US2516640A - Hydraulic fluids - Google Patents

Description

Patented July 25, 1950 HYDRAULIC FLUIDS 1 Char-les W. Montgomery: and William L Gilbert,

Oakmont; and Robert E. Kline, ienna 'lown- Research Developmentddompany, r Pitts- 1 .burgh, .-1a.-, a corporation .01 Delaware I *No Drawing Arn ti =..1.Serial N0.*7 8

i t v s16,- -Claims.

,-';1his:;invention1 relates toi :hydraulic -fluids,.and more; particularly to fluids for "11863111 -*hydraulially operated-apparatus, wsuchas brake :mechanlsms, fluid flywheels, shock u absorbers,control mechanisms and similar hydraulically operated quipment.

V arious Jfluids have previouslvbeen proposed for use inr hydraulic systems ashydraulic power ransmission mediator the like; In a great numer ofthe previously. proposed-fluids, there have een many disadvantages attendant to their use, A uch,-;aslcorrosive and degrading effects'ofsuch fluids -on metaland rubber-parts of the hydraulic vequipment, actendency towardsqvolatilization at a perating; temperatureswlack' oi nsuificient lubriatieawm ti etc.

It -is an object of this-inventiomtherefore, to provide a-hydraulic fiuid which overcomes the @disadvantage of many of the prior artmaterials.

51b is a further object of this invention to provide hydraulic fluids which have general utility if under variable operating conditions.

-,-These and other objects are accomplished by the-present invention wherein we provide as a hypdraulic fluid for hydraulic equipment a liquid 1-; omprising a substantially neutral ester of a monohydric alcohol and the mixture of acids obg tained by the oxidation with gaseous oxygen of an aqueous alkaline slurry of a finely divided car- ---bonaceous material selected frcm'the group conistingof. coal and coke obtained by the carbonzation of coal at temperatures below 700 C. For -.convenience, the acids described above are here- '-,-.,inafterereferred to as coal acids.

w We have found that the substantially neutral ,trnonohydric alcohol esters of the mixture of :coal -acids described above provide excellent hydraulic -i-iuids,whlch are characterized by general utility wunder a wide variety of operating conditions. These esters may be readily and cheaply prepar ed,-and therefore are an attractive source of "hydraulic fluids.

As has been stated, the acids usedin the preparationof our new hydraulic fluids-,areobtained by the oxidation with gaseous oxygen 40L; an aqueous alkaline slurry of a finely divided carbonaceous material selected from the group consisting' 01";0031-8111'1 cokeobtained by the carbonization of coal at temperatures below 700? C Suitable coals. comprise anthracite, bituminous,

