Modified Petroleum Coke As Sorbent/catalyst For Flue Gas Desulfurization

This thesis focus on the preparation of petroleum coke to be applied to remove SO₂ from flue gases. Several desulphurizers are prepared through high-pressure hydrothermal activation, acidification,alkali modification, calcinations, H₂O₂ oxidation and the loading of Cu²⁺. The fixed-bed reactor is employed to investigate the activity of desulphurizers and the influence of temperature,time,space velocity,water vapour content and oxygen content. The prepared desulphurizers were characterized by BET,XRD and scanning electron microscope.The initial specific surface area of petroleum coke is only 2.67m /g with almost no adsorptivity. Owing to the preence of low content sulphur,ash and volatile matter as well as high content fixed carbon built into a compact structure, the activation of petroleum coke requires strong activating agent to break up the structure.The experimental results indicate that treatments by high-pressure hydrothermal activation, acidification,alkali modification and finally by calcination is quite effective for the promotion of desulfurization performance.Calcination is proved to be the key step to acquire high performance desulphurizers. The intrinsic hole structure is changed and the specific surface area, pore volumn are greatly increased after activation. The desulfurization performance of modified petroleum coke is attributed not only to open up of pore structure, but also to the creation of new chemical groups on the surface.The oxygen functional groups on the surface play an important role in desulfurization; high temperature can lead to the decomposition of oxygen functional groups and therefore improving the surface alkalinity.Because of the strong oxidizing property of HNO₃, more new oxygen functional groups can be created on the surface of petroleum coke; functional groups beneficial to be adsorption of SO₂ can be generated through calcination. Desulphurizers prepared using KOH have an obvious de- SO₂ effect, alkali can diffuse into the minicrystal structure of petroleum coke, cellular structure are created when KOH reacting with carbide, agraphitic carbon and active point. As the alkalinity of KOH is stronger than NaOH, it is more effective in the breaking of the inner structure of petroleum coke and hencer more effective to desulfurization.H₂O₂ can open up the close hole and expang the micropore in the petroleum,resulting in the improvement of desulfurization performance.The loading of Cu²⁺ can synergistically improve the SO₂ removal effect of the desulphurizers. The result of the experiment indicates that favourable loading content ofCu²⁺ is 5%.Petroleum coke modified by KOH(4:1 KOH/C) is choosen for further study on the effects of operation paramenters.The results show that the optimum desulfurization temperature is 120℃; the de-SO₂ effect is decreases with the increase of space velocity; the feed gas concentration of SO₂ have no marked effect on desulfurization; the favourable water vapour content is 8% to 10%; an oxygen concentration of 4 %-6 % is necessary to maintain a high removal efficiency of SO₂.The result of XRD test indicates that the raw petroleum coke have compact structure,with high extent of crystalization.The use of KOH, especially at large dosage, can destroy the crystal structure, and therefore improve the de-SO₂ performance.The SEM study of desulphurizers show that the surface of raw petroleum coke have a crinkled or coarse surface with no hole.Treatment by KOH and HNO3 can lead to the increase of the amount of micropore and mesopore, giving rise to the improvement of desulfurization performance.