US2153895A - Solvent and process for dewaxing mineral oils - Google Patents

Description

UNETED STATES GFFIQE SOLVENT AND PROCESS FOR DEWAXING MINERAL OILS Donald S. McKittrick, Oakland, and Hilary J. Henrlques, Berkeley, Calif., assignors to Shell Development Company, San Francisco, Calif.,

I a corporation of Delaware No Drawing. Application June 20, 1936, Serial No. 86,356

10 Claims. (Cl. 196-18) This invention relates to a process for separatsolvent is used to dissolve the desired oil .which, ing various waxy substances from mineral oil in the case of extraction processes, it is desired containing the same. More particularly, it perto recover in the liquid phase insoluble in the tains to an improved diluent for decreasing the solvent. q

' viscosity of the oil and the solubility of the wax, Certain of such selective solvents may,'however, while improving the solubility of the oil in the be employed for dewaxing purposes by adding liquid phaseproduced when solid wax is separated thereto a quantity of a secondary solvent, somefrom oil, whereby the wax and the oil are sepatimes referred to as a solubility enhancing solrated more readily than has been possible heretovent. The addition of the secondary solvent iml0 fore. proves the miscibility of oil and selective solvent,

Mineral oils naturally contain varying amounts but inmost cases destroys the selectivity of the of waxy hydrocarbons, often designated as parafresulting mixture between wax and oil, so that fin wax or petrolatum, and hereinafter genericalthe resulting mixture of primary selective solly designated as waxes, which at normal or elevent and solubility enhancing solvent is to a great vated temperatures are dissolved in the liquid extent equivalent to a non-selective diluent, and 15 hydrocarbons, hereinafter referred to as oil. but functions only to reduce the viscosity of the which solidify or become extremely viscous at chilled oil. lower temperatures. If these oils are to be used We have discovered that mixtures of a propyl as lubricants at these reduced temperatures the alcohol with dihalogenated aliphatic hydrocarsolidified or highly viscous wax causes the oil to bons having between one and four carbon atoms, 20

resist flow. When the wax content is too low to particularly 1,2 dichloro ethane (ethylene dichloimpede flow, it may, nevertheless, cause cloudiride) and 1,2,dichlor propane (propylene dichlo ness in the oil. It becomes necessary, therefore, ride), are particularly suitable for use as dewaxto effect the removal of all or some of the wax. ing solvents. Other halogenated hydrocarbons,

- The first step in such a process is the creation such as 1,2, dichloro ethene (dichlor ethylene), 25

of conditions under which the wax has a miniand 1,1, dibromo ethane (ethylidine bromide) may mum solubility in the phase containing the oil. also be employed, but we prefer the above named This wax probably contains aliphatic hydrocar chlorinated compounds. Isopropyl alcohol is subons and/or naphthenic and other hydrocarbons; perior to normal propyl alcohol, and shows a it belongs to the group of components of pehigh selectivity between wax and oil when diluted 30 troleum which are the least soluble in selective with these dihalogenated hydrocarbons and solvents. The removal of wax may be accommakes it possible to obtain unusually high yields plished by any of several methods. of dewaxed oil of moderately low pour points.

In accordance with one of these methods, the Suitable solvent mixture may, for example,

oil is chilled to a temperature substantially below consist of from 15 to 90% isopropyl alcohol and 35 that at which the wax solidifies and the wax is from 10 to 85% of a di-halogenated hydrocarbon, separated from the liquid oil by mechanical such as 1,2, dichloro ethane. means. As an improvement in such a process, it The method which is subject to our invention is common to add a non-selectivediluent, such as relies primarily on the peculiar properties of the 0 liquefied, normally gaseous hydrocarbons, light above mixtures of solvents, which were found to naphthas, etc., to the oil to reduce its viscosity create a condition in which there is a large difand facilitate the mechanical separation. ference between the solubility of the solid or waxy In another method, a selective solvent medium components of the initial oil and the solubility is added to the initial oil, and the waxfree comof the liquid or oil components thereof. In one ponents of the initial oil are dissolved there n. aspect, our method comprises the steps of mix- 45 This method necessitates the use of a solvent ing a waxy oil, such as lubricating oil, fuel oil,

- medium which is sufliciently selective to dissolve etc., which may be either a residual or a distillate the oil at a suitable dewa-xing temperature withoil, with our selective solvent and solubility enout dissolving the wax. The ordinary selective hancing solvent, and chilling the resulting m xsolvents which are employed for example in liqture to a dewaxing temperature to solidify the 50 uid-liquid solvent extraction processes to dissolve wax, which may then be separated from the liqcertain types of oils which arelless paraflinic in uid portion of the system by any mechanical nature from those which'are more parafiinic in means, such as filtration, cold settling, or cennature are not in general suitable for use as trifuging, depending upon the character of the solvent media, because in dewaxing processes the wax. Our process is, however, particularly suitperature may, for example, be slightly below the melting point of the lowest melting wax which it is desired to remove. The pour point of the dewaxed oil may in certain cases be slightly higher than the dewaxing temperature, but by adiusting the proportions of selective solvent and solubility enhancing solvent, as described below, pour points which are as much as 20 F. below the dewaxing temperature may be obtained.

