US1956780A - Dewaxing mineral oils - Google Patents

Description

Patented May 1, 1934 UNITED STATES DEWAXING MINERAL OILS Vandcrveer Voorhees, Whiting, Ind., assignor to Standard-Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Application December 11, 1931, Serial No. 580,493

6 Claims. (01. 196-19) 7 This invention pertains to the removal of wax from oil and particularly to the removal oi. mineral wax from mineral oil.

One object of the invention is to provide a process for the removal. of wax from oil more completely than has heretofore been possible.

Another object is to provide a more eflicient method for the removal of wax from oil.

Another object is to provide for the removal 10 of wax from oil in a plurality of stages at different temperatures in such manner as to effect the maximum possible removal of wax at each temperature.

Still another object is to provide suitable diluents for operating this process.

, Further objects of the invention will appear as the description thereof proceeds.

.The removal of wax from oil, and more particularly the removal of mineral wax from mineral oil, has in the past generally been accomplished by the dilution of the wax bearing oil with a suitable diluent or diluent mixture followed by chilling the solution to precipitate the wax, and removal of the wax by some suitable means such as filter pressing. The diluent most commonly used in this process has been a petroleum naphtha, but more recently it has been found advantageous to use a diluent mixture which will .more completely remove the wax from the ,oil.

These newer diluent mixtures most commonly comprise two substances, one of which has a *relatively high solvent powerfor wax and the other of which has a relatively low solvent power for wax. These two components are blended together in such proportion that the wax will be precipitated as completely as possible at thedesired dewaxing temperature. In such a diluent mixture the component of high solvent power may be called the solvent and the component 4 of low solvent power may be called the antisolvent. As much anti-solvent is used as can be used without throwing some of the oil out of solution at the dewaxing temperature. The result is that when the composition is so adjusted that the oil is on the verge of precipitation the solution will have the minimum solvent power for wax.

As an exampleof such a process, lOObarrels of an overhead lubricating oil made by the fractional distillation of Mid-Continent crude and having a viscosity of 74 seconds Saybolt at 210 F. maybe diluted with 95 barrels of acetone and.

155 barrels of benzol to give a homogeneous solution at ordinary temperatures. This solution may then be cooled down to about -10 F. at which removal of oil from the wax cake is much easier.

-filter rate, since the amount of wax to be retemperature most of the wax will be precipitated. The precipitated wax may then be removed by any suitable means, such as filter pressing.

Although such a process has many advantages over the use ofan ordinary naphtha diluent, it has also many disadvantages. One of these is I that the wax is not always completely removed.

Another disadvantage is that at the necessarily low dewaxing temperatures the viscosity of the solution is relatively high, which leads to poor filter rates and to a wax filter cake from which it is diflicult to remove entrained 011. Still anotherdisadvantage is that in chilling the waxbearing oil solution, the wax begins to precipitate at temperatures well above the filter temperature and this precipitated wax often leads to dimculties in the chilling operation. When chillers of a tubular type are used it is particularly prone to clog the chilling equipment.

My invention'overcomes these difficulties by removing the greater portion of the ,wax at a relatively high temperature. At this elevatedtemperature, the viscosity of the solution is much lower, filter rates are therefore much higher and the Furthermore, when the partially dewaxed oil is cooled down to the final dewaxing temperature,

the relatively small amount of residual wax is able to crystallize unencumbered by the larger portion of wax, with the result that there is ultimately more complete wax .removal. This effect maybe enhanced by using a moreclosely woven filter medium at the lower dewaxing temperature which can be done without seriously impairing the moved at the lower temperature is relatively small. This use of two or more dewaxing stages at successively lower temperatures largely eliminates the trouble due to clogging of the chilling equipment, since most of the wax is removed at a relatively high temperature before much refrlgeration is necessary.

