US2679470A - Process and apparatus for continuously treating a fluid with an immiscible liquid - Google Patents

Description

May 25, 1954 w, KRESS 2,679,470

PROCESS AND APPARATUS FOR CONTINUOUSLY TREATING A FLUID WITH AN IMMISCIBLE LIQUID Filed Feb. 12, 1952 n- 0 sum mamas r 9 n 5 LIQUID l G no a FRESH TREATING is uquno Patented May 25, 1954 PROCESS AND APPARATUS FOR CONTINU- OUSLY TREATING A FLUID WITH AN IM- MIS CIBLE LIQUID Walter E. Kress, Wood River, 111., assignor to Shell Development Company, Emeryville, Calif., a corporation of Delaware Application February 12, 1952, Serial No. 271,086

8 Claims.

This invention relates to a method and apparatus for continuously treating a fluid with a treating liquid which is immiscible therewith,

for example, treating sour hydrocarbon distillates with aqueous alkaline solutions. More particu- 5 with aqueous solutions of hydrotropic agents, larly, this invention is concerned with the ree. g., potassium butyrate, potassium or sodium moval of interfacial emulsions from the stratipropanesulfonate, and the like to recover the fied mixture resulting from such treatment. oxygenated compounds from the hydrocarbon It is Well known to treat various fluid (liquid solution thereof; various hydrocarbon fractions or gaseous) streams with a stream of an imcontaining basic nitrogeneous compounds are miscible treating agent by intimately contacting treated with sulfuric acid or with an organic (mixing) the two streams, e. g., in a centrifugal acid (formic acid) to extract the basic nitropump by passage through a vessel such as a geneous compounds; and various gaseous streams mixing valve, provided with suitable baffles or (hydrogen, natural gas, refinery gases, synthesis other obstructions to cause turbulence, or by pasgas, and the like) are treated with alkaline sage through a vessel provided with a stirrer, or liquids (aqueous potassium phosphate, aqueous the like, then to pass the mixture to a suitable caustic soda, ethanolamines, and the like) for settler wherein a relatively quiescent state is the purpose of removing acidic substances, such maintained and wherein the mixture is permitted as hydrogen sulfide, with or without carbon dito stratify into at least two layers, one of the oxide removal. tWO layers C p ng treating liquid and ma- However, a serious difficulty often encountered terial dissolved therein resulting from the treatin such mixer-settler treating systems is the ment, and the other of the two layers being the formation of a third phase or layer of material treated fluid, the layer of highest density (usually in the settler comprising a rather stable emulsion the treating agent) being lowermost, and to which accumulates as an interfacial layer bewithdraw both the treated fluid and treating tween the stratified layers of treated fluid and agent from the settler in a continuous manner treating agent to an extent which cannot be while maintaining a body of both layers or phases tolerated. The rate at which this emulsion acin the settler, often with recycling of at least cumulates generally is too small to make its com a portion of the treating agent from the settler tinuous removal feasible. Therefore, it is preferto the mixing zone, with or without intermediate ably removed periodically. In existing systems regeneration thereof. Thus, sour hydrocarbon this emulsion is removed by periodically withdistillates aso kelosenfi. gas 0 1) are treated drawing from the settling zone the entire treatwith alkaline solutions (e. g., aqueous caustic ing' ggllltion together with the emulsion layer soda or caustic potash solutions, aqueous meththereabove. This results in a period or" nonanolic caustic soda solutions), for the removal treatment of the fluid stream passing through of acidic sulfur compounds, e. g., hydrogen sulthe system or a shutdown of the system which fid I mercaptans; heal/181 hydrofiarbim d usually is not desirable, and contaminated hydrol te fr ti n (ke gas il, and lu ricatin carbon distillate is discharged from the settling oil) are extracted with selective solvents such 40 zone until fresh treating solution has been added as furiural, phenol, cresols, nitrobenzene, sulto the system. This arrangement is obviously folane, and the like, to improve the properties unsatisfactory. of the oil fraction for the intended purpose, such It is, therefore, a principal object of this inas for use as diesel engine fuel in the case of vention to provide an improved process for conthe kerosene and gas oil, and as a lubricating 5 tinuously treating a fluid with a treating liquid oil in the case of the lubricating oil distillate; which is immiscible therewith. A more specific mixtures of oxyhydrccarbons, e. g., as obtained object is to provide a method for removing interin the Fischer-Tropsch process, particularly of facial emulsions from a settling zone of a system aldehydes, ketones and alcohols, are treated with for continuously treating a fluid with a treating 5 liquid immiscible therewith without interrupting ,an aqueous solution of sodium bisulfite to eifect a selective separation of various ones of the oxygenated compounds; mixtures of hydrocarbons and oil soluble oxy-compounds, e. g., as obtained by the Fischer-Tropsch process, are extracted treating liquid in the treatment. Still another object is to provide a method for removing interracial emulsions from the settling zone of a system for continuously treating a sour hydrocarbon distillate with an aqueous alkaline solution, such as an aqueous solution of an alkali metal hydroxide. Other objects and advantages will be apparent from the following description.