sub-bituminous, lignite and other low grade coals. Suitable cokes are those produced by the carbonization of a coal at a temperature below 700C; in a manner known tothe art. 1 If the cokes are pro- 12 -.':Z'I.beC0me'r graphi-ticiandrunsnitable; for .thezmroduction or coal acids axsatisfaetory gyield. The;.fbllowingvis an exampleiof theapreDfl-ration: of the-coal acids. Finely groundibituminous: coal, :alkali; :such;v as sodium hydroxide and qwatemare mixed}; in a nickel-lined autoclave:equipped -with a: turbomixer and with means for.heatin zandncoolinggthe charge. The iamountiofialkali:usecL is ,inexc.ess 0 of that requiredrcfimpletely-q towneutra liz all: of rthegcoallgacids lfqtmem in" thew-oxidation ,p cess. "'By wayofjyexamplenthe proportion l'ofrthedncgredients 'may-wbe" '15 -pQundS of coal, 15cgallons -of-;. ;water and 45,: pounds' jof causticisqdan i'Ihe 15 charge wis heateduand irthenwoxysen is cbubbled therethrough. r-w'lhe temperature of'thej'charge is maintained: from-- 200? to300 Cc; at a total -pres- 1surewof= from.500 ;to@1 200;p0unds per-squarerinch. The reaction? is; exothermic and therltemperature: 3151f main ained "Wi t1hl1'1.3th8ijimit-sfi'statedjby P cooling; zsucheas by passin awaterithroughssanrinternal' COO1jiI1g"CO -1Zfin:the autoclave; zThel oxida- I '1 :tion is contin-lled 'xuntil -=all of; the i, carbonaceous .a-material; oi -the coal passes intossolutionrand usu- .-ally requires-between" 21 31116. 3 hours l-Hali-ofiathe carbon of the coal isroxidizedeto-porganicizaeids wand the remai-nderwto carbon-dioxide. i-iAtzzthe com letion-ofrtheoxidation thechargegisrcooled to about L10g 0.: and is? discharged: rfromstherz auto- 0. clave. The ash ofathe coal which is *rlargelyrun- -attacked; is removed: byvfllteringcthrough zalifilr press. l '2 i' her l er lrrprqduct aisacan :ealkaline-esclution containing the sodium salts of the organ \gaeids obtained bymthe: oxidation: of thew coal. Enough sulfuric acid-is:added; to this 'solutior'mto, liberate i the free vacids. Any-:insoluble material: appearing: after qacidificat-ion withsuliuric acidadszremoved'by %fi;lte ring.;-; 'l'herlfreewoalracids obtained 5 are water-soluble and may conveniently be robstained from, their; solutionaimwater;-by;nextraction with a water-immiscible organic solvent. I'IEFOI' exampleqmethyl ethyl ketone may-bemseddor this purpos in e; nzthe: p esence; .oifrthe sodium; su fate produced by the acidification withpsulfuric acid, methyl ethyl ketone is water-immiscible. Thelextract phase may then be transferred to a still for recovery of the bulk ofathe solvent, and the. product remaining in the still may. ,thenbejecl 0. to. alvacuum rotary drier for removalofwthe remainder of -the solvent. For convenience inrsub- .sequent handling, the dried product: may; be

ground to a fine powder in a pebble mill.

*The product obtainedappears to be amixture ducedat--temperatures in excess of "700" C., they "56"01' aromatic acids. ,This mixture is a free-iflo'wing 3 yellow powder which is hygroscopic and substantially completely soluble in water. The average molecular weight of the acids is 250 and the average equivalent weight is 80. Accordingly, the average number of carboxyl groups per molecule is somewhat more than 3. The exact nature of the acids is unknown, but they are believed to contain triand tetra-carboxylic benzene acids, as well as acids having a more,

complex nucleus than the benzene ring.

In order to obtain the hydraulic fluids of our invention, the coal acids as obtained above are esterifled with a monohydric alcohol to produce substantially neutral esters. Esteriflcation may conveniently be carried out by refluxing 6 moles of the alcohol with 1 mole of the coal acids for several hours while continuously adding'small.

as methyl, ethyl, propyl, butyl, amyl, hexyl, octyl,

decyl, lauryl, myristyl, palmityl and eicosyl alcohols yield excellent products. Branched chain alkanols such as isopropyl alcohol, 2-ethyl-hexyl alcohol, and the individual by product alcohols obtained from the methanol synthesis may also be employed. Other monohydric alcohols which may be employed are the unsaturated aliphatic alcohols such as allyl alcohol, crotonyl alcohol, oleyl alcohol and the like. Alicyclic and aromatic service conditions extremely remote.

