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Regeneration of granular activated carbon (GAC) exhausted by model diesel fuel

2010 Annual ChE Graduate Student Conference , Head Hall, UNB Fredericton, May 14 th. Regeneration of granular activated carbon (GAC) exhausted by model diesel fuel. --Characterization of the spent GACs. Xue Han Supervisor: Dr. Ying Zheng. Hydroprocessing Laboratory

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Regeneration of granular activated carbon (GAC) exhausted by model diesel fuel

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  1. 2010 Annual ChE Graduate Student Conference, Head Hall, UNB Fredericton, May 14th Regeneration of granular activated carbon (GAC) exhausted by model diesel fuel --Characterization of the spent GACs Xue Han Supervisor: Dr. Ying Zheng HydroprocessingLaboratory Department of Chemical Engineering University of New Brunswick

  2. Dibenzothiophene(DBT, 761.6 ppmw S) , indole (333.33 ppmw N) , carbazole (333.33 ppmw N) , 0.31 wt% naphthalene and 26.5 wt% ethyl acetate in dodecane. • Composition of model diesel fuel: • Regeneration method: • Thermal regeneration (450 oC for 2 h in nitrogen) • Ultrasound regeneration in dimethylfomamide (US-DMF, at room temperature for 1 h) • Solvent extraction by dimethylfomamide in Soxhlet (Sol-DMF) • Solvent extraction by toluene in Soxhlet (Sol-Tol) • Adsorbent: • Granular activated carbon (GAC)

  3. Textural data of the spent GACs • The SBET, total volume and micropore volume of GAC samples decrease with the increase of regeneration cycle. • More micropores of GAC are lost in thermal regeneration.

  4. Effect of specific surface area on regeneration efficiency For the regeneration of adsorptive sites taken by N in indole, the regeneration efficiency changed randomly with SBET, which means surface area is not the dominant effect on the regeneration. For the other two cases, surface area seems to play a key role in the regeneration of adsorptive sites occupied by S and N species. Linear relationship is found between regeneration efficiency and SBET, indicating regeneration is governed by surface area. When Sol-DMF is used for regeneration, the slopes of the trendlines are smaller than those in the other regeneration processes in both cases. Considering the higher regeneration efficiency, it is likely that this method is fit for long run operation. The effect of micropore volume and total pore volume on the regeneration efficiency are similar to that of specific surface area.

  5. Peak attribution in TPD spectrum The peaks in TPD spectrum are divided into two parts: the peaks at low temperature (below 300 oC) can be mainly ascribed to CO2 release from the decomposition of carboxylic and lactonic groups (strong acidity); the peaks at high temperature (above 400 oC) can be mostly attributed to CO from the decomposition of phenolic and carbonylic groups (weak acidity). Surface groups on carbon and their decomposition by TPD • Figueiredo JL, Pereira MFR, Freitas MMA, et al. Carbon, 1999, 37(9): 1379-1389.

  6. TPD results of GACs in Cycle 9 For the GAC regenerated by Thermal method, an additional peak shows up at 760 oC, which can be attributed to the decomposition of carboxylic anhydrides groups. The carboxylic anhydrides groups come from the dehydration of carboxylic acids under the conditions of Thermal regeneration, which can be verified by the significant decrease of peak area of the peak at low temperature and the FTIR results. 5

  7. Effect of regeneration method on the strong acidic groups • In Cycle 9, the amount of strong acidic groups increase in the order of Thermal<US-DMF<Sol-DMF<Sol-Tolin terms of regeneration method, which is more or less accordant to that of regeneration efficiency. • Thermal regeneration results in the least strong acidic groups, which is benefit to the adsorption. This might be another reason to the lowest regeneration efficiency.

  8. TPD results of GACs regenerated by Sol-Tol With the increase of the regeneration cycle, the center temperature of the peak attributed to both CO2 from strong acidic groups and CO from weak acidic groups shift to lower temperature, which indicates the decrease of the stability of the oxygen surface functional groups. This shift may be resulted from the change of the kinds of strong/weak acidic surface functional groups, which happens in the solvent extraction process.

