Experimental study of high-pressure ultrasound-assisted oxidative desulfurization (UAOD) and sulfone adsorption/desorption using zeolite-13X

Abstract

The sulfurous compounds in natural gas liquids should be reduced to the extent of satisfying the standard recipes due to corrosion, poisoning of catalysts in downstream processes, reduction in the quality of hydrocarbon products and environmental issues. Ultrasound-assisted oxidative desulfurization is an emerging method for sulfur removal from natural gas liquids. Since natural gas liquids exist in the liquid form of hydrocarbons at high pressures and ambient temperature (25 °C), this work aims to investigate the optimal conditions governing ultrasound-assisted oxidative desulfurization for various sulfurous compounds including mercaptan, sulfide and thiophene at high pressure and finally to appraise the adsorption of oxidized sulfurs and the regeneration of the adsorbent using elution with hot water. So, the effects of sulfur content and ultrasonication time were evaluated at 30 bar. Results showed that as the initial sulfur concentration in normal heptane was increased from 0.00 to 3000 ppmS, the sulfur removal efficiency was enhanced by less than 2 % of 95.9 % and of course, the increased ultrasonication time improved the sulfur removal efficiency. Next, results of the sulfone adsorption using zeolite-13X at 30 bar in continuous mode confirmed that the breakthrough time was reduced from 63 to 12 min as the weight hourly space velocity was increased from 5 to 20 h⁻¹ and pursuantly, the mass transfer zone diminished. Besides, the breakthrough time decreased by 45 - 10 min for increasing the initial sulfur content from 200 to 1000 ppmS. Changing the pressure of the adsorption process from 1 to 30 bar caused the improvement of sulfone adsorption capacity by approximately 3.75 times. In continued, the regeneration of zeolite-13X contaminated with sulfone by flowing hot water was evaluated and the zeolite-13X bed was completely regenerated.