SOLVENT FOR USE IN AROMATIC EXTRACTION PROCESS

Abstract

Oxidized disulfide oil (ODSO) compounds, derived from disulfide oil (DSO) compounds produced as by-products from the generalized mercaptan oxidation (MEROX) sulfur removal process, are effective as aromatic extraction solvents, thereby converting the low value or waste oil DSO products into a valuable commodity that has utility in improving the extraction of aromatics from hydrocarbons derived from fossil fuels.

Claims

1. An aromatic extraction solvent that comprises one oxidized disulfide oil (ODSO) compounds selected from the group consisting of (RSOOSOR), (RSOOSOOR), (RSOSOOOH), (RSOOSOOOH), (RSOSOOH), and (RSOOSOOH), where R and R are alkyl groups comprising 1 to 10 carbon atoms.

2. The aromatic extraction solvent of claim 1, wherein the number of carbon atoms in the one or more ODSO compounds is in the range of from 1 to 20.

3. The aromatic extraction solvent of claim 1, wherein the solvent is water soluble.

4. The aromatic extraction solvent of claim 1, wherein the one or more ODSO compounds of the solvent has at least three oxygen atoms.

5. The aromatic extraction solvent of claim 1, wherein the density of the solvent is greater than 1.0 g/cc.

6. The aromatic extraction solvent of claim 1, wherein the density of the solvent is in the range of from 1.1 g/cc to 1.7 g/cc.

7. The aromatic extraction solvent of claim 1, wherein the solvent has an average boiling point greater than 80 C.

8. The aromatic extraction solvent of claim 1, wherein the solvent comprises water in the range of from 0.1 W %-50 W % of the solvent.

9. The aromatic extraction solvent of claim 1, wherein the solvent comprises water in the range of from 1.0 W %-30 W %.

10. The aromatic extraction solvent of claim 1, wherein the solvent is a mixture comprising one or more non-ODSO aromatic extraction solvents.

11. The aromatic extraction solvent of claim 10, wherein the one or more non-ODSO aromatic extraction solvents is selected from the group consisting of diethyleneglycol, triethyleneglycol, tetraethylene glycol, sulfolane, furfural, N-methyl-2-pyrrolidone, N-formylmorpholine and dimethylsulfoxide.

12. The aromatic extraction solvent of claim 11, wherein the one or more non-ODSO aromatic extraction constitutes from 0.1 W %-99.9 W % of the total weight of the solvent mixture.

13. The aromatic extraction solvent of claim 1, wherein the one or more ODSO compounds is selected to remove mono- and poly-aromatic compounds from the hydrocarbon stream.

14. The aromatic extraction solvent of claim 1, wherein the one or more ODSO compounds is selected to remove benzene from the hydrocarbon stream.

15. The aromatic extraction solvent of claim 1, wherein the solvent is liquid at ambient conditions.

16. The aromatic extraction solvent of claim 1, wherein the one or more ODSO compounds are derived from catalytically oxidized disulfide oils present in an effluent refinery hydrocarbon stream recovered downstream of a MEROX process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The process of the disclosure will be described in more detail below and with reference to the attached drawings in which:

[0036] FIG. 1 is a graph illustrating the selectivity and capacity of the selected traditional industrial solvents for dearomatization from the prior art that are useful for blending with one or more ODSO compounds to provide a solvent, data points reproduced from Wauquier, Jean Pierre, Petroleum Refining, Vol. 2, Separation Processes, editions TECHNIP, page 430.

[0037] FIG. 2 is a graph illustrating the simulated distillation data of various oxidized oil fractions.

DETAILED DESCRIPTION OF THE INVENTION

[0038] Aromatic compounds are selectively extracted from a hydrocarbon feed using an aromatic extraction solvent derived from a disulfide oil. In general, any feed containing aromatics is a suitable feed. Preferred feedstocks include naphtha boiling in the range of from 36 C. to 180 C., gas oil boiling in the range of from 180 to 370 C. and vacuum gas oil boiling in the range of from 370 C. to 650 C. The source of the feed can include crude oils, coal liquids, cellulose-based bio liquids and intermediate refinery streams from hydrotreaters, hydrocracking units, delayed cokers, catalytic reformers, fluid catalytic cracking thermal cracking units, fluid catalytic cracking units, etc.

[0039] In embodiments where the targeted aromatic compound is benzene, a preferred aromatic extraction solvent is one or a mixture of neat ODSO compounds, i.e., used alone. In embodiments where one or more ODSO compounds are blended with traditional aromatic solvents, any aromatic-containing feed can be treated.

