Optimized methods for preparing activated carbon from rock asphalt using orthogonal experimental design

This work evaluated three activation methods, physical activation, chemical activation and combined physical–chemical activation, for preparing activated carbon (AC) from rock asphalt. A high carbon content and the low cost of rock asphalt makes it a good possible raw material for the preparation of activated carbon. The objective of this research was to establish what preparation conditions resulted in the AC with the best performance. Orthogonal experimental design was used to optimize preparation conditions. The criteria for evaluating the AC preparation methods were yield, surface area and mercury adsorption performance of the AC samples prepared with each technique. The optimum experimental conditions for AC preparation using the chemical activation method are: a carbonization heating rate of 12 °C min⁻¹, a carbonization temperature of 400 °C, a carbonization time of 60 min, an activation temperature of 850 °C, an activation time of 120 min and a KOH/asphaltene mix rate of 3 (w/w). The potassium hydroxide added in the chemical activation method reduced the formation of volatiles during the carbonization process. The KOH/asphaltene mix rate and the carbonization temperature play a decisive role on the specific surface area and Hg adsorption capacity of AC. The optimum experimental conditions for AC preparation using the combined physical–chemical activation method are: a carbonization temperature of 450 °C, a carbonization time of 40 min, an activation temperature of 800 °C, an activation time of 60 min, a KOH/asphaltene mix rate of 1 and a steam flow rate of 8 g h⁻¹. In the combined physical–chemical activation method, the KOH/C mix rate, activation temperature and steam flow rate are the primary factors affecting the surface area and Hg adsorption capacity. The surface areas of the AC samples prepared under the optimum experimental conditions in the chemical activation method and the combined physical–chemical activation methods were 2834.3 m² g⁻¹ and 2102.2 m² g⁻¹, respectively. The physical activation method was not suitable for preparing AC from rock asphalt due to low char yields.