Evaluation of Activated Carbon Fibers for Removal of Volatile Organic Compounds in Indoor Environments

1. Evaluation of Activated Carbon Fibers for Removal of Volatile Organic Compounds in Indoor Environments Huajun Lu Neil Zimmerman PhD CIH Purdue University School of Health Sciences Oct., 17th, 2003

2. OVERVIEW • Introduction of Indoor air quality (IAQ) • Purposes of Study • Materials and Methods • Theoretical Background • Results • Conclusions

3. IAQ Background • In developing countries, use of biomass fuels for cooking and heating • Result in 2 million death annually. • Associated with adverse pregnancies • Increase the risk of young child’s serious respiratory infection • One-half of U.S schools have problems linked to indoor air quality problems • Ranks among top five environmental risks to public health • Lost productivity estimated $60 billion per year

4. Sources of Concern for IAQ • Inadequate ventilation • Hazardous gases such as CO, NOx, etc. • Formaldehyde • Respirable particles • Pesticides • Biological contaminants • Bacteria • Mold • Viruses • Pollen • Volatile organic compounds (VOCs)

5. Adsorption • Adsorption is the process of trapping gas and vapor molecules within the pores of a microporous solid such as activated carbon. • Influence factors • Surface interactions between adsorbate and adsorbent • Surface area of adsorbate • Pore size of adsorbate • Adsorption media • Alumina / potassium permanganate • Zeolite (molecular sieve) • Granular activated carbon (GAC) • Activated carbon fiber (ACF)

6. Why ACF? • Compared to GAC, ACF has the following advantages: • Greatly improved contact efficiency with adsorbates leading to greater rates of adsorption, • Superior breakthrough capacity and excellent adsorption properties to low concentration of contaminants (Yue, et al., 2001). • Availability of felt or fabric forms: occupying smaller space • Electrical reactivation: saving reactivation cost (Suzuki, 1994, Economy and Lin, 1976).

7. What Does the Fiber Look Like? Typical SEM micrograph of ACF-15 Dia.=16 m Reference: Foster, K.L., Doctoral dissertation, UIUC, IL, 1993

8. Typical Surface Image of Single Fiber Reference: Foster, K.L., Doctoral dissertation, UIUC, IL, 1993

9. Typical Cross-section Image of Single Fiber Reference: Foster, K.L., Doctoral dissertation, UIUC, IL, 1993

10. Purposes of Study • To determine adsorption and desorption parameters for selected VOCs on ACF and typical indoor materials; • To establish an IAQ model based on the sink effects of indoor materials and adsorption by ACF

11. Materials and Methods---Chamber Test System

12. Chamber Diagram Injection port Fan Incoming air Outgoing air

13. Materials and Methods---Test chemicals

14. Test Materials • Test Materials: • Cotton: 100% cotton cloth • Carpet: • Polyester • Wallboard: Gold Bond® regular gypsum board with 100% paper in both sides, 12.7mm in thickness • ACF Surface area (m2/g) • ACF-10 738 • ACF-15 1390 • ACF-20 1600 Reference: Foster, K.L., et al., Chem.Mater., 4: 1068-1073, 1992 Mangun, C.L., et al., Chem. Mater. 11, 3476-3483, 1999

15. Sampling Strategies • Sampling and analysis of samples • Sampling intervals vary from 3 minutes to 3 hours • Sampling time ranges from 1 minutes to 10 minutes • Sampling flowrate: 80 ml/min • Active sampling with activated coconut charcoal tubes • CS2 as desorber • Gas chromatography/Flame ionizing detector

16. Model Development Chamber interior surfaces Adsorption materials

17. IAQ Model • For empty chamber: With initial conditions: C0=Ce, M0=Me • For chamber with ACF or indoor materials: Initial values: t=0, C0=0, M1=0, M2=0

18. Equations for Prediction of Adsorption Capacity • Freundlich isotherm equation: Where: m ----- The mass of adsorbate adsorbed per unit adsorbent, mg/g C ----- Concentration in bulk gas phase K, n --- Empirical constants • Dubinin-Radushkevichequation: Where: V----Volume of the adsorbate adsorbed at temperature T, cm3/g V0---- Total active volume of ACF, cm3/g A---- RT*ln(P0/P), adsorption potential, J/mol, P0, saturation vapor pressure, P, partial pressure of adsorbate at equilibrium β ---- Affinity coefficient, with respect to benzene in this project E0----Characteristic adsorption energy

19. Static ACF Adsorption Profile of Toluene

20. Freundlich Isotherm—Log-transformation

21. Freundlich Isotherm Parameters Freundlich Equation after log-transformation

22. Dubinin-Radushkevich Isotherm

23. Dubinin-Radushkevich Isotherm Parameters

24. ACF Adsorption--Dynamic Test in Chamber

25. Sink Strengths of Indoor Materials

26. Conclusions • For ACF static adsorption of toluene, the correlation coefficients for the experimental data were >0.97 based on both Freundlich and Dubinin-Radushkevich equations. • For ACF static adsorption, the adsorption capacity correlates with surface area, and pore size distribution. • Among tested indoor building materials, carpet has the greatest adsorption capacity for toluene. • Qualitatively speaking, ACF has significantly greater adsorption capacity than indoor building materials, thus, making it possible to aid removal of VOCs in passive mode.

27. Acknowledgements • Committee members: • Dr. Neil Zimmerman • Dr. Gary Carlson • Dr. Herman Cember • Dr. Yan Chen • Dr. George Sandison • Dr. Frank Rosenthal • Mr. Xinzhu Pu • Dr. Zhishi Guo (EPA, Research triangle park) • Dr. Jianshun Zhang (Syracuse University) • Mr. Miao Yang (Syracuse University) • This research study was (partially) supported by the NIOSH Pilot Project Research Training Program of the University of Cincinnati Education and Research Center Grant #T42/CCT510420.