The Preparation Of Nitrogen-doped Carbon Cryogel And Its Study On CO₂ Adsorption Performance

In recent years,the global warming caused by the "greenhouse effect"is extremely serious.A series of events such as high temperature in the Antarctic,rising sea level and frequent forest fires have sounded the alarm to us.Therefore,it is of great practical significance to study the capture of carbon dioxide.Carbon cryogels is a nano-carbon material with high specific surface area and high porosity,which can be applied to the fields of adsorption.Traditional carbon cryogels have high cost and complex preparation process,and pore structure is not suitable for CO2 adsorption.In view of the above problems,this paper will focus on the low cost preparation of carbon aerogels and their application in the field of CO2 adsorption.In this paper,Taking Pekala’s resorcinol(R)-formaldehyde(F)aerogel preparation method for the study of the foundation,with cheap phenol(P)instead of resorcinol,with relative economic security freeze drying instead of supercritical drying,respectively using melamine(M)and urea(U)as a nitrogen source,a relatively low cost nitrogen doped monolithic carbon cryogel was prepared by using in situ method.At the same time,according to the CO2 adsorption property,the technological parameters of preparing carbon cryogels were optimized,and finally the nitrogen-doped carbon aerogels with good mechanical strength and excellent CO2 adsorption property were obtained.In this paper,the influence of process parameters on the physical and chemical structure of carbon cryogels was analyzed,and the influence of physical and chemical structure on CO2 adsorption performance was discussed.The main research contents and conclusions are as follows:1.Nitrogen doped carbon cryogels were prepared by using phenolmelamine-formaldehyde as the main raw material.The effects of raw material ratio,catalyst dosage and dilution ratio on the properties of carbon cryogels were analyzed.The results show that:a)Changing the ratio of raw materials can change the crosslinking degree of reaction and the nitrogen content of precursor,affect the pore structure and nitrogen content of carbon cryogels,and then affect the CO2 adsorption capacity.b)Changing the amount of catalyst can change the cross-linking structure of the gel system and affect the molding of the carbon cryogel.The monolithic carbon cryogels can be formed with the appropriate amount of catalyst.c)The change of dilution ratio mainly changed the pore structure of cryogels,which had important effects on the CO2 adsorption properties.The carbon cryogels obtained under optimal conditions have the characteristics of high nitrogen content(1.89%),high compression strength(0.67 MPa),high specific surface area(1406 m2/g),high porosity(96.9%)and low density(102 mg/cm3).The CO2 test results showed that the carbon cryogels had high adsorption capacity(5.75mmol/g,0℃,lbar),superior to that of similar carbon cryogels,and CO2 adsorption properties of carbon cryogels were mainly related to pore volume and nitrogen content.2.The use of cheap urea instead of melamine as a nitrogen source,reducing the cost from raw materials,successfully prepared phenol-ureaformaldehyde based nitrogen doped carbon cryogels,in order to play a positive role in industrial applications.Meanwhile,the effects of raw material ratio,gel condition and carbonization temperature on the performance of carbon cryogels were analyzed.The results show that:a)The ratio of raw materials has an important effect on the pore structure of carbon cryogels,and further affects the CO2 adsorption properties.b)The sol-gel conditions affected the molding,mechanical strength and CO2 adsorption of carbon cryogels.Within suitable range,the molding conditions of carbon cryogel is good.On the premise of forming the sample,changing the gel condition can change the compression strength of the carbon cryogel.The gel condition also had a great influence on the CO2 adsorption performance.c)The influence of carbonization temperature on the pore structure of carbon cryogels is significant,and the volume of micropores increases first and then decreases with the increase of carbonization temperature.Under certain conditions,The carbon cryogels have the characterized of high strength(0.70 MPa),high specific surface area(1160 m2/g),low density(74.0 mg/cm3)and high CO2 adsorption.The CO2 adsorption up to 5.85 mmol/g(0℃,1bar).In summary,nitrogen doped carbon cryogels can be successfully prepared with melamine or urea as nitrogen source.The two kinds of carbon cryogels have high specific surface area,low density,high compressive strength and high CO2 adsorption capacity.The carbon cryogels with urea as the nitrogen source had more advantages,mainly in the following:the cost of urea was lower than that of melamine,and the PUF carbon aerogels had slightly higher compressive strength and CO2 adsorption properties than PMF carbon cryogels.Therefore,the preparation of PUF carbon cryogel can play a positive role in its industrial application.