US2305024A - Method of refining paraffin waxes - Google Patents

Description

Dec. 15, 1942. H. J. MOYER 2,305,024

METHOD OF REFINING PARAFFIN WAXES 'Filed Nov. 30, 1940 PAN JWEATER.

Patented Dec. 15, 1942 METHOD OF REFI NIN G PARAFFIN WAXES Harold J. Moyer, Summit, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application November 30, 1940, Serial No. 367,940

Claims.

Ihe present invention relates to the refining of 'parafiin waxes obtained from petroleum or other mineral oil sources. The invention is especially concerned with improvements in the so-called sweating operations in which the final amounts of oily constituents are removed from the waxy constituents. In accordance with the present invention, improvements in sweating operations are secured by charging the sweating apparatus with presolidified crude wax instead of with molten crude Wax. When operating in this manner, the efficiency and capacity of a sweating apparatus is materially increased, since it is no longer necessary to solidify the molten wax in the sweater apparatus. A preferred adaptation of my invention utilizes a cooling fluid by which a relatively small wax particles size is secured.

The cooling fluid also functions as a carrier medium for charging the trays of the sweating apparatus in a manner to secure a uniform and even distribution of the small solid wax particles.

It is well-known in the art to separate waxy constituents from petroleum oils by various processes and to refine the crude separated waxes by subjecting them to carefully regulated heat treatment, usually in a sweater house. Separation of the waxy constituents from a feed oil by conventional method usually comprises chilling the waxy feed oil to a temperature at which the wax crystallizes and passes out of solution, followed by filtering the chilled mixture. The waxes so obtained usually retain appreciable amounts of the oily constituents, the concentration of which may vary from about 10% to 50% or more based upon the oily wax. These waxes, due to the amount of oil present, are semi-solid and unctuous in nature, particularly so when the amount of oil present is relatively high. The slack wax cake is removed from the filter press, melted in a suitable receptacle and then conveyed in a molten state to sweating apparatus, the conventional form of which comprises a multiplicity of shallow metal pans stacked one above the other. Each pan is equipped with a false, perforated bottom and a continuous coil of pipe through which a heating or cooling fluid may be circulated. The stack of pans is closed within the building, commonly known as a sweater house. The usual practice, in charging the sweater pans, is to fill each pan with water to the age receptacles.

height of the false bottom which is withdrawn from the bottom of the pan after the wax charge has solidified. The molten wax is then charged to the pan in such a Way that it floats upon the Water and so that the interface between the wax and oil is in contact with the perforated plate. Under these conditions the pipe coil which is disposed immediately above the false bottom is submerged in the wax.

The molten wax is solidified by circulating cooling water or an equivalent cooling medium through the coil, and by means of cool air which is passed through the sweater house. After the crude wax is solidified, it is sweated and the oily constituents removed by gradually raising the temperature or" the oil-wax cake by circulating a heated fluid in the submerged coil and heated air within the sweater house. As the temperature of the crude wax cake rises, the oily constituents are first removed. After removal of an appreciable amount of the oily constituents, waxes of gradually increasing melting points areremoved. These waxes contain gradually diminishing percentages of oil as the sweater house temperature and the melting points of the fused waxes increase. Finally, the sweating operation progresses to the point where only the porous structure of the highest melting point wax remains in the solid state on the perforated false bottom since the other wax fractions have melted out and have been drained off by grades to stor- The remaining solid, relatively high melting point wax is substantially oil-free and is known in the art as crude scale wax. Crude scale wax contains approximately 2% of oil based upon the wax and is hard and firm, and generally possesses some discoloration. This crude scale wax is generally subjected to further refining and sweating in order to remove the remainder of the oil by methods similar to those described above for slack wax sweating except for some variations in temperatures employed for the fractional fusion of the crude scale wax. This method for refining waxes is applicable to waxes obtained by any manner such as those obtained when using dewaxing solvents of the character of propane, various ketones, and the like. Thismethod of refining waxes possesses. a distinct disadvantage that an appreciable time period required in order to solidify the wax,

which may amount to 14 hours or more. That this factor is critical is apparent when it is considered that a cycle of this character may require about 27 hours or so.

In conventional wax-sweating operations, the crude oil containing wax is charged to the sweating apparatus pans in liquid form and there cooled and solidified. This materially limits the capacity of the sweating apparatus by appreciably increasing the time cycle. In order to shorten the time cycle, Various suggestions have been made that the time period necessary for solidifying the wax be eliminated by charging the wax directly to the trays in the solid form. However, suggestions heretofore made of this character have not been successful due to the fact that the waxes removed from the filters, centrifuges, or plate and frame presses are irregular and lumpy in form, and thus cannot be readily transferred to the sweater pans. Furthermore, practice has demonstrated that waxes which are relatively large in form, or in which the wax particles are irregular in size cannot be successfully sweated.

