US2137209A - Dewaxing mineral oil - Google Patents

Description

Patented Nev. 15, 193s 2,137,209`

UNITED STATES PATENT oFF1cE- DEWAXING MINERAL UIL Edwin C. Knowles, Beacon, N. Y., assigner to The Texas Company, NewYork, N. Y., a corporation of Delaware Application September 20, 1935, Serial No.`41,`393

5 Claims. ((1196-18) This invention relates to the separation of wax jected to the preliminary heating stepoi' my infrom oil. vention.

'I'he invention contemplates a process of de- The filter cake obtained by the practice of my waxing wax-bearing mineral oil containing either invention is less voluminous, retains less oil, and

5 a naturally-occurring or an added wax crystal comprlsesahigher content of parafiin wax. Fur- 5 modifying substance, wherein the oil is mixed thermore, there is an increase in the yield ofwaxwith a solvent liquid, the resulting mixture of oil free oil obtained as a result of followingthe proand solventheated to an elevated temperature, cedure of my invention.

and the heated mixture thereafter chilled to pre- This improvement in filtration rate is apparcipitate the wax constituents which are subseently due to the beneficial change inthe nature quently removed. mmof the crystal formation of the'wax precipitated The invention has particular reference to defrom mixtures which have been subjected to the waxing relatively viscous oils having a Saybolt preliminary heating'step, although the reason for Universal viscosity above about 80 seconds at 210 this change in' the crystal structure is not en- F. as, for example, an oil of around 90 or 100 sectirely understood. 15 onds at 210 F. and containing naturally-occur- It is my thought that, in the case of viscous ring asphaltic and resinous constituents which zoils, certain of the naturally-occurring asphaltic apparently modify the crystal form of the wax, and resinous hydrocarbon constituents constitute as will be more fully explained below. The inwax crystal modifying substances. These convention involvesI dewaxing oil of this 'character stltuents are believed to be less soluble than wax 2o under conditions such that these naturally-ocin the dewaxing solvent liquid, and at the mincurring constituents apparently facilitate crysimum temperature at which the wax-bearing oil tallization of the wax in a more readily separable appears to be in complete solution, these constitand iterable form. uents are not in true solution but rather are pres- 'The invention is also applicable todewaxing ent as a colloidal solution. 25 oils containing Wax crystal modifying substances In this form,theSE SubSianCeS DOSSblXfOIm'mS or materials which have been added thereto. I 011 the-Small Plate-WPG paraffin Crystals formed have found it advantageous toV add wax crystal during preliminary precipitation of the wax from modifying materialto relatively low viscosity oils the solution, and these films inhibit the normal 3o which are dencient in the naturallyeoc'urring transformation of the plate-type wax crystals 30 modifying material above referred to, and then 111130 the mOI'e easily lterable type of crystals. dewax them by the process of my invention. By 'heating t0 temperatures 0fA 15 to 50. F.

The invention specifically contemplates heating above this minimum temperature of apparent the mixture of dewaxing solvent and waxmermg complete solution, these colloidal or lowI solubility 36 oil containing such Wax crystal modifying sub- "substances are apparently completely disolved in 35 stance to a. temperature of around 15 to 50 F the solvent. It is believed that upon chilling the above the minimum temperature at which the heated solution, they precipitate f rom the soluoil and wax appears to be completely dissolved ,tion substantially 5o-extensively with the wax m in the solvent, and thereafter chilling the heated the form of nuclear particles which actually fa" l 40 mixture to a temperature of the order of o., E cilitate crystallization. of wax in a more readily 4 .in order to precipitate the wax constituents in separable and mtemble form' .It is thought that l readily separable form the optimum effect is realized when the modify- I have discovered thatwhen such wax-bearing ing substance continues to preciplta'te from .the oil and solvent mixture is subjected to heating'y mon over the entire range of Wax crystalhzaon. at thefe elevated temperatures prior to chilling' Ihave found that the modifying action of added there 1s a marked improvement in the character of the wax precipitated from the chilled i wax crystal modiers may be greatly enhanced t Th t l t t m x' by the procedure of my invention, and particuure' e YS -2' s fue ure of the Wax is Such l. larly in the case of relatively less viscous oils as,. that the wax 1s more readily separated from the for example' oils having a, viscosity up to about -50 mxtme and can be more fapldly led there- "15 Saybolt Universal seconds at 210 F. Some .fIOm- AS a CODSSQUDCG, the filter rates can be improvement results, however, even in thecase increased ten 'or twelve times over the rate obof the more viscous oils by adding some of this taining in the ordinary de-waxing procedure material thereto and lproceeding by the method where the mlxtule 0f Oil and Solvent 1 not Subof this invention. Such added modiers may 55 comprise small amounts of Montan wax, or synthetic modifying substances such as derived by condensation of chlorinated wax and naphthalene, and aluminum stearate, etc. The amount of such modifying material added may be of the order of 0.20 to about 1% by weightof the waxbearing oil.

