US2983676A - Hydrorefining of heavy mineral oils - Google Patents

Description

May 9,' 1961 w. w. HOWLAND 2,983,676

HYDRCREFINING OF HEAVY MINERAL OILS Filed Jan. 13, 1958 JEP/IRTOR HYDROREFINING OF HEAVY MINERAL OILS Ward W. Howland, Anaheim, Calif., assignor to Union 011 Company of California, Los Angeles, Calif., a corporation of California i Filed Jan. 13, 1958, Ser. No. 708,708

17 Claims. (Cl. 208-218) This invention relates to methods for the catalytic hydrorefining of heavy mineral oils, particularly crude oils, and including specifically crude shale oils. In broad aspect, the process consists in first preheating the feedstock to approximately the desired hydrorelining temperature, then partially vaporizing the heated oil to recover a light overhead fraction and a heavy bottoms fraction, the fractionation being carried out at a pressure substantially lower than the pressure to be used in hydroreining. The resulting heavy fraction is then contacted in liquid phase with the hydrorefining catalyst in the presence of added hydrogen but in the absence of said light fraction. The light fraction p-lus added hydrogen is contracted in vapor phase with hydrorefining catalyst in a second hydrorelining zone. If desiredy the initial hydrorelining of the heavy fraction may be incomplete, and the partially refined product may be blended with the light feed fraction, and the blend then subjected to hydrorelining in the second zone. In either case, the final products of hydroreiining are cooled and condensed in conventional manner, and hydrogen-rich gas for recycle is separated. This recycle gas is returned either in whole or` in part to the second hydrorening zone, while all the fresh makeup hydrogen for the two contacting zones is admitted to the lirst zone wherein said heavy fraction is treated.

The principal object of this invention is to provide methods for contacting heavy mineral oils with catalysts in such manner as to minimize the deposition of carbonaceous deposits upon the catalyst. Another object is to prolong the total life of hydrorening catalysts, and to prolong the life cycle between regenerations thereof. Another object is to prevent the deposition of tarry materials in the feed preheater and the cooler sections of,

the hydrorefining catalyst, such as normally tend to cause plugging of the system. Still another object is to provide a contacting process of the nature described which will permit a maximum recovery of liquid product. Other objects will be apparent from the more detailed description which follows.

The catalytic hydrorefining of hydrocarbon oils to effect selective decomposition of organic sulfur, nitrogen and oxygen compounds is well known. Such processes consist essentially in contacting the oil at temperatures of about 600-900 F. with an active hydrorening catalyst in the presence of added hydrogen. Pressures between about 30D-5000 p.s.i.g. are employed. Difficulties are encountered in the operation of this process when the feed oil consists of a crude oil or residual fraction, and to a lesser extent when heavy distillate fractions are treated. The principal diiculties encountered involve the precipitation upon the catalyst of asphaltic materials or other gummy materials, which then are decomposed to form carbonaceous deposits which rapidly deactivate the catalyst. This is particularly troublesome in the treatment of crude shale oils, as well as the treatment of heavy petroleum crude oils. In these cases, the depo- States atent ice vsiton of tarry materials in the cooler sections of the catalyst bed often will elect a plugging of the reactor so that operation must be suspended within a few hours. Similar difficulties often arise from the deposition of tarry deposits in the preheater and transfer lines.

In the past, these difficulties have been attacked in several different ways. ln one method, the feed oil may -be subjected to a deasphalting operation to remove as phaltenes, carboids, and the like. This is disadvantageous because it results in a substantial reduction in liquid yield, and is also expensive in requiring a complete extraneous treating unit. VAlternatively, the oil may be subjected to thermal coking to convert asphaltenes, carboids and the like to coke, and the coker distillate is then used as feed to the hydrorener. This operation is also expensive, and results in an even greater reduction in over-all liquid yield. The process of this invention is designed to overcome these major draw backs.