[0040] In a preferred embodiment, the number of carbon atoms in the ODSO aromatic extraction solvent is in the range of from 1 to 20.

[0041] The ODSO aromatic extraction solvent has a boiling temperature higher than that of benzene (80 C.) which is the least volatile of the aromatics to be extracted. In some embodiments, the ODSO aromatic extraction solvent has a boiling point at least 10 C. or at least 20 C. higher than the extract. Preferred boiling temperatures for the aromatic extraction solvent are in the range of from 80 C. to 140 C., 90 C. to 140 C., or 100 C. to 140 C. The solvent can thereafter be regenerated from the extracted aromatic mixture by a simple and, consequently, economical distillation process.

[0042] The water soluble ODSO aromatic extraction solvent has a specific gravity close to or greater than 1.38, thereby ensuring a gravity differential with the hydrocarbons in the feed. Typically, the hydrocarbons in the feed have a density at 20 C. that is between 0.660 and 0.880 g/cm.sup.3 which promotes rapid phase settling of the denser solvent and solute and efficient operation of the liquid/liquid separation vessel.

[0043] In preferred embodiments, the aromatic extraction solvent has a density greater or equal to 1.0 g/cc. In certain embodiments, the aromatic extraction solvent has a density in the range of from 1.1 g/cc to 1.7 g/cc.

[0044] In general, ODSO aromatic extraction solvents that include mainly water insoluble ODSO compounds will have a lower density than aromatic extraction solvents that include mainly water soluble ODSO compounds.

[0045] It may be possible to isolate individual groups, or more narrow cuts, of ODSO compounds from a mixture of ODSO compounds based on their individual densities and temperatures for inclusion in the aromatic extraction solvent.

[0046] The aromatic extraction solvent has a sufficiently low crystallization temperature so that aromatic extraction can occur without complex equipment and controlled systems. In contrast, traditional industrial solvents such as sulfolane, DMSO and NFM have relatively high crystallization temperatures which may require steam tracing on steam-heated storage tanks and lines depending upon the operating conditions, unit design, and the feedstocks.

[0047] The ODSO aromatic extraction solvent has a high viscosity at ordinary temperatures especially for mixtures with glycols, but has a viscosity always lower than 2.5 mPa s at the operating temperature in the extractor. This allows for favorable rapid mass transfer kinetics.

[0048] The presence of water will decrease extraction capacity, but improves selectivity for the one or more targeted aromatics. Therefore, for aromatic extraction solvents including ODSO compounds without the addition of traditional solvents, when the ODSO already possesses enhanced selectivity, lower water concentrations are preferred in order avoid negatively effecting the capacity of the overall aromatic extraction solvent.

[0049] In preferred embodiments, the aromatic extraction solvent comprises water in the range of from 0.1 W %-50 W % of the solvent. In preferred embodiments, the aromatic extraction solvent comprises water in the range of from 1.0 W %-50 W % of the solvent, or 1.0 W %-30 W % of the solvent.

[0050] For blended solvents, i.e., solvents where one or more ODSO compounds are blended with one or more traditional solvents, the preferred water content will depend of the properties of the traditional solvent.

[0051] In a preferred embodiment, the aromatic extraction solvent is a mixture of ODSO compounds, each compound having a distinct boiling point which can vary over a significant temperature range. The boiling point of the individual ODSO compounds in the mixture depends on the degree of oxidation in the di-sulfide moiety. It is therefore possible to have selective aromatic extraction for different aromatic components of the hydrocarbon feed.

[0052] In preferred embodiments, the aromatic extraction process is conducted under ambient conditions. In other embodiments, the aromatic extraction process is conducted at temperatures above ambient.

[0053] In certain embodiments, a hydrocarbon feed is contacted with one or a mixture of neat water soluble ODSO compounds to remove some or all of benzene in the feed. The benzene-lean stream is then contacted with a traditional industrial solvent to remove other aromatic compounds. In this embodiment, two aromatic streams are produced: (1) a benzene-rich stream and (2) and an aromatic-rich stream.

[0054] In certain embodiments, a hydrocarbon feed is contacted with one or a mixture of water soluble ODSO compounds to produce a hydrocarbon stream of reduced aromatic content. The hydrocarbon stream of reduced aromatic content can then be contacted with a non-ODSO aromatic extraction solvent to further reduce the aromatic content. In certain embodiments, the resulting hydrocarbon stream is essentially aromatic free.

Extraction Capacity and Selectivity

[0055] The aromatic extraction solvents for use in aromatic extraction processes have a molecular structure made up of a radical moiety or a relatively small hydrocarbon ring, and a polar group. These structural properties allow the aromatic extraction solvent to be miscible with each other and with water and also provide the desired selectivity for aromatic hydrocarbons.

[0056] In a given hydrocarbon, the aromatic extraction solvent's solubility depends on the chemical nature of the hydrocarbon and to a lesser degree, its molecular size. Specifically, when considering the different chemical families of hydrocarbons, there is a decreasing solubility in the order for components with the same number of carbon atoms as follows: aromatics>diolefins>olefins>naphthenes>paraffins. In the same chemical family, solubility decreases moderately with an increase in the molecular weight of the hydrocarbon.

[0057] For example, it has been found that benzene, MW=78.11 g/mol, has a higher solubility than toluene, MW=92.14 g/mol in an ODSO aromatic solvent that comprises all water soluble ODSO compounds produced in the oxidation reaction described herein.

[0058] Capacity is defined as a distribution coefficient which is the ratio of the concentration of aromatics in the solvent phase to the concentration of aromatics in the raffinate phase.

[0059] Selectivity is defined as the ratio of the distribution coefficient for aromatics divided by the distribution coefficient for non-aromatics.

[0060] Capacity increases as the solvent dissolves more aromatics, and selectivity increases as the ability of the solvent to reject aliphatics increases.

[0061] The selectivity and capacity of the commonly used solvents of the prior art are illustrated in FIG. 1. Solvent capacity or solvent power is expressed by the distribution coefficient of benzene at the origin in volume fractions. Solvent selectivity is expressed as the ratio of the distribution coefficients of benzene and hexane. The data points on the graph in FIG. 1 show a clear tendency to follow a law of inverse variation between selectivity and capacity. Two solvents, dimethylsulfoxide and sulfolane, appear from this graph to be good candidates for use in the present process, in view of the similar selectivity and capacity of these two solvents. The properties of a blended mixture is expected to have capacity and selectivity values between the values of the two individual components.

[0062] The addition of water to the mixture and a change in the temperature at which the extraction is conducted will both change the extraction performance. Adding water to a solvent decreases its capacity and increases its selectivity. In contrast, raising the extraction temperature improves solvent capacity at the expense of reducing its selectivity.

Example 1

[0063] A sample of gas oil derived from Arabian medium crude oil containing aromatics was used as a feedstock for extraction of the aromatics using an oxidized disulfide oil (ODSO). The number of carbon atoms in the individual water soluble OSDO compounds of the solvent used in Example 1 is in the range of from 2 to 4 carbon atoms. The properties and composition of the gas oil are shown in Table 4.

TABLE-US-00004 TABLE 4 Composition of Gas Oil in Example 1 Parameter Unit Value Density g/cm3 0.842 Refractive index @ 20 C. 1.47 Hydrogen W % 13.21 Carbon W % 85.27 Sulfur Ppmw 13,090 Nitrogen Ppmw 71 Cetane Number 59.5 Paraffins W % 44.5 Naphthenes W % 23.4 Aromatics W % 32.1 Distillation (ASTM 2887) 0 W % C. 141 10 W % C. 204 30 W % C. 249 50 W % C. 285 70 W % C. 319 90 W % C. 351 100 W % C. 400

[0064] Simulated distillation of the oxidized oil at various stages of oxidation is shown in FIG. 2. It is clear that a significant difference, i.e., about 156 C., is shown between the mid-boiling points of the original disulfide oil and the oxidized water soluble oil. The water soluble oil shows an increase in mid-boiling points.

[0065] The increased boiling points of the water soluble ODSO imply a reduced vapor pressure of the components. This in turn reduces issues relating to the sour/foul smell of the disulfide derivative compounds.

[0066] The increase in boiling points reflect heavier compounds being formed as a function of increased oxidation. The increased oxidation results in phase transfer from the water-insoluble phase to the water-soluble phase.

[0067] Water soluble ODSO compounds are immiscible with aromatic-containing streams, e.g., gas oil, and after intense mixing is discontinued, two separate layers are formed from the mixture which results in easier separation of the aromatic-containing ODSO solvent and the raffinate phase.

[0068] Density of the water soluble ODSO solvent is also higher when compared to the water insoluble ODSO solvent. This is advantageous in counter-current mixing processes.

Example 2

[0069] The aromatic extraction process was carried out on gas oil at 20 C. and atmospheric pressure. The gas oil and water soluble ODSO were mixed in equal volume and vigorously shaken for 10 minutes. The number of carbon atoms in the individual water soluble OSDO compounds of the solvent used in Example 2 is in the range of from 2 to 4 carbon atoms. There were two distinct phases at the start and end of the reaction.

