US2964579A - Selective hydrogenation of diolefins with copper chromite catalyst - Google Patents

Description

United States Patent SELECTIVE HYDROGENATION OF DIOLEFINS WITH COPPER CHROMITE CATALYST Francis William Kirsch, Wilmington, Del., and Sol W. Weller, Drexel Hill, Pa., assignors to Houdry Process (Iorporation, Wilmington, Del., a corporation of Delaware The present invention relates to selective hydrogenation of diolefins in hydrocarbon streams containing monoolefins and is especially concerned with selective conversion of butadiene contaminant in butene charge stocks employed in alkylation processes for production of aviation and motor gasoline. The invention, in certain of its aspects, also is applicable to selective conversion of diolefins, particularly C diolefins, to monoolefins; as for example in production of butylenes for use in synthetic Butyl rubber or for other uses.

The C fraction employed in alkylation processes is principally that obtained from thermal or catalytic cracking of higher boiling hydrocarbons or from a hydrocarbon coking operation. Such C fraction may generally contain in the order of about 0.3 percent and up to about 1% or more of diolefin; the 0., fraction from a cracking operation rarely contains as much as 2% of diolefin. Even this small content of diolefin in the feed for the alkylation process has been widely recognized as being extremely undesirable for the one reason, among others, of the greatly increased consumption of acid made necessary thereby, as a result of forming tarry acid-diolefin condensation products, adversely affecting the over-all economics of the alkylation process. Severalsuggestz'ons for the conversion or removal of the diolefins from hydrocarbon miXtures also containing monoolefins have not proved attractive, because of accompanying concomitant disproportionate loss of monoolefins in the treated product, and high operating and investment costs.

In the case of a C fraction derived from a coking operation which may contain even higher proportions of diolefins, going up to 5% or more, the problem is even more acute, and the use of such fractions for alkylation has been largely avoided.

Among the objects of the present invention is the provision of an improved process for selective conversion of C or C diolefins in a monoolefin-containing hydrocarbon fraction, wherein the monoolefin content is about 5 or more times the diolefin content, by catalytic hydrogenation of diolefins to more saturated product and with minimum hydrogenation of monoolefins in such fraction.

Such selective conversion of the diolefins is accomplished, in accordance with the present invention, by effecting the hydrogenation over a selected catalyst and under carefully controlled operating conditions. By this controlled operation the butadiene content of a C -olefincontaining fraction can be lowered to 0.1 weight percent or less and with a net loss of less than about 1% of butenes.

The process of the invention involves hydrogenation of a C or C hydrocarbon fraction comprising monoolefins and which contains a minor quantity of diolefins,

over catalyst comprising copper-chromite; such hydrogenation being effected at a temperature in the range of about 125 to 250 F., and at pressures of about 1 to 20 atmospheres. The hydrogen added in the process is maintained as low as possible but at least in excess of the stoichiometric requirement for full conversion of the diolefins to monoolefins. In practice generally as applied, for example, to selective hydrogenation'of an 01c ample less than about 2%.

finic C fraction containing up to about 2% diolefins, hydrogen is employed in a ratio of at least about 1.5 mols per mol of diene in the hydrocarbon feed and generally not in excess of about 20/1. Space rate of hydrocarbon feed may be from about 1 to 15 volumes of hydrocarbon (determined as liquid) per hour per volume of the catalyst in the reactor. Substantially the same reaction conditions are applicable to C hydrocarbon mixtures comprising a small quantity of C diolefins, operating in the higher portion of the described temperature range and permissibly as high as 300 F.

While the greatest advantages of the described process are obtained in the treatment of olefinic C hydrocarbon streams containing less than about 2% butadiene by weight of total hydrocarbons, the process is also applicable, but not necessarily with equal results, to the treatment of olefinic C fractions of higher diolefin content, such as a butane-butylene fraction obtained from a thermal coking operation which may include up to about 5-6% diolefins. A further application of the invention lies in the treatment of a butylene-rich stream from a dehydrogenation process containing from a fraction of a percent up to 5% or more diolefin. For example, in the dehydrogenation of butane, for production of butadiene, particularly after separation of the product butadiene by tractionation and extraction, there still remains in the monoolefin-rich raffinate a small percentage of butadiene of from about a fraction of a percent up to about 2%, depending upon the efiiciency of the separation. This small amount of butadiene cannot be economically recovered as such, and interferes with the possible uses of the rafiinate, for instance as feed to alkylation. Some butadiene is also produced in those processes designed principally for conversion of butane to butene. If the quantity of butadiene in the product is sufiiciently great, say in excess of about 5%, its recovery by known procedures may be warranted. Smaller quantities of butadiene, as between about 3 to 5% may or may not be worth recovering as such, depending upon recovery costs versus market demand and value. In either of the above instances, the enhancement of the butene product by selective hydrogenation of diolefins in accordance with the present invention, comes into consideration.

