COMBINED SOLID ADSORPTION-HYDROTREATING PROCESS FOR WHOLE CRUDE OIL DESULFURIZATION

Abstract

A whole crude oil desulfurization system and process includes a combination of an adsorption zone and a hydroprocessing zone. This combined process and system reduces the requisite throughput for the hydroprocessing unit, conventionally a very costly and process both in terms of energy expenditures and catalyst depletion. By first contacting the whole crude oil feedstock with an adsorbent for the sulfur-containing compounds, the adsorption effluent having a relatively lower sulfur content can be collected and provided to refiners without further treatment. The adsorbates, including adsorbed organosulfur compounds, are solvent desorbed resulting in a stream containing high levels of organosulfur compounds and a solvent. Following recovery of the solvent, the volume of the sulfur-containing feedstream that remains to be desulfurized in the hydroprocessing zone is substantially less than the original amount of whole crude oil feedstock.

Claims

1. A process for treating whole crude oil containing organosulfur compounds comprising: a. contacting, upstream of a crude distillation unit, a whole crude oil feed stream containing organosulfur compounds with a solid porous adsorbent material having average pore diameter in the mesoporous range to about 50 nanometers, wherein organosulfur compounds are adsorbed by the adsorbent material; b. recovering a treated effluent stream having a reduced level of organosulfur compounds; c. desorbing at least a portion of the organosulfur compounds from the adsorbent material, and recovering a purge stream having an increased level of organosulfur compounds from the adsorbent material; and d. hydroprocessing the purge stream and recovering a hydroprocessed stream having a reduced level of organosulfur compounds.

2. The process as in claim 1, wherein the adsorbent material is contained in at least one fixed bed.

3. The process of claim 1, wherein the hydroprocessed stream is combined with the treated effluent stream.

4. The process of claim 1, wherein the treated effluent stream is further subjected to a fractionation process to remove a gas phase that contains at least hydrogen sulfide gas.

5. The process of claim 1, wherein the treated effluent stream contains at least about 5 to 53 weight percent less organosulfur compounds than the whole crude oil stream.

6. The process of claim 1, wherein the treated effluent stream contains at least about 30 to 53 weight percent less organosulfur compounds than the whole crude oil stream.

7. The process of claim 1, wherein the desorbing step employs a stripping solvent.

8. The process of claim 7, wherein the purge stream contains at least a portion of the stripping solvent, and organosulfur compounds, and wherein at least a portion of the stripping solvent in the desorbed purge stream is distilled and recycled.

9. The process of claim 7, wherein the stripping solvent comprises a solvent selected from the group consisting of toluene, hexane, butane, pentane and combinations comprising at least one of the foregoing solvents.

10. The process of claim 7, wherein the stripping solvent comprises toluene.

11. The process of claim 1, wherein the desorbing step employs a supercritical fluid.

12. The process of claim 11, further comprising recovering the desorbed purge stream containing at least a portion of the supercritical fluid and the increased organosulfur compound purge stream, and wherein at least a portion of the supercritical fluid in the desorbed purge stream is compressed and reused as the stripping solvent.

13. The process of claim 11, wherein the supercritical fluid comprises a supercritical fluid selected from the group consisting of supercritical carbon dioxide, ethane, supercritical ethylene, supercritical propane, supercritical butane and combinations comprising at least one of the foregoing supercritical fluids.

14. The process of claim 11, wherein the supercritical fluid comprises supercritical carbon dioxide.

15. The process of claim 1, wherein the adsorbent material has an adsorbent capacity, and wherein contacting comprises: passing the whole crude oil feed stream through a first adsorbing bed containing adsorbent material until the adsorbent material in the first adsorbing bed has reached a predetermined percentage of its adsorbent capacity; and passing the whole crude oil feed stream through a second adsorbing bed containing adsorbent material when the adsorbent material in the first adsorbing bed has reached the predetermined percentage of its adsorbent capacity.

16. The process of claim 15, further comprising desorbing the first adsorbing bed while the whole crude oil feed stream is passed through the second adsorbing bed.

17. The process of claim 15, wherein the predetermined percentage is greater than at least 95%.

18. The process of claim 1, wherein the adsorbent material is selective to organosulfur compounds including benzothiophenes dibenzothiophenes, other multi-ring thiophenes, and combinations comprising at least one of the foregoing organosulfur compounds.

