US2489608A - Process for producing acetaldol - Google Patents

Description

Nov. 29, 1949 ALHERITIERE 2,489,608

PROCESS FOR PRODUCING ACETALDOL Filed Feb. 10, 1947 2 She'ets-Sheet 1 CONDENSER I 7/ W1.

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SEPARATIZQ COLUMN INVENTOR.

Lows ALHIERITIERE.

av W /W ATTO R N EIYS.

Nov. 29, 1949 1.. ALHERITIERE I 2,489,608

PROCESS FOR PRODUCING ACETALDOL FiledFeb. 10, 4947 2 Sheets-Sheet 2 20 I CONDENSER.

SEPARATINYCQLuMN INVENTOR- LOUIS'ALHERITIEREL.

ATTORN EYS.

Patented Nov. 29, 1949 UNITED STATES PATENT OFFICE PROCESS FOR PRODUCING ACETALDOL Louis Alhritire, Beau-Soleil, Melle, France,

assignor to Les Usines de Melle Saint-Leger-les-Melle, France, a

Anonyme corporation of France Application February 10, 1947, Serial No. 727,491 In France February 18, 1946 6 Claims. (Cl. 260-602) From aldol, crotonaldehyde is formed by removal of water. The reaction which occurs may be represented as follows:

Acetaldehyde Aldol CH3CH=CI-ICHO+H2O Crotonaldehyde One of the main difficulties encountered in effecting this reaction on an industrial scale, lies in the considerable release of heat in the production of aldol which must be carefully controlled to prevent a violent reaction. To assure the regular elimination of the heat, several methods have been suggested. There has been recommended especially the dilution of aldehyde by water, alcohol, etc., in order to reduce the speed of aldolizing and at the same time the speed of the secondary reactions which lead to the formation of the poly aldols. The efforts of the research workers have been mainly concerned with the means of refrigeration used; thus there has been recommended, for example, the use of plate heat exchangers, having a, very high heat exchanging coefficient.

Irrespective of the diversity of the devices evolved up to date, both for continuous and for interrupted operation, in using the known procedures one has always been forced to operate at the lowest possible economic temperature, so as to maintain the conversion at the upper limit. It is known that with high temperatures only a small percentage of conversion of acetaldehyde to aldol is effected.

In the processes known, the aldolizing was carried out either in strongly cooled vats or incountercurrent heat exchangers or in apparatus combining these two means. When the desired conversion degree had been obtained, the mixture was brought to a suitable pH to stop the reaction The principal object of the present invention. accordingly is to provide a simple process which These necessity for isolating the aldol to produce such" liquid.

(Socicte shall do away, at least in part, with the disadvantages mentioned of the prior processes. Another object of the invention is to provide a process of the kind described which may alternatively produce either aldol or crotonaldehyde as desired and in which the crotonaldehyde may be produced directly from the aldol as a continuation ofthe process for producing aldol without crotonaldehyde. Another object of the invention is to provide a simple apparatus which may be used for carrying out the process.

The invention accordingly comprises the novel apparatus and combinations thereof, as well as' the novel processes and steps of processes which may be carried out in such apparatus, specific embodiments of which are described herein by way of example only and in accordance with the manner in which I now prefer to practice the invention.

I have found in accordance with my invention that operating at a low temperature is not indispensable and that it is, on the contrary, im-

portant to operate at a high temperature. The present invention, based on this surprising observation, is characterized by the fact that the aldolizing is carried out in a medium at boiling point. The vapors emitted consisting mostly of the condensed product to the apparatus.

