Effects of CO2 activation on porous structures of coconut shell-based activated carbons

Abstract In this paper, textural characterization of an activated carbon derived from carbonized coconut shell char obtained at carbonization temperature of 600 °C for 2 h by CO2 activation was investigated. The effects of activation temperature, activation time and flow rate of CO2 on the BET surface area, total volume, micropore volume and yield of activated carbons prepared were evaluated systematically. The results showed that: (i) enhancing activation temperature was favorable to the formation of pores, widening of pores and an increase in mesopores; (ii) increasing activation time was favorable to the formation of micropores and mesopores, and longer activation time would result in collapsing of pores; (iii) increasing flow rate of CO2 was favorable to the reactions of all active sites and formation of pores, further increasing flow rate of CO2 would lead carbon to burn out and was unfavorable to the formation of pores. The degree of surface roughness of activated carbon prepared was measured by the fractal dimension which was calculated by FHH (Frenkel–Halsey–Hill) theory. The fractal dimensions of activated carbons prepared were greater than 2.6, indicating the activated carbon samples prepared had very irregular structures, and agreed well with those of average micropore size.

[1]  V. Likholobov,et al.  Palladium catalysts on activated carbon supports: Influence of reduction temperature, origin of the support and pretreatments of the carbon surface , 2000 .

[2]  Peter Pfeifer,et al.  Chemistry in noninteger dimensions between two and three. I. Fractal theory of heterogeneous surfaces , 1983 .

[3]  G. Zgrablich,et al.  Characterization of active carbons: the influence of the method in the determination of the pore size distribution , 1998 .

[4]  F. Rodríguez-Reinoso,et al.  The use of steam and CO2 as activating agents in the preparation of activated carbons , 1995 .

[5]  S. J. Gregg,et al.  Adsorption Surface Area and Porosity , 1967 .

[6]  J. Lahaye,et al.  Fundamental issues in control of carbon gasification reactivity , 1991 .

[7]  D. Stoyan,et al.  Mandelbrot, B. B., Fractals: Form, Chance, and Dimension. San Francisco. W. H. Freeman and Company. 1977. 352 S., 68 Abb., $14.95 , 1979 .

[8]  Kenneth E. Noll,et al.  Adsorption technology for air and water pollution control , 1991 .

[9]  K. Gubbins,et al.  Pore size distribution analysis of microporous carbons: a density functional theory approach , 1993 .

[10]  R. Leboda,et al.  Estimation of the pore-size distribution function from the nitrogen adsorption isotherm. Comparison of density functional theory and the method of Do and co-workers , 2003 .

[11]  Osei-Wusu Achaw,et al.  The evolution of the pore structure of coconut shells during the preparation of coconut shell-based activated carbons , 2008 .

[12]  V. Gomes,et al.  Fractal dimensions of activated carbons prepared from lignin by chemical activation , 2002 .

[13]  A. Neimark,et al.  Density functional theories and molecular simulations of adsorption and phase transitions in nanopores. , 2001, Physical review. E, Statistical, nonlinear, and soft matter physics.

[14]  Wei Li,et al.  Preparation of high surface area activated carbons from tobacco stems with K2CO3 activation using microwave radiation , 2008 .

[15]  K. Krishnaiah,et al.  Experimental study of the production of activated carbon from coconut shells in a fluidized bed reactor , 1991 .

[16]  Aik Chong Lua,et al.  Microporous activated carbons prepared from palm shell by thermal activation and their application to sulfur dioxide adsorption. , 2002, Journal of colloid and interface science.

[17]  Douglas M. Smith,et al.  Characterization of Porous Solids , 1994 .

[18]  G. Halsey,et al.  Physical Adsorption on Non‐Uniform Surfaces , 1948 .

[19]  David Avnir,et al.  The Fractal approach to heterogeneous chemistry : surfaces, colloids, polymers , 1989 .

[20]  W. Su,et al.  Preparation of microporous activated carbon from coconut shells without activating agents , 2003 .

[21]  N. Seaton,et al.  A new analysis method for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements , 1989 .

[22]  S. Bhatia,et al.  A modified pore-filling isotherm for liquid-phase adsorption in activated carbon , 2001 .

[23]  K. Gergova,et al.  Effects of activation method on the pore structure of activated carbons from apricot stones , 1996 .

[24]  A. Gil,et al.  Extension of the Dubinin-Astakhov equation for evaluating the micropore size distribution of a modified carbon molecular sieve. , 2003, Journal of colloid and interface science.

[25]  F. Cannon,et al.  Overcoming calcium catalysis during the thermal reactivation of granular activated carbon , 2000 .

[26]  P. Tarazona,et al.  Free-energy density functional for hard spheres. , 1985, Physical review. A, General physics.

[27]  A. Fernández-Nieves,et al.  Structure formation from mesoscopic soft particles. , 2001, Physical review. E, Statistical, nonlinear, and soft matter physics.

[28]  A. Razafitianamaharavo,et al.  Investigation of activated carbon surface heterogeneity by argon and nitrogen low-pressure quasi-equilibrium volumetry. , 2005, Langmuir.

[29]  Aik Chong Lua,et al.  Influence of pyrolysis conditions on pore development of oil-palm-shell activated carbons , 2006 .

[30]  J. F. González,et al.  Carbon dioxide-activated carbons from almond tree pruning: Preparation and characterization , 2006 .

[31]  Anastasia Zabaniotou,et al.  Agricultural residues as precursors for activated carbon production—A review , 2007 .

[32]  E. Teller,et al.  On a Theory of the van der Waals Adsorption of Gases , 1940 .

[33]  K. Henning,et al.  Impregnated activated carbon for environmental protection , 1993 .

[34]  Robert Evans,et al.  Fundamentals of Inhomogeneous Fluids , 1992 .

[35]  D. Henderson.  Fundamentals of Inhomogeneous Fluids , 1992 .

[36]  W. Heschel,et al.  On the suitability of agricultural by-products for the manufacture of granular activated carbon , 1995 .