Assessing the viability of electro-absorption and photoelectro-absorption for the treatment of gaseous perchloroethylene

Abstract

This work focuses on the development of electro-absorption and photoelectroabsorption technologies to treat gases produced by a synthetic waste containing the highly volatile perchloroethylene (PCE). To do this, a packed absorption column coupled with a UV lamp and an undivided electrooxidation cell was used. Firstly, it was confirmed that the absorption in a packed column is a viable method to achieve retention of PCE into an absorbent-electrolyte liquid. It was observed that PCE does not only absorb but it was also transformed into phosgene and other by-products. Later, it was confirmed that the electro-absorption process influenced the PCE degradation, favoring the transformation of phosgene into final products. Opposite to what expected, carbon dioxide is not the main product obtained, but carbon tetrachloride and 2 trichloroacetic acid. Both species are also hazardous but their higher solubility in water opens possibilities for successful and more environmental-friendly removal. The coupling with UV-irradiation has a negative impact on the degradation of phosgene.Finally, a reaction mechanism was proposed for the degradation of PCE based on the experimental observations. Results were not as expected during the planning of the experimental work but it is important to take in mind that PCE decomposition occurs in wet conditions, regardless of the applied technology, and this work is a first approach to try to solve the treatment problems associated to PCE gaseous waste flows in a realistic way.

Continuous electro-scrubbers for the removal of perchloroethylene: Keys for selection

“…Operation conditions: j=100 mA cm -2 ; 6.0 L h -1 PCE/air flow. Regarding the formation of phosgene and carbon tetrachloride during the PCE treatment, this is in agreement with the reactivity of PCE observed in previous works [35,36,40] in which the system was operated in discontinuous mode: in wet conditions PCE is converted into phosgene (non-electrochemical process) which is very unstable and it is transformed into CCl4 and TCA during electrolysis. Depending on the electrolysis conditions, they can be further oxidized to form carbon dioxide and chlorohydric acid as final products which indicates that pollution would be totally removed at the end of the process.…”

“…Other operating conditions are as follows: the mobile phase, 1% phosphoric acid (H3PO4); column temperature, 30 °C; flow rate, 0.8 mL min −1 ; injection volume, 20 μL. More details can be found in previous works [34][35][36].…”

Cobalt mediated electro-scrubbers for the degradation of gaseous perchloroethylene

“…Four main components integrate the experimental system: a glass column absorber, two storage tanks and an electrochemical cell as shown in Figure SM1. More details can be found elsewhere (Castañeda-Juárez et al, 2020;González-Pérez et al, 2020;Munoz-Morales et al, 2020)This setup is divided in two interconnected circuits: a liquid circuit which mainly contains the electrolyte/absorbent and a gaseous circuit. Firstly, 1.2 L of an aqueous solution of 150 mg L -1 of PCE was stored in the liquid waste desorption (LWD) tank and from here, the volatilization of PCE was promoted by bubbling a carrier air stream generated with a 3.8 W air compressor (Silent Pump (8) model SI6000, ICA SA, Toledo-Spain) with a flowrate of 360 L h −1 .…”

“…In another investigation, the treatment of a mixture of gases (NH3, (CH3)3N, CH3SH, H2S and CH3CHO was carried out using as absorbent electrolyte a 0.75 M Co(II) solution in 4 M H2SO4 Pt/Ti as anode, where, working at 10°C, removal efficiencies close to 100% were obtained, except for CH3SH, which exhibited an efficiency of 95% (Govindan and Moon, 2013). In this line, chlorinated hydrocarbons have caused many environmental and health problems (Bhatt et al, 2007;Huang et al, 2014) and lately, some studies have carried out their removal in liquid phase (Semitsoglou-Tsiapou et al, 2016;Dominguez et al, 2018) and soil polluted (Santos et al, 2019;Raimondo et al, 2020), but also their transference to gaseous currents to avoid the widespread of persistent pollution (Lopes et al, 2013;Muñoz-Morales et al, 2019;Munoz-Morales et al, 2020).…”