US2275802A - Treating azeotropic condensate - Google Patents

Description

March 10, 1942. QTHMER AL 2,275,802

TREATING AZEO'IROPIC CONDENSATE Filed Aug. 10, 1939 CONDENSERS 0R 4 2| Fig.1. 4 HEAT EXCHANuuo AGENT AND WATER 6 -&coo|.mc k FLUID 4 3 DECANTER AGENT AGENT k WATER (cooLEo) DECANTER AGENT '2 A8 //17 AGENTAND Comm ,ISTRIPPING WATER E COLUMN WATER f I4 fifig /AZEOTROPIC FEED Z --CONDEN5ER 0R w ACID AND ACID HEAT EXCHANGER WATER VAPORS ACID ACID FLQ HEAT 7 i CONDENSERSOR HEAT EXCHANGERS s2 36 5s AZEOTROPE WATER I ACID AGENT 4 WATER EXTRACT-OR LIQUID AGENT REFLUX uouw 4| AZEOTROPIC ams COLUMN HEAT gwue/wtou Donald F. Oflmwr Robert E.Whue

Patented Mar. 10, 1942 TREATING AZEOTROPIC CONDENSATE Donald F. Othmer, Coudersport, Pa., and Robert E. White, Cincinnati, Ohio, assignors to Eastman Kodak Company, Rochester, N.

poration of New Jersey Application August 10, 1939, Serial No. 289,451

Claims.

This invention relates to an improved process of azeotropic distillation and more particularly to improved procedure for decanting the azeotropic condensate produced in such type distillation.

Various processes of azeotropic distillation are used in industry. One example of such industrial uses is in the dehydration of aliphatic acids. As shown in Othmer Patent No. 2,028,800, mixtures of aliphatic acids and water may be distilled withan agent which carries over the water as an azeotrope, thereby leaving a dehydrated acid. The water-agent azeotrope is condensed, decanted and the decanted agent returned to the process. The water layer from the decantation is passed to further distillation. In azeotropic processes as previously carried out, it will be observed that condensers of substantial size were employed for cooling the azeotropic mixture. In addition, in commercial operation the cooling medium employed in many instances comprises water pumped from rivers or other large bodies of water. Consequently, the cooling medium was usually well below atmospheric and room temperatures and below -20 C. Therefore, in prior art processes, although the azeotropic vapors might be at a temperature of 80-90 C. or higher, the condensate therefrom and the agent separated in accordance with procedure prior to our invention would be cooled to relatively low temperatures, as for example -30 C. or lower. It is readily apparent that the production of such temperature differentials not only requires heat for raising the ingredients to a vaporous condition, but also involves costs in cooling, pumping the cooling fluid, and other factors which will be pointed out as the description proceeds.

We have found improved procedure for operating azeotropic distillation processes and handling the azeotropic condensates, whereby not only heat economies are obtained, but added apparatus capacity and other advantages are also obtained.

This invention has for one object to provide improved procedure for operating azeotropic distillation processes and in particular azeotropic distillation processes for the dehydration of aqueous solutions of lower aliphatic acids. A still further object is to provide improved procedure for handling azeotropic condensates obtained in the azeotropic distillation of lower aliphatic acids. A still further object is to provide improved separation procedure for condensates obtained during azeotropic distillation. Still another object is to provide special decantation procedure in azeoadmixture with lower aliphatic acids.

Y., a cortropic distillation. Another object is to provide a method of separating azeotropic-forming agents from condensates, whereby particularly complete separation is obtained. A still further object is to provide improved operatory procedure which may be applied to existing systems for the azeotropic dehydration of aqueous solutions of lower aliphatic acids to obtain increased capacities and other economies from such existing systems.

In the present application, by the term agent" we referto any of the various chemical compounds such as esters, ethers, ketones and hydrocarbons such as, fofiexample, described in Othmer 2,028,800 and 2,050,234, which are capable of forming an azeotrope withwater, and thereby assisting in the separation of water in By the term liquid as employed herein, we refer to various constituents such as methyl alcohol, solvents such as halogenated hydrocarbons, or other similar constituents which may be present in the aqueous solutions of aliphatic acids being treated by azeotropic distillation. For example, if the aqueous solution aliphatic acid is obtained from pyrollgneous liquor, a content of methanol may be present with the acid.

