Nitrogen compounds in crude oil

The amount of nitrogen in different crude oils varies from 0.02 to 1.5%. There are many types of nitrogen compounds in crude oil. The example shown in Figure 1.1 is only one of them. 

The above are some examples of nitrogen compounds in crude oil. It is however difficult to show all the possible nitrogen compounds present in crude oil. Recent investigations have shown that compounds with two nitrogen atoms or one nitrogen atom and one sulfur atom in one molecule can be found in crude oil. 

Figure 5.1.24 Typical nitrogen compounds in crude oil - 1 indole, 2 acridine, 3 methylcarbazole, 4 hydroxyquinoline, 5 aniline.

Figure 9.2. Typical sulfur- and nitrogen-containing compounds in crude oil.

One of the most ubiquitous multiple-component contaminants that reaches the soil and deeper subsurface layers is crude oil and its refined products. In the subsurface, these contaminants are transformed differently by various mechanisms (Cozzarelli and Baber 2003). Crude oil contains a multitude of chemical components, each with different physical and chemical properties. As discussed in Chapter 4, the main groups of compounds in crude oils are saturated hydrocarbons (such as normal and branched alkanes and cycloalkanes without double bonds), aromatic hydrocarbons, resins, and asphaltenes, which are high-molecular-weight polycyclic compounds containing nitrogen, sulfur, and oxygen. 

The main groups of compounds in crude oils are saturated hydrocarbons (such as normal and branched alkanes and cycloalkanes that contain no double bonds), aromatic hydrocarbons, resins and asphaltenes (higher molecular weight polycyclic compounds containing nitrogen, sulfur. 

The nitrogen compounds are very important in their role as natural surfactants. The concentration of these compounds in crude oil has a great influence on the chemical and physical activities of the crude oil, on metal/crude oil interface and ground/crude oil interface. This property of nitrogen compounds is used during the production of crude oil from the oil well. For example, hinoline can prevent the corrosion of metal parts this is very important for the continuous working of many oil production plants. 

Crude oils contain nitrogen compounds in the form of basic substances such as quinoline, isoquinoline, and pyridine, or neutral materials such as pyrrole, indole, and carbazole. 

Various types of non-hydrocarbon compounds occur in crude oils and refinery streams. The most important are the organic sulfur, nitrogen, and oxygen compounds. Traces of metallic compounds are also found in all crudes. The presence of these impurities is harmful and may cause problems to certain catalytic processes. Fuels having high sulfur and nitrogen levels cause pollution problems in addition to the corrosive nature of their oxidization products. 

Examples of the nitrogen compounds commonly found in crude oil were included in Table 2. In the diesel fraction, the population comprises basic and non-basic compounds, such as quinoline, indole, and carbazole families. 

Pollution associated with petroleum refining typically includes volatile organic compounds (volatile organic compounds), carbon monoxide (CO), sulfur oxides (SO c), nitrogen oxides (NO ), particulates, ammonia (NH3), hydrogen sulfide (H2S), metals, spent acids, and numerous toxic organic compounds (Hydrocarbon Processing, 2003). Sulfur and metals result from the impurities in crude oil. The other wastes represent losses of feedstock and petroleum products. 

Crude oil is composed primarily of hydrocarbon compounds. Organic and inorganic sulfur-, oxygen-, and nitrogen-containing species are also found in crude oil. Additionally, water, vanadium, nickel, sodium, and other metals may be present. 

A significant portion of the sulfur- and nitrogen-containing species in crude oil can be found in heterocyclic form within the asphaltene, maltene, and resin compounds. Oxygen-containing heterocycles may also be present. Examples of high-molecular-weight aromatic, resinous, and polar compounds found in crude oil are provided in TABLE 3-1. 

It has been determined that certain nitrogen-, oxygen-, and sulfur-containing aromatic compounds contained in crude oil can lead to darkening of refined fuels and oils. Often, these compounds are found in fuels refined from naphthenic crude oil or asphaltic, high-sulfur crudes. Compounds such as indoles, quinolines, and naphthenobenzothiophenes can lead to darkening of fuel. 

Asphaltenes These are complex high-molecular-weight polycyclic aromatic compounds which may contain oxygen, sulfur, or nitrogen heteroatoms. They are found in crude oil and in certain heavy fuel oils in micellar form. Their dispersion throughout oil can be stabilized by asphaltene precursors called resins and maltenes. 

Very little is known about nitrogen compounds found in crude oils. Apparently, the nitrogen atoms are included in the complex ring structures. Simple examples are given below. 

A further chracterization of these pyrrole type nitrogen compounds in the very weak base concentrate can be made by using the colorometric pyrrolic nitrogen value of 6.8% (Table III) as the value for a, -unsub-stituted pyrrole type compounds. This leaves 22.2% of the nitrogen in pyrroles and indoles which have both a- and -substitution. The affi-unsubstituted pyrroles and indoles also have no N-substitution because these N-substituted compounds would titrate as weak bases and not as very weak bases. The lack of N-substitution on the pyrroles and indoles is consistent with the research of Jacobson (18, 19) who reported that N-alkylpyrroles and N-alkylindoles thermally and irreversibly isomerize to give the a and alkyl isomers and therefore would not likely be present in crude shale oil. 

In the present context, heavy oils and residua can also be assessed in terms of sulfur content, carbon residue, nitrogen content, and metals content. Properties such as the API gravity and viscosity also help the refinery operator to gain an understanding of the nature of the material that is to be processed. The products from high-sulfur feedstocks often require extensive treatment to remove (or change) the corrosive sulfur compounds. Nitrogen compounds and the various metals that occur in crude oils will cause serious loss of catalyst life. The carbon residue presents an indication of the amount of thermal coke that may be formed to the detriment of the liquid products. 

Crude oils contain a certain amount of combined nitrogen which sometimes breaks down in thermal crackers to form these harmful nitrogen compounds. California, West Texas, and Venezuelan crudes seem to break down this way much more readily than other crudes. Catalytic-cracking units convert the nitrogen compounds in their feed to these polymerization catalyst poisons almost without exception. Other basic materials which have poisoned polymerization catalyst at times are sodium hydroxide and diethanolamine. Both of these materials are used extensively for the removal of hydrogen sulfide from the feed to polymerization units. Catalyst poisons of a basic nature can be removed from the... 

Crude oil is a complex mixture of chemicals. The relative composition of these chemicals will be different in crude oil from different sources. However, the overall composition (i.e., the chemicals present) remains fairly consistent between sources. The chemical classes present in crude oil include paraffinic hydrocarbons, long-chain straight or branched carbon-based chemicals and naphthenic hydrocarbons, multiple-ringed carbon-based chemicals. Also present will be low percentages of sulfur, nitrogen, and oxygen compounds, and trace quantities of many other elements. 

Nitrogen-containing compounds always pose problems for oil refinery industry via catalyst poisoning (1). Their combustion products also cause great concern in air pollution (2). Due to higher nitrogen content in shale oil and coal liquid (1-2%) than in crude oil (<0.5%), it is essential to lower the nitrogen content in shale oil before any refinery processes are performed. 

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