CHARACTERIZATION AND APPLICATIONS OF ACTIVATED CARBON PRODUCED FROM MORINGA-OLEIFERA SEED HUSKS BY SINGLE-STEP STEAM PYROLYSIS

The seed husks of the multipurpose tree Moringa oleifera are potential ly a waste product that may be available in large quantities, and prev ious work has demonstrated that a microporous activated carbon can be produced from them by carbonisation under nitrogen followed by activat ion in steam. This research examines the efficacy of a simpler and che aper activation process, single-step steam pyrolysis activation, with a view to promoting the production of low-cost activated carbon in the developing world. Husks were heated in a steam atmosphere to 750 degr ees C for 30 or 120 min, or 800 degrees C for 30 min, then the resulti ng carbons were tested to determine their iodine numbers and adsorptio n isotherms for phenol, 4-nitrophenol and methylene blue. Phenol and 4 -nitrophenol were adsorbed rapidly by all three carbons, with 80-90% w /w adsorbed in the first 30 min, whereas methylene blue adsorption was slower. Pyrolysis at 800 degrees C for 30 min produced a carbon (yiel d 12.2% w/w) with an iodine number of 703 mg g(-1), a phenol specific surface area (SSA) of 629 m(2) g(-1), a 4-nitrophenol SSA of 664 m(2) g(-1) and a methylene blue SSA of 211 m(2) g(-1). The carbon produced at 750 degrees C for 120 min (yield 11.9% w/w) had similar properties, but the one produced at 750 degrees C for 30 min (yield 16.6% w/w) ha d a less developed porosity. The adsorbance characteristics of the two best carbons were superior to those produced previously by the conven tional two-stage carbonisation-activation, and were competitive with c ommercial carbons. These results demonstrate that steam pyrolysis acti vation of M. oleifera husks could provide a low-cost, local source of high quality activated carbon in the developing world. (C) 1997 Elsevi er Science Ltd.