HK1182043B - Separation process - Google Patents

Description

Separation method

Cross Reference to Related Applications

This application claims the benefit of U.S. patent application 12/849,408 filed on 3.8.2010, which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates generally to a novel separation technique that uses the high surface area and coalescing properties of high surface area vertical hanging fibers to achieve rapid separation of two immiscible liquids. A particular application of the present invention relates to an improved separation process carried out in a single vessel wherein a mixture of disulfides and caustic solution produced in the process of removing sulfur and other contaminants from hydrocarbons including liquefied petroleum gas ("LPG") is separated into an aqueous caustic stream for recycle and an organic stream containing disulfides. The present invention significantly reduces separation residence time, thus reducing equipment costs and improving the overall efficiency of the process.

Background

The separation of two immiscible liquids into two distinct liquid layers for recovery is well known in the art. However, most separation devices rely primarily on large vessels that use gravity and long residence times to achieve phase separation or to form distinct layers. Alternatively, the forced physical separation of the two liquids is accomplished using complex mechanical equipment such as centrifuges (which also require large energy inputs) or using membranes with perm-selective characteristics. In the case of an urgent need for a more economical process, which is also more compact to save space, a smaller, more efficient separation is required.

The U.S. clean air act (US CleanAirAct) enactment in 1990 has peaked in North America, requiring gasoline pool (gasolin pool) to contain less than 10-wppm sulfur. From a practical standpoint, this means that refineries typically produce gasoline pools containing less than 5-wppm to allow for pipeline contamination of residual wall "attached" sulfur from previous shipments and the accuracy of test methods prescribed by the air cleaning laws.

Another consequence of the 1990 air clean laws was the shutdown of small, inefficient refineries in the united states, from 330 refineries in 1980 to less than 175 refineries in 2007. No new refineries have been built in the past 25 years, but refineries have expanded and imported to meet the gasoline demand in the united states.

Existing refineries have also turned to more severe fluid catalytic cracking unit operations to reduce burner fuel quantities while producing additional higher octane gasoline and increased olefin production. These olefins are propane/propylene and butane/isobutane/isobutylene. These are the feeds for the subsequent processing steps, which are the alkylation unit. Some refiners alkylate pentenes (pentenes) depending on their economic model.

Most refineries alkylate mixed butenes or mixed propylene and butenes using HF (hydrofluoric acid) or sulfuric acid alkylation units. Alkylation is the process of reacting isobutane with olefins to produce branched chain alkanes. Since sulfur is detrimental to the alkylation process, most refineries are equipped with caustic treatment systems to extract the easily extracted methyl-, ethyl-, and more difficult propyl-mercaptans present in the mixed olefinic liquefied petroleum gas ("LPG") stream.

Typically, the caustic treatment uses a liquid-liquid contactor, in some cases a FIBERContactors, marketed and sold by the Merichem Company (Houston, TX) and described in U.S. Pat. nos. 3,758,404; 3,977,829 and 3,992,156, all of which are incorporated herein by reference. To conserve caustic, a caustic regenerator is almost always used. A typical process flow scheme for treating LPG involves a first caustic treatment using at least one liquid-liquid contactor to extract sulfur contaminants (typically mercaptans) from the LPG feed, which produces a "spent" caustic solution rich in mercaptans or a so-called rich caustic solution (rich calstic), separating the LPG in the contactor, oxidizing the rich caustic solution to convert the mercaptans to disulfides (commonly referred to as disulfide oils ("DSO")) (which produces an "oxidized" caustic solution), and then separating the DSO from the oxidized caustic solution using a gravity separator. In some cases, a bed of granular coal (granular coal) is used in conjunction with a gravity settling device as a coalescer to further assist in the separation of DSO from the oxidized caustic. Once the DSO is removed, the regenerated caustic solution can then be recycled and mixed with fresh make-up caustic solution and used in the liquid-liquid contactor to treat the LPG feed.