Another advantage of operating in two or more steps is that the wax removed at the higher temperatures is a high melting point wax, having an enhanced market value which it would nothave if contaminated with the low melting point wax removed at the lower dewaxing temperatures. Still another advantage of operating in two or more stages is that any wax which may pass thru the filter medium in the first stage will probably be removed in the second stage, whereasin a onestage process more wax inevitably passes thru the filter medium to contaminate the oil.

'These theoretical advantages of operating in two or more stages have never been accomplished in practice when using special diluents. This is due to the fact that if the diluent composition is adapted to the complete removal of wax at the lower dewaxing temperature it will be inefiicient or even completely ineffectual at the higher temperature. On the other hand, if the diluent composition is adapted to. the efiicient removal of wax at the higher dewaxing temperature and it is attempted to chill the unmodified solution to the lower dewaxing temperature, it will be found that part of the oil and/or part of the diluent will separate out of the solution, resulting in many dificulties. If the composition of the diluent. is selected in such manner as to be intermediate be tween the composition desirable for operating at the higher dewaxing temperature and the composition desirable for operating at the lower dewaxingtemperature it is found that unsatisfactory results will be obtained in both stages, i. 'e. dewaxing will be very incomplete in the first stage and there will be trouble from the precipitation of oil and/or the separation of part of the diluent in the second stage.

This situation has been remedied by my invention which comprehends the modification of the composition of the diluent mixture to adapt it to the most eflicient removal of wax at each of the successively lower dewaxing temperatures. Thus in the first dewaxing step a diluent composition is selected which will permit the removal of most of the wax at a relatively high temperature, say

-+5 F. to +50 F. This can be done with relatively little refrigeration and will therefore avoid difiiculties due to clogging of the chillers. It willalso permit the recovery of an uncontaminated high melting point wax. Furthermore, the high filtration temperature and good crystalline form of the precipitated wax will permit exceptionally high filter rates and will promote the efficient washing of the wax cake.

All these results are brought about by using an initial diluent composition with a relatively 'high anti-solvent content in order to precipitate as much wax as possible without throwing any oil out of solution. This procedure will remove the great bulk of the ,wax at a relatively high temperature. l

In order to secure a low cold test lubricating oil, however, it is necessary to remove the small amount of residual low melting point wax which can only; be done at a much lower temperature If the original filtrate from the first dewaxing step is cooled to this'final low dewaxing tempera ture, oil will be thrown out-oi solution and in many cases part of the diluent will separate as an additional liquid phase. Either of these events leads to prohibitive difllculties in the filtering op- I eraton.

In operating my invention the filtrate from the first dewaxing stepis modified by the addition of more solvent or the removal of part of the antisolvent so -as to render the solution capable of retaining the oil and diluent as a single liquid phase at the lower dewaxing temperature. In order to remove substantially all of the wax at .this lower temperature, however, the properties of the modified solution must as previously pointed out, be such as to just retain the oil in solution. Therefore, it is necessary or desirable to add just sufiicient solvent or remove just sufiicient anti-solvent to accomplish this result. In other words if the solution has too high a solvent power acetone.

the wax will be incompletely removed and if the solution has too low a solvent power some of the oil will be thrown out of solution.

' The following is an example of my process:

100 barrels of the above mentioned wax-bearing lubricating oil is dissolved at ordinary or slightly elevated temperatures in a mixture of 95 barrels of acetonexand 80 barrels of benzol. This solumay then be removed by filter pressing or other suitable means. 'The filter cake may be washed with more of the same or another diluent. The

-diluents may be recovered from both filtrate and filter cake by distillation.-

Although theabove example mentions specific temperatures and amounts of acetone and benzol, it is to be understood that the dewaxing temperatures, and diluent composition should be varied to suite the individual situation. The exact conditions will depend upon the character of the oil, the character of the wax, the percentage of wax in the oil, the pour point characteristics which are desired for the dewaxed oil, etc. The most suitable conditions for any individual case can readily be determined by simple experi-- ments which will be apparent to those skilled in the art.. I

It is to be understood that other substances having a relatively high solvent power for wax may be substituted for all or part of the benzol. Examples of such substances are toluol,"highly unsaturated or aromatic petroleum naphtha, etc.