It has been found that the deposition of plugging and deactivating deposits upon the catalyst is an end result which-is usually initiated by precipitation from the liquid phase in the hydrorener ofthe more insoluble heavy materials high in carbon content. These materials precipitate first as a heavy tar or gum, which is thereafter gradually decomposed to form coke-like bodies, if the temperature is sufficiently high. According to the present invention, these effects are avoided by providing methods for preventing the initial precipitation of the more insoluble materials in the preheater or on the catalyst.

It has been found that the asphaltic and/or gummy materials are most completely` precipitated at hydroreiiner pressures by the combined precipitating action of the light hydrocarbon components of the feed and the hydrogen employed therein. When the heavy fraction of the feed is subjected to hydrorener pressures in the presence of hydrogen alone, substantially less precipitation occurs than would occur under like conditions in the presence of the light fraction of the feed. Also, when the total feed is subjected to hydrorening pressures in the absence of hydrogen, less precipitation occurs than if hydrogen were also present. The process of this invention is hence directed toward methods of treating the feed which will avoid the simultaneous presence of both hydrogen and the light portions of the feed during the initial stages of contacting. By first contacting only the heavy portion of feed with hydrogen and the catalyst, the asphaltenes and carboids remain in solution to a greater extent, and are hydrogenated to form more soluble materials before beingl admixed with the light fraction of the feed. After the asphaltenes have been hydrogenated, they are must more soluble in the liquid phase and hence are not so readily precipitated by the combined action of hydrogen and the light feed fractidns. Hence by this contacting sequence, the gumand coke-producing materials are caused to remain effectively in solution throughout the contacting sequence.

The process of this invention may be conducted either in two separate reactors, or in a single reactor. Where two reactors are used, the heavy fraction of feed plus hydrogen is passed through onereactor, and the light fraction, with or without the partially hydroreiined heavy fraction, is treated in the second reactor. Where a single reactor is used, the heavy fraction plus hydrogen may be conveniently introduced at the top thereof, and the light fraction of feed may be admitted to the reactor at an intermediate point downstreamwardly. The heavy fraction may be withdrawn at a point above the point of introduction of the light fraction, or said heavy fraction may be allowed to mingle with the light fraction and continue downwardly in admixture therewith. Either the same or different conditions of temperature, pressure and hydrogen ratios may be empolyed in the two contacting zones, but ordinarily it is preferably to employ 'substantially the same conditions.

l The catalyst used in the two contacting zones may be the same or diterenn-but ordinarily the same catalyst is used. The catalyst may be disposed in a fixed stationary bed, or various moving bed or iluidized bed techniques may be used. Generally, the fixed bed technique is most satisfactory. Suitable catalysts may comprise any of the oxides and/or suldes of the Vtransitional metals, and especially an oxide or sulfide of a group VIII metal (particularly iron, cobalt or nickel) mixed with an oxide or sulfide of a group VIB rnetal (preferably molybdenum or tungsten). Such catalysts may be employed in undiluted form, but preferably are distended and supported on an adsorbent carrier in proportions ranging between about 2% and 25% by weight. Suitable carriers include in'general the difcultly reducible inorganic oxides, c g. aluminia, silica, zirconia, titania, clays such as bauxite, bentonite, etc. Preferably the carrier should display little or no cracking activity, and hence highly acidic carriers are generally to be avoided. The preferred carrier is activated alumina, and especially activated alumina containing about 3-15% by weight of coprecipitated silicagel.

The preferred hydrorening catalyst consists of cobalt oxide plus molybdenum oxide supported on silica-stabilized alumina. Compositions containing between about 2% and 8% of CoO, 4% and 20% of M003, 3% and 15% of SiO2, and thebalance A1203, and wherein the mole-ratio of COO/M003 is between about 0.2 and 4, are specically contemplated. These catalysts are preferably prepared by alternate impregnation with aqueous solutions of ammonium molybdate and cobalt nitrate, as described in U.S. Patent No.2r,687,381.

