US2573727A - Apparatus for distillation of fatty acids, tall oil, and the like - Google Patents

Description

1951 R. H. POTTS ET AL 2,573,727

APPARATUS FOR DISTILLATION OF FATTY ACIDS, TALL OIL, AND THE LIKE Filed Dec. 15, 1947 Z4 Z8 26 /6 .77 'J J J I I? a H TOWER-1 IE: =i=== 1 I &

Patented Nov. 6, 1951 UNITED STATES PATENT OFFICE APPARATUS FOR DISTILLATION OF FATTY ACIDS, TALL OIL, AND THE LIKE Ralph H. Potts, La Grange, and Roy N. Olson,

Chicago, Ill., assignors to Armour and Company, Chicago, IlL, a corporation of Illinois Application December 15, 1947, Serial No. 791,856

2 Claims. (Cl. 202-154) This invention relates to apparatus for the distillation of fatty acids, tall oil and like material in which there is danger of decomposition upon the use of relatively high distillation temperatures.

In the distillation of fatty acids, tall oil and similar materials in which the product is adversely affected by decomposition at high temperatures, it has heretofore been felt desirable to limit the amount of steam employed in the distillation of such products. The' use of steam in somewhat larger amounts is desirable from the standpoint of reducing the temperature differentials existing in the top and bottom portions of the fractionating or distillation tower and particularly for reducing the temperature in the lower portion of the tower. However, the use of such large amounts of steam has a disadvantage in that a substantial entrainment occurs. This entrainment in addition to the actual loss incurred, passes into the vacuum equipment, solidilies in the condensers, resulting in costly shutdowns. For this reason, the quantity of steam has been restricted and in some cases dispensed with altogether.

The following example illustrates the advantage in using larger amounts of injected steam and emphasizes the unfortunate limitation of steam required to avoid entrainment losses. Consider a system operating with a feed composed of 50% palmitic acid and 50% stearic acid, a pressure of 5 mm. at the top of the tower and 45 mm. at the base of the tower. The vapor temperature at the top of the tower would then be the temperature at which the vapor pressure of palmitic acid is 5 mm. or 385 F. The temperature at the base of the tower would be the temperature corresponding to a vapor pressure of stearic acid of 44 mm. or 514 F.

If we now consider a system in which the partial pressure of the palmitic acid at the top of the tower is again 5 mm. but the total pressure is 30 mm. the remaining 25 mm. being the result 01' the admission of 5 mols of steam per mol of fatty acid then we will find a considerable ditierence in the conditions existing at the base 01' the tower even though the top tower temperature remains the same, i. e., 386 F. The 20 fractionating trays can again be designed for a pressure drop of 2 mm. per tray and the total pressure existing at the base of the tower will be 70 mm. The partial pressure of the fatty acid vapor will be ,4,- of '70 mm. or 11.6 mm., and the corresponding vapor temperature at the base of the tower will be the temperature at which stearic 2 acid exhibits a vapor pressure of 11.6 mm. or 450 F.

From the above it will be noted that the use of steam considerably reduces the temperature required in the base of the tower and such reduced temperature sharply reduces the thermal decomposition of the product and results in a much improved product.

It will be obvious from the foregoing that if some simple means can be provided which will take care of the entrainment and prevent serious entrainment losses while at the same time permitting the use of large amounts of steam, a decided advance will have taken place. In the first place, a temperature difierence existing between the top and bottom of the tower will be reduced, as in the example above, from F. to 64 F. This difference more nearly represents the difference that exists between the respective boiling points of palmitic and stearic acid and is not so dependent upon tower pressure as in the first instance. This should provide for better fractionating conditions, as pressure changes due to fractionating vacuum will not cause as much change in still conditions. In the second place, the temperature existing in the base of the tower is 64 F. lower when using steam, and consequently, decomposition is greatly reduced.

An object of the invention is to provide apparatus in which steam may be utilized inlarge amounts in a distillation operation, the apparatus being provided with means for supplying the steam from the steam ejector pumps whereby entrainment produced in the apparatus is carried to preceding or succeeding distillation operations and thereby recovered. Yet another project is to provide highly effective apparatus permitting the utilization of steam and the recovery of materials entrained by directing steam employed in steam ejector pumps lying in communication with one tower into the base of another tower while also providing means for reheating such steam which is introduced into the base of the tower. Other specific objects and advantages will appear as the specification proceeds.

The invention, in a specific embodiment, is illustrated by the accompanying drawing in which there is given a diagrammatic layout of apparatus embodying the invention.

