US2054096A - Fatty acid distillation - Google Patents

Description

lime/abr.; 1 ,1h40/UHU@ Sept. l5, 1936. R. H. PoTTs ET AL.

FATTY ACID DISTILLATION Filed April 24, 1935 Patented Sept. l5, 1936 UNITED STATES Application April 24, 1933, Serial No. 667,568

3 Claims. (Cl. 87--4l The present isvention relates to the treatment of oleaginous materials having a fatty acid content, and has particular reference to an improved process for treating fatty material obtained, for

5 instance, from the product known as foots" in a particularly advantageous manner.

Animal oils and vegetable oils, such as cottonseed oil, corn oil, and cocoanut oil, are customarily subjected to a process of alkali rening, whereby ll free fatty acids in the oil are neutralized. The

resultant soap ilocks to thel bottom of the relining kettle, together with some neutral oil that is held by the soap particles. The material thus separating from the oil is known as foots", and

l ordinarily will contain on the order of 50 per cent fatty acids, the remainder being impurities and,

primarily, water. Of the fatty acid content of foots, approximately 60 per cent may be free fatty acids and the remainder glycerides.

The foots are acidulated with sulfuric acid in order to break the mass into oil and water. That is, the acid breaks the soap into fatty acid and the sulfate salt of the positive radical combined with the fatty acid. The mass then separates into an v oil layer and a water layer, which layers may be separately recovered by decanting or other suitable process.

The fatty material obtained from acidulation of the foots is usually termed raw fatty acid stoc 3o and for purposes of description, our invention will be described in particular with reference to this material.

It has been customary heretofore to recover the fatty acids from fatty acid stock by saponifying this stock and then subjecting the saponied stock thus obtained to distillation in an intermittent or batch distillation system, with the aid of superheated steam injection into the charge, the entire system being maintained under diminished pressure. The stills employed in such distillation are generally heated by direct fire, in which case the bottom of the still is always at a considerably higher temperature than the temperature of the major portion of the material contained therein. That is, there are local areas of highly heated stock adjacent the metal of the still. Invariably, this high temperature, and the extended period of heating, causes a thermal decomposition of constituents of the stock, giving rise to a viscous residue which cannot be further purified without great cost. Also, the distillate is of poor color and odor. In some instances superheated steam and high vacuum have been employed in distilling the stock. but this method has proved unsatisfactory from many stand- PATENT for-FICE Fam acm nrs'rniLA'rloN Ralph H. Potts, Chicago, and John E. McKee, Western Springs, lll., assignors to Armour and Company, Chicago, Ill., a corporation of Illipoints, such as cost, time and eiliciency of recovery of the fatty acids.

A primary object of the present invention is the provision of a yprocess for distilling fatty acid materials in an improved manner. l5v

v An additional object is to provide a process for distilling fatty acids in which material decom-v position is avoided.

A further object is the provision of an improved process for treating raw fatty acid stock conlo taining free fatty acids andvneutral oil.

A still further object is the provision of a ,l process for separating the various constituents of a mixture of different fatty acids.

These and other objects will be apparent from 15 a consideration of the following illustrative and explanative description and with reference to the accompanying drawing, in which the single figure represents, diagrammatically, suitable apparatus in which to carry out our improved process. 20

In accordance with our invention, the stock, containing free fatty acids, is heated quickly to a temperature of incipient vaporization, and then subjected to flash distillation. to remove the fatty acids therefrom. The neutral oil remaining as 25 an undistilled residue may be subjected to further treatment, such as saponication, while the dis,- tillate, which contains a mixture of fatty acids, may be'subjected to further treatment, such as fractionation, whereby to separate the various 3o' acids.

'I'he apparatus shown in the drawing is somewhat similar, in many respects, to that employed, for example, in the petroleum industry.

