US2527951A - Hydrocarbon separation - Google Patents

Description

Oct. 3l, 1950 B. J. MAYLAND ETAL HYDRoCARBoN SEPARA'IION Filed Sept. 27, 1948 2 Sheets-Sheet 1 Oct. 31, 1950 B. J. MAYLAND ETAL 2,527,951

x-xYnRocARBoN SEPARATION Filed sept. 27, 1948 2 sheets-sheet 2 A TTORNEVS Patented Oct. 31, 1950 UNITED STATES PATENT OFFICE 2,527,951 HYDROCARBON SEPARATION Bertrand J. Mayland, Bartlesville, Okla., and Edward E. White, Covington, Va., assignors to Phillips Petroleum Company, a corporation of Delaware Application September 27, 1948, Serial No. 51,444

'1y Claims. (Cl. 260-68L5) This invention relates to a process for resolvingl mixtures of aliphatic hydrocarbons having at least three degrees of saturation. In a speciiic embodiment it relates to a process for resolving mixtures of aliphatic parailln, olefin and diolen hydrocarbons into the respective components. This invention is useful for the resolution of mixtures of butanes, butenes and butadiene.

'I'his application is a, continuation-impart of our copending application, Serial No. 691,148, tiled August 16, 1946, now U. S. Patent 2,484,305.

The separation of olefins or dioleflns from paramnic hydrocarbon streams to obtain a subphatic hydrocarbons having -at least three degrees of saturation into the respective components of the mixture. Another object is to provide an improved method of resolving mixtures of aliphatic paramns, oleiins and diolelns into the respective components of the mixtures. It is a further object of this invention to resolve mixtures of butanes, butenes and butadiene by liquid-liquid extraction. Numerous other objects will appear more fully hereinafter.

The accompanying drawings portray diagrammatically one arrangement of equipment which has been found very satisfactory for carrying out liquid-liquid extraction as a means of sepastantially pure paraiiinic stream and unsaturate rating aliphatic hydreearbens of different destream usually cannot be simply accomplished grees of saturation; the arrangement shown repbecause of the close boiling range of the comresents a preferred embodiment of our invention, pounds and because of the tendency to formv but obviously other arrangements may be used azeotropes. For example the separation of Without going beyond the SCODe 0f 0111 invention. butadiene and butenes from n-butane by straight The present invention Provides a Solution to fractionation is not possible due to the formation the problem Outlined above in that it makes of a constant boiling mixture between butadiene vailabIe Solvents having bOth high selectivity and n-butane. Similarly the separation of diand good Solvent power or capacity for the oleflns from oleiins by ordinary fractionation is hydrocarbons. We have discovered that a often not possible, solvent having greatly improved properties over It has heretofore been attempted to solve this problem by the use of azeotropic or extractive distillation whereby another component is added to the system which makes possible fractionation by changing the relative volatilities of the hydrocarbon. If the added component goes overhead this method of separation is referred to as azeotropic distillation, and the added component is commonly termed an entraining agent. If the added material is removed in the kettle product, the process is known as extractive distillation, and the added material is termed a selective solvent. Generally, a greater change in relative volatilities is obtained by adding a component of higher selectivity. Polar compounds (i. e., compounds having a high dipole moment and a high internal solution pressure) are used as selective solvents for extractive distillation. In general, the greater the polarity of the selective solvent, the greater the selectivity but the lower the solvent power or capacity. To decrease the height of a column necessary to effect the desired separation a highly selective added component is desired as the selective solvent. On the other hand, the hydrocarbons must have a moderate solubility in the solvent to limit the amount of solvent required to be added and to keep the diameter of the column within reason. The polar solvent chosen represents a compromise between these two extremes; i. e., selectivity is sacrificed for solvent power or capacity.

An object of this invention is to provide an improved method for resolving mixtures of allordinary polar solvents is obtained by blending a polar solvent with a solvent which exhibits compound-forming tendencies with the unsaturated hydrocarbons. The resulting solvent has improved selectivity over either of the solvents alone and greater solvent power or capacity for the hydrocarbons. The blended solvent may be used in an extractive distillation process of the type now well known in the art. In conventional extractive distillation, the mixture of aliphatic hydrocarbons of varying degrees oi saturation ranging from diolens vto paramns is fed continuously to a combined fractional distillation-extraction column at an intermediate point therein, the relatively non-volatile selective solvent is continuously introduced at the top of the column and iiows downwardly therein, the bottom of the column is reboiled in the usual way to drive out any of the more saturated hydrocarbon dissolved therein and to supply the heat required for the distillation, the top of the column is reuxed by returning a portion of the condensed more saturated hydrocarbon taken overhead, and the solvent rich in more unsaturated hydrocarbon is continuously fed to a stripping column where the unsaturated hydrocarbon content is stripped from the solvent.

