US3347780A - Naphtha hydroconversion to produce lower boiling hydrocarbon products - Google Patents

Description

United States Patent NAPHTHA HYDROCONVERSION T0 PRODUCE LOWER BOILING HYDROCARBON PRODUCTS Robert H. Lindquist, Berkeley, and Clark J. Egan, Piedmont, Califi, assignors to Chevron Research Company, San Francisco, Calif., a corporation of Delaware No Drawing. Filed Feb. 4, 1966, Ser. No. 525,150 Claims. (Cl. 208-111) ABSTRACT OF THE DISCLOSURE Producing C to C hydrocarbons by hydrocracking petroleum naphtha feed having a maximum end point of 385 F. with at least 1500 s.c.f. of hydrogen per barrel of naphtha with a consumption of at least 500 s.c.f. of hydrogen per barrel of feed converted to lower boiling products, at more than 350 p.s.i.g. hydrogen partial pressure and below 800 F. at more than 0.2 v./ v./ hour liquid hourly space velocity with a conversion per pass of at least 30% to lower boiling products over a presulfided catalyst prepared by chemisorbing a fluoride of a hydrogenating met al of the iron transition group (e.g., nickel) on an active cracking support containing at least of alumina or magnesia in a substantially dehydrated state, while maintaining a sulfur content of at least 10 p.p.m. in the naphtha feed. Preferably the naphtha feed boils above 170 F. and at least 50% is converted per pass to products boiling below 150 F.

This invention relates to a process for the catalytic conversion of naphtha fractions to light gases and more particularly to the catalytic conversion of naphtha predominantly to light hydrocarbons having 3 to 5 carbon atoms.

Naphthas, particularly paraffinic naphthas such as straight-run naphthas boiling in the range of about 170 to 450 F., have a low octane rating and are not desirable as reforming feeds. Hence the refiner is faced with the problem of disposing of these low octane naphthas. Also, in some areas the demand for propane and normal butane used in LPG and isobutane used in preparing alkylate exceeds the normal supply. While heavier hydrocarbons such as gas oils can be converted to useful products such as gasoline for long periods of time over the better hydrocracking catalyst, it has been found that these hydrocracking catalysts lack the ability to operate for long periods of time without fouling when employed for conversion of naphthas to light hydrocarbons having 3 to 5 carbon atoms.

In accordance with this invention there is provided an improved process for converting petroleum naphtha to light hydrocarbons having 3 to 5 carbon atoms. This process employs the catalyst prepared in a certain manner and operating conditions such that the catalyst does not become rapidly fouled and hence the naphtha conversion can be continued for long periods of time without catalyst regeneration or replacement. The process comprises contacting the naphtha, along with at least 1500 s.'c.f. of hydrogen per barrel of said naphtha feed with a consumption of at least 500 s.c.f. of hydrogen per barrel of naphtha converted to lower boiling products, at more than 350 p.s.i.g. hydrogen partial pressure and below 800 F. at

-mixing with a die lubricant and hours at 900 more than 0.2 v./v./hour liquid hourly spaced velocity over a hydrocracking catalyst prepared by chemisorbing a fluoride of a hydrogenating metal of the iron transition group on an active cracking support containing at least 10 percent by weight of alumina or magnesia in a substantially dehydrated state and, even though the resulting catalyst may be presulfided before use, maintaining a sulfur content of at least 10 p.p.m. in the naphtha feed being brought into contact with said catalyst.

The process of the present invention is beneficial in that conversion of naphtha to light hydrocarbons can be ac complished in high yields for long periods without the catalyst being fouled rapidly and requiring frequent regenerations or replacement. The process is particularly advantageous when substantial portions or all of the reaction efiluent boiling above about 200 F. is recycled. It is especially advantageous when the reaction effluent boiling above about 160170 F. is recycled since such operation is even more difiicult to conduct with appreciable catalyst life; the present process can be operated for extended periods with this lower recycle cut point. In the process into contact with the catalyst must be maintained above 10 p.p.m., preferably above 50 p.p.m. Where the catalyst has not been sulfided prior to use, it is preferable to use a higher sulfur content such as above p.p.m., at least until the hydrogenating metal component of the catalyst has become sulfided.

, The catalyst is prepared by chemisorbing a fluoride of a .hydrogenatingmetal of the iron transition group, preferably nickel or cobalt fluoride, on an active cracking support containing at least 10% of alumina or magnesia. In some instances, a plurality of metal fluorides may be desirable. For example, fluorides of nickel and cobalt may be employed as well as fluorides of nickel or cobalt with fluorides or other metals such as copper and tungsten. The chemisorption is obtained by contacting the support with the alumina or magnesia in a substantially dehydrated state with an aqueous solution of the metal fluoride and the contacting is continued until the catalyst has acquired a hydrogenating metal content of at least 3% on a dry weight basis. The support is preferably a siliceous alumina cracking catalyst such as silica-alumina, silica-aluminazirconia, and silica-alumina magnesia but also may be one of the natural or synthetic aluminosilicates such as the zeolitic crystalline aluminosilicates described in Patents 3,130,006; 3,130,007 and 3,140,249.

Following chemisorption, the catalyst is usually dried,

such as, for example, by heating in a relatively dry at- -m0sphere for 16 hours at F. Thereafter, the dried desired shape, such as by tableting. Likewise, other methods of shaping such as extrusion may be used. Usually the catalyst is then calcined in air, for example, for 4 F. to remove the organic materials and to catalyst may be formed into the Y and normally from about convert the chemisorbed hydrogenating metal component to the oxide on the catalyst surface.

Further details and variations with respect to the preparation of the catalysts for use in the present process are set forth in Lindquist and Billman Patent 3,140,925.

With many hydrocracking catalysts which are composed of iron transitional group metal hydrogenating components, the activity of the catalyst is increased by a dry thermactivation treatment. Such thermactiv-ation involves passing a dry, non-reducing gas through a mass of particulate catalyst at a rate of at least cu. ft. per hour per cu. ft. of catalyst at temperatures of 12001600 F. for times ranging from 0.25 to 48 hours. Therefore, it is surprising that with the present catalyst prepared by chemisorption of a fluoride of an iron group transition hydrogenating metal, the activity as well as the resistance to fouling is further improved by subjecting the catalyst, usually after shaping and partial drying, as a preferred procedure to calcination in an atmosphere containing at least 10% steam for at least one hour at 850-l100 F. Preferably the calcining atmosphere containing -90% steam and the temperature is 9001000 F. Preferably the catalyst is calcined with a flowing stream containing steam for 2-10 atmosphere-hours (i.e., the partial pressure of steam in atmospheres times the hours). For example, with 0.1 atmosphere hours of steam calcination a catalyst of the present invention gave a naphtha conversion at 700 F. to C of 56% but with 4%. atmosphere-hours the catalyst gave a conversion of 84%. Most especially the steam calcination is continued until the catalyst bulk density is at least 0.5 (gms./cc.), preferably at least 0.65, as measured by displacement after compacting with agitation in a glass cylinder whose diameter is 5 times larger than catalyst pellet diameter. During the high temperature water vapor treatment some rearrangement of the catalytic surface apparently occurs and results in increased activity and decreasing fouling rate. The preferred activation with steam is set forth in more detail in copending application Serial No. 525,122 filed concurrently herewith by R. H. Lindquist and C. J. Egan and entitled: Improved Fluoride Catalyst.

In using the foregoing catalyst in the present process, it is prefer-red that catalyst be sulfided. Most conveniently, this is done by passing a gaseous sulfiding agent through the catalyst after it has been placed in the reactor. Likewise, the sulfiding can be effected by contacting the catalyst with a feed containing a suflicient concentration of sulfur compounds.

