US2031117A - Process for dewaxing oil - Google Patents

Description

Feb- 18, 1936 D. R MERRILL Er AL PROCESS FOR DEWAXING Filed 00%,. 24,' 1932 Nm, W a n om d N ww w f E W\\\ Nm Nu /wm KW bhwmwN NW.\ Nm m. um.. Wm, @Mmmw mm. Nv Q $3 mm b w Rm. QR V TQQ N 1% l n N I INVENTORS Q 1 Dax/ldRMerrl/Ph1p'ubkow BY l ATTORNEY.i

Patented Feb. 18, 1936 UNITED STATES PATENT OFFICE PROCESS FOR DEWAXING OIL ration of California Application October 24, 1932, Serial N0. 639,340

11 Claims.

This invention relates to a process for the separation from petroleum of those hydrocarbons which are normally solid at ordinary temperatures. According to our process We are able to separate from petroleum or mineral oil such substances as asphalt, paraiiin, crystalline or amorphous wax, or gummy or resinous substances which may be present. While our invention is particularly adapted to the removal of paraffin, amorphous or crystalline wax, or gummy or resinous substances from lubricating oil, it may be utilized in the treatment of any other petroleum fraction where it is desirable to separate the oil from the foregoing substances.

Many crude oils from which lubricating oil is produced contain paraiiin or wax. It is found associated with the lubricating oil fractions of parain base crude oil and with the lubricating oil fractions produced from any of the mixed base and asphalt base crude oils. It is not only of doubtful lubricating value but also limits the temperature at which lubricants containing it may be used by congealing at the lower temperatures. Therefore, in the production of lubricating oils from petroleum fractions containing wax or parafn, it is customary to remove a substantial portion of the wax or parain present in the oil in order to lower the temperature at which the nal product congeals. 'Ihe temperature at which an oil congeals is commonly referred to as its pour point and this value is usually obtained according to method D-97-30 of the American Society of Testing Materials.

Several methods well known in the art are employed at present for the production of low pour point lubricating oil stock from petroleum fractions which contain substances congealing at high temperatures as set forth above and to which we shall hereinafter refer as wax. In the cold settling process, the wax-containing oil is rst diluted with a light hydrocarbon diluent, such as naphtha, gasoline or kerosene. The diluted oil and wax are then run into a tank of large capacity and slowly chilled by the aid of brine circulated in coils located within the tank. The chilling process is carried out for a period of from 20 to 50 hours until a temperature is reached at which there exists a substantial separation of the wax in the form of a slimeor'g'el from the solution of oil. By allowing the cold solution of oil containing precipitated wax to stand for a period of several days the precipitated wax settles to the bottom of the settling tank. While this method has been used extensively for the separation of wax from lubricating oil, it is objectionable because of the cost of refrigerating the diluted oil over so long a period, lfurthermore, because of the large tank and refrigerating capacity required for the treatment of the oil and lastly on account of the usual poor separation 5 obtained between the wax and the oil.

Another method for dewaxing petroleum which has been used to a large extent is the cold pressing process. Wax distillate produced from those fractions of petroleum distilling over between the 10 approximate temperature limits of 450 F. and 725 F. is slowly chilled to a temperature of about 15 F. to 30 F. whereupon the wax present in the oil precipitates to form a product having av mushy consistency. The cold, mushy mass is 15 then pumped through a lter press under a pressure of 300 to 350 pounds per square inch. The wax present is collected upon the filter and the oil is recovered as a pressed distillate relatively free from wax. When the oil under treatment 20 contains a relatively large quantity of wax it is sometimes necessary to re-chill and re-iilter it in order to obtain an oil having the desired pour point. The length of time required to lter the chilled oil depends upon the crystalline struc- 25 ture of the wax. A distillate which is poorly crystallized, i. e., with crystals in the form of plates, or in which the wax crystals are small, requires a much longer period of filtration than does a distillate in which the wax crystals are large and 30 of needle structure. This process has found commercial application onlyin conjunction with oils having the wax present in a crystalline form, as so-called amorphous wax or micro-crystalline wax is extremely diicult to separate by ltra- 35 tion from the oil. Consequently, oils containing amorphous wax cannot be treated onl a commercial scale by this process.

