US2656342A

US2656342A - Hydrocarbon segregation utilizing

Info

Publication number: US2656342A
Authority: US
Publication date: 1953-10-20
Anticipated expiration: 1970-10-20

Description

Oct. 20, 1953 c. N. KHVIBERLIN, JR., ETAL 2,656,342

HYDROCARBON SEGREGATION UTILIZING UREA AND A NITRILE Filed July 8, 1949 I2 UREA uappzn.

nvonocanaolv FEED 3 UREA COMPLEX FORMAT/ON ZONE A Tau/r1: 11.: v

camuzx SEPARATION 2 A ND wnsmue 2 cm:

.Snsnr was ze'cvcLzo ro l CQMPl-EX UNREACTED HYDRO CARBONS AND A CT1v1 7'4 ILE UREA RECYCl-E ---p l5 N-AI. IPHATI 8 I nvozocmzson's 6 BIG FRACTION M .avwwvtom Patented Oct. 20, 1953 UNITED STATES PATENT OFFICE HYDROCARBON SEGREGATION UTILIZING UREA AND A NITRILE Delaware Application July 8, 1949, Serial No. 103,562

4 Claims. (Cl. 260-965) This invention relates to a process for separating hydrocarbons and particularly for separating normal aliphatic hydrocarbons. The invention also concerns a process for separating one type of normal aliphatic hydrocarbon from another type of normal aliphatic hydrocarbon. In accordance with the process of this invention, feed stocks containing hydrocarbons to be segregated are contacted with urea in the presence of a nitrile, resulting in the formation of a ureanormal aliphatic hydrocarbon solid complex which may be separated and decomposed to release the normal aliphatic hydrocarbon.

While many methods are known in the art for segregating hydrocarbon fractions or particular hydrocarbon types, a need still exists for separating particular types of hydrocarbons or for fractionating particular types of hydrocarbons. The present invention concerns a process for separating normal aliphatic hydrocarbons from other types of hydrocarbons, utilizing a nitrile such as acetonitrile and urea. While urea extractive crystallization processes of this general character have been known, the process of this invention does not require the presence of water, alcohol, or any of the other auxiliary liquids heretofore employed in urea extractive crystallization processes. It is contemplated that the process of this invention will find application in systems not well adapted for the use of alcohol or water as the auxiliary liquid. It is furthermore contemplated that in particular systems, the selectivity of the hydrocarbon segregation will be improved over that formerly obtainable.

As indicated, the process of this invention is adapted to the segregation of normal aliphatic hydrocarbons from other types of hydrocarbons. Thus, urea in the presence of a nitrile will selectively form solid complexes with normal hydrocarbons to the exclusion of complex formation with hydrocarbons of other types. Hydrocarbons which form crystalline complexes with urea in the presence of a nitrile include the parafiinic hydrocarbons such as butane, pentane, hexane, etc., having 4 or more carbon atoms. Similarly, normal aliphatic olefinic hydrocarbons such as the butenes, pentenes, hexenes, etc., having 4 or more carbon atoms may be treated by the process of this invention. Normal diolefins and triolefins as well as the normal alcohols, esters, ketones, ethers, and other compounds containing a normal alkyl group of 4 or more carbon atoms may also be treated with urea to form solid complexes therewith. It is therefore to be understood that this invention is of general application to the treatment of any feed stocks containing normal (1. e, straight chain) organic compounds of the general classes indicated.

It is to be understood that the terminology complex formation is intended merely as being descriptive in so far as the nature of the interaction between urea and normal aliphatic hydrocarbons is not fully understood. The term urea-hydrocarbon complex is therefore simply used as indicative of the nature of the interaction between the urea and normal aliphatic hydrocarbons whatever the exact mechanism of this interaction may be. In this connection it is significant that definite and characteristic crystals of urea and normal aliphatic hydrocarbons may be observed differing in characteristics from crystals of urea and differing in characteristics dependent upon the particular normal aliphatic hydrocarbon with which the urea was reacted.

In order to successfully form urea-normal aliphatic hydrocarbon complexes in accordance with this invention, a quantity of a nitrile is mixed with the urea and the stock containing the normal hydrocarbons to be treated. In the presence of the nitrile, the urea will react with straight chain hydrocarbons which form ureahydrocarbon complexes. The amount of nitrile employed is not particularly critical. Thus even a trace of nitrile in the presence of urea and a normal aliphatic hydrocarbon will cause the formation of urea hydrocarbon complexes. In certain cases it may be preferred to use a greater quantity of the nitrile in proportions which may equal or in some cases exceed the volume of the liquid feed stock being treated with the urea. It is therefore to be understood that the process of this invention may be conducted using a volume of a nitrile varying from what may be described as a trace of the nitrile to any desired upper limit.

