US2514966A

US2514966A - Refining and concentrating crude unsaturated aldehydes by extractive distillation

Info

Publication number: US2514966A
Application number: US1314A
Authority: US
Inventors: Gino J Pierotti; Arthur E Handlos; Charles M Reider
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1948-01-09
Filing date: 1948-01-09
Publication date: 1950-07-11
Anticipated expiration: 1967-07-11

Description

-ing means.

Patented July 11, 1950 REFINING AND CONCENTRATING CRUDE UNSATURATED ALDEHYDES BY EX- TRACTIVE DISTILLATION Delaware Application January 9, 1948, Serial No. 1,314

This invention relatesto the production of 7 high purity unsaturated aliphatic aldehydes from hydrocarbon oxidation products comprising the unsaturated aldehydes in admixture with close boiling saturated carbonylic compounds inseparable therefrom by practical scale fractionat- The invention relates more particularly to the separation of alpha-beta unsaturated aliphatic aldehydes in a state of high purity from mixtures comprising the unsaturated aldehydes in admixture with saturated aldehydes and/or ketones having the same number of carbon atoms as said unsaturated aldehydes. Still more particularly the invention relates to the production of acrolein in a state of high purity from mixtures comprising acrolein in admixture with propionaldehyde and/or acetone.

Production of the unsaturated aldehydes on a practical scale generally results in the obtaining of a crude product comprising the unsaturated aldehydes in admixture with substantial amounts of by-products unavoidably formed during the process. The ability to utilize the unsaturated aldehyde efficiently in many of its fields of application is often dependent upon the absence therein of any substantial amount of impurities. The large scale production of an unsaturated aldehyde of relatively high purity is, of necessity, limited to methods enabling the obtaining of a product comprising the unsaturated aldehyde in admixture with impurities which are readily separable therefrom by available practical scale separating means. Thus the production of acrolein .from such starting materials as, for example, acetaldehyde and formaldehyde under carefully controlled conditions often enables the attainment of a product comprising the acrolein in admixture with impurities consisting essentially of acetaldehyde, formaldehyde and relatively high boiling organic materials. All of such impurities are readily separable from the acrolein on a-practical scale by methods available heretofore comprising such steps as simple fractionation, water scrubbing, distillation and the like. Although acrolein of relatively high purity is often obtained by such methods these processes are generally handicapped by unavailability at sufliciently low cost of the starting materials. A particularly valuable source of the unsaturated aldehydes comprises the products obtained by the oxidation of the readily available hydrocarbons. It has recently been found that the readily available olefinic hydrocarbons can be converted efliciently to products consisting predominantly of un- 16 Claims. (Cl. 202-395) saturated aldehydes such as, for example, the alpha-betaunsaturated aliphatic aldehydes, by catalytic oxidation in the presence of specific catalysts. Thus acrolein is obtained by the catalytic oxidation of propylene. obtained in such catalytic hydrocarbon oxidations, however, comprise besides the desired unsaturated aldehydes, saturated carbonylic compounds such as, saturated aldehydes and ketones inseparable therefrom on a practical scale by methods disclosed heretofore. The production of an alpha-beta unsaturated aliphatic aldehyde from the corresponding olefin, such as, for example, the production of acrolein from propylene results in the production of a product comprising the acrolein in admixture not only with readily separable impurities such as high boiling material, formaldehyde and acetaldehyde, but also close boiling carbonylic compounds such as, for example, propionaldehyde and acetone, inseparable therefrom on a practical scale by separating means available heretofore. Inability to effect the eflicient and yet substantially complete removal of close boiling carbonylic compounds from the unsaturated aldehydes has militated against any full realization of the substantial advantages inherent in the utilization of the readily available hydrocarbons as a source of these highly desirable and valuable compounds.

It is an object of the present invention to provide an improved process for the more eificient purification of the crude unsaturated aliphatic aldehydes obtained by the oxidation of hydrocarbons.

Another object of the invention is the provision of an improved process for the more efiicient purification of crude alpha-beta unsaturated aliphatic aldehydes obtained by the oxidation of the corresponding olefini'c hydrocarbon.

A more particular object of the invention is the provision of an improved process for the more eflicient purification of the crude acrolein obtained by the catalytic oxidation of propylene.

A further object of the invention is the provision of an improved process for the more efficient separation of an aliphatic unsaturated aldehyde from admixture with saturated carbonylic compounds not readily separable therefrom by practical scale fractionating means.

Another object of the invention is the provision of an improved process for the more eflicient separation of an alpha-beta unsaturated aliphatic aldehyde from admixture with saturated carbonylic compounds having the same number of carbon atoms to the molecule.

The products .with. a saturated aliphatic aldehyde and/or ketone having the same number of carbon atoms I to the molecule.