It is desirable, although not essential. to produce a homogeneous wax-oil-solvent system prior to the precipitation step. To achieve this, the

temperature of the system may initially be raised to somewhat above the dewaxing temperature. We have, moreover, found that excellent filtration rates are obtained by heating the oil-solvent mixture to a temperature within the-range from 65 C. to 100 C. or higher, and then cooling it slowly to the dewaxing temperature. When the mixture is initially warmed, it is necessary to cool the oil-solvent mixture, and this may be eifected by indirect cooling or self-refrigeration. Where very low pour points are not essential, our solvent mixtures may often be mixed with the oil at ordinary temperatures of the order of 18 (3., thereby obviating the necessity of chilling the oil.

The chilling, when used, is not only for the purpose of merely freezing out the wax, as in the processes now practiced, but also for the purpose of increasing the selectivity of the solvent mixture which may have been added to the oil at a temperature at which it is less selective. This feature distinguishes our process from those in which the wax is caused to separate by mere chilling, and a non-selective solvent or diluent is added to reduce the viscosity oi the oil and to expedite the separation of the solidified wax. In this connection it should be noted that the above selective solvents become more selective at lower temperatures.

Under certain conditions the wax which is precipitated according to the procedure outlined above, either with or without chilling during precipitation, may be so soft as to make its separation diflicult. It is in these cases advantageous to chill the precipitated wax during or just prior to its final removal to harden it. Subsequently the solvent mixture is removed from the separated liquid by any means, such as distillation. I

To be fllterable or otherwise separable from the oil-solvent phase, the wax particles must be of suitable form, size and strength and/or hardness. We have found that if in precipitating the wax a very small amount of liquid oil is separated out from the .oil with the wax crystals, clusters of crystals are formed and theseparation of wax from the solution of oil and solvent is facilitated. The amount of oil necessary for this purpose depends upon the size of the initial wax crystals, which, in turn, depends among other things, upon the nature of the wax and the rate of chilling. In processes in which the crystals are extremely small and the wax content of the initial oil is high, as much as 1.0% of the main body of the oil may be desirable. In other cases, as when the crystals are larger, and/or when less wax is present, lesser amounts of oil may be desirable, and it is frequently practical to permit substantially no oil to be separated out with the wax. Since the separation of an excess quantity of oil reduces the yield of dewaxed oil, it is desirable to control the amount of the oil which is separated with the wax, as described below.

2,158,895 able for filtration methods. The dewaxlng tem- A convenient method of controlling this amount of oil is to regulate theconcentration of the halogenated hydrocarbon gas in the solvent mixture. A The necessary dilution ratio, 1. e., the ratio of the combined solvent mixture to the initial oil, is generally determined by the viscosity of the oil and the solvent mixture and by the selectivity of the solvent mixture at the dewaxing temperature, and is made as low as possible with a view of conserving the solvent. When using the new solvent mixtures of our invention, the

dilution ratio may be much lower than the ratio employed with the known solvent mixtures. For

example, we have obtained excellent results when using a dilution ratio of 2:1,hnd even lower ratios, such as 1:1 may be employed, although we prefer to employ ratios of about 4:1. At very lowtemperatures. ratios as high as 8:1 maybe desirable.

For a given dilution ratio, the greater the concentration of the propyl alcohol, in the dewaxing mixture, the more complete will be the precipitation of wax, and extremely low pour points may often be obtained. However, since the alcohol has a relatively low solvent power for the oil, the oilsolvent system will in this case form two liquid phases, in addition to the solid wax phase, and the yield of the dewaxed oil will be extremely low. When a high concentration of halogenated hydrocarbons is employed, the oil-solvent system may exist as a homogeneous liquid phase, and

both pour points and yields of dewaxed oil will be increased, although the usev of'an excess 'of halogenated hydrocarbons may again cause the formation of two liquid phases. There is, therefore, at least one, and sometimes two compositions of the combined solvent mixture forming a transition point between the liquid-solid and liquid-liquid-solid phase systems. The transition composition will, of course, depend upon several factors such as the dilution ratio, the dewaxing temperature, the specific solvents employed, and the character of the oil, but may be easily determined empirically for any given situation.

We have found that when the volume concentration of the halogenated hydrocarbons in the mixed dewaxing solvent is lower than about 10% below the concentration corresponding to the' quantities of solubility enhancing agent results in greater yields, but the pour points of the dewaxed oil will often be undesirably high. A refer-1 ence to a transition point is, in the present paragraph and in the claims, intended to refer to that transition composition which contains the higher concentration of alcohol, in situations in which the systemhas several transition points.

