Method for separating sulfone from a hydrocarbon stream having a small concentration of sulfone

Abstract: Described is a process for separating sulfone from a hydrocarbon having a small concentration of said sulfone by use of water as an extraction solvent.

Description: The present invention relates to a process for separating sulfolane from a hydrocarbon stream which contains a small concentration of sulfolane. It has recently been discovered that sulfolane additives can be utilized in combination with traditional hydrogen fluoride alkylation catalysts as a means for reducing the volatility of the resultant catalyst mixture. An alkylation catalyst which is used in processes for alkylating olefin hydrocarbons with isoparaffin hydrocarbons to produce high octane alkylate products is, for example, known from the European Patent Application No. 0 568 089. That catalyst comprises a mixture of a hydrogen halide and a sulfone. One side effect from utilizing a sulfolane additive in combination with a hydrofluoric acid alkylation catalyst is that small concentrations of sulfolane become dissolved in the resultant alkylate product. The small concentration of sulfolane in the alkylate product can have a negative impact on the alkylate as a gasoline blend component. Thus, even though the concentration of sulfolane is very small, it is desirable to remove such small concentrations of sulfolane from an alkylate product in order to prevent its negative economic consequences on refiners who use the alkylate as a gasoline blending component. It is thus an object of this invention to provide a method for removing sulfolane that is contained in an alkylate reaction product. It is further an object of this invention to provide a process for separating a small concentration of sulfolane contained in an alkylation reaction product which contains a concentration of sulfolane, which concentration is less than 1 wt.-%. Thus, the process of the present invention includes separating sulfolane from a hydrocarbon stream which contains a concentration of sulfolane. This process includes extracting the sulfolane from the hydrocarbon stream by contacting such hydrocarbon stream with water. The water serves as an extraction solvent and thus extracts at least a portion of the sulfolane contained in the hydrocarbon stream and provides an extract stream which is enriched with sulfolane and comprises water. A raffinate stream is produced which has a concentration of sulfolane that is smaller than the concentration of sulfolane in the original hydrocarbon stream which is contacted with the extraction solvent. As mentioned above, the present invention relates to a method for removing sulfolane from a hydrocarbon stream having a sulfolane concentration of less than 1 weight percent. The hydrocarbon stream is contacted with a water solvent, and an extract stream enriched with sulfolane and comprising water is recovered. Also recovered is a raffinate stream comprising a hydrocarbon having a concentration of sulfolane that is below that of the sulfone concentration of the hydrocarbon stream. In the accompanying drawings: FIG. 1 provides a schematic representation of the process which is one embodiment of the instant invention; and FIG. 2 is a plot of extraction data for water as an extractant for removing sulfolane from alkylate. The process of this invention contemplates the resolution of problems associated with a gasoline blending component containing a small concentration of a sulfolane. The sulfolane, in sufficient concentrations, is a contaminant to a gasoline end-product when it is contained in a gasoline blending component such as an alkylate product produced by the catalytic alkylation of olefins and isoparaffins. In particular, recently it has been discovered that a novel catalyst which utilizes sulfolane as one component in combination with hydrogen fluoride can provide for a suitable alkylate product. One problem encountered, however, is that when utilizing a mixture of the hydrogen fluoride and sulfolane as an alkylation catalyst, due to the slight solubility of sulfolane in hydrocarbon, there is a small concentration of sulfolane that passes from the alkylation reaction system along with the alkylate end-product. It is, thus, critical that a significant portion of the sulfolane contained in the alkylate end-product be removed prior to utilizing it as a gasoline blending component. The need to remove the sulfolane is important, even though the sulfolane is only slightly soluble in the alkylate hydrocarbon and the concentration typically will not exceed 2 or 3 weight percent of the alkylate product. It is, therefore, important to remove a significant portion of the sulfolane in a hydrocarbon stream, which contains such sulfolane. Generally, it is necessary that at least a portion of the sulfolane is removed from the hydrocarbon stream, which can be at least 70 weight percent of the sulfolane concentration. Preferably, it is desirable to remove at least 80 weight percent of the sulfolane contained in the hydrocarbon stream and, most preferably, it is desirable to remove at least 90 weight percent of the sulfolane in the hydrocarbon stream. In fact, the novel process described herein has the exceptional ability under proper process conditions of removing at least 99 weight percent of the sulfolane contained in the hydrocarbon stream when the sulfolane concentration is less than 1 weight percent. The hydrocarbon stream of the invention generally will include hydrocarbons having from 3 to 12 carbon atoms and with the most common hydrocarbons being paraffins. Specifically, the hydrocarbon stream will be an alkylate hydrocarbon product comprising paraffins produced by the catalytic reaction of olefins and isoparaffins