Performance Evaluation of Chemically Modified Sawdust as Lignocellulosic Adsorbent for Aqueous Ethanol Purification.
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Date
2016
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Publisher
Obafemi Awolowo University
Abstract
This research investigated the applicability of a lignocellulosic adsorbent such as chemically modified sawdust for aqueous ethanol purification with a view to producing fuel-grade ethanol. It also determined the optimum condition for water adsorption and evaluated the performance of the modified sawdust samples as alternative to the costly commercial adsorbents.
The sawdust were modified using 25% (weight of H2O/weight of adsorbent) H2SO4 and 15% (weight of H2O/weight of adsorbent) CaCl2 at temperature range of 30 – 90 0C. The physical characterization of the screened sawdust were determined and used to select the likely optimum particle size for the adsorption process. The samples were analyzed using refractive index and density methods. Liquid phase adsorption experiments were conducted at room temperature with initial concentration of 92.85% (w/w) aqueous ethanol. Adsorption isotherm parameters were determined from equilibrium experiments carried out using different adsorbent doses of range 0.5 - 2.0 g. The adsorption performance of the modified sawdust samples were determined from the kinetic models using pseudo-first order, pseudo-second order kinetics and intraparticle diffusion as the rate controlling mechanism. The evaluation of the performance of the modified sawdust samples for equilibrium isotherm was done using Langmuir, Freundlich and Brunauer-Emmett-Teller (BET) adsorption isotherm.
The results showed that adsorption capacities at equilibrium for the 0.425 mm particles modified in 15% (w/w) CaCl2 (MC90) and 25% (w/w) H2SO4 (MH90) had the highest adsorption capacities of 0.774 and 0.731( g H2O g-1 adsorbent) respectively and percentage water removal of 88.81 and 83.50% respectively .The acid and salt modified sawdust samples attaining equilibrium within 50 min. The calculated adsorption capacities for pseudo-first order model (0.1910 – 0.9036 ml/g) were closer to experimented data (0.3080 – 0.7530 ml/g) than those obtained from pseudo-second order model (0.6620 – 0.9880 ml/g). Statistical evaluation of kinetic models showed that total error (Err2) and standard deviation (SSE) for pseudo-first order (0.0084 – 0.0298) and (0.1726 – 0.1170) respectively were smaller compare to that of pseudo-second order model of range (0.0072-0.1253) and (0.354 – 0.0847).The adsorption parameter for Langmuir isotherm ranges between 0.9220-0.9695 and Freundlich isotherm ranges between 0.568 and 0.9251. Since conditions of (0 < RL < 1) and (0 < 1/Nf < 1) were met by the process, this implied that the adsorption system is favorable.
The study concluded that CaCl2 modified sawdust has higher adsorption performance than H2SO4 modified sawdust. The smallest particle sizes of CaCl2 (MC90) modified adsorbent gave the highest yield of 0.774 g/g adsorption capacity using 92.85% w/w initial ethanol concentration. Pseudo-first order model and Freundlich adsorption isotherm were the most appropriate models that described the adsorption process.
Description
xix,101
Keywords
Chemically Modified Sawdust, Lignocellulosic Adsorbent, Aqueous Ethanol, Langmuir, Freundlich, Brunauer-Emmett-