US2576034A - Catalytic dehydrogenation of paraffins - Google Patents

Description

Patented Nov. 20, 1951 CATALYTIC DEHYDROGENATION OF PARAFFIN S John W. Myers, Bartlesvilie, kla., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application February 28, 1949, Serial No. 78,891

This invention relates to the catalytic dehydrogenation of parafiln hydrocarbons to produce olefins and diolefins. In one of its more specific aspects it relates to an improved process for the dehydrogenation of aliphatic paraffin hydrocarbons in the presence of steam and steam insensitive alumina-metal oxide catalysts to produce the corresponding olefins and diolefins and is particularly applicable to the production of olefins and diolefins from aliphatic parafilns containing from four to five, carbon atoms per molecule. In the dehydrogenation of paraflins to the corresponding diolefins, two dehydrogenation steps are customarily employed. In the first step the parafiins are dehydrogenated to olefins which are then subjected in a second step to a separate dehydrogenation treatment to produce diolefins. The olefins may or may not be separated from the effluent of the first dehydrogenation step prior to dehydrogenation to dioleflns.

The customary procedure for the production of diolefins by dehydrogenation of corresponding parafiins involves separate dehydrogenation oi! parafiins and olefins using somewhat different conditions for each dehydrogenation reaction. The paraffins are first dehydrogenated to olefins in the presence of a highly active dehydrogenation catalyst, the olefins are separated from the eflluent of the paraffin dehydrogenation step, and separately converted to the corresponding diolefin at a temperature somewhat higher and in the presence of a less active dehydrogenation catalyst than employed for the paraffin dehydrogenation step. Chromium oxide is the active dehydrogenation catalyst conventionally used for the dehydrogenation of paraflins but it is much too severe for olefin dehydrogenation. Separate dehydrogenation of parafiins and olefins requires the use of diflicult and relatively expensive separation steps to segregate the parafiin and olefin feed stocks, but the separation procedure is justified on the basis of improved yields and operation. I

In the dehydrogenation of paraflins some diolefins are formed; however, the dehydrogenation of parafiins directly to diolefins is not practical by present dehydrogenation processes. Attempted combinations of concurrent dehydrogenation reactions involved in converting paramns to diolefins in a single dehydrogenation step encounter serious difliculty due to the fact that optimum conditions for the conversion of paraflins to olefins are quite different from theoptimum conditions for the conversion of olefins to dioleflns.

8 Claims. (Cl. 260683.3)

For the dehydrogenation of paraffins, such as normal butane, the catalyst ordinarily employed comprises approximately 10 weight per cent chromium oxide (ClzOs) deposited on a suitable carrier, such as aluminum oxide. As might be expected from the law of mass action, the dehydrogenation reaction is favored by low absolute or partial pressures. Low absolute pressures, i. e., below atmospheric pressure, whilefavorable to the dehydrogenation reactions, are undesirable in commercial operations due to the difiiculty of preventing leakage of air into the system. For

this reason it is customary to employ pressures somewhat above atmospheric pressure, generally in the neighborhood of about 30 pounds per square inch gage. A low partial pressure of the reactants, e. g., normal butane, may be obtained by dilution with an inert gas; It has been found that steam is undesirable as a diluent for the dehydrogenation of paraflins since it poisons or reduces the activity and life of the chromium oxide catalyst of the conventional type. While other gaseous diluents, such as propane and lighter hydrocarbons, are not subject to this disadvantage they are generally not employed because the handling and recycling of large amounts of gaseous diluents represents a large item in plant investment and operating cost. The dehydrogenation of parafiins containing four or five carbon atoms per molecule may be conducted in the absence of a diluent with an efficient separation of olefin products from the parafiin recycle stock.

From the standpoint of chemical and physical characteristics, the most desirable diluent for dehydrogenation is water vapor. This diluent may be cheaply provided in any desired amount and may be removed from the hydrocarbon stream by simple condensation, thereby eliminating a large part of the compression and fractionation equipment necessary when other diluents are used. Steam has been used as a feed diluent in several different types of catalytic and thermal processes for hydrocarbon conversion such as cracking and olefin dehydrogenation. In such processes, particularly those in which solid catalysts are used, the steam serves not only as a diluent, but also as a reagent for the removal of carbon that deposits on the catalyst.

