US2377049A - Extraction process - Google Patents

Description

May 29, 1945- M. souDERs, JR 2,377,049

EXTRACTION PROCESS Filed Nov. 5, 1942 2 Sheets-Sheet 1 buianzs +Acz1onz f II8 l cous Andorre Concen'ra'fzd) Solvzn Edurn Line Figi May 29, 1945. M, SOUDERS, JR 2,377,049

EXTRACTION PROCESS Filed Nov. 3, 1942 2 Sheets-Sheet 2 queoueAczione Conccnfmred) Fig. n

Patented May 29, 1945 Ex'mAo'rIoN raocEss Mott Souders, Jr., Piedmont, Calif., assigner to Shell Development Company, San Francisco, Calif., a corporation of Delaware Appuootiop November s, 1942, serial No. 464,403

(ci. iss- 115) 6 Claims.

This invention relates to the separation of hydrocarbon mixtures of narrow boiling range which are diflicultly separable by ordinary fractionation. More particularly, the invention relates to the separation lof narrow boiling hydrocarbon mixtures containing two vor more components of diii'erent degrees of saturation.v

The invention is especially valuable in connection with the separation of olefins of four car bon atoms from normal butane and as so applied constitutes an improvement on the process described in copending application S'erial No. 332,366, which issued as Patent No. 2,371,908 on March 20, 1945.

In the process of the above-identified copending application, mixtures of olefins and parailins or mono-olefins and dioleflns are separated by contacting them with an aqueous organic solvent, the organic constituent of which may be acetone, for example, to selectively dissolve the more unsaturated component which isL obtained as a highly purified material upon subsequent regeneration of the solvent solution as by distillation. The process is conveniently executed by passing the mixture to be separated in countercurrent relation to the aqueous solvent in a 'column provided with suitable contact and/or acetone to the treatment of mixtures of olefins of four carbon atoms as normal butylenes and isobutylene with normal butane has given rise to considerable operating difficulty because of loss of acetone with the overhead vapors. This is believed to result, partially at least, from the formation of an azeotrope of normal butane and acetone, since the diiculty is not corrected by the employment of additional rectifying plates between the solvent inlet port and the top of the column. By means of such rectifying or knockdown plates it is sometimes possible in distillation or extraction processes of the type involved to prevent any substantial loss of solventwith the overhead, but this expedient has been found valueless as to mixtures containing normal butane.

A further operating diflioulty, experienced not only during the treatment of mixtures containing normal butane but also during the treatment of mixtures free of this hydrocarbon, results from the accumulation in the aqueous organic solvent of hydrocarbons of a higher molecular weight than the hydrocarbons inthe mixture being separated. Mixtures of the type subjected to the treatment according to the process of application, Serial No. 332,366, are obtained, for example, by the pyrolysis of petroleum or petroleum fractions. Although by ordinary fractionation it is relatively easy to obtain cuts or fractions from the pyrolyzed product which predominate in hydrocarbons of the same number of carbon atoms, it is practically impossible to achieve absolutely clean separation. Thus, a C4 hydrocarbon cut will invariably be contaminated with at least minor amounts of amylenes, pentanes, pentadienes, etc. Upon subsequent continuous extraction of the C4 fraction these higher molecular Weight hydrocarbons tend to build up in the solvent with a consequent adverse eii'ect upon its emciency.

A principal object of the present invention is to provide an improved process for effecting the recovery of acetone from the overhead produced when a mixture comprising one or more oleflns together with one or more parailins, particularly a mixture comprising one or more oleflns of four carbon atoms together with normal butane, is extracted with an aqueous acetone solvent. Another object is to effect continuous recovery of the acetone content of the overhead in a manner providing for its immediate recirculation. Still another object is to provide an improved process for separating olefins from parafllns by means of an aqueous acetone solvent wherein the lean or regenerated solvent produced incident to the recovery of the extracted olefln is continuously or intermittently freed of undesirable hydrocarbon accumulate. A still further object is to provide an improved process which is generally applicable to the separation of narrow boiling hydrocarbon mixtures containing components of different degrees of saturation as mixtures of mono-olens and diolens, mono-oleflns and/or diolens and parailins, etc.