,I-Iowever, I have now discovered a process by which, wax may be charged to the sweaters in solid form in an efficient and economical manner and by which it is possible to sweat the solid wax in a manner to secure results superior to the resultssecured when. sweating wax charged to the sweaters "in the liquid state. By operating in a manner which eliminates the solidification period from the sweater apparatus cycle, the efficiency 7 of the sweaters can be greatly increased and the capacity of same more than doubled. My invention entirely eliminates the solidifying and cooling period which is required when charging the sweaters by the conventional method. In accordance with the present invention, the oily wax cake as it is removed from the filters, centrifuges, plate and frame presses or ,aprior sweater is handled in a manner to secure vwax particles having a uniform relatively small size which are then charged to the sweater. Wax particles of this character are preferably secured byintermittently ejecting the wax from a multiplicity of suitable relatively small apertures in the form of small pellets or globules into a stream of cold Wateror an equivalent cooling fluid. In accordance with the preferred modi- I lficatijon of the present invention, this cooling fluid also functions as a carrier medium for introducing the small solid Wax particles into the sweating trays. V i

operating in this manner, utilizing the cooling fluid as the carrier medium, the small. wax particles are distributed uniformly and evenly ever the wax trays to the desired height. The cooling fluid, preferably water, is allowed to drain from the pan after distributing the wax particles on the tray. In this manner any desired depth of crude wax, limited only by the "height of the sidewalls, may be readily attained on each tray. The cooling fluid after removal from the tray may be cooled and recycled, or discarded as desired. After the cooling fluid is removed from the tray, the sweating operation may be immediately started by gradually raising the temperature of the solid small wax particles.

The process of my invention may be readily understood by reference to the attached drawing'illustrating modifications of the same. Fig- "ure '1' illustrates a diagrammati'cal flow plan of a "conventional sweating operation adapted in "accordance with the present invention. Figure sired size.

2 illustrates in some detail a sweater tray, while Figures 3 and 4 illustrate preferred modifications of securing the relatively small solid wax particles.

Referring specifically to Figure 1, it is assumed that the crude, oil-containing wax fractions have been secured from conventional deoiling operations. The crude wax fraction is melted in vessel I by means of steam pipe coil 2. Liquid wax is withdrawn from vessel I by means of line 3 and pump 4 and is ejected at point A into a stream of cold water by means of an ejector arrangement ii. The water is withdrawn from water storage 6 by means of pump I and is introduced into ejector arrangement 5 by means of line 8. Beyond point A the ejected waxes along with the water flow upwardly through ejector arrangement 5 under conditions whereby the ejected wax particles tend to form spherical pellets. The solid wax particles and water are withdrawn from ejector arrangement 5 by means of line 9 and passed to trays or pans ll! of the sweater apparatus I I. The water utilized in conveying the wax functions to distribute the wax uniformly into pans I0. After the pans Ifi have been filled to the desired depth with the wax pellets, the water is drained from the respective pans by means of withdrawal line I2 controlled by valves iii. The wax pellets are retained in the pans by means of the perforated bottom plates Id. The cooling carrier fluid which comprises water and which is withdrawn from sweater apparatus II by means of line I2 is passed through cooler I5 and recycled to water storage 4 by means of line I6.

Figure 2 illustrates in some detail a pan or tray arrangement I0, Carrier fluid containing the solid wax particles is introduced by means of line 9 and the fluid Withdrawn by means of line I2 controlled by means of valve IS. The solid wax particles are retained on the tray by means of perforated plate I4. After the removal of the carrier and cooled fluid the sweating operation is started and controlled by means of heat which is introduced into pans ID by means of a heating fluid conducted through coil ll and then withdrawn.

Figure 3 illustrates in some detail ejecting ,arrangement 5. Water is introduced into ejecting arrangement 5 by means of line v8 while the molten wax is introduced by means of line 3. A suitable cutting arrangement 20 powered in any desirable manner is provided for securing the desired pelleted size. The arrangement shown for the purposes of illustration comprises an apparatus which is provided with an oscillatory motion which cuts the extruded wax to the de- Figure 4 illustrates the cutting arrangement 20 in some detail. Cutting arrangement 20 is provided with an oscillating cap 2| which opens and closes a series of apertures through which the molten wax is protruded in a manner to cut the molten wax to the desired particle size.

7 The present invention may be widely varied. The size of the wax pellets may vary considerably and in general is of such a diameter that they may be readily carried along with the cooling fluid and may be readily sweated. However, in order to secure rapid solidification of the wax on contact with the water, it is preferred that the'diameter of the particles be less than /2 inch.

I have found that particularly desirable results aresecured when the diameter of the wax particles is in the range from about V8 to inch.

