Desulfurization and optimization of low-grade local coal by sequential KOH and HCl treatment

Due to abundance and low cost coal remains the world’s most preferred energy source. With energy demand on the rise, the need for low sulfur coal is increasing. Therefore, it is necessary to treat the local low-grade coal in an effective way to reduce its sulfur contents for subsequent use in industrial and domestic applications. In this study, the desulfurization of coal samples from Choa-Saidan Shah (Jhelum, Pakistan) coal fields, with potassium hydroxide (KOH) and hydrochloric acid (HCl) at a temperature ranging from 25 to 70°C, at a time ranging from 30 to 150 min., with particle size ranging from 60 to 220 mesh (63–250 µm), and KOH concentration varying from 5 to 10% was investigated. The maximum desulfurization of 74.2% was achieved by combined treatment with 50% KOH and 10% hydrochloric acid. Moreover, the decrease in particle size results in an increase in desulfurization characterized by a 72.6% sulfur removal at a particle size of 220 mesh (63 µm). The results also showed that an increase in time and temperature increases the desulfurization of coal. Independent variables were co-related by using response surface methodology in central composite design to achieve maximum desulfurization. The results of experimentation show that the KOH concentration is the most critical factor in the removal of sulfur from low-grade coal as it has the highest F statistic value.