According to the present invention, as carried out using an aqueous solution of acetone as the selective solvent, the acetone-containing overhead vapors from the extraction column are condensed with the formation of two liquid phases. The upper or hydrocarbon phase is ree turned to the extraction column as reflux, while the lower phase, which is relatively rioher in acetone, is introduced into ascrubbing zone, which may conveniently be a second column or tower, wherein it is scrubbed with water. The acetone solution obtained through the scrubbing operation is separated from the undissolved component or components and conveyed to a distillation unit which is operated under such conditions as to produce an aqueous acetone solution of a strength equivalent to that of the solution being employed in the extraction tower. I'he aqueous acetone solution so produced may be returned' to the extraction tower either directly or from intermediate storage.

In the execution of the invention using aqueous acetone as the selective solvent, water washing is also employed to eiect the removal ofthe undesirable hydrocarbon accumulate from the regenerated solvent produced upon distillation of the olen solution from the extraction column. According to one embodiment of the invention the water washing of the regenerated or lean solvent is carried out in the same scrubbing zone into which the acetone rich phase of the extraction column overhead is introduced.

The invention will be more clearly understood from the following detailed description and the accompanying flow diagrams illustrative of methods of applying it. Figure I represents a system adapted especially to the separation of mixtures of normal butane and other hydrocarbons of four carbon atoms having a lesser degree of saturation by means of an aqueous acetone solvent. Figure II represents a modification of this system. The drawings indicate only the essential and/or desirable apparatus elements and their relation to each other, minor elements such as pumps, compressors, valves, and the like being in the main omitted. Proper lplacement of these auxiliaries will at once be evident to those skilled in the art to which the invention pertains.

With reference to Figure I, the numeral IIl denotes an extraction column provided with the heat source shown as a closed heating coil II through which may be circulated a heating medium, such as steam, hot oil, and the like. The mixture to be separated, which will be considered as consisting of alpha and beta butylenes, normal butane and isobutane, is introduced into column I via line I2 at approximately the point indicated. As the gaseous mixture ascends into the column III, it is met by a descending stream of an aqueous acetone solution, having an acetone concentration of from about 75 to about 90 percent, introduced into the column III'via line lI3 at a. point below the point of introduction of the feed mixture. The olenic content of the feed mixture is selectively dissolved by the aqueous acetone solvent which has a preferential aflinity therefor. Any paraflln hydrocarbon, e. g. butanes, dissolved by the solvent is substantially completely removed therefrom in the lower portion of the column, which is maintained at a relatively higher temperature than the rest of the column by means of the heating coil II. The solution of olenns in the aqueous acetone solvent is conveyed from column IIJ through line I4 to stripping column I5, which is provided with a heat source I6 also indicated as a closed heating coil. Column I is operated at a temperature sufiicient to remove the dissolved olens which are recovered as overhead. The stripped or lean solvent is Withdrawn from column I5 through line I'I which communicates with solvent feed line I3 as shown.

The top or overhead product from extraction column I0 consisting of the butanes present in the original mixture plus acetone is conveyed through an overhead vapor line I8 to a condenser and phase separator I9. Two liquid layers arey formed in condenser I9. Each layer contains both acetone and paraflin hydrocarbon but the lower layer is relatively richer in acetone than the upper. Controlled quantities of the liquid in the upper layer are preferably returned to the extraction column as reux via reflux line 2U, while the lliquid in the lower layer is conveyed through linev 2I to a scrubbing tower 22 wherein it is scrubbed with water admitted through line 23. This serves to' separate substantially all of the butanes which have only negligible solubility in water. The dilute aqueous acetone solution resulting from the scrubbing operation is withdrawn through line 25 to a concentrating column 26. It should be noted that if desired all of the liquid which accumulates in condenser-separator I9 may be conveyed to tower 22, but best results have been found to follow by operating with reflux as described.

