Patent Grant
8778173
The present invention relates to a process for desulfurizing heavy oil feedstreams with alkali metal compounds and improving the compatibility of the stream components in either the feed stream, an intermediate product stream, and/or the reaction product stream in the desulfurization process. These high compatibility feed, intermediate, and product streams have reduced incompatible asphaltene levels, thereby improving the overall reaction process, the reactor life, and quality of the final produced desulfurized heavy oil product stream.
As the demand for hydrocarbon-based fuels has increased, the need for improved processes for desulfurizing heavy oil feedstreams has increased as well as the need for increasing the conversion of the heavy portions of these feedstreams into more valuable, lighter fuel products. These heavy oil feedstreams include, but are not limited to, whole and reduced petroleum crudes, shale oils, coal liquids, atmospheric and vacuum residua, asphaltenes, deasphalted oils, cycle oils, FCC tower bottoms, gas oils, including atmospheric and vacuum gas oils and coker gas oils, light to heavy distillates including raw virgin distillates, hydrocrackates, hydrotreated oils, dewaxed oils, slack waxes, raffinates, and mixtures thereof. Hydrocarbon streams boiling above 430° F. (220° C.) often contain a considerable amount of large multi-ring hydrocarbon molecules and/or a conglomerated association of large molecules containing a large portion of the sulfur, nitrogen and metals present in the hydrocarbon stream. A significant portion of the sulfur contained in these heavy oils is in the form of heteroatoms in polycyclic aromatic molecules, comprised of sulfur compounds such as dibenzothiophenes, from which the sulfur is difficult to remove.
The high molecular weight, large multi-ring aromatic hydrocarbon molecules or associated heteroatom-containing (e.g., S, N, O) multi-ring hydrocarbon molecules in heavy oils are generally found in a solubility class of molecules termed as asphaltenes. A significant portion of the sulfur is contained within the structure of these asphaltenes or lower molecular weight polar molecules termed as “polars” or “resins”. Due to the large aromatic structures of the asphaltenes, the contained sulfur can be refractory in nature and can be difficult to remove.
These heavy oils typically contain significant amounts of sulfur. Sulfur contents of in excess of 2 to 5 wt % are not uncommon for these heavy oil streams and can often be concentrated to higher contents in the refinery heavy residual streams, such as atmospheric and vacuum gas oils. Additionally, most conventional catalytic refining and petrochemical processes cannot be used on these heavy feedstreams and intermediates due to their use of fixed bed catalyst systems and the tendency of these heavy hydrocarbons to produce excessive coking and deactivation of the catalyst systems when in contact with such feedstreams. Also, due to the excessive hydrocarbon unsaturation and cracking of carbon-to-carbon bonds experienced in these processes, significant amounts of hydrogen are required to treat high aromatic and asphaltene containing feeds. The high consumption of hydrogen, which is a very costly treating agent, in these processes results in significant costs associated with the conventional catalytic hydrotreating of heavy hydrocarbon feedstreams for sulfur removal.
One problem that exists in the industry is that heavy oil streams can be difficult to process even when utilizing an alkali metal salt treatment process due to the tendency of these asphaltene components of these heavy oils and their reaction products to precipitate during processing conditions thereby fouling the associated equipment and catalyst as well as requiring expensive and complicated facilities to handle and process the increased solids content in the reactor feed or intermediate process streams. This also leads to increased disposal costs for these hydrocarbon solids as well as a significant loss in alkali metal catalysts which can be bound to and removed with these hydrocarbon solids.
An additional problem exists in that many of these heavy oils, such as crudes, synthetic crudes, rough crude distillation cuts, and bitumens often need to be transported over pipelines spanning hundreds of miles for further processing at refineries and other related upgrading facilities. These pipelines have strict regulations on the solids content of the streams and therefore, the product stream to the pipeline must be low in solids as well as be stable such that the incompatible hydrocarbon compounds, in particular asphaltenes, in the product stream do not precipitate out of the stream during pipeline shipments as well as in the storage facilities associated with the pipeline transport.
Therefore, there exists in the industry a need for an improved process for improving the compatibility of the feed, intermediate, and/or product heavy oil streams associated with an alkali metal reagent desulfurization process.
The current invention embodies a process for improving the desulfurization of sulfur-containing heavy oils utilizing an alkali metal reagent. The process of the present invention improves the solubility of the components in the feed, intermediate, and/or product streams associated with the alkali metal desulfurization reaction process resulting in improved reaction efficiency, lower hydrocarbon product losses, lower solids disposal costs, lower alkali metal reagent losses and improved product stability.
A preferred embodiment of the present invention is a process for producing a stable desulfurized hydrocarbon product stream, comprising:
a) contacting a sulfur-containing heavy oils feedstream with an API gravity of less than about 20 with a first alkali metal reagent stream, and a first aromatic stability stream containing least 50 wt % aromatic hydrocarbons in a first reaction zone, thereby producing a desulfurized reaction stream comprised of desulfurized hydrocarbon compounds, spent alkali metal compounds, and hydrogen;
b) conducting the desulfurized reaction stream to a hydrocarbon product separator;
c) obtaining an aqueous spent alkali metal product stream from the hydrocarbon product separator; and
d) obtaining a desulfurized hydrocarbon product stream from the hydrocarbon product separator;
wherein less than 3 wt % of the asphaltenes present in the heavy oil feedstream precipitate out in the first reaction zone, and the desulfurized hydrocarbon product stream has a sulfur content by wt % that is less than 40% of the sulfur content by wt % of the heavy oils feedstream.
In a preferred embodiment, at least two desulfurization reaction zones are utilized in the process described wherein a second alkali metal reagent stream and a second aromatic stability is contacted with the desulfurized reaction stream and is thereafter conducted to a second reaction zone prior to the hydrocarbon product separator.
In yet another preferred embodiment, less than 1 wt % of the asphaltenes present in the heavy oils feedstream precipitate out in the first reaction zone and the desulfurized reaction product stream has a sulfur content by wt % that is less than 25% of the sulfur content by wt % of the heavy oils feedstream.
The present invention is a process for desulfurizing heavy oil feedstreams with alkali metal reagent compounds and improving the compatibility of the stream components in either the feed stream, an intermediate product stream, and/or the reaction product stream in the desulfurization process. These high compatibility feed, intermediate, and product streams have reduced incompatible asphaltene levels, thereby improving the overall reaction process, the reactor life, and quality of the final produced desulfurized heavy oil product stream.
The alkali metal reagents as utilized in the present invention for the desulfurization and demetallization of heavy oils streams are preferably selected from alkali metal hydroxides and alkali metal sulfides. The alkali metal hydroxides are preferably selected from potassium hydroxide, sodium hydroxide, rubidium hydroxide, cesium hydroxide, and mixtures thereof. The alkali metal sulfides are preferably selected from potassium sulfide, sodium sulfide, rubidium sulfide, cesium sulfide, and mixtures thereof. These alkali metal reagents are particularly useful in the desulfurization and demetallization of a heavy oil feedstream wherein a significant portion of asphaltenes may be present in the heavy oil stream. These hydrocarbon streams to be treated contain sulfur, much of which is part of the polar fraction and higher molecular weight aromatic and polycyclic heteroatom-containing compounds, herein generally referred to as “aphaltenes” or they are associated in the emulsion phase of such asphaltene species. “Asphaltenes” or the “asphaltene content” of a hydrocarbon stream as used herein are measured by ASTM D 6560-00 “Standard Test Method for Determination of Asphaltenes (Heptane Insolubles) in Crude Petroleum and Petroleum Products”.
It should be noted here that the terms “heavy oil feedstream” or “heavy oil stream” as used herein are equivalent and are defined as any hydrocarbon-containing streams having an API gravity of less than 20. Preferred heavy oil feedstreams for use in the present invention include, but are not limited to low API gravity, high sulfur, high viscosity crudes; tar sands bitumen; liquid hydrocarbon streams derived from tar sands bitumen, coal, or oil shale; as well as petrochemical refinery heavy intermediate fractions, such as atmospheric resids, vacuum resids, and other similar intermediate feedstreams and mixtures thereof containing boiling point materials above about 650° F. (343° C.). Heavy oil feedstreams as described herein may also include a blend of the hydrocarbons listed above with lighter hydrocarbon streams, such as, but not limited to, distillates, kerosene, or light naphtha diluents, and/or synthetic crudes, for control of certain properties desired for the transport or sale of the resulting hydrocarbon blend, such as, but not limited to, transport or sale as fuel oils and crude blends. In preferred embodiments of the present invention, the heavy oil feedstream contains at least 60 wt % hydrocarbon compounds, and more preferably, the heavy oil feedstream contains at least 75 wt % hydrocarbon compounds.
In preferred embodiments of the present invention, the heavy oil feedstream that is desulfurized in the present process contains at least 1 wt % sulfur and more preferably at least 3 wt % sulfur. In other preferred embodiments of the present invention, the heavy oil feedstream that is desulfurized in the present process contains polycyclic sulfur heteroatom complexes which are difficult to desulfurize by conventional methods.
