Preparation And Desulfurization Performance Of ZnAl LDO Based On Hydrotalcitr-like Compounds

With the rapid development of economy,the demand for energy has risen sharply.In the three major fossil fuels?coal,oil and natural gas?,coal still occupies the main position of the energy source and guarantees people's material well-being life.In the process of coal combustion,a large number of SO₂ will be produced,which will harm the environment.Therefore,it is imperative to promote clean coal technology.Coal gasification technology is a crucial step in clean coal technology.There are 0.1%-1.5%sulfur in coal.In the process of gasification,coal will produce H₂S,SO₂,COS and various organic sulphides.Among them,H₂S accounts for more than 90%.If these harmful gases are not being well treated,they will be highly corrosive to the mechanical equipment and poison the catalyst.Moreover,SO₂ will be produced after combustion,which is detrimental to the environment.Therefore,coal gas must be desulphurized before combustion.At present,ZnO is acknowledged as the most efficient desulfurizer for it can reduce the concentration of H₂S to fractions of ppm.However,ZnO-based sorbents would sinter and ZnO can be reduced to the elemental zinc in the syngas reductive atmosphere when the reaction temperature above 600°C.Zinc will volatilize subsequently,leading to the loss of the active component and low efficiency of the desulfurizer.Therefore,a good thermal stability material—hydrotalcite zinc aluminum composite metal oxide?ZnAl LDO?was synthesized to remove H₂S from hot coal gas in this paper.Firstly,the optimal ratio of zinc and aluminum was selected by investigating the physical and chemical properties of ZnAl LDHs and ZnAl LDO with the Zn/Al ration of 1-4.The desulfurization performance of ZnAl LDO with different Zn/Al ration was also studied.Afterwards,the thermal decomposition behavior of ZnAl LDHs was studied by means of TG-DSC,TG-MS,XRD,FTIR and SEM,and the activation energy of ZnAl LDHs during the thermal decomposition process was calculated.Finally,the optimum conditions for the regeneration and desulfurization reaction and the desulfurization-regeneration cycles performance of ZnAl LDO was investigated.The conclusions as follows:?1?The optimal molar ration of Zn/Al is 3.The sulfur capacity of ZnAl-3LDO is 26.83 g S/100 g sorbent at 500 ^oC in simple atmosphere?2000 ppm H₂S and N₂ as balance?.The morphology of ZnAl LDHs and ZnAl LDO are both hexagonal lamellar sheets.?2?There are two major stages of the thermal decomposition of ZnAl LDHs:Stage I with an intense endothermic peak at 196°C in DSC curve is ascribed to the removal of water?both the physically absorbed water and the interlayer water?and a small loss of CO₂.Stage II with a broad endothermic peak is due to the decomposition of the carbonate anions and a little part of dehydroxylation from brucite-like sheets.The activation energies calculated by the Kissinger and FWO method are 110.7 and 112.8 KJ mol^-1 of stage I and 94.3 and 98.1 KJ mol^-1of stage II,respectively.?3?The optimal desulfurized temperature of ZnAl LDO in simulated gas?2000 ppm H₂S,18%CO,10.5%H₂,5%CO₂ and N₂ as balance?is 600 ^oC,and the sulfur capacity is 26.06 g S/100 g sorbent.?4?The optimum condition for regeneration experiments is regeneration temperature is 650 ^oC,regeneration space velocity is 12000 h^-1 and oxygen concentration is 6 vol%.Under this condition,the regeneration rate is 98.29%.?5?The results of desulfurization-regeneration cycles experiments shows that the 1st regenerated sorbent has the highest sulfur capacity—33.68 g S/100 g sorbent.After that,with the increase of the number of sulfurization and regeneration cycles,the sulfur capacity of the desulfurizers decreased gradually but all of them were higher than the sulfur capacity of fresh sorbent.