US1998747A - Wax recovery - Google Patents

Description

April 23, 1935. c. E. ADAMS WAX RECOVERY Filed Sept. 29,

no 385 N5} 9 .5 33

C72 mmgg 8.5 67 .fidama 1,2, 2

ATTORNEY Patented AI. 23, 19 35.

UNITED STATES PATENT i OFFICE H WAX RECOVERY Chester E. Adams, Hammond, 'Ind., assignor to Standard Oil Company, Chicago, 111., a cor- 1 notation of Indiana Application September 29,1933, Serial No. 891,532

" --10 Claims. (Cl- 198-20) This invention relates to the refining of wax bearing mineral oils; and it pertains. more particularly to the dewaxing of paraifin distillates or other stocks containing sweatable wax by the use of crystallization regulators, the dewaxing being etl'ected by means of propane and the crystallize and for increasing cooling rates from a few degrees per hour to several degrees pervminute,

but it has shown remarkable and unexpected results as a diluent. The propane diluent causes the crystallization of wax-mixtures in filterable' and settleable form, increases filtering and settling rates to a remarkable-degree, and does not dissolve even as-much waxl'as .light gasoline. The propane dewaxin'gzsystem'ior obtaining low pour point lubricatin'g'oils (iromabout 60 to 110 seconds Saybolt viscosity at ZIO K F.) has proven to be extremely successfulon' ac'ommercial scale and has been found to oflferan unsurpassed flexibility and economy of operation. The object 01' the present inventionis to extend the scope of this propane dewaxingqizocessto lighter oils, the

' so -called paramndl's tillates', and to combine propane dewaxingwith-ajwax-sweating operation so that. wax of a,..desired melting point, can be obtained from the process as well as dewaxed ,1. A further object ot my invention is to provide- [a means'tor obtaining an extremely rapid separation of sweatable wax from paraflindistillate dry wax cakes which contain minimum amounts of oil-and which will not have to be washed with propane or deoiled .prior to sweating. A

further. object is to increase the amount of salable wax that can be obtained from a given paraflin '7 distillate'and to improve the value of the dewaxed oil. A further object is to avoid the necessity of;

that in factv it appears to increase the yield of continuously supplying crystallization regulators or pour point depressors which are expensive and which might otherwise detract vfrom the :com-v .mercial success of the process. v A further object 'is to, simplify the dewaxing of paraflin distillate and the apparatus therefor, to dewax such distillates continuously, and to decrease the costs of equipment and operatingexpense. Other ohand the like. A further object is to obtain dense, with the advantage of more complete wax tre- Jects will be apparent from the following detailed description 01' the invention:

- v This invention is particularly applicable to a different type of 011 than is generally used i'or the crankcase lubrication oi. automobile engines. 5'

It specifically relates to fparaflln distillates" or stocks containing sweatable wax, a preferred example being a fraction of Mid-Continent crude between 62% and 74% distilled,-this fraction having a viscosity of about 136 seconds Saybolt at 100 F., a gravity of about 27.8 A. P. I. and a wax content oi' about 10.4% (determined by a 50-50 acetone-benzol mixture at 10 F.) Heretoiore it has been common practice to merely chill such distillates and press them in Carbondale presses,

the chilling often requiring several hours and the filtering or pressing requiring a like amount of time. I dilute the warm stock with a limited amount of propane, add a small amount 01' a crystallization regulator, chill by vaporizing some of the propane, leaving or adding enough propane to insure about 35% to 50% for use as diluent, and i flnally filter the wax from the oil on a continuous filter. The cooling may be effected in ten or fliteen minutes and the filtering may be efiected infrom three to ten minutes. The crystallization regulator appears to prevent interlacing of wax crystals and consequent entrainment oiunduiy large amounts of oil, and by using such materials I can obtain a very dry,

