US2191136A - Solvent and process for dewaxing mineral oils - Google Patents

Description

ravine SGLVENT AND PROCESS FUR. DEWAKING WEB-AL OHS Sijbren 'Iijmstra, Berkeley, and Donald S.

McKittrick, Gakland,

Caliil, assignors to Shell No Drawing.

Application July 3.7, 1934,

Serial No. 735,826

' 7 Claims.

This invention relates to a process for separating from mineral oils various waxy substances occurring therein. More particularly it pertains to a diluent for decreasing the viscosity of the oil and the solubility of the wax, whereby the wax and the oil are separated more readily than has been possible heretofore.

Mineral oils naturally contain varying amounts of waxy paraihns or petrolatum, hereinafter designated as waxes, which at normal temperatures are dissolved in the liquid hydrocarbons, but which solidify at lower temperatures. If these oils are to be used as lubricants at these low temperatures these waxy constituents tend to solidify and may cause the oil to resist fiow. When the wax content is too low to impede the flow it may, nevertheless, cause cloudiness in the oil. It becomes necessary therefore, to efiect the removal of these waxy constituents.

The first step in such a process is the creation of conditions under which the wax has a minimum solubility in the phase containing the re mainder of the oil. This probably contains aliphatic hydrocarbons and belongs to the group '01" components of petroleum which are the least soluble in selective solvents. The removal of wax may be accomplished by any of the following methods.

In accordance with one method, the oil is chilled to a temperature substantially below that at which the wax solidifies and the wax may be removed from the oil by mechanical means. As an improvement in such a process, it is common to add a non-selective diluent, such as liquefied v normally gaseous hydrocarbons, light napthas,

etc., to the oil to reduce its viscosity and facilitate the mechanical separation.

In another method, a selective solvent is used, and the wax-free components of the oil are dissolved therein. This method necessitates the use of a solvent which is sumciently selective to dissolve at a suitable temperature the oily components of the wax containing mixture without sub stantially dissolving the waxy components.

The most selective solvents, however, are not suficiently soluble in even the nonwaxy components for emcient dewaxing. To obviate the resulting dificulties, it was proposed to dilute the oil with a non-selective solvent which would dB- solve the wax as well as the oil. A second solvent, often called an antisolvent, which was a poor solvent for wax, was added to the mixtures of the oil and the first non-selective solvent. This second solvent was not, however, chosen on the basis of its selective properties, but merely to counteract (Cilite-433 the solvent eflfect of the first solvent when the oil was chilled to precipitate the wax. 7

It is an object of our invention to provide a process for the efiicient dewaxing of oil. It is a further ob ect of our invention to provide a sol-. vent mixture which is suitable for this process. Further objects of our invention are; to provide a solvent mixture which will produce an oil which has a pour point which is near to or even substantially below the temperature at which the wax is separated; to provide a solvent mixture which will cause the paraiiln wax to separate in a much purer form and in a form in which it can be more readily separated from the oil, than has been possible with the solvents now known; to provide a solvent mixture which will overcome the disadvantages of solvents heretofore known, and which can be used on all types or mineral oils by a slight variation in the properties of its constitutents. Other objects or our invention Will be apparent to those skilled in the art from a reading of this specification.

The method which is the subject of our invention relies primarily on the peculiar properties oi mixtures of solvents, at least one of which possesses selective properties, to create a medium in which there is a large difference in solubility of the difierent components of oil and especially between the solubility of the solid or waxy com= ponents and the solubility of the liquid or nonwaxy components.

, It is well known that the presence of a selective solvent in a liquid phase containing on components creates a medium in which there is a xiiiierence in the solubility of the various oil components. it has been round, however, that the effect of the selective solvent in creating such a difierence in solubility of the various oil components depends on the concentration of the selective solvent in the liquid phase, sometimes known In dewaxas the solvent rich or extract phase. ing processes this is the phase which contains primarily the non-waxy components. It is apparentthat as the solubility of the wax component in this phase is made smaller the eficiency of the dewaxing process is increased.