Embodiments of the present invention utilizes at least one aromatic stability stream as a stabilizer in the overall alkali metal hydroxide desulfurization process to improve the overall process performance and products as described above. As defined herein, the term “aromatic stability stream” is defined as a hydrocarbon-containing stream which contains at least 50 wt % of aromatic compounds based on the overall aromatic stability stream. The term “aromatic compounds” as utilized herein is defined as hydrocarbon compounds containing one or more unsaturated carbon rings.
Embodiments of the present invention are best described by referring to the process diagrams as shown in
Beginning with
The aromatic stability streams utilized in the present invention preferably have an aromatics content of at least 50 wt % based on the total weight of the aromatic stability stream. More preferably, at least one of the aromatic stability streams utilized in the present invention preferably have an aromatics content of at least 60 wt %, and even more preferably at least 75 wt % based on the total weight of the aromatic stability stream. Preferred sources for the aromatic stability streams utilized in the present invention are high aromatic content product streams from a Fluid Catalytic Cracking Unit (“FCCU”), product streams from a pyrolysis unit, product streams from a visbreaking unit, or product streams from a coking unit. These process units and the products that are derived from these process units are well known in the art.
Even more preferred embodiments include wherein at least one of the aromatic stability streams is comprised of an FCCU product stream selected from a light catalytic cycle oil, a heavy catalytic cycle oil, and a catalytic bottoms oil. These stream terms are well known to those in the art, but for purposes of this application, a light catalytic cycle oil is a distillation stream obtained from an FCCU process wherein the hydrocarbon components of the stream boil substantially in the range of about 450° F. to about 650° F. (232° C. to 343° C.). A heavy catalytic cycle oil is a distillation stream obtained from an FCCU process wherein the hydrocarbon components of the stream boil substantially in the range of about 550° F. to about 750° F. (288° C. to 399° C.). A catalytic bottoms oil is a distillation stream obtained from an FCCU process wherein the hydrocarbon components of the stream boil substantially in the range of about 650° F.+ (343° C.+). The catalytic bottoms oil is a distillation stream obtained from the bottom of the distillation column from an FCCU and typically contains entrained catalyst particles, and therefore is also sometimes referred to as a “cat slurry oil”. By the term “substantially”, it is meant that at least 85 wt % of the overall hydrocarbon stream boils within the temperature range as designated under atmospheric pressure.
Additional preferred embodiments include wherein at least one of the aromatic stability streams is comprised of a visbreaking unit or coking unit distillation product stream selected from a naphtha distillation product stream, and gas oil distillation product stream, and a bottoms distillation product stream. These stream terms are well known to those in the art, but for purposes of this application, a naphtha distillation product stream is a distillation stream obtained from a visbreaking or coking process wherein the hydrocarbon components of the stream boil substantially in the range of about 450° F. to about 650° F. (232° C. to 343° C.). A gas oil distillation product stream is a distillation stream obtained from a visbreaking or coking process wherein the hydrocarbon components of the stream boil substantially in the range of about 550° F. to about 750° F. (288° C. to 399° C.). A bottoms distillation product stream is a distillation stream obtained from a visbreaking or coking process wherein the hydrocarbon components of the stream boil substantially in the range of about 650° F.+ (343° C.+).
Continuing with
Herein, the desulfurization reactor (120) can be comprised of a vessel or even simply piping which provides sufficient time and conditions for the heavy stream, the aromatic stability stream, and the alkali metal hydroxide to contact sufficiently to allow for the hydrocarbon portion of the overall process stream to be desulfurized. In the present invention, the aromatic stability stream prevents significant asphaltene precipitation during the desulfurization reaction process, thereby improving the overall desulfurization process, reducing hydrocarbon losses, and reducing alkali metal compound losses as these alkali metal compounds tend to get bound to and removed with the precipitated asphaltene components of the heavy oil feedstream in conventional processing.
Following the process scheme of
It is preferred that the amount of the pre-reaction aromatic stability stream (110) that is added in to the process is controlled to the point at which less than 3 wt % of the asphaltenes in the heavy oil feedstream precipitate out in the heavy oils desulfurization reactor (120). More preferably, the amount of the pre-reaction aromatic stability stream (110) that is added in to the process is controlled to the point at which less than 1 wt % of the asphaltenes in the heavy oil feedstream precipitate out in the heavy oils desulfurization reactor (120).