'The blended solvents of the present invention may also be used in liquid-liquid extraction processes. For example, a mixture of two or more of paraffins, oleflns and diolens may be contacted countercurrently with a blended solvent in any suitable type of equipment such as a vertical column provided with means of obtaining intimate contact such as bailles, packing, bubble trays, etc. The resulting extract consisting essentially of solvent and dissolved more unsaturated hydrocarbons may then be stripped in a separate zone to recover the more unsaturated hydrocarbons. The extracted hydrocarbon stream, i. e., the raffinate, is composed essentially of the more saturated hydrocarbon, which was undissolved by the solvent, together with a small amount of dissolved solvent. This raffinate may be stripped or otherwise treated to separate essentially pure more saturated hydrocarbon from the dissolved solvent.

We much prefer, however, to use a special liquid-liquid extraction process which we have discovered and which provides a large saving of heat over either extractive distillation or conventional liquid-liquid extraction processes. Such a special process is described in detail below.

It can be shown that the selectivity of a polar solvent depends on the degree of polarity as well as on the difference of polarity between the compounds being separated. In the order of increasing polarity the C4 hydrocarbons are n-butane, butenes, and butadiene. These compounds actually are relatively non-polar and form nonideal solutions with highly polar compounds. The differences in polarity of these hydrocarbons determine their relative deviation from ideal solution laws. Butadiene being more polar will be more soluble in a polar solvent than n-butane under comparable conditions of temperature, pressure and concentration.

Blendingf two polar solvents results in a polar mixture having a polarity somewhere between the polarity of the individual solvents. The mixture exhibits about the same degree of selectivity as a single solvent having a polarity corresponding to the mixture and the hydrocarbon solvent power or capacity is similarly related. Thus the solvent obtained by blending two polar solvents has little or no advantage over a single solvent of the same degree of polarity.

Some compounds show a tendency to form loose chemical compounds with the hydrocarbons. If this tendency is more pronounced with one type of hydrocarbon than with another or if the tendency is present with one of the hydrocarbon types and not with another, the solvent will have a certain amount of selectivity depending on the strength of the effect. A compound of this type may or may not be polar. If it is polar, the selectivity is due to the polarity as well as to the bonding tendency and the selectivity will be greater than that of an ordinary polar compound which does notI exhibit the bonding tendency.

In accordance with our invention selective solvents for the separation of aliphatic hydrocarbons of varying degrees of saturation are made by blending a polar solvent having no bonding tendency or only poor bonding tendency with the unsaturates with a solvent having such bonding tendency with the unsaturates. The resulting mixture shows selectivity due to the resulting polarity of the mixture and due to the bonding tendency with the unsaturates and is greatly superior to either component by itself.

By the term polar as used herein we mean a compound having a high polarity, i. e. a compound in which a dissolved non-polar compound such as gaseous normal butane at atmospheric condition has a high activity coeiiicient, namely above 10. Methods of determining the activity coeflicient of a compound such as normal butane in solution are well-known to those skilled in the art and need not be detailed herein. The activity coeilicient is a measure of the deviation of the solution from ideality, a vcoeicient of -unity indicating ideality. A coefficient greater than unity indicates solubility or solvent power less than ideal (positive deviation), and a coefficient less than unity indicates solubility or solvent power greater than ideal (negative deviation).

In general the polar compounds used in practicing our invention do not exhibit a bonding tendency with unsaturates. Conversely the compounds exhibiting a bonding tendency with unsaturates used in accordance with the present invention are, generally speaking, non-polar.

We have found that blending highly polar solvents with relatively non-polar solvents that exhibit strong valence forces with the unsaturates is a means of approaching theideal solvent.

The compound exhibiting bonding tendency may display such tendency with dioleflns but not with olens or parafiins or with both dioleilns and oleflns but not with paraiiins. In the first case the resulting blended solvent may be employed to separate dioleiins from olefins and/or paramos. In the second case it may be employed to separate diolens and/or olens from parains.

