Patent Application
20110155647
The present invention relates to processes for de-acidifying hydrocarbons such as crude oil and hydrocarbon fractions produced from the crude oil. More particularly, the invention relates to such processes using an ionic liquid.
Crude oil and hydrocarbon fractions thereof are known to contain organic acids, e.g., naphthenic acids that cause corrosion problems in transportation pipelines and in oil refinery equipment used to process the oil.
In a conventional de-acidification process, an acidic oil, i.e., a hydrocarbon containing a naphthenic acid, is mixed with an alkali such as sodium hydroxide or potassium hydroxide and water. The mixing produces an emulsion which may be separated into an aqueous phase and an oil phase with addition of a de-emulsifier. The neutralization reaction produces an alkali metal salt in the aqueous phase which is removed from the resulting oil phase having a reduced acid content. The acidic oil may be a whole or full range crude that is suitable as feed to a crude distillation zone or an acidic hydrocarbon fraction produced by the crude distillation zone or other process zones in a refinery.
PCT application PCT/GB2007/001985 published as WO 2007/138307 A2 discloses a sulfur-containing acid removal process for deacidifying a crude oil and/or crude oil distillate containing sulfur-containing acids comprising the steps of: (a) contacting the crude oil and/or crude oil distillate containing sulfur-containing acids with a basic ionic liquid having a melting point of below 150° C., and extracting at least a portion of the sulfur-containing acids into the basic ionic liquid as an extract phase; and (b) separating a crude oil and/or crude oil distillate phase which is reduced in acidity from the basic ionic liquid phase.
There remains a need in the art for improved or alternate processes that reduce the acid content of crude oil and acidic hydrocarbon fractions.
In an embodiment, the invention is a process for de-acidifying a hydrocarbon feed comprising: contacting the hydrocarbon feed containing an organic acid with a feed-immiscible phosphonium ionic liquid to produce a mixture comprising the hydrocarbon and the feed-immiscible phosphonium ionic liquid; separating the mixture to produce a hydrocarbon effluent and a feed-immiscible phosphonium ionic liquid effluent comprising the organic acid; and optionally adding a de-emulsifier to at least one of the contacting step and the separating step.
In another embodiment, the mixture further comprises water in an amount less than 10% relative to the amount of the feed-immiscible phosphonium ionic liquid in the mixture on a weight basis.
In further embodiment the feed-immiscible phosphonium ionic liquid comprises a non-basic ionic liquid.
In general, the invention may be used to de-acidify, that is, reduce the acid content of a hydrocarbon through use of a feed-immiscible phosphonium ionic liquid. In an exemplary embodiment, the feed-immiscible phosphonium ionic liquid comprises a non-basic ionic liquid.
Hydrocarbons to be de-acidified by processes of this invention contain an organic acid. The hydrocarbon may be any hydrocarbonaceous stream containing one or more organic acid compounds. Examples of organic acids include naphthenic acids, such as cyclopentyl and cyclohexyl carboxylic acids. In an embodiment, the organic acid ranges in molecular weight from about 120 au to about 700 au or higher. The acidity of the hydrocarbon is reported as the Total Acid Number (TAN) in units of mg KOH/g and is determined by ASTM Method D-0664, Acid Number of Petroleum Products by Potentiometric Titration. Unless otherwise noted, the analytical methods used herein such as ASTM D-0664 are available from ASTM International, 100 Barr Harbor Drive, West Conshohocken, Pa., USA. In an embodiment, the hydrocarbon feed to the process has a TAN in the range of from about 0.1 mg KOH/g to about 9 mg KOH/g. In another embodiment, the hydrocarbon has a TAN in the range of from about 0.3 mg KOH/g to about 4 mg KOH/g; and the TAN may range from about 0.5 mg KOH/g to about 8 mg KOH/g.