As mentioned above, the problem of using gravity settling equipment in prior art processes isLong residence times are required, especially when used to separate DSO from an oxidized caustic solution. These long residence times adversely affect the economics of the caustic treatment process. In addition, the prior art gravity settlers are relatively large pieces of equipment. Also, forced separation devices such as centrifuges are complex mechanical devices that require a large energy input to operate. The present invention now solves the problems found in prior art separation devices when two immiscible liquids need to be separated and in particular when used to separate DSO from a caustic solution. In particular, the present invention implements the entire process in a single column. The present invention also utilizes two new improvements that can be used alone or in combination. The first involving the use of FIBERThe second involves the use of solvent injection (solvation) prior to oxidizing the spent caustic solution. The process of the present invention may also employ one or more refining steps (refining steps) after DSO separation to further remove residual DSO from the oxidized caustic solution. The greatly reduced residence time and reduction in equipment size translates into a very economical process for removing sulfur compounds from LPG and thus minimizes capital and operating costs. These and other advantages will become apparent from the following more detailed description of the invention.

Disclosure of Invention

As mentioned above, the present invention relates to the use of FIBER in a single column, column or vesselImproved separation methods for technically separating mixtures of at least two immiscible liquids and find particular application in the separation of DSO and other hydrocarbons from caustic solutions. The present invention achieves separation residence times many times faster than conventional gravity settlers, whether or not such conventional settlers use coal bed coalescers. Furthermore, the inventors have found that use in oxygenThe small amount of solvent added prior to the formation step further improves the separation performance relative to conventional gravity settling techniques.

Although FIBER is used in co-current (co-current) liquid-liquid contactor applications where two immiscible liquids are in contact with each other for enhanced mass transfer of certain compoundsThe technique is well known, but FIBER is not recognized in the artThe technology enables the actual separation of two immiscible liquids fed as a mixture in a single stream, and two or more contactor stages (contactors) each containing a plurality of vertically suspended fibers can be arranged in a convective manner to achieve even better separation without increasing solvent consumption. Despite the fact that the FIBER isThe technology has been commercialized for over 35 years, and a need for an efficient and improved separation process has been present. Also, one is not aware of FIBERThe technology is used for separation purposes because the fibers do not provide selectivity due to physical size limitations as does membrane technology, nor do they force physical separation by large energy inputs as does centrifuge technology. In contrast, the present invention utilizes large surface area fibers to form a thin liquid film in which a coalescing effect is achieved due to a strongly restricted path length.

In prior art processes, such as those taught in U.S. Pat. nos. 5,017,294(Derrieu) and 5,480,547(Williamson), the process is designed to separate aqueous droplets (where the aqueous phase is discontinuous) from organic hydrocarbons (which are continuous). When fibers are utilized, the aqueous droplets wet the fiber surface and coalesce to coat and flow out along the fibers. However, it is not known or clear when the fibers areSuch FIBER when wetted with an aqueous phaseWhether the technique can be used to separate organic droplets from a continuous aqueous phase. Also, it is not known what level of organic hydrocarbon separation can be achieved by this technique. In fact, the inventors have unexpectedly found that using FIBERTechniques are possible to separate organic droplets or dissolved organics from aqueous caustic solutions. In the present invention, the fibers are still wetted by the aqueous phase, however, the organic hydrocarbon droplets and dissolved organic matter coalesce, not because they are in contact with the fibers, but because their restriction is imposed by the short path that can move around in the aqueous phase film formed around the fibers. Further observations of the above-described prior art processes indicate that those processes are aimed at removing aqueous droplets or so-called free "water", which is not effective for removing dissolved water from the organic phase. In the present invention, the inventors removed free organic droplets as well as dissolved organic (solvent + DSO).

The disulfide oil or DSO used herein is meant to include mixtures of possible disulfides including dimethyl disulfide, diethyl disulfide, methylethyl disulfide and higher disulfides. Likewise, the term mercaptan is intended to include any kind of organosulfur compound similar to alcohols and phenols, but containing a sulfur atom in place of an oxygen atom. Compounds containing-SH as the predominant group attached directly to carbon are referred to as 'thiols'.

One aspect of the present invention involves oxidizing an organic stream to convert contaminants using only a single apparatus (i.e., a single column) followed by separation of at least two immiscible liquids, such as, but not limited to, water or a mixture of an aqueous solution and a hydrocarbon. This mixture is fed to the separation device as a single stream, wherein the single stream contacts the high surface area fiber bundle. When the mixture contacts and flows down a plurality of individual fibers, a thin film of liquid forms around each fiber, and due to the thorough exposure in the liquid filmThe limited path length achieves a coalescing effect. Together with the particularly high surface area of the fibre membranes, the two liquids separate rapidly from one another and form two distinct layers in the collecting zone at the bottom of the separating device. The two different liquid layers (the lower layer comprising the higher density liquid and the upper layer comprising the lower density liquid) allow each liquid layer to be withdrawn separately from the separation device. Examples of mixtures that benefit from the novel separation process of the present invention include, but are not limited to, mixtures of hydrocarbons such as propane, butane, pentane, condensate, natural gas, molecular sieve regeneration gas, diesel, kerosene, gasoline, lubricating oil, light crude oil, edible oil, biofuel, biodiesel reaction products, and any reaction product of a petrochemical plant such as polyols, POSM, and vinyl chloride, and water, with water or aqueous solutions, including acidic, neutral, or basic solutions that may contain dissolved salts and other organic or inorganic components. As using FIBERAs a result of the technology, the inventors have unexpectedly found that residence times are greatly reduced, by an order of magnitude, compared to conventional gravity settling equipment. The inventors believe that this is caused by the increased interfacial surface area compared to Conventional Gravity Separators (CGS), even where the CGS uses a coal bed as a coalescer.

The present invention also finds particular application in the removal of sulfur contaminants from LPG and other hydrocarbon streams, wherein a thiol compound-containing rich caustic stream is supplied to an oxidizer. Oxidizing a mercaptan compound in the presence of an oxygen-containing gas at a conversion level of 90% or more to form DSO, which results in the formation of a mixture of DSO, caustic and gas; supplying this mixture as a single stream to a separation device, wherein the mixture contacts a vertically suspended fiber bundle; separating the DSO from the caustic liquor in a separation device by forming two distinct liquid layers in a collection zone at the bottom of the separation device, wherein the lower layer comprises a caustic liquid phase and the upper layer comprises the DSO; and removing the DSO from the separation device by withdrawing a portion of the upper layer and removing the caustic from the separation device by withdrawing a portion of the lower layer.

Although it has been recognized in the art that gravity settling can be used to separate water (or aqueous solution) from hydrocarbons, these prior art separation techniques typically require the use of one or more liquid-liquid contactors downstream of the CGS, wherein the separated oxidized caustic solution is washed with a solvent stream to extract residual DSO, reducing the residual DSO to acceptable levels, so that the caustic liquor is suitable for recycling back to the main liquid-liquid contactor section where the contaminated hydrocarbons, such as LPG, are fed. The present invention replaces the CGS and downstream liquid-liquid contactors with a single processing vessel containing an oxidizer and one or more separation stages (stages) utilizing vertically suspended fibers. This provides significant savings in capital and operating costs, as well as valuable real estate, since its footprint (foot print) is much smaller than the combination of CGS and liquid-liquid contactors. As described above, FIBER is used in liquid-liquid contactor applicationsThe techniques are well known; however, none has been realized with any FIBER that performs the separation of two immiscible liquids, such as DSO-rich hydrocarbons and causticProvided is a technique. The present invention also does not require any solvent addition to separate the DSO from the oxidized caustic solution. The present invention is unique in that only a single stream containing a mixture of immiscible liquids needs to be fed to a separation device containing a fiber bundle. No additional process flow (processflow) is required to implement the separation. In one particular application of the process of the present invention, the inventors were able to separate DSO from an oxidized caustic solution such that the DSO was less than 5ppm in the caustic solution. The invention will also find application in reverse process applications, where an acidic aqueous solution is used to extract a basic mixture from a liquid, such as a hydrocarbon-based liquid. The only important factor is the use of only a single vessel and feeding at least two immiscible liquids leaving the oxidizer section as a mixture in a single stream to at least one separator using suspended fibers.

These and other objects will become more apparent in light of the detailed description of the preferred embodiments contained below.

Drawings

FIG. 1 schematically illustrates the use of FIBEROne possible embodiment of the process of the present invention for the separation of DSO from caustic solution is a technique wherein a small solvent stream is added prior to the oxidation step;

figure 2 is a graph showing the effectiveness of the present invention compared to a conventional gravity separator.

FIG. 3 shows another possible embodiment of the invention with a single column design, oxidizer at the top and two FIBERsA separator (FFS) is connected in series below the oxidizer; and

FIG. 4 shows the oxidizer at the top and four FIBERsSeparator (FFS) is a schematic of the single column design of the present invention in series below the oxidizer.

