US3496100A - Electrostatic technique for the contacting and mixing of non-miscible liquids - Google Patents

Description

Feb. 17, 1970 F. J. WRIGHT ELECTROSTATIC TECHNIQUE FOR THE CONTACTING AND MIXINGOF NON-MISCIBLE LIQUIDS Filed Dec. 7, 1967 25:5 25:3 5 8.5: Ewan 1 3 3 S 3 $32 hzmmw FUDOONE L 0w TwmDOI QmmI l nvantor F. J. Wright I Patent Attorney United States Patent O 3,496,100 ELECTROSTATIC TECHNIQUE FOR THE CON- TACTING AND MIXING OF NON-MISCIBLE LIQUIDS Franklin J. Wright, Watchung, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Dec. 7, 1967, Ser. No. 688,858 Int. Cl. Cg 19/02;B01k J/00; B01f 3/08 U.S. Cl. 208265 4 Claims ABSTRACT OF THE DISCLOSURE The instant disclosure is directed towards a method and apparatus for electrostatically mixing and contacting liquids. The method is particularly useful for obtaining large surfaces of contact between nonconducting liquids such as hydrocarbons with conducting liquids such as caustic or acid solutions or water. The teachings herein disclose the transferring of electrical charges to the conducting liquid by passing the same through a metallic nozzle which is connected to a high voltage supply. By using the method and apparatus of the instant disclosure, an extremely fine dispersion of the conducting liquid may be obtained in the nonconducting liquid.

BACKGROUND OF THE INVENTION In many refinery and other industrial operations which involve the contacting of immiscible or partially miscible liquids, the efficiency of the operation depends greatly on the thoroughness of the contacting and mixing of the two phases. The higher the degree of dispersion of the one phase with the other and the greater the degree of agitation, the greater is the contact achieved.

In practice, dispersion has generally been accomplished in the prior art by means of propeller bladed mixers or other mechanical devices, all of which require moving equipment, such as impellers, circulating pumps and the like. It will be appreciated by those skilled in the art that when mechanical devices such as propellers are used for stirring and mixing, various associated problems exist. For example, when stirring and mixing in pressure vessels, packing glands for the rotating propeller shafts are necessary. The use of packing glands often results in associated undesirable maintenance problems. In addition, moving parts are prone to mechanical failures, particularly in the presence of corrosive solutions which may be undergoing processing. Aside from these purely mechanical and/or maintenance problems, ditficulties still exist in obtaining adequate contacting and mixing of the immiscible or partially miscible liquids by purely mechanical means.

The novel technique and apparatus for contacting liquids which form the basis of the disclosure for the present invention is based on the use of electrostatic fields and not only can provide equal or better dispersion and agitation than can be obtained by mechanical means but can achieve this without resorting to any moving parts. Thus, servicing and maintenance are held to a minimum, particularly since all electrical components to be used can be considerably overdesigned at little or no extra cost.

SUMMARY OF THE INVENTION By way of example and obviously not by way of limitation, the novel electrostatic mixing technique of the instant invention will be discussed in the environment of an acid washing of a hydrocarbon feed.

The mixing of sulfuric acid with a hydrocarbon is selected as an example because of its importance in processes such as alkylation and also in order to clearly demonstrate the difference and substantial improvements presented by the present invention over the prior art, which describes the use of electrostatic fields to mix liquids (see in this regard U.S. 2,884,375).

The prior art teaches that dispersion can be produced by applying a voltage across the boundary between two liquids. This technique is limited, however, to a few special combinations of liquids such as, for instance, heptane and nitrobenzene or aniline. The technique fails if one of the liquids is a good conductor of electricity such as caustic or acid solutions or even water. Unfortunately, these are the very types of liquids which are of the greatest interest in many refinery operations. The reason for the breakdown of the technique with good conductors is that with a conducting liquid, the boundary between the two liquids becomes in essence the electrode and hence only the nonconducting hydrocarbon is subjected to the field.

