Production of activated carbon from sugar beet pulp, its characterisation and use in adsorption of Cu(II) ions

IV SUMMARY Master Thesis Production of Activated Carbon From Sugar Beet Pulp, Its Characterisation and Use in Adsorption of Cu(II) Ions Muhammet Şaban TANYILDIZI Fırat University Graduate School of Natural and Applied Sciences Department of Chemical Engineering 1999, Page 77 Activated carbon is one of the adsorbents used widely in the removal of heavy metals from wastewater systems. Although activated carbons were commercially produced from wood, anthracite, lignite and bituminous coal, some agricultural by products such as almond, apricot, hazelnut and coconut shells, olive and grape stones and sugar cane bagasse have also been used for this purpose. In this study, the production of activated carbon was aimed by carbonizing sugar beet pulp, which is a by product of sugar industry, in carbon dioxide flow. In addition, after some characteristics of prepared activated carbons were determined, these samples were used in adsorption of Cu(II) ions from aqueous solutions. Carbonization procedure carried out in a fixed bed where 50 gram of sugar beet pulp was carbonized for the times ranging from 15 to 120 min at different temperatures (350- 750 °C). The yield of activated carbon from sugar beet pulp was decreased depending on the rise in time and temperature of carbonization process. The ash content of activated carbon samples is quite high. The pH of aqueous suspensions of prepared activated carbons changed in the range of 8.55-11.0 and the pHs of samples obtained by longperiod carbonisation at elevated temperatures are higher. Iodine number (IS) of activated carbon samples does not show a regular change depending upon carbonisation conditions. Iodine number of activated carbon obtained by carbonising sugar beet pulp at 400 °C for 120 min is 417.2 mg-Iî/g. This is the highest value of iodine number determined. Surface area of activated carbons, which is determined by phenol adsorption, increased by increasing time and temperature. Although the carbon contents of activated carbons were decreased with a rise in temperature and time of carbonization, amount of acid insoluble inorganic material was increased. In the experiments that the adsorption of Cu(II) ions was examined, the most effective removal was provided by activated carbons (A- 120-750) obtained from sugar beet pulp carbonised at 750 °C for 120 min. Optimum pH for Cu(II) ions was determined as 5.30. At this pH, by contacting Cu(II) solution of 50 mg/1 with activated carbon (A-120-750) the dosage of which is 1 g/L, 72.2 % of present Cu(II) ions was removed (at room temperature for 180 min.) at the same conditions. When the pH of mixture was raised to 7.8, the removal percentage of Cu(II) ions reached to 100 %. However, since Cu(II) ions may precipitat in the form of hydroxide at the pHs higher than 5.30, the experiments related to other parameters of adsorption were carried out at pH 5.30. The equilibrium time for the adsorption process of Cu(II) ions was determined as 180 min. Adsorption yield increased with increasing the dosage of activated carbon and when the dosage of 3 g/1 was used, the removal yield of Cu(H) ions reached to 99.6 % for the Cu(ü) solution of 50 mg/1. On the other hand, the results of the experiments carried out at 20, 40 and 60 °C were applied to Langmuir and Freundlich isotherms. The constants calculated from isotherm equations showed that the adsorption yield of Cu(II) ions was increased with rise in temperature of solution. Maximum adsorption capacity (qmax) were calculated as 63.69, 74.63 and 78.12 mg/g at 20, 40 and 60 °C, respectively. Although the values of Kf are lower compared to the values of qmax, the increase in their values with temperature is more outstanding. Enthalpy change for the process was calculated to be 8373.2 j/mol at the temperature intervals examined. The free energyVI change is negative and its value changed in the range of 22.11-25.14 depending upon the temperature. As a consequence, activated carbons obtained from sugar beet pulp may be effectively used in the adsorption of Cu(II) ions from aqueous solutions. That the adsorption capacities calculated from isotherm equation are high, confirms the deduction mentioned above. However, that the carbonization of sugar beet pulp have been carried out at high temperature is disadvantageous in point of cost. Key Words: Activated carbon, Copper, Adsorption, Sugar beet pulp.