US2066165A - Process of purifying and dewaxing mineral oils - Google Patents

Description

Dec. 29, 1936..

PRocEss .oF PURIFYING AND DEWAXING MINERAL oILs V Filed June 27, 1935 Apo/r/a/VAL Pl/MPJ G. J. sTREzYNsKl 26,066,165

Patented Dec. 29, 1936 UNITED STATES PROCESS OF PURIFYING AND DEWAXING MINERAL OILS George J. Strezynski, Poughkeepsie, N. Y., as-

signor to The De Laval Separator Company, New York, N. Y., a corporation of New Jersey Application June 27, 1935, Serial No. 28,656

2 Claims.

In an application led by me June 27, 1935, Serial No. 28,655, I describe a process for purifying and dewaxing mineral oil containing both amorphous and crystalline waxes and producing therefrom a dewaxed lubricating oil having a high pour test. In this process, which is preferably applied to crude oil from which no or feW light fractions have been distilled, but which is also applicable to any heavy fraction of the crude, such as the long residuum containing all or most of the lubricating fractions, the crude is blended with any suitable light diluent, such as naphtha or other light hydrocarbon, and the blend is subjected to chilling, preferably shock chilling with pronounced agitation, to reduce its temperature to approximately 35 F. below the desired pour point of the finished oil. The diluent is added in such proportion that the treated blend, after addition of acid, will, when centrifuged with a force 6000 times gravity, gives a heavy layer of waxy acid sludge not less than 15% or more than 30% of the mass of the chilled and treated blend. After the chilling step, wherein all the wax, amorphous and crystalline, is precipitated (that is, all the wax is precipitated down to the temperature of the pour point desired), a continuous stream of acid is added to the continuous stream of the mixture of oil and wax owing from the chiller and the two streams are subjected to a mixing action, the acid combining with undesirable compounds (impurities) in the oil and wax to form a waxy acid sludge. The treated mixture then flows continuously to a centrifuge wherein a purified completely dewaxed oil is separated from the sludge.

In the process set forth in said application, the oil is chilled, for example, to a temperature of approximately 16 F. if it is desired to produce a finished lubricating oil having a pour point of 20 F., or to approximately 35 F. if the nished lubricating oil is desired to have a pour point of F. In the specific example of the process therein given, there is treated a typical east Texas paraffin base (more accurately mixed base) crude containing gasoline about 29%, kerosene about 14%, gas oil about 21%, wax and asphaltic material about 12% (wax about 8%) and lubricating oil constituents 1'7-18%, which, when separated, give a lubricating oil having a pour point of 20 F., viscosity index 86 and viscosity 67.

The present process is not concerned with the centrifugal separating step of the process whereby there is secured a maximum yield of the quality of oil desired, but relates to the acid. addition step of the process and particularly to the temperature of the acid added in its relation to the temperature to which the oil ischilled. The temperature of chilling, dependent Aon the desired pour point of the finished oil, may vary from about 0 F. to 50 F. Since the freezing point of sulfuric acid of the high concentrations that give the best results may vary from about 8 F.

to not much above 30 F. (usually in the upper mixture of cold oil and wax. 'Ihe reaction con- Y sequently proceeds so slowly that eventually a certain amount of acid freezes into hard crystals and causes clogging and overflow. The use of fuming acid has been suggested, but the freezing point of fuming acid is higher than that of 98% acid.

I have found, however, that if the oil is chilled to a temperature more than 30% below that of the desired pour point of the finished oil, that is, below what has been deemed necessary, and if the added acid is at a substantially higher temperature than that hitherto employed, the chemical reaction is so far expedited and the heat generation so far accelerated that the reaction will be completed before the acid is sufciently reduced in temperature to freeze, thereby eliminating the clogging elfect of acid crystals. While the temperature of the oil and Wax mixture is thereby raised more than it otherwise would be, it Will not be raised above the permissible maximum if, in the initial chilling, it is chilled to only a very few degrees below the temperature required if the acid were added while comparatively cold. To prevent freezing, the temperature of the acid sho-uld be above 110 F. More desirably it should be added at a temperature within about F. of 150 F. It will be understood that the hotter the acid, the greater must be the degree of refrigeration. It is permissive to add the acid at a temperature substantially higher than 150 F., but it is uneconomical to do do so, since it involves the expense of refrigeration to a lower temperature with no corresponding gain.

The amount of acid added may be varied Within limits at the discretion of the operator. The

desirable amount will vary with the desired pour test of the finished oil. Thus, in producing 20 F. pour test oil, a preferable addition of acid is about 12 to 14 pounds per barrel of oil, or about 21/2%; While in producing 0 F. pour test oil, a preferable addition of acid is about 24 to 28 pounds, or about 5%. The amount of acid in these examples is about 20% moreL than is used in conventional methods and is distinctly above the amount required to produce the necessary reaction. The addition of acid in such substan- 5 tial excess is of advantage invseveral respects. It insures a sufficient gravity differential between the oil and sludge. It speeds the reaction. It results in the production of a lubricat-` ing oil having a higher viscosity index number than is obtainable by the addition of a smaller quantity. It decreases the temperature spread between the operation temperature and the pour point of the finished oil. I Referringto the drawing, which is a diagram or flow sheet of an apparatus for practicing the above described process: Separate streams of the oil tor be dewaxed and purifiedV (which may be crude oilV of the character hereinbefore described) Yand a diluent, such as naphtha, are delivered'to a blending tank I0, whence the oil is pumped through a chiller II and therein sub-cooled to a temperature. of about l35 `F. below the desired pour test of the finished oil. The chilling operation will precipitate all the wax which precipipitates at the temperature of chilling. By means of a pump I2 the mixture of oil and wax is conveyed to a mixer I4, which may be a centrifugal pump. YInto the oil line leading to the mixer I4 is conveyed, through a pump I3, a stream of concentrated sulfuric acid (preferably about 98% H2804) at a temperature of about 150 F. The mixing may be completed in the pump I4, or it may berun through an additional mixer I5, which maybe a series of centrifugal pumps. The acid reacts with the oil and forms a mixture of waxy acid sludge and oil, the latter usually containing'wax in ne suspension but otherwise purified. The mixture is then conveyed to a centrifuge I6, which is specially designed to act upon the mixture so as to enable the recovery of completely dewaxed oil. Suitable centrifuges are shown in patents granted to me December 3, 1935, No. 2,022,814, No. 2,022,815, No. 2,022,816, and No. 2,022,817.

It will be understood that I do not herein claim, separate and apart from the above described process, certain novel features thereof, such as the regulation of the percentage of the diluent, which form the subject matter of an application filed by Strezynski and Pfau July 25,1935, Serial No. 33,073. n n

What I claim and desire to protect by Letters Patent is:

1. In the process of purifying and dewaxing mineral oil to obtain therefrom high test pour oil, which comprises chilling the oil to a temperature below 0 F. to precipitate the wax, mixing concentrated sulfuric acid with the mixture of oil and precipitated wax and centrifuging the resultant mixture of waxy acid sludge and purified dewaxed oil and thereby effecting their separation; the improvement which comprises,in the chilling operation, sub-cooling the oil below the temperature that would be required, if cold acid were added, to subsequently produce purified dewaxed oil of the desired pour point, and, in the acid treating operation, adding the acid While at a temperature above F. to thereby, by accelerating the generation of heat by the reaction, prevent freezing of the acid before completion of the raction.

2. In the process of purifying and dewaxing mineral oil to obtain therefrom high testV pour oil, whichfcomprises chilling the oil to a temperature below 0 F. to precipitate the wax, mixing concentrated sulfuric acid with the mixture of oil and precipitated wax and centrifuging the resultant mixture of waxy acid sludge and purified dewaxed oil and thereby effecting their separation; the 'improvement which comprises, in the chilling operation, sub-cooling the oil below the temperature that would be required, if cold acid were added, to subsequently produce purified dewaxed oil of the desired pour point, and, in the acid treating operation, adding the acid while at a temperature Within 10 F. of 150 F. to thereby speed the reaction and prevent freezing of the acid before the completion of the reaction.

' GEORGE J. STREZYNSKI.

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