US2412645A - Treating hydrocarbon fluids - Google Patents

Description

. 17; 1946. J. c. MUNDAY TREATING H/YDROCARBON FLUIDS Filed Oct. 14, 1943 Patented Dec. 17, 1946 UNITED STATES PATENT oFElcE 2,412,645 TREATING mmRocAaBoN FLUms John C. Monday, Cranford,-N. J., assigner to Standard Oil Development Company, a corporation oi' Delaware Application October 14, 1943, Serial No. 506,169

v naphtha to produce aviation gasoline. My present invention is an improvement over such other processes. y

According to my invention, a relatively heavy hydrocarbon, such as gas oil, is cracked in the presence'of a catalyst at a relatively high temperature and from the cracked products are separated a light naphtha fraction, a heavy naphtha fraction, and a heavier oil'fraction. The light naphtha fraction is alkylated with isobutane, and

'the heavy naphtha fraction is 'subjected to 'a catalytic recracking operation. The products from these steps are then fractionated to separate light hydrocarbon fractions boiling in the aviation gasoline range, and the fractions are blended to produce a finished aviation gasoline of high stability, high octane number, high susceptibility to tetraethyl lead and high rich mixture performance. Furthermore, the ethylene and butylenes produced in the cracking and recracking steps may also. be subjected to alkylation with isobutane since the product alkylate is of high quality and augments the yield of aviation gasoline.

The light fraction of the catalytically cracked naphtha which is fed to the alkylation step should be substantially free of aromatics. The end p-oint should be chosen to exclude benzene, if an appreciable amount is formed in the cracking step. For example, the end point may be 165 or 170 F. In some cases wherein the amount of benzene is very small the end point may be 200 or somewhat higher, but it should be borne in mind that the presence of even small amounts of aromatics in the alkylation feed stock results in rapid degradation of alkylation catalysts, as well as in lower yields and lower octane number products. This will be evident from the following Examples 1, 1A and 1B, Example 1 showin-g my preferred alkylation step and EX- amples 1A and 1B showing poorer results when selecting improper fractions.

Example 1 A Sil-150 F. fraction containing no aromatics from catalytically cracked gasoline was alkylated With isobutane at 45 F. employing a 10/1 isobutane/olefin ratio andI sulfuric acid catalyst in 'a 1/1 acid/hydrocarbonV ratio for 30 minutes contact time in a continuous run of 103 hours duration. An acid replacement Arate of 0.5 to 0.7 pound per gallon of alkylate'was required in or- (Cl. 20o-683.4)

2 der to maintaincatalyst activity. The. yield of aviation alkylate was 125% of the 60-150 F.

fraction and the A. S. T. M. octane number was 87.5. The aviation octane number-|-4 cc. llead per gallon was equivalent to iso-octane+0.24 cc. lead per gallon.

Example 1A y.

A 60-200 F. fraction from the same gasoline containing 8.8% aromatics when alkylated under the same conditions required an acid replacement rate of Y1.5-1.8 pounds per gallon of alkylate in order to maintain activity. The yield of alkylate was 118% and` thel A. S. T. M. octane number was 85. Y

Example 1B If a 400 F. end point naphtha is subjected to alkylation. the yield is very low and the octane number of the product may actually be lower than that of the `feed stock as a result of the absorption of aromatics by the catalyst and the alkylation of aromatics thus forming compounds boiling above the gasoline range.

In the alkylation step, the oleiins react With isobutane to form saturated hydrocarbons of high clear octane number, high octane number appreciation on the addition of tetraethyl lead,

high blending octane number, and high performance when employing rich fuel/air ratios as in take-oil or under heavy loads as measured by the AFD-3C test method. Each of these factors is of prime importance in the production of large quantities of aviation gasoline having octane numbers of or above. Removal or conversion of the olelns in the naphtha is necessary to achieve this end, and the alkylation ofl the light catalytic naphtha originally containing about 40% olens lowers the bromine number from about 82 ogs/gm. to less than l.