As mentioned hereinbefore, the use of water vapor has previously been condemned in the art because of its deleterious effects on the activity of conventional catalysts employed for the dehydrogenation of paraflins. The catalysts now used for the dehydrogenation of parafiins in commercial operations show poor conversion when steam is used as a diluent. Present practice is to dehydrogenate undiluted paraflins or to use a feeds are, in many cases, substantially unreacted (see Schulze et al., U. S. 2,367,623)

Catalysts have recently been devised in contact with which paraflins may be efiectively and efficiently dehydrogenated in the presence of major amounts of steam, as is disclosed in application Serial No. 683,996, now Patent No. 2,500,- 920, filed July 16, 1946, of' which I am one of the joint inventors. The catalysts disclosed therein consist essentially of a major proportion of alumina and minor amounts of one or more of the oxides of molybdenum, tungsten, and vanadium. It is also disclosed that these catalysts may be further improved by the addition of from 1 to 15 weight per cent chromium oxide.

I have now found that catalysts consisting essentially of alumina and the above enumerated dehydrogenating oxides, in which the alumina is in minor amount by weight of the composite catalyst, have substantially longer life than catalyst composites of the same constituents but in which the alumina is present in major proportions.

An object of this invention is to provide an improved process for the production of olefins and diolefins from corresponding parafiins. Another object of the present invention is to provide a process for the dehydrogenation of paraflins wherein steam or water vapor may be effectively and efficiently employed as the diluent. A more .specific object is to provide a process which is particularly applicable to the dehydrogenation of butane to produce butylenes and butadiene. It is also an object of the invention to provide catalysts for the conversion of paraflins to olefins and diolefins in the presence of water vapor as a diluent, which catalysts maintain higher conversion activity for longer periods of time than catalysts heretofore known. Still another object of the present invention is to provide catalysts which give efiicient conversion of parafllns to olefins and diolefins in the presence of water vapor as a diluent. Other'objects and advantages will become apparent to those skilled in the art from the accompanying disclosure of the invention.

It has been found that parafilns may be advantageously dehydrogenated in the presence of steam as a diluent to produce olefins and diolefins. Advantages obtained by steam dilution are longer reaction cycles, obviation of the necessity for using reactors made of special heat and corrosion resistant alloys, and the feasibility of using comparatively large reactors. The longer reaction cycles result from the chemical reaction of steam on deposited carbon, known as the water gas reaction, which enables the catalyst to be used for long periods without regeneration with an oxygen-containing gas. Large reactors of the 'bed type, in contrast to reactors comprising complex heat exchange systems, may be employed in this process as a result of the heat-carrying capacity of steam. This represents a tremendous saving in investment and operating costs.

It has also been found that catalysts that are 4 satisfactory for the dehydrogenation of undiluted parafflns are relatively unsatisfactory for the dehydrogenation of paraflins diluted with steam because of low yields and short process cycles. It has been further found that a catalyst containing a major portion of alumina and a minor proportion of at least one oxide of the group molybdenum oxide, tungsten oxide, and vanadium oxide is satisfactory for dehydrogenating paranins diluted with steam. The catalysts of the present invention consist essentially of a minor amount of alumina, preferably in the range of 10 to 45 per cent by weight of the composite and the balance at least one, and preferably more than one, of the oxides of molybdenum, yanadium, and tungsten, each in the amount of at least 5% of the weight-of the catalyst. While a catalyst of alumina and chromia alone is unsatisfactory for dehydrogenating in the presence of steam, it is desirable to incorporate from 1 to weight per cent, preferably 5 to 50 weight per cent, of chromia in a catalyst composition of alumina and one of the oxides just named. Pieierred combinations of these dehydrogenating metals in combination with alumina are chromiavanadia, chromia-molybdena, and vanadia-molybdena. These catalysts are especially effective and efficient in the dehydrogenation of paraiiins diluted with steam inlarge amounts and have considerably longer life before regeneration is required than catalysts containing the same constituents with a major proportion of alumina.

