US2478456A

US2478456A - Solvent dewaxing

Info

Publication number: US2478456A
Application number: US654790A
Authority: US
Inventors: Lloyd E Boudreaux; Owen R Mitchell
Original assignee: Socony Vacuum Oil Co Inc
Current assignee: ExxonMobil Oil Corp
Priority date: 1946-03-15
Filing date: 1946-03-15
Publication date: 1949-08-09
Anticipated expiration: 1966-08-09

Description

Patented Aug. 9, 1949 UITED STATS NT FF SOLVENT DEWAXIN-G No Drawing, Application March 15', 1946, Serial No. 654,790

15.4 Claims- 1 This invention relates to air-improvement inv the operation of solvent dewaxingpetroleum hydrocarbons and; more particularly, is directed to preventing the formation andadherence of hard ice on the interior surfaces of chillers conventionally employed insaid operation.

Petroleum fractions of the nature of distill-ates and residues andrnixtures thereof containing waxy materials are. normally treated to remove the wax therefrom byaddi-ng to the waxyoil a diluent material, chilling the mixture to a tern-- perature at which the wax or a substantial por tion thereof is precipitated and thereafter filtering, centrifuging or otherwise physically separating the wax from the oil. Those methods in which the diluent used is one tending to exert a preferential solvent action for oil over waxy material at low temperatures are commonly known assolvent dewaxing methods.

One widely used method of chilling the blend of waxy oil and solvent tothe desired lowtemperature isby passing: the same through a double pipe chiller of the Garbondale type. This ma chineconsists or a number ofpipes in series, each jacketed by an outer pipe of larger diameter. A cooling medium, such as brine-solution or the like, is circulated between the two pipes, thus chill-ingthe surface'of the inner pipe through which the blend of waxy oil and solventis passed. Inside of each of the inner pipes is a screw-like scraper composed of acentral shaft witha helical scraper blade attached thereto. The scraper is revolved: during the chilling operation, the blade thereof touching the: inner surface of the pipe, removing; adhering solid matter therefrom and forcing-conegealed wax along and out of the pipe as a slurry in the diluted oil. I

It has been heretofore noted in solvent dewaxing operations employinga chiller of the type described that a small amount of water COR-F tively high proportion of water dissolved therein; or when the dewaxing solvent or solvent mix:- ture employed has the tendency toidissolve waten. In practice, it is necessary to recover the: solvents employed for further usein: treating: fresh oil wax' mixtures. A customary method or 116v This problem is of particular importance when theoil tobe treated has a. rela;--

tails. in the, chilling oneratiom. iving. rise to-tlie metho however. has: otbeen em lo ed to ny reat extent. due primarily to the expense of the operation; involved. In some ins ance a -rvineaeenthas been used. such as concen r ted odium].carbonatesolution;for dry n thesolv rats ilati m In. practic pro-- cedure has consisted of contacting the solvent containin a small quanti rofwat r wi h. h solution oi drying a ent until. the dr ms. agent is so dilut. that: no; further water.- s. absorbedfrom the solvent. A portion of the di t -solution: is; than discarded: and: fresh concen rated lu ion i added to the r ma nder. to m n ain he bso p ion. capa i y of he dryin agent at the; prope ev l d scard n a o on o he diluted soluti m. not only some. o t e dry ng; a en l stbu an.approo a lo quantity of solvent is lost, s nce such dilu d sol tion sa urated solvent, at the treating, empera re- It is an objectof; the'presentinvention to over-- come. the above: mentioned dif i lt n h chilling; operation of: so t dewaxina y P venting the. f rma ion ot a. hard ad e ent. i e t the. walls oi: blilixfilli l i- A: mo pe i object is. to; prev nt the breakage of ch ller scrape bladesolua to contact. with saidhard ce f rmeg; n: the sur ace of. the ner p pe of double nioezohillers co v 'on llv employed in th -art, for; example. th lla b nda oz chiller. A fur her ob-ieotis oi rovent. he luaa ne of hi e p p s- .S ti1li further bjec s to inhibit th formation Qf=an:ioe :ooatine on hoohiller pip s.- Whiohtends todecrease the ch lling, effect of. the sur oundma cooling; mediulaaot e a a pa ial: n ulator against. I I the use. or a ewaxins solvent in whioh. small. quantiti szotwater ma be tolerated .withoutload- 1m; tozthez hard. ice; formation. here ofore. en ountered in: the 1 chillin op a io Bhese: and; her ob ects: which will; be reads.- iz dzby those: skilled n the an are realized n accordanc with the. present. invention. It, has. oom found that; the iormat on. of hard. iicia in; the. dewaxine. hiller. canbe. sub tantially in? hibitedi by the; incorporation. ot, a small; quantity,

covered titer-n; the: oil and; war

the sauna. A very important object s of a water miscible, oil immiscible organic acid or alcohol in the dewaxing solvent containing a minor proportion of aqueous contaminant. The resulting mixture of solvent containing small quantities of the order of from about 0.02 to about 0.8 per cent by weight of a water miscible, oil immiscible alcohol or organic acid even at the lowest chilling temperatures employed in dewaxing operations was found to inhibit the formation of a solid ice having a tendency to adhere to the surface walls of the chiller.

On the other hand, a soft or mushy non-adherent ice tends to form, which readily moves through the chiller pipes along with the waxy fraction being treated. The plugging of the chiller pipes due to hard ice formation therein, with resultant chipping and breaking of the chiller scrapers, is thus overcome.

The amount of alcohol or organic acid to be incorporated in the dewaxing solvent will be dependent upon the temperature at which chilling is carried out, upon the amount of water contained in the solvent or in the oil to be treated and upon the nature of the alcohol or acid employed. The present invention has been found to be particularly useful in solvent mixtures which have a relatively high tendency to dissolve water, such as those containing ketones. Hence, the incorporation of small amounts of water miscible, oil immiscible organic acids and alcohols has been found to be suitable for the ketonebenzol dewaxing solvents, such as mixtures containing 25 to 40 per cent acetone or methyl ethyl ketone, 12 to 25 per cent toluol and 40 to 60 per cent benzol conventionally employed in dewax- The particular ratio of solvents to be used will be largely dependent on the characteristics of the oil undertreatment. V In general, a larger proportion of benzol or toluol necessitates the use of lower chilling temperatures to obtain an oil of a given pour test. In practice, the oil to be dewaxed is diluted with 3 to 4 volumes of the solvent mixture, chilled to a temperature at which the waxy constituents precipitate, generally to about 5 F. below the desired pour point of the oil and usually not lower than about 35 F. The precipitated waxy constituents are then separated from the dewaxed oil by filtration. 1

As those in the art know, blended dewaxing solvents are composed of a mixture of a solvent, for example, benz'ol'or toluol, and an anti-solvent, such as methyl ethyl ketone or acetone. The alcohols and organic acids to be used in the present invention for inhibiting hard ice formation are of the anti-solvent type. For this reason it is possible to incorporate, a fairly large volume of these additives in the dewaxing mix-- 7 ture provided a suitable adjustment is made in the solvent to anti-solvent ratio. Thus, by reducing the percentage of acetone or methyl ethyl .ketone contained in the conventional benzolketone solvent mixture, a relatively large amount of alcohol or organic acid may be added. The

4 Without substantially affecting the dewaxing ef ficiency thereof. The lower limit of alcohol or acid to be used will largely depend on the amount of aqueous contaminant contained in the solvent. Accordingly, a sufficient proportion of alcohol or organic acid is contemplated to prevent the formation of a hard ice in the dewaxing process.

The alcohols or organic acids to be used in the present invention are water miscible, oil immiscible and include monohydric aliphatic al-- cohols, preferably those having less than four carbon atoms, such as methyl, ethyl, propyl, isopropyl alcohol; dihydric alcohols, such as ethylene glycol; trihydric alcohols, such as glycerol; fatty acids, preferably those having less than four carbon atoms, such as acetic and propionic acids. The above list is not intended to be restrictive and other water soluble alcohols and organic acids which will occur to those skilled in the art may likewise be used. However, as a practical matter, the less expensive and more easilyavailable members of this group of compounds will generally be employed.

Having described in a general way the nature of this invention, it may bemore readily understood by the following specific example.

A'mixture of dewaxing solvent consisting of about 40 per cent methyl ethyl ketone, about 40 per cent benzol and about 20 per cent toluol and having a small amount of water present in about 1.0 per cent by weight based on the weight of solvent, and an oil to be dewaxed were chilled by.

flowing through a cooled pipe, employing a chilling temperature of 20 F. A hard ice formed under these conditions, preventing further flow of the liquid mixture.

A second sample of the above mixture of oil to be dewaxed, solvent and water having incorporated therein about 0.2 per cent by weight of methyl alcohol based on the weight of solvent, was treated under the same conditions and in this instance a mushy, soft, non-adherent ice formed which'flowed along through the chiller tube with the waxy oil under treatment without interfering with the dewaxing efficiency of the solvent employed.

