US2885347A - Hydroforming in presence of recycled pentane and heart cut fractions - Google Patents

Description

United States Patent HYDROFORMING IN PRESENCE OF RECYCLED PENTANE AND HEART CUT FRACTIONS Charles E. Hemminger, Westfield, N.I., assignor to Esso Research and Engineering Compan a corporation of Delaware Application August 31, 1953, Serial No. 377,607 9 Claims. (Cl. 208-102) The present invention relates to improvements in the hydroforming of naphthas. More particularly, the present invention relates to the hydroforming of naphthas in a process whereby not only is the octane number or value of the said stock improved but also the product is improved as to volatility characteristics.

Hydroforming is an operation in which virgin naphtha, cracked naphtha, or Fischer naphtha, or a mixture of two or more of these naphthas is treated at elevated temperatures and pressures in the presence of a solid catalytic material and hydrogen whereby the said naphtha is converted into a product of improved octane value. The main reaction involved in hydroforming is the dehydrogenation of naphthenes. However, other reactions occur during hydroforming such as isomerization of normal paraffins to form iso-parafiins, cyclization of parafiins such as normal heptane, followed by dehydrogenation to yield aromatics, and some hydrocracking of heavier or higher boiling paraflins to form lower boiling products.

The catalysts most commonly employed in hydroforming are platinum group metals supported on active alumina or group VI metal oxides such as molybdenum oxide or chromium oxide similarly supported.

As indicated previously, the present invention involves treating a feed naphtha under conditions which will not only yield a product of improved octane rating in good yields but will also possess the desired volatility required in a premium gasoline. In brief compass, the present invention involves treating the naphtha in a first stage, preferably in the presence of a fluidized bed of catalyst under hydroforming conditions, withdrawing the product from the first hydroforming stage and subjecting the product to fractional distillation to recover separately the following fractions:

(1) A fraction boiling within the range of about 225 to 300 F. which fraction is recycled to said hydroforming zone;

(2) A normal C fraction which is also recycled to the said hydroforming zone;

(3) A fraction boiling substantially in the range of about 125 to 225 P. which is product as such; and and finally,

(4) A high boiling fraction, namely, a fraction boiling above about 300 P. which also is recovered from said distillation for product.

Another feature of the present invention involves feeding with the naphtha, which normally boils within the range of about 200 to 350 F., a virgin or natural C fraction which may contain, for example, 75% normal pentane and 25% isopentane, the purpose here being to isomerize a substantial portion of the normal C fraction to isopentanes.

Another feature of the present invention involves charging the hydrogen-containing gas to the reaction zone at a point located downstream from the bottom of the bed at about the mid-point of the bed of catalyst or at a point below the mid-point of the bed of catalyst. The

purpose of so operating is to carry out a greater portion of the dehydrogenation in the lower portion of the bed in low concentrations of recycle hydrogen-containing gas and the final portion of the dehydrogenating reaction in the upper portion of the bed in the presence of larger quantities of recycle hydrogen-containing gas.

The main object of the present invention, therefore, is to provide a hydroforming process adapted to produce a hydroformed naphtha of good anti-detonation quality in good yields and at the same time to produce a hydroformate improved as to volatility characteristics.

Another object of the present invention is to provide a process adapted to hydroform naphthas to produce a product suited for blending in premium motor gasoline.

Another object of the present invention is to hydroform naphtha to yield hydroformed product possessing the following characteristics when blended to form a premium motor fuel, namely, (1) quick starting; (2) a volatility which, although it permits quick starting, is not over-volatilized to the extent that it may cause vapor lock; (3) the hydroformed product of the present invention has a relatively low final boiling point, namely, about 350 F.

Another object of the present invention is to produce a hydroformate which is a substantial portion of a premium motor fuel possessing the valuable properties of substantially complete saturation of hydrocarbons and the further valuable property of being substantially free of sulfur.

Other further objects of the present invention will appear in the following more detailed description and claims.

In the accompanying drawing there is shown diagrammatically an apparatus layout in which a preferred modification of the present invention may be carried into effect.