In a preferred embodiment of the process of the present invention the reactor, after being charged with catalyst for fixed bed operation, is operated under a total pressure ranging from about 400 psig up to about 3000 p.s.i.g., referably below 2500 p.s.i.g., and at an average catalyst temperature in the range of 400 to 800 F. preferably below 750 F. with the temperature usually being so regulated to initiate the desired conversion at as low a temperature as possible. The naphtha feed is introduced in admixture with at least 1500 s.c.f. of hydrogen per barrel of total feed. At least 500 s.c.f., 1000 to 2000 s.c.f. of hydrogen are consumed in the hydrocracking reaction zone per b-arrel of naphtha converted to lighter hydrocarbons boiling below the initial boiling point of the feed naphtha. Generally the naphtha feed is introduced into the hydrocracking reaction zone at a liquid hou-rly space velocity (LHSV) of from about 0.2 to 5 volumes of hydrocarbon (calculated asliquid) per superficial volume of catalyst with a preferred rate being from about 0.4 to 3 LHSV. The conditions of temperature, pressure and space rate are preferably such that at least 20 volume percent of feed naphtha is converted per pass to lighter hydrocarbons. Preferably the reaction conditions are adjusted such that the per pass conversion to lighter hydrocarbons is in the range of from to 90%. Usually it is preferred to operate the hydrocracking process at a selected per pass conversion while periodically increasing the reaction temperature so as to maintain the conversion at a relatively constant level. In some instances the process is desirably operated on a. once-through basis, particularly where the product demand is for both LPG (e.g., propane and butanes) and C -C hydrocarbons, predominantly isoparafiins, which are suitable as high octane light gasoline blending stock. In such operation the lower octane components are selectively cracked to LPG components and/ or converted to higher octane gasoline components, so that gasoline octane requirements can be met without overloading the reforming facilities in a refine y. In other situations, it will be more desirable to recycle a substantial portion or all of the reaction efiluent boiling above a certain cut point such as 125 F. In order to obtain greater yields of propane and butanes which may be separated into propane and n-butane for use in LPG and isobutane for use in alkylation. As indicated hereinbefore, a partcular advantage of the present process is the long catalyst life that can be obtained when operating with extinction recycle of all hydrocarbons boiling above hexane and especially when recycling all reaction eflluent boiling above pentane.

In accordance with the present process of employing a chemisorbed metal fiuoride catalyst and maintaining a sulfur content in the feed naphtha above a certain level, long periods of operation are obtained with minimum catalyst fouling which in turn determines the useful life of the catalyst. Since, when running at a constant space velocity and pressure, the temperature must be raised to maintain the conversion constant, the fouling rate can be expressed in terms of temperature rise per unit of time, i.e., degrees per hour.

The following examples are presented toillustrate preferred embodiments of the naphtha conversion process of the present invention (all percentages are by weight unless otherwise specified) Example 1 A sulfided nickel fluoride catalyst was prepared by contacting with stirring at room temperature for 78 hours one volume of powdered calcined silica-alumina cracking catalyst containing 25 of alumina with eight volumes of water containing powdered nickel fluoride tetrahydrate in a proportion of 6.23 parts of nickel fluoride tetrahydrate to 8 parts of silica-alumina. Although the nickel fluoride has a low water solubility, a saturated aqueous nickel fluoride solution was in contact with the silicaalumina and nickel fluoride dispersed in the water until all the nickel fluoride Was depleted by the chemisorption. Thereafter the catalyst was dried at 300 F. for 12 hours. With the addition of die lubricant, the treated catalyst powder was tableted and crushed to 8-14 mesh particles which were then calcined in air for 4 hours at 900 F.

to remove the organic materials and to convert the nickel components to nickel oxide on the catalyst surface. The

calcined catalyst was reduced in hydrogen at 900 F. for 4 hours and then calcined in air containing 13% steam at 900 F. for 24 hours. Analysis of the catalyst showed 18% Ni, 5% F, 284 m. gm. surface area and 0.76 bulk density gms./ cc.