A third sample of the above mixture of oil to be dewaxed, solvent and water having incorporated therein 0.05 per cent by weight of ethyl alcohol based on the weight of solvent, was treated under the same conditions. tion of alcohol was sufficient to modify the appearance of ice crystals.

of the solvent mixture, ice formation was completely eliminated at a temperature of 20 F.

Thus, the above experiments clearly show that the incorporation of a minor proportion of a water miscible, oil immiscible alcohol or organic acid in a dewaxing solvent, particularly the benzol-ketone mixtures conventionally employed, gives rise to an improved dewaxing solvent which in operation leads to formation of a soft, mushy, non-adherent ice. Hard ice crystal formation is thus substantially inhibited, leading to an improved flow rate of the liquid mixture through the chiller tubes, preventing the expensive and troublesome breakage of chiller scrapers and eliminating pre-treatment of solvents with drying agents to remove water therefrom, as has heretofore been necessary.

We claim:

1. In the method of dewaxing, apetroleum hydrocarbon, comprising blending said hydrocarbon with a dewaxing solvent consisting of from about This minor propor- When th amount of 7 alcohol was increased to 0.6 per cent by weight airs-,4

to about 40- per cent acetone, from about 12 to about 25 percent-toluol and from about 40 to about 60 per cent benz ol, and passing the resultant mixture through a chiller to precipitate wax therefrom, the improvement which comprises the addition to said solvent, prior to said passing, of a compound selected from the group consisting of water miscible, oil immiscible alcohols and organic acids in an amount less than about 0.8 per cent by weight of said solvent but sufiicient to inhibit the formation of a hard, adherent ice on the inner surfaces of said chiller due to the freezing of water contained in the mixture under treatment.

2. In the method of dewaxing a petroleum hydrocarbon, comprising blending said hydrocarbon with a dewaxing solvent consisting of from about 25 to about 40. per cent methyl ethyl ketone, from about 12 to about 25 per cent toluol and from about 40 to about 60 per cent b e nzol, and passing the resultant mixture through a chiller to precipitate wax therefrom, the improvement which comprises the addition to said solvent, prior said passing, of a compound selected from the group consisting of water miscible, oil immiscibile alcohols and organic acids in an amount less than about 0.8 per cent by weight of said solvent but sufficient to inhibit the formation of a hard, adherent ice on the inner surfaces of said chiller due to the freezing of water contained in the mixture under treatment.

3. A dewaxing solvent consisting of benzol, toluol, and a low boiling aliphatic ketone in such proportion that a selective action is exerted as between wax and oil at reduced temperature and having incorporated therein a minor proportion of a compound selected from the group consisting of water miscible, oil immiscible alcohols and organic acids in an amount less than about 0.8 per cent by Weight of said solvent but suflicient to inhibit hard, adherent ice formation during the dewaxing operation.

4. A dewaxing solvent consisting of from about 25 to about 40 per cent of a ketone selected from the group consisting of acetone and methyl ethyl ketone, from about 12 to about 25 per cent toluol, from about 40 to about 60 per cent benzol, and having incorporated therein from about 0.02 to about 0.8 per cent by weight of said solvent mixture of a compound selected from the group consisting of water miscible, oil immiscible alcohols and organic acids.

5. A dewaxing solvent consisting of benzol, toluol, and methyl ethyl ketone in such proportion that a selective action is exerted as between wax and oil at reduced temperature and having incorporated therein a minor proportion of a compound selected from the group consisting of water-miscible, oil-immiscible alcohols and organic acids in an amount less than about 0.8 per cent by weight of said solvent but sufficient to inhibit hard, adherent ice formation during the dewaxing operation.

6. A dewaxing solvent consisting of benzol, toluol, and acetone in such proportion that a selective action is exerted as between wax and oil at reduced temperature and having incorporated therein a minor proportion of a compound selected from the group consisting of water-miscible, oil-immiscible alcohols and organic acids in an amount less than about, 0.8 per cent by weight of said solvent but sufficient to inhibit hard, adherent ice formation during the dewaxing operation.

