US2329887A - Method of desalting crude petroleum - Google Patents

Description

Sept. 21, 1943. H, EGGLESTON ET AL 2,329,887

METHOD OE DESALTING CRUDE PETROLEUM Filed July 9, 1940 HERBERT L. EGGLESTON RAYMOND H. PIERSON JAMES B. MULLIN p INVENTORS, lama-(0.1. i

, JEIORNEY.

Patented Sept. 21 1943 METHOD or DEsAL'rIno CRUDE PETROLEUM Herbert L. Eggleston, Glendale, Raymond H. Pierson, Alhambra, and James B. Mullin, San Marino, Calif., assignors to Gilmore Oil Company, a corporation of California Application July 9, 1940, Serial No. 344,610

- 7 Claims.

The object of the invention is to provide a rapid and economical method for removing the salt (mainly sodium chloride) which occurs in many crude petroleums either as finely disseminated strong brine or as solid crystals or even in both forms in the same oil.

Reduced to its simplest terms, the method consists in adding to a stream of the solt-bearing petroleum a minor stream of an aqueous alkali solution, so proportioned and under such conditions as to produce an immediate and intimate dispersion of the solution through the petroleum, and immediately passing the mixed stream into a zone in which rapid separation of the phases is produced. From this zone are withdrawn separate streams of clean oil and of an aqueous solution which contains substantially all of the salt originally carried by the petroleum.

The preferred manipulation of the invention may best be described with reference to the attached drawing, which shows in a diagrammatic manner an apparatus suitable for putting the.

method into effect. It will be understood that all of the elements of this apparatus are wholly conventional and subject to substitution by functional equivalents, and that the assembly shown is illustrative only. v

Referring to the drawing, the salt-containing petroleum, the initial condition of which will be described, is drawn from any source not shown through pipe I by pump 2 and is discharged through pipe 3 and a meter 4.

An aqueous solution of an alkali, later to be described, is prepared in any tank 5, from which it is withdrawn through pipe 6 by a pump fl and discharged through pipe 8 and a meter 9.

Pipes 3 and 8 join in pipe Ill which conducts a mixed stream of oil and alkaline solution into a heating element i I, which may be a tubular heat interchanger warmed by the stream of clean "oil later provided.

From this element the warmed mixture passes through pipe i2 into a second heating element l3 supplied with steam under pressure by a valved pipe l4 and relieved of condensed water by a valved pipe l5. In this element the temperature of the mixture is raised to the preferred level, which may be about 220 Fahr. for heavy and viscous oils and materially lower; say 150 Fahr., for crude oils of low viscosity. y

In the heating units the alkaline solution becomes thoroughly dispersed and disseminated throughout the oil and reaction between the alkali and saponifiable constituents contained in or added to the oil takes place. It is not essential that just two heating elements be used-one or any greater number may be employed and they -may be heated in any desired manner. It is not desirable, however, to heat the oil by means of high temperature fire gases nor to inject open steam into the mixture for heating purposes.

From heating element I3 the heated mixture flows through pipe it into the upper end of a separating chamber I'l. Ordinarily it is necessary to pack this chamber or column with baffling material, such as broken glass or pottery, smal lump coke, Raschig rings or excelsior, the latter being preferred. If packing is used it rests ona perforated plate or grid l8 so spaced from the bottom of the shell as to leave a settling space I9 of ample capacity.

In some cases the oily and aqueous phases will separate spontaneously, without the use of bailling material, but in most cases the presence of a liberal quantity of contacting solids is desirable and in many instances, particularly if the oil be viscous, it is completely essential to successful separation. Where it is present, and assuming correct operating conditions, the dispersed alkaline solution is collected in films on the surfaces of the packing material and flows downwardly and concurrently with the clean oil v into space 19, in which the two liquids immediately stratify.

A valve 20 controlling a water drain pipe 2| and controlled in turn by float mechanism generally indicated at 22 withdraws the alkaline solution (now a dilute salt brine) as fast as it separates and thus maintains a constant oil-water parting level. The clean oil collects above the brine layer and is withdrawn through pipe 23.

The first contacting column usually removes most of the brine from the oil, sometimes a l of it, but it is desirable to provide a second column 24, identical with the first, to remove the last traces lof brine.== From this tower the aqueous liquid is drained as above described while the oil, now substantially free from water, is finally withdrawn through pipe 25. This pipe should be provided with some pressure control mechanism, illustrated as a relief valve 26, so adjusted as to prevent the liberation of steam or oil vapors within the system. For example, if the maximum temperature is maintained at 220 Fahr. the relief valve may be set to maintain a pressure of 20 pounds gauge at the outlet of column 24.