A particular object of the invention is the provision of an improved process enabling the more efllcient separation of acrolein from mixtures comprising acrolein in admixture with propionaldehyde and/or acetone. Other objects and advantages of the invention will become apparent from the following detailed description thereof.

In co-pending application Serial No. 49,816, filed September 17, 1948, there is described and claimed a method enabling the production of an unsaturated aldehyde of relatively high purity from a crude unsaturated aldehyde containing saturated carbonylic impurities having boiling temperatures closely approximating that of the unsaturated aldehyde, by subjecting the crude material to two consecutive extractive distillations in the presence of a suitable solvent. It has now been found that an unsaturated aldehyde, such as, for example, an alpha-beta unsaturated aliphatic aldehyde, is obtained in a high state of purity with substantially improved efficiency from the crude unsaturated aldehydes comprising it in admixture with saturated carbonylic impurities having boiling temperatures closely approximating that of the unsaturated aldehyde by a method of purification employing a single low temperature extractive distillation step in the presence of a specific solvent under well-defined conditions. The process of the invention enables the separation of the unsaturated aliphatic aldehyde from admixed saturated carbonylic impurities including saturated ketones and saturated aldehydes having the same number of carbon atoms to the molecule as the unsaturated aldehyde, in a single low temperature extractive distillation. The single extractive distillation step of the process furthermore enables the simultaneous removal of any water from the unsaturated aldehyde to a greater degree than possible by ordinary fractionating conditions.

The process of the invention may be applied broadly to the separation of an unsaturated aldehyde from a mixture comprising it in admixture with saturated aldehydes and ketones having the same number of carbon atoms to the molecule as the unsaturated aldehyde regardless of the source of the mixture. Because of its ability to effect in a single extractive distillation the substantially complete removal from an unsaturated aldehyde a plurality of close boiling saturated carbonylic impurities, such as saturated ketones and saturated aldehydes having the same number of carbon atoms to the molecule as the unsaturated aldehyde as well as water, the process of the inventions is applied with particular advantage to the purification of the crude unsaturated aldehydes, such as the alpha-beta unsaturated aldehydes obtained by the oxidation of the corresponding hydrocarbons.

In accordance with the process of the invention a crude unsaturated aliphatic aldehyde, such as a crude alpha-beta unsaturated aliphatic aldehyde containing close boiling saturated car- .bonylic impurities comprising saturated aldehydes and ketones having the same number oxidation of propylene and containing propionaldehyde and acetone, is subjected to extractive distillation at a temperature below about (35 C2) in the presence of a suflicient amount of water to maintain a single liquid phase in the extractive distillation zone. It has been found that under the above-defined conditions substantially all of the saturated carbonylic impurities including the unsaturated aldehydes and ketones havin the same number of carbon atoms to the molecule as the unsaturated aldehyde are removed as bottoms from the extractive distillation zone together with the water. Overhead from the extractive distillation consists essentially of the unsaturated aldehyde free not only of any substantial amount of saturated carbonylic impurities inseparable therefrom on a practical scale by methods disclosed heretofore, but containing substantially less water than comprised in the unsaturated aldehyde-water azeotrope obtained under normal fractionating conditions.

In order that the invention may be more readily understood it will be described in detail herein in its application to the production of acrolein of high purity from crude acrolein obtained by the catalytic oxidation of propylene. Reference will be had to the accompanying drawings wherein Figure I illustrates more or less diagrammatically one form of apparatus suitable for executing the process of the invention, and Figure II illustrates graphically the variation of the relative volatility of acrolein-propionald'ehyde, acrolein-acetaldehyde, and acrolein-acetone mixtures, with variations in temperaturein the presence of 83% by weight water.

When the alpha-beta unsaturated aliphatic aldehyde-containing mixture to be purified in accordance with the invention consists essentially of a mixture such as that eliminated from a reaction zone wherein the unsaturated aldehyde is produced by oxidation of the. corresponding hydrocarbon, the charge is first freed of at least the greater part of normally gaseous and relatively high boiling components prior to its passage to the extractive distillation zone of the process. Referring to Figure I of the drawings, a crude acrolein-containing mixture consisting essentially of the eflluence from the reaction zone wherein it was produced by the catalytic oxidation of propylene, and optionally emanating directly from such reaction zone, is passed through line l0 into a separating zone. When the charge emanates directly from the reaction zone and is at an elevated temperature it is preferably passed through suitable cooling means, such as, for example, a cooler H. Optionally additional cooling means comprising the addition of a quenching medium, such as water to the stream by means of valved line l2, may be employed.

The propylene oxidation product will comprise besides the crude acrolein containing the acrolein in admixture with acetaldehyde, acetone, propionaldehyde and water, certain amounts of formaldehyde, high boiling organic materials, and substantial amounts of normally gaseous materials. The normally gaseous materials will comprise unconverted propylene, some other low boiling hydrocarbons, and varying amounts of gaseous products such as nitrogen, carbon dioxide, carbon monoxide and the like.

