US1860838A - Method of preparing lubricants - Google Patents

Description

E. H. LESLIE METHOD OF PREPARING LUBRICANTS May 31, 1932.

Filed March 7, 1928 5 Sheets-Sheet Elvwwnboz Zugene h [es/A3.

Ju flbtome c4 0 [1932- E. H. LESLIE 1,860,838

METHOD OF PREPARING LUBRICANTS Filed March 7, 1928 3 Sheets-Sheet 5 i222; z z V 95 H 1 j 103 1 0 42 1:111:11: 111112 fixowhq-nmmig 7 Svwemtoz [Page/we H [es/[e 851 a-ttozmm d Patented May 31, 1932 UNITED STATES rArsN-rerr-Ice Imam n. LEsLm, or ANN Anson, u'rcnrem, nssrenon zro E. '3. Banana &. sons com-m, or nos'ron, mssacnusnr'r s, A CORPORATION OF mssAcHUsEr'rs METHOD or Panama LUBRICANTS Application filed Mar ch 7, -1e2s. sefiaimasasst My invention relates to a method'ffor economically securing a high yield of lubricants from a petroleum or like material.

. Many crude petroleum materials from 5 which lubricants are derived contain a considerable amount of tarry oras haltic ma terials, which are either ractlcally nonvolatile or have boiling polnts higher than those of the highest boiling lubricants.

10 These tarry or asphaltic materials must not,

bedpresent in the finished lubricants and in or er to remove them b distillation the temperature must be sufliclently high to distill and separate from them the desired lubriis cants. The lubricants of the hi hest viscosity which in many instances are tie most valuable, are'those havin the highest boiling points, and it is there ore desirable to use a maximum distillation temperature and at so the same time to avoid substantial cracking. It is well known that the rate of cracking is a function of temperature, the amount of cracking being generally directly propor tional to the time and increasing rapidly with increase in temperature. Extended researches have been made by others to determine the time and temperature factors contributing to a maximum amount of cracking, as this information has been of great 80 importance to the tremendous industry of producing gasoline by cracking. Iam concerned on the other hand with obtaining a minimum of cracking of the lubricating portions of a material from which lubricants are 85 derived, in order to prevent loss of the lubricants, and at the same time with utilizing temperatures that will permit distilling a maximum of lubricants in an economical manner. The precise influence of the fac- 40 tors of time and temperature on the loss of.

lubricants by cracking has not been previously determined, and the method of this invention is based on careful investigation and experimental work in this field.

In the ordinary present day commercial oin' crude petroleum are lowbecause of plant procedures that destroy the viscous oil ythermal decomposition or cracking. Us ually one or more distillations from large shell stills are employed, and the petroleum is heated to a'relatively high temperature for a period of many hours, thereby causing 1 "cracking in the bed of the .oil. Moreover, the temperature of t e oil close to the heating surfaces is necessarily materially higher than that of the body of the oil, and hence considerable cracking takes place in the relativel quiescent film next to the heating suraces. Endeavors have been made to reduce the decomposition'of the lubricants by reducing the temperature or time of distillation or both. One process employs shell stills and lowers the temperature required by distilling under a low absolute pressure. The long time of heating and the'film overheating efl'ect referred to above, are necessary consequencesof the use of shell stills, hence it follows that it is essential, if any substantial cracking is to be avoided, to maintain a very low absolute pressure, thereby permitting the use of a relatively low temperature. The

use of shell stills under such very low absolute pressures involves relatively high initial installation costs and operating ex penses. Another expedient in common use is to distill in shell stills and to inject steam into the oil. The effect of the steam is to lower the distillation temperature in accord- I ance with well known principles. In addition to the disadvantages of a long time of heating and overheating of the oil next to the heating surfaces, suchpractice involves ,a.

through tubes heated externally, the time of prractice, the yields of lubricants obtainedheating and therefore the amount of cracking bem less for any given temperature than in s ell stills at the same temperature.

In all such heaters, however, so far as I am aware, the viscous material or lubricant has been subjected to a time of heating such that substantial cracking of lubricants results when raising the temperature to a point where the desired amount of lubricant will be distilled. In some cases steam has been introduced into the heating tubes to lower the distillation temperatures, and to increase velocity, thus decreasing the time element. In one installation a tubular type of heater has been employed in which the tubes are not filled with the material being distilled and provision is made for the removal of vapor as formed.

