US2170834A - Process for the dehydration of lower fatty acids with ketones and ethers - Google Patents

Description

Aug. 29, 1939. D. F. OTHMER 2,170,834

PROCESS FOR THE DEHYDRA'I'ION OF LOWER FATTY ACIDS WITH KETONES AND ETHERS Filed July 3, 1936 2 Sheets-Sheet 1 KETONE LAYER GRAMS ACETIC ACID PER CCSOLVENT WATER LAYER 2a FIG.2. l- 526 51124 Z2 4-] l 2 $7 I 1 Q g. r/ 346 f ,Rf q 3,. z rn w DISTRIBUTION I ACETIC ACI BET EN 55. WATER AND ETHE .4 I. .42 .68 .7? .60 502 T f T F U INV OR.

mem 5&5? :51,

BY W

PER CC. WA V v ATroaEYs Aug. 29, 1939. D. F. OTHMER 2,170,334

PROCESS FOR THE DEHYDRATION OF LOWER FATTY ACIDS WITH KETONES AND ETHERS Filed July 3, 1956 2 Sheets-Sheet 2 FIG. 3.

CONDE DECANTER D/LUTE ACID IN VAPOR LIQUID DEHYDRATED ACID our ACETIC' ACID WATER" ENTRAINER (KETONE, ETHER, ETC.)

" DOnaZdFOIhmeP INVENTOR Patented Aug. 29, 1939 UNITED STATES PATENT OFFICE PROCESS FOR. THE

DEHYDRATION'OF LOW- ER. FATTY ACIDS WITH KETONES AND ETHERS poration of Virginia.

Application July 3, 1936, Serial No. 88,823

13 Claims.

for extracting acetic acid from its aqueous solutions by counter-current liquid contact. The acetic acid after extraction may be more readily recovered from the solvent thanfrom the water originally present. Still other methods have concerned themselves with the distillation. of the aqueous solution in the presence of an auxiliary liquid, which by reason of its insolubility in water and the vapor pressure relations dependent thereupon, brings over the water in a low boiling vaporous mixture. In such methods (see for example, Othmer, U. S. Patent No. 1,917,391), it

is usual practice to condense the vaporous mixture of water and withdrawing agent, separate the two layers of water and water insoluble third liquid respectively, discharge the water layer to waste (or to an auxiliary still for removing the trace of third liquid dissolved therein) and return the third liquid or withdrawing agent to the head of the column as reflux wash for the purpose of bringing over more water in a continuous operation.

I have found that certain materials of a somewhat difierent boiling range than those ordinarily. used and exemplified by various ketones and ethers are satisfactory materials to be used in the extraction process; in the azeotropic distillation process when the operation is changed as will be noted hereinafter; or in the combined operation wherein, after systematic extraction of the aqueous acetic, the water dissolved with the acetic in the solvent layer is ejected in a socalled azeotropic distillation with the solvent itself.

The use of low boiling materials such as ethylone dichloride and ethyl acetate is old in the art of removing water from acetic acid by these several practices, but these low boiling materials require an excessively large distillation column and considerable more heat because of the very high ratio of withdrawing agent to water in the azeotropic mixture.

One of the difliculties which has prevented the use of various materials for azeotropic withdrawing agents is their "tendency to come out of the system with the acetic acid because their boiling points are so close to that of acetic acid that they cannot be satisfactorily separated therefrom by distillation and rectification.

I have found, however, that this tendency for the acetic acid to come out of the system contaminated by withdrawing agent may be readily overcome by the correct operation of the process as hereinafter explained in a continuous manner and in an efficient column of the usual type fitted with still pot or heating section, condenser and decanter as is usual practice in the use of azeotropic withdrawing materials. The type and arrangement of equipment is described in. Othmer, United States Patent No. 1,917,391; but the method of operation is substantially different, as will be indicated.

This invention has for an object to provide a process, including azeotropic distillation with oxygenated agents, wherein the azeotropic composition is formed and maintained separate from concentrated aliphatic acid. Another object is to provide a process for operating a distillation unit employing oxygenated withdrawing agents wherein the lower part of the unit is operated in accordance with the simple principles of ordinary rectification.

