USRE21932E - Processes for converting hydro - Google Patents

Description

Reissued 0a. 28, 1941 L UNITED STATES '21,: raocsssas Foa commune muocsanoss Frederick E. Frey, Bartlesvllle, Okla and Walter F. Huppke, Lomita, Callf., assignors to Phillips Petroleum Company, poration of Delaware No Drawing. Original Bartlesvllle, 0th., a cor- No. 2,o9a,seo, dated November 18, 1937, Serial No. 16,512, April 15," 1935, which is a division oi erial No. 723,808,

May 2, 1934.

Application for rcissn 25, 1941, Serial No. 408,238

August 1: Claims. (c1. zen-ewe) This application is a reissueof a division of copending application Serial No. 723,608, filed May 2, 1934; v

I This invention relates processes wherein saturated hydrocarbons are converted into oleiins by catalytic dehydrogenation at elevated temperatures, the nature of the catalyst and the a corresponding aromatic hydrocarbons by a small group of catalysts comprising the most active oi .thehydrogenation catalysts. Both alcohols and 'hexamethylene hydrocarbons can be successfully dehydrogenated to yield molecular hydrogen and the corresponding dehydrogenation product at moderate temperatures. which need not exceed 300 C. The paraflln-hydrocarbons, on the other hand, cannot be dehydrogenated at .such low temperatures because of the unfavorable thermodynamic relationships. Temperatures in the range 450 to 800 C. are required to obtain high extents oi conversion and while temperatures somewhat below 400 C. will give a measurable 'dissociatlon. a prohibitively low pressure or. other.

artifice must be resorted to it extensive conversion, exceeding ten per cent or so is to be eil'ected.

In this higher temperature range ordinary decomposition or cracking will take place in the absence or acatalyst to yield smaller molecules by fracture oi'the carbon chain. and furthermore Y a protracted exposure to such temperatures will lead to theformation of tar and carbon which will. deposit on any catalytic surfaces present and be high to allow the dehydrogenation to be accomplished in a timo'lo short that cracking is not marked: the active nature or the surface must not be destroyed by the high temperatures;

- the composition and mechanical structure of the catalyst sboulddiscourage'tar and for-,-

mation. Nickel, platinum, and palladium comprise the efl'ective catalysts for dehydrogenating hexamethylene hydrocarbons but these fall under the conditions required for paraflins. Many hydrogenation of parafllns which fail in one or more respects. Many difllcultly reducible oxides, such as zinc oxide, magnesia, chromic oxide and others prepared in ordinary ways; show high de hydrogenatlng activity when applied to alcohols, but exhibit little or no dehydrogenating activity when applied. to parafllns. Theultimate mechanisml-ot the reaction is probably quite different from that of the alcohol dehydrogenation. The objectives to be achieved by the use of mixtures as catalysts are far from parallel for the two fields of catalysts and the most eflective compositions for the two purposes are widely ditierent.

In U. S. Patent 1,905,383 there has been described the use of chromium oxide in. the form of a hard dark colored vitreous gel for thepurpose of dehydrogenating paraillns. This catalyst is highly active in the useful temperature range. The activity falls of! during use and can be restored by heating to 400-550 C. in an oxygen containing gas which eiieets oxidation oi deposate in and carbon. At 550" c. to 600 0. howflo ever it passes over into the common inert form be restored by the oxygen treatment. At somewhat lower temperatures the transformation requires one or more days but ultimately takes place within the elevated temperature range useful in. practice for obtaining high conversions.

to be the iniuslble oxides, alumina, zlrconia, tho-. rium oxide, silicon dioxide. borie oxide, magneslum 'oxide and titanium dioxide incorporated in :the chromium oxide in sucha way that' thesel characteristics are conserved; This may be accomplished by precipitating together from-aqueous solution the gelatinous hydrous oxides of chromium and one or more or the elements named. The two or more metallic salts may be ably ammonium, sodium or hydroxide.

The addition oi a small amount of. acid. 5 -prior to precipitation assists in mmun other substances have been suggested for the deof chromic oxide; the activityis lost and cannot.

