Methods and systems for purifying caustic fluids containing sulfur.

Abstract

Methods and systems for purifying caustic fluids containing sulfur are provided.

Description

Background of the Invention

[0001] In mercaptan removal systems, disulfide oil (DSO) in the caustic soda feed stream is carried back to the final hydrocarbon products, which may include propane, butane, liquefied petroleum gas (LPG), fuel gas, naphtha, or gasoline, resulting in increased sulfur content that exceeds target specifications.

[0002] Improved systems and methods are needed for removing sulfur from caustic soda feed streams.

[0003] This invention provides improvements over at least some of the disadvantages of the prior art. These and other advantages of this invention will become apparent from the description listed below.

[0004] Brief Overview of the Invention

[0005] One aspect of the present invention provides a method for purifying a caustic alkali fluid comprising sulfur, the method comprising: (a) mixing the caustic alkali fluid comprising sulfur with a hydrocarbon solvent, comprising injecting the hydrocarbon solvent into a mixing valve at a pressure greater than the pressure of the caustic alkali fluid comprising sulfur at a rate in the range of 3% to 10% of the flow rate of the caustic alkali fluid comprising sulfur, the mixing valve operating at a pressure differential in the range of 10 psid to 50 psid; (b) passing the caustic alkali fluid comprising sulfur mixed with the hydrocarbon solvent through a pre-filter assembly operating at a temperature in the range of 50°F to 150°F at a pressure differential in the range of 1 psid to 25 psid, the pre-filter assembly comprising a housing, the housing including an inlet and an outlet and defining a fluid flow path between the inlet and the outlet, wherein at least one porous pre-filter element passes through the fluid flow path within the housing, thereby improving the purification efficiency. (c) A sulfur-containing caustic alkali fluid of lean solids mixed with a hydrocarbon solvent is supplied; (d) the sulfur-containing caustic alkali fluid of lean solids mixed with a hydrocarbon solvent is passed through an inlet of a liquid-liquid coalescing assembly at a temperature in the range of 50°F to 150°F, the liquid-liquid coalescing assembly comprising a liquid-liquid coalescing assembly housing including the inlet and at least one liquid-liquid coalescing filter element in the liquid-liquid coalescing assembly housing having an upper portion with an upper orifice and a lower portion with a lower orifice, wherein the liquid-liquid coalescing assembly operates at a pressure differential in the range of 1 psid to 15 psid, wherein the flow rate of each liquid-liquid coalescing filter element is in the range of 10 gpm to 50 gpm; (i) coalescing droplets containing sulfur and a hydrocarbon solvent are passed through the upper orifice; and (ii) purified caustic alkali fluid with a reduced sulfur content is passed through the lower orifice.

[0006] In one aspect of the method, (a) involves mixing a sulfur-containing caustic fluid with a caustic alkali concentration in the range of 1 Baume to 10 Baume with the hydrocarbon solvent.

[0007] In a preferred aspect of the method, the caustic fluid comprising sulfur contains disulfide oil (DSO).

[0008] On the other hand, a system for purifying a caustic alkali fluid comprising sulfur includes: (a) a mixing assembly having at least a first inlet orifice, a mixing valve, and an outlet orifice; (b) a first conduit for receiving the caustic alkali fluid comprising sulfur, the first conduit having a first conduit first end in fluid communication with a source of the caustic alkali fluid and a second conduit second end in fluid communication with the at least one inlet orifice of the mixing assembly; (c) a second conduit for receiving a hydrocarbon solvent, the second conduit having a second conduit first end in fluid communication with a source of the hydrocarbon solvent and a second conduit second end in fluid communication with the first conduit; and (d) a pre-filter assembly comprising a housing having a pre-filter assembly inlet and a pre-filter assembly outlet and defining the pre-filter assembly inlet. A fluid flow path between the inlet and the outlet of the pre-filter assembly, and having at least one porous pre-filter element arranged within the housing of the pre-filter assembly through the fluid flow path, wherein the pre-filter assembly inlet is in fluid communication with the outlet orifice of the mixing assembly, and the pre-filter assembly outlet is in fluid communication with the inlet of the liquid-liquid coalescing assembly; (e) a liquid-liquid coalescing assembly comprising a housing, the housing including at least one liquid-liquid coalescing filter element therein, the housing having a liquid-liquid coalescing assembly inlet and an upper and a lower portion, the upper portion having an upper orifice for receiving coalesced droplets containing sulfur and hydrocarbon solvents, and the lower portion having a lower orifice for receiving purified caustic alkali fluid with reduced sulfur content.