The charge of stock is run into two deodorizers 35 l0 and Il wherein volatile color and odor imparting impurities and `moisture are removed by means of closed steam coils I2 and I3 andopen steam coils I4 and I5, the impurities and moisture passing from the deodorizers through pipe 40 I6 into a suitable condenser l1. The deodorizers are preferably maintained under a partial vacuum by means of a suitable vacuum line I8 connected to the condenser l1. When a sufficient charge of stock is admitted to the deodorizers, 4.5 steam is turned into the closed coils i2 and i3 and steam is passed directly into the charge by means of the open coils i4 and I5. Under the elevated temperature and steam injection, volatile impurities and moisture are removed within 5o a few hours and the fatty acid material is'ready for subsequent operations. It will be understood that the deodorizers lll and Il are used intermittently, that is, while the stock in one deodorizer is being treated, the other deodorizer may bevused l5 as a source of stock for the subsequent treatments. lIn this manner the operation of the remainder of the apparatus is made continuous. Primarily, the deodorization serves to remove certain light unsaturated products, volatile color and odor imparting bodies,V permanent gases, and moisture from the stock, the presence of these impurities being objectionable in the subsequent treatment to which the stock is subjected, as well as in the nal products. For instance, moisture vaporizes in the pipe still, to be described hereinafter, with explosive violence, thereby causing undue entrainment and subsequent contamination of the distillate.

When suiiciently deodorized, the stock is transferred through line I9 by means of pump 20 into a pipe still 2|. The still is provided `with 'a re box 22 and a steam superheater 23, the latter belng used to supply steam for the various open coils of the apparatus. A meter 24 is connected in line I9 by means of which the rate of flow of stock through the line is indicated. 'As the stock passes through tubes 25 of the pipe stili, which deilne a tortuous passageway, they are raised quickly to a temperature which is high enough to impart a sufficient quantity of sensible heat to the stock above that required for the vaporlzatlon of the fatty acids at reduced pressure to cause their distillation when subsequently passed into a flash chamber maintained at reduced pressure. In the batch stills of the prior art the fatty acids remain in the high temperature of the still about eight or ten hours, the stills being maintained at about a 10,000 lb.charge, distilling at the rate ofabout 1,000 lbs. per hour. Also, as before stated, such stills have local areas which are heated considerably higher than the temperature of the mass, the time involved, and the highv temperature causing objectionable deterioration of the materials. Our process is so regulated that the stock passes through the pipe still in a few minutes, the large area of heating surface being suillcient to cause a very rapid increase in the temperature of the stock.

Experiments show that fatty acid stock is subject to thermal decomposition, which proceeds more rapidly as the material is continuously vaporized. In accordance with our invention, the stock is controlled while in the pipe still so that the vaporization therein is maintained at a minimum. This may be accomplished by suitable control of the pressure within the still, a higher pressure acting to retard vaporization.. When the heated stock enters the flash chamber, vaporization is practically instantaneous and decomposition is thereby reduced to a minimum.

The stock preferably is heated in the deodorizers by the open and closed steam coils therein to a temperature of the order of 300 F., and are rtransferred to the pipe still at substantially the same temperature.- By controlling the temperature of the fire box 22, the length and size of pipes in the pipe still,'and the velocityoi!V the material transferred therethrough, it is possible to obtain any desired result with respect to temperature and time of treatment. In a preferred modication, the speed of the stock through the pipe still is on' the order of two feet per second, substantially six minutes being required for the stock to pass completely through the still. The temperature vof the still is preferably controlled so as to raise the temperature of the stock to substantially 450 to 550 F., a slight pressure, sufllcient to retard vaporization, being malntained within the pipe still; the exact temperature and pressure being dependent upon such factors as the nature of the particular material being treated.

A steam line 26 communicates with the pipe still at a point intermediate the length of the pipe 25 thereof, whereby steam, preferably superheated, is added to the stock during the heating process, creating a partial pressure that will lower the boiling point and assist in the subsequent vaporization to maintain a low distillation temperature. l

ItA will be seen that the heating period of our process, which may be `from 4 to 10 minutes, for example, compares very favorably to the heating period of 8 to 10 hours which is employed in`batch stills. The heat is applied evenly by the pipe stills,v and in the'short time involved. thermal decomposition is reduced to the minimum.