Still another objectis to provide a process for dehydrating aliphatic acids employing oxygenated withdrawing agents. It is also an object to provide a process for concentrating the lower fatty acids which is continuous. Another object is to provide a process in which the same agent may be used both as an extracting agent and as a water entraining agent.

A further object is to provide a distillation process employing oxygenated agents for remov- 'ing water from dilute solutions of acetic, propionic and butyric and other lower fatty acids or mixtures thereof. A further object is to provide an extraction and distillation process whichis applicable to lower aqueous fatty acid solutions of various concentrations. Another object is to provide a process employing oxygenated agents in which the water removed from aliphatic acids carries with it to waste only a very small amount of acid.

The efficient and almost complete separation of water and acid without the discharge of withdrawing agent, such as ketones or ethers, in the acetic acid may be accomplished, by the control of the amount of the withdrawing agent in the system so that it is only in the upper part of the column; and considerable water is present in the acid below the lowest point where the withdrawing agent reaches. Heretofore, it has been thought necessary either to have an excess of withdrawing agent in the column so that it will exist in the column below that point Where the last of the water has disappeared; or, at the east, the right amount so that in working down the column, the last of the water and the last of the withdrawing agent will be vaporized togcther and hence removed from the acetic acid. I have found that, by removing a part of the quantity of withdrawing agent (ketone or ether), the acid may be discharged free of the withdrawing agent.

By such operation it will be seen that liquid passing down the column will flow out of the section-in which there is azeotropic withdrawing agent, still containing more or less water. Heretofore, such operation of the distilling column has been considered fatal to the removal of the last of the water to give the anhydrous acid which is desired at the base. I have discovered, however, that it is possible to obtain substantially dry acid at the base even though considerable water flows down with the acid out of that section which is charged with the azeotropic withdrawing agent. I explain this ability to accomplish the dehydration in a column, which according to previous practice would be regarded as insufficiently charged with withdrawing agent, on the ground that the fraction of water present is removed from the acid in the lower part of the column by the ordinary rectification process; and this water, containing considerable acid, is passed up into the azeotropic distillation range in which the water is separated from substantially all of the accompanying acid. In the usual case, it is not desirable to have more than ten to twenty percent of water in the acid passing out of that part of the column which has present the withdrawing agent; and this maximum amount of water which can besatisfactorily separated by straight rectification in the lower part of the column wtihout the aid of withdrawing agent depends on the water present in the dilute acid fed to the column, and also on the latent heat and azeotropic ratio of the withdrawing agent used.

If less than 25% water is present in acetic acid,- it may be separated from most of the acid without the expenditure of an excessive amount of heat-supplied in the still pot and removed in the dephlegmator condenser-by ordinaryrectification. The Water so removed will contain considerable acid; in the usual case, about an equal amount. The heat requirements are excessive, however, when dilute acids are submitted to ordinary rectification, and especially is this the case when it is desired to remove all of the water substantially free of acid.

I have discovered now, that by using the lower part of a distillation column in continuous operation for ordinary rectification of the last water from the acetic acid, the vapors, containing all of the water and considerable acid, may be passed into the upper part of the column wherein the water is completely separated in an azeotropic distillation; and the acid is allowed to fiow back into that part of the column wherein ordinary rectification is proceeding. The liquid flowing from the upper part of the column to the lower, commonly called reflux wash is used in this rectification just as that returned from a dephlegmator would be if this rectification was proceeding in a separate column. Actually, the loW- er part is factionating from the anhydrous acetic acid which is discharged in the usual way from the column base, eighty or ninety per cent acid (for example) which is passed as vapors across the hypothetical division into that part of the column where the withdrawing agent per sists and removes the water from the acid in substantially the usual azeotropic distillation.

There is used in the lower part of the column to remove the final amount of water from acid by straight rectification the same vaporous heat as is used in the upper part of the column to complete the separation by distillation with the withdrawing agent. That is, in my distillation column the bubble platesare covered with liquid.

