Removal of Polar VOCs at Low Concentration Using a Sacrificial Carbon Bed

• Author / Creator

  Nusrat Nayan

• Volatile organic compounds’ (VOCs) emissions from automotive painting operations consist of a mixture of polar and nonpolar compounds. Adsorption is a widely used method for capturing VOCs from industrial gas streams. Typically, most of the non-polar pollutants are captured using adsorption onto activated carbon. Polar VOCs can be challenging to control, particularly at very low concentrations, due to the hydrophobic nature of activated carbon. Moreover, the driving force at low concentration is not high enough to readily overcome mass transfer resistances during the adsorption. Since adsorption is a selective capture process, it is of great interest to find the most suitable adsorbent with high capacity and affinity for the target polar pollutants, especially when dealing with VOCs at low concentrations.
  In the present study, a sacrificial fixed bed containing carbon adsorbents is utilized to treat a VOC-laden air stream. Adsorption of several polar VOCs (ethanol, acetone, 2-propanol, isobutanol, and 1-butanol) on different carbon materials with distinct properties was investigated. Eleven activated carbons from three major types namely beaded activated carbon (BAC), granulated activated carbon (GAC) and activated carbon clothes (ACFCs) were tested in this project. In order to acquire information regarding the key properties of the adsorbents, nitrogen adsorption isotherms, X-ray photoelectron spectroscopy, pHpzc and Boehm titration analyses were performed. BET surface area and micropore volume for wood based crushed GACs (OVC and VC48C) and ACFC 15 were close to virgin BAC and higher than coal-based ones (BPL and VCRSD) and ACFC 10. Pelleted GACs showed highest BET surface area, lowest micropore volume and considerable amount of mesopore volume. Based on XPS analysis, oxygen content for BACs, crushed GACs and pelleted GACs was more than 5% up to 8%, but less than 4% for activated carbon fiber clothes. Findings from Boehm titration analysis were consistent with pHpzc values.
  Adsorption capacity of activated carbons challenged with polar compounds such as ethanol, acetone and 2-propanol were not high enough (maximum 6% for 2-propanol with ACFC-10) but less polar compounds such as iso-butanol and n-butanol showed up to 26% and 33% capacity respectively. In general, adsorption capacity of carbon samples did not follow any specific trend which could be accurately described by their chemical or physical properties. Adsorption capacity of activated carbons challenged with polar compounds better corelated with micropore volume while total acidity contributed highest to the less or non-polar compounds.
  
  Based on the experimental data, several performance indicators including adsorption capacity, 5 % breakthrough time, throughput value and length of unused bed were determined. Considering cost, adsorption capacity and ease of handling pelleted carbon samples were recommended for the design of the sacrificial bed.

• Subjects / Keywords

  • Adsorpsion of polar VOCs at low concentration

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-05rx-0n35

• License

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