A comparative optimisation study of activated carbon production from hazelnut shells by thermal and microwave heating methods

• Main Author: Sharifan, Suzan
• Other Authors: Fowler, Geoffrey
• Published: Imperial College London 2014
• Subjects: 624
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.592751

This research has studied the optimisation of activated carbon production from waste hazelnut shells, using both conventional and microwave heating techniques. A comparative study was conducted on the results obtained from both production methods to provide information on the characteristics, advantages and disadvantages of each production technique from a physical and chemical perspective. The study of the conventional production method was carried out using a comprehensive two- stage Response Surface Methodology (RSM). The microwave production method was studied using a combination of RSM and the traditional single-factor-at-a-time experimental design. The comparison of the two production methods showed that at a similar degrees of carbon burn- off, much lower pore volume and internal surface area was achieved for the microwave produced samples. The highest BET surface area produced with the conventional production method was 1777 m2/g, obtained from the activation of carbonised char with 0.67 ml/min water for 4 hours at 900°C. This value was nearly 2.5 times larger than the maximum BET surface area achieved from the microwave production method (715 m2/g) (50 min at 1000W). Similar results were also obtained for the aqueous phase adsorption of phenol and methylene blue; 2.2x and 2.3x larger adsorption capacity for thermal sample, respectively. In general, the microwave production method was found to be less effective in the production of highly microporous carbon. While the rate of micropore development with carbon burn-off in microwave heating was much lower than the conventional method, mesopore volume was found to be close and even comparable with that achieved with the conventional method. Considering that the microwave heating resulted in lower energy consumption per unit carbon burn-off, this heating system can be energy efficient in the production of mesoporous adsorbents. The energy efficiency could be of great importance when a two step carbonisation- activation is to be employed, since it could considerably reduce the heating time to the final activation temperature.