Another process has been suggested which consists in diluting the oil containing wax with such 40 light petroleum hydrocarbons as gasoline, naphtha or kerosene, adding to the diluted oil a waxadherent material, chilling the mixture of oil and wax-adherent material with constant agitation until a temperature is reached which is suili- 45 ciently low to cause the wax present in the oil to precipitate and `collect upon the wax-adherent materialand nally separating the substantially wax-free oil byltration from the wax-adherent material' and weer,l this process is objec- 5o tionable because-f the long period of time required to obtain suitable wax separation from the diluted oil land also because of the large chilling and filtering capacity required to make the process commercially possible.

It has been found that many of the disadvantages present in the foregoing processes may be overcome by removing the waxy constituents of petroleum in the presence of light hydrocarbons, such as propane.

The liquid propane lowers the Viscosity of the chilled mass sufficiently to facilitate the separation of the precipitated wax from the chilled solution of propane and oil.

We have found that waxes which have been precipitated from gasoline or naphtha by chilling a light waxy oil dissolved in these solvents are usually highly amorphous in structure. Likewise, we have found that when wax-containing oil is rapidly chilled in the presence of propane, the wax precipitates in so ne a form of subdivision that filtering or settling is substantially impeded. Such waxes are in the nature of gelsy or slimes and as such offer many difiiculties in their removal from the chilled solution of oil and solvent. As already discussed, they are unusually hard to separate by ordinary filtration methods as the slimy wax forms an impervious layer upon the filter plate of the lter press which obstructs free movement of the dewaxed oil through the lter plate and filtration is usually possible only if excessive amounts of lter aid are employed. Furthermore, the wax flocks or aggregations which are formed during the chilling operation will not readily settle out by cold settling methods even in the presence of propane which increases the difference in the specific gravity between the solution of oil in the solvent and the wax.

We have discovered that the precipitation of the wax in the presence of propane into a form too finely divided for elcient settling and/or filtration is caused by a too rapid cooling of the solution of oil, wax and propane. This rapid cooling we call shock chilling. .We have invented a process whereby shock chilling is prevented, the oil, wax and propane solution being cooled in successive stages while sulcient time is allowed to permit the wax crystals to re-crystallize and grow, the crystals for ed in an earlier stage forming nuclei for the fu her development of crystals in the later stages of crystal formation.

Due to the granular structure which the wax possesses when precipitated from a chilled propane solution of waxy oil in this manner, it may be separated commercially from the propane solution of oil by filtration or settling with none of the attending difliculties present when ltering or settling waxy slimes. When filtering, the granular structure of the wax does not form the impervious nlm over the filter plate which is characteristic of waxy slimes or gels. Instead, such granular waxes form a porous layer upon the illter plate through which the wax-free oil dissolved in solvent may freely flow. When settling, the long period necessary to obtain separation of the precipitated wax is obviated.

Another advantage of. using a light liquid hydrocarbon as a diluent for the oil containing wax is that by allowing a portion of the solvent to vaporize under reduced pressure, the necessary refrigeration is obtained to chili the oil to the desired dewaxing temperature. The waxy oil is first dissolved under pressure in alight liquid hy drocarbon. A portion of the light liquid hydrocarbon is vaporized or allowed to boil off at reduced pressure which thereby lowers the temperature of the waxy oil dissolved in the remaining solvent to a point suiciently low to precipitate the wax. Thus, the light liquid hydrocarbon functions as a diluent for the waxbearing oil and also as an internal refrigerant to chill the solution of oil and wax to the proper dewaxing temperature. Furthermore, this internal refrigeration may occur in the propane itself prior to intermixture with the oil and wax.