For the purpose of illustrating the function of the various apparatus parts, such parts will be described in conjunction with the processes which may be eifectively carried on, by such apparatus.

In the illustration given, it will be noted that 3 there are three towers. Tower I receives the incoming feed in line It and the residue from tower l passes from pipe H to tower 2 where fractional distillation is carried out. Residue from tower 2 passes through line I2 into tower 3. It will be noted that a single-casing provides towers 2 and 3 and that the two towers are separated by an imperi'orate wall l3.

Tower I is employed for steam distillation and in the preferred process is employed mainly for stripping a relatively light vapor fraction from the feed material. Such a fraction is condensed in condenser l4 and the liquid product is recovered through line I5. A reduced pressure is maintained by a structure which is well known and which will be briefly described. Communicating with the condenser I4 is a vapor pipe l8 leading to a catch-all II. A reflux line pipe l8 leads from the bottom of the catch-all l1 and returns to an intermediate portion of tower l. A vapor pipe i9 leads from the catch-all I! to a barometric condenser 20. Communicating with the top of the barometric condenser is an ejector pump 2|. Since such apparatus for maintaining reduced pressure is well known. a further detailed description is believed unnecessary.

The feed material consisting of fatty acids, tall oil or similar types of material enters the stripping tower I through line I'll and the unvaporized residue passes downwardly and flows through line H into tower 2 where it is further fractionated. The line II is provided with an electrically controlled valve 22 which in turn is controlled by a level controlling electric mechanism 23. Since such level maintaining mechanism is well known in the art, a detailed description here is believed unnecessary.

In tower 2, vapors are condensed in the condenser 24 and a second liquid fraction drawn oil through the pipe 25. It will be understood that a number of liquid fractions may be recovered from different portions of the tower. Leading from the condenser 24 is a vapor pipe 26 which communicates with a steam ejector pump 21. Steam is introduced into the pump 21 through the valve controlled line 28.

denser 24 and tower 2. The steam discharged through the pump 21 is conducted by a pipe 29 to a heater 30 in which the temperature of the steam may be raised. The steam is heated by steam coils 3| or by any other suitable means. The reheated steam enters the bottom of tower l and is effective in the steam distilling of the product 'in that tower.

We have already referred to the withdrawal of residue from tower 2 and the passing of the same through pipe l2 into the lower tower 3. The

pipe I2 is provided with an electrically controlled valve 32 which in turn is controlled by an electrically operated level control device 33 similar to the structure 23 employed in tower I. Heating coils for steam or other material 34 may be employed in connection with tower 3. I1 desired, the tower 3 may be left unheated and employed solely as an unheated flash drum. If desired, entrainment eliminators 35 may be supported in the upper portion of tower 3. A withdrawal pipe 36 for residue is controlled by the electrically operated valve 31 which is in turn controlled by the electrical level maintaining device 38.

Communicating with the top of tower 3 is .a vapor withdrawal pipe 39 leading to a condenser 40. A liquid fraction is recovered from the con: denser through the ipe 41. Communicating Such a pump is efiective in reducing the pressure within con-.

with the condenser 43 is a vapor pipe 42 to which is connected a two-stage steam ejector pump. Steam is introduced through the valve controlled pipe 43 into the pump 44 and steam is also introduced through the valve controlled pipe 45 into the pump 46. The steam outlet from pump 44 communicates with pump 46 and the combined output of steam passes through pipe 41 into the reheater 43 where a steam coil 49 may be used for raising the temperature of the steam. It will be understood that any type of heating means may be employed for this purpose. The steam passes from the heater 43 into the lower portion of tower 2.

As an example of the process, the following may be set out. A fatty acid compounded mainly of palmitic and oleic acids was passed through feed line in into tower I. The top of tower l' was maintained at a temperature of 315 F. while the tower bottom was maintained at about 400 F. Tower 2 had a top temperature of 382 F. and a bottom temperature of 456 F. Tower 3 had a top temperature of about 375 F. with the temperature of the liquid in the bottom being about 425 F.

The fraction I recovered from tower i through pipe I! consisting mainly of an odoriferous material was withdrawn mainly for the purpose of removing this constituent from the remaining material. The fraction II recovered from tower 2 through pipe 25 consisted mainly of palmitic acid while fraction III from pipe 4| leading from tower 3, consisted mainly of oleic acid. The residue through pipe 36 was a heavy tarry material. The proportions in the specific example were 5% in fraction I (odoriferous material). 20% in fraction II (palmitic), 55% in fraction III (oleic) and 20% in residue.

In the above specific example, lbs. of steam was introduced through pipe 43. 600 lbs. through pipe 45 and 400 lbs. through pipe 28. Tower i had a top pressure of 40 mm. of mercury. Tower 2 had a top pressure of 30 mm. and a bottom pressure of 70 mm. while tower 3 had a pressure of 2 mm. Hg.

The heaters 30 and 48 were efiectively employed not only as steam reheaters but also as reboilers. They were effective in introducing additional heat into the material being vaporized as well as in raising the temperature of the incoming steam. 1

In the operation of the process as described above, it was found that entrainment losses were nullified bycarryin the entrainment through the medium of the thermo-compressor steam back into the next tower so that such entrainment materials were wholly recovered. Whether entrainment was large or small was of little consequence because the material entrained was immediately subjected to a steam distillation in the next tower. The process results in a saving of steam but more important is the fact that the steam is employed as a vehicle for the return of entrained material so that it can be recovered. With the new process and apparatus any desired large amount of steam may be employed with all the attendant advantages which have been described as flowing from such use while at the same time the disadvantages heretofore following the use of such large amounts of steam are eliminated.

The apparatus is compact and provides a highly efficient arrangement for the reutilization of the thermo-compressor steam while also preparing it for reuse at the desired temperature.

By combining towers 2 and 3 in a single structure, an effective arrangement.v is set out whereby the lower tower I or flash drum serves as a means for directing heat upwardly against the residue in tower 2 while the lateral arrangement of the condenser separates the condenser itself from the hot areas where the two towers Join. The heater tructures 30 and 48 serve the double function of reheating steam while also reboiling the material within the tower, such structures being in alignment with the lower portionsof their respective towers and being equipped with separately controlled heating means.

The foregoing process involving fractional distillation or straight distillation has been described in connection with fatty acids, tall acids, etc., for the purpose of specifically illustrating the invention. It will be understood that the invention is applicable for the treatment of fatty acid derivatives, such as their esters, alcohols, nitriles, amines, etc. The invention is particularly effective with fatty acids and such derivatives having from 8 to 24 carbon atoms in their hydrocarbon radical. Broadly, the invention applies to all organic materials whose 1 distillation temperature is such that decomposition occurs or is likely to occur in the range of the distails of tructure may be varied widely by those skilled in the art without departing from the spirit of our invention.

- We claim:

1. In apparatus of the character'set forth, a steam stripping tower, a steam distilling tower. and a flash drum, means for passing charging stock successively through said stripping tower.

fractionating tower and flash drum, condensers communicating with each of said towers, a steam ejector pump communicating with the condenser for said steam distilling tower, a steam ejector pump communicating with the condenser for said flash drum, and conduit means directing the steam from the pump communicating with said steamdistilling tower to the lower portion of said steam stripping tower and directing steam from the pump communicating with said flash drum into the lower portion of said steam distiliation tower.

2. In apparatus of the character set forth, a steam stripping tower, a steam distilling tower, and a residue distilling tower, means for passing charging stock successively through said stripping tower, steam distilling tower, and residue distilling tower condensers communicating with each of said towers, a steam ejector pump communicating with said condenser for said distilling tower, a steam ejector pump communicating with the condenser for said residue distilling tower, and conduit means directing the steam from the pump communicating with said steam distilling tower to the lower portion of said steam stripping tower and directing steam from the pump communicating with said residue distilling tower into the lower portion of said steam distillation tower.

RALPH H. POTTS. ROY N. OLSON.

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

UNITED STATES PATENTS

Claims (1)

1. IN APPARATUS OF THE CHARACTER SET FORTH, A STREAM STRIPPING TOWER, A STEAM DISTILLING TOWER, AND A FLASH DRUM, MEANS FOR PASSING CHARGING STOCK SUCCESSIVELY THROUGH SAID STRIPPING TOWER, FRACTIONATING TOWER AND FLASH DRUM, CONDENSERS COMMUNICATING WITH EACH OF SAID TOWERS, A STEAM EJECTOR PUMP COMMUNICATING WITH THE CONDENSER FOR SAID STEAM DISTILLING TOWER, A STEAM EJECTOR PUMP COMMUNICATING WITH THE CONDENSER FOR SAID FLASH DRUM, AND CONDUIT MEAND DIRECTING THE STEAM FROM THE PUMP COMMUNICATING WITH SAID STEAM DISTILLING TOWER TO THE LOWER PORTION OF SAID STEAM STRIPPING TOWER AND DIRECTING STEAM FROM THE PUMP COMMUNICATING WITH SAID FLASH DRUM INTO THE LOWER PORTION OF SAID STEAM DISTILLATION TOWER.

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