Effect of the Selective Removal of Non-basic Nitrogen Compounds on the Hydrotreatment of Light Gas Oil

Abstract

Nitrogen compounds are strong inhibitors of catalyst activity in downstream chemical processes. Two distinct types of nitrogen compounds are present in light gas oils: basic and non-basic. Basic nitrogen compounds are generally considered to have stronger inhibitory effects on hydrotreating; however, non-basic nitrogen compounds are known to undergo inhibition reactions that can be generated during the hydrogenation process. This can cause the formation of basic nitrogen compounds, which are challenging to hydrotreat. Non-basic nitrogen compounds have also been proven to hinder further hydrodesulfurization due to competitive adsorption on the catalyst active sites during hydrotreating. With more stringent environmental laws regarding allowable sulfur limits, it is important to find ways to decrease the amount of sulfur, nitrogen and aromatics contents even further, in hydrotreating products. In this thesis, the effect of the selective removal of non-basic nitrogen compounds on hydrotreating was studied. An absorbent material consisting of three basic components, namely, a polymer support, poly (glycidyl methacrylate-co-ethylene glycol methacrylate) (PGMA-co-EDGMA), a π-acceptor moiety (2, 4, 5, 7-tetranitroflorenone, TENF) and a linker, three- (diaminopropane, DAP (3)), was synthesized to create a PGMA-DAP(3)-TENF polymer. The polymer was used to selectively target non-basic nitrogen compounds from light gas oil through a mechanism known as charge transfer complex. The resulting light gas oil was referred to as the pretreated feed. To measure the effect of selective removal of non-basic nitrogen compounds on hydrotreating, the pretreated feed was further hydrotreated and the extent of hydrodesulfurization, hydrodenitrogenation and hydrodearomatization was measured. Hydrotreating experiments were executed in a trickle-bed reactor using a NiMo/γAl2O3 commercial catalyst. These measurements were compared with results from the untreated feed. Any improvement before and after the hydrotreatment of the pretreated feed was associated with the removal of non-basic nitrogen compounds. The first phase of this thesis involved the synthesis, adsorption and regeneration studies of the PGMA-DAP(3)-TENF polymer. Adsorption studies were carried out using a bulk mass quantity of the polymer. The effectiveness of the polymer on a bulk scale was measured and compared to a batch scale. Regeneration studies were carried out to determine if the polymer was reusable. Characterization techniques including BET and FTIR analysis were performed on each polymer, before and after adsorption and regeneration studies to determine any physical and/or chemical changes to the polymer. The second phase of this thesis focused on the hydrotreatment of the pretreated and untreated feeds to measure the effectiveness of the polymer. Statistical significance of selectively removing non-basic nitrogen compounds was also examined after hydrotreatment studies. Results from this thesis show that there was an overall improvement in nitrogen, sulfur and aromatics removal after pretreatment. The PGMA-DAP(3)-TENF polymer selectively removed 24.9% of non-basic nitrogen compounds in the untreated feed, which led to a 18.7%, 8.3% and 9.4% decrease in the total nitrogen, sulfur and aromatics content respectively, after hydrotreatment. Based on this result, pretreatment of light gas oil can serve as a useful industrial application in reducing impurities in petroleum product streams.