US2627513A - Segregation of hydrocarbons with - Google Patents

Description

Patented Feb. 3, 1953 SEGREGATION OF HYDROCARBONS WITH UREA AT LOW TEMPERATURES i William F. Arcy, Jr., Baton Rouge, La., assig'nor to Standard Oil Development Company, a corporation of Delaware Application April 6, 1949, Serial No. 85,867

(Cl. ZBO-96.5)

2 Claims.

The present invention is concerned with a process for the segregation of normal aliphatic hydrocarbons from other types of hydrocarbons. The process of this invention may also be adapted to the separation of one type of normal aliphatic hydrocarbon from another type of normal aliphatic hydrocarbon. In accordance with this invention, urea is employed for the extractive crystallization of various hydrocarbons employing an improved technique wherein relatively low temperatures are employed in conjunction with critical amounts of a solvent. A specific adaptation of the present invention is the contact of hydrocarbons with urea at temperatures below about 32 F. utilizing relatively small amounts of a suitable solvent.

It is well known in the art to segregate hydrocarbon fractions and particularly hydrocarbon constituents from each other by the use of various processes. These processes comprise for example, distillation operations, solvent extraction operations, solid adsorption operations, extractive distillation operations and the like. It has also been suggested to use urea as a chemical reagent for the segregation of relatively high molecular weight hydrocarbons. Urea segregation processes depend upon the interaction of urea and certain specific types of hydrocarbons to form solid, crystalline, urea-hydrocarbon complexes. Urea segregation processes of this nature have generally been carried out at temperatures of about 70 F. and higher. However, it has been suggested that if urea be contacted with a hydrocarbon fraction at relatively low temperatures, as for example, in the range from about 40-60 F., unexpected and desirable results can be secured when contacting hydrocarbon fractions having relatively low molecular weights. It is the particular object of this invention to improve the segregation of hydrocar- Cil bons which may be obtained at or somewhat below 40 F.

In urea crystallization operations it is essential to employ a suitable solvent. The solvent may be one in which both the urea and the normal aliphatic hydrocarbon to be segregated are soluble. Suitable solvents are the alcohols, the alcohol amines. and the nitriles. Specific solvents for example are methyl alcohol, ethyl alco-VH hol, the propyl alcohols, the butyl alcohols, the

amyl alcohols, ethanol amine, propanol amine. di-

vent is methyl alcohol.

The organic compounds which may be treated e' drocarbon stream in line I.

by the process of this invention are broadly those compounds having substantially normal structure both of the saturated and unsaturated types. This class includes olefins, dioleiins, parailins, alcohols of six or more carbon atoms, ketones, esters, ethers, and aldehydes. Olenic and parafnic hydrocarbons of 3 to about 16 carbon atoms are particularly adapted for segregation by the process of this invention.

As pointed out heretofore, it has been suggested that relatively low molecular weight hydrocarbons, as for example, those having from 3 to 9 carbon atoms in the molecule, as well as higher molecular weight hydrocarbons, can readily be segregated employing urea in conjunction with a suitable solvent provided the temperature is maintained below about 70 F., generally in the range from about l0-60 F. In these operations it was also known that unsatisfactory results were secured if the temperature used was too low, as for example, below about 3240 F. It is theorized that at these temperatures the ureahydrocarbon complex reacts with the solvent. such as methyl alcohol, to produce free hydrocarbon and a urea-solvent complex.

It has now been discovered that very low temperatures can be employed in the treatment of hydrocarbon fractions providing the volume of the solvent when using these temperatures is controlled` within critical limits. In particular, it is necessary that less than one mole of solvent be used per mole of urea.`

The process of the present invention may be readily understood by referring to the drawing illustrating one embodiment of the invention. Referring specifically to the drawing, a hydro-- carbon feed stream which for the purpose of illustration is assumed to consist of normal heptane and isooctane is introduced into reaction zone I0 by means of feed line I. For the purpose of illustration it is assumed that the solvent utilized is methanol. The solvent may be introduced through line 2 for admixture with the hy- As will be disclosed, a critically small amount of solvent is employed which is generally less than 5% by volume based upon the hydrocarbon stream. The urea employed is introduced to reaction zone I0 from hopper 3 by suitable means, such as the screw conveyor illustrated.