. It is thought that, as in the case ofthe naturally-occurring Wax crystal modifying substances, these added substances probably are precipitated from the previously heated solution in a form in which they act as nuclear particles serving to modify wax crystallization, with the result that the Wax can be more readily filtered from the chilled solution.

'I'he minimum temperature at which the waxbearing oil appears, on visual inspection, to be completely soluble in the dewaxing` solvent, orin homogeneous admixture therewith, depends upon the nature of the oil as weil as upon the solvent.

In the case of a selective dewaxing solvent of the .character of a mixture of about 30% acetone and 70% benzol, for example, the minimum temperature of apparent complete solution of wax-bearl`such as a mixture of acetone and benzol, to temperatures in the range of about 125 to 175 F., and then chilling the heated mixture to tempera'- tures of 0 F. and below in order to precipitate the wax constituents. These wax constituents are then separated from the cold mixture, advantageously by filtration.

l drawings.

'I'he invention is particularly advantageous as applied to the dewaxing of distillate and residual wax-bearing oils which contain small amounts of asphaltic and resinous matter. For this reason, it is particularly adapted to dewax relatively viscous oils, including those which have been subjected to previous solvent rening action to remove relatively low viscosity index constituents, and which are ordinarily rather difficult to dewax.

The improvement in filtration rate is indicated by reference to Figure 1 of the accompanying Curves A1, A2 and B in this 'figure represent graphically the relationship between filtration rate and the temperature of heating prior tchilling in the case of dewaxing both a distillate and a residual type of stock, each of which had been previously subjected tg solvent extraction for the removal of relativelyv low viscosity index constituents. Cur'v/es A1 and Az relate to dewaxing the same ,distillatestock, while curve B relates to dewaxing the residual stock,

using methyl ethyl ketone and benzol as a dewaxing solvent. Laboratory inspection tests made on these two stocks gave the following results:

In both cases, the solvent comprised a mixture composed of 40% methyl ethyl ketone and 60% benzol, mixed with the oil in the proportion of four parts of solvent mixture to one part of oil. After heating the mixture to the desired solution temperature, it was then introduced to a chilling vessel wherein it was chilled by indirect contact with cold brine to a temperature of -10 F. 'Ihe chilled mixtures were all filtered at this temperature to remove the wax and produce nitrates containing oil of about 0 F. pour. Filter rate calculations are all based on the passage of an equal volume of wax-free oil through the filter surface, that is, 0.2 gallon of wax-free oil per square foot of ltering surface.

As shown by curve A1 where the solvent and wax-bearing oil mixtures were heated to a temperature of only F. prior to chilling, a filtration rate of about 1.7 gallons of wax-free oil per square foot of filtering surface per hour was realized. On the other hand, when the solution was heated to a temperature of F. prior to chilling, the filter rate was increased to 24 gallons of Wax-free oil per square foot of ltering surface per hour. 1

It will be observed that heating the mixtures to temperatures in the range below 120 F. andV also in the range above i60-170 F. does not appear to affect the filtration rate, but between these points the increase in filtration rate with increasing mixing temperatures is quite rapid;

In the experiments represented by curve A1, the mixture of wax-bearing oil and solvent was subjected during the chilling step to mild agitation by bubbling pre-cooled nitrogen gas through the mixture at the rate of about 4.8 cubic feet of gas per hour per square foot of horizontal cross-sectional areal of the vertical chilling vessel. The chilling vessel comprised a vertical cylindrical vessel, and the gas was introducedl into the battom thereof and caused to bubble upwardly through the mixture of oil and solvent contained therein.

Curve Az represents the filtering rates obtained with the same stock, using the same solvent but employing mechanical stirring instead of gaseous agitation. The mechanical stirring in this instance .-was effected by inserting a mechanical stirring arm into the same chilling vessel used in the preceding experiments. The stirring arm was rotated 'at a uniform rate of about five revolutions per minute.

Under these conditions, the optimum ltration 5.0i

ever, without such preliminary heating as, for

example, when heating the oil and solvent to a temperature of around 120 F., the filtration ratev is only about one gallon per square foot of filtering surface per^hour at the same rate of mechanical agitation.