Processes according to the invention remove an organic acid from the hydrocarbon. That is, the invention removes at least one organic acid compound. It is understood that the hydrocarbon will usually comprise a plurality of organic acid compounds of different types and in various amounts. Thus, the invention removes at least a portion of at least one type of organic acid compound from the hydrocarbon. The invention may remove the same or different amounts of each type of organic acid compound, and some types of organic acid compounds may not be removed. In an embodiment, the organic acid content of the hydrocarbon is reduced by at least 50% based on the Total Acid Numbers of the hydrocarbon introduced to the process and the hydrocarbon effluent from the process. In another embodiment, the organic acid content of the hydrocarbon is reduced by at least 65% based on the Total Acid Numbers of the hydrocarbon introduced to the process and the hydrocarbon effluent from the process; and the organic acid content of the hydrocarbon may be reduced by at least 70% based on the Total Acid Numbers.
The hydrocarbon feed to the process contains an organic acid and may be a single hydrocarbon compound or a mixture of hydrocarbon compounds. In an embodiment, the hydrocarbon comprises a crude oil. As used herein term “crude oil” is to be interpreted broadly to receive not only its ordinary meanings as used by those skilled in the art of producing and refining oil but also in a broad manner to include hydrocarbon mixtures exhibiting crude-like characteristics. Thus, “crude oil” encompasses any full range crude oil produced from an oil field and any full range synthetic crude produced, for example, from tar sand, bitumen, shale oil, and coal. Crude oil may be passed to a crude oil distillation zone wherein the crude oil is fractionated into multiple product streams, such as, light ends, naphtha, diesel, and gas oil. A crude oil distillation zone may comprise multiple distillation columns. In another embodiment, the hydrocarbon comprises a high boiling hydrocarbon fraction, i.e., boiling above the end of the diesel range, including straight run fractions such as atmospheric gas oil, vacuum gas oil, atmospheric crude tower bottoms, vacuum crude tower bottoms and similar boiling fractions. A high boiling hydrocarbon fraction may also be produced by various refining processes such as visbreaking, coking, deasphalting, and fluid catalytic cracking (FCC) processes.
One or more ionic liquids may be used to extract one or more organic acids from a hydrocarbon. Generally, ionic liquids are non-aqueous, organic salts composed of ions where the positive ion is charge balanced with negative ion. These materials have low melting points, often below 100° C., undetectable vapor pressure and good chemical and thermal stability. The cationic charge of the salt is localized over hetero atoms, such as nitrogen, phosphorous, sulfur, arsenic, boron, antimony, and aluminum, and the anions may be any inorganic, organic, or organometallic species.
Ionic liquids suitable for use in the instant invention are feed-immiscible phosphonium ionic liquids. As used herein the term “feed-immiscible phosphonium ionic liquid” means an ionic liquid having a cation comprising at least one phosphorous atom and which is capable of forming a separate phase from the hydrocarbon feed under operating conditions of the process. Ionic liquids that are miscible with hydrocarbon feed at the process conditions will be completely soluble with the hydrocarbon feed; therefore, no phase separation will be feasible. Thus, feed-immiscible phosphonium ionic liquids may be insoluble with or partially soluble with the hydrocarbon feed under operating conditions. A phosphonium ionic liquid capable of forming a separate phase from the hydrocarbon feed under the operating conditions is considered to be feed-immiscible. Ionic liquids according to the invention may be insoluble, partially soluble, or completely soluble (miscible) with water. In an embodiment, the feed-immiscible phosphonium ionic liquid comprises tetrabutylphosphonium methanesulfonate, [(C4H9)4P]+[CH3SO3]−. Tetrabutylphosphonium methanesulfonate is a non-basic ionic liquid. As used herein, the term “non-basic ionic liquid” means an ionic liquid with a pH equal to or less than 7.
In an embodiment, the invention is a process for de-acidifying a hydrocarbon comprising a contacting step and a separating step. In the contacting step, the hydrocarbon feed containing an organic acid is contacted or mixed with a feed-immiscible phosphonium ionic liquid. The contacting may facilitate transfer of the one or more organic acid compounds from the hydrocarbon to the ionic liquid. Although a feed-immiscible phosphonium ionic liquid that is partially soluble with hydrocarbon feed may facilitate transfer of the organic acid from the hydrocarbon feed to the ionic liquid, partial solubility is not required. Insoluble hydrocarbon/feed-immiscible phosphonium ionic liquid mixtures may have sufficient interfacial surface area between the hydrocarbon and ionic liquid to be useful. In the separation step, the mixture of hydrocarbon and feed-immiscible phosphonium ionic liquid settles or forms two phases, a hydrocarbon phase and a feed-immiscible phosphonium ionic liquid phase, which are separated to produce a feed-immiscible phosphonium ionic liquid effluent comprising the organic acid and a hydrocarbon effluent.
