Effect of Ethylene Glycol on the Dissolution of Palladium with HCl Solution Containing Oxidizing Agents and Selective Precipitation of Pd(IV) Compound

Structural properties of gelatin—pectin gels. Part I: Effect of ethylene glycol

Palladium (Pd) present in spent electroplating solutions is concentrated by cementation with zinc (Zn) metal powder. Therefore, it is necessary to recover Pd from the cemented Pd. In this work, recovery of pure Pd(IV) compounds from the leaching solutions of the cemented Pd was investigated by using selective precipitation method. It was found that the existence of Pd(IV) in the aqueous solutions is critical for the precipitation with NH4Cl. Precipitation experiments of Pd(IV) from the synthetic aqua regia solution containing Pd(IV) and Zn(II) was tested. Afterwards, the optimum precipitation conditions were applied to recover Pd(IV) precipitates from the real H2SO4 and HCl leaching solutions containing NaClO as an oxidizing agent. The selective precipitation resulted in the recovery of extra pure (NH4)2PdCl6 from real leaching solutions under the conditions of 1:30 molar ratio of Pd(IV) to NH4Cl at 60oC within 30 min. The precipitation percentage of Pd(IV) from the H2SO4 and HCl solutions was over 99.9 and 98.2%, respectively. A simple hydrometallurgical process consisting of cementation, leaching, and precipitation was proposed for the recovery of pure Pd(IV) compounds from spent electroplating solution.

Spent electroplating solutions contain small amounts of Pd(II). Cementation of Pd(II) with zinc metal powder is practiced to concentrate the Pd. Dissolution of the cemented Pd metal is necessary to recover pure Pd metal or compounds. In this work, the leaching behavior of Pd metal in inorganic acid solutions (hydrochloric and sulfuric acid) in the presence of an oxidizing agent such as H2O2, NaClO3, or NaClO was investigated. To determine the optimum conditions for Pd leaching, experiments were conducted by adjusting the concentration of the acids and oxidizing agents, reaction temperature and time, and pulp density. Complete leaching of Pd was possible using a hydrochloric acid solution with 3 kinds of oxidizing agents, whereas only NaClO was effective in the leaching with sulfuric acid solution. The chloride ions of HCl and NaClO3/NaClO play an important role in enhancing the leaching of Pd, due to the formation of Pd chlorocomplexes and by decreasing the reduction potential of Pd(II). Compared to H2O2, NaClO3 and NaClO showed some merits as oxidizing agents in terms of reaction time, temperature and low acid concentration. Based on the optimum leaching conditions of single Pd metal, the conditions for the complete leaching of Pd and Zn from the metallic mixtures were obtained.

Among platinum group metals, palladium and platinum are in the same group, and thus their chemical properties are very similar. Therefore, many methods have been reported on the separation of the two metal ions from the leaching solutions. In this work, separation of the two metals by selective dissolution was investigated. For this purpose, sulfuric acid solutions containing oxidizing agents, like sodium hypochlorite and sodium chlorate were employed. The leaching behavior of the two metals was investigated by varying the concentration of sulfuric acid, oxidizing agents, and pulp density at ambient temperature. In most of the leaching conditions using sulfuric acid, the leaching percentage of Pt metal was negligible, while Pd metal was selectively dissolved, resulting in the separation of the two metals. The conditions for the complete dissolution of Pd metal were found to be 5 M H₂SO₄, 0.2 M NaClO, 20°C, and 60 min. The chemical reactivity of NaClO and NaClO3 in sulfuric acid solution was compared on the basis of their chemical structure. The platinum metal present in the residue was completely dissolved by 5 M HCl solution containing 0.3 M NaClO₃ at 60°C for 60 min. Since palladium and platinum metals can be separated by selective dissolution, the recovery process of the two metals from secondary resources would be simpler and can be commercially applied.

