US2287966A - Process for dewaxing mineral oils - Google Patents

Description

June 30,'1942.` DLG. BRANDT PROCESS FR DEWXING MINERAL OILS Filed May 11, 1938 Kul-...IU v ...93.1

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lslvfmd v x ATTQRNEY Patented June 30, 1942 PROCESS FOR DEWAXENG MHNERAL OILS David G.V Brandt, Westfield, N. J., assignor to Cities Service Oil Company,- New York, N. Y., a corporation of Pennsylvania Application May 11, 1938, Serial No. 207,232 4 Claims. p (01.196-18) This invention pertains to a process for dewaxing petroleum oils, and more particularly to the dewaxing of petroleum lubricating oil stocks.

The invention of the present application is an improvement on the process of the applicants` pending application Serial No. 670,066, filed May 9, 1933, for improvements in the Art of dewaxing oils. The said application discloses a process for dewaxing petroleum oil stocks to be used for lubricating purposes in which the stock is dissolved in a liqueiied normally gaseous hydrocarborn diluent such as liquid propane or any similar hydrocarbon or mixture having less than ve carbon atoms to the molecule. In that process a portion of the chilling is eected by vaporizing some of the solvent, although provision is made for mixing precooled diluent such as liquid propane with the oil solution at various stages of the chilling operation.

In carrying out the chilling process in accordance with the disclosure of said application, the oil-propane mixture is passed through a series of chambers and additional quantities of cold liquid propane is added to the mixture for the purpose of maintaining the desired gravity and viscosity of the oil mixture. After the precipitation of the Wax in the oil solution, the wax is separated by gravity separation in an externally cooled separator in which provision is made for accelerating the removal of wax.

Repeated tests have shown that in the dewaxing of petroleum oils in which propane is used as a diluent and internal refrigerant, the chilling of the mixture by vaporizing propane apparently breaks up the wax crystals or prevents the formation of large wax crystals because of the intense agitation of the oil due to the vaporization of the propane.

Therefore, the primary object of the present invention is to provide an improved process for the use of a low molecular weight diluent such asv liquid propane in which the wax precipitation will be greatly improved.

A further object of the invention is to provide an improved apparatus particularly adapted for carrying out the improved process of the present invention,

With these objects in mind the process of the present invention in general comprises the steps of forming a solution of the petroleum lubricating oil stock to be dewaxed in liquid propane or similar low molecular weight hydrocarbon, cooling the solution by indirect heat exchange with .a cooler i'luid to Aa point just short of wax precooled solution into a chilling zone maintained at a pressure adapted to prevent 'vaporization of the diluent and introducing prechilled diluent into the solution in sufficient quantity to eiect the precipitation of all of the wax content of the oil desired to be removed therefrom, the introduction of the chilled diluent being effected in such a manner as to cause only a mild eddying of the oil mixture to bring it and the introduced diluent to equilibrium temperature conditions. After the wax has been precipitated in the manner described, it may be separated from the diluted mixture by settling, centrifuging or ltering, or any combination of these common practices.

Other objects, features and advantages of the process and apparatus of the present invention will be apparent to those skilled in the art from the following more detailed description thereof taken in connection with the accompanying drawing in which:

The single ligure is a diagrammatic flow sheet of apparatus particularly adapted for carrying out the improved process, and in which certain of the elements of the apparatus are shown in vertical position.

Referring to the drawing, the oil stock to be dewaxed is conducted through a line I, and introduced into a mixer 2 where the voil is mixed with liquid propane introduced through aline 3. A solution of the oil stock in propane is effected in the mixer 2 and the resulting solution is passed from the mixer downwardly through a heat eX- changer column 4, rst in indirect heat exchange with a cooling liquid such as Water which is passed through a cooling coil 6, and then in heat exchange with a relatively cold liquid Vsuch Aas cold dewaxed oil which is passed through a heat exchange coil 8. The diluted oil stock introduced into the tower i may contain about 50% of liquid propane, and'may be at an initial temperature of from 125 F. to about 145 F. or at the temperature of the solution leavingthe mixer 2 in which the oil stock was brought into'solution with liquid propane. In some'cases particularly where the temperature of the oil or propane is too low, Vit is necessary to heat the oil or propane, or both, to the temperatures referred to, inv order to eliect thorough solution of the oilstock in the propane. The dilution at this point should not be greater than necessary to insure easy handling of the oil stock at temperatures approaching its pour point, orlthe Vpoint at'which Wax Would begin to precipitate out. However, `the oil mixture should contain at least 30% or 40% of Vcipatition in the solution, thereafter passing the :55 DlOpane at this Stage 0f the Operation.

