US2367622A - Process for dehydrogenation of hydrocarbons - Google Patents

Description

' Jan. 16, 1945. w A SCHULZE ErAL 2,367,622

PROCESS FOR DEHYDROGENTION 0F HYDROCARBONS ',Fled Sept. 27, 1941 2 Sheets-Sheet 1 JOHN C. HILLYER BY HARRY E DRENNAN ATI'ORN Jan. 16, 1945. w, A SCHULZE ErAL 2,367,622

PRocEss FOR DEHYDROGENATION oF HYDRocARBoNs Filed Sept. 27, 1941 2 Sheets-Sheet 2 Patented Jan. 16, 1945 PROCESS FOR DEHYDROGENATION OF HY DROCARBON S Walter A. Schulze, John C. Hillyer, and Harry E.

Drennan,

Bartlesville, Okla.,

assignors to Phillips Petroleum Company, a corporation of Delaware Application September 27, 1941, Serial No. 412,636

3 Claims.

This invention relates to the catalytic dehydrogenation of hydrocarbons to produce oleiins and diolens. It relates more specically to an improved process for the dehydrogenation of paraffin and/or olen hydrocarbons to produce diolens and has particular application to the production of diolens from low boiling aliphatic hydrocarbons of said classes.

In the preparation of valuable diolens by catalytic dehydrogenation, the corresponding olens may be treated to yield dioleiins directly, or the corresponding parains may be the starting material for a two-stage dehydrogenation treatment in which olefins are an intermediate product of the initial dehydrogenation. In the latter instance the olens may or may not be segregated prior to conversion todiolens. The combination of the dehydrogenation treatment hydrogenation of paraiiins such as normal buinto a'single operating stage wherein the paran-olen and olefin-diclefin conversions are concurrent, has'been described. However, such combinations of the concurrent reactions have usually encountered serious difculties due to the fact that optimum conversion conditions are quite different for the two dehydrogenation reacti'ons.` Thus the conditions of temperature, iiow rate, catalyst activity vand the like which promote satisfactory conversions of olens have previously caused overconversion o'f parafllns with consequent losses due to cracking, carbon formation and the ensuing complications due to side reactions and curtailed catalystlife.

An alternative procedure starting with lowboiling paratlins such as normal butane has in-l volved the separation of the two dehydrogenation reactions into two operating stages wherebythe olens formed under optimum conditions for paraiin dehydrogenation are segregated and used as the feed stock for a second conversion step to produce the diolen. This procedure has been based on the necessity of having low concentrations of parans present during olefin de-v hydrogenation. Conversely, low concentrations of olens are desirable in the parailin dehydrogenation step. This procedure introduces a dificult and relatively expensive operation to segregate the. paraiiln and olefin stocks, but is often justified on the basis of improved yields and operation. t

Because of the relatively higher conversion temperatures, the large concentrations of unsaturated hydrocarbons. and the instability of the reaction products, the dehydrogenation of. olefins is carried out at low partial pressures of reactants. In this manner excessive decompositane may be conducted in the absence of a diluent with principal attention being devoted to an eicient separation of olen products from the parains feed stock.

The application of catalytic dehydrogenation to the low-boiling parafiins and to the corresponding oleiins has developed certain novel op-` erating methods and processes which have been disclosed in co-pending applications Serial Numbers 352,786, 352,787, 353,961, 353,962, and 355,- 710.' Said disclosures have dealt with the preferred catalysts, methods of obtaining feed y stocks, and the operating conditions for the dehydrogenation of low-boiling parains and olefins respectively. In general, the use of extremely acting catalysts at relatively low temperatures for normal butane dehydrogenationhas been disclosed. Further, the use of higher temperatures and catalysts of lower but maintained and f specic activity have been designated for the deof normal butane step or secured from other.

sources is used as the diluent in the dehydrogenation of butenes. This process provides certain advantages in the physical and chemical characteristics o1' the C3 hydrocarbon diluent, but the handling and recycling of large amounts of Cs hydrocarbons represents a larger item in plant investment and operating costs. It is an object of this invention 'to describe an improved method for the production of dlolens from corresponding parailins. vMore particularly.- it is an object of this invention to produce lower boiling aliphatic dioleiins such as butadiene from corresponding paramns, such as butane.

One of the specific objects of this invention is to provide an efficient process for producing diolens such as butadiene by a two-stage vdehydrogenation of parains such as butane in which different catalytic and other conditions are utilized in each stage, said catalysts and the condtions of their use being adapted to produce optimum results in each stage and in the combination of steps hereinafter more fully described.