19. The process of claim 1, wherein the adsorbent material is selected from the group of materials consisting of Y-zeolites, active carbon powders and a combination comprising at least one of the foregoing materials.

20. The process of claim 1, wherein hydroprocessing is selected from the group consisting of hydrodesulfurization, hydrocracking, hydrodenitrification, hydrodealkylation and hydrotreating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The foregoing summary, as well as the following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings the same numeral is used to refer to the same or similar elements, in which:

[0024] FIG. 1 is a schematic diagram of one embodiment of an improved whole crude oil desulfurization system in accordance with the invention;

[0025] FIG. 2 is a schematic diagram of another embodiment of an improved whole crude oil desulfurization system in accordance with the invention; and

[0026] FIG. 3 is a schematic diagram of a further embodiment of an improved whole crude oil desulfurization system in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] A process for treating whole crude oil containing organosulfur compounds is generally described with respect to FIG. 1. A system 10 includes an adsorption zone 14 and a hydroprocessing zone 20. The process includes contacting a whole crude oil feed stream 12 containing organosulfur compounds with a solid adsorbent material in the adsorption zone 14, wherein organosulfur compounds are adsorbed by the adsorbent material. A treated effluent stream 16 having a reduced organosulfur compound content is recovered from the adsorption zone 14.

[0028] When the adsorbent material has reached a predetermined percentage of its adsorption capacity, organosulfur compounds are desorbed from the adsorbent material, e.g., by contacting the adsorbent material with a solvent for the organosulfur compounds. An increased organosulfur compound purge stream 18 is recovered. The increased organosulfur compound purge stream 18 is then desulfitrized in the hydroprocessing zone 20, from which a reduced organosulfur compound hydroprocessed stream 22 is recovered. Accordingly, the treated effluent stream 16 having a reduced organosulfur compound content (as compared to the whole crude oil feed stream 12) bypasses the hydroprocessing zone 20. In certain embodiments, the reduced organosulfir compound hydroprocessed stream 22 and the treated effluent stream 16 recovered from the adsorption zone 14 can be collected in a common location 24 or stream 24 (e.g., reservoir, tanker, pipeline, refinery crude feed stream). Alternatively, (not shown), the hydroprocessed stream 22 and the treated effluent stream 16 are collected or transported separately.

[0029] The sequence of hydroprocessing after adsorption allows the use of commercial hydroprocessing plant reactors and equipment such as hydrotreating units and provides a significant economic advantage. The cost of building and operating a hydroprocessing unit is generally proportional to the feed volume, and is generally not sensitive to the sulfur content up to about 6 wt %. Therefore, since the cost of adsorption, desorption and other unit operations equipment is generally much less than the cost of hydroprocessing equipment such as hydrotreating units, the same amount of whole crude oil can be desulfurized at a reduced cost using relatively smaller hydrotreating units downstream of the adsorption unit(s), as compared to using only a relatively larger hydrotreating unit to achieve the same or similar level of desulfurization of a give whole crude oil feedstream.

[0030] The adsorbent zone 14 can include any type of adsorbent bed or other structure and associated systems for containing adsorbent material. In certain embodiments, the adsorbent material is contained in at least one fixed bed. The adsorbent zone 14 can also be a plurality of fixed beds in parallel, series, or a combination including parallel and series; one or more agitated or non-agitated slurry vessels; or one or more moving bed adsorbers. The whole crude oil feed 12 can be treated in batch, semi-continuous or continuous operation, depending on the type and number of adsorbing units in the adsorption zone 14.

[0031] The adsorbent material is characterized by a high capacity and high selectivity for the sulfur compounds that are present in whole crude oils. In general, the adsorbent material has an adsorbent capacity suitable to remove at least about 5 to about 53 weight percent of the organosulfur compounds contained in the original whole crude oil feed stream 12. In certain preferred embodiments, the adsorbent material has an adsorbent capacity suitable to remove at least about 30 weight percent, and in certain embodiments higher levels, of the organosulfur compounds contained in the whole crude oil feed stream 12.

[0032] In addition, a suitable adsorbent material can be readily regenerated for repeated use if the adsorption unit. For instance, suitable adsorbent material can be used for at least about 50 cycles, preferably at least about 200 cycles of adsorption and desorption.

