US2007546A - Fractional crystallization of waxes - Google Patents

Description

July 9, 1935. E. PET'TY.

FRACTIONAL CRYSTALLIZATION OF WAXES Filed July 27, 1935 INVENTOR Ear/Pf/y www All

Patented July 9, 1935 FRACTIONAL CRYSTALLIZATION 0F WAXES v Earl Petty, New York,

N. Y., assignor to Alco Products, Incorporated, New York, N. Y., Aa corporation of Delaware Application July 27, 1933, Serial No. 682,446

6 Claims.

My invention relates to a method of fractional crystallization of waxes and more particularly to a method of removing wax from hydrocarbon oils in stages in order to obtain segregated wax fractions.

Currently lubricating oils are made preponderantly from distillates procured by vacuum distillation. The lubricating oils are obtained by dewaxing two or more segregated fractions of 1ubricating oil-bearing distillates, namely, pressable wax distillate, slop wax, and vacuum steam refined stock. The pressable wax distillate is cold pressed to remove the wax and segregate the lubricating oil. The slop wax distillate is processed by a centrifugal operation in which residuum stock or vacuum steam refined stock and retarders such as Paraflow or filter aid systems are used. The vacuum steam refined stock is processed by centrifuging or by the use of a filter aid process employing wax precipitating retarders such as Paraflowf or residuum retarder stock. Parailow is the trade name for a wax-aromatic hydrocarbon condensation product which has the property of lowering the cold test by retarding the crystallization of waxes which may be present in the oil.

These conventional methods of processing distillatesto produce lubricating oils have as their byproducts the regular market grades of waxes, namely crude scale wax, refined paraffin wax, and petrolatum.

In my co-pending applications, Serial No. 632,- 278, filed September 9, 1932, now Patent 1,940,015, issued December 15, 1933,v and Serial No. 651,- 497, led January 13, 1933; I have disclosedaprocess of dewaxing in which a normally gaseous diluent such as propane, is liquefied and a solution made therewith with a wax-bearing hydrocarbon oil. Upon chilling this solution, wax is precipitated, due to the fact that the diluent at low temperatures acts as an oil solvent and a wax anti-solvent. By means of my dewaxing process, I have been enabled to dewax the entire lubricating oil-bearing distillates in-one fraction. 'I'his fraction includes all the wax distillate, the slop fraction, and the vacuum steam refined stock. The resulting characteristics as to viscosity, falls in the approximate range of to 85 seconds, (Saybolt universal) at 210 F. Y

It will be obvious that the operation by which the entire lubricating oil-bearing distillates are dewaxed in a single operation has numerous advantages in so far as the lubricating oily compo'nent is concerned. The wax which results from these processes, however, is a mixture of (Cl. 12W-,18)

commercial paraffin wax and petrolatum, and the 'wax requires further special processing to isolate the different types of waxes. This has been a disadvantage. It may be desirable to dewax an entire wax-bearing lubricating oi1-fraction and then practice fractional crystallization on the wax only by diluting with a non-viscous oil such as gas oil or naphtha in the first stage of dilution and then dilute with propane thereafter in the subsequent stages.

One object of my invention is to provide a process for dewaxing hydrocarbon oils while crystalliziiig the wax fractionally in order to obtain grades of wax which will meet thestandard specifications and quality with respect to paraiiin.

Another object of my invention is to provide a method of precipitating waxes from hydrocarbon oils in a series of stages in order to obtain different grades of wax.

Another object of my invention is to provide a method of fractional crystallization of waxes in a lubricating oil dewaxing process which will produce an improved quality of petrolatum,

In general, my invention contemplates a dewaxing process in which a normally gaseous liquefied diluent is employed to make a solution of a wax-bearing oil and the diluent. The concentration of the solution is carefully controlled. The solution is chilled to predetermined temperatures at which I have found various types of waxes precipitate. It will be seen that the type of wax which will be obtained will be a function of the type of wax-bearing oil used, the coneentration of the solution and the temperature to which the solution is chilled. The concentration of the solution and the temperature to which the solution is chilled can be controlled. The ,solu- ,tion is chilled to a predetermined temperature to ,precipitate a desired type of wax which is then 'tliltered from the solution and the remaining solution further chilled to further precipitate the wax in a stepwise manner.

'Ihe accompanying drawing represents a schematic view 'of one form of apparatus capable of carrying out my invention. More particularly, I use as a solvent a normally gaseous liqueed diluent. I prefer to use propane, though it is to be understood that any equivalent solvent having a boiling range falling between 65 F. and 32 F. may be used. Such hydrocarbon gases as butane, iso-butane, or mixtures thereof, either -alone or with' propane, would be eiective invmy process. It is possible to use ethane, though this has a lower boiling point than necessary, or mixtures of such compounds of acetone or other chemical compounds which would serve as crystal accelerators, with desired portions of propane.