We have noted that from the standpoint of chemical and physical characteristics, the `most promising diluent for olefin dehydrogenation is water vapor. This diluent may be cheaply provided in any desired amounts 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. However, the use of water vapor has previously been condemned in the art because of its deleterious effects on the activity of conventional dehydrogenation catalysts and hence on the conversions obtained by the use of said catalysts in prior dehydrogenation processes.

By extensive investigation we have determined the extent to which substantially all suggested dehydrogenation catalysts are susceptible to deterioration and loss of activity by water vapor, and the conditions which govern the use of water vapor in hydrocarbon conversions. We have discovered certain new catalysts, furthermore, which -are water-resistant and which may be satisfactorily employed in dehydrogenation reactions in a manner hereinafter described. 'Ihe application of our discoveries to the dehydrogenation of both paramns and olefins and the improved dehydrogenation process thereby evolved are described below in detail.

The conversion of paraffin hydrocarbons such as n-butane to oletlns is promoted by dehydrogenation catalysts operating with maximum activity at temperatures below those causing excessive thermal or catalytic rupture of the carbon chain. Said catalysts often exhibit suitable activity in the temperature range of 850 to 1150 F. and produce substantially equilibrium conversion with moderate contact times. Said catalysts, however, are characterized by inhibition of activityv in the presence of water vapor so that even relatively minor amounts of steam inhibit conversion. We prefer, therefore, to perform the paraffin-olefin conversion in the presence of a, highly active although watersensitive dehydrogenation catalyst and 1' in the substantial absence of water vapor.

In the dehydrogenation of olefins to diolefins, however, we have found that at the temperatures of about 1100 to 1300 F. desirable for conversion, the presence of water vapor does not inhibit conversion when the catalyst is water-resistant either inherently or by reason of a modifying an effective method for the vconversion of butane to butadiene is described, in which the first stage of dehydrogenation produces a feed particularly suitable for the second stage of dehydrogenation and in which conditions in each stage are effective for maximum operating efficiency, the combination of steps thus giving optimum results. By the use of our invention, the necessity or desirability of segregating olefins from paraflins prior to dehydrogenation is wholly or partially eliminated with consequent savings and simplification in operations: Also, the use of the steam diluent in olefin dehydrogenation tends to reduce the rate and amount of deposition of carbonaceous material on the catalyst. This effect results in increased operatingcycles for the catalyst as well as a reduction in the time required for reactivation. These and other advantages of our process will be apparent from the following disclosure.

In a more specific embodiment, our process may include the following steps: 1) ldehydrogenation of n-butane over a water-sensitive catalyst in the substantial absence of water vapor to producesubstantially equilibrium conversion to n-butenes; (2) treatment of the products from (1) to remove lower-boiling material from the C4 fraction comprising substantially butenes and unconverted butane; (3) charging the C4 fraction from (2) diluted with steam to a second dehydrogenation stage using a -waterresistant catalyst to produce butadiene; (4) treatment of products from (3) to segregate a C4 fraction comprising butadiene, butenes and nbutane; (5) removing the butadiene from-the pre-treatment. Said water-resistant properties are obtained by experimental selection or by pre-treatment of certain catalytic materials to impart water-resistance. In fact, we have discovered that the quality of water-resistance may be imparted in certain instances by treatments designed to produce stability at high temperatures and specific activity in certain valuable catalytic materials. We have further discovered that in the presence of water vapor and a waterresistant catalyst, the dehydrogenation reaction is specific for olefins to the extent that the corresponding parafllns if present in normal concentrations are substantially unconverted. This discovery makes possible the dehydrogenation of butenes, for example, in the presence of relatively large amounts of n-butane with excellent yields of butadiene and negligible conversion of the parailln hydrocarbon. In such an operation C4 fraction of step (4) and returning the butenes and n-butane to the first and/or the second dehydrogenation stage for further conversion.

The process may be illustrated by reference to Figure 1 which is a flow diagram of one arrangement of conventional equipment for application of our invention to normal butane.

Figure 2 is a fiow diagram of an alternative manner of performing the second' stage dehydrogenation.

In Figure 1 the fresh n-butane feed enters by line I and passes to heater 2 where the charge is heated to reaction temperature. The hot vapors then pass by line 3 to catalyst cases l containing a water-sensitive dehydrogenation catalyst, and the-treated vapors exit through line 5 to cooler 6. A portion of the eluent vapors may be recycled through line 5A to the inlet of the catalyst cases. The cooled vapors from 6 pass through polymer separator 1 in which minor .amounts of heavy material are removed, then are compressed in unit 8, and pass to accumulator4 9. The compressed gas then passes byline I0 to stripper column Il where C: and lighter material is removed by line I 2. A portion of this latter stream which contains hydrogen may be returned to the feed line l through line l! if dedred. The accumulator liquid yfrom 9 passes to column li through line id, while the liquid from column ii is taken through -line I to column iti, a portion being returned through line il to column ll as absorbent. Column I6 operates to yremove C3 and lighter hydrocarbons from the C4 mixture and the former material is removed through line i8. The C4 mixture which is the bottoms fraction from column i8 is taken through line i9 to line Z as fresh feed to the second-dehydrogenation stage.