of an alkylation process. The alkylation catalyst utilized in the alkylation process comprises sulfolane and hydrogen fluoride. The alkylation catalyst utilized in the alkylation of the olefins and isoparaffins generally will have a weight ratio of hydrogen fluoride to sulfolane in the range of 1:1 to 40:1. A preferred weight ratio of hydrogen fluoride to sulfolane in the alkylation catalyst can range from 2.3:1 to 19:1 and, more preferably, it can range from 3:1 to 9:1. Alkylation processes contemplated in the present invention are those liquid phase processes, wherein mono-olefin hydrocarbons such as propylene, butylenes, pentylenes, hexylenes, heptylenes, and octylenes are alkylated by isoparaffin hydrocarbons such as isobutane, isopentane, isohexane, isoheptane, and isooctane for production of high octane alkylate hydrocarbons boiling in the gasoline range and which are suitable for use in gasoline motor fuel. Preferably, isobutane is selected as the isoparaffin reactant, and the olefin reactant is selected from propylene, butylenes, pentylenes and mixtures thereof for production of an alkylate hydrocarbon product comprising a major portion of highly branched, high octane value aliphatic hydrocarbons having at least seven carbon atoms and less than ten carbon atoms. Sulfolane that is to be removed from hydrocarbon streams according to this invention has the formula and offers the advantage of being liquid at process operating conditions of concern herein. Because of the slight solubility of sulfolane in the alkylate hydrocarbon product, there will be a small concentration of sulfolane therein. The sulfolane concentration is less than 1 weight percent of the total weight of the alkylate hydrocarbon product and, specifically, it can range from 0.01 weight percent to 1.0 weight percent depending on processing conditions. Ordinarily, the sulfone concentration in the alkylate hydrocarbon product can range from 0.1 weight percent to 0.9 weight percent and, most likely, it can range from 0.15 weight percent to 0.5 weight percent. Because of the contamination caused by an excessive concentration of sulfolane in the alkylate hydrocarbon product, it is desirable to remove at least a portion of the sulfolane in the alkylate hydrocarbon product so as to have a gasoline blending component that can suitably be blended with other gasoline components to produce a desirable gasoline end-product. Thus, a substantial portion of the sulfone content of the alkylate hydrocarbon product is removed by the inventive process which can be at least 70 weight percent of the sulfolane contained in the alkylate hydrocarbon product. Preferably, it is desirable to remove at least 80 weight percent of the sulfolane of the alkylate hydrocarbon product and, most preferably, it is desirable to remove at least 90 weight percent of the sulfolane. Because of the efficiency of the process of this invention, it is even possible under appropriate process conditions to remove upwardly to 99 weight percent, or more, of the sulfolane contained in the hydrocarbon alkylation product. The alkylate hydrocarbon product is contacted with an extraction solvent comprising, consisting of, or consisting essentially of, water. Any suitable contacting means for contacting the extraction solvent with the alkylate hydrocarbon product can be used for providing intimate mixing or contacting the extraction solvent with the alkylate hydrocarbon product. Such contacting means as plate columns, packed columns or single stage contacting means, which include static mixers and mechanically agitated vessels, may be used. Thus, any means which provides for the intimate contacting or mixing of the extraction solvent with the alkylate hydrocarbon product may be used as a part of this invention. Any amount of extraction solvent relative to the quantity of the alkylate hydrocarbon product can be utilized in the process, provided the amount of extraction solvent contacted with the alkylate hydrocarbon product is effective for the removal of at least a portion of the sulfolane contained in the alkylate hydrocarbon product. Generally, contacting efficiency requires an amount of extraction solvent with the alkylate hydrocarbon product such that the volumetric ratio of water contacted with the alkylate hydrocarbon is at least about 0.01:1 water to hydrocarbon. Preferably, the volumetric ratio of water contacted with hydrocarbon is at least about 0.05:1 and, most preferably, the volumetric weight ratio can exceed 0.1:1. Economics will generally set the upper limit for the volumetric ratio of water to alkylate hydrocarbon product. An extract stream enriched with sulfolane and comprising water is recovered from the contacting means. The extract stream will contain at least a portion of the sulfolane contained in the alkylate hydrocarbon product and can contain, as earlier described herein, at least 70 weight percent of the sulfolane contained in such alkylate hydrocarbon product. Also recovered from contacting means is a raffinate stream which comprises the alkylate hydrocarbon product and has a reduced sulfolane concentration below that of the alkylate hydrocarbon product. Referring now to FIG. 1, there is presented a schematic representation of process 10 which depicts a liquid-liquid extraction process system utilized for the extraction of a sulfolane solute from an alkylate hydrocarbon product. The alkylate hydrocarbon product stream, which comprises an alkylate product having a concentration of sulfolane, passes by way of conduit 12 to extractor 14. Extractor 14 defines a contacting zone and provides contacting means for contacting the alkylate hydrocarbon product with an extraction solvent comprising water. The extraction solvent is introduced