US2177664A - Distillation and purification of carbonizable organic materials - Google Patents

Description

y A. P. LEE DISTILLATIN AND PURIFICATION OF CARBONIZABLE ORGANIC MATERIALS Filed June 24, 1936 Oct. 31, 1939.

' ATTORNEY.

Patented Oct. 3l, 1939 PATENT lol-FICE DISTILLATION AND PURlFICATI-ON F CAR- BONIZABLE ORGANIC man Porter n, New York. N. Y.

Application June 24. 1936, Serial No. 86,912 e claims` (ci. 2oz-5s);

' This invention relates to improvements in methods of distillation and puriiication of such organic materials as are readily charred or carbonized when heated to temperatures` in the 5 neighborhood of their' volatilization points, more particularly' when subjected to local overheating vdue to unequal contact with the heat transfer medium. An important example of suchmaterials is found in mixed fatty acids, the product l0 of hydrolysis of tallows, greases, fatty oils, soapstocks and similar products.

Distillation of .such mixed fatty acids in batch, or Senn-continuous' processes Lhas-been carried out in industry for many years in -various countries,

the methods being well-known to those skilled in the art; 'I'he usual equipment heretofore employed has been a reheated batch-typesteam still operated under atmospheric or subatmospheric pressure. Superheated steam has been generally injected into the mass of material in the still'in order that the partial pressure of the steam may reduce the distillation temperature. Condensation has been carried out generally in tubular surface condensers interposed between 'the still and the vacuum-producing apparatus, -if vacuum is employed, or merely connected to the vaporl outlet of the still in atmospheric distillation outfits. In the distillation of fatty'acids in suchA apparatus there has been considerable loss due to local overheating of the still bottom, particularly of the lm of material directly adjacent to the bottom; also in a considerable zone near it. This overheating has caused marked voharring .and

' l degradation of the stock being distilled, resulting in low yields of distilled products and high yields of tar or pitch. There has been also considerable damage -to the still itself, necessitating frequent renewalof the still bottom.

In recent years various efforts have been di 40 recte'd toward improvement of equipment and processesfor distillation of fatty acids-and similar materials. Most methods proposed have attempted to reduce the percentage of carbonization by reducing the time during which the stock to be '45 distilled is subjected to heating action, chiefly' by heating said stock while it is in motion through (or other inert gas or vapor) is permitted to contact the heated stock, intimate contact being secured by,bailies or Aother well-known means of securing counter-current travel and intimateadmixture of the steam with the heated stock. 5

' In commercial application of these principles to the distillation of fatty acids and other similar delicate organic products, one of the dilculties to be overcome is local overheating of the charge in the course of passage through the tubes of the 10 heating zone, due to the difficulty of preventing the formation of avsluggish lm of material on the inner surface of the tube. It is a well-known principle of chemical engineering that no-matter how turbulent the now of the' main body of a l5 stream through a tube, there must be a 111m of uid moving in viscous or sluggish flow in the outer annular portion of the cross-section of the tube, that is, near the wall of the tube. The rate of heat thransferthrough such a lm is very 20 low, therefore when it is necessary to heat the entire contents of the tube to a temperature near the decomposition point there is great danger of decomposing and (in'the case of delicate organic materials) carbonizing the material in the film. 25

Such carbonizing is progressive and once started, rapidly proceeds toward the center of the tube as new and thicker sluggish films are formed on'the rough surfacel of the carbon which becomes de- -posited upon the inner surface of the tube. It 30 becomes apparent, then, that in applying heat to a tube heater for distillation of those organic products which decompose at temperatures only slightly above their respective vaporization points, it is necessary to control the temperature of the heat transfer medium within very close limits,

relatively near the temperature'desired Vin the heated stock, or to seek means of overcoming the above-described lm effect.

Methods proposed for close control of heating in a tube for distillation purposes have included lo, such expedients as- 1. Immersion ofthe tube in a lead or oil bath,`

heated by suitable means.

2. Transfer of heat to the tube through the medium of superheated steam, which is inturn i heated by gases of combustion in a suitable iur-- heating and carbonization in the tube, thus permltting the use of such economicalsmeans of heat transfer to the stock in the tube as is provided by gases from the combustion of any suitable fuel. This invention also provides new methods 'of con-l densation which facilitate the production of animproved distillate and a new method of circu` ble to other organic materials of similar lcharac-v teristics and is not limited to fatty acids.v

In order that my invention may-be clearly understood, I refer to the drawing herewith in which:

moisture.

