An extremely rapid, convenient and mild coal desulfurization new process: Sodium borohydride reduction

The present work describes the desulfurization of coal using mildly reductive method. Both a Yanzhou and a Yanshan coal (referred to as YZ and YS coal, respectively), were treated in an aqueous media employing sodium borohydride (NaBH4) as reducing agent, which is a well known hydrogen storage. Reaction variables investigated include concentration of reductant, time, pH of initial media, temperature, stirring rate and particle size. The calorific values and ignition temperatures of the coal samples before and after treatment were determined. Results show that the total sulfur removal improved with the increase in the concentration of NaBH4, shaking rate and temperature and with the decrease in the particle size. Meanwhile, decreasing the particle size from - 250 to - 109 mu m increased the organic sulfur removal by more than six times for either of the coal samples. Considering economic rationality and operational convenience, the desulfurization conditions determined were 1.6 mM of NaBH4 concentration, - 109 mu m of particle size, neutral pH of initial media, 1 min of treated time, 100 rpm of shaking rate, 30 degrees C of temperature. This led to 23.8% and 59.0% reduction in the pyritic, 70.4% and 100% reduction in the sulfate, and 11.0% and 15.0% reduction in the organic sulfur, giving 31.3% and 40.8% reduction in the total sulfur for the YZ coal and the YS coal, respectively. Moreover, this resulted in the increase in the calorific values by 3.4-6.9% and the decrease in the ignition temperatures by 2-21 degrees C for the coal samples. The desulfurization method described here is extremely rapid, convenient, inexpensive and mild, and therefore, has considerable technological interest. (C) 2010 Elsevier B.V. All rights reserved.