examine the surface morphology of polished carbon steel surfaces and those immersed in 1 M HCl in the absence and presence of 400 ppm of inhibitor (IV).     

Electrosynthesis of lactic acid on copper and lead cathodes in aqueous media

The present study concerns the electrochemical reduction of pyruvic acid in different aqueous media on lead and copper electrodes. Some parameters such as electrode material, nature of the electrolyte, reduction potential and concentration of the organic substrate were systematically studied. The cathodic behavior of pyruvic acid was studied by cyclic voltammetry and suitable conditions were found in order to optimize the conversion of pyruvic acid during prolonged electrolyses. The results obtained showed that the pH of the solution (pH 10), the electrode material (Pb) and potential of electrode (−2.0 V (MSE)) allowed to enhance the selectivity of lactic acid which reached 90% with a conversion yield of 92%.     

Electrosynthesis of iminodiacetic acid from nitrilotriacetic acid

The electrosynthesis of iminodiacetic acid by electrooxidation of nitrilotriacetic acid in undivided cells has been studied using Zn, Cu, PbO₂, DSA^®O₂, DSA^®Cl₂, C, Ni and porous carbon as anodes. Results show that the synthesis is possible in both acid and basic mediums. The best results were obtained in aqueous 40% w/w sulphuric acid with porous carbon RVC-4000 as anode and SUS 316 as cathode, at 60 °C, 400 mA cm^-2 and charge 95% of theoretical. Under these conditions, nitrilotriacetic acid conversion was 92%, current efficiency 80% and selectivity 85%. Loss of selectivity was due to chemical side reaction between iminodiacetic acid and HCHO electrogenerated in the electrolysis.     

Evaluation of problematic indigenous phosphate deposits for phosphoric acid manufacture

To examine the possible utilization of indigenous phosphate reserves, bench scale studies were under-taken to assess their suitability for phosphoric acid manufacture.It was found out that in spite of few problems, the Silicious phosphate reserves of 2–3 million tons could be utilized for phosphoric acid manufacture, because low sulphuric acid consumption 2.52 ton acid/ton P₂O₅ and better P₂O₅ recovery yield (94.71) was achieved. The dolomitic phosphate reserves of 4–5 million tons (having 5–6% MgO) remained problematic, giving low P₂O₅ recovery yield (89.25) and higher sulphuric acid consumption 4.08 tons acid/ton P₂O₅.Product acid from the dolomitic reserves upon concentration became paste like at 36–38% P₂O₅ and therefore, these indigenous dolomitic phosphate reserves could not be utilized for the production of phosphoric acid.     

3-Hydroxybenzoic acid as AISI 316L stainless steel corrosion inhibitor in a H<Subscript>2</Subscript>SO<Subscript>4</Subscript>–HF–H<Subscript>2</Subscript>O<Subscript>2</Subscript> pickling solution

3-Hydroxybenzoic acid (3-HBA) was studied for possible use as a AISI 316L stainless steel (SS) corrosion inhibitor in an environmental-friendly aqueous pickling solution of 75 g l^–1 sulphuric acid (H₂SO₄), 25 g l^–1 hydrofluoric acid (HF) and 30 g l^–1 hydrogen peroxide (H₂O₂). 3-HBA was tested in concentrations from 5 × 10^–5 to 5 × 10^–1 M at 298 and 313 K temperature. Inhibition efficiency increased with the 3-HBA concentration. The inhibitor mechanism is discussed in terms of the properties of the isotherm equations of Frumkin, Hill-de Boer and Kastening–Holleck mainly. The shape, the trend of the slopes along the curve and the existence of inflection points, were analysed as the characteristics that differentiate one adsorption equation from another. The best fit was obtained using the Frumkin isotherm model. The projected molecular area of 3-HBA was calculated as a structural parameter to elucidate its optimal inhibition mechanism.     

Recovery of pyruvic acid with weakly basic polymeric sorbents

BACKGROUND: Carboxylic acids are among the most important substances that can be manufactured from biomass. However, the recovery of carboxylic acids from fermentation broths presents a challenging separation problem. To avoid the production of waste salts and net consumption of chemicals in the calcium carboxylate salt process, the use of reversible chemical complexation with polymeric sorbents and extractants is attractive for carboxylic acid recovery. Pyruvic acid is widely used in the manufacture of medicines, pesticides and foodstuffs and can be produced by fermentation. Since the acidity of pyruvic acid (pK_a = 2.49) is stronger than that of normal carboxylic acids, and as few reports on the recovery of pyruvic acid are available, the sorption of pyruvic acid from aqueous solution on two types of weakly basic polymeric sorbent, tertiary amine D301R and primary amine D392, was investigated over a wide pH range and at various salt (MgSO₄) concentrations. RESULTS: Overloading adsorption of pyruvic acid on both weakly basic polymeric sorbents occurred, with the overloading of D392 being greater than that of D301R. The adsorption of pyruvic acid on both sorbents was greatly affected by the solution pH and the salt concentration in the aqueous phase. An overloading model was able to predict the experimental uptake data very well. CONCLUSION: Solution pH is one of the most important operating conditions, and both polymeric sorbents D392 and D301R can be used to recover pyruvic acid from dilute aqueous solution with high efficiency at a solution pH around 2. The uptake by D392 is greater than that by D301R owing to steric hindrance of the tertiary amine. Copyright © 2008 Society of Chemical Industry     

Effect of some polymeric materials on the corrosion behaviour of tin in succinic acid solution

The anodic behaviour and corrosion of tin in various concentrations (0.05–0.7M) of succinic acid were studied using cyclic voltammetry. The potentiodynamic anodic polarization curves exhibit active/passive transition. The active dissolution of tin involves one anodic peak. The cathodic curve exhibits one cathodic peak corresponding to the reduction of the passive layer. The ratio of the anodic charge/cathodic charge is more than unity indicating that the passive layer is very thin and the dissolution products are mainly soluble species. Additions of some polyethylene glycols to the succinic acid solution decrease the anodic peak current and shift the peak potential in the negative direction. These changes depend on the concentration and molecular weight of the polyethylene glycol added. The effect of the inhibitors decreases in the following order: (PEG)₆₀₀₀ > (PEG)₄₀₀₀ > (PEG)₁₂₀₀. The inhibition efficiency decreases with increase in temperature, suggesting physical adsorption.     

Chemical beneficiation of coal with aqueous hydrogen peroxide/sulphuric acid solutions

The removal of sulphur and ash from coal treated with aqueous hydrogen peroxide/sulphuric acid solutions has been studied at ambient temperature, under a variety of experimental conditions. Almost complete elimination of the sulphate and the pyritic sulphur was observed in most cases, as well as substantial reduction in the ash content. The other components of the organic coal matrix were not affected to a significant extent, indicating high selectivity of the $\text{H}{}_2\text{O}{}_2\text{H}{}_2\text{SO4}$ system towards sulphur oxidation. An optimal H₂SO₄ concentration was established, above which the acid was found to have an adverse effect on the oxidation of pyrite by hydrogen peroxide.     

The polymerization of acenaphthylene by sulphuric acid in methylenedichloride

Summary Acenaphthylene was polymerized in methylenedichloride at 273, 291 and 308 K by sulphuric acid. The initiation step takes place by addition of the proton of sulphuric acid to the monomer. The propagation step is through ion-pairs, and the propagation constants are first-order with respect to the monomer and initiator(k_p = 0.22 M^–1. s^–1(273K), k_p=0.88 M^–1. s^–1(291K), k_p = 2.81 M^–1. s^–1 (308K)). There is not appreciable loss of active centres, being this confirmed by experiments carried out with succesive additions of monomer. The molecular weights obtained confirm the importance of processes to monomer in this polymerization.     