In contrast to present practice, my procedure is designed to secure larger yields of lubricants economically from material containing the same by distillation in such man ner as to prevent any substantial amount of cracking. By my process, average distillation temperatures higher than those that have previously been considered possible may be employed without diminishing the yield of lubricants or impairing their viscosity.

According to my invention, I heat the lubricant containing material in a tubular heater to the temperature required to vaporize the desired lubricating fractions, which temperature is normally considerably above the cracking temperature of 'the material, in such a manner that the period of time during which the material is subjected to temperatures above its crackin temperature is too short to permit any su stantial cracking to take place, and that the oil next to the heating surface is not heated to a temperature considerably exceeding that of the body of the oil. After heating the material to the required temperature I subject it to flash vaporization in a suitable vaporizer or flash chamber. I have demonstrated by complete experimental work the advantages of flash vaporization as *compared with incremental or stepwise vaporization. By means of flash vaporization approximately 30% more Inbricants can be vaporized by heating to any given temperature than by stepwise vaporization, or the same percentage can be vaporized by heating to a lower temperature. Furthermore,-at agiven temperature the desired lubricants will be more sharply separated from the viscous bottom by flash vaporization than by stepwise vaporization. To reduce the temperature required to vaporize a large part or substantially all of the ris- 'cous oils I preferably operate under a vacuum as described more fully hereinafter. After separating the desired lubricants from the h avy residues by flash vaporization, I prefe ably employ counter current fractionation in a suitable plate column to separate the after.

vapors from the vaporizer into the desired fractions. The use of a plate fractionating column is essential to secure the highest yieldsof lubricants and the advantages thus obtained will be pointed out in detail herein- My process is particularly advantageous bearing oils, and an important feature of my invention resides in the treatment of these oils in such a manner as to secure in a single operation a maximum amount of so-called pressable wax distillate. In the commercial shell still processes heretofore employed, the wax distillate out either does not contain the wax in a form suitable for pressing or is divided into two portions during distillation, thefirst portion to go overhead being pressable, and the second and usually larger portion being non-pressable. Thecustomary procedure is to redistill the wax distillate or the non-pressable part thereof in shell stills under cracking conditions, whereby a secondary wax distillate, which is pressable, is pro duced. Obviously, however, this procedure is wasteful of heat and. destroys some of the valuable lubricants. According to my invention, on the other hand, as will appear from the detailed description given hereinafter, a larger yield of pressable wax distillate may be obtained directly from the original distillation, which is carried out under substantially non-cracking conditions as above de' scribed.

These and such other objects and advantages of my invention as may hereinafter appear will be best lmderstood in connection with a description of suitable apparatus for carrying out my process, such as is illustrated diagrammatically in the accompanying drawings, which form a part of this specification and-in which;

, Figure 1 is a diagrammatic side elevation, partially in section, of a complete plant adapted to carry out my process;

Figure 2 is a horizontal section through a tubular heating unit which may be used in place of the heating unit shown in Figure 1;

Figure 3 is. a central vertical section through the heating unit shown in Figure 2;

Figure 4 isa horizontal section through anotherform of heating unit; and

Figure 5 is a central vertical section through'estill another suitableform of heating unit.

Referring more particularly to Figure 1 of the drawings, 10 indicates generally a suitable tubular heater or pipe still for bringing the lubricant containing material to the desired distillation temperature. The pipe still 10 comprises a preheating or economizer section 11 and a high temperature or radiant heat section 12. The radiant heat section 12 is preferably constructed in the form of an upright cylinder and is provided at its upper P economizer section 11. From the economizer arranged circumferentially'around a portion heat section 12. In other words, for a typical 5 relatively slowly in the preheating or econoend with a centrally locatedoil burner 13. The-hot products of combustlon from the burner 13 pass downwardly through the center of thera'diant heat section 12 and thence through the flue 14 to the economizer section 11 and out through the stack 15. In the embodiment'shownin this figure, the oilto be heatedjis divided into a plurality of independent streams, four of such streams being illustrated. The oil is picked up from each of the four supply pipes16, connected to a source of supply not, shown, by a separate pump 17, and forced through a heating c011 '18 in the eeonomizer section 11. The four independent heating coils 18 are horizontally disposed in direct contact with the products of combustion. If desired, the oil maybe preheated in'suitableheat exchan ers (not illustrated) before being introduce into the section, each of the four streams of oil is separately conducted through aline 19 to the radiant. heat section 12, where it passes through a vertically disposed heating coil 20 of the inner Wall of the radiant heat section. The four coils 20 taken together form'a hollow vertical cylinder. By this construction,

