US2281667A - Method for treating oils - Google Patents

Description

May 5 1,942 u. B. BRAY METHOD FOR TREATING OILS Filed July 22, 1955 XSS hlOm, X QQSQ @QN @W Q@ WQN Al QW Y IVENTOR Ulr'z'c Bray uw Nw bh, wm,

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Patented May 5, 1942 2,281,667 I RIETHD FR TREATNG GILS Ulric B. Bray, Palos Verdes Estates, Calif., asy signor to Union Oil Co Angeles, Calif., a corp mpany of California, Los eration of California Application July 22, 1933, Serial No. 681,726

` 3 Claims.A (Cl. 196--18) The present invention relates to a method for separating Wax from oils containing the same. More specically, it relates to -a method for separating Wax in a plurality oi stages and in the presence of a solvent. This invention is a continuation, in part, of my co-pending application Ser. No. 672,433, filed May 23, 1933 now Patent Number 2,041,277.

In the aforementioned co-pending application, I disclosed a plural stage process for the separation of asphalt and wax from oils containing the same to produce lubricating oil. In the first stage of the process, the asphalt and Wax containing oil was commingled with a liqueed normally gaseous hydrocarbon solvent, such as liquid propane, under pressure sufficient to maintain the propane in a liquid state. This permitted a hard asphalt to precipitate and settle to the bottom of the decanter depending upon the volumetric ratio of solvent to oil.- When using a high volumetric ratio of solvent to oil, the asphalt settling to the bottom of the decanter Was a substantially hard or heavy asphalt. The precipitation was carried out at a temperature substantially atmospheric, i. e. about 70 F. to 80 F.

The oil solvent solution was separated or decanted from the precipitated asphalt and was then chilled to a suiiiciently low temperature, i. e. 40 to 0 F. by evaporating a portion of the propane under reduced pressure. 'Ihis eiiected precipitation of further quantities of asphaltic material which I termed a soft asphalt or pseudo asphaltic material. The refrigeration to the low temperature also caused precipitation of Wax from solution. However, due to the longer pe-` riod of time required to settle the light fiocculent Wax, the latter remained in suspension in solution of oil and solvent during the period required for settling the heavier asphaltic material. The supernatant solution of oil and solvent containing the suspended precipitated Wax was then decanted and transferred to Wax settling chambers Where longer settling periods were provided to permit the Wax to settle from. solution.

In the present discussion of my invention by the term propane I intend to include such hydrocarbons as are normally vaporous at ordinary temperature and pressure; such hydrocarbons include methane, ethane, propane, butane, iso-butane and mixtures thereof. These normally gaseous hydrocarbon solvents may be obtained by rectification of casinghead gasoline by the socalled stabilizing method now conventional. in the natural gasoline industry. They are the overhead fractions obtained. Theyare liquefied by compression and cooled in the conventional manner and are drawn off into pressure chambers Where they are maintained in a liquid state until used. A typical analysis of such a fraction is 6.72% ethane, 72.2% propane, 19.91% butane and 1.17% normal lontane. Such a fraction may be maintained in a liqLLd state at a pressure of 125 lbs. per sq. in. at a temperature of about 757 F. The predominating member in this mixture is propane and hereafter when I use the Word propane or liquid propane I am referring to such a fraction. f

In the foregoing process, I observed that the soit asphaltic material settling to the bottom of y the decanter and precipitated by refrigerating the solution of solvent and oil to a low temperature contained Wax and that this wax was a hard, heavy and granular-like material having physical characteristics substantially unlike the light iiocculent Wax which remained in suspension in the oil and solvent during the settling of the commingled pseudo asphaltic material and hard Wax.

By the present invention, I propose to separate the Wax from cils containing the same in a plurality of stages, in particular, in two stages. I have discovered that I may precipitate and recover two diiferent types of Wax, that is, a hard Wax and a soft Wax, if the Wax bearing oil such as a parafnic crude or a residue obtained therefrom or a distillate containing wax, is chilled in the presence of a solvent and the separation from the oil solvent solution is eiected in two stages. In one stage of the process, the Wax bearing oil is v commingled With a liquened normally gaseous hydrocarbon solvent under pressure suiiicient to maintain the solvent in the liquid state and at a temperature of approximately atmospheric, i. e. about 70 F. to 80 F. The mixture is then transferred into a chilling column Where the temperature of the mixture is gradually reduced, preferably at a rate not in excess of 4 F. per minute, to a suiiiciently low temperature, i. e. about 40 to 0 F. to effect precipitation of substantially all of the Wax present in the oil. When the desired low temperature has been attained, the mixture of cil, solvent and precipitated Wax is permitted to settle so that Wax will settle to the bottom of the chilling column or any decanter in which the mixture is permitted to settle.