Within separator l3 a liquid layer comprising crude acrolein, close boiling carbonylic impurities, formaldehyde, water, and high boiling organic material is separated from a gaseousfractlon comprising the normally gaseous materials as well as substantial amounts of acrolein containing close boiling carbonylic impurities. The gaseous phase is passed from separator it through line it into a scrubbing zone. The scrubbing zone may comprise a scrubbing column l0, optionally containing suitable packing material, baille plates, or the like. Within column [6 the charge thereto is brought into countercurrent contact with a suitable scrubbing medium such as, for example, water, selectively dissolving or absorbing the acrolein. Water is introduced into the upper part of column 16 by means of valved line l1. Normally gaseous material comprising propylene and fixed gases is eliminated from column it by means of valved line l9. Acrolein in admixture with close boiling saturated impurities such as propionaldehyde, and acetone as well as acetaldehyde and formaldehyde is taken from the lower part of column I6 together with the scrubbing water by means of valved line it. s A superatmospheric pressure, for example, in the range of from about 50 to about 500 pounds, and preferably from about 150 to about 250 pounds is maintained in column iii to assure substantially complete absorption of the acrolein. The temperature within column It may range, for example, from about 10 C. to about C. Higher or lower tempera-- acetaldehyde, propionaldehyde and acetone as well as water, is separated from a liquid fraction consisting essentially of water, formaldehyde and high boiling organic material.

The liquid fraction is taken from stripping column 22 by means of valved liner" and eliminated from the system. The vapor fraction is taken overhead from stripping column 22 by means of valved line 26.

The amount of saturated carbonylic impurities contained in the crude acrolein taken overhead from stripping column 22 through valved line 26 will vary considerably often depending upon the specific condition employed in producing the crude acrolein. In general the amount of close boiling carbonylic impurities contained in the crude acrolein passed through valved line 26 will not substantially exceed about 10% by weight of the acrolein. It is to be understood. however, that the invention is in no wise limited to the purification of a crude acrolein containing close boiling carbonylic impurities in any specific amount The water content of the crude acrolein overhead from stripping column 22 will be at least equivalent to that of the acrolein-water azeotrope which is 2.7% by weight of water based on acrolein. The saturated carbonylic impurities will generally consist essentially of acetaldehyde, propionaldehyde and acetone in varying amounts.

The following table is illustrative of the comscrubbing and stripping of oxidation products of propylene as herein described: 7

Per cent by weight Acrolein I '80to 90 Acetaldehyde 3 to 10 Propionaldehyde 0.5 to 3 Acetone 1.0to5 High boiling organic material 1.0 to2.0 Water 2.4 to 6.0

It is seen that in addition to acetaldehyde the crude acrolein contains propionaldehyde and acetone in contaminating amounts. These saturated compounds are not only lower boiling and higher boiling respectively, than acrolein but have boiling temperatures closely approximating that of acrolein and therefore preclude their separation by ordinary practical scale fractionating means. It is apparent that the production of substantially pure acrolein from such a mixture by methods available heretofore, if feasible at all, necessitates the use of such a plurality of steps and operations of such complexity as to render itslarge scale application highly impractical. The reduction of its water content below the relatively large amount contained in the acrolein-water azeotrope normally obtained in fractionation would occasion the resort toadditional complex and costly operative steps.

A study oi. the distillation of crude acrolein mixtures in the presence of polar solvents revealed that whereas the relative volatility (alpha) for the separation of acrolein from acetone is approximately 1.12 in the absence of a solvent the presence of most polar solvents results in a reduction of the relative volatility I value below unity, that is acrolein is the more polar compound and is taken off with the bottoms of the column. It was found, however, that water, quite contrary to the behavior of otherv polar solvents in the presence of acrolein, instead of decreasing the relative volatility value for the separation of acrolein from acetone increased it markedly, and that extractive distillation of crude acrolein in the presence of water resulted in the taking off overhead of a fraction containing acrolein that was poorer in acetone. Acetaldehyde is also removed to a substantial degree in the bottoms.

The overhead of such an extractive distillation at substantially atmospheric or higher pressures will still comprise, however, not only a considerable portion of the acetone and acetaldehyde contaminants but will contain substantially all of the propionaldehyde.

