US2800428A - Combination pretreating-hydroforming with platinum-type catalysts - Google Patents

Description

July 23, 1957 v R. J. HENGSTEBECK 2,800,428

COMBINATION FRETREATING-HYDROFORMING WITH PLATINUM-TYPE CATALYSTS 2 Sheets-Sheet 1 Filed Sept. 14, 1953 Hydrafarmed Producf %l aa aosw Naphf/ra Charge INVENTOR. Ruben J. Hengsfebec/r A TTOR/VEY July 23, 1957 J HENGSTEBECK 2,800,428

COMBINATION PRETREATING-HYDROFORMING WITH PLATINUM-TYPE CATALYSTS Filed Sept. 14, 1953 2 Sheets-Sheet 2 A/apf/Ia Charge /0 HYDROFO/W/NG 93 SYSTEM /2 I a a3 a4 /5 I g E w L z m /4 L nu m/Vm/mfi.

Haber! J. Hengslebeck United States 2,800,428 Patented July 23,. 1957 COMBINATION PRETREATING-HYDRGFORMING WITH PLATINUM-TYPE CATALYSTS Robert J. Hengstebeck, Valparaiso, Ind, assignor to Standard Oil Company, Chicago, 11]., a corporation of Indiana Application September 14, 1953, Serial No. 379,810

1 Claim. (Cl. 196-24) This invention relates to an improved combination pretreating and hydroforming system employing platinumtype catalysts, and it pertains more particularly to an integrated system for handling high sulfur naphthas.

In copending application Serial No. 347,635, filed April 9, 1953, a process is described for reforming naphthaboiling-range-hydrocarbons with platinum catalysts and for periodically regenerating and rejuvenating the catalyst in said system. It has been found that when the sulfur content of the charging stock is about .1 percent or higher the catalyst becomes deactivated more quickly and the problem of regenerating and rejuvenating the catalyst to substantially its original activity and original rate of de cline becomes more difiicult. While the desirability of de sulfurizing the charging stock has been appreciated, prior systems for efifecting said desulfurizations have been unduly expensive both from the standpoint of capital investment and from the standpoint of operating costs.

An object of my invention is to provide a unitary pretreating-hydroforming system which not only eifectively desulfurizes the charging stock before it is subjected to hydroforming conditions, but which also removes from the charging stock other components which have a tendency to decrease the activity of platinum hydroforming catalysts. A further object is to minimize the investment and operating costs of charge stock pretreating and overall operation. Another object is to provide an improved method and means for utilizing the heat contained in products leaving the desulfurization zone of a hydroformer charge preparation system. A still further object is to provide an improved method and means for minimizing the deactivation of platinum-containing hydroforming catalyst in a hydroforming system for effecting conversion of naphtha components boiling above 360 F. as well as components boiling below that temperature. Other objects will be apparent as the detailed description of the invention proceeds.

In practicing my invention a naphtha charging stock which may have an end point of about 400 F. or higher and which may contain about .02 to 2 percent or more of sulfur is preheated in heat exchangers, heated to a temperature of about 600 to 800 F. and desulfurized by contacting at said temperature under a pressure of about atmospheric to 500 p. s. i. g. or more with a desulfurization catalyst such as bauxite, fullers earth, group Vi metal oxides on alumina such as chromia-on-alumina, group V and VI metal oxide mixtures on alumina such as nickel tungstate, cobalt molybdate or even a platinum-onalumina catalyst which may have previously become relatively deactivated in hydroforming operations. The space velocity in the pretreating or desulfurizing zone will depend upon the particular charging stock and catalyst and whether or not hydrogen is passed through the desulfurizing zone with the charging stock; generally speaking, the space velocity is of the order of about 1 to liquid vol umes of charging stock per hour per volume of catalyst in the reactor. The hot efiluent from the desulfurizing zone supplies the required heat not only for effecting fractionation of the naphtha (either before or after the desulfurizing step) but also for recovering condensable hydrocarbons which are absorbed from net tail gas in the heavy naphtha fraction removed from the fractionator and for supplying preheat to the charging stock entering the desulfurizing zone.