In the catalytic recracking step, also, olens are converted. so that the blend of alkylated light naphtha and atalytically r'ecracked heavy naphtha has a low bromine number and low acid heat and easily passes specications. Since in the recracking of the heavy naphtha lower boilingolens are produced, in a preferred modiiication of my process the light naphtha produced in the recracking step is passedto the alkylation unit along with the light naphtha produced in the catalytic cracking. In this manner there is produced an aviation gasoline of quite low olen content and very high quality.

Apparently the oleiin content is reduced in the catalytic recracking step partly by polymerization and partly by hydrogenation through hydrogen exchange with naphthene hydrocarbons. The recracking causes a sharp reduction in the .amounts of naphthenes and paralns present, particularly in the high boiling portions which are very high in aromatic content.

3 The heavy fractionof the catalytically cracked naphtha which is subjected to catalytic recracking must likewise be a selected fraction if high yields of high octane number aviation gasoline are to be realized, as shown by the following examples. Example 2C shows improved yields obtained when catalytically recracking a selected heavy naphtha fraction, whereas Examples 2,12A and 2B show that best results are not obtained with improperly selected fractions.

Example 2 A 'l0-410 F. naphtha produced by catalytic cracking at a temperature lin the range 925-975 F. with powdered synthetic silicaalumina gel was recracked at 900 F. with the same catalyst and the product was fractionated.

The yield of 335 F. end point aviation base stock.

exclusive of pentane was 46.8% and the yield of pentane was 25.9%. The aviation octane number+4 cc. tetraethyl lead per gallon of the feed.

stock to recracking was 88.7 while that of the depentanized aviation base product was 94.2.

Example 2A A 11o-220? F. fraction of the same gasoline as employed in Example 2 was recracked under the same' conditions. The yield of aviation gasoline base exclusive of pentane was 58% and the yield of pentane was 14%, while aviation octane numbers+4 cc. lead of the feedand ofthe depentanized aviation base product were86.4 and y 92.6, respectively.

V A' Example 2B i a' A 11G-289 F.

employed in Example 2 was recrackedunder-the same conditions, and. yields `of 61% vof dac-'.-

pentanized aviation' base and 11.3% of 'pentane were obtained. The feed hadan aviation octane number-F4 cc. lead of 88, while that of the depentanizeal aviation b ase product was 92.5.

Example 2C A 220410 F. fraction4 of the gasoline employed f in Example 2 was recracke'd'under the same conditions. The feed' stock .contained 38.2% ,of

material boiling in the .aviation gasoline range below 3 35" F. The yield ci depentanizedaviation base was 5,8%; the pentaneyield being 4.4%, and

the yield of C4 hydrocarbons being 5.5%. Whereas .the aviation octane .number-r4 cc. leadof the feedstock was 87, that lof the depentanized aviation base product was' 98.2.' It has Abeen foundthat ,the fractionofa catalytically cracked gasoline boilingbetween about 160 or 170v F. and-"about 220 F. has va fraction of the same gasolineas' As pointed out'above, the yield and quality of the aviation gasoline maybe augmented by alkylation of the ethylene and butylenes produced by cracking and recracking with the isobutane produced by cracking and recracking. In view of the requirements of normal butene and isobutylene as feedstocks 4in synthetic rubber production, it may be desirable vto``alkylate only the ethylene at the present time.V The ethylene should be alkylated with isobutane in a separate unit not in the presence of sulfuric. acid catalyst but in the presence ofa halide catalyst, such as aluminum chloride or bromide, employing about 3/1v to. 5/1 isobutane-ethylene ratio at 100-150 F. and 250-350 lbs./sq. in. pressure. The product contains 'I0-85% of Ce hydrocarbons, predominantly v2,3-dimethyl butane'which has a very high rich mixturerating on the AFD-3C y scale.

The ethylene alkylate, or only the Cs fraction therefrom, is blended with the aviation fractions produced by alkylation of the light catalytic naphtha and by recracking the'heavy fraction of thecatalytic naphtha. When operating sol as to alkylate ethylene and C4l oleiins as well as thelight catalytic naphtha, the yield of finished high quality aviation gasoline'is more than 100% based on' the original catalytic naphtha.

In contrast to ethylene alkylation, either the Vnormal butenes or isobutylene or both can be alkylated with isobutane in-the presence of sulfuric acidcatalyst with good results, and it is preferred 'to do thissimultaneously and in the same unit as employed in the alkylation of the light naphtha fractions.