The catalyst was then placed in a reactor and presulfided with four theories of ethyl mercaptan in hexane (a theory of sulfiding agent is equivalent to the stoichiometric amount required for conversion of all the nickel present to nns Sulfur-free n-heptane along with hydrogen (at a mol ratio of hydrogen to heptane of 12:1) was passed through the catalyst at a heptane space velocity of 1.5 LHSV at an initial temperature of 586 F. The conversion to lower boiling products initially was 89%. While maintaining the temperature at 586 F. and doubling the hydrogen/heptane ratio, the conversion dropped to 83% after 5 hours and to 50% in 30 hours. The temperature was then raised to 601 F. at 32 hours at which time the conversion was 5 61% but at 48 hours had dropped to 32%. This decrease in conversion indicated a substantial decrease in activity of the catalyst. At 52 hours the catalyst temperature was raised to 632 F. at which time the conversion was 58%. Thereafter the n-heptane feed was discontinued and the hydrogen was continued for 68 hours after which period n-heptane was reinjected and conversion then at 126 hours was 35%. At 146 hours, with the temperature still at 632 F., introduction of dimethyl disulfide with the feed was started at a rate to give a concentration of 190 p.p.m. of sulfur in the heptane feed. After an additional 24 hours, the conversion due to the effect of the added sulfur had risen to 48%. At 173 hours (the sulfur addition being continued) the temperature was raised to 660 F. at which point the conversion became 71%. After an additional 48 hours the conversion was still high at 69%,

i.e., essentially constant. A sample of the product of the reaction taken at the end of the run analyzed as follows:

Component: Weight percent C 0.2 C 0.3 C 30.5 i-C 30.0 I'l-C4 iC 3 0.5 11-C5 K4 C s 0.7 C 31.0

The last portion of this test illustrates that with an appropriate sulfur content in the feed contacting the cat- .alyst nickel fluoride silica-alumina catalyst, high conversions of n-heptane and the like to lower boiling hydrocarbons can be achieved under stable conditions with essentially no catalyst fouling or decrease of catalyst activity.

Example 2 Another test was conducted on a once-through basis .using the same catalyst as in Example 1 and a naphtha .feed having a distillation range of 215 F. start, 252 F.

50% point, and 322 F. end point and the following com- The naptha feed together with hydrogenat a rate of 6200 s.c.f. of H per barrel of feed was passed through the catalyst at 1.5 LHSV and 1205 p.s.i.a.' and 580 F. The conversion to products boiling below O; was 75% at the start and was 74% after 77 hours on stream. A sample 7 of the product taken at 71 hours analyzed as follows:

Component: Weight percent 0 v 0.05

' iC 24.4 n-c. 7.9 i-C 17.6 I'll-C5 2.]. C578 11.2

C and higher 26.4

This test also illustrates that high conversions canbe obtained with essentially no catalyst fouling.

Example 3 Another test was conducted on a once-through basis (i.e., no recycle of unconverted hydrocarbons) with the same catalyst as in Example 1 and a straight run naphtha feed having a distillation range of 162 F. start, 202 F.- 50% point and 306 F. end point and the following composition:

Component: Weight percent C 2.6 C 27.4 C 37.9 C 28.3 C 3.8

as follows:

Component: Weight percent C1 0 -3 C 0.6 C 26.7 i-C 27.3 nC 11.3 iC 11.1 nC 4.6 C 18.0

Example 4 A sulfided nickel fluoride silica-alumina catalyst was prepared by contacting with stirring at room temperature for 48 hours one volume of powdered calcined silicaalumina cracking catalyst (25% alumina) with 8 volumes of water containing powdered nickel fluoride tetrahydrate (6.23 parts by weight per 8 parts of silica alumina). After decanting the remaining aqueous solution, the catalyst was dried at 150 F. for 16 hours, and formed into $4 inch tablets. The tablets were crushed to 8-14 mesh particles and calcined in air for 4 hours at 900 F., reduced in flowing hydrogen at 900 F. for'4 hours and then calcinediat 900 F. for 21 hours in air containing 13% steam. The catalyst had the following properties: 18.9% Ni, 8.5% F., 247' rn. /gm. surface area and 0.77 bulk density -grns./cc. The catalyst was then placed in a reactor .and sulfided in the same manner as the catalyst in Example 1. Naphtha feed was passed through the catalyst at 0.75 LHSV along with 5000 s.c.f.