Figure 1 is an elevation, partly in section, of the apparatus in one form of design.

Figure 2 is a detail of one form of the steam or inert gas atomizer for atomization of the material to be distilled.

Referring to Figure l, which is an elevation, partly in section, of suitable equipment for carrying out of my process, pipe-line I is the chargingline through which the mixture of fatty acids or fatty-acid-containing stock is fed to the apparatus by gravity or by other suitablemeans. In the usual operation of commercial fatty acid distillation the stock' fed may contain from 90% to 98% of mixed fatty acids, the remainder consisting of neutral fat, unsaponifiable material and traces of The material fed into the system through charging line I may be at any suitable temperature for its pipe-line flow, varying from room temperature for liquid fatty acids to 150- 175 F. for higher melting mixtures. The stock to be distilled is fed thus through pipeline I into and through the shell-and-tube heat exchanger` 2, where it is heated by means of any suitable hot fluid, preferably steam, to any convenient temperature of initial heat or preheat, such as225 to 300 F., and preferably not over 275 F., for avoidance of local overheating and consequent decomposition. The temperature of the heating fluid may be from 300 to 375 F. or lower, but not substantially higher. l

From the preheater 2 the stock to be distilled passes through the pipeline 3 to'the atomizer 4, where it is thoroughly mixed, atomized and sprayed with from five to fifty or more times its own volume of steam. The effect of this atomization is to break up the solid stream of owing liquid into a mist or spray of dissociated liquid particles or droplets, each being fully surrounded and encased by a protective atmosphere of steam. In this mixture the steam forms a; continuous phase and the stock a discontinuous phase consisting of a plurality of separate particles. The possibility of formation of any film of liquid. on the interior surfaces of thetubes 5, 5 in the heater, through which the mixture next passes is thus avoided. In this manner any local overheating,

decomposition, charring or carboniratiomis prevented. The atomization with steam also increases the velocity of flow and the turbulence,Y thus contributing further to the avoidance of nlm formation in the tubes of the heater. Y

The atomization of the stock with steam may be accomplished by anysuitable means, such as a steam ejector, revolving vanes, spray nozzles, mixing valve, burner-type atomizer or any suitable combination of such'means. In the processherein described the atomizing means consists of a steam-ejector-type mixing valve as shown in cross-section in Figure 2.

The preheated charging stock is supplied under pressure through pipe 3 while superheated or saturated steam is supplied at slightly higher pressure through valve b. Valve c is a throttle valve by means of which the volume of steam used in mixing can be regulated within close limits. The steam passing through the .constricted throat d exerts a suction effect upon the stock surrounding the nozzle e in the chamber f, drawing the stock in the form4 of fine atomized drops or particles' Awhich case the atomizing gas would preferably be preheated to a' temperature equal to or slightly higher than that of the stock to 'be atomized. When steam is used it may be saturated or slightly superheated steam.

Thel atomized mixture of stock and steam passes through the heating tubes 5, 5 of the mist heater coil, (Figure 1), being heated therein by direct contact on the outer Walls of the tubes of the gases of combustion of suitable fuel, as for example, natural gas, fuel oil or coal. In one application of my invention, ywastegases whichhave previously been utilized for superheating steam are employed to heat the mixture of steam and fatty acids passing through the tubes 5, 5, means being provided to control the temperature of the gases .when contacting the tubes 5, 5, raising this temperature by admission throughV bypass I0 (shown in closed position) of some gases not previously utilized and lowering it by admission of air through `the tempering damper or dampers, Ilfand Ila. Suitable temperature of gases entering the stock-steam heater pass 9a have'been found to be between 650 and 950 F., preferably 850 F.

The atomized mixture .of Vsteam and stock is heated very rapidly while passing through the tubes 5, 5 of the pass 9a, a convenient ratebeing about 800 F. per minute, the 'heating being car- 'upon' the composition of the stock and the absolute pressure conditions in the distilling apparatus. After being heated in `the .tubes 5, 5, where the pressure is maintained at an average of 8 lbs. per square inch gauge or less, the mixture of stock and steam passesthrough the pipe 6 and the control valve 8 into the distillation chamber I2, which is maintained `under relatively low subatmospheric pressure, from 1" to 10" mercury absolute, and preferably about 2" absolute in its upper portion. although the operation may be performed atother pressures, .depending upon the amount of distillation steam employed. The distillation chamber may take any well-known form, as, for example, a plain cylinder, a tower packed with materialfor increasing evaporative surfaceI a screen-bao tower or a bubble-cap tray tower.l In this instance thel chamber is shown as a bubble-cap plate When ,the atomized mixture of'steam and stocl: enters the vacuum chamber I2 through the valve 3, the steam expands, and the stock, being above its'volatilizationtemperature for the pressure conditions of the vacuum chamber, commences to volatilize rapidly. Both these conditions cause considerable drop in temperature in the stock, which drop` amounts in practice to 40 to 90 F.