Referring to the details in the drawing, 1 represents a hydroforming reactor which, in a preferred modification, contains a fluidized bed of catalyst C which extends from a grid G to an upper dense phase level or interface L. Gasiform material including naphtha vapors are fed to the reactor 1, as will subsequently appear, and the superficial velocity of these gases and vapors in reactor 1 are controlled so as to provide the dense fluidized bed previously referred to. Above L in reactor 1 there is a light phase suspension of catalyst and gasiform material. That is to say, the concentration of catalyst in the gasiform material in reactor 1 in the space above L is much lower than the concentration of catalyst and gasiform material in the dense fluidized bed C. In other words, the space in reactor 1 above L serves as a catalyst disengaging space wherein the main bulk of the catalyst is separated from the gases and vapors.

It will be noted that reactor 1 is provided with two gas distributors, namely, G and G These are foraminous members such as screens or grids. In charging reactor 1, a naphtha enters the system through line 2 and thus passes into a furnace 3 wherein the naphtha is vaporized and superheated to a temperature of about 950 to 1025 F. Care must be taken in preheating the naphtha to avoid thermal cracking of naphthenes contained in the feed naphtha. There may also be fed to the reactor 1 a C hydrocarbon fraction, namely, one which may contain say normal pentane and 25 isomers thereof. This hydrocarbon enters the present system through line 4. The preheated naphtha and C fraction are with covered from the product purification system as will sub.-

sequently appear .is charged from ,line 37 into line. 6 and passes with the hydrocarbons into reactor 1. Under conditions of temperature and pressure, contact time and the like, more fully set forth hereinafter, the desired hydroforming reaction occurs in reactor 1 in the presence of catalyst C. The crude product emerges from the dense bed of catalyst C, passes through the disengaging space above the dense phase level L and is withdrawn from the reactor through line 7. However, since the product gases and vapors about to emerge from the reactor 1 contain entrained catalyst the said gases and vapors are forced through one or more cyclones S wherein entrained catalyst is separated from the said vapors and gases and returned to the dense fluidized bed C through one or more dip pipes d.

The crude product in line 7 thence passes through a heatexchanger 8 wherein it is cooled by heat interchange with say some of the feed naphtha wherein the latter is preheated. The cooled naphtha is withdrawnfrom heat exchanger 8 through line 9 and thence passed into a second cooler 10 wherein it is cooled to a temperature of about 100 F. In other words, to a temperature sufficiently low to condense the major portion of the clear liquid constituents. From condenser 10 the product passes via line 11 into a separation drum 12 wherein gaseous material is separated from liquid product. The latter is withdrawn from separation drum 12 through line 13 and passed to a fractional distillation column 14. A side stream comprising fraction boiling within the range of from about 140 to 225 F. is passed directly to product receiving drum16. A high boiling fraction, namely, one boiling fro-m about 300 to 350 F., is withdrawn as bottoms from fractionator 14 and also delivered to product receiving drum 16.

Referring again to separation drum 12 a fraction is taken overhead through line 17 from this drum, thence passed via line 18 into a scrubber or absorber 19. An absorbing oil boiling substantially in the range of about 225 to 300 F. is withdrawn from fractional distillation column 14 through line 20, thence passed via l ne 21 into a point near the top of absorption drum 19 wherein it flows downwardly against the upflowing gasiform material charged to a point near the bottom of said drum as shown whereby normal liquid constituents are dissolved out of said charged gasiform material. The absorber oil and the dissolved constituents are withdrawn from absorber 19 through line 22 and charged to line 13 and thence passed to fractional distillation column 14 with the mate rial in line 13. There is withdrawn overhead from ,absorber 19 via line 23 unabsorbed hydrogen and C -hydrocarbons. The material in line 23 may be rejected from the system or it may be treated in known manner to recover the said C -hydrocarbons.

Referring again to the fractional distillation column 14, a portion of the hydrocarbons withdrawn through line are charged via line 24 into line 25 for recycling via lines 2 and 6 to reactor 1. This fraction which boils substantially in the range from about 225 to 300 F. is an intermediate or heart cut and the purpose of recycling this fraction to the hydroforming zone is to improve the intermediate volatility for some of the final octane product. Thisinterrnediate fraction which is -recycled to hydroformer 1 for additional conversion, .after reheating in furnace 3, as shown in the drawing, contains hydrocarbons more difiicult to treat to secure the desired result, than the fraction boiling above about 300 F.