It appears, therefore, that in order to rea the optimum effect of preliminary heating, it is desirable to employ relatigely mild agitation during the subsequent chilling "step, and preferably the type of agitation such yas is realized by bubbling a stream of gas at a relatively low rate through the chilling mixture. cessiveqmechanical agitation or violent l.agit tion of any type tends to deform the wax crystals and ender the wax much more difficult to filter.

Curve B represents the results obtained in the case of a residual lubricating oil stock, and since mechanical agitation, rather than gaseous agitation, was lemployed in chilling the solutions of residual oil and solvent, the curve is very similar to curve Aa for the distillate oil dewaxed under CIL the same conditions. In any case, as shown by curve B, heating the mixture of residual stock and solvent to a temperature of about F. results in a very great increase in the rate of filtration. The general characteristic of curve B is similar to that of curve A1, indicating that the application of the'process of this invention to residual stocks produces the same improved results as in the case of -viscous distillate lubricating oil stocks, providing that the mixture, during the chilling step, is subjected to relatively mild agitation.

The following tabulation affords a comparison of the eiect upon filter rates -by varying thel degree and type of agitation employed during the chilling step in dewaxing a distillate stock, such as that described above, with the same proportion of solvent mixture of the same solvent composition 2` Mechanical agitation Tempera Filter rateture of Revolugallons of waxsolution tions per free oil per prior to minute square foot chilling per hour 165 `l00 Y l. 4

Gaseous agitation Tempera- Cubic Filter rateure of feet of gas gallons of waxsolution persquare free oil per prior to foot per square foot chilling hour per hour F. 15. 1 16.8 170 4. 8 16. 8 170 l. 6 12. 0 150 22. 0 12. 5 `150 18.0 15.3 150V 15.1 i7. 7

In making these comparisons, the mixture of wax-bearing oil and solvent was subjected to chilling in the same chillingvessel, regardless of the type of agitation employed. Mechanical agitation comprised the insertion of a rotating stirrerin the chilling vessel which was caused to revolve at rates varying from 5 to 140 revolutions per minute. v

The gaseous agitation was effected by bubbling nitrogen gas through the mixture in the chilling vessel, with the stirrer removed, at rates of from 1.6 to 22 cubic feet of gas per hour per square foot of horizontal cross-sectional area of the vertical chilling vessel.

In the runs in which the mechanical stirrer was employed, the mixture of wax-bearing oil vand solvent was heated to the same solution temperature of 165 F. prior to chilling. 'I'he results obtained indicated that where rapid mechanical agitation is employed as, for example,' at rates of around 50 to 140 revolutions per minute of the stirrer, the filtration rate is relatively low, in the neighborhood of one or two gallons per square foot of filtering surface per hour.v However, by reducing the stirring rate to around ve revolutions per minute, there is a very marked increase in the filtration rate; that with this low-rate-of stirring, a filter rate of 11:4 gallons It appears, therefore, that when the mixture l is agitated by bubbling gas therethrough. at a relatively low rate, the wax crystals are subjected to less deformation than when subjected to mechanical stirring. is necessary in ord-er to realize uniform chilling of the mixture.

I have also found `that the obtaining of the maximum degree of benefit by preliminary heating of the wax-bearing oil and solvent is dependent upon employing the proper ratio of solvent mixture to oil. In the case of oils up to about '15 seconds viscosity at 210 a suitable mixture comprises one part of oil to one part of sol- 'vent. For more viscous oils, the \mixture may comprise two parts 'of solvent to onpart of oil. Larger proportions of solvent may be used if -desired as, for example, as high as four lor six parts of solvent to yone part of oil. v

In order to more fully describe the operation of my invention, reference will now be made vto Figure 2 of the drawings, illustrating a method of flowadapted to the practice of my invention. Wax-bearing oil from a source not shown .is delivered by a pump I to a mixer and heater 2. The dewaxing solvent, from a source not shown, is delivered by a pump 3 to the mixer and heater ."2 wherein it undergoes mixing with the Waxbearing oil, and theresulting mixture is heated to a super-solution temperature, for example, in the range -of about 130 to 170 F.

From this mixer, the heated mixture is then conducted through a pre-cooler 5 wherein it is cooled by indirect heat exchange with a cooling medium which may comprise water.

The cooled mixture is thereafter conducted through heat exchanger 6 wherein it is further cooled as, for example, by indirect heat exchange` with a flowing stream of dewaxed oil, leaving the filter-referred Ato later.

