US2112350A - Process for the manufacture of lubricating oils - Google Patents

Description

March 29, 1938. J. E. SCHULZE PROCESS FOR THE MANUFACTURE OF LUBRICATING OILS Original Filed May 5, 1932 3.2mm Au ATTORNEY Patented Mar/29,1938 I I I 2,112,350

UNITED STATES PATENT OFFICE PROCESS FOR THE MANUFACTURE OF .LUBRICATING OILS John E. Schulze, Chicago, IlL, assignor, by mesne assignments, to Red River Refining Company, Chicago, 111., a corporation of Delaware Original application May 5, 1932, Serial No. 609,508. Divided and this application June 4,

1937, Serial No. 146,496

4 Claims. (Q1. ice-s3) This invention relates generally to'processes for exceeding, and most desirably materially below, the manufacture of lubricating oils; and in par- 25 millimeters of mercury, and at temperatures ticular it relates to the manufacture of lubricatincreasing only very gradually and uniformly, ing oils by straight overhead distillation under the lubricating oil constituents being thus pro 5 high vacuum, that is, under very low absolute gressively vaporized in the order of their boiling pressure. However, the invention is not restricted points and obtained as lubricating oil distillates to distillation of lubricating oils under vacuum, requiring no acid treatment or filtration to render but it is of greatest present utility in that field them finished marketable lubricating oils of good P a which will therefore be more particularly referred color and stability.

to in explaining the principles of the invention. The process of the present invention is a part 10 In prior copending application Serial No. of the complete process disclosed in said prior 'ap- 609,508, filed May 5, 1932, of which the present plication and is directed more particularly to application is a division, this applicant has disnovel features of procedure forming a part of the closed and claimed a novel process of manufacsecond stage or phase of said complete process.

1.3 turing high grade lubricating oils directly by An object of this invention is to provide a straight overhead distillation under high vacuum, method or process of recharging a distillation the distillates thus obtained requiring no acid unit or system of the type used in practicing the treatment or filtration to render them finished second phase of the aforesaid process whereby high grade lubricating oils of good-color and stait is not necessary to shut the unit down, or rebility. The complete process of said prior applilease the vacuum, or clean out the still, before cation comprises generally two principal stages introducing another charge to be run, thus not or phases: only saving time, but minimizing heat losses.

In the first stage, there is effected a relatively Qther objects and advantages of theinvention quick separation of lubricating 011 components will become apparent as the description proceeds. from the heavier components of a given crude In order to afford a full understanding of the mineral oil material or charging stock by a conprinciples of the invention, a typical practical tinuous procedure which includes rapidly heating embodiment thereof will now be described in dethe crude material to temperatures sufiiciently tail in connection with the accompanying drawhigh to vaporize all the desired lubricating oil ing which illustratesmore or less diagrammaticomponents under absolute pressure on the order cally and to some extent in the form of a flow 30 of 50 millimeters of mercury or lower, vaporizing sheet, a typical distillation unit or plant wherein such components at such low absolute pressure, the process can be effectively carried out, the and condensing them under such low pressure principal apparatus or equipment parts being as one or more lubricating oil distillates substanshown in side elevation, with portions broken tially free of tarry and other heavier constituents away to disclose certain structural details.

of the crude starting material employed, as well Referring to the drawing, in utilizing the apas from nearly all of the lighter constituents paratus system there illustrated in practicing the thereof. The lubricating oil distillates thus obdistilling process of this invention, the distillatained by quick separation, while superior in some tion, although essentially batch or discontinuous 40 respects to those heretofore obtainable by comin character so far as the nature of the distilla- 40 parable procedure, are nevertheless charactertion itself is concerned, is nevertheless semi-conized by a small content of unstabilizing constiiutinuous from the standpoint of plant manipulaents, and they are not the finished, stable lubri-, tion. That is to say, although the lubricating eating oils desired. Said distillates are employed, oil components are vaporized in the order of their either singly or together, as high grade charging respective boiling points, which is characteristic stock in the second stage or phase of the comof batch distillation, the arrangement of the applete process of said prior application. paratus is such that, after running a given charge Inthe second stage'or phase of the complete down to a residue or bottoms of, say, 5 to 6 per process of said prior application, the quickly sepcent, it is not necessary to shut the unit down,

arated and unfinished lubricating oil distillates or release the vacuum, or clean out the stlll beare subjected, either singly or in mixtures of two' fore introducing another charge to be run. This or more, to redistillation by batch or discontinis a point ofgreat practical advantage as can uous distillation in which vaporization and subreadily be seen. sequent condensation of the lubricating oil con- Generally described, the distillation unit, in