the hot produetsof combustion from the burner 13 pass centrally downward through the radiant heat section, and transmit their heat thereto mainly by radiation.. The products of combustion are. cooled materially before they come into direct contact with the heating coils located in the 'economizer section 11-, thus preventingthe burning or'oxidation of the heating tubes. The ends of the four coils 20 in the radiant heat section 12 are all connected to the common outlet header 21 disposed above the radiant heat section.-

1 preferably design'and operate the pipe still 10 in such manner that the oil undergoing treatment does not reach a cracking temperature until after it enters the radiant lubricant containing petroleum oil the maximum temperature reached inthe eeonomizer. section 11 will be, in, the neighborhood of 600 F. It is thus feasible to heat the oil mizer section. Therefore, I employ relatively large heating tubes in the economiz er section 11, thereby securing a cheaper andmo're dur its . the heating depends upon the character of the 105 I have found thatlwhen a distillationtemapproximately 650 F., to the maximum temture is lower, and vice versa; However, in.

exist in the portion of the tubes near the outlet header 21.

mum temperature which must be obtained depends of course upon the characterof the material and the percentage thereof which it is desired to vaporize. The first requirement in the design of the heater obviously is that the area of the heating surface must be large 9 enough so that the amount of heat required to raise the oil to the desired distillation temperature can be put into the oil.

The maximum time during which the mate'- rial is above its cracking temperature may be determined by dividing the material capacity ofthe portion of the'heater in which the material is aboi e its cracking temperature, in this case the radiant heat section 12, by the amount of said material which passes through this portion of the heater in a unit of time.- For instance, if the material capacity of the radiant heat section 12 should be thirty gallons and the material put through one gallon per second, it would require a maximum of thirty seconds for the material to pass through this portion of the pipe still. 7 Throughout this specification I have defined the time during which the material is held at 'I a temperature above its cracking temperature in this manner, disregarding such variations as may result'from' theformation of gas or vapor.

The permissible time for this final stage of material undergoing treatment and the maximum temperature to which it is -to be heated.

perature of about 850 F. is desired, it is possible to avoid substantial cracking if the oil is raised from its cracking temperature, or

perature in about 60 seconds. A longer time is permissible if the distillation temperaorder to secure the best results, I prefer not to heat the oil at temperatures above its crackingtemperature for more than 35 seconds.

, have further found that the velocityat which the material passes through the heat- 12 ing tubes is of great importance, and that this velocity must be high. In order to prevent any substantial cracking of the oil being heated, it is necessary that no portion of the oil stream be materially higher in temperature than the main body of the oil. The velocity of flow determines to a large extent the temperature gradient between the oil v close to the tube walls and that at the center 13 of the tubes. A high velocity of flow apparently sets up a turbulent condition which aids in preventing any great differences of temperature in the oil stream.

There are thus three major factors which I consider in the design of the tubular heater:

First, the area of the heating surface must be great enough-so that the required amount of heat can be put into the oil; second, the ma terial capacity of the heating tubes must be sufiiciently small so that the time of passage of the oil will be 60 seconds or less; and, third, the velocity of the oil through the tubes must be such that high film temperatures on the tube walls are avoided. At the same time, care must be taken that the velocities and tube lengths used are not such as would give an excessively high pressure drop through the heater.

As a result of my experimental work, I have found that for commercial size plants,

--tub es of 1% inside diameter or less are desirable, and that velocities of 10 feet per second or over must be used. For large units in which a single tube of the required area would be so long that the pressure drop would be excessive, I may use several tubes in parallel.

The oil after being heated to the required final temperature is discharged into the flash vaporizer 30, which may be, as shown in Fig-- ure 1, interposed in the periphery of the outlet header 21. The material entering the vaporizer 30is above its boiling point at the pressure existing therein, and a substantial portion of the material will therefore immediately. flash into vapor, which leaves the vaporizer through the overhead pipe 31.

One or more baffle plates 32, which may be of I viscous lubricants.

the usual bubble tower type, are, if desired, placed in the top of the vaporizing chamber 30 to prevent entrainment of liquid in the vapors leaving the chamber. I have illustrated the flash vaporizer 30 only diagrammatically as any suitable type thereof may be employed.

