The Law And Mechanism Of N₂O Adsorption/desorption Of Coal With Different Metamorphic Degrees

Nowadays,the global warming issue has gained broad concern.The Fourth Assessment Report of Working Group I of the Intergovernmental Panel on Climate Change?IPCC?has pointed out that the global temperature has increased by approximatley 0.74±0.18 ^oC over the past 100 years.The increasing greenhouse gas concentration in the atmosphere caused by human activities is the main cause of climate change.Followed by carbon dioxide?CO₂?and methane?CH₄?,the nitrous oxide?N₂O?is ranked as the third greenhouse gas in the atmosphere,the Global Warming Potential?GWP?of which is 190-290 times that of CO₂ and 4-21times of CH₄.Moreover,N₂O is stable in chemical properties and will not be decomposed in the atmosphere for 100 years.It can enter the stratosphere and destroy the ozone layer.Thus,reducing the emission of N₂O into the atmosphere is of great significance to mitigate global warming.Numerous studies show that the agriculture source accounts for one third of the total N₂O emission.The N₂O emitted from the soil occupies 72%of the agriculture source.Thus,how to reduce N₂O emitted from the soil is meaningful to mitigate greenhouse effect.The emission of N₂O from soil is mainly caused by the large use of nitrogen fertilizer.At present,the measures for reducing N₂O emissions from soils mainly include reducing the use of nitrogen fertilizer,controlling irrigation methods and times,using nitrification inhibitors and biochar,etc.Considering the shortcomings of the above-mentioned methods,to develop a method of low cost and high efficiency to control N₂O emissions,a method using coals with develped pore system and abundant functional groups as adsorbent for N₂O was raised in this study.This proposal is expected to immobilize N₂O in soils and further its emmisions into the atmosphere.Atempting to verify the feasibility of this proposal,this paper investigated N₂O adsorption equilibirum and kinetics behaviors on the four rank coals.Furthermore,the potential interaction mechanism between N₂O and coals is addressed by applying some related characterization methods.The main contents and conclusions derived from this study are summarized as follows:?1?The volumetric method was applied to measure the adsorption equilibrium and kinetics data of N₂O on coals,and the related models were also employed to fit the experimtal data.The results indicate that the Langmuir can well describe the adsorption equilibirum relationship between N₂O and coals.The Langmuir model-derived maixmum adsorption capacity of N₂O on the four selected coals is in the range of 1.01-1.62 mmol/g.Moreover,the pseudo-second-order kinetics model is applicable to the adsorption kinetics behavior of N₂O within coals.The kinetics parameter regarding the four coals generated from the pseudo-second-order kinetics model varies between 0.082-3.31 g/mmol/s??2?The pore characteristics including micro-,meso-and macropore of coals were determined by CO₂ adsorption and N₂ adsorption/desorption.The influence of pore system of coals on its N₂O adsorption performace was also studied.The result shows that the micropores accommodate the space for the adsorbed N₂O.To be specific,the coal with abudant micropores exhibits higher adsorption performance for N₂O.?3?Using the volumetric method to measure the desorption equilibrium data of N₂O on coals,the results show that the adsorption/desotion hysteresis is prounounced for the low rank.Such finding is associated with the fact that the amout oxygen containing functional groups of coals decreases with the degree of metamorphism.?4?To further study the adsorption mechanism between N₂O and coals,the X-ray photoelectron spectroscopy?XPS?characterization was used in this work.The characterizarion indicates that the chemisorption effect may exist between N₂O and coals.To be specific,the total nitrogen content of coals after N₂O interaction increases,and the pyrrole/pyridone-N content decreases.Therefore,the N₂O molecule may interact with pyrrole/pyridone-N in coals and further form amines or amides.In addition,the oxygen functional groups including-C=O and-COOH of coals after N₂O interaction decrease.It's worthy noting that the existing chemisorption effect is helpful to stable immobilization of N₂O within coals.?5?In order to bridge the gap between the laboratory investigation and the pratical N₂O mitigation from soils,the study on N₂O adsorption on the moist coals was also performed.The results show that H₂O molecules decrease the N₂O adsorption capacity of coals.The decreasing N₂O adsorption on coals may be associated with the following two aspects.H₂O can be easily adsorbed on the functional groups on coals and occupy the adsorotion sites which are also avaliable for N₂O adsorption.In addition,H₂O molecules may block the pore throat and prevent N₂O from reaching the adsorption sites in coals.