I have observed that a portion of the wax precipitated, that is, released from solution by refrigeration, settles rapidly and in a relatively short time, while the remaining portion remains in a cloudy .suspension in the solution of solvent and oil and requires considerable time to settle. This is due to the different physical characteristics of the two types of waxes. The first portion of the wax which settles rapidly to the bottom of the decanter is a hard, heavy and solid wax. It is granular and crystalline and has a larger particle size than the wax remaining in suspension. It may be separated from the remaining portion of the wax substantially as a separate fraction by dec-anting off the supernatant solution of oil, solvent and suspended wax after the mixture has been allowed to settle for a short period of time. In some cases, depending upon the type of oil treated, this wax may be contaminated with light asphalt or pseudo asphaltic ma terial which also precipitates from solution when the oil is chilled to a dewaxing temperature.

The wax remaining suspended in the supernatant solution is soft and slime-like when the temperature has not been reduced sufficiently low but is substantially flocculent when the solution of oil and solvent has been chilled to a suiiiciently low temperature, i. e. approximately 40 F. This portion of the wax may be recovered as a separate fraction by decanting and transferring the solution containing the supernatant wax to separate wax settlers and allowing suiiicient time for settling. It may also be recovered by filtration, lter pressing or by oentrifuging.

To obtain the desired refrigeration of the solution of oil and solvent such as propane and thus effect precipitation of wax, I prefer to gradually.

reduce the pressure in the chilling column and thus vaporize propane which will gradually chill the oil and precipitate the wax. The ebullition accompanying the vaporization of the propane will agitata the solution of oil, solvent anclprecipitated wax and thus will prevent substantial amounts of light iiocculent wax from settling and mixing with the hard, heavy Wax settling to the bottom of the column. The light flocculent wax will remain in suspension in a solution of oil and solvent during the period required for settling the heavier wax. The supernatant solution of oil and remaining solvent containing the suspended flocculent wax may then be transferred to other settling chambers where a longer settling period may be provided. If suiricient propane is not present in the mixture to give good settling of the light flocculent wax, a further quantity may be added to the mixture.

Instead of employing the uniform slow cooling rate of not in excess of 4 F. per minute throughout the entire range of chilling down to 40 F., the propane solution may be chilled more rapidly, i. e., F. per minute until a temperature of approximately 35 to 45 F. is reached provided the remainder of the chilling down to 40 F. is performed at a slow, controlled rate not in excess of substantially 3 F. per minute. The temperature in the neighborhood of 40 F. to which the propane solution maybe chilled rapidly corresponds to the point at which wax begins to precipitate from. the propane solution.

With the above discussion in mind, it will be perceived that it is an object of my invention to separate wax from oil by means of solvents in a plurality of stages. It is a particular object of my invention to separate wax from wax bearing oils by chilling the oil to precipitate the wax and then separating the precipitated wax in a plurality of stages;

It is a further object of my invention to separate wax from oils by means of solvents in two stages wherein a substantially hard Wax is recovered in the first stage and a light, softer wax is recovered in the second stage, both types of wax being precipitated by refrigeration from the solution of oil and solvent.

A further object of my invention resides in commingling a wax bearing oil with a liquefied normally gaseous hydrocarbon solvent such as propane under pressure suiicient to maintain the solvent in a liquid state and at an atmospheric temperature of about '70 F. to 80 F. and then gradually reducing the temperature of the oil solvent solution to approximately 40 F. to 0 F. by lowering the pressure to eect vaporza tion of a portion of the solvent and thus precipitating wax from solution, then allowing the chilled solution to settle for a short period of time to permit a hard wax to settle from the solution but to retain a softer wax in suspension in the solution, then decanting the solution of oil and remaining solvent containing the suspended wax from the settled hard wax, allowing the suspended wax to settle from solution and then separating the settled wax from the solution of oil and solvent and removing the solvent from the oil.

Other objects and advantages of my invention will be apparent from the following description of my invention taken from the drawing which refers to a schematic arrangement of apparatus for carrying out my invention.

