US2392579A - Process for the treatment of olefinic sulphur-bearing gasoline to effect substantialdesulphurization and refining - Google Patents

Description

Jan. 8, 1946. R; M. COLE 2,392,579

PROCESS FOR THE TREATMENT OF OL'EFINIC SULPHUR-BEARING GASOLINE TO EFFECT SUBSTANTIAL DESULPHURIZATION AND REFINING Filed Feb. 10, 1945 InvenTor'. Robcrt' M. Cow.

Es his ATTornzL &l

Patented Jan. 8, 1946 PROCESS FOR THE TREATMENT OF OLE- FINIC SULPHUR-BEARING GASOLINE TO EFFECT SUBSTANTIAL DESULPHURIZA- TION AND REFINING Robert M. Cole, Oakland, Calii'., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application February 10, 1945, Serial No. 577,181

Claims.

This invention relates vto the treatment of thermally cracked gasolines, catalytically cracked gasolines, thermally reformed gasolines, and similar materials of the gasoline boiling range containing substantial amounts of olefins and/or other unsaturated bodies and other impurities such as sulphur compounds, nitrogen compounds. etc.. to effect a substantial desulphurization and to remove and render innocuous various gum-forming bodies. More particularly the invention relates to the treatment of such materials by the combined action of hydrogen and catalysts under such conditions and in such a manner as to afford the desired finishing or refining treatment with a minimum loss of material, minimum consumption of hydrogen, and with substantially no depreciation of the antikncck characteristics.

Gasolines produced by thermal cracking, gasolines produced by catalytic cracking, and gasolines produced by thermal reforming of various gasoline stocks usually have the following characteristics: They contain appreciable quantities of olefins and other unsaturated bodies and consequently have a high bromine number and high acid heat. They contain appreciable amounts of sul hur compounds. nitrogen compounds. etc. They have poor color stability, poor gum stability, andpoor lead susceptibility. Consequently these stocks generally require some sort of finishing treatment to make them acceptable for use in gasoline of present-day quality. The conventional method of finishing these materials is the conventional sulphuric acid treatment followed by a doctor treatment and rerunning. This method has the recognized disadvantages of incomplete sul'ohur removal, high acid consumption, poor yields, and an appreciable de reciation of anti knock properties. In view of these disadvantages considerable attention has been given to the finishing of such materials by catalytic hydrogenation. Certain such processes have been proposed. However, the proposed processes have certain disadvantages-and furthermore are usually too costly to make their use economical exce t in the special case of the production of substantially saturated blending materials for premium grade aviation gasoline.

The present process provides a means for effecting excellent desulphurization and refining while affording a product of excellent anti-knock characteristics. These desirable results are obtained with a low consumption of hydrogen and with excellent catalyst life. Consequently the process of the invention is also applicable and tion. The loss of octane number usually encountered in the catalytic desulphurization by bydrogenation of olefinic gasolines of the type described is due largely to the fact that these relatively drastic hydrogenation conditions are re- 'quired. Thus, when eflecting the hydrogenation in the usual manner to the extent necessary to effect a satisfactory removal of sulphur an appr'eciable amount of the aromatic hydrocarbon constituents of the gasoline is hydrogenated to naphthenic hydrocarbons of relatively low antiknock value. Also, at least a large part of the normal oleflns which have good anti-knock properties are hydrogenated to the corresponding normal paraffin hydrocarbons having very poor anti-knock properties. These undesired hydrogenations are. not only particularly detrimental in decreasing the anti-knock properties of the gasoline, but also account for a large part of the hydrogen consumption.