'Referring again to fractional distillation column14, a light fraction, namely one boiling from C hydrocarbons to'about 225 F., is taken.offlfrom,saidfractionator via line .49 and passed directly toproduct storage 16. Atthe sametime a heavy bottom fraction is takenofi from fractionator14 via line .15,,and also passed to product storage :16, this particular fraction being the one boiling about..-300 F. .The intermediate fraction, that is, the fraction boiling substantially within the range of about 4 225 to 300 F., is withdrawn from fractionator 14 through line 48 and passed to product storage 16. This is the fraction which has been recycled for further treatment in reactor 1, as previously stated, to produce a premium gasoline of improved volatility for a given octane rating.

Still referring to fractional distillation column 14 it will be noted that a cut or fraction is taken off overhead from said distillation column 14 through a line 26. This fraction is passed to a fractional distillation column 27 which may contain as many as 60 plates wherein C and C hydrocarbons are separated from C and C hydrocarbons. The C and C hydrocarbons are withdrawn overhead from 27 through line 28, and these hydrocarbons may be processed in any known manner as where, for example, the C hydrocarbons after separation from the C hydrocarbons may be converted to, say, butadiene or other chemicals by conventional processes. The C hydrocarbons may'also be blended intomotor fuel to improve the Reid vapor pressure of said fuel. In like manner, the C hydrocarbons may be used as a fuel or treated in known manner to form chemicals by known means.

The bottoms fraction from fractionator 27 is withdrawn through line 29 and fed to the middle of fractional distillation column 30 wherein isopentanes are separated from the normal pentane and recovered overhead through line 31 and delivered to product storage 16. The higher boiling normal pentane is withdrawn from fractional distillation column 30 through line 32 and delivered to line 25 and thereafter recycled with the said heart cut material in that line via lines 2 and 6 to reactor 1 wherein these normal paraffins, which may be mixed with some C hydrocarbons, undergo isomerization to form theiso derivatives possessing higher anti-detonation qualities than the normal parafiins.

Referring again to separation drum 12, the overhead gasiform material in line 17 is in part recirculated via line 33 and reheat furnace 34 and line 35 to line 37 from which it is passed into line 6 for return to the bottom portion of reactor 1. A portion of the gas in line 35, however, may be passed via line 38 into reactor 1 at a point above grid G In order to control temperature, a portion of the recycle gas in line 33, which is a cold gas, is passed via branch line 36 into line 38 and flows with the hot gas in this line into reactor 1 as shown in the drawing. It will be noted that only a portion of this recycle hydrogencontaining gas is charged to the bottom of reactor 1. The purpose of so operating is to provide an atmosphere in reactor 1 which contains lesshydrogen in the lower portion of reactor 1 than is contained in the portion above G The portion of the reactor below 6;, therefore, contains the lower hydrogen concentration and dehydrogenation reaction is favored whereas the bed above G which contains the greater hydrogen concentration, has the optimum atmosphere for hydrocracking and isomerization of parafiins. While the amounts of hydrogen which are charged to reactor 1 at the two points indicated may vary, a good way to operate with respect to the hydrogen feed to the said reactor is to bypass about of the hydrogen-com taining gas in line 33 around furnace 34 via line 36 into line 38 and thence'to reactor 1; whereas about' of the total gas in line 33 is passed to reactor 1 via line 38 while the remaining portion of the gas in line 33 is charged to reactor 1 via lines 37 and 6. It will thus be noted that according to the present invention no attempt is made to provide an inverse temperature gradient in catalyst bed C. As armatter offact, the catalyst bed temperature on'the lower portion thereof may be higher than thatin the upper portion of the bed of catalyst in reactor 1. The advantages of so operatingare as follows:

(a) The feed doesnot contact hot catalyst in the first section of the bed, as will be described later, and (b) the initial dehydrogenation reactions where naphthenes are converted to aromatics is speeded by the low hydrogen partial pressure. Thus the conversions of naphthenes to aromatics and the isomerization of C and C hydrocarbons is faster than if the total recycle gas were present. The two competing reactions in hydroforming are dehydrogenation and thermal cracking. Since the temperature coeflicients of the two reactions are about the same the relative rates cannot be altered by different temperatures in the reactor. However, when the hydrogen concentrations are kept low the rate of dehydrogenation reaction is increased relative to the rate of the cracking reactions. However, large quantities of recycle gas or hydrogen are necessary, to repress excessive coke formation in the upper portion of the reactor where the hydrocyclization and the greater portion of the coke formation takes place. It has been shown that in fluid hydroforming units equal or improved selcctivities are obtained when a positive temperature gradient (i.e. higher at the lower portion of the catalyst bed) exists in the reactor.

During the course of the reaction, the catalyst in reactor 1 acquires carbonaceous deposits and perhaps also deposits containing sulfur. It is necessary to regenerate the catalyst to remove such deposits and to restore the catalyst activity. Toward this end catalyst is withdrawn from reactor I through a stripping zone 40, the catalyst entering said stripping zone through an opening or orifice 39. Steam is charged to the bottom of said stripping zone 40 through a pipe 41, which steam passes upwardly against the downflowing catalyst, and dislodges volatile hydrocarbons therefrom, which hydrocarbons are carried upwardly with the steam into the reactor at a point above the dense phase level L, thus avoiding contacting steam with the main body of catalyst C. As shown in the drawing, the catalyst from stripper 40 is charged into a stream of air flowing in pipe 42 wherein it is formed into a suspension and carried into regenerator 43. The bottom of standpipe or stripper 40 is provided with a valve V to control the flow of catalyst into the air stream in 42. The quantity of air in line 42 is about 10% of the total air required in regenerator 43 to consume the deposits on the catalyst. Supplemental air is added to regenerator 43 through line 44. Regencrator 43 may be of the same construction as reactor 1 but very much smaller. As usual, it is provided with gas distributing means G through which the suspension and the air pass into the regenerator to form a fluidized mass extending from G to an upper dense phase level L formed by controlling the superficial linear velocity of the gasiform material in regenerator 43. The space above L in regenerator 43 is a catalyst disengaging space wherein the main bulk of the catalyst is separated from the gas. In the top of regenerator 43 there is disposed one or more cyclones S or dust separators which separate entrained catalyst which is returned to the main fluidized bed C through one or more dip pipes al The fumes pass from the regenerator through exit pipe 45, and since they contain appreciable quantities of sensible heat and also some potential chemical heat, the heat content thereof may be utilized in the present system, according to conventional means.

The conditions under which the regeneration is carried out will be described in detail hereinafter. The regenerated catalyst is withdrawn from regenerator 43 through line 46 and returned to reactor 1 at a point in close proximity to but above the grid G at a point spaced from stripper pipe 40. Thus, the freshly regenerated hot catalyst is not charged to the lower portion of the hydroformer 1 for the reason that hot vapors and gas enter at the bottom of the reactor supplying heat. It should be noted, however, that catalyst above G passes downwardly through a downcomer 47 into a bed of catalyst between G and G and catalyst passes upwardly from this region through grid G into the upper portion of the catalyst bed C.

It will be understood that the present drawing is diagrammatic, and only the essential apparatus have been indicated therein to illustrate the present process. Thus, a person familiar with the present art will appreciate that accessory apparatus such as temperature and pressure recorders, flow meters, etc., not shown in the drawing,

would be included in a commercial unit. Also, stand-' Range Preferred Catalylsto Composition, Percent M003 5-20 9-12.

011 z 3. Catalyst particle size in microns 10-200 20-110 (65% 3y wt. 20-

Temperature, F- 850-975 890-925. Pressure, p.s.i -400 175-250. Feed Rate, lbs. oil/hr./lb. catalys 0. 2-1. 5 0.4-1.0. Catalyst/Oil Ratio 0. 3-5.0 0.8-2.0. Standard Cu. ft. of hydrogen ted to Reactor llbarrcl of oil 1, 500-7, 000 2,000-4,000. Concentration of hydrogen in gas ted to 45-90 50-75.

reactor, percent. Superficial gasil'orm velocity in ft./sec-. 0.2-1.5 0.5-0.8.

