Fiber membrane desulfhydration technology

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Fiber membrane desulfurization technology I: Working principle of gasoline fiber membrane desulfurization. The working principle of gasoline fiber liquid membrane desulfurization is shown in Figure 1. The catalyst-containing alkaline solution (aqueous phase) first enters the reactor from the side at the top of the fiber liquid membrane reactor, where it forms an alkaline liquid film on the fiber bundles inside the reactor. Gasoline (hydrocarbon phase) and oxidizing air enter 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 gasoline. Due to the difference in surface tension between gasoline and the alkaline solution, the fiber strands have a greater affinity for the alkaline solution. Additionally, the flow rates of the alkaline solution and gasoline are different, which results in the liquid film formed by gasoline 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 flow in the same direction, forming sodium thiol. Under the action of the catalyst and oxidizing air, sodium thiol is oxidized into disulfides, which are then returned to the gasoline phase. Upon reaching the end of the inner cylinder of the reactor, the density difference between the hydrocarbon phase and the alkaline solution causes the aqueous phase and the hydrocarbon phase to separate automatically rapidly in the sedimentation and separation tank, thereby completing the deodorization process of gasoline. During this process, the large number of fiber filaments significantly increases the mass transfer area. At the same time, 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 gasoline 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 contain as little water as possible, while 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 reason why the fiber liquid film reactor enables non-diffusive mass transfer between the hydrocarbon phase and the aqueous phase, allows for the removal of impurities from the hydrocarbon phase, and can **increase the mass transfer rate**, can be explained by the following mass transfer equation: (Equation-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-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. Figure 1: Principle of the fiber liquid film reactor process. II. Chemical reactions in the gasoline desulfurization and dewaxing system. In this process, the removal of hydrogen sulfide from gasoline occurs within the fiber liquid film reactor through the following reactions: H2S + 2NaOH → Na2S + 2H2O (1). The extraction of thiol compounds from gasoline takes place as follows: RSH + NaOH → NaRS + H2O (2). The oxidation of sodium thiol compounds occurs as follows: 4NaRS + O2 + 2H2O → 2RSSR + 4NaOH (3). III. Advantages of the fiber liquid film desulfurization and dewaxing process for gasoline. Compared with traditional gasoline desulfurization processes, this method offers the following advantages: a large mass transfer area per unit volume, resulting in high processing capacity; short mass transfer distances, longer effective treatment time, and continuous renewal of the mass transfer surface, which enhances mass transfer efficiency and enables more thorough removal of hydrogen sulfide and thiol compounds from gasoline. It utilizes a non-diffusive mass transfer mechanism, avoiding emulsification and entrainment, and thus minimizing the occurrence of alkaline solution entrainment in the treated gasoline. The process is simple to operate, stable in performance, and easy to adapt to existing facilities. It requires less space, makes efficient use of available space, and is simple to maintain. It also results in low consumption of alkali, reduced amounts of alkaline waste, and lower operating costs. The continuous operation rate is close to 100%. Last edited by gylai490 on 2008-12-3 15:02