For example a blended solvent consisting of ethanolamine-saturated with tetraethylorthosilicate may be used to separate diolelns or oleiins or both from parailins in accordance with our invention. However a solvent consisting of ethanolamine saturated with paraldehyde has an activity coefficient of less than unity with butadiene but greater than unity with butene-l and n-butane and therefore can be used to separate butadiene from butene-l or n-butane or both.

The process of our invention may be defined as a two-stage process for resolving a hydrocarbon mixture containing at least one saturated aliphatic hydrocarbon, at least one unsaturated aliphatic hydrocarbon containing one double bond per molecule and at least one unsaturated aliphatic hydrocarbon containing at least two double bonds per molecule into the respective components. In the first stage the hydrocarbon mixture is intimately contacted with a blended solvent which will effect preferential solution of either the unsaturated hydrocarbons or the more unsaturated hydrocarbons, viz. those containing the two double bonds per molecule. As a consequence one of the hydrocarbon types in the mixture is separated from the other two types, and in the second stage the other two types are separated from each other by intimately contacting them with a selective solvent which will eifect preferential solution of the more unsaturated of the two hydrocarbon types. Hence, the ultimate result of practicing our invention is a resolution of the hydrocarbon mixture into its respective components.

The second component, which is the compound that exhibits bonding tendencies1 of the selective solvent of the present invention exhibits compound-forming tendencies with oleiins or diolens or both but is to be distinguished from a compound `which actually forms compounds with.

olefins or diolefins. Examples of the latter type of compound are sulfur dioxide, cuprous salts, maleic anhydride. The compounds which we employ are generally characterized by being nonpolar, i. e. in which n-butane has an activity coefficient greater than 1.0 but not greater than 2.0 and either butene or butadiene less than 1.0.

The hydrocarbonseparation may be conducted vapor phase simple gas scrubbing may be practiced but extractiva distillation is preferable. We prefer liquid-liquid extraction. The temperature may range from the freezing point of the solvent' or components thereof up to the point of complete miscibility between the solvent Vand the. hydrocarbon mixture. Temperatures below the critical temperature of the hydrocarbon mixture should of course be employed. Generally the temperature of extraction will be atmospheric or substantially atmospheric.

The pressure may vary over wide limits but should be suillcient to hold the hydrocarbon mixture in the liquid phase in order that liquidliquid extraction may be practiced. At ordinary atmospheric temperatures of, say, 60 toA 110 F., pressures of the order of 80 to 200 pounds per square inch gauge will be sulcient to. prevent appearance of a gaseous phase to any appreciable extent.

The relative amounts of the blended solvents and the hydrocarbon feed employed will depend upon the concentration of the hydrocarbon to be preferentially separated. It is of course preferable to use enough solvent to dissolve a substantial proportion or all of the .hydrocarbon to be separated. In the interest of economical operation the amount of solvent should preferably be kept as close as is practical to the minimum required to dissolve completely the hydrocarbon to be separated.

We have found it highly desirable and advantageous to carry out the separation steps in vertical elongated columns or contacting zones, introducing the hydrocarbon mixtures to be separated at an intermediate point in these columns and the solvent at one end, most conveniently at the top, contacting the feed countercurrently with the feed in one end of the extraction zone and passing the resulting extract past the feed entry into the other portion, usually the lower, of the zone, and to introduce near the other end of the extraction zone a continuous stream stripping the resulting extract the more unsaturated hydrocarbon or hydrocarbons is obtained. A portion' of this is vwithdrawn as the more unsaturated hydrocarbon product of the process and the balance is returned for injection as "reflux" into the nrst extraction zone as described above. v

Extraction of the first extract with the single l component of the blendedsolvent in the manner (which may be termed reflux") oi' more unsaturated hydrocarbon or hydrocarbons separated from the resulting extract. Introduction of this more unsaturated stream effects displacement from the solvent of any dissolved more saturated hydrocarbon and gives a much purer fraction of more unsaturated hydrocarbon or hydrocarbons.

The ramnate from the extraction step consists essentially of the more saturated hydrocarbon or hydrocarbons containing a small amount oi!v dissolved solvent. This may be stripped to recover the more saturated hydrocarbon or hydrocarbons.