Suitable hydroretning conditions are as follows:

Operative Preferred Temperature, F 650-720 Pressure, p.s.i.g. 50G-3, 500 Liquid hourly space velo 0, 5-15 1-10 Hydrogen ratio, s.c.f./bb1 300-8, 000 50G-5, GGO

Feedstocks which may be treated herein include specically crude shale oil, reduced crude shale oil, petroleum crude oils, or reduced crudes, residual fractions from the topping of such crude oils, heavy distillate fractions therefrom, or in general any mineral oil having an end boiling point in excess of about 700 F. and also containing'components boiling below about 500 F. According to one modification of the invention, where a particularly refractory crude oil is being treated which is very high in asphaltenes, the precipitation of gum in the hydroretner is further inhibited by adding to such oils a small proportion, egg. 1-l0% by volume, of a highly aromatic cycle oil from a thermal or catalytic cracking operation. Such heavy aromatic oils further assist in preventing the precipitation of gums.

The process may be more readily understood with reference to the accompanying drawings, which are flow sheets illustrating two different modifications. In Figure ll, a single reactor is used, and the heavy fraction of feed is treated in both hydrorening zones. The initial feedstock is brought in through line 1, preheated to about 60G-875 F. in preheater 2 and thentransferred via line 3 to a gas-liquid separator 4. The pressure in separator 4 is so adjusted as to achieve the desired separation into a heavy fraction and a lighter fraction. Pressures between about 0 and 2000 p.s.i.g. are contemplated, but in most cases the pressure will range between about 50 and 400 p.s.i.g., and preferably at least about 300 p.s.i.g. lower than the pressure prevailing in the hydrorefiner. The higher the pressure, the greater will be the volume of liquid phase recovered, land vice versa. It is preferred to maintain pressure and temperature conditions such that the vapor phase will comprise substantially all of the feed components boiling below about 250 F., and most of the feed components boiling below about 500 F. The vapor phase will also comprise most of the light gases resulting from thermal decomposition in the preheater, eg. H2, HZS, CO, CO2, CH4,VC2H4, etc. The optimum proportion of feed to be vaporized `depends upon the nature of the feedstock, and particularly its aromaticity and asphaltene content. Oils rich in aromatics and/or lean in asphaltenes require proportionately less vaporization of the light components than oils which are lean in aromatics and/or rich in asphaltenes. In the case of crude shale oils for example it is preferred to volatilize about .20-60% by volume of the feed in this stage.

The liquid phase in separator 4 is continuously withdrawn via line 6 in response to liquid-level-controlled valve 7, and pressured up to the hydrorener pressure in pump S. This liquid fraction is then blended with hydrogen in line 10 and admitted into the top of hydrorener 12 wherein the mixture of hydrogen and oil ows downwardly through catalyst bed 13. In catalyst contacting bed 13 it is preferred to maintain the concentration of light parains as low as possible to avoid their precipitatingaction. The recycle gas from line 30 ordinarily will contain a small proportion of the light gases, methane, ethane, propane, etc. The concentration of such parains is minimized by introducing into line 10 via line 11 the entire amount of fresh makeup hydrogen required for the process. The .mixture of fresh and recycle hydrogen is preheated to reaction temperature in heater 14. In some instances, as for example where the liquid phase from separator 4 is a minor proportion .of the feed, it is possible to use only fresh hydrogen in catalyst bed 13, thereby completely eliminating .light hydrocarbon gases.

The vapor phase from separator 4 .is withdrawn via line 15 and cooled in condenser 5 to effect total or partial condensation, whereby it may be more economically pres sured up to hydrorener vpressure by means of pump .16. Without precondensation, a pum-p of much larger capacity would be required. The liquefied vapor phase fraction then passes from pump 16 through auxiliary preheater 14, wherein it is raised lto reactor temperature, and then passed via, line 17 into a feed header-distributor 18 located between catalyst bed 13 and catalyst bed 20. Preheated recycle hydrogen from line 22 may be blended with the light feed fraction inline 17.

It is contemplated that all of the recycle hydrogen may be admitted to the reactor Via line 10 with the liquid phase feed, or only a portion is so added and the remainder is recycled via line 22. It is preferred however to recycle as much of the rhydrogen as possible via line 2?., diverting only as much recycle hydrogen through line 10 as is needed to maintain the desired hydrogen partial pressure in catalyst zone 13. As indicated above, this desired partial pressure in many instances can be maintained solely by means of the fresh hydrogen admitted via line 11, in which case all of the recycle hydrogen is returned via line 22.