In the drawing, the figure represents one form of apparatus which may be used to practice my process.

low 'octane number, fory example, about 84 aviation+4 cc. lead, and that recracking improves it lonly slightly, for example,to about 88. It is generally preferred to discard this'fraction, which may amount to 10 or 12% of the catalytic gasoline, and to use it in automotive fuels. When 'a discarding this fraction the charge'to the alkylation unit is about.48% of the catalytic gasoline exclusive of C4 hydrocarbons, and the 220410 F. fraction charged to the recracking step amounts to about 40% of the catalytic gasoline. t

As shown in VExample 1, the yield Vfrom alkylation is 125%.of the chargeor 60% based on the catalytic gasoline, and this alkylate has an aviation octane number-i4 cc. lead greaterthan 100 (isooctane+0.24 cc. lead) As shown in Example 2C, the yield of depentanized aviation base stock from the recracking step is 58% of the charge, or 23% based on the` catalytic gasoline.

vReferring now to the drawing, the reference character'lll designates aline through which the hydrocarbon oilfeed stock is introduced to the system. For example, the feed` may comprise gas .oil vapors4 or votherrelativelyheavy vaporv ized petroleum stock.v

catalyst, it is also possible to startv with a partly 1 When4 using powdered preheated liquid stock andto supply the heat of vaporization and conversion by contact with a suilicient quantity of hot catalyst. The hydrocarbons are cracked at atmospheric pressure or thereab'outs at'a temperature of about 900 F. to

1000. F., preferably about-975 F. when cracking a relatively heavy gas oil having an A. P. I.

gravityof 25430"v and a mid-boiling point of about 60G-750 F.

Thecatalyst may be 'any suitable cracking catalyst, such as synthetic silica alumina gel, synthetic silica magnesia gel, acid-treated bentonites, etc. For the preparation of aviation gasoline and relatively large amounts of oleiins, it is preferred to use the synthetic silica alumina gel. The preparation of such a catalyst is well known and is ,not described here.l Instead of vusing powdered catalyst, it is within the contemplation of my invention to use larger particles of amaca mesh or finer.

The hydrocarbon feed stock is passed through line I0 into the bottom portion of a reaction vessel I8 which contains dry powdered catalyst at reaction temperature. The velocity of the vapors passing throughreaction vessel I8 is controlled so that the catalyst particles remain in the vessel for a much longer period of time than the vapors, and preferably such that a relatively densev layer of catalyst is present in the lower portion ofthe vessel. Suitable velocities lie in the range from 0.5 to 10, preferablyvl to 3, linear feet per'second when employing 200-400 mesh catalyst having a density when freely settled of from 35 to 60 lbs/cu. ft.' Under these conditions the relatively dense catalyst phase has a density of the order of to 30 lbs./cu. ft. The relatively dense catalyst phase is aerated by the rising vapors and has the appearance of a violently boiling liquid, and possesses properties of liquids such as fluidity, the ability to exert hydrostatic pressure and a level or meniscusY which is especially noticeable when low vapor velocities are employed. Also, when employing relatively low velocities, such as from 0.5 to 2 ft. per second, the carry-over of catalyst by the cracked produots is very small, of the order of 0.003-0.01

lbs/cu. ft. of vapors.

The cracked products leave the top of the reaction vessel I8 through line 22, after lpassing through cyclone separator 24 where entrained 'in iixed bed operation. Preferably the .powdered tower 32 through line-38 and are subjected to l fractionating and/or scrubbing operations to separate fractions rich in ethylene and in C4 hydrocarbons. These operations, which are well known and need not be described in detail here, are indicated on thedrawing by numeral 43. Light gases pass overhead through line 44. A C3 fraction is withdrawn through line 45. The septhe upper portion of vessel I8. Other forms of separating means may be used. Separated catalyst is returned to the reaction zone proper through linie 25. During the conversion operation the powdered catalyst becomes contaminated with coke or carbonaceous material and lt is necessary to regenerate the catalyst in any known manner,l preferably by burning with air or oxygen-containing gas at about 1000-1l00"l F. toV remove the carbonaceous deposit. Catalyst for regeneration is withdrawn from reaction vessel I8 through line 26 in a luidized condition and is passed to a regenerator (not shown) Ywhich may be similar in construction to vessel i8. Hot regenerated-catalyst is returned to line I0 and to the reactor through line 28 at a suiiicient rate to maintain reactor` temperature and catalyst activity at the desired levels, vand if liquid feed stock is being supplied to the reaction, to absorb or vaporize the liquid cornpletely. The weight ratio of catalyst to oil. employed is generally above 3, for example, from 5 to 20.

