US3094481A - Hydrofining process with temperature control - Google Patents

Description

June 18, 1963 R. M. BUTLER ETAL 3,094,431

HYDROFINING PROCESS WITH TEMPERATURE CONTROL Filed Sept. 9, 1960 I 2 Sheets-Sheet 1 FEED 3L, xpREACTOR PREHEAT FURNACE 20 34 TAIL ,A A A L ma l v v v %5 l5 SEPARATOR g |31J 33 PREHEAT 25 FURNACE ABSORBER 23 STRIPPER A A A r v v v 26 HYDROFORMER REACTOR SYSTEM 32 COMPRESSOR 3| F lG.-l 29 PRODUCT 3o SEPARATOR l 2 Roger M. Butler John A Bichord Inventors WPatenT Attorney June 18, 1963 Filed Sept. 9, 1960 RECYCLE TEMPERATURE, F.

R. M. BUTLER EIAL 3,094,481

HYDROFINING PROCESS WITH TEMPERATURE CONTROL 2 Sheets-Sheet 2 TYPICAL RELATIONSHIP OF VARIABLES F LINES OF CONSTANT FEED TO RECYCLE RATIO LINES OF CONSTANT ATF.

IN THE REACTOR BED uoo lzl I000 A O so 15 I00 EAT o 20 40 so I00 PERCENT OLEFINS m FRESH FEED Roger M. Butler Inventors John A. Bichurd By K 32 a 2 Patent Attorney United States Patent 3 094 481 HYDROFINING PROESS WITH TEMPERATURE CONTROL Roger M. Butler, Sarnia, Ontario, and John A. Bichard,

2 but below the temperature at which substantial deposits are formed.

It is the object of this invention to provide a simple, efiicient method whereby naphtha feedstocks can be Point Edward Ontario Canada, assignors to Essa 5 heatelcll tio temperatures above about 500 F. for charging search and Engineering Company, a corporation of O a mn'eatmg Delaware It is also an ob ect of this invention to provide a Filed Sept. 9, 1960, SenNo. 54,867 method for heating naphtha feedstoclcs, along with by- 5 Claims. (Cl. 208-255) drogen-containing treat gas to temperatures above 500 F. while avoiding the formation of solid deposits on heat This invention pertains to a hydrocarbon conversion exchanger or furnace tube process and more particularly to an impr ved Process for These and other objects will appear more clearly from the catalytic conversion of petroleum naphthas in the th d t il d ifi i and l i hi f H presence of added hydrogen. It has now been found that fouling of heat exchanger It is known that the quality of virgin or straight run or preheat furnace tubes can be avoided by mixing the as well as cracked or thermally reformed naphthas can relatively cold naphtha feed with a recycled stream of be improved by reacting such feedstocks with added hyheated hydrofined naphtha product and hydrogen. It has drogen .at elevated temperatures and superatmospheric been found that the h'ydrofined naphtha can be heated to pressures in the presence of hydrogenation-dehydrogenatemperatures of about 900-1000 F. at pressures of 200- tion catalysts. Such operations are referred to as hydro- 450 p.-s.i.g. and at hydrogen partial pressures of about forming, hydrofining, hydrocracking, hydrodesu g 100-350 p.s.i.g. with little or no thermal cracking and and the like. The purpose and result of these treatwithout the formation of deposits upon the preheater ments are to eifect a substantial reduction of the sulfur tubes that are formed when the fresh feed is heated to content, to saturate certain highly unsaturated gum-formvaporization in such tubes. While this procedure reing constituents and to saturate at least a part of the quires the recycle of hydrofined product and thus subolefins present, to improve the color and odor of the stantially increases the total throughput of the reactor, product, to produce aromatic hydrocarbons by the catathis can be taken care of by increasing the size of the lytic dehydrogenation of naphthenic and cyclic Olefin reactor, by increasing the space velocity or by a comcomponents. bination of the two. In existing plants the increase in In most of these processes the feed is supplied alon throughput will ordinarily be effected by increasing the or in admixture with the added hydrogen to the catalystspace velocity since rather large changes in space velocity containing reaction zone at temperatures in the range of can be made without any significant change in product from about 300 F. to 950 F. It is the general practice quality. In some instances dilution of the fresh feed to obtain such temperatures by passing the feed through with good quality recycle could improve the overall a heat exchanger provided with a large number of tubes quality of the feed to such an extent that running this of small diameter. It has been found, however, that as high quality feed at the necessary higher space velocity temperatures about 300 F. are reached, many naphtha would produce a better quality product than could be feeds tend to form deposits on the walls of the heat exobtained by running the fresh feed in a once-through changer and thus decrease the efliciency of the unit. In operation at low space velocity. some cases these deposits have even plugged the heat It has been disclosed in Pichler U.S. Patent 2,910,433 exchanger tubes. The main constituent of these deposits that cracked stocks contain appreciable proportions of diis iron and iron sulfide which is bound extremely tightly olefins and other gum-forming compounds which are conto the inside of the preheat exchanger tubes 'by a hydroverted to gums which deposit on heat exchanger surfaces carbon binder. The following table summarizes the when the oils are heated to temperatures in excess of analysis of typical deposits from a naphtha hydrofiner about 500 F. The Pichler patent proposes to overcome feed heat exchanger. this problem by preheating the charge stocks to such Elemental Analysis 1 Spectrophotometric Analysis 1 Deposit Source P r en Percent Percent Percent Percent Major Minor Large Trace Small Trace Ash 0 H N S y) (Oxide) ExchangeInletBonneL. 14.66 0.90 0.11 19 Fe Si M,Mn,Gi Mg,Pb,Cu,Zn 70.1 ReamcdFromTubes.. 8.46 0.52 Fe Si,Mn M0,Or,N1 Pb, 04, Sn, Mg 78.2

