Influence of Purge Gas Flow and Heating Rates on Volatile Organic Compound Decomposition during Regeneration of an Activated Carbon Fiber Cloth

Abstract

Five-cycle adsorption/regeneration experiments using 1,2,4-trimethylbenzene (TMB) were completed at different purge gas flow and heating rates to identify their impact on heel buildup. Regeneration of a saturated activated carbon fiber cloth was completed at 400 °C using resistive heating at different heating rates and purge gas flow. At 1 standard liter per minute (SLPM) desorption purge gas, increasing the regeneration heating rate from 5 to 100 °C/min increased heel buildup from 4.6 to 10.4 wt % and adsorption capacity loss from 7.8 to 52.0%. On the other hand, at 70 °C/min heating rate, increasing the purge gas flow rate from 0.1 to 5 SLPM decreased heel buildup from 14.6 to 1.4% and capacity loss from 82.3 to 2.1%. Increasing the heating rate or decreasing the purge gas flow results in higher TMB concentrations being exposed to the high desorption temperature and higher residence time of TMB in the adsorbent pores. This increases adsorbate decomposition, causing deposition of pore-blocking, high carbon content residue (coke) onto the adsorbent surface. These results show the importance of optimizing desorption conditions to minimize heel buildup during cyclic use, contrary to conventional wisdom, suggesting that higher heating rates are consistently preferred, and provide improvements in energy use.

Adsorbing Volatile Organic Chemicals by Soluble Triazine-Based Dendrimers under Ambient Conditions with the Adsorption Capacity of Pyridine up to 946.2 mg/g

“…VOCs, including aromatics, alkanes, amines, and oxygenated or halogenated hydrocarbons [ 4 , 5 , 6 ], are often produced by chemical and pharmaceutical industries [ 7 , 8 , 9 ]. Porous materials currently used for adsorbing VOCs are zeolites (Zs) [ 10 , 11 , 12 ], activated carbons (ACs) [ 13 , 14 , 15 , 16 ], polymeric resins (PRs) [ 17 , 18 , 19 , 20 ], and metal-organic frameworks (MOFs) [ 21 , 22 , 23 , 24 ]. In these systems, a pre-drying column to remove the moisture of absorbed chemicals is generally required to maintain the adsorbing efficiency [ 24 ], which is an additional cost for VOC adsorption.…”

Regeneration of beaded activated carbon saturated with volatile organic compounds by a novel electrothermal swing adsorption system

“…This may result in more heel formation at a rapid heating rate. Niknaddaf et al [35] indicated that increasing the heating rate or lowering the purging gas flowrate leads to higher 1,2,4-trimethylbenzene exposure at higher temperatures; therefore, residence time was extended, leading to pore-blockage or high carbon residue (i.e., coke) within the inner structure of adsorbents. This suggests a higher chance of heel formation after regeneration.…”

Adsorption of Volatile Organic Compounds and Microwave Regeneration on Self-prepared High-surface-area Beaded Activated Carbon

“…Notably, the weight loss of saturated BACs became slower at rapid heating rates, resulting from the heel buildup within the adsorbents. Niknaddaf et al (2020) pointed out that the increase of heating rate from 5 to 100°C min -1 led to 8-52% of capacity loss as well as 4.6-10.5% of heel buildup for activated carbon fiber cloth (ACFC) in five consecutive adsorption/regeneration operations, respectively.…”