The liquid residue remaining in the vaporizer 30 may be drawnofl through the valve 33 into a cooling coil 34, which discharges into a receiving tank 35 provided with a drawofl pipe 36.

The vapor leavmg the vaporizer through the pipe 31 mayv be led to a suitable fractionating column 40 where the lubricating stock may be cut into fractions of desired viscosity and, if. desired, the lighter nonviscous material may be stripped from the The column 40 is provided with a series of plates 41 which may be of the usual bubble tower type. The heavy lubricant collecting in the bottom of the fractionating column d 40 may be drawn off through the pipe 42 controlled by the valve 43 into a cooling coil 44. The cooling coil 44 discharges into a receiving tank 45 provided with a drawoif 46.

' drawofl'pipe 40 which is connected to a cooling coil 51 discharging into a receiving tank] 52. It will be understood that more thanone intermediate drawofl. such as may be provided if desired.

The overhead vapors from the fractionating column 40 are conducted through the pipe to a condenser 61. The condenser 61' discharges into a trap 62 from which the condensate is conducted through a pipe 63 to 'a cooler 64, discharging into a receiving tank 65. The vapor space of the trap 62 is connected bythe pipe 66 to a vacuum pump 67, v

by means .of which the desired low absolute pressure may be maintained in the-vaporizingsystem.

The receiver is provided with a valve controlled drawofl pipe 70 and also wlth a valve controlled pipe 71 leading to a ump 7 2, which pumps the desired quantity 0 con-' densate through the line 73into the top of the fractionating column 40 to provide the necessaryreflux to secure the proper operation of the fractionating column. The valve 74 may be used to control the amount of reflux introduced into the column.

The manner of carrying out the'flash vaporization and the counter current fractionation steps of my method depends, to a considerable extent, upon the character of the oil being treated. A broad line of division may be made between the handling of non-waxbearing oils and of oils containing wax, and the latter classification may be sub-divided again into those of mixed base and'thoseof parafiin base.

In the treatment of non-wax-bearing oils, a-temperature in the vaporizer 30 is prefer ably maintained such that the residue remain ing therein and drawn ofi through the valve 33 forms. but a small proportion ofthe'stock charged, and consists largely of tarry, vasphaltic, gummy, andcoloring substances.

The viscous stocks vaporized overhead and recovered in the bottom of the fractionating column 40 are oils of good color as well as of high viscosity and may be sold as cylinder stock without filtration and with very little refining treatment. In previous processes in which cylinder stocks have been made from various oils, on the contrary, these stocks or the most viscous lubricants remain as a still residue, and filtration or a heavy treatment with sulphuric acid, or both, are usually necessary,particularly in the production of bright stocks from mixed base oils such as Mid-Continent oils.

Non-wax-bearing oils may be cut in the fractionating column 40' directly into frac- Isa tions of the desired viscosity. Thus, for ex-- am ss through the pipe 50, and a heavirlubricant from the bottom of the column t ough the pipe 42. If the chargin stock contains only enough gas oil or other hght fractions to obtain an overhead roduct of the desired viscosity, a light lu ricating materialmay be taken overhead from the column 40 and collected in the receiving tank 65.

Most present day commercial methods of lubricatm oil manufacture are, I believe,

based on t e method of simple distillation or difierential vaporization with little or no fractionation of the vapor so formed. Most stills-have no fractionating devices or even partial condensers. In actual practice, the

lubricating oil in the" still may contain considerable gas-oil. The presence'of this gas oil lowers the viscosity of the lubricating oil,

p not only in proportionrto the concentration 2 of the gas oil but considerably more because viscosities are not additive. In other words, blending equal parts of two oils, one of 200 ;,viscosity and the other of 100 viscosity will j give a blendnot of 150viscosity'but of considerably less. In the reduction of petroleum oils torequired viscosity by simple distillation in a shell still, the distillation must-be carried to such a point that the gas oil con centration in the still is .low,-,which results,