An essential feature of this invention is that I eifect conversion of ethanal to aldol in a body of liquid medium mainly comprised by ethanal, i. e.

a volatile substance, so that a considerable" amount of ethanal is vaporized by reaction heat and thus acts as a cooling fluid that carries heat to the condenser, and then is refluxed as a cool of the cooling agent as has been done for example where water was employed as a cooling agent, I use the total heat including the latent heat of evaporation so that for a given amount of cooling fluid, the latter is used much more efficiently. Hence it is possible according to the preferred embodiment of my invention to provide an aldolization zone of so small a volume that an adequately efiicient heat exchanger for cooling purposes as conventionally employed in the past could not be accommodated therein.

invention, I make provision whereby acetalde- In other words, through the reaction zone and a condenser I provide a cycle of ethanal, whereby instead of using only the specific heat hyde is in contact with aldolization catalyst only for a very short period of time, specifically not longer than about minutes. For this purpose, in a reaction zone I maintain a shallow body of liquid mainly composed of acetaldehyde in major proportion and acetaldol in minor proportion, for example by providing a weir or overflow in a reaction chamber or by providing a. number of capless trays in the top zone of a distillation column, and I continuously supply this shallow body of liquid with acetaldehyde at a rate of at least twelve times the volume of said body per hour, together with an alkaline aldolization catalyst in such a proportion as to cause conversion of about 35 to per cent of acetaldehyde to acetaldol; with such a rate of conversion, heat developed by the aldolization reaction keeps the body in steady, strongly boiling condition at a temperature of about 30 to about 45 0., producing a considerable evolution of acetaldehyde vapors which provide for dissipation of heat produced in the body. The liquid which overflows from said body still contains aldolization catalyst, which I thereafter immediately render ineffective, e. g. by adding acid.

The period of contact is preferably from 1 to 5 minutes and consequently the rate of supply of liquid acetaldehyde to the body of liquid per hour should be from about 60 to about 12 times the volume of said body.

According to the preferred embodiment of my invention, the vapours of acetaldeyde evolved from the boiling body of liquid are condensed in a. separate condensation zone; furthermore unconverted acetaldehydein the liquid overflowing from. the body is recovered, and; the condensed acetaldehyde, the reconnected acetaldehyde and a proper amount of fresh acetaldehyde are com bined to form the aforesaid supply of acetaldehyde to said body; the proportion of fresh acetaldehyde in the supply of acetaldehyde continuously fed to the body is from about 23 to about 12.5 per cent with respect to the total supply where a rate of conversion of 35 to 15 per cent is secured. As to the proportion of' alkaline aldolization catalyst with respect to fresh acetaldehyde, it amounts to about 0.2-0.3 per cent expressed in terms of caustic.

As stated, the. process is preferably operated in a continuous manner. It includes the maintenance of a shallow body, preferably shallow pools of liquid, contained in an aldolizing chamber and which liquid consists mainly of acetaldehyde in major proportion and acetaldol in minor proportion. This chamber constitutes a reaction zone which has a greater volume than the total volume of the pools. Liquid acetaldehyde is fed to. the uppermost of these pools and it overflows to the next poolv below, the depth and consequently the volume of the liquid in any pool being controlled by the height of the overflow above the bottom of the pool. The rate of feed. of the acetaldehyde is at least 1 times the total combined volume of the pools per hour. To. the uppermost or first pooI, an aldolization catalyst is fed in a proportion to cause conversion of about 35-15% of the acetaldehyde fed to the first pool. The pools are kept in a strongly boiling condition at a temperature of about 30 to 45 C. The acetaldehyde is constantly boiled off, condensed and returned to the aldolizing chamber. The rate of flow of freshly supplied acetaldehyde plus that recycled is equal to at least 12 times the volume of liquid in the pools of the aldoli'zing chamber. The rate of sup- 4 ply of fresh acetaldehyde is about 12.5 to 23% of the combined total of acetaldehyde recycled and acetaldehyde freshly added. An aldolization catalyst is added to the shallow body of liquid at a rate of about 0.2 to 0.3% with respect to the rate of supply of acetaldehyde.

Thus, where there is approximately 40 liters of liquid on the capless plates in chamber A as discussed below in connection with the drawings, the acetaldehyde is supplied at a rate of at least 480 liters per hour and the aldolization catalyst is supplied at a rate of about at least 9.6 to about 14.4 liters per hour.

To replace the aldolizing equipment heretofore used and the consequent complex refrigerating circuit, it sufiices in accordance with my invention, to provide a simple aldolizing chamber connected with the aldol-acetaldehyde separation column in such a manner that the vapors which carry off the calories of the reaction and which are emitted during the aldolizing, join the vapors originating from the column while the condensed liquid passes through the aldolizlng zone or chamber and thence to the column. In both of the apparatuses described below, the acetaldehyde is in an enclosed circuit and losses are consequently cut down.

