Calcium-promoted catalytic degradation of PCDDs, PCDFs, and coplanar PCBs under a mild wet process.
The authors achieved highly efficient degradation of polychlorinated aromatic compounds, including polychlorinated dibenzo-p-dioxins, dibenzofurans, and dioxin-like compounds such as coplanar polychlorinated biphenyls (co-PCBs), which are known as persistent organic pollutants. Degradation was accomplished in 24 h through a simple stirring operation using safe and high workability metallic calcium, which acts as both a scavenger and a reducing agent, and Rh/C catalyst in an alcohol solution under mild conditions in a sealed tube at 25 degrees C without a temperature increase within 0.15 MPa of increasing internal pressure during the reaction. In this system, reductive dechlorination by metallic calcium and catalytic reduction by Rh/C and generated hydrogen gas, without any external addition of hydrogen, exert a synergistic effect on the degradation of chlorinated compounds. Alcohol was used as a proton source and hydrogen, which was generated by a side reaction, causes an increase in the activity of Rh/C catalyst. Through the degradation of 4-chloroanisole in ethyl alcohol, anisole and cyclohexyl methyl ether were obtained in good conversions. Using ethyl alcohol as a solvent, treatment of dioxins and co-PCBs in a solution was markedly effective for degradation to reduce 2806 pg TEQ/ml of initial concentration to 31.8 pg TEQ/ml; its yield was 98.5%. Moreover, degradation in methyl alcohol took place in a 99.3% yield. That concentration ultimately reached 20.3 pg TEQ/ml under a mild wet process. All congeners of dioxins and co-PCBs were degraded in high conversions. In this degradation, lower aliphatic alcohol, such as methyl alcohol, is effective for making a new calcium surface as compared to alcohol with more methylene chains. In addition, it seemed that a higher pressure of hydrogen was easily generated in methyl alcohol, and then catalytic degradation was effectivley influenced.
Department of Environmental Sciences, Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara City, Hiroshima, 727-0023, Japan. mitomay@pu-hiroshima.ac.jp
Yoshiharu
Y
Mitoma
Norie
N
Tasaka
Maki
M
Takase
Taizo
T
Masuda
Hideki
H
Tashiro
Naoyoshi
N
Egashira
Takashi
T
Oki
D000840:Anisoles / Q000737:chemistry; D001572:Benzofurans / Q000737:chemistry* / Q000302:isolation & purification / Q000633:toxicity; D002118:Calcium / Q000737:chemistry*; D002384:Catalysis; D002713:Chlorine / Q000737:chemistry; D000072338:Dibenzofurans, Polychlorinated; D000431:Ethanol / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry; D006859:Hydrogen / Q000737:chemistry; D007564:Japan; D000432:Methanol / Q000737:chemistry; D008738:Methyl Ethers / Q000737:chemistry; D010084:Oxidation-Reduction; D011078:Polychlorinated Biphenyls / Q000737:chemistry* / Q000302:isolation & purification / Q000633:toxicity; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000737:chemistry / Q000302:isolation & purification / Q000633:toxicity; D011522:Protons; D013696:Temperature; D018508:Water Purification / Q000379:methods*
D000840:Anisoles; D001572:Benzofurans; D000072338:Dibenzofurans, Polychlorinated; D008738:Methyl Ethers; D000072317:Polychlorinated Dibenzodioxins; D011522:Protons; D000431:Ethanol; D002713:Chlorine; D006859:Hydrogen; C060998:anisole; D011078:Polychlorinated Biphenyls; D002118:Calcium; D000432:Methanol