[0033] Further, the adsorbent material preferably does not react with sulfur gases that can be present in the whole crude oil stream 12, such as hydrogen sulfide gas. Accordingly, unlike other prior art processes that use beds of catalytic to remove hydrogen sulfide, generally by oxidation, organosulfur compounds are adsorbed in a manner that utilizes the purge stream to recover whole crude oil, in a purge stream 18 having increased levels of organosulfur compounds.

[0034] The adsorbent material/materials can include materials such as zinc oxide. manganese oxide, metals over high surface area supports like silica, alumina, zeolites, activated carbon, mesoporous silica molecular sieves (e.g., Al-MCM-41), and bauxite. Particularly suitable adsorbents that have been identified as having suitable adsorbent capacity for adsorbing organosulfur compounds from whole crude oil streams include alumino silicates such as type Y zeolite (metal promoted, ion-exchanged and other forms) and activated carbon powders. In certain embodiments, a combination comprising at least one of the above mentioned adsorbent materials can be used. For instance, these different adsorbent materials can be admixed, or in staged sections or adsorbent beds (in the case of series adsorbent beds).

[0035] The adsorbent preferably includes properties such as pore size that permits the large organosulfur compounds access to the internal adsorption sites. For instance, in a preferred embodiment, adsorbent material is selected that has an average pore diameter of about 10 to about 50 nanometers, a surface area of about 100 to about 500 square meters per gram, a pore volume of about 0.5 to about 0.8 cubic centimeters per gram, and a bulk density of about 0.55 to about 0.75 grams per cubic centimeter. In addition, preferred adsorbent particles are extrudates having a diameter of about 1 to about 5 millimeters and a length of about 0.5 to about 2.5 centimeters.

[0036] In preferred embodiments, large pressure drops (e.g., greater than about 0.25 bar/meter) are avoided by selection of suitable adsorbent material (including selection of suitable particle size), and suitable operating conditions such as temperature, pressure and space flow velocity. Operating conditions during adsorption can include: a temperature of ambient to about 70 C., and in certain embodiments ambient to about 50 C.; a pressure of ambient to about 5 bars, and in certain embodiments ambient to about 3 bars; and a liquid hourly space velocity of about 0.5/hour to about 10/hour, and in certain embodiments about 1.0/hour to about 8.0/hour.

[0037] The organosulfur compounds from the whole crude oil stream can include mercaptans, organic sulfides, organic sulfoxides, organic sulfones, thiophenes, multi-ring thiophenes, benzothiophenes, dibenzothiophenes and other sulfur-containing organic compounds, and combinations comprising at least one of the foregoing organosulfur compounds. During hydroprocessing, the amount of organosulfilr compounds in the purge stream 18 having increased levels of organosulfur compounds are converted to the reduced organosulfur compound hydroprocessed stream 22.

[0038] In certain embodiments, sulfurous gases (such as hydrogen sulfide gas) can be removed from the treated effluent 16 with a fractionation process to further reduce the overall sulfur content, as in known to those of ordinary skill in the in the art of hydrotreating. The elemental sulfur can be recovered for commercial sale.

[0039] Referring now to FIG. 2, an embodiment of a process and system for desulfurizing whole crude oil (more generally shown with respect to FIG. 1) is shown. A whole crude oil desulfurizing system 110 generally includes at least two parallel adsorption units 34, 54 in an adsorption zone 114. During the adsorption cycle, in which one adsorption unit 54 is adsorbing organosulfur compounds from the whole crude oil stream 32, the other adsorption unit 34 is in the desorption cycle, where it is desorbing the previously adsorbed organosulfur compounds into an increased organosulfur compound purge stream 38.

[0040] During an adsorption cycle of the adsorption unit 34, a treated effluent stream 36 having a reduced organosulfur compound content is recovered from the adsorption unit 34. Likewise, during an adsorption cycle of the adsorption unit 54, a treated effluent stream 56 having a reduced organosulfur compound content is recovered from the adsorption unit 54. The treated effluent streams 36, 56 can be directed, for instance, into a treated effluent stream 116.

[0041] During a desorption cycle, shown with respect to the adsorption unit 34 in FIG. 2, the adsorbates (including organosulfur compounds adsorbed to the adsorbent material) are desorbed to remove the increased organosulfur compound purge stream 38. A desorption cycle is also carried out in the adsorption unit 54 (not shown). The desorption cycle can commence, for instance, when the adsorbent material in the adsorption unit 34 or 54 has reached a predetermined percentage of its adsorbent capacity. In certain embodiments, the whole crude oils stream 32 is adsorbed until the level of organosulfur compounds has been reduced by a predetermined percentage. The amount of sulfur reduction can be monitored in the treated effluent stream 36, by various processes including but not limited to X-ray florescence.