The present invention on the other hand operates best in these very situations, i.e., when a conducting liquid is to be dispersed in a nonconducting one. If two nonconducting liquids were required to be mixed, considerable improvement in the effectiveness of the electrostatic technique could be achieved by making one of the liquids slightly conducting by the addition of a very small concentration of a soluble polar substance capable of enhancing the conductivity of hydrocarbons. Examples of such additives are bifunctional compounds such as dinitriles, diamine alkanes, hydroxy nitriles, hydroxy amines, dihalo alkanes, halo-cyano alkanes and also esters of phytic acids. Concentrations of 1 p.p.m. to 0.1% are effective, the preferred concentrations being in the range of 10 to 1000 p.p.m.

The hydrocarbon is contained within a suitable tank while the acid wash solution is introduced into the hydrocarbon by means of an injector comprising a suitably sized electrically conductive nozzle or through a plurality of such nozzles. The injector, which serves as an electrode, is connected to a high voltage power supply, another electrode being immersed in the hydrocarbon itself. With the application of a high voltage from the power supply to the injector, the acid solution issues from the nozzle or nozzles as a very fine mist of droplets. An extremely high contact surface is thus presented to the oil by the acid droplets. Furthermore, since these droplets are charged as they enter the electrical field between the nozzle or nozzles and the electrode in the hydrocarbon feed, they are greatly agitated.

As will be appreciated by those skilled in the art, the nozzle or nozzles can be made either the positive or the negative electrode, the formation of the dispersed droplets being unafiected by the polarity of the field. It was unexpectedly found that AC voltages were equally effective. While the voltage necessary to produce these droplets is in the range of 20 to 30 kilovolts, the resultant currents are quite small (usually less than 10* amps) and thus the power consumed is of a low magnitude, being on the order of 1 or 2 watts at the most.

It will be further appreciated that the acid droplets continue to move towards the electrode in the hydrocarbon and they will eventually coagulate in its vicinity. Thus, the equipment operates, in addition to a contacting means, as an electrical coagulator. This, of course, greatly improves the efiiciency of the overall Wash process since it ensures that no treating agent (in this case acid) is carried over to the next processing stage with the treated hydrocarbon feed.

In spite of its apparent simplicity, the instant device and method produce a great many advantages over contacting processes used in the prior art. For example, contacting time between the hydrocarbon and the acid used in the above example can be greatly reduced because of thehigh degree of dispersion. Thus, the possibility of undesirable side reactions leading to sludge formation and acid consumption is reduced. Furthermore, the process can easily be operated under superatmospheric conditions since there is no requirement dictating the use of usually troublesome packing glands around rotating shafts. Under such conditions oxygen may be readily excluded, thereby preventing gum formation and the like; and, hence problems such as pumping of a gummy acid wash solution are avoided. It will also be seen that because no moving machinery is involved, service factors and maintenance, as "well as the cost of initial installation, are all minimized.

Thus, an object of the instant invention is to provide a method and apparatus for the mixing and contacting of nonmiscible liquids or partially miscible liquids.

Another object of the instant invention is to provide an electrostatic technique for mixing and contacting immiscible liquids which avoids the necessity of using mechanical agitation means.

Still another object is to provide an electrostatic mixing and contacting method and technique which is particularly useful for obtaining large surfaces of contact be tween a nonconducting liquid such as a hydrocarbon with a conducting liquid such as a caustic or acid solution of water wherein the technique also operates as an electrical coagulator.

These and further objects as well as a fuller understanding of the invention may be had by referring to the following description and appended claims taken in conjunction with the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 shows schematically a mixing and contacting apparatus according to the teachings of the instant invention.