1 Atomic ratio of hydrogen to carbon in bonnet deposit is 0.74; atomic ratio of hydrogen to carbon in tubing deposit is 0.74.

2 Major: 10%; Minor: 110%; Large trace: 0.11%; Small trace: 0.17

It should further be noted that the inlet =bonnet which moderate temperatures, generally of the order of 500 normally operates at less than about 300 F. has about 15-16 wt. percent of the hydrocarbon binder. The deposit reamed from further down the tubes where temperatures as high as 900 F. are reached has only about 9 wt. percent of the binder.

It has been proposed to overcome this difficulty in various ways such as by distillation or by passing an inert gas through the feedstock to strip oif the free oxygen content, by 'blanketing the feedstock to minimize contact with air and by giving the feedstock a pretreatment with hydrogen in contact with a hydrogenation-dehydrogenation catalyst at temperatures above about 300 F.

F., at which no gum deposits take place and to make up the heat requirements of the hydrogenation system by higher preheats of the treated and stabilized recycle oil. It should be noted that this patent was concerned with the treatment of oils boiling essentially above the gasoline range and in an operation wherein the oil remains in liquid phase so that there is continuous washing of the heat exchanger surfaces and the catalyst bed with a recycle stream of the heated oil. In contrast to the Pichler teachings the naphtha feedstoclcs cannot be preheated to the moderate temperatures of about 500 F. without seriously fouling the heat exchanger surfaces and more importantly the preheat applied is sufficient to effect vaporization and, accordingly, there is no washing of heat exchanger and catalyst surfaces with liquid phase oil.

The feedstocks that can be treated advantageously by the process of the present invention are those hydrocarbons which boil within the gasoline boiling range, for example, straight-run naphtha, coker naphtha, thermally or catalytically cracked naphthas, and steam cracked naphthas. Ordinarily the fee-dstocks boil in the range of from about 150 to 450 F., but may be narrow boiling cuts from within this range. The process of this invention is particularly adapted for the treatment of cracked or coker naphthas especially those which tend to form deposits when heated to vaporization temperatures in heat exchangers or preheat furnace tubes.

In carrying out the process in accordance with the present invention, any conventional hydrofining or hydrogenation-dehydrogenation type catalyst may be used. Such catalysts include various oxides and sulfides of metals of groups VI and VII such as molybdenum, tungsten, vanadium, chromium and the like, or mixtures such as nickel-tungsten sulfide and cobalt molybdate, or mixtures of cobalt oxide and molybdenum oxide preferably deposited on a support or carrier material such as activated alumina, silica gel or activated alumina containing small amounts (2 to 10 wt. percent) silica. The preferred catalyst is one containing from about 5 to about 25 wt. percent of cobalt oxide and molybdenum oxide with the ratio of the former to the latter in the range of from about 1 to 5 to about 5 to 1, supported upon an adsorptive or activated alumina containing about 25 wt. percent of silica. Such catalysts are prepared by first forming adsorptive alumina, containing silica if desired, in any suitable or known way and then compositing molybdenum oxide and cobalt oxide therewith. The molybdenum oxide can, for example, be added as a slurry or it may be applied as a solution of ammonium molybdate. The cobalt oxide is conveniently added as a salt such as cobalt nitrate or acetate, salts which are readily decomposed to cobalt oxide and volatile materials. The catalyst may, if desired, be given an activation treatment prior to use in the hydrofiner by reacting the same with a suitable sulfiding agent such as a sulfur-containing feedstock, hydrogen sulfide, carbon disulfide, and the like. The amount of sulfur added for preactivation of the catalyst may vary from about 100% up to about 1500% of the stoichiometric quantity necessary to convert the cobalt oxide and molybdenum oxide to the corresponding sulfides.