Although, as described heretofore, it is preferable to retard vaporization in the pipe still, in some cases ity/'may be found desirable to allow incipient vaporization in the pipe' still, and to complete the vaporization by subsequent introduction into a flash chamber. In this case, it is not necessary to heat the stock to as high a temperature as Iwhere sumcient sensible heat must be added to the liquid stock to substantially completely vaporize the volatile constituents thereof. It will be understood that the particular pressure in the flash zone will depend upon such factors as the type of equipment employed, the nature of the material treated, and the rate of distillation. By way of example, it

may be stated thatv a pressure of 45 to 60 anni.

Hg. has been employed to advantage in the ash zone. In such instances, the pressure in the upper part of the fractionating tower through which the vapors subsequently are passed may be of the order of 10 mm. Hg.`

'I'he heated stock passes from the pipe still into a valve controlled line 2'|-which communicates with the interior of a flash chamber 20. The stock, heated to a temperature which may be between 450 and 550 F., is released into the flash chamber which is maintained under reduced pressure. It is preferred to spray the stock into the flash chamber to facilitate subdivision and vaporization of the Vfatty acids therein. The sensible heat in the stock is suillcient to cause a flash distillation of the volatile constituents thereof, that is; to supply the latent heat of vaporization. The temperature of the distillation `of the1stock will ordinarily be in the neighborhood of 400 F., which is considerably below the temperature of the stock in the pipe still, therebyl preventing excess decomposition which would-` result from vaporizatlon of the stock at a high temperature.

In the case of said stock vbeing introduced into the flash chamber the fatty acid content is vaporized, while the remainder of the stock, which is mostly neutral oil, retains itsy liquid form.

Thf` flash chamber Ais preferably a vessel of fairly large volume and may contain a number of bubble trays. Above the point at which the stock is introduced into the flash chamber are mounted a series of mist extractors 29 which serve to remove entrained unvaporized materials from the fattyA acid vapors. The entralnedvliquid, together with the unvaporized portions of the stock, falls toward the bottom of theash chamber and is received by a series of bubble trays -30 of suitable construction. As the unof steam from the open coil 3| positioned in the lower portion of the ash chamber, thereby stripping this unvaporized residue of its residual portion of fatty acids. This steam and the removed residual portions of the fatty acids pass upwardly through the flash chamber and are mingled with the fatty acids volatilized during the distillation'process. i i

Communicating with the bottom of the chamber isa tank 32 in which the unvaporized residuum of the stock is collected. 'Ihis residuum may be collected until a sulcient quantity is'obtained for further treatment. In the case of raw stock, the portion which is not vaporized contains quite a large percentage of neutral oil. Since the raw stock already contains a-considerable quantity of free fatty acids, the further splitting or saponification was expensive and ineillcient, a greater amount of handling being required due to the large volume of material and a larger quantity of reagents being used to provide the proper concentration. By first distilling the free fatty acids from the raw stock by the method described herein and then splitting the neutral oil in the residue by the Twitchell process or other treatment, a higher percentage of recovery of fatty acid and glycerine is obtained. After splitting the residue, as by the Twitchell method, it is possible to recover the glycerine from the mixture, the fatty acids being again distilled as described heretofore. The distillation may be eiected by adding the split material to a fresh batch of stock. Heretofore millions of pounds of glycerine have been lost by the costs necessary to recover the same from raw stock. When recoveredv in accordance with our process this glycerine is of a good grade and the process economical.

In other words, where the raw material, which may contain onthe, order of 60 per cent free fatty acids, is subjected to a further splitting in accordance with Twitchells process, the entire amount of the oil is treated by boiling for 18 hours in admixture with about 2 per cent reagent, 1 per cent sulfuric acid, and 40 per cent of water by weight of the whole batch of oil, including the 60 per cent free fatty acids. A second boil is generally made with substantially 0.5 per cent acid and per cent additional water. The total split from this operation is about 94.- per cent. There results from this operation a glycerine water of about 2 per cent or 3 per cent concentration. In accordance with my invention, the raw material is ilrst distilled as described to remove the free fatty acids, and then subjected to the splitting operation, whereby only about 40 per cent of the material is handled and a glycerine water of about 8 per cent concentration is obtained. Glycerinel of goodV quality may be obtained from this water at a reasonable cost.