Most of the selective solvents are very slightly soluble in theoil or in the non-waxy components of the oil at the low or moderate temperatures of the dewaxing operation and the effect of the selective solvent in creating or enhancing the difierence in solubility between solid and liqud components is limited by its solubility. This limit can be increased by adding a secondary solvent which is a good solvent for both the oil and the selective or primary solvent. 1

We, therefore, select a highly selective solvent as a primary solvent, and add to it (in any manner as by physically mixing together, or adding separately to the oil, etc.,) a secondary solvent, which may be known as a solubility enhancing agent, and which dissolves both the oil and the primary solvent, and use the mixture of the two solvents (in whatever manner produced) as a diluent to dissolve the liquid components of the oil, and to precipitate the Wax. Under certain conditions this mixture has the further effect of reducing the viscosity .of the oil to aid in the separation of the liquid and solid phases.

In our process the components precipitated are primarily waxy components, both light and heavy, having a melting point above the temperature at which the dewaxing operation is cairried out. There is, however, no sharp distinction on the basis of the melting point, and a certain amount of hydrocarbons having melting points below the said operating temperature will be removed with the precipitated hydrocarbons of higher melting points. It is not, therefore, necessary to operate at a temperature which is as low as the lowestmelting fraction of the wax which it is desired to remove. I

In one aspect, this method, therefore, comprises the steps of mixing oil containing wax with a selective solvent mixture, and chilling to a temperature which is below the melting point of the highest melting components of the wax to be removed and separating precipitated wax at this temperature. This will result in the removal or not only those components of wax which are normally solid at the temperature at which separation occurs but also of some of those which have melting points which are below that temperature.

It is desirable, although not essential, to produce a homogeneous oil-solvent system prior to the precipitation step. To achieve this, the temperature of the system will often be initially raised somewhat above the dewaxing temperature. In this event the oil-solvent mixture must be chilled to the temperature necessary to solidify certain portions of the wax, as explained above.

Some of our dewaxing mixtures may, however,

be used at ordinary temperatures, and require no chilling.

The chilling, when used in this process, 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 of the oil and expedite the separation of the solidified wax.

After the oil-solvent system of the proper ternperature has been created, the waxy constituents are separated from the liquid phase by means of any appropriate mechanical means, as filtering, settling or centrifuging. 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 then 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 phases by any means, such as distillation.

In operating according to the method of our invention it becomes possible to precipitate the wax in a form in which it can be removed more readily, particularly by filtration. When oil which does not contain a solvent or diluent is chilled to separate out the wax, the latter often assumes an amorphous form known as petrolatum. Separation by filter pressing is obviously extremely difficult. The same results may be obtained when a diluent is used which exercises no selective solvent action. When, however, the wax is precipitated from an oil in the process of our\invention, the wax will generally separate out in filterable particles.

a To be filterable or otherwise separable from the oil-solvent phase, these particles of wax must be of suitable size and strength and/or hardness. We have found that if in precipitatingthe wax a very small amount of liquid oil is separated out from the oil with the wax crystals, clusters of crystals will be formed and the separation of the wax from the main body of the oil is facilitated. The amount of oil necessary for this purpose depends on the size of the wax crystals. In processes in which the crystals are extremely small and the wax content of the oil is high, as much as 1.0% of the main body of the oil may be desirable. When the crystals are larger in size or smaller in amount, lesser amounts of oil are desirable, and it is frequently practical to permit no oil to be separated out. If more than such a small quantity of oil is lost to the wax, the yield of the wax-free oil will be decreased and the precipitated wax becomes difiicult to separate. It will, therefore, often be desirable to precipitate a small amount of oil with the wax, but it is then necessary to control carefully the amount of oil which is to be carried away with the wax.

A convenient method of controlling this amount of oil is to control the quantity of the solubility enhancing agent in the solvent mixture. The necessary dilution ratio, i. e., ratio of the combined solvent mixture to the oil, is generally determined by the viscosity of the oil and the solvent mixture and by the selectivity of the solvent mixture, and is made as low as possible with a view of conserving the solvent. For this given dilution ratio, the greater the concentration of the selective solvent in the oil, the more complete will be the precipitation of wax. As was pointed out above, since pure selective solvent is not. sufliciently soluble in the oil, a solubility enhancing agent is added to achieve a homogeneous liquid phase. If more of this agent than is required for homogeneity is added,

this condition will still be retained. In this case i the concentration of the selective solvent in the liquid phase for the given dilution ratio is not, however, at its maximum, although the extraction can be conducted under these conditions. It is desirable, for the purpose of increasing the selective solvent concentration, to use only that quantity of solubility enhancing agent as is required to insure the desired degree of solubility.