The nitrile to be used may consist of aoetonitrile, propionitrile, butyronitrile or any other nitrile having about 2 to 11 carbon atoms. preferred nitrile for use in the process of this invention, however, is acetonitrile and the description of this process will be drawn with particular reference to the use of the acetonitrile for illustrative purposes.

A critical factor affecting the formation of urea hydrocarbon complexes is the temperature at which the reaction is carried out. In particular it is necessary that this temperature be below about F. as urea-hydrocarbon complexes will not be formed and are not stable above this The 6 carbon atoms, when contained in 50% con.- centration in a hydrocarbon mixture, above a temperature of about '70 R, while complex formation can successfully be carried out with hydrocarbons of less than ,6, carbon atoms at 50 F. or lower. Due to the temperaturesensitivity of the urea complex formation, it is possible tofractionate hydrocarbons by conducting a first stage segregation at a diiferent. temperature than a second stage segregation. Other factors aife'cting the fractionation obtainable are the time of the urea hydrocarbon contact, the extent of mixing employed, and the amount of nitrile present. All of these variables may be controlled to permit the fractionation of one type of normal aliphatic hydrocarbon from another type of normal aliphatic hydrocarbon or of similar types of normal aliphatic hydrocarbons. having different molecular weights.

A wide variety of techniques may be employed for contacting the urea, nitrile, and feed stock to be treated. Thus, any suitable batch mixing methods may be used or continuous processes may be employed, utilizing slurries or suspensions of urea. gain, if desired the contact of the urea with the nitrile and the feed stock to be treated may be carried out in columns or towers in which the urea is maintained as a fixed bed or moving bed. It is. therefore to be understood that any suitable solid-liquid contacting processmaybe adapted for the conduct of the process of this invention.

As indicated, urea-normal aliphatic hydrocarbon complexes will readily form in the presence of a nitrile. The resulting complex will be of a solid crystalline form which may readily be separated from the remaining liquid by settling, by filtering, or by centrifuging, It is particularly preferred that. the solid crystals of urea-hydrocarbon complexes be. washed with previously extracted material prior to decomposition of these complexes, This Washing technique, as. also been. foundv to; be. favorable in washing ureahydrooarhon complexes. formed in the.- presence of; the conventional auxiliary liquids such as alcohols. or Water. Use of previously extracted material to wash, the urea complex eliminates. the necessity for distillation and recycling facilities, eliminates the necessity for any auxiliary washing, agent, and permits handling: of the washing; operationsin the equipment used for forming and. decomposing the, urea complex. Thus from 10 to 50 percent of the normal: aliphatic. hydrocarbon fraction. .from a. previous urea. crystallization. operation may: be utilized as a wash liquid, recycling the spent: wash liq.- uid to. the feed stock ofthe next urea treating cycle..

.After suitable washing of. the urea complex crystals, preferably inthe. manner indicated; or alternatively by using any otherzdesired wash liquid, theurea complex crystals. are decomposed any one of several techniques. .Thus the urea complex crystals may.- be. decomposed; by, heating; the; crystals to; a temperature. somewhat above 120 F., orby exposing. the. crystals to either a. solvent for. the urea. or: to; a solvent for composition of the complex.

the organic compound combined in the complex with urea. Suitable urea solvents which may be utilized for example are water or amines, while suitable hydrocarbon solvents which may be employed are, for example, petroleum hydrocarbon fractions. When employing a-solvent to decompose the urea complex, it is generally necessary to apply mild heating to secure the de- This will result in the regeneration of free urea which may be separated for reuse in the process. In the event that heating is employed as the method of urea complex decomposition, the heating may be conducted so as to distill overhead the hydrocar- Icons released from the complex, particularly when steam distillation is employed.

As developed therefore the process of this invention involves the reaction of urea with normal aliphatic hydrocarbons in the presence of a nitrile. In general. modifications and im--' provements of conventional urea and thiourea extractive crystallization processes may be adaptedto the process of this invention. Similarly the process of this invention utilizing a nitrile may be adapted for extractive crystallation process utilizing thiourea and in particular, the feature herein disclosed of using hydrocarbons released from the urea complex as a washing agent, may be employed in urea or thiourea processes.

