US2219109A - Process of desulphurizing petroleum oils - Google Patents

Description

Oct. 22, 1940. T. F. MccoRMlcK PRocEss oF DESULPHURIZING PETROLEUM ons Filed Nov. 16, 1955 'T'Sheets-Sheet l //v Vf/v TOR MOM/45 FMC @ORM/CK f 0% ATTIOAWEK T. F'.i MccoRMlcK PROCESS 0F' DESULPHURI'ZING PETROLEM lOILS Filed NOV. 16, 1935 '7 Sheets-Sheet 2 Oct. 22. 1940.

Oct. 22. 1940. T. F. MccoRMlcK 2,219,109 PRocEssoF DESULPHURIZING PETROLEUM oILs Filed Nov. 16,'- 1935 v sheets-sheet s Fig. 5.

A rroQ/vfy Oct. 22. 1940. T. F. McCoRMlC'K 2,219,109

PROCESS 0F DESULPHURIZING PETROLEUM OILS Filed Nov. 16, '1935 7 ,Sheets-Sheet 4 Oct. 22. 1940.

T. F. MCCORMICK PRDCESS OF DESULPHURIZING PETROLEUM OILS Filed Nov. 1e, 1955 '7 Sheets-Sheet 5 Odi. 22, 1940. T F. MCCORMlCK 2,219,109

PROCESS 0F DESULPHURIZING P ETRULEUM. OILS i y Filed Nov. 1e, 1955 7 sheets-sheets //v L/ E/V TOR THON/4 6j EMC CoRM/CK A TroR/VEK Oct. 22., 1940.

T; F. MccoRMlcK 2,219,109l

PROCESS 0F DESULPHURIZING PETROLEUM= OILS Filed Nov. 16, 1935 Pity-2:

7 Sheets-Sheet 7 jy Y A r'roR/vex Patented Oct. 22, 1940 PROCESS F DESULIIILUSRIZING PETROLEUM Thomas F. McCormick, Martinez, Calif., assignor, by mesne assignments, to Tide Water Associated Oil Company, San Francisco, Calif., a corporation 0f Delaware Application November 16, 1935, Serial No. 50,206

11 claims. (c1. 19a-31) This invention relates to the treatment of petroleum oil, or distillates thereof, and has for a particular object the reduction of the sulphur content of cracked distillates with concomitant improvement in color, odor and octane rat- The invention is particularly applicable for the above purposes to a distillate derived from crack. ing petroleum, or its fractions, such as cracked gasoline which is selected -or illustration herein, but the invention is not necessarily limited to processing such gasoline, being in a broad sense directed to the-treatment of Aany petroleum or distillate thereof, having` characteristics in conber.

The remaining 60% of the cracked distillate shows increasing sulphur content up to about 70% and from there -on to the end of the fractionation a slight drop in sulphur occurs, but

in no way to a degree approaching the low sul- The reason for this is believed to be that the formity with this disclosure and responsive to Fm N pmt sulphur the steps outlined herein. "n oi original percent Cracked gasoline is particularly useful for use as a fuel in internal combustion engines which, 1

with modern high compression pressures, require 2 i8 gi:

a fuel with relatively high octane number to pre- 2 10 0.00

vent detonation. 5 g h1 This octane number with ordinary cracked s lg gasoline may be obtained by the addition thereg m L69 to of well known anti-knock compounds such as 1in lg g tetra-ethyl lead, etc., but it is much more preferable and economical to utilize as far as possible4 y the anti-knock values in the crude cracked gas- The above fractions are of course, taken ln A oline itselg g the usual manner in accordance'with volatility This accomplished by the herein aescrbed the fractions and the r Show a maxprocess in so treating a crude cracked gasoline mmm Sulphur content l5 reached When from with sulphuric acid that the semeuve savent about '10% t0 80% of the distillate has been taken action of the acid is exercised in at least two olf. directions, which may be termed a split-treat, lf eall Ofthe above 10% fractions is then with great economy of acid and large reduction treated mdivldllally With the Same amount 0f in sulphur. sulphuric acid., for instance 98% acid, for the Cracked gasoines vary in chemical structure, .purpose 0f reducing the sulphur content to a percentage 0f sulphur, etc" the type of desired maximum, it may be Seen there is 8| large stock used for cracking aswell as the type of lllmp in the Sulphur Content 0f the heavier fraccracking process employed. In general, cracked tlons of the distillate from 40% on as Shown in 40 gasolines contain increased percentages of unthe folloWlng table:

saturatedhydrocarbons over the stock from which they were derived and usually contain a sul h sulphur substantial quantity of sulphur compounds. P r