Conditions in regenerator 43 Range Preferred Temperature, F- 1, 000-1, 300 1, 075-1, Pressure, p.s.i Contact Time, min 3-60 5-20 Regeneration vent gas, con of oxygen,

vol. percent 0. 2-4. 0 0.8-2. 0 Superficial gas velocity 1 Practically same as reactor 1.

2 See rates in reactor 1 above.

A fed was hydroformed using a catalyst consisting of about 10% molybdenum oxide and 90% aluminum oxide, the foregoing percentages being by weight. A naphtha containing 10% aromatics, 45% naphthene and 45 paraffins with 55 research octane number and the natural C fraction containing 75% normal pentane and 25% isopentane were mixed and fed to the hydroforming zone. For each barrel of oil feed, barrel of the said components derived from natural gas was fed to the reaction zone. The hydroforming operation was carried out at a temperature of 935 F. in the lower portion of the bed and 905 F. in the upper portion of the bed. The oil was fed to the reaction zone at a rate of 0.6 lb. of oil per hour per lb. of catalyst in the reactor and a pressure of 200 lbs. per square inch was maintained in the reactor. A heart out boiling substantially within the range of 225 to 300 F. from the previously hydroformed naphtha was also fed to the reaction zone as recycled material. The amount of the said heart cut with respect to the fresh oil feed was 0.3 barrel per barrel of fresh feed. There was also fed to the reaction zone a quantity of recycle normal C hydrocarbon. The amount of normal C hydrocarbons recycled to the hydroforming zone, with respect to the fresh naphtha feed, was 0.6 barrel per barrel of fresh 1 Exclusive 01 extraneous 0 added to system.

It will be noted from the above that for an octane 7 number of 90, the recycle operation gave a volatility (percent D+L at 212 F.) of '32 as against 25 for the run with no recycle of the 225 to 300 F. cut. It should be explained that a 32 or a 25 (percent D+L at 212 F.) means that those percentages of naphtha distill from the naphthas when'heated to 212 F. at 1 atmosphere.

It will be understood that the foregoing conditions and results are illustrative of a good way to carry out the present invention, and the specific details therein contained are not to be construed as placing any limitations on the invention.

To recapitulate, briefly, the present invention involves a hydroforming process preferably using a fluidized bed of hydroforming catalyst characterized in that a middle fraction of the reformed naphtha is recycled to the reforming zone. This recycling effects a distinct improvement in the volatility, at a given octane rating, of the reformed naphtha which is an important factor in the manufacturing of preminum quality gasoline.

The present invention is not limited to the use of a molybdenum oxide catalyst but rather a platinum group metal catalyst may be used. Thus, an alumina-platinum group metal catalyst containing 0.05 to 5 weight percent platinum or 1.5 weight percent palladium may be used. The operating conditions in the case of these catalysts would be: temperature of catalyst bed-800900 F., pressure in hydroformer 100700 p.s.i.g.; hydrogen charged to reactor per barrel of oil feedl0005000 standard cubic feet; residence time of oil in reactor as represented by oil feed rate-1 to 10 lbs. of oil per hour per lb. of catalyst in reactor.

Many modifications of the present invention will be apparent to those who are familiar with the present art.

What is claimed is:

1. The method of hydroforming hydrocarbon fractions boiling in the naphtha boiling range which comprises contacting the naphtha vapors at elevated temperatures and pressures with a bed of a hydroforming catalyst in the presence of hydrogen in a hydroforming zone for a suflicient period of time to effect the desired conversion, withdrawing crude product from the hydroforming zone, subjecting the hydroformate to fractional distillation to separate the 125225 F. fraction, the C fraction, a 225 300 F. heart cut fraction and a 300 F.+ fraction, passing the entire 125-225 F. fraction and the entire 300 F.+ fraction to product, passing a portion of the 225 to 300 F. fraction to product, subjecting the C fraction to distillation whereby isopentane is separated overhead and passed to product while the normal pentane is recovered as bottoms and recycling the normal pentane to the hydroforming zone together with the remainder of the 225 -300 F. fraction in order to improve the volatility of the product.