'i'he catalysts of this invention may be prepared by any of the methods of preparing solid porous oxide catalysts known in the art. Such methods include mixing of the powdered nongel components, coprecipitation of the components as gel, and impregnation of the carrier material, 1. e., aluminum oxide, with an aqueous solution of a salt of the other metal, with subsequent ignition to the oxide. An example of the latter method of preparation is the use of an aqueous solution of a molybdenum salt, preferably ammonium molybdate, to impregnate a porous alumina carrier, suitably in the form of small pellets, followed by ignition to molybdenum oxide by passing an oxygen-containing gas over the catalyst at a moderately' elevated temperature. Catalysts of the invention may also be prepared by coprecipitating the hydrous oxides from mixed aqueous solutions of their salts so as to form a composite with less than the desired amount of oneor more of the constituents and, after forming the composite into pellets, adding the remainder of said constituent by single or multiple impregnation with a suitable salt solution followed by calcination to convert to the oxide. The catalyst may be used in the form of granules of approximately 5 to 60 mesh size, in the form of pills or pellets, in the form of fluidized powder, or in the form of dust suspended izi'the feed. In the operatic of the present invention the paraffin feed, e. g., normal butane, is admixed with steam in the ratio of between 1 to l and 1 to 30. The mixture is heated to the conversion temperature and passed into contact with the catalyst. The eiiluent from the dehydrogenation zone may be processed in known manner for the separation of substantially pure olefins and diolefins. The olefins may be separately dehydrogenated in a known manner for conversion to diolefins. Unconverted parafllns are recycled to the dehydrogenation step. If desired, the diolefins may be separated from the eiiluent and the fin at a temperature slightly below the desired reous'volumes (S. T. P.) per volume oi. catalyst per hour. The hydrocarbon and the steam may be mixed before charging to the reaction zone or the steam may be separately injected at a plurality of points along the reaction zone. The steam is preferably preheated to a temperature at least as high as the temperature employed in the reaction and in some cases it may bepreferable to separately preheat the hydrocarbons and the steam before mixing. It is sometimes desirable to preheat the steam to a temperature somewhat above the desired conversion temperature and to admix the preheated steam with preheated parafand so forth. When the activity of the catalyst becomes undesirably low because of carbon depositions, the flow of hydrocarbons is interrupted, and steam is allowed to contact the catalyst until the carbon is removed. Air may be added to the steam during the regeneration period if desired.

In order to illustrate specific advantages of the invention, three catalysts containing minor amounts of alumina and major amounts of the dehydrogenating metal oxides disclosed, and one of the catalysts of the aforementioned application containing a major amount of alumina were utilized under comparable reaction conditions in a butane dehydrogenation process in the presence of considerable steam. All of the catalysts were in the form of one-eighth inch by one-eighth inch cylindrical pellets. In the several runs the steam was admixed with normal butane, the mixture preheated to the conversion temperature and passed over the pelleted catalyst. The effluent was condensed and analyzed. The space velocity is expressed in terms of volumes of normal butane per volume of catalyst per hour. The total conversion per pass represents the percentage by volume of normal butane reacted in passing over the catalyst. The yield of normal butylenes and butadiene per pass represents the percentage by volume of the normal butane feed which was converted to these products in passing over the catalyst. The ultimate yield indicates the percentage by volume of normal butane reacted which was 50 The compositions of the catalysts shown in Table I are as follows: Catalyst A consisted 01' alumina, 30% vanadia, and 10% chromia. (All per cents are by weight.) Catalyst B con sisted of 25% alumina, 50% chromia, and 25% vanadia. Catalyst C consisted of 42% alumina, 40% chromia, and 18% vanadia. Catalyst D consisted of 38% alumina, 47% chromia, and 15% vanadia. All of the catalyst composite of catalysts A and B and the major portion of the the catalysts C and D were prepared by precipitating the hydrous oxides from mixed solutions of chromium and aluminum nitrates and vanadium pentoxide dissolved in hydrogen peroxide by addition of 3 per cent aqueous ammonia followed by recovering the precipitate and treating in the usual manner in order to form the composite into pills consisting of the metal oxides. Catalyst C was made by impregnating the coprecipitated composite in the form of pellets three times with 30 per. cent chromium trioxide solution so as to deposit 23 per cent of chromium oxide; and catalyst D was made in a similar mannor by impregnating six times with 30 per cent chromium trioxide solution so as to deposit an additional 37 per cent chromium oxide thereon.

The rates oi. activity decline oi the various catalysts tested during the dehydrogenation cycle are shown in Table II.

Table II Catalyst Activity During Cycle; Time in Hours After Start 0! Cycle Catalyst 0.5 hr. 2 hrs. 4 hrs. 6 hrs. 8 hrs.

The catalyst activity readings in the above table are those recorded by a thermal-conductivity hydrogen-sensitive gas analyzer and 211178 approximately 2-5 units above the total hydrocarbon convers on.

