US2099835A - Process of producing gasoline from cracked naphtha - Google Patents

Description

3 E. H. BARLOW ET AL 7 PROCESS OF PRODUCING GASOLINE FROM CRACKED NAPHTHA Filed Sept. 2, 1933 2 Sheets-Sheet l Nov. 23, 1937. E. H. BARLOW ET AL I 2,099,835

PROCESS OF PRODUCING UASOLINE FROM CRACKED NAPHTHA Filed Sept. 2, 1935 2 Sheets-Sheet 2 Patented Nov. 23, 1937 UNITED STATES PATENT OFFICE PROCESS OF PRODUCING GASOLINE FROM CRACKED NAPHTHA Application September 2, 1933, Serial No. 688,046

1 Claim.

This invention relates to a process of producing a finished gasoline from cracked naphtha and will be understood from the following description when read in conjunction with the drawings,

tion, partly in section of the apparatus used for carrying out the invention, and

Figure 2 is a similar representation illustrating the improvements of rerunning the acid treated heavy naphtha.

The main object of the invention is to efiect savings in the cost of producing finished gasoline by cutting an intermediate fraction which requires neither high pressure stabilization nor alkali or acid treating.

' Referring now to the Figure 1, the apparatus shown will be described in conjunction with a method of operating the same. Cracked distillate from feed accumulator or tank I and preferably before the disengagement of very light hydrocarbon vapors, is pumped through heat exchanger 9 into an intermediate portion of a fractionating or debutanizing tower 3. In this tower, which is maintained under appropriate pressure, the raw 5 distillate is separated by distillation and fractionation into four fractions; the overhead distillate cut, consisting of a very volatile light naphtha which is removed in vapor'form through line 4, condensed in condenser 5 and collected in drum Q, the non-condensable gas which is vented from drum 6 through line 22 and pressure regulator 23; an intermediate cut which is removed in liquid form through side stream line 7; and a bottoms out which is removed through line 8, heat exchanger 9 and cooler Hi. Reflux pump back is supplied at the top of the tower from the reflux drum 6 through line H by means of pump 24. Part of the bottoms is continuously Withdrawn through line l2 by pump 25and returned v through line 83, after heating in fired tubes It.

Other methods of heating the bottoms may also be employed. The side stream is conducted through line i into a steam stripper i5 and then cooled in cooler it. The stripped vapor and steam are returned to the tower through line H. The

light naphtha from the reflux drum 6 is conducted to the naphtha stabilizer which is diagrammatically shown and designated by Hi. An alkali treater 98 follows the stabilizer E8. The

debutanized heavy naphtha from line 8 is led through the acid treating plant E9. The light naphtha from the stabilizer, the intermediate fraction after its passage through cooler l6, and the heavy naphtha from the acid treating plant, are combined, doctor sweetened, if necessary, in

5 Figure 1 of which is a diagrammatic side elevasweetening plant 20, and then stored in storage tank 2L, The gas vented through line 22 may be burned. or sent to an absorption plant for recovery of its gasoline constituents.

In carrying out the invention the pressure and 5 temperature in the fractionating or debutanizing tower 3 are so regulated that the overhead distlllate and gas containat least half the hexane present in the raw distillate and substantially all "the lighter components. Usually it is desirable to 10 include slightly heavier fractions also, the desirable end point being 200-300 F. .The overhead distillate does not require acid treating but contains a sufiicient amount of undesirable light components, such as propane, to require stabiliza-' 15 tion at 175-250 pounds per square inch in the high pressure stabilizer 18 in order to substantially eliminate the propane and all lighter hydrocarbons. The methods of stabilizing and caustic washing in themselves do not form part of the 20 invention and are known in the art so that they do not need to be described in further detail.

The intermediate side stream cut will consist of progressively higher boiling naphtha fractions treating. This cut will consequently by-pass the acid treating "operation and in addition has been 30 freed from undesirable light ends in the stripper IS without recourse to the more expensive high pressure stabilization process and caustic washing. The size of the cut as defined by the above limits will vary. considerably for cracked dis- 35 tillates produced from different crudes. In the case of sour crudes, the amount of the intermediate side stream will be small as compared to the amounts of the overhead distillate and the bottoms cuts. Conversely, in the case of a sweet 40 crude, an intermediate cut of 30% of .the total distillate or even higher maybe possible. In many cases a final end point of 300 to 350 F. will be suitable for the intermediate cut.

The bottoms cut will consist of all fractions not 45 included in the above two cutsand will be substantially' free of propane and butane. This fraction must be acid treated and its size will, of

course, be influenced by the same factors which influence the size of the intermediate out. After 50 4 acid treating, the bottoms cut will usually be rerun soas to separate out a fraction which has no components heavier than such as can be included in the final gasoline and to remove high boiling sulfur compounds resulting from reactions in acid treating. After rerunning, the bottoms cut may be doctor sweetened either separately and then blended with the intermediate and overhead distillate cuts, or first blended and then the total gasoline thus obtained is doctor sweetened. If desired the intermediate cut or a blend of the intermediate cut with. the caustic washed light out may be sweetened separately and, if desired, a gum inhibitor added immediately after sweetening.