The unsaturated hydrocarbons, which include Fraction No' Per nl (rg-m mmf the olefines and aromatics, are highly desired in Pam* moto:` fuel as anti-knock compounds to reduce, or suppress, detcnation and the problem of reg g2g. gig; taining the same during treatment with sul- 10 0.00 0.04 phuric acid for the removal of undesired sulphur lg agg is solved herein in a novel and highly useful mani0v ig 8.734 ner.

It has been fileterminaithat when al .total 3 i3 112% 3;14 cracked distillate is carefully fractionated by tak- 1 1 v L37 0'7"' ing a 10% cut comprising each fraction that the first few cuts up to about 40% are relatively lowin "This indicates that an amount of sulphuric sulphur while being the highest in octane numacid which-is suilicient to desulphurize more volber. Also, the same first few cuts are relativelyv atile fractions up to about 40% of the cracked high in percentage of unsaturated compounds distillate is insuicient to desulphurize the heavi- 6 which shows conformity with high octane numer fractions from 40% on.

sulphur in the lighter andl more easily desulphurized fractions is largely in the form of sulphides and mercaptans while in the heavier fractions the sulphur is in a diierent form, probably as thiophenes.

From this it may be seen that if a cracked total distillate is treated as a whole with sufficient concentrated sulphuric acid to remove the sulphur from the heavier fractions thereof, the lighter fractions must then be subject to a sulphuric acid treat far in excess of requirements to remove only sulphur and therefore the desired antiknock compounds of the lighter fractions will re- Spond to the sulphonating and polymerizing action of the excess concentrated acid and are removed in the acid sludge and re-run distillation with large losses of the very constituents desired to be retained.

This defect fin treatment is overcome in the present invention by utilizing methods of treating the total cracked distillate wherein the distillate is first separated by fractionation according to the sulphur content of the different fractions and each fraction thus separated is then treated separately with just suicient sulphuric acid to remove the desired amount of sulphur and then the treated fractions may be blended to form the total nished gasoline containing a minimum percentage of sulphur and a high percentage of the unsaturates present in the stock before acid treatment.

The total cracked distillate may be separated into any desired number of fractions to be separately treated with sulphuric'acid, but in commercial refinery operations, it is generallysumcient in obtaining the desired results to fractionate the crude cracked distillate, in accordance with boiling ranges, into two or possiblyV three fractions and then separately treating each fraction in accordance with its sulphur content.

The simplest way is, of course, to divide the total cracked distillate into two parts by fractionation, one part containing from about to 60% of the lighter fractions relatively low in sulphur and relatively high in unsaturates, and the other part containing from about 80% to 40% of the heavier fractions relatively high in sulphur. Each fraction may then be separately treated with sulphuric acid of the same degree of concentration to assure the desired desulphurization but the rate of treatment, or pounds of sulphuric acid per barrel,l for the lighter fraction will be far less than that required for the heavier fraction.

At times it may be desirable to similarly separate the crude total cracked distillate into three fractions:

(1) Light fractions relatively low in sulphur and relatively high in unsaturates comprising for instance about from 20% to 40% of the distillate.

(2) Intermediate fractions relatively high in sulphur which, however, is contained in cornpounds easily absorbed by, or reactive with, sulphuric acid, and comprising about from to 50% of the distillate.

(3) Heavy fractions relatively high in sulphur which, however, is contained in compounds of the residual type requiring comparatively large amounts of concentrated sulphuric acid for their removal.

The distillation range of each fraction to be thus separately treated may be easily determined by simple laboratory control to fix the points at which the cuts should be made and at the same centrations of sulphuric acid as, for instance, the

removal of olefines from the lighter fractions relatively high in unsaturates to recover alcohols from the oleiine containing acid sludge by hydrolysis.

The preferred application of the invention is, however, directed to the production of a motor fuel retaining the bulk of the unsaturates and one method of treating is shown in the accompanying drawings, in which:

Fig. 1 is a diagrammatic flow sheet showing a split-treat in' which a two, or three fraction cut can be used.