In the instance shown the stock and steam mixture is introduced just above the lowest upper tray I3c of the bubble tower. The steam and the immediately vaporized fatty acids rise in the tower toward the next tray above, while that part of the stock which remains unvaporized falls toward the tray I3c. The mixed vapors pass through the chimneys and caps inthe next upper tray I3b and much of the vaporized fatty acids is condensed, forming on ,the tray a pool of fatty acids of considerably purer quality than the original stock. The depth of this poolis controlled by the overflow pipe ISb, which carries to the next lower tray all condensation in I1 and superheated in the pipe coil I8 in furnace 9 to ilnal temperature of 900 to 1000 F. In passing through the pressure reducing and regulating valve I9, its pressure is reduced to 3-10 lbs.

per square inch gauge and its temperature falls to 750-900 F., normally 850i F. Any suitable fuel is burned at the burner 35 in furnace 9, the

gases of combustion passing over the steam superheating coil I8 in space 36, then through pass 9a over the heatingtubes 5, 5' through which latter tubes is passed the atomized stock-steam mixture which is to be distilled, the gases passing ilnally out through the breeching 38 and the stack 39. Control of temperature of the gases .passing over the tubes 5, 5 is 'secured by means of the hot-gas bypass damper I0 and the tempering dampers II and IIa.

The reduced-pressure superheated steam is conducted through pipe 20, control valve 2I and nozzle 22 to the center of the tower I2 at a point just below the bottom bubble-cap plate I3f. This superheated steam serves two purposes, rst, to aid distillation of the fatty acids and second, to supply heat to replace that consumed in evaporation of the stock and in radiation :from the apparatus.

As the steam expands through the control valve 2I out of thesupply pipe zone of 'pressure of 3 to 10 lbs. per square inch gauge, into the .bottom area o'f the tower at pressure of 21A" to 3" of mercury absolute, there is marked cooling of' the steam due to expansion, which enables rregulation of the temperature of this bottom area at between' 575 and 650 F., when using steam at temperatures betweenl 800 and 900 F. before expansion into the tower.

the surplus stock over-lows to the next lower tray I 3d, where it forms a new pool of materiall lower in fatty acid content than the original stock. In similar manner pools are formed on each succeeding tray below the point where the atomized stock-steam mixture enters the tower.

As the superheated steam entering the bottom of the tower expands, rises through the bubblecap chimneys and is distributed by the bubblevcaps through the pool of material on the lowest is repeated on each succeeding bubble tray from bottom to top of the tower, the rising vapor mixture becoming progressively richer in distillate vapors as the top tray is approached and the descending unvaporized stock becoming progressively poorer in vaporizable material as it approaches the bottom tray.

'Ihe rising mixed vapors of superheated steam and distillate become progressively cooler as they pass upwardl through the tower. from the effects of expansion, evaporation and radiation. The descending stream of liquid material likewise tends to b'ecome progressively cooler in descending through the tower, from the effects of evaporation and radiation. As the operation progresses, this tendency of the descending stock to become cooler isovercome', in 'part by the heating effect of partial condensation of distillate vapors in the pool of liquid on each tray and partly by the heat supplied by the superheated steam, so that when the operation reaches the desired'state of continuous equilibrium, the descending liquid stock increases in temperature on each succeeding lower tray, while the ascending vapors decrease in temperature as they rise through the tower. The liquid residue flowing away from the bottom tray I3f, in fatty acid distillation is at a temperature of 505 to 595 F. and preferably 580 F. when distilling standard mixed fatty acids from tallow grease. It is to be noted that for best results. this temperature of material leaving the bottom tray may suitably be varied over a wide range, depending upon the type of material treated. For certain fatty acids of vegetable origin, this bottom' tray temperature suitably may be carried as low as 400 F., or even lower.

'Ihe residue flows from the bottom plate through the overflow pipe I6! into the cup seal 23, out of which ii falls to the bottom of the tower, forming there a pool, the depth of which is controlled by the inverted syphon pipe-loop 2l.

