Synthesis Of Nitrogen-Rich Microporous Organic Polymers For CO₂ Adsorption

Nitrogen-rich microporous organic polymer has outstanding performance of CO2 adsorption and separation. Therefore it has potential applications to deal with environmental issues caused by excess CO2 emissions. As the nitrogen atom has lone pair of electrons which provide a good interaction with CO2, it can significantly increase the amount of CO2 adsorption and improve the separation abilities of CO2/N2 and CO2/CH4. Microporous polymers with cross-linked network structure were synthesized by using different nitrogen-containing monomers so that a large amount of nitrogen atoms could be introduced into microporous organic polymer. The effect of monomers with different lengths and side group sizes on pore structureand adsorption and separation of CO2 was explored. Special works of this paper can be detailed as follows.1) Microporous polybenzimidazole PBI-Ad-1 and PBI-Ad-2 were made by reacting 1,3,5,7-tetrakis(4-aldehydephenyl)adamantane with 3,3'-diaminobenzidine and 1,2,4,5-tetraaminobenzene, respectively. Due to tetraphenyladamantane's tetrahedron structure, the cross-linked networks of PBI-Ad-1 and PBI-Ad-2 have larger specific surface area of 1023 m2/g and 926 m2/g, respectively. The pore size of the samples are concentrated at 0.58 nm and 0.6 nm, which are belong to the scope of ultramicro pore structure. As molecular chains interpenetrate with each other, PBI-Ad-1, with longer linking arm, has a smaller pore size and higher BET surface areas. Therefore, CO2 adsorption capacity of PBI-Ad-1 reached 17.3 wt% and the separation of CO2/N2 and CO2/CH4 reached to 72 and 9.9, respectively. All of the values are higher than PBI-Ad-2. Because of containing naphthenic and aromatic structure, the sample exhibit excellent benzene vapor and cyclohexane vapor adsorption capacities. The adsorption of benzene and cyclohexane vapor can reach 98 wt% and 53.6 wt%, respectively.2) Melamine and 1-Naphthaldehyde,1-Pyrenecarboxaldehyde were selected to build up microporous polyaminals (PAN-7 and PAN-8). As the side group of PAN-8 is bigger, the BET surface area of PAN-8 (865 m2/g) is higher than PAN-7 (615 m2/g). The greater pi electron delocalization system makes PAN-8 have a higher CO2 adsorption capacity (13.2 wt%) than PAN-7. The high contents of secondary amine structure in the PANs can effectively enhance CO2 affinity under low pressure and make a high CO2 adsorption capacity (5.8 wt%) at 0.15 bar. In addition, the samples also show a good adsorption capacity for benzene vapor and cyclohexane vapor. Because of cheap raw materials and simple synthetic process, the microporous polyaminal provides a way for the industrial application and has a great practical application value.