'Ihe charge may be the wax solution obtained by dewaxing the entire lubricating oil bearing fraction or cut in one operation taking the wax solution as a charging stock.

The normally gaseous liquefied diluent isstored in a tank I. The stock to be dewaxed is stored in tank 2. Pump 3 pumps the oil to be dewaxed from the tank 2 through line 4 to a mixing tank 5 where the propane from tank I is pumped by pump 6 through line 1 to a mixing tank 5. 'Ihe ordinary blend comprises about 50% lubricating oil stock and 50% diluent by weight. The mixture under pressure is passed through heating and blending equipment 8 to form a solution. The temperature is raised to a point well above the melting point of the wax, while sufficient pressure is maintained to keep the -diluent in a liquid state. I have foundthat a temperature range from to 150 F. and a pressure range from 180 pounds to 250 pounds per square inch gauge will be involved. The solution is then passed through a cooler 9 of any suitable type, and through line I0 into crystallizer evaporator II. In the crystallizer evaporator, a portion of the propane is evaporated through line I2 which communicates with separator I4 which is in communication with low pressure propane main I5. Any liquefied propane or oil carried overhead through line I2 will be separated in separator I4 and be returned to evaporator crystallizer through line/I 6. The amount of chilling in evaporator crystallizer I I is such that the solution will be chilledto a temperature range varying from 30 to 50 F. depending upon the type of oil being dewaxed. At this point, the solution is still under pressure and a crystal type of wax will largely be precipitated.

The chilled oil-diluent solution containing precipitated crystalline wax is Withdrawn from the evaporator crystallizer II through line I1 and is pumped by pump I8 through line I9 into filter 20. The Wax-oil-diluent slurry fromfi1ter20ispumped by pump 2| through liney 22 into filter 23. The wax-oil-diluent slurry is pumped from filter 23 through line 24 by pump 25 through line 26 to lter 21. The filter structure involved in filters 20, 23, and 21 is that shown in my co-pending application Serial No. 679,358, filed July 7, 1933. The filter arrangement comprises filter tanks in which edge filtration apparatus is installed. The filters are provided with means for keeping the Wax in a slurry form by the addition of added amounts of diluent. The filters are also provided with a kick-back arrangement or a method of introducing fluid in the reverse direction through the filter in order to clear the same. These details are disclosed in my last mentioned co-pending application. In this connection, however, it might be well to point out that any diluent which is added to maintain the wax in the form of a slurry is added at a temperature from 10 to 20 F. or, if desired, at a lower temperature in order to prevent re-dissolving of the wax. vThe filters, of course,'will operate at pressures at or above the pressure of equilibrium for the temperature at which the separation is being made. The oildiluent solution containing unprecipitated waxes passes from filters 20, 23, and 21 into manifold 28 which enters crystallizer evaporator 29. The Wax solution slurry is withdrawn from filter 21 through line 30 and pumped by pump 3.I through line 32, through heat exchanger 33 in which the temperature of the slurry is raised sufficiently to melt the solution slurry wax. The slurry is then passed through contactor 34 in which it is treated for color and then passed into steam still stabilizer 35 in which the propane is distilled off overhead through line 36, condensed in condenser 31 and accumulated in tank 38 from which it may be pumped by pump 39 to the propane working tank I. The first wax fraction, preponderantly of the crystalline type and oil free, will be withdrawn from the bottom of stabilizer 35 through line 40. This wax will have a melting point falling within the range of 120 to F.

The oil-propane solution is then chilled by evaporating a portion of the normally gaseous liquefied diluent in crystallizer evaporator 29 The propane being evaporated passes from the evaporator crystallizer through line 4I into separator 42 which communicates through line 43 to the low pressure propane main I5. Any liquid propane or oil carried overhead is separated in separator 42 and is returned to the evaporator crystallizer through line 44. It will be observed that I have pointed out, in order to maintain the wax in the form of a slurry, I propose to add as needed, additional amounts of liqueed diluent. The oil-diluent solution, therefore, entering evaporator crystallizer 29 may have a dilution which is too high. I propose, in evaporator crystallizer 29, to evaporate a sumcient amount of propane to adjust the concentration to the desired point, which will depend, of course, on the type of charging stock. Obviously, evaporation of a large amount of propane will result in a temperature which will be too low for the desired fractional crystallization of the Wax. I overcome this disadvantage by installing a heat exchanger 45 in evaporator crystallizer 29. Any suitable material to be cooled may be passed through pipe 46, through heat exchanger 45, in order to permit the desired concentration to be reached, while allowing the temperature to fall within the range of 20 to 0 F. The concentration of the diluent which is desirable is again approximately 50% by weight to 50% by weight of the oil being dewaxed. The oil-diluent solution at proper temperature and proper concentration, is withdrawn from evaporator crystallizer 29, through line 41 and is pumped by pump 48 through line 49 to filters 50, 5I and 52. The diluent-wax-oil slurry passes between filters through lines 53 and 54. The oil-diluent solution is withdrawn from filters 50, 5I, and 52 into manifold 55 from which it passes to evaporator crystallizer 56. The wax is withdrawn from filter 52 through line 51 and is pumped by pump 58 through heat exchanger 59 in which the temperature ofthe solution is raised in order to melt the wax, and the entire solution is contacted for color in contactor 60 and passedto steam still stabilizer 6I, from which the propane is withdrawn overhead through line 62, condensed in condenser 63 and accumulated in tank 64 from which it may pass through line 65 to line 66 and will be pumped by pump 39 to. propane tank I. The second Wax Will be a parafiinwax of a lower melting point and is Withdrawn from the stabilizer 6I through line 61 and will be passed to storage.