dense waxcake which does not have to be washed or 'de-oiled and which, after the removal oi. propane, may be readily sweated. In previous propane dewaxing processes it has been necessary to use much larger amounts of propane of the order or 75-80%, in order to obtain satisfactory filter rates. By the use of a continuous filter and a crystallization regulator, I have been able to reduce the amount of propane inthe mixture and still obtain as good or even higher fllter rates, but 40 recoverable wax or a given melting point. I have further discovered that the crystallization regulator is not combined with the high melting wax I but that after the sweating operation it is concentrated almost entirely in the drips or roots oil, it may be recovered for reuse by distillation of the drips or foots oil, or thisoil may be r'eturned to the dewaxing step with the crystallization regulator admixed therewith.

The accompanying drawing which forms a part of this specification diagrammatically represents an elevational plan of my improved system, parts of the apparatus being broken away and parts shown in section.

I will describe my invention as applied to the recovery of wax from 136 sec. viscosity (Saybolt 100 F.) pipe still paraflln distillate from Mid- Continent crude, but it should be understood that the invention is applicable to any other oil containing sweatable wax. As a crystallization regulator I prefer to use Pourex, which is a product made as follows: 180 parts by weight of chlorinated wax (130 F. melting point parafiln wax chlorinated to 13% chlorine content) are heated with 20 parts by weight of naphthalene to a temperature of 300 F.; two to four parts by weight of aluminum chloride are gradually introduced into this mixturfi. the addition requiring only a few minutes. The mixture is stirred and maintained at a temperature of about 300 F. for a period of about 2 to 20 minutes, preferably about 10 minutes. The hot products are then separated from the granular sludge by filtration and/or by gravity, and the reaction products are neutralized with hot caustic soda to completely remove all uncombined and loosely bound chlorine, hydrochloric acid, etc. The neutralized products are washed with water and are then ready for use. The product prepared in this manner is designated by the trade mark "Pourex and is my preferred crystallization regulator. I may, however, employ the substance which'is made in accordance with Davis Patent 1,815,022 and commercially known by the trade mark Paraflow". I may also use'highly refin'ed pitch still residues or gum fractions, residues from the distillation of petrolatum, asphaltic residues, soaps, and equivalent substances which have the desirable properties of preventing the interlacing of the wax crystals, and the present invention is not limited to any specific crystallization regulator.

Referring to the drawing, propane from pipe 10, a small amount of Pourex from pipe II and the parafiin distillate from pipe |2 are introduced into mixer II which is maintained at a sumciently hightemperature and pressure to effect a homogeneous mixture of the wax, Pourex and oil in the propane. I employ a sufiicient amount of propane to leave about 35% to 50% propane by volume in the chilled slurry which is charged to the filter. The amount of propane introduced through pipe 10 must be sufiicient to effect the refrigeration and to compensate for heat absorption, or additional propane or similar refrigerant must be subsequently added. The amount of Pourex may vary from about .05 to 2.0% based on the oil, but it is preferably about .1% to .2% by weight. The Pourex may, of course, be introduced in the oil solution and may be dissolved in the incoming oil. The temperature of the mixer is preferably about 80-100 F., the temperature.

Valve Ila is closed and valve la is opened so that the mixture is refrigerated by removing propane vapors through pipe l8 by means of compressor 20, the compressed propane vapors being condensed in coil 2|, and cooled by a cooling medium in box 22. The condensed propane is then introduced into separator 23, air and non-condensible gas being vented from the top thereof through valve 24 and liquid propane being conducted through pipe 25 to propane storage tank 26.

As soon as the propane-oil-wax slurry in chiller A reaches a temperature of about '10 to +10 F., preferably 0 F., valve I80. is closed and the cold slurry is withdrawn through opened valve Ila. and pipe 21 by pump 28, which is controlled by a liquid level device 29 in trough 30 in the pressure filter chamber 3|. stood, of course, that while the mixture in chamber A is being cooled, chamber B is being filled and chamber C is being emptied,-the arrangement of batch chillers being designed to permit the operation of a continuous filter. I may employ continuous pipe chillers and I may employ a receiver or storage tank to maintain a suitable volume of wax slurry for charging to the filter.

