METHOD FOR PRODUCTION OF MINERAL OILS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application Nos.60/903,763, filed February 26, 2007; and 60/910,207, filed April 4, 2007, the entirety of each is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] Mineral oils are liquid hydrocarbon products with very little (generally less than 1%) aromatic content. Mineral oils frequently are used as baby oils, in oil well drilling mud, in low odor industrial and household products, for aluminum rolling, and for many other uses and products. Waxes and petrolatum are similar but generally have a higher boiling point and higher viscosity.

[0003] The production of mineral oils was formerly achieved via sulfonation with oleum; however, environmental considerations made this process obsolete. Hydrogenation is more commonly used at present due to its wide range of uses and qualities. But high capital costs, and the requirement for relatively sophisticated operators, make this process less economical. Synthesis of mineral oils is also an option but is even less suitable for medium- to small-size operations.

[0004] Production of mineral oils by liquid-liquid extraction (LLE) of a light distillate feedstock is theoretically possible. In a typical LLE process, aromatic hydrocarbons (and other unsaturated and polar species) can be removed from non-polar (saturated) hydrocarbons by extraction with a polar solvent which is immiscible with non-polar hydrocarbons. This extraction step results in formation of two liquid phases conventionally called the extract (containing the desired hydrocarbons) and the raffϊnate (a mixture containing the undesired species). Many solvents, and mixtures of solvents, have been used for LLE in the production of "BTX" (benzene, toluene, xylene) as well as lubricant base oil preparation.

[0005] For economic and environmental reasons, it is desirable to recover the extraction solvent from the extract stream. In some cases, solvent can be recovered by distillation of the raffmate and/or the extract. However, when the boiling range of two or more components,

including the solvent, are similar, distillation becomes difficult.

[0006] When a sufficiently hydrophilic extraction solvent is used, the extraction solvent can be separated from the extract by addition of water (or other solvents or solvent mixtures) to the extract stream. The addition of water results in the formation of a biphasic system in which the water and extraction solvent form an aqueous phase, and the (partially purified) desired product or extract forms a second phase. In order to recover the extraction solvent, and the aqueous phase can be distilled. Water can also be used to control the solubility of aromatic species in the solvent.

[0007] However, this LLE approach has certain difficulties. First, the distillation of large quantities of water requires large energy inputs with associated costs. Second, mixtures of water, hydrocarbon, and solvent may form emulsions rather than cleanly separating into two phases as described above; these emulsions can be difficult to manage. Third, the process results in formation of an aromatic phase which is of limited economic value because it typically contains considerable non-aromatic hydrocarbon. It is therefore more expensive to provide hydrocarbon products which boil at a temperature range similar to the extraction solvent, and which have very low aromatic content.

SUMMARY OF THE INVENTION

[0008] The present invention provides improved methods and systems for preparing highly purified mineral oils. The inventive methods and systems are generally less expensive and more environmentally-friendly than previously-known methods.

[0009] In one aspect, the invention provides an improved liquid-liquid extraction process, in which a mixture of solvents is used for extraction, resulting in a mineral oil with low levels of aromatics (e.g., less than 5% or less thanl%), and purified aromatics with low levels of mineral oil (e.g., less than 1%), which allows for efficient production of purified mineral oil and highly valuable purified aromatics. In certain embodiments, the invention also features improved management of emulsions, which makes the process more feasible. In certain embodiments, the invention also features modem purification technologies, such as reverse osmosis, which reduces operating costs.

In one aspect, the invention provides a process for producing mineral oil from a light hydrocarbon feedstock. The process comprises the steps of a) contacting the light hydrocarbon feedstock with

an extraction solvent; (b) separating a mineral oil phase from the extract phase;

(c) contacting the extract phase with water to form a wetted solvent phase and an aromatic phase;

(d) separating the wetted solvent phase from the aromatic phase; (e) distilling the purified wetted solvent to recover regenerated solvent and regenerated water, (f) contacting the aromatic phase of step (d) with the regenerated water and contacting the mineral oil phase of step (b) with the regenerated water to remove solvent traces from the aromatic phase of step (d) and the mineral oil phase of step (b). In certain embodiments, the solvent comprises up to 20% propylene carbonate in N-methyl pyrrolidone.

In certain embodiments, the process further comprises the steps of: (h) contacting the aromatic phase of step (d) with regenerated water of step (e) to provide a purified aromatic phase and water with solvent traces; (i) contacting the wetted solvent phase of step (d) with the purified aromatic phase of step (h) to provide a partially purified wetted solvent and an aromatic phase; and (j) contacting the partially purified wetted solvent of step (i) with the light hydrocarbon feedstock to provide a purified wetted solvent and a modified feedstock (e.g., a feedstock enriched in saturates extracted from the solvent). In certain embodiments, the water with solvent traces from step (h) is purified with reverse osmosis to remove solvent traces prior to contacting the aromatic phase of step (d) and the mineral oil phase of step (b). In certain embodiments, the purified wetted solvent of step (j) is further treated by nano-filtration.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention is further described below with reference to the following non-limiting examples and with reference to the following figures, in which:

[0011] Figure 1 is a flow diagram illustrating one embodiment of a purification process according to the invention.

[0012] Figure 2 is a flow diagram illustrating another embodiment of process for producing mineral oils.

[0013] Figure 3 is a schematic showing the flow of liquids in one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention relates generally to improved methods and systems for the production of mineral oils from light distillate feedstock.

[0015] The hydrocarbon feedstock which may be treated by the process of this invention is preferably a lighter boiling feedstock (such as a distillate, preferably a light distillate) from petroleum or synthetic sources. In particular, the feedstock may be derived from a synthetic liquid such as shale oil, coal liquid, or mixtures thereof.

[0016] The solvent used for extraction of the hydrocarbon feedstock is preferably a mixture of N-methyl pyrrolidone (NMP) and propylene carbonate (PC). NMP is a superior extraction solvent because it effectively solubilizes aromatics, permitting the production of a high quality, low-aromatic mineral oil. NMP is also relatively hydrophilic; therefore, addition of water to an NMP-aromatic solvent system results in effective separation and recovery of the aromatics. In addition, NMP is relatively environmentally friendly and has low toxicity, and boils at a moderate temperature (especially under vacuum), so high temperature distillation, and its attendant costs and hazards, is not required.

[0017] In certain embodiments, the solvent mixture comprises at least 75% NMP and not more than 25% PC; in certain embodiments, the solvent mixture comprises at least 80% NMP and not more than 20% PC. PC has low water affinity (e.g., it accepts less than 10% of water-in-PC dilution), but in mixtures of up to 20% PC in NMP, this characteristic is not significant in the NMP-PC mix. Thus, in certain embodiments, PC is used for selectivity control, i.e., to minimize the amount of aliphatics that can become dissolved in the solvent, and thereby to maximize the purity of the aromatics.

[0018] The contacting of the feedstock with the solvent (e.g., a blended solvent) is carried out, and/or the mixture is maintained, at a temperature of from about 5 to about 20 ⁰ C, preferably from about 5° to 10 ⁰ C, below the critical solution temperature of the mixture. The critical solution temperature is the highest temperature at which the particular mixture of solvents and feedstock becomes miscible, i.e., the solvents form only one homogeneous phase. The temperature to which the components of the mixture are exposed should maintain the solvent- feedstock system as a two-phase system. The exact temperatures which will be employed for this purpose depend on many factors such as the specific feedstock utilized and particular solvent

system employed. In addition, the temperatures employed during the contacting must be sufficient to achieve relatively low phase viscosities in continuous countercurrent towers if such towers are employed to extract the solvents.

[0019] One of the two phases formed during this contacting period where the temperature is adjusted to the appropriate level, sometimes referred to herein as the extract, will generally contain the asphaltenes, aromatics, and a small amount of low molecular weight polars from the feedstock, as well as most of the solvent. The second phase, sometimes referred to herein as the mineral oil phase, generally contains non-polar molecules (also known as saturates) and a lesser amount of polars from the feedstock along with some amount of solvent.

