US2438445A - Process for the acid-treating of catalytically cracked naphtha - Google Patents

Description

Patented Mar. 23, 1948 PROCESS FOR THE ACID-TREATING OF CATALYTICALLY CRACKED NAPH'IHA Arnold F. Kaulakis, Roselle, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application September 15, 1943, Serial No. 502,440

2 Claims. 1

This invention relates to treating hydrocarbons, and more particularly, relates to acid-treating of catalytic naphthas to improve the anti-knock quality of aviation gasoline or blending stock.

It is known that certain olefins are undesirable constituents in aviation gasolines and difierent methods have been described for removing undesirable olefins from such fractions. Some of these methods are referred to hereinafter. It has been reported that sulfuric acid treatment of low sulfur catalytic naphthas in the aviation gasoline boiling range results in no significant improvement in either AFD-lC and AFB-3C anti-knock quality (presently to be described), and in some cases results in decrease in AFD-3C quality. These results apply particularly to the sulfuric acid treatment of a total aviation naphtha in the 05-350 F. range.

The AFD-lC method of evaluating aviation gasoline anti-knock quality is carried out in accordance with Army-Navy specification AN-VV-F-746. This rating is designed to be a measure of the anti-knock quality of the fuel under lean-mixture conditions such as would exist under cruising conditions in aircraft. The rating is expressed in terms of the volume per cent of iso-octane that must be blended with normal heptane to give a blend which will just equal the anti-knock quality of the test sample in the AFD-1C engine.

The AFB-3C rating is designed to indicate the anti-knock quality of the gasoline under rich mixture conditions such as are encountered in aircraft operations under take-off or combat operations. The rating is generally expressed in terms of the volume of lead tetraethyl (milliliters per U. S. gallon) that must be added to S Reference fuel (commerc al iso-octane) to match the anti-knock quality of the test samples in the AFB-3C test engine. The rating is sometimes expressed in terms of the indicated mean effective pressure (IMEP) developed in the AFB-3C test engine. The AFB-3C rich mixture testing is made according to Army-Navy specifications AN-VV-F-748, and the rating obtained is directly proportioned to the maximum knock-free power of an engine using this fuel. Therefore, fuels of high AFB-3C quality are more desirable since they will give more knock-free power in the aircraft engine.

I have found that by separating catalytically cracked naphtha of relatively high olefin content into two or more fractions and separately treating these fractions with concentrated sulfuric acid rather than acid-treating the total naphtha cut, substantial increases in AFB-1C, and more particularly in AFB-3C anti-knock quality are obtained. The total catalytically cracked naphtha fraction contains olefins, aromatics, naphthenes, and paraffins, and if the total naphtha fraction containing a large percentage of olefin-s is treated with sulfuric acid, some aromatics are lost by the alkylation of aromatics with olefins.

'If the separate fractions are acid-treated, there is less loss due to alkylation because the aromatics are concentrated in the higher boiling fraction .or fractions and the ratio of aromatics to olefins is then unfavorable to the alkylation reaction. My improved results are apparently due to the more selective removal of olefins, the removal of which results in the concentration of aromatics and naphthenes.

In addition to the possibility of acid-treating naphthas in conventional equipment, my process can readily be installed in refineries where sulfurie acid alkylation is practiced with a small expenditure for contacting and rerunning.

In the drawing;

Fig. 1 represents one form of apparatus which may be used to carry out my process; and

Fig. 2 represents another form of apparatus wherein my process may be used in a refinery which practices sulfuric acid alkylation of lower boiling hydrocarbons.

In the catalytic cracking of relative y heavy hydrocarbons, such as gas oils. to produce lower boiling hydrocarbons. the gasoline produced contains aromatics, olefins, naphthenes, and paraflins. The aromatics, naphthenes and branched chain parafiins are desirable constituents for aviation gasoline but olefins are generally undesirable.

,One method for removing olefins is acid-treating, which has long been practiced in petroleum refineries.

ever, not desirable for treating catalytically cracked fractions. For example, in the production of aviation gasoline, it has been reported that there is a loss in AFB-3C rating of the aviation gasoline if it is acid-treated with concentrated sulfuric acid. I have found, however, that if the aviation gasoline or naphtha fraction is divided into two or more fractions, and each fraction treated separately with sulfuric acid of concentrations and acid oonsumptions optimum for each fraction, that an actual increase in the AFB-3C rating is obtained.

There are other ways of removing olefins or separating aromatics or naphthenes from the cracked gasoline, and my process compares favorably with them. Other processesare catalytic after treating of the catalytically cracked gasoline, hydrogenation of the catalytica-ll'y crackedmv naphtha and solvent extraction of the catalytically cracked naphtha.

Referring now to Fig. 1 of theurawings. the if referencecharacter l designates a line for con veying catalytically cracked naphtha to a fractionating tower I2 for separating the naphtha into desired fractions. For example, a gas oil is cracked at a temperature of about 925-1500 F.,opreferably 975 F. in the presence of a catalyst, such as, synthetic gels, acid-treated. bentonites, etc., preferably silica-alumina gelcatalyst. 'The cracked naphtha is separated from'the cracked products.

Conventional acid-treating is, how- C4 and lighter are taken overhead 'tower 42 as reflux liquid. The rest of the liquid 4 and condenser 46 to a liquid gas separator 52 wherein uncondensed gases and vapors are separated from liquid. The gases or vapors pass overhead through line 54 and the liquid is withdrawn from the bottom of the separator 52 through line 56. At least a portionof the liquid withdrawn through line 56 is passed through line 58 by pump 62 and. returned to the fractionating from line 56 forms the desired lighter treated fraction and will be referred to hereinafter.

Bottoms from the fractionator 42 are withdrawn through line 64. These bottoms contain higher boiling constituents in the gasoline'boiling'range and may be used as blending agents for ordinary motor gasoline.

The 225 to 350 F. fraction is given a similar treatment though the optimum treating condithrough line [4 and may be sent to storage or when the composition of these fractions is given.

However, both fractions contain olefins and it is preferred to acid-treat both of the fractions.

The C5 to 225 F. fraction is introduced into an acid-treating tank 24 provided with a stirrer26,

or other suitable means of providing intimate contact between acid and naphtha. Concen- A heavier fraction having a boiling,

tions may differ from those for thelight fraction.

The 225-350 F2. fraction is passed to an acidtreating tank 65 provided with a stirrer 68 or other meansof providing required mixing. Concentrated sulfuric acid having a concentration of about 85 to 98% is introduced into the tank 6 6 through line i2 and after sludge is withdrawn through line 14. The amount of sulfuric acid 1 used is about 5 to 60 pounds per barrel of oil fraction treated, dependingon acid strength, the olefin content of the fraction, etc. v of mixing and reaction in the acid tank 55' is from about2 to 120 minutes,longer times being usedwith weaker acid. The temperature during treating is about 30? F. to 120 F. a 7

The acid-treated225 to 3'50 F. fraction is then passed through line T5 to another wash tank 18 where the fraction is washed with alkaline water to remove entrained acid. The washed 225- 350 F. fraction is'then passed through line 82 to V a second fractionating tower 84"for recovering the desired-treated fraction. 'Instead' of using two fractionators 42* and 8d for the separate fractions, the fractions may be: combined and fractionated in one fractionator. H V V As above pointed out, the heavier fraction also contains olefins and the acid; treatment removes a large part of the olefins. In the fractionating tower 84 the treated: heavier fraction is heated and fractionated to separate a desired 225 to 350 F. fraction. Higher boiling constitutrated sulfuric acid having a concentration of 7 about 85 to 98% is introduced into the tank 24 through line 28 and acid sludge is withdrawn through line 32. The amount of acid used may vary between about 5 to 60 pounds of sulfuric acid per barrel of oil treated, depending on the olefin content of the naphtha,v the improvement desired, and the strength of acid that is to'be used in treating. Preferably, about 20 to 30 pounds of sulfuric acid (98%) per barrel of oil is used. The temperature may vary between about 30 to 120 F. V

The time of contact of the acid and'the oil fraction is from 2 to 120 minutes, longer times being used with weaker acid. The acid treatment removes a large part of the olefins and the treated C5 to 225 F. fraction is withdrawn through. line 34 and passed through a wash tank 35 where the fraction is Washed with alkaline water to remove entrained acid. The Washed fraction is then passed through line 381:0 a fractionating. tower 42 for rerunning. the treated fraction.

' The desired volatile fraction passes overhead from the fractionating tower 42 through line 44 cuts are drawn off 'asbottom'sthroughline and may be used as blending agents for ordinary motor gasoline.

The vapors pass overheat from the fractionating tower 84' through line 86 and condenser 88 to a liquidgas separator 92 for separating liquids from gases and vapors. The gases and vapors pass overhead through lineo94. .The liquid is withdrawn from the bottom of the separator 92 through line'9B and at least a portion thereof is passed through line 98 by pump [02 and returned to the top of the fractionating tower 84 as reflux liquid. The rest of the liquid. is passed through line I04 and combined with the. treated lighter fraction passing through line I06 which forms a continuationof line 56. The combined naphtha fractions are withdrawn from. the system through.

line M8. The combined treated naphtha fraction has a higher AFD-IC and a higher AFB-3C rating than the totalnaphtha fraction. would,

have if acid-treated as a single fraction.

The following datairepresent one example to line fractions containing substantialproportions of olefins and aromatics:

The time Table 1.Acid treated fractions compared with acid treated total naphtha Treating uality Increase gfig Ioss Vol. l'limg of Q er cen rea mg Decrease on Feed AFD-lO AFB-30 1 HeS0498% l#/Bbl. of Oil Treated: Minutes (ls-225 F 23 1 3 3. 3 8.1 225-350 F 7 6. O 3 3. 5 12. 7

Total Recombined 10. 5 3. 4 10. 0

Treat Cu350 F. (Total) 10# HzSO4 98%/Bblof Oil 9.0 3 1.8 -l. 6

H2SO198% #/Bbl. of Oil Treated:

Oe- 225 F 46 28 3 6.3 15. 7 12 11 3 5. 0 25. 5

Total Recombined 17 3.8 19 7 Treat Ct350 F. (Total) 20# H2SO4-98%/Bbl.'

of Oil 14. 0 3 3. 3 -3. 6

1 Ratings based on fuel containing 4 ml. TEL/gal.

The above table discloses data to show that there is a quality increase in the aviation naphtha when the naphtha is divided into two fractions and each fraction separately acid-treated. These data show that the total recombined naphtha after separate acid-treating of the fractions has a much greater AFD-lC increase than the total naphtha C6 to 350 when it is acid-treated as a single fraction. These data further show that there is an increase in AFB-3C rating when the fractions are separately treated whereas when the total naphtha fraction is acid-treated as a single fraction there is a decrease in AFB-3C rating,

Table 2.-Composition 0f fraction-vol. percent composition of such a naphtha is given in Table 2. A catalytically cracked gasoline of this type having a boiling range of about 100-335 F. has and AFB-3C rating at about 170-180 IMEP.

Only one example of catalytically cracked naphtha has been given and it is to be understood that the amounts of the different constituents may vary with different feed stocks and different cracking conditions, such as temperature, time of cracking and amount and kind of catalyst used, but it is generally true that the amount of olefins in the lighter fraction is greater than in the heavier fraction and the amount of aromatics in the lower boiling fraction is much less than the amount of aromatics in the higher boiling fraction.

The amount of improvement to be gained in Aromat- Naph- Ole- Bromine Fmctwn ics themes fins Pamfins No. treating the naphtha fractions varies with the amount of acid employed as well as the strength gt-225:1? 3 rig-2g of the acid. The following Table 3 discloses the 2 effect of acid quantity on the light and heavy TotalFractiOn 36 7 3 -75 naphtha fractions when treating with 98% 50 strength used:

Table 3 VOL Quality Improvement Treating Number AFD-lC IMEP Minutes 225-350 2o 11 12 s. o 25. 5

1 Rating with 4 cc. tetraethyl lead added to samples.

Table 2 discloses a typical composition of catalytically cracked gasoline. Paraflinic gas oil having an A. P. I. gravity of 315 and a mid boiling point of 650 F. was cracked at a temperature of about 975 F. in the presence of synthetic silica alumina gel at about conversion, which means that about 65% of the original gas oil is converted to gas, coke and gasoline, and that there is 35% cycle oil left. Cracked naphtha is From the above Table 3 it will be seen that with the more drastic sulfuric acid treats greater improvement in the AFD-lC and AFB-3C ratings is obtained but at the same time greater loss of feed results. Table 3 also illustrates that the quality improvements to be gained, at fixed treating conditions, vary, depending on the boiling range and/or composition of the naphtha; thus, to obtain a given overall quality improvement my separated from the cracked, products and the .75 process of treating selected fractions is also a WWWUIOOW more efiicient scheme from a standpoint of acid consumption and treat severity inasmuch as each and. butenes.

fraction can be treated separately more efiecbutane/olefin'ratio of 250/1.

V The C and C5 alkylate and pentanes are with.-

Table 4.E17ect of given acid treat on oarious fractzons o 1 i 11 o k 1 L t d ata yt ca y me e ig an Naphtha Fraction Lght Heavy Total Heavy Recombined Treat# of acid /Bbl. of

Fraction 20 20 20 20 Bromine No. Decrease. 46 '12 28 Loss. Vol. Per centt 28 11 17 20 AFD-lC Improvement. 6.3 5.0 3.8 5. 7 AFB-3O IMEP Improvement 15. 7 25. 3 4. 7 20. 0 Loss/AFD-IC Improvement 4. 5 2. 2 4. 5 3. 5 Loss/AFD-3C IMEP 1111-; r I

provement 1. 8 0. 4 l. 0

1 4. 2 Negative.