Fig. 2 is a diagrammatic flow sheet taken from the co-pending application of Edwards and Stark, Ser. No. 532,000, filed April 22, 1931, for use with Fig. 1 and showing a preferred form of contacting the acid and distillate.

Fig. 3 is a chart illustrating the eiliciency of a true countercurrent treatment of a cracked total distillate as shown in Fig. 2 over a batch treatment of the same distillate when treating in both cases with acid of the'same concentration to effect the removal of the same percentage of sulphur.

Fig. 4 is a chart showing the efciency of treating a selected light fraction from a cracked end point distillate lby the countercurrent method of Fig. 2 over a batch treatment of the same fraction when treating in both cases with acid of the same concentration to eect the removal of the same percentage of sulphur.

Fig. 5 is a chart illustrating the eillciency of treating a selected heavy fraction from a cracked end point distillate by the countercurrent method of Fig. 2 over a batch treatment of the same fraction when treating in both cases with acid of the same concentration to effect the removal of the same percentages of sulphur.

Fig. 6 is a chart illustrating the efficiency in sulphur removal by batch treatment, comparing the results obtained in sulphur removal by splitting a cracked end point distillate into 50% of a light fraction and 50% of a heavy fraction and treating each fraction separately with acid to the results obtained by treating the cracke end point distillate as a whole; in both cases ing sulphuric acid of the same concentration. 60

Fig. 'l is a chart showing the efficiency of treating the light and heavy fractions obtained from a cracked end point distillate separately in true countercurrent flows according to Fig. 2 over treating the unsplit distillate by the same method; sulphuric acid of the same concentration being used in both cases and the light and heavy fraction each consisting of 50% of the unsplit distillate according to volatility.

Referring to Figs. 1 and 2, it will be seen that 7o the cracked distillate may be passed continuously through line l 0 into a still, or fractionator,

I l, wherein controls are established in well known manner to pass say 50% of thedistillate according to volatility throughY suitable condensers (not 75 shown) in line l2 and through an alkaline-wash I3 such as caustic soda. or sodium carbonate, or other suitable solution, to remove certain impurities such as hydrogen sulphide and organic acids,

and the thus treated liquid fraction is then passed through a treating plant 'I4 (which is preferably of the type shown in Fig. 2) wherein the fraction is subject to true countercurrent contacting with the required rate of sulphuric acid supplied from tank I5, the acid sludge being continuously drawn oi through line I6.

The light fraction thus treated with relatively low rates of sulphuric acid may now to a run down tank I1 whence it is withdrawn to a rerun still i3, from which rerun bottoms comprising polymerized bodies are withdrawn through line I9.

In similar fashion and simultaneously with the light fraction, the heavy 50% fraction from still I I passes through line 20, alkaline wash 2|, treating plant 22, run down-tank 23 to rerun still IB where it blends with the light treated fraction and is distilled therewith to end point gasoline,

which is then subjected to the usual sweetening process 24 by means of doctor solution, or other sweetening process, and is thus finished ready for use.

The heavy fraction is, of course, subject to countercurrent treatment with concentrated sulphuric acid in treating plant 22 at a much higher rate than that applied tothe light fraction in treating plant I4 and the acid sludge from treating plant 22 is collected in tank 25.

It is found that such acid sludge obtained from treating the heavy fraction in plant 22 with high acid rates contains sumcient reactive sulphuric acid to function eiliciently for the desulphurization of `the light fraction in treating plant I4, hence a preferred f orm of the invention includes the supply of acid sludge derived from the treatment of the heavy fraction from sludge tank 25 through line 26 to treating plant I4 for the treatment of the light fraction therein and the rate of such supply is, of course, in conformity with requirements for efficient desulphurization of the light fraction to the desired degree.

Apparently, the acid sludge produced from the treatment of the heavy fraction at relatively high acid rates to remove a relatively high percentage of sulphur from the heavy fraction, although hav- 1 ing accomplished maximum desulphurization of the heavy fraction still retains suillcient chemical reactivity to treat effectively vthe more unsaturated light fraction without substantial loss of unsaturates therefrom. -In addition, the use of such sludge accomplished the removal of unstable unsaturates such as the gum forming constituents like di-olenes together with acid soluble sulphur' compounds, all of which improves the odor and stabilizes the color of the light fraction.