The second stage feed enters the heater 22 through lines and 2i together with steam from line 23 and recycled material from line 55. The butene-butane-steam mixture is heated to reaction temperature and passes through line 2li to catalyst cases 25 filled with a water-resistant catalyst. The treated effluents exit by line 26. and a portion thereof may be returned to the catalyst case inlet through line 2'1.

Thevhot vapors passing through line 26 are chilled by Water injection through line 28, and pass to condenser 29 wherein water vapor is condensed and condensate removed through line 30. The hydrocarbon vapors then pass to compressor @i and accumulator 32. The material from accumulator 32 enters column 33 through lines 3d and 35, and said column operates to remove C2 hydrocarbons and lighter material overhead through line 3S. taken through line 3'! to column 38 or zpartly as absorbent through line 39 to column 33. Column 38 operates to remove C3 and lighter material overhead through line dil, while the depropanized liquid is taken through line il to solvent extrac- I tion unit t2.

in unit l2 a separation is made by a selective solvent between the n-butane and the unsaturated C4 hydrocarbons. The n-butane which is not dissolved passes through line d3 and may be returned through line lili, and if necessary through dehydrator liti, to the rst dehydrogenation stage. The solvent passes from unit i2 through line it to stripper il where the C4 unsaturates are separated, and the solvent is returned to unit t2 through line d8. The butenes-butadiene mixture thus substantially freed of n-butane then is taken through line t@ and fractionated in column El! to separate butene-i as an overhead product. The'bottoms fraction comprising'butenes-Z and butadiene is withdrawn'through line 5i to fractionator t2, where substantially pure butadiene is taken overhead through line 53 to storage and butenes-2 pass through line 5d to recycle line 55 or through line 56 to chemical extraction unit 5l. The butene-i stream passing from column Eid through lines 5d and 59 is treated in chemical extraction unit 5l' for the separation of the relatively low percentages of butadiene present in the butene-l. The butadiene recovered therein from either or both of the butene streams is removed through line d@ and the butenes pass through line di to recycle line 55. The recycle material from line 55 is returned to the second dehydrogenation stage for further conversion to butadiene.

Various modifications of the process outlined in Figure l will be obvious from our disclosure and no attempt will bel made to discuss all the possibilities within the scope of our invention.

For example, the separation of C3 and lighter material from the products of dehydrogenation The liquid from column 33 is ond stage total C4 mixture may be utilized without departing from the present disclosure.

Certain devices for obtaining essentially adi- 4 abatic reaction conditions in the second stage catalyst cases may be employed particularly Well with steam diluent, such as the multi-point injection of steam into different sections of the catalyst cases. In this arrangement the steam may be superheated to or above reaction temperatures in a separate furnace coil and injected into the catalyst bed to offset falling temperatures due to endothermal heat of reaction.

This last-named arrangement is illustrated by the ow diagram of Figure 2. This shows the parain-olencharge passing through line lili and admixed with steam from line |02 prior to entering heating coil [03. The mixture is heated to reaction temperature, and passes through line lii to catalyst cases m5. The concentration of the pre-mixed steam from line 02 is adjusted somewhat below the desired eventual steam concentration. Additional steam from line |06 passes through auxiliary heating coil I 01 and then after being heated up to or somewhat above the reaction temperature attained by the vapors in lineil is injected into the transfer line 104 and/or the catalyst cases as indicated through lines Hi8 and ISA at a plurality of points, The eiiluent vapors may be divided at the exit of the catalyst cases Ed with a portion being recycled to line mit throughy line Htl. The remainder passes through line Hi@ into which cooling water may be injected from line Hl, and thence through line H2, condenser HS and line il@ to further processing for the recovery of butadiene as illustrated in Figure 1. The condensed water is withdrawn through line H5.

n the rst stage of our process, the dehydrogenation to produce olens is desirably performed in both stages may be performedin a single fractionation or with other auxiliary operations such as refrigeration and the like. Similarly other methods for separating butadiene from the secon substantially dry feed stocks at pressures of about atmospheric to pounds gage. Temperatures and pressures are selected within a range suitable for the catalyst used, and temperatures within the range of 850 to 1150 F. are ordinarily employed. At these conditions ow rates of the order of l to 1) liquid volumes of hydrocarbons per hour per volume of catalyst are usually maintained. Particular conditions of flow rate, ternperature and pressure are usually chosen to conform to the characteristics of the specic catalyst used.