Another feature of my invention, is my method of recycling and reheating residues for further recovery of distillate therefrom. It is well known that almost any distilling column can be reduced in overall height and number of trays by reuxing a portion of the residue to the lower portion of the tower (below the feed inlet). In the distillation of fatty acids, tars, waxes and similar` heavy, viscous materials, the residues are of such heavy, tarry nature, even at the elevated tempern ature of the still, that recirculation by ordinaryI means becomes difllcult and often impossible. In addition such residues tend to cool rapidly, becoming on cooling very much more viscous.

In my invention I utilize a lift-pump operated by superheated steam at a temperature considerably above that of the residues to draw such residues from the bottom of the vacuum chamber l2 through the skimming pipe 25 and the liftpump 26, discharging through the discharge pipe 21 and the valve 28 into the distillation chamber at a point above the third tray from bottom,

i3d, or alternatively to the next lower tray Ile through the valve 28a, or through both these' valves to both the trays simultaneously. Superheated steam at 3 to 10 lbs. gauge pressure and into the tower.

temperature of about 850 F. is taken from the for operation of the lift-pump 26.

The use of the, lift-pump operated by superheated steam has several advantages. The temperature of the residues is raised, thus aiding further distillation of Ivaporizable material from these residues. The superheated steam used for the lift-pump mixes with the residues and its vapor pressure is utilizable in the distillationo from the trays above the point of its entrance 'I'he addition yof the extra heat units of this superheated steam is useful in economical` replacement of heat lost by radiation,V from the central and upper portions of the tower and in maintenance of vaporizing temperatures on the upper plates.

Despite the admixture of steam with the residues and .the injection of this mixture into the median portion of` the distilling zone, in my process no entrainment of coloring' matter from the residues is apparent in the distilled fatty acid vapors leaving the upper exit of the tower.

By variation of the volume of superheated steam fed to the lift-pump, the quality and amount of final residue can be controlled, the amount recirculated controlling the net amount of nal residue outflow. As the amount of material recirculated is increased, the amount of distillation steam added to the tower through the 'supply pipe nozzle 22 likewise must be increased.

to provide for the increasing distillation burden on thelower trays. The amount of steam utilized by the recycling lift-pump, however, is also used as distillation steam and does not increase the total steam input which would be required to obtain comparable distillation results in similar apparatus without this feature.

The heavier residues, sinking to the lowest point of the pool formed on the tower bottom and comprising all surplus which is not recycled by the lift-pump 26, flow through the pipe 3| and inverted syphon 24 into the pitch receiver 32, which is connected to the tower I2 by the vacuum-vent pipes 33 and 33a. The pitch receiver is shut off intermittently from the vacuum tower and, by means of steam pressure through the line 34 from the header 1, the pitch is 4discharged from the receiver 32 to storage, through valve 1,5 and pipe 16. When the pitch receiver is being discharged. the residues are permitted to accumulate further in.i the bottom `of the tower |2,"to the extent of surplus above the amountbeing -recirculated, without" deleterious -effect upon the color of the distillate. In fact,

after they continuous operation of the distilling apparatus has become stabilized, a vpool of residue is maintained on the bottomv of the tower I2, to the depth permitted by the height of the inverted syphon loop 24. This pool is heated by the superheated steam issuing from the nozzle 22 just above the pool and is also heated by the metal of the tower bottom, which in turn, derives its heat from the superheated steam. In operation the temperature of the residue pool is maintained at from 15 to 50 above that of the partially nished stock on the bottom tray l3f. The vapors of pure f atty acids or other disilled material, which are volatilized from the upper tray.- Ila. of the flashing chamber, byl heat from the condensation of less pure vapors in the pool ot liquid on that tray, and which are mixed with vapors of supherheated steam, may be freed of entrained liquid by any well-known means 4(such as the baille-plate 40 in this instance), and

then condensed, also by any means well-known to those skilled in the arts of distillation; the nal residual water vapors, which contain traces of distillate, being condensed in the vacuum'producing apparatus or allowed to escape to the atmosphere (in atmospheric pressure adaptations of my process). l

-In practice heretofore in fatty acid distillation it has been customary to condense the distillate at such temperatures and pressures and under such conditions that the condensate obtained contained `considerable liquid water or at least traces thereof.