FIGURE 2 illustrates a typical acid and caustic washing process to be performed on a hydrocarbon feed, which process employs the method and apparatus of the instant invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIGURE 1 in detail and again using by way of illustration concentrated sulfuric acid and a hydrocarbon as the liquids to be contacted, the apparatus and method of operation is as follows:

The hydrocarbon 14 is placed in a suitable container 12. The sulfuric acid (or other conducting liquid) is stored in a suitable vessel designated by the reference numeral 2. Vessel 2 has at its lower end a metallic nozzle 4. It will be appreciated by those skilled in the art that nozzle 4 may take on any number of configurations and is to be sized in accordance with the amounts of fluids being handled. Thus, for example, in small scale laboratory work, this nozzle can be fabricated of stainless steel hypodermic tubing having a gauge number of 22. As may be seen in FIGURE 1, the end or tip of noz zle 4 is submerged beneath the surface of hydrocarbon 14. A suitable high voltage power supply 6, such as a transformer, maintains nozzle 4 at a high potential (with respect to ground) in the range of from about 1 kilovolt to about 50 kilovolts through the lead 8. Another electrode held at a lower potential {c.g. ground) is submerged in the hydrocarbon below nozzle 4. It will be understood that in the absence of a voltage across the two electrodes 8 and 10, large drops of the sulfuric acid would form at the tip of the nozzle, then break off and slowly sink to the bottom of the vessel 12. However, in the presence of a field, the sulfuric acid issues from the nozzle as a fine mist of droplets of colloidal dimensions. Due to the existence of the field between electrodes 4 and 10, these droplets are violently excited in a random fashion as they travel towards the submerged electrode 10. Eventually the acid droplets reach the electrode 10 where they coagulate and fall to the bottom of the vessel 12 as indicated at 16. Thu h q ipment not only serves as a contacting means but also operates as an electrical coagulator. This effect, of course, increases the efiiciency of the overall process since it assures that no acid is retained in the hydrocarbon.

In order to disperse the sulfuric acid, electrical charges must be transferred to the acid from the nozzle which is acting as an electrode. This transfer is dependent on the conductivity of the liquid, the nature and extent of the contact between the charged surface of the electrode and the liquid, the flow rate and the magnitude and type of high voltage. In this regard polarity of the field is not of sufficient importance so the nozzle can be made with a positive or the negative electrode or it can be attached to an AC power supply. From a practical point of view, the fact that AC is eifective is useful since, in general, equipment to generate high AC voltage is cheaper and less bulky than high voltage DC power supplies.

Example Using concentrated sulfuric acid and heptane as the liquids to be mixed, and employing a nozzle made from a stainless steel hyprodermic tubing (No. 22 gauge) a voltage of about 20 to 30 kilovolts applied to the nozzle resulted in a spray angle of over emanating from the tip of nozzle 4. This angle and the fine mist of sulfuric acid droplets which formed at the tip of nozzle 4 produced highly satisfactory contacting and mixing of the sulfuric acid with the heptane. While the voltages were as indicated, the currents measured were quite small (being in the range of about 10- amperes). Thus, the power consumed is normally very low, being on the order of l or 2 watts at the most.

A flow scheme exemplifying the use of the instant apparatus and method in acid and caustic washing of a hydrocarbon feed is shown in FIGURE 2. The hydrocarbon feed to be treated is introduced into a tank 12 via the line 11. Two electrodes 20 and 10 are provided within the tank 12. Electrode 20 is in the form of a manifold portion 21, to which are affixed a plurality of injection nozzles 4. A potential difference is imposed between electrodes 20 and 10 by use of the high voltage power sup ply 6 which is operatively connected to electrode 20. An acid solution such as H 50 and water contained in tank 2 is pumped via pump 32 and the line 34 into manifold 21. As hereinbefore indicated, due to the high voltage applied to electrode 20, the acid solution issues from nozzles 4 as a very fine mist of droplets. Thus, an extremely high surface is presented to the hydrocarbon within the tank 12. Furthermore, as these charged droplets enter the electrical field between the two electrodes 20 and 10, they are greatly agitated. Eventually, the acid droplets 13 move towards the ground electrode 10 where they coagulate, the equipment operating as an electrical coagulator at this juncture. The coagulator acid exits the tank 12 via the line 22. A portion of this material may then be recirculated via the line 24, the remainder exiting the system via the line 26. An acid make-up line 28 provides additional acid to the tank 2. It will be appreciated by those skilled in the art that the coagulation effect above mentioned greatly improves the chiciency of the overall process since it ensures that none of the acid wash is carried over to the next, i.e. caustic wash, stage.