Column 25 shown as equipped with a heat source 2l, an overhead vapor line 28, and a condenser 29 is operated to produce an overhead fraction consisting of acetone and water, which fraction has an acetone concentration substantially equivalent to the aqueous acetone solvent being employed in extraction column ID and a bottom fraction consisting of water. The condensed overhead is withdrawn from condenser 29 through line 30 which communicates with lines Il and I3 as shown, while the water fraction may be recycled as in the drawing to the scrubbing tower.

As previously herein indicated, it is highly desirable that the solvent recycled to the extraction column I0 be substantially completely free of hydrocarbon material. For the purpose of avoiding the accumulation in the solvent of hydrocarbon material not removed by the stripping operation in column I5, a line 3l, which may be called the regenerated solvent clean-up line, is provided. This line terminates near the bottom of scrubbing column 22.

The rate of take-off or the amount of regenerated solvent withdrawn from line II through line 3I and thence to column 22 varies within wide limits, being determined primarily by the purity of the khydrocarbon fraction beingseparated. This in turn depends upon the source of the fraction, or in the case of cuts derived from pyrolyzed petroleum fractions upon the efliciency of the available prefractionation equipment. In operating upon a butylene-butane fraction separated from a pyrolyzed petroleum fraction with ordinary refinery fractionating equipment, it has been found that the solvent may be maintained in near optimum condition by directing from about 1,4m to about 1/10 of the regenerated solvent into line 3I. The hydrocarbon material separated from the regenerated solvent withdrawn from line I'I via line 3| is recovered from column 22 as overhead along with the butanes separated from the extraction column overhead.

It should be mentioned that, if desired, all of the regenerated solvent from the stripping column may be water-washed before its re-introduction into the extraction column. The waterwashing of either all or a part of the regenerated solvent may be carried out in tower 22 as shown, that is in the same tower in which the overhead from the extraction column is scrubbed or in a second scrubbing tower.

Still further modifications of the invention will immediately suggest themselves. For example, it may be advantageous where it is desired to continuously water-wash all or a large portion of the regenerated solvent prior to its re-use in the extraction column to employ both the column in which the overhead from the extraction column is scrubbed and a second column, the regenerated solvent to be washed being proportioned either equally or otherwise between the two columns. Also, the employment of a second or, for that matter, a third or a still greater number of scrubbng columns or towers may be coupled with water scrubbing of all or a part of the stripping column overhead, that is the overhead from column I which, under certain circumstances, may contain sulcient acetone to justify such op.. eration. Thus the system used may approximate the modification disclosed in Figure II wherein like numerals refer to like parts in Figure I.

In Figure II the overhead from stripping column |5 is conveyed via line 32 to a second scrubbing tower or column 33. Water is supplied to column 33 through line 35. A line 33 extends from stripping column exit line I1 to column 33, terminating near the bottom of the column, while a branch line 31 extends from line 36 to the bottom portion of the scrubbing tower 22. Under this arrangement, and assuming of course the incorporation of suitable control valves in the system, any desired amount of the regenerated solvent from the stripping column may be conveyed to either of the two scrubbing towers. The top fraction produced by column 33 consists of the olens dissolved by the aqueous acetone solvent in the extraction column plus the hydrocarbon accumulate separated from the regenerated s01- vent by the washing operation. The dilute aqueous acetone solution produced as bottom product may be concentrated to the desired strength for use in the extraction column either in a second concentrating column 38, as shown, to which column it is conveyed by line 39, or, if desired, in column 26. In the latter event column 28 is necessarily of greater capacity than where only the dilute solution from column 22 is concentrated therein.

When operating with a single concentrating column, the bottom products of each of the scrubbers may be combined and introduced into the concentrating column at a single point, while the water fraction constituting the bottom product of the concentrating column may be split in proper proportion between the two scrubbing towers.

If the system comprises the use of a second concentrating column, as shown in the drawings, that is column 38, the concentrated overhead is introduced after condensation into the solvent return line just as in the case of the concentrated overhead from column 26, while the water bottom fraction is recycled to scrubbing tower 33 via line 35.

It is to be understood that execution of the invention may not entail the water scrubbing of the extraction column overhead but only water scrubbing of the overhead from the stripping column I5. In this case columns 22 and 26 may or may not form part of the system.