Uturebelow about 50 F. and is preferably maintained at a temperature below about 32 F. After `suiilcient time has been permitted for the reactdrawn through line 4 and passed to settling zone 20. In settling zone 20, essentially a two phase system separates, the lower phase comprising crystals of urea-normal aliphatic hydrocarbon complexes plus any unreacted urea crystals, and urea alcohol complex, and the upper phase will comprise the hydrocarbons which have not reacted with urea. To secure separation of these crystals a centrifuge may be used or a continuous settler such as a Dorr Thickener.

The liquid phase comprising primarily unreacted hydrocarbons, is withdrawn from zone' 20v by means of line 5 and is introduced into separation zone SiS-wherein any solvent remaining inthe:

hydrocarbon may be removed by distillation or Water Washing or by use of solid adsorbents, etc. The solvent that is recovered is preferably recycled to the system by means ol line 6, while the unreacted hydrocarbons are removed from zone 30 by means of line 'l and may be handled as desired.

In accordance with one modiiication of the present invention the hydrocarbon stream of line 5 may be further contacted with urea prior to removal of solvent from the stream to secure further segregation in a manner similar to that described with respect to the feed stream introduced by means of line l. This essentially provides a two stage treatment which may beconducted to secure fractionation of normal aliphatic hydrocarbons as by maintaining the temperature and other factors eect'ingl complex formation different in the two stages.

Urea complexes formed in zone I0 are withdrawn from settling zone 20 by means of line 8 and are passed to ltering and washing-zone dil. In this zone the urea complex is washed Withan inert solvent, such as isopentane Whichv is intro duced by means of line 9 andv withdrawn by means of line Il. If desired a small amount of the solvent employed in zone l0, particularly if saturated with urea may be used as the Wash liquid or preferably `a portion of the hydrocarbons obtained on decomposition of the complex may be employed. In the latter casev` the` used wash liquidmay simply be recycled to zone. l0 while if an inertsolvent is employed distillation must be used for solvent recovery. The urea complex is withdrawn from zone 40 by meansl of line i2 and is lntroducedinto decomposition zone 50.

The decomposition of the urea, normal aliphatic hydrocarbon complexes may be achieved by washing the crystals with water orv any urea solvent or hydrocarbon solvent if desired. However. it is preferred not to use arsolvent for this purpose as it is generally simpler to heat the d crystals in zone 50. It is only necessary that the crystals introduced into zone be subjected to temperatures of about F. to 160 F., and preferably 15G-160 F. For this purpose hot gases may be used, heat exchanger i4 may be employed, or the substantially dry crystals may simply be stirred in zone 50 so as to be exposed to radiant heat from the Walls of the zone. The hydrocarbons released from the urea hydrocarbon complexes may be removed from the decomposition zone by decreasing the pressure or increasing the temperature of this zone until the hydrocarbone are' distilled overhead, or if desired the hydrocarbonsy may be Washed from zone 50 in liquid phase together with a `wash liquid introduced through line I3.

The hydrocarbons obtained by the decomposi tion ofthe urea complexes are withdrawn from zone 50 by means of line I5 and may be further treated as desired While the urea crystals are withdrawn from zone 50 by means of line I0 and are recycled to zone l0. As described, a portion of the hydrocarbon stream of line I5 may be recycled in liquid phase to zone do for use as a Wash liquid.

The process is particularly directed to the treatment of hydrocarbonV fractions having not in excess of 9 carbon atoms in the molecule employing temperatures below about 50 F. It is more specifically concerned with the treatment of these fractions at temperatures in the range from 10 to 32 F. utilizing less than 5 volume per cent of solvent in zone Ib-as compared to the hydrocarbon feed. A preferred adaptation is to use less than 1% of solvent by volume based upon the hydrocarbon feed. Although the hy= drocarbon may be recovered from the urea complex by heating or by Washing with a suitable urea solvent as described, one adaptation of the present invention is to decompose the urea complex at temperatures in the range from about -10 to 32 F. by utilizing excess amounts of the solvent used to form the complexes. Any amount greater than one mole of solvent per mole of urea will decomposethe urea complexes. Thus in the example given, an excess amount oi methanol may be used for this purpose.

The'process of the present invention may be further understood by the following examples illustrating embodiments of the saine:

EXAMPLE 1 A hydrocarbon mixture consisting of normal heptane and iso-octane was treated with various quantities of methanol at about 57 F. Theresults of these operations are listed in the following table:

e Specliled amount of alcohol added to a mixture of 200 cc. iso-octane, 200 cc. n-heptaneendA-ISO grams of urea at 57 F. and mechanically agitated tovattain-equilibrium;

b O11 total hydrocarbon. Y v

Complex separatedbyfltrationiand decomposed bytreating with excessw'ater.