86 therefore, in a large loss of valuable lubrieating oil in the gas oil vapors normally passed overhead. Byemploying'a'fractionating column according to my invention, on the other hand, I can cleanly strip the lubricating stock from inclusions of non-viscous lighter oils which may beseparated overhead without loss ofvaluable lubricants, and can sharply separate heavy viscous lubricants from those of lower viscosity. 46 In the manufacture of lubricants from wax-bearing oils it is, of course, essential to separate the wax from the -lubricatingoil in some manner, The wax present in pe- 8 troleum oils maybe classified accordingto 4 talline waxnot in pressable form, and (a) In this classification amorphous wax is wax the crystal growth of which has been practically completely prevented by inhibiting substances. 7 These substances are heat sensitive and can be destroyed by cracking; They are high boiling-and can be removed from the lower boiling lubricating fractions by counter, current fractionatiom As an example of amorphous wax it'may be noted that thewell:

known petrolatum of commerce containsa large part of itswax in the amorphous oi' ncmcrystalline state. By crystalline wax not in pressable form is meant wax the crystal growth of which has been partially inhibited, that is, to suchan extent that the crystals cannot easily 'be removed by filtratidn in a filter press. Amorphous wax and crystalline wax not in pressable form are reits state, as: (a) amorphous'wax,"(b) erysferredto collectively in this specification as non-pressable wax. Pressable wax, as the term isused herein, is wax in the form of crystals that deposit on the press cloth and on the frame of the press to form a reason- ,ably open crystal mass through the interstices of which oil can flow.

In handling wax-bearing lubricatin oils the usual shell still practice is to disti ofi successively ,the gasoline, kerosene and gas oil and then to take overhead a so-called wax distillate, the difierent fractions being conducted to separate receiving tanks. The distillation is usually conducted at atmospheric pressure, steam being employed during the later stages -to avoid excessive cracking. The wax distillate is ordinarily collected as a single fraction, but in some cases it is divided into two cuts, thevfirst cut to 0 overhead being usually much smaller t an the second. Where a'single wax distillate cut is made,-it is not pressable in the-form in which it isoriginally obtained, andthe same is true of thesecond out where two outs of wax distillate are made.- This non-pressable wax distillate must be redistilled to secure a pressable wax distillate. In redistilling this'wax distillate, which operation like the original distillation is usually carried out at atmospheric pressure, the heat treatment is intentionally made such that considerable cracking takes place; The substances inhib iting wax crystal growth areheat sensitive and aredestroyed to such an extent that wax crystals of reasonable size will grow in the 10o so-called crystalli wax-distillate taken overhead from the crystallizing still. Thiscracking operation has heretofore always been considered essential to convert the wax in the wax distillate into pressable form. The redistilled wax distillate contains the wax in pressable form and the still residues. remaining from'this second distillation is commonly-sold as a cheap lubricant or black oil. The wax is removed from the pressable no wax distillate by filtering throu h a filter press and the resulting pressed istillate is then redistilled into cuts of suitable viscosi-- ties or boiling points. It will be understood that the wax distillate contains sufiicient gas. "5

" the presence of these wax crystallization inhibitors that renders the original wax distillate in the usual'shell still operation nonpressable. I have "further discovered that these wax, crystallization inhibitors are high boiling substances that can be separated from the wax distillate by counter current'fractionation, thus making it possible to obtain directly a pressable wax distillate without the step of redistilling and cracking. For

example, traces of high boiling, resinous,

tarry or asphaltic substances in the wax distillate may act as wax crystallization 1nh1b- .itors and prevent obtaining the crystallizable wax in pressable form.- These high boiling substances appear to interfere with the growth ofthe wax crystals by retarding the movement of the crystallizable wax molecules in the solution and by coating the wax crystal nuclei. Moreover, these same inhibiting substances or other high boiling substances in the oil increase the solubility of wax in oil and oil in wax, thus interfering with the separation and proper growth of wax crystals.

According to my invention wax crystallization inhibitors are partially left in the residue of the vaporizer. The vapors leaving the vaporizer are subjected to counter current fractionation in the fractionating column as described and the high boiling, resinous, tarry and asphaltic substances are removed from the wax distillate containing the crystallizable wax thus obtaining a maximum yield of pressable wax distillate in a single operation. It will be apparent that bymy process I avoid the destruction of valuable lubricants by cracking and also avoid the heat loss incident to a second distilling operation. Furthermore, I am enabled to get a sharper separation between the crystallizable wax and the amorphous wax than is possible in prior processes. This permits me in the rimar distillation to obtain a larger part 0 the orl as directly pressable wax distillate than is ordinarily obtained as pressable distillate after the primary and crystallizing distillations. Since pressing is a less expensive operation. than either of the other well known methods of wax removal, namely, cold set tling and centrifuging, it is, of course, desirable to secure as large a proportion of the oil as is possible in the form of pressable wax distillate.