In the upper part of the column the liquid will include withdrawing'agent. The vapors from the lower system contact by bubbling through liquid and in doing so new vapors are formed which in turn contact the liquid on the plate above. It is therefore apparent in my process that the vapors from the straight rectification may supply heat to accomplish the azeotropic distillation.

My process is the exact reversal of the former method of azeotropic distillation using comparatively low boiling materials such as ethylene dichloride isee U. S. Patent No. 1,917,391) wherein the upper part of the column" accomplishes the azeotropic distillation and the lower part of the column is used for a straight rectification of an excess of withdrawing agent rather than an excess of Water as in the present invention.

In the use of these lower boiling withdrawing agents I have found that it is also advantageous to work with insufiicient azeotropic liquid in the lower part of the column.

I have found that the use of the lower part of the column for straight rectification of water from acetic acid in a two component system enables the use of various ketones and ethers as withdrawing agents which boil closely to the boiling point of acetic acid, or indeed at the same temperature or above. be more diflicult to separate from acetic acid by straight rectification than the water itself, and in the older processes were considered quite impossible of utilization. It is from these liquids that the most efficient azeotropic withdrawing liquids may be chosen; and I have found that much smaller amounts of liquids having these comparatively high boiling points are required to bring over a unit amount of water than will be required of those having lower boiling points. This means that the column will have less vapors to handle and hence a smaller column can be used; and since less vaporous heat is required, a corresponding reduction in the amount of steam used will also be possible.

By the proper operation of this continuous process. I ha e found that the number of liquids which may be used for azeotropic withdrawing agents has been greatly extended. In general, the use of less than the required amount extends the boiling range of suitable azeotropic liquids from 102 (1., which was formerly regarded as the unpcr limit for continuous operation to about C. Many liquids in this boiling range have been found satisfactory and those listed below are to be regarded merely as examples of thosz which may be used when the lower part of the column is allowed to separate the aliphatic acid from the last of the water by straight rectification and the upper part substantially separates the water from the aliphatic acid by the azeotropic distillation.

Among some of the agents which may be used Such liquids may even.

are the following, with their normal boiling points-dichloromethyl ether106; allyl iso amyl acid based on the use of methyl propyl ketone as an azeotropic withdrawing agent employed in accordance with the procedure set forth herein. This ketone may contain, in the nature of an impurity, approximately 10% or less diethyl ketone. Either of these two ketones or their mixture may be used with the same results.

These ketones, individually, have maximum constant boiling mixtures withformic acid at,

105 C. containing respectively 48 mol% di-ethyl ketone and 47 mol% methyl-propyl ketone. The well known constant boiling mixture of water with formic acid has a boiling point-of 107 C. and contains 43 mol% of water.

It would seem at first thought that either of these ketones would be very unsatisfactory for use due to the fact that they would be as hard to separate from formic acid as the water itself.

This is, of course, the case, unless theketones are properly employed.

It would be seen, however, that anoutstanding advantage at the start over such prior art materials as pro-pyl formate, would be that the ketones would increase the relative boiling point of formic acid-or decrease its vapor pressure and thus make it somewhat easier to separate from water.

It has been found possible to remove the water from formic acid by the use of these ketones at set forth in Othmer Patent No. 2,028,800 or in,

accordance with the procedure described in the present application.

In accordance with the procedure in the present application the lower part of the column will be used as a rectifying column to separate the water and formic acid, producinghighly concentrated or anhydrous acid at the base. .In this later case. it will be seen that it is necessary to than 43 mol% at that point where the lastof the withdrawing agent leaves in order that the rectifying may proceed along with part of the vapor composition curve between the constant boiling mixture and anhydrous formic acid.

Because of the closeness of the vapor composition curve to the 45 diagonal-i.e., the little difference between composition of vapor and liquid, or the difficulty in rectification--this dependence on the lower part ofthe column for straight rectification requires a very efllcient distilling unit. It is therefore preferred to operate according to the principle of Othmer 2,028,800 to carry off the Water: and while this is a somewhat difficult condition to keep balanced, it issimpler than the operation of prior art methods for formic dehydration.