[0020] The extraction process of this invention is particularly suited for being conducted in a continuous mode with reference to the schematic diagram of FIG. 1. As shown in FIG. 1, a feedstock 30 from line 2 is contacted in a first contacting zone 4 with a solvent 32 via line 6. First contacting zone 4 may be any apparatus suitable for obtaining an intimate mixture of hydrocarbon feedstock and solvents at temperatures up to and above 100 ⁰ C, such as a contacting tower or a mixer-settler. The mineral-oil containing phase 34 is drawn off, and the remaining phase 36 (containing the aromatics and the solvent 40) is transferred via line 8 through area 10 to second contacting zone 12.

[0021] Second contacting zone 12 may be any apparatus where mixing and separation of the liquid phases may take place, such as a settler where the aromatics-containing phase settles to the bottom. Water 42 is added via line 20 to the mixture in second contacting zone 12; the aromatic-containing layer then separates and is removed from the second contacting zone 12 via line 14 as aromatics 44. The remaining phase is transferred to separation zone 18, where the water is removed and recycled to second contacting zone 12 via line 20 and the solvent is recovered and returned via line 6 for further extraction procedures.

[0022] The separation zone 18 preferably comprises a distillation tower for separating water from the extraction solvent. However, the water and NMP need not be separated from each other by distillation; instead, the distilled mixture of water and NMP can then be separated by a two-stage process: an evaporator to recover the solvent to its original condition (not more than about 3% water); and reverse osmosis to yield highly purified water. For such a reverse osmosis process, it is desirable to use a reverse osmosis membrane which is resistant to NMP.

[0023] When a mixer is required, many conventional mixers known in the art can be used. For example, static mixers include, for example, Multiflux, Sulzer, PMR, McHugh, Komax and Honeycomb, X, Ross-ISG and helical mixers.

[0024] In general, water must be purified prior to use in the removal of remaining traces of solvent in the aromatics and in the aliphatics. While water can be purified by any technique known in the art, it is somewhat difficult to completely separate pure water from solvents such as NMP by distillation. Advantageously, the water can be purified in two steps, e.g., by (i) contacting the water with the aromatic (to remove aromatics from the water and to remove traces of solvent from the aromatic) and (ii) purifying the water by reverse osmosis to remove traces of solvent from the water. As noted elsewhere herein, it is necessary to use a reverse osmosis membrane which is resistant to NMP in this step; for example, polytetrafluoroethylene polymer membranes are relatively NMP resistant.

[0025] Upon mixing of two immiscible phases, it is known that emulsions can form. Emulsion formation is undesirable because it slows processing and increases the likelihood of contamination of the desired products.

[0026] It is also desirable to free the wetted solvent from aromatics and aliphatics before distillation. This can advantageously be achieved in three steps:

(i) The wetted solvent is mixed with the same aromatic produced in the process disclosed herein, but it is preferably cleaned of solvent traces. In this step, the ratio of aromatics to solvent can be about 2:1; therefore a recirculation scheme must be used (the overall production of aromatics in the process does not generally approach a level required to sustain this ratio); (ii) The wetted solvent is cleaned of aliphatics, by contacting the wetted solvent with the feedstock for the process. Aliphatics are a major cause of emulsions, specially the denser type which do not separate fast enough in the decanters. Before this step, the aromatics must be removed (see step (i)) and taken out of the process. If aliphatics are removed (e.g., by contacting with the raw material (feedstock), but aromatics remain to contaminate the wetted solvent, then some aromatics will go back into the process and potentially diminish the capacity of the process.

(iii) If steps (i) and (ii) are not sufficient to provide clean wetted solvent, a nano-filtration step can be used to further reduce the hydrocarbon content in the wetted solvent.

[0027] Thus, in certain embodiments, the invention provides a process in which distilled

water is freed of solvent and aromatics, and the recovered solvent is freed from aromatics and aliphatics. This can be accomplished without using additional inputs by careful recirculation and purification of the materials (water, solvent, feedstock) used in the process, e.g., as described below.

