Decomposition of dichloromethane and in situ alkali absorption of resulting halogenated products by a packed-bed non-thermal plasma reactor

Abstract

For an effective decomposition and removal of organic halogenated compounds, a packed-bed non-thermal plasma reactor with in situ absorption of the resulting halogenated products by alkaline sorbent incorporated was proposed. In the plasma reactor, a-Al 2 O 3 particles of 1 and 3 mm (mean particle diameter) were packed as solid dielectric medium to enhance the plasma power density in the reactor. Further, alkaline sorbent of Ca(OH) 2 was doped onto the surface of a-Al 2 O 3 particles, in order to remove halogenated products by in situ absorption with Ca(OH) 2 . A high-voltage and high-frequency pulsed power of -15 to 15 kV and 1 kHz was applied to the wire electrode of the plasma reactor by means of a DC power source. In the present study, as the sample of an organic halogenated compound that is most popularly used, we selected dichloromethane (CH 2 Cl 2 ), and 500 ppm of the initial concentration of CH 2 Cl 2 was fed into the reactor accompanied by air at a fixed flow rate of 500 9 10 -6 m 3 min -1 at room temperature. As a result, it was recognized that the amount of CH 2 Cl 2 decomposed by nonthermal plasma in an a-Al 2 O 3 particle bed increased with an increase in plasma input power. The ratio of decomposition of CH 2 Cl 2 was almost 100% at 13 kV of electric power and 1 kHz frequency, and CO 2 , CH 3 Cl, COCl 2 , HCl, and Cl 2 were observed as the major reaction products. On the other hand, when CH 2 Cl 2 was introduced into the plasma reactor where a-Al 2 O 3 particles doped with Ca(OH) 2 were packed, the ratio of decomposition of CH 2 Cl 2 became higher, compared to the case that a-Al 2 O 3 particles were not doped with Ca(OH) 2 . Moreover, there were no halogenated by-product gases detected in the outlet gas from the reactor. As the solid reaction products, CaClOH and Ca(ClO) 2 Á4H 2 O were detected on Ca(OH) 2 by X-ray diffraction. From these findings, it was recognized that CH 2 Cl 2 was decomposed more effectively without producing unwanted harmful halogenated byproducts in the proposed non-thermal plasma reactor where a-Al 2 O 3 particles doped with Ca(OH) 2 sorbent were packed.

Enhanced performance of non-thermal plasma coupled with TiO2/GAC for decomposition of chlorinated organic compounds: influence of a hydrogen-rich substance

“…However, when TiO 2 /GAC was tested without NTP, no significant catalytic activity detected. Several studies have discussed the dependence of RE on energy density, supporting the observations made in the present study [ 33 , 34 ]. The main reason for this marked improvement may be the increased number of accelerated electrons due to higher input energy.…”

“…It was observed in several earlier studies that when the oxidation of chlorinated compounds occurs in a plasma reactor in an oxygen-rich environment such as air, a considerable amount of different chlorinated products can be produced, which could be more hazardous than the initial compound itself [ 44 ]. Among them, COCl 2 , Cl 2 , and CO seems to be the main harmful by-products [ 34 ]. The formation of products containing oxygen and chlorine is attributed to the reaction between chloride and oxygen atoms as described by Indarto et al, and Foglein et al [ 23 , 24 ].…”

Competitive Adsorption Mechanism Study of CHClF2 and CHF3 in FAU Zeolite

“…In fluorocarbons, chlorodifluoromethane (CHClF 2 ) is the highest demand HCFC widely used in air conditioners, commercial refrigerating, and extruded polystyrene foams as well as the manufacture of pentafluoroethane and fluoropolymers. , In manufacturing CHCIF 2 , the generation of trifluoromethane (CHF 3 ) is unable to be avoided. As a very effective greenhouse gas, according to the Kyoto Protocol, CHF 3 has the potential for global warming of 14 800 in a 100 year period, and its life in the atmosphere is 270 years. − To our knowledge, effective separation of CHClF 2 and CHF 3 mixtures have not been studied by using cationic faujasites like NaX and NaY distinguished by their Si/Al ratios [Si/Al (X) < 1.5, Si/Al (Y) > 1.5].…”