Akitsugu Okuwaki

New method of treating dilute mineral acids using magnesium–aluminum oxide

Mineral acids, such as H(3)PO(4), H(2)SO(4), HCl, and HNO(3,) were treated with magnesium-aluminum oxide (Mg-Al oxide), which behaved as a neutralizer and fixative of anions. Anion removal increased with increasing Mg-Al oxide quantity, time, Mg/Al molar ratio, and initial acid concentration. Up to 95% removal of anions was achieved in 0.5 N acids using a stoichiometric quantity of Mg(0.80)Al(0.20)O(1.10) for H(3)PO(4), 1.75 stoichiometric quantities for H(2)SO(4), or 2.5 stoichiometric quantities for HCl or HNO(3) at 20 degrees C over a period of 6 h. The final solutions were found to have a pH in the range of 8-12. Selectivity of acid removal was found to follow the following order: H(3)PO(4) > H(2)SO(4) > HCl > HNO(3). The equivalent of acid removal per 1 g of Mg-Al oxide decreased as the Mg/Al molar ratio of Mg-Al oxide increased.

Photocatalytic Properties of Layered Hydrous Titanium Oxide/CdS-ZnS Nanocomposites IncorporatingCdS-ZnS into the Interlayer

H 2 Ti 4 O 9 /Cd 0.8 Zn 0.2 S nanocomposites incorporating Cd 0.8 Zn 0.2 S particles, less than 1 nm in thickness, were fabricated by the chemical reaction between a Cd 2+ -Zn 2+ mixture and H 2 S in the interlayer of H 2 Ti 4 O 9 . H 2 Ti 4 O 9 /Cd 0.8 Zn 0.2 Z nanocomposites were capable of efficient hydrogen evolution following irradiation with visible light in the presence of Na 2 S as a sacrificial donor. The hydrogen production activity of the H 2 Ti 4 O 9 /Cd 0.8 Zn 0.2 Z nanocomposite was superior to those of unsupported Cd 0.8 Zn 0.2 S and the mixture of H 2 Ti 4 O 9 and Cd 0.8 Zn 0.2 S. The hydrogen production was enhanced by doping Pt together with Cd 0.8 Zn 0.2 S in the interlayer, but was depressed by depositing Pt on the outer surface of the H 2 Ti 4 O 9 /Cd 0.8 Zn 0.2 S nanocomposite.

The simultaneous removal of calcium and chloride ions from calcium chloride solution using magnesium-aluminum oxide.

We investigated the removal of Ca(2+) and Cl(-) from CaCl(2) solution at 20-60 degrees C, using magnesium-aluminum oxide, Mg(0.80)Al(0.20)O(1.10), prepared by the thermal decomposition of a hydrotalcite-like compound, Mg(0.80)Al(0.20)(OH)(2)(CO(3))(0.10).0.78 H(2)O. The degree of Ca(2+) and Cl(-) removal from the solution increased with increasing initial CaCl(2) concentration, temperature, and quantity of Mg(0.80)Al(0.20)O(1.10) added. When Mg(0.80)Al(0.20)O(1.10) was added to 0.25 M CaCl(2) solution in a Mg(0.80)Al(0.20)O(1.10)/CaCl(2) molar ratio of 20, the degree of Ca(2+) and Cl(-) removal from the solution at 60 degrees C after 0.5 h was 93.0% and 98.2%, respectively. These results reveal that Mg(0.80)Al(0.20)O(1.10) has the capacity to remove Ca(2+) and Cl(-) simultaneously from aqueous solution.

Dehydrochlorination behavior of rigid PVC pellet in NaOH solutions at elevated temperature

Rigid PVC pellet was treated at 150–250 °C in 0~7M NaOH solutions for 0~12h. The degree of dehydrochlorination increased with increasing reaction temperature, and reached about 100% at 250 °C over 3h. A porous char, 2 μm pore size, was produced. The dehydrochlorination proceeded by a first order reaction in the alkaline solution. Maximum rate of the dehydrochlorination for rigid PVC was at 3 M NaOH. The apparent activation energy was 96 kJ mol−1 in 3 M NaOH for rigid PVC.

Chemical recycling of flexible PVC by oxygen oxidation in NaOH solutions at elevated temperatures

Oxidative degradation of a flexible PVC pellet (F-PVC) with oxygen was carried out in 1–25-mol/kg(m)-H2O NaOH solutions, at 150–260°C and 1–10 MPa. Dehydrochlorination of F-PVC occurred first, followed by oxidation. The major products were oxalic acid, a mixture of benzenecarboxylic acids, and CO2. We obtained 320 g of oxalic acid and 130 g of benzenecarboxylic acids (as phthalic acid) from 1 kg of F-PVC under conditions of a 15-m NaOH solution at 250°C and a of 5 MPa for 5 h.

Chemical recycling of rigid-PVC by oxygen oxidation in NaOH solutions at elevated temperatures

Abstract Oxidative degradation of rigid-PVC pellets (R-PVC) with oxygen was carried out in 1–25 mol/kg-H2O (m) NaOH solutions, at 150–260°C and Po2 of 1–10 MPa in order to investigate the chemical recycling of PVC materials. The apparent rate of oxidative degradation of R-PVC progressed as a zero order reaction, and the apparent activation energy was 38.5 kJ mol−1. The major products were oxalic acid, a mixture of benzenecarboxylic acids, and CO2. The tin in R-PVC was extracted completely. This paper reports the possibility of converting PVC materials into raw materials such as carboxylic acids by chemical recycling.

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.

Solubility of hematite in LiOH, NaOH and KOH solutions

Abstract The dissolution behavior of hematite in 1–10 M LiOH, NaOH and KOH solutions was investigated at 303–349°K. The solubility of hematite increased with increasing temperature and alkali hydroxide concentration, although it remained very low. The solubility changed greatly depending on the kind of alkali hydroxide used, in the order NaOH > KOH > LiOH.

Formation of aromatic carboxylic acids from coal-tar pitch by two-step oxidation with oxygen in water and in alkaline solution

Abstract The production of benzenecarboxylic acids by oxidation of coal-tar pitch with oxygen in the aqueous phase was studied. To reduce the amount of unreacted pitch observed in one-step oxidation in NaOH solution, two-step oxidation was explored: preoxidation with oxygen in water and subsequent oxidation with oxygen in NaOH solution. Char formed in the oxidation of pitch in water was easily oxidized in a 5 molal NaOH solution without formation of troublesome residue. By optimum combination of the oxidation in water and in NaOH solution, the yield of water-soluble aromatic acids (WSAA) was improved from 51 to 79 wt%. The content of benzenecarboxylic acids in the WSAA reached 40–50 wt%.

Plasticizer leaching from flexible PVC in low temperature caustic solution

By separating plasticizer using alkali solution at low temperature, the recycling of PVC and plasticizer is possible. A low temperature leaching process has been developed and the performance of the process investigated. An experimental study using various concentrations of NaOH solutions at different temperatures and processing time shows that treatment with 5 M NaOH solution at 100 °C gives a selective separation of the plasticizer without dechlorination of PVC. Surface changes of the treated PVC have also been examined.