If the first heating element I3 is an interchanger as above described, pipe 25 may be connected to discharge into the space surrounding the tubes, to supply heating fluid, the final point of discharge of clean oil being then through pipe 21. If an interchanger is not used at this point some other means of cooling the oil stream to a temperature at which it may safely be discharged into the final receiving tank should be provided in its stead.

Control The proper functioning of this system depends on control of the condition of the oil entering the system and of the quantities of water and of alkali introduced into the oil in the form of the dilute alkaline solution above referred to. These controls will now be described.

Condition of feed oil It should be premised that the method herein described is limited to petroleums containing constituents which saponify or form water soluble salts with alkalis in dilute aqueous solution. This formation of soaps is essential to the dissemination of the aqueous liquid throughout the oililow, and this intimate dispersion in turn is essential to bringing the salt content of the oil into solution in the aqueous liquid. Most crude petroleums, even of low specific gravity, contain enough'saponifiable matter for this purpose, in 1 the form of naphthenic acids; lactones or acid anhydrides, though some of the very pure parafiinic petroleums are deficient in this respect and do not respond to the treatment. Oils which do not contain enough saponiflable matter initially may be made responsive to the treatment by the addition of very small quantities of readily saponifiable matter, as for example oleic acid or resin acids. Without limitation, the method is particularly applicable to the asphaltic oils which are adapted to the manufacture of road oils-and asphalts.

The oil supplied to the system should be brought in advance to a low water content, not to exceed pipe line specification (3% by volume of water and suspended matter). The system will break a small amount of emulsion, but not economically, and if the crude as produced does not meet the requirements of low water content and substantial freedom from emulsion and -sus-. pended solids it should first be demulsified in separate apparatus and in any preferred or conventional manner.

Control of water dosage The alkaline solution supplies to the oil stream both water and alkali. Fortunately the volume of water supplied is not critical, though it should be kept within limits. We ha e found in experience that satisfactory results are had with such quantity of water that the withdrawn brine contains about 3 pounds salt per barrel (42 gallons) of brine. Thus if the crude contained 200 pounds total salt per 1,000 barrels oil and was reduced by the treatment to say or 12 pounds Control of alkali dosage The control of the. quantity of alkali introduced into the oil is effected roughly by controlling the strength of the alkali solution, taking into account the proportion of water which it is considered desirable to add, after which finer adjustments may be made by varying the volume of this solution in its relation to the volume of oil being fed. If the strength of the solution be adjusted initially to give an approximation to the optimum alkali dosage when the water dosage is at its optimum, such variations in solution supply as are required for exact adjustment of the alkali dosage can be made without vary-' mental operation of the plant, though only with the risk of producing some oil which is incompletely desalted and which may contain a stable emulsion, and preliminary tests by one or the other of the following laboratory methods is recommended.

Both of these laboratory methods depend on observations of the behavoir of agitated mixtures of the unknown crude with aqueous al-,

same quantity, say 5 to 7 ml. of one of the test solutions, and all the bottles then brought to a constant temperature of say 200 Fahr. in a water bath. Each bottle is then shaken vigorously for two minutes and an observation is made of the manner in which the solution disperses in the oil. The bottles are then allowed to stand for one hour in the water bath at the same temperature and the appearance of the settled samples is observed.

As the results of this method as well as of the second to be described are essentially comparative, either'may be modified as regards temperature, time and dosage to adapt it to a variety of crudes.

Inthe second method, samples ofthe oil are measured, dosed and heated as above described but are agitated by means of a power mixer. Portions of the mixed samples are then diluted and centrifuged according to A. S. T. M. Test Method D96-35. In either case the behavior and appearance of the tested samples is interpre'ted as 'follows:

If the alkali dosage is deficient, dispersion of phases separate rapidly on standing or centrifuging and the removal of salt from the oil approaches completion. The settled aqueous liquid is characteristically cloudy and opalescent with a slight yellowish undertone.

With an excessive alkali dosage dispersion is stillrapid and complete but, on settling or cen-.

are quite marked and readily observable and permit the selection of the one test solution which comes the closest to introducing theoptimum proportion of alkali into the .oil. The actual alkali dosage corresponding to this test is then calculated by multiplying the percentage 7 dose of solution by the alkali content of the selected testsolution. The alkali-dosage so determined, which' will be an approximation to the correct dose, may then be applied to the stream of oil passing through the system, in the form of an aqueous solution of such strength as will carry into the oil the preferred quantity of water. As a precaution, in starting up the system with an unknown oil, it is desirable to start with less than the determined dosage and gradually build up to the optimum, to avoid the possibility of plugging packed contacting towers with an emulsion resulting from initial overdosage. The incompletely desalted oil produced during this building-up stage may be returned for retreatment.