For convenience of consideration in Table 1 below there is a list of eight ketones which fall within the boiling range 102 C.-150 C. and which are commercially available. This by no means exhausts the list of ketones which are known and which boil within this range and which would be useful for this purpose but these materials are examples and all are commercially available at the present time. The data in this list includes the molecular weight, the specific gravity at the boiling point at atmospheric pressure, the solubility in water-end water in, the latent heat in calories per gram, the azeotropic boiling point with water, and the azeotropic ratio of solvent to water by volume. This last point is found by carefully obtaining thy azeotropic ,vaporous mixture. condensing thesl vapors, and measuring the solvent and water layers. Finally there is listed the maximum strength of acetic acid which may be best extracted by these solvents, or in other words, the strength of acid in contact with the solvent just below the point at which perfect miscibility is obtained. This data is believed accurate within a reasonable range allowed for experimental error.

Because of the considerable insolubility of these materials in water, these materials will give a much sharper separation in the decanter,

x will carry back less water to the distilling column .for re-evaporation and will carry less solvent to the stripping column and therefore decrease the load and steam consumption of the stripper than *is the case with certain prior art esters.

Because of the very satisfactory distribution ratios of these materials as illustrated in the attached drawing, Fig. 1 the efficiency of the rectifying column is very considerable as has been explained before; and for a given desired sweet Water concentration, the column may be comparatively short.

Table 1 Solubilitv by weight Maximum i A Azeo 111K- Mnle- Specific Latent Area boilw tune by Ketone cular gravity at 332 a; 1 ing point volume weight '20 f. j with water be ketone In water Water in Lmcted water ill-ethyl. Methyl pro; iyl l i i v llexonc (methyl isnbutyl) Higher ketones 4:01 65 70% li-isonropyl. 35-30% ethyl isopropyL IMethyl n butyl 80 to l Mesityl oxide 34% 46 to l Dipropyl i r r Methyl n amyl 45% 1 4 to l While the above description has been directed to the consideration of the group of oxygenated compounds, the aliphatic ketones; I have also found and as already described that there are anumber of ethere, which are satisfactory for use in my novel process. There is following detailed information concerning some of the ethers which are more orless commercially available together with their physical properties. Other ether-s would be those boiling within the boiling range of approximately 102 C.-to 150 Such ethers as those not'speciflcally mentioned may .be readily determined by a consideration of the permutations and combination of alcohols togive ethers in this boiling range.

, Dibutyl' Ethyl hexyl Ether other other Molecular. weight 130 130. Specific gravity 20/20. 0. 7713 0. 8327. Boiling poiut. 142.6 143-144. Solubility in water percent by wt. 0. 04 Insoluble .l. Solubility of water in percent by wt 0.05 Insoluble .l. Azootropic boiling point with wager 02.9 92. 9. Azcotropic mixture by voluinei g: 2' 6 2, 45, Max. strength acetic which is best ex 70 70 or above.

trocted, percent. ,1

The ethers, such as di-butyl and the like are particularly suitable for acetic and higher aliphatic acids. However, there are a number of ethers which may be employed in accordance with my novel procedure for dehydrating formic Iso propyl 675 C. Methyl-n butyl '70.0 C. Ethyl-n propyl 61.4 C. Ethyl t butyl73.1 C. Ethyl isobutyl 81.1 C. Ethyl isobutyl 80 C. Propyl isopropyl 80 C. Methyl t butyl 552 C. Ethyl sec butyl 81.2 C.

The ethers containing an alcohol not of the straight chain configuration are advantageous for two reasons: (1) They may be readily produced compared with the tedious and expensive method for making mixed ethers containing two normal alcohol groups, (2) in decomposing they give respecti've alcohols rather than explosive peroxides.

In further reference to the use of ethers for dehydrating formic acid, special mention is made of isopropyl ether.

Because of the fact that formic acid has a maximum boiling azeotropic mixture with water itself, it is even more difficult to separate from water than is the more familiar acetic acid. The choice of azeotropic withdrawing agents has consequently been more limited. In previous patents, (U. S. 1,826,302 and 1,930,146) the use of. propyl formate was covered as being suitable I 'still pot.

for this operation and also for liquid-liquid ex- .tration of the aqueous formic acid.