To advance the optimal design of amines for postcombustion CO2 capture, a sound mechanistic understanding of the chemical process of amines with good CO2 capture performance is advantageous. A sterically hindered alkanolamine, 2-(tert-butylamino)ethanol (TBAE), in ethylene glycol (EG) solution was recently reported to have better CO2 capture performance and unusual reactivity toward CO2, in comparison with those of the prototypical alkanolamines. However, the reaction mechanism of TBAE with CO2 in EG solution is unclear. Here, various quantum chemistry methods were employed to probe the reaction mechanism of TBAE with CO2 in EG and aqueous solution. Six reaction pathways involving three kinds of possible reactive centers of TBAE solution were considered. The results indicated that the formation of anionic hydroxyethyl carbonate by the attack of -OH of EG on CO2 is the most favorable, which is confirmed by complementary high-resolution mass spectrum experiments. This clarified that the speculated zwitterionic carbonate species is not the main product in EG solution. The reaction process of TBAE in aqueous solution is similar to that in EG solution, leading to bicarbonate, which agrees with experimental observations. On the basis of the unveiled reaction mechanisms of TBAE + CO2, the role of the key tert-butyl functional group of TBAE was revealed.

Separation of transition metals from rare earths by non-aqueous solvent extraction from ethylene glycol solutions using Aliquat 336

Glass fiber reinforced nylon 6,6 (GFNY66) composites widely used for automotive applications undergo degradation when repeatedly exposed to aqueous ethylene glycol (EG) solution, resulting in significantly reduced mechanical properties. Hence, it is important to clearly understand the degradation and hydrogen bond breaking mechanism of nylon 6,6 (NY66) and interfacial failure mechanism in GFNY66 (when exposed to aqueous EG solution) in order to improve the mechanical properties of recycled NY66. From ATR‐IR spectra of NY66 immersed in aqueous EG solution at 108°C for varying intervals of time, the shifting of amide‐I band (νCO) at 1640 cm−1 towards lower frequency with increasing immersion time may be attributed to the breakage of intra‐ and intermolecular H‐bonding between amides in NY66 followed by the new formation of H‐bonding between amide group in NY66 and hydroxyl group in the absorbed EG. GPC data revealed the reduction in molecular weight due to the absorption of EG into NY66 matrix leading to chain scission of NY66. GFNY66 samples treated with aqueous EG solution exhibited pronounced deterioration in mechanical properties because of the interfacial failure between glass fiber and NY66 matrix as well as molecular weight reduction caused by the absorbed EG solution. POLYM. COMPOS., 28:778–784, 2007. © 2007 Society of Plastics Engineers

Viscosity measurements of ethylene glycol solution with flow drag reduction additives

Unveiling the role of ethylene glycol for enhanced performance of PEDOT:PSS/Silicon hybrid solar cells

Summary Nanofluids, particularly water-based nanofluids, have been extensively studied as liquid–solid phase change materials (PCMs) for thermal energy storage (TES). In this study, nanofluids with aqueous ethylene glycol (EG) solution as the base fluid are proposed as a novel PCM for cold thermal energy storage. Nanofluids were prepared by dispersing 0.1–0.4 wt% TiO2 nanoparticles into 12, 22, and 34 vol.% EG solutions. The dispersion stability of the nanofluids was evaluated by Turbiscan Lab. The liquid–solid phase change characteristics of the nanofluids were also investigated. Phase change temperature (PCT), nucleation temperature, and half freezing time (HFT) were investigated in freezing experiments. Subcooling degree and HFT reduction were then calculated. Latent heat of solidification was measured using differential scanning calorimetry. Thermal conductivity was determined using the hot disk thermal constant analyzer. Experimental results show that the nanoparticles decreased the PCT of 34 vol.% EG solution but minimally influenced the PCT of 12 and 22 vol.% EG solutions. For all nanofluids, the nanoparticles decreased the subcooling degree, HFT, and latent heat but increased the thermal conductivity of the EG solutions. The mechanism of the improvement of the phase change characteristics and decrease in latent heat by the nanoparticles was discussed. The nanoparticles simultaneously served as nucleating agent that induced crystal nucleation and as impurities that disturbed the growth of water crystals in EG solution-based nanofluids. Copyright © 2016 John Wiley & Sons, Ltd.

