Study of the Adsorption of Nitrogen Compounds for Diesel Fuel Production Using Three Commercial Materials
Chemical Science International Journal,
The aim of this work was to study the removal of nitrogen (N-) compounds for ultra-low sulfur diesel (ULSD) production purposes by using three commercial materials: selexsorb® CDX (CDX), silica gel (SG), and activated carbon VG-077 (VG-077). The experiments were conducted in three steps: (1) Adsorption of quinoline, indole, or carbazole from model fuels (300wppm in a 1:1g/g n-hexadecane:toluene mixture) in a batch setup; adsorption of N- compounds from straight run gas oil (SRGO): (2) in a batch setup, and (3) in a fixed-bed column (FBC). Langmuir and Freundlich models were considered for modeling the adsorption isotherms of quinoline, indole, carbazole from model fuels and N-compounds from SRGO. Clark and Thomas models were employed for fitting the FBC experimental data. In the batch experiments, the adsorption capacities (qm) for neutral N-compounds were 0.795mmol/g (VG-077), 0.287mmol/g (CDX), and for basic N-compounds were 0.708mmol/g (SG), 0.385mmol/g (CDX), and 0.242mmol/g (VG-077). The goodness of the fit for the Langmuir and Freundlich models strongly depended on the N-compound and the adsorbent when treating model fuels. Treating SRGO, VG-077 presented a higher qm (0.855mmol/g) than the other two materials (0.687mmol/g (SG) and 0.372mmol/g (CDX)), which is understandable because neutral N-compounds represent 75% of nitrogen in this fuel. The Langmuir model was better than the Freundlich model to reproduce the adsorption isotherms properly with SRGO (R2>0.9966). Besides, the pseudo second-order model performed better than the pseudo first-order model to simulate the adsorption rates in almost all cases, although the comparison was not straightforward, because the values depended highly on the N-compound and the material studied. In the FBC experiments, the Clark model agreed better with the experimental data than the Thomas model did. VG-077 achieved the highest N-adsorption (0.38mmol/g vs. 0.18mmol/g (SG) and 0.15mmol/g (CDX)). However, according to the preliminary estimation carried out, a higher adsorption capacity is still required for commercial application of this process.