Starting the oil through the plant system with the approximate alkali dosage determined as above, closer regulation and a better final result may be obtained by observing the behavior of the system. An

increase in pressure drop through the contacting towers is an indication of emulsion accumulation and overdose of alkali, while a rise in the salt content of the product oil indicates a deficiency. Such minor variation in alkali dosage may be compensated by varying the relative volume of solution feed to volume of the oil stream.

The pH value of the withdrawn aqueous liquid may also be used as a guide to plant regulation. The original alkali solution has a high pH value, from 11.0 to 12.0. For the attainment of the most complete desalting and the smoothest operation the pH value of the withdrawn aqueous liquid should range from 8.4'to 8.9, and so far as our experience goes the optimum figure is PH 8.7.

The appearance of the aqueous liquid withdrawn from the system varies as above described as the alkali dosage departs in either direction from the optimum, and after a little experience may be used as a closely approximate guide to correct dosage. The time factor of the system must be considered in observing the effect of any change in regulation. The final test, of

course, is the attainment of the maximum salt content of the clean oil to less than 0.012 pound per barrel. The clean oil withdrawn from the system should be substantially free from water and ,in good practice will show from 0.2% to a mere trace. 4

In the desalting in this manner of heavy California crude oils the best results have been attained with doses of alkali (calculated as normal sodium carbonate) ranging from 0.015 gram to 0.050 gram per ml. of 0il,i0r from 0.052 to 0.173 ppund per barrel; 7

Other alkalis, to-wit the carbonates, hydroxides or borates of any of the alkali metals, may be substituted for sodium carbonate in the proportions represented by their combining weight.

The similar compounds of the alkali earth metals cannot be so substituted.

In the event that no one of the test samples in the laboratory methods above described produces rapidand intimate dispersion of the alkali solution through the oil, it may be well to determine whether the oil actually contains saponifiable substances. This may be determined indirectly by initially adding to the oil a very small proportion of a fatty acid, preferably oleic acid, a suitable proportion being of the order of 0.01% to 0.03% by volume. the oil amenable to the treatment a variation of the dosage of acid may then be tried in order to determine the minimum quantity necessary. Oleicor naphthenic acids may be used in this manner to supplement a deficiency of natural acid constituents or to replace such constituents where they are completely lacking in the crude oil. a

We claim as our invention:

1. The method of desalting petroleum originally deficient in saponifiable substances which comprises: blending with said petroleum a minute proportion of a soap-forming organic acid; saponifying said acid by intermixing with said blended petroleum a dilute aqueous solution of an alkali, the proportion of said solution being so controlled as to cause the intimate and rapid dispersion of said solution throughout said petroleum and the avoidance of the formation of permanent emulsion, and substantially completely separating from said petroleum the aqueous liquid containing the soaps so formed together with a part of the salt originally contained in said petroleum.

2. The method of desalting petroleum containing soap-forming organic acids which comprises: gently agitating with said petroleum a dilute aqueous solution of an alkali, said solution having initially an alkalinity not substantially less then pH 11.0; producing reaction between said alkali and said soap-forming acids; controlling the quantity of said solution to bring the alkalinity of said solution after said reaction within the range pH 8.4 and pH 8.9, and partingisaid solution from said petroleum after said reaction takes place.

3. The method of desalting petroleum which comprises: ascertaining whether said petroleum contains suflicient saponifiable matter to produce dispersion therein of a dilute aqueous solution 01' an alkali; correcting any deficiency of saponifiable matter by blending with said petroleum a soap-forming organic acid; creating separate flow=streams of said petroleum and said solution and blending said flow-streams; so proportioning said solution stream to said petroleum stream as to cause the saponification 01' at least a part of said saponifiable matter, the intimate If this addition renders and rapid dispersion of said solution throughout said petroleum and the avoidance of the formation of permanent emulsion, and substantially completely separating from said petroleum the aqueous liquid containing soapy reaction produid containing soapy reaction products and salt.

5. A method substantially as and for the purpose set forth in claim 4, including a preliminary ucts together with a part of the salt originally contained in said petroleum.

4. The method of desalting petroleum which comprises: ascertaining whether said petroleum contains sufiicient saponifiable matter to produce dispersion therein of a dilute aqueous solution of an alkali; correcting any deficiency of saponfiable matter by blending with said petroleum a soap-forming organic acid; intermixing with said petroleum a quantity of said alkali solution so proportioned as to cause the intimate and rapid dispersion of said solution throughout said petroleum and the avoidance of the formation of permanent emulsion, and substantially completely separating from said petroleum the aqueous liq- 'step of removing from said petroleum any water in excess of about 3% by volume together with any emulsion originally present in said petro-

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