In the accompanying drawings is shown an apparatus in accordance with my invention which may be employed to carry out my above described process, in which Figure 1 represents a diagrammatic elevation showing in cross section a column of which the upper portion constitutes the reaction chamber, and

Fig. 2 shows a similar elevation of a modified device in which a separate reaction chamber is used.

Referring now to these drawings, the numeral l represents an aldolizing chamber containing plates 2. These plates are provided with the customary overflows 3 which permit the flow of liquid from plate to plate but instead of being provided with bubble caps, they are provided with uncapped flues 4 and 5 which permit the free passage to a condenser l of all vapors originati'ng in the aldolizing chamber and in the column below. With these vapors flows heat from the exothermic reaction, thus preventing excessive rise of temperature in the reacting mixture. These vapors ma then flow freely through the conduit 6 at the top of the chamber to the condenser and upon condensation may be returned through pipe 8 to the chamber above the upper- I most plate 2.

This aldolizing chamber I is placed directly on top of the separating column 9 which is provided with the usual plates H3 and also provided with the usual overflows ll. Each of the plates ID has the usual central flue 22 provided with a bubble cap l3.

Liquid collectin at the base chamber M of the column 9 may be heated by a steam coil 55 to the boiling point and removed through conduit [5a controlled by valve E 8.

A supply of acetaldehyde and water is. fed through pipe I! to pipe 8 and thus passes into the aldolizing chamber along with condensate from the condenser 1. Through a pipe 8 a solution of an alkaline agent, as sodium, po-

chloric acid, is passed. onto the uppermost plate.

separate chamber and. its connections, the-r characteristics of Figs. 1 and 2 are substantially. It is connected with the uppermost plate ID of the separating column by a pipe 2I.. Water and acetaldehyde are admitted through- I! and sodium hydroxide is admitted:-

the same.

D 1 through pipe I8. These pipes join pipe 8 which return condensate from the condenser I to the aldolizing chamber. A pipe 22 leads directly from the top of the separating column 9 to the condenser I. It is joined by the pipe 8 leading from the aldolizing chamber I and through it pass the. acetaldehyde vapors from both the chamber I and the column 9.

The following are examples of my process. These examples are illustrative and the process is not to be restricted thereto except as indicated in the appended claims.

Example 1 into the top of the aldolizing chamber I flowing in over the top plate 2..

2. An exothermic reaction occurs as the aldolizing is efiected in the aldolizing chamber.

theuppermost plate I0 of the separating column 9. The aldolizing is effected on the plates Z of the aldolizing chamber and the flow of material overtheseplates is regulated in such a manner thatthe liquid held by them remains there for about five minutes.

vapors consisting substantially of pure acetaldehyde escape from the column through pipe Ii, are

condensed at I and returned to the uppermost. plate 2 of the aldolizing chamber through pipe 8.:

liquid or pool on the capless plates'in chamber I amounts to about 40 litres, and its free or exposed surface has an area of about 4 square decimeters it should be understood that the foregoing figures are not limitative (thus for example an area larger than 4 square decimeters may be provided) but they readily show that I can efiect' aldolization efiiciently in a quite small reaction chamber.

Acetic acid of 50 grams per liter is introduced through pipe I9 onto the uppermost bubble plate I0 of the separating column at the rate of about 16 liters per hour. mixture and brings its pH to a value of between about 4 and about 5. This causes the aldol reaction to stop. The separation of the acetaldehyde and aldol formed is effected on the succeed- 16 liters of aqueous: sodium hydroxide containing 20 grams of NaOH per liter are introduced through pipe I8 to mix. with the water and acetaldehyde above the plate- Themixture of acetaldehyde, water and sodium hy-,-' droxide overflows through pipes 3 from each of, the two plates 2 in this chamber and descends to The heat released by the reaction v causes the liquid to boil at about 33 C. The

Acetic acid neutralizes the" 107 kgs. per hour of acetaldehyde and 20 kgs.; per hour of water are introduced through pipe I! ingplates III of the separating column. The liquid collecting in the base chamber Id of the separating column is heated by steam passing through pipe I5 and is accordingly maintained at its boiling point. It consists of a solution of aldol with .the diluent water and sodium acetate. This mixture is drawn off at the base of the column through the pipe II and the aldol is recovered from the mixture in a known manner. The yield of aldol is approximately 97 The above process is carried out at atmospheric pressure. It may also be carried out at a slightly higher pressure, namely, about .5 kg./cm. above atmospheric pressure, in order to facilitate the condensation of the vapors of acetaldehyde. For this purpose, nitrogen or other inert gas may be introduced through the pipes 20 and 8 in regulated amount to give the desired pressure. The liquids then introduced through the pipes leading to the aldolizing chamber I and to the fractionating column 9 are then admitted under suitable pressure. The gate valve I6 regulates the release of the aldol-containing liquid from the chamber I4.

Crotonaldehyde may be directly manufactured from aldol thus formed without isolating the aldol. For this purpose, a pressure from 1 to 5 lag/cm. is maintained throughout the apparatus. This pressure results in uniformly increasing the entire range of temperatures prevailing throughout the apparatus, thus causing the dehydration of aldol in the separating column 9 to form crotonaldehyde. In other words, using exactly the same number of plates with the increased pres-' sure, the product accumulating in the base chamber I 4 of the separating column 9 will be crotonaldehyde instead of aldol.

It is more convenient in the case of an apparatus as shown in Fig. 2 to cause the superatmospheric pressure suitable for crotonisation pur-' poses to be set up only in the distillation zone 9, by providing pressure retaining means in pipes 2I and 22, so that aldolization proper in chamber I may be effected under atmospheric pressure or an only slightly increased pressure.

Example 2 I introduce through pipe I! and thence into the aldolizing chamber 107 kgs. per hour of acetaldehyde, and through pipe I8 I introduce 14 1. of aqueous potassium hydroxide solution containing 30 grams of KOH per liter. Note that no water need be introduced with the acetaldehyde for the manufacture of crotonaldehyde.

The mixture remains in the aldolizing chamber I The crotonaldehyde formed in the column 9 by dehydration of aldol in acid medium under pressure, accumulates in the base chamber I4 under hydrated condition due to the presence of the dehydration Water and may be drawn off through the gate valve I6. The length of time in which the aldol flows over the plates and in the base chamber I4 under the above conditions is about 30 minutes to form crotonaldehyde. The crotonaldehyde may be recovered from the mixture 7 flowing from the base chamber M in 'a' k'nown manner.

Instead of increasing the pressure, the number and/or capacity of the plates of the separating column may be increased in order to increase the time in which the aldol in the pot remains in the acid medium, which also causes the formation of crotonaldehyde.

Instead of employing a pressure of 2 kgs./cml a greater number or capacity of plates maybe employed with a slightly elevated pressure, say, 1,kg./cm.

It is also possible to draw off crotonalde'hyde in the Term of a vapor consisting of an azeotrop'ic mixture thereof with water. This may be done through the pipe 22 located a few plates above the base chamber l4. Under these circumstances, residual liquors consisting of practically pure water flow off through pipe I I.

'What I claim is:

1. In a continuous process for the production of acetaldol, continuously feeding acetaldehyde and acetaldol catalyst into a shallow body "of liquid largely composed of a mixture of acetaldehyde and acetaldol and containing an acetaldol catalyst in a reaction zone of greater volume than said body, thereby producing an exothermic reaction between acetaldehyde and catalyst causing the mixture to boil strongly, retaining the fed liquid in the reaction zone for "a period of not over minutes approximately at-a temperature of from 30-45 C., converting about 35 to of the acetaldehyde to acetaldol, continuously withdrawing at a temperature not exceeding 45 C. acetaldol, acetaldehyde and unspent catalyst from the reaction zone and rendering the unspent catalyst ineffective.