The hydrofining reaction conditions vary somewhat, depending upon the nature of the feedstock, the character and quantity of the impurity or contaminant to be reerably 575-650 F, reaction pressure 50-500 p.s.i.g., preferably 200-250 p.s.i.g., and feed rate 1-20 v./v./hr.,

preferably about 2-10 v./ v./ hr. The hydrogen-rich treat gas which should contain at least about 25 volume percent hydrogen is supplied to the hydroiining reaction zone i at the rate of about 50-3000 s.c.i./b., usually about 500 s.c.f./b., and the hydrogen consumption in the hydrofining operation is about 1 to 600 s.c.'f./b., usually about 30 s.c.'f./b. V

In view of the exothermic nature of some of the reactions that occur in hydrofining, the temperature of the feed charged to the reaction zone is adjusted so that the temperature rise that occurs in the reaction zone will bring the reaction mixture up to the desired temperature level. In accordance with the present invention a portion of the hydrofined liquid product, preferably in admixture with the hydrogen-rich treat gas which may be recycle or fresh or a mixture of recycled and fresh hydrogen-rich gas is heated in a preheat furnace to a temperature sufliciently above the hydrofining reactor temperature that, upon mixture with the fresh feed at ambient temperature or at an elevated temperature in the event that the fresh feed is obtained directly from a fractionator, the resultant mixture will be at the desired temperature for introduction into the hydrofining reactor. Normally the hydrofined liquid product, in admixture with the treat gas, can be heated to 900-1000 F. for recycling in accordance with this invention with very little if any thermal cracking provided that the pipe layout and flow are suitably engineered. For example, at a design velocity of 40-60 ftJsec. for the recycle stream, the stream plus hydrogen can be conveyed up to about 4500 it. at 900 F. or up to about 330 it. at 1000 F. while holding cracking to less than about 1%.

Processing of stocks high in olefin content would ordinarily result in severe hydrofiner preheat exchanger fouling, rapid deactivation of the catalyst and a temperature rise, approximately five times the bromine number of the feed. A recycle rate of about 1:1 to fresh feed, and a recycle temperature of about 950 F. would provide suflicient heat to maintain a reactor inlet temperature of about 600 F. and a temperature rise within the reactor of about 50 F. with 25% olefins in the original feed. The lower the olefin content of the fresh feed, the higher the recycle rate must be. For example, a feed with zero percent olefins would require a recycle (at 950 F.) to fresh feed ratio of about 13:1 for a 650 F. operation.

Reference is made to the accompanying drawings wherein FIGURE "1 is a diagrammatic flow plan of one embodiment of the present invention and FIGURE 2 illus- :trates typical relationship of variables when operating in accordance with this invention.