The extract consists essentially of the more unsaturated hydrocarbon or hydrocarbons dissolved in the solvent. While this may be stripped directly to give a fraction consisting essentially of the more unsaturated hydrocarbon or hydrocarbons we have found -it much superior to extract the extract with a solvent composed chiefly of the component of the blended solvent which exhibits bonding tendencies with the unsaturated hydrocarbon content of the extract. This effects transfer of the more unsaturated hydrocarbon or hydrocarbons from the original extract to the second solvent leaving a rafllnate consisting essentially of the blended solvent suitable for recycle to the first extraction. Upon just described efi'ects great savings in heat since the large amount of blended solvent in the first extract is replaced by a relatively small amount of the single solvent. The single solvent is capable vof dissolving very much more of the more unsaturated hydrocarbon or hydrocarbons. In fact the single solvent is generally completely miscible in all proportions with aliphatic unsaturated hydrocarbons. Thus, the second extraction greatly reduces the volume of solvent associated with the more lunsaturated hydrocarbon orhydrocarbons and efl'ects a correspondixgly great saving in the heat required for strip- D D8- Y We have found that tetraethylorthosilicate exhibits a bonding tendency with olefins and dioleflns but not with paramns. The bonding tendency of this compound is shown by the following tabulation which gives the solubility of three gaseous C4 hydrocarbons in this compound and their calculated activity coefllcients.

[ F.. 1 atm., 5 ml. solvent.]

An activity coemcient less than unity indicates negative deviation from ideal solution laws and is an indication of attraction between the solvent and hydrocarbon. This attraction is called loose chemical bonding but may be thought of as simply an attraction between unlike molecules. Whereas n-butane shows positive deviation, the 1izlinsaturated hydrocarbons show negative devia- We have found that blending tetraethylorthosilicate with a polar solvent not exhibiting a bonding tendency with the unsaturated hydrocarbons gives a solvent having greater selectivity than either solvent alone and greater solubility or solvent power for the hydrocarbons than the polar solvent. A typical polar solvent, namely ethanolamine, was blended with tetraethylorthosilicate by saturating the ethanolamine with tetraethylorthosilicate. The resulting blend was compared with ethanolamine by itself for the relative solubility of the three gaseous Ct hydrocarbons. The following tabulation shows the results which were obtained.

[85 F., l atm.. 5 ml. solvent] It will be seen that the blended solvent has a selectivity between parafllns and the unsaturates greater than either solvent alone. The solubility oi.' the hydrocarbon in the blended solvent is greater than in the polar solvent alone.V In addition, whereas the greater amount oi hydrocarbon dissolved in the blended solvent tends to decrease the selectivity, actually the selectivity is shown to be greater. Other polar compounds may be used instead of ethanolamine. anolamine is a good example because it has high selectivity but it is of doubtful usefulness by itself because of low solubility for the hydrocarbons. The presence oi' the tetraethylorthosilicate increases its capacity for dissolving hydrocarbons and also increases its selectivity between parailins and unsaturates.

We have found that paraldehyde tends to form loose chemical compounds (i. e. exhibits a bonding tendency) with diolefins but not with oleflns or paratiins. This is indicated by the data below where butadiene-1,3 has an activity coei'licient of less than unity in the hydrocarbonparaldehyde system whereas butene-l and nbutane show positive deviation and so do not tend to form loose chemical compounds with the solvent.

[Vapor-Liquid Equilibrium 180 F., 100 p. s. i. n.1

Eth-

This solvent by itself would be useless for liquidliquid extraction operations because it is miscible in all proportions at ordinary temperatures. However, by blending with a polar solvent to cut down the solubility, the selectivity due to formation of loose chemical bonds of the diolefin plus the selectivity due to the polarity of the solution is obtained and the degree of miscibility can be SdJusted.

For example, the solvent ethanolamine, a polar compound characterized by low solubility for hydrocarbons, was saturated with paraldehyde and tested for selectivity. The following tabulation compares the blended solvent with pure ethanolamine.

[85 F., 1 atm., l0 nil. solvent] Ethanolamlne Satu- Ethanolumino rated with Paraldehyde at 75 F.