Aluminium alloys in sulphuric acid Part I: Electrochemical behaviour of rotating and stationary disc electrodes

Anodic oxidation of various aluminium alloys was investigated by means of rotating disc electrodes in 3 M H₂SO₄ as a function of Cl^–, F^–, Zn²⁺ and In³⁺ concentration. Al-In, Al-Zn/In and Al-Zn/Sn alloys yielded current-potential curves at the lowest overpotentials and faradaic efficiencies for anodic oxidation of up to 98% at currents 50 mA cm^–2. While these alloys were electrochemically active in the presence of chloride as the only additive in sulphuric acid, binary aluminium alloys with Ce, Ga, La, Nd, Sn, Ta, Te, Ti or Tl were only active when Cl^–, Zn²⁺ and In³⁺ species were added to the electrolyte. With the exception of Al-Ga, binary alloys displayed high faradaic efficiencies of up to 95%. Fluoride additives resulted in current-potential curves at even more negative potentials than those with chlorides. In contrast to Cl^–, fluoride ions are consumed during the aluminium oxidation process due to complexation with Al(III).     

Lithium recovery from pretreated α-spodumene residue through acid leaching at ambient temperature

A novel alkaline hydrothermal approach for low-temperature conversion of α-spodumene into Li₂SiO₃ residue was proposed, providing a promising method for extracting lithium from α-spodumene as a pretreatment process. This work proposed a systematic investigation for extracting lithium from the residue by acid leaching and preparing lithium carbonate. The reaction feasibility between Li₂SiO₃ and acids (HCl and H₂SO₄) was first evaluated through thermodynamic calculation. Compared with the leaching effects of hydrochloric acid and sulphuric acid, sulphuric acid is the preferred leaching agent due to its higher extraction efficiency for lithium and lower acid consumption. Lithium extraction efficiency from the residue achieved up to 87.48% under the following optimized conditions: 0.75 mol/L H₂SO₄, 0.4 times the theoretical amount of acid, 10 min, 30°C, and 100 rpm. Based on the optimized conditions, the lithium-containing solution was concentrated through three consecutive cycles of leaching, which obtained a concentration of 17.78 g/L for lithium. The leaching solution was purified by CaO-Na₂CO₃, resulting in the removal rates of SiO₃²⁻, Mg²⁺, and Ca²⁺ of 84.22%, 95.51%, and 90.55%, respectively. Finally, the solution was precipitated with sodium carbonate to prepare Li₂CO₃. This paper facilitates the development of an economical process for efficient lithium extraction from spodumene at low temperatures.     

Purification and utilisation of iron-contaminated sulphuric acid

The purification and utilisation of sulphuric acid contaminated with iron is discussed in detail. It is found that treatment of the acid with FeSO₄·7H₂O resulted in complete removal of the iron impurity. Partial removal of the iron was affected by treatment with acetone and ammonium sulphate. Treatment with activated carbon was not found to be effective. The study shows that the contaminated sulphuric acid can be utilised to prepare sodium sulphate and calcium sulphate.     

Synthesis and characterization of copolyesters based on tartaric acid derivatives

A series of aliphatic copolyesters based on naturally occurring l-tartaric acid amenable to facile post-polymer modification have been synthesized and characterized. The hydroxyl groups of the tartaric acid were protected and copolyesters were synthesized by taking different feed molar ratio of dimethyl 2,3-O-isopropylidene tartarate and dimethyl succinate with 1,6-hexanediol. Then, a series of copolyesters were synthesized by taking equal feed molar ratio of dimethyl 2,3-O-isopropylidene tartrate and dimethyl succinate or dimethyl adipate with different alkane diols. The acetal protecting groups were then selectively hydrolyzed to prepare a new series of copolyesters with pendant hydroxyl groups along the copolymer chain. The number average molecular weights (M _n) of the copolymers were found to vary in the range of 3.7–8.4 × 10³ g mol⁻¹. The hydroxy copolyesters show higher glass transition (T _g) and melting (T _m) temperatures as compared to isopropylidene copolyesters and the T _g varies from −8.0 to −48.2 °C depending on the feed ratio of the comonomers. The hydrolytic degradation studies of copolyesters revealed that hydroxyl copolyesters degrade faster than isopropylidene copolyesters.     