The relative volatility value for the separation of propionaldehyde from acrolein in the absence of a solvent was found to be about 1.12 and therefore is separable to at least a substantial degree by fractionation. In the presence of substantial amounts of water it was found that the relatively volatility value was increased somewhat attaining a value of about 1.4 in the presence of about 90% of water at atmospheric pressure. A second extractive distillation of the crude acrolein in the presence of water at substantially atmospheric pressure or higher would therefore enable the removal to some extent of propionaldehyde overhead from a crude acrolein mixture. Such a plurality of steps will, however, occasion a reduction in overall recovery due to losses caused by hydra-- tion, polymerization etc. Notonly is such a process handicapped by the disadvantages inposition of crude acrolein obtained by water herent in the plurality of operative procedures tent of at least 2.7 per. cent by weight based on acrolein, thereby generally necessitating a further complex dehydration step.

It has now been found, however, that whereas the extractive distillation, in the presence of water, at substantially atmospheric conditions of the crude acrolein results in the obtaining of propionaldehyde in the overhead product, a, lowering of the temperature below a definite critical temperature in the presence of water in an amount at least equal to about 80% by weight of the aqueous mixture, results in the appearance of all of the saturated carbonylic impurities including, propionaldehyde in the column bottoms leaving substantially pure acrolein as the sole overhead product. A study has indicated, as graphically illustrated by the curve A of Figure 11 of the attached drawings, that the relative volatility value (alpha) for the separation of propionaldehyde from acrolein in the presence of water not only increases with decrease in temperature but that at the temperature of about 35 C. it becomes unity and thereafter increases markedly in positive value with further decrease in temperature. Thus whereas the relative volatility value for the separation of propionaldehyde from acrolein in the presence of water is only about'0.71 at a temperature of 60 C. it has a value of 1.32 at 20 C. and 2.0 at C.

It has furthermore been found that the low temperature extractive distillation not only results in the obtaining of a product which is substantially free of propionaldehyde but which no longer contains the still considerable amounts of impurities such as acetone, acetaldehyde and water which are comprised in the product obtained at temperatures above about 35 C. It was further found, as indicated graphically by curves B and C, Figure 11 of the drawing, that the values for the relative volatilities for the separation of acetaldehyde and acetone in the presence of water increased at a markedly rapid rate with'decrease in temperature below about 35 C. Thus whereas these values (alpha) are only 1.15 and 2.1 at 60 C. for acetaldehyde and acetone, respectively, they are as high as 2 and 4, respectively, at 0 C.

A further signal advantage of the low temperature extractive distillation resides in the obtaining of acrolein of high purity containing substantially less water than that of the acroleinwater azeotrope obtained at higher temperatures or normal fractionating conditions. Thus whereas the normal acrolein-water azeotrope contains about 2.7% of water, the acrolein overhead obtained in the low temperature extractive distillation of the invention has a water content below about 0.4%.

The low temperature extractive distillation of the invention therefore enables the simultaneous separation of all saturated carbonylic impurities, including those having the same number of carbon atoms to the molecule as the acrolein, as well as at least a substantial amount of water, from acrolein in a single highly efficient and economical operation.

In accordance with the invention the crude acrolein containing acetaldehyde, propionaldehyde, acetone and water is passed from line 26 through

valved lines

28 and 29 into an extractive distillation zone. The extractive distillation zone may comprise an extractive distillation column 3| provided with suitable heating means, such as, for example, a reboilcr, or a closed heating coil 32. Line 29 is provided with suitable means enabling thelntroduction or removal of heat from g the crude acrolein stream passing therethrough, such as, for example, an indirect heat exchanger 33. The charge may be introduced into the extractive distillation column 3|. in the liquid, vapor or mixed phase. Within. column 3| the crude acrolein subjected to extractive distillation conditions in the presence of water introduced into the upper part of the column by means of valved line 35. Means for controlling the temperature, of the water introduced into column 31 through valved line 35 such as, for example a cooler 35, is provided.

Crude acrolein, comprising acrolein in admixture with one or more close boiling saturated carbonylic impurities such as, for example, acetone,

propionaldehyde and acetaldehyde may be introduced into the system from any outside source by means of

valved lines

31 and 38 leading into line 29. Crude acrolein introduced into the system by means of valved line 31 may constitute a part or all of the crude acrolein charge to the system.

Conditions within column 3| are controlled to maintain the temperature therein below about 35 C. and preferably below about 20 C. Thus the temperature within column 3| may be maintained within the broad range of, for example, from about 35 C. to about 10 C. and preferably from about 20 C. to about 0 C. The temperature within column 3| is maintained within the prescribed range by control of the temperature of the materials introduced therein and by the maintenance therein of asufliciently low subatmospheric pressure by any suitable conventional means not shown in the drawing.

Essential to the attainment of the objects of the invention is the .introduction into column 3| of sufiicient water to maintain a single liquid phase throughout the column. The introduction of water into the column is controlled to maintain the water content of the total mixture therein at least equal to about by weight. Without intent to limit the scope of the invention by any theories advanced herein to set forth more fully the nature of the invention it is believed that below the temperature of about 35 C. under the conditions within column 3|, acrolein will not form a hydrate whereas the saturated carbonylic constituents will undergo hydrate formation. Conditions in column 3| are preferably controlled within the prescribed conditions 'to obtain a throughput rate assuring attainment of equilibrium with respect to the formation of the hydrates of substantially all of the saturated carbonylic compounds introduced into the column. Thus the relative volatility value for the separation of acrolein from propionaldehyde under the low temperature extractive distillation conditions was found to be about 0.71, 1.1 and 1.5 for residence times of 6, 20 and 30 seconds respectively. Suitable throughput rates comprise those enabling a residence time per transfer stage of from about 20 to about '75 seconds, and preferably from about 25 to about 50 seconds within low temperature extractive distillation column 3 I. Aminimum residence time of about 30 seconds is particularly preferred when effecting the low temperature extractive distillation at a temperature of from about 0 C. to about 10 C. Higher minimum residence times may, however, be employed within the scope of the invention. The minimum residence time of the charge within the low temperature extractive distillation column 3|, it has been found, may be reduced materially bythe acrolein is extractively distilled within column 31 with the formation of liquid bottoms consisting essentially of water, acetaldehyde, propionaldehyde and acetone, and a vapor overhead consisting essentially of acrolein in a high state of purity, substantially free of saturated carbonylic steps as distillation, fractionation and the like,'

to effect the recovery of saturated carbonylic compounds therefrom.

The vaporfraction is taken overhead from column 3| through valved. line 4| provided with suitable cooling means such as, for example, a condenser 42, and passed into an accumulator 43. Acrolein in a high state of purity is drawn from accumulator 43 by means of valved line 44 as a final product. A part of the acrolein withdrawn through valved line 44 is passed through valved line 45, provided with suitable cooling means such as a cooler 46, into the upper part of column 3| at a point above that of introduction of the water into the column.

The eiilciency with which acrolein is separated in a high state of purity from a crude acrolein obtained by the catalytic oxidation of propylene and comprising saturated carbonylic compounds having the same carbon atoms to the molecule as acrolein is illustrated by the following example:

Example I A crude acrolein-containing mixture, obtained a by the catalytic oxidation of propylene, is subjected to phase separation in a separator., The

gaseous phase is scrubbed with water at a pres-' sure of about 125 lbs. gauge to recover crudeacrolein therefrom. The rich scrubbing water is combined with the liquid phase from the separator and subjected to distillation. Crude acrolein is separated as a vapor fraction from a liquid bottoms comprising water, formaldehyde and high boiling organic material. The crude acrolein thus obtained has the following composition:

Weight per cent Acrolein 90.0 Acetaldehyde 6.0 Propionaldehyde 2.0 Acetone and is subjected to extractive distillatiofi'in the presence of water under the following'lconditions:

Top column temperature, C.'. 9.'7

Reflux to feed ratio The composition of the overhead and bottoms of the column in per cent by weight are indicated in the following table:

Overhead Bottom wt. t.

. Acetaldehyde, having a boiling temperature substantially below that of acrolein, and a relative volatility of about 3.5 in the absence of a solvent, may be separated to at least a substantial degree from the crude acrolein by fractionation. In a modification of the invention, the load on the extractive distillation column 3| is reduced by the passage of at least a part of the crude acrolein containing acetaldehyde fi'om line 28 into a fractionating zone. The fractionating zone may comprise a suitable column such as, for example, fractionating column 50. Acetaldehyde-containing crude acrolein, introduced into the system through line 31, may be passed in part or in its entirety into column 50 by means of valved line 5|. Within column 50 the crude acrolein is subjected to fractionation to effect the separation of a vapor fraction comprising acetaldehyde from a liquid fraction comprising acrolein in admixture with acetone and propionaldehyde.

The vapor fraction is passed overhead from fractionator 50 through line 53, provided with cooling means 54, into accumulator 55. Liquid condensate comprising acetaldehyde is taken from accumulator 55 through valved line 58 and eliminated from the system. A part of theliquid passed through valved line 56 is passed through valved line 5'! as reflux to the top of fractionatpr 50. Such fractionation enables the elimination of at least. a substantialpart of the acetaldehyde from the charge to the extractive distillation zone as exemplified by the following example:

Example II Crude acrolein obtained by the catalytic oxidation of propylene was freed of acetaldehyde by fractionation. The resulting crude acrolein-containing fractionator bottoms were subjected to a low temperature extractive distillation in the presence of water under the following conditions:

Top column temperature, "C -9.l Bottom column temperature, C 16 Top column pressure, mm. Hg abs 50 Bottom column pressure, mm. Hg abs. 152 Water content of column percent by weight of total liquid on trays in column 83 Reflux ra i 2 Composition of the. crude-acrolein charge and the products of the distillation are indicated in th following table:

Extractive Distillation Crude was Feed Botfmcfiom toms from anon Crude Overhead Bottoms Fractionator 102.7 wt? 10!.7 wt.'7 Acroleiu 03 0597 05.4 3.10 Propionaldehyde. 2. 0 2. 16 0. 2 0. 2i Acetone 2. 0 2. 15 0. 0 0. 23 Aoetaldehyde.-. 6. 0 0. 2 0. 0 02 Water I 0. 4 99. 40

1 1 Although the detailed description of the invention has stressed the purification of crude acrolein containing both acetone and propionaldehyde it is to be understood that it may be applied to the separation of acrolein from mixtures containing Example III A mixture of acrolein and propionaldehyde, containing" 2.0% by weight of propionaldehyde is extractively distilled at low temperature in the presence of water. A temperature of 4 C. and a pressure of 62 mm. Hg abs. are maintained in the upper part of the extractive distillation column and a temperature of C. and a pressure of 152 mm. Hg abs. in the lower part of the column. A reflux ratio of 2 is employed. Water is continuously introduced into the upper part of the column, below the point of introduction of reflux, in sufficient amount to maintain a ratio of water to feed charged to the column of 9.8. 99% of the acrolein charged is recovered in the column overhead as acrolein of 99.3% purity.

Example IV A mixture of acrolein and acetone, containing 2% by weight of acetone is extractively distilled at low temperature in the presence of water. A temperature oi 0 C. and a pressure of 62 mm. Hg abs. are maintained in the upper part of the extractive distillation column and a temperature of C. and a pressure of 150 mm. Hg abs. in the lower part of the column. A reflux ratio of 2.0 is employed. Water is continuously introduced into the upper part of the column, at a point below the introduction of reflux in suflicient amount to maintain a ratio of water to feed charged of 9.8, 99% of the acrolein charged was obtained overhead from the column as acrolein of 99.7% purity.

The process of the invention thus not only enables the large scale production of acrolein from crude acrolein, such as obtained for example by the catalytic oxidation or propylene, in a substantially higher state of purity than possible by practical scale methods disclosed heretofore but makes possible its production with markedly improved efllciency.

Although the illustrative description of the invention has stressed the separation of acrolein from saturated carbonylic compounds the invention may be applied to the separation of unsaturated aldehydes other than acrolein from saturated carbonylic impurities having boiling temperatures closely approximating that of the unsaturated aldehyde. The invention is applied with particular advantage to the separation of alpha-beta unsaturated aldehydes from the crude unsaturated aldehydes obtained by the oxidation of the corresponding hydrocarbons. Thus the invention may be applied to the separation of methacrolein from admixture with acetalde- 1. The process for separating acrolein in a high state of purity from a mixture comprising acrolein in admixture with propionaldehyde which comprises extractively distilling said mixture at a temperature below 35 C. in the presence of a suflicient amount of water to maintain substantially a single liquid phase in the extractive distillation zone, thereby separating a vapor fraction consisting essentially of acrolein free of any substantial amount of propionaldehyde from liquid bottoms comprising water and propionaldehyde in the extractive distillation zone.

2. The process for separating acrolein in a high state of purity from a mixture comprising acrolein in admixture with propionaldehyde which comprises extractively distilling said mixture at a temperature above about -10 C. and below 35 C. in the presence of a suflicient amount of water to maintain substantially a single liquid phase in the extractive distillation zone, thereby separating a vapor fraction consisting essentially of acrolein free of any substantial amount of propionaldehyde from liquid bottoms comprising water and propionaldehyde in the extractive distillation zone.

3. The process for separating acrolein in a high state of purity from a mixture comprising acrolein in admixture with propionaldehyde which comprises extractively distilling said mixture at a temperature of from about 0 C. to about 20 C. in the presence of a sumcient amount of water to maintain substantially a single liquid phase in the extractive distillation zone, thereby separating a vapor fraction consisting essentially of acrolein free of any substantial amount of propionaldehyde from liquid bottoms comprising water and propionaldehyde in the extractive distillation zone.

4. The process for separating acrolein in a high state of purity from a mixture comprising acrolein in admixture with propionaldehyde and acetone which comprises extractively distilling said mixture at a temperature above about l0 C. and below 35 C. in the presence of a sufficient amount of water to maintain substantially a single liquid phase in the extractive distillation zone. thereby separating a vapor fraction consisting essentially of acrolein free of any substantial amount of propionaldehyde and acetone from liquid bottoms comprising water, propionaldehyde and acetone in the extractive distillation zone.

5. The process for separating acrolein in a high state of purity from a mixture comprising acrolein in admixture with propionaldehyde and acetone which comprises extractively distilling said mixture at a temperature of from about 0 C. to about 20 C. in the presence of a sufllcient amount of water to maintain substantially a single liquid phase in the extractive distillation zone, thereby separating a vapor fraction consisting essentially of acrolein free of any substantial amount of propionaldehyde and acetone from liquid bottoms comprising water propionaldehyde and acetone in the extractive distillation zone.

6. The process for separating acrolein in a high state of purity from crude acrolein comprising acrolein in admixture with propionaldehyde-containing saturated carbonylic compounds having the same number of carbon atoms to the molecule as acrolein, which comprises extractively distilling said crude acrolein at a temperature below 35 C. in the presence of a sufficient amount of water to maintain substantially a single liquid phase in the extractive distillation zone, thereby" separating a vapor traction consisting essentially of acrolein free or any substantial amount of saturated carbonylic compounds from liquid bottoms comprising water and said saturated carbonylic compounds in the extractive distillation zone.

7. The process for separating acrolein in a high state of purity from crude acrolein com- I prising acrolein in admixture with propionaldehyde-containing saturated carbonylic compounds having the same number of carbon atoms to the molecule as acrolein which comprises extractively distilling said crude acrolein at a temperature of from about -1 0, C. to about 20 C. in the presence of a suflicient amount of water to maincomprising acrolein in admixture with close boiling saturated carbonylic impurities, which comprises extractively distilling said crude acrolein at a temperature of from about -l C. to about 20 C. in the presence of a sufficient amount of water to maintain substantially a single liquid phase in the extractive distillation zone, thereby separating a vapor fraction consisting essentially of acrolein free of any substantial amount of saturated carbonylic compounds from liquid bottoms comprising water and said saturated carbonylic compounds in the extractive distillation zone.

9. The process for the separation of an alphabeta unsaturated aliphatic aldehyde having from three to four carbon atoms to the molecule in a high state of purity from a mixture comprising said alpha-beta unsaturated aldehyde having from three to four carbon atoms to the molecule in admixture with a saturated aldehyde having the same number of carbon atoms to "the molecule as said unsaturated aldehyde which comprises extractively distilling said mixture at subatmospheric pressure and at a temperature below 35 C. in the presence of a sufiicient amount of water to maintain a single liquid phase in the extractive distillation zone.

10. The process for separating an alpha-beta unsaturated aliphatic aldehyde having from three to four carbon atoms to the molecule from a crude alpha-beta unsaturated aliphatic aldehyde having from three to four carbon atoms to the molecule obtained by the oxidation of the corresponding olefin, said crude unsaturated aldehyde comprising said alpha-beta unsaturated aldehyde in admixture with saturated carbonylic impurities having the same number of carbon atoms to the molecule as said unsaturated aldehyde, which comprises extractively distilling said crude unsaturated aldehyde at subatmospheric gaseous hydrocarbons, formaldehyde, acetaldehyde, acetone, propionaldehyde and high boiling organic impurities, which comprises scrubbing said reaction products with water at superatmospheric pressure to obtain a rich scrubbing medium comprising water and said reaction products substantially free of normally gaseous hydrocarbons, distilling said rich scrubbing medium to separate crude acrolein comprising acrolein in admixture with propionaldehyde and acetone therefrom, and extractively distilling said crude acrolein at a temperature below 35 C. in the presence of a suflicient amount of water to maintain substantially a single liquid phase in the extractive distillation zone, thereby separating a vapor fraction consisting essentially of acrolein free of any substantial amount of propionaldehyde and acetone from liquid bottoms comprising water, propionaldehyde and aceton in the extractive distillation zone.

12. The process for purifying crude acroleincontaining reaction products obtained by the oxidation of propylene, said reaction products comprising acrolein in admixture with normally gaseous hydrocarbons, formaldehyde, acetaldehyde, acetone, propionaldehyde and high boiling organic impurities, which comprises separating a fraction consisting essentially of crude acrolein comprising acrolein in admixture with propionaldehyde and actone from said reaction products, and extractively distilling said crude acrolein at a temperature of from about -10 C. to about 20 C. in the presence of a sufficient amount of water to maintain substantially a single liquid phase in the extractive distillation zone, thereby separating a vapor fraction consisting essentially of acrolein free of any substantial amount of propionaldehyde and acetone from liquid bottoms comprising water, propionaldehyde and acetone in the extractive distillation zone.