The oil stock mixture passed through the cooling tower 4 is cooled to a temperature just above that at which wax precipitation would take place, and then conducted through a valved line I@ into a compartmented chilling chamber I2, in which vaporization of propane is prevented and in which the compartments are merely separated by baiiles around which the oil mixture passes. As the oil mixture enters the rst compartment, it is mixed with a proportion of cold liquid propane which is used exclusively as the cooling medium for precipitating the wax. As the oil mixture passes through the compartments of the chilling cha-mber I2 it is cooled to successively lower temperatures at any desired rate by the introduction of increments of extremely cold propane through a plurality of valved injection lines I4. In each compartment the cold propane is injected through an injector type of nozzle which prevent-s shock chilling by creating a flow of the oil mixture past the nozzle and by producing a gentle circulation of the mixture in each compartment. This method vof injection insures thorough mixing of the cold propane and the oil stock mixture without causing any substantial agitation of the mixture which would tend to break up the wax crystals as they form,

`Oil stocks which are more effectively handled by rapid chilling, may be chilled almost instantaneously in a single compartment of the chamber I2 or in a single chilling chamber, by rapidly mixing with the oil stock mixture the required amount of extremely cold liquid propane. The series of compartments in the chilling chamber I2 maybe utilized to eiect gradual chilling of the oilstock and the gradual building up of the wax crystals as the mixture advances through the chamber. The oil stock mixture in the chamber I2 may be cooled to a temperature of 20 to 40 F. or to any other temperature found to be necessary for completely precipitating the wax content desired to be removed from any selected oil'stock under treatment.

The chilled oil mixture containing the precipitated wax in suspension is conducted from the chilling chamber I2 through a valved line I6, Yand forced by means of a pump II, or passed through a valved by-pass line VI3 vand a line I9 into a wax separating apparatus 20 in which the wax is removed-from the diluted oil mixture. The apparatus '20 may 'comprise any suitable wax separating equipment suitable for the particular stock such as 'centrifuged lters, or settling chambers. The separated wax is conducted from the apparatus 20 Vthrough a line 22 into a wax washing unit 24, while the wax-free oil solution is conducted through a line 26 and passed by means of a pump 28 and 'a line 30 throughthe heat exchanger coil 8 mounted in the cooling` tower 4.

While it is not necessary to ymaintain a superatmospheric pressure on a propane oil solution at temperatures below about 40 F. to prevent vaporization of propane, substantial pressures are maintained on the oil mixture in the cooling tower 4, the chilling chamber I2 and the wax separating apparatus 20, in order to prevent any evolution of vapor. The pressure required in the cooling tower 4 and chilling chamber I2 will depend upon the temperature of the mixture as introduced into these chambers Aand must be sufciently high to maintain the propane in liquid phase. Except for natural pressure drop due to flow resistance through these-elements of the apparatus, the same pressure -may be employed,

but a slightly lower pressure may be used in chamber I2. The valve in line I6 may be used to reduce the pressure a substantial degree, but where lter presses are used the pressure for effecting the ltration operation may be derived from the high pressure in the chamber I2 and tower 4 by-passing the pump I1,

