Granular nitrogen-doped carbons with ultra-high C2H2/CO2 adsorption selectivity for C2H2 purification

Purification of C2H2 from C2H2/CO2 mixtures such as cracked gas through the adsorptive separation technology based on porous adsorbent with highly selective adsorption capability is considered as the promising and energy -efficient process in petroleum industry. Herein, granular nitrogen-doped carbons derived from coconut shell were obtained through the urea modification with steam assisted hydrothermal method followed by calcination. They were characterized and their adsorption and separation properties for C2H2/CO2 mixture were systemat-ically investigated. It was found that they macroscopically present the uniform particle sizes (median diameter D50 at around 700 mu m), and structurally have the characteristics of developed porosities (Brunauer-Emmett-Teller surface areas up to 430.2 m2/g) and abundant nitrogen-containing functional groups. In particular, their adsorption selectivities for C2H2/CO2 were significantly improved to 7.5 at 25 degrees C and 1.0 bar, outperforming the granular carbons without nitrogen doping (4.0) and some benchmark powdery adsorbents. Breakthrough ex-periments indicate that the granular nitrogen-doped carbons can be directly packed in a fixed bed to separate C2H2/CO2 mixture completely under dry conditions (relative humidity = 0 %) and humid conditions (relative humidity = 75.1 %) at 25 degrees C, and their dynamic separation performance could be well remained during the cyclic experiments. Molecule simulation results further reveal that the pyridinic-N with great binding energy (BE) interactes with C2H2 (-16.27 kJ/mol), and great absolute difference of binding energies (Delta BE) between C2H2 and CO2 (Delta BE pyridinic-N = 5.04 kJ/mol) plays the significant role in improving the C2H2/CO2 adsorption and separation performance of granular nitrogen-doped carbons. Therefore, the granular nitrogen-doped carbons are very promising for purification of C2H2 from C2H2/CO2 mixtures.