Experimental Study On Absorption Removal Of H₂S From FCC Dry Gas Using Fe-Zn-TMS System

Fe-Zn-TMS?tetramethylene sulfone? desulfurization system,which was consisted of ferric chloride hexahydrate?FeCl₃·6H₂O? as oxidizer, zinc chloride?Zn Cl? as precipitant, TMS as physical solvent and ethanol?C2H5OH? as co-solvent, were used for absorption removal H₂S from the cracking gas in fluid catalytic cracking?FCC? unit of petroleum refining process, the rich liquor was regenerated by 30% H₂O2 and recovered sulphur.This desulfurization system innovative compound chemical desulfurization system?Fe-Zn? with physical desulfurization agent?TMS? for the physical and chemical desulfurization system, compared with the traditional desulfurization process, this system maintained for a long time effective desulfurization at high load H₂S concentration; the rich liquor was regenerated by 30% H₂O2, 30% H₂O2 not only regenerated the chemical desulfurization system and physical desulfurization agent by one time, but also the suytem could recovery sulphur.In the single factor experiment of Fe-Zn-TMS desulfurization system synthesis and removal H₂S. In order to preliminary ensure the best mole ratio of each active ingredient and removal H₂S condition, the effects of different mole ratio of FeCl₃·6H₂O and Zn Cl and TMS? n?FeCl₃·6H₂O?: n?ZnCl₂?: n?TMS??, volume concentration?W? and p H value of the absorbing liquid on H₂S removal were evaluated. The results showed that maximum H₂S removal rate of 99.82% in effective desulfurization time was achieved and maintained for a long time at n?FeCl₃·6H₂O?:n?ZnCl₂? n?TMS? of 0.45:0.55:1, absorption solution p H of 0.75, and volume concentration?W? of 50%, FCC dry gas flow?Q? of 400 m L·min-1 and H₂S initial concentration of 3183 mg·m-3⁸643 mg·m-3. In the single factor experiment of rich liquor regeneration, the impacts of different mole ratio of Fe2+ and H₂O2?n?Fe2+?:n?H₂O2?? and p H value in the concentrate on oxidation rate of Fe2+ were also examined. Results showed that the oxidation rate of Fe2+ reached 96.7% at n?Fe2+?:n?H₂O2? of 2:1, rich liquor p H of 0.65, regeneration time of 1.5 min.The response surface methodology?RSM? with Box-behnken and equation of linear regression were used to optimize the results of the single factor experiment. The interaction effects of percentage of each active ingredient, volume concentration and p H value of the absorbing liquid on H₂S removal and FCC dry gas flow in H₂S removal experiment,?n?Fe2+?:n?H₂O2?? and rich liquor p H value and regeneration time in regeneration experiment on the response surface value were evaluated. According to the response surface 3D map and the correponding contour map, the results showed that the interaction was significant between two parameters in each stage, H₂S removal rate as the response surface value reached 99.99% by equation of linear regression at n?FeCl₃·6H₂O?:n?ZnCl₂? n?TMS? of 0.53:0.61:1.1, absorption solution p H of 0.74, and volume concentration of 47.89%, FCC dry gas flow of 308.58 m L·min-1, the oxidation rate of Fe2+ as the response surface value reached 99.6% by equation of linear regression at n?Fe2+?:n?H₂O2? of 1.58:1, rich liquor p H of 0.43, regeneration time of 1.8 min. Results of RSM were optimized with the prospect of industrial application, absorption solution p H was 0.73, and volume concentration was 49.6%, FCC dry gas flow was 420 m L·min-1, n?Fe2+?:n?H₂O2? was 1.82:1, rich liquor p H was 0.68, regeneration time was1.62 min. The absorbent could be reused for 3 times while H₂S removal rate maintained above 99% from continuous desulfurization experiment, SO42- of desulfurization by-product was produced at rich liquor stage and stabilized at 20 mg·L-1 within effective desulfurization time. SO42-had little effect on desulfurization system. The sulphur recovery rate stabilized at around 95%.A combination of the single factor experiment and RSM showed that the Fe-Zn-TMS desulfurization system compared with the traditional desulfurization process, it could work well at normal temperature and pressure with simple operation, rich liquor regenerated with a low energy consumption, by-products generated less and had a single product, high sulphur recovery rate, the Fe-Zn-TMS desulfurization system had good prospects for industrial applications.