Another new feature of my invention is a new and unique means of distillate condensation, whereby the condensate in a distillation process is recovered entirely free of any trace of liquid water. Its application to the process of fatty acid distillation herein described is as follows:

As stated above., the pure distillate vapors mixed with superheated steam rise from the top l). The mixed vapors travel through the annular space surrounding the entranment baille 40,

' pass above the bailleand out of the distillation chamber through the vapor nozzle 4I and the elbow 42. Exit vapor temperaturefor fatty acids ymay be 375 to- 475 F. (preferably 415 to 430 F. for the mixed fatty acids of tallow greases).

In applying'the well-known water spray condensation system at points 43 and/or 44, 45, it was found that the distillate recovered in the receiver-separator 46 was small in quantity and contained appreciable amounts of free liquid water as well as some emulsiled water. In my invention, surprisingly, I overcome these drawbacks entirely by heating the water us'ed in the condensing sprays nearly to its boiling point at atmospheric pressure. This heatedwater is conveyed under positive pressure to the condensing spray-heads and when4 released through these spray-heads into the reduced pressure zone .of the vapor pipes 41 and 48, all of the water is completely vaporized, absorbing the heat necessary for its vaporiza-tion from the mixed distillate and superheated steam vapors coming from the tower I2. `This absorption of heat causes the bulk of the distillate vaporsl to condense as liquid, entirely freeof any liquid water. This liquid condensate may be collected inthe receiver-separator 48.

Description of the spray-.condensation system as operated in my invention is as -follows (refer to Figure l):

SteamV at lbs. gauge pressure is taken from the main steam header ,fl through the valve 49 and the pipe line 50 to the steam space of the preheater 2 where it is utilized to preheat the charging stock of the still by means of heat-- 'tray na of the disuuauon chamber l2 (Figure the reservoir 54.

exchange. The steam condenses in the preheater and the condensate water is'automatically removed through the pipe line l by the steam trap 82, discharging through the pipe line 83 into 'I'he pure condensed water is pumped by the pump 55 through the heating coil 58 in the heat exchanger 51 and on through the pipe line 58 to the spray nozzles at 43, 44 and 45. These nozzles may be utilized in any suitable manner, each being controlled by a valve.

the steam main 1 through the pipe line 4a and reduced to 15 to 20 lbs. gauge pressure by means of the pressure-reducing and regulating valve 4b.

v A portion of this steain 1s uunzed for atomization of the charging stock in the steam-atomizer 4 and another portion passes to the heat exchanger 81 through the pipe line 4c. In the heat exchanger 51, this steam is used to heat the water passing through the coil 56. This water is heated to 180 to 205 F. and preferably as high as possible without substantial vaporization in the coil 58 or the pipe line 58. Operation of the pump 55 is so controlled that a pressureof from 6 to 12 lbs., normally 8lbs. gauge is maintained in the spray water supply pipe 58 at the gauge point 58 close to the spray-nozzle locations.

'I'he meansherein described for supplyingv hot water to the spray-nozzles is one example only and its description is not to be 'construed 'as limiting my invention, as any suitable means of heatingf'the water may be employed, my invention being comprised in the heating of water or other vaporizable liquid for use in spray condensation, to insure full absorption of the latent heat of vaporization when thev liquid is discharged through the spray-nozzle or other spray device. The sensiblev heat which is added to the water -in the heating is sol small in quantity in proportion to the latent heat which is absorbed. when the water is vaporized that it is not an important factor.

If cold, or only moderately warm water is used for spray condensation in vacuum apparatus, the water will be vaporized eventually, but the advantage of using water or other liquid which has been heated to a temperature closely approaching its atmospheric vaporization point is to be found in the rapidity with which it will be completely vaporized under the reduced pressure conditions in the vacuum apparatus.; It

, is obvious that the water or other liquid selected as a spray condensation means must have a vaporization point well below thatv of the distillate to be condensed and must have a relatively latent heat of vaporization for cooling and condensirg purposes; third, complete freedom of the condensatefrom traces of'the cooling liquid.

The spray condensing system may be coni- 4 bined with any suitable collecting system for recovery of the condensed distillate.A In the example shown (Figure 1), the mixed Avapors of steam and distillate entering the'outlet pipe 4I at '415 to 430 F., are cooled to 325? to '365 (normally. 350 F.)'by means of the hot- water sprays 43, 44 and 45. Passing through the vapor pipe 41 into the receiver-separator 46, the bulk of the distillate vapors separates out as liquid fatty acids in the receiver-separator, from which the liquid condensate ilows by gravity through the pipeline 80, the shell-and-tube cooler 6| and the pipe 82 to the, collector 63. In passing through the shell-and-tube cooler 6|, the liquid condensate is cooled to 125 to 175 (normally 135 F.) by means of water or other cooling fluid and collected in a pure moisture-free state in the collector 88. .From this container it may be pumpedcontinuously by means of the pump 64 and the pipe 88 to a receiving and storage tank (not shown). The collector 63 iskjoined to the receiver-separator 48 by theadditional vacuum- Aventfpipe 88.