Ml. Relativo Sol. Ml. Relative Bol.

n-Butane 1l. 3 1.00 13. 4 1.00 Butn-l 25. 1 2. 22 l. 00 27. 2 2. 03 l. 00 Butadiene-LB 61.4 5. 43 2. 45 76. 0 6T 2. 80

The above data concerns C4 hydrocarbons but 75 the principle of blending the solvents of the prsent invention can be applied to any mixture of saturated and unsaturated aliphatic hydrocarbons. Usually, if not always, the hydrocarbon mixture treated by the process of the present invention will consist of hydrocarbons having the same number oi.' carbon atoms per molecule, because it is a simple matter to separate hydrocarbons having different numbers oi carbon atoms per molecule by ordinary fractional distillation. The hydrocarbon mixtures treated may range from Cz to Ca or even higher. Generally a C4 or a C5 hydrocarbon stream will be treated by the present invention.

Practically any polar solvent may be employed in carrying out the present invention. As stated above we prefer to use a highly polar compound, i. e. a compound in which normal butane at atmospheric condition exhibits an activity coefilcient greater than 10. Examples of such highly polar compounds are: ethanolamine, furfural. furfuryl alcohol, aniline, nitrobenzene, phenyl hydrazine, methyl sulfate, ethylene chlorohydrin, tetraethylene pentamine, diethylene glycol monoethyl ether, levulinic acid, o-anisidine, triethylene glycol, B-hydroxypropionitrile.

Instead of tetraethylorthosilicate and paraldehyde, we may employ other solvents having a bonding tendency with hydrocarbon, but not with saturated hydrocarbons. Examples of other solvents are: 1,1-bis-tert-butyl mercapto ethane, tert-dodecyl thioacetate, dioctyl disulfide, diethyl carbitol. In order to practice our two-stage process one o! the solvents exhibiting a bonding tendency must exhibit such tendency with unsaturated aliphatic hydrocarbons in preference to saturated aliphatic hydrocarbons, and the other of such solvents must exhibit its bonding tendency with more unsaturated aliphatic hydrocarbons in preference to less unsaturated aliphatic hydrocarbons.

While the preferred solvents for use in carrying out the present invention are saturated solutions of tetraethylorthosilicate and paraldehyde in ethanolamine, we may employ other blends of polar solvents and solvents exhibiting a bonding tendency with unsaturates. The blend should contain a substantial amount of each solvent. Preferably the solvent will consist of the polar solvent saturated with the solvent exhibiting bonding tendency with the unsaturates.

The blended solvents of the present invention may be employed in extractive distillation processes for the separation of aliphatic hydrocarbons oi differing degrees of saturation such as paraiiins and unsaturates. However, liquid-liquid extraction possesses a number of economical advantages over extractive distillation and is theefore more desirable. Liquid-liquid extraction has not been used heretofore on a commercial scale for the separation of aliphatic hydrocarbons of diiferent degrees of unsaturation. As pointed out above, it is probable that the reason for this failure to use liquid-liquid extraction processes is the limited hydrocarbon solubility in the selective solvents heretofore available. The present invention overcomes this drawback and makes feasible the use of liquid-liquid extraction for this type of separation.

The drawings show in simplified flow diagram how the separation of a mixture of aliphatic 'nydrocarbons of different degrees of saturation may be accomplished using the blended solvents of the present invention with a double liquid-liquid extraction process which results in a great saving of heat over either extractlve distillation or simple liquid-liquid extraction.

Referring to Figure 1, a feed stream oi' aliphatic hydrocarbons to be separated and comprising, for example, paranins together with oleflns and diolefins, is fed via line I into the center of a multiple stage liquid-liquid contacting column 2 operated at a pressure suilicient to maintain liquid conditions. The blended solvent, typically a polar compound, such as ethanolamine, saturated with tetraethylorthosilicate is fed from storage 3 via line 4 into column 2 near or at the top and contacted countercurrntly with the rising hydrocarbon stream. The upper section of column (i. e. the part above the point of feed entry) acts as a stripping section where the unsaturates are nearly all or completely removed from the hydrocarbon stream. The overhead stream, constituting the raffinate, is removed via, line 5. This rafnate consists essentially'of paraftln hydrocarbon and dissolved solvent constituents. The parainic hydrocarbon is recovered as a nearly pure stream by stripping the rafdnate in a distillation column 6. The resulting bottoms product, consisting essentially of recovered solvent components may be returned via line I to blended solvent storage 3. The solvent may be cooled in cooler 'IA prior to its return. As is usual, stripper column t is provided with a reboiler 8 and the feed to the column is introduced at the top. The stripped essentially pure paralnic hydrocarbon overhead is withdrawn from column 6 via line 9. A portion oi this overhead stream may be condensed and returned as reflux (not shown) to the top of column 6. Of course, enough solvent must be used in the extraction conducted in extractor 2 so that all the non-polar constituent, tetraethylorthosilicate in this case, is not dissolved in the hydrocarbon stream 5 from the extractor 2.