In accordance with the present invention, it has been found that, in a process for continuously treating a fluid with a treating liquid substantially immiscible therewith wherein the resultin treated fluid is continuously separated from treating liquid in a settling zone, and a portion of the separated treating liquid is recycled in the process for treating a further portion of the fluid, suflicient of the interfacial emulsion which accumulates in the settling zone can be removed to prevent excessive build-up, yet without in-- terruption of the treatment,'by a method cornprising continuously passing the resulting mixture of treated fluid and treating liquid to a settling zone or" extended horizontal cross-sectional area comprising two separated horizontally contiguous lower sections and an upper section which is in substantially unobstructed communication with both of the lower sections, permitting the mixture to stratify in the settling zone under substantially quiescent conditions into a lowermost layer of treating liquid distributed. in the two lower sections, an uppermost layer of treated fluid in the upper section, and an interfacial emulsion layer therebetween, essentially at the uppermost level of the two lower sections, continuously and simultaneously separately withdrawing treated fluid and treating liquid from the settling zone while maintaining a substantial body of each therein and returning at least a portion of the withdrawn treating liquid for treatment of further portions of incoming untreated fluid, and intermittently withdrawing from one of said lower sections of the settling zone all of the treating liquid contained therein and the interfacial emulsion layer disposed thereon while maintaining a body of the the other lower section. Described in greater detail, the present process comprises continuously contacting an untreated 'fluid, particularly a liquid, such as a sour hydrocarbon distillate, with a treating liquid which is substantially immiscible therewith and which has a different density therefrom (preferably a higher density), such as an aqueous caustic soda solution for treating a sour hydrocarbon distillate, continuously passing the resulting mixture to a settling zone, the lower portion of which is divided, as by a baflle, into two sections, A and B, and wherein said mixture continuously separates or stratified into three layers: a layer of treated fluid, an interfacial emulsion layer, and a layer of treating liquid, continuously with-- drawing treated fluid (hydrocarbon) from said settling zone, continuously withdrawing treating liquid (aqueous caustic soda) from section A of said settling zone, continuously withdrawing treating liquid (aqueous caustic soda) from section B of said settling zone while maintaining substantial bodies of treating liquid in each of sections A and 13, until an undesirable amount of interfacial emulsion accumulates in the settling zone, continuously recycling at least a portion of the treating liquid withdrawn from sections A and B for treatment of further portions of untreated fiuid, intermittently removing interfacial emulsion from said section B by withdrawing therefrom all of the treating liquid therein and interfacial emulsion collected thereabove and thereafter introducing, into the treating system, an amount of fresh treating liquid equal to the amount of used treating liquid withdrawn from section B during removal of the interracial emulsion layer contained therein.

The apparatus which makes it possible to carry out the method of the invention in a practical and efficient manner comprises in combination: a mixing vessel provided with inlet for untreated fluid and treating liquid and outlet for resulting mixture, a settler connected to the outlet of the mixing vessel and having a partition therein extending upwardly from the bottom and extending only to an intermediate level of the height from bottom to top providing two lower sections and an upper section in substantially unobstructed communication with both of the lower sections, treated fluid outlet in the upper section and treating liquid outlets in each of the lower sectionsof the settler, a pump connectedto the outlets in the lower sections and adapted to return liquid withdrawn therethrough to said mixing vessel and valved outlet means in one of the lower sections adapted for intermittently discharging the treating liquid contents thereof and interracial emulsion collected thereon independently of withdrawal or" treating liquid from the other lower section. The last mentioned valved outlet can be operated manually, with visual observation of the interfacial level in the lower section under consideration, or it can be provided with a valve control which is set to close the valve when substantially only treated fluid fills said lower section.

The apparatus and method or the present invention may be used in any system for continuously contacting two substantially immiscible fluids having different specific gravities where separation of the treated fluid from the treating solution is efiected in a settling vessel and an undesirable emulsion accumulates between the two fluids being separated. Illustrative processes include the refining of petroleum oils with aqueous caustic solutions or with acid solutions, the treat ment of mineral oils with li uid sulfur dioxide, furfural, phenol and the like, the extraction of water-soluble compounds from oils, the extraction of ether-soluble compounds from water, the extraction of alcohol-soluble compounds from oil, and the like.

The present invention is of particular utility in the treatment of sour hydrocarbon gases or sour hydrocarbon distillates boiling in the gasoline or kerosene boiling range, 1. e., having a boiling point range between about F. and about 760 F., preferably between about F. and about 500 F., with about 19% to about 30% by volume, based in the incoming hydrocarbon stream of an aqueous solution of an alkali metal hydroxide, such as an aqueous caustic soda solution, containing from about 5% to about 50% by weight of alkali metal hydroxide.

The process or" the present invention will be more fully understood from the following detailed description made with reference to the accompanying drawing wherein the single figure thereof represents a simplified flow diagram of the process and which illustrates an improved settler for carrying out the present process.

Referring to the drawing the numeral I represents a horizontal, elongated, cylindrical settling vessel. An imperforate (i. e., solid) baffle 2 is installed in the bottom of the settler and divides the lower portion of the settler into two sections, A and B. The baflle is preferably located just beyond the midpoint of the settler. The baITle is of such size that sufiicient treating solution is retained upstream of the bafile (when the interface between the treated fluid and treating liquid is just below the top of the bailie) that satisfactory treatment and separation of incoming fluid can be maintained.

An untreated fluid is introduced through line 3, from a source not shown, and is combined with treating liquid, introduced through line 5. A flow rate control valve 6 (either manual or automatic) limits the flow of treating liquid as dictated by the required ratio of treating liquid to the volume of untreated fluid to be handled. The resulting mixture is passed through mixing valve 7 and into settler I wherein the mixture continuously separates into three layers: an upper treated fluid layer, an interfacial emulsion layer, and a lower treating liquid layer.

During normal treating operations, after the normal treating liquid level in the settler has been reached, all valves should be open except valve 8 in the fresh treating liquid line Ill, valves I I and I2 in spent treating liquid discharge lines I4 and I5, respectively. Used (only partially spent) treating liquid is continuously withdrawn from both sections A and B through lines I6 and I1, respectively, and is recycled for treatment of further portions of the incoming fluid stream. Treated fluid is continuously withdrawn from the settler through line I8.