In the flow plan of FIGURE 1, feedstock such as a naphtha fraction boiling between about 100 and 350 F. is supplied at system pressure through inlet line 10 at ambient temperatures. Recycle product and hydrogen containing treat gas is supplied through line 11 in sufiicient amount and temperature that upon mixing with the fresh feed supplied through line '10, the resultant mixture will be at the desired temperature for charging through inlet line '12 to the reactor 13. The reactor is charged with a suitable hydrogenation-dehydrogenation catalyst, preferably a cobalt oxide-molybdenum oxide on alumina catalyst as described above. The reaction mixture passes through the reactor '13 at a suitable rate to obtain the desired treatment of the feedstock, principally hydrogenation and hydrodesulfurizat-ion. The reaction products are withdrawn from the reactor via line 14, cooled and discharged into separator 15 wherein the normally liquid products are separated from the normally gaseous materials, the latter being removed as tail gas from the system via line 16. The normally liquid products are withdrawn from separator 15 via line .17 and discharged into the upper part of absorber stripper column .18. Hydrogen, or hydrogen-rich gas, is supplied through line 19 to the bottom of the column .18 in order to contact the hydrofined liquid product countercurrently, thereby shipping off hydrogen sulfide, ammonia, and the like from the nor-' mally liquid products. The gases pass overhead from column 18 and sufiicient gas is withdrawn through line 20 to serve as treat gas in the hydrofiner while the excess gas is discharged from the system through line 21. When hydroformer tail gas is used as the stripping gas in column 18, hydrocarbons contained therein, particularly C -C hydrocarbons, are absorbed in the liquid hydrofined product. The stripped, hydrofined liquid product containing hydrocarbons absorbed from the stripping gas are withdrawn from column 18 through line 22. Part of this liquid prodnet is discharged into line 26, mixed with hydrogen-rich recycle gas supplied through line 24, and passed through preheat furnace 25 where the mixture is heated to suitable temperatures for charging via line 26 to the hydroformer reaction system 27. it will be understood that this showing is purely diagrammatic and that this system may be a conventional fluid or moving bed hydroforming systeni charged with a molybdenum oxide or platinum-alumina catalyst, or it may be a fixed bed system preferably charged with a platinum-alumina catalyst which may be operated nonregeneratively, semiregeneratively, or regeneratively, all as well known in the art.

The hydroformer reaction products are discharged from the hydroformer reactorsystem through line 28, cooled and passed into product separator 29 wherein the normally liquid products are separated from the normally gaseous products. The liquid products are discharged from separator 29 through line 30 to suitable product blending or storage. The normally gaseous products, containing about 60-90% or more of hydrogen are taken overhead from separator 29 via line 31, passed to compressor 32 and thence recycled via line 24 to the hydroformer reactor system or passed through line 19 to the absorber stripper 18 as described above.

In accordance with this invention, a portion of the hydrofined liquid product is discharged from line 22 into line 3-3 for recycle to the hydrofiner. The hydrofined liquid product is mixed with the hydrogen-rich treat gas supplied via line 20 and the mixture is passed via line 34 into preheat furnace 35. Because of the improved stability of the hydrofined liquid product, it may be heated to temperatures of about 900-1000 F. in the coils in preheat furnace '35 without forming any appreciable deposits upon the coils. The preheated mixture of hydrofined liquid and hydrogen-rich treat gas is then passed from preheat furnace 35 through line 11 for intermixture with the fresh feed supplied through line 10. Ordinarily the fresh feed to recycle ratio will be selected depending on the olefin content of the fresh feed, the temperature rise in the reactor, the temperature of operation, and the temperature of the recycle stream as illustrated by the example in FIGURE 2. The relationship of these variables shown in FIGURE 2 is for a typical operation at about 355 p.s.i.g. 650 F. average reactor temperature, 1160 set. recycle gas (85 mol percent H per barrel of fresh feed which is a 165/320 F. VT naphtha at 275 F. The principal variables are the percent olefins in the fresh feed and the temperature of the recycle stream.

Working examples of this invention can be readily deduced from the correlation of variables shown in the attached FIGURE 2, for example:

At the aforesaid conditions, i.e. 355 p.s.i.g., 650 F. average reactor temperature, 1160 s.c.f. recycle gas rate, and 165/ 320 F. VT naphtha feed at 275 F., and with (1) 15%olefins in the feed,

(2) 50 F. temperature rise in the reactor, i.e. 625 F.

inlet temperature and 675 F. outlet temperature,

(3) 975 F. temperature of the recycle stream, i.e. hy-

drofined product plus hydrogen.

Then a fresh feed to recycle ratio of 1:14 would be used. This corresponds to point A in FIGURE 2.

The foregoing description contains a limited number of embodiments of the present invention. It will be understood that numerous variations thereof are still within the scope of the present invention.

What is claimed is:

1. A method for catalytically hydrogenating naphtha feedstocks which tend to form deposits upon heat transfer surfaces when heated to temperatures above about 300 F. which comprises hydrogenating the feed at elevated temperature and pressure to improve the stability of the naphtha, separating the hydrogenated liquid product from the accompanying gases, preheating a portion of the hydrogenated liquid product to a temperature of about 900-1000 F., mixing the preheated hydrogenated product with naphtha feed at a temperature substantially below 300 F. in suflicient amount that the resultant mixture may be charged directly to the hydrogenating step without further heating.