From the above it is apparent 'that the separation of hydrocarbons in alltests 1-5 was substantially the same although some improvement was secured utilizing 0.5% and 2.5% of solvent as compared to the operation where 100% solvent was used.

EXAMPLE 2 Additional operations were carried out at ternperatures which varied from about -4 to 32 F. The results of these operations are as follows:

Table II ,e 6 that the recovery at low temperatures is mate-f rially improved by using a relativelyI low percentage of the solvent. l' The invention is broadly concerned with an improved process for the segregation of normal parain hydrocarbons from,l hydrocarbon mixtures. It is particularly directed to the'segregation of normal paraffin hydrocarbons from isoparaflins. As pointed out heretofore, it has been disclosed that relatively low molecular weight SEPARATION OF N-HEPTANE ISO-OCTANE MIXTURES AT LOW TEMPE RATURES l Mixture of 300 cc. iso-octane, 100 co. n-heptane and 150 grams urea cooled to ternperature noted, specied amount of alcohol added, and mixture agitated until equihbrium conditions were reached.

b Based on total hydrocarbon,

Complex separated by filtration and decomposed by treating with excess water.

From the above it is apparent that a marked increase in the recovery of hydrocarbons is secured when a relatively small quantity of solvent is used at the relatively low temperatures.

EXAMPLE 3 Other operations were conducted wherein the temperatures were varied and the cc. of heptane recovered was determined when using various mixtures of normal heptane and iso-octane. The results of these operations are listed in the following table:

From operations 1 and 2 it is apparent that th recovery of C7 hydrocarbon is materially increased by decreasing the temperature from 80 to 55 F. A comparison between operations 2 and 3 indicates that an increase in yield is secured by decreasing the volume of solvent at 55 F. Operation 4 is striking in that the recovery of C7 is Zero when a relatively large volume of solvent is utilized at a temperature of F. On the other hand, operations 4 and 5 clearly show that the recovery will continue to increase providing the volume of solvent is substantially reduced at relatively low temperatures.

From the data presented in runs 6 to 12 employing feed mixture B it is readily apparent paramns can be segregated from hydrocarbon mixtures containing the same provided relatively low temperatures are employed, as for example in the range from about 40 to 60 F. In these prior disclosures it was assumed that any amount of a solvent could be employed in the Separation operation. However, in accordance with the present discovery, it is apparent that if temperatures below about 40 F. are utilized and especially if the temperatures employed are below about 32 F. adverse results will be secured unless the amount of the solvent is critically controlled. Thus, in accordance with the process of the present invention low boiling hydrocarbon fractions, as for example, those fractions boiling in the range from about F. to 250 F., are preferably treated at temperatures in the range from about -15 F. to 32 F. with urea and with a relatively small amount of a solvent. The amount of urea employed may vary appreciably depending upon the composition of the feed stock. However, in general it is preferred to use from about 10% to 40% by weight of urea. based upon the feed material. The amount of solvent employed when the operation is conducted in the range from about 15 to 32 F. is preferably below about 10 mol per cent of solvent Ibased upon the amount of urea employed. A particularly desirable amount of solvent to be used is in the range from about 2 to 8 mol per cent of solvent based upon the urea utilized.

Having described the invention it is claimed:

1 Improved process for the segregation of normal aliphatic hydrocarbons from other types of hydrocarbons which comprises contacting said hydrocarbons with urea at temperatures below 32 F. in the presence of less than 5 volume per cent methanol based on the feed.

2. Process according to claim 1 in which the amount of methanol is 6 mol per cent based on the urea.

WILLIAM F. AREY. JR.

(References on following page) A REFERENgI'ZS CITED OTHER RFERENCES f LThe vfollmvng references are of record `in the Bengen: Technical Oil'Msson, Reel ,143, May le of this patent: "22, 1946.

A UNITED STATES PATENTS 5 Number Name Date '2,520,716 Fetter1y7 Aug. 29, 1950

Claims (1)

1. IMPROVEMENT PROCESS FOR THE SEGREGATION OF NORMAL ALIPHATIC HYDROCARBONS FROM OTHER TYPES OF HYDROCARBONS WITH WHICH COMPRISES CONTACTING SAID HYDROCARBONS WITH UREA AT TEMPERATURES BELOW 32* F. IN THE PRESENCE OF LESS THAN 5 VOLUME PER CENT METHANOL BASED ON THE FEED.

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