Sulfur compounds in crude oil

Rail, H.T., C.J. Thompson, H.J. Coleman and R.L. Hopkins (1972), "Sulfur compounds in crude oil". Bureau of Mines Bull. No. 659. Distributed by National Technical Information Service (NTIS), US Dpt of Commerce, Springfield, VA. 

Identifying sulfur compounds in crude oils and their products is of little use to a refiner because all sulfur compounds can easily be hydro-desulfurized to hydrogen sulfide and the corresponding hydrocarbon. 

A summary of the work on the identification of sulfur compounds in crude oils has been given recently by Ball, Rail, Waddington, and Smith (31), who list the sulfur compounds isolated from petroleum by earlier investigators and, in addition, give several new compounds which have recently been isolated from a Wasson, Tex., crude petroleum by the API Research Project 48. Birch and Norris (5) isolated a substantial number of the thiol (mercaptan) type of sulfur compounds from an Iranian crude petroleum. 

The positive identification of the sulfur compounds in crude oils is a difficult problem often complicated by the lack of reference compounds. This difficulty has been overcome by hydrodesulfurization (see Section VIII), which converts the sulfur compounds into known hydrocarbons. Treatment of a petroleum oil fraction with calcium hexammine converts the benzo[6]thiophenes present into aryl mercaptans, which are readily separable from accompanying aromatic hydrocarbons (e.g., naphthalene) and then identified by hydro-... 

The distribution of sulfur compounds in crude oils has been studied extensively since the 1890s and it has become possible to note various generalities. For example, the proportion of sulfur will increase with the boiling point... 

Figure 1.2 Types of sulfur compounds in crude oil and distillates.2...

API and Bureau of Mines Projects. Some of the most important current work on the sulfur compounds present in petroleum is being carried out under the auspices of the American Petroleum Institute under Project 48 which was organized in 1948 to conduct fundamental studies on the synthesis, properties, and identification of sulfur compounds in petroleum. At present. Project 48 consists essentially of four phases (1) production and purification of sulfur compounds and the determination of their common physical properties (2) measurement of thermodynamic properties of pure sulfur compounds (3) identification and measurement of sulfur compounds in crude oil and (4) development of methods of synthesis and identification of sulfur compounds. Work on the first three phases, combined as Project 48A, is being conducted at the U. S. Bureau of Mines under the supervision of H. M. Smith as project director. Work on the fourth... 

Sulfur compounds in crude oil sharply decreases the quality of fuels and oils produced from the crude oil. They cause corrosion of equipment during treatment, reduce activity of antidetonation additives and antioxidizing stability of gasoline, raise the propensity to form hard residues in cracking gasoline fractions, and result an environment pollution. 

Utashiro, S. and Hatsuo, H., 1977. Studies on the sulfur compounds in crude oils and heavy fuel oils exposed on the sea surface by the FPD gas chromatography. Kaijo Hoan Daigakko Kenkyu Hokoku, Dai-2-Bu, 23(1-2, Sekt. 2) 37—54. 

Sulfur is one of the more common constituents of the earth s crust and can be ranked as the 16th or 17th most abundant element [68]. The mean sulfur content-of the rocks forming the crust of the earth is estimated to be about 400 ppmw. Sulfur naturally occurs as elemental sulfur, metal sulfides in coal and mineral ores, sulfates, hydrogen sulfide in natural gas, and complex organic sulfur compounds in crude oil and coal. All of these various forms of sulfur are used as sulfur sources, but the most important sources are elemental sulfur, hydrogen sulfide in natural gas, and iron pyrites. 

The sulfur compounds in crude oil can be separated into two classes aliphatic and aromatic hydrocarbons. The aliphatic hydrocarbons are characterized by open carbon chains, which can be branched. One or several sulfur atoms are inserted into these carbon chains in different ways, as shown in Table 34.2. These compounds are denoted sulfides, disulfides, and thiols [11]. 

Table 34.2 Different ciasses of aiiphatic sulfur compounds in crude oil...

A number of transition metal sulfide catalysts have been studied for the HDS of thiophene (C H S), which is commonly used as a simple model for the sulfur compounds in crude oil. Typically, there are two types of difficult steps, the breaking of the C-S bond and the removal of adsorbed S from the catalyst surface. 

Sulfur Compounds. All crude oils contain sulfur in one of several forms including elemental sulfur, hydrogen sulfide, carbonyl sulfide (COS), and in aliphatic and aromatic compounds. The amount of sulfur-containing compounds increases progressively with an increase in the boiling point of the fraction. A majority of these compounds have one sulfur atom per molecule, but certain aromatic and polynuclear aromatic molecules found in low concentrations in crude oil contain two and even three sulfur atoms. Identification of the individual sulfur compounds in the heavy fractions poses a considerable challenge to the analytical chemist. 