We have found that in azeotropic distillation processes the mutual solubilities of the agent in water and/or liquid may not necessarily be most favorable from the separation standpoint, when the mixture is at a substantially reduced temperature. While in the instance of dissolving solids in solvents the quantity of solid in the solvent may be increased by increasing the temperature of the solvent and conversely the cooling of supersaturated solutions will cause the separation of solid, such generalities do not necessarily follow in liquid-liquid systems. In the case of liquid-liquid components, the action is quite unpredictable and the inter-relation of the factors of mutual miscibility of two layers at elevated temperatures apparently may not follow definite rules.

After considerable investigation, we have found that treating condensates resulting from the vapors evolved during azeotropic distillation, under varying conditions, that certain heat economies may be effected, as well as better separation obtained of the components comprising the condensate.

For a more complete understanding of our invention, reference is made to the attached drawing forming a part of the present application Fig. 1 is a semi-diagrammatic side elevation view of one apparatusarrangement that may be employed for carrying out our process.

Fig. 2 is also a semi-diagrammatic side elevation view of another arrangement of apparatus which may be employed for carrying out a modification of our process.

Referring to Fig.1, 2 represents a distillation column suitable for carrying out azeotropic distillation of aliphatic acids. The-column might comprise .a 30-60 plate unit or two or more columns could be employed. The construction. of suitable azeotropic columns are described in the patents aforementioned or in various other patents as for example 1,908,508, 2,049,440 and 2,049,441. Hence, further description thereof is unnecessary.

Also, as described in the patents above-men tioned, the column would be connected by a vapor oiftake conduit3 to condenser or heat exchanger 4. However, in accordance with this invention the vapor ofltake conduit would enter the condenser at a lower point, as for example point 6. Furthermore, the condenser may be of consider- The condensate formed by cooling device 33 is discharged through conduit 31 into decanter 38 as described with respect to Fig. 1. However, in accordance with the arrangement shown in Fig. 2, one of the layers from the decanter would be conducted through conduit 39 through the extractor 4!, wherein not only may cooling be caused to take place, but certain components in the agent may be removed. This may be done by the introduction of a cold solvent as for example, water into the conduit 42. Conduit 42 is provided for conducting the water and any liquid extracted away from extractor to the stripping. column 43. A secondconduit 44 is provided for conducting the other layer from decanter 38 to stripping column 43. a I

Stripping-column 43 is provided with a vapor offtake conduit 46 which leads through condenser 41 so asto discharge intodecanter 38 similar to the arrangement described with respect to Fig. 1. However, in accordance with the con struction of Fig. 2, an additional group of plates ably smaller construction, inasmuch as the condensate formed therein is not to bematerially cooled. Conduit I is provided for conducting the condensate to a decanter 8. This decanter may be of construction such as described in the patents aforementioned.

However, in accordance with this invention, the draw-oil 9 for the agent layer (which, for the purposes of convenience will be assumed to be the upper layer in the decanter) would be conducted to a cooling device or heat exchanger H. This cooling device is connected by conduit l2 to another decanter 13, which decanter is con- 48 are positioned above the section 43 for the purpose of permitting the separation of the liquid aforementioned. This additional construction includes vapor offtake conduit 5| and condenser 52 which discharges into the weir box 53. Provisionis made for the reflux line 54 and draw-off line 55. I H

Likewise, in the construction of Fig. 2it is to be understood that suitable provision would be made for supplying heat tothe' columns, cooling nected by conduit l4 to the azeotropic column 2.

The decanter is also connected by another conduit I6 to a stripping column I1.

This stripping column is connected to the firstmentioned decanter 8 by means of conduit l8) The purpose of this arrangement is to permit the water layers from all decanters to be withdrawn to the stripping column. The stripping column may be of a construction as described in, for example, Patent 2,028,800, aforementioned, and include a vapor ofitake conduit l9 which passes through condenser 2| so as to discharge condensate into the first-mentioned decanter 8.

It is, of course. understood that the respective columns-will be ,equipped'with suitable means for supplying heat thereto, temperaturerecord ing devices and other such means for facilitating distillation as, described in the patents aforementioned; hen e, detailed description thereof in the present'application is unnecessary. Howeveninthe present construction, as will be medium to the condensers. etc.

In our investigation relative to the separation of condensates resulting in the azeotropic distillation of lower aliphatic acids, we have found that the relative solubilities, hot and cold, of each liquid layer in the other layer, may vary independently. Thus,- one layer may 'be' more soluble hot and theother more soluble cold, or vice versa. Or, both layers may be more soluble hot or both may be more soluble cold. We have found, however, that it is most advantageous to accomplishthe main decantation step immediately following the condensation as heretofore, excepting in those'case's where both layers have lower miscibility cold.

