983686 - Application of Honeycomb Structured Zeolite Adsorbent for Adsorption/Regeneration of Volatile Organic Compounds from Industrial Streams

Adsorption is a widely used process for abatement of volatile organic compounds (VOCs) from gas streams due to its low cost, effectiveness for a wide range of pollutant types and concentration, and by enabling adsorbate recovery and reuse. Granular activated carbon (GAC) has long been applied for removal of VOCs; however, structured adsorbents including honeycomb structured zeolite have recently emerged as an alternative to GAC. Honeycomb zeolite adsorbents, in either fixed bed or rotary wheel configuration, offer several advantages over GAC including lower pressure drop, higher thermal stability, and adjustable hydrophobicity.
This study compares the adsorption-regeneration performance of a honeycomb structured zeolite adsorbent with that of beaded activated carbon (BAC) for a VOC (1,2,4-trimethylbenzene (TMB)) present in paint booth air, under industrially-relevant operating conditions. Adsorption capacity and breakthrough time, VOC removal efficiency, and heel formation were selected as performance metrics. Moreover, adsorption isotherms of both materials for TMB were obtained to assess their affinity for TMB as indicated by the equilibrium adsorption capacity measured at different VOC concentrations. surface area and pore volume of BAC samples and thermal stability of formed heel after 5 cycles of TMB adsorption-desorption were determined by N2 adsorption analysis and thermogravimetric analysis (TGA), respectively. Due to its larger surface area and total pore volume relative to the honeycomb zeolite, BAC achieved considerably higher TMB adsorption capacities and removal efficiencies in the first three cycles. However, after 5 adsorption-regeneration cycles, the amount of heel over the BAC bed was almost 9 times greater than that over the honeycomb zeolite. This severe heel formation within BAC’s narrow micropores led to a sharp decline in its adsorption capacity, which after five cycles declined by 55% (versus 17% for zeolite). Furthermore, the TGA results for exhausted carbon and zeolite samples revealed that the formed heel on BAC can only be removed at a substantially higher temperature than the zeolite honeycomb (270 ºC vs. 140 ºC), implying that the nature of heel (strongly physisorbed or chemisorbed) depends on the adsorbent’s properties.