' of recycled gases (about 97% hydrogen). The conversion 'with recycle of high boiling portions of the reaction eflluent was run continuously for 790 hours with the other operating conditions varied to maintain a 60% conversion to the recycle cut point as indicated below. For the first 176 hours, the naphtha feed was the same as for Example 2 and thereafter the feed was a similar naphtha having a distillation range of F. start, 222 F.,-50% point, 334 F. end point, an analysis of 71.2% paraffins, 18.9 naphthenes and 9.8% aromatics and a sulfur content of 304 p.p.m. In the following table, C recycle cut point indicates that heptanes and higher boiling components were recycled to the reactor and 0 recycle cut point indicates that hexanes and higher boiling material were recycled.

Time on Stream Recycle Cut Total Pressure,

( t gg g Point RS1. g Temperature, F.

1 Adjusting to higher temperature.

Example In the following tests, catalyst A was prepared as described in Example 1. The other catalysts B, C, D and E were prepared by contacting with stirring 1 volume of powdered alumina-silica (25% alumina, surface area. 550 m. /gm., bulk density 0.63) gm./cc. with 8 volumes of water and nickel fluoride in proportion of 6.23 parts to 8 parts of silica-alumina. The contacting period for the chemisorption of the nickel fluoride on the silica-alumina was 48 hours at room temperature. The catalysts were then formed into 1/ inch tablets. Then the catalysts were dried for 16 hours at 150 F. Thereafter the catalysts were crushed to 8-14 mesh particles and calcined in air for 4 hours at 900 F. Thereafter the catalysts (catalyst A included) were variously treated as shown in the table below. In the steam treatments, the air was saturated with water vapor at 125 F. which is equivalent to 13% steam. The catalysts were sulfided as described in Example 1. The activity tests were carried out in the name manner and conditions in Examples 2 and 3, Feed'2 being that of Example 2 and Feed 3 being that of Example 3, the conversion being measured after 6 hours on stream.

measured, and the activities ofthe catalysts determined. All the catalysts were prepared by chemisorbing nickel fluoride on powdered activated silica-alumina (25% alumina) as follows: One volume of silica-alumina was contacted with five volumes of water having dispersed therein 7.8 parts of nickel fluoride tetrahydrate for each 10 parts of silica-alumina until substantially all the nickel fluoride was chemisorbed. Thereafter the catalysts were dried at 150 F. for 16 hours and then reduced in flowing hydrogen for 4 hours at 900 F. Then the catalysts were calcined in flowing steam for 4 hours at the temperatures shown below. The surface areas were measured by nitrogen absorption by the method of Brunauer et al. (I. Am. Chem. Soc. 60, 309, 1938). The activities of the catalysts in sulfided form were determined by measuring the amount of conversion of a naphtha to products boiling below C The naphtha had the following inspections: D-86 distillation: 209 F. start, 270 F.50% point and 384 F. end point, and a sulfur content of 750 p.p.m. The results of the tests are as follows:

Steam Bulk Surface Activity, Cat. No. Treatment, Density Area, Percent F. (gnL/cc.) mfllgrn. Conversion The foregoingillustrates that the activities are higher with the steam treatments which give the higher bulk densities. In the foregoing tests the activities were determined at 595 F, 1.5 LHSV, and 1185 p.s.i.a.

What is claimed is:

1. A process for converting petroleum naphtha having a maximum end point of 385 F. to light hydrocarbons having 3 to 5 carbon atoms which comprises contacting said naphtha as feed, along with at least 1500 s.c.f. of hydrogen per barrel of said feed with a consumption of at least 500 s.c.f. of hydrogen per barrel of feed converted to lower boiling products, at more than 350 p.s.i.g. hydrogen partial pressure and below 800 F. at more Cat. No.