[0009] Brief description of several views in the attached diagram

[0010] The accompanying drawing is a schematic diagram showing a system according to one aspect of the present invention. Invention Details

[0011] One aspect of the present invention provides a method for purifying a caustic alkali fluid comprising sulfur, the method comprising: (a) mixing the caustic alkali fluid comprising sulfur with a hydrocarbon solvent, comprising injecting the hydrocarbon solvent into a mixing valve at a pressure greater than the pressure of the caustic alkali fluid comprising sulfur at a rate in the range of 3% to 10% of the flow rate of the caustic alkali fluid comprising sulfur, the mixing valve operating at a pressure differential in the range of 10 psid to 50 psid; (b) passing the caustic alkali fluid comprising sulfur mixed with the hydrocarbon solvent through a pre-filter assembly operating at a temperature in the range of 50°F to 150°F at a pressure differential in the range of 1 psid to 25 psid, the pre-filter assembly comprising a housing, the housing including an inlet and an outlet and defining a fluid flow path between the inlet and the outlet, wherein at least one porous pre-filter element passes through the fluid flow path within the housing, thereby improving the purification efficiency. (c) A sulfur-containing caustic alkali fluid of lean solids mixed with a hydrocarbon solvent is supplied; (d) the sulfur-containing caustic alkali fluid of lean solids mixed with a hydrocarbon solvent is passed through an inlet of a liquid-liquid coalescing assembly at a temperature in the range of 50°F to 150°F, the liquid-liquid coalescing assembly comprising a liquid-liquid coalescing assembly housing including the inlet and at least one liquid-liquid coalescing filter element in the liquid-liquid coalescing assembly housing having an upper portion with an upper orifice and a lower portion with a lower orifice, wherein the liquid-liquid coalescing assembly operates at a pressure differential in the range of 1 psid to 15 psid, wherein the flow rate of each liquid-liquid coalescing filter element is in the range of 10 gpm to 50 gpm; (i) coalescing droplets containing sulfur and a hydrocarbon solvent are passed through the upper orifice; and (ii) purified caustic alkali fluid with a reduced sulfur content is passed through the lower orifice.

[0012] In one aspect of the method, (a) involves mixing a sulfur-containing caustic fluid with a caustic alkali concentration in the range of 1 Baume to 10 Baume with the hydrocarbon solvent.

[0013] In some respects, the method is carried out at system pressures ranging from 50 psig to 600 psig, for example to ensure that the hydrocarbon solvent remains in a liquid state.

[0014] In a preferred aspect of the method, the caustic fluid comprising sulfur contains disulfide oil (DSO), and in a more preferred aspect, the method includes a thiol removal process.

[0015] On the other hand, a system for purifying a caustic alkali fluid comprising sulfur includes: (a) a mixing assembly having at least a first inlet orifice, a mixing valve, and an outlet orifice; (b) a first conduit for receiving the caustic alkali fluid comprising sulfur, the first conduit having a first conduit end in fluid communication with a source of the caustic alkali fluid and a second conduit end in fluid communication with the at least one inlet orifice of the mixing assembly; (c) a second conduit for receiving a hydrocarbon solvent, the second conduit having a second conduit end in fluid communication with a source of the hydrocarbon solvent and a second conduit end in fluid communication with the first conduit; and (d) a pre-filter assembly comprising a housing having a pre-filter assembly inlet and a pre-filter assembly outlet and defining the pre-filter assembly. A fluid flow path between the inlet of the mixing assembly and the outlet of the pre-filter assembly, and having at least one porous filter element arranged across the fluid flow path within the housing of the pre-filter assembly, wherein the inlet of the pre-filter assembly is in fluid communication with the outlet orifice of the mixing assembly, and the outlet of the pre-filter assembly is in fluid communication with the inlet of the liquid-liquid coalescing assembly; (e) a liquid-liquid coalescing assembly comprising a housing, the housing including at least one liquid-liquid coalescing filter element therein, the housing having a liquid-liquid coalescing assembly inlet and an upper and a lower portion, the upper portion having an upper orifice for receiving coalesced droplets containing sulfur and hydrocarbon solvents, and the lower portion having a lower orifice for receiving purified caustic alkali fluid with reduced sulfur content.

[0016] The system may also include a first container for receiving coalesced droplets containing sulfur and hydrocarbon solvents passing through an upper orifice of the liquid-liquid coalescer assembly, and a second container for receiving purified caustic alkali fluid with reduced sulfur content passing through a lower orifice of the liquid-liquid coalescer assembly.

[0017] In some aspects of the system, the system can operate at system pressures ranging from 50 psig to 600 psig.

[0018] In alternative aspects of the method and system, the liquid-liquid coalescer assembly may include at least one porous pre-filter element (instead of a separate pre-filter assembly or as a supplement to a separate pre-filter assembly) arranged upstream of at least one liquid-liquid coalescer filter element in the liquid-liquid coalescer assembly housing, wherein the at least one porous pre-filter element may be in the form of, for example, a cylindrical or planar element.

[0019] The various components of the invention will now be described in more detail, wherein similar components have similar reference numerals.

[0020] Using the aspects illustrated in the accompanying drawings, system 1000 includes: a mixing assembly 150 having at least a first inlet port 101, a mixing valve 100, and an outlet port 102 (a differential pressure gauge 175 is arranged across the mixing assembly in the illustrative aspect); a first conduit 10 for receiving a caustic alkali fluid comprising sulfur, the first conduit having a first conduit end 10a in fluid communication with a source of the caustic alkali fluid and a second conduit end 10b in fluid communication with the at least one inlet port of the mixing assembly; a second conduit 20 for receiving a hydrocarbon solvent, the second conduit having a second conduit end 20a in fluid communication with a source of the hydrocarbon solvent 50 and a second conduit end 20b in fluid communication with the first conduit (in the illustrative aspect, a pump 22, a flow control valve 23, and a flow meter 24 are inserted between the second conduit ends 20a and 20b); and a third conduit 30 for receiving the mixed fluid exiting the mixing assembly, the third conduit having a third conduit end 30a in fluid communication with the outlet port of the mixing assembly and a pre-filter assembly 200. The pre-filter assembly has a second end 30b of a third conduit in fluid communication with the inlet 201 of the pre-filter assembly. The pre-filter assembly includes a housing 210 having the pre-filter assembly inlet 201 and a pre-filter assembly outlet 202 and defining a fluid flow path 250 between the inlet and outlet. It also has at least one porous filter element (e.g., a porous pre-filter cartridge) 251 arranged within the housing through the fluid flow path. The pre-filter assembly outlet is connected to the liquid via a fourth conduit 40 having a first end 40a and a second end 40b. The liquid-liquid coalescer assembly 300 is in fluid communication with a liquid-liquid coalescer assembly inlet 301, the liquid-liquid coalescer assembly including a housing 310, the housing including at least one liquid-liquid coalescer filter element 351 in the housing, and an upper portion 360 having an upper orifice 361 for receiving coalesced droplets containing sulfur and hydrocarbon solvents, and a lower portion 370 having a lower orifice 371 for receiving purified caustic alkali fluid with reduced sulfur content, wherein the purified caustic alkali fluid can be introduced from the lower orifice 371 into, for example, a thiol removal extractor.

[0021] In a preferred aspect, the system includes a collection tank 400 communicating with an upper orifice 361, the tank receiving coalesced droplets containing sulfur and hydrocarbon solvents, wherein the hydrocarbon extract can be distilled or hydrogenated from the collection tank orifice 401 along a fifth conduit 50 having a first end 50a and a second end 50b via a pump 62, and subsequently via sixth and seventh conduits 60 and 70, or via an eighth conduit 80 into a source 50 of hydrocarbon solvents for recycling.

[0022] Suitable hydrocarbon solvents include, for example, naphtha, hexane, liquid propane, and other hydrocarbon solvents with low sulfur content.

[0023] Various mixing assemblies, including mixing valves, are suitable for use in various aspects of the invention. In one aspect, the mixing valve comprises a ball valve.

[0024] The hydrocarbon solvent can be injected into the mixing assembly by means of, for example, a pump or a pressurized reservoir using inert gas to increase the pressure above that of the caustic alkali stream, so that the hydrocarbon solvent flows into the caustic alkali stream.

[0025] Suitable pre-filter components include, for example Filters and II filters are commercially available from Pall Corporation (Port Washington, NY). Pre-filter assemblies may have any number of porous pre-filter elements, and in some respects, at least two porous pre-filter elements, such as three or more.

[0026] Preferred liquid-liquid coalescer assemblies include those described in U.S. Patents 5,443,724 and 5,480,547, U.S. Patent Application Publication 2001 / 0047967, and EP 0,831,958. Suitable liquid-liquid coalescer assemblies are commercially available from Pall Corporation (Port Washington, NY). Liquid-liquid coalescer assemblies may have any number of liquid-liquid coalescer filter elements (e.g., cartridge-type liquid-liquid coalescer filter elements), typically at least two, such as three or more, and in some aspects, at least four fluoropolymer liquid-liquid coalescer filter elements.

[0027] Preferably, the coalescer and pre-filter cartridge are constructed using fluoropolymer media such as ethylene chloride trifluoroethylene (ECTFE) or polyvinylidene fluoride (PVDF), nylon media, polyphenylene sulfide (PPS) media, or other materials compatible with caustic alkalis and hydrocarbons, and may contain stainless steel support material and end caps. The housing accommodating the pre-filter and coalescer may be made of carbon steel or stainless steel.

[0028] The following examples further illustrate the present invention, but should not be construed as limiting the scope of the invention in any way. Example

[0029] This embodiment demonstrates a reduction of sulfur from a caustic fluid comprising DSO according to one aspect of the invention.

[0030] Using the system schematic shown in the accompanying drawings, a first fluid stream containing a caustic alkali with >350 ppmw of DSO and a solid phase is run at 100 gpm, and a low-sulfur naphtha hydrocarbon solvent (using a pump, with flow control valves and flow meters controlling the flow rate) is injected into the first fluid stream at a flow rate of 5 gpm (5% of the caustic alkali flow rate).

[0031] The caustic alkali and solvent are mixed together by a spherical mixing valve that generates a pressure differential of 15 psid as measured by a differential pressure gauge (thus creating shear, resulting in micron-sized droplets to improve subsequent coalescence and mass transfer of sulfur from the caustic alkali phase to the hydrocarbon solvent phase), and the mixture passes through a pre-filter assembly (trade name) with two nylon porous depth pre-filter cartridges (each 60 inches long by 6 inches in diameter). The filter (Pall Corporation, Port Washington, NY) removes the solid phase and initiates a coalescence process that increases droplet size, and the mixture of the solid-lean phase is passed through a cylinder with four fluoropolymer liquid-liquid coalescers (each 40 inches long by 3). 3 A horizontally configured liquid-liquid coalescer assembly (approximately 4 inches in diameter) provides a coagulated emulsion of solvent and DSO, which coalesces and is more easily separated from the caustic alkali by buoyancy. This emulsion is collected from the top of the liquid-liquid coalescer assembly in a hydrocarbon storage tank and periodically discharged as part of a continuous process. Purified caustic alkali (reduced to <180 ppmw DSO) is passed from the bottom of the liquid-liquid coalescer assembly into a thiol extraction tower, thus providing a reliable, continuous supply of final product hydrocarbons with low sulfur content below target specifications.

[0032] All references cited in this article, including publications, patent applications and patents, are incorporated herein by reference to the same extent that each reference is individually and explicitly stated to be incorporated by reference and listed in its entirety herein.

[0033] Unless otherwise stated herein or obviously contradicted by the context, the terms “a,” “an,” “the,” “at least one,” and similar indicators used in the context of describing the invention (especially in the context of the following claims) shall be interpreted to cover both the singular and the plural. Unless otherwise stated herein or obviously contradicted by the context, the use of the term “at least one” followed by a list of one or more items (e.g., “at least one of A and B”) shall be interpreted to mean either one of the listed items (A or B) or any combination of two or more of the listed items (A and B). Unless otherwise stated, the terms “comprising,” “having,” “including,” and “containing” shall be interpreted as open-ended terms (i.e., meaning “including but not limited to”). Unless otherwise stated herein, the descriptions of numerical ranges herein are intended only as a shorthand method for individually referring to each individual value falling within the range, and each individual value is incorporated into the specification as if it were individually stated herein. Unless otherwise stated herein or obviously contradicted by the context, all methods described herein may be performed in any suitable order. Unless otherwise claimed, the use of any and all examples or exemplary language (e.g., “for example”) provided herein is intended only to better illustrate the invention and not to limit its scope. The language in the specification should not be construed as indicating that any unclaimed element is necessary for the practice of the invention.

[0034] This document describes preferred aspects of the invention, including the best modes of carrying out the invention known to the inventors. Variations of those preferred aspects will become apparent to those skilled in the art upon reading the foregoing description. The inventors intend that those skilled in the art will suitably employ such variations, and the inventors intend that the invention be practiced in a manner different from that specifically described herein. Therefore, the invention includes all modifications and equivalents of the subject matter recited in the appended claims as permitted by applicable law. Furthermore, unless otherwise stated herein or clearly contradicted by the context, the invention includes any combination of the foregoing elements with all possible variations.

Claims

1. A method for purifying a caustic alkali fluid containing sulfur, the method comprising: (a) Mixing the sulfur-containing caustic alkali fluid with a hydrocarbon solvent, including injecting the hydrocarbon solvent into a mixing valve at a rate in the range of 3% to 10% of the flow rate of the sulfur-containing caustic alkali fluid at a pressure greater than the pressure of the sulfur-containing caustic alkali fluid, the mixing valve operating at a pressure differential across the mixing valve in the range of 10 psid to 50 psid. (b) A pre-filter assembly that operates a sulfur-containing caustic alkali fluid mixed with a hydrocarbon solvent at a temperature in the range of 50°F to 150°F under a pressure differential in the range of 1 psid to 25 psid, the pre-filter assembly comprising a housing having an inlet and an outlet and defining a fluid flow path between the inlet and the outlet, wherein at least one porous pre-filter element passes through the fluid flow path within the housing, thereby providing a sulfur-containing caustic alkali fluid with a lean solids content mixed with a hydrocarbon solvent; (c) Passing the sulfur-containing caustic fluid, which is a lean solid mixture with a hydrocarbon solvent, through the inlet of a liquid-liquid coalescing assembly at a temperature in the range of 50°F to 150°F, the liquid-liquid coalescing assembly comprising a liquid-liquid coalescing assembly housing, the liquid-liquid coalescing assembly housing including the inlet and at least one liquid-liquid coalescing filter element in the liquid-liquid coalescing assembly housing having an upper portion with an upper orifice and a lower portion with a lower orifice, wherein the liquid-liquid coalescing assembly operates at a pressure differential in the range of 1 psid to 15 psid, wherein the flow rate of each liquid-liquid coalescing filter element is in the range of 10 gpm to 50 gpm; (i) passing a coalesced droplet containing sulfur and hydrocarbon solvent through the upper orifice; and (ii) Pass the purified caustic fluid with reduced sulfur content through the lower orifice.

2. The method of claim 1, wherein the caustic fluid comprising sulfur comprises disulfide oil (DSO).

3. The method according to claim 1 or 2, wherein (a) comprises mixing a sulfur-containing caustic alkali fluid with a caustic alkali concentration in the range of 1 Baume to 10 Baume with the hydrocarbon solvent.

4. The method according to claim 1 or 2, comprising a thiol removal process.

5. The method according to claim 1 or 2, wherein the method is performed at a system pressure in the range of 50 psig to 600 psig.

6. A system for purifying caustic alkali fluids containing sulfur, comprising: (a) A mixing assembly having at least a first inlet orifice, a mixing valve, and an outlet orifice; (b) A first conduit for receiving a caustic fluid comprising sulfur, the first conduit having a first conduit first end in fluid communication with a source of the caustic fluid, and a first conduit second end in fluid communication with the at least one inlet orifice of the mixing assembly; (b) A second conduit for receiving a hydrocarbon solvent, the second conduit having a first end in fluid communication with a source of the hydrocarbon solvent and a second end in fluid communication with the first conduit; (d) A pre-filter assembly comprising a housing having a pre-filter assembly inlet and a pre-filter assembly outlet and defining a fluid flow path between the pre-filter assembly inlet and the pre-filter assembly outlet, and having at least one porous pre-filter element disposed within the pre-filter assembly housing through the fluid flow path, wherein the pre-filter assembly inlet is in fluid communication with the outlet orifice of the mixing assembly, and the pre-filter assembly outlet is in fluid communication with the inlet of the liquid-liquid coalescer assembly; (e) A liquid-liquid coalescer assembly comprising a housing including at least one liquid-liquid coalescer filter element therein, the housing having a liquid-liquid coalescer assembly inlet and an upper and a lower portion, the upper portion having an upper orifice for receiving coalesced droplets containing sulfur and hydrocarbon solvents, and the lower portion having a lower orifice for receiving purified caustic fluid with reduced sulfur content.

7. The system of claim 6, which is capable of operating at system pressures in the range of 50 psig to 600 psig.

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