In an embodiment, a de-emulsifier is added to the contacting step and/or the separation step to facilitate or enable the phase separation of the hydrocarbon and the feed-immiscible phosphonium ionic liquid, for example, when contacting or mixing the hydrocarbon and the feed-immiscible phosphonium ionic liquid forms or would otherwise form an emulsion. In an embodiment, the de-emulsifier is added to the contacting step simultaneously with the hydrocarbon and/or the feed-immiscible phosphonium ionic liquid. The optional de-emulsifier addition step may be used after an emulsion has formed.
De-emulsifiers suitable for use in the invention are any ethoxylated and/or propoxylated polyamines, di-epoxides or polyols. Examples of such de-emulsifiers include alcohol-based de-emulsifiers available from Baker Petrolite Corporation such as BPR23025 and BPR27330. In an embodiment, the weight ratio de-emulsifier to hydrocarbon feed ranges from about 1:10,000 to about 1:1000. In another embodiment, the weight ratio of de-emulsifier to hydrocarbon feed ranges from about 1:1000 to about 1:10.
Processes of the invention may be conducted in various equipment which are well known in the art and are suitable for batch or continuous operation. For example, in a small scale form of the invention, the hydrocarbon, a feed-immiscible phosphonium ionic liquid, and optionally a de-emulsifier, may be mixed in a beaker, flask, or other vessel, e.g., by stirring, shaking, use of a mixer, or a magnetic stirrer. The mixing or agitation is stopped and the mixture forms a hydrocarbon phase and an ionic liquid phase after settling. In an embodiment, the mixture is centrifuged to facilitate formation of the two phases. The phases can be separated, for example, by decanting or use of a pipette to produce a hydrocarbon effluent having a lower organic acid content relative to the hydrocarbon feed. The process also produces an ionic liquid effluent comprising the one or more organic acid compounds and the feed-immiscible phosphonium ionic liquid.
The contacting and separating steps may be repeated for example when the organic acid content of the hydrocarbon effluent is to be reduced further to obtain a desired organic acid content in the ultimate hydrocarbon product stream from the process. Each set, group, or pair of contacting and separating steps may be referred to as an acid removal step. Thus, the invention encompasses processes having single and multiple acid removal steps.
An acid removal zone may be used to perform an acid removal step. As used herein, the term “zone” can refer to one or more equipment items and/or one or more sub-zones. Equipment items may include, for example, one or more vessels, heaters, separators, exchangers, conduits, pumps, compressors, and controllers. Additionally, an equipment item can further include one or more zones or sub-zones. The acid removal process or step may be conducted in a similar manner and with similar equipment as is used to conduct other liquid-liquid wash and extraction operations. Suitable equipment includes, for example, columns with: trays, packing, rotating discs or plates, and static mixers. Pulse columns and mixing/settling tanks may also be used.
Consistent with common terms of art, the ionic liquid introduced to the acid removal step may be referred to as a “lean ionic liquid” generally meaning a feed-immiscible phosphonium ionic liquid that is not saturated with one or more extracted organic acid compounds. Lean ionic liquid may include one or both of fresh and regenerated ionic liquid and is suitable for accepting or extracting organic acid from the hydrocarbon feed. Likewise, the ionic liquid effluent may be referred to as “rich ionic liquid”, which generally means a feed-immiscible phosphonium ionic liquid effluent produced by an acid removal step or process or otherwise including a greater amount of extracted organic acid compounds than the amount of extracted organic acid compounds included in the lean ionic liquid. A rich ionic liquid may require regeneration or dilution, e.g., with fresh ionic liquid, before recycling the rich ionic liquid to the same or another acid removal step of the process.