It will be seen that my process possesses three major advantages over the prior art processes in the treatment of wax-bearingoils, first, substantially no cracking takes place during the original distillation of the oil; second, the necessity of redistilling and cracking to produce a pressable wax distillate is eliminated; and third, a clean separation among the various cuts may be ob-- tained. Each of these advantages assists in obtaining a final maximum yield of valuable lubricants.

When a mixed base oil containing wax is being treated, the vaporizer residue will be relatively small as described in connection with the treatment of non-wax-bearing oils, and will contain the asphalt and a large part of the tarry wax crystallization inhibitors The fractionating co umn bottoms will com prise a heavy lubricant containing the high boiling, non-pressable waxes, but the larger proportion o the wax present in the crude will be contained in the light fraction drawn oflf through the pipe 50. This fraction is amorphous wax or mineral jelly referred to above, and in addition will contain some of the higher boiling paraflins which may be pressed only with great difliculty. The heavy lubricant drawn from the bottom of the fractionating column may be subjected to refining treatment only, or may be subjected to col settling or centrifuging followed by refining treatment. In some cases, it is advisable to combine the heavy stocks collected in the tanks 35 and 45 and subject the mixture to a cold settlin or centrifuging to remove the wax, and, i desirepili to subsequent'refining treatment such as tering.

During all of the operations above described, I- preferably maintain an absolute pressure of about 25 mm. in the vaporizer 30 y operation of the vacuum pum 67. The absolute pressure at the pump itse f will usually be appreciably less than the ressure in the vaporizer, the pressure dro t roughthe fractionating column 40 and t e connecting piping being responsible for the difference. It will be apparent that the pressures at the pump and inthe fractionating column are-absolutely immaterial except in so far as they determine the pressure in the va orizer. In order words, the function of the ow absolute pressure in the vaporizer is to enable the vaporization of the required percentage of the charging stock at a lower temperaturethan would otherwise be necessary and once this object is accomplished and the vaporshave dropped below their cracking tempera ture, the pressure under which the subsequentstarting material for my process a. reducedcruderather than a crude containing the This is adnatural gasoline and kerosene. visable in order to reduce the burden upon the lac apparatus and to make the operation more economical.

The foregoing operations have been sucillustrative runs made in accordance with I this invention on two of the three types of charging stock above discussed:

I Asphaltz'c base permeate-bearing oil Charging stock, Orange County Gulf Coast reduced crude (70% bottoms).

Charging rate, 50 gallons per hour.

Products g Viscosity Totalvaporized 88. 1 Light overhead out... 34. 6 Medium out. 34.2 60 sec. 210 F. Heavy viscous cut 19. 3 161 sec. 210 Tar bottoms 11. 7

Temperatures Outlet of heater 845-860 F. Vapor from vaporizer 719731 F. Vapor (mm column 390 F.

Pressures (absolute) Top of column-.. mm. Vaporizer. 1 r 31-32 mm. Velocity of oil in heater 1.79 ft./sec. Total time of oil in heater 112 seconds Probable time in heater at temperature above 650 F 60 seconds II. M iced base wee-bearing oz'l Charging stock, mixture of Powell and Prairie Pipe Line Midcontinent reduced crudes (47% bottoms).

Gravity, 245 A. P. I.

Charging rate, 61.5 gallons per hour.

Products m Viscosity Total vaporized 82. 5 I

Wax distillate 63. 2 29. 3 79. 5 sec. 100 F. Heavy viscous cut 19. 3 .138 sec. 210 F. Tar bottoms 17. 5 I

Temperatures 5 Outlet 01 heater 826 F.

Vapor from vaporizer 724 728 F. Vapor from column 530 F.

Pressures (absolute) Top of column 20 mm.

a rizer 36-38 mm. 50 Ve ocity of oil in heater 2.20 ttJsec. "Total time of oil in heater" 91 seconds Probable time in heater at temperature above 650 Ft. 50 seconds It will be understood that the pressures, temperatures and other data given in these runs are not in any sense limiting values, but are simply illustrative of suitable values for the particular charging stocks. In computing the velocity of the oil in the heater and the timewhich the oil is in the heater, it was assumed, first, that the oil remainsin the liquid phase throughout its passage through the heater, and second, that the average density of the oil is its density at 500 F.