The water-sensitive catalysts which are useful in the first stage of our process are those having suitable activity at temperatures below those causing excessive cracking of the paran hydrocarbone and capable of promoting substantially equilibrium conversion under the designated conditions. Said catalysts include the conventional high-activity dehydrogenation catalysts such as metals. metal oxides or composites thereof alone or supported on suitable carriers. Of particular value are the oxides of aluminum and magnesium which possess considerable activity in themselves, and are preferably promoted with more or less minor quantities of oxides of metals of Groups IV, V, and VI of the Periodic Table. Specic examples are alumina catalysts promoted with the oxides of chromium and zirconium. Also of particular value are certain active chromium oxide catalysts with or withouty carriers. of valuable water-sensitive catalysts are the natural mineral ores such as bauxite and activated clays promoted with chromium or other metal oxides or salts. g

These catalysts are characterized by loss of ac- Another class A.

y tivlty due to the presence in the hydrocarbon vapors of water vapor, even in relatively minor quantities at temperatures corresponding to the range of optimum activtiy. However, for the paraffin-olefin dehydrogenation, said catalysts are preferred because of their high-activity and satisfactory yields of olens without excessive loss of charge stock or oleflnic products through carbon and fixed gas formation and/ or polymerization reactions.

The effluent vapors from the first stage of our process are processed to separate any high-boiling material formed by the catalytic treatment, and to remove propane and lower-boiling gaseous products. 'I'he separation of light gases is indicated in two stages, and the gas from the deethanizing column containing hydrogen may be partly returned to the feed stock vapors ahead of the catalyst to reduce the rate of catalyst poisoning. Precautions are observed in such an operation to avoid building up concentrations of hydrogen which will suppress the dehydrogenation reaction.

The completeness with which C3 hydrocarbons' are'separated from the. first stage eluents may vary somewhat, and the retention of a propylenepropane mixture inthe charge to the second stage may not be undesirable since said gases are essentially diluents in the second stage dehydrogenation. Further, the propylene is a potential .hydrogen acceptor capable of promoting dehydrogenation. In fact, the depropanizing step may be omitted following our first stage if desired, and the separation of C3 hydrocarbons performed following the second stage. Our purpose is to remove the C3 hydrocarbons at at least one point in the system to prevent the pyramiding and recirculation of this relatively inert material which increases the compression requirements of the process. Also, the substantially complete separation of propane is desirable ahead of the dioleln purification steps indicated in our second stage.

In the operation of the second dehydrogenation step, the charge stock is prepared in such proportionsrthat the partial pressure of olefins-is less than one atmosphere and ordinarily in .the range of 0.2 to 0.5 atmosphere. The other constituents of the mixture are principally undonverted parafns and steam together with any C3 hydrocarbons remaining in the product from the first stage. After steady state conditions are obtained in an integrated operation, the relative propor- In the treatment of butane-butene-butadiene mixtures these operations produce a substantially propane-free mixture which may then be treated by solyent extraction, azeotropic distillation or the like to produce the desired degree of separation and recovery of the parainic hydrocarbons. In many cases it is desirable to segregate a butadiene-containing fraction substantially free of butane and for economic reasons. the butane `concentrate returned to the, first stage is ordinarily substantially denuded of butadiene. The recycled butane concentrate may contain varying amounts of butenes and, although we usually prefer to maintain a relatively low degree of unsaturation in the feed to the first stage, the dehydrogenation will proceed as longv as equilibrium concentrations are not exceeded.

The recovery of diolefln from the resulting unsaturated hydrocarbon mixture may be effected by the methods illustrated or by other known processes which produce substantially equivalent results. Thus, the first operation on a butenes-butadiene mixture may be a fractionation to separate a bottoms fraction comprising butenes-2 and butadiene and an overhead fraction comprising principally butene-l with minor amounts of butadiene. This overhead fraction may then be treated by a chemical extraction process for the removal of butadiene, and the butene-l returned to the second stage of dehydrogenation.

The bottoms product is then fractionated to produce Substantially pure butadiene as the overf head product, while the butenes-2 bottoms frac- 'tion is returned to the second stage catalyst along with the above-mentioned butene-l. Or, if desired, the butene streams may be combined ahead of the chemical extraction step to effect more complete recovery of butadiene.

In certain instances it may be desirable to treat the entire C4 mixture from the second dehydrogenation stage, without preliminary fractionation, in a chemical extraction unit for the recovery of butadiene. In this embodiment the residue from the chemical separation unit comprises butenes and n-butane which may be recycled to either or both of the catalytic treatments for further conversion, with precautions being observed to avoