Nitrogen-containing compounds of Kazakhstan petroleum vacuum gas oil

Abstract

Relevance. The need to accumulate data on nitrogen-containing compounds of heavy fractions, the share of which in secondary oil refining is steadily increasing every year. With the weight of raw materials the amount of sulfur-, nitrogen- and oxygen-containing components in it increases. The high content of heteroatomic compounds has a negative impact on catalytic processing, the quality and performance characteristics of the products obtained, and the environment. One of the widespread processes for upgrading crude oil, in particular, vacuum gas oil, is hydrotreating. However, during the catalytic hydrodesulfurization of heavy distillates the reactions of hydrogenolysis of organic sulfur compounds are inhibited in the presence of nitrogen-containing compounds. At the same time, the degree of hydrodenitrogenation of heavy oil fractions is relatively low. It is known that petroleum nitrogen-containing compounds are divided into nitrogenous bases titrated with acid solutions and nonbasic nitrogen compounds. Nitrogenous bases are represented mainly by alkylbenzo- and alkylnaphthenobenzo derivatives of pyridine. Nonbasic compounds may include benzologs of pyrrole and amides. Determining the composition of nitrogen-containing compounds in vacuum gas oil and studying their transformations during hydrotreatment is an important and actual problem. Aim. Comparative study of high- and low-molecular nitrogenous bases and nonbasic nitrogen-containing compounds of vacuum gas oil of Kazakhstan oil before and after hydrotreating. Objects. Samples taken before and after the catalytic hydrotreatment of vacuum gas oil from Kazakhstan oil. Methods. Hydrotreatment, elemental analysis, potentiometric titration, benzene cryoscopy, IR and 1H NMR spectroscopy, structural group analysis. Results. The paper introduces a comparative characteristic of the composition and structure of high and low molecular weight nitrogenous bases from the original and hydrotreated vacuum gas oil. Under the conditions of hydrotreatment, the total removal of nitrogen was 6.56 wt %, and the content of Nbas. decreased by 36%. At the same time, nitrogenous bases in the hydrotreated product are characterized by low molecular weights. Using IR spectroscopy, similar structural fragments were identified in the nitrogen compounds of the original and hydrotreated vacuum gas oil: pyridine rings (1573–1574 cm–1), carboxylic (3209–3225 and 1701–1709 cm–1) and sulfoxide (1032–1033 cm–1) groups. Among the nitrogen-containing compounds of the original vacuum gas oil, amides (1647–1648 cm–1) were identified, which are absent in the composition of nitrogen-containing compounds of the hydrotreated vacuum gas oil. Hydrocarbon skeletons of molecules include aromatic (1599–1602 cm–1) and aliphatic fragments (2860–2960 and 1454–1460, 1377, 723–727 cm–1). In accordance with the results of the structural group analysis, the averaged molecules of high and low molecular weight nitrogenous bases of the original and hydrotreated vacuum gas oil are represented by naphthenoaromatic structures with different alkyl framing. The differences observed between the values of individual structural parameters of the nitrogenous bases average molecules of the original and hydrotreated vacuum gas oil may indicate the compounds transformations under study during hydrotreatment.