If the minimum amount of solubility enhancing 4 agent for complete solubility is used, substantially no oil will separate from the oil solvent mixture when the oil-solvent mixture is chilled to precipitate wax. A good yield is produced and, under many conditions, this is the optimum quantity of solubility enhancing agent. But, as was pointed out above, it may often be diiiicult to separate the wax from the oil-solvent phase. Under these conditions it is desirable to separate some oil with the wax. This may be accomplished by using less of the solubility enhancing agent. A very small quantity of oil is then lost, but the separation of the wax is made easier. This condition sometimes represents the optimum amount of solubility enhancing agent. Beyond this point a further reduction in the quantity of the solubility enhancing agent will be undesirable because of decreased yield and increased filtering difficulties.

When using the new solvent mixtures of our invention, the dilution ratio, mentioned above, may be much lower than the dilution ratio used with the known solvent mixtures. For example, excellent results have been obtained when using a dilution ratio of 2: 1, and even lower ratios may at times, be suitable. With the solvents and/or solvent mixtures of the prior art much greater ratios are necessary.

As used in the claims, the term "suiiicient to prevent the separation of free oil, as applied to the quantity of solubility enhancing agent, means the amount necessary to permit no more oil to be carried away with the wax than is necessary to form a readily separable Wax. In situations in which no oil is needed to produce a readily separable wax, all .oil not retained by the solvent is regarded as free oil.

In another aspect, therefore, our invention comprises the steps of mixing oil containing wax with a primary selective solvent and precipitating the wax at a desired temperature in the presence of a controlled quantity of a solubility enhancing agent so as to prevent more than certain small desired amounts of oil from separating from the solvent phase.

Another advantage-of our process and solvent mixtures is that it becomes possible to obtain a pour point which is near to or often, substan tially below the temperature to which the oilsolvent mixture is chilled. This makes it possible to operate at substantially higher temperatures than heretofore. It is to be understood,'however, that our invention is not limited to operating at any particular temperature, inasmuch as the advantages of this process and of our new solvent compositions will be realized although the extraction is practiced according to the number of alternate procedures coming within the scope and spirit of our invention. In all of these, the wax separates as a result of the action of the selective solvent or solvents and not of simple freezing out.

Selective solvent mixtures suitable for a dewaxing process of the type described must'have a sufficiently high solubility for the liquid constituents of the oil at the temperatures at which the wax is separated therefrom to keep substantially all of these liquid constituents in solution. As pointed out above, since selective solvents usually possess either a low solubility for petroleum oils at the low temperatures which obtain during separation, or a low selectivity for liquid oil componcnts at normal room temperatures, it is usually necessary to blend them with a secondary solvent, which may be known as a solubility enhancing agent, and which in combination with the primary solvent produces a solvent mixture of suitable selectivity for oil components at dewaxing temperatures.

Of the many substances which can be used as secondary solvents those should, preferably, be selected which have a low solubility for paraifin wax. While a degree of selectivity of the secondary solvent is not an absolute requirement, it will be found that a greater efficiency often results in cases of using for that purpose a fairly selective solvent. For example, butyl alcohol usually gives better results than hexane or benzol. We have found that there exists two broad groups of substances, the first of which includes substances which are good selective solvents but in which the oil is generally not sufficiently so1-' uble. The second group includes substances which are primarily good solvents for both the primary solvent and for the oilfbut which may possess selective properties of a certain degree.

The first group includes the following substances:

I. Non-hydrocarbcn derivatives of the following cyclic compounds: benzene rings (CsHs), heterocyclic rings (of the type CiHiO, C4H4 S .or C4H4NI-I), pyridine rings (CsHsN) or sixmembered rings with two atoms of N, or O, or N plus 0, or N plus S, each with at least one of the following substituents: OH, =CO, CI-IO, COOH, --R, COOR (where R stands for an alkyl or a'ryl radical), Cl, Br, I, NO2, -NH2, ONO, SH, =CS, CONHz, SCN, CN. Also condensed ring systems containing one or more of the above ring types and certain products of industrial processes having complex compositions.

Eramplea-Benzene nitrile, benzene nitrite,

nitrobenzene, nitrotoluene, aniline, diphenyl amine, phenol, chlorophenol, cresol, cresylic acid, acid oils described hereinbelow, quinoline, pyridine, furfural, thiophene, thiophenol, lutidine, picoline, thionaphthol,

II. Lower aliphatic acids, hydroxy or keto aliphatic acids, anhydrides of aliphatic acids, and sulphur analogues of the above acids, all containing not more than four carbon atoms in the molecule.