When we use the term light liquid hydrocarbon, we mean those hydrocarbons which are normally in the vapor state at atmospheric pressure and temperature. Such hydrocarbons include propane, isobutane, butane, ethane, methane and mixtures thereof. These may be olotained by the rectification of casinghead gasoline by the so-called stabilizing method. They are the overhead thus obtained. They are liquefled by compression and cooling in the conventional manner and are drawn 0E into pressure chambers where they are maintained in a liquid state until they are used. For example, a fraction composed of 6.72% ethane, 72.2% propane, 19.91% isobutane and 1.17% normal butane is satisfactory. It will be understood, however, that this merely illustrates the type of fractions which may be used and that the composition may vary. This fraction will hereafter be referred to as "propane for purposes of simplicity.

It is an object of our invention to precipitate granular wax from wax-bearing oil and separate said wax from said oil.

It is another object of our invention to precipitate wax in granular form from wax-bearing oil by the use of liquid propane and subsequently to separate the wax, oil and propane from each'l other.

Another object is to chill the wax-bearing oil in stages by the successive introduction of pro- --pane into said oil whereby granular wax precipitates from the solution.

A further object is to chill the wax bearing oil in stages thereby permitting crystal growth in order to avoid the production of amorphous wax or wax gels or slimes.

An additional object is to so control the time and degree of chilling that crystal growth is aided and granular wax is produced.

In the drawing, Fig. 1 is one form of apparatus which we may employ to carry out our process. Fig. 2 is a cross sectional view of the expansion valve 54 which we prefer to use in chamber 55. Fig. 3 is a cross section of an orifice mixr which we may employ to produce an intimate mixture between two liquids.

Referring more particularly to Fig. 1, propane in liquid form is held under pressure in tank I0 and waxy oil is contained in tank II. The waxy oil is removed therefrom by pump I2 via line I 3 controlled by valve I4 and is passed through orifice mixers I 5,- I6 and I1 into crystallizer tank 2U. During 110W of the waxy oil through line Il and the orice mixers, liquid propane is introduced into the oil through lines 24, 21 and 50 in the manner described below. Preferably the liquid propane is introduced at successively lower temperatures. The orifice mixer of Fig. 3 may be any one of the mixers I5, I6, I1. The fluids in pipe I3 pass successively through diaphragms 6 which are provided with openings 1. After leaving the constricted openings 1, the fluid passes into chambers 8. 'Ihe successive passage of the liquids through the diaphragms into the enlarged chambers 8 produces sufficient intermixture to insure intimate contact of these uids.

Liquid propane from storage I0 issues therefrom by action of pump 2|via line 22 controlled by valve 23. 'I'he flow of liquid propane is then split, 75

part passing via line 24 controlled by valve 25 to join with the waxy oil traveling through line I3 prior to passage into orifice mixer 5 while the remainder of the liquid propane passes in chamber 55. Valve 54 may be provided with venturi 10 disposed at the outlet 59. Line 1| is connected with the venturi. The reduction of pressure effected by valve 54 and the operation of through line 26 in heat interchange with the maventuri 10 causes material to enter chamber 55 via 5 terial passing through line I |1 described below. line 1| in a. manner described below.

From line 26, the stream of liquid propane is again Preferably, the liquid level in 55 is maintained split, part passing via line 21 controlled by Valve above the outlet of venturi 18 whereby the mate- 28 to line I3 at a point intermediate orifice mixers rial introduced through valve 54 is jetted directly I5 and 6 while the remaining liquid propane into the liquid maintained in 55 causing turbu- 10 passes via line 29 into evaporator 38. The flow lence thereof and aiding uniform temperature through line 29 is regulated by float controlled conditions, and washing of the valve seat to avoid valve 35 operated in the usual manner by the wax precipitation and clogging of the passages. amount of liquid maintained in evaporator 38. Referring again to Fig. l, chamber 55 is con- The pressure in the evaporator is reduced sufnected to propane vapor line 38 by line 12 con- 15 ficiently to partially vaporize the propane controlled by valve 13. Propane vapors from chamtained therein. ber 55 pass therethrough by action of pump 39 Propane vapors in tank 38 are removed thereand compressor 40 into condenser 42 and liquid from through line 36 controlled by valve 31 and propane storage I0.