In each of these runs the distillation was effected without any substantial cracking taking place even though the final temperature The following are lar heater. .It will be noted that the lowest at the outlet of the heater was well above the 1cracking temperature of the charging. stoc t. plished without the use-of steam in the tubu- Moreover, this result was accom--- absolute pressure used in the vaporizer in either of these runs was 31 mm., but I have found it advisable in some instances to uti-- lize considerably lower pressures in the vaporizer. Ordinarily, however, I maintain an absolute pressure in the vaporizer in the neighborhood oft25 mm. of mercury.

At first glance the velocity of the oil in the neighborhood of two feet er second, appears to be far outside the pre erred range of veter of 0.49. With pipe of this internalj diameter, a velocityof about two feet per secs end is sufiicient to avoid any injurious skin effect and to secure a turbulent flow. The velocity of ten feet per second referred to above is applicable to tubes'of the ordinary sizes used in commercial pipe stills. In this connection it may be stated here that the velocity of ten feet per second is higher than that ordinarily used' in such pipe stills.

heater in the foregoing runs, which'is in the Knowing the velocity required with one size of pipewhenheating a given oil to a specified maximum temperature to obtain a suitable temperature gradient between the oil at the outside of the pi e'and that at the center, that is to say, t e velocity required. to. I

avoid injurlo'us skin efiect, it is possible to compute by well known formulae the velocity which must be maintained to obtain the same temperature gradient when using a pipe still having pipes ofa different size. In other words, the relationship between velocity and temperature gradient has been already drawings, these figures disclose a modified form of pipe still which may be advantageously employed in carrying out my process. The furnace 80 is provided with a burner 81 arranged at one end' of the furnace near the floor thereof and discharging into a re diant heat or combustion chamber 82. The products of combustion are forced to pass upwardly over a bridge wall 83, down through a convection heat chamber 84 and thence u wardly through a stack 85. A depending aflie 86 is arranged in front of the bridge wall 83, forming a passageway 87 between the bridge Wall and the baflle through preferablyso designed that the oil does. not

reach a cracking temperature until it enters the coils 90.

It will be understood that in carrying out the process of my invention, the pipe still 80 is simply-substituted for. the pipe still 10 in the plant shown in Figure. 1. The pipe still 80 has the advantage of being cons'iderably simpler in construction than the pipe still 10 andinay be used whenever it is not necessary to divide the oil t6 be heated into a plurality of streams as shown in Fig- "ure 1.

Figure 4 shows still. another form of pipe still in which the oil is passed through t e convection heat section in a single stream and is then split into a plurality of streams be fore passing through the radiant heat section in which it reaches a cracking temperature. In this figure, 95 represents the pipe still as a whole, and the constructional details of the furnace may be exactlythe same as those shown in Figures 2 and 3 except for the arrangement of the heating tubes.

The same reference characters are therefore used for similar parts. In the furnace illustrated in Figure 4, the oil to be heated is introduced into the heating coils 89 located in the convection heat chamber 84 and passes thence into a manifold 96 from which the oil is delivered to the radiant heat or high temperature section of the furnace. A plurality of high temperature heating coil-s 97, in this instance four, are located along the roof of the combustion chamber 82, and have their inlet ends connected to the manifold 96 and their outlet ends to a manifold 98. A valve 99 is located at the inlet endof each (if the coils 97 to regulate the. quantity of oil flowing therethrough. If desired, a separate pump may be placed at the inlet of each of the coils 97 to pick up the preheated oil from the manifold 96 and force it through'the. high temperature coils. I

In the pipestill 105 shown in Figure 5, a

burner 106 is located in a small combustion.

chamber 107 anterior to the main radiant heat chamber 82. The heating tubes 89 located in the convection heat chamber 84 discharge into a radiant heat coil 108 located along the roof of the chamber 82. The coil 108, is formed of tubes of smaller diameter than those in' the coil 89, and is connected to a helical coil 109 located directly in front of the burner 106 and through which: the

- products of combustion from the burner'pass.

The coil 109 is made of tubing still smaller in diameter than that of the coil 108. .-By this construction the oil is given a final very short exposure to the highest temperature action, and that the rate of cracking increases very rapidly as the temperature is raised.