Operation of our process will depend in detailv to separate the various constituents of a mixture of distilled fatty acids obtained from splitting a neutral fat or oil, such as cottonseed oil or tallow. Where the` stock distilled has been obtained from cottonseed oil, the composition of the distilled free fatty acids may be approximately 50 per cent linoleic acid, 25 per cent oleic acid, and 25 per cent palmitic acid. The oleic and the linoleic acids are unsaturated acids which are liquid at ordinary temperatures. Oleic acid congeals at about 4 C. and linoleic acid at about 16 C. Palmitic acid, on the other hand, is a saturated solid acid having a melting point of 62 C. These acids have been used in the soap industry for many years. 'I'here has been a demand for higher titered fat, such as palmitic acid, for use in the composition oi' many soaps, it being recognized that a saturated fat is more desirable in this connection. Considerable effort has been made toward the separation of the palmitic constituents of the fatty acid mixture in the production of soaps, one method which has gone into extensive use consisting in subjecting the mixture of fatty acids to a fractional crystallization. However, the method has proved unsatisfactory, due to the inefcient degree of removal, the high cost and the cumbersome apparatus necessary to carry out the process.

In accordance with our invention, the constituents of the fatty acid mixture are separated by a, fractional distillation process in which the fatty acids vaporized in the flash chamber pass upwardly through the mist extractors 29, through a line 33 communicating with the top of the flash chamber and into a fractionating tower 34 at an intermediate portion ,.thereof. In the lower portion of the fractionating column or tower 3E are a series of bubble plates 35 of suitable structure and design. The fatty acid vapors entering the fractionating tower arise therethrough and are met with a downwardly flowing stream of a reflux which is preferably composed of the condensate of the lighter fraction of the fatty acids which is taken from the top of the fractionating column. This condensate flows downwardly across a second series of bubble plates 36 similar in design to the plates 35. In traveling upwardly through the fractionating column the higher boiling constituents of the fatty acid vapors are condensed by the reux and the material on each succeeding higher plate Vis of a lower boiling point. That is, the fractionating column reaches the state of equilibrium in which the composition of the material on each plate remains substantially constant and the boiling point of the material on each higher plate is lower than the liquid on the next lower plate.

Somewhere in the fractionating column will be found a plate which will contain the largest percentage of linoleic acid. The liquid is drawn from this plate by line 31 and passed into a stripper 38. In the bottom of this stripper is an open steam coil 39, the live steam passing through the liquid acting to remove residual portions of palmitic acid, the vapors of palmitic acid returning directly to the column through line 39. A line 40 communicates with the bottom of the stripper and passes, through a suitable pump, to a storage tank. This liquid is fairly pure linoleic acid but will be found to contain a certain amount of oleic acid, a more complete separation, if desired, being dependent upon further treatment. The stripper contains an open steam coil Il in its bottom portion, by means e c Y, n

of which the lower boiling palmitlc acid is stripped from the linoleic acid mixture.

The liquid collecting in the bottom of the fractionating column, consisting primarily of oleic acid, is drawn oil! through line 42 and passed through a. pump to a suitable place of storage. Fractionation in the lower portion of the fractionating tower is made possible by passinga current of steam from the open steam coil 4l positioned in the bottom of the fractionating column upwardly through the succeeding bubble plates, the downwardly flowing fatty acid mixture acting as reflux and being separated into portions of successively higher boiling point toward the bottom of the tower.

From the upper bubble plate 36 of the fractionating column the vapors, consisting principally of steam and palmitic acid, pass through a partial or reflux condenser 43 which furnishes suiiicient reflux for the desired fractionation. From the reflux condenser 43 the vapors, which consist primarily of steam and palmitic acids,

pass through a line 44 into a vapor condenser 45. 'I'he condenser preferably is provided with large vapor spaces, thereby permitting a minimum pressure drop across it. The temperature of the condenser is so regulated that practically all of the palmitic acid vapor is liqueed, the condensate being drawn 0E through a line 46 and transferred through a pump to any suitable source of disposition.

The vapors which leave the condenser 45 will preferably be almost entirely steam. However, experience has shown that the steam will contain an appreciable amount of mechanically incorporated or entrained fatty acids in the form of mist. To removethe entrained fatty acids from the steam, the steam vapors are passed through a mist remover or catch-all 41, the temperature of which is preferably above the melting point of the fatty acids, whereby the particles of fattyacid are removed.

