Adsorptive removal of nitrogen from coal-based needle coke feedstocks using activated carbon.

摘要

A low percentage of nitrogen in needle coke feedstocks is desired for the reduction of puffing during the process of graphitization of needle coke. The purpose of the present study is to investigate the removal of nitrogen species from a coal-based needle coke feedstock, when treated with both commercial activated carbon, Nuchar SA 20 and "coal-derived" activated carbon, WVUAC 900-15. Koppers coal tar distillate (CTD), which has 1.1% wt starting nitrogen content, is selected as the needle coke feedstock. A series of experiments was performed to establish a standard procedure for the removal of nitrogen species. Using the established experimental procedure, experiments were conducted to determine the effect of solvent, time and amount of activated carbon on the adsorption capacity of nitrogen for both Nuchar and WVUAC 900-15 activated carbons. Also, the surface properties of both the activated carbons were modified via oxidation with nitric acid and air. The oxidized activated carbons were then tested as adsorbents for the de-nitrogenation of CTD. From the pH test results, it is observed that oxidation modification has improved acidic surface functional groups on activated carbons. In an experiment it is observed that 92% of the nitrogen was removed from the CTD with 9 g of Nuchar SA20. Unfortunately the result was not repeatable. No reasonable explanations were found for this but it is suspected that aging of the CTD which may change the nitrogen compounds in CTD and error in the sampling technique are possible reasons. Oxidized activated carbons performed 10--15% better than unoxidized activated carbon in removing nitrogen species. The coefficient of thermal expansion (CTE) of the graphite test specimen prepared with de-nitrogenated CTD is measured as 0.209 ppm/°C while CTE of the graphite test specimen prepared with a petroleum-based needle-coke feedstock, decant oil, is 0.250 ppm/°C.