Oxygen compounds in crude oils are more complex than the sulfur types. However, their presence in petroleum streams is not poisonous to processing catalysts. Many of the oxygen compounds found in crude oils are weakly acidic. They are carboxylic acids, cresylic acid, phenol, and naphthenic acid. Naphthenic acids are mainly cyclopentane and cyclohexane derivatives having a carboxyalkyl side chain. 

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. 

Tn this work the sulfur compounds in the gas oil of three Cretaceous - heavy oils from the edge of the Alberta sedimentary basin were investigated. These crude oils were obtained from the Athabasca, Cold Lake, and Lloydminster deposits and are believed (I) to belong to the same oil system which implies like modes of origin. The geographic location of these deposits is shown in Figure 1. This investigation was conducted to develop the analytical capability used to follow the maturation of the sulfur compounds in these oils (2). 

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 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. 

Photometry and colorimetry are used by crude oil chemists to determine the content of different metals and heteroatomic compounds in crude oil and petrochemical products. Many references on photometry and colorimetry are given at the end of this chapter. Many authors have described the successful analysis of different metals in motor fuels by photometric and colorimetric methods. The composition of additives used during fuel production can be characterized by photometric and colorimetric methods because very many additives contain metals. It is not only fuels that can be characterized by photometry and colorimetry. Lubricants, which contain metals as an important component, can be successfully determined by these methods. These methods can quickly give qualitative information on heavy metals and heteroatomic compounds such as oxygen and sulfur in crude oil. More on this topic can be found in references 76 and 77 at the end of this chapter. 

Catalytic methods of gas cleaning are used very often in modern industry as a result of the possibility of very deep cleaning of the waste gas. Up to 99.9% of pollutant can be separated from the waste gas by this method. However, the disadvantage of this method is the formation of new compounds, which must be use-able. In the example shown of waste gas cleaning from the H2S, the formed byproduct can be used in the chemical industry. However, the amount of sulfur formed in crude oil refineries is often so high that it cannot be moved completely to the chemical industry. It then becomes important to find new ways of using sulfur. 

There are those happy users who dissolve their sample in the mobile phase and inject right away. If you are one of these and you also have isocratic conditions with acetonitrile/water, you can forget about sample preparation for now. There are however those users who need to quantify minor unknown impurities of a metabolized metabolite from bile fluid and others who hunt after heterocyclic sulfur-containing compounds in crude oil residue from Iran and compare it with Iraqi oil. They all have my sympathy. In the following table, a few typical errors occurring in a normal sample preparation are listed. 

These processes result in a large number of different sulfur-containing compounds in crude oil. The substances cover the whole range of molar masses present in crude oil. Therefore, almost any fraction of crude oil includes sulfur-containing substances and the sulfur content of the fractions rises with increasing boiling range [10]. 

The basis of aromatic sulfur-containing compounds in crude oil is the thiophene molecule, which consists of four carbon atoms and one sulfur atom (cf, Table 34.3). 

Sulfur for commercial purposes is derived mainly from elemental sulfur mined by the Frasch process or from the sulfur by-products of purified sour natural gas and petroleum. (The term sour is generally associated with high-sulfur petroleum products.) During World War n, sulfur was first produced commercially from sour natural gas by the early 1970s, sulfur from sour natural gas and organosulfur compounds in crude oil already exceeded that produced by mining elemental sulfur. 

Hua, R.X. Wang, J.H. Kong, H.W. Liu, J. Lu, X. Xu, G.W. (2004), Analysis of sulfur-containing compounds in crude oils by comprehensive two-dimensional gas chromatography with sulfur chemiluminescence detection. Journal of Separation Science, Vol.27, No.9, pp.691-698, ISSN 1615-9314... 

Free sulfur is rarely present in crude oils, but it can be found in suspension or dissolved in the liquid. The crude from Goldsmith (Texas, USA.) is richest in free sulfur (1% by weight for a total sulfur content of 2.17%). It could be produced by compounds in the reservoir rock by sulfate reduction (reaction 8.2). 

Of the general formula, R - S — H, where R represents an aliphatic or cyclic radical, the thiols —also known as mercaptans— are acidic in behavior owing to their S—H functional group they are corrosive and malodorous. Their concentration in crude oils is very low if not zero, but they are created from other sulfur compounds during refining operations and show up in the light cuts, as illustrated in Table 8.6. 

Mercaptans are naturally present in crude oil (Chapters 1 and 8), or they result from the decomposition of other sulfur compounds during thermai or catalytic cracking operations. 

---