In order to more fully understand the prin ciples of this invention a diagrammatic flow plan of a urea extractive crystallization process is illustratedin. the drawing, embodying the principles of this invention. Referring to this drawing, the three necessary processing steps of urea complex formation, complex separation and washing, and complex decomposition are each indicated as being carried outinseparate zones I-, 2 and 3. In actual. practice only two, or even one zone may be. employed. as all the necessary process steps can be carried out if desired a single reactor. Urea is introduced to the urea complex formation zone I, as for example from g the urea hopper 12, through line I3. A screw conveyor, orsimilar mechanical means may be used for introducing the urea. tozone I The feed stock to be treated. with the urea, such as a. hydrocarbon feed from which itis desired to remove normal. aliphatic hydrocarbons, may. be introduced to zone i,, through line.- 4. Similarly, a nitrile, such. as acetonitrile, may be intro! ducedto zone. I- through line 5.- As formerly brought out the. relationship. of the quantity; of urea, hydrocarbon feed and nit-rile, is. notcritical. However, it is, apparent. thatfor besttreating results relatively high. proportions of urea to hydrocarbon feed should be used. The amount of urea required, depends upon the. con;- centration of straight chaincompounds in. the feed. It. is 'preterred. to employ at. least three mols. of urea per mole of. straight chain: hydro-v carbon to be removed: from themixtu-ra- Ifzone I is. cooled to a temperature below about 70 F.=, it is possible to achieve complex formation of relatively low. molecular weight. hydrocarbons which do not form complexes at higher temperatures. Hydrocarbons having lessthanabout '7 carbon atomsfall inthis. class. Furthermore, by cooling zone. I,. it is possible to increase the yield; of complex. as inmostv cases lower tern.- peratures favor the equilibrium: reaction. involving; complex formation. Any desired type. or. degree of agitation may be applied! 119...ZQ1IE15. The complex formation occurs-readily and rapidly so that a relatively short reaction time may be employed in zone I, of the order of 10 to 120 "any other desired means to separate the solid urea complex crystals from the unreacted liquids. If, for example, zone 2 comprises a filtration zone unreacted hydrocarbons and acetonitrile may be removed from the filtration zone through line I leaving the urea complex crystals and unreacted urea crystals in zone 2.

These crystals are then subjected to a suitable washing action to eliminate traces of liquids adhering to the crystals. Virtually any organic liquid agent may be used for washing purposes, but 'in accordance with a preferred adaptation of this invention, a part of the normal aliphatic hydrocarbons, subsequently released from the complexes in zone 3 are recycled to zone 2 to achieve the washing. Thus from 10% to- 50% of the hydrocarbons obtained on decomposition of the complexes in zone 3 may be recycled to zone 2 through line 8, so as to wash the crystals in zone '2. This spent wash may then be removed from zone 2 through line 9 and is preferably recycled to the complex formation zone I.

The washed crystals consisting of unreacted urea and urea hydrocarbon complexes are then withdrawn from zone 2 through line H), and are introduced to the complex decomposition zone 3. Again, as formerly indicated a variety of means may be employed to decompose the urea hydrocarbon crystals. One of the most attractive methods for accomplishing this is to simply heat the crystals of zone 3 to a temperature above about 120 F. At temperatures of this order, the urea hydrocarbon complexes decompose, freeing the hydrocarbons comprising the complexes and yielding free urea. Alternatively, the urea complex crystals may be contacted with a urea solvent, or a hydrocarbon solvent to secure their decomposition. If it be assumed that zone 3, illustrated in the drawing represents a heating zone, decomposition of the complex in zone 3 may be carried out so as to distill the freed normal aliphatic hydrocarbons overhead. This distillation may be aided by the introduction of steam so as to enable removal of the freed hydrocarbons by steam distillation after which the hydrocarbons may be separated from the steam or condensed water. After suitable decomposition of the urea complexes, free urea may be obtained from zone 3 for removal through line l5 and preferably for recycle to zone l. The freed hydrocarbons constituting a stream rich in normal aliphatic hydrocarbons may be removed through line [6. As formerly stated, in a preferred adaptation of this invention, from about to 50% of the freed hydrocarbons are recycled through line 8 to zone 2.

The process of this invention may be better understood from a consideration of the following examples indicative of the results which may be obtained according to this process:

Example I 56 cc.s of iso-ootane, 56 cc.s of normal heptane and 850 cc.s of acetonitrile solution which 6: had been saturated with urea at F. were cooled to 34 F. During this cooling operation a crystalline precipitate consisting at least in part of urea-hydrocarbon complexes was formed and was removed by filtration. Water was used to decompose thecomplex. The hydrocarbons liberated from the complex amounted to 3 vol. per cent of the hydrocarbon feed and analyzed 73% n-heptane and 27% isooctane.