Separation vessel 165 may contain a solid media 175 and/or other coalescing devices which facilitate the phase separation. In other embodiments the separation zone 300 may comprise multiple vessels which may be arranged in series, parallel, or a combination thereof. The separation vessels may be of any shape and configuration to facilitate the separation, collection, and removal of the two phases. In a further embodiment not illustrated, acid removal zone 100 may include a single vessel wherein lean ionic liquid stream 4 and hydrocarbon feed stream 2 are mixed, then remain in the vessel to settle into the hydrocarbon effluent and rich ionic liquid phases. In an embodiment the process comprises at least two acid removal steps. For example, the hydrocarbon effluent from one acid removal step may be passed directly as the hydrocarbon feed to a second acid removal step. In another embodiment, the hydrocarbon effluent from one acid removal step may be treated or processed before being introduced as the hydrocarbon feed to the second acid removal step. There is no requirement that each acid removal zone comprises the same type of equipment. Different equipment and conditions may be used in different acid removal zones.
The acid removal step may be conducted under acid removal conditions including temperatures and pressures sufficient to keep the feed-immiscible phosphonium ionic liquid and hydrocarbon feeds and effluents as liquids. For example, the acid removal step temperature may range between about 10° C. and less than the decomposition temperature of the ionic liquid; and the pressure may range between about atmospheric pressure and 700 kPa(g). When the feed-immiscible phosphonium ionic liquid comprises more than one ionic liquid component, the decomposition temperature of the ionic liquid is the lowest temperature at which any of the ionic liquid components decompose. The acid removal step may be conducted at a uniform temperature and pressure or the contacting and separating steps of the acid removal step may be operated at different temperatures and/or pressures. In an embodiment, the contacting step is conducted at a first temperature, and the separating step is conducted at a temperature at least 5° C. lower than the first temperature. In a non limiting example, the first temperature is about 70° C. and the second temperature is about 25° C. Such temperature differences may facilitate separation of the hydrocarbon and ionic liquid phases.
The above and other acid removal step conditions such as the contacting or mixing time, the separation or settling time, and the ratio of hydrocarbon feed to feed-immiscible phosphonium ionic liquid (lean ionic liquid) may vary greatly based, for example, on the nature of the hydrocarbon feed, the acid content of the hydrocarbon feed, the degree of acid removal required, the number of acid removal steps employed, and the specific equipment used. In general it is expected that contacting time may range from less than one minute to about two hours; settling time may range from about one minute to about eight hours; and the weight ratio of hydrocarbon feed to lean ionic liquid may range from 1:1,000 to 1,000:1. In an embodiment, the weight ratio of hydrocarbon feed to lean ionic liquid may range from about 1:100 to about 100:1; and the weight ratio of hydrocarbon feed to lean ionic liquid may range from about 1:10 to about 10:1. In an embodiment the weight of hydrocarbon feed is greater than the weight of the lean ionic liquid.
In an embodiment, more than about 40% of the acid may be extracted or removed from the hydrocarbon feed 2 in a single acid removal step as determined by the Total Acid Numbers of the hydrocarbon feed 2 and the hydrocarbon effluent 6. That is, the Total Acid Number of the hydrocarbon effluent 6 is less than about 60% of the Total Acid Number of the hydrocarbon feed 2. In another embodiment, the Total Acid Number of the hydrocarbon effluent 6 is less than about 50% of the Total Acid Number of the hydrocarbon feed 2; and the Total Acid Number of the hydrocarbon effluent 6 may be less than about 40% of the Total Acid Number of the hydrocarbon feed 2. The degree of phase separation between the hydrocarbon and ionic liquid phases is another factor to consider as it affects recovery of the ionic liquid and hydrocarbon. The degree of acid removed and the recovery of the hydrocarbon and ionic liquids may be affected differently by the nature of the hydrocarbon feed, the de-emulsifier, if used, the equipment, and the acid removal conditions such as those discussed above.
