US2231446A - Treatment of hydrocarbons - Google Patents

Description

Patented Feb. 11, 1941 UNITED STATES PATENT osmos versal Oil Products company, Chicago, Ill, a corporation of Delaware No Drawing.

Application A?! 14, 1937,

Serial No. 136.80

7 Claims. (cl- 260-677) This invention relates particularly to the treatment of hydrocarbons for the dehydrogenation thereof and is applicable to the treatment of any type of hydrocarbons containing more hy- 5 drogen than aromatics to produce more highly unsaturated derivatives either by simple dehydrogenation or dehydrocyclization reactions.

In a more specific sense the invention is concerned with a process employing specific types of catalysts and specific types of containers for said catalysts which are constructed of metals having substantially no direct influence upon the course of the dehydrogenation reactions so that the reactions may be better controlled and the 15 life of the catalysts extended.

It has been shown by extensive experiments that the course of dehydrogenation reactions involving for example the production of mono oleflns from parafflns, the production oi diolefins 20 from mono oiefins, the formation of aromatics from naphthenes and also the formation of aromatics by the' dehydrogenation and subsequent cyclization of aliphatic hydrocarbons can be influenced in the direction of greater selectivity by the use of proper catalysts so that the formation of undesirable by-products coresponding to secondary reactions is kept at a practical minimum. In large scale operations, however, it has been found that as a rule adverse influences are exerted on the course of these reactions by the I ordinary materials of construction including ordinary steels and also special alloy steels comprising the elements cobalt, nickel, and chromium. In the case of steel tubes which contain dehydrogenating catalysts, there is a pronounced tendency for carbon to deposit where the hydrocarbon stream contacts the steel so that not only is the real catalyst contaminated but difficulties arise in temperature control on 40 account of the insulating eifect of the carbon film. These difflculties are, of course obviated if tubes of ceramic material or silica are employed, but these materials are fragile and in general not adapted to service when pressures either above or below atmospheric are employed on account of the dimculty of properly cementing or packing joints to prevent le=. i: e.

In one specific embodiment the pt invention comprises the use of aluminum-bronze al- 50 loys as containers for granular dehydrosenating catalysts comprising relatively inert supporting materials having deposited thereon minor percentages of oxides of elements in the left-hand columns of the fourth, fifth and sixth groups of th: Periodic Table.

be described in more detail. The term aluminum bronze as used in the present connection refers to alloys which contain as their essential components aluminum and copper with perhaps minor traces of iron and other elements. This definition is given to distinguish the present type of materials from those which might contain definite quantities of other elements such as those which contain as high as 3% iron and those which contain tin as well as copper and 1 still fall under the definition of bronze. Materials oi' the present character can be worked into tubes and chambers of considerable size and the alloys themselves have suificlent tensile strength to permit the use of subatmospheric and moderately superatmospheric pressures at temperatures of the order of 450-650 C. which include most of those used in connection with the preferred hydrogenating catalysts. It is also within the scope of the invention to employ steel tubes which have been properly lined by aluminum-bronze alloys.

The dehydrogenating catalysts which are employed in aluminum bronze tubes in accordance with the present invention comprise a particular group of composite catalytic materials which employ as supporting materials certain refractory oxides which in themselves may have some slight specific catalytic ability in dehydrogenation reactions but which are improved greatly in this respect by the addition of certain promoters or secondary catalysts in minor proportions. These supporting materials are preferably of a rugged and refractory character capable of withstanding the severe use to which the catalysts are put in regard to temperature during service and in regeneration by means of air or other oxidizing gas mixtures after they have become fouled with carbonaceous deposits after a period of service. The preferred supporting materials 4 comprise oxides of aluminum and magnesium oxide.

The mamesium and aluminum oxides mentioned may be considered as base catalytic materials which may have some slight specific dehydrogenating action in themselves but which are improved materially in this respect by the addition of morecatalytically active promoters.

'Either of these oxides may be prepared by the controlled calcination of either suitable ores or genating reactions over a considerable temperatrolled calcination of natural magnesite is in itself a fairly good catalyst for accelerating the rate'andcontrolling the character of dehydro- NazAKCOrla, an alkalized aluminum oxide is preparable directly.

The promoters which are used on the supporting materials include preferably oxides of certain elements which occupy what may be termed a definite area in the periodic table, and which therefore may be classed as a natural group. The elements whose oxides have been found to exert the best catalytic eflects in paraiiln dehydrogenation reactions are those in the lefthand columns of groups 4, 5, and 6, and for indicating these elements and their relative positions the following tabulation is introduced which is an abbreviated section of the periodic table of the elements as at present accepted. The table also includes the elements in the right-hand columns, though these are not included as sources of catalysts according to the present invention.

Group 1'! Group V Group Vl Left Right Leit Right Leit Right Titanium Vanadium Chromium rm ni (Arsenic) (Selenium) Zirconium Columbium Molybdenum (Antimony) (Tellurium) Hsinium Tantalum Tungsten 'ture range. However, an extensive series of experiments has demonstrated that this catalytic property is greatly improved by the addition or certain promoting substances in minor amounts. usually in the order of less than 10% byweight of the oxide.

The mineral magnesite is most commonly encountered in a massive or eathy variety and rarely in crystal form, the crystals being usually rhombohedral. In many natural esites, the magnesium oxide may be replaced to the extent of several percent by ferrous oxide. The mineral is of quite common occurrence and readily obtainable in quantity at a reasonable figure. The pure compound begins to decompose to form the oxide at a temperature of 350 0., though the rate of decomposition only reaches a practical value at considerably higher temperatures, usually of the order of 800 C. to 900 C. Magnesite is related to dolomite, the mixed carbonate of calcium and magnesium, the latter mineral, however, not being of as good service as the relatively pure, magnesite in the present instance. Magnesium carbonate prepared by precipitation methods may also be employed as a source of magnesium oxide with any type of activation which may be employed to produce a material of good porosity and structural strength.

Aluminum oxide to be used as a carrier for the preferred metal oxide catalysts may be prepared by the ignition either of precipitated aluminum hydroxide or by ignition of such natural minerals as bauxite as already mentioned. The

.ignited aluminum oxide which is apparently in the carbonaceous deposits are removed by air or other oxidizing gas mixture. By ignition of the mineral dawsonito having the formula The elements given above whose oxides are preferred as dehydrogenating catalysts according to the present invention are apparently further characterized by a variation in catalytic eiiectiveness in a horizontal direction and are also characterized by the fact that in general the most effective catalysts are oxides of elements which are most readily oxidizable and reducible. Thus in a general way the efiectiveness of the catalysts increases from Group IV to Group VI and decreases in Group VI downwardly. There are some irregularities in these characterizations. particularly in regard to compounds of vanadium which are particularly efilcient catalysts, although the oxides of vanadium are not the most easily reducible of the preferred elements of Groups IV and V.

Catalyst composites comprising supporting materials of the types indicated and oxides of the elements shown'may be prepared by utilizing by prepared granular carriers or from which they are deposited upon the carriers by evaporation of'the solvent. In order to promote completevadsorption of the salts the solutions may be concentrated by evaporation in the presence of the adsorbent material or even evaporated to complete dryness in some cases. In the latter case it is obvious that good distribution of the promoting material will be assisted by thorough mixing during the drying period.

The most general method for adding the preferred oxide catalyst to the supporting materials (which if properly prepared have a high adsorptive capacity) is to stir prepared granules of from approximately 4 to 20 mesh into solutions of salts which will yield the desired promotin compounds on ignition under suitable conditions, such as the nitrates, in some instances the sulfates. and in other instances acids corresponding to the hydratedoxides, for example, chromic acid in the case of chromium. In some instances the granules maybe merely stirred in slightly warm solutions of salts until the dissolved compounds have been retained on the particles by absorption or occlusion, after which the particles are separated from the excess solvent by settling or filtration, washed with water to remove excess solution, and then ignited to produce the desired residual promoter. In cases of certain compounds of relatively low solubility it may be necessary to add the solution in successive portions to the adsorbent base catalyst with intermediate heating to drive oil solvent in order to get the required quantity of promoter deposited upon the surface and in the pores of the base catalyst. The temperatures used for drying and calcining after the addition of the promoters from solutions will depend entirely upon the individual characteristics of the compound added and no general ranges of temperature can be given for this step.

Catalytic promoters may be added to the supports by precipitating the hydroxides of certain elements onto the granular supports suspended in aqueous solution, by adding alkali hydroxides, aluminum hydroxideor the corresponding oarbonates. The occluded hydroxides are then calcined at suitable temperatures for producing the corresponding oxides. Experience has shown that it is better to subject the oxides to a reducing action before employing the catalyst composites in dehydrogenating reactions since evidently the best catalytic eflects are accomplished by the lower oxides such as the sesquioxide CrzO: in the case of chromium and the corresponding oxide V203 in the case of vanadium. If this is not done thereis usually an induction period" in which the catalyst is gradually reduced to its lower valence by the hydrocarbon vapors passing over it In regard to the relative proportions of supports and catalysts it may be stated in general that the latter are generally less than 10% by weight of,the total composites. The effect upon the catalytic activity of the composite caused by varying the percentage of any given oxide deposited thereon is not a matter for exact calculation but more one for determination by experiment. Frequently good increases in catalytic efiectiveness are obtainable by the deposition of as low as 1% or'2% of a promoting compound upon the surface and in the pores of the base catalyst, though the general average is about 5%.