7 In the method of dewaxing a petroleum hydrocarbon, comprising blending said hydrocarbon with a dewaxing solvent consisting of benzol, toluol, and a low boiling aliphatic ketone in such proportion that a selective action is exerted as between wax and .oil at reduced temperature and passing the resultant mixture through a chiller to precipitate wax therefrom, the improvement which. comprises the addition to; said solvent, prior to said passing, of an aliphatic alcohol having less than 4 carbon atoms, in an amount less than about 0.3 per cent by weight of said solvent but sufficient to inhibit the formation of a hard, ad: herent ice on the inner surfaces of said chiller. due'to the freezing of water contained in the mix: ture under treatment. V

8. In the method of dewaxing a petroleum by..- drocarbon, comprising blending said hydrocarbon with a dewaxing solvent consisting of benzol, toluol, and a lowboiling aliphatic ketone in such proportion that a selective action is exerted as between wax and oil' at reduced temperature and passing the resultant mixture through a chiller toprecipitate wax therefrom, the improvement which comprises the addition to said solvent, prior to said passing, of methanol, in an-amount less thanabout 0.8 per cent by weight of said solvent but sufficient to inhibit the formation of a hard, adherent ice on the inner surfaces of said chiller due to the freezing" of water contained in the mixture under treatment.

9. In the method of dewaxing a petroleum hydrocarbon, comprising blending said hydrocarbon with a dewaxing solvent consisting of benzol, toluol, and a low boiling aliphatic ketone in such proportion that a selective action is exerted as between Wax and oil at reduced temperature and passing the resultant mixture through a chiller to precipitate wax therefrom, the improvement which comprises the addition to said solvent, prior to said passing, of glycerine, in an amount less than about 0.8 per cent by weight of said solvent but suflicient to inhibit the formation of a hard, adherent ice on the inner surfaces of said chiller due to the freezing of water contained in the mixture under treatment.

10. In the method of dewaxing a petroleum hydrocarbon, comprising blending said hydrocarbon with a dewaxing solvent consisting of benzol, toluol, and a low boiling aliphatic ketone in such proportion that a selective action is exerted as between wax and oil at reduced temperature and passing the resultant mixture through a chiller to precipitate wax therefrom, the improvement which comprises the addition to said solvent, prior to said passing, of ethanol, in an amount less than about 0.8 per cent by weight of said solvent but sufficient to inhibit the formation of a hard, adherent ice on the inner surfaces of said chiller due to the freezing of water contained in the mixture under treatment.

11. In the method of dewaxing a petroleum hydrocarbon, comprising blending said hydrocarbon with a dewaxing solvent consisting of from. about 25 to about 40 per cent of a low boiling aliphatic ketone, from about 12 to about 25 per cent toluol and from about 40 to about 60 per cent benzol, and passing the resultant mixture through a chiller to precipitate wax therefrom, the improvement which comprises the addition to said solvent, prior to said passing, of a compound selected from the group consisting of water-miscible, oil-immiscible alcohols and or-' ganic acids in an amount less than about 0.8 per cent by weight of said solvent but sufficient to inhibit the formation of a hard, adherent ice on 7 the inner surfaces of said chiller due to the freezing of water contained in the mixture under treatment.

12. A method of dewaxing a petroleum hydrocarbon comprising blending said hydrocarbon with a dewaxing solvent consisting of benzol, toluol, and a low boiling aliphatic ketone combined in such proportion that a selective action is exerted as between wax and oil at reduced temperature and having incorporated therein a minor proportion less than 0.8 per cent by weight of said solvent mixture of a compound selected from the group consisting of water-miscible, oilimmiscible alcohols and organic acids, chilling the resulting mixture to precipitate wax therefrom, and thereafter separating the wax-oilsolvent mixture into its components.

13. A method of dewaxing a petroleum hydrocarbon comprising blending said hydrocarbon with a dewaxing solvent consisting of from about 25 to about 40 per cent of methyl ethyl ketone, from about 12 to about 26 per cent toluol, and from about 40- to about 60- per cent benzol, and having incorporated therein from about 0.02 to about 0.8 per cent by weight of said solvent mixture of a compound selected from the group consisting of water-miscible, oil-immiscible alcohols and organic acids, chilling the resulting mixture to precipitate wax therefrom and thereafter separating the wax-oil-solvent' mixture into its components.

14. A dewaxing solvent comprising an oil solvent mixture of benzol and toluol and a wax anti-solvent consisting'of a low boiling aliphatic ketone combined in such proportion that a selective solvent action is exerted as between wax and oil at reduced temperature and having incorporated therein a minor proportion of a compound selected from the group consisting of watermiscible, oil-immiscible alcohols and organic acids in an amount less than about 0.8 per cent by weight of said solvent but sufficient to inhibit hard, adherent ice formation during the dewaxing operation.

LLOYD E. BOUDREAUX. OWEN R. MITCHELL.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,848,636 Livingstone Mar. 8, 1932 1,981,758 Svanoe Nov. 20, 1934 2,061,541 Govers Nov. 17, 1936 2,062,355 Ellis Dec. 1, 1936 2,324,303 Johnson July 13, 1943 2,358,921 Gee Sept. 26, 1944