WVhen, therefore, I refer to a temperature below the cracking temperature, Iintend to define a temperature such that even though a normal time be allowed for the .reaction,

no substantial amount of cracking will occur,

and when I refer to a temperature above the cracking temperature, I mean a temperature such that under such time conditions a substantial amount of cracking will occur.

VVher'e thev expression temperature gradient is employed in the claims, it is intended to mean the difference in temperature between the oil near the surface of the tubes of the tubular heater and that at the center of the tubes. y

' It will be understood that my invention is not limited to the specific embodiments described and that various deviations may be made therefrom. It will be apparent also that some of the features of my invention may be used entirely independently of the employment of other features herein disclosed. I desire to be limited, therefore, only by the scope of the appended claims. I I

I. The method of preparing. lubricants from non-overhead wax-bearing lubricating oil which comprises passing the material under treatment under an initial pressure through a tubular heater, heating said material during its passage through said heater-to a temperature above its cracking temperature, the period during which the material is heated above its cracking temperature and the velocity of the material during said period ,being such. that no substantial amount of cracking ofthe material takes place, subjecting said material to flash vaporization'under a low absolute pressure to vaporize a substantial portion thereof and to separate certain wax crystallization inhibitors therefrom, subjecting the resulting vapors to counter-current fractionation, and

cutting said lubricants into arelatively light lubricating fraction containing wax in pressable form and-a relatively heavy lubricating fraction containing the balance of the wax crystallization inhibitors.

2. The method of preparinglubricants from wax-bearing lubricating oil which comprises passing the material under treatment under aninitial pressure through a tubular heater, heating said material during its passage, through said heater to a temperature of over 750 F., the period during which the material is heated above its cracking temperature being less than 35' seconds and the velocity of the material during said period being such as to produce a low temperature gradient, subjecting said material to flash vaporization to vaporize a substantial portion thereof and to separate certain wax crystallization inhibitors therefrom, subjecting the resulting vapors to counter-current fractionation, and cutting said lubricants into a relatively light lubricating fraction containing wax in pressable form and a relatively heavy lubricating fraction containing the balance of the wax crystallization inhibitors.

3. The method of preparing lubricants from wax-bearing lubricating oil which comprises passing the material under treatment under an initial pressure in the absence of steam through a tubular heater, heating said material during its passage through said heater to a temperature of over 750 F., the period during which the material is heated above its cracking temperature being less than 35 seconds and the velocity of the material during said period being such as to produce a low temperature gradient, 'subjecting said material to flash vaporization under a low. absolute pressure to vaporize a substantial portion thereof and to separate.

certain wax crystallization inhibitors therefrom, subjecting the resulting vapors to counter-current fractionation, and cutting said lubricantsinto a relatively light lubrieating fraction containin wax in form and a relatively eavy lu ricating fraction containing the balance of the wax crystallization inhibitors.

4. The method of preparing lubricants from non-overhead wax-bearing lubricating oil which comprises heating the oil in a con fined flowing stream to a point well above its cracking temperature for a period of time insuificient to cause any substantial amount of cracking of the oil subjectin said oil to flash vaporization under a low a solute pressure to vaporize a substantial portion thereof and to separate certain wax crystallization inhibitors therefrom, subjecting the resulting vapors to counter-current fractionation,

and cutting said lubricants into a relatively light lubricating fraction containing wax in {from the remaining vapors a directly pressable wax distillate.

6. The method of preparing lubricants from non-overhead wax-bearin lubicating oil which comprises passing t e material under treatment through a tubular heater, heating said material during its passage through said heater to a temperature above its cracking temperature, the period during which said material is heated above its cracking temperature being such thatno substantial amount of cracking of the material takes said material during its passage place, subjecting said material to flash vaporization under a low absolute pressure to vaporize asubstantial portion thereof, subjecting. the resulting vapors to counter-current fractionation to separate wax crystallization inhibitors therefrom, withdrawing the remaining vapors, and condensing the same to form a directly pressable wax distillate containing the major portion of the crystallizable wax initially present in the material.

In testimony whereof, I have signed my name to this specification this 27th day of February, 1928.

' EUGENE H'. LESLIE.

pressable pressable form and a relativeli heavy lubrieating fraction containing the alance of the wax c stallization inhibltors.

. 5. 0 method of preparing lubricants

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