Sustainable synthesis of green adsorbent pellets with optimal attributes of capacity, strength, and cost from powdered activated carbon

Abstract

Powdered Activated Carbon (PAC) particles packed in tall industrial fixed bed columns pose practical problems such as high column pressure drop and solid losses during handling. Hence, the PACs are shaped in form of pellets using a suitable combination of binders. PAC made from coconut shells is mixed with bentonite and carboxy methyl cellulose (CMC) to form pellets. The problem is to identify an optimal blend of binders and PAC that satisfies multiple objectives viz. mechanical strength, gas adsorption capacity and cost. The first two objectives were quantified in terms ball pan hardness (BPH), and carbon tetra chloride activity test (CTC). Since CTC is a banned chemical reagent, its equivalence viz. n-butane adsorption test was performed. An experimental mixture design methodology is presented where these multiple objectives were described through correlations that were optimized either singly or together. Different proportions of binders and PAC were suggested for the different objectives. Hence, a benefit to cost ratio (BCR) response was further defined to identify the final proportion of binders and PAC in the pelletized adsorbent that was economical and did not compromise on its hardness and adsorption capacity. This strategy contributed to synthesis of carbon pellets that simultaneously satisfied structure, performance, and cost requirements. The final pellet with maximum BCR exhibited a BPH of 98.55%, CTC of 67.65% and a scaled cost of 96.79.