The lower part of extraction column 2 (i. e. the portion below the point of entry or feed line I) acts as an enriching section whereby the solvent from the stripping section is contacted with a hydrocarbon reilux stream consisting essential-- ly of the unsaturated hydrocarbons and introduced near or at the bottom of column 2 via line I0. The stream withdrawn via line II from the bottom of column 2 consists essentially of mixed solvent and dissolved unsaturates. The unsaturated hydrocarbons may be recovered by a stripping operation at this point but the amount of solvent is large and the heat consumption would be excessive.

We have found that a large saving in heat consumption may be effected by carrying out another extraction by contacting the stream flowing in line I I with a stream of tetraethylorthosilicate introduced via line I2 to a second multiple stage liquid-liquid extracting column i3. This gives a stream of polar solvent saturated with tetraethylorthosilicate (railinate), withdrawn from column I3 via line I4 and a stream of tetraethylorthosilicate saturated with the polar solvent and containing the unsaturated hydrocarbons (extract), withdrawn via line I5. The rallnate is returned via line I4 to blended solvent storage 3. The extract is passed via line I5 to distillation column I6 which serves to strip the unsaturated hydrocarbons from the solvent. The stripped solvent is returned via line Il and cooler I'IA to tetraethylorthosilicate solvent storage I8.

The -unsaturated hydrocarbons stripped in column I6 is withdrawn overhead via line I9. Condenser I9A may be employed to cool and condense the overhead vapors. A portion of the resulting liquid condensate may be returned as reflux (not shown) to the top of stripper I6. The balance of the condensate is split into two streams, one stream being returned via line I0 tothe bottom of extractor 2 and the other stream being withdrawn via line 20 as the unsaturated hydrocarbon product of theV first stage of our process.

An important advantage of the second extraction carried out in extractor I3 is that, tetraethylorthosilicate bein'g completely iniscible with the hydrocarbon, the second extraction greatly reduces the volume of solvent associated with the hydrocarbon before the stripping operation carried out in column I6 thus resulting in a large saving in the heat required for the stripping.

It is noted that whereas the feed line I enters the rst extractor 2 at an intermediate point therein, say at or near the mid-point, the resulting extract flowing in line II enters the second extractor I3 at a point adjacent the top thereof. The reason for this is that column 2 is effecting a separation between parafllns and unsaturates and embodies an upper or stripping section wherein the unsaturates are substantially completely removed from the hydrocarbon stream and a lower or enriching section wherein the downwardly flowing solvent is contacted with a stream consisting essentially of unsaturated hydrocarbons to eifect displacement of paraffin from solution in the solvent; Whereas column I3 is eecting only separation of a major portion or substantially all of the mixed solvent from the unsaturated hydrocarbons by employment of tetraethylorthosilicate as a solvent which functions to selectively dissolve the hydrocarbons from the blended solvent.

Countercurrent liquid-liquid extraction is conducted in each of extractors 2 and I3, conditions being such that all components are in liquid phase and proportions of incoming streams and conditions being such that two phases are present, each in substantial amount. The extractions are ordinarily carried out at atmospheric temperature.

In operation the stream of tetraethylorthosilicate owlng in line I2 from storage I8 to the bottom of extractor I3 is saturated with the polar solvent. This is for the reason that the equilibrium attained in extraction unit I3 is such that the extract withdrawn via line I5 comprises tetraethylorthosilicate saturated with the polar solvent as well as containing the unsaturated hydrooarbons. amount of polar solvent in the tetraethylorthosilicate fed via line I2 to unit I3 does not affect the operation adversely so that no means for separating the polar solvent from the tetraethylorthosilicate is necessary.

In practice a phase of tetraethylorthosilicate saturated with the polar solvent tends to build up in the blended solvent storage 3 and must be withdrawn occasionally in order that proper operation may be attained.