In one embodiment of the invention the entire naphtha stream may be desulfurized prior to fractionation so that the fractionator serves the function of a stripper to remove C5 and lighter hydrocarbons, HzS, oxygen and moisture from the naphtha fractions which are subsequently hydroformed with platinum-containing catalysts. The naphtha fraction boiling in the range of about to about 360 F. is charged to the first hydroforming stages together with recycled hydrogen so that the platinum catalyst will not be unduly deactivated by the presence of hydrocarbons boiling above 360 F. When the heavy ends are excluded from the hydroforming system, the hydroformed product does not require rerunning since it Will contain substantially no components boiling above the desired gasoline end point. However, when it is desired to hydroform the naphtha fraction boiling above 360 F., it may be mixed with the effluent from a first or intermediate hydroforming vessel which efiluent may serve as a heat carrier for supplying endothermic heat of hydroforming the heavy fraction in the final hydroforming step. The by-passing of the initial hydroforming reactors, the mild conditions in the final reactor, and the presence of the aromatics in the efiluent with which heavy ends is admixed minimizes catalyst deactivation so that it requires less frequent regeneration and rejuvenation.

In another embodiment of the invention the naphtha may be fractionated before desulfurization so that only that fraction which boils in the range of about 150 to about 360 F. is desulfurized. Here again the hot desulfurization product stream supplies not only the heat required for naphtha fractionation but also the heat required for recovering light hydrocarbons from absorber oil which has been used to scrub net tail gas.

The invention will be more clearly understood from the following detailed description of specific examples read in conjunction with the accompanying drawings which form a part of this specification and in which:

Figure 1 is a schematic flow diagram of a commercial unit for pretreating and hydroforming a high sulfur naphtha with platinum-containing catalyst wherein the entire naphtha charge is desulfurized,

Figure 2 is a schematic flow diagram of such a unit wherein high boiling naphtha fractions are not desulfurized and fractionation precedes desulfurization.

The charging stock in these examples is a naphtha containing about .05 weight percent sulfur and having an end point in the range of about 400 to 450 F. which contains substantially no olefins (although the invention is not limited to olefin-free charging stocks), and consists chiefly of parafiins and naphthenes, the naphthene content preferably being in the range of about 30 to 50 percent. Such a charging stock may have an F] clear octane number of about 50.

Referring to Figure 1, about 10,000 barrels per day of such naphtha at about 100 F. is introduced by line 10 at a pressure of about 100 p. s. i. g. through heat exchanger 11 wherein it is heated to about F. It then passes by line 12 through heat exchanger 13 wherein it is heated to about 400 to 500 F. Next it passes through coils 14 of preheater furnace 15 and thence is intro duced by line 16 to desulfurizing vessel 17 at a transfer line temperature of about 750 F.

The desulfurization vessel in this example is charged 3 with a bauxite desulfurizing catalyst but it should be understood that any known types of desulfurizing catalysts may be employed. Since these catalysts per se form no .:.;...part of the. present invention and the. catalysts and condi .,tions..for employing them are welLknowntothose skilled in the.art,..no detailed description of the ,desulfurizing step .is necessary.

A The hotdesulfurizedproduct,vaporstream leaves desulfurizingvesselfl through linelS and. ispassed through heat exchanger 19 wherein it is, cooled to .about 550 F.,

the base .thereofby line 23,..passing the withdrawnliquid through heat exchanger; andreturning itby line 24 to the base of the towerso. that thetower operates at a i .bottomtemperaturebf about 490 F.