The selective hydrogenation of butadiene in a monoolefin-rich mixture by the present invention is more easily accomplished and with greatest etliciency when the proportion of diolefin in the mixture is quite low, for'ex- In such instance catalytic hydrogenation under the described operating conditions can be accomplished in isothermal or adiabatic reactor systems, and some variation from the optimum in process variables can be tolerated at the expense of some sacrifice .in yield and purity of product. In the case of butenerich hydrocarbon fractions containing a larger amount of diolefin contaminant, more precise handling is needed for selective hydrogenation of the diolefin. Since the hydrogenation is an exothermic reaction and the relative quantity of heat evolved at the selected operating conditions will depend on diolefin content, care must be taken to avoid the development of excessive temperatures which may give rise to undesired extensive hydrogenation of the monoolefin. Moreover, the hydrogen to diolefin ratio in'the reaction must be carefully controlled. For

, part of the advocated range, and provisions are made 3 for heat removal from areas nearer the outlet of. the reac: tron zone, such as by cooling coils or in other known manner.

The copper chromite catalyst employed is one having 4 It will be seen from the foregoing that at high hydro: gen/diene ratios there was a considerable conversion of the monoolefins. From the standpoint of selectivity, best over-all results were obtained atapproximately the cona substantial Surface a a. a companying, high ac ivity. ditions of Run #4. As the temperature is increased, the u h ca y y be P p d y I Q 'PQ Z i n 0f the residence time should be accordingly reduced to maincopper and chromium oxides in a porous; relatively inert tain comparable selectivity as can be seen in comparing JJPP H P as alumina, y imu a e s g ma nn Runs 1 and 3. Reduction of butadiene to below about of these oxldes Q-lz s) v the senc Q a a ri r 0.01% of product is ordinarily not required for most purtr m a opp and chr iumontaini mp ac nt: it) poses and is not advocated it this can be accomplished Pound, h a a i pp m i m ehromate to P only at the expense of disproportionate extent of hydroduce so-called massive copper chromite.- While the genafign of h l fi rm pp chromite i here p y on is With The catalyst employed in the above example was preart terminology to describe catalysts containing these pared as foflg oxides of copper and chromium in various proportions (a) The water-absorption capacity of the activated pp c mg Steiehiemetrie, it is to be und a the alumina pellets (having a surface area of about 80 m.'*/ g.) finished catalyst in heat-treated and/or reduced state is was d t rmined as being 47% by weight, so that it was not necessarily or entirely in the form s i y of the npredicted that 2000 grams of the pellets would absorb p e CUPIZOII' The catalysts employed P a Of about 940 cc. of solution containing the required content the invention contain oxides of copper andchromiumin f copper d h i To b i complete i Pf p furnishing substantially qu o P p sion of the pellets in the solution, a 50% excess of solu-, of C11 and Q 85 from 0.7 to 1.3 mols of C ppe tion was employed, to provide a catalyst composed of per mol of chromium, and have a surface area in bulk or 2000 parts 1 0 parts f 0 and 242 parts f supported form of not less than about 50 mF/g.