The improved process of the present invention is advantageous in the two major respects that the solvent employed in .the extraction column is completely recovered for re-use and is at the same time maintained in a state of highest operating eiilciency. Although especially applicable,

as stated, to the separation of vnarrow boiling hydrocarbon fractions comprising normal butane, as mixtures of butadiene and/or butylenes with normal butane, it may be applied with equal success to the treatment of other narrow boiling hydrocarbon mixtures as mixtures of ethylene and ethane, propylene and propane, butadiene and butylenes, amylenes and pentadienes, amylenes and/or pentadienes and pentanes, etc.

The invention is not limited to extraction or distillation operations involving the use of aqueous organic solvents but may be put into effect where the extraction is carried out with an anhydrous solvent having the required degree of selectivity. Nor is it necessary for the solvent to have a greater aillnity for the more unsaturated of the components to be separated as the process is ap.- plicable where non-polar solvents, such as ether, trichlorethylene, carbon tetrachloride, etc., are used. In non-polar solvents, such as those specically named, parafllns are relatively more soluble than olens and mono-olens are relatively more soluble than dioleilns; hence, the more saturated component is extracted rather than the more unsaturated.

Among the many solvents, which like aqueous or anhydrous acetone have a. preferential solvent power for the more unsaturated components as between components of different degrees of saturation, may be mentioned: furfural, ethylene chlorhydrin, epichlorhydrin, nitriles, as acetoand propionitrilesy dichlorethyl ether, dimethyl glycerol ether, isocrotyl chloride, acid anhydrides, as the anhydrides of acetic and propionic acids, etc.

When operating with an anhydrous solvent, the solvent concentrating column or columns are of course operated to produce an anhydrous product for recycle. It should also be mentioned that it may be advantageous in some cases to use a liquid other than water as the scrubbing agent to produce the dilute substantially hydrocarbon-free solution or solutions of the solvent. Like water, the liquid used should have relatively little solvent power for hydrocarbons. For example, ethylene glycol, glycerol, trimethylene glycol, ethylene diamine, ethanolamine, etc. may be used in lieu of water when operating with anhydrous acetone.

I claim as my invention:

l. In a process which comprises contacting a gaseous mixture containing a butylene and normalv butane with an aqueous acetone solvent to produce a solution of the butylene in the aqueous acetone solvent, which solution after separation from the residual mixture is subsequently treated to recover the butylene therefrom and to produce a regenerated acetone solvent, the improvement which comprises subjecting the residual mixture to condensation conditions under which two liquid phases are formed, the lower of said phases being relatively richer in acetone than the upper, passing the liquid in the lower phase and at least a part of the regenerated solvent produced upon recovery of the butylene into a scrubbing zone, scrubbing the said liquid and the regenerated solvent passed into said zone with water to separate hydrocarbon material therefrom and to produce a dilute aqueous solution of acetone, concentrating the dilute aqueous solution of acetone to an acetone concentration substantially equivalent to the acetone concentration of the aqueous acetone solvent employed to produce the solution of the butylene, and employing the concentrated solution to extract additional quantities o! the butylene.

2. In a process which comprises contacting a mixture containing an oleiin and a parain of similar boiling temperatures and having the same number of carbon atoms per molecule, with an aqueous acetone solvent to produce a solution of the olen in the aqueous acetone solution, which solution after separation from the residual mixture is subsequently treated to recover the olefin therefrom and to produce a regenerated acetone solvent, the improvement which comprises subjecting the residual mixture to condensation conditions under which two liquid phases are formed, the lower of said phases being relatively richer in acetone than the upper, passing the liquid in the lower phase and at least a part of the regenerated solvent produced upon recovery of the olefin into a scrubbing zone, scrubbing the said liquid and the regenerated solvent passed into said zone with water to separate hydrocarbon material therefrom and to produce a dilute aqueous solution of acetone, concentrating the dilute aqueous solution of acetone to an acetone concentration substantially equivalent to the acetone concentration of the aqueous acetone solvent employed to produce the solution of the olen, and employing the concentrated solution to extract additional quantities of the oleiin.