The overheadfrom tower22 passes by line 25 through heat exchangerv 11 and cooler 26 to receiv'er27. which is held at about 100,F. and 20. p. s. i. ,g. HzS and other uncondensed gases are vented ,from thereceiver by line 28. A suflicient amount of reflux .condensateis returned by pump 29 and line 30 to maintain a top temperature in the vfractionator of about 215 F. Light hydrocarbons boiling below about 200 F. are withdrawnby line 31.

about 850 to 950 F. with an overall space velocity of about 1 to 5 and in the presence of about 1,000 to 8,000 standard cubic feet of recycled hydrogen per barrel of fractionated naphtha charged.

The product stream from the final hydroforming reactor is passed by line,,47. through heat exchangers 48 and 34 and thence through cooler 49 to separator 50 wherein tail gas, consisting chiefly of;hydrogen, is separated from the remaining product. The product withdrawn through line 51 may bedepropanized and/or debutanized but it will require no, rerunningto, remove heavy ends if the initial charging stock introduced through line 32 is of the order of 350 to 370 F. end point.

The required hydrogen recycle is returned -by compressor 52 through line 53, heatexchanger 48 and heating coils 54 and 55, then returned by line 56 for admixture with preheated charge in line 37.

The net tail gas producedin the system is withdrawn from separator. 50 through line,.57 and introduced at the base of absorberor scrubbing -.vessel 58. ;The absorber or scrubbing .oil is high boiling ,naphtha withdrawn. from thebaseof fractionator 22'through line 59, heat exchanger 60 and ,cooler 70, the cooled liquid being intro- The fraction of desulfurized. naphtha boiling in the range of about 200 to 360 F. is withdrawnby line 32 to intermediate storage, or surge tanks (not shown) and is passed by pump 33 through heat exchanger 34, preheater coils 35 in furnace 36 and line 37 to first hydroforming reactor vessel 38 together with recycled hydrogen as will be hereinafter described. The total stream from vessel 38 is passedvby line 39-through heating coils 40 and line 41 to the second hydroforrning vessel 42., The hydroformed product from the second reactor passes by line 43 through heating coils 44 and 1ine 45 to third hydroforming reactor 46. It should be understood that four or more hydroforming vessels may thus be employed with reheatpercent of platinum, preferably about .3 to .5 weight percent, and is prepared by contacting an aqueous solution of chloroplatinic acid containing about 3.5 grams of platinum per liter with an ammonium sulfide sulfurizing agent for converting the platinum into a sulfurized form of platinum sulfide in a stable aqueous solution, then combining this true or colloidal solution with hydrous alumina prepared as taught in U. S. Re. 22,196, the resulting mix- ,ture then being dried and calcined. Thecatalyst may contain about thesame amount, by weight, of a halogen such as chlorine or fluorine as platinum, but it should be substantially free from sodium, iron and molybdenum oxides. Other methods of preparing the alumina base may be employed but best results are obtained by using an alumina of the highest purity obtainable. Also, other methods may be employed for incorporating the platinum and other types of supports may be used but, since the catalyst per se forms no part of the present invention, they will not be described in further detail.

No novelty is claimed in the hydroforming step per se and this step, together with the steps of regenerating and rejuvenating the catalyst, is described in some detail in copending applications, Serial No. 347,635, filed April 9, 1953, and Serial No. 355,004, filed May 14, 1953. The naphtha fraction which is charged to the hydrofonning system through line 32 should boil within the range of 150 to 360 F. and have a sulfur content below .02 1 weight percent and as low as commercially feasible. The hydroforming may be effected at a pressure of 200 to 500 p. s. i. g.- or more at a temperature in the range of duced by pump 71 vat the top of the absorbeL'HUnabsorbed gas is withdrawn through line 72 for utilization elsewhere. The base of the absorber may beheated to a temperature of about 230,F. by suitable reboiler or heat exchange coils 73;, such a heateris not essential and if it is employed the heat may be derived, from hot desulfurized product from vessel 17. The purpose of the absorber is to recover C3 or C4 and heavier. condensable hydrocarbons from net tail gas. The rich absorber oil containing such condensable hydrocarbons passes by line ,74 through exchanger 60 and line 75 at a temperature of about 328 F. either to line21or directly to fractionating tower 22. It will thus be seenthat heat exchanger 19, which serves as areboiler and asource of heatsupply for the fractionator, supplies not only the heat required for fractionating the naphtha charge but also serves to supply the heat for stripping condensables out of absorber oil.