[0042] A semi-continuous operation can be established by adsorbing in the adsorption unit 54 during the desorption cycle of adsorption unit 34, where the whole crude oil stream 32 is directed to the adsorption unit 54 for adsorptive desulfurization. The process can cycle between desorption and adsorption as needed.

[0043] The adsorption bed 34 can be regenerated by various methods. Furthermore, upon regeneration of the adsorbent material, at least about 95%, preferably at least about 99%, of the adsorbate is removed.

[0044] In the schematic diagram of FIG. 2, the desorption cycle employs a stripping solvent. The stripping solvent used in the process of the present invention is characterized by the following properties: [0045] a. the ability to dissolve sulfur organic compounds; [0046] b. it is in a liquid phase or supercritical state at the stripping conditions; and [0047] c. sufficiently volatile for reuse after separation of sulfur compounds.
In addition, economic considerations are important. Examples of suitable stripping solvents include toluene, hexane, butane, pentane, or combinations comprising at least one of the foregoing solvents. In certain embodiments, toluene is a desirable stripping solvent as it is an inexpensive aromatic solvent, thereby increasing the solubility of a greater portion of aromatic organosulfur compounds. Hexane, pentane and butane will dissolve a smaller portion of the aromatic sulfur compounds, especially those with multiple aromatic rings and nitrogen heteroatoms, in addition to sulfur, but energy savings in recovering the solvent are realized.

[0048] The adsorbent in the adsorption unit 34 is contacted with a stripping solvent in a desorbing stream 128. The purge stream 38 from the desorption cycle therefore includes organosulfur compounds and stripping solvent. All or a substantial portion of the stripping solvent used in the purge stream 38 is recovered, for instance, in a distillation unit 126.

[0049] The effluent from the distillation unit 126, a hydrocarbon stream 118 having an increased level of organosulfur compounds, is then processed in the hydroprocessing zone 120 for desulfurization. A hydroprocessed stream 122 having a reduced level of organosulfur compounds is recovered.

[0050] In certain embodiments, the hydroprocessed stream 122 and the treated effluent stream 116 recovered from the adsorption zone 114 can be collected in a common location 124 or stream 124. Alternatively, (not shown), the hydroprocessed stream 122 and the treated effluent stream 116 are collected or transported separately.

[0051] Operating conditions during desorption, for instance using toluene as a stripping solvent, can include: a temperature of ambient to about 70 C., and in certain embodiments ambient to about 50 C.; a pressure of ambient to about 5 bars, and in certain embodiments ambient to about 3 bars; and a liquid hourly space velocity of about 0.5/hour to about 10/hour, and in certain embodiments about 1.0/hour to about 8.0/hour.

[0052] The operating conditions for adsorption and desorption can be similar, realizing process economics and configuration advantages related to heating or cooling the bed. Since typical stripping solvents have relatively low viscosity levels, there is a lower pressure drop across the bed, or a higher velocity at the same pressure drop. For butane and lighter hydrocarbons, stripping can be accomplished in a liquid phase or supercritical state, and the pressure and temperature conditions should be set accordingly, i.e., such that the fluid is in its liquid state with the temperature below the solvent's critical temperature and the pressure above the solvent's vapor pressure, and such that the fluid is in the supercritical state with the temperature slightly above the solvent's critical temperature point and the pressure around the solvent's critical pressure.

[0053] In a further embodiment of a process and system for desulfurizing whole crude oil, and referring now to FIG. 3, a system 210 is shown similar to system 110 described with respect to FIG. 2, with the use of compressed gas or supercritical solvent. For instance, system 210 can use as a stripping agent one or more of supercritical carbon dioxide, supercritical ethane, supercritical ethylene, supercritical propane and supercritical butane.

