Effect of phosphoric acid concentration on properties of peanut shell adsorbents

Carbon adsorbents from peanut shell have been produced batchwise by reacting with 10–60 wt% phosphoric acid solutions at 473 K for 120 min. Both BET surface area of each adsorbent obtained, as well as iodine amount adsorbed, has been measured at conventional conditions. In addition, adsorption of benzene vapour on each adsorbent produced has been carried out under chromatographic conditions at 473 and 493 K. The effect of initial phosphoric acid concentrations on the specific surface area and adsorptive properties has been investigated. Correlations of surface area and adsorptive properties of the adsorbents produced with the initial concentrations have been proposed. Peanut shell could be converted completely to carbon adsorbents with the initial concentration of 20–60 wt% under the selected conditions. In these circumstances, the adsorbent yield has reduced from 60% to 45% of the original mass. BET surface area of peanut adsorbent has been increased to almost 1000 m2 g−1 with the increase in the initial phosphoric acid concentration to 60 wt%. For adsorptive properties, both iodine amount adsorbed and benzene adsorption equilibrium constants have been increased in the same manner as the surface area. All adsorptive properties of the adsorbents have been proportional to the surface area created. In addition, the incremental surface area improvement, as well as all adsorptive properties, has distributed quite symmetrically around the arithmetic mean of experimental phosphoric acid concentrations. Consequently, the symmetrical expressions for the relationship of specific surface area and corresponding adsorptive property with the initial concentration have been proposed.