Thermal cracking of Al-Dora asphalt for the simultaneous production of light fuel and activated carbon for desulfurization process

Abstract

Thermal cracking of an Iraqi asphalt, namely Al-Dora asphalt, at multiple temperatures for various durations was first achieved. The main target of this investigation was to produce an upgraded liquid fuel and microporous activated carbon. The thermal pyrolysis of asphalt was carried out in the temperature range of 400–600 °C for different durations (30–150 min) at a 20 °C/min heating rate. The maximum liquid fuel yield (51.55%) was produced at 450 °C for 1 h. This treatment process raised the American Petroleum Institute (API) gravity of the original asphalt from 3.26 to 34.54, while its viscosity was reduced from 422.0 mm2.s−1 to 3.76 mm2.s−1. Analysis of the produced liquid fuel by 1H NMR spectroscopy,13C NMR spectroscopy, and GC-MS disclosed that it was a mixture of n-paraffins (57.05%), isoparaffins (12.68%), and alkenes (30.27%) with a C6 and C19 carbon distribution. The physical and chemical features of the liquid were also determined following ASTM procedures, and the outcomes revealed that the produced liquid fuel had preferable properties to that of the authentic asphalt, suggesting its suitability as an alternative to diesel fuel. The coke produced after thermal pyrolysis of Al-Dora asphalt was successfully converted into active carbon (AC) via the optimized KOH-activation route, and the selected AC was prepared using a 2:1 KOH: coke impregnation ratio at 750 °C for 1 h. The AC was characterized by various techniques, including BET surface area and pore volume, X-ray diffractometry (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis (EDX), and infrared spectroscopy (FTIR). The total acid and basic surface groups besides the pHPZC of the AC were also determined. The adsorption efficiency of the as-obtained AC was tested in the adsorptive desulfurization process. For this target, dibenzothiophene (DBT) in n-hexane was selected as a model fuel. The AC showed an excellent efficiency of 99.33% for eliminating DBT from a model fuel containing 500 mg/L DBT using 0.35 g of AC at 40 °C for 30 min. Moreover, the removal of S- compounds from commercial gasoline using the AC under typical experimental conditions reached 65.12%. The adsorption of DBT by the produced AC offered an excellent fitting for Freundlich isotherm and the pseudo-2nd-order kinetics model. Finally, the regenerated AC demonstrated its ability to eliminate DBT up to the 6th reuse cycle efficiently.