The filter is preferably of the continuous type and is shown in the drawing as a drum with a peripheral canvas or filter element 32, the drum being formed of a plurality of segments 33, 33, etc., each of which is connected to a port in the supporting shaft. The filter shown in the drawing rotates in a clockwise direction, the cake being built up while the segment is immersed in the slurry, being dried as the cake advances out of the slurry, being washed, and finally being discharged, as will be hereinafter described. I may use any type of filter instead of the continuous type described. I

The wax-free diluted oil passes through pipe 25 to filtrate storage tank 28, from which it is forced by pump 31 through pipe 38 to steam still 39. This still is heated by steam coil 40 or other suitable means, and propane is vaporized under pressure and conveyed by pipe 4| to condenser coils 2|. The hot oil is then passed through pipe 42 and reducing valve 42 into low pressure chamber 44, wherein the last traces of propane are vaporized and removed through pipe 45 to pipe I! and compressor 20. If desired, I may employ a suitable stripping means for insuring desired flash characteristics of the finished oil which is removed through pipe 4' to asuitable storage tank.

The wax on the filter may be washed with propane which is led into the filter by pipe 41 and sprayed onto the cake by nozzles 4|. It should be understood that I may maintain the pressurev in the filter by means of an inert gas or a lower boiling gas, such as ethane, and I may employ butane or other solvent instead of propane as a washing liquid.

The wax cake is preferably removed from the filter by a blow-back system, port 48 being connected by pipe 50 to the top of storage tank 28 or to some other source of pressure. Other cake discharge means may, of course, be employed. The wax cake is scraped from bulged filter cloth by'scraper 52, and is conveyed by wax screw 53 to a wax melting tank I4, which is heated by steam coils. Liberated propane is removed through pipe 56 to propane line l8, and the hot liquid wax is forced by pump 51 to crude wax storage tank 58.1mm which it is introduced by pipe 59 into sweating oven 00.

It should be under-' It should be understood that any number of sweating ovens may be employed and that they may be of any type or design. The wax is first solidified in,the swea oven by introducing cold water through pipe ooh, I, and the temperature is thereafter gradually raised by circulation of warm water through coil to cause the softening and separation from high melting waxes" It will be understood to those skilled in the art I that suitable plumbing fixtures, valves, pressure regulators, insulating means, etc. will be supplied when necessary, that a pump it will be necessary in propane line III, etc. I do not limit myself to any of these details except as defined by the appended claims.

Some outstanding features of the invention are:' wax can be solidified and filtered in a few minutes while prior art methods require several days; dewaxed oils of much lower pour points can be obtained than were otherwise obtainable; the yield of to melting point waxes from any given crude are markedly increased, and

the process is extremely economical in operation.

The process is made commercially feasible because of the peculiar and unexpected effect of the crystallization regulator and because this crystallization regulator can be readily recovered for reuse from the drips or foots oil.- 'When Pourex, Paraflow and the like are employed with paraflin distillates which have been diluted with naphtha, they have little effect, filter rates are not materially increased, and the sweatability of the wax is not improved. However, when Pourex is used with a propane-diluent, phenomenal results are obtained. A 50-50 mixture of parafiin distillate and propane cooled and filtered in the absence of Pourex yields only 50% of dewaxed oil; when .03% Pourex is added to the oil the yield of dewaxed oil is increased to 87.2%. When a 35% propane,65% parafiin distillate mixture is filtered at about 0 F., the reduced wax cake is 55% of the original oil charge. When .2% of Pourex is added to the oil the 35:85 mixture gives a wax cake of 19.2% of the original oil charged. When .3% Pourex is added to the oil in the 35:65 mixture the yield of wax cake is only 12.5%. At the same time the addition of the Pourex effects a considerable increase in the filter rate; without Pourex-the rate is 10 galions per square foot per' hour, based on the viscous oil charge, and with 3% Pourex the filter rate is increased to 16.6 gallons per hour. ,Without Pourex the thickness of the wax cake is about three-fourths of an inch, and with 2% to 3%. of Pourex the cake is only one-fourth to one-half inch in thickness, illustrating the increased compactness of the wax. Without Pourex the wax cake is mostly oil and contains only about 15% of wax. With Pourex the wax content of the filter cake is about 50% to 55% Without Pourex the melting point of the reduced wax cake is so low that it cannot readily be determined, and even when 50% propane is used the meltingpoint of the wax cake is only 89 F. When Pourex is employed the melting point of the wax cake is 'from 108-114" F. It is significant to note also that the melting point of the dry wax is several degrees higher when Pourex is used. In all of these tests the chilling rate can be about 2 to 3% F. per minute, the filtering temperature about 5 to +5 F., and the filter pressure may be about 15 lbs. per square inch. The filtering rates are very rapid.