If desired, the unsaturated hydrocarbon produots of our invention may be withdrawn via line 20, but We prefer to separate these products further in a second stage liquid-liquid separation step. The apparatus for and the operation of the second stage of our process is identical to that of the rst stage, and for that reason we will not encumber our disclosure with a detailed description of the second stage. It will be understood that the products from the first stage of our process are the more saturated hydrocarbons or paraflins and a mixture of the unsaturated hydrocarbons or oleflns and diolefins. We separate The presence of the resulting small this latter product into its components in a. second stage, identical to that described above, wherein the hydrocarbon mixture to be separated is the unsaturated hydrocarbon product from the ilrst stage and it is the feed ior the second stage separation. Improved operation may be obtained in some cases by diluting the olendiolen feed with a paraflin that is readily removable by distillation. For example a butenebutadiene stream wlthdrawn through line may be diluted with a pentane, a hexane, or other easily removable paramn prior to resolution in the second stage extraction. This feed passes through a separation process identical to the first stage except that the blended solvent for the second stage is a polar compound saturated with a compound that exhibits a compound forming tendency with dioleiins in preference to oleiins. An example is ethanolamine saturated with paraldehyde which we use in the second stage instead of the ethanolamine saturated with tetraethylorthosilicate of the iirst stage of our process. The second stage of our process is readily understood by considering the description oi.' the iirst stage and replacing tetraethylorthosilicate with paraldehyde and realizing further that the hydrocarbon feed contains olens and diolefins and that the resulting products are a stream oi oleilns and a stream of dioleiins. Hence, the ultimate result of our two-stage process is a resolution of a hydrocarbon mixture containing hydrocarbons of at least three degrees oi' saturation into the components of the mixture.

Figure 2 portrays the complete process of our invention. This drawing is self-explanatory, and it will be understood that both the ilrst and second stage extraction steps are carried out in a, manner similar to that of Figure 1, more fully described above.

From the above description numerous modifications of our invention will be apparent to those skilled in the art. For example, in an alternative embodiment the original leed is contacted with a blended solvent of ethanolamine and paraldehyde, and the more unsaturated hydrocarbon or the diolefin is one of the products of this iirst stage. In the second stage the other product of the first stage which contains the more saturated hydrocarbons, or parailins and olens, is contacted with a blended solvent of ethanolaminc and tetraethylorthosilicate, and the resulting products are a stream of the paramns and a stream of the oleiins. This embodiment along with other modifications are Well within the scope of our invention.

We claim:

1. The method of resolving a mixture of aliphatic hydrocarbons containing hydrocarbon types of at least' three degrees of saturation r'which comprises intimately contacting said mixture with a liquid selective solvent consisting essentially of ethanolamine and a non-polar solvent in which N-butane has an activity coeicient between 1.0 and 2.0 and in which at least one of butene and butadiene has an activity coeillcient less than 1.0 and selected from the group consisting of paraldehyde and tetraethylorthosilicate and thereby effecting a preferential dissolution of at least one of the unsaturated hydrocarbon types in said selective solvent as the extract phase and separation of at least one of the more saturated hydrocarbon types in the raillnate phase, and intimately contacting the hydrocarbon content of the phase containing more than one hydrocarbon type from the iirst-named con-' tacting step with a second liquid selective solvent consisting essentially of ethanolamine and a nonpolar solvent which is paraldehyde when tetraethylorthosilicate is the first-named polar solvent and tetraethylorthosilicate when paraldehyde is the iirst-named polar solvent, and thereby effecting preferential dissolution of the more unsaturated hydrocarbon type in said second selective solvent.

2. The method of resolving a mixture of aliphatic hydrocarbons containing hydrocarbon types of at least three degrees of saturation which comprises intimately contacting said mixture with a liquid selective solvent consisting essentially of ethanolamine and tetraethylorthosilicate and thereby effecting preferential dissolution of the unsaturated hydrocarbon types in said selective preferential dissolution of the unsaturated hydrocarbon types in said selective solvent, separating said unsaturated hydrocarbon types from said sci vent, and intimately contacting the thusseparated unsaturated hydrocarbons with a liquid selective solvent consisting essentially of ethanoiamine and paraldehyde and thereby effecting preferential dissolution of said more unsaturated hydrocarbon type of said separated unsaturated hydrocarbons in said second selective solvent.