3. In a process for the separation of a narrow boiling hydrocarbon mixture containing a component of a different degree of saturation but having the same number of carbon atoms as a component from which it is to be separated, which process comprises contacting said hydrocarbon mixture with a selective solvent to produce a solution of the said component in the solvent, which solution after separation from the residual mixture is subsequently treated to recover said hydrocarbon component therefrom and to produce a. regenerated solvent, the improvement which comprises subjecting the residual mixture to condensation conditions under which two liquid phases are formed, the lower of said phases being relatively richer in selective solvent than the upper, passing the liquid in the lower phase and at least a part of the regenerated solvent produced upon recovery of the aforementioned hydrocarbon component into a scrubbing zone, scrubbing the said liquid and the regenerated solvent passed into said zone with a liquid having relatively little solvent power for hydrocarbons to produce a diluted substantially hydrocarbon-free solution of the selective solvent, concentrating said diluted solution to substantially the strength of the solvent employed to produce the solution of the said hydrocarbon component, and employing the concentrated solvent to dissolve additional quantities of the said hydrocarbon component.

4. In a process for the separation of a narrow boiling hydrocarbon mixturecontaining a diolen and a more saturated hydrocarbon of similar boiling temperature and having the same number of carbon atoms per molecule, with an aqueous acetone solvent to produce a solution of the dioleiin in the aqueous acetone solution, which solution after separation from the residual mixture is subsequently treated to recover the diolen therefrom and to produce a regenerated acetone solvent, the improvement which comprises subjecting the residual mixture to condensation conditions under which two liquid phases are formed, the lower of said phases being relatively richer in acetone than the upper, passing the-liquid in the lower phase and at least a part of theregenerated solvent produced upon recovery of the diolen into a scrubbing zone, scrubbing the said liquid and the regenerated solvent passed into said zone with water to separate hydrocarbon material therefrom and to produce a dilute aqueous solution of acetone, concentrating the dilute aqueous solution of acetone to an acetonev concentration substantially equivalent to that of the aqueous acetone solvent employed to produce the solution of the diolen, and employing the concentrated solution to extract additional quantities of the diolefln.

5. In a process which comprises contacting a gaseous mixture containing a butadiene and a butylene with an aqueous acetone solvent to produce a solution of the butadiene in the aqueous acetone solvent, which solution after separation from the ,residual mixture is subsequently treated to recover the butadiene therefrom and to produce a regenerated acetone solvent, the improvement which comprises subjecting the residual mixture to condensation conditions under which `two liquid phases are formed, the lower of said phases being relatively richer in acetone than the upper, passing the liquid in the lower phase and at least a part of the regenerated solvent produced upon recovery of the butadiene into a scrubbing zone, scrubbing the said liquid and the regenerated solvent passed into said zone with water to separate hydrocarbon material therefrom and to produce a dilute aqueous solution of acetone, concentrating the dilute aqueous solution of acetone to an acetone concentration substantially equivalent to that of the aqueous acetone solvent employed to produce the solution of the butadiene, and employing the concentrated solution to extract additional quantities of the butadiene.

6. In a process which comprises contacting a gaseous mixture containing a pentadiene and an amylene with an aqueous acetone solvent to produce a solution of the pentadiene in the aqueous acetone solvent, which solution after separation from the residual mixture is subsequently treated to recover the pentadiene therefrom and to produce a regenerated acetone solvent, the improvement which comprises subjecting the residual mixture to condensation conditions under which two liquid phases are formed, the lower of said phases being relatively richer in acetone than the upper, passing the liquid in the lower phase and at least a part of the regenerated solvent produced upon recovery of the pentadiene into a scrubbing zone, scrubbing the said liquid and the regenerated solvent passed into said zone with water to separate hydrocarbon material therefrom and to produce a dilute aqueous solution of acetone, concentrating the dilute aqueous solution of acetone to an acetone concentration substantially equivalent to that of the aqueous acetone solvent employed to produce the solution oi the pentadiene, and employing the concentrated solution to extract additional quantities of the pentadiene.

MOTT SOUDERS, Jn.

Images