Preparation of activated carbons from macadamia nut shell and coconut shell by air activation

a novel, three-step process for the production of high-quality activated ca rbons from macadamia nut shell and coconut shell charcoals is described. In this process the charcoal is (i) heated to a high temperature ("carbonized "), (ii) oxidized in air following a stepwise heating program from low (ca, 450 K) to high (ca. 660 K) temperatures ("oxygenated"), and (iii) heated a gain in an inert environment to a high temperature ("activated"). By use of this procedure, activated carbons with surface areas greater than 1000 m(2 )/g are manufactured with an overall yield of 15% (based on the dry shell f eed). Removal of carbon mass by the development of mesopores and macropores is largely responsible for increases in the surface area of the carbons ab ove 600 m(2)/g. Thus, the surface area per gram of activated carbon can be represented by an inverse function of the yield for burnoffs between 15 and 60%. These findings are supported by mass-transfer calculations and pore-s ize distribution measurements. A kinetic model for gasification of carbon b y oxygen, which provides for an Eley-Rideal type reaction of a surface oxid e with oxygen in air, fits the measured gasification rates reasonably well over the temperature range of 550-660 K.