US2034175A - Settling aid - Google Patents

Description

March 3 G. F. CHASE El AL SETTLING AID Filed Dec. 29, 1952 BQN EN Q QQ q V m Jrwentorazqj zfifi-ndarsow ATTORNEY Patented Mar. 17, 1936 I 2,034,175

UNITED STATES PATENT OFFICE SETTLING AID George F. Chase, Hammond, Ind., and John A. Anderson, Chicago, Ill., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana Application December 29, 1932, Serial No. 649,420 6 Claims. (Cl. 196-19) This invention relates to the separation of wax wax in distillate stocks can be materially altered from mineral oil distillate stocks and it pertains by the presence of crystallization regulators or more particularly to a method of congealing wax settling aids, and our invention relates more in a particular manner so that it may be readily particularly to the preparation and use of these separated from the oil by cold settling. particular materials. Their exact chemical or 5;

The modern trend in the manufacture of lubriphysical action cannot be definitely determined, cating oils is to use overhead or distillate stocks, but their effect is to cause the separation of wax even for the heavy oils, instead of .using residual n a compact form which will readily settle. Mistocks or blends of residual with distillate stocks. e e pic studies show that when these inhibitors These overhead or distillate lubricating stocks are p the a crystallizes in clusters 01 10 contain mixtures of parafiin and petrolatum waxes h p or r nd d particles rather than in which must be removed if the finished lubricant interlocking interlacing e s 0 p a es- .is to have a low pour point The object of our These materials are added before the dewaxlng invention is to provide a simple and economical p, n hey a e removed with the wax so that method and means for separating such wax from the finished oil is not contaminated and so that distillate lubricating stocks. no expensive treatments are required for remov- Heretofore these lubricating stocks have been ing m f om the dewaxed oil. Their use in diluted t naphtha, or other lighi; diluehts t cold settling offers the further advantages that diluted mixture has been chilled to crystallize the superna ent O l is characte ized by a ve y out the wax, and the wax has been separated 10W D point, that the Settling rate is much from t diluted n by means of filtration th higher than can otherwise be obtained, and that filter aids or special wax antisolvents, by centrimarkedly increased y e ds are efiected. fuging, or by cold settling in the presence of The broad idea of using settling aids in naphadded petrolatum, etc. This latter method is the the solutions is t new,many attempts have simplest and most desirable if it can be used, but e made mechanically accelerate the Selimany waxes will not settle at all and many other tllng of Wax c ystals or to change the crystal waxes will not settle sufllciently to make the procformation y p y cal or chemical means. The ess commercially feasible. If the chilled, diluted, only P i methods Whlch v Shown y Pr mwaxy oil is settled in a tank 100 units deep, the ise are the use Of pe atum and the use of wax crystals may only settle a, fewu ic from asphaltic bodies or residues. Our invention is the top; if they settle 10 units it is saidthat the n improvement over these substances. our oil is settled t 90% b tt Unless th 11 is settling aids are efiective with oils in which both settled to very low bottoms, the yield of finished petrolatum and asphaltic materials or residues oil will be so small that the process is useless. are inefieetive, and 0111 Settling a ds mpart no The object of our invention is to provide a method contamination and add no wax to the i ic so and means whereby these distillate stocks may is being Wa dbe settled to very low bottoms. In other words, n our p e d odiments our settling aids we want to minimize the amount of oil which is p e a n c tu nts of petroleum resientrained by wax and we want to eiiect a sharp du s which are segregated and removed from separation of wax from oil so that the clear oil the wax o O -S u asphaltie t a W ic will have a low pour point. has heretofore been present in settling aids. The

A further object of our invention is to provide materials a be prepared m petroleum resia process of dewaxing which will require a minidues such as residuum from ma k ver. Wl mum initial plant cost, a minimum amount of Mid-Continent or other crudes. Starting, for refinery space, and a minimum operating ex-' instance, with a 38% reduced Mid-Continent pense. Other objects will be apparent from the crude, we may extract the ineffective and undetollowing detailed description of the invention. sirable components with alight hydrocarbon sol- It is known that wax in residual stocks may vent, such as propane, hexane, petroleum ether be readily settled and that wax in dlstillate stocks or gasoline. The extraction may be made at'orusually contains crystals in the form of plates dinary room temperatures, using about one to or needles which are rather irregular in outline four volumes of light hydrocarbon per volume of and which may interlock or interlace to set up residual stock. When the extraction is made at a. skeleton framework throughout the entire body room temperature it is necessary to'thoroughly of oil, causing the body of oil to solidify. We mix the materials for obtaining the contact me nave discovered that the crystal formation of essary to dissolve the undesirable substances in the solvent. We may dissolve the residual stock in the light gasoline or hexane at high temperatures and then eifect separation at ordinary room temperatures. In any case, the oil soluble fraction is discarded and the precipitate is ready for use as a settling aid without further treatment. The precipitate or insoluble residue may be distilled to remove the light hydrocarbon, but since it is to be used in a propane settling plant, this distillation is usually unnecessary. The settling aid so prepared may be added to a lubricating distillate stock in amounts of about .1 to about 2.0%. Usually about 1.0% is sufilcient, especially when the substances have been precipitated from propane.