The cold liquid propane used in effecting the chilling operation in the chamber I2 may be obtained by the auto-refrigeration of liquid propane initially at atmospheric temperatures. For example, liquid propane at atmospheric temperature is conducted from a propane storage 32, which of course will be maintained under suitable superatmospheric pressure to retain the propane in liquid state, through lines 34 and a series of indirect heat exchange coolers 36 and 38, and through a pressure reducing valve 40, into a propane chilling chamber 42. The expansion of the propane into the chamber 42 vaporizes a portion of the propane and chills the remaining portion; and the temperature to which the remaining liquid is reduced may be controlled by the pressure maintained in the chamber 42. The vapor evolved. upon the p ressure reduction in the .chamber 42 is ,conducted through a valved line 44 and through the series of heat exchange coolers 38 and 36 by means of lines 46 and 48. The vapors evolved in the chamber 42 are naturally much cooler than that of the liquid propane prior to expansion, so that it is an ideal cooling agent for precooling the liquid propane in the coolers 36 and 38. The propane vapor in the line 48 is picked up by a compressor 50 which compresses the propane to a 'high superatmospheric pressure and forces it through a line 52, a condenser 54 and a line 56 into the propane lstorage 32. 4In this operation the pressure in the storage chamber 32 is maintained by the compressor 56. Propane from an outside source may be introduced into the system through a valved line 58 which connects into the line 52. A vacuum of any desired degree may be maintained on the `propane chiller 42 by the suction created by the compressor 50, so that the liquid propane obtained in Chiller 42 may have an extremely low temperature such as for example minus 55 F. to minus 85 F.

:The cold propane distributed through the injection lines i4, is drawn from the Chiller 42 through a line 60, and forced by means of a ypump 62 and a valved line 64 into any or all of the Vlines I4 which may be in use for supplying cold propane to the oil stock mixture passing through the chilling chamber I2. Liquid propane from the chiller 42 may also be utilized in washing the oil from the wax in the washing unit 24 by merely withdrawing cold liquid propane from the line 64 through a valved line 66 which connects into the washing unit 24. The cold propane and .oil washed from the wax in the unit 24 is removed through a valved line 68, while the washed wax is removed 'through a line 16. The cold oil-propane mixture from the line 68 maybe introduced into any orall of the lines I4 and used as a chilling medium. The wax or wax slurry discharged through the line 22 is at a very low temperature and the cold liquid `propane introduced through the line 66 .is also at a very vlow temperature, so that the maintenance oflsubstantial pressures .in the wax .Washing unit 24 is .not necessary.

In .the dewaxing of many petroleum oil stocks, it isprefera'ble to maintain the dilutionof rthe stock as low as reasonably possible until the wax precipitation is' substantially complete, in order to insure the formation of relatively large wax crystals. Some stocks may not require very low temperatures in the chilling chamber l2 in order to precipitate the wax desired to be removed therefrom, but relatively low temperatures are usually necessary in order to prevent any rise in temperature above a certain maximum during the wax separation step. Minimum chilling for precipitation may be effected in the chamber I2 by the addition of extremely cold liquid propane, and the additional chilling necessary may be effected by conducting the oil stock mixture containing the precipitated wax from the line I6 through a connecting valved line 'I2 into a flash chilling chamber M in which the additional chilling is effected by vaporization of a portion of the liquid propane diluent under reduced pressure. In this operation, the vaporized propane is conducted from the flash chiller 14 through a valved line 'I5 into the line Q4, and the chilled wax-stock mixture at the desired low temperature is conducted through a line i8 into the line I6 beyond the valve, and forced by means of pump l1 into the dewaxing apparatus 2D. The temperature to which the oil stock is chilled in the chiller 14 is controlled by the pressure or vacuum maintained in this chamber, by regulating the Valve in line 16.

Where it is necessary to chill the oil stock solution to extremely low temperatures for the p-recipitation of the wax content, a portion of the precipitation may be eiected in the chilling chamber i2 and the remaining portion in the iiash chiller lli in order to avoid excessive dilution of the mixture during the wax precipitating operation. However, it is preferred to effect all of the wax precipitation in the chamber l2 under conditions such that there will be no agitation suicient to break up wax crystals as is usually the case where prop-ane vaporization is relied upon for chilling and precipitating purposes.

While various modifications may be made in the improved process and apparatus, as described above, the primary feature of precipitating the wax by addition of cold diluent has been found to materially increase the wax precipitation for a given chilling temperature and facilitate the separation of the precipitated wax. While liquid propane has been referred to as the diluent and chilling agent in the example, it is to be understood that other similar hydrocarbons or other compounds of low speciiic gravity may be employed, and the hydrocarbons may be saturated or unsaturated hydrocarbons preferably of lower molecular weight than butane.

1t is to be understood that in utilizing the apparatus, all elements, lines and pumps will be insulated where the temperatures therein are below normal.

