LPG desulfurization

The technologies for desulfurization of liquefied gas are now pretty similar, with little change in the process flow. The new process currently does not have a pre-alkaline washing tower; instead, a fiber membrane reactor is added to the top of the alkaline washing tank, usually in one or two stages. The rest is not much different from the traditional methods. Basic principle of the fiber liquid film reactor: The working principle of liquefied gas fiber liquid film desulfurization and denaturation is shown in Figure 2.1. The alkaline solution (aqueous phase) first enters the reactor from the side, where it forms a liquid film of the alkaline phase on the fiber bundles inside the reactor. Liquefied gas (hydrocarbon phase) enters the reactor from the top of the fiber liquid film reactor. As the alkaline solution flows downward along the surface of the fiber strands inside the reactor, it reacts with the liquefied gas. Due to the difference in surface tension between the liquefied gas and the alkaline solution, the fiber strands have a greater affinity for the alkaline solution. Additionally, the flow rates of the alkaline solution and the liquefied gas are different, which results in the liquid film formed by the liquefied gas and the alkaline solution on the fiber bundle being continuously renewed. The impurities in the hydrocarbon phase (such as hydrogen sulfide and thiols) react continuously with the alkaline solution film as they move in the same direction. By the time they reach the end of the reactor’s inner cylinder, the density difference between the hydrocarbon phase and the alkaline solution phase enables rapid automatic separation of the aqueous phase and the hydrocarbon phase in the sedimentation and separation tank, thereby completing the desulfurization process of the liquefied gas. During this process, the large number of fiber filaments significantly increases the mass transfer area. Meanwhile, since the reaction takes place between the liquid films, the mass transfer distance is reduced, which **improves the mass transfer efficiency and enhances the chemical reaction between sulfides and the alkaline solution on the liquid films. As a result, impurities in liquefied gas can be removed to a large extent. This non-diffusive separation between the aqueous phase and the hydrocarbon phase enables the refined hydrocarbon phase to have as little water as possible entrained in it, and the aqueous phase does not contain any hydrocarbons. The hydrocarbon phase flows to the downstream equipment at the other end of the separation tank, while the alkaline solution at the bottom of the separation tank is pumped by a circulation pump to the top of the reactor for reuse. The ability of the fibrous liquid film reactor to achieve non-diffusive mass transfer between the hydrocarbon phase and the aqueous phase, thereby removing impurities from the hydrocarbon phase and **increasing the rate of mass transfer**, can be explained by the following mass transfer equation: (Equation 2-1) Where: ——mass transfer reaction rate ； ——Mass transfer constants of hydrocarbon-aqueous systems ； ——Effective contact area between hydrocarbon and water phases ； ——The concentration difference driving the transfer of impurities from the hydrocarbon phase to the aqueous phase. In Equation 2-1, the value related to temperature varies slightly depending on the properties of the hydrocarbon phase and the aqueous phase. It can be seen that the changes in these values are not significant; however, the large number of fibers in the fiber-membrane reactor increases the effective contact area between the hydrocarbon and aqueous phases**, thereby increasing the mass transfer rate as well.

Basic principle of desulfurization of thiols: This device uses an alkaline solution together with sulfonated cobalt phthalocyanine to remove trace amounts of hydrogen sulfide from the liquefied gas, as well as most of the thiols present in it. The alkaline desulfurization process is a typical absorption-regeneration reaction process. Principle of the desulfurization of thiols: An aqueous sodium hydroxide solution combined with titanium cyanocobalt sulfonate is used as an absorbent in a fiber membrane reactor, where the catalyst and alkaline solution react with H2S and thiols present in the feed gas. The removal of trace hydrogen sulfide and most thiols from liquefied gas occurs as follows in a fiber membrane reactor: The reaction for the removal of trace hydrogen sulfide is: H2S + 2NaOH → Na2S + 2H2O (1). The reaction for the extraction of thiols from liquefied gas using alkali is: RSH + NaOH → NaRS + H2O (2). The oxidation of sodium thiolates and the regeneration of the alkaline solution take place as follows: 4NaRS + O2 + 2H2O → 2RSSR + 4NaOH (3)

What are the reasons for the failure of desulfurization alcohols?