In the zone surrounding distributor 18, the partially refined liquid phase from catalyst zone 13 is blendedwith the light feed fraction entering through line 17, and the mixture then continues downwardly through catalyst zone 20 and is withdrawn via line 2S, condensed in condenser 26, and transferred via line 27 to high pressure separator 29. Hydrogen-rich recycle gas is withdrawn via line 30 and recycled as previously described. liquid phase in separator 29 may then be `flashed into low pressure separator 32 via line 34. Low pressure olf-gases are Withdrawn via line 35 and utilized for fuel or any other conventional purpose. The nal liquid product is withdrawn via line 36 and sent to Vstorage not shown.

Referring now to Figure 2, this modification illustrates tine method for utilizing two separate hydroreiiners,

. wherein the heavy feed fraction is completely treated in j drawn via line 43, pressured up to the desired hydrorefining pressure, blended with preheated hydrogen from line 46, and then passed into liquid phase hydrorefiner 48. The conditions of hydrorening in reactor 48 are sulficiently severe to accomplish the desired desulfuri'zation, denitrogenation, etc. The resulting product is withdrawn through line 49, condensed, and transferred via line 50 to high pressure separator 58.

The vaporphase in separator 42 is taken overhead via line 50, pressured up to the desired hydroreiining pressure in line 53, and blended with preheated recycle hydrogen from line 51. The resulting mixture is then passed into the top of hydrorener 54, wherein it is subjected to suitable conditions for effecting the desired degree of desulfurization, denitrogenation, etc. The resulting product is withdrawn via line 56 and blended with the liquid phase product from line 49. The mixture of products is cooled and condensed in condenser 57, and subjected to gas-liquid phase separation in separator 58. The combined liquid product is withdrawn via line 60 and subjected to iinal nishing treatments which form no part of the present invention.

'The hydrogen-rich gas in separator 58 is withdrawn via line 61 and as in the case of the Figure 1 modification, may be recycled entirely via line 51 to vapor phase reactor 54, in which case the hydrogen utilized in liquid phase` hydrorefiner 48 consists entirely of fresh hydrogen brought in through line 46. It will be understood that in liquid phase hydrorefining, the critical operative hydrogen requirement is merely to keep the liquid phase saturated with hydrogen at reactor pressure. In cases where the fresh hydrogen from line 46 is insutiicient to meet this requirement, a portion of the recycle hydrogen from line 61 is diverted through line 45 to supplement the fresh hydrogen in line 46.

Each of the foregoing modifications displays its own peculiar advantages and disadvantages. In the case of the Figure l modification, the principal advantage resides in minimizing the extent of hydroretining which must be conducted principally in the liquid phase. When the liquid phase from contacting zone 13 is admixed with the light feed fraction plus added hydrogen from line 17, an additional quantity of liquid phase feed will be vaporized and its hydroreiining completed in vapor phase. Vapor phase catalytic hydroreiining is generally most eilicient .from the standpoint of catalyst treating capacity, due mainly to increased diffusion rates in the gas phase. However, rather careful control is required in order to obtain the desired hydrogenation of deposit-forming constituents in contacting zone 13 without at the same time effecting more or less complete hydrorefining. The process of Figure 2 is generally more easily controlled because, since the liquid phase products from hydrorefmer 48` are never` admixed with the light fractions in hydroreiiner S4, the degree and type of hydrogenation which is elfected in reactor 48 is not so critical. The choice of these two alternatives hence depends largely upon the type of feed being treated, the catalysts, the hydrorening conditions, and the desired product specifications.

Manifestly, the details of each of the above processing schemes may be varied considerably without departing from the essential scope of the invention. The following example is cited to illustrate the nature of the-diliiculties encountered in conventional operations, and one way in which they are solved according to the present invention.