[0028] In certain embodiments, the invention features a process depicted schematically in FIG. 2. As shown in FIG. 2, the extraction process begins when the feedstock and solvent enter stage 100. The solvent and the raw material should be intimately mixed, e.g., in very small drops, in order for the solvent to extract the aromatics. Then the solvent and the (now de-aromatized) hydrocarbon (also known as aliphatic or saturated phase) must be separated, e.g., by mixing the feedstock and the solvent in a static mixer and then separating them by settling in a decanter. For efficient extraction, it is contemplated that stage 100 will include 3-6 countercurrent extraction stages, and that the solvent will be present at about 200%-300% by weight of the feedstock. However, additional solvent or countercurrent extraction stages can be used if required (e.g., with feedstocks containing larger amounts of aromatics). An equivalent mass- transfer column can also be used. Thus, the inputs into stage 100 are feedstock and solvent; outputs are solvent plus aromatics (extract) and an aliphatic phase retaining traces of solvent.

[0029] At stage 200 of FIG. 2, the aliphatic material is further purified by removal of remaining solvent. In certain embodiments, the solvent so separated can be recovered and re-used, as described herein. The aliphatic phase and purified water are mixed, e.g., in a static mixer, and then separated, e.g., by settling in a decanter. For efficient extraction, it is contemplated that stage 200 will include 1-2 countercurrent extraction stages, and that the water will be present at about 100%-200% by weight of the aliphatic. An equivalent mass-transfer column can also be used. Thus, the inputs into stage 200 are partially-purified aliphatic and water; outputs are water (with some solvent) and purified aliphatic phase.

[0030] At stage 300 of FIG. 2, aromatic material is separated from solvent. In certain embodiments, the solvent so separated can be recovered and re-used, as described herein, and the aromatic can be further purified so as to be sufficiently pure to be used or re-sold. The solvent (extract) phase from stage 100 is mixed with water from stage 200, e.g., in a static mixer, and then separated, e.g., by settling in a decanter. For efficient extraction, it is contemplated that stage 300 will include one countercurrent extraction stage, and that the water will be present at about 80% by weight of the solvent phase (extract). An equivalent mass-transfer column can also be used. Thus, the inputs into stage 300 are solvent phase (extract) from stage 100 and water with solvent traces from stages 200 and 600; outputs are wetted solvent (with traces of

hydrocarbons) and aroniatics (with traces of solvent).

[0031] At stage 400 of FIG. 2, aromatic material is purified. At this stage, the traces of solvent remaining in the aromatic phase can be recovered, and any aromatics remaining in the distilled water are transferred to the aromatic phase. The aromatic material from stage 300 is mixed with water, e.g., in a static mixer, and then separated, e.g., by settling in a decanter. For efficient extraction, it is contemplated that stage 400 will include one countercurrent extraction stage, and that the water will be present at about 100-200% by weight of the aromatic phase. An equivalent mass-transfer column can also be used. Thus, the inputs into stage 400 are aromatic phase and water; outputs are water (with traces of solvent) and purified aromatics.

[0032] At stage 500 of FIG. 2, the wetted solvent is cleaned of traces of aromatics before distillation, to avoid contamination of the aliphatic material at stage 200 and to ensure that the solvent capacity is maximized for re-use in Stage 100. The aromatic purified in stage 400 is mixed with wetted solvent from stage 300, e.g., in a static mixer, and then separated, e.g., by settling in a decanter. For efficient extraction, it is contemplated that stage 500 will include one extraction stage, and that the wetted solvent will be present at about 50-100% by weight of the aromatic phase. A recirculation circuit will preferably be used. An equivalent mass-transfer column can also be used. Thus, the inputs into stage 500 are aromatic phase and wetted solvent; outputs are purified aromatics (with traces of solvent) and wetted solvent with only traces of aliphatic.

[0033] At stage 600 of FIG. 2, the aromatics are again purified, to remove (and re-use) traces of solvent and ensure pure aromatics for use or sale. The aromatic from stage 500 is mixed with pure water, e.g., in a static mixer, and then separated, e.g., by settling in a decanter. For efficient extraction, it is contemplated that stage 600 will include one extraction stage, and that the water will be present at about 100-200% by weight of the aromatic phase. An equivalent mass- transfer column can also be used. Thus, the inputs into stage 600 are aromatic phase from stage 500 and pure water; outputs are purified aromatics and water with traces of solvent.

