CWAO of phenol over activated carbon catalysts with hydrogen peroxide as promoter
Sustainable process-product development & green chemistry
Environmental Engineering & Management (T1-3P)
Keywords: wastewater treatment; wet oxidation; hydrogen peroxide;phenol; activated carbon
Catalytic Wet Air Oxidation (CWAO) with activated carbon catalysts is presented as an effective technology to treat aqueous hazardous wastes, especially when these are too dilute to incinerate and too concentrated for a biological treatment. CWAO process uses molecular oxygen as oxidant and operates at T< 200 ºC and P< 100 atm. The employ of activated carbons implies some particularities such as the specially mild operating conditions required (T<160 ºC and P<10 atm) to avoid combustion of the carbon itself. To enhance activity at these operating conditions, some metals can be incorporated on the activated carbon. Also, the addition of free radical promoters can be an option.
In this work, the addition of hydrogen peroxide as promoter in the CWAO of phenol with activated carbon catalysts has been studied in a trickle-bed reactor at T=127 ºC and P= 8atm in a wide range of space time values (20-320 gCAT•h/gPhenol). The experimental profiles for phenol and TOC conversions using hydrogen peroxide as promoter in the CWAO have been compared to those obtained in the CWAO. Toxicity of the effluents (Microtox, ISO 11348-3, 1998) have been also measured since although the same intermediate species were identified different intermediate distribution was observed in both treatments.
Results show that the effect of hydrogen peroxide on the efficiency of the process is significant, making possible the CWAO with activated carbon at shorter space times and mild conditions. It has been shown that in the CWAO promoted by hydrogen peroxide, phenol and TOC conversions of 95% and 70%, respectively, can be achieved at 40 gCAT•h/gPhenol but higher space times are required (up to 160 gCAT•h/gPhenol) to reduce the toxicity of the effluent. These yields in phenol, TOC and toxicity removal were not observed in absence of hydrogen peroxide even at the highest space time value tested.
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Presented Monday 17, 13:30 to 15:00, in session Environmental Engineering & Management (T1-3P).
