Enhanced microwave regeneration of a polymeric adsorbent through carbon nanotubes deposition

Abstract

Microwave (MW) regeneration can be an effective alternative to conventional adsorbent regeneration methods; however, regeneration of MW-transparent adsorbents can be challenging. In this study, multiwall carbon nanotube (CNT) was used to enhance the MW absorption and regeneration of Dowex Optipore V503, a commercial hypercrosslinked polymeric adsorbent with low dielectric loss factor. CNTs were dispersed in sodium dodecyl sulfate solution and physically deposited on the surface of the adsorbent at different weight percent (wt %). On average, coating the adsorbent with 0.1 to 0.3 wt% of CNT resulted in a 3 to 24% decrease in its surface area. Dielectric properties measurement revealed a sharp increase in the loss factor from 0.05 to 1.30 after coating the adsorbent with 0.3 wt% of CNT. MW energy needed to heat the adsorbent by 1 °C decreased from 722 to 13 J/g at 0.3 wt% of CNT owing to improved MW absorption by CNT-coated adsorbent. Finally, 5 cycles of n-heptane adsorption and MW-assisted regeneration were completed for CNT-coated and as-received adsorbent samples. The deposition of a very small amount of CNTs (0.1 to 0.3 wt%) on the adsorbent increased the MW-assisted desorption efficiency by 103% to 284% compared to the as-received adsorbent. These results are encouraging because they show that addition of small amounts of CNT can be effective in enhancing the MW regeneration of MW-transparent adsorbents.