INDUSTRIAL PROCESS OF VOLATILE ORGANIC COMPOUND TREATMENT BY ADSORPTION ONTO ACTIVATED CARBON FIBER CLOTH AND DESORPTION BY JOULE EFFECT

摘要

Previous studies have shown a good adsorption of volatile organic compounds present in air onto activated carbon fiber cloths (ACCs). It was found that the mass transfer between the solid and the fluid phase was 2 to 20 times faster than on activated carbon grains. With ACCs, the desorption was performed in situ applying an electrical current on the cloth. Operating conditions were optimized at a laboratory scale on pilot units. An industrial process was carried out in a chemical plant. A gaseous emission (about 100 m~3 h~(-1)), loaded with dichloromethane at concentrations ranging between 3 and 18 g m~(-3) had to be treated to get a final mass flow lower than 100 g h~(-1) From the lab studies, an industrial VOC removal process using an ACC adsorption module and an electrical desorption system was developed and studied in this industrial site. A microporous ACC was carried out in two identical cylindrical modules of 20 cm diameter and 50 cm length. The modules worked altematively in an adsorption desorption cycle of about 1 h. Data (inlet and outlet pollutant concentrations, adsorption and desorption temperatures, dichloromethane mass balance) were continuously collected during several days to determine the best operating conditions and to evaluate the performances of the system. The polluted air velocity through the module was of 320 m h~(-1) The outlet pollutant concentrations were less than 120 mg m~(-3), i.e. less than 12 g h~(-1) with an average value of 3 g h~(-1). To periodically regenerate the filters, an electrical current was applied to the module to get by Joule effect an ACC surface temperature close to 60 °C. A flow of gaseous nitrogen (5 m~3 h~(-1), i.e. 16 m h~(-1)) was used to put the desorbate out of the system and to pass it through a liquid nitrogen trap. Liquid dichloromethane was recovered and reused in the chemical processes of the plant. This system was continuously working for more than 17 months (24 h a day) with no operating problem and giving good performances according to the regulations on the VOC outlet emissions.