The above comparisons of 36:65 propane parafiln distillate mixtures with and without Pourex are even less striking than the results obtained with 50-50 propane parafiln distillate mixtures. Here again the wax cake, in the absence of Pourex, is 50% by volume of the oil charged while a wax cake of only about 12%% is obtained by using from .2% to .3% of Pourex. "Quantities of Pourex larger than 0.3% based on wax-bearing oil are not necessary on this particular stock, but it is found that sweatable wax cakes cannot be obtained with less than .05% of Pourex.

I have discovered that Pourex is thrown out of solution with the wax in the chilling step. This is proved by the complete recovery of the Pourex, as will be hereinafter described, and it is also proved by the fact that the cold tests on oils dewaxed with Pourex are not lower than oils dewaxed without added Pourex.

However, the efiect of Pourex on the wax cake is found to be beneficial rather than detrimental. The finger test on the mixture indicates that its sweating properties are not impaired and the comparison of slack wax sweating with and without Pourex is shown by the following table:

rim IV- Sweating plant slack was-with and without Pourex 'M. P. of slack wax-110 v A sample-of the drips from the sweating of the slack wax containing Pourex was, mixed with completely dewaxed Mid-Continent 60 stock and vacuum distilled until a volume equal to the drips charged had been taken overhead. The maximum still temperature during the distillation was 540 1". under the pressure of 3 mm. Assuming that all of the Pourex added to the slack wax was in the drips, then all of the Pourex should be in the bottoms from the vacuum distillation. On that basis the bottoms were added to 180 pale oil to give different concentrations of Pourex and the cold tests compared with cold tes'ts obtained on the same oil with original Pourex added. The comparison is shown in the following table:

TABLE V Recovered Pom-ea: or. original Pourex as cold test depressor: for 180 pale Thus it is. seen that Pourex does not impair sweating and that it can be completely recovered from the drips by vacuum distillation, or equivalent distillation with steam. The usual practice, however, is to return the drips with incoming oil, and tests have proven that the mixture of incoming oil with about 8% of foots oil (containing Pourex) can be filtered at rates of about 14 gallons per square foot per hour to give a cake containing about 57% wax which, when dry, hasa meltingpoint of 127 F.

It should be understood that instead of effecting all of the refrigeration by vaporizing propane, as hereinabove described, I may cool the mixture by introducing cold propane into warm oil and venting the propane during the addition. I have found, however, that this process cuts down markedly on filter rates and increases the amount of .oil in the wax cake. It is more desirable to introduce warm propane and to efiect all of the refrigeration by vaporization of propane rather than by heat exchange or the use of sensible heat.