Having thus described the invention in its preferred form, what is claimed as new is:

1. In the process of dewaxing petroleum lubricating oil stocks in which the oil stock to be dewaxed is diluted with liquid propane in suicient quantity to completely dissolve the oil stock and provide a solution which will be fluid and readily handled at temperatures below the pour point of the oil stock, the improvement which comprises cooling the solution by indirect heat exchange with a cooler low gravity liquid to a temperature just short of that of wax precipitation in the solution, thereafter passing the oil mixture to be dewaxed through a series of relatively large zones in which the mixture is gradually chilled to progressively lower temperatures by mixing therewith precooled liquid propane under conditions adapted to prevent vaporization of any of the propane, introducing the cooled propane into the oil mixture in each zone in a jetting action adapted to cause only mild eddying currents in each of said zones to effect equilibrium between the oil mixture and the introduced cold propane, maintaining a superatmospheric pressure in each zone and preventing substantial agitation therein, introducing a suiicient proportion of cold liquid propane into said zones to completely precipitate the wax content of the oil desired to be removed therefrom by the time the oil has passed through said series of zones, and separating the precipitated wax from the resulting chilled oil mixture to produce a dewaxed petroleum lubricating oil stock.

2. The process of dewaxing petroleum lubricating oil stocks in which the oil stock to be dewaxed is diluted with a liquefied normally gaseous hydrocarbon which is liquid at low dewaxing temperatures, said hydrocarbon being used in sufficient proportion and under conditions such as to completely dissolve the oil stock and provide a solution which will be uid and readily handled at temperatures at and somewhat below the pour point of the stock, thereafter passing the diluted mixture -to be dewaxed through a series of relatively large chilling Zones through which the mixture is passed in series and gradually chilled by mixing therewith in each zone an increment of precooled liquid normally gaseous hydrocarbon, maintaining a substantial body of the mixture being chilled in each zone, introducing the precooled liquid normally gaseous hydrocarbon into the oil mixture in each zone in a jetting action adapted to cause only a gentle local circulation of the mixture therein to eect equilibrium between the oil-mixture and the introduced cold hydrocarbon, maintaining a superatmospheric pressure in each Zone sufficient to prevent vaporization of any of said hydrocarbon and preventing substantial agitation in said zones, introducing a suii'icient proportion of the cold normally gaseous hydrocarbon into said series of Zones to completely precipitate the Wax content of the oil desired to be removed therefrom by the time the oil mixture has passed through said zones, and separating the precipitated wax from the resulting chilled oil mixture to produce a dewaxed petroleum lubricating oil stock.

3. The process of dewaxing petroleum lubricating oil stocks in which the oil stock to be dewaxed is diluted with a liquid normally gaseous hydrocarbon which is liquid at wax separation temperatures, diluting the oil stock with a sufcient proportion of said hydrocarbon and under such conditions as to completely dissolve the oil stock and provide a solution which will be fluid and readily handled at temperatures as low as the pour point of the stock, thereafter passing the solution to be dewaxed into one end of an enlarged elongated chamber and then through a series of distinct cooling zones in said chamber, maintaining a substantial body of the mixture in each zone, gradually chilling the mixture as it passed through said series of zones in said chamber by mixing with the body of material in each zone an increment of extremely cold liquid normally gaseous hydrocarbon thereby gradually building up wax crystals in the mixture as it advances through said chamber, introducing the cold hydrocarbon into the b-ody of oil mixture in each zone in a manner adapted to cause only a gentle local circulation of the mixture therein to eiiect. temperature equilibrium between the oil mixture and the introduced cold hydrocarbon, maintaining a superatmospheric pressure in said chamber suicient to prevent vaporization of any of said hydrocarbon and preventing substantial agitation of the mixture in said chamber, said hydrocarbon introduced into said zones being of sufciently low temperature and of sufficient proportion to completely crystallize and precipitate the Wax content of the oil desired to be removed therefrom during the passage: of the oil through said chamber, discharging the chilled mixture from said chamber and separating the precipitated wax therefrom to produce a dewaxed petroleum lubricating oil stock.

4. The process of dewaxing petroleum lubricating oil stocks as defined by claim 3 in which said chamber is a vertical chamber and the solution to be dewaxed is introduced into the upper part thereof, and in which said zones are dened by vertically spaced baies in said chamber around which the oil mixture ows toward the bottom of the chamber.

DAVID G. BRANDT.

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