Dehydrogenating catalysts of the character described may be used over a considerable range of temperatures and pressures and hydrocarbons to be dehydrogenated more or less extensively may be contacted with the catalytic materials for widely varying times. In general the temperatures vary from Mill-700 C.. pressures from about 0.25 atmospheres absolute to superatmospheric of the order of 100 lbs. per square inch and times from 0.1 to as high 50 seconds. When paraflins are dehydrogena to the corresponding mono olefins temperatures of the order of 500-600 C., atmospheric or slightly superatmospheric pressures and times of contact up to 6 seconds are usually adequate. When using the same catalysts to produce dioleflns from mono olefins the same general range of temperatures are applicable but best results are usually obtained with subatmospheric, pressures of the order of 0.25 atmospheres and relatively short times of contact, commonly less'than 1' second. When. dehydrogenating aliphatic hydrocarbons with the object of producing aromatic hydrocarbons by successive dehydroe and cyclization reactions, the temperatures may be raised to points approaching the upper limit of 700 C. and the times of contact may be extended to as high as tions may be employed.

Any of the alternative catalysts prepared by the previously described methods may be pretreated if desired by any necessary method at elevated temperatures to increase their activity. In the heat treatment gases such as air, steam, carbon dioxide, hydrogen, nitrogen, etc. are passed over the catalyst particles at elevated temperatures. No general rule can be laid down for the temperature and time necessary to activate the catalysts, the best activating temperature sometimes being higher'and sometimes lower than the optimum temperature at which they may be employed for treatments. The use of hydrogen or other reducing gas mixture prior to putting the catalyst in service will usually eliminate an induction period corresponding to the time necessary to reduce the oxides to those of lower valence, which are apparently the active catalysts.

The following illustrative data are introduced to show the improved results obtainable when employing aluminum bronze tubes instead of steel tubes or even certatin special alloys in current use although the scope of the invention is not to be exactly limited to the data presented.

Using a catalyst comprising approximately 95% by weight of an activated alumina supporting 5% by weight of chromium sesquioxide, runs were made to dehydrogenate a mixture of bu tanes to produce a mixture of butenes. When a steel tube was employed as a catalyst container the carbon formation at 500 C. and atmospheric pressure was very rapid so that the tube became plugged with carbon in a few hours operation. Using a tube of nickel-chromium-steel the operation was improved to the extent that a run of 250 hours was possible before carbon deposition rendered continuing the process impractical. When an aluminum-bronze tube having a composition of approximately 10% aluminum and 90% copper was employed, there was substan tially no carbon deposits after a period of 1000 hours operation which indicates the marked superiority of this type of material over those in common usage in hydrocarbon conversion reactions.

The nature of the invention is evident from the preceding specification and the numerical data although neither section is intended to be unduly limiting upon those generally broad in scope.

I claim as my invention:

1. A process for the catalytic dehydrogenation of hydrocarbons which comprises subjecting said hydrocarbons at temperatures of the order of 400-700 C. to contact with dehydrogenating sentially 01 aluminum and copper and; substa tially free oi iron and tin.

3. A process for the catalytic dehydrogenation of hydrocarbons of approximate gasoline boiling range which comprises subjecting said hydrocarbons at temperatures of the order of 400-700 C. to contact with dehydrogenating catalysts in containers whose inner surfaces exposed to the hydrocarbons and catalyst are composed of an alloy consisting essentially of aluminum and copper and substantially free of iron and tin.

4. A process for the catalytic dehydrogenation of hydrocarbons which comprises subjecting said hydrocarbons at temperatures of the order of 400-700 C. to contact with dehydrogenating catalysts comprising essentially relatively inert granular materials supporting less than 10% by weight of oxides of elements in the lefthand columns of groups IV, Y- and VI of the periodic table in containers whose inner surfaces exposed to the hydrocarbons and catalyst are composed of an alloy consisting essentially of aluminum and copthan 10% by weight of oxides of elements in the.

lefthand columns of groups IV, V, and VI of the p riodic table in containers whose inner surfaces exposed to the hydrocarbons and catalyst are composed of an alloy consisting essentially of aluminum and copper and substantially free of iron and tin.

6. A process'for the catalytic dehydrogenation of hydrocarbons of approximate gasoline boiling range which comprises subjecting said hydrocarbons at temperatures of the order of 400-700 C. to contact with dehydrogenating catalysts comprising essentially relatively inert granular materials supporting less than 10% by weight of oxides of elements in the lefthand columns oi groups IV, V, and VI of the periodic table in containers whose inner surfaces exposed to the hydrocarbons and catalyst are composed of an alloy consisting essentially of aluminum and copper and substantiallyiree or iron and tin.

7. A process for the catalytic dehydrogenation of hydrocarbons which comprises subjecting said hydrocarbons at temperatures of the order of 400-700" C. to contact with 'dehydrogenating catalysts comprising essentially aluminum oxide supporting less than 10% by weight of the oxides of the elements in group VI of the periodic table in containers whose inner surfaces exposed to the hydrocarbons and catalyst are composed of an alloy consisting essentially of aluminum and copper and substantially free of iron and tin.

ARISTID V. GROSSE.