Detailed Description

As mentioned above, the present invention relates to the use of FIBERA novel method of separating at least two immiscible liquids in a mixture is disclosed. One particular application of the invention relates to the caustic treatment of hydrocarbons such as LPG to remove contaminants such as sulfur compounds which are detrimental to downstream processes. In particular, the present invention replaces a conventional gravity settler with a separation vessel utilizing high surface area fibersOr forced separation techniques such as centrifuges to separate the oxidized sulfur contaminants from the caustic solution. This new use of vertically suspended fibers with high surface area greatly reduces the residence time typically required for separation by an order of magnitude. In addition, the inventors have found that when using FIBERTechnically, adding a small solvent stream to the oxidizer or upstream of the oxidizer further improves downstream separation performance.

Figure 1 illustrates an embodiment of the invention wherein LPG feed contaminated with mercaptan compounds such as ethyl mercaptide is fed via line 1 to the caustic treatment section 3. The specific design of the caustic treatment section is not critical to the present invention; however, preferred designs include a staged contactor operating in a convection configuration, with the most preferred contactor configuration using suspended fibers in a liquid-liquid contactor. These and other contactor configurations are well known to those skilled in the art. Lean (lean) caustic is fed via line 5 to the contactor treatment section 3 where it is mixed with the LPG introduced via line 1. The caustic used in the present invention may be any type of desulfurized hydrocarbon known in the art, including solutions comprising NaOH, KOH, Ca (OH)2, Na2CO3, ammonia, organic acid extracts (organic acids), or mixtures thereof. Preferably, the caustic solution comprises an aqueous solution of potassium hydroxide and an aqueous solution of sodium hydroxide, the alkali hydroxide concentration being from about 1% to about 50%, more preferably from about 3% to about 25%, and even more preferably from about 5% to about 20% by weight.

Substantially sulfur-free LPG is removed from contactor section 3 via line 7 and used in subsequent processes, for example, in an alkylation unit. By substantially free of sulphur is meant that the sulphur level of the LPG is <150ppm total sulphur, preferably <20ppm total sulphur and more preferably <10ppm total sulphur. The caustic solution from contactor section 3 is a rich caustic solution which is removed via line 9. The rich caustic contains mercaptans and other sulfur contaminants extracted from the LPG feed.

Then will come fromThe rich caustic of the caustic treatment section is fed to the oxidizer 10. As with the liquid-liquid contactor, the precise design of the oxidizer is not important to the present invention, and any number of oxidizer designs may be used, such as bubble oxidizers, non-catalytic solid packing, and solid catalyst technologies. The preferred oxidizer is one containing a solid mat of catalyst, preferably a catalyst containing an active metal such as cobalt attached to a solid support such as activated carbon. The most preferred catalyst is the catalyst sold under the trade name ARI by Merichhem company^TMCatalyst sold at 120L. In an alternative embodiment of the invention, a small volume solvent stream 11 is introduced to the oxidizer 10 along with a rich caustic stream. This solvent stream can be mixed with the rich caustic prior to entering the oxidizer or injected into the oxidizer as a separate stream. The solvent can be any light hydrocarbon that will aid in the separation of the DSO downstream from the caustic solution after oxidation. Any relatively light hydrocarbon or mixture of such hydrocarbons may be used as a solvent in the present invention, however, preferred solvents include naphtha and kerosene. Although it is unclear how the exact mechanism of how the solvent improves the separation of the DSO from the oxidized caustic, one theory is that the solvent has much higher DSO solubility than the caustic, and their poor solubility provides the driving force for extraction. By FIBER providing a higher interfacial surface areaThe method is implemented in a device, and this effect is further amplified. The amount of solvent injected into the oxidizer, either with the rich caustic or separately, based on the volume percent of the rich caustic feed, is not particularly important to the present invention, so long as a minimum amount is used to improve downstream separation performance. As noted above, only a small volume of solvent is required, with a preferred range for minimum solvent injection being from about 0.1% to about 10.0% by volume, preferably from about 0.5% to about 5.0% by volume of the rich caustic fed via line 9.

In addition to feeding the rich caustic and solvent to the oxidizer, air or one or more other oxygen-containing gases are introduced to the oxidizer via line 12. The amount of oxygen containing gas added to the oxidizer is sufficient to achieve 95+% oxidation, most preferably 99+% oxidation, of the mercaptan compounds initially present in the LPG to disulfide compounds. Preferred ranges of operating conditions for the oxidizer include temperatures of about 75 ° F to about 200 ° F and caustic flow rates of up to 10LHSV, but preferably from about 100 ° F to about 150 ° F and less than 5 LHSV. The operating pressure of the process of the present invention is not critical as long as it maintains the process stream in a liquid state.