through line 38 by action of pump 39. These Unvaporized material in chamber 55 passes 20 vapors are compressed in compressor 40 in line therefrom by action of pump 11 via line 18 con- 4| connected with line 38 and after condensation trolled by valve 19 into settling chamber 88. Proin condenser 42 the liquid propane is passed via pane vapors from 88 pass into line 38 controlled line 43 to propane storage I8. by valve 8| for treatment in a manner already The chilled propane which remains liquid in described. 25 evaporator passes therefrom by action of pump Due to the suction produced by venturi 18, a 41 via line 48 controlled by valve 49. This stream portion of the mass in settling tank 88 may be reof liquid propane may then be split, part passing turned to chamber 55 via line 82 controlled by via line 58 controlled by valve 5I to intermix with valve 83 connected with line 1I or via line 84 con- 30 the waxy oil flowing through line I3 at a point trolled by valve 85 connected with line 1I. Fur- 30 intermediate orifice mixers I6 and I1 and part thermore, the action of pump 88 in line 86 may passing through line |00 for use in the manner be employed to force waxy oil from tank 88 into described below. line 1I and thence into chamber 55 by proper Thus, the propane in liquid state is introduced manipulation of valves 81, 89, 92 and 94. The

3f in successive stages into the stream of wax-bearpurpose of the ire-introduction 0f the wax into 35 al, ing Oil, and the propane introduced in each succhamber 55 from settling tank 80 is to allow said i cessive stage is at a lower temperature t'han that wax to contact with the propane for a sufiicient ,.f added to the oil in the preceding stage. Sudden length of time to cause crystal growth and re- "L local excessive chilling is thus avoided, i. e. shock crystallization to prevent the production of amor- .ml chilling is thereby prevented by a gradual reducphous wax which is dinicult to remove either by tion of temperature and the resultant precipitated Wax tends to be in granular form Whereas shock chilling produces gel-like wax which is diflicultly separable by settling or filtration, as 45i`stated above.

settling or filtration. The re-introduced wax forms nuclei for the growth of crystals and aids in the formation of macro-crystals rather than miggg-crystals. W

Pumpv 88 may also be used to force waxy oil 45 We have found that the production of wax in granular form is aided by allowing the propane to contact with the Wax bearing oil for a suiiicient time after intermixture therewith. Consequentfrom 80 through either or both of lter presses 95 and 96 via lines 86, 98, 9| and 93 by proper manipulation of valves 81, 88, 92 and 94. Liquid propane from evaporator 30 may also be introduced ly, we have provided crystallizer chamber 20 in in line 9| and/or 93 by action of pump 41 via 50 which the oil, wax and propane flow in intimate line 48, |00, I0|, |03 by proper manipulation of contact for the time necessary to cause crystal valves 49, 5I, |82 and |94. growth and recrystallization. The evil effects The wax remaining in the lter press may be of shock chilling and the production of amorremoved in any manner desired. 'I'he wax free phous wax are thereby substantially avoided. oil from presses 95 and 86 is removed therefrom 55 The mixture of oil, wax and liquid propane in via lines |05 and |01, respectively, controlled by tank 28 is withdrawn therefrom by pump 52 in valves |86 and |88, respectively, by action of line 53 and is sent through valve 54 preferably pump in line ||0 to which lines |05 and I 81 disposed in chamber 55. are' connected. Wax free oil from settling tank A preferred structure of valve 54 is shown in 80 may likewise be removed by action of pump 60 Fig. 2. This valve is formed by abarrel 68 having via lines ||4 controlled by valves I|5 and via a seat 6| and a valve 62 with handle 56 attached line I|6 connected with line |I0. to valve stem 63 which may be threaded or The wax free oil flowing through line ||0 passes otherwise engaged at 64. The barrel 68 is prothrough line II1 in heat exchange with the liquid 65 vided with an inlet 53 and an outlet 59. A steam propane passing through line 26 and then passes B5 jacket 65 is disposed about barrel 68 and is through line II8 into line IIS for further heat exequipped with steam inlet 61 and a steam outlet change with the material passing through line 66. Heavy insulation 68 may be provided be- |52. From line I|9 the wax free oil travels via tween steam jacket 65 and outer casing 69. The line 28 into column still |25 heated by closed 70 purpose of this construction is to provide means steam coil |26 and provided with conventional 70 to prevent clogging the valve if wax crystals would fractionating plates |21. 'I'he fractionation tend to build up -at the seat. Steam may be adplates in column |25 which are positioned bemitted into the'stcam jacket to melt the wax and tween lines |28 and |48 are preferably heated by free the orifice if any collects. Also, the insula.- steam coils not shown. Line |20 may be protion minimizes the leakage of heat to the mixture vided with high pressure pump I2|. Vapors em- 75 anating in tower |25 pass therefrom via line |28 controlled by valve |29 into condenser |30 and thence vialine |33 into liquid vapor separator |34. Uncondensed propane issues therefrom by action of pump |31 via line |35 controlled by valve |36. Line |35 connects with line 4| and the propane is condensed in the manner described above.