into extractor 14 via conduit 16 which is operably connected in fluid flow communication between fractionator 18 and extractor 14. An extract is recovered from extractor 14 by way of conduit 20 which is operatively connected in fluid flow communication between extractor 14 and fractionator 18. The recovered extract comprises water with at least a portion of the sulfolane contained in the alkylate hydrocarbon product and passes to fractionator 18. Fractionator 18 defines a fractionation zone and provides for the separation of water and sulfolane. A raffinate stream, which is the alkylate hydrocarbon product stream having a substantially reduced concentration of sulfolane contained therein passes from extractor 14 by way of conduit 22. The recovered water from fractionator 18 may, if desired, be returned to extractor 14 by way of conduit 16. Makeup water is conveyed to extractor 14 through conduit 23. The sulfolane recovered from the extraction solvent passes by way of conduit 24 from fractionator 18 to vacuum tower 26. Conduit 24 is operatively connected and provides for fluid flow communication between fractionator 18 and vacuum tower 26. Vacuum tower 26 defines a fractionation zone and provides means for separating the sulfone from the water contained in the sulfolane stream exiting fractionator 18. The overhead from vacuum tower 26 passes by way of conduit 28 and comprises primarily water recovered from the fractionator 18 bottoms stream. The purified sulfolane will pass from vacuum tower 26 by way of conduit 30. The recovered sulfolane, which passes from vacuum tower 26 by way of conduit 30, can be recycled or reused as sulfolane in an alkylation reaction process. The water recovered by way of conduit 28 can be either disposed of or reused as an extraction solvent. The following examples are provided to further illustrate the present invention. The examples are provided by way of illustration only. They are not intended as a limitation upon the invention as set out in the appended claims. EXAMPLE 1 The following calculated example is to illustrate the benefits achievable from the novel process as illustrated in FIG. 1. Table I shows the mass flows corresponding to the numbered streams of FIG. 1. As can be seen from the material balance of Table I, the alkylate hydrocarbon product passing through conduit 12 contains more than 0.1 weight percent sulfolane, and the raffinate stream contains less than 0.001 weight percent sulfolane. Over 99 weight percent of the sulfolane contained in the alkylate hydrocarbon product is removed therefrom by the novel process. Material Balance for Process of Figure 1 Stream 12 16 20 22 23 24 28 30 Mass Flows Pentanes 118828.2 0.3 0.3 118828.2 0.0 0.0 0.0 0.0 Hexanes 118828.2 0.0 0.0 118828.2 0.0 0.0 0.0 0.0 Heptanes 962097.5 0.9 0.9 962097.5 0.0 0.0 0.0 0.0 Octanes 1950013.0 0.1 0.1 1950013.0 0.0 0.0 0.0 0.0 Nonanes 124974.5 0.0 0.0 124974.5 0.0 0.0 0.0 0.0 C10+ 821143.8 0.0 0.0 821143.8 0.0 0.0 0.0 0.0 Water 0.0 377520.2 381335.5 3837.4 7652.7 3815.3 3800.7 14.6 Sulfolane 4889.2 4.0 4856.5 36.7 0.0 4852.5 0.5 4852.0 Total 4100774.2 377525.5 386193.3 4099759.2 7652.7 8667.8 3801.2 4866.6 EXAMPLE II Example II presents data obtained from extraction experiments using water as an extraction solvent for removing sulfolane from alkylate. An alkylate feed containing, on average, 1082 wppm sulfolane was charged to a commercially available 2.54 cm (1 inch) stirred York-Scheibel extractor containing approximately 8 theoretical stages. The data obtained are present in Table II and are charted in FIG. 2. As the data show, water can be an effective solvent for extracting sulfolane contained in a hydrocarbon solution. The water solvent is effective in removing more than 99 weight percent of the sulfolane contained in an alkylate. The weight percent sulfolane removed increases with increasing water to alkylate ratios. Water/Alkylate Ratio (vol/vol) Sulfolane Removal (weight percent) Alkylate/Water Ratio (vol/vol) 0.050 98.8 20 0.083 98.8 12 0.167 99.0 6 0.250 99.3 4 0.250 99.4 4 0.330 99.7 3 While this invention has been described in terms of the presently preferred embodiment, reasonable variations and modifications are possible by those skilled in the art. Such variations and modifications are within the scope of the described invention and the appended claims.

Claims: A process for separating sulfolane from a hydrocarbon stream, wherein the concentration of sulfolane in the hydrocarbon stream is less than 1 weight percent, said process comprising the step of contacting said hydrocarbon stream with an extraction solvent comprising water to extract at least a portion of the sulfolane from said hydrocarbon stream, thereby providing an extract stream, which is enriched with sulfolane and which comprises water, and a raffinate stream having a concentration of sulfolane smaller than the concentration of sulfolane in the hydrocarbon stream prior to the contacting step. The process of claim 1, wherein the extract stream and the raffinate stream are recovered. The process of any of the preceding claims, wherein at least 70 weight percent of the total sulfolane content in said hydrocarbon stream are extracted. The process of any of the preceding claims, wherein said hydrocarbon stream comprises paraffin compounds, in particular paraffins produced by the catalytic reaction of olefins and isoparaffins. The process of any of the preceding claims, wherein the weight ratio of water to hydrocarbon is at least 0.01.

Inventors: ELDRIDGE ROBERT B, HOVIS KEITH W, HUNT HAROLD R, ELDRIDGE, ROBERT B., HOVIS, KEITH W., HUNT, HAROLD R.
Applicants: PHILLIPS PETROLEUM CO, PHILLIPS PETROLEUM COMPANY
Application year: 1996
Main classification: C07C7
IPC codes: B01D11, C07C7, C07C21, C07C9