The effluent from the oxidizer 10 or oxidized caustic (which is a mixture of caustic and DSO) is removed from the oxidizer 10 via line 13 and sent to a separator 14 where DSO is separated from the caustic using vertically suspended fibers. The separator 14 may be any device that uses a column of tightly packed fibers and provides a large surface area. As mentioned above, this fibre membrane technology has been used in the past in liquid-liquid contactors to facilitate mass transfer of chemical compounds from one liquid to another, but has never, as is known, been used solely for the purpose of separating a mixture of two or more immiscible liquids. The design of these fibrous membrane liquid-liquid contactors is described in various references, for example, in U.S. Pat. nos. 3,758,404, 3,992,156, 4,666,689, 4,675,100 and 4,753,722, all of which are incorporated herein by reference. The present invention utilizes fiber membrane technology in separation applications for the first time. The inventors did not use it as a mass transfer liquid-liquid contactor. Thus, only a single feed stream needs to be fed to the high surface area fiber bundle. In the particular application shown in FIG. 1, the mixture comprises an oxidized aqueous caustic solution containing DSO and residual gases. This mixture is fed via a single line 13 to a separator 14. The oxidized aqueous caustic containing the DSO and gas enters the top of the fiber bundle 20, which fiber bundle 20 comprises substantially elongated fibers mounted in a cover and contained in a conduit. This conduit is provided with an inlet flange (flare) and a flow distribution device for distributing the oxidized caustic solution with DSO from line 13 over the fibers. The fibers in the separator 14 are selected from (but not limited to) metal fibers, glass fibers, polymer fibers, graphite fibers, and carbon fibers that meet the following two criteria: (1) the fibrous material must be preferentially wetted by a mixture of at least two immiscible liquids; and (2) the fibers must be of a material that does not contaminate or be destroyed, e.g., corroded, by the process.

During operation of the separator 14, two layers are formed at the bottom of the collection vessel 21; a lower layer 23 comprising regenerated caustic solution and an upper layer 22 comprising separated DSO. Figure 1 also shows an alternative embodiment in which a small solvent stream is added upstream of the oxidizer 10. When this alternative is used, the added solvent is removed in the upper layer 22 along with the DSO. Off-gas is removed from the top of collection vessel 21 through line 15. The covering and fibres of the fibre bundle extend partly in the boundary of the separator 14, the downstream end of the fibre bundle being positioned in the collecting container 21 so that the downstream end is in the lower layer 23. The DSO and solvent in upper layer 22 are removed from separator vessel 14 via line 16 and sent to storage or for further processing.

The residence time in separator 14 is selected to achieve maximum removal of DSO from the caustic liquid phase, with a target concentration of 5ppm or less. Unexpectedly, the inventors have found that the use of vertically suspended fibers (with or without added solvent) greatly reduces the required residence time by an order of magnitude compared to conventional gravity settling equipment. As explained more fully below in the examples, the use of hanging fibers reduces residence time from about 90 minutes for a gravity settler to less than 5 minutes for the separator of the present invention using vertically hanging fibers. The addition of solvent as explained above further improves the separation performance as shown in the chart described in the examples below.

The rate of removal of the caustic solution in lower layer 23 via line 17 is adjusted to maintain the appropriate residence time required to achieve a DSO level in this layer of 5ppm or less (measured as sulfur). The separated caustic solution in stream 17 may be further purified in polishing unit 24 to ensure that its DSO content is below 5 ppm. Various refining operations are known in the art, most of which involve liquid/liquid contact techniques. The final purified caustic is then removed from vessel 24 as lean caustic and recycled via line 5 to the caustic treatment section 3.

