Study On Carbon Monoxide And Carbon Dioxide Synergistic Removal From Fire Smoke In Enclosed Space

When a fire breaks out in enclosed spaces such as submarines and manned spacecraft,toxic smoke may accumulate in the cabin easily.It is necessary to remove fire smoke and restore the environment quickly after a fire accident.However,the present comprehensive air purification system in submarine and spacecraft is mainly applied to remove several specific toxic gases such as CO and CO2 produced in daily operation.Whether that could meet the need for rapid removal of high-concentration smoke under the fire emergency requires further studies.Besides,the air purification strategy for the submarine or manned spacecraft is still to adopt different removal methods for different gas components,which results in the large mass/volume,high energy consumption and low efficiency of the system.CO and CO2 are two key toxic gas components which must be removed in both daily and emergent situations.In recent years,the single gas component removal methods such as CO catalysis and CO2 sorption under ideal atmosphere have been well studied.However,there are few studies on the toxic gas removal under fire smoke atmosphere,and the research on the integrated elimination of multiple components in fire smoke has not been reported.Therefore,this thesis was going to study the CO and CO2 synergistic removal from fire smoke in enclosed space.The study attempted to obtain a suitable coupled catalyst for CO and CO2 synergistic removal and propose a multi-component combined elimination method of fire smoke in closed space,through the multiple component coupling of CO catalyst and CO2 sorbent.The major work was summarized as follows:1.Preparation and optimization of high-activity CO catalyst at low temperature.Cu-Mn-Ce oxide catalysts(CuMnCe)were prepared by impregnation(IM),deposition-precipitation(DP),traditional coprecipitation(CP),coprecipitation with cetyl trimethyl ammonium bromide(CC),and sol-gel(SG)methods,and further tested for CO catalysis and characterized by XRD,etc.Results showed that the supported CuMnCe catalysts obtained by IM and DP had higher CO catalytic activity than the bulk/unsupported CuMnCe catalysts prepared by CP,CC,and SG.Particularly,CuMnCe-IM exhibited outstanding CO oxidation performance.The presence of more isolated CuO and MnOx entities on the supported catalyst surface might contribute to the efficient utilization of both lattice oxygen and spillover oxygen to improve the activity.Further study revealed that CuMnCe catalyst had higher CO catalytic activity than CuCe and MnCe catalysts,and as Cu/Mn mass ratio varied from 1/0.2 to 1/9,the activities presented unimodal distribution.When Cu/Mn=1/1,CuMnCe showed the highest activity.And calcination temperature(160??400?)affected the pore formation and metal element valence of CuMnCe.Calcination at 320? was decent pretreatment to obtain desired metal oxides along with fine textural properties for the ceria supported Cu-Mn oxides catalysts.2.Coupling of the CO oxidation catalyst and CO2 sorbent.CuMnCe catalyst was coupled with CO2 sorbent KOH,LiOH or K2CO3 by wet impregnation(WI),solid-state impregnation A(SI-I)and B(SI-II),and wet/solid-state impregnation(WSI)methods,and further tested for CO/CO2 removal and characterized by XPS,etc.Results showed that CuMnCe/LiOH,CuMnCe/KOH,and CuMnCe/K2CO3 were all able to oxidize CO and absorb CO2 in situ.Coupling methods affected the sample performance,and the sorbent dispersion state was a key factor.Taking KOH as an example,CuMnCe/KOH-WSI with the large KOH bulk phase exhibited the outstanding CO catalytic activity and CO2 sorption efficiency,higher than the uncoupled sample.Besides,CuMnCe/LiOH,CuMnCe/KOH,and CuMnCe/K2CO3 coupled samples all presented high CO oxidation activities,while their CO2 sorption performances were quite different.CuMnCe/LiOH showed the best performance which could be a good alternative for CO/CO2 synergistic removal from fire smoke.Particularly,through the catalyst and sorbent coupling,their oxidation and adsorption performances were both improved,due to the competitive adsorption of CO2 on catalyst surface by the sorbent in the coupled sample,which induced the synergistic effect between catalyst and sorbent,i.e."sorption enhancement" effect.It was further summarized as the concept of sorption-enhanced CO capture.3.Deactivation and modification of catalyst in impurity atmosphere.Catalyst deactivation in H2O,SO2,and NO2 is a common issue.Fire smoke usually contains high-concentration water and other impurity gases.Hence,CO2 sorbent coupling was used as the modification method of CO catalysts.CuMnCe catalyst and CuMnCe/LiOH,CuMnCe/KOH,CuMnCe/K2CO3 coupled catalysts were tested for CO removal under H2O,SO2,and NO2,and further characterized by XRD.Results showed that water vapor could decrease CO oxidation activity of the pure catalyst and coupled catalysts to different degrees.LiOH coupling could restrain the adverse effect of H2O to a certain extent,while KOH coupling would intensify the effect.And H2O could improve the CO2 sorption efficiency of three coupled catalysts.Meanwhile,SO2 could reduce the activity of CuMnCe catalyst in both the presence and absence of water.At the high concentration of 0.04%,SO2 would even lead to the complete deactivation of catalysts.While the deactivation effect could be effectively inhibited through coupling LiOH or K2CO3 sorbent.Compared with SO2,the adverse effect of NO2 was very limited.4.Performance validation of coupled catalyst for fire smoke circulation removal in enclosed space.Scaled closed test chamber system was set up to reveal CO/CO2 cycle removal efficiency of CuMnCe/LiOH coupled catalyst under polyethylene smoke.Results showed that CuMnCe/LiOH showed good performance of CO/CO2 integrated removal from complex polyethylene smoke.Under the benchmark condition of 50.0g CuMnCe/LiOH with 72.4g LiOH dosage and 5 L/min purification flow rate,the average CO removal efficiency of the sample was 96.4%,and the average CO2 removal efficiency was 70.3%.Furtherly,increasing the purification flow rate could improve CO/CO2 removal reaction rate and shorten purification time,while reducing the sample dosage would reduce the efficiency and reaction rate per unit mass sample.Among the different conditions,the CO/CO2 removal reaction rate of the sample was highest under 50.0g CuMnCe/LiOH with 72.4g LiOH dosage and 10 L/min rate,and its average CO removal efficiency was 98.1%along with 46.6%of CO2 removal efficiency.These confirmed that CuMnCe/LiOH was suitable for CO/CO2 synergistic removal from fire smoke in enclosed spaces such as submarines.Finally,experimental data was used to modify the gas concentration variation model obtained by theoretical analysis as follows:...