Condensed propane in separator |34 passes therefrom via line |38 controlled by valve |39 by action of pump |40. The stream may then be split, part passing into propane storage I via line |4| controlled by valve |42 and via line 43. Another part may pass into still |25 via line |43 controlled by valve |44 for use as a reuxing medium.

Unvaporized dewaxed oil issues from still 25 via line |45 and valve |46 by action of pump |41. This stream may be split, part returning via line |48 controlled by valve |49 into the still 25 as a reiiux medium while the other portion travels via line |50 controlled by valve |5| through line |52 into heat exchange with the dewaxed oil flowing through line 9. From |52 the unvaporized dewaxed oil flows through line |53 into dewaxed oil storage tank |55.

As illustrative of the operation of our process for one type of oil and without intending to limit our invention, the oil in tank may be a lubricating oil containing wax. It is maintained therein above the wax congealing temperature. Part of the propane from storage I0 at about 60 F. intermingles with the oil in mixer after passage through valve 25. If nesswthgl Aii'tli'ifrtion of the' propane'is chilled in line 26 before introduction into the waxy oil via valve 28. If the cooling in 26 by heat exchange with dewaxed oil in is not suiicient, additional cooling, not shown, before passage through valve 28 may be provided. The temperature in I6 is for example, about 20 F. to 30 F. The third portion of propane, subjected to partial evaporation in evaporator 30, is preferbaly at a still lower temperature. If desired, the vaporization in 30 may take place under vacuum whereby extremely low temperatures will prevail in the remaining liquid propane. The temperature in mixer |1 and tank 20 may be approximately 5 F. to 5 F.

In insulated crystallizer tank 29, which is of larger cross-sectional area. and larger volume than line I3 the rate of iiow of oil and precipitated wax is substantially reduced whereby the Wax is given suflicient time to crystallize, recrystallize and grow into the desired form.

' Final refrigeration occurs in chamber 55 by expansion through valve 54 and vaporization of the propane. The temperature in 55 may be 10 F. to 20 F. although 40 F. or lower can sometimes be advantageously employed. The tempcrature can be varied by employing appropriate pressures or vacuum depending upon the cold test desired for the oil obtained as a. iinal product.

By these gradual, successive reductions in temperature and by giving the Wax ample time to crystallize, an easily separable, granular wax is produced. Chamber 55 may also be suiciently large to provide additional time for crystallization during iiow of the mixture therethrough. However, it is also desired to provide an additional chamber to act as a settling tank. The oil, .wax andliquidpropane in 5 5 exiting via line 18 is pumped intosettlirigclilnber 89 where settling of the wax takes place and additional time for crystallization is provided. Due to the low viscosity of the propane solution and the wide difference in the gravity of the wax and the gravity of the propane solution of oil and due to the granular nature of the wax crystals, the-latter tend to settle rapidly to the bottom of settling tank 80 leaving a clear layer at the top.

The temperature in 80 should approximate that in 55. Preferably, we desire to prevent vaporization in settling chamber 80 because of the turbulence produced thereby. Stratification has been found to take place more readily in a quiescent state. Accordingly, settling chamber 80 should be maintained at the same pressure as Vaporizer 55; or if desired, a higher pressure may be employed in 80 by re-pressuring with gasepuspropanegor other gasuto prevent boiling and avoid interferce""'with settling. If it is desired to discharge any propane from 80 this may be accomplished via valve 8| in line 38.

In order to provide additional nuclei for the precipitation of wax crystals in 55 and permit additional time and opportunity for the recrystallization of the wax precipitated in 80, provision is made for the retum of a portion of the wax precipitated in 80 to the crystallizer 55. This may be accomplished in either or both of two ways. By operating valves 85, 81, 89, 92 and 94, wax crystals as a slurry may be returned either by the jetting action of the expanding propane and oil solution through venturi or by the pump 88 or by both.

A portion of the wax slurry is sent through either filter press 95 or 96 by operation of the valves 92 and 94. Assuming press 95 has been filled with wax cake, valves |04 and 92 are closed and valve 94 is opened to permit the wax, oil and propane mixture to pass through filter press 96. The ltrate leaving the lter press via line |01 and valve |08 commingles with the supernatant oil from 80 passing valves ||5 and lines ||4 and I6 to line H0. This mixture is forced by pump into heat exchange in line ||1. with the propane in line 26, then into heat exchange in line ||9 with hot oil passing through line |52. The heated mixture then iiows through line into still |25.

While oil is being iiltered through press 96, the wax caked on the plates of filter 95 is washed with cold propane coming through lines |00 and |0| and valve |02. The cold propane dissolves oil remaining in the wax cakes and this solution of oil in propane in passed via line |05 and valve |06 to commingle, if desired, in line ||0 with the filtrate from filter press 96 and with the supernatant oil from settling chamber 80 entering line ||0 via line H6.

While lter press 96 is operating and after the wax cakes in press 95 have been washed with the cold propane, the press 95 may be cleaned of Wax in any manner desired. When press 95 is ready for operation and 9E has become filledwith wax, valves 94 and |02 are closed and valve 92 is opened, permitting flow of the waxy oil and propane mixture into press 95. Valve |04 may be opened to permit the wax cakes in press 96 to be washed free of oil with cold propane. This oil and propane solution passes to line ||0 via line |01 and valve |08 to commin'gle with the filtrate from press 95 entering line ||0 via line |05 and valve |06.

The preheated oil and propane solution in line 20 is introduced into column still |25 which may be operated at high or low pressure. If the pressure is to be high so that the propane may be condensed by ordinary cooling water, an additional high pressure pump |2I may be provided inline |20. The column is additionally heated by steam passing through coil |26.

Part oi' the condensate in |34 produced from the vapors leaving column still |25 via line |28 and condenser |30, is forced by pump |40 as reiiux to still |25 via line |44 and the rest is returned via line |4| to propane storage I0. The uncondensed vapors pass via line 135 and pump |31 to compressor 40 and cooler 42 and thence to storage I0. The vapors from 55, and 30 are first compressed by compressor 39 in line 38 and then are finallycompressed in 40 and passed to storage, as described above. The stripped dewaxed oil is withdrawn by pump |41 and part is recirculated via valve |49 and line |40 to the column still, while part passes through |52 in heat exchange with the incoming material passing through ||9. The desired stripped and dewaxed lubricating oil is stored in storage |55.

'I'he foregoing exemplary description is merely illustrative of a preferred mode of carrying out our invention and is not to be taken as limiting, as many variations may be made within the scope oi' the following claims by a person skilled in the art without departing from the spirit thereof.

In our divisional application, Serial Number 34,664, filed August 5, 1935 we claim the recirculation of the separated wax to the chilling zone.

We claim:

Al. A process for the separation of wax from oil containing wax which comprises precipitating said wax during the flow of said oil through a line of relatively small cross-sectional area and introducing a liqueiied normally gaseous hydrocarbon at successively lower temperatures in stages at successive points along said ilow of wax and oil toavoid shock chilling the wax.

2. A process for the separation 'of wax from oil containing wax which comprises precipitating said wax during the flow of said oil through a line of relatively small cross-sectional area and introducing liquid propane at successively lower temperatures in stages at successive points along said flow of wax and oil to avoid shock chilling the wax.

3. A process for the separation of wax from oil containing wax which comprises mixing said waxy oil with liquid propane. precipitating wax therefrom during flow of said oil, wax and propane through a line of relatively small crosssectional area and introducing further quantities of liquid propane in stages at successive points along said flow of wax, propane and oil at successively lower temperatures to avoid shock chilling the wax. l Y

4. A process for the separation of wax from oil containing wax which comprises commingling said waxy oil with liquid propane under pressure, precipitating said wax during ow oi said oil and propane under pressure through a line of relatively small cross-sectional area and introducing further quantities of liquid propane under pressure in stages at successive points along said iiow of wax, oil and propane at successively lower temperatures to avoid shock chilling the wax.

5. A method of chilling a wax-containing oil which comprises mixing said oil with a liqueed chilled liquefied normally gaseous hydrocarbon diluent into said flowing stream between the initial mixing zone and the iinal zone of chilling, said introduction of chilled diluent being in an amount regulated to avoid shock chilling the wax.

6. A process for the separation of wax from oil containing wax which comprises introducing a liquid normally vaporous hydrocarbon into said wax bearing oil, subjecting said mixture of wax, cil and hydrocarbon to pressure suicient to maintain said hydrocarbon liquid, flowing said mixture through a constricted line in a confined stream and successively through a plurality of constricted openings in said line, introducing a further quantity of liquid normally vaporous hydrocarbon into said flowing mixture at a lower temperature at a point intermediate said plurality of constructed openings and thereafter reducing the pressure on said mixture in an expansion zone to vaporize the liquid normally vaporous hydrocarbon, chill the oil and precipitate the wax.

'7. A process for the separation of wax from oil containing wax which comprises precipitating wax during ow of said oil through a line of relatively small cross sectional area and introducing liquid Anormally vaporous hydrocarbon under pressure at successively lower temperatures in stages at successive points along said ilow of oil and wax, subsequently reducing the pressure on said partially cooled mixture of oil, wax and hydrocarbon in a pressure reducing zone to vaporize the liquid normally vaporous hydrocarbon, further chill the oil and precipitate the wax without shock chilling andseparating said precipitated wax from said oil and liquid normally vaporous hydrocarbon.

8. A process for the separation of wax from oil containing wax which comprises introducing liquid propane into said wax bearing oil, subjecting said mixture of wax, oil and propane to pressure sufdcient to maintain the propane liquid, flowing said mixture through a constricted line in a connned stream and successively through a plurality of constricted openings in said line, introducing a further quantity of liquid propane into said. owing mixture at a lower temperature at a point intermediate said plurality of successive constricted openings 4and thereafter reducing the pressure on said mixture in an expansion zone to vaporize the propane, chill the oil and precipitate the wax.

9. A process for the separation of wax from oil containing wax which comprises precipitating wax during flow of said oil through a line of relatively small cross-sectional area and introducing liquid propane under pressure at successively lower temperatures, in stages at successive points along said ow of wax and oil, subsequently reducing the pressure on said partially cooled mixture of oil, wax and propane in a pressure reducing zone to vaporize the propane, further chill the oil and precipitate the wax without shock chilling and separating said precipitated wax from said oil and propane.

10. A process for dewaxing oil which comprises commingling wax containing oil and propane at temperature and pressure suiiicient to maintain said propane liquid, passing said mixture in av flowing stream to a zone of final wax crystallization and introducing additional liquid propane at a lower temperature than said mixture into said propane and oil mixture at an intermediate 'point during said flow from the point of said first mentioned propane intermixture to said zone of final wax crystallization said introduction of chilled propane being in an amount regulated to avoid shock chilling the wax.

11. A process for dewaxing oil which comprises commingling wax containing oil and propane at a. temperature and pressure suiicient to maintain said propane liquid, passing said mixture in a owing stream to a zone of inal wax crystallization and then to a zone of wax separation, and introducing additional liquid propane at a lower DAVID R. MERRILL. PHILIP SUBKOW.

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