The acid 'washed hydrocarbon feed exits tank 12 via the line 38 and enters a caustic wash tank 39. The operation of this portion of the process is exactly analogous to the acid wash portion just described. Thus, a caustic wash is contained within the tank 46, which wash is pumped via the line 36 to the manifold portion 21 of electrode 20'. As before, electrode 20- is supplied with a high voltage from a high voltage power supply 6'. The spent caustic exits tank 39 via the line 40, a portion being recycled via the line 44 and the remainder leaving the system via the line 42. Fresh make-up caustic is supplied to the tank 46 via the line 48. The caustic wash hydrocarbon feed exits the tank 39 via the line 46.

Although the invention has been described with a certain degree of particularity, it is to be understood that the present disclosure has been made by way of example and that obviously changes in the details of construction and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed. It is also to be appreciated that the invention is obviously not limited to the acid and caustic washing of a hydrocarbon feed and that the flow diagram represented in FIGURE 2 is intended to be illustrative in nature.

In view of the above, reference should be had to the following appended claims in determining the full scope of the instant invention.

What is claimed is:

1. A method of forming a dispersion between an electrically conducting liquid with a nonconducting liquid, said conducting liquid being at least partially immiscible in said nonconducting liquid, which method comprises the steps of:

(a) maintaining a body of non-conducting liquid;

(b) maintaining an electrical field in said body of nonconducting liquid;

(c) feeding said conducting liquid to an ejector suspended in said body of non-conducting liquid;

((1) maintaining said ejector at a potential of from about 20 to about 30 kilovolts with respect to ground potential;

(e) passing said conducting liquid through said ejector whereby said conducting liquid emanates from the tip of said ejector as a plurality of electrically charged fine droplets, said droplets being dispersed in said body of non-conducting liquid under the infiuence of said electrical field.

2. The method of claim 1 wherein said conducting liquid is selected from the group consisting of aqueous caustic solutions and aqueous acid solutions and said nonconducting liquid is a hydrocarbon.

3. A method of forming a dispersion between a first normally nonconductive liquid and a second normally nonconductive liquid, said first liquid being at least partially immiscible in said second liquid, which comprises the following steps in combination:

(a) maintaining a body of said second normally nonconducting liquid;

(b) injecting an amount of a soluble polar substance into said first liquid whereby the conductivity of said first liquid is enhanced;

(c) feeding said first liquid through an ejector suspended in said body of said second normally nonconducting liquid;

(d) maintaining said ejector at a potential from about 20 to about kilovolts with respect to ground potential;

(e) maintaining an electrical field in said second normally non-conducting liquid; and

(f) passing said first liquid through. said ejector whereby said first liquid emanates from the tip of said ejector as a plurality of electrically charged fine droplets, said droplets being dispersed in said body of said second liquid under the influence of said electrical field.

4. The method of claim 3 wherein the amount of said soluble p'olar substance is sufiicient to obtain a concentration of said substance in said first liquid in the range of from about 10 p.p.m. to about 1000 p.p.m.

References Cited UNITED STATES PATENTS 2,033,446 3/1936 Pettefer 204302 3,169,915 2/1965 Kennedy 204171 1,565,992 12/1925 Eddy 208187 2,050,301 8/1936 Fisher 20'4l85 2,884,375 4/1959 Seelig et a1. 208146 3,309,413 3/1967 Ferrara et a1. 208-267 DELBERT E. GANTZ, Primary Examiner G. J. CRASANAKIS, Assistant Examiner US. Cl. X.R.

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