When the interfacial emulsion accumulates to such an extent that it must be discarded, valve II, in spent treating liquid discharge line I 4 is opened, and treating liquid is discharged from the settler until the treating liquid level in the settler reaches the top of the bafile 2. The battle serves to divide the interfacial emulsion layer into two parts. Valve I I in line It and valve I9, in line I l, are then closed and valve I2 is opened. All of the spent treating liquid in section B and substantially all of the interfacial emulsion layer disposed thereon are removed therefrom. Ac cording to an alternative procedure when it is necessary to discard the interfacial emulsion layer, valve I 9 can be closed and valve I2 opened, and all of the spent treating liquid and interfacial emulsion which is contained in section B and which passes into section B are removed therefrom.. The gauge glass 22 can be used to determine when all of the treating liquid and interfacial emulsion layer have been removed. Treating liquid from section A is lated via line 5 for treatment of further portions of the incoming fluid stream, thereby maintaining satisfactory treatment of the fluid stream during removal of the interfacial emulsion layer from section B. After removal of treating liquid and interfacial emulsion from section B, valve I2 is closed, and valve 8 is then opened to introduce sufiicient fresh treating solution to make up to normal treating level; then valve 8 is closed. Valve I9 is also opened to permit recirculation of treating liquid from section B.

The spent treating liquid discharged from the settler may be regenerated for use as fresh treating liquid.

The above-described procedure is particularly suitable for such processes as the caustic treatment of sour hydrocarbon distillates wherein the consumption of treating liquid per pass is relatively small and, therefore, it is not necessary to continuously introduce fresh caustic solution continuously recircuin order to maintain satisfactory treatment. However, it is possible to vary the above procedure so that fresh treating liquid may be continuously introduced during the normal treating operation.

For example, according to one possible variation, used treating liquid is continuously withdrawn from section A, and returned to the system through line 5, together with fresh treating liquid introduced through line I8, for treatment of further portions of the incoming fluid stream. Used treating liquid is continuously withdrawn from section B, through line I5, at essentially the same rate at which fresh treating liquid is added to the system. When the interfacial emulsion accumulates in the settler to such an extent that it must be discarded, valve 8, in fresh treating liquid line I 0, is closed, and all of the used treating liquid and interfacial emulsion layer contained in section B is withdrawn therefrom. Used treating liquid withdrawn from section A is continuously recycled to maintain satisfactory treatment of the incoming fluid.

After removal of the interfacial emulsion layer from section B, valve I2 is closed and valve 8 is opened. When sufficient fresh treating liquid has been added to the system to make up to normal treating level, valve I2 is again opened and used treating liquid is withdrawn from section B at essentially the same rate at which fresh treating liquid is added to the System.

Although the invention has been described somewhat in detail with references to a preferred form of apparatus, it is to be understood that the present invention is not limited to the par-' ticular detailed structure hereinbefore disclosed. Many modifications which fall within the scope of the present invention are possible. For example, the baflle or partition which serves to divide the lower section of the settler into two parts can be placed either vertically or at an angle within the settler, and can be disposed horizontally, as well as transversely, of the settler. The inlet means for the mixture of fluid and treating liquid and the outlet means for treated fluid can be located either at opposite ends of the settler or on opposite sides thereof.

The following example serves to illustrate the present invention.

Example A petroleum naphtha having a boiling point range of from about F. to about 325 F. and which was strongly positive (about 0.01% by weight H23) to the lead acetate test was continuously contacted with an aqueous caustic sodasolution, and the resulting mixture was continuously passed to a horizontal cylindrical settling vessel about 20 feet long and about 8 feet in diameter. The lower portion of the settling vessel was divided into two sections by a transverse internal baffle which was located just beyond the midpoint of the vessel and which extended upwardly from the bottom of the settler for about 1 foot 4 inches. During normal treating operations, the percentage of caustic soda, solution in the incoming hydrocarbon stream was maintained at about 21% by volume, based on the hydrocarbon stream. The treated naphtha was lead acetate negative.

When the interfacial emulsion layer in the settler had built up to excess, all of the caustic soda solution and interfacial emulsion layer downstream of the baffle were drained from the settling vessel. The treated naphtha withdrawn from the settling vessel during this draining period was also lead acetate negative. No noticeable changes in operation or degree of treatment were observed during removal of the interfacial emulsion layer.

The above-described treatment was carried out, using a conventional settler. When excess interfacial emulsion accumulated in the settler, all of the caustic soda solution in the settler and the interfacial emulsion disposed thereon were removed from the settler prior to fresh caustic soda charge. During this draining period, the naphtha product from the settler became lead acetate positive. Sufficient HzS bearing naphtha escaped treatment to cause corrosion of equipment beyond the settler to an extent requiring replacement of parts in an abnormally short time.

I claim as my invention:

1. In the process of continuously treating a sour hydrocarbon distillate with an aqueous alkaline solution, the improvement comprising continuously passing the resulting mixture of treated hydrocarbon distillate and aqueous alkaline solution into a settling zone, the lower portion of which is divided by an upright baffle into two sections, A and B, and wherein the mixture separates into a layer of treated hydrocarbon distillate, an interracial emulsion layer, and a layer of aqueous alkaline solution, continuously withdrawing treated hydrocarbon distillate from the settling zone, continuously withdrawing aqueous alkaline solution from section A of the settling zone and recycling the withdrawn alkaline solution for treatment of further portions of incoming sour hydrocarbon distillate, continuously withdrawing aqueous alkaline solution from section B of said settling zone and recycling the withdrawn aqueous alkaline solution for treatment of further portions of the incoming sour hydrocarbon distillate, intermittently interrupting the recycle of alkaline solution from section B and withdrawing from said section B all of the aqueous alkaline solution therein and interfacial emulsion disposed thereon while maintaining a body of aqueous alkaline solution in said section A and the upper level thereof at the top of the baffle, and thereafter adding to the system an amount of fresh aqueous alkaline solution equal to the amount of used alkaline solution withdrawn from section B during removal of the interfacial emulsion layer therefrom.

The process according to claim 1, wherein the sour hydrocarbon distillate has a boiling range between about 100 F. and about 500 F. and wherein the aqueous alkaline solution is an aqueous solution of an alkali metal hydroxide.

3. In the process of continuously contacting a sour hydrocarbon distillate with an aqueous alkaline solution, the improvement comprising continuously passing the resulting mixture of treated hydrocarbon distillate and aqueous alkaline solution into a settling zone, the lower portion of which is divided by an upright bafile into two sections, A and and wherein the mixture is allowed to separate into a layer of treated hydrocarbon distillate, an interfacial emulsion layer, and a layer of aqueous alkaline solution, continuously withdrawing treated hydrocarbon distillate from the settling zone, continuously withdrawing aqueous alkaline solution from section A of the settling zone and recycling the withdrawn alkaline solution for treatment of further portions of incoming sour hydrocarbon distillate, together with fresh aqueous alkaline solution. continuously withdrawing used alkaline solution from section B of said settling zone at essentially the rate at which fresh alkaline solution is added to the system, and intermittently withdrawing from said section B all of the alkaline solution therein and interfacial emulsion disposed thereon while maintaining a body of aqueous alkaline solution in said section A and the upper level thereof at the top of the baflie.

4. In the process of continuously treating a sour hydrocarbon distillate with an aqueous alkaline solution, the improvement comprising continuously passing the resulting mixture of treated hydrocarbon distillate and aqueous alkaline solution into a settling zone, the lower portion of which is divided by an upright baffle into two sections and wherein the mixture is allowed to separate into a treated hydrocarbon distillate layer, an interracial emulsion layer, and a layer of aqueous alkaline solution, continuously withdrawing said treated hydrocarbon distillate from the settling zone, continuously withdrawing said aqueous alkaline solution from the settling zone and recycling at least a portion thereof for treatment of further portions of sour hydrocarbon distillate, and intermittently withdrawing from one of said sections of the settling zone all of the aqueous alkaline solution therein and interfacial emulsion disposed thereon while maintaining a body of aqueous alkaline solution in the other of said sections and the upper level thereof at the top of the bafile.