It is generally desirable to use a withdrawing agent for dehydrating formic solutions having a lower boiling point than would be usually regarded as desirable with'acetic acid. This lower boiling point means a lower boiling azeotropic mixture which in turn means a larger amount of withdrawing agent in the azeotropic mixture and hence a larger amount of reflux to the column. This large amount of reflux helps to accomplish the separation, and turns out a very small amount of formic acid at the top of the .column in the water while maintaining a concentrated acid at the base.

An azeotropic withdrawing agent of higher .boiling point would give a smaller amount of reflux; but because of the difficulty of separating the water from the formic acid, would bring over considerable acid in the water discharge from the decanter.

In my search for suitable materials, it. was .found that isopropyl ether, having a normal boilingtpoint of approximately 69 C., is satisfactory .for this separation because it requires approximately 31 parts of ether by weight to bring over one part of water by weight. Thus there is a very large amount of reflux available to accomplish the separation of water from formic acid in the column. The azeotropic boiling point is approximately 2.6 lbs. of steam per lb. of water removed, in addition to the heat of vaporation of the water itself (i. e. the total heat requiredexcept radiation and other losses per lb. of water removed is approximately that of 3.6 lbs. .of steam.

The following is an example of a run carried out employing isopropyl ether for dehydrating formic acid and my process wherein the lower part of the column was operated in straight rectification.

90% formic acid was diluted with water (5 to 4) to give approximately 50% formic acid. This was fed into a fifteen foot column, packed with glass beads, at a height of ten feet above the Iso-propyl ether was used as the azeotropic withdrawing material. Water was discharged with no taste of formic acid but a taste of the isopropyl ether. About 0.3% acid by titration in water layer. The process continued unchanged until the acid in the still pot-originally 50% approx-came up to the azeotropic point. The boiling point in the still pot had then reached 1065 where it stayed constant. Still not acid titrated about 72% acid, water practically ceased coming off the top, isopropyl ether circulated around. This isopropyl at the top titrated less than 0.1% acid. Temperature 64 to 66.

For further consideration of my invention, reference may be had to the attached drawings.

Fig. 1 is a graphic representation showing the distribution of acetic acid between water and the ketones of the present invention.

Fig. 2 is a similar representation concerning some of the ethers of the present invention.

Fig. 3 is a diagrammatic side elevation View of one form of appropriate apparatus which may be used in carrying out my process.

It isxtherefore, apparent from the above description that my process may employ a variety of different agents including both ketones and ethers. For convenience of reference I may hereinafter term these ketone and ether aliphaticwithdrawing agents or entrainers as oxygenated.

Since the legends appearing on the drawings terials which are suitable for the azeotropic' render the figures self explanatory, further description is unnecessary.

Certain of the liquids are more efficient from the standpoint of heat costs, others may be more efficient from the standpoint of ease of separation of substantially pure water at the still head. In some case, as, for example, with butyl ether, I have discovered that some acid may be found in the water at the still head unless one of the longer columns are used. This is not always undesirable, but when acid entirely free water is wanted, choice may be made of another material.

It will be apparent to those skilled in the art that the calculation of the number of bubble cap plates-if the usual plate column is used-necessary for the lower part of the column can readily be made by setting up the customary heat balances. The maximum amount of reflux wash entering the top of this section may also be obtained by the same calculation. With a known number of plates, and theamount of reflux wash which is available thus calculated, it is simple to determineby the usual methods of design for a column the maximum amount of water which may be allowed in the acid descending from the azeotropic section if glacial acid is to be obtained at the column base. The upper part of the column in which the azeotropic distillation'is conducted may be a continuation of the lower section with no mechanical transition or differences; and it is made of a suitable height to give the required freedom of acid in the water discharged. If this is exceeded in practice, it is merely necessary "to charge a small additional amount of withdrawing agent so that it will work down and thus lengthen the sectionin which the azeotropic distillation is being conducted. A skilled operator will immediately recognize a change of conditions in practice by observation of changes'in the temperatures of thermometers inserted along the side of the column, and will readily apply the proper corrections.