A preferred embodiment of the application of our invention will be described in connection with the accompanying drawing in which:

Figure 1 is a diagrammatic plan of our cold settling dewaxing system;

Figure 2 is a representation of wax crystallized under usual conditions in the absence of crystallization regulator;

Figure 3 is a representation of wax crystallized in star-shaped aggregates because of added crystallization regulator; and

Figure 4 is a representation of wax crystallized in agglomerated particles by the addition of crystallization regulator.

As a diluent in this process we may use any light liquid which has the necessary low viscosity and low specific gravity at dewaxing temperatures and which at the same time is an antisolvent for wax or which has very low solvent power for wax. We prefer to use commercial propane for this purpose, or mixtures of propane, butane, isobutane, propylene, etc., because when the normally gaseous diluents are used in the liquid form they offer the advantage of extremely low viscosities and densities, and at the same time they may be partially evaporated to effect the necessary refrigeration. We may also use other normally gaseous diluents, such as methyl ether, diethylamine, etc., or we may, under some condi tions, use light gasoline or naphtha. The invention is particularly applicable, however, to the extremely light diluents which will, for simplicity, be referred to as propane.

The invention will be described in connection with the dewaxing of Mid-Continent treated distillate having a viscosity of about 80 seconds Saybolt at 210 F. The invention, however, is equally applicable to other distillate stocks, treated or untreated.

The distillate lubricating oil stock is introduced from a suitable storage tank (not shown) through line In, and it is mixed with about one percent of our settling aid from storage II, the settling aid (which is heated by steam coil Ila to about IUD-150 F. or which has previously been dissolved in some of the 011) being withdrawn through pipe I2 by proportioning pump l3 and mixed with the oil in pipe 14 and mixer l5. Propane from storage tank I6 is admitted through line I1 to mixer 15, a suitable pump being employed, if necessary,the volume of; propane being preferably six or eight times the volume of distillate stock. In mixer I5 the oil is dissolved in the propane and, if desired, a steam coil may be employed to efiect complete solution of the stock therein. The propane solution is then passed through pipe l8 and pipes l9 or 20 to chill chambers 2| or 22. Refrigeration is effected by removing propane vapors through valves 23, pipes 24 and line 25 by means of compressor 26, the

vapors being liquefied in condenser 21 and re-' turned through heat exchanger 28 to diluent storage tank l6. When the pressure in the respective chill chamber is reduced to about zero pounds -gauge and the temperature of the propane mixture is about -40 F., the slurry is passed through pipes 29 or 30 and pipe 3| to continuous settler 32. The temperature may be maintained at low level in the settler by removing propane vapors through pipe 33. Instead of using separate chill chambers we may use a continuous chiller, the slurry being passed through an elongated conduit and vapors being removed at intervals along its length. If additional propane is required in the chillers it may be introduced through pipe 34.

The rapidity with which the wax crystals settle out in settler 32 will depend to a large extent upon the nature of the waxy oil, the nature of the diluent and the amount and quality of the settling aid. If the Mid-Continent stock above described is' chilled in the absence of a settling aid the wax will crystallize in the form of needles or plates 35 as shown in Figure 2. By using effective settling aids, the wax assumes the form of star-shaped aggregates 36 or rounded particles 31 (see Figure 2) which settle rapidly and to very low bottoms, and which give a dense wax cake. When about 1% or 2% of a propane extract of an asphaltic residue is added to the oil there is no improvement in its settling properties.

However, when about three-tenths percent of the propane insoluble material from 38% reduced Mid-Continent crude is added to the oil, it settles to very low bottoms, andwhen one percent of the same material is used instead of three-tenths percent, we obtain a still denser wax cake and a still larger yield of wax-free oil.

The clear oil is decanted from the settling tank through pipe 38, and wax slurry is continuously removed at the bottom through wax screw 39 to suitable diluent recovery means. The wax may be washed several times with propane or reprecipitated (repulped), such expedients being. familiar to those skilled in the art.

