| Hydrogen sulfide（H2S）is major gaseous pollutant,which is widely present in natural gas,petroleum cracking gas,coke oven gas,biogas and so on.H2S has strong toxicity and corrosivity,and at a certain concentration,it can endanger human health and corrode metal pipes and equipment.In the air,H2S is easily oxidized to SO2,which contributes to the formation of acid rain.Therefore,it is essential to remove H2S from industrial gas.At present,activated carbon adsorption method is considered to be one of the most potential desulfurization methods due to its convenient operation process,better pore structure and reproducibility.However,due to the limitation of raw materials,it has high application cost,restricting its large-scale application.Biomass is regarded as a potential substitute for activated carbon because of its rich yield and high specific surface area after carbonization.Compared with terrestrial biomass,microalgae widely exist in the natural water,and the culture cycle is very short.Meanwhile,microalgae（e.g.,chlorella and spirulina）are widely used in the preparation of biomass fuels.After the preparation of biomass fuels,microalgae will produce a large number of microalgae biochars by-products.The effective utilization of these by-products to achieve resource utilization has important scientific significance and industrial value for improving the economy of biomass fuels preparation and reducing the potential solid waste pollution.In this dissertation,chlorella and spirulina were used as raw materials to prepare microalgae-based biomass porous carbon by KOH thermal activation and microwave-assisted KOH activation to adsorb H2S from gas stream.Then,the spent adsorbent after desulfurization was used to remove elemental mercury from flue gas.The research content and achievements are as follows:Two kinds of microalgae biochars（chlorella and spirulina）were modified by KOH thermal activation,and the obtained modified microalgae-based porous carbons were used for H2S removal.The physicochemical properties of the modified microalgae-based porous carbons were analyzed by various characterization methods.The effects of preparation parameters and process parameters on the desulfurization performance of porous carbons were investigated in the reaction system.Based on characterization analysis,adsorption kinetic model and thermodynamic calculation,the adsorption mechanism of H2S over porous carbon was studied.In addition,the removal performance of elemental mercury from flue gas using sulfur-containing spent adsorbent after desulfurization was studied.Results showed that KOH thermal activation greatly improved the desulfurization performance of porous carbons via improving the pore structure of porous carbon and increasing the surface oxygen-containing groups.The modified microalgae-based porous carbons（CK2 and SK2）achieve optimal desulfurization performance.Low concentration of water vapor can improve the desulfurization performance of modified microalgae-based porous carbon,while high concentration of water vapor can inhibit the adsorption of H2S on modified microalgae-based porous carbon.The increase of H2S,SO2,NO and CO2concentration and gas flow have negative impact on the adsorption of H2S by the modified microalgae-based porous carbon.S0and sulfate were successfully detected on porous carbon surface after adsorption via XPS and XRD analysis,indicating that chemical adsorption occurred in the H2S adsorption.The oxygen-containing functional groups（C-O）on the surface of porous carbon promote the adsorption of H2S.The pseudo-first order kinetic model can better fit the desulfurization process of porous carbon,and external mass transfer is the main control step of the desulfurization process.Thermodynamic analysis shows that physical adsorption is dominant in H2S adsorption process of modified microalgae-based porous carbons.The spent adsorbents（containing-sulfur porous carbons）could effectively capture Hg0from flue gas,and its mercury removal performance is better than that of commercial activated carbon under the same conditions.Two kinds of porous carbons were prepared by microwave-assisted KOH modified microalgae biochar for H2S removal.The physical and chemical properties of the microalgae-based porous carbons surface activated by microwave were investigated by characterization methods.And the effects of two activation methods（thermal activation and microwave-assisted activation）on on the physicochemical properties and adsorption properties of porous carbon were compared.The effects of activation method,impregnation ratio,adsorption temperature and gas composition on the desulfurization performance of porous carbon were investigated in the adsorption reactor.The desulfurization mechanism of microalgae-based porous carbons were studied with adsorption kinetics and thermodynamics.In addition,the removal performance of elemental mercury from flue gas using sulfur-containing spent adsorbent after desulfurization was studied.The study found that for the two activation methods,the modified microalgae-based porous carbon obtained by microwave-assisted activation has better desulfurization performance.The improvement of the desulfurization performance of porous carbon is mainly due to the improvement of specific surface area and total pore volume.25℃is the best adsorption temperature.Appropriate water vapor can improve the desulfurization performance of porous carbon,while high concentration of water vapor inhibits the adsorption of H2S.The increase of H2S inlet concentration and gas flow rate has negative impact on the adsorption of H2S.The competitive adsorption between SO2/CO2/NO and H2S has been formed,which reduces the desulfurization effect.The pseudo first-order kinetic model can better describe the desulfurization process of modified microalgae-based porous carbon,and the external mass transfer is dominant in the adsorption process of H2S.Thermodynamic analysis shows that the adsorption process of H2S is a spontaneous exothermic process,and low temperature is conducive to the removal of H2S.Physical adsorption is the main process in the desulfurization process,while chemical adsorption is the auxiliary.At the same time,the spent adsorbent after desulfurization successfully captured elemental mercury in the simulated flue gas,and its mercury removal performance was better than that of commercial activated carbon under the same experimental conditions. |