Crfraction contains normal butane and isobutane Isobutane from an extraneous source may be added if desired. The C4 and Cs fractions are combined and passed through line I34 to an acid alkylation unit I36 where the mixture is treated with sulfuric acid having a.

concentration of about 98%. The sulfuric acid is introduced into the unit I36 through line I38.

The temperature during alkylation is about 40 F. The alkylation is carried out at an internal isodrawn through line I42.

7 The spent acid having a concentration of abou V 85 to 95% is withdrawn through line ld l'and may be used in acid-treating the Q5 to 225? F. cut (or C6 to 225 F.) and the 225 to 350 F. Or the spent acid may be passed through an acid recoveryunit M6 for concentrating the acid to the desired concentration for reuse and recycling to the alkylation unit I36. 7. f r V V The C6 to 225 F. fraction is withdrawn from unit I22 through line I48 and passed to an acidtreating unit I52 where it is mixed with spent acid introduced through line I5 3. The spent acid is part of the acid leaving the alkylation. unit through line HM. If desired, fresh acid may be introduced into line I54 through line I56.. Ihe acid tank I52 is provided with a stirrer such as shown in'Fig. 1 or other stirring means for intimately contacting the light fraction and the sulfuric acid. When using a weaker acidof 85 to 95% concentration, the amount of acid to light fraction may be about 20 to 100 lbs./bbl..of light fraction. The temperature during the Table 5.-Acz'd treat for substantially complete olefin removal o s. 1. Highlunsaturated naphtha irom 975? F., 65% conversion cracking of heavy Tinsley gas 01 2. Low unsaturate gas oil, using higher catalyst to oil'ratio than for the 65% conversion.

A typical application of my process in a refinery producing aviation gasoline is illustrated in 2. Referring now to Fig. 2 of the drawings,

the line I20 designates a line for conducting a heavy oil stock, such as gas oil, to a cracking unit for the Production of lower boiling constituents including gasoline. The cracking unit is diagrammatically shown at I22 and also includes means for separating the reactionproducts into desired fractions. The gas oil or other stock is cracked in the presence of powdered catalyst having a size of about 200 tov 400 standard mesh or finer. The catalyst may be acid-treated bentond naphtha from 975 F., 80% conversion cracking of heavy Tinslcy treatment is about F. to 120 F. and the time of contact is about 6 minutes to 60 minutes.

The acid-treated C6 to 225 fraction is withdrawn through line I 58 and is preferably given an alkaline wash (not shown in Fig. 2) and then reiteor synthetic. silica-alumina or silica magnesia gel. The temperature during cracking is about 825 to I000 F. The amount of catalyst to liquid oil by weight is in the ratio of from about 2/1 to 20 1. 7

Gases are taken overhead through line I25 and bottoms are withdrawn through line I25. A Q4 fraction, is Withdrawn through line I28 and a C5 fraction iswithdrawn through line I32. The

run to remove light and heavy ends. The resulting C6 to 225 F. fraction has an improved AFB-1C and AFB-3C rating as above pointed out in the description of Fig. 1 andthe data included in connection therewith. Spent acid from the acid tank 152 is withdrawn through line I62 and may be recycled to the acid recovery unit I46 through line I44. Part of the spent acid may be withdrawn through line I52. I

The heavier fraction (225 to 350 F.) from unit I22 is passed through line I56 to another aci'dtreating tank Iiit'i where it is mixed with acid introduced through line I22. The acid comprises the spent acid from the .alkylation unit I36 and 7 may include fresh acid introduced through line 555.. The acid-treating tank I68 may be provided with any desirable stirring means for mixing the heavier fraction and the sulfuric acid. The sulfuric acid has a concentration of about 85 to 95%. About 20 to 100 pounds of acid are used per barrel of heavy fraction. The time of treating is about 6 to 60 minutes and the temperature during the treating is about 60 to 120 F. Spent acid is Withdrawn through line I'M and returned to the acid recovery unit 55 for reconcentrating the sulfuric acid.

The acid-treated 225 to 350 fraction is with drawn from the acid-treating unit E08 through line I76 and is preferably given an alkaline wash to remove entrained acid and rerun to remove light and heavy ends. The treated heavier fraction has an increased AFB-1C and AFB-3C IMEP rating as above pointed out in the description of Fig. 1 and the data included therewith. The treated light and heavy fractions may be combined and further processed in one system including a fractionator.