The esters of the coal acids obtained as described hereinabove present a number of properties making them eminently suitable as hydraulic fluids. The high initial boiling points and extremely low vapor pressures of the esters, even at elevated temperatures, render any loss of these hydraulic fluids by vaporization under As a matter of fact, the esters of the coal acids cannot be distilled in appreciable amounts by ordinary distillation techniques and can only be partially fractionated by molecular distillation. The esters are very stable, particularly with respect to oxidation. They also have high viscosity indexes, high flash points and excellent lubricating properties. In general, the lower straight chain alkanol esters of the coal acids, including the octyl ester, have pour points sufficiently low to give them general utility as hydraulic fluids. For those monohydric alcohol esters having a relatively high pour point, such as the lauryl ester, the addition of solvents or diluents in the proportions hereinafter disclosed serves very effectively to lower the pour points without materially affecting the desirable properties of the esters. By reason of the fact that the esters are anticorrosive, they may safely be used in contact with the metal parts of hydraulic equipment without requiring the addition of a corrosion inhibitor. The esters have a high specific gravity and are therefore excellently adapted for use as fluid flywheels. In brief, the esters of the coal acids present an aggregation of properties in a single material which renders them particularly suitable for general use as hydraulic fluids, and in addition, it is unnecessary to add corrosion inhibitors and lubricants which are normally required to be added to prior art hydraulic fluids. Although we have disclosed the use of the esters monohydric alcohols such as cyclohexanol and of the coal acids as hydraulic fluids by thembenzyl alcohol are also suitable. Mixtures of selves, diluents and/or solvents may be added to monohydric alcohols may also be employed, parthe coal esters to produce homogeneous hydraulic ticularly the mixture of alcohols obtained by the fluids. When a diluent is used it will ordinarily reduction of coconut oil fatty acids and known be present in an amount from about 5 to about commercially as Lorol, the mixture of higher .45 p r cent by Weight 011 the esters of t e 811 ac s molecular weight alcohols obtained as a product depending uopn the particular requirements, in the synthesis of methanol from carbon such as whether a light or heavy grade of fluid monoxide and hydrogen, as well as the mixture of is required for a particular application. Alalcohols obtained as a by product in the synthough the esters of coal acids are soluble in a thesis of hydrocarbons from carbon monoxide 50 wide variety of solvents, it is preferred to use and hydrogen. A preferred subgroup of monorelatively non-volatile solvents boiling in the hydric alcohols comprises the straight chain kerosene range or above as diluents of the esters aliphatic alcohols containing from 4 to 12 carbon in our hydraulic fluids. Thus the lower aliphatic atoms. alcohols, such. as methanol, ethanol and propanol,

- If desired, the esters obtained as indicated and the low boiling hydrocarbons, such as benabove may be treated with lime and an adsorbent zene and toluene, are not desirable as diluents. such as fullers earth in order to purify the crude Typical solvents which may be used as diluents product. For example, in one such treatment the are (l) the glycol ethers including the monoestcrs are stirred with 4 per cent by weight of butyl ether of ethylene glycol, the monoethyl fullers earth and 4 per cent by weight of lime at {30 ether of ethylene glycol, the 'methyl ether of a temperature of 150 to 200 C., and are then ethylene glycol monoacetate, the butyl ether of flltered. diethylene glycol and the diethyl ether of ethylene Representative properties of some of the esters glycol; and (2) hydrocarbon solvents such as of this invention are shown in the following light lubricating oils, gas oils, kerosene and'the table: like.

Ester Inltai%17:6B0.gfiL C. Sp Gm Visibg slljl at ViSiOS SUI at VI PourF 1.t.,

' n-Butyl (crude)... greater than 27l 1.094 at 130l60 F 2,479 130 76 n-Bntyl (treated 1 greater than 27l 10,210 360 92 n-Octyl (crudc) greater than 380 1.654 117 95 0 n-Octyl (treated) greater than 380"... 1,820 123 94 0 n-Lauryl (crude) greater than 366.-. 0.9659 at 60l60 F l, 218 116 +55 n-Lauryl greater than 366 0.9659 at 60 'l60 F 1,267 116 +50 1 Treated with 1611a"; earth and lime as disclose din the preceding paragraph.

The following data illustrate some of the properties of the coal acid esters containing diluents. Data for the ester per se are included for comparison.