[0034] At stage 700 of FIG. 2, the distilled water is purified before use in stages 200 and 600, to ensure that the water is free of solvent. Water is purified by reverse osmosis with an NMP- resistant membrane. Thus, the input into stage 700 is water with traces of solvent; outputs are purified water and rejected water with higher concentrations of solvent.

[0035] At stage 800 of FIG. 2, the wetted solvent is purified, to remove traces of aliphatic that could contaminate solvent during distillation of the solvent. The wetted solvent from stage 500 is mixed with the feedstock, e.g., in a static mixer, and then separated, e.g., by settling in a decanter. For efficient extraction, it is contemplated that stage 800 will include one extraction stage, and that the feedstock will be present at about 100-200% by weight of the wetted solvent. An equivalent mass-transfer column can also be used. Thus, the inputs into stage 800 are raw material and wetted solvent with traces of aliphatics; outputs are raw material and cleaned wetted solvent.

[0036] If desired, an optional stage 900 (not shown in FIG. 2) can be employed, in which the wetted solvent is purified by ultrafiltration.

[0037] The invention provides several advantages. Using the process of the invention, highly purified aromatics and aliphatics (such as mineral oil) can be obtained, using less costly, environmentally damaging, and operationally risky processes than previously known processes (i.e., sulfonation and hydrogenation). Thus, the present invention provides an efficient, economical, and environmentally friendly process for producing aliphatic and aromatic products from a feedstock.

[0038] In certain embodiments, the aromatics recovered from the process according to this invention can have not more than 10% aliphatics, more preferably not more than 5% aliphatics after purification according to the disclosed process. More highly purified aromatics generally can be sold for a higher price than less-purified aromatics. In addition, a higher proportion of aliphatics are recovered from the raw material, increasing the overall efficiency of the process.

[0039] In certain embodiments, the water used in the extraction process has no more than 0.5% NMP after purification and before recirculation and re-use of the water. In certain embodiments, the water has no more than 0.2% or 0.1% NMP after purification and before recirculation and reuse. Low levels of NMP in the water permits better recovery of the NMP in the final products, further reducing operating costs.

[0040] In certain embodiments, the water used in the extraction process has no more than 1% hydrocarbons after purification and before recirculation and re-use of the water. In certain embodiments, the water has no more than 0.5% or 0.1% hydrocarbons after purification and before recirculation and re-use. As a result, the disclosed process is capable of providing an aliphatic

product with a very low content of aromatics (e.g., less than 1000 ppm, 500 ppm, or 100 ppm).

[0041] In certain embodiments, the solvent (NMP) used in the extraction process has no more than 1 % hydrocarbons after purification and before recirculation and re-use of the solvent. In certain embodiments, the water has no more than 0.5% or 0.1% hydrocarbons after purification and before recirculation and re-use. Thus, the present invention can use lower amounts of solvent and therefore lower amounts of energy to evaporate, and recover, the water, via a lower solvent-to-raw material ratio.

[0042] The amount of contaminants present in the aliphatics, aromatics, water and solvent can be determined according to methods known to one of skill in the art, for example, by gas chromatography (GC), mass spectrometry (MS), nuclear magnetic resonance spectroscopy (NMR), or by combined techniques such as GC/MS.

[0043] Example 1

[0044] Figure 3 shows a schematic diagram of a system according to one embodiment of the present invention. Referring to Figure 3:

[0045] Processor 100 receives the hydrocarbon feedstock via fluid conduit or pipe 8A; extraction solvent is also supplied via a fluid conduit, e.g., a conduit from the distillation unit 1000 as shown in Fig. 3. After mixing of the feedstock with the extraction solvent, the aliphatic (mineral oil) fraction (which at this stage will contain traces of solvent) is separated and transferred via conduit IA to processor 200, while the extraction solvent phase (which also contains aromatics extracted from the feedstock) is transferred to processor 300.