Pretreatments of sugarcane bagasse by three high boiling-point polyol solutions were compared in acid-catalysed processes. Pretreatments by ethylene glycol (EG) and propylene glycol solutions containing 1.2 % H2SO4 and 10 % water at 130 °C for 30 min removed 89 % lignin from bagasse resulting in a glucan digestibility of 95 % with a cellulase loading of ~20 FPU/g glucan. Pretreatment by glycerol solution under the same conditions removed 57 % lignin with a glucan digestibility of 77 %. Further investigations with EG solutions showed that increases in acid content, pretreatment temperature and time, and decrease in water content improved pretreatment effectiveness. A good linear correlation of glucan digestibility with delignification was observed with R2 = 0.984. Bagasse samples pretreated with EG solutions were characterised by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction, which confirmed that improved glucan enzymatic digestibility is mainly due to delignification and defibrillation of bagasse. Pretreatment by acidified EG solutions likely led to the formation of EG-glycosides. Up to 36 % of the total lignin was recovered from pretreatment hydrolysate, which may improve the pretreatment efficiency of recycled EG solution.

The thermal denaturation of ribonuclease A(RNase A) and chymotrypsinogen A in aqueous solutions of ethylene glycol (EG) was investigated by differential scanning calorimetry at several pH values in the acidic region. The calorimetric enthalpies of denaturation, ΔHd, of these proteins increased monotonously with increasing the EG concentration under all the conditions studied. These proteins, however, differed from one another in the variation of the denaturation temperature, Td, with the addition of EG. The Td of chemotrypsinogen decreased slightly with an increase in EG concentration under all the conditions, producing a greater effect at high pH. The Td of RNase A, on the other hand, was almost independent of the EG content at pH 3.8, while at pH 2 and 3, the Td increased slightly with increasing the EG concentration and decreased slightly at pH 5. That is, EG stabilized or unstabilized these proteins against thermal denaturation, in a way which seemed to be dependent on temperature rather than the pH. The standard thermodynamic parameters for denaturation, ΔG°, ΔH°, and ΔS°, which were calculated using Td and ΔH° and assuming a constant heat capacity change, suggested that the slight increase or decrease in ΔG° induced by EG is attributed to whether ΔH° increases as much as ΔS° does or not. These results may be explained on the basis of the effect of EG on the solvation around hydrophobic groups of the protein. The EG effect may depends on the structural properties of proteins such as hydrophobicity and polarity, as well as on temperature.

Thermotropic and barotropic phase transitions of dilauroylphosphatidylcholine bilayer

Electrochemical polishing with glycol-based electrolyte of the curved internal channels fabricated via laser powder bed fusion

Platinum group metals (PGMs) are important for the manufacture of advanced materials in the field of catalysts and electronic devices. Since the chemical properties of PGMs are very similar to each other, hydrometallurgical processes should be employed to recover PGMs with high purity from either ores or secondary resources. In hydrometallurgical processes for PGMs, the first step is the dissolution of PGMs. For this purpose, inorganic acid solutions with oxidizing agents are generally employed. In this work, nonaqueous solvent leaching systems with a relatively cheap price were employed to investigate the dissolution of pure palladium (Pd) metal. The solvent leaching systems consisted of concentrated hydrochloric acid solution and commercial extractants such as tributyl phosphate (TBP), 7-hydroxydodecan-6-one oxime (LIX 63), and di-n-octyl sulfide (DOS) in the presence of H2O2 as an oxidizing agent. Among the three systems, TBP showed the best efficiency for the dissolution of Pd. The effect of several parameters like TBP concentration, temperature, time, stirring speed and the weight ratio of Pd to TBP/HCl/H2O2 was explored. The dissolution percentage of Pd by the HCl–H2O2–TBP system was higher than by the HCl–H2O–H2O2 system at the same concentration of HCl and H2O2. The role of TBP in enhancing the dissolution of Pd was discussed on the basis of the interaction between HCl and TBP. Compared to aqueous systems, mass transfer is important in the dissolution of Pd metal by the solvent leaching system. Optimum conditions for the complete dissolution of Pd were obtained.