5. The process, according to claim 4, wherein the sour hydrocarbon distillate has a boiling point range between about F. and about 5 0 F.

6. The process, according to claim 4, wherein the aqueous alkaline solution is an aqueous solution or an alkali metal hydroxide.

'7. In the process of continuously treating a fluid with a treating liquid which is substantially immiscible therewith and which has a density higher than that of said fluid, the improvement comprising continuously passing the resulting mixture treated fluid and treating liquid into a settling zone, the lower portion of which is divided by an upright baffle into two sections, A and B, and wherein the mixture separates into an uppermost layer of treated fluid, an interfacial emulsion layer, and a lowermost layer of treating liquid, continuously withdrawing treated fluid from the settling zone, continuously withdraw ing treating liquid from section A of the settling zone and. recycling the withdrawn treating liquid for treatment of further portions of incoming untreated fluid, continuously withdrawing treating liquid from section B of said settling zone and recycling the withdrawn treating liquid for treatment of further portions of the incoming untreated fluid, intermittently interrupting the recycle of treating liquid from section B and withdrawing from said section B all of the treating liquid therein and interfacial emulsion layer disposed thereon while maintaining a body of treating liquid in said section A and the upper level thereof at the top of the baffle, and thereafter adding to the system an amount of fresh treating liquid equal to the amount of used treating liquid withdrawn from section B during removal of the interfacial emulsion layer therefrom.

8. In the process of continuously treating a fluid with a treating liquid which is substantially immiscible therewith and which has a density higher than that of said fluid, the improvement comprising continuously passing the resulting mixture of treated fluid and treating liquid into 10 ing liquid therein and interfacial emulsion disposed thereon while maintaining a body of treating liquid in the other of said sections and the upper level thereof at the top of the bafile.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,030,245 Crosby et a1 Feb. 11, 1936 2,556,438 Parker et a1. June 12, 1951 2,594,311 Johnson et a1 Apr. 29, 1952

Claims (1)

1. 8. IN THE PROCESS OF CONTINUOUSLY TREATING A FLUID WITH A TREATING LIQUID WHICH IS SUBSTANTIALLY IMMISCIBLE THEREWITH AND WHICH HAS A DENSITY HIGHER THAN THAT OF SAID FLUID, THE IMPROVEMENT COMPRISING CONTINUOUSLY PASSING THE RESULTING MIXTURE OF TREATED FLUID AND TREATING LIQUID INTO A SETTLING ZONE, THE LOWER PORTION OF WHICH IS DIVIDED BY AN UPRIGHT BAFFLE INTO TWO SECTIONS, AND WHEREIN THE MIXTURE IS ALLOWED TO SEPARATE INTO AN UPPERMOST LAYER OF TREATED FLUID, AN INTERFACIAL EMULSION LAYER, AND A LOWERMOST LAYER OF TREATING LIQUID CONTINUOUSLY WITHDRAWING TREATED FLUID FROM SAID SETTLING ZONE, CONTINUOUSLY WITHDRAWING TREATING LIQUID FROM SAID SETTLING ZONE AND RECYCLING AT LEAST A PORTION THEREOF FOR TREATMENT OF FURTHER PORTIONS OF INCOMING UNTREATED FLUID, AND INTERMITTENTLY WITHDRAWING FROM ONE OF SAID SECTIONS OF THE SETTLING ZONE ALL OF THE TREATING LIQUID THEREIN AND INTERACIAL EMULSION DISPOSED THEREON WHILE MAINTAINING A BODY OF TREATING LIQUID IN THE OTHER OF SAID SECTIONS AND THE UPPER LEVEL THEREOF AT THE TOP OF THE BAFFLE.

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