Example II A mixture of 200 cc. n-heptane, 250 cc. isooctane, and 150 grams of solid urea was cooled to 13 C. (555 F.) by means of a cold water bath.

10 cc. of acetonitrile were added and the mixture was mechanically agitated for 10 minutes. Visual observation indicated complex formation within a minute after the nitrile addition. Solid crystals of complex and unreacted urea were removed by filtration and decomposed by dissolving in water. Both the filtrate and the hydrocarbon recovered from the complex were water washed three times and dried over calcium chlo- Example III The procedure was the same as above except that a hydrocarbon mixture of 200 cc. n-heptane and 200 cc. methyl cyclohexane was employed. Results were as follows: I

Amount, Analyses v01. per- Percent Percent n-heptane MCH Hydrocarbon from complex 33 68 32 Hydrocarbon from filtrate 67 41 59 Example IV 200 cc. n-heptane, 200 cc. methyl cyclohexane, 150 grams urea, and 4 cc. acetonitrile were agitated at 10 C. (14 F.) On decomposition of the complex, results were as follows:

Analyses Amount, vol. E301;-

cen 0 Percent Percent feed methyl nheptane cyclohexane Hydrocarbon from complex... 38 65 35 Hydrocarbon from filtrate. 62 42 58 Example V cc. n-heptane, 300 cc. methyl cyclohexane, grams urea, and 4 cc. acetonitrile were agi- 7 Example VI A mixture of 260 to. ii=heptane, 200 cc. isooctane, 150 grams oi solid urea arid 10' do. of scetomtriiewas chilled, with agitation, to a tempfatilr or -1o= c. (14 F.). Complex was removed by filtration and decomposed with Water. the filtrate and the hydrocarbon recovered from the complex were water washed and dried over anhydrous calcium chloride. Results were as follows:

Alfie-flit, glasses V' .Ijf-

Percent 3 Percent e n-heptane iso-octane fli t rbqn om mp e 81; 5 9 8 ydrocarbon from filtrate. 68. 5 39 61 Amount, Analyses vol perl cent of feed-Fwash Percent Percent use n-heptane iso-octane Hydrocarbon from complex... 26. 8 8 8 12 Hydrocarbon wash filtrate. 9. 8 50 50 Hydrocarbon from filtrate 63. 4 39 61 What is claimed is:

1. A urea extractive crystallization process in which urea is contacted with a liquid containing normal aliphatic hydrocarbons and a nitrile of 2 to 11 carbon atoms in a first step of the process whereby urea hydrocarbon complexes are formed and subsequently said complex isdecomposed to yield liquid rich in normal aliphatic hydrocarbons,- including the step of washing the said. urea hydrocarbon complexes prior todecomposltion with about 10 to of liquid rich in nor-- mal aliphatic hydrocarbons obtained from prior complex decomposition.

2. The process of claim 1 in which the said contact of the urea with the normal aliphatic hydrocarbons in the presence of a iiitrile is conducted at temperatures below about F.

3. The process of claim 1- in which the said nltrile" is aoetonitrile.

4. The process of claim 1- in which the said decomposition is achieved by contacting the urea complex crystals with water;

CHARLES N. KIMBERLIM JR.

F. AREY, Ja.

References Cited in the file of this patent UNITED STATES PATENTS Name Dat Fetterly Aii. 29', 1950 Fetterly f. Cit. 2.- 1951 OTHER REFERENCES Behgen, Tech. 0. T. Mission, Reel 143 (6 pages), May 22, 1946.

Claims

1. A UREA EXTRACTIVE CRYSTALLIZATION PROCESS IN WHICH UREA IS CONTACTED WITH A LIQUID CONTAINING NORMAL ALIPHATIC HYDROCARBONS AND A NITRILE OF 2 TO 11 CARBON ATOMS IN A FIRST STEP OF THE PROCESS WHEREBY UREA HYDROCARBON COMPLEXES ARE FORMED AND SUBSEQUENTLY SAID COMPLEX IS DECOMPOSED TO YIELD LIQUID RICH IN NORMAL ALIPHATIC HYDROCARBONS, INCLUDING THE STEP OF WASHING THE SAID UREA HYDROCARBON COMPLEXES PRIOR TO DECOMPOSITION WITH ABOUT 10 TO 50% OF LIQUID RICH IN NOR-