13. The process for purifying crude acrolein-. containing reaction products obtained by the oxidation of propylene, said reaction products comprising acrolein in admixture with normally gaseous hydrocarbons, formaldehyde, propionaldehyde-containing saturated carbonylic compounds having boiling temperatures closely approximating that of acrolein, and high boiling organic impurities, which comprises scrubbing said reaction products with water at superatm'ospheric pressure to obtain a rich scrubbing medium comprising water and said reaction products substantially free of normally gaseous hydrocarbons, distilling said' rich scrubbing medium to separate crude acrolein comprising acrolein in admixture with close boiling saturated carbonylic impurities therefrom, and extractively distilling said crude acrolein at a temperature below 35 C. in

. eous v hydrocarbons, formaldehyde, propionaldehyde-containing saturated carbonylic compounds having boiling temperatures closely approximating that of acrolein and high boiling organic impurities, which comprises separating a fraction consisting essentially of crude a'crolein comprising acrolein in admixture with said close boiling saturated carbonylic compounds from said reaction products, and extractively distilling said crude acrolein at a temperature of from about C. to about 20 C. in the presence of a suiiicient amount of water to maintain substantially a single liquid phase in the extractive distillation zone, thereby separating a vapor fraction consisting essentially of acrolein free of any substantial amount of said close boiling saturated carbonylic compounds from liquid bottoms comprising water and said saturated carbonylic compounds in the extractive distillation zone.

15. The process for purifying crude acroleincontaining reaction products obtained by the oxidation of propylene, said reaction products comprising acrolein in admixture with normally gaseous hydrocarbons, saturated carbonylic impurities substantially lower boiling than acrolein comprising formaldehyde and acetaldehyde, saturated carbonylic impurities having boiling temperatures closely approximating that of acrolein comprising propionaldehpde, and high boiling organic impurities, which comprises scrubbing said reaction products with water at superatmospheric pressure to obtain a rich aqueous scrubbing medium comprising water and said reaction products substantially free of normally gaseous hydrocarbons, distilling said rich scrubbing medium to separate crude acrolein comprising acrolein in admixture with said close boiling saturated carbonylic impurities comprising propionaldehyde therefrom, and extractively distilling said crude acrolein at a temperature below 35 C. in the presence of a suflicient amount of water to maintain a single liquid phase in the extractive distillation zone, thereby separating a vapor fraction consisting essentially of acrolein substantially free of any saturated carbonylic impurities from liquid bottoms comprising water and saturated carbonylic impurities comprising propionaldehyde in the extractive distillation zone.

16. The process for the purification of crude acrolein-containing reaction products obtained by the oxidation of propylene, said reaction products comprising acrolein in admixture with normally gaseous hydrocarbons, saturated carbonylic impurities substantially lower boiling than acrolein comprising formaldehyde and acetaldehyde, saturated carbonylic impurities having boiling temperatures closely approximating that of acrolein comprising propionaldehyde, and high boiling organic impurities, which comprises separating a fraction consisting essentially ofcrude acrolein comprising acrolein in admixture with said close boiling saturated carbonylic impurities comprising propionaldehyde from said reaction products, and extractively distilling said crude acrolein at a temperature of from about 10 C. to about 20 C. in the presence of a sufilcient amount of water to maintain a single phase in the extractive distillation zone, thereby separating a vapor fraction consisting essentially of acrolein substantially free of any saturated carbonylic impurities from liquid bottoms comprising water and said saturated carbonylic impurities comprising propionaldehyde in the extractive distillation zone.

GINO J. PIEROTTI. ARTHUR E. HANDLOS. CHARLES M. REIDER.

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

UNITED STATES PATENTS Number Name Date 2,033,539 Ralston et al Mar. 10, 1936 2,179,991 Bright et a1 Nov. 14, 1939 2,198,651 Bludworth Apr. 30, 1940 2,261,704 Wagner -Nov. 4, 1941 2,283,911 Brant et al May 26, 1942 2,290,636 Deanesly July 21, 1942 2,334,091 Herstein Nov. 9, 1943 2,341,748 Hopkins June 15, 1943

Claims

10. THE PROCESS FOR SEPARATING AN ALPHA-BETA UNSATURATED ALIPHATIC ALDEHYDE HAVING FROM THREE TO FOUR CARBON ATOMS TO THE MOLECULE FROM A CRUDE ALPHA-BETA UNSATURATED ALIPHATIC ALDEHYDE HAVING FROM THREE TO FOUR CARBON ATOMS TO THE MOLECULE OBTAINED BY THE OXIDATION OF THE CORRESPONDING OLEFIN, SAID CRUDE UNSATURATED ALDEHYDE COMPRISING SAID ALPHA-BETA UNSATURATED ALDEHYDE IN ADMIXTURE WITH SATURATED CARBONYLIC IMPURITIES HAVING THE SAME NUMBER OF CARBON ATOMS TO THE MOLECULE AS SAID UNSATURATED ALDEHYDE, WHICH COMPRISES EXTRACTIVELY DISTILLING SAID CRUDE UNSATURATED ALDEHYDE AT SUBATMOSPHERIC PRESSURE AND AT A TEMPERATURE BELOW 35*C. IN THE PRESENCE OF A SUFFICIENT AMOUNT OF WATER TO MAINTAIN SUBSTANTIALLY A SINGLE LIQUID PHASE IN THE EXTRACTIVE DISTILLATION ZONE.