'I'he fatty acid passing from the fractionating column and liquefied in the condenser 45 is substantially pure palmitic acid. It will be seen from the foregoing description that we have provided a process by which animal or vegetable fatty acid mixtures may be separated into their various constituents, thereby making the latter available for manyl uses to which the mixture of fatty acids are not adaptable. c

In some instancesit may be found desirable to flash the heated stock directly from the pipe still into the fractionating column, rather than into a separate ilash chamber as described hereinbefore. This is 'particularly true where it is desired to operate at as low a pressure as possible.

The steam after being scrubbed of its sus-Y pended fatty acid mist is passed directly .to a barometrc condenser 4l to which is connected suitable vacuum pumps, not shown. These pumps serve to maintain the entire system, including the flash chamber and fractionating tower, under a suitable reduced pressure.

It will be observed by one skilled in the art that the foregoing specific description is subject to modification, and such variations as come within the spirit of our invention are intended to be included in the appended claims.

.We claim:

1. The process of treating oleaginous materials containing a mixture of volatile fatty acids having different boiling points, which comprises passingl said material through a tortuous passage subject to a temperature suiiiciently high to raise the temperature of the' material hi\gher than necessary for vaporization of fatty acids at reduced pressure and sumciently high for ilash distillation, maintaining said materials under presure din-ing the heating period, subjecting said materials t`o flash distillation in a xone'of reduced pressure and forming a mixture of vapors tainingsaidfatty acids heated sumciently high for fractional distillation, and subjecting said vapors to a fractionalx distillation procedure for the separation of the fatty acids into volatile fractions having different boiling points, said procedure including the steps of passing the heated vapors' through a series of heat-exchanging pools of condensed fatty acid mixtures having successively lower boiling points, condensing the low-boiling vapors passing through the last of said pools, returning a portion of said condensed low-boilingvapors to said pools as reflux liquid, and withdrawing from said pools a liquid volatile fatty acid fraction of higher boiling point than said low-boiling fraction.

2. The process of treating oleaginous materials containing a mixture of volatile fatty acids having different boiling points, which comprises subjecting said materials to continuous distillation in which said fatty acids are heated quickly to a temperature above the temperature required for vaporization. at reduced pressure, then producing under reduced pressure a mixture of vapors -containing said fatty acids and being heated sufliciently higher than that temperature which is the boilingl point of said vapors at the pressure thereof, for fractional distillation, and subjecting said heated vapors to a fractional distillation procedure for the separation of the fatty acids into volatile fractions having different boiling points, said procedure including the steps of passing the heated vapors through a series of heatexchanging pools of condensed fatty acid mixtures having successively lower boiling points, condensing the low-boiling vapors passing through the last of said pools, returning a portion of said condensed low-boiling vapors to said pools as reflux liquid, and withdrawing from said pools a liquid volatile fatty acid fraction of higher boiling point than said low-boiling fraction.

3. 'I'he process of treating oleaginous materials containing a mixture of fatty acids having different boiling A points, which comprises subjecting said materials to a continuous distillation step in which said fatty acids are heated quickly to a tem- Y perature of incipient vaporization above thetemperature required for vaporization 'at reduced pressure and producing a mixture of vapors at reduced pressure containing said fatty acids heated suil'lciently for fractional distillation, and sub- Jecting the heated vapors to a fractional distillation procedure for the separation of the fatty acid into volatile fractions having different boiling points, said procedure including the steps of passing the heated vapors through a series of heatexchanging pools of condensed fatty acidmixtures having successively lower boiling points, condensing the low-boiling vapors passing through the last of said pools, recirculatin'g a major portion of said condensed low-boiling vapors to said pools as reflux liquid for reboiling at a lower temperature than the temperature of said heated vapors and withdrawing from the lower of said pools a liquid volatile fatty acid fraction of higher boiling point than said low-boiling fraction, said higher boiling fraction being heated to a temberanire above the temperature of the upper of said pools.

RALPH H. POTI'S. JOHN E. McKEE.

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