Abstract:
To investigate the effect of parameters on the preparation of activated carbon from sewage sludge for crude glycerol purification. Types of activating agent (KOH, K₂CO₃ and H₃PO₄), weight ratio of activating agent to char (1.0-6.0 w/w), impregnation time (5-25 hrs) and carbonization temperature (500-900℃) were explored. The results showed that the purity of crude glycerol depended significantly on either the quantity of carbonyl group or the surface properties. The KOH activation can enhance the quantity of oxygen functional groups and the BET surface area than the solely thermal treatment, the K₂CO₃ and H₃PO₄ activations. Weight ratio of activating agent to char, impregnation time and carbonization temperature affected the quantity of carbonyl group and the surface properties as well as the ability to purify crude glycerol. Among the as-prepared sludge-derived activated carbon, the activated carbon prepared by KOH at the weight ratio between KOH to char of 5, impregnation time of 25 hr and carbonization temperature of 800℃ for 30 min by using the dose of activated carbon of 67 g/l with 120 min adsorption time and shaking rate of 250 rpm exhibited appropriate surface properties to enhance the purity of pre-treated crude glycerol up to 93.0 wt. %, which was greater than that by commercial activated carbon of around 1.05-fold. The repetitive purification can enhance the purity of pre-treated crude glycerol up to 96.9 wt.%. The regeneration of sludge-derived activated carbon by hexane was better than diethyl ether.