2. A process in accordance with claim 1 "in which the acetaldol catalyst is a caustic alkali and is supplied at a rate of about 0.2 to about 0.3% with respect to the fed acetaldehyde.

3. In a continuous process for the production of acetaldol, maintaining a succession of constant volume shallow pools of liquid composed principally of a mixture of acetaldehyde and acetaldol and containing an acetaldol catalyst, in a reaction zone of greater volume than the total volume of said pools, continuously feeding acetaldehyde and acetaldol catalyst through the first pool so as to cause the same to pass through the successive pools, causing the liquid in the pools to boil strongly, retaining the fed liquid in the reaction Zone for a period of not over five minutes approximately at a temperature of from -45 C., converting about to 15% of the acetaldehyde to acetaldol, continuously Withdrawing from the reaction Zone at a temperature not exceeding C. acetaldol, acetaldehyde and unspent catalyst, and rendering the unspent catalyst ineffective.

4. A continuous process for the production of acetaldol which comprises, maintaining a shallow body of liquid having an overflow controlled constant volume, said liquid being mainly composed of acetaldehyde in major proportion and acetaldol in minor proportion in a reaction zone having a greater volume than said body, continuously supplying fresh liquid acetaldehyde and an acetaldol catalyst to said body, said catalyst being supplied at a rate of about 0.2 to about 0.3% with respect to the fresh acetaldehyde supplied,

, 8 maintaining the body thereby in a strongly "bolling condition at a temperature of 30 to 45 (7.,

leading acetaldehyde vapors from the reaction zone to a condensation zone, retaining the body of liquid in the reaction zone for a period of not over five minutes at the boiling temperature of 30 to 45 C., converting about 35 to 15% of the acetaldehyde to acetaldol, continuously withdrawing at a temperature not exceeding '45 :6. the liquid acetaldol, acetaldehyde and unspent catalyst f-romthe reaction zone, rendering the unspent catalyst ineffective, distilling acetaldehyde "from the withdrawn liquid and condensing same .in said condensation zone, and returning acetaldehyde continuously to the reaction 'zone along with said fresh acetaldehyde.

5. A continuous process for the production of acetaldol which comprises, maintaining a shallow body of liquid having an overflow controlled constant volume, said liquid being mainlycomposed of acetaldehyde in major proportion and acetaldol in minor proportion in a reaction zone having a greater volume than said body, continuously supplying fresh liquid acetaldehyde and an acetaldol catalyst to said body, said catalyst being a solution of caustic alkali and being supplied at a rate of about 0.2 to about 0.3% with respect to the fresh acetaldehyde supplied, maintaining the body thereby in a strongly boiling condition at a temperature of 30 to 45 0., leading acetaldehyde vapor from the reaction zone to-a condensation zone, retaining the body "of liquid in the reaction zone fora period of notover five minutes and approximately at the boiling temvperature of 30 to 45 C., converting about 35 to I5 of the acetaldehyde to acetaldol, continuously withdrawing at a temperature not exceeding 45 C. the liquid acetaldol, acetaldehyde and unspent catalyst from the reaction zone, continuously adding acid to the liquid thus withdrawn to bring the pH value thereof to about! to 5, continuously distilling the acidified liquid in a distillation zone, to expel unconverted acetaldehyde contained therein as vapors, continuously condensing the last named vapors in said condensation zone to obtain liquid acetaldehyde, and continuously returning the liquidacetaldehyde obtained in the condensation zone tosa'id body.

'6. A process in accordance with claim 1 in which the process is efiected under an inert :gas pressure of zero to 0.5 kg. per square centimeter above atmospheric pressure.

LOUIS ALI-IERITIERE.

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

UNITED STATES PATENTS Number Name Date 1,432,511 Young Oct. 1'7, 1922 1,466,411 Peters, Jr Aug. 28, 1923 1,693,907 Luscher Dec. 4, 1928 1,905,290 .Horsley Apr. 25, 1933 2,260,111 Caldwell Oct. 21, 1941 2,341,229 .Mueller-Cunradi et a1. Feb. 8, 19.44

FOREIGN PATENTS Number Country .Date

58,068 Sweden .Apr. 3, .1923

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