I have found that with a bubble plate column of standard design, that from about thirty to fifty plates are required, depending to some extent upon the strength of the acid to be concentrated; but to a greater extent on the boiling point and some other physical properties "of the withdrawing agent used.

In many cases, the same ketones'and ethers which I have found to be suitable for azeotroplc,

withdrawingagents by the use of the process described, may be used as extracting agents for the separation of the acetic acid or other aliphatic acid from the bulk of the water before distillation. While the use of extracting solvents having relatively high boiling points is known (U. 8. Patent 1,839,932,) it has hitherto been necessary to add still another liquid to perform the azeotropic withdrawal of the water which necessarily accompanies the acetic acid.

By the use of my method of azeotropic distillation above described, it is possible to accomplish the extraction first and then' the azeotropic distillation with the same material. While all madistillation are not usefulfor a preliminary extraction step, the ketones and ethers which I have described are satisfactory for both operations. I have also found that this process of azeotropic disti11ation-whereby insufficient Withdrawing agent is present in the distillation system to form the azeotropic mixture with the water present closure as limited and defined by the appended claims.

In particular, it may be noted that any standard type of extractorv and/or distilling column or columns which are efficient for this purpose may be used; that a single column may be used for both the azeotropic distillation and the straight rectification of water from acid or acids, or that two columns may be used with or without a still pot and heating unit in between. The dilute acid may be fed into the distilling column or columns either in a liquid or vaporous state; and the discharged acid may be either partly or completely dehydrated and passed from the distillation system in either a liquid or vaporous condition. Aso, after the azeotropic distillation, the condensate from the condenser may be separated into layers comprising substantially pure water and substantially pure withdrawing agent respectively, and the former discharged to waste or to an auxiliary still for.recovering the trace of withdrawing agent dissolved therein, while the latter is returned to the head of the still as reflux wash, or divided into two or more streams. one of which. enters the top of the distilling column and the rest of which enters the column at a lower point or points. Likewise, it isapparent that in some cases other chemical materials'than the withdrawing liquid itself may be added in such a way that the withdrawing liquid will be manufactured in the column. Also as already described various mixtures of withdrawingliquids may be used in combination.

Having described my invention, what I claim and desire to secure by Letters Patent is, as follows:-

aqueous solutions of the lower fatty acidsby distillation in the presence of withdrawing agents y from the group'gbgnsisting of ketones and ethers for the uyai' ;.oi; water, the separation of the last'partioftheimater from the lower aliphatic .acid by straight "rectification, said rectification using the same vaporous heat which is thereafter passed to the 'azeotropic distillation and keeping said withdrawing agent out of the resultant dehydrated fatty acid at all times that it occurs dehydrated acid.

2. The process for group consisting of ketones and ethers which separating water from lower fatty acid or acids by distillation with an' aliphatic oxygenated withdrawing agent from the forms an azeotropic mixture in the still head,

the vaporous mixture is condensed, the con 'densate separated into a water and a withdraw- V ing liquid layer, the water layer discharged and the oxygenated withdrawing liquid layer returnedto the still head to remove more water, the partially concentrated lower fatty acid or acids passed out of the upper part of the distilling column containing withdrawing liquid to a. lower part which contains no withdrawing liquid, additional water separated by straight rectification of the lower fatty acid or acids in the lower part of the column, the highly concentrated or anhydrous lower fatty acid or acids removed from the column base, keeping said withdrawing agent out of said concentrated fatty acid at all times that it occurs as concentrated acid, and a vaporous mixture, containing most or substantially all of the water, passed upwardly from said lower part of the distilling column to said upper part.

3. In the process of dehydrating aqueous solutions of the lower fatty acids by extraction and distillation in the presence of oxygenated aliphatic withdrawing agents from the group consisting of ketones and ethers having a normal boiling point between 102 and 150 C. for the removal of water, the use of insufficient withdrawing agent to form an azeotropic mixture with water n the lower part of the distilling column and keeping said oxygenated aliphatic withdrawing agent out of the dehydrated acid at all times.