Referringto the drawing, a wax containing oil, such as crude oil or a residue obtained from a parainic crude oil or a distillate containing wax, is taken from tank l and is drawn into line 2 by pump 3 where it meets a liquefied normally gaseous hydrocarbon solvent, such as liquid propane taken from storage tank 4 via line 5 and pump E which forces the liquid propane through valve 'l into line 2. The amount of propane introduced into line 2 will depend upon the character of the oil and the temperature desired in the subsequent chilling column Il, that is, sufficient propane must be introduced into the oil to be treated so the desired temperature may be eiected in the chilling column by evaporation of propane as will be described hereinafter. Preferably, the amount of propane mixed with the oil should be sufficient so that subsequent to obtaining the desired low temperature in the chilling column, a suicient quantity of liquid propane will remain in the oil to provide for adequate settling of the precipitated wax from the solution of oil and propane. During Wax settling, it is desirable to maintain a ratio of substantially or in excess of four volumes of propane to one volume of the oil which is adequate for good settling of the precipitated wax. This applies to both the chilling column ll and the settler 10. If sufcient propane is not present during chilling, make-up propane may be introduced so that the final volumetric ratio of propane to oil subsequent to the'completion of the chilling operation will not be substantially below 4 to 1. The makeup propane may be gradually introduced into the chilling column at such rate as to maintain a constant ratio of 4 to l in the chilling column l l.

It will be observed that other solvents may be employed which are capable of dissolving the oil and wax and that the present invention is not limited merely to the use of propane. Thus, other light petroleum fractions as naphtha and casinghead gasoline or mixtures thereof may be used. Other solvents which may be used are alcohol, ether, mixtures of alcohol andy ether, acetone, etc.

'I'he mixture of liquid propaneand oil contain ing wax is passed through turbulence or mixing coil 8 into line 9 controlled by pressure reduction valve I into a combined decanter and chilling column II. If` desired, the mixture of oil and propane may be acid treated and neutralized by methods now conventional prior to itsvintroduction into the column I I. In column I I, sufficient propane vaporizes to reduce the temperature of the remaining solution of oil and solvent to a suiciently low temperature which causes wax to precipitate from solution. It is preferable to lower the temperature gradually to the desired temperature, that is, at a rate not in excess of 4 F. per minute. This is accomplished by controlling the pressure in the column II by the proper operation of valve I4 on line I2 and compressor I'I which is connected to the column by lines I2 and I8. The pressure will be gradually lowered in the column I I to about 0 to 25 lbs. gauge which corresponds to a. temperature of approximately -40 F. to 0 F. If desired, the temperature in column I I may -be lowered rapidly, as, for example, at a rate of approximately F. per minute until a temperature of approximately to 45 F. is attained after which the temperature may be lowered gradually to approximately F. to 0 F. at a rate of approximately 2 F. or 3 F. per minute. The propane evaporating in the column I I will pass out of the top through line I2 controlled by valve I4 and then into line I6 to the suction of compressor I1 Where its pressure is raised to approximately 125 to 175 lbs. per sq. in. in order to liquefy the propane vapors by cooling to atmospheric tem perature. The compressed vapors are then cooled in cooler I9 where they are liquefied and then run down into propane storage tank 4.

Due to the fact that sulicient time must be given to gradually chill the oil and solvent passing into the column II and to make the process continuous, a plurality of chilling columns I I may be provided and operated alternately. However, when operating a batch process merely one of such chilling columns will -be sufficient. Thus, the introduction of oil and solvent into decanter II may be continued until any desired level in the decanter is reached after which the flow into the column II may be discontinued and the mixture chilled by controlling the operation of the valve I4 on line I2. In the chilling column II, the refrigeration of the oil and solvent causes the heavy, hard and solid granular wax to precipitate from solution as well as the light occulent wax but due to the differences in physical state, i. e., presumably crystal structure and particle size of the two types of wax, the former will settle rapidly to the bottom of the chiller before any substantial amounts of the light flocc-ulent wax will settle. This will require from 5 to 30 minutes depending upon the volumetric ratio of propane to oil. In other Words, at a relatively high ratio as for example, about eightvolumes of propane to one volume of oil, the hard wax will settle from solution in approximately 5 minutes. At lower volumetric ratios of propane to oil, the time required for settling ofthe hard wax will be pro# portionately increased. Moreover, the agitation accompanying ebullition by the evaporation of propane will prevent substantial quantities of light flocculent wax to settle. The hard granular wax settling to the bottom of the column I I is removed by line 22 controlled by valve 23and pump 24 as a Vslurry cfwax and propane containing some oil. If desired, this mixture may be washed with cold propane to remove the. oil constituents present. As the wax present in the mass containing oil and propane recovered from the bottom of the column II is in a form which settles rapidly from the chilled propane it can be Washed with cold propane and then passed to a settling device to separate the wax from propane solution of oil.