While I have shown only one cyclone separator on the drawing, it is to be understood that more than one cyclone separator may be used in series 4arated C4 fraction withdrawn through' line 45 contains isobutylene which is useful in the production of synthetic'rubber and the isobutylene may be recovered by scrubbing with acid. The acid used is preferably sulfuric acid having a concentration of about 65% by weight. The C4 fraction is introduced into the bottom portion of an acid scrubbing vessel 48, the acid is introduced at the top through line 52, and the acid extract is removed through line 53. In the scrubbing vessel 48 the temperature of the sulfuric acid is about 75 F. The isobutylene is recovered from the`acid by treating with steam, thus raising the temperature to about 250 F. and lowering the acid concentration to Ll045%. Isobutylene and di-isobutylene are ashed overhead and the latter is cracked to form isobutylene. If isobutylene is not desired for synthetic rubber, the entire C4 cut is by-passed around acidv scrubber 48 through line 54 to line 56 leading to alkylation unit 51.

, 'I'he rest of the C4 fraction containing isobutane and butenes leaves scrubber 48 through the line and is mixed with a light naphtha fraction introduced through line 58. This light naphtha fraction is withdrawn from the upper part of fractionating tower 32 wherein the catalytically cracked products -are fractionated. The light naphtha fraction collects on trap-out tray 62 in the fractionating tower 32 and is passed through line 58 by pump 64. The light naphtha fraction contains olens and paralins, but as mentioned above, should be substantially free of aromatics. The light naphtha fraction has a boiling range of about 60 to about 170 F. or 200 F. .l

The mixture of the light cracked naphtha and the C4 fraction is passed through line 58 to the alkylation unit or reactor 51 wherein the olens are alkylated with isobutane to transform the olefins to branched parafns. Any suitable alkylation -catalyst is used, such as sulfuric acid, boron fluoride-water, hydrogen fluoride, etc. Where sulfuric acid is used, the titratable acidity of the acid is maintained above about 82%, preferably at about 85-90%, by continuous .replacement with 94-98% acid. The temperature during alkylation is preferably in the range li5`80"` F. The ratio of isobutane to oleflns in the feed is generally maintained at 3/1ior higher by reto effect a better separation of powdered catalyst I Vhydrocarbons leave the top of the fractionating cycling isobutane separated from the products, and the vinstantaneous isoparaiiin/olen ratio in the reactor is maintained considerably higher, for

example, 30/1 or 100/1 or'greater, by recycling,

products which are low in olens to the inlet of the reactor.

The acid for the alkylation unit is introduced through line 'l2 and spent acid sludge is withdrawn through line 'M The products of alkylation are passed through line 76 into a second fractionating tower I8 for separating the desired light hydrocarbons boiling in the aviation gasoline range from higher boiling constituents. The

light hydrocarbon constituents lpass overhead through line 82, are partially condensed in condenser 84, and passed to a separator 86 wherein gases are separated from liquid. The gases comprising C4 and lighter pass overhead through line I8 -and are fractionated in equipment (not shown) fraction is withdrawn froml separator 86 as a liquid through line 82. This light fraction boils up to the end point of the desired aviation gasoline, generally 30D-330 F. and is substantially free of olens. Higher boiling constituents are.with drawn from the bottom of the fractionator 18 through line 94. These higher boiling constituents may be addedtogordinary motor gasoline.

As mentioned earlier, it is frequently desirable to alkylate the ethylene produced in the cracking and recracking operations with isobutane. To this end the ethylene separated in fractionating and scrubbing equipment 43 and which may have a purity from`25 to 80% is passed through line 85 to an alkylation unit 86 where it isalkylated with isohutanel in the presence of aluminum ch1o' ride. Isobutane is introduced through line 91.