We have discovered that-the addition offcertain V dissolved together in water and the hydrous oxides precipitated by excess of alkali; prefergel structure during the subsequent drying of the precipitate. 'ntanium dioxide; boric oxide and silicon dioxide are of an acidic nature and are best introduced in the form of their alkali salts in aqueous solution. Such a solution may be introduced into the alkali solution used for the precipitation before the solution of the chromium or other salts is introduced, or alternatively the two salt solutions may be poured at the same time into the alkali solution with vigorous stirring. In some cases. particularly when silica is to be incorporated in a mixture with chromium oxide, the hydrous oxides may best be precipitated separately and the gelatinous precipitates mixed before drying. Five per cent or more of the difliculty reducible oxide incorporated in chromium oxide is usually required to eflect stabiliza tion to heat. Higher proportions impart greater stability but a proportion so great as to reduce the chromium oxide content to below five per cent is usually undesirable since the activity is unduly decreased; The gelatinous-precipitate The reaction rate with the catalysts described in high and equilibrium extent of dissociation is readily attained. We have found that the lower temperature at which equilibrium dissociation is small may be used at the lower pressures which favor dissociation s, or when treating the higher mospheric give good results, and pressures below obtained by this procedure is washed with water,

dried slowly in air, granulated, and finally heated to reaction temperature. Prepared in this way,

the catalyst is obtained in hard glass granules. It is preferable to perform the heating prior to use in a stream of hydrogen whereupon some reduction of the chromium oxides is eiiected with formation of water.

The catalyst prepared in this way may be supported in a suitable container and the paraiiin to be dehydrogenated passed over the catalyst while a suitable reaction temperature of preferably 450-550 C. is maintained.

The chromium oxide gel thus'stabilized by the addition of a diilicultly reducible oxide will lose activity duringuse, but the activity can be restored repeatedly by passing over the catalyst for a short time an oxygen containing gas while -molecular weight hydrocarbons, for which the thermodynamic equilibrium dissociation is large at the lower temperatures. The dissociation is repressed by high pressures, /and pressures exceeding a few atmospheres are accordingly undesirable. Pressures in the neighborhood of atatmospheric'permit still greater dissociation.

Where the catalysts are used to effect hydrogenation of oleflns or diolefins, temperatures of 200 to 500 C. may be used, preferably the, lower temperatures and a high partial pressure of hydrogen and pressures above atmospheric are desirable but not necessary. These catalysts exhibit good activity at low hydrogen pressures and resist poisoning by sulfur compounds.

Example.1.-An aqueous solution of .chromic nitrate and aluminum nitrate containing thesalts in the molarratios of one to one was introduced into an excess of dilute aqua ammonia. The gelatinous precipitate of the mixed hydrous oxides was then washed with water thoroughly, iiltered 'ofi, dried slowly in air to a glassy gel and maintaining. a temperature of 400-550 C. During the decay in activity, tar and carbon form in the catalyst granules and it is probably to this that the loss in activity must be attributed. We

have found that the addition of small amounts of certain heavy metal oxides incorporated in the catalyst will bring abouta decrease in the rate at which activity is lost and the rate at which carbon forms. Thallium and bismuth oxides are most eifective, lead andmercury oxides less so. Since these oxides are readily reduced, they are no doubt finely distributed, for the most part, in the metallic form in the catalyst during use. The heavy metal oxides are incorporated in the catalyst most conveniently by adding a soluble salt of the metal, preferably the nitrate to the chromium salt prior to dissolving" and precipitating the hydrous oxides as described, Large proportions of the heavy metal oxides cannot be introduced without loss 01" the coherent gel structure. Usually less than mol. per cent should be incorporated in the catalyst and an addition of 0.5 to 5 per 'cent will produce a great lessening in decay of activity during continued dehydrogenation.

- The improved catalysts are effective for converting not only paraiiins but also alicyclic or granulated. A 5 cc. portion of the granular gel was supported in a catalyst 'tube and a stream of n-butane passed over it at rate of tenliters per hour while the temperature was maintained at 450 C. -A 12 per cent conversion into butenes plus hydrogen was obtained. The'activity decayed during use; the conversion fell to 6 per, centduring li hours. The flow of butane was interrupted, the catalyst treated with oxygen at 450 C. and the catalyst was found to have been restored to original activity. The catalyst was used and restored to original activity in this way many times. A chromium oxide gel containing no added metals or other oxides which was used a and reactivated in the same way suffered a serious loss inactivity after two reactivations by Example 2 .A chromium oxide-aluminum oxide gel was prepared as in Example lexcept that- 2'mol. per cent of thallium nitrate was incorporated in the solution of the other metallicsalts. The conversion of butane, carried out in the same way, proceeded for 72 hours before extent of conversion fellto 6 per cent and thecatalyst was successfully reactivated many times by oxygen.

Having described our invention, what we claim is:

1. In a process forhydrogenating unsaturated hydrocarbons, the steps which comprise passing the said unsaturated hydrocarbons together with hydrogen at temperatures above 200 C. in contact with a vitreous gel catalyst comprising chromium oxide and a dimcultly reducible oxide of the group aluminum, zirconium, titanium, silicon, thorium, boron, and magnesium, the said oxides having been combined in a state of intimate association effected while'the oxides are in a highly hydrous condition.

2. In a process for hydrogenating unsaturated hydrocarbons, the'steps which comprise passing the said unsaturated hydrocarbons together with hydrogen at temperatures'above 200 C. in contact with a vitreous gel catalyst comprising chro-.

mium oxide and a diflicultly reducible oxide of the group aluminum, zirconium, titanium, sili con, thorium, boron, and magnesium, the said oxides having been combined in a state of intimate association efiected while the oxides are in a highly hydrous condition, and also at least .5 mol. percent of a readily reducible'oxide oi the group, thallium oxide, mercury oxide, bismuth oxide and lead oxide.

3. In a process for hydrogenating unsaturated hydrocarbons, the steps which comprise passing the said unsaturated hydrocarbons together with hydrogen at temperatures above 200 C. in con-- tact with a vitreous gel catalyst comprising chromium oxide and a diiiicultly reducible oxide of the group aluminum, zirconium, titanium, silicon, thorium, boron, and magnesium, the said oxides having been combined in a state of intimate association eflected while the oxides are in a highly hydrous condition, continuingsaid passage until the activity of said catalyst becomes reduced, and then restoring-the activity of said catalyst by subjecting it to treatment with an oxygen containing gas at an elevated temperature.

hydrocarbons, the steps which comprise passing the said unsaturated hydrocarbons together with hydrogen at a hydrogenating temperature above 200' C. in contact with a vitreous gel catalyst comprising not less than five per cent of chromium oxide and at least five percent of a, dimcultly reducible oxide of the group aluminum, zirconium, titanium, silicon, thorium, boron, and magnesium, the said oxides having been combined in a state of intimate association eiifected while the oxides are in a highly hydrous condition.

4; In a process for hydrogenating unsaturated 5. In a process for hydrogenating unsaturated hydrocarbons; the steps which comprise passing the said unsaturated hydrocarbons together with hydrogen at a hydrogenating temperature above 200 C. in contact with a vitreous gel catalyst comprising not less than five per cent chromium oxide and' at least five per cent of aluminum oxide, the said oxides having been combined in a state of intimate association eflected while the oxides are in a highly hydrous condition.

6. In a process for hydrogenating unsaturated hydrocarbons, the steps which comprise passing the said unsaturated hydrocarbons together with hydrogen at a hydrogenating temperature above 200 C. in contact with a vitreous gel catalyst comprising not less than five per cent chromium oxide and at least five per cent of zirconium oxide, the said oxides having been combined in a state of intimate association effected while the oxides are in a highly hydrous condition.

7. In a process for hydrogenating unsaturated hydrocarbons, the steps which comprise passing the said unsaturated hydrocarbons together with hydrogen at a hydrogenating temperature above 200 C. in contact with a vitreous gel catalyst comprising not less than five per cent chromium oxide and at least five per cent of magnesium oxide, the said oxides having been combined in a state of intimate association effected while the oxides are in a highly'hydrous condition.

FREDERICK E. FREY WALTER F. HUPPKE.