5 stituents is effected under absolute pressures not the specific form here illustrated, comprises a relatively large capacity vaporizer I I adapted to contain a suitably large volume of the oil to be processed, in a body having an extensive free upper surface to facilitate rapid vaporization. This oil may be one or more of the lubricating oil distillates obtained from the first stage or phase of the complete process of said prior application aforesaid. The vaporizer, which in this instance takes the form of a shell still, is surmounted by a reflux fractionating tower III containing fractionating elements I I2. These should most desirably be of such character that resistance to vapor flow is reduced to the utmost possible minimum consistent with sufficiently intimate and prolonged contact between the counterflowing Vapor and liquid to ensure adequate fractionation and clean separation of impurities from the desiredlubricating oil distillate under the conditions of operation. Liquid reflux is delivered to the top of the series of annular plates II 2 by distributor I 23 the liquid dropping from one plate to the next lower one in filming downwardly over the plate surfaces. By means of curved vanes (not shown) associated with said plates, the ascending vapors are given a whirling movement and are also alternately divided into' three passes or streams and reunited into a single stream, as they ascend.

In order to reduce to a minimum any possibility of locally overheating and thus cracking the oil to be run, the vaporizer I I0 is not itself heated by contact with flame or hot furnace gases, but the oil to be processed is heated by continuous passage through a pipe still H3, oil being continuously discharged into the vaporizer through line II 4 and withdrawn therefrom through line I I5 by a centrifugal circulating pump I I6 and returned through line H! to the pipe still for further heating to progressively higher temperatures. The oil passes through the tubes 01' the pipe still heater at high velocity (e. g. 6 m8 feet per second) and in a stage of extreme turbulence, thereby practically eliminating any chance of locally overheating and cracking portions of the oil being processed. In order to permit very rapid circulation of a large volume of oil per minute through the pipe still heater and vaporizer the pipe still may desirably be of what is known as multi-pass construction, four passes being indiitial charge of material to cated at H3 for and at H3 for the radiant bank, the several passes being connected in parallel by suitable headers in a known manner. Such an arrange ment, together with the ample size of the circulating connections H4, H5, H1, and high operating capacity of pump I I6, permits circulation of the oil through the system proximately 650 gallons per minute where, in a typical instance, the total initial charge to the system is 21,000 gallons. circulation of the charge through the system, throughout the distillation, at a per minute rate of about 2 to 4 per cent of the volume of the inthe unit, is desirable in practice. Since the volume of the charge in the unit decreases to a residue of say, 5 to 6 per cent, the circulating rate, in terms of the proof only 2 to 3 the convection bank of tubes I at the rate of ap- Generally speaking,

circulating pump in operation, the oil is clrculated rapidly through the system in closed circuit, as previously described. The rate of circulation may be observed by means of a suitable flow meter I22 interposed at any convenient point in the circulating lines connecting the heater and the shell still vaporizer. The pipe still heater, in the prevent example, may be of sufficient capacity (i. e. heating surface area) to raise the temperature of the oil in the shell still approximately 70 F. per hour, and during-the initial heating up of the charge, the pipe still heater may be fired at this rate; so that within a period of from 3 to 5 hours, depending on the type of charge being run and other factors, the oil is heated to its initial boiling point. It may be stated that prior to running the charging stock into the vaporizer, it is desirable to treat it with approximately 0.2 per cent by volume of a neutralizing agent such as caustic soda of about 40 Baum strength, this neutralizing solution being thoroughly mixed with the charging stock'.

The system comprising the shell still, the fractionating tower, the reflux condenser I23, and final condenser I24, is held under high vacuum throughout the entire distillation of the lubricating fractions by powerful exhausting means which pull all fixed gas and uncondensed vapor out of the system at high velocity through largediameter oiftake I 28. In a typical instance, the absolute pressure in line I25 at the outlet of condenser I24, may be 3 millimeters of mercury, while in the vapor space above the charge in shell still II II it may be 5 to 6 millimeters, a loss millimetersin vacuum. Any suitable exhausting means of suflicient capacity may be used for this purpose, but in practice it is found practical in this instance to use a 3-stage ejector equipment, such as that indicated generally at I26, or a 3-stage reciprocating Worthington pump especially developed for this purpose. The tail water from operation of the ejec- -ers I23, I24, together with controlling valves I 29,

I30, whereby the operation of reflux condenser I23 can be regulated and controlled to best advantage.

