title: Enhanced removal of sodium salts supported by in-situ catalyst synthesis in a supercritical water oxidation process.
abstract: For practical applications of supercritical water oxidation to wastewater treatment, the deposition of inorganic salts in supercritical phase must be controlled to prevent a reactor from clogging. This study investigated enhanced removal of sodium salts with titanium particles, serving as a salt trapper and a catalyst precursor, and sodium recovery by sub-critical water. When Na(2)CO(3) was tested as a model salt, sodium removal efficiency was higher than theoretically maximum efficiency defined by Na(2)CO(3) solubility. The enhanced sodium removal resulted from in-situ synthesis of sodium titanate, which could catalyse acetic acid oxidation. The kinetics of sodium removal was described well by a diffusion mass-transfer model combined with a power law-type rate model of sodium titanate synthesis. Titanium particles showed positive effect on sodium removal in the case of NaOH, Na(2)SO(4) and Na(3)PO(4). However, they had negligible effect for NaCl and negative effect for Na(2)CrO(4), respectively. More than 99% of trapped sodium was recovered by sub-critical water except for Na(2)CrO(4). In contrast, sodium recovery efficiency remained less than 50% in the case of Na(2)CrO(4). Reused titanium particles showed the same performance for enhanced sodium removal. Enhanced salt removal supported by in-situ catalyst synthesis has great potential to enable both salt removal control and catalytic oxidation.
authors.affiliation: Faculty of Urban and Environmental Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan. f-takahashi@doc.kyushu-u.ac.jp
authors.forename: F
authors.initials: F
authors.lastname: Takahashi
authors.forename: Z R
authors.initials: ZR
authors.lastname: Sun
authors.forename: K
authors.initials: K
authors.lastname: Fukushi
authors.forename: Y
authors.initials: Y
authors.lastname: Oshima
authors.forename: K
authors.initials: K
authors.lastname: Yamamoto
mesh_terms: D002384:Catalysis; D008855:Microscopy, Electron, Scanning; D010084:Oxidation-Reduction; D010087:Oxides / Q000138:chemical synthesis; D012964:Sodium / Q000737:chemistry*; D014025:Titanium; D014865:Waste Disposal, Fluid / Q000379:methods*; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D010087:Oxides; D014874:Water Pollutants, Chemical; D014867:Water; C471701:sodium titanate; D012964:Sodium; D014025:Titanium