The resulting cooled mixture is then introduced to the top of a vertical pipe chiller or series of such vertical pipe chillers 1. The chiller 'l advantageously comprises a vertical vessel provided with an annular jacket through which cold brine is circulated.

f 'Ihis chiller 1 is provided with an internal scroll type of scraper il adapted to scrape adhering Wax from theinterior surfaces of the chiller. A distributor 9 is positioned in the bottor'n of the chiller for introducing gas to the lower portion thereof.

The mixture of wax-bearing oil and solvent introduced to the upper portion of the chiller 1 moves downwardly therethrough countercurrent- 1y to the rising gas, which latter is introduced at a rate suiicient to eect relatively mild agitation of the body of liquid within the chiller 1.

From vthe bottom of the chiller 1, the chilled mixture, at a temperature of the order of 0 F. and below, and containing precipitated wax, is removed, either directly to a filter I0, or to a surge tank ll.

Mild agitation, of course,

Thesurge tank Il also advaitageously'bom- 75 prises a vertical vessel provided-with means for introducing gas through a distributor I2 for the purpose of maintaining the contents in a gently agitated condition.

The iilter I advantageously comprises a continuous type of vacuum filter` by means of which the precipitated wax is removed from the cold solution as a filter cake.

The resulting ltrate, which is still at a low temperature, may be passed, all or in part, in heat exchange relationship with the fresh charge flowing through the heat exchanger 6.

Thereafter, the warm dewaxed solution is conducted to a solvent recovery system not shown, wherein the solvent is stripped from the dewaxed oil and returned for further use.

The gas used for agitation purposes in the chiller l and the surge tank Ii may comprise any suitable inert gas, such as carbon dloxidefnitrogen, ilue gas, or a volatile petroleum hydrocarbon.

The make-up gas is taken from a gasometer I3 by means 'of a pump or compressor I4 and delivered along with the recycling gas to the lower portion of a gas chiller I5 wherein it is chilled to the appropriate temperature, preferably around 0 F. and below.

In the gas chiller I5, the circulating gas is brought into indirect heat exchange relationship with a refrigerant, such as vaporizing ammonia.

If desired, the circulating gas may be caused to bubble through a body of liquid, such as a portion of the dewaxing solvent, which ls maintained in indirect contact with a refrigerant fluid.

It may be of advantage to employ the latter means of cooling the circulating gas so that the latter will always be saturated with dewaxing solvent vapor, and thus not disturb the ratio of solvent to oil being maintained within the chiller 1.

The chilled .circulating gas is conducted from the upper portion of the gas chiller I5 to the distributor 9 in the bottom of thel chiller 1.

In a similar manner, a portion of the chilled gas is circulated through the contents of the surge tank I I, and from there returned to the gas chiller I5. As a specific example in the carrying out of the process of my invention, a sample of wax distillate was ilrstextracted with furfural to remove the relatively low voscoslty index coiistituents, then dewaxed according to the following procedure.

This wax distillate was derived from Mid-Continent crude, and after solvent extraction with furfural had tests similar to those of the distillate "v stock already referred t6 in connection with the discussion of Figure 1.

This=furfuralreiinediwax distillate was mixed with a mixture consisting of 40% methyl ethyl ketone and 60%- benzol in the proportion of four parts of solvent mixture to one part of distillate. This mixture of oil and solvent was then heated toa temperature of 140 F.

Following this, the hot mixture was cooled to a temperature of -10 F. during which cooling it was subjected to mild agitation by bubbling nitrogen gas therethrough. The cooling was effected in a vertical cylindrical vessel provided with means for introducing gas to the lower portion thereof. The gas was thus introduced to the chilling vessel at the rate of aboutiive cubic feet per hour per square foot of horizontal crosssectional area of the chiller. A

The -cold mixturewas then ltered in a vacuum lter to remove the solidified wax as a lter cake. The-lter cake was removed without washing with a solvent. This cake, after removal of the solvent, comprised -slack wax containing around 44% to 46% of paramn wax of 146 to 148 F. melting point.

The filtrate, after removal of the solvent, had a pour test of around 0 F. and comprised 71% of the undewaxed distillate. This filtrate was produced at the rate of 22 to 25 gallons per hour per square foot of filtering surface, when calculated on the basis previously given.

The results thus Obtained indicated that the illter rate was increased approximately twelve times over that obtained when the mixture of wax-bearing oil and solvent wasv not subjected to heating above 115 or 120 F. prior to chilling. The yield of wax-free oil, without subjecting the filter cake to a solvent wash.' was increased around 10%. At -the same time, the volume of the wax cake was about 35% less, While the paraiiln vwax content of this wax cake was ini creased by about '7% or 8%.- o

The lter cake comprised crystalline wax which was compact and relatively free from oll, characterized by the fact that it ltered or 'drained quite easily as contrasted with the mushy, bulky and slow-filtering filter cakes obtained in prior methods of dewaxing.