2. A method for hydrofining naphtha feedstocks which tend to form deposits upon heat transfer surfaces when heated to temperatures above about 300 F. which comprises treating the feedstocks at temperatures of about 500-750 F., at pressures of about 50-500 p.s.i.g. in the presence of about 5 0-3000 s.c.f./ b. of hydrogen-rich treat gas and in contact with an active hydrogenation catalyst, separating the hydrogenated liquid product from the accompanying gases, heating a portion of the hydrogenated liquid product to a temperature well above the temperature in the hydrogenation reaction step, mixing the hot hydrogenated product with naphtha feed at a temperature substantially below 300 F. in sufiicient amount that the resultant mixture can be charged directly to the hydrogenation reaction step without further heating.

3. A method for hydrofining naphtha feedstocks which tend to form deposits upon heat transfer surfaces when heated to temperatures above about 300 F. which comprises treating the feedstocks at temperatures of about 500-750 F., at pressures of about 50-500 p.s.i.g. in the presence of about 50-3000 s.c.f./b. of hydrogen-rich treat gas and in contact with an active hydrogenation catalyst, separating the hydrogenated liquid product from the accompanying gases, heating a portion of the hydrogenated liquid product to a temperature of about 900-l000 F., mixing the hot hydrogenated product with naphtha feed at a temperature substantially below 300 F. in sufiicient amount that the resultant mixture can be charged directly to the hydrogenation reaction step without further heating.

4. A method for hydrofining naphtha feedstocks which tend to form deposits upon heat transfer surfaces when heated to temperatures above about 300 F. which comprises treating the feedstocks at temperatures of about 500-750 F., at pressures of about 50-500 p.s.i.g. in the presence of about 50-3000 s.c.f./b. of hydrogen-rich treat gas and in contact with a cobalt oxide-molybdenum oxidealumina hydrogenation catalyst, separating the hydrogenated liquid product from the accompanying gases, heating a portion of the hydrogenated liquid product to a temperature well above the temperature in the hydrogenation reaction step, mixing the hot hydrogenated product with naphtha feed at a temperature substantially below 300 F. in suflicient amount that the resultant mixture can be charged directly to the hydrogenation reaction step without further heating.

5. A method for hydrofining naphtha feedstocks which tend to form deposits upon heat transfer surfaces when heated to temperatures above about 300 F. which comprises treating the feedstocks at temperatures of about 500-750 F., at pressures of about 50-500 p.s.i.g. in the presence of about 50-3000 -s.c.f./b. of hydrogen-rich treat gas and in contact with a cobalt oxide-molybdenum oxidealumina hydrogenation catalyst, separating the hydro genated liquid product from the accompanying gases, heating a portion of the hydrogenated liquid product to a temperature of about 900-1000 F., mixing the hot hydrogenated product with naphtha feed at a temperature substantially below 300 F. in sufiicient amount that the resultant mixture can be charged directly to the hydro genation reaction step without further heating.

References Cited in the file of this patent UNITED STATES PATENTS 2,866,750 Mosesman Dec. 30, 1958 2,901,417 Cook et al Aug. 25, 1959 2,910,433 Pichler Oct. 27, 1959 2,927,891 Weikart Mar. 8, 1960

Claims (1)

1. A METHOD FOR CATAYLSTICALLY HYDROGENATING NAPHTHA FEEDSTOCKS WHICH TEND TO FORM DEPOSITE UPON HEAT TRANSFER SURFACES WHEN HEATED TO TEMPERATURES ABOVE ABOUT 300*F. WHICH COMPRISES HYDROGENATING THE FEED AT ELEVATED TEMPERATURE AND PRESSURE TO IMPROVE THE STABILITY OF THE NAPHTHA, SEPARATING THE HYDROGENATED LIQUID PRODUCT FROM THE ACCOMPANYING GASES, PREHEATING A PORTION OF THE HYDROGENATED LIQUID PRODUCT TO A TEMPERATURE OF ABOUT 900-1000*F., MIXING THE PREHEATED HYDROGENATED PRODUCT WITH NAPHTHA FEED AT A TEMPERATURE SUBSTANTIALLY BELOW 300*F. IN SUFFICIENT AMOUNT THAT THE RESULTANT MIXTURE MAY BE CHARGED DIRECTLY TO THE HYDROGENATING STEP WITHOUT FURTHER HEATING.

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