In my co-pending application, Serial No; 568,843, filed December 19, 1944, .of which this application is a continuation-in-part, I have shown that the various normal constituents of such gasolines differ somewhat in their susceptibilities toward hydrogenation. I have shown that when treating aromatic fractions such as toluene, the hydrogenation of the toluene may be prevented while allowing the hydrogenation of 'thiophenic sulphur compounds to be carried substantially to completion by maintaining a small concentration of oleflns in the hydrogenation reaction zone. For this purpose, small amounts of olefins are added, preferably at points along the length of the reaction zone. v A similar 7 principle may be applied also to preventto a certain extent the undesired hydrogenation of normal olefins. The process of the present invention makes use of both of the above principles for the 'catalytic treatment of cracked gasolines and similar oleflnic materials of the type described and allows such materials to be substantially de-- sulphurized and hydrofined with minimum con-.

ing' the olefinic gasoline in the presencev 61 a fraction or the partially-treated Product, obtained as later specified, with hydrogen in the presence of a sulph-active hydrogenation catalyst under" suitable conditionaseparating the product into a plurality of fractions having different boiling ranges, withdrawing the lowest boiling fraction and blending it with a portion of the higher boiling material, and recycling at least a portion of the higher boiling material to the hydrogenation zone, the through put rate and recycle ratio being adjusted to provide the desired quality of the blend withdrawn.

The process will be described in more to scale, a suitable assembly of conventional apparatus arranged and adapted for operationaccording to the process of the invention. Referring to the drawing the oleflnic gasoline, which may be any gasoline of the type described and may boil from about 100 F. up to about 425 F.or withinthis range,-is introduced via line I and pump 2. 'Ihisgasoline, which for the The higher scum; fraction a withdrewninmm via line II to' a second fractionating tower l'l wherein it is again separated into a lower boiling fraction and a'higher boiling fraction. The higher boiling fraction from fractionator I1 is withdrawn in part via line is to a third fractionating tower I! wherein it is againseparated into a lower boiling fraction and a higher boiling fraction. The higherboiling fraction is withdrawn via line 20. Part of it is recycled as hereinaiter specified and the remainder is withdrawn via line 25. Thelower boiling fractions from the 1 three fractionating towers are. withdrawn via purpose of illustration may be considered to be a debutanized catalytically cracked gasoline boiling up to about 360 F.,'is mixed with an appropriate amount of heavy gasoline, obtained as hereinafter specified, entering via line 3. The

mixture is preheated in coil 4 of furnace 5. Re-

- cycled gas rich in hydrogen is simultaneously preheat edin coil ii of furnace 5 and is mixed with the hydrocarbon feed. 'Iihe. mixture at aboutthe desired reactor inlet temperature passes vialine late a catalytic converter or reactor 8 provided- 'with-.a p sulph-active hydrogenation catalyst. :The' catalyst .inreactor 8 may be any 01' :thecknown conventional-I sulph-active hydrogen'ation catalysts. ,Suitable catalysts, by way of example, are tungsten sulphide-nickel sulphide, cobalt sulphiiie, molybdenum sulphide, cobalt thiomolybdate, iron sulphide, molybdenum oxide and the various composites thereof which, furthermore, may or may not contain such materials as alumina, ma'gnesia,silica, ,zinc oxide,

chromium oxide, etc as stabilizers, promoters, or supports. The temperature in reactor is maintained below about 950 F., and is usually above about 400 F. Thus, typical temperatures arc -for example, between about 450 F. and.

850 F. The pressure is usually in the order of 200-1000 p. s. i. The mol ratio of hydrogen to hydrocarbon in the feed to the reaction zone is preferably between about 2 and 30.

The treated product leaves the reactor via I line 9. and cooler II and passes to a separator. Gas rich in hydrogen is removed from the upper part of separator l0. This gas is usuall subjected to one or'more compression and cooling steps to separate condensablehydrocarbonsand 7 is then usually cycled through aJ-hydmgen sulphide removalsystem, such as a Shell phosphate.

system, to remove hydrogen sulphide formed in reactor 8.. These refinements form n'o part of the invention, arewell understood in the. art,

" withdrawn via line 20 may have been treated at 7 an efl'e'ctive liquid hourly space velocity of 1.

and are consequentlynot shown in the drawing.

The hydrogen gas isrecycled to the heater via line 1 Hydrogen for the process is supplied via line I 3. V

The liquid product fromiseparator I 0 is boiling fraction 9. higher boiling fraction,

or asingle fractionation .colinnn adjusted and a designed to'aflord a lower boilingov'erhead prode a" d P s a'z tionatin tower l wherein'it is separated :into .a lower lines 22, 23 and 24 to .line 25. This mixture is combined with a portion of the higher boiling,

fraction from line and the blend, now corresponding approximatelyin boiling curve to the original feed. P 5 8 to a caustic scrubber 21 to remove dissolved hydrogen sulphide. The treated product is withdrawn via line 28. A substantial part of the higher boiling fractions from the respective fractionators is withdrawn via lines 29, and zo saa. recycled via line 2|, pump 32 and line 3. .This blend is the heavy gasoline referred to above.

The cut points between the various fractions are not critical and may be made at any convenient points. In general, however, the end point of the first or lowest boiling fraction withdrawn via line 22 is in the order of 180 F.-225 F. Thus, for instance,'the initial boiling points'of the three heavy fractions in the operation described above may be 200 F., 250 F.,and 300 respectively.

The composition and amount of the heavy gasoline recycled via line 2i depends upon the particular character of the feed and is preferably adjusted during operation to obtain the optimum results. In general, the amounts of the higher, 9

boiling fractions recycled are roughly proportionalto their molecular weights or boiling points. Thus,-in the described operation, by way ofexample, the heavy gasoline may consist of 40% of the heavy material withdrawn from fractionator 15, of the heavy material withdrawn from fractionator l1, and of. the heavy material withdrawnv from fractions-hr It. Since the heavy fraction from fractionator I5 contains considerable amounts of the same components as found in the heavy fractions from fractionators "and I9 it is seen that the'concentration of heavy materials is greatest in the higher boiling range. Likewise, the treatment afforded the product is approximately inversely proportional to the molecular weight or boiling range. For example, the material withdrawn via line 22 may have been treated at an effective liquid hourly space velocity of 15; that withdrawn via line 23 may have been. treated at an eflective liquid hour-' 1y space velocity of 8; that withdrawn via. line 24 may have. been treated at an effective liquid hourly space velocity of 3: and' the material While the pro'cess described above for purposes of illustration involves three separate fractionation steps and consequently involves six separate hydro'carbonfractions it will be appreciated. that the principle of the invention may be applied with two or even one distillation st ps uct, -a heavy'bottonji product, one'or' more intermediate side streams may be-employed. For

100- r. meteor l'tma'ybe treated and the products separated into three fractions boiling. for

instance, between 100 I".-200 l"., 200' 15-800 1,]

s n-sao' R, respectively. .The lower or 100' l t-200 F., fraction of the product may be withdrawn and blended with appropriate amounts of the two heavier fractions. andporamounts to afford the desired results. "Hills. when treating a thermally cracked gasoline as the ieed to a very mild 'hydrogeiiation treatment, is thereby to preserve the maior part of the oleflns in this portion of the feed and at the same time tions or the zoor.-'aoo r. fraction and the 300 l".-880 1''. fraction may be recycled in such described. the liquid hourly 8M velocity may i be adjusted, for example, so that the 100 l".-200

1''. fraction has the following properties:

The properties oi the corresponding fraction of the feed are given for comparison. The amount to utilize these lower boiling oleflns to prevent i hydrogenation of aromatic hydrocarbons in the more drastically treated higher boiling fraction of the feed. Expressed in another way, the oleflnic constituents of the feed are hydrogenated in the present process approximately in proportion to their molecular weights or boiling points.

Thus, the lowest boiling oieflns, for instance those boiling below about 200 F.,' are hydrogenated only to a minor extent, for, instance or less, and the highest boiling oleflns, for instance in the heaviest 50 F. boiling range portions of the ole- .finic gasoline. are substantially hydrogenated; for

instance, 75% or more. It will be noted that in the present process. the feed and product have essentially the same boiling curve as measured, for example, by an AS'I'M distillation, whereas the boiling curve of the combined feed to reactor 0 is concentrated in higher boiling constituents.

' The above objects cannot be obtained eitherby of 200 F.-300 F. fraction of the product blended with the feed and hence recycled may be adjusted to aflord a product having, for instance, either of the twofollowing sets of properties:

,3 200 F.300 F. iraction- Of the 0f the 0f the prufiuci rufiuui feed Percent sulphun 0. 2 0. 4 0. 7 Brominenumber 56 76 87 ASTM octane number (clear) 69. l 70. 7 70. 4 ASTM octane number (1 cc. 'lEL) 75 74. 7 73. 4

The treatment required for attaining these results in the hydrogenation process described above corresponds, for example, to an effective liquid hourly space velocity of about 20 at a temperature of about 550 F.-600 F., i. e. a liquid hourly space velocity affording a contact time equivalent to that in treating this fraction in the absenceof other fractions in a single pass at a liquid hourly space velocity of 20. The amount of the 300 F.-380 F. fraction recycled maybe adjusted to afford a product having, for instance, the following properties:

In order to obtain such results an effective liquid hourly space velocity between about 0.5 and 2 is generally required.

