Comparison of Kinetic Models for CO2 Gasification of Coconut-Shell Chars: Carbonization Temperature Effects on Char Reactivity and Porous Properties of Produced Activated Carbons

Abstract

Solid chars were prepared from coconut shell at different carbonization temperatures in the range from 250-750°C and gasified in a thermogravimetric analyzer under the atmosphere of carbon dioxide at 850 o C. The kinetic analysis showed an accelerating increasing of char conversion with reaction time, indicating an increase in the instantaneous gasification rate as the reaction proceeded. Four kinetic models for gas-solid reactions including, the volume-reaction model (VRM), the shrinking-core model (SCM), the random-pore model (RPM) and the modified volume-reaction model (MVRM) were tested against the measured kinetic data and the MVRM was found to predict the gasification kinetics most accurately. The char reactivity index was computed from the apparent rate constant of the MVRM and used to assess the reactivity of char towards carbon dioxide gasification. It was found that the char reactivity index decreased with increasing carbonization temperature, with the char produced at the lowest temperature of 250°C giving the highest reactivity. Surface area of activated carbon, produced from the gasification of various chars at 850°C for 60 and 120 min, correlated well with the char reactivity index, showing a proportional increasing of surface area with increasing reactivity index and passing through a maximum near the reactivity index of 0.02 min-1 .

Assessment of steam gasification kinetics of the char from lignocellulosic biomass in a conical spouted bed reactor

“…The reaction zone then moves into the solid, leaving behind completely converted material. Thus, at any time during the reaction, there exists an unreacted core of material which shrinks in size during reaction [16,25,53]. The nth model is an empirical model, and is not therefore based on any theoretical consideration for the reaction mechanism inside the char particle.…”

“…Char steam gasification has been assumed to be a simple heterogeneous reaction controlled by the chemical reaction step, and therefore without mass transfer limitations [53] (Section 3.1 deals with this point). The reaction rate is described by a general kinetic expression considering the evolution of conversion with time as a function of temperature and steam concentration: …”

Controlling Synthesis of Polymer-Derived Carbon Molecular Sieve and Its Performance for CO2/CH4 Separation

“…Basically, carbonbased porous material such as CMS can be made by controlled pyrolysis of various natural carbonaceous materials such as coal, nut shell and wood [13][14][15][16] or synthetic polymer such as polyvinylidene chloride, polyimide and phenol formaldehyde [17][18][19][20]. It has been generally known that the pore structure of the carbon molecular sieve is affected by the nature of the precursor, pyrolysis method, and post-treatment conditions.…”

Simplification of Gibbs Free Energy Equation for Predicting the Gas Composition of Steam Gasification of Pattukku Coal Char

“…Based on the concept of mass balance, the mass of each element is conserved. The mass balance of component i can be written as follows: (10) …”

“…For this reason, mathematical equations or modeling that could be used to perform the optimization of the process is of importance [8,9,10,11]. Some researchers already proposed modeling the process of gasification by using the equilibrium approach.…”