In'the event that the agent layer, for example has lower mutual solubility cold than hot, it is passed from the hotdecantationthrough a heat exchanger or cooler to cool it down to the desired temperature; thence, to a subsequent dedescribed in further detail with respect to Fig. 2,

provision may bemade for passing v the agent layereither through the azeotrope -condensers or in contact with'the outgoing concentratedacid in order that the agent be substantially heated prior to its introduction into the column as-reflux.

Referring to Fig. 2, 3| represents a distillation column and 32 a vapor oiftake conduit therefrom, as described with respect to Fig. 1. Conduit 32 leads to the condenser or heat exchanging device 33. However, in the arrangement of Fi 2, this device is adapted to receive the decanted cool agent through conduits 34 and 36 on its return as reflux to the column 3|. By this arrangement, as previously discussed, the separated agent may be returned to the column in a heated condition.

canter where the water precipitated out in the cooling process is; then. decanted. The agent layer from this cold decantati'on is then passed to the top of the az eotropic column or through a heat exchanger or passedthrough heating tubes in the condenser and then to the top of the azeotropic column as reflux thereto.

A complete understanding of our process will beapparent from a consideration of the following example, .as carried out in the apparatus of Fi .1;

Referring to Fig. 1, it will be assumed that the column 2 is operating for the continuous dehydration of acetic acid by means of a butyl acetate containing agent. That is, the butyl acetate in the column 2 forms an azeotrope with the water and upon distillation, the water is carried out of the column through conduit 3, thereby leaving the dehydrated acetic acid in the column.

From a study of the solubility of water and butyl acetate at different temperatures, it was found that water was more soluble in hot butyl acetate, than in cold butyl acetate. However. if

butyl acetate-water azeotrope were extensively cooled, it is apparent that greater heat requirements would be placed upon the process. Thus, the two effects were seen to be tending in opposite directions. 7

However, by means of the arrangement of Fig. 1, it will be seen that this diillculty is overcome. Butyl acetate and water-azeotrope entering condenser 4 at point 6 would be cooled only about suflicient to cause the condensation of the azeotrope. By the condenser arrangement shown, whereby the vapors enter the lower portion of the condenser, close control of the cooling may readily be obtained.

The butyl acetate-water condensate in a relatively warm condition then flows through conduit 1 into decanter 8. In decanter. 8 separation takes place and the butyl acetate layer forms in the upper portion of the decanter and is substantially continuously withdrawn through conduit 9 The water layer forms in the lower portion of A the decanter and is withdrawn through conduit l8. However, while there is more water dissolved in the butyl acetate layer flowing through conduit IS, the butyl acetate is considerably less soluble in the hot water flowing through conduit l8. Consequently less heat is required in column l| because there is less dissolved butyl acetate to be distilled oil and furthermore, the liquid to be vaporized is already in a heated condition.

Referring to the butyl acetate layer flowing from the decanter through conduit 9, this layer is passed through the condenser ll wherein the temperature of the butyl acetate is substantially lowered, the cooled butyl acetate being withdrawn through conduit l2 into the second decanter l3, which, in contrast to the hot decanter 8, may be considered as a cold decanter. By this cooling, water dissolved in the butyl acetate has been caused to separate out with the result that a relatively non-aqueous butyl acetate layer may be withdrawn through conduit l4 for reflux to the azeotropic column 2. In accordance with preferred procedure, this reflux layer would, in accordance with the arrangement shown in Fig. 2, be passed through the azeotrope condenser in order that the reflux would be heated before returned to the column. It is apparent from the foregoing that since the butyl acetate returned as reflux has been efiectively freed of water, (and possibly other liquids as will be pointed out with respect to Fig. 2) the load on the column 2 has been alleviated by this elimination of components which it is one of the objects of the distillation to remove. Hence, heat economies and increased capacity may be obtained in column 2 by our arrangement.

The water layer from the cold decanter I3 which may contain some butyl acetate, is conducted through conduit l6 into stripping column H, where butyl acetate is volatilized through conduit l9, condenser 2| and recovered in the decanter during the continuous operation.

In accordance with the foregoing example, it will thus be seen that the azeotrope was separated under conditions favorable to separation of the butyl acetate and then by the second treatment conditions favorable to the separation of water. -Hence, optimum separation is obtained by the arrangements described. Heat economies and increased apparatus capacity may also be obtained. While in the foregoing example we have described butyl acetate-water as the material comprising the azeotrope, it is understood that this is merely for the purposes of illustration and that other comparable azeotropic mixtures wherein, for example, the agent is less soluble in hot water, than in cold water, etc., may be similarly treated in accordance with our invention. Likewise, although we have referred to a binary azeotrope or butyl acetate-water, similar procedure may be applied to azeotropes comprised of butyl acetate-butyl alcohol-water and other azeotropes comprising a plurality of components.

Referring to Fig. 2, operations in accordance with this arrangement would be somewhat similar to that described with respect to Fig. 1. That is, an azeotrope of agent and water would be distilled through conduit 32. However, in accordance with this example, the azeotrope might also contain additional liquids such as methyl alcohol, halogenated hydrocarbons, or the like. For example, if the acetic acid being dehydrated in column 3| had been obtained from pyroligneous liquor, it might include a content of methyl alcohol which wouldv distill over through conduit 32 together with the water and agent. Or, if the acetic acid had been obtained from certain cellulose manufacturing processes in addition to water it mightalso contain halogenated hydrocarbons which would distill over with the agent and water azeotrope. For the purpose of convenience, this third liquid will merely be referred to as liquid. The azeotropic mixture of agent, water and-any liquid is cooled in condenser 33 as already described, merely suflicient to cause the condensation of the vapors but insuflicientto materially reduce the temperature.

of the condensate. The condensate flowing through conduit 31 is introduced into decanter 38, wherein it is decanted. This decantation takes place with the components in a relatively warm condition as described with respect to the first decanter in Fig. 1. The liquid might be present in the agent layer, the water layer or in both layers. The water layer from the decanter may be conducted through conduit 44 to the stripping column 43. The agent layer, together with any liquid contained therein, .is conducted through the extractor 4| wherein not only by virtue of cooling, but by introduction of a solvent for the liquid as for example water, assuming the liquid was methyl alcohol, the agent is depleted of the undesired constituents. The water and liquid from this treatment are conducted through conduit 42 to column 43. The improved agent is then passed through conduit 34 through the heat exchanger 33 where its former temperature is restored and the hot agent may then be returned through conduit 36 as reflux to the column. This procedure not only economizes on the heat requirements but permits the separation of mixtures containing in addition to the acid other ingredients such as methyl alcohol or the like, as described.

Referring to the stripping column 43, any agent which may have been carried over in the water is readily volatilized through conduit 46, condensed in condenser 41 and discharged into the decanter 38. The methyl alcohol or other liquid conducted to column 43 is rectified in the superimposed plates 48, a portion of the liquid being returned through conduit 54 for reflux and another portion being withdrawn at 55.

The foregoing examples have been set forth primarily for illustrating the preferred operation of our process and it is to be understood that our invention is not restricted thereto. For exbe made. For example, it is apparent that since the temperature of the azeotrope condensate is not materially reduced, the azeotrope condenser may be smaller than heretofore employed. Since the water layer being passed to the stripping column contains less agent than formerly, and since the agent layer being returned to the column contains less water than formerly, benefits are.

obtained in this respect.

It is therefore apparent, from the foregoing that our invention is susceptible of some modification. Hence, we do not wish to be restricted,

excepting insofar as may be necessitated by the prior art and the spirit of the appended claims;

What we claim and desire to be secured by the Letters Patent of the United States is: v

1. An improved process for the azeotropic dis-- tillation of aqueous solutions containing at least one lower aliphatic acid, which comprises distilling the aqueous solution in the presence of an agent which forms an azeotrope with water, distilling offthe vapors containing water and said agent, cooling the vapors sufiiciently to'produce a condensate therefrom but insumciently to cool the condensate 15 C. below theboili'ng point of said azeotrope, decanting the condensate in the relatively warm condition into a water layer and an agent layer, subjecting the agent layer to further cooling and decantation which canting the condensate while stillfin thewarm condition to obtain a 'water' layer and an agent layer, subjecting the agent layer tofurther cooling and decantation and returning the agent obtained from this latter decantation to the .azeotropic distillation for refluxv v 4. An azeotropic process for the distillation of aqueous aliphatic acid solutions wherein vapors of agent and water are distilled off, the steps which comprise condensing at least a part of said vapors, decanting the condensate in a heated condition a few degrees below the temperature of the boiling point of said azeotrope, and further cooling the solvent layer obtained from the first mentioned decantation, and subjecting it to a further decantation and returning solvent from this further decantation to the aforesaid distillation step as reflux.

5. A process for the azeotropic distillation of aqueous solutions containing at least one lower aliphatic acid which comprises distilling the aqueous solution in the presence of an agent essentially comprised of an ester which will form an azeotrope with water, distilling off vapors of said ester and water, cooling the vapors sufllcientlyto' obtain a condensatetherefrom but insufficiently to substantially cool the condensate, decanting the condensate into a water layer and an ester layer, subjecting the ester layer to further cooling and decantation which causes the separation of further water therefrom and returning at least a part of the ester which has causes the separation of further water from the agent, conducting this water and the first-mentioned water to treatment for the distillation therefrom of any agent contained in the water, and returning agent processed in accordance with the aforementioned steps as a heated reflux to the azeotropic distillation, by passing the agent in heat exchange with outgoing hot products of the azeotropic distillation.

2. The process of azeotropic distillation of aqueous solutions containing acetic acid, which comprises distilling the aqueous solution in the presence of an agent which forms an azeotrope with the water, distilling ofi azeotropic vapors comprised of water and agent, cooling the vapors sufficiently to form a condensate but insufficiently to cool the condensate substantially below its dew point, decanting the condensate in a warm condition into a water layer and an agent layer, subjecting the agent layer to further cooling and decantation, which causes the separation of water therefrom, and conducting the resultant agent to the azeotropic distillation.

3. A process for the distillation of aqueous solutions containing at least one lower aliphatic acid, whieh comprises distilling the aqueous solution in the presence of an agent which forms an azeotrope with the water, distilling off azeotropic vapors containing the water and agent,

cooling the vapors sufficiently to cause the formation of a condensate but insufliciently to reduce the tempearture of the condensate tomcre than 25 below the boiling point of the azeotrope, de-

been so treated to the distillation for removing further water from the aqueous-solution, there- .by leaving a dehydrated acid.

6. A process for the azeotropic distillation of aqueous solutions containing at least one lower aliphatic ,acid which comprises distilling the aqueous solution in the. presence of an agent essentially comprised 'of an ether'which will form an azeotrope with water, distilling off vapors of said-ether, and-'water, cooling the vapors sufficiently to obtain a condensate therefrom but insufficiently to substantially cool the condensate, decanting the condensate into a water layer and an ether layer, subjecting the ether layer to further cooling and decantation which causes the separation of further-water therefrom and returning at least a part of the ether which has been so treated to the distillation for removing further water from the aqueous solution, thereby leaving a dehydrated acid.

'7. A process for the azeotropic distillation of aqueous solutions containing at least one lower aliphatic acid which comprises distilling the aqueous solution in the presence of an agent essentially comprised of a ketone which will form an azeotrope with water, distilling off vapors of 7 said ketone and water, cooling the vapors sufficiently to obtain a condensate therefrom but insufficiently to substantially cool the condensate, decanting the condensate into a water layer and a ketone layer, subjecting the ketone layer to further cooling and decantation which causes the separation of further water therefrom and returning at least a part of the ketone which has been so treated to the distillation for removing further water from the aqueous solution, thereby leaving a dehydrated acid.

8. A process for the azeotropic distillation of aqueous solutions containing at least one lower aliphatic acid which comprises distilling the aqueous solution in the presence of an agent which will form an azeotrope with water, distilling off vapors of saidagent and water, cooling the vapors sufliciently to obtain a condensate therefrom but insufiiciently to substantially cool the condensate, decanting the condensate into a water layer and an agent layer, subjecting the agent layer to further cooling and decantation which causes the separation of further water therefrom and returning at least a part of the agent which has been so treated to the distillation for removing further water from the aqueous solution, thereby leaving a dehydrated acid.

9. A process for the distillation of aqueous solutions containing at least one lower aliphatic acid in the presence of a volatile constituent, which comprises distilling the aqueous solution in the presence of an agent which forms an azeotrope with water, distilling off vapors comprised of the agent, water and said volatile component, cooling the vapors sufficiently to obtain a condensate therefrom, decanting the condensate into an agent layer and a water layer, passing the agent layer to an extraction treatment wherein at least some of said constituent is removed therefrom and returning the extracted agent in a. heated condition to the distillation, conducting said water layer to distillation wherein any of said volatile constituent and agent are separated therefrom.

10. A process for the azeotropic distillation of aqueous solutions containing at least one lower aliphatic acid which comprises distilling the solution in the presence of an agent which will form an azeotrope with water, said agent being less soluble in hot water than cold water, distilling an azeotropic mixture comprising the agent and water vapor, cooling the vapors sufficiently to obtain a condensate therefrom but insufliciently to substantially cool the condensate, decanting the condensate into a water layer and an agent, subjecting the agent to further cooling and decantation which causes the separation of further water therefrom and returning at least a part of the agent which has been so treated to the distillation for removing further water from the aqueous solution, thereby leaving a dehydrated acid.

DONALD F. OTHMER.

ROBERT E. WHITE.

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