As soon as the temperature of initial vaporization is reached in the shell still, the rate of firing of the pipe still heater is controlled to conform with the rate of distillation desired. In a typical instance, where the initial charge consists of the combined lubricating distillates obtained from tower II of the primary system of said prior application aforesaid, vaporization of relatively light products begins at around 350 to 360 F., and the rate of firing is thereafter so regulated as greatly to reduce the rate at which the temperature of the oil increases, especially during the distillation of the lubricating oil fractions proper, which may betaken to begin when the stream coming over shows a viscosity of 50 to 60 seconds Saybolt (at 100 F'.). The temperature of the charge at this point is ordinarily about 375 to 400 F. From then on until the heaviest lubricating oil fractions have been distilled over, which usually requires around 12 to 14 hours in accordance with the present process, the temperature of the charge is raised very slowly and at a substantially uniform rate to a final distillation temperature of about 560 to 575? F., and not exceeding 600 F. as a maximum.

The residue of 5 or 6 per cent, to which the charge.

is run down, is a very heavy high grade lubrieating stock which may be accumulated and rerun by batch distillation, yielding, directly, overhead distillates as finished high grade lubricating oils of good color and stability, with viscosities as high as seconds Saybolt (at 212 F.).

Distillation in the manner just described means a temperature rise approximating to 200 F. during 12 to 14 hours of, distillation, which is an average rise of less than 0.25 F. per, minute or 15 F. per hour. It may be stated that, in practicing the present process, the rate of temperature increase during distillation should not average more than 05 per minute at the most.

The discharge from the pipe still heater to the shell still is controlled by a valve 4' in such manner that a slight positive back pressure (e. g. 5 lbs.) is maintained on the oil to minimize vaporization in the tubes of the pipe still heater. After entering the shell still, the line II4 bends down wardly as shown and terminates in a discharge header I30 extending longitudinally of the still and close to the bottom thereof. This discharge header is provided throughout its length with numerous small diameter discharge openings I3I whose total area may desirably be less than the cross-sectional area of the discharge header. This restriction of discharge opening area permits the discharge of the hot oil from the pipe still heater at very high velocity into the lower part of the shell still in many small jets, thus constantly maintaining the body of oil in the shell still in highly turbulent condition and ensuring substantial uniformity of temperature throughout said body. The velocity of the oil at the point of discharge through the small openings I 3| is on the order of about 30 feet per second. This provision is of great importance in increasing the efficiency and uniformity of vaporization at the extremely low rate of temperature increase above referred to, thus further favoring uniformity in composition (narrow cut) of the vapors evolved during a given period of time, say several minutes, a fact which, in spite of the very low pressure drop through the fractionator and condenser, as already pointed out, makes for relatively highefiiciency in the subsequent fractionation of said vapors and clean separation from the lubricating distillate of the small quantity of relatively volatile malodorous and unstabilizing contaminants included therewith.

The vapors rising from the oil in the shell still pass through the large diameter vapor offtake I32 into the fractionating tower and through the entrainment separator I33 located in the base thereof. The vapors then pass upwardly through the system of fractionating plates or trays II2, previously referred to.

The vapor temperature at the top or outlet of reflux condenser I23 is carefully regulated and controlled throughout the distillation in such manner that no condensation of malodorous or unstabilizing products, which are relatively low boiling as compared to the lubricating constituents of the distillation vapors, can occur in the reflux condenser. That is to say, care is taken throughout the distillation to so adjust the water cooling of reflux condenser I23 that the temperature of the uncondensed vapors and gases leaving the same is always high enough to ensure that, at any given time, said vapors include not only those of the aforesaid malodorous and unstabllizing constituents, but also a small proportion of vapors of the considerably higher boiling lubricating constituents then coming over.

Vapors escaping condensation in reflux condenser I23 pass into condenser I24 where they are cooled to a much lower temperature sufficiently low to compel most of the residual vapors to condense. This condensate, which is of unpleasant odor and unstable, is led away through line I34 and look box I35 to tank I36.