The amount of water present in the hydrocarbon/ionic liquid mixture during the acid removal step may also affect the amount of organic acid removed and/or the degree of phase separation or recovery of the hydrocarbon and ionic liquid. In an embodiment, the hydrocarbon/feed-immiscible phosphonium ionic liquid mixture has a water content of less than about 10% relative to the weight of the feed-immiscible phosphonium ionic liquid. In another embodiment, the water content of the hydrocarbon/feed-immiscible phosphonium ionic liquid mixture is less than about 5% relative to the weight of the feed-immiscible phosphonium ionic liquid; and the water content of the hydrocarbon/feed-immiscible phosphonium ionic liquid mixture may be less than about 2% relative to the weight of the feed-immiscible phosphonium ionic liquid. In a further embodiment, the hydrocarbon/feed-immiscible phosphonium ionic liquid mixture is water free, i.e. the mixture does not contain water.
An optional hydrocarbon washing step may be used, for example, to recover ionic liquid that is entrained or otherwise remains in the hydrocarbon effluent stream by using water to wash or extract the ionic liquid from the hydrocarbon effluent. In this embodiment, a portion or all of hydrocarbon effluent stream 6 (as feed) and a water stream 12 (as solvent) are introduced to hydrocarbon washing zone 400. The hydrocarbon effluent and water streams introduced to hydrocarbon washing zone 400 are mixed and separated to produce a washed hydrocarbon stream 14 and a spent water stream 16, which comprises the ionic liquid. The hydrocarbon washing step may be conducted in a similar manner and with similar equipment as used to conduct other liquid-liquid wash and extraction operations as discussed above. Various hydrocarbon washing step equipment and conditions such as temperature, pressure, times, and solvent to feed ratio may be the same as or different from the acid removal zone equipment and conditions. In general, the hydrocarbon washing step conditions will fall within the same ranges as given above for the acid removal step conditions. A portion or all of the washed hydrocarbon stream 14 may be passed to crude oil distillation zone 800.
An optional ionic liquid regeneration step may be used, for example, to regenerate the ionic liquid by removing the organic acid compound from the ionic liquid, i.e. reducing the organic acid content of the rich ionic liquid. In an embodiment, a portion or all of ionic liquid effluent stream 8 (as feed) comprising the feed-immiscible phosphonium ionic liquid and the organic acid and a regeneration solvent stream 18 are introduced to ionic liquid regeneration zone 500. The ionic liquid effluent and regeneration solvent streams are mixed and separated to produce an extract stream 20 comprising the organic acid compound, and a regenerated ionic liquid stream 22. The ionic liquid regeneration step may be conducted in a similar manner and with similar equipment as used to conduct other liquid-liquid wash and extraction operations as discussed above. Various ionic liquid regeneration step conditions such as temperature, pressure, times, and solvent to feed may be the same as or different from the acid removal conditions. In general, the ionic liquid regeneration step conditions will fall within the same ranges as given above for the acid removal step conditions.
In an embodiment, the regeneration solvent stream 18 comprises a hydrocarbon fraction lighter than the hydrocarbon feed stream 2. The lighter hydrocarbon fraction may consist of a single hydrocarbon compound or may comprise a mixture of hydrocarbons. In an embodiment, the lighter hydrocarbon fraction comprises at least one of a naphtha, gasoline, diesel, light cycle oil (LCO), and light coker gas oil (LCGO) hydrocarbon fraction. The lighter hydrocarbon fraction may comprise straight run fractions and/or products from conversion processes such as hydrocracking, hydrotreating, fluid catalytic cracking (FCC), reforming, coking, and visbreaking. In this embodiment, extract stream 20 comprises the lighter hydrocarbon regeneration solvent and the organic acid compound. In another embodiment, the regeneration solvent stream 18 comprises water and the ionic liquid regeneration step produces extract stream 20 comprising the organic acid compound and regenerated ionic liquid 22 comprising water and the feed-immiscible phosphonium ionic liquid. In an embodiment wherein regeneration solvent stream 18 comprises water, a portion or all of spent water stream 16 may provide a portion or all of regeneration solvent stream 18. Regardless of whether regeneration solvent stream 18 comprises a lighter hydrocarbon fraction or water, a portion or all of regenerated ionic liquid stream 22 may be recycled to the acid removal step via a conduit not shown consistent with other operating conditions of the process. For example, a constraint on the water content of the ionic liquid stream 4 or ionic liquid/hydrocarbon mixture in acid removal zone 100 may be met by controlling the proportion and water content of fresh and recycled ionic liquids.