ErampZes.--Diacetone alcohol, acetic acid, butyric acid, lactic acid, acetic anhydride, th1oacetic acid,

III. Aliphatic alcohols, aldehydes, ketones, ethers, acids, acid anhydrides, hydroxy or keto acids, and sulfur analogues of the above oxygenated aliphatic compounds, all containing not more than sixteen carbon atoms in the molecule and containing at least one substituent from the group: Cl, --Br, I, CN, SH, CS, CONH2, SCN, N'Ha.

Eramples.-Chlorex (,BB dichlorethyl ether), dichlorbutyl ether, dibromethyl ether, chloracetic acid, ethanol amine, triethanol amine, lactic ac d,

IV. Relatively unreactive liquid inorganic compounds of S, Se, Te, Sn, Sb, as, for example, 502, SnClq,

The acid oil contained in the above list may be prepared as follows: petroleum oil, preferably cracked distillate oil, is treated with a concentrated sulfuric acid, and the sludge is removed from the mixture. The oil is then neutralized with caustic soda and the second sludge, or spent alkali, separated from the oil. Upon acidification of this second sludge ,either with an acid or with the acid sludge, an oil known as acid oil" is produced. This oil apparently contains hydroxy-aromatics and possesses selective solvent action. This property can be modified by the presence of solubility enhancing agents, such as an alcohol, to produce a selective solvent mixture which is useful in our dewaxing process.

The second group, (which contains compounds suitable for use as the secondary solvent) includes:

I. Aliphatic alcohols, aldehydes, acids, others, methyl ethyl or higher symmetrical or mixed ketones, and sulphur analogues of the above oxygenated aliphatic compounds, all containing not more than twelve carbon atoms in the molecule.

Examples-Primary butyl alcohol, secondary butyl alcohol, isopropyl alcohol, propylaldehyde, diethyl acetone, diethyl ether, diethyl thioether.

II. Carbon bisuli-lde, aliphatic amines, esters of lower iatty acids and lower alcohols containing more than four and not more than twelve carbon atoms in the molecule, branched chain and cyclic aliphatic hydrocarbons (containing not more than twelve carbon atoms in the molecule), polycyclic (and particularly bicyciic) aromatic hydrocarbons, such as naphthalene and its homologues, preferably dissolved in benzol or its homologues or equivalents.

Although the solvents of each or the two broad groups set forth possess the properties of their respective group, we have found that certain of these substances possess these properties to an appreciably greater degree, and form distinct subgroups. Furfural, Chlorex, quinoline, nitromethone and nitrobenzene constitute the subgroup of the first group; and the following substances co'nstitute the corresponding subgroup of the second group: butyl, amyl and hexyl alcohols( secondary, tertiary, normal or iso-); ethyl, propyl, isopropyl, butyl, and isobutyl ether carbon disulflde; aliphatic amines; and isopentane.

With regard to the relative eiliciency o! the alcohols, better results are usually obtained with n than th nd b t r r mo dary wi primary et 8 g gure of acetone and benzol.

with tertiary than with secondary alcohols. alcohols of low molecular weight are not ve soluble in mineral oils, so that when operating at low temperatures it is preierable'to use amyl and/or even hexyl or higher alcohols.

Mixtures of two or more diflerent primary and secondary solvents can be used in our solvent mixture. When used in a process in which it is desired or necessary to separate the primary solvent from the solubility enhancing agent, it be comes desirable to choose a pair or substances having substantially diii'erent boiling ranges. This is, however, not necessary in certain other processes in which our solvent mixture can be used.

Pairs of substances which we have found to be especially useful, and which constitute a preten-ed embodiment oi our invention are: (1) Iurfural and secondary butyl alcohol, (2) furfural and trlmethyl carbinol, (3) furfural and methyl normal propyl carbinol, (4) turfural and dimethyl ethyl carbinol, (5) furfural and methyl normal butyl carbinol, (6) turfural and dimethyl normal propyl carbinol, (7) Chlorex and second- My butyl alcohol, (8) Chlorex' and trimethyl carbinol, (9) Chlor'ex'and methyl normal propyl carbinol, (10) Chlorex and dimethyl ethyl carbinol,. (11) Chlorex and methyl normal butyl carbinol, (12) Chlorex and dimethyl normal propyl carblnol, (13) Chlorex and mopentane, (14) nitrobenzene and secondary butyl alcohol, (15) nitrobenzene and methyl normal propyl carbinol, (16) nitromethane and secondary butyl alcohol, (17) nitromethane and methyl normal propyl carbinol, (18) furiural and ethyl ether, (19) furfural and isopropyl ether, (20) furfural and isobutyl ether, (21) Chlorex and ethyl ether, (22) Chlorex and isopropyl ether, (23) Chlorex and isobutyl'ether,

(24) qulnollne and secondary butyl alcohol, (25) quinoline and trlmethyl carblnol, (26) quinoline and methyl normal propyl carbinol, (27) quincline and dimethyl ethyl carbinol.