6 `Example A crude shale oil educted from Colorado shale rock, said oil having a 50% boiling point of 680 F., a gravity of 20.4 API, containing 1.84 weight-percent nitrogen, and a Ramsbottom carbon residue of 3 weight-percent, was subjected to conventional hydrorening using a catalyst consisting of-3 weight-percent CoO and 9 weight-percent M003, impregnated on a carrier consisting of A1203 and 5% coprecipitated SiO2. The conditions of hydroreiining were: pressure 3000 p.s.i.g., liquid hourly space velocity 2.0, hydrogen/oil ratio 6000 s.c.f./ bbl., and temperature 735 F. After operating under these conditions for 35.5 hours, the pressure drop across the reactor had risen from about l inch of water to 27 inches, indicating that excessive plugging of the reactor had occurred. The operation was hence discontinued and it was found that the catalyst contained coke and gum deposits amounting to 0.06 weight-percent of the total feed processed.

By rst subjecting the above feedstock to a liquid-v Vapor phase separation at 700 F., and a pressure of 100 p.s.i.g., a heavy liquid phase is recovered amounting to about 45% by volume of the initial stock. Upon passing this liquid phase into the top of the reactor in admixture with 2000 s.c.f./bbl. of hydrogen, and passing the vapor phase into the midsection of the reactor in admixture with about 8000 s.c.f./bbl. of hydrogen, and withdrawing the combined product from the bottom of the reactor, satisfactory operation can be continued for in excess of 30 days without appreciable increase4 in pressure drop across the reactor, and without prohibitive decline in catalyst activity. It is hence apparent that by iirst eecting at least a partial hydrorefining of the heavy portion of the feed in the absence of the light portion, it is possible to complete the hydrorefining of the mixture of light and heavy fractions with much less precipitation of deposits than would occur without such pretreatment.

The foregoing description of specific methods is not intended to 'oe limiting in scope except where indicated. Many variations will occur to those skilled in the art and all such variations which yield essentially the same result are intended to be included. The true scope of the invention is' intended to be embraced within the following claims.

I claim:

1. A process for the hydrorefining of a crude mineral oil having an end-boiling-point in excess of about 700 F. and containing components boiling below about 500 F., and which normally tends to deposit carbonaceous materials upon hot surfaces, and wherein the hydrogen utilized comprises both a relatively pure makeup hydrogen stream and a recycle hydrogen stream contaminated with light hydrocarbons, which comprises heating said oil to substantially the desired hydrorelining temperature, subjecting the heated oil to partial vaporization in the absence of hydrogen and at a pressure substantially lower than the pressures to be employed in the hereinafter-dened liquid phase and vapor phase hydroretining zones, said pressure and temperature of vaporization being adjusted to produce (l) a Vapor phase comprising substantially all of the oil components boiling below about 250 F. and the predominant portion of oil components boiling below about 500 F. and (2) a liquid residual oil phase, subjecting said liquid phase to catalytic hydrorefining in a first catalytic contacting zone in admixture with substantially all of said makeup hydrogen stream and in the absence of said vapor phase, subjecting said vapor phase to catalytic hydrorelining in a second catalytic contacting zone in admixture with at least a substantial portion of said recycle hydrogen stream, and recovering a reblended mixture of hydrorefined oils from said contacting zones, the total hydrogen admixed with said liquid phase being relatively less contaminated with light hydrocarbons than the total hydrogen stream admixed with said vapor phase.

2. A process as defined in claim 1 wherein the hydroreiining of said vapor phase is carried out in the absence of said liquid phase.

3. A process as defined in claim 1 wherein the4 hydroreiining of said vapor phase is carried out in admixture with the partially hydroreiined product from said liquid phase hydroreiining.

4. A process as defined in claim 1 wherein the hydroreining of said liquid phase and vapor phase fractions are each conducted at a temperature between about 650 and 780 F. and a pressure between about 500 and 3500 p.s.i.g., and said separation of liquid phase from vapor phase is carried out at a pressure at least about 300` p.s.i.g. below the pressure in said liquid phase hydroreining zone.