The lubricating oil distillate condensed in the tower III is led away in side stream from collecting plate I31 through line I38 to constant level seal tank I39. The operation of the fractionating system is so regulated and controlled that the lubricating distillate leaving the tower at any given time is very hot, being practically at its point of initial vaporization. During the greater part of the distillation, the temperature at which it leaves the column or tower is not more than 50 to 60 degrees Fahrenheit below that of the vapors entering the base of the column, and only near the commencement of the distillation is it sometimes as much as 100 degrees below that of the vapors entering the column. This aids greatly in preventing absorption of malodorous constituents from the distillation vapors by the condensate while it remains in the tower; and the possibility of absorption is still further minimized by the maintenance of the extremely high vacuum on the hot condensate even after it leaves the column, thus ensuring withdrawal therefrom of even minute traces of such volatile contaminants. The condensate is withdrawn through line I40 and cooler I4I by pump I42,

.which then pumps it through line I43 to storage.

Line I43 may be provided with sight glass I44 and meter I45, as shown. The lubricating oil cooler I4I may utilize as cooling medium the water discharged through line I 21 from the ejector system and condensers at the top of the tower. The

operation of lubricating oil pump I42 is automatically regulated by float control device I46, as indicated.

The lubricating oil distillate going to storage through line I43 is the desired final product of the process. When the initial charge is one or more of the unfinished lubricating oil distillates obtained from the first stage or phase of the complete process of said prior application, or any similar charging stock, the product obtained is sweet, stable, finished lubricating oil, of excellent color, resulting directly from straight overhead distillation and requiring no further refining or purifying as by acid treatment and/or filtration. Its particular specifications as toviscosity, boiling range, etc. depend, of course. upon the character of the charging stock used.

The procedure thus far described is typical of the second stage or phase of the complete process disclosed and claimed in said prior application Serial No. 609,508 aforesaid. The process of the present application has to do with that part of the second stage or phase of the aforesaid process whereby the unit may be recharged after running a given charge down to a desired point, without having to shut the unit down, or release the vacuum, or clean out the still, so that the operation of the unit may be semi-continuous in the sense already explained hereinabove.

Referring again to the drawing, a stand-by pump I41, which may desirably be steam operated, serves in the capacity of a residue pump when. a distillation run or cycle is completed, and also serves to some extent as a charging pump in such manner that the operation of the unit may be semi-continuous, as just mentioned. When a given still charge has been distilled off until a residue of about 6% remains in the shell still, firing of the pipe still heater is discontinued, centrifugal circulating pump I I6 is stopped, valve I52 is closed, and circulation of the aforesaid residue is continued at a reduced rate by means of the steam stand-by pump I"; which is arranged in parallel with pump H8 by valved suction and discharge connections I41 and l respectively, the valves in these connections having been opened for the purpose. While the described distillation has been going on, a fresh supply of charging stock has been prepared for running and has been placed in the charging tank II8.

When the steam stand-by pump has been operating for some time as just described and the -stream of lubricating oil condensate flowing from tower III through line I38 has ceased, valve II! in discharge or delivery line Ill from the pipe still heater is closed, and valves I and. I49 in residue discharge line I50 are opened, thus causing the hot residue to be pumped from the system through residue cooler I5I to storage. Knowing the actual quantity of residue remaining in the system at the end of the distillation, and knowing the capacity of the steam stand-by pump I41 or observing the rate of flow of the residue as indicated by flow meter I22, an operator can determine the exact time when all of the residue has been removed from the shell still. At this time, the suction valve I52 in line II! leading from the shell still remaining closed the valve I53 in line I20 leading from the still charging tank H8 is opened and the valve in line I41 is closed,

so that the steam stand-by pump then draws fresh charge from the tank through branch line I54 in which valve I55 has been opened for the purpose. The stand-by pump continues to operate until the remaining portion of the residue, which is thus forced through the pipe still ahead of the fresh charge from tank I I8, is entirely removed from the system, whereupon valve H4 in the heater discharge line III is opened, and valve I49 in the residue discharge line I50 is closed. The proper time for effecting this operation is readily determined from a knowledge of the capacity of the tubes in the pipe still heater and the transfer lines, and the rate at which the steam stand-by pump is operated. A further guide is afforded by noting the temperature drop which suddenly occurs at the outlet in the pipe still heater as the last of the hot residue leaves it. Shortly after the first portion of the fresh charge reaches the shell still, the steam stand-by pump I" is shut down, the valves in lines III and I" are closed, and the centrifugal circulating pump is started to complete the charging of the system with fresh lubricating oil distillate stock to be run; valve III in the suction connection of the pump to the charging tank H8 being opened and remaining open until the charging operation is finished, whereupon it is closed and valve I52 is opened again. In the meantime firing of the pipe-still has been resumed.