While a specic example using a solvent mixture composed of methyl ethyl ketone and benzol has been referred to, nevertheless the method of this invention is also applicable to dewaxing with other solvents or solvent mixtures. I have found that substantially the same results are obtained when employing a solvent mixture consisting of 30% acetone and 70% benzol with the same wax-bearing stock.

As examples of other solvents which may be used in connection with this invention, methyl isobutyl ketone may be mentioned, and mixtures of methyl ethyl ketone and aliphatic ethers, such as isopropyl ether and dibutyl ether. I have found that the method of this invention is particularly advantageous in the'case of mixtures consisting of about equal parts of methyl ethyl ketone and isopropyl ether, for example.

Solvent mixtures composed of mixed aliphatic ketones, suchas a mixture of dipropyl ketone with methyl ethyl ketone or with methyl isobutyl ketone, may also be advantageously .employed in the practice of my invention.

I have found that the application of the step of heating the wax-bearing oil and solvent mixture prior to chilling produces improved results in the case of dewaxing with the foregoing solvents or solvent mixtures.

Thus, for example, when dewaxing the above lubricating oil distillate stock and methyl isobutyl ketone, I have found that a illtering rate as high as 63 gallons per square foot of filtering surface per hour may be -obtained by ilrst heating the mixture of oil and solvent to a temperature of 175 F. prior to chilling. This is to be compared with a ltering rate of only about one gallon per square foot of filtering surface per ho'ur where the mixture is not heated to temperatures above 130 F. prior to chilling. This comparison was made using four parts of solvent to one part of oil and dewaxing at 0 F. to produce` an oil of around zero pour test.` v

The examples referred to above specifically describe dewaxing relatively viscous oils. Itis contemplated, however, that the invention is applicable to the treatment of relatively less viscous oils containing wax crystal modifying substances.

should be imposed as are indicated in the ap pended claims.

I claim:

1. The method of separating wax from mineral oil which comprises mixing the oil and Wax containing Wax crystal modifying material with a selective solvent such that the wax and oil appear to be completely dissolved therein at a temperature not in excess of about 125 F., and such that upon chillinga mixture of the oil and solvent to precipitate wax, and removing the wax so precipitated, the resulting dewaxed oil, after removal of the solvent, will have a pour test corresponding lsubstantially to the temperature at which the wax was removed, heating the solution to a temperature above 150 F. such that uponlchilling to about F. and filtering, the rate of filtration is substantially greater than that obtained, and a wax cake is secured having a bulk not more than two-thirds the bulk secured, by heating only to about 125 F., chilling theheated mixture to precipitate wax and removing lthe wax thus precipitated.

2. The method, according to claim 1, in which I the selective solvent comprises a mixture consisting of a. low molecular weight aliphatic ketone and an aromatic hydrocarbon.

3. The method, according to claim 1, in which the selective solvent comprises an aliphatic ketone containing up to seven carbon atoms.

v4. The method of separating wax from mineral oil which comprises mixing the oil and wax containing wax crystal modifying material with a selective solvent such that the wax and oil appear to be completely dissolved therein at a temperature not inexcess of about 125 F., and such that upon chilling amixture of the oil and solvent to precipitate wax, and removing the waxso precipitated, the resulting dewaxed oil, after removal of the solvent, will have a pour test corresponding Isubstantially to the temperature at which the wax was removed, heating the solution to a temperature around 160 to 170 F. such that upon chilling to about 0 F. and filtering, the rate of iltration is substantially greater than that 0btained, and a waxv cake is secured having a bulk not more than two-thirds the bulk secured, by

Vheating only to about 125 F., chilling the heated mixture to precipitate wax and removing the Wax thus precipitated.

5. The method of separating wax from mineral oil which comprises mixing the oil and wax containing wax crystal modifying material with a selective solvent comprising a mixture of a low molecular I weight aliphatic ketone and an aromatic hydrocarbon such that the wax and oil appear to be completely dissolved therein at a temperature not in excess of about 125 F., and such that upon chilling a. mixture of the oil and solvent to precipitate wax, and removing the 'wax so precipitated, the resulting dewaxed oil, after removal of the solvent, will have a pour test corresponding substantially to the temperature at which the wax was removed, heating the solution to a temperature around 160 to 170 F. such that upon chilling to about 0 F. and ltering, the

the wax thus precipitated.

Enwm c. rcuovvrnsus.A i

Images