It will also be understood that the acetone may be wholly or partially replaced by other substances having a relatively low solvent power for wax such as methyl acetate, ethyl acetate, methyl carbonate, ethyl formate, methyl ethyl ketone, butyl alcohol, etc.

Although the invention in the above form comprehends the use of a diluent mixture comprising a solvent and an'antisolvent (in the example benzol and acetone respectively) it is to be understood that in somecases a one-component diluent (the anti-solvent) can be used in the first dewaxing stage-and that the second component having a higher solvent power (the solvent) can be added prior to further chilling.

As an example of this type of process, 100 barrels of a wax-bearing lubricating oil fraction may be diluted with 200 barrels of ethyl acetate and chilled to +30 F., the precipitated wax may be removed at that temperature, 55 barrels of benzol may be added, the modified solution may be I chilled to l0 F., the residual wax may be removed at that temperature, the diluent may be recovered from the separated oil and wax by distillation, and the benzol and acetone may be separated by fractionation and returned to the respectivelysuitable points in the process.

It will also be understood that in some cases a three component mixture may be used. An example of such a diluent mixture is one containing a solvent, an anti-solvent and a third substance having an intermediate solvent power for wax.

An example of the use of a diluent mixture fo the latter type in my process is as follows:

100 barrels of the above described oil are dis l l l tures in a mixture isopropyl ether, 50 barrels of ethyl'alcohol and I "ture containing suflicient anti-solvent to cause solved at ordinary or slightly elevated temperacomprising 125 barrels of 25 barrels of benzol. This solution is then cooled down to +35 F. at which temperature the greater part of the wax is precipitated and removed. The filtrate is then further diluted with 50 barrels of benzol and chilled to 15 F. at which temperature the remaining small amount of wax is precipitated and removed. In the above example the benzol is the solvent, the ethyl alcohol is the antisolvent and the isopropyl ether is a substance of intermediate solvent power.

To summarize, my invention comprehends the dilution of a wax-bearing oil with a diluent or diluent mixture adapted to precipitateall or most'of the wax which can be precipitated at a certain dewaxing temperature, chilling to that temperature, removing the precipitated wax, adjusting the composition of the solution to adapt it to precipitate substantially all the remaining wax at a lower dewaxing temperature, chilling to said lower dewaxing temperature and removing the wax at that lower temperature.

Although the above description contemplates the removal of wax in two steps at two dewaxing temperatures, it will be readily understood that the process may be adapted to the removal of wax in three or more steps at a corresponding number of successively lower dewaxing temperatures, the composition of the solution being adjusted at each step in order to effectuate sub-- stantially the maximum possible wax removal in each step which is possible at that temperature with a solvent-antisolvent mixture without causing the precipitation of oil.

'As a part of my invention I also intend to include the improved method of refrigeration of the oil solution wherein a highly volatile normally gaseous liquefied hydrocarbon is incorporated in the solution and permitted to evapcrate. As such a refrigerant, I may use liquid propane 0r butane. Thus, I may dilute the wax-- bearing oil with a substantial quantity of liquid propane under pressure and add to this mixture an antisolvent, for example, diethyl-ether for the purpose of decreasing the solubility of the wax in the mixture. from this mixture, chilling will result from the evaporation of part of the propane, causing the crystallization of most of the wax from the other-propane-oil-solution. After filtering off the wax which has separated, additional propane diluent may be added to the filtrate and a part thereof subsequently evaporated to reduce the temperature of the mixture still further, thereby causing the separation of the remainder of the wax. Operating in this fashion no additional refrigeration is needed beyond that ob tained by evaporation of the propane employed in the mixture. It should be understood that other highly volatile solvents or antisolvents may be employed without departing from the spirit of this invention which is-particularly concerned with the dewaxing of lubricating oils in a plurality of stages with modification of the composition of the diluent or diluent mixture between the dewaxing stages in order to adapt it to the efficient separation of wax from oil in each stage.