[0054] During a desorption cycle, shown with respect to the adsorption unit 34 in FIG. 3, the adsorbates (including organosulfur compounds adsorbed to the adsorbent material) are desorbed to remove purge stream 38 having an increased level of organosulfur compounds. A desorption cycle is also carried out in the adsorption unit 54 (not shown). The desorption cycle can commence, for instance, when the adsorbent material in the adsorption unit 34 or 54 has reached a predetermined percentage of its adsorbent capacity. In certain embodiments, the whole crude oils stream 32 is adsorbed until the level of organosulfur compounds has been reduced by a predetermined percentage, for instance, ranging from about 5 to 53 weight percent, preferably about 30 to 53 percent.

[0055] A solvent desorbing stream 228 is passed through the adsorption unit 34. The purge stream 38 from the desorption cycle therefore includes desorbed adsorbate, i.e., organosulfur compounds, and solvent. At least a portion, and preferably, substantially all, of the solvent used in the desorption cycle purge stream 38 is recovered, for instance, in a separation unit 226, such as a distillation unit. The solvent is recompressed in a compressor 230, for instance, during continued desorption in a desorption cycle, or when needed in a subsequent desperation cycle. The increased organosulfur compound whole crude oil stream 118 can then be processed in the hydroprocessing zone 120 for desulfurization, and a hydroprocessed stream 122 having a reduced level of organosulfur compounds is recovered, as discussed above.

[0056] Operating conditions during desorption, for instance using supercritical carbon dioxide as a stripping solvent, can include a temperature of generally about 31 C. to about 70 C. and a pressure of about 72 to about 1000 bars with a liquid hourly space velocity of about 0.5/hour to about 20/hour. In preferred embodiments, operating conditions during adsorption can include a temperature of generally about 31 C. to about 70 C. and a pressure of about 72 bars to about 200 bars with a liquid hourly space velocity of about 1.0/hour to about 0/hour.

[0057] In the processes described herein, unlike conventional desulfurization processes, gaseous sulfur components of the whole crude oil stream (such as hydrogen sulfide) are not the targets of the adsorption process. Rather, organosulfur compounds, mercaptans, organic sulfides, organic sulfoxides, organic sulfones, thiophenes, benzothiophenes, multi-ring thiophenes such as dibenzothiophenes, and other sulfur-containing organic compounds are the desired adsorbates, and hydrogen sulfide is substantially not adsorbed. Thus, the reduced organosulfur compound adsorbent effluent stream is discharged having substantially the same amount of hydrogen sulfide gas as the whole crude oil stream. This treated effluent stream can be further subjected to a fractionation process to remove the gas phase containing hydrogen sulfide gas prior to delivery, storage or combination with the hydrotreated desultfurized stream described herein.

EXAMPLES

[0058] The following examples illustrate specific embodiments of the method(s) of this invention. The scope of this invention is not to be considered as limited by the specific embodiments described therein, but rather as defined by the claims.

Example 1

[0059] In this example, 3 grams of type Y zeolite powder was activated in a vacuum oven at 175 C. and a gauge pressure of 14 psig overnight. The Y zeolite powder was then cooled to room temperature and placed in a 100 ml wide-mouth bottle, to which 15 grams of crude oil having a total sulfur content of 3.01 wt % was added. The mixture was mechanically shaken for 8 hours to reach adsorption equilibrium. After the shaking was stopped, the zeolite powder was allowed to settle by gravity and the upper liquid layer was analyzed for total remaining sulfur which was found to be 1.4 wt %. The liquid was then decanted from the bottle and the remaining solid was washed with 30 grams of toluene. Analysis by X-ray fluoresce indicates that the toluene removed 67% of the total sulfur from the adsorbent.

Example 2

[0060] Example 1 was repeated, except that NiY zeolite powder (prepared by ion exchange) was employed as the adsorbent. The remaining total sulfur in the liquid was 1.2 wt % and toluene removed 54 wt % of the total sulfur from the adsorbent.

Example 3

[0061] Example 1 was repeated, except that 1-Y zeolite pellets were employed as the adsorbent. The remaining total sulfur in the liquid was 2.87 wt % and toluene removed almost 100 wt % of the total sulfur from the adsorbent.

Example 4

[0062] Example 1 was repeated, except that activated carbon powder was employed as the adsorbent. The remaining total sulfur in the liquid was 2.61 wt % and toluene removed 100 wt % of the total sulfur from the adsorbent.

[0063] The process of the invention has been described and explained with reference to the schematic process drawings and examples. Additional variations and modifications will be apparent to those of ordinary skill in the art based on the above description and the scope of the invention is to be determined by the claims that follow.