Development Of Desulfurization Technique For Improving Removal Efficiency Of Mercaptans From Liquefied Petroleum Gas (lpg)

The sulfur content of coking liquefied petroleum gas (LPG) is rising and the sulfur compounds distribution is becoming more and more complex because of using heavy and high sulfur content crude oil as feed. As a result, present process and technology for LPG desulfurization are showing some limitations with the rigorous desulfurization and environment reqirements. This research for improving sulfur removal efficiency from LPG was carried out in this paper. The relationship between the quality of alkaline and sulfur content in LPG was inveatigated. Meanwhile, the desulfurization performances were comparied between series liquid film contactor and general process. Then alkaline solution was regenerated by using micro-bubble oxidation and stripping process with the laboratory and pilot scale. The LiFT-HR technology was developed for removing sulfur from LPG based on some improvements in mercaptans removal unit and regeneration unit. Furthermore, the LiFT-HR technology has been used in industrial plant for mercaptans removal in Maoming petrochemical branch of Sinopec (MMPC).Some potential problems in present desulfurization industrial plants were analyzed and indicated. Analysis results show that the low mass transfer efficiency of extraction process restrictes the desulfurization performance. The large amount of alkaline residue is mainly derived from H2S which exists in the entrained amine solution by LPG. Desulfurization performance showed periodic change because the oxidation products accumulate in regenerated alkaline solution and release into LPG.With above results, amine concentration in LPG can be controlled below 200 ppm by using an amine coalescence separator. As a result, the Na2S content in alkaline solution from pre-alkaline washing process shows a significant decrease and the alkaline solution can also be regenerated. Besides, the mass transfer property is intensified by using liquid film contactor. Meanwhile, the oxidation regeneration efficiency of alkaline solution and the separation degree of disulfide are largely improved. The results of中试indicate disulfide content in regenerated alkaline solution can be reduced to 340 ppm and the separation efficiency of disulfide is about 70% by efficient oxidation and stripping process.The industrial application results of LiFT-HR fiber liquid film technology in mercaptans removal plant in MMPC indicated that mercaptans content can be reduced to 40 mg/m3 after treating with liquid film contractor. The removal efficiencies of mercaptans, disulfides and total sulfides can reach 97%,70% and 93%, respectively. The low concentrations of disulfides and Na2S as well as high quality of regenerated alkaline solution can be retained. The using period of alkaline solution can reach 5 to 6 months. LiFT-HR process show the alkaline residue emissions of 1.04kg/(t LPG) which is 80% lower compared with general technology.