Dehydrochlorination behavior of flexible PVC pellets in NaOH solutions at elevated temperature

Flexible PVC pellets were treated at 150–250°C in 0–7M NaOH solutions for 0–12 h. The degree of dehydrochlorination of flexible PVC pellets increased with increasing reaction temperature and was about 100% at 250°C over 5 h. A porous char, 2–16 μm in pore size, was produced. The dehydrochlorination of PVC in the flexible PVC was proceeded by a first-order reaction in alkaline solution. The maximum rate of the dehydrochlorination for flexible PVC was reached at 5M NaOH. The apparent activation energies were 22–35 kcal/mol in 1–7M NaOH for flexible PVC. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2171–2177, 1998     

Photochemical reduction of nitrate to ammonia using layered hydrous titanate/cadmium sulphide nanocomposites

The photocatalytic activity of H₂Ti₄O₉/CdS nanocomposites incorporating CdS particles, less than 0·8 nm thick, in the interlayer of H₂Ti₄O₉ was evaluated for the reduction of NO₃⁻ with and without methanol. NO₃⁻ was photochemically reduced by bandgap illumination in the presence of H₂Ti₄O₉/CdS nanocomposites with and without methanol although unsupported CdS showed no noticeable photocatalytic activity for NO₃⁻ reduction. The oxidation of CdS in H₂Ti₄O₉/CdS to SO₄^2- was accompanied by NO₃⁻ reduction without methanol, whereas addition of methanol was useful to promote the NO₃⁻ reduction and depress the oxidation of CdS. The catalytic activity of H₂Ti₄O₉/CdS greatly increased with doping Pt particles in the interlayer.     

Corrosion Behavior of Alumina Ceramics in Caustic Alkaline Solutions at High Temperatures

The corrosion rate and changes in the microstructure and fracture strength of alumina ceramics (93.0% Al₂O₃ and 99.5% Al₂O₃) were studied in 0.1 m to 25 m NaOH solutions at 150°C to 200°C, where m = mol/(kg of H₂O). The attack of the caustic alkaline solution started at the grain boundaries. Consequently, the corrosion resistance increased with decreasing SiO₂ content in Al₂O₃ ceramics, and the corrosion resistance of 99.5% pure Al₂O₃ was similar to that of Si₃N₄ ceramics. Since large pits are formed by corrosion, the surface area increased first and the apparent corrosion rate increased with time in the initial stage of the corrosion. The corrosion rate of Al₂O₃ increased linearly with increasing NaOH concentration, and the activation energy was 102 kJ/mol. The fracture strength of corroded Al₂O₃ decreased monotonically as the degree of dissolution of alumina increased.     

Uptake of benzenecarboxylate ions by magnesium aluminium oxides

The behaviour of uptake of the benzenecarboxylate ions, C₆H_6-n(COO)_nⁿ (n = 1–6), in aqueous solutions by rock-salt type magnesium aluminium oxide, Mg_(1-x)(2+x)Al_2x/(2+x)O (x = 0.17, 0.30, 0.33) was investigated at 0.70°C. All the benzenecarboxylate ions were taken up from solution competitively with OH- to form the hydrotalcite-like layered double hydroxides. The uptake rate could be adequately described by a surface chemical reaction controlled shrinking core model, and the apparent activation energy was c. 60 kJ mol^?1. The selectivity of anion uptake increased with increasing the charge density of the benzenecarboxylate ions. The amount of benzenecarboxylate ions incorporated in the interlayer of hydrotalcite and the selectivity of uptake for benzenecarboxylate possessing higher electric change increased with increasing aluminium content in the magnesium aluminium oxide.     

Effects of pH and concentration on ability of Cl<Superscript>−</Superscript> and NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> to intercalate into a hydrotalcite-like compound during its synthesis

In this study, we confirmed that the characteristics of anion intercalation into the interlayer of a hydrotalcite-like compound (HT) during synthesis are similar to those of the anion-exchange reaction of HTs as well as the reconstruction reaction of HTs from Mg-Al oxide. We demonstrated that (i) Cl⁻, which has a higher charge density than NO₃⁻, more easily reacted with Mg and Al species to form HT structure, resulting in greater intercalation of Cl⁻ into the HT interlayer; and (ii) for HTs with lower Mg: Al molar ratios, OH⁻, which has a higher charge density than Cl⁻ and NO₃⁻, was more likely to interact with Mg and Al species to form HT structure, blocking the intercalation of Cl⁻ and NO₃⁻. Furthermore, we showed that high concentrations of Cl⁻ and NO₃⁻ in solution regulated their intercalation into the HT interlayer. The high activity of Cl⁻ and NO₃⁻ in solution would facilitate the anions’ reactions with Mg and Al species to form HTs, resulting in a high degree of anion intercalation into the interlayer of HTs.     

Decomposition of 2-bromophenol in NaOH solution at high temperature

2-Bromophenol was reacted in aqueous sodium hydroxide at 200-250 degrees C. The decomposition rate was remarkably faster at 250 degrees C than at 225 or 200 degrees C, and the percentage debromination reached almost 100% in 1M NaOH at 250 degrees C for 4h. The percentage increased with NaOH concentration over the range 0.1-1M. Aliphatic compounds, such as 2,2-dimethoxypropane and 4-hydroxy-4-methyl-2-pentanone, and aromatic compounds, such as phenol and cresol, were formed as decomposition products. The formation of carboxylic acids, such as formic, acetic, and propionic acids, in the presence of oxygen was also confirmed. Under a nitrogen atmosphere, the oxidation caused by oxygen in solution was suppressed and hydrolysis became the dominant reaction in the decomposition of 2-bromophenol.