[0046] At processor 200, water (received from processor (e.g., reverse osmosis unit) 700 via conduit 7B) is mixed with the aliphatic fraction from processor 100; the phases are separated, removing much of the remaining traces of extraction solvent from the aliphatic fraction (and preferably recovering the solvent for reuse in the aqueous fraction). After separation, the aliphatic fraction is removed via a conduit and prepared for further processing or for sale, while the aqueous fraction (which contains some solvent extracted from the aliphatics) is removed via conduit 2B to processor 300.

[0047] At processor 300, the aqueous fraction from processor 200 is mixed with the

aqueous fraction from processor 600 and with the extraction solvent phase from processor 100. Optionally, wetted solvent may be added from reverse osmosis unit 700 via conduit 7A, and additional recovered hydrocarbons may be added from mixer 900 via conduit 9A. After mixing, the phases are separated, and the aromatics-containing phase (at this point containing some traces of solvent) is drawn off via conduit 3A to processor 400. The solvent-containing phase is transferred to processor 500 via conduit 3B.

[0048] At processor 400, water from the distillation unit 1000) is added to the aromatics-containing phase from processor 300, to remove traces of extraction solvent from the aromatics and to transfer hydrocarbon traces from the distilled water to the aromatics phase. After mixing, the aqueous phase (now containing traces of extraction solvent) is removed via conduit 4B to reverse osmosis unit 700, while the purified aromatics phase is transferred through conduit 4A to processor 500.

[0049] At processor 500, which is preferably capable of high volume recirculation of the aromatics phase from processor 400, the aromatics phase is mixed with the solvent-containing phase from processor 300, to recover traces of aromatics from the solvent-containing phase. After the phases are separated, the aromatics phase (now having traces of extraction solvent) is transferred via conduit 5A to processor 600, while the solvent-containing phase (now having traces of aliphatics but with most of the aromatics removed) is drawn off to processor 800 via conduit 5B.

[0050] At processor 600, the aromatics phase from processor 500 is combined with water received via conduit 7C from reverse osmosis unit 700. After mixing and separation, the aromatics phase, now largely free of extraction solvent, is removed via conduit 6 A to be stored for further processing or sale.

[0051] At processor 700, extraction solvent present in the aqueous phase recovered from processor 400 is separated from the water by reverse osmosis. The separated extraction solvent can be recycled, e.g., by transfer to processor 300 via conduit 7A. After reverse osmosis treatment, the purified water is recycled, e.g., to processors 200 and 600 via conduits 7B and 7C.

[0052] At processor 800, the wetted solvent received from processor 500 via conduit 5B is mixed with the hydrocarbon feedstock. This mixing removes traces of hydrocarbons from the extraction solvent; after phase separation, these hydrocarbons are extracted into the feedstock and

are transferred with the feedstock to processor 100 via conduit 8A. The wetted solvent is removed via conduit 8B to processor 900.

[0053] At processor 900, the extraction solvent is treated by ultrafiltration to remove traces of hydrocarbons from the extraction solvent. These recovered hydrocarbons can be discarded or can be recycled, e.g., by transferring to processor 300 via conduit 9A. The wetted solvent, now largely tree of hydrocarbons, is recovered for recycling or reuse. For example, water can be removed from the wetted extraction solvent by distillation as described below.

[0054] The wetted solvent passes through a conduit to distillation unit 1000, where the wetted solvent is heated to cause vaporization and separation of the solvent from the remaining water. The distillation process can be performed under reduced pressure to reduce the boiling point of the components and thereby minimize the damage to the solvent. Also, the distillate may be fractionated using distillation columns or other means to ensure separation of the components. Some modern distillation technologies allow for very low operating costs, e.g., by recovery of heat (energy inputs). Technologies are known in the art for recovery of up to 95% of heat input in the recovery of sweet water from sea water, and such technologies can be used to reduce the energy costs. The recovered solvent can be returned via a conduit 1OA to processor 100 for reuse; similarly, the recovered water can be returned via conduit lOBto processor 400 for reuse.

[0055] The disclosures of each and every patent, patent application and publication cited herein are hereby incorporated herein by reference in their entirety.

[0056] Although the invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of the invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention. The claims are intended to be construed to include all such embodiments and equivalent variations.