My invention is applicable to the dewaxing of heavy .distillates and residual stocks as well as light parafiln distillates, but in this case it is necessary to use larger amounts of propane, and to filter at lower temperatures. When residual stocks are employed I prefer to precipitate the asphalt by means of propane before dewaxing and proceed directly with dewaxing and deasphaltized propane solution. A Mid-Continent residue (298 viscosity at 210 F. Saybolt) deasphaltized with 25% of propane at to F., gives a yield of about deasphaltized oil. When this oil is dewaxed using 70% by volume of propane as a diluent I obtain a wax cake containing 70.3% wax. My invention is also applicable to both treated and untreated wax-bearing oil stocks and, in fact, to any wax-bearing material containing sweatable wax.

With regard to the. percent of wax removed. from the 136 viscosity at F. pipe still paraflin distillate, a comparison was made between the Pourex-propane method and the present methods. Assuming a solid point (dewaxed oil) of 30 F. with present methods against 15 F. for the .propane-Pourex method it was found that the wax recovery is approximately 30% greater using the propane-Pourex method than with the present method.

An extremely important feature of my invention is the low operating cost. Estimates in one instance show that the cost per 100 gallons of solution charged will be less than one-third the cost per 100 gallons with present methods. The cost of removing sweatable wax from parafiln distillate is, of course, much less than the cost of and solvents where convenient. Thus I may dilute very viscous oils with hexane or naphtha to facilitate handling in the various steps of the process. I may also add-certain other solvents to the mixture to decrease thesolubility of the wax and provide a more complete separation thereof. Acetone, sulfur dioxide, ethyl and methyl ether are examples of such solvents.

I claim:

1. The method of recovering sweatable wax from a wax mixture, which comprises mixingsaid wax mixture with propane and a crystallization regulator at an elevated temperature and pressure to effect a homogeneous mixture thereof, chilling the mixture by vaporization of propane to effect the solidification of wax which can be readily filtered to give a dense sweatable wax cake, filtering the diluted oil from the wax and crystallization regulator, sweating the wax to remove the foots oil and crystallization regulator therefrom, and returning the crystallization regulator for admixture with further amounts of sweatable wax.

2. The method of claim lwherein the foots oil containing the crystallization regulator is admixed with further amounts of thegmineral oil stock containing sweatable wax.

3. The method of claim 1 wherein the crystallization regulator is recovered from the foots oil by distillation.

4. The method of claim 1 wherein the crystallization regulator is a condensation product obtained by the reaction of a chlorinated wax with naphthalene brought about by the catalytic action of aluminum chloride.

5. The method of claim 1 wherein the wax mixture undergoing treatment is a paraiiin distillate having a viscosity of about 136 seconds Saybolt at 100 F.

6. The method of obtaining maximum yields of high melting point wax from mineral oil stocks containing wax, which comprises mixing said stocks with propane and a crystallization regulator, chilling the mixture to about 0 F. to efi'ect solidification of wax which, on filtration, will yield a relatively dry wax cake, filtering said mixture to obtain said dry wax'cake, sweating said wax cake to remove low melting point waxes, oil and crystallization regulator from the high melting point waxes, and recovering the crystallization regulator for reuse.

7. The method of claim 6 wherein the crystallization regulator is a condensation product obtained by the reaction of a chlorinated wax with naphthalene brought about by the catalytic action of aluminum chloride.

.8. The method of claim 6 wherein the oil stocks containing wax are parailln distillates having a viscosity at 100 F. of about 136 seconds Saybolt.

9. A processfor recovering high melting point wax from a mineral oil stock, which comprises mixing said stock with a crystallization regulator and a liquefied normally gaseous hydrocarbon diluent, refrigerating the mixture by vaporization of a portion of said diluent, leaving about 35% .to 50% ofthe diluent admixed with 65% to 50% of the chilled stock, filtering the mixture to separate diluted wax oil from wax cake containing crystallization regulator, removing diluent from the wax cake, sweating the wax cake to separate high melting point wax'from low melting point wax and crystallization regulator, and returning the crystallization regulator for reuse.

10. The process of claim 9 wherein the mineral oil stock is a paraflin distillate having a viscosity at 100 F. of about 136 seconds Saybolt.

CHESTER E. ADAMS;

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