5. In a process for the catalytic hydrorening of a heavy mineral oil having an end-boiling-point in excess of about 700 F. and containing components' boiling below about 500 F., and which normally tends to deposit carbonaceous materials upon hot surfaces, the improvement which comprises separating said oil into a heavy liquid fraction containing heavy ends of said oil, and a light vapor fraction, said vapor fraction comprising most of the oil components boiling below about 500 F. and substantially all of the components boiling below about 250 F., preheating said liquid `traction to hydrorening temperature in the absence of added hydrogen, said separating and said preheating being carried out at a pressure substantially below the pressures prevailing in the hereinafter-definedV liquid phase and vapor phase hydrorefining zones, blending said preheated liquid fraction with hydrogen and immediately contacting the mixture with a hydrorening catalyst at an elevated pressure in a liquid phase hydroreining zone, separately contacting said vapor fraction plus added hydrogen with a hydroreining catalyst at an elevated pressure and temperature in a vapor phase hydrorefining zone, and recovering a reblended mixture of hydroreflned oils from said contacting zones.

6. In a process for the catalytic hydroretlning of a heavy mineral oil having an end-boiling-point in excess of about 700 F. and containing components boiling below about 500 F., and which normally tends to deposit carbonaceous materials upon hot surfaces, the improvement which comprises iirst preheating said oil in the absence of added hydrogen to substantially the desired hydroreining temperature, etecting a vapor-liquid phase separation of the preheated oil in the absence of added hydrogen and at a pressure substantially lower than the pressures prevailing in the hereinafter-defined liquid phase and vapor phase hydroreiining zones, recovering from said separation a preheated liquid fraction containing heavy ends of said oil, and a preheated vapor fraction, said vapor fraction comprising most of the oil components boiling below about 500 F. and substantially all components boiling below about 250 F., blending said preheated liquid fraction with hydrogen and immediately contacting the mixture with a hydroretining catalyst at an elevated pressure in a liquid hydrorefining zone, separately contacting said vapor fraction plus added hydrogen with a hydroreiining catalyst at an elevated pressure and temperature in a vapor phase hydroreiining zone, and recovering a reblended mixture of hydroreiined oils from said contacting zones'.

7. A process as delined in claim 6 wherein said mineral oil is essentially a crude petroleum oil.

. 8. A process as dened in claim 6 wherein said mineral oil is essentially a crude shale oil.

9. A process as defined in claim 6 wherein the catalyst employed in said hydrorefining zones consists essentially of a minor proportion of cobalt oxide plus molybdenum oxide distended upon an adsorbent carrier which is predominantly activated alumina.

10. -A process as defined in claim 6 wherein the condi-` tions of hydroretning in said contacting zones include a temperature between about 600 and 875 F., a ,pres. sure between about -5000 p.s.i.g., a liquid hourly space velocity between about 0.5 and 15, and a hydrogen ratio between about 300 and 3000 s.c.f./ bbl.

11. A process as defined in claim 6 wherein the hydroreliining of said vapor phase is carried out in the absence of said liquid phase.

12. A process as defined in claim 6 wherein the hydrorefining of said vapor phase is carried out in admixture with partially hydrorened product from said liquid phase hydroreiining.

13. A process as delined in claim 6 ywherein the hydrorelining of said liquid phase and vapor phase fractions are each conducted at temperatures between about 650 and 780 F. and pressures between about 500 and 3500 p.s.i.g., and said separation of liquid phase from Vapor phase is carried out at a pressure at least about 300 p.s.i.g. below the pressure in said liquid phase hydrorening 14. A process as defined in claim 6 wherein the hydrogen blended with said ypreheated liquid fraction is relatively pure, being composed mainly of fresh makeup hydrogen to the process, and wherein the hydrogen added to said vapor fraction is relatively impure, being composed mainly of recycle hydrogen from the process and containing substantial proportions of light hydrocarbon gases.