0 Nature of Treatment A B O D E Reduced. Reduced Reduced No Steamed an not an Reduction not Steamed Steamed Steamed No Steam Reduced calcining:

4 Hrs. in H, at F 900 21 Hrs. in Air and Steam, F. 1 900 Ni, Wt. percent. F, Wt. percent.

Activity Tests:

Conversion of Feed 3 to C at 700 F Conversion of Feed 2 to (Jr-at 580 F 1 24 hours.

Example 6 A series of steam calcination treatments on nickel fluoride silica-alumina catalysts were made, the bulk denthan 0.2 v./v./hour liquid hourly space velocity over a presulfided hydrocracking catalyst prepared by chemisorbing a fluoride of a hydrogenating metal of the iron transition group on an active cracking catalyst support containing at least 10% of alumina or magnesia in substantially dehydrated state, said catalyst having a hydrogen-ating metal content of 3-40% on a dry weight basis and sulfiding the resulting catalyst, and maintaining a sulfur content, of at least 10 p.p.m. in the naphtha feed being brought into contact with said catalyst, the operating conditions including temperature being sufficient to convert at' least 30% of said naphtha feed to products sities and surface areas of the resulting catalysts were 75 boiling below the initial boiling point of said feed.

2. The process of claim 1 wherein a substantial portion of the product which does not boil below the initial boiling point of said feed is recycled for contact with said catalyst.

3. The process of claim 1 wherein said naphtha feed has an initial boiling point above 170 F. and the operating conditions including temperature are suflicient to convert at least 50% of said feed on a per pass basis to products boiling below 150 F.

4. The process of claim 1 wherein said fluoride of hydrogenating metal is nickel fluoride.

5. The process of claim 1 wherein said active cracking catalyst support is silica-alumina.

References Cited UNITED STATES PATENTS 2,982,719 5/1961 Gilbert et a1 20s 120 5 3,140,925 7/1964 Lindquist et a1 252-441 3,157,589 11/1964 Scott et al. 20s s0 3,213,012 10/1965 Kline et a1 2os 110 10 DELBERT E. GANTZ, Primary Examiner.

ABRAHAM RIMENS, Examiner.

Claims (1)

1. A PROCESS FOR CONVERTING PETROLEUM NAPHTHA HAVING A MAXIMUM END POINT OF 385*F. TO LIGHT HYDROCARBONS HAVING 3 TO 5 CARBON ATOMS WHICH COMPRISES CONTACTING SAID NAPHTHA AS FEED, ALONG WITH AT LEAST 1500 S.C.F. OF HYDROGEN PER BARREL OF SAID FEED WITH A CONSUMPTION OF AT LEAST 500 S.C.F. OF HYDROGEN PER BARREL OF FEED CONVERTED TO LOWER BOILING PRODUCTS, AT MORE THAN 350 P.S.I.G. HYDROGEN PARTIAL PRESSURE AND BELOW 800*F. AT MORE THAN 0.2 V./V./HOUR LIQUID HOURLY SPACE VELOCITY OVER A PRESULFIDE HYDROCRACKING CATALYST PREPARED BY CHEMISORBING A FLUORIDE OF A HYDROGENATING METAL OF THE IRON TRANSITION GROUP ON AN ACTIVE CRACKING CATALYST SUPPORT CONTAINING AT LEAST 10% OF ALUMINA OR MAGNESIA IN SUBSTANTIALLY DEHYDRATED STATE, SAID CATALYST HAVNG A HYDROGENATING METAL CONTENT OF 3-40% ON A DRY WEIGHT BASIS OF SULFIDING THE RESULTING CATALYST, AND MAINTAINING A SULFUR CONTENT OF AT LEAST 10 P.P.M. IN THE NAPHTHA FEED BEING BROUGHT INTO CONTACT WITH SAID CATALYST, THE OPERATING CONDITIONS INCLUDING TEMPERATURE BEING SUFFICIENT TO CONVERT AT LEAST 30% OF SAID NAPHTHA FEED TO PRODUCTS BOILING BELOW THE INITIAL BOILING POINT OF SAID FEED.