The preferred operating range for selective hydrogena- 25 (b) 11 3 parts o CMNOS) were heated until f of 4 dlelefin over the alumina-Supported Catalyst the crystals melted, dissolving the salt in its water of hymcludes temperatures in the order of ISO-225 F. and d g 480 parts f CrO (:363 parts Cr O were pressures of from about 75 to 0 p -s, employing y dissolved in 375 parts water with warming and stirring. P PP rates from about one Volume The molten copper salt solution was added to the chromic mined as q P 110111 P' vehlme 0f Catalyst pw acid solution with stirring and the solution diluted with as P about Hydrogen 15 added Somewhat 111 water to a total volume equivalent to that occupied by cess of the stoichiometric requirement for conversion of 4 2 parts water h dlolefin t0 monoolefin as from 1015 2 P mo! (c) 2000 parts of the activated alumina pellets were drolefins 1n the charge up to about 20:1. As noted above, immersed in the impregnating solution 5 and allowed less severe operating conditions on the low side of the to Soak therein f hours The pellets were then temperature range and lower hydrogen ratios in the drained free of excess solution and dried in hot air for scribed range are employed when the hydrocarbon charge 2 hours at 75 cfmtams f than Sever? P of diolefinwith (d) The dried pellets were then calcined for 8 hours higher activity catalyst having a surface area in the order at 5 F. in a Steamgdr atmosphere comprising 20 mol of 80 m. g. or more, lower pressures can be employed 40 percent H2O down to about 70 if desired somewhat Using the catalyst of Example I above, the activity and f Space rates may be employed as to about selectivity of the catalyst for butadiene hydrogenation m the treatment f hydrocarbon Streams contammg without excessive hydrogenation of monoolefins in the less than about 2% dlolefinsfeed, are maintained over long operating periods of sev- EXAMPLE I eral months or more, provided that the catalyst is periodicall ur ed with h drogenation. Such hydrogenation The .catalyst employed m the Sever-a1 runs W purge is b elieved to IY6II10V from the catalyst polymeric apliroxlmately Cuo and.10% Craoa by welght on hydrocarbon materials which become deposited therein act vated alumina, prepared 1n the manner-hereinafter during the reaction Thus in runs made over the f The charge Stock had the followmg compo' scribed catalyst operating continuously on a two-shift Smon' period and overnight shutdown, the flow of hydrocarbons hwelght Percent of was discontinued during the shutdown and hydrogen flow Butane ydmcarb'on g i continued at about the same rate as during the on-stream period (approximately 12 hours on stream and 12 hours Butemfs on purge). In over twelve days operation with the de- Butadlene scribed intervening hydrogen purges, there was no sig- The catalyst was brought to reduced state and the renificant loss in the activity or selectivity of the catalyst. actor and contents brought to required pressure by cir- The results obtained after about 146 hours of such operaculation of hydrogen-rich gas. The described C hydrotion (at about 175180 F. average hydrocarbon inlet carbon charge was then cut inand passed over the catatemperature, 150 p.s.i.g., 3 LHSV, and 5 mols H per mol lyst contained in the fixed bed reactor at an average temdiene in feed) are reported below: perature and under the conditions set out in Table I below with the results therein reported. B tane, B teues, Butadiene,

Wei ht \Veit'ht W'eivht Table l Percent Percent Percent 1M0 1 2 3 4 23;; at is Product at 108 hrs so. 4 a0. 6 o; 00 Conditions:

Temperature, F. (a 212 215 238 148 P e ans" 1 50 1 0 150 To determine the frequency of purging that may be igjgifigg gfii Z 2 2 2 required, the operation was run conti o y over the & catalyst of Example I Without intervening purge. It was 222 found that after about 40 hours of such operation the activityofthe catalyst began to decline significantly and at a continuously increasing rate in the next several hours.

The results obtained at 38 hours of such continuous operation (during which the temperature rose to 224 F.) are reported below:

Accordingly for those catalysts which begin to show loss of activity or selectivity in continuous running of about 36 to 48 or more hours, it is proposed to subject the same to a purge in hydrogen at about run temperature or somewhat below for 6 or more hours. The continuous running without purge should not be extended beyond the time that the catalyst begins to decline rapidly in activity, since once that the activity has been largely lost it has been found then impossible to restore the activity by the proposed hydrogen treatment.

Of course, with those catalysts which do not show appreciable activity decline on continuous operation of a week or more, the hydrogen purging step need not be practiced. When such catalysts eventually begin to decline in activity as a resutl of coke accumulation or other deactivating influences, these can be restored to activity by oxidative regeneration in air at about 700 F. or higher but short of damaging temperatures.

Prior to going on stream in treatment of hydrocarbons with fresh catalyst or with regenerated catalyst, the catalyst should be first reduced in hydrogen at temperatures above about 180 F., and preferably no higher than 300 F., for one or more hours. It was found that lower reduction temperatures (150 F.) failed to initiate the desired activity in the catalyst for hydrogenation of diolefin at space rates of 3 LHSV or higher.