The cold wax-free diluted oil may be collected in a suitable sump or receiver 39 and then passed by means of pump 40 through pipe 4| to exchanger 28 wherein it absorbs the heat from liquefied propane. The warm mixture is then passed by pipe 48 to stripping still 43 equipped with steam heater coil 44, the finished oil being withdrawn through pipe 45 and propane being rilatumed by pipe 46 and condenser 21 to storage An important feature of our invention is the use of only that portion of the residual stock as a settling aid which is precipitated from propane or other light hydrocarbon diluent. We may use butane, pentane or hexane, etc. for precipitating the desirable substances from the residual stock, but as the viscosity or molecular weight of the precipitating agent increases, its solubility for the effective settling aid materials also increases and we therefore prefer to precipitate our active substances by means of extremely non-viscous or low molecular weight hydocarbons. By thus segregating the active ingredients we not onlymake these ingredients much more effective as crystallization inhibitors, but we also remove from them deleterious substances which would otherwise contaminate the finished oil and which would require expensive treating processes for removal therefrom. As a matter of fact, we have found that the color of our dewaxed oil is not perceptibly worse than that of the original waxbearing stock which shows that whatever coloring matter may be present in our settling aid is carried down with the wax.

In some cases it may be undesirable to have the wax contaminated with the fractions of pe-- troleum residues hereinabove described. In such cases we may first extract the residuum with hexane or light naphtha, which dissolves large amounts of the inhibitor or settling aid present in the residuum. The hexane or light naphtha extract, after removal of the block residue, is then precipitated with propane as hereinabove described, and the precipitate is used as a settling aid in proportions and in the manner hereinabove described. This fraction of the petroleum residuum which is soluble in hexane but insoluble in propane will be precipitated with the wax when oil is settled from a propane solution. We may also obtain a similar material by dissolving the residuum in propane at an elevated temperature, e. g., F., and separately collecting the precipitate fraction obtained on successive cooli We do not limit ourselves to a fraction which is soluble in hexane and insoluble in propane, but we contemplate in any case the use of that particular fraction which is found by simple tests to be the most efiective. For instance, we may extract a residue with naphtha, distil the naphtha from the extract, and then fractionate the extract by the selective solvent action of hexane, pentane, butane, propane, etc. In this way the crystallization regulators or settling aids may be concentrated to produce powerful material containing a amount of undesirable color bodies, carbonaceous materials or other impurities.

Since the crystallization regulator is thrown down with the wax, it may be recovered therefrom for reuse either by distillation (the crystallization regulator remaining in the residue) or by reprecipitation from propane or other suitable diluent at a sufiiciently high temperature to maintain the waxin solution.

We have found on highly paramnic oils or oils which have been selectively extracted with solvents such as dichlor 'ethyl ether, chlor aniline, nitfif'obenzene, S02, etc., it is more diificult to obtain low cold tests than on oils which contain naphthenic constituents. Our invention is therefore particularly applicable to the dewaxing of highly. paraffinic oils or oils from which naphthenic constituents have been removed by solvent extraction.

The propane or other purifying agent used in the precipitation of the settling aid from the residuum may be at a higher temperature in'this precipitation step than the temperature which is to be used in the dewaxing step. By segregating or purifying the settling aid at higher temperatures the product is less soluble in oil than the product which is removed at lower temperatures.

If the active precipitated filter aids are dimcult to separate from the propane or other light hydrocarbon precipitating agent, we have found that a desirable way of recovering them is by percolation through a bed of clay. The clay will absorb the desired substances which are efiective as settling aids, and these substances may be recovered from the clay by extraction with chloroform, acetone, benzol-alcohol, or other suitable solvent. Other modifications of our invention will be apparent to those skilled in the art.

We have also found that our crystallization regulators are a definite aid in the filtration of wax from oil. They apparently cause the separation of the wax crystals in a. more compact form which facilitates their removal by filtration, resulting in higher filter rates, larger yields of ofl, and denser wax cakes.

While we have disclosed a preferred embodiment of our invention, it should be understood thatwe do not limit ourselves to any of the details hereinabove set forth except as defined by the following claims which should be construed as broadly as the prior art will permit.-

We claim:

1. The method of dewaxing a wax-containing petroleum distillate stock which comprises adding to said stock a small amount of a crystallization regulator derived from a mineral oil residuum by selective precipitation from a 2 to 4 carbon atom hydrocarbon solvent and extraction with naphtha, diluting saidoil to reduce its viscosity, chilling said diluted oil to a low temperature for congealing the wax, and separating said wax from said 011. f

2. The method of claim 1 wherein the separation of wax from oil is efiected by cold settling.

3. The method of claim 1 wherein the separation of wax from oil is effected by filtration.

4. The method of claim 1 wherein the crystallization regulator is recovered from the wax for reuse.

5. The method of regulating the crystallization of wax from oil in the form of star-shaped aggregates or rounded particles instead of interlacing needles or plates, which comprises the step of adding to the mixture of wax and oil a sniall amount of a fraction of a-petroleum residuum which is insoluble in ethane but soluble in naphtha.

6. The method of dewaxing a wax-containing petroleum distillate stock which comprises addme: to said stock a small amount of a crystallization regulator derived from a mineral oil residuum soluble in light naphtha and insoluble in propane, diluting said oil to reduce its viscosity, chilling said diluted oil to a low temperature for congealing the wax, and separating said wax from said oil.

' GEORGE F. CHASE.

JOHN A. ANDERSON.

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