In the particular installation here illustrated, the discharge side of stand-by pump I41 is also connected by valved line IlI to discharge line I 50, whereby the pump may draw oil from the shell still through line I" and discharge it directly into line I50, which may be hecessary or desirable upon occasion. 1 it The,manipulation of the unit to render its operation virtually semi-continuous may of course be accomplished in other ways than that described in specific detail hereinabove, such description being given merely by way of concrete example for purposes of explanation. This method of procedure is very advantageous because it renders operation of the distillation unit materially more economical and efficient. Since the shell still, fractionating tower, pipe still heater and all lines connecting the heater with the shell still are insulated, the whole system which is at a temperature well above 500 F. at the end of the distillation, retains a large amount of heat which is thus conserved and utilized to impart a rise in temperature to the fresh charging stock amounting to 70-80 F. before firing of the pipe still heater is begun. Also, the interval during which the fresh charge is being heated up to initial boiling point for the next distillationis reduced by about one hour as compared to the time required to heat a fresh charge up to the same temperature in a cold unit.

Seal tank I38 has a pressure balancing connection I39 to tower III, as shown. Seal tank- I requires a similar pressure balancing connection unless, as in the illustrated installation, it is located far enough below condenser I! to provide a balancing leg of oil in line Ill.

The temperatures and other detailed operating conditions hereinabove given are to be understood merely as indicative of good practice in handling typical topped crudes such, for example,

'asfUrania (Louisiana) and Columbia (South America) crudes. Obviously such operating conditions will vary to some extent with the type of crude charging material, and hence the operating data are to be regarded as given for purposes of illustration and not as rigidly restrictive.

It is very important to rigidly exclude access of air into the distilling system, since the occurrence of even very slight oxidation makes it impossible to produce directly, as overhead distillates, finished lubricating oil products of the character here in question. All seams and joints exposed to temperature changes should be welded, and the entire system should be made absolutely tight.

By a stable lubricating oil, as the expression is herein employed, is meant one that does not undergo changes in storage and use which are in the nature of breakdown or decomposition and which are recognized by the industry as characterizing inferior lubricating oils. A lubricating oil which, upon being heated to 300 F. andbcing held at this temperature for 10 minutes, does not darken in'color more than one-half point on the standard Saybolt color scale, does not acquire a bluish cast in place of the desired greenish bloom, and, does not have or develop an unpleasant odor, is a stable oil.

What is claimed is:

1. In a'process of manufacturing lubricating oil, wherein lubricating 011 components of a charge of suitable mineral oil are distilled off while the charge is being circulated in a closed path orcircuit which includes a tube or pipestill heater, a vaporizer and the necessary connecting conduits for delivery of oil from the heater to the vaporizer and for return of oil therefrom to the heater, respectively, the method of auasso vaporizer and to pass it through said heater, .and then, when substantially all or most or the residue has been withdrawn from said vaporizer, introducing a fresh charge of mineral oil into the circuit at a point in said return conduit in order to force any remaining residue through said heater and into said delivery conduit for discharge therefrom, resuming delivery of oil to said vaporizer when substantially all the residue has been thus discharged'from the circuit, and continuing introduction ofiresh charge until the circuit is fully re-charged, whereby the circuit may be re-charged in a relatively short time while minimizing heat losses and without endangering the heater tubes through overheating.

2. The method as defined in claim 1 which furtherincludes reducing the speed or oil flow ,in the circuit while the residue is being discharged'therefrom and the first portion of the fresh charge is being introduced.

3. The method as defined in claim 1 which further includes maintaining a low absolute pressure in the circuit during the distilling and recharging operations. p

4. The method as defined in claim 1 whichiurther includes maintaining an absolute pressure of about 6 millimeters of mercury in the vaporizer during the distilling operation and preventing any substantial increase in pressure in the circuit during the recharging operation.

JOHN E. SCHULZE.

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