FIG. 3 shows the process of the present invention conducted in a single vessel, wherein either the rich caustic solution 100 or the spent caustic solution 100 enters the top of the oxidizer section 160 along with air 200 and solvent 500. The streams are combined and introduced through distributor 150 to the top of solid catalyst pad 350. Oxidation of mercaptides to disulfide oil (DSO) occurs in catalyst pad 350, which results in a mixture comprising a continuous phase of caustic, discontinuous phase of organic (solvent + DSO) droplets distributed in the caustic phase, and gases (nitrogen from air and unreacted oxygen). The mixture exiting the oxidizer 160 enters a first cover containing vertically suspended fiber bundles with an inlet distributor 210, which is located in section 170. The gas from the oxidizer 160 is stripped from the liquid stream at the fiber bundle cast (fiber bundle cast) outlet and exits as off-gas 330 through a demister 340. The two immiscible liquids flow down the vertical fibers as a single stream during which the organic hydrocarbon droplets coalesce and form a top organic layer 250, while the aqueous caustic liquid adheres to the fibers and flows further down forming a bottom caustic liquid layer 260.

A spent solvent stream containing DSO400 is withdrawn from the top organic layer 250 in the separation section 170. A caustic stream 800 having a substantially reduced amount of DSO is withdrawn from the bottom caustic liquid layer 260. The caustic stream 800 is further mixed with fresh solvent 300 to form stream 900 and enters the second separation section 180 containing vertical fiber bundles with inlet distributor 220. The liquid stream flows down the vertical fibers during which the remaining organic droplets coalesce and form a top organic layer 270, while the aqueous caustic adheres to the fibers and flows further down forming a bottom caustic layer 280. A recycle solvent stream 500 containing a low level of DSO is withdrawn from the top organic layer 270 in the separation section 180 and recycled to the top of the oxidizer vessel 160. A regenerated caustic liquid stream 140 or a lean caustic liquid stream 140 having a very low DSO content is withdrawn from the bottom caustic liquid layer 280 in the second separation section 180.

Figure 4 shows another embodiment of the present invention,in which two other FIBERs are combinedA separation (FFS) portion is added to the single column to achieve even better purification of the caustic. This embodiment has four FFS stages, namely FFS1, FFS2, FFS3 and FF4, namely 170, 180, 190 and 200, wherein the solvent and caustic streams are in principle counter-current. The convective flow configuration is achieved by: the solvent is removed from FFS (n) and fed to FFS (n-1) while the caustic stream flows from FFS (n-1) to FFS (n). Here n =2, 3, 4, representing FFS2, FFS3, and FFS 4. The spent solvent stream containing DSO400 is withdrawn from top organic layer 250 in FFS1 portion 170. The caustic stream 800 is mixed with recycled solvent 600 from the third separation section 190 to form stream 900 and enters the second separation section 180 containing vertical fiber bundles with inlet distributor 220. The third separation section 190 contains a vertical fiber bundle with an inlet distributor 230 and has a top organic layer 290 and a bottom caustic liquid layer 300 in FFS 3. A recycle solvent stream 500 containing a low level of DSO is withdrawn from the top organic layer 270 in FFS2 portion 180 and recycled to the top of oxidizer vessel 160. The caustic stream 120 is mixed with fresh solvent 3000 to form stream 130 and enters a fourth separation section 200 containing vertical fiber bundles with an inlet distributor 240. A regenerated caustic stream 140 or lean caustic stream 140 having little or no DSO is withdrawn from the bottom caustic liquid layer 320 in the FFS4 portion 200.

Examples

To illustrate the surprising and unexpected performance of the present invention, laboratory tests were conducted to compare a Conventional Gravity Settler (CGS) to the high surface area fiber separator of the present invention. A rich caustic solution containing about 7000ppm sulfur of ethanethiol was oxidized at a temperature of about 125 ℃ F., 4.0LHSV and 25psig back pressure (back pressure) using a 1-inch diameter oxidizer loaded with ARI-120L of solid catalyst to a conversion level of 99+% conversion. Air was injected at about 300 ml/min. In a separate experiment, kerosene was injected into the oxidizer at a rate of about 1.5 ml/min.

The effluent from the oxidizer containing about 7000ppm DSO sulfur as diethyl disulfide was first fed into a 3-inch diameter CGS and settled by gravity. After residence times of 5 minutes and 90 minutes, the DSO level in the caustic decreased to about 76 and 6ppm, respectively (FIG. 2).

Then using FIBERThe separator replaces CGS and the fibers provide a very large surface area. FIBERThe separator contained 150 metal fibers placed in a covering in an 3/8 inch diameter catheter. This same arrangement is used when injecting solvent into the oxidizer.

