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.
Mitoma
Yoshiharu
Y
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
Tasaka
Norie
N
Takase
Maki
M
Masuda
Taizo
T
Tashiro
Hideki
H
Egashira
Naoyoshi
N
Oki
Takashi
T
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