  9. FT-IR spectrums of GACs after different cycle’s regeneration by different methods in S and N adsorption 746 746 1457 1457 746 1457 Peak attribution: 1457 cm-1--skeletal C=C vibrations in aromatic rings [1] 746 cm-1--ortho-aromatics [2]; C-S bond in DBT [3] • The adsorbates left on the GAC since the first cycle’s regeneration, especially for the samples regenerated by ultrasound and thermal methods. • The amount of accumulated adsorbates increased with the regeneration cycle. • 1 Wang CT, Chen SH, Ma HY, et al. JOURNAL OF APPLIED ELECTROCHEMISTRY, 2003(33): 179-186. • 2 Masson JF, Gagne M. ENERGY & FUELS, 2008 (22): 3402-3406. • 3 Castillo K, Parsons JG, Chavez D, et al. JOURNAL OF CATALYSIS, 2009 (268): 329-334.

  10. Conclusion • The structure of GACs can be better maintained when the ultrasound and solvent method is used for regeneration. • The texture of the GACs has little influence on the regeneration of the adsorptive sites taken by N in indole. • The regeneration of the adsorptive sites occupied by N in carbazole and S in DBT is governed by the structure of GACs. • Loss of strong acidic surface functional groups takes a negative effect on the regeneration of GACs. • FTIR results indicate that the adsorbates left on the GAC since the first cycle’s regeneration, and the amount of adsorbates increased with the regeneration cycle.

  11. Future work • Finish TPD tests of the other GAC samples • Nitrogen and sulfur analysis in the spent GAC samples • TGA characterization of the spent GAC samples

  12. Acknowledgement • Thank my supervisor Dr. Ying Zheng for her guidance and support! • Thank Dr. Hongfei Lin for his helpful suggestion and discussion about my experiment! • Thank the planning committee of this conference!

  13. Content • BET analysis of the spent GAC samples • TPD analysis of the spent GAC samples • FTIR analysis of the spent GAC samples • Accumulated sulfur and nitrogen content on the spent GAC samples • Conclusion • Future work • Acknowledgement

  14. Effect of micropore volume on regeneration efficiency Similar conclusions are obtained on the relationship between micropore volume and regeneration efficiency, as shown in the previous slide. When Sol-Tol is taken as the regeneration method, the micropore volume decreases little since the third cycle, which demonstrates that this approach can maintain most of the micropores of the adsorbent.

  15. Effect of total pore volume on regeneration efficiency The effect of total pore volume on the regeneration efficiency is similar to that of micropore volume. The higher pore recovery is, the higher regeneration efficiency for sulfur and nitrogen compounds is obtained.

  16. Effect of specific surface area on the capacity of nitrogen and sulfur In the case of regeneration of nitrogen in indole,

  17. Effect of micropore volume on the capacity of nitrogen and sulfur

  18. Effect of total pore volume on the capacity of nitrogen and sulfur

  19. Area of the peaks in TPD spectra • With the increase of regeneration cycle, the area of peaks at low temperature decrease, which means the consumption of strong acidic sites; while the area of peaks at low temperature increase, suggesting the introduction of weak acidic groups during the regeneration under atmosphere, especially when solvents are used. • In the same cycle, e.g. Cycle 9, the amount of both strong and weak acidic groups increase in the order of Thermal<US-DMF<Sol-DMF<Sol-Tol, which is same as that of regeneration efficiency.

  20. Area of the peaks in TPD spectra • With the increase of regeneration cycle, the area of peaks at low temperature decrease, which means the consumption of strong acidic sites; while the area of peaks at high temperature increase, suggesting the introduction of weak acidic groups or conversion of the strong acidic groups to the weak ones during the regeneration processes and the desorption of the adsorbates. • In the same cycle, e.g. Cycle 9, the amount of both strong and weak acidic groups increase in the order of Thermal<US-DMF<Sol-DMF<Sol-Tol, which is same as that of regeneration efficiency.

  21. Effect of acidic groups on regeneration efficiency • The more strong acidic groups, the higher regeneration efficiency. • A linear relationship exists between the amount of strong acidic groups and regeneration efficiency of adsorptive sites occupied by N in carbazole, which means the carboxylic groups may play a dominant role in this regeneration process. Relationship between strong acidic groups and regeneration efficiency. Regeneration method: Sol-DMF.

  22. (2) (1) • When the GAC samples are regenerated by Sol-Tol, the strong acidic groups take little effect on the regeneration of GACs exhausted by either S or N compounds. • Weak acidic groups, such as phenolic groups seem to influence the recovery of the adsorptive sites taken by S in DBT and N in carbazole when Sol-Tolmethod is used. • The effect of total acidic groups is similar to that of weak acidic groups. (3) Relationship between acidic groups and regeneration efficiency: (1) strong acidic groups (2) weak acidic groups and (3) total acidic groups. Regeneration method: Sol-Tol.

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