Study On Desulfurization Of Gasoline By Selective Adsorption Over Modified Activated Semi-coke

With the increasingly stringent environmental laws and regulations, reducing the SO_X in motor vehicle exhaust, producing and using environmental friendly low sulfur content gasoline becomes a universal attention question by the governments and refining enterprises all over the world. Although the traditional hydrodesulfurization (HDS) process can effectively remove the majority of sulfur-containing compounds in gasoline, it meets difficulty in achieving ultra-deep desulfurization. It needs stricter requirement for both production equipments and technology, and most middle and small refining enterprises encountered the difficulties in deep desulfurization for both technology and economy. Development of non hydrodesulfurization process as an effective supplement becomes more and more significant, among them the adsorptive desulfurization is considered to be one of the most promising desulfurization methods.In this paper, the lignite semi-coke from Ordos Inner Mongolia is selected as raw material to prepare adsorbents. The semi-coke is first modified by multiple chemical and physical activation methods, and then impregnated with transition metal oxide. Desulfurization performance of FCC gasoline is evaluated using dynamic adsorption in a fixed bed reactor. The optimum preparation parameters of adsorbents and operating conditions on desulfurization performance of FCC gasoline are obtained. The category of sulfide in FCC gasoline and desulfurized gasoline is analyzed by gas chromatography with a flame photometric detector (GC-FPD). The inactivated semi-coke adsorbent is regenerated by several methods in order to find the optimum regeneration way. The physical and chemical properties of adsorbent are characterized by several analytical instruments, and the adsorption of model compound is studied to calculate the thermodynamics and kinetics of adsorption. The adsorptive mechanism is analyzed to provide practice experiences for the industrialization of adsorptive desulfurization. The results of dynamic adsorption experiment shows that the preparation conditions play important roles in desulfurization performance of semi-coke adsorbent. The desulfurization efficiency of raw semi-coke is only 20.03%; it can be up to 34.78% after nitric acid activation, 44.19% after vapor activation, 48.95% after potassium hydroxide activation, and 46.46% after zinc chloride activation. The impregnation of metal oxide on activated semi-coke can improve the desulfurization performance, and the amount of metal oxide has an optimal one, 3% for CuO, and 1% for ZnO, respectively. The one impregnated with CuO has better performance in desulfurization than that with ZnO. The semi-coke first activated by vapor activation, then by phosphoric acid activation has a desulfurization efficiency of 81%, the activation condition is: the volume ratio of phosphoric acid and semi-coke 1.5, concentration of phosphoric acid 50%, dipping temperature 95℃, calcination temperature 650℃, then loading 4% CuO. The semi-coke activated by vapor activation and by sulfuric acid activation in order has a desulfurization efficiency of 89.22%, the activation condition is: the volume ratio of sulfuric acid and semi-coke 1.5, dipping temperature 90℃, calcination temperature 200℃for one hour, then loading 3% NiO. The breakthrough sulfur capacity of three adsorbents named HNVP₃%CuO, VPHP₄%CuO and VPHS₃%NiO is respectively 0.1430%, 0.2454% and 0.1806%, the adsorbent activated with vapor activation, phosphoric acid activation and loading 4%CuO has the best desulfurization performance.The GC-FPD chromatogram shows that the semi-coke adsorbent exhibited a quite high selectivity on benzothiophene, and lower on other sulfur containing compounds, the sequence of sulfur-containing compounds adsorption on semi-coke from ease to difficulty is benzothiophene (and its derivatives), thiophene (and its derivatives), and nonaromatic cyclic compounds (Tetrahydrothiophene). The result of model compounds experiment indicates that unsaturated hydrocarbon and heterocyclic compounds have a competitive adsorption with thiophene and its derivatives on semicoke, and the sequence of them influence from big to small is pyridine, benzene, cyclohexene. Thiophene is easier to be influenced than benzothiophene. The adsorption isotherm of thiophene adsorbed on semi-coke can be described by Freundlich adsorption model, and lower temperature is beneficial to adsorption of thiophene. The adsorption isotherm of benzothiophene adsorbed on semi-coke can be described by Langmuir model, and higher temperature is beneficial to adsorption of benzothiophene. The kinetic adsorption behavior shows that the adsorption of thiophene and benzothiophene is a process that starts from pseudo first order kinetic equation and end to pseudo second order kinetic equation, in initial stage, it fits pseudo first order kinetic equation, and at last stage it accords with pseudo second order kinetic equation. The kinetic adsorption behaviors of real gasoline can be described by pseudo second order kinetic equation. The adsorption of aromatic sulfur containing compounds on semi-coke is dominated byÏ€-Ï€complexation, S-M coordination, and Van Der Waals force. And the selective desulfurization depends mainly on the first two terms(Ï€-complexation and S-M coordination). The thiophene adsorbed on semi-coke should be possible to vertical adsorption and the benzothiophene inclined to parallel.The inactivated semi-coke of VPHP3%CuO regenerated by heat method at the temperature 650℃has better performance but its regeneration sulfur capability is only 0.1351%, regenerated ratio is 52.81%, it can improved to 0.1527% and 52.81% regenerated with vapor. The sequence of solvent extraction regeneration from easy to difficulty is xylene, toluene, benzene, n-heptane and ethanol. The regeneration sulfur capability can be up to 0.1788%, the regenerated ratio being 69.91%, by regeneration with xylene, and secondary regeneration sulfur capability being 0.1722%, secondary regenerated ratio being 67.32%. The regeneration sulfur capability can reach to 0.1877%, the regenerated ratio being 73.38% by Soxhlet extraction. And the regeneration process combined with Soxhlet extraction and vapor regeneration can achieve a sulfur capability of 0.2083%, regenerated ratio of 81.41%, and is the best one in this study.