That portion of the heavy naphtha boilingaboveabout 360 P. which is not required for use as absorber oil may be withdrawn by line 76 from the system. When it is desired to hydroform this fraction it may be. introduced by li'ne'77 for admixture with the hydroformed product stream in line 43 and preheated with this stream in-coils 44 and charged to the final hydroforming reactor 46. Alternatively it may be introduced through 'line 78 directly to line 45, with or without a preheating to bring it up to conversionternperature. In fact, the final hydroforming stage may be at a sufficiently lower temperature (i. e.

. about 50 F. to 100 F. lower) than the preceding stage volume of hydroformed product from line. 43 thus stores sufiicient heat to effect both, its final conversion in the last reactor and also the totalconversionof the heavy fraction. The dilution effect of the partially hydroformed product coupled with its heat carrying capacity, thus provides a method of hydroforming the heavy fraction with minimum catalyst deactivation.

In Figure 2;the naphtha charge from source ,10 is preheated in exchanger 11 and passed by line 12-together with richabsorber oilfrom line 74 trough line 79, exchangers 80 and 81 and line 82 to 'fractionator22"'which in this case fractionates the naphtha before it undergoes desulfurization. The naphtha fraction boiling in the range of 200 to about 360 F. is withdrawn through line 83 and introduced by pump 84 through coils 14 in preheat furnace 15', thence through line 16' to desulfurization vessel 17 at a transfer line temperature of about 750 F. The hot desulfurized product stream passes from vessel 17' through line 18', heat exchanger 19 and heat exchanger 81 and thence through line 85 to stripper 86. Overhead from the stripper is cooled in cooler 87, introduced into receiver 88 from which H28 and other uncondensed gas is vented through line 89. The condensate is withdrawn by pump 90, a part being returned by line 91 for use as reflux in the top of the stripper and the remainder withdrawn as light product through line 92. The stripped stream passes by line 93 to the hydroforming system 94 from which hydroformed product is withdrawn by line 95. Net tail gas is introduced by line 57' to the base of absorber 58. High boiling fractions from fractionator 22 are withdrawn from the fractionator at about 490 F. through line 59', cooled to about 225 F. in exchanger 80, further cooled to about 100 F. in cooler 70' and introduced by pump 71 to the top of the absorber. Unabsorbed gases are vented through line 72. In this case the high boiling fraction has not been desulfurized and it is preferably withdrawn from the system through line 76.

In the system of Figure 2, as well as that of Figure 1, the heat content of products leaving the desulfurizing vessel supplies not only the heat required for fractionating the naphtha but also for boiling condensables out of absorber oil and preheating incoming charging stock. The mixed absorber oil and preheated feed enters exchanger 80 at 167 F. and leaves the exchanger at 250 F. and it is further heated in exchanger 81 to 335 F. at approximately which temperature it enters the fractionator. The hot desulfurized stream enters exchanger 19 at 750 F. and is therein cooled to 550 F., it being further cooled to 290 F. in exchanger 81 before being introduced to stripper 86. No further description of Figure 2 appears to be necessary in view of the previous description in connection with Figure 1, the chief difierence being that in Figure 2 fractionation precedes desulfurizing so that the heavy naphtha fraction is not desulfnrized and so that the desulfurized fraction requires a stripping in a vessel which is separate from fractionator 22'. The hydroforming system may be substantially the same as described in connection with Figure 1.