The graph shown in FIG. 2 shows the FIBERComparison of the separator to the CGS. In the case of CGS, the caustic contained 76ppm DSO at a residence time of 5 minutes. Surprisingly, the FIBER of the present inventionThe separator gave a DSO content of caustic solution of only 12ppm at the same residence time of 5 minutes.

The effect of adding 5 vol% solvent (as kerosene) to the oxidizer is also shown in fig. 2. Injection solvent and FIBERThe combination of separations reduced the DSO content to 4ppm at a residence time of 5 minutes.

The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

The means, materials, and steps for carrying out various disclosed functions may take a variety of alternative forms without departing from the invention. Thus, the language "means for … (means to..)" and "means for …" (means for …) "or any method step language that may be used after a functional statement found in the above specification and the following claims is intended to define and encompass any structure, physical, chemical, or electronic element or structure, or any method step, which may or may not be present in the future, that performs the recited function, whether or not exact equivalent to one or more of the embodiments disclosed in the above specification, i.e., other means or steps that perform the same function may be used; and is intended to be given the broadest interpretation of such expression within the scope of the following claims.

Claims (6)

1. A process for separating mercaptan compounds from a caustic rich stream comprising, in combination:

a) feeding a stream of solvent, an oxygen-containing fluid and a thiol compound-containing rich caustic to a single column having a top section comprising an oxidizer and a bottom section containing at least two fiber-containing contactors in series below the oxidizer;

b) contacting the stream from step a) with a catalyst in the presence of oxygen in the oxidizer to oxidize the mercaptan compounds to disulfide oils (DSO) at a conversion level of 90% or more and form a mixture comprising DSO, solvent and caustic;

c) directing the mixture formed in step b) from said oxidizer as a single stream to a first separation section in said single column where said mixture contacts a vertically suspended fiber bundle;

d) separating the DSO and solvent from the caustic liquor in the first separation section by flowing the mixture through the fiber bundle to form two distinct liquid layers in a first collection zone, a first lower layer comprising a caustic liquid phase and a first upper layer comprising a DSO/solvent phase;

e) continuously removing a portion of said DSO/solvent phase from said first separation zone;

f) continuously removing a portion of said aqueous caustic phase and mixing with fresh solvent to form a second separated feed, said second separated feed being supplied to a second separated portion of said single column where it contacts a second vertically suspended fiber bundle;

g) forming two distinct liquid layers in a second collection zone, a second lower layer comprising a caustic liquid phase and a second upper layer comprising a DSO/solvent phase, by flowing the second separation feed through the fiber bundle in the second separation section, thereby separating any remaining DSO and solvent from the caustic liquid in the second separation section;

h) continuously removing a portion of said DSO/solvent phase from said second separated portion and recycling it as solvent for step a); and

i) continuously removing a lean caustic stream from the second lower layer.

2. The process of claim 1, wherein the stream of thiol compound-containing rich caustic is oxidized by: the stream is contacted with a solid pad containing a metal-supported catalyst.

3. The process of claim 1, wherein residual gases are removed in the first separation section as off-gas.

4. A single column for treating a stream of rich caustic containing mercaptan compounds, comprising:

a) an upper section comprising an oxidizer; and

b) a lower portion comprising at least two separate portions in series flow, wherein each separate portion contains a covering of vertically hanging fibers and a liquid collection area.

5. A convective process for separating mercaptan compounds from a caustic rich stream comprising, in combination:

a) feeding a stream of solvent, an oxygen-containing fluid and a thiol compound-containing rich caustic to a single column having a top section comprising an oxidizer and a bottom section comprising at least three separation sections in series below the top section, the separation sections comprising a contactor comprising fibers;

b) contacting the stream from step a) with a catalyst in the presence of oxygen in the oxidizer to oxidize the mercaptan compounds to disulfide oils (DSO) at a conversion level of 90% or more and form a mixture comprising DSO, solvent and caustic;

c) directing the mixture formed in step b) from said oxidizer as a single stream to a first separation section in said single column where said mixture contacts a vertically suspended fiber bundle;

d) separating the DSO and solvent from the caustic liquor in the first separation section by flowing the mixture through the fiber bundle to form two distinct liquid layers in a first collection zone, a first lower layer comprising a caustic liquid phase and a first upper layer comprising a DSO/solvent phase;

e) continuously removing a portion of the DSO/solvent phase from the first separated portion;