2. The process as defined in claim 1 in which a virgin natural C fraction containing about 75% normal pentane and 25% isopentane is fed to the hydroforming zone with the fresh feed naphtha.

3. A continuous method for hydroformig hydrocarbon fractions boiling in the naphtha boiling range which comprises charging the naphtha vapors to a hydroforming zone containing a fluidized bed of a hydroforming catalyst which bed of catalyst is disposed, in part, in the lower portion of a hydroforming zone and, in part, in another portion disposed immediately above the firstnamed portion, the two portions being separated and in communication with each other, charging preheated naphtha and a hydrogen-containing gas to the hydroforming zone, permitting contact between the said naphtha vapors and the portions of said bed of catalyst at hydroforming conditions of temperature and pressure for a sufficient period of time to effect the desired conversion, withdrawing a product from said hydroforming zone, subjecting the hydroformate to fractional distillation to separate the -225 F. fraction, the C fraction, a 225 300 F. heart cut fraction and a 300 F.+ fraction, passing the entire 125-225 P. fraction and the entire 300 F+ fraction to product, passing a portion of the 225 to 300 F. fraction to product, subjecting the C fraction to distillation whereby isopentane is separated overhead and passed to product while the normal pentane is recovered at bottoms and recycling the normal pentane to the hydroforming zone together with the remainder of the 225 -300 F. fraction in order to improve the volatility of the product.

4. The method set forth in claim 3 in which a C fraction from natural gas is fed to the hydroforming zone with the fresh feed naphtha.

5. The method set forth in claim 3 in which the said lower portion of the catalyst bed is maintained at a higher temperature than said upper portion of said catalyst bed.

6. The method set forth in claim 3 in which the catalyst is composed of molybdenum oxide carried on alumina.

7. The method set forth in claim 3 in which the catalyst is composed of a platinum group metal carried on alumina.

8. The method set forth in claim 3 in which catalyst is withdrawn from the hydroforming zone, regenerated with an oxygen-containing gas in a separate regeneration zone and thereafter returned to the upper portion of said catalyst bed.

9. The method set forth in claim 3 in which catalyst is permitted to circulate between both portions of said bed of catalyst.

References Cited in the file of this patent UNITED STATES PATENTS 2,349,045 Layng et al. May 16, 1944 2,374,095 Helmers Apr. 17, 1945 2,380,938 Burk Aug. 7, 1945 2,389,342 Conn Nov. 20, 1945 2,472,844 Monday June 14,1949 2,484,381 Johnson et al Oct. 11, 1949 2,596,145 Grotze May 13, 1952 2,697,684 Hemminger et al Dec. 21, 1954 2,718,535 McKinley et al Sept. 20, 1955 2,736,684 Tarnpoll Feb. 28, 1956 2,740,751 Haensel et a1 Apr. 3, 1956 2,776,247 Anhorn et al. Jan. 1, 1957 2,781,298 Haensel et a1. Feb. 12, 1957 OTHER REFERENCES Fulton: Petroleum Refiner, volume 29 (1950), pages 109 to 112.

Claims (1)

1. THE METHOD OF HYDROFORMING HYDROCARBON FRACTIONS BOILING IN THE NAPHTHA BOILING RANGE WHICH COMPRISES CONTACTING THE NAPHTHA VAPORS AT ELEVATED TEMPERATURES AND PRESSURES WITH A BED OF A HYDROFORMING CATALYST IN THE PRESENCE OF HYDROGEN IN A HYDROFORMING ZONE FOR A SUFFICIENT PERIOD OF TIME TO EFFECT THE DESIRED CONVERSION, WITH DRAWING CRUDE PRODUCT FROM THE HYDROFORMING ZONE, SUBJECTING THE HYDROFORMATE TO FRACTION DISTILLATION TO SEPARATE THE 125*-225*F. FRACTION, THE C5 FRACTION, A 225* 300*F. HEART CUT FRACTION AND A 300*F.+ FRACTION, PASS-

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