'Ihe filtration in filters 5I, 5I, and 52 ls again conducted in such a manner as to permit the wax to remain in the form of a slurry. Due to the fact, however, that a lower temperature is now needed, I have found that it usually is not necesary to employ a heat exchanger in evaporator crystallizer 56. A portion of the propane is again evaporated from the oil-diluent solution until a temperature of from 20 F. to 40 F. is obtained. The chilled oil solution containing wax precipitated bythe low temperature and by- 12, passing between iilters through lines 13 and 14. The dewaxed oil solution is withdrawn from iilters 10, 1|; and 12, and passed into manifold 15 which discharges to steam still stabilizer 18 in which the propane is distilled and passed overhead through line 11, through condenser 18, and 4 accumulated in tank 18, from which it passes through line into line 66 from which it is pumped by pump 39 to propane tank I. 'Ihe fully dewaxed oil is withdrawn from the bottom of the stabilizer 16 through line 8| and passed to storage. The wax slurry is withdrawn fromllter 12 through line 82 and is pumped by pump I3 through heat exchanger 84 in which the temperature is raised in order to insure that the wax is melted.' The wax is then contacted for color in contacter 85 and the slurryor solution is passed into steam still stabilizer 86 in which the propane is evaporated from the wax. The propane passes overhead through line 81 and is condensed in condenser 88 and accumulated in tank 89 from which it is withdrawn through line 90 to line 66 and pumped by pump 39 to propane tank l. The wax which is withdrawn from the bottom of stabilizer 86 through line 9i is a highly rened petrolatum of an unusuallylow oil content and resembles beeswax in physical characteristics.

lIt is to be understood, of course, that any number-of suitable stages of wax crystallization may be employed in order to obtain diierent types of waxes which may be useful in the different arts. The resulting oil is fully dewaxed.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is Within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is,

by evaporating a portion of the liqueiled normally gaseous diluent sufficient to producea solution of predetermined concentration, adding heat to the solution during chilling in suiicient quantity to prevent the temperature of the solution from dropping below a predetermined low temperature and separating precipitated wax from the chilled solution.

2. The method of dewaxing a hydrocarbon oil including the steps of chilling a solution of wax bearing oil inaliqueed normally gaseous diluent toa predetermined low temperature, separatingV from the chilled solution wax precipitated by the chilling, further chilling the partially dewaxed' solution by evaporating a portion of the liquefied normally gaseous diluentsuilcient to produce a solution of predetermined concentration while adding heat to the solution during chillingsufiicient to prevent the temperature of the solution from dropping below a predetermined tempera'- ture lower than the rst mentioned temperature and separating from the chilledsolution Wax precipitated during the last mentioned chilling operation.

3. A method as defined by claim 1 in which the normally gaseous liquefied diluent is a hydrocarbon which at wax precipitating temperatures exhibits wax anti-solvent, oil solvent properties.v

4. A method as deilned by claim 2 in which the normally gaseous liquefied diluent is a hydrocarbon which at wax precipitating temperatures exhibits wax anti-solvent, oil solvent properties.

5. The method of fractionally separating waxes from Wax bearing hydrocarbon oils including the steps of dissolving a waxbearing oil in a liquefied normally gaseous diluent, chilling the solution to a predetermined,wax-precipitating temperature, filtering the precipitated wax from the solution, recovering a iirst wax, chilling the partially dewaxed solution to a lower wax precipitating temperature at which a second type of wax precipitates by evaporating a portion of the normally vchilled in suiiicient quantity to prevent the temperature of the solution from dropping below the predetermined lower wax precipitating temperature, filtering the precipitated wax from the solution and recovering a second wax.

'6. A method as in claim 5 in which the normally gaseous liqueed diluent is a hydrocarbon which at wax-precipitating temperatures exhibits wax anti-solvent, oil solvent properties.

EARL PETI'Y.

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