In some instances, the precipitation point to which one may want to control the pre-reaction aromatic stability stream (110) may not be at the conditions of the heavy oils desulfurization reactor (120). In some instances, the asphaltenes may be soluble under the heavy oils desulfurization reactor (120) conditions which typically run at temperatures of from about 600° F. to about 900° F. (316° C. to 482° C.). At higher temperatures, the asphaltenes tend to increase in stability and therefore a higher wt % of asphaltenes can be retained in a hydrocarbon stream without precipitating than at lower temperatures. Therefore, the amount of the pre-reaction aromatic stability stream (110) added to the present process may be controlled by the asphaltene precipitation rate at the lower storage or pipeline temperatures.
While the addition of the pre-reaction aromatic stability stream can be added at element (110), a post-reaction aromatic stability stream (130) can either be added to the process either alternatively or in addition to the pre-reaction aromatic stability stream (110). While the pre-reaction aromatic stability stream (110) assists in reducing fouling of the heavy oils desulfurization reactor (120) and improves the overall desulfurization performance, some or all of an aromatic stability stream can be added after the heavy oils desulfurization reactor as a post-reaction aromatic stability stream (130). In this instance, the post-reaction aromatic stability stream (130) assists in stabilizing the desulfurized reaction product stream (125) to prevent solids precipitation in downstream equipment particularly as the product stream is reduced in temperature. This has an additional benefit to the overall process by not reducing the capacity of the heavy oils desulfurization reactor (120) since this post-reaction aromatic stability stream is added after the reactor, thereby not displacing the heavy oil feed stream (101) to the heavy oils desulfurization reactor (120).
In the present invention, it is important that there is proper mixing and contact between the heavy oil feedstream (101), the alkali metal reagent stream (105), and the aromatic stability stream(s), especially when a pre-reaction aromatic stability stream (110) is utilized upstream of the heavy oils desulfurization reactor (120). Therefore in preferred embodiments, a slurry reactor or ebulating bed reactor design is preferred for use as the heavy oils desulfurization reactor (120). Additionally, static, rotary, or other types of mixing devices can be employed in the feed lines to heavy oils desulfurization reactor (120), and/or mixing devices can be employed in the heavy oils desulfurization reactor (120) to improve the contact between the heavy oil feedstream, the alkali metal reagent stream, and the pre-reaction aromatic stability stream.
After the desulfurized reaction product stream (125) is removed from the heavy oils desulfurization reactor (120), the desulfurized reaction product stream is preferably sent to a low pressure separator (135) wherein at least a portion of the of the hydrogen, light hydrocarbons, and non-condensable components of the desulfurized reaction product stream (125) can be removed via line (140). A degassed reaction stream (145) containing desulfurized hydrocarbons and spent alkali metal compounds is then sent to a hydrocarbon product separator (150) wherein the desulfurized hydrocarbons and spent alkali metal compounds are separated by various methods known in the art, e.g., a water wash. The spent alkali metal compounds tend to be more soluble in the water-based phase than the desulfurized hydrocarbon. As such, preferred methods of separation include gravitational (or density based) separations processes known in the art such as, but not limited to, the use of settling vessels, hydroclones, or centrifuges. In these processes, it is generally advantageous to keep the temperatures in the range of from 50° F. to about 300° F. (10° C. to 149° C.) in order to improve the contacting of the hydrocarbon with the water phase. A desulfurized hydrocarbon product stream (155) is thus obtained from the hydrocarbon product separator (150) and an aqueous spent alkali metal product stream (160) is also obtained. Filtering can also be utilized to remove some of the solids compounds formed, such as, but not limited to, coke and precipitated asphaltenes, as well as iron, vanadium, and nickel compounds derived from the heavy oils feedstream.
By the term “desulfurized hydrocarbon product stream” it is meant that the sulfur content by wt % of the desulfurized hydrocarbon product stream is less than 40% of the sulfur content by wt % of the heavy oils feedstream. In a more preferred embodiment of the present invention, the sulfur content by wt % of the desulfurized hydrocarbon product stream is less than 25% of the sulfur content by wt % of the heavy oils feedstream. In a most preferred embodiment of the present invention, the sulfur content by wt % of the desulfurized hydrocarbon product stream is less than 10% of the sulfur content by wt % of the heavy oils feedstream. These parameters are based on water-free hydrocarbon streams.