However, as shown in the drawing the material removed from the bottom of decanter I I is passedv via line 22 and 25 to heater 26 and thence through line 2l into evaporator 28. Superheated steam is circulated through closed coil 29 to supply additional heat and to vaporize propane and light oil present in the mixture.. The overhead from evaporator 28 passing through mist extractor 30 is sent through line 3I controlled by valve 32 to cooler 33 and then via line 34 intov separator 35. The uncondensed propane from separator 35 is sent through line 36 controlled by valve 3l to cooler 38 and thence via lines 39 and I6 to the suction of compressor II where its pressure is raised and is then sent to cooler I9 where the propane is liquefied and runs down into propane storage tank 4. light oil is withdrawn from the separator 35 through line 40. The hard wax is taken from the bottom of evaporator 28 via line 45 and pump 4E which forces the hard wax via line 4T and line 48 controlled by valve 49 to storage tank 50. The hard wax recovered in tank 50 is suitable for use in candle making by blending with stearic acid after rening by methods now conventional forpurifying scale wax. This wax is distinguishable from thelight ilocculent Wax remaining in suspension in decanter II which is not suitable for use in candle making due to its softness. However, the soft wax may be used as a component of lubricating greases such as those employed for lubricating ball or roller bearings.

If desired, the precipitated wax slurry containing propane settling at the bottom of the wax separator or decanter II may be removed via line 22 and commingled with a hot fluxing oil coming from tank 5I via line 52 controlled by valve 53 and pump 54 which forces the uxing oil through line 55 and heater 56 and thence into line 57 controlled by valve 58 and line 25 where it is commingled with the wax slurry.

proximately 500 F. prior to commingling it with the wax slurry. If the wax is to be converted into fuel oil, the wax slurry containing the residual propane and oil may be mixed with ordinary renery residuum at a temperature of f 500 F. and the heat required for vaporizing the propane and iiuxing the wax is supplied in the form ci sensible heat from the preheated re- Any condensed 4 in which unvaporized propane is withdrawn via line 36 and passed to propane storage tank 4 in the manner heretofore described. The condensed oil is removed via line 40. The fuel oil is withdrawn from the bottom of evaporator 28 and passed to storage tank 50 or a portion thereof maybe recirculated to line via heater G14 in the manner hereinafter described.

However, if the wax is to be recovered as a crude petrolatum which may then be processed in some desired manner, the wax slurry may be mixed with an initial amount of petrolatum preheated to a temperature of approximately 350 F. and introduced into line 25. The mixture preferably corresponds to the proportions ci two volumes of preheated petrolatum to one of wax slurry. The mixture is then passed into the evaporator 28 where propane is vaporized. Heater 26 may be omitted. The crude petrolatum is withdrawn from evaporator 28 at a temperature of approximately 200 F. which is sufficiently high above the melting point of the petrolatum for enicient pumping and handling and is then passed through line 45, pump 46 and line 41, one volume of the material passing into tank 50 and the other two volumes are recirculated into line 25 via line 60, controlled by valve 5Il and pump 62 which forces the material through line 63 and heater 64 where the temperature is :again raised to 350 F. and then passed into lines 65 and 25. The cyclic circulation through lines 60 and 63, heater 64 and line 65 into lines 25 is carried on continuously.

If desired, the initial amount oi preheated petrolatum introduced into line 25 may be substituted by an initial volume of preheated petroleum residuum which is circulated through the apparatus in the manner described above, one volume being passed to tank 50 while the remainder is recirculated and mixed with the Wax slurry coming from decanter I I. After a number of such circulations, the material passing into line will be sufliciently free from petroleum residuum and will comprise a crude petrolatum. Consequently, the material cooling in tank and the portion circulated through heater 64 will also comprise a crude petrolatum.

Chilling column II is provided with a plurality of side draw-off lines 66 located at any desired position above the bottom outlet employed for withdrawing the hard granular wax slurry. Each of these lines is provided with a valve 6l. By proper operation of these valves, the supernatant solution of oil solvent and precipitated occulent wax will be Withdrawn from the column II as a solution substantially free from hard wax. The propane, oil and precipitated wax suspended in solution is withdrawn from column II via said draw-off lines 56 and pumped by pump 68 via line 69 and valve 69 into the vapor tight wax separator or settler lll. In batch operation only one of these settlers will suice but to make the process continuous a plurality of these settlers may be provided operated alternately in order to provide for sucient settling periods. In order to prevent ebullition in the Wax separator 10 during the wax settling operation, pressure is imposed upon the solution of oil. This is accomplished by maintaining pressure within the separator by pump 68. As the chilled mass in the wax separator remains in a non-ebullient state, the wax settles out and is collected by vanes 'II operated by pulley I2 connected to a suitable source of power not shown. The time required for settling the nocculent Wax insettler l0 will vary from one-half to two hours depending upon the volumetric ratio of propane to oil as described above. If desired, the wax settler 'I0 may be replaced by a filter through which the solution of oil, solvent and precipitated wax may be passed to separate the suspended wax from the remaining oil and liquid propane. This may be accomplished by passing the chilled mixture via line H0 and valve IIU to filter III. The ltrate may be passed via line II2 into line 'i4 while the separated wax may be passed via line H3 into line 50. If desired, a lter aid such as diatomaceous earth, clay, sawdust or wood iiour may be mixed with the chilled propane solution of oil containing the precipitated wax and passed through the filter.