Electrochemical regeneration of ceric sulphate in an undivided cell

Ceric sulphate (0–0.5 m) was generated electrochemically from cerous sulphate slurries (0.5–0.8 m total cerium) in 1.61 m sulphuric acid, at 50 °C, using a bench scale differential area undivided electrochemical cell with an anode to cathode ratio of eleven. A cell current efficiency for Ce(IV) of 90% was obtained at an anode current density of 0.25 A cm^–2. An empirical model illustrates an increase in overall current efficiency for Ce(IV) with an increase in electrolyte velocity, an increase in total cerium concentration, and a decrease in the cell current. From separate kinetic studies on rotating electrodes, both, anode and cathode kinetics were found to be affected by cerium sulphate adsorption processes. Anode adsorption of cerous sulphate species leads to inhibited mass transfer and negatively affected current efficiencies for Ce(IV). Cathode adsorption of cerium sulphate is thought to be responsible for high cathode current efficiencies for hydrogen (93–100%). The dissolved cerous sulphate concentration increased with increasing ceric sulphate and total cerium sulphate concentrations resulting in slurries with a stable dissolved cerous sulphate concentration of as high as 0.851 m in 1.6 m H₂SO₄ at room temperature.     

Oxygen reduction on poly(4-vinylpyridine)-modified ordinary pyrolytic graphite electrodes with adsorbed cobalt tetra-sulphonated phthalocyanine in acid solutions

Poly(4-vinylpyridine) (PVP) has been used to modify ordinary pyrolytic graphite (OPG) electrodes with adsorbed cobalt tetra-sulphonated phthalocyanine (CoTsPc) in acid solutions. These modified electrodes were prepared in different manners and characterized by cyclic voltammetry. Their electrocatalytic activity for oxygen reduction and stability in 0.05M H₂SO₄ solutions was examined at room temperature. The OPG/CoTsPc/PVP modified electrodes were found to be more active for oxygen reduction in 0.05M H₂SO₄ solutions as compared to the electrode with adsorbed CoTsPc on OPG without PVP. The increase in activity is due to the formation of an adduct between PVP and CoTsPc. U.v.-visible and FTIR studies provide evidence for such adduct formation. Over a 10 h period the activity of the OPG/CoTsPc/PVP system was essentially constant while that of OPG/CoTsPc without polymer decreased by a substantial amount (about 37%). The PVP layer inhibits the diffusion of the CoTsPc and/or Co out of the complex into the solution phase. The stability of the OPG/CoTsPc/PVP system may also be due to low solubility of the adduct between PVP and CoTsPc in a 0.05M H₂SO₄ solution. Thicker films of PVP decreased the diffusion limiting oxygen reduction current. The effect of pH of the electrolyte solution on the activity of such PVP-modified electrodes for oxygen reduction has also been investigated.     

Boric acid binding studies with diol containing polyethylenimines as determined by 11B NMR spectroscopy

Three water‐soluble polymers incorporating increasing levels of 2,3‐dihydroxy propyl attached to polyethylenimine (PEI) backbone were synthesized, characterized by NMR, and investigated for their ability to bind boric acid (BA). ¹¹B NMR spectroscopy showed that BA interacted with the polymeric 2,3‐dihydroxy propyls by forming borate monoester and borate diesters in the boron concentration range of 100–1000 ppm and at 0.0775M polymer. Borate monoester species predominated for low functionalization levels (33% of the PEI amines functionalized), whereas borate diester species dominated for the higher functionalized polymers (66–100% of the PEI amines functionalized). All three polymers showed that 100% of the BA was bound as a mixture of borate mono‐ and diesters at 100‐ppm boron. The overall best performer based on total borate ester formation was the 2/3‐PEI, with a binding K_d of 631 at 200 ppm boron. Borate ion concentration was measured from the ¹¹B NMR chemical shift of the BA/borate peak and it decreased as 1/3‐PEI > 2/3‐PEI > 3/3‐PEI. Variable temperature ¹¹B NMR showed drastic reduction of borate ester species at 65°C. Thus, PEI polymers, as the ones investigated in this work, are reasonable candidates for the selective recovery and recycle of BA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4411–4418, 2006