15. `In a process for the catalytic hydrorelining of a heavy mineral oil having an end-boiling-point in excess' of about 700 F. and containing components boiling below about 500 F., and 4which normally tends to deposit carbonaceous materials upon hot surfaces, the improvement which comprises separating said oil into a heavy liquid fraction containing heavy ends of said oil, and a light vapor fraction, said vapor fraction comprising -most of the oil components boiling below about 500 F. and substantially all components boiling below about 250 F., preheating said liquid fraction to hydrorefining temperature in the absence of added hydrogen, blending said preheated liquid fraction with relatively pure hydrogen comprising makeup hydrogen for both of the hereinspecified hydrorening zones, and immediately thereafter contacting the mixture with a hydroreining catalyst at an elevated pressure in a liquid phase hydroreining zone, blending said vapor phase with a relatively impure hydrogen stream comprising recycle hydrogen from both of the herein-specified hydroreiining zones, and containing substantial proportions of light hydrocarbon gases, preheating the resulting vapor phase mixture to hydrorelining temperature and separately contacting said preheated mixture with a hydroreiining catalyst at an elevated pressure and temperature in a vapor phase hydrorelining zone.

16. A process as defined in claim 15 wherein said relatively pure hydrogen stream comprises substantially all of the fresh makeup hydrogen required for both of said hydrorening zones, and wherein said relatively impure hydrogen stream is' recycle hydrogen from each of said hydroreining zones.

17. A process as dened in claim l5 wherein the hydrorening of said vapor phase is carried out in admixture with partially hydrorelined effluent from said liquid phase hydrorening.

References Cited in the tile of this patent UNITED STATES PATENTS

Claims (1)

1. A PROCESS FOR HYDROREFINING OF A CRUDE MINERAL OIL HAVING AN END-BOILING-POINT IN EXCESS OF ABOUT 700* F. AND CONTAINING COMPONENTS BOILING BELOW ABOUT 500* F., AND WHICH NORMALLY TENDS TO DEPOSIT CARBONACEOUS MATERIALS UPON HOT SURFACES, AND WHEREIN THE HYDROGEN UTILIZED UPON HOT SURFACES, AHD WHEREIN THE HYDROGEN GEN STREAM AND A RECYCLE HYDROGEN STREAM CONTAMINATED WITH LIGHT HYDROCARBONS, WHICH COMPRISES HEATING SAID OIL TO SUBSTANTIALLY THE DESIRED HYDROREFINING TEMPERATURE, SUBJECTING THE HEATED OIL TO PARTIAL VAPORIZATION IN THE ABSENCE OF HYDROGEN AND AT A PRESSURE SUBSTANTIALLY LOWER THAN THE PRESSURES TO BE EMPLOYED IN THE HEREINAFTER-DEFINED LIQUID PHASE AND VAPOR PHASE HYDROREFINING ZONES, SAID PRESSURE AND TEMPERATURE OF VAPORIZATION BEING ADJUSTED TO PRODUCE (1) A VAPOR PHASE COMPRISING SUBSTANTIALLY ALL OF THE OIL COMPONENTS BOILING BELOW ABOUT 250* F. AND THE PREDOMINANT PORTION OF OIL COMPONENTS BOILING BELOW ABOUT 500*F. AND (2) A LIQUID RESIDUAL OIL PHASE, SUBJECTING SAID LIQUID PHASE TO CATALYTIC HYDROREFINING IN A FIRST CATALYTIC CONTACTING ZONE IN ADMIXTURE WITH SUBSTANTIALLY ALL OF SAID MAKEUP HYDROGEN STREAM AND IN THE ABSENCE OF SAID VAPOR PHASE, SUBJECTING SAID VAPOR PHASE TO CATALYTIC HYDROREFINING IN A SECOND CATALYTIC CONTACTING ZONE IN ADMIXTURE WITH AT LEAST A SUBSTANTIAL PORTION OF SAID RECYCLE HYDROGEN STREAM, AND RECOVERING A REBLENDED MIXTURE OF HYDROREFINED OILS FROM SAID CONTACTING ZONES, THE TOTAL HYDROGEN ADMIXED WITH SAID LIQUID PHASE BEING RELATIVELY LESS CONTAMINATED WITH LIGHT HYDROCARBONS THAN THE TOTAL HYDROGEN STREAM ADMIXED WITH SAID VAPOR PHASE.

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