DECOMPOSITION OF ORGANIC COMPOUNDS BY MOLTEN SALTS

Shukuji ASAKURA* , Eisuke KURAYA **, Yuichi SHOJI*** Ritsuo YOSHIOKA***

Yuichi FURUDATE**** and Shengyao JIANG*****

       *   Graduate School of Engineering, Yokohama National University, Japan

      **  Department of Materials Science and Chemical Engineering,

          Faculty of Engineering, Yokohama National University, Japan

       *** Power & Industrial Systems R&D Center, Chemical Systems R&D Dept.,

           Toshiba Corporation

           Ukishimachou 4-1, Kawasaki-ku, Kawasaki-city. Japan

     ****  TOMSIC Corporation, Japan

    *****  Institute of Nuclear Energy Technology, Tsinghua University, China

 

     The decomposition technology of harmful chemical wastes with sodium hydroxide molten salt has been developed. The authors summarize the decomposition examination results of organic chlorine compounds such as carbon tetrachloride (CCl₄), chlorobenzene (C₆H₅Cl), and dioxins

     Various conditions such as type of molten salts, temperatures, and carrier gases (air and nitrogen), were studied to investigate the influence to decomposition rates of carbon tetrachloride. Consequently, compared with molten carbonates and chlorides, molten sodium hydroxide was found to have such superior characteristics as faster decomposition capability and less by-products generation. And it was revealed that decomposition rates depend on temperature and atmospheric condition. For example, the decomposition rate in N₂ carrier was higher than that of air carrier. A chemical reaction formula was supposed to be an equation (1) from thermodynamic data.

            CCl₄ (g)+ 6NaOH (l)  =  Na₂CO₃ (l)+ 4NaCl (l) + 3H₂O (g)……  equation(1)

It was found that the contact surface area and retention time between CCl₄ and NaOH affected decomposition rates. For example, the decomposition rate was able to be raised from about 47% to about 99%, by increasing the depth of molten salts from 50mm to 250mm.

     In case of aromatic organic chlorine compounds, chlorobenzene, the decomposition rate was about 56% in 600 degrees C at 50mm depth of molten salts. So, it was revealed that aromatic organic chlorine compounds were able to be decomposed similar to carbon tetra chlorides.

     Dioxins vaporized from fly ash heating at 500 degrees C was treated with molten sodium hydroxide. At the depth of 100mm, the decomposition rate was about 96%, and higher rate of 99% was achieved at 300mm. A chemical reaction formula was supposed to be an equation (2) as similar to equation (1). In this case, H₂O was supplied from the content moisture in NaOH and fly ash used.

C1₂H(8-x)Cl_ｘO₂＋(24+x)NaOH＋(10－x)H₂O＝12Na₂CO₃＋xNaCl＋(26-x)H₂　(x=0～7)…(2)

     From these experimental data, it was revealed that the molten alkaline salt such as sodium hydroxide reacts to the organic chlorine compounds to decompose them completely at about 600 degrees C, without producing any harmful compounds.