Instead of passing the 225 to 350 F. fraction through the acid-treating unit 100, in some'cases it may be used as such without acidetreating. In such case, the heavier fraction is icy-passed around the acid-treating unit or tank I68 through line I78 and used as such in the final product.

The final product is formed by combining the acid-treated 225 to 350 F. fraction, the acidtreated C6 to 225 F. fraction, the alkylate passing through line I42 and an extraneous natural base passing through line I02. The final product in one specific case has the following composition but it is understood that this is given by Way of example only as the final product will vary with the quality and nature of the fractions:

Per cent by volume Cs-225 F 12.7 225 F.-350 F. 17.0 Pentanes in alkylate 11.7 C4 and C5 alkylate 40.2 Natural base 18.4

The combined product is withdrawn through line I84 and has an AFD-BC rating of 203 IMEP. The extraneous natural base may have the following composition:

The extraneous natural base has a boiling range of about 100 F. to 200 F. and has an AFD3C rating of 140-170 IMEP.

Since aviation gasoline is an extremely high grade product, there does exist a supply of readily available natural base stocks, so-called marginal bases, which are of a high quality compared to normal motor fuel, but are relatively low compared to final 100 octane aviation product. Since this natural base material can be obtained without the installation of any processes or equipment over that available in normal crude processing, the volume of aviation gasoline can be increased by mixing this natural base with higher octane stocks, such as alkylation and/or catalytically cracked naphtha acid treated according to my invention. The losses which accompany acid treating, although high, represent material considerably poorer than the marginal stock, and by removing this poorer material, aviation production is increased. Further, the loss is not a complete one as the polymers recovered from the sul- 10 furic acid used for treating may be used in motor asolines.

Optimum treats for individual fractions are such that will eliminate substantially all olefins with a minimum of loss of aromatics. Splitting of the total naphtha assures the minimizing of alkylation by providing unfavorable aromatic to olefin ratios, and one advantage of split treating results from this fact. Since the higher boiling olefins in the heavy fraction are more difiicult to remove than the olefins in the light fraction, a more severe acid treat is required to obtain a given quality improvement for the heavy fraction as compared to the light.

My process may be used with low or high sulfur stocks. When using my process for treatment of low sulfur stocks, the improvement in quality is due primarily to the removal of olefins. Naphthas containing sulfur to the extent of about 0.20% are improved to a higher degree because of sulfur removal in addition to the removal of olefins.

While I have specifically set forth fractions of Cs225 F. and 225 to 350 F., it is to be under- I stood that the split between'the fractions may occur anywhere between 175 F. and 275 F., depending on the nature of the catalytically cracked naphtha being treated. Also, more than two outs may be made and treated, if desired.

While I have shown two forms of apparatus for carrying out my invention and have included specific compositions, conditions, etc., it is to be expressly understood that these are by way of example only and my invention is not to be restricted thereto.

I claim:

1. A method of improving the IMEP of catalytically cracked aviation gasolines containing olefins and aromatics which comprises separating a catalytically cracked aviation gasoline into a (JG-225 F. fraction containing a major portion of the olefins and a 225-350 F. fraction containing a major portion of the aromatics, separately treating each fraction with concentrated sulfuric acid having a concentration of about to 98% to remove olefins and then recombining the treated fractions.

2. A method according to claim 1 wherein the sulfuric acid is used in the amount of about 5-60 pounds per barrel of fraction treated, the temperature during treating is 30120 F. and the time of treating is about 2 to minutes.

ARNOLD F. KAULAKIS.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,827,537 Morrell Oct. 13, 1931 1,873,728 Wagner Aug. 23, 1932 2,099,835 Barlow et al Nov. 23, 1937 2,109,446 Kendall Feb. 22, 1938 2,252,082 Lloyd et a1 Aug. 12, 1941 2,258,512 McCormick Oct. 7, 1941 2,264,447 Meier Dec. 2, 1941 2,267,458 Goldsby Dec. 23, 1941 2,276,081 McGrew Mar. 10, 1942 2,293,705 Bloch Aug. 25, 1942 2,310,327 Sweeney Feb. 9, 1943 2,311,096 Strawn Feb. 16, 1943 2,315,738 Ryan et al Apr. 6, 1943 2,336,736 Kanhofer Dec. 14, 1943 2383.056 Goldsby Aug. 21, 1945 2,388,087 Ryan et a1 Aug. 30, 1945

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