[0070] Visual observations show that the bottom phase, which includes the ODSO and solute, changed from colorless/white to a dense black, indicating that some aromatic extraction occurred. The feedstock and the extract phase were analyzed using FT-ICR MS, with the results shown in Table 5 as a function of Double Bond Equivalence (DBE).

TABLE-US-00005 TABLE 5 FT-ICR MS results showing the percent of aromatics as a function of DBE Gas Oil, Aromatic DBE % Extract, % 4 0.2 5.0 5 0.2 3.9 6 1.4 3.7 7 14.2 32.8 8 48.8 34.7 9 23.9 11.0 10 9.3 6.5 11 1.2 1.6 12 0.7 0.7 13 0.0 0.1 14 0.1 0.00 Total 100.00 100.0

[0071] Referring to Table 5, the results of the FT-ICR MS analysis report the percent of aromatics is shown as a function of DBE. The Aromatic Extract, % column is the DBE number ratio of the gas oil-extracted ODSO fraction from the total accumulated DBE number intensity of that particular sample.

[0072] The concentrations shown are based on the peak intensities obtained in the FT-ICR MS analysis and are relative to each other.

[0073] As also shown by the data in Table 5, the water soluble ODSO mixture extracted aromatics from the gas oil phase is indicated by change in the amount of a particular DBE from the original gas oil (Gas Oil, %) and the gas oil-extracted ODSO (Aromatic Extract, %), and indicates that the gas oil components are in the ODSO solvent layer.

[0074] During aromatic extraction of the gas oil, a portion of the gas oil is extracted into the ODSO. For the extract layer comprising the ODSO solvent with a portion of the aromatics derived from the gas oil for DBE values across the range of 4-14, FT-ICR MS (not shown) has detected compounds having carbon numbers above 4, with a minimum carbon number of 10 and a maximum carbon number of 26. Since the disclosed ODSO molecules used in Example 2 have a DBE value of 0 and have a maximum of four (4) carbon atoms in their structures, it is clear that the hydrocarbon components in the water soluble ODSO solvent must derive from the gas oil and hence extraction of aromatics has occurred.

[0075] The data of Table 5 clearly demonstrates that the ODSO solvent is a powerful extraction solvent for the aromatics in the gas oil sample of Example 1.

Example 3

[0076] An n-dodecane stock solution spiked with BTX was used as a feedstock for the extraction of the aromatics using separately a water soluble oxidized disulfide oil (ODSO) solvent and a sulfolane solvent. The number of carbon atoms in the individual water soluble OSDO compounds of the ODSO solvent used in Example 3 is in the range of from 2 to 4 carbon atoms. The feedstock contained approximately 5 wt. % of benzene, 5 wt. % of toluene, 5 wt. % of o-xylene, 5 wt. % of m-xylene and 5 wt. % of p-xylene, as indicated in Table 6.

TABLE-US-00006 TABLE 6 GS-MS results showing selectivity of the ODSO compounds vs. sulfolane Sulfolane Extraction (wt. %) ODSO Extraction (wt. %) Normalized Normalized Stock Extract Selectivity Stock Extract Selectivity Benzene 4.12 0.69 100 4.49 0.26 100 Toluene 4.4 0.37 50 4.95 0.02 7 m-Xylene 4.81 0.58 72 5.08 0 0 p-Xylene 4.67 0.21 27 4.95 0 0 o-Xylene 4.66 0.09 12 4.93 0.06 21

[0077] The feedstock and solvent were vigorously shaken for 10 minutes at room temperature and atmospheric pressure.

[0078] After mixing, two distinct phases separated and were isolated. The raffinate layer comprised the feedstock with a portion of its aromatics removed. The extract layer comprised the solvent with the portion of aromatics removed from the feedstock.

[0079] Table 6 includes the results of a GC-MS analysis showing the wt. % of the BTX in the extract layer. When the selectivity is normalized, it is clear that the sulfolane solvent extracts all BTX components with no significant distinction between the different types of aromatics. In contrast, it is also clear from the results in Table 6 that the water soluble ODSO solvent has excellent selectivity for one specific aromatic, i.e., benzene.

[0080] It is clear from Table 6 that in embodiments where the targeted aromatic compound is benzene, a preferred aromatic extraction solvent is one or a mixture of ODSO compounds used alone, i.e., without other types of solvents.

[0081] The methods and compositions of the present invention have been described in detail above and in the attached drawings; however, modifications will be apparent to those of ordinary skill in the art from this description and the scope of protection for the invention is to be determined by the claims that follow.