Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
2000-01-11
2002-06-25
Myers, Helane E. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S210000, C208S211000
Reexamination Certificate
active
06409912
ABSTRACT:
BACKGROUND OF THE INVENTION
Many crude oils contain significant quantities of asphaltenes. It is desirable to remove the asphaltenes from the oil, because asphaltenes tend to solidify and foul subsequent processing equipment, and because removal of asphaltenes lowers the viscosity of the oil.
Solvent extraction of asphaltenes is used to process residual crude that produces deasphalted oil which is subsequently catalyticly cracked and made into predominantly diesel. The deasphalting process typically involves contacting a heavy oil with a solvent. The solvent is typically an alkane such as propane to pentanes. The solubility of the solvent in the heavy oil decreases as the temperature increases. A temperature is selected wherein substantially all the paraffinic hydrocarbons go into solution, but where a portion of the resins and the asphaltenes precipitate. Because solubility of the asphaltenes is low in this solvent-oil mixture, the asphaltenes precipitate, and are separated from the oil.
Then high pressure steam or a fired heater is typically used to heat the deasphalted oil-solvent mixture to sufficient temperature. The oil portion then separates from the solvent by vaporizing solvent. The choice of solvent depends on the quality of the oil. As the molecular weight of the solvent increases, the amount of solvent needed decreases but the selectivity, for example to resins and aromatics, decreases. Propane requires more solvent but also does not extract as much aromatics and resins. Solvent recovery costs are generally greater with lower molecular weight solvents.
The extraction of asphaltenes from an asphaltene-containing hydrocarbon material with a low-boiling solvent is known. See, for example, U.S. Pat. No. 4,391,701 and U.S. Pat. No. 3,617,481, the disclosures of which are incorporated herein by reference. The deasphalting step involves contacting the solvent with the asphaltene-containing hydrocarbon material in an asphaltene extractor. It is advantageous to maintain the temperature and pressure such that the asphaltene-containing hydrocarbon material and the low-boiling solvent are fluid or fluid like. The contacting may be done in batch mode, as a continuous fluid—fluid countercurrent mode, or by any other method known to the art. The asphaltenes form solids and can be separated from the deasphalted hydrocarbon material via gravity separation, filtration, centrifugation, or any other method known to the art.
Most deasphalting solvents are recycled, and therefore generally contain a mixture of light hydrocarbons. Preferred solvents are alkanes having between three and five carbon atoms.
The deasphalted oil can easily be broken down into high-value diesel oil in a fluidized catalytic cracking unit. The deasphalted oil generally contains significant quantities of sulfur- and nitrogen-containing compounds. This deasphalted oil may also contain long chain hydrocarbons. To meet environmental regulations and product specifications, as well as to extend the life of the catalyst, the fluidized catalytic cracking unit feed is hydrotreated first to remove sulfur components.
In hydrotreating and hydrocracking operations, hydrogen is contacted with hydrocarbons typically in the presence of a catalyst. The catalyst facilitated the breaking of carbon—carbon, carbon-sulfur, carbon-nitrogen, and carbon-oxygen bonds and the bonding with hydrogen. The purpose of this operation is to increase the value of the hydrocarbon stream by removing sulfur, reducing acidity, and creating shorter hydrocarbon molecules.
An excess amount of hydrogen is present during the reaction. When the gas stream leaves the reactor, it is still primarily hydrogen. The gas stream also contains vaporized hydrocarbons, gaseous hydrocarbons such as methane and ethane, hydrogen sulfide, and other contaminants. This gas stream is treated to remove condensables and is then recycled to the hydrotreating reactor. However, by-products of the hydrotreatment reaction build up, and a purge stream must be taken off the recycled gas stream to keep the impurities from building up to concentrations that would inhibit the hydrotreating reaction.
The process and advantages of gasifying hydrocarbonaceous material into synthesis gas are generally known in the industry. Hydrocarbon materials that have been gasified include solids, liquids, and mixtures thereof. Gasification involves mixing an oxygen-containing gas at quantities and under conditions sufficient to cause the partial oxidation of the hydrocarbon material into carbon monoxide and hydrogen. The gasification process is very exothermic. Gas temperatures in the gasification reactor are often above 1100° C. (2000° F.).
Gasification of hydrocarbonaceous material, i.e., the asphaltenes and optionally other hydrocarbonaceous material, occurs in a gasification zone wherein conditions are such that the oxygen and hydrocarbonaceous material react to form synthesis gas. Gasification thereby manufactures synthesis gas which is a valuable product. The components of synthesis gas, hydrogen and carbon monoxide, can be recovered for sale or used within a refinery.
The integration of these processes has unexpected advantages.
SUMMARY OF THE INVENTION
The present invention provides a process of liquid hydrocarbon product and hydrotreater gas from a hydrotreater effluent. The process includes introducing a hydrotreater gas and a liquid hydrocarbon stream to a hydrotreater and then reacting a portion of the hydrotreater gas with the hydrocarbon stream in the hydrotreater, thereby forming a reaction mixture. This reaction mixture is removed from the hydrotreater and sent to a stripper. The gaseous phase and the fluid phase are then separated. There, steam or nitrogen is introduced, and as the stream contacts the reaction mixture, volatiles are stripped from the reaction mixture.
The hydrocarbon stream can be deasphalted oil. Deasphalting an oil is performed by contacting the oil with a light alkane solvent, and then recovering the solvent. The asphaltenes recovered during solvent extraction are advantageously gasified, producing a gas comprising hydrogen and carbon monoxide. The hydrogen gas from this gasification process is advantageously utilized in the hydrotreating process.
During the hydrotreating process, hydrogen sulfide and short chain hydrocarbons such as methane, ethane, propane, butane and pentane are formed. When the gas stream leaves the hydrotreater, it is still primarily hydrogen. The gas stream and the hydrocarbon stream also contains vaporized hydrocarbons such as methane through pentane, hydrogen sulfide, and other contaminants. This gas stream is separated from the hydrocarbon liquid, treated to remove condensables, and is then is advantageously recycled to the hydrotreating reactor.
A schematic of one embodiment of the process is shown in FIG.
1
. In this embodiment, the hydrotreater gas and the liquid hydrocarbon stream are admixed prior to entering the hydrotreater. Then, after hydrotreating, steam is admixed. Some of the heat is recovered, and then the gas and fluid phases are separated. The gas is cooled and condensables are obtained. The gas remains at high pressure. Most of the gas is compressed and reintroduced to the hydrotreater.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process of liquid hydrocarbon product and hydrotreater gas from a hydrotreater effluent.
Hydrotreating takes place at pressures of between about 800 psi (5516 kPa) and about 3000 psi (20684 kPa), and the contaminants are dissolved in the hydrocarbon liquid. In conventional hydrotreating, the separation of contaminants from hydrotreated liquid hydrocarbons is achieved by flashing and distilling the oil from the hydrotreater.
The separation of gas from hydrotreated liquid hydrocarbons in this invention is achieved using a high pressure steam or nitrogen stripper and a flash drum. High pressure steam or nitrogen is contacted with the hydrotreated liquid hydrocarbon material. This high pressure steam strips the volatiles, i.e., hydrogen, the volatile hydrocarbons, hydrogen
Johnson Kay Anderson
Wallace Paul S.
Myers Helane E.
Texaco Inc.
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