3. A method according to claim 2 wherein the aliphatic hydrocarbon mixture to be resolved contains parafflns, oleilns and' dioleilns.

4. A method according to claim 3 wherein the aliphatic hydrocarbon mixture to be resolved contains butanes, butenes and butadiene.

5. The method of resolving a mixture of aliphatic hydrocarbons containing hydrocarbon types of at least three degrees of saturation which comprises intimately contacting said mixture with a liquid selective solvent consisting essentially ci ethanolamine and paraldehyde and thereby effecting preferential dissolution of the more unsaturated hydrocarbon type in said selective solvent, separating the hydrocarbon types more saturated than the selectively dissolved hydrocarbon from said selective solvent, and intimateiy contacting the thus-separated more saturated hydrocarbons with a liquid selective solvent consisting essentially of ethanolamine and tetraethylorthosilicate and thereby eiecting preferential dissolution of said more unsaturated hydrocarbon type of said separated more saturated hydrocarbons in said second selective solvent.

6. A method according to claim 5 wherein the aliphatic hydrocarbon mixture to be resolved contains paramns, oleflns and dioleins.

7. A method according to claim 6 wherein the aliphatic hydrocarbon mixture to be resolved contains butanes, butenes and butadiene.

BERTRAND J. MAYLAND. EDWARD E. WHITE.

REFERENCES CITED The following references are of record 1n the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,365,898 Morris et al. Dec. 26, 1944 2,379,332 Arnold June 26, 1945 2,396,300 Cummings et al. Mar. 12, 1946 2,422,341 Crouch June 17, 1947 Certificate of Correction Patent N o. 2,527,951 October 31, 1950 f BERTRAND J. MAYLAND ET AL.

` It is hereby certified that error appears in the printed specification ofvr the above numbered patent requiring correction as follows:

Column 12, lines 19 and 20, strike out the Words preferential dissolution of the unsaturated hydrocarbon types in said selective;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Olice.

Signed and sealed this 22nd day of May, A. D. 1951.

THOMAS F. MURPHY,

Assistant ommz'sszoner of Patents.

Claims (1)

1. THE METHOD OF RESOLVING A MIXTURE OF ALIPHATIC HYDROCARBONS CONTAINING HYDROCARBON TYPES OF AT LEAST THREE DEGREES OF SATURATION WHICH COMPRISES INTIMATELY CONTACTING SAID MIXTURE WITH A LIQUID SELECTIVE SOLVENT CONSISTING ESSENTIALLY OF ETHANOLAMINE AND NON-POLAR SOLVENT IN WHICH N-BUTANE HAS AN ACTIVITY COEFFICIENT BETWEEN 1.0 AND 2.0 AND IN WHICH AT LEAST ONE OF BUTENE AND BUTADIENE HAS AN ACTIVITY COEFFICIENT LESS THAN 1.0 AND SELECTED FROM THE GROUP CONSISTING OF PARALDEHYDE AND TETRATHYLORTHOSILICATE AND THEREBY EFFECTING A PREFERENTIAL DISSOLUTION OF AT LEAST ONE OF THE UNSATURATED HYDROCARBON TYPES IN SAID SELECTIVE SOLVENT AS THE EXTRACT PHASE AND SEPARATION F AT LEAST ONE OF THE MORE SATURATED HYDROCARBON TYPES IN THE RAFFINATE PHASE, AND INTIMATELY CONTACTING THE HYDROCARBON CONTENT OF THE PHASE CONTAINING MORE THAN ONE HYDROCARBON TYPE FROMT HE FIRST-NAMED CONTACTING STEP WITH A SECOND LIQUID SELECTIVE SOLVENT CONSISTING ESSENTIALLY OF ETHANOLAMINE AND NONPOLAR SOLVENT WHICH IS PARALDEHYDE WHEN TETRAETHYLORTHOSILICATE IS THE FIRST-NAMED POLAR SOLVENT AND TETRAETHYLORTHOSILICATE WHEN PARALDEHYDE IS THE FIRST-NAMED POLAR SOLVENT, AND THEREBY EFFECTING PREFERENTIAL DISSOLUTION OF THE MORE UNSATURATED HYDROCARBON TYPE IN SAID SECOND SELECTIVE SOLVENT.

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