It seems that the abstracted organic matter in` the acid sludge acts as a diluent and its effect on the more stable and desired unsaturated compounds in the light fraction appears to be the same as that of a treatment with dilute sulphuricl acid so that excessive sulphonation and polymerization of desired unsaturates is prevented.

Depending, of course, on the degree of desulphurization required, the light fraction may or may not be desulphurized to a point suicient for commercial requirements by the use of the acid sludge from the heavy fraction treating, inasmuch as the sulphur thus removed from the light fraction may only vary from to 50% of the removable sulphur which is often sufilcient. Y

- However, the use of other suitable sludges as, for instance, the acid 'sludge obtained from the sulphuric acid treatment of straight run gasoline or kerosene, or from other sources, is contemplated herein for the treatmentl of the light frac.- tion in place of .the straight acid treatment, 4it being understood, of course, that if any of the sludges utilized for this purpose are deficient in acid value for treatment of the light fraction, such sludge can be increased in acid concentration by the addition of a required amount cf fresh acid from tank I5.

Alternatively, if the acid sludge derived from the heavy fraction is not suiliciently reactive to reduce the sulphur content of the light fraction to a very low figure, the light fraction may be further separately treated with fresh acid at a rate of say up to ve pounds per barrel of 98% acid and in accordance with the true counterbe withdrawn through line 3l.

Treating plants I4, 22 and-28 are preferably constructed and operated in accordance with the process disclosed in said co-pending application Ser. No.; 532,000, as illustrated in Fig. 2 hereof, in which any of the fractions, or the unsplit total distillate, is passed by pump 3l through a cooler 32 into the bottom of a contact tower 33 substantially filled with a suitable contact material 34, comprising Raschig rings, glass beads', crushed gravel or other well known material, and meets therein in true countercurrent flow acid sludge from a spray 35 derived from the succeeding treatment of the distillate and forced through spray 35 by pump 36.

The distillate thus treated with relatively spent acid sludge passes through a valve 31 into line 39 being alternatively by-passedv if desired through valve 38) and is cooled to a desired degree by cooler 40 before passage into the bottom of a second similar contact tower 4I, supplied with less spent acid sludge derived from a succeeding tower through pump 42 to spray'43.

The more treated distillate then passes through aline 44 and cooler 45 to the next similar contact tower 43 which is supplied with fresh acid through a pump 41 and spray 48.

In,l this manner, there is provided truc countercurrent contacting of the distillate with the. acid, or acid sludge, in each towertogether with true countercurrent ow ol distillate with acid sludge through the system so that maximum desulphurization combined with minimum losses of desired hydrocarbons is assured.

The temperature during the acid treats in each contact tower should be sufficiently low to permit selective solvent action of the ,sulphuric acid on undesired sulphur` compounds and gum forming constituents While preventing excessive sulphonation and polymerization of unsaturates. Depending onthe type of stock treated. concentration of acid used, etc., such treating temperatures may range during reaction from 0 F. to 40 F. or even lower or higher. Simple laboratory tests,

well known to-those skilled in the art, will determine the optimum temperatures taking all things into consideration.

The countercurrent acid treatment of the distillate being finished in tower 46, the distillate may be passed through line 49 into a settling chamber 50, similarly lled with contact material to separate any entrained acid sludge, and thence through line I into a similarly iilled contact tower 52, receiving spent caustic sludge through pump 53 and spray 54 from the bottom of a second caustic contact tower 55 supplied with fresh caustic solution, the spent caustic from both towers 52 and 55 being discharged through square inch on the system for the purpose of holding SO2 gas in solution.

The discharge of acid sludge is controlled by a valve 62 and the discharge of caustic sludge is controlled by a valve 64 which, together with valve 63, maintain the desired pressure on the system.

As before stated, the acid sludge derived from the treatment of a heavy fraction may be run into tank 25 to be supplied through line 26 for treating the light fraction.