After collection of the bulk of the condensed distillate in the receiver-separator 46, the residual water vapors, containing a small percentage of uncondesed distillate vapors, pass through the vapor pipe 48 to the shell-and-tube condenser 81, wherethe vapor stream is further cooled to 115 to 140 F.- (normally 120 FJ, by heat exchange with water or other suitable cooling iluid. Here the remaining distillate vapors are condensed, the liquid condensate collecting in the hot-well receiver 88 and flowing by gravity through the pipe 68 tothe second collector 18, from ,which this condensate is pumped continuously through the pipe 1I by means of the pump 12 to a,receiving and storage tank (not bulk of the distillate vapors being condensed byv the spray. condensing system.

The ilnal water vapor, practically free of dis .tillate (vapor or liquid), leayes the shell-andtube condenser 81 by the vapor pipe 14, passing to standard vacuum apparatus of any suitable type (not shown). Y

As an example of-operation under the process hereinbefore lvdescribed, the following distillation has been carriedout, vThe distillingbubble tray column utilized1 -was .approximately 15' high .and f 6'6" ininternal diameter at the top"(cross.sec tional area 33.2 square feet). The tower contained sixbubble trays spaced 22" apart, the

bottom tray being 30l above the bottom of the tower. The upper tray contained 84 bubble caps. each cap being 5" in external diameter. The total effective distilling area of the upper plate was therefore 21.75 square feet. The top vapor outlet of the towerv was 16". internal diameter. Below the vapor outlet a conical shaped baille plate' 41" in greatest diameter was inserted. The ,annular space through which all vaporspassed between this bai'e plate and the upper portion of the tower wall was 28.25 square feet in area.

Steam was admitted to the tower through a 3 pipe below the bottom tray, but above the maximum height of the pool of residue on the bottom of the A tower. The vmaterial to be distilled, after atomization by steam, was admitted to the heater through two two-inch tubes inparallel and af-ter leaving the heating zone the two portions were combined in one three-inch pipe through -which the mist Aof atomized .fatty acids and )steam enteredI the distilling tower'in its upper portion. Pressure slightly in excess Materials, which are well-known to those skilled in the art of distillation.)

During this period 3202 lbs. of steam were fed to the charge through the atomizing devic an average ofI 35 lbs. per hour.

There was added also a total of 86,790 lbs. ofl superheated steam (an average of 949.5 lbs. per hour), through the three-inch pipe at the bottom of the tower and through the bottoms recirculating lift-pump. The stream of fatty acids entered the steam preheater at about 160 F.

and was heated therein to temperature of 215 to 230 F. with normal temperature of 225 F. It then passed to the atomizing and steam-mixing valve wherein it was atomized and thoroughly mixed with an average of 35 lbs. of steam per 1977 lbs. of charge, or approximately 29 parts of steam by volume to each part of fatty acid charge.

This atomized mixture of fatty acids and steam entered the heating mist- heater tubes 5, 5 at a temperature of 227 F. and was heated therein to 495 to 530 F. with a normal temperature of 510 F. Passing then to the d istilling column through the line 6 and the valve 8, the atomized mixture entered the column above the tray I3c and was cooled by expansion and evaporation so that the temperature of the liquid pool formed on thel tray I3c was 425 to 440 F., normally 430 F.

A large portion of the fatty acids was-vaporized. at once and -passed upward as vapor through the distilling column. The unvaporized portion formed a pool on the tray |3c and overflowed therefrom to the lower trays in sucession. As the unvaporized residue of the stock descended through the tower, successive additional portions of the fatty acids were vaporlzed from each tray and the temperature o f theresidue gradually rose until on the bottom tray 3f) the temperature was 525 to 550 FI. with normal temperature of 525 F. From this tray the remaining unvaporized residue overilowed into the cup 23 and thence to the bottom of the tower. the bottom of the tower reached the height of the intake of 'pipe 25, 4 inches above the bottom of the tower', they lift-pump 26 commenced drawing the residue through the pipe 25, mixing it with superheated steam to reheat it and discharging it above the plate I 3d where it joined the stream of unvaporized stock descending through 'the distilling column. Whenthe total of unvaport ized stock descending in the tower became greater than the amount returned by the liftpump to plate i3d, a pool was formed in the bottom of the tower. The depth of thispool was controlled (by the outlet pipe loop 24) at 13 .inches above Athe bottommf the tower., When were as follows:

When the pool of residue so formed in from the pipeline 34.