Referring to the drawings again, Figure lustrates the apparatus used in the preferred form of the present invention in which the heavy naphtha fraction is redistilled after the acid treat. It may be that the heavy naphtha fraction already contains some gas oil. If not, 5 to 10% of gas oil is added from a gas oil tank (not shown) through line 26 by pump 21. The acid treat in the treating plant 19 is carried out in the usual way with strong sulfuric acid. Water.washing and neutralizing follows the treatment with sulfuric acid as usual.- The neutralized stock is then discharged into still 28 provided with .a fractionating column 29. The charge is heated until all the heavy naphtha distills off and is united with the light and intermediate naphtha fractions after being condensed in condenser 30. The gas oil together with sulfur-containing reaction products remains as a residue in the still and is emptied therefrom aft- =er cooling. The purpose of adding the gas oil is to prevent the decomposition of the sulfurcontaining reaction products and the subsequent contamination of the overhead naphtha distillate with sulfurous gases.

The principal advantage of the invention lies in the fact that the intermediate cut requires neither treatment with the usual strong sulfuric acid nor high pressure stabilization and caustic washing. Our experiments have proved that the sulfur reduction secured with the same quantity of chemicals is greater in the process of the present invention than inprior processes in which the entire out which by-passes acid treating is submitted to washing with caustic. The sulfur reduction is also greater than in the case of prior processes in which the entire distillate is caustic washed and then acid'treated. This is due to the fact that the removal of sulfurbyzcaustic washing is most efficient when only the ghter portion of the by-passed cut is washed. It was also found that the present process-offers the greatest advantages when treatinghigh sulfurcontaining distillates such as distillates containing above 0.12% sulfur as' determined by the lamp method. The following example will illustrate the invention:

-A cracking coil distillate of 56.7 A. P. I. gravity and 265% sulfur containingcracking coil gas dissolved under pressure and having a final boiling point (Engler) of 439" F., is fed to the apparatus. The pressure regulator (23) is set for 140 lbs per sq. in.gauge, which is approximately therefore the operating pressure in the tower (3) At 47.5% by volume cut of heavy distillate is withdrawn from the bottom of the tower at a temperature of 580 F. This out has 41.9 A. P. I. gravity and its gasoline content to 392 F. has a sulfur content of 0.298%.

This heavy naphtha is acid treated and rerun to give a stock of 0.065% sulfur content.

An intermediate cut of 10.5% by volume on the feed is withdrawn at a temperature of 470 F.

It is of 535 A. P. I. gravity and has a sulfur content of. 0.23%, the Engler final boiling point being 315 F. A light distillate cut of 37.0% by volume on the feed is taken overhead, together with 5% of gas (based on the feed) at a vapor line temperature in line (4) of 280 F. and the distillate is condensed and withdrawn from the reflux drum (6) at a temperature of 80 F. This light distillate is of 80 A. P. I. and has a sulfur content of 0.225% the Engler F. B. P. being 270 F. This cut is stabilized and caustic washed to .give a stock having a sulfur content of 0.1.

The stabilized and caustic washed light distillate, the untreated intermediate cut and the. acid treated and rerun heavy cut are blended to give a stock of 58 A. P. I. gravity and 390 F. Engler final boiling point, with a sulfur content of 0.1%. This blend is then doctor sweetened to give a finished gasoline.

The invention may be modified in several ways, thus for example, the acid treating of the heavy 'cut may sometimes be replaced by treating with clay, or treating with metallic halides suchas ZnClz, with mineral acids other than sulfuric acid such as H01 in the presence of a zinc bearing contact agent, with non-metallic halides such as BFa, etc.

The figures show an apparatus in which a separate debutanizer tower is, provided for obtaining the three cuts. It is evident, however, that the invention may be applied to other types of debutanizers such as for example the type which is made an integral part of the single or the secondary bubbletower of the cracking coil in which case the heat exchanger 9 and reheating circuit I2-l4 may be eliminated.

Another type which maybe employed is a pair of shell stills, which may operate at atmospheric pressure, the gas and light distillate out being taken overhead in the first still, the intermediate cut in the second still, and the heavy cut taken as a-bottoms from the second still. In this case the light distillate cut may require only caustic washing or may require both stabilization and caustic washing.

Other variations of the invention will be apparent to those skilled in the art. The invention is not to be limited by the example but only by the following claim in which it is our intention to claim all novelty inherent in the invention.

What we claim is:

The method of producing a finished gasoline from a cracked naphtha having a sulfur content of at least 0.12 which comprises fractionating it to remove any gas and to obtain three liquid portions, namely, a light portion having a final boiling point (Engler) of about 270 F. greatly susceptible to sulfur reduction by alkali treatment, an intermediate portion having a final boiling point (Engler) of about 315 F. only slightly susceptible to sulfur reduction by alkali treatment and greatly susceptible to sulfur reduction by treatment with sulfuric acid but also susceptible to large losses by acid treatment, and a heavy portion greatly susceptible to sulfur reduction by acid treatment with only slight treating losses, separately stabilizing the light naphtha portion and treating it with alkali, separately treating the heavy naphtha portion with sulfuric acid and redistilling it to remove polymers, blending the treated light naphtha portion and the treated heavy naphtha portion with the untreated intermediate portion and doctor sweetening the blend to obtain-a finished gasoline.

EDWIN H. BARLOW. AMIOT P. HEWLE'I'I. PAUL E. KUHL.

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