The present invention significantly improves the processes of the prior art by reducing the amount of precipitated solids in these intermediate and product to streams. However, as discussed prior, the asphaltene solids may precipitate out at the lower temperatures described herein for the hydrocarbon product separator (150) than for the higher temperatures found in the heavy oils desulfurization reactor (120). Therefore, in a preferred embodiment, the amount of either one or both of the aromatic stability streams (110 and/or 130) added to the overall reactor feedstream may be controlled such that a minimal amount of asphaltene precipitates in the hydrocarbon product separator (150). In a preferred embodiment, the amount of aromatic stability stream(s) (110 and/or 130) that is incorporated into the process is controlled to the point at which less than 3 wt % of the asphaltenes in the heavy oil feedstream (101) precipitate out in the hydrocarbon product separator (150). More preferably, the amount of aromatic stability stream(s) that is incorporated into the process is controlled to the point at which less than 1 wt % of the asphaltenes in the heavy oil feedstream (101) precipitate out in the hydrocarbon product separator (150).
It should also be noted that after separating the desulfurized hydrocarbon product stream (155), this product is typically further sent to storage tanks and then further to a pipeline. A problem that exists is that if the desulfurized hydrocarbon product stream being sent to the pipeline is not stable, asphaltenes can precipitate from the product stream into the pipeline thereby exceeding the maximum solids content specification for the pipeline. Therefore, the pipeline product control requirements may be such that they are the ultimate control limit for the amount of aromatic stability stream(s) (110 and/or 130) that is added in to the process. In a preferred embodiment of the present invention, the amount of aromatic stability stream(s) that is added in to the process is controlled to the point wherein the portion of the desulfurized hydrocarbon product stream (155) that is sent to a pipeline has a solids content lower than the allowable solids content specification for the pipeline.
In another embodiment of the present invention, an additional aromatic stability stream (165) may be, added to the desulfurized hydrocarbon product stream (155) to improve the stability of the resulting blended product stream. Preferably, the amount of the aromatic stability stream (165) is controlled to the point wherein the portion of the desulfurized hydrocarbon product stream (155) that is sent to a pipeline has a solids content lower than the allowable solids content specification for the pipeline. In another preferred embodiment, the aromatic stability stream (165) is added to the desulfurized hydrocarbon product stream (155) in an amount wherein less than 3 wt % of the asphaltenes in the heavy oil feedstream precipitate out in the downstream storage associated with a transportation pipeline. More preferably, the amount of the aromatic stability stream (165) is added to the desulfurized hydrocarbon product stream (155) to wherein less than 1 wt % of the asphaltenes in the heavy oil feedstream precipitate out in the downstream storage associated with a transportation pipeline.
It should also be noted that a preferred embodiment of the present invention can be utilized with a similar sulfur reduction process utilizing multiple desulfurization reactors than just a single desulfurization reactor as shown in
Therefore,
In the multi-reactor embodiment shown in
Following the process scheme of
A final desulfurized reaction product stream (245) is comprised of desulfurized hydrocarbon compounds, spent (e.g., sulfurized) alkali metal compounds, and hydrogen is removed from the second heavy oils desulfurization reactor (240). If desired, a post-reaction aromatic stability stream (250) can be added to the final desulfurized reaction product stream (245) to improve its stability. The final desulfurized reaction product stream (245) is preferably sent to a low pressure separator (260) wherein at least a portion of the hydrogen, light hydrocarbons, and non-condensable components of the final desulfurized reaction product stream (245) can be removed via line (265). A degassed reaction stream (270) containing desulfurized hydrocarbons and spent alkali metal compounds are then sent to a hydrocarbon product separator (275) wherein the desulfurized hydrocarbons and spent alkali metal compounds are separated by various methods known in the art, e.g., a water wash. Similar processes and conditions as described for the hydrocarbon product separator in the embodiment of
In another embodiment of the present invention, a product aromatic stability stream (290) may be added to the desulfurized hydrocarbon product stream (280) to improve the stability of the resulting blended product stream. Preferably, the amount of the product aromatic stability stream (290) is controlled to the point wherein the portion of the desulfurized hydrocarbon product stream (280) that is sent to a pipeline has a solids content lower than the allowable solids content specification for the pipeline. In another preferred embodiment, the product aromatic stability stream (290) is added to the desulfurized hydrocarbon product stream (280) in an amount wherein less than 3 wt % of the asphaltenes in the heavy oil feedstream precipitate out in the downstream storage associated with a transportation pipeline. More preferably, the amount of the product aromatic stability stream (290) added to the desulfurized hydrocarbon product stream (280) to wherein less than 1 wt % of the asphaltenes in the heavy oil feedstream precipitate out in the downstream storage associated with a transportation pipeline.
Similar to the single reactor process as embodied in
Although the present invention has been described in terms of specific embodiments, it is not so limited. Suitable alterations and modifications for operation under specific conditions will be apparent to those skilled in the art. It is therefore intended that the following claims be interpreted as covering all such alterations and modifications as fall within the true spirit and scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 61/203,048 filed Dec. 18, 2008.
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