ADSORBENTS FOR METHANE STORAGE MADE BY PHOSPHORIC-ACID ACTIVATION OF PEACH PITS

Powdered peach pit was impregnated with various concentrations of phos phoric acid and then heated to temperatures between 350 and 900 degree s C. The resulting chars were characterized by nitrogen isotherms at 7 7 K and mercury porosimetry. Methane isotherms were measured gravimetr ically at 298 K to 3.5 MPa. Although many of the chars had relatively high 77 K nitrogen BET surface areas and micropore volumes, they consi stently adsorbed less methane at 298 K than expected. A linear relatio nship between surface area and methane uptake for many different carbo ns had previously been observed [1]. With increasing heat treatment te mperature, these chars followed more closely the predicted relationshi p. From reflectance IR absorption and temperature-programmed desorptio n, it is apparent that these chars cannot be considered as only carbon because of their high oxygen and hydrogen content. Only at temperatur es above 700 degrees C do they begin to show the methane uptake expect ed from their surface area and micropore volume. The adsorption potent ial of the char pore towards methane at 298 K appears to be lower than that of a truly carbonaceous adsorbent. Alternatively, the adsorption potential to nitrogen at 77 K may be greater for these chars than the adsorption potential of a microporous carbon. The chars produced in t his study by phosphoric acid treatment of peach pit do not adsorb suff icient methane to be considered as suitable adsorbents for natural-gas storage applications. Copyright (C) 1996 Elsevier Science Ltd