`.The isobutane may come from cracked products v in my process or froman extraneous source. The conditions of operation are similar to those emboiling above the aviation gasoline range reduces their boiling points and thereby increases the yield of aviation naphtha.

The'vaporous reaction products pass overhead from reactor through line |24 to a third of the heavy naphtha fraction additional amounts of isobutane are formed together with other valployed in alkylation unit lexcept that the temperatureis higher (1D0-150 F.).andthe pressureV may be 250K-350 'lha/sq. in.1The `products are passed through'1ine98`into fractionatorJB along with the products from 'alkylationunit v51.

Returning now to the first-mentionedl fractionating tower 32, the catalytically crackedproduable light olenic hydrocarbons. These light hydrocarbons are withdrawn from the top of the fractionating tower |34 through line |36 and are .combined withthe gaseous products leaving the rst fractionator 32 through line 36. This mixture is then treated to separate isobutane and olefins from the other gases vfor use in the alkylation units 51 and 86.

Ihe reaction products in the iractionator |34 are fractionated to separate an aviation naphtha fraction vwhich collects on trap-out tray |40. Thisfraction is relatively heavy, boiling for ,the most 'partbetween about 190 and 335 F. and contains high quality constituents for aviation gasoline. The aromatic content of the naphtha is very high, lparticularly of the 22o-335 F. fraction which mayfbe v8090% aromatics or higher.

' The naphtha fraction is withdrawn from trapucts are further fractionated to separate aheavyf naphtha fraction which is .withdrawnv from trapout tray |02 through line |04 by pump |06. Ihis higher, and contains olens, parafilns, aromatics andnaphthenes. vThe paraflinsand some of the .oleiins are ofr poor- Isome of the alkylated aromaticshave a high boil-l ing point and. it i s desirable to break oft'part of the chains of the alkylated aromatics to reduce their boiling point.

To improve the quality ofthe heavynaphtha u :outtray |40through line |42 and is mixed with the, light .alkylate fraction withdrawn through linef92 and the mixture is Withdrawn through line V| 44 as 'an aviation gasoline.y The addition of 4 or 4.5`cc.-` of tetraethyl lead per gallon andadjustment of 'the vapor pressure by adjustment of heavy naphtha fraction has'an initial' boiling point from about 170 F. to about 4220" F. and may have an end point of 350 or -400 lor somewhat 1theisopentane content of the gasoline produces -a finished aviation gasoline of high stability and high octane numberby both the aviation octane number 'and the AFD-3C methods of testing.

A heavier `fraction collects on lower trap-out tray |46'in.th e fractionating tower |34 and this fraction is withdrawn through line |48. This heavier fraction may be added to motor gasoline. In a preferred modication, a light fraction of 'the recrackedproducts, and which contains olefraction, it is passed through a second catalytic cracking operation in reactorl'll. Therecracking unit is` operated in the same manner as the cracking unit described earlier, employing vpow.-v

dered cracking catalystof thesame or different composition.' Synthetic silica-alumina gel is a` preferred catalyst. The temperature of operation is generally slightly lower than in cracking,

V "for example, '700'tof950 F., particularly if the cracking unit is `operated to give -high conversions. With cracking conversions of the order of -80%, 900 F. is a suitable temperature for Withdrawn from the reactor through line |'|2, re-

generated and returned through line I4. A cy-i clone separator H6 and return pipe |'l8 are used.-`

A common regeneratoris preferably employed for passing to the reaction zone ||0 remain as aromatics, but de-alkylation of alkylated aromatics and modifications may be 'made without depart ing' from'the spirit of my invention.

II claim:

` A methodbt 'producing aviation 'gasoline which 1 recraclnng. A stream of catalyst is continuously G0- boiling frange o f about Gti-165 F., an intermecomprises. separating a catalytically Acracked riaphthaintoalightlnaphtha fraction having a diate naphthafraction having a boiling range ot about ITG-'220 F.,'and a heavy naphtha fraction having a boiling range of about 22o-410 F., a1-

kylating the separated light naphtha fraction with isobutane to transform olens to branched chain hydrocarbons.' discarding the separated in-

Images