As an alternative method of operating continuously, I may effect chilling in column I'I as aforesaid and without providing for any substantial settling in column II, the entire charge is Withdrawn from the bottom into separate settlers connected in series so that the overow from the first settler constitutes the feed to the second settler. In the rst settler, a relatively short settling time is allowed to permit the hard wax to settle and in second settler, a longer settling time is provided. In order to withdraw a substantiaily homogeneous mixture from the bottom of column II, I prefer to employ positive agitation in column II during the chilling and transferring operation. Ii desired, a pump may be located at the bottom of column II for continuously circulating a portion of the mixture Withdrawn back into the column at a higher point while the remainder of the mixture Withdrawn is forced through the settling vessels.

The proportions of hard and soit wax recovered will depend upon the stock being dewaxed. For example, approximately one fourth of the total Wax recovered from de-asphaltized Kettleman residuum can be obtained as a hard Wax and the remainder as a petrolatum by the operation of my process.

The wax free oil dissolved in propane is withdrawn from the separator l0 and pumped by pump 'i3 through line 'E4 controlled by valve 'i5 into heater 'I6 provided with mist extractor 'l where the propane present is vaporized by the aid of steam circulated through the closed steam coil 18. The vaporized propane passes out from the heater through lines 'I9 controlled by valve 80. cooled in cooler 8I and then passed through lines 82 and I5 to compressor I1, cooler I9, into storage tank 4. The dewaxed propane free oil passes from heater 'I5 by means of line 83, controlled by valve 84 to pump 85 which forces the heated oil solution through heat exchanger and then through line 81 into tank 88. If the oil had been previously treated with acid and alkali, it may be treated in its chilled condition prior to the separation of the propane in the evaporator or heater 16.

The precipitated wax slurry settling to the bottcm of the wax separator I0 is removed from the separator through line and is passed through heat exchanger 86 where it extracts heat from the dewaxed oil from heater 16. The wax slurry is then pumped by pump 9|, into line 92, through heater 93 and line 94, into separator 95. Vaporized propane is passed to the storage tak 4 via line 9B controlled by valve 91 and line 36, cooler 30, lines 39 and I6, compressor I'I and cooler I9. The propane free wax is withdrawn from the separator 95 through line I 00 and pumped by pump. UJI into line |02 controlled by valve |03 into storage tank Ind. If desired, the wax slurry a settling tank to thereby separate high melting separated from settler 10 may be treated in like Wax from the oil mixture by settling, passing the manner as that separated from the column Il, oil mixture from the settling tank, and then septhat is, it may be commingled with hot uxing oil arating the remaining portion of the wax content and converted into a fuel oil as previously de- 5 by ltration.

scribed or the wax slurry may be treated for the 2- In the meilhOd 0f relng Petroleum Oil C011- production of crude petrolatum in the manner taining paraflin waxes, the steps which comprise,y heretofore described mixing the oil with liquefied hydrocarbon gases It is to be understood that the above is merely having a vapor pressure greater than atmospheric illustrative of preferred embodiments of my inl0 at Ordinary atmOSDheTC temperature, Cooling the vention of which many variations may be made mixture t0 a temperature SUIiCiSIIt t0 COIlgeal by those skilled in the art Without departing from the Wax content, passing the cooled mixture the spirit thereof. through a settling tank to thereby separate wax I claim: from the oil mixture by settling, passing the oil l. In the method of rening petroleum oil con- 15 mixture from the settling tank, and then separattaining paraffin waxes, the steps which comprise, ing the remaining portion of the Wax content by mixing the oil with lqueed hydrocarbon gases ltration. having a Vapor pressure greater than atmospheric 3. A process as in claim 2 in Which the liquefied at ordinary atmospheric temperature, cooling the hydrocarbon gases are preponderantly propane. mixture to a temperature suincient to congeal the 20 Wax content, passing the cooled mixture through ULRIC B. BRAY.

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