Optional ionic liquid drying step is illustrated by drying zone 600. The ionic liquid drying step may be employed to reduce the water content of one or more of the streams comprising ionic liquid to control the water content of the acid removal step as described above. In the embodiment of
Unless otherwise stated, the exact connection point of various inlet and effluent streams within the zones is not essential to the invention. For example, it is well known in the art that a stream to a distillation zone may be sent directly to the column, or the stream may first be sent to other equipment within the zone such as heat exchangers, to adjust temperature, and/or pumps to adjust the pressure. Likewise, streams entering and leaving washing or extraction zones including acid removal zone 100, hydrocarbon washing zone 400, and ionic liquid regeneration zone 500 may pass through ancillary equipment such as heat exchanges within the zones. Streams, including recycle streams, introduced to washing or extraction zones may be introduced individually or combined prior to or within such zones.
The invention encompasses a variety of flow scheme embodiments including optional destinations of streams, splitting streams to send the same composition, i.e. aliquot portions, to more than one destination, and recycling various streams within the process. Examples include: various streams comprising ionic liquid and water may be dried and/or passed to other zones to provide all or a portion of the water and/or ionic liquid required by the destination zone. The various process steps may be operated continuously and/or intermittently as needed for a given embodiment, e.g., based on the quantities and properties of the streams to be processed in such steps. As discussed above the invention encompasses multiple acid removal steps, which may be performed in parallel, sequentially, or a combination thereof. Multiple acid removal steps may be performed within the same acid removal zone and/or multiple acid removal zones may be employed with or without intervening washing, regeneration and/or drying zones.
The examples are presented to further illustrate some aspects and benefits of the invention and are not to be considered as limiting the scope of the invention.
A commercial sample of a Medium Arabian Crude Oil having the following properties was obtained for use as the hydrocarbon feed stream: Total Acid Number of 0.116 mg KOH/g, 128 ppm water; 1000 ppm nitrogen, 2.88% sulfur. The Total Acid Number was determined by ASTM Method D-0664, Acid Number of Petroleum Products by Potentiometric Titration. The water content was determined by ASTM Method D1364-02, Karl Fisher Reagent Titration. The nitrogen content was determined by ASTM Method D4629-02, Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection. The sulfur content was determined by ASTM Method D5453-00, Ultraviolet Fluorescence.
The Medium Arabian Crude Oil of Example 1, the ionic liquid listed in Table 1 and a de-emulsifier containing butanol (BPR 27330 from Baker Petrolite Corporation) in a weight ratio of Medium Arabian Crude Oil to ionic liquid to de-emulsifier of 1:0.5:0.05 were mixed at a pressure of 43 kPa(g) for two hours at 300 rpm using a digital magnetic stirrer hot plate. Examples 3 and 4 were mixed at 50° C. and Examples 2 and 5 were mixed at 70° C. After mixing was stopped, the mixtures were centrifuged for 5 minutes at 25° C., then a sample of the hydrocarbon phase (hydrocarbon effluent) was removed with a pipette and analyzed by for Total Acid Number by ASTM Method D-0664. The results are compared in Table 1.
Example 2 demonstrates that processes of the invention using a feed-immiscible phosphonium ionic liquid may provide up to 80% removal of organic acids from a hydrocarbon as determined by the Total Acid Numbers of the hydrocarbon feed and effluent. Example 2 is a non-basic ionic liquid. However, comparative Examples 3-5 using non-basic imidazolium and pyridinium ionic liquids did not remove organic acids from the hydrocarbon feed at the conditions employed, but caused a net increase in the Total Acid Number of the hydrocarbon.
This application claims the benefit of U.S. Provisional Application No. 61/291,289 filed Dec. 30, 2009.
| Number | Date | Country | |
|---|---|---|---|
| 61291289 | Dec 2009 | US |