f) continuously removing a portion of said caustic liquid phase and mixing with the DSO/solvent stream removed from the third separation section to form a second separation feed, said second separation feed being supplied to a second separation section in said single column where it contacts a second vertically suspended fiber bundle;

g) forming two distinct liquid layers in a second collection zone, a second lower layer comprising a caustic liquid phase and a second upper layer comprising a DSO/solvent phase, by flowing the second separation feed through the fiber bundle in the second separation section, thereby separating any remaining DSO and solvent from the caustic liquid in the second separation section;

h) continuously removing a portion of said DSO/solvent phase from said second separated portion and recycling it as solvent for step a);

i) continuously removing a caustic stream from said second lower layer and mixing with fresh solvent to form a third separated feed, said third separated feed being supplied to a third separation section in said single column where it contacts a third vertically suspended fiber bundle;

j) separating any remaining DSO and solvent from the caustic in the third separation section by flowing the third separation feed through the fiber bundle in the third separation section to form two distinct liquid layers in a third collection zone, a third lower layer comprising a caustic liquid phase and a third upper layer comprising a DSO/solvent phase;

k) continuously removing a portion of said DSO/solvent phase from said third collection zone to mix with the caustic liquid phase of step f); and

l) continuously removing a lean caustic stream from said third lower layer in said third collection zone.

6. A convective process for separating mercaptan compounds from a caustic rich stream comprising, in combination:

a) feeding a stream of solvent, an oxygen-containing fluid and a thiol compound-containing rich caustic to a single column having a top section comprising an oxidizer and a bottom section containing at least four separation sections in series below the top section, the separation sections containing contactors comprising fibers;

b) contacting the stream of step a) with a catalyst in the presence of oxygen in the oxidizer to oxidize the mercaptan compounds to disulfide oils (DSO) at a conversion level of 90% or more and form a mixture comprising DSO, solvent and caustic;

c) directing the mixture formed in step b) from said oxidizer as a single stream to a first separation section in said single column where said mixture contacts a vertically suspended fiber bundle;

d) separating the DSO and solvent from the caustic liquor in the first separation section by flowing the mixture through the fiber bundle to form two distinct liquid layers in a first collection zone, a first lower layer comprising a caustic liquid phase and a first upper layer comprising a DSO/solvent phase;

e) continuously removing a portion of the DSO/solvent phase from the first separated portion;

f) continuously removing a portion of said caustic liquid phase from said first collection zone and mixing with the DSO/solvent stream removed from the third separation section to form a second separation feed, said second separation feed being supplied to a second separation section in said single column where it contacts a second vertically suspended fiber bundle;

g) forming two distinct liquid layers in a second collection zone, a second lower layer comprising a caustic liquid phase and a second upper layer comprising a DSO/solvent phase, by flowing the second separation feed through the fiber bundle in the second separation section, thereby separating any remaining DSO and solvent from the caustic liquid in the second separation section;

h) continuously removing a portion of said DSO/solvent phase from said second separated portion and recycling it as solvent for step a);

i) continuously removing a caustic stream from said second lower layer and mixing with the DSO/solvent stream removed from the fourth separation section to form a third separation feed, said third separation feed being supplied to a third separation section in said single column where it contacts a third vertically suspended fiber bundle;

j) separating any remaining DSO and solvent from the caustic in the third separation section by flowing the third separation feed through the fiber bundle in the third separation section to form two distinct liquid layers in a third collection zone, a third lower layer comprising a caustic liquid phase and a third upper layer comprising a DSO/solvent phase;

k) continuously removing a portion of said DSO/solvent phase from said third collection zone to mix with the caustic liquid phase of step f);

l) continuously removing a caustic stream from the third lower layer in said third collection zone and mixing with fresh solvent to form a fourth separation feed, said fourth separation feed being supplied to a fourth separation section in said single column where it contacts a fourth vertically suspended fiber bundle;

m) forming two distinct liquid layers in a fourth collection zone, a fourth lower layer comprising a caustic liquid phase and a fourth upper layer comprising a DSO/solvent phase, by flowing the fourth separation feed through the fiber bundle in the fourth separation section, thereby separating any remaining DSO and solvent from the caustic liquid in the fourth separation section;

n) continuously removing a portion of said DSO/solvent phase from said fourth collection zone to mix with the caustic solution in step i); and

o) continuously removing a lean caustic stream from the fourth lower layer in said fourth collection zone.