To illustrate the improved results obtained with our new solvent mixtures, the following examples are set forth:

Table I Diluent Final Exp. 7 83%} poor tration point Select solvent 801. enhancing agent of 011 r. o r. ,1 Furtunlw fin- B-but lalcohol 70 60 9 .do ma 50% 35 so 3 do .do l0 4 Acetone 36%-... Benzol 66% 0 20 These results indicate that our solvent mixture will produce an oil having a pour point which is substantially below the temperature to which the oil-solventmixture is chilled. They also demonstrate the increased efliciency of our solvent mixture as compared with a solvent mix- It is apparent that ur solvent mixture makes it possible to operate at substantially higher temperatures than heretofore if an oil of the same pour point is desired. On the other hand, if the same temperature is used, an oil with a lower pour point is produced.

Exam II To compare the efllciencies of our various new solvent mixtures and the acetone-benzol mixture, propane-deasphaltized Venture, residue having a pour point of 80 F. was diluted with several solvent mixtures, chilled, and filtered. The results are shown in Table II.

Table II Ratio F1118] Exp. 3 l 1 BoLenhancing' of oil EP' pour No. agent todiluint out :011

1 Furluml 26%.. s-gabu tyl alcohol 1:4 32 25 2 Furlural 20%. Mot lfyl normal in 1a propyl carbi- DO]. 71%. 8 Furlurall8%.. s-gityl alcohol 1:2 26 4 Acetone 35%-- 1:611:31 65%-..- 114 4o ll to be dea ened, the yield of oil l The only requirement is that the so enhancing agent be in such a that when the oll-sclvent mixture is recipitate the wax, the oil will remain in the solvent mixture to such a degree oil will be substantially prevented from away with the War. The declaring duct-ed either as a continuous or a It is obvious, also, at the ratio will vary with the solubility of the oil in the particular selective solvent processes involving the use thereof are claimed in c 239212,] applications.

We claim as our invention: 4

l. A selective solvent dewaxing mixture for petroleum oil comprising furfural and a secondary or tertiary alcohol containing more than three and less than seven carbon atoms, said alcohol being present in an amount suficient to prevent the separation of free 011 from an oilsolvent mixture formed by adding an effective quantity of said dewaxing mixture to said petroleum oil when said oil-solvent mixture ischilled to a temperature at which the wax is precipitated. therefrom. 2. a selective solvent dc mixture is petroleum oil comprising iurfurel secondary hutyl alcohol, said alcohol being present. in an amount suhiclent to prevent the separation of free oil from an oil-solvent mixture formed by adding an cfiectlve quantity of sairl de'svaxihg mixture to said petroleum oil W118i" id oil-sol vent mixture is chilled to a tempera r the wax is precipitated therefrom.

3. selective solvent olevvaxing sisting of between 15% and its tween 85% and *lil% secondary or alcohol.

4. A selective solvent ciewaxing sisting of between 29% and. in tween 30% secondary or alcohol.

5. The process of dewaxing min oils which comprise mixing said 5 with furfural and a butyl alcohol of the group: secondary and tertiary butyl alcohol, chilling said mixture to precipitate wax, and removing the precipitated war; from the oil-so1vent mixture.

6. The process of claim 5 wherein the solvents used are taken in such proportions and quantity as to cause the cold test of the dewaxed oil to be not above the temperature at the wax is separated from the oil-solvent mi zture.

7. The process of deivaxing mineral lubricating oils which comprises mixing said oil with at least one part of a solvent mixture consisting of between 15% and 30% furfural and octween 85% and secondary or tertiary loutyl alcohol; chilling the mixture to precipitate wax; and removing the precipitated wax from the oil solvent mixture.

con-

tertiary outyl SIJBREN TIJMS'IRA. DON s. McIC".

meal and he- ."al lubricating