Altho my invention has been described in connection with various specific embodiments thereof, I do not desire to be restricted thereby but only by the scope of the appended claims.

I claim:

l. A process of the class described for dewax- On partial release of pressure ing oil first at a low temperature and th n at a lower temperature, which comprises dissolving a wax-bearing :oil in a, solvent anti-solvent mix separation of oil from the solution at said lower temperature, but not at said low temperature, chilling the mixture tosaid low temperature, separating wax which has solidified at said low temperature, increasing .the solvent-anti-solvent ratio to prevent the separation of oil from the solution at said lower temperature, chilling to said lower temperature, separating substantially all of the wax which is solidified at said lower temperature, and removing the solvent and antisolvent from the dewaxed oil.

' 2. A process of the class described for dewaxing oil first at a low temperature and then at a lower temperature, which comprises dissolving a wax-bearing oil in an anti-solvent adapted to cause separation of oil from the solution at'said lower temperature but not at said low temperature, chilling the solution to said low tempera ture, separating wax which has precipitated at said low-temperature, adding solvent to the dewaxed oil solutlon'in quantity suflicient to prevent the separation of oil from 'thesolution at said lower temperature, chillingto said lower temperature, separating substantially all or the wax which has precipitated at said lower temperature, and removing solvent and anti-solvent from the dewaxed oil.

3. A process for dewaxing oil with solvent-- anti-solvent mixtures in a series of consecutively lower temperature stages which comprises solving a wax-bearing oil in a soivent-anti-solvent mixture containing sufiicient anti-solvent to cause separation of the oil therefrom in the second stage; cooling the mixture to the first stage dewaxing temperature, separating was from diluted oil in said first stage, changing the ratio of solvent to anti-solvent in the mixture to prevent the separation 'of oil therefrom in the second stage but to cause the separation of oil therefrom inlthe third stage, cooling the mixture to the second stage dewaxing temperature, separating wax from diluted oil in said second stage, and continuing to change the ratio of solvent to anti-solvent at successively lower temperature stages so that the oil will be in solution at each dewaxi-ng temperature but would be thrown out of solution at a lower temperature.

4. A process of the class described, comprising dissolving a wax-bearing oil under pressure in adiluent mixture comprising a solvent and an anti solvent and having at least one normally gaseous constituent, said diluent mixture having a composition adapted to precipitate most of the total wax content at a selected dewaxing temperature lower than the temperature of the aforementioned dissolving step, reducing the pressure to evaporate a portion of said normally gaseous constituent thereby cooling said solution, precipi tating said wax at said selected dewaxing temperature, increasing the ratio of solvent to antisolvent in the partially dewaxed oil solution to a point at which substantiallyall the remainng war will be precipitated at a second selected dewaxing temperature lower than said first-mentioned selected dewaxing temperature without precipitation of oil from the solution, further reducing the pressure to evaporate a furtherportion of normally gaseous constituent thereby cooling said solution, precipitating said wax at said second selected dewaxing temperature, and removing 3 i 3 i l said precipitated wax substantially at said lastmentioned temperature. I 3 v j5.-cA-processlotv-thelclass described, comprising dissolving'a wax-qbearing oil in a mixture comprising benzol and sufficient acetone to precipitate most of the total wax content at a selected dewaxing temperature lower than the temperature of the dissolving step, precipitating said wax from the solution at said selected dewaxing temperature, removing precipitated wax substantially at said selected dewaxing temperature, adding to the partially dewaxed oil solution an additional quantity of benzol suflicient to alter the composition of said solution to a point at which substantially all the remaining wax will be precipitated at a second selected dewaxing temperature lower than said first-mentioned selected dewaxing temperature without precipitation of oil from the solution, precipitating said wax at said second selected dewaxing temperature, and removing. said'fprecipitated wax' substantially at said lastmentioned temperature.