The hydraulic. fluids of the present invention, whether comprising the esters of the coal acids alone or in combination with a diluent as described above, may be used as fluid power and transmission media in any of the common hydraulic systems wherein power is transmitted from an actuable element to an actuated element by means of a fluid, the most common form of such a system comprising a. pair of variable volume chambers with, connecting conduit means, the chambers and the conduit means being filled with a fluid hydraulic power transmission medium. The hydraulic fluids of the present invention may also be used in analogous equipment in which power transmission is not the primary purpose as, for example, in power absorption systems, such as damping mechanisms, shock absorbers and the like.

What we claim is:

l. The process which comprises transmitting power by means of a liquid containing a. substantially neutral ester of a monohydric alcohol and the mixture of acids obtained by the oxidation with gaseous oxygen of an aqueous alkaline slurry of a finely divided carbonaceous material selected from the group consisting of coal and coke obtained by the carbonization of coal at temperatures below 700 C.

2. The process of claim 1, wherein the monohydric alcohol is an alkanol containing up to 20 carbon atoms.

3. The process of claim 1, wherein the monohydric alcohol is an alkanol containing from 4 to 12 carbon atoms.

4. The process of claim 1, wherein the monohydric alcohol is butyl alcohol.

5. The process of claim 1, wherein the monohydric alcohol is octyl alcohol.

6. The process of claim 1, wherein the monohydric alcohol is lauryl alcohol.

L'The process of claim 1, wherein the finely divided carbonaceous material is bituminous coal.

8. The process of claim 1, wherein the liquid contains additionally a relatively non-volatile diluent boiling at least in the kerosene range.

9. A homogeneous hydraulic fluid comprising (1) a substantially neutral ester of a monohydric alcohol and the mixture of acids obtained by the oxidation with gaseous oxygen of an aqueous alkaline slurry of a finely divided carbonaceous material selected from the group consisting of coal and coke obtained by the carbonization of coal at temperatures below 700 0., and (2) a relatively non-volatile diluent therefor boiling at least in the kerosene range and being present in an amount of from 5 to per cent by weight.

10. The fluid of claim 9, wherein the diluent is a glycol ether.

11. The fluid of claim 9, wherein the diluent is a hydrocarbon solvent.

12. The fluid of claim 9, wherein the monohydric alcohol is a straight chain al'kanol containing from 4 to 12 carbon atoms.

13. The fluid of claim 9, wherein the monohydric alcohol is butyl alcohol.

14. The fluid of claim 9, wherein the monohydric alcohol is octyl alcohol.

15. The fluid of claim 9, wherein the monohydric alcohol is lauryl alcohol.

16. The fluid of claim 9, wherein the finely divided carbonaceous material is bituminous coal. 1

CHARLES W. MONTGOMERY. WILLIAM I. GILBERT. ROBERT E. KLINE.

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

UNITED STATES PATENTS Number Name Date 2,390,258 Katz et al. Dec. 4, 1945 FOREIGN PATENTS Number Country Date 429,175 Great Britain May 20, 1935 454,628 Great Britain Oct. 5, 1936 OTHER REFERENCES Chemical Abstracts, vol. 40 (1946), page 5223. Beilstein: vol. IX, 4th ed., page 1010, and the 1st supplement thereto on page 443.

Claims (1)

1. 9. A HOMOGENOUS HYDRAULIC FLUID COMPRISING (1) A SUBSTANTIALLY NEUTRAL ESTER OF A MONOHYDRIC ALCOHOL AND THE MIXTURE OF ACIDS OBTAINED BY THE OXIDATION WITH GASEOUS OXYGEN OF AN AQUEOUS ALKALINE SLURRY OF A FINELY DIVIDED CARBONACEOUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF COAL AND COKE OBTAINED BY THE CARBONIZATION OF COAL AT TEMPERATURES BELOW 700*C., AND (2) A RELATIVELY NON-VOLATILE DILUENT THEREFOR BOILING AT LEAST IN THE KEROSENE RANGE AND BEING PRESENT IN AN AMOUNT OF FROM 5 TO 50 PER CENT BY WEIGHT.