If the wax particles are too small, emulsions tend to form which impair the sweating process, hinder separation of oil from wax, and decrease the oil-free wax yield from a given oil-wax mixture. If the wax particles are too large, they are difficult to handle in the described manner. Furthermore, non-uniform sweating also results.

It is to be understood that the oil-containing crude wax may be ejected into the stream of cooling fluid either as a liquid or as a plastic solid. When the wax is ejected into the cooling fluid as a liquid, the crude wax will be both solidified and cooled by the cooling fluid. However, when the wax is ejected as a solid, heat may or may not be removed and will depend upon the relative temperatures of the extruded wax and the cooling fluid. When solid wax is ejected into the water or an equivalent cooling fluid, it is preferably accomplished by an extrusion means known in the art. Waxes which have a relatively high oil content and are, therefore, relatively plastic and soft, such as slack waxes, are preferably extruded in the solid form rather than ejected into the cooling fluid in the liquid state. By operating in this manner the necessity for melting the wax for transferring to the sweater is eliminated. Waxes which have a relatively low oil content, such as scale waxes, are preferably melted and formed into pellets by ejection of the molten wax as small globules into a stream of cooling fluid. Due to the low oil content of these waxes, they are less plastic and, therefore, more readily assume a permanent shape than plastic waxes when solidified. Whether the crude wax to be sweated is pelleted from a liquid or a solid state depends upon the nature of the wax being processed.

In order to avoid agglomeration of the globules or pellets of the ejected wax, it is desirable to eject the wax vertically upward and to have the same flow concurrently with the cooling fluid. The ejecting means is of a sufficiently large diameter so as to minimize turbulence and is long enough to insure complete solidification of the outer surface of the pellet before it reaches a line of a reduced diameter. By operating in this manner, the wax globules will not become concentrated in the upper part of the pipe, as they would were the pipe placed in horizontal position. Agglomeration and plugging of the equip- 1 ment are thus avoided. It is also extremely desirable to adjust the temperature of the molten wax so that it is ejected into the cooling fluid only a few degrees above its melting point in order to avoid undue delay in the solidification period. In general, the temperature of a liquid wax as it is ejected into the cooling fluid should be less than 5 above its melting point and preferably less than 3 above its melting point.

Any suitable inert cooling fluid may be used as a cooling medium. However, in general, the cooling fluid preferably comprises water.

In order further to illustrate the invention, the following examples are given which should not be construed as limiting the same in any manner whatsoever. In various operations, a slack wax of about 107 F. melting point, containing about 26% of oil, was prepared in three forms and charged to a sweater pan. All forms were sweated for crude scale wax. The results of these operations were as follows:

Method of charging sweater pan Conven- Extruded tional, i. e., wax pellets gi sf g f molten wax of about Sion of ax allowed 34" dia. char to solidify charged to i in pan to pan p Temp. at start of opern. F 75 78 Sweater yields:

Foots oil, vol. percent of charge to pan 35 26 20 Intermediate slack wax, vol. percent of charge to pan 25 33 54 Crude scale wax, vol. percent of charge to pan.-. 4O 41 26 Oil in crude scale wax percent.. 2 2. 2 1 4 Melting point of crude scale wax F- 120 1 120 1 Above. 9 Below.

From the above it is apparent that the pelleted wax of the present invention sweats as satisfactorily as does wax charged in the conventional manner to the pan. It is also apparent that the size of the wax particles is critical in order to V avoid emulsiflcation and poor sweating.

The invention may be adapted to all present conventional forms of sweating crude petroleum waxes for the purpose of separating oil and wax. It may be readily adapted to charge both the tank and pan type of sweater.

The invention is not to be limited by any theory or mode of operation but only in and by the following claims in which it is desired to claim all novelty in so far as the prior art permits.

I claim:

1. Improved process for sweating crude solid waxes comprising extruding the same into a cooling fluid under conditions to secure relatively small solid wax particles, passing the fluid containing the solid wax particles to a sweating pan, withdrawing the cooling fluid and then subject: ing the wax particles to gradually increasing temperatures.

2. Process as defined by claim 1 in which said particles have a diameter in the range from about to inch, and in which said cooling fluid comprises water.

3. Improved process for sweating crude solid waxes comprising melting the same, ejecting the melted wax into a cooling fluid under conditions to secure solid relatively small wax particles, passing the fluid containing the wax particles to a sweating pan, withdrawing the cooling fluid and then subjecting the wax particles to gradually increasing temperatures.

4. Process as defined by claim 3 in which said wax particles have a diameter in the range from about to A inch, and in which said cooling fluid comprises water.

5. Process as defined by claim 3 in which said melted wax is injected upwardly into upflowing cooling fluid comprising water.

HAROLD J. MOYER.

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