Petroleum oxygen compounds

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. 

Snyder, L.R. Nitrogen and Oxygen Compound Types in Petroleum. Total Analysis of a 400-700oF Distillate from a California Crude Oil, Anal. Chem. 1969, 41, 314. 

Redman, A. 2005. Production of olefins and oxygenated compounds from Fischer-Tropsch. Paper presented at the 18th World Petroleum Congress, Johannesburg, cdl79. 

In very general terms, petroleum is a mixture of (1) hydrocarbon types, (2) nitrogen compounds, (3) oxygen compounds, (4) sulfur compounds, and (5) metallic constituents. Petrolenm prodncts are less well defined in terms of heteroatom compounds and are better defined in terms of the hydrocarbon types present. However, this general definition is not adequate to describe the true composition as it relates to the behavior of the petroleum, and its products, in the environment. For example, the occnrrence of amphoteric species (i.e., compounds having a mixed acid-base natnre) is not always addressed, nor is the phenomenon of molecnlar size or the occnrrence of specific functional types that can play a major role in petrolenm behavior. 

Oxygen is one of the five (C, H, N, O, and S) major elements in resids and asphalt, although the level rarely exceeds 1.5% by weight. Many petroleum products do not specify a particular oxygen content, but if the oxygen compounds are present as acidic compounds such a phenols (Ar-OH) and naphthenic acids (cycloalkyl-COOH), they are controlled in different specifications by a variety of tests. 

The separation of coal liquids by gel permeation chromatography using lOOA Styragel columns and solvents such as THF and toluene has been reported elsewhere (7.8.9.13.14). Coal liquids and petroleum crude are similar in their physical appearance as well as the complexity in composition. The major difference between the two is that petroleum crude does not contain oxygenated compounds, such as alkylated phenols, in substantial quantity. In addition, the average linear molecular size of petroleum derived asphaltenes (15.16) is much larger than that of coal derived asphaltenes (. ... 

Application of fluidized catalyst techniques to the Fischer-Tropsch synthesis (30) has yielded a process that produces chiefly (about 70%) motor gasoline, with minor amounts (about 30%) of fuel oil and oxygenated compounds. The fluidized iron catalyst process is outstanding because of its very high space-time yield and because it may be competitive with existing petroleum production and refining processes, if natural gas at 10 cents or less per 1000 cubic feet is available as the raw material for synthesis gas production. 

In the following paragraphs the developments of the past 25 years are reviewed primarily on the basis of the various processes whereby the basic oxygenated compounds are produced from the original petroleum raw materials ... 

Isopropyl alcohol production in 1950 exceeded 800,000,000 pounds, all made from petroleum. This alcohol is used mainly as a raw material for the production of acetone and also as a solvent. Acetone is made by the catalytic high temperature dehydrogenation or air oxidation of isopropyl alcohol. A much smaller part of the total acetone supply comes from fermentation and from hydrocarbon oxidation. Like isopropyl alcohol, part of the consumption is for solvent uses, but most serves as a raw material for other oxygenated compounds. 

Thus, the hydrodesulfurization process is a very complex sequence of reactions due, no doubt, to the complexity of the feedstock. Furthermore, the fact that feedstocks usually contain nitrogen and oxygen compounds (in addition to metal compounds) increases the complexity of the reactions that occur as part of the hydrodesulfurization process. The nitrogen compounds that may be present are typified by pyridine derivatives, quinoline derivatives, carbazole derivatives, indole derivatives, and pyrrole derivatives. Oxygen may be present as phenols (Ar-OH, where Ar is an aromatic moiety) and carboxylic acids (-C02H). The most common metals to occur in petroleum are nickel (Ni) and vanadium (V) (Reynolds, 1997). 

The stability of the products from coal-derived syncrudes must be examined carefully. Many unique compounds are present in these syncrudes peri-condensed aromatics and naphthenes, oxygen compounds, and asphaltene-like hydrocabons. Traces of these compounds may remain in the hydrotreated product and their effect on jet, thermal, and oxidation stabilities cannot be predicted from the behavior of petroleum products. 

In addition to the effects of crystal lattice energy, choice of solvent other than n-paraffins can also be important. For example, Corbett and Swarbrick (10) have shown that a number of oxygenated compounds can precipitate asphaltenes from petroleum residua in quantities varying from 12 wt % to 100 wt % on resid. Clearly, the shape of the precipitation curves for the different solvents should be different from that for n-paraffins and from each other. However, the use of a solubility parameter type of polarity scale should permit rationalization of the results when considered along with the solubility parameter of the particular solvent. 

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