Pumps 36 and 42 serve to withdraw acid sludge as rapidly as possible from the bottom of towers 4I and 46, respectively, together with a portion of the distillate from each of said towers for the purpose of establishing rst a circulatorysystem for the distillate between two of the towers and secondly to pass the sludge from a succeeding tower to the top of a preceding tower for contacting the cooled distillate therein, the sludge being separated from the accompanying distillate from each pump in the top of each tower due to a reduction in velocity therein where it is sprayed on the contact material evenly and descends countercurrent to the rising distillate.l

The increased velocity of the distillate stream thus circulated between two towers adds largely to the eiliciency of the interposed cooling sections 40 and 45.

As an example of treating eiliciency in utilizing the acid sludge from the heavy fraction for desulphurizing the light fraction, the following data, derived from operating the above described split-treat when the total cracked distillate is split according to volatility into 55% of a light fraction and 45% of a heavy fraction and treating the heavy fraction with pounds of 98% sulphuric acid to the barrel to recover an acid sludge used on the light fraction, is illustrative:

the chemical structure of the sulphur compounds present and also on the characteristics and quantity of the sludge obtained from the treatment of the heavy fraction. With acid rates higher than 10 pounds of 98% acid to the barrel there is naturally a higher desulphurization of the light fraction due to the greater reactivity of the sludge and also the desulphurization is greater, when using a true countercurrent contact of acid sludge and oil as before described. l The relative efllciencies of batch and true countercurrent contacts are well illustrated in Fig. 3 as well as the relative eiiiciencies of the batch and true countercurrent contacts of the light fraction and of the heavy fraction which are shown in Figs. 4 and 5. The relative efiiciencies between batch treatment of the complete cracked distillate and the same distillate split into a light and a heavy fraction and treated as above described are shown in Fig. 6. The relative eiiiciencies between true countercurrent treatment of the complete distillate and true countercurrent treatment of the light and heavy fractions separately are shown in Fig. 7.

These charts shown in Figs. 3 to 7 inclusive are self-explanatory to those skilled in the art and show improved desulphurization in every case by use of the herein described process.

In all cases herein where sulphuric acid is used, the tests were made with 98% sulphuric acid and the same is used as illustration only and not as a limitation.

Other strengths of acid can be used depending on operating conditions such as a range of from 66 acid up to 20% fumlng sulphuric acid, the concentration being determined for optimum results by laboratory control. Likewise, the temperature may vary with the concentration of acid and consequent degree of reaction heat between V-0 F. up to 80 F.v

'I'he rerunning of the light and heavy fractions may be done at one time, or separately, or, when only a light sludge treatment is given the light fraction for stabilization, the rerun distillation thereon may be eliminated.

The total cracked distillate referred to herein is a distillate made from the pyrolytic cracking of various stocks and is usually a distillate cut to an end point by A. S. 'I'. M. distillation stance, as those made by polymerization of hydrocarbon gases and sulphur bearing distillates from other sources.

The sulphur removal will depend in part on A typical California cracked distillate responcaisson sive to the herein described process may have The distillation characteristics of such unsplit distillate, or an unsplit distillate of closely simi.- lar boiling 'range will, of course, vary and when the same are split to be treated according to the described process there will be some variations in result.

'I'he following table illustrates distillation char-'- acteristics oi' various percentage splits taken from the processing of diii'erent stocks.

compared with the heavy fraction, treating the heavy. fraction with sulphuric acid at such a rate as to reduce the sulphur content thereof a desired amount while at a temperature below 60 F. sumcient to minimize the eiIect of the acid upon unsaturated compounds, recovering the acid sludge from treatment of the heavy fraction, and treating lthe light fraction with said sludge.

3. A process of removing sulphur from hydrocarbon oils which comprises: ractionating a total cracked distillate into'a plurality of fractions, one of which consists of not more than 50% -of the total distillate and contains lower boiling constituents and another of which consistsl of heavier boiling constituents, treating the heavier boiling fraction with sulphuric acid at such a rate as to reduce the sulphur content thereof while leaving the resulting acid sludge in reactive condition, removing the said reactive sludge from the heavy fraction, and treating the light iraction with said sludge.