It can be seen from the data in Table I that the efliciency of the catalysts of this invention containing minor amounts of the aluminum oxide compare very favorably with similar compositions which include a major amount of alumina in their composition. It should also be noted that the amount of conversion to butadiene is considerably higher for the lower content alumina catalysts. However, the outstanding advantage of the catalysts of the invention in the dehydrogenation of paraflin hydrocarbons to olefins and diolefins in the presence of relatively large proportions of steam is shown in the data in Table II, which clearly indicate that catalysts containing minor amounts of alumina in combination with the dehydrogenating metal oxides have at least as high initial activity and maintain their activity at a high level over longer dehydrogenation periods than catalysts containing a major amount of alumina and the same Table I 5 Yield of m v01. Total mama-elm, Per Cent oi Temp., y Ratio Convsr- Mo] Per Cent 04H. Catalyst F. Steam to sion, in

" Butane Per Cent CH|+nCH| J per pass ultimate 722 18.8 24. 22 14. 82 61.19 26. s 719 18.9 25. 29 1s. 66 e1. 02 40. 2 car 20. 2 23. 4s 1s. 00 5.5. 31 27. 2 730 18. 7 20. e4 10. as 53. 20 40. a

metal oxide dehydrogenating catalyst. This is a highly desirable characteristic since the onstream dehydrogenating cycle can be substantially increased so as to reduce the number 01' regeneration periods required and, therefore, substantially increase the yield per day from a given amount of catalyst.

Certain modifications of the invention wi1 become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A process for the dehydrogenation of an aliphatic paramn hydrocarbon which comprises contacting said hydrocarbon diluted with from 1 to 30 volumes of steam per volume of hydrocarbon under dehydrogenating conditions, including a temperature within the range 01' 1000 F. to 1400 F. with a catalyst consisting essentially of alumina in the range of 10 to 45 weight per cent of the catalyst and the balance of at least one oxide selected from the group consisting of molybdenum oxide, tungsten oxide, and vanadium oxide.

2. The process of claim 1 in which the catalyst also contains at least 5 weight percent chromium oxide.

3. A process for the dehydrogenation of an allphatic parafiin hydrocarbon containing from four to five carbon atoms per molecule which comprises passing said hydrocarbon in admixture with from 1 to 30 volumes of steam per volume of hydrocarbon under dehydrogenating conditions, including a temperature within the range of 1000 F. to 1400 F. into contact with a catalyst consisting essentially of aluminum oxide in the range of to 45 weight per cent and the balance of chromia and at least one oxide selected from the group consisting oi molybdenum oxide, tungsten oxide, and vanadium oxide.

4. The process of claim 1 in which said catalyst includes at least 5 weight per cent vanadia.

5. The process of claim 1 in which said catalyst includes at least 5 weight percent molybdena. 6. The process of claim 3 in which said catalyst includes at least 5 weight per cent vanadia.

7. The process of claim 3 in which said catalyst includes at least 5 weight per cent molybdena.

8. A process for the dehydrogenation of an allphatic paraflln hydrocarbon containing from four to five carbon atoms per molecule which comprises passing said hydrocarbon in admixture with from vanadium oxide.

JOHN W. MYERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,406,646 Webb et al Aug. 27, 1946 2,423,163 Thomas July 1, 1947 2,477,740 Grote Aug. 2, 1949 2,500,920 Pague et a1 Mar. 21, 1950 FOREIGN PATENTS Number Country Date 115,967 Australia Oct. 15, 1942

Claims (1)

1. A PROCESS FOR THE DEHYDROGENATION OF AN ALIPHATIC PARAFFIN HYDROCARBON WHICH COMPRISES CONTACTING SAID HYDROCARBON DILUTED WITH FROM 1 TO 30 VOLUMES OF STEAM PER VOLUME OF HYDROCARBON UNDER DEHYDROGENATING CONDITIONS, INCLUDING A TEMPERATURE WITHIN THE RANGE OF 1000* F. TO 1400* F. WITH A CATALYST CONSISTING ESSENTIALLY OF ALUMINA IN THE RANGE OF 10 TO 45 WEIGHT PER CENT OF THE CATALYST AND THE BALANCE OF AT LEAST ONE OXIDE SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM OXIDE, TUNGSTEN OXIDE, AND VANADIUM OXIDE.