As hereinabove pointed out other known desulfurizing catalysts may be employed instead of bauxite. When a hydrofining catalyst such as alumina-supported cobalt molybdate is employed, the hydrogen stream removed from separator 50 through line 57 is introduced by line 57a to line 12 and passed through the desulfurizing zone 17 along with charging stock. In this case net tail gas from line 28 is introduced through line 28a to the base of absorber 58 so that the absorber will recover condensable hydrocarbons produced in the hydrofining step as Well as in the hydroforming step although the off gas from line 72 in this case will contain H2S. When a molybdenacontaining catalyst is employed in the desulfurizing step the system of Figure 1 is preferred so that any molybdenum contaminant in the desulfurized product stream may be removed from the fraction which is introduced by line 32 to the hydroforming step. If the heavy fraction withdrawn through line 76 contains molybdenum contaminant it is preferably not charged to the hydroformer.

When a desulfurizing catalyst such as platinum-onalumina is employed in vessel 17 somewhat lower temperatures may be used than are employed in the case of bauxite and, here again, the hydrogen stream from separator 50 may be admixed with charge entering the desulfurizing step and net tail gas from separator 27 may be introduced by line 28a to absorber 58. When desulfurizing catalysts are employed which are more eifective in the presence of hydrogen and which contain no component which might poison the platinum catalyst, the system of Figure 2 may be modified by introducing the hydrogen stream from line 57 through line 57a to the charging stock stream entering preheater 14' and the net tail gas from the separator 88 may be introduced by line 89a to absorber 58. Other modifications and alternative operating conditions will be apparent from the above description to those skilled in the art.

It should be noted in the system of Figure 2 that stripper 86 operates at approximately 300 F. so that the stripped stream which enters the preheater of the hydroforming system through line 93 is relatively hot. A small amount of stripping gas may be introduced at the base of column 86 if desired and sufiicient reflux is returned through line 91 to prevent the loss of any substantial amount of hydroformer charge with lighter products which are withdrawn through line 92.

I claim:

In a process for treating a naphtha containing more than about .02 weight percent of sulfur wherein at least -a part of said naphtha is desulfurized by contact with a desulfurization catalyst in a desulfurization zone at 600 to 800 F. to convert its sulfur content to HzS, said HzS is removed from desulfurization zone effluent, at least a part of the efliuent is charged to a hydroforming operation comprising contact with platinum-on-alumina catalyst in at least three heating-reaction stages at pressures in the range of about 200 to 500 p. s. i. g. and temperatures in the range of about 850 to 950 F. in the presence of recycled hydrogen and wherein a net gas stream containing hydrogen, H28 and light hydrocarbons is obtained, the improved method of operation which comprises countercurrently contacting said net gas stream with an absorber oil to obtain enriched absorber oil containing light hydrocarbons, introducing said enriched absorber oil with said naptha to a fractionating zone, returning a part of the bottoms from the fractionating zone as said absorber oil to said countercurrent contacting step, pumping a fraction of the naphtha boiling chiefly in the range of about to 360 F. from the fractionating zone to the desulfurizing zone, introducing hydrogen produced in the hydroforming operation to said desulfurization zone, heat exchanging efliuent from the desulfurizing zone with liquid entering the fractionating zone whereby the heat contained in said efliuent is utilized not only for fractionating said naphtha but also for distilling light hydrocarbons from enriched absorber oil, stripping said efliuent at a temperature of about 300 F. after said heat exchange step whereby not only HzS but water and light hydrocarbons are removed as said net gas stream from said effluent and introducing the hot stripped efiiuent as charging stock to said hydroforming operation.

References Cited in the file of this patent UNITED STATES PATENTS 1,981,305 Bray Nov. 30, 1934 2,035,467 Faragher Mar. 31, 1936 2,273,299 Szayna Feb. 17, 1942 2,338,573 Creelman Jan. 4, 1944 2,642,381 Dickinson June 16, 1953 2,651,597 Corner et a1 Sept. 8, 1953 2,671,754 De Rosset et al Mar. 9, 1954 2,691,623 Hartley Oct. 12, 1954

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