By means of the superheated steam entering the distilling column and in the lift-pump 26, the temperature of the recycling stock and of the descending stock in the'lower portion of the column was gradually raised until the temperature on the bottom tray became 580 to 610 F.,

normally 595 F. and the temperature of thel pool o f residue in the bottom of the tower became 610 to 635 F., normally 615 F.

'I'he vapors rising in the'distilling -column had an exit temperature of 410 to 430 F., normally 420 F. and were cooled immediately upon leaving 'the tower, so that the residual vapors leaving the receiver-separator 46 had a temperature of 340 to 367 F., normally 350 F. In the shelland-tube condenser 61, the vapors were further cooled to an `eidt temperature of to 140, normally F. and here substantially the entire remainder of the uncondensed fatty acid vapors was condensed, collecting in the hot-well 68 and flowing to the second collector 10. The

' condensed fatty acids flowing from the receiverseparator I6 were cooled in the shell-and-tubev cooler 6| to 125 to 160F., normally 135 F. This condensate was free of water. The condensates from both collectors were pumped to a of steam pressure admitted to the receiver 32 single storage tank, where they were combined in anticipation of further processing or shipment.

The temperature ofthe water used in the sprays' was 198 to 200 F., normally 200 F. The pressure of this water in' the supply pipe near the spray-outlets wa's 3 to 8 lbs. per square inch, normally 6'lbs. per square inch, above atmospheric pressure.

I The plant steam pressure utilized was 148 lbs.

'per square inch gauge with total temperature of 365 F. 'I'he superheated steam had 'pressure of 6.5 lbs. gauge and temperature of 850 F. before entering the bottom of the tower and the lift-pump, variations of pressure being observed between 5 lbs. and 7 lbs. gauge and temperature range from 830 to 880 F. vThe pressure of steam before entering the atomizing mixer was 18 lbs. gauge, temperature 255 F.

Absolute pressures maintained in the system Inches of mercury At the vacuum condenser 0.5 At the shell-and-tube`condenser 1.0 1.5 At the receiver-separator 1.5 2.0 At the tower top 1.752.25 Aty the `tower bottom na 2.5 3.0

The yield was as follows:

Pounds 4Percent Dumme 113,390 95.8 Pitch i645 3.1 ses 0.5

My new process may be used likewisein other distillations where it is desirable to protect the .charge from local overheating in passing through tubes in a'heating zone. It may be used also for the d eodorization and/or purification of fatty oils or mineral oils or other delicate organic substances containing volatile components. The fatty acids mentioned in the foregoing can be substituted, for instance, by petroleum oils, particularly lubricant stocks, or by glycerine, without' any change of procedure other than those which would be evident from a knowledge loi? the f chemical and physical properties of those materials. 1

The foregoing detailed description has been given only for clarity of understanding and no unnecessary limitations should be understood therefrom, but'theappended claims should be construed as broadly as permissible, in view of the prior art.

What I claim is:

1. In a process for distillation of organic liquids with avoidance of decomposition, the steps which comprise atomizing `such liquid at atmos-A pheric or higher pressure with not less than approximately ve times its own volume of suitable inertgas to form an atomized mist consisting ofa continuous phase of said inert gas containing and surrounding a discontinuous phase of said liquid, heating said atomized mist as such in a continuous tubular structure to a temperature below the initial vaporization temperature of said liquid at the pressure of4 said heating, but which temperatureis higher than the initial vaporization temperature oi' said liquid at a subsequent sub-atmospheric distilling pressure and is within the normal temperature range of incipient decomposition of said liquid if subjected to flow as a liquid'stream through a heated tube, expanding said heated atomized mist lthrough suitable control means into a distilling zone of` sub-atmospheric pressure and passing inert gas into said distilling zone to promote vaporization of liquid from said atomized mist.

2. In a process for distillation of fatty acids with avoidance of decomposition, the steps which comprise atomizing `material containing fatty acid at atmospheric or higher pressure with not less than approximately ve times its own'volurne of suitable inert gas to form an atomized mist consisting of a continuous phase of said inert gas containing and surrounding a discon-f` tinuous phase of said material, heating said atomized mi t as such in a continuous tubular Y s Vvprises'moderatelyl preheating such liquid below structure to a temperature below the initial vaporization temperature of the contained fatty acid at the pressure of said heating, but which temperature is higher than the initial vaporization temperature of said fatty acid at a subsequent sub-atmospheric distilling pressureand is within the normal temperature range of incipient decomposition of said material if subjected to ow as a liquid stream through a heated'tube, expanding said heated .atomized mist through suitable control means into a distilling zone of sub-atmospheric pressure and passing inert gas into said distilling zone to promote vaporization of fatty acid from said atomized mist.

3. 'Ihe process for distillation of organic'liquids with avoidance of decomposition which comprises moderately preheating such liquid below its vaporizing temperature, atomizing a flowing stream'of said preheated liquid at atmospheric or higher pressure with not less than approximately five times its own volume of suitable inert gas to form an atomized mist comprising a continuous .phase of said inert gas containing and surrounding a discontinuous phase consisting of discrete particles of said liquid, heating `said atomized mist as such in a continuous tubular structurev to a temperature below the initial vaporization temperature'of said liquid at the pressure of said heating, but which temperature is higher than the initial v'aporization temperature of said liquid at a subsequent sub-atmos pheric distilling pressure and is within the normal temperature range of incipient decomposition of saidliquid if subjected to iiow as a liquid stream through a heated tube, expanding said heated atomized mist through suitable control means into a distilling zone of sub-atmospheric pressure, passing inert gas into said distilling zone to promote vaporization of liquid from said atomized mist, passing the vapors of distillation into a condensing zone and` condensing and removing the resultant distillate.

4. The process of distillation for obtaining purified fatty acid from material containing fatty acid with avoidance of decomposition which comprises moderately preheating such material below the initial vaporizing temperature of its contained fatty acid, atomizing a ilowing stream o1' said preheated material at atmospheric or higher pressure with notless than approximately five. times its own volume of suitable inert gas to form an `atomized mist comprising a continuous phase of said inert gas containing and surrounding a discontinuous phase consisting of discrete particles of said material, heating said atomized mist as such in a continuous tubular structure to a temperature below the initial vaporization temperature of the contained fatty acid at the pressure of saidheating, but which temperature is higher than the initial vaporization temperature of said Dfatty acid at a subsequent sub-atmospheric distilling pressure and is within the normal temperature range of incipient decomposition of said material if subjected to ilow as a liquid stream through a heated tube, expanding said heated atomized mist through suitable `control means into a distilling zone of sub-atmospheric pressure, passing inert gas into said distilling zone to promote vaporization of fatty acid from said atomized mist, passing the vapors of distillation into a condensing zone and condensing and removing the resultant fatty acid distillate.

5. The process for distillation of organic liquids with avoidance of decomposition which comits vaporizingl temperature, -atomizing a flowing stream oi' said preheated liquidlrwithnot less than approximately iive'timesritsown bvolume of suitable inert gas to form anatomi'zed 'mist comprising a continuous phase of said inert gas containing and surrounding a discontinuous phase consisting of discrete particles o, of said liquid, heating said atomized mist as such in a continuous tubular structure to a temperature below the initial vaporization temperature of said liquid at-the pressure of said heating, but which temperature' is higher than the initial vaporization temperature of said liquid at a suitable subsequent reduced distilling pressure and is within the normal temperature range of incipient decomposition of said liquid if subjected to now as a liquid stream through a heated tube, ex-

panding said heated atomized mist through suitable control means into a distilling zone maintained at pressure lower than the pressure normally prevailing in saidy continuous tubular structure vaporizing liquid Afrom said heated atomized mist in said distilling zone, passing the vapors of distillation into a condensing zone and condensing and removing the resultant distillate.

6. The process of distillation for obtaining purifled fatty acid from material containing fatty acid with avoidance of decomposition which comprises moderately preheating such material below the initial vaporizing temperature of its contained fatty. acid, atomizing a flowing stream ofv cuff' said preheated material with not less than approximately ve times its own volume of suitable inert gas to form an atomized mist comprising a continuous phase of said inert gas containing and surroundinga discontinuous phase consisting of discrete particles of said material, heating said atomizedmist as such in a continuous tubular structure to a temperature belofw the initial vaporization temperature of said fattyv aci'd at the pressure of said heating, but which temperature is higher than the initial vaporization temperature of said fatty acid at asuitable subsequent reduced distilling pressure and heated atomized mist in said distilling zone, passing the vapors of distillation into a condensing zone and condensing and removing the resultant fatty acid distillate.

ALAN PORTER LEE.

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