4. A process of removing sulphur from hydrocarbon oils which comprises: fractionating a total cracked distillate into a plurality of frac'- tions, one of which consists of not more than 50% of the total distillate and contains lower boiling Fraction Light Heavy Light Heavy Light Heavy Approximate percentage. of cut percen 30 70 50 60 60 40 E.l P 182 400 276 402 313 407 Recov 92.5 98.0 96.0 98.0 95.5 98.0 Residue 1.0 1.0 1.0 1.0 1.0 1.0 Loss 6. 6 1. 0. 3. 0 1 '0 3. 5 1. 0

and the other fraction consisting of about 80% to 40%A of the total distillate and inwhich the light fraction is relatively low `in sulphur and relatively high in unsaturated hydrocarbons when compared with the heavy fraction, treating the heavy fraction with sulphuric acid at such a rate as to reduce the sulphur content thereof a desired amount, recovering the acid sludge from treatment of the heavy fraction, and treating the light traction with said acid sludge.

2. A process of removing sulphur from hydrocarbon oils which comprises: fractionating a total cracked distillate into two fractions, one fraction consisting of about 20% to 60% of the lower boiling constituents of the total distillate and the other fraction consisting of about 80% to 40% of the total distillate and in which the light fraction is relatively low in sulphur and relatively high in unsaturated hydrocarbons when constituents and another of which consists of heavier boiling constituents, treating the heavier boiling fraction with sulphuric acid at such a rate as to reduce the sulphur content thereof` while leaving the resulting `acid sludge in reactive condition, removing the said reactive sludge from the heavy fraction, treatingl the light fraction with said sludge, then further treating the thus treated light fraction with fresh acid.

5. In a process of removing sulphur from petroleum distillates'in which a total distillate is split into a. plurality of fractions of varying degrees of volatility to provide a. light fraction consisting of not more than 60% of the total'distillate and a heavy fraction and of which fractions the light fraction is relatively low in sulphur and relatively high in. unsaturated compounds when compared with the heavy fraction, the combination of steps which comprises: treating the heavy fraction with sulphuric acid o! such concentration and at such a rate as to reduce its sulphur content a desired amount and to produce a reactive acid sludge, then treating the light fraction with said acid sludge.

6. A process ofremovingsulphur from hydrocarbon oils which comprises: Ira'ctionating a cracked distillate to yield a relatively low boiling range fraction [relatively low insulphur and high Ain unsaturated hydrocarbons and a relatively high boiling range fraction relatively high in sulphur and low in unsaturated hydrocarbons,v

treating the high boiling fraction with as low as 10 pounds per barrel of concentrated sulphuric acid, removing the acid sludge, and treating the low boiling fraction with said removed acid sludge.

7. A process of removing sulphur from hydrocarbon oils which comprises: fractionating a cracked distillate to yield a relatively low boiling range fraction relatively low in sulphur and high in unsaturated hydrocarbons and a relatively high boiling range fraction relatively high in sulphur and low in unsaturated hydrocarbons, treating the high boiling fraction with as low as 10 pounds per barrel of concentrated sulphuric acid, removing the acid sludge, and immediately treating the low boiling fraction with said removed acid sludge.

8. A process of treating hydrocarbon distillates containing sulphur-bearing, color and gum forming compounds, said distillates being fractional condensates of a common vapor body including the steps of treating one of the distillates with acid and then treating a lighter one of the distillates containing a less amount of sulphur and color-forming compounds with acid sludge formed in the first treating step.

9. A process of treating hydrocarbon distillates containing sulphur-bearing, color and gum forming compounds, said distillates being fractional condensates of a common vapor body including the steps of treating one of the distillates with acid, then treating a lighter one of the distillates containing a less amount of sulphur compounds with acid sludge formed in the first treating step, removing the major portion of thesludge, and then treating the thus puried light distillate with an alkaline solution; thereby reducing the tendency of the sludge treated light distillate to become color unstable.

10. A process of treating hydrocarbon distillates containing sulphur-bearing, color and gum forming compounds,- said distillates being fractional condensates of a common vapor body including the steps of treating one of the distillates with acid, then treating a lighter one of the distillates containing a less amount of sulphur compounds with acid sludge formed in the first treating step, and then treating the thus purified distillates, after removal of acid sludge therefrom, with an alkaline solution; thereby reducing the tendency of the treated distillates to become color unstable.

11. In a process of treating hydrocarbon distillates containing sulphur-bearing, color and gum forming compounds, said distillates being fractional condensates of a common vapor body; the steps of treating one of the distillates with sulphuric acid and then treating a lighter one of the distillates containing a less amount of sulphur compounds with the sulphuric acid sludge formed in the first treating step.

THOMAS F. MCCORMICK.

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