EXAMPLE II The following example relates particularly to the treatment of a refinery C fraction of higher diolefin content, such as one of the following typical composition from mixed refinery sources:

The charge is fed to the catalyst, such as one described in the previous example, at a temperature of about 150- 180 F. maintained in an isothermal reactor, at a pressure of 150 p.s.i.g. together with 2 mols hydrogen per mol of diolefin, the hydrocarbon charge rate corresponding to a liquid hourly volume space velocity of 5. Under these conditions the diolefins can be reduced to below 0.5% of product with less than about 3% net loss in monoolefins.

In the treatment particularly of hydrocarbon fractions of higher diolefin content in excess of about 2%, it is especially important that the hydrocarbon feed temperature be kept as low as possible to avoid the initiation of excessive exothermic temperature rise. Thus, it was found that even for a charge of only about 1% butadiene content, introduction of the hydrocarbon charge at 198 F. resulted in 82 F. temperature rise (at 5H :diene mol ratio), while at an inlet temperature of 150 F., the temperature rise was only 17 F. (at 2.5H zdiene mol ratio).

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. The method of selectively hydrogenating diolefins present in minor quantity in a mixed hydrocarbon stream composed essentially of hydrocarbons in the range of 4-5 carbon atoms, said stream also containing monoolefins, which method comprises subjecting such mixed stream with added hydrogen to contact with active copper chromite catalyst having an initial surface area of not less than 50 square meters per gram, said contact being effected at temperatures in the range of -250 F. and at a pressure of 1 to 20 atmospheres.

2. The method according to claim 1 wherein said bydrocarbon stream is composed essentially of C hydrocarbons.

3. The method according to claim 2 wherein said hydrocarbon stream contains up to about 2% by weight butadiene.

4. The method according to claim 1 wherein said bydrocarbon stream is one containing up to about 6% diolefins.

5. The method of selectively hydrogenating butadiene in a C hydrocarbon fraction containing monoolefins in an amount of at least several times the butadiene content, which method comprises contacting the hydrocarbon fraction with a catalyst comprising oxides of copper and chromium wherein the Cu to Cr mol ratio lies between 0.7 to 1.3, said contacting being effected in the presence of free hydrogen in quantity in excess of that stoichiometrically required for hydrogenation of the butadiene content of the charge to butene, and said contacting being at conditions including temperature in the range of about 250 F. and at pressure of 70 to 250 pounds per square inch gauge.

6. The method according to claim 5 wherein said catalyst is unsupported copper chromite.

7. The method according to claim 5 wherein said catalyst comprises a porous inert carrier for said oxides.

8. The method according to claim 7 wherein said carrier is activated alumina.

9. The method according to claim 5 wherein said operating conditions include hydrogen to diene mol ratios of between 1.5 and 5.

10. The method according to claim 5 wherein the catalyst is subjected to a hydrogen purge in the absence of hydrocarbon feed for at least several hours between successive contacts with the hydrocarbon fraction.

11. The method according to claim 5 wherein said catalyst prior to hydrocarbon contact is treated in flowing hydrogen gas at above 180 F. for at least 6 hours.

Adkins: Reactions of Hydrogen, Univ. of Wis. Press, Madison, Wis., 1937, pp. 47-48.

Emmett et al.: Catalysis, vol. 3, Reinhold Publishing Corp., New York, 1955, p. 81.

v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No; 2 964579 I Decemher 13 1960 Francis William Kirsch et all,

it is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below,

Column .3 line 8 for "surh" read such column 4 line 46, for "hydrogenationi each occurrence read hydrogen column 5, line 26 for "resutl" read Signed and sealed this 24th day of October 1961o (SEAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents USCOMM-DC v

Claims (1)

1. THE METHOD OF SELECTIVELY HYDROGENATING DIOLEFINS PRESENT IN MINOR QUANTITY IN A MIXED HYDROCARBON STREAM COMPOSED ESSENTIALLY OF HYDROCARBONS IN THE RANGE OF 4-5 CARBON ATOMS, SAID STREAM ALSO CONTAINING MONOOLEFINS, WHICH METHOD COMPRISES SUBJECTING SUCH MIXED STREAM WITH ADDED HYDROGEN TO CONTACT WITH ACTIVE COPPER CHROMITE CATALYST HAVING AN INITIAL SURFACE AREA OF NOT LESS THAN 50 SQUARE METERS PER GRAM, SAID CONTACT BEING EFFECTED AT TEMPERATURES IN THE RANGE OF 125-250*F. AND AT A PRESSURE OF 1 TO 20 ATMOSPHERES.