Such solven't mixtures as are used in accordance with the present invention may, for example, at temperatures of about 0 F. to 10 F., have complete or substantially complete solubility for oil having specific gravities (115 between 0.90 and 0.94 and refractive indices 1m between 1.50 and 1.52, and substantially no solvent power for wax which is solid at the said temperatures, i. e., not more than a few tenths of one per cent of wax arsasss I will be dissolved at these temperatures: such an oil may, for example, have a viscosity 01 between 50 and 55 sec. Say. Univ. at 210 F. Mixtures of solvents having this characteristic may, of course, be used also with oils of different refractive indices, specific gravities or viscosities.

The dewaxing process may'also be carried out in several steps, the c mposition of the solvent mixture being regulated, and the process being carried out as described in the U. 8. Patent No.

' The yields of dewaxed oil, of a given pour point and the filtration rates can often be further increased by adding a smallamount, generally be-' tween 0.2% and 1% of a pour point reducing substance, such as tetrastearyl glucose, pentaerithritetetrastearate distearyl'picene, cracked resitures. For comparison, the same oil was dewaxed' withoutmixtures and with acetone-benzol mixtures, the latter mixture being commonly regarded as standard for dewaxlng mineral oils.

Example-Several samples of a Venture distillate having apour point of 95 F. were each diluted with tour volumes of various solvent mix-- tures, heated to about 100 0., gradually cooled,

and filtered at between and 19O. The

compositions of the solvent s and the yieids'are given as percent by volume. The iresuits are shown in the table:

Dliuent Yisldciderims E3? oil {WT-L 1% new some risoho etheno P's: are 9F, L.........- at so as, Y -v.s w 40 -1.s s...-........ so a -m.s s...........- es lo 14 -m.s s. so s m -15 Acetone was P v V as so 91 1s is as co m so so so s so 40 av 10 so as o u. 7s 25 as Y +5 Oontained 10 percent toluene.

It be noted that our dewamng mixtures may he used over a wide range of cotlons, and that throughout the range the pour points of the dewaxed oil are materially lower than the mu! points obtained with acetone-benzol mixtures. I'he lowest pour point obtainable with the latter dew mixture when dewaxing at -20 C. was 0 F.

with a dilution ration of 1:4 at -20 0., the iollo compositions of solvent dewaxing mixtures corresponded to the transition point between one and two liquid phase systems: 83% isopropyl alcohol, 17% 1, 2, dichloro ethane: 55% acetone; 45% (A second transition point precpiating occurs at the composition 24% isopr op yl alcohol, 76% 1, 2, dichloro ethane, two liquid phases being towed when less than 24% isopropyl alcohol is in the solvent mixture, but, as is apparent from the above figures, the best results are obtained when operating in the vicinity of the transition point corresponding to an 83% alcohol concentration.)

The above example is presented only for the purpose of illustrating the efliciency of our new solvents, and to show the manner in which the pour point and yield may be varied by varying the relative concentrations of alcohol and halogenated hydrocarbon. Our invention is in no way limited to the specific mode of operation described in this example, since it ispossible to employ other specific halogenated hydrocarbons, or other oil-solvent ratios.

We claim as our invention: 1'. A selective solvent dewaxing mixture for petroleum oils, consisting of between 15 and 90% isopropyl alcohol and between 10 and 85% of a dichlorinated aliphatic hydrocarbon having two carbon atoms.

,2. Thedewaxing mixture according to claim 1 in which the chlorinated hydrocarbon is 1, 2, dichloro ethane.

3. 'the dew mixture according to claim 1 in which the chlorinated hydrocarbon is 1, 2,;

dichloro ethene. 4. In the process of manufacturing low pour pointlubricating oil from wax-bearing mineral solid wax from the oil, said solvent mixture comprising a propyl alcohol (and a (ii-halogenated aliphatic hydrocarbon having two carbon atoms,

-.. sumciently low to solidify the I e process according to claim 4 in which e process according to claim 4 in which 8. the alcohol is isoprcp'yl alcohol.

according to claim 4 in which ted from the oil-solvent mixfiltration.

of dewa mineral oils which a said oil with a propyl alcohol, solid wax from the resulting 011- e in the presence of a di-halogeni. e process n; 1!, is 81:." ture by 8. The process cipitated wax from the oil-solvent mixture.

equal volume of a solvent mixture containing between 15 and isopropyl alcohol and g tween 10 and 85% of 1, 2, dichloro ethane, z the resulting oil-solvent. mixture to precipitate the wax, and removing the precipitated wax from the oil-solvent mixture by mechanical means.

DONALD S.

ogenated hydrocarbon is 1, 2, dichloro ated aliphatic hydrocarbon having-twdcarbon