An object of the described operation is to subject in a single apparatus and in a most advantageous way the higher molecular weight and higher boiling constituents of the feed stock to a a substantial and relatively thorough hydrogenation treatment approximately proportional to the molecular weight or boiling point to remove thiophenic sulphur compounds while at the same time subjecting the lower boiling components of separating the feed initially into separate frac-- tions and treating each fraction separately or by treating the whole fraction under different conditions adapted to efiect the desired hydrogenation of the higher boiling olefins. The first method doesnot aflord the desired protection of the high anti-knock aromatic hydrocarbons by the lower boiling oleflns and the second method produces excessive saturation of lower boiling Oleflns and loss in anti-knock properties.

I claim as my invention:

1. A process for the treatment of olefinic sulphur-bearing gasoline to effect a substantial desulphurization and refining thereof which comprises-adding to said gasoline a portion of heavy gasoline obtained as hereinafter specified, subjecting the mixture to the action of a mo] excess of hydrogen in the presence of a sulph-active hydrogenation catalyst at a temperature between about 400 F. and 950 F. and under superatmospheric pressure and at a space velocity adjusted to give hydrogenation of only a part of the lowest boiling olefins, separating the product of said' treatment into a plurality of fractions of different boiling ranges, reble'nding the lowest boiling fraction with amounts of the higher boiling material suflicient-to produce a blend having cssentially the ASTM distillation curve of the untreated gasoline and recycling a second substantial portion of the higher boiling material as the boiling ranges, reblending the lowest boiling fraction'with amounts of the higher boiling material sufficient to produce a blend having essentially the ASTM distillation curve of the untreated gasoline and recycling a second substantial portion of the higher boiling material as the heavy gasoline specified above, the relative proportions of said sulphur-bearing gasoline feed and said heavy gasoline being adjusted to afford a si'ibstantial hydrogenation of olenn sin said heavy z'asolineand only a minor hydrogenation of the lower boilingoleflns. c 1 3. A process for the treatment of 'oleflnie sulphur-bearing gasoline to eiiect a substantial desulphurization and thereof which opinprises adding to said gasoline a portion or heavy v gasoline obtained as hereinafter. specified. sub-,

Jecting the to the actibnQf g, mol excess "oi hydrogen in the presence, or a suIph-acti've by drogenation catalyst at a temperature between about 400 F. and 950 F; and und p ranno pherjici pressure and at a space velocity adjusted a treatment into a plurality of'jfractions or t ili e ranaes i l ding a. low b i in timer; and 225 1"., reblendinz isaidllower oleilnic fraction with amountsot the materialfsuflicient to produce a v essentially AB'I'M distillation emeot m untreated gasoline and recycling a second T'gnbstantial portion of the higher boiling as the heavy gasoline specified above, the amount of said higher boilinz material recycled such that the portion ofthe am or the heaviest soa'r 'boiling tion of said oleflnic gasoline feed is ai-alienated. 4. Process according to claim 1; in, which Peratulfe between $50 F.'.and, 859? FQ I l 5.,In'a process for -treatmen't oi oleflnic lflphurqbearins gasoline; .to eflectv. a substantial desulphuriaation and refining thereoiby catalytic h dro enationin the presence oLasu'lpm-active hydrogenation treatment is ,carried.o1,itatla ten1- hydrogenationicatalystlat a temperaturebetween about, 4009.1, and 95 0?Fb,:.theimprovementwhich comprises charging to the treatment olefinic sulphi.1r-bearinxv 8asollne,'with from said v gi've hydrogenation oi'only a minor-part0! the lowest boiling oleflns. separating the product of c fraction having an end point. between 4 ROBERT M. com.

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