' 4. In the continuous process of dehydrating aqueous solutions of the lower fatty acids by distillation in the presence of a ketone withdrawing agent, the separation of the last part of the water from the acid or acids by straight rectification and keeping the ketone out of the dehydrated acid at all times that it occurs as dehydrated acid 5. In the continuous process of dehydrating aqueous solutions of the lower fatty acids by distillation in the presence of an ether withdrawing agent, the separation of the last part of the water from the acid or acids by straight rectification and keeping the ether out of the dehydrated acid at all times that it occurs as dehydrated acid.

6. In the continuous process of dehydrating aqueous solutions of the lower fatty acids by distillation in the presence of oxygenated aliphatic withdrawing agents from the group consisting of ketones and ethers, the separation of the last part of the water from thefatty acids by straight rectification, said rectification using the same vaporous heat which is thereafter passed to the azeotropic distillation and keeping the oxygenated Withdrawing agents out of the dchydrated acids at all times that they occur as dehydrated acids.

'7. In the continuous process of dehydrating aqueous solutions of the lower fatty acids by distillation in the presence of ketone withdrawing agents from the group consisting of ethyl propy ketone, methyl butyl ketone, allyl acetone, dipropyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl normal butyl ketone, methyl normal amyl ketone for the removal of water, the separation of the last part of the water from the acetic acid by straight rectification, said rectification using the same vaporous heat which is thereafter passed to the azeotropic distillation and keeping the ketone withdrawing agents out of the dehydrated fatty acids at all times that they occur as dehydrated acids.

8. In the process of dehydrating aqueous solutions of the lower fatty acids by distillation in the presence of ethers boiling within the range 50-150 C. and capable of the removal of water as an azeotrope, the use of insufiicient ether to form an azeotropic mixture with water in the lower part of the distilling column and keeping the ethers out of the dehydrated fatty acids at all times that they occur as dehydrated acids.

9. In the continuous process for dehydrating aqueous solutions of formic acids including azeotropic distillation in the presence of isopropyl ether for the removal of water, the separation of the last part of the water from the formic acid by straight rectification, said straight rectification supplying at least a part of the same vaporous heat which is thereafter passed to the azeotropic distillation and keeping the isopropyl ether out of the dehydrated formic acid at all times that it occurs as dehydrated acid.

10. In a process for dehydrating aqueous solutions containing at least one of the lower fatty acids by distillation in the presence of ethyl hexyl ether as a withdrawing agent for the removal of water, the separation of the last part of the water from the acid or acids by straight rectification and keeping the ethyl hexyl ether out of the dehydrated acid at all times that it occurs as de-' hydrated acid.

11. In a process for dehydrating aqueous solutions containing at least one of the lower fatty acids by distillation in the presence of normal butyl ether for the removal of water by azeotropic distillation in the upper part of the distilling unit, the use of insufficient normal butyl ether to form an azeotropic mixture with the water in the lower part of the distilling unit andkeeping the butyl ether out of the dehydrated acid at all times that it occurs as dehydrated acid.

12. The process for separating water from aqueous formic acid solutions, which comprises distilling the aqueous formic acid solutions in a distilling column having a still pot,with ketones which form an azeotropic mixture with the water, condensing the azeotropic mixture, permitting the condensate to separate into a water layer and a ketone layer, discharging the water layer and returning the ketone layer to distillation for re moving more water, employing insufficient ketone agent to form an azeotropic mixture with the water in the lower part of the distilling column and separating the last part of the water from the formic acid by straight rectification so as to give dehydrated formic acid in the still pot and keeping the ketone out of the dehydrated formic acid at all times that it occurs as dehydrated acid.

13. In the continuous process of dehydrating aqueous solutions of the lower fatty acids by distillation in the presence of ketone withdrawing agents from the group consisting of ethyl propyl ketone, methyl butyl ketone, allyl acetone, di-' propyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl normal butyl ketone, methyl normal amyl ketone for the removal of water, the use of insufficient ketone withdrawing agent to form an azeotropic mixture with water in the lower part of the column and the separation of the last part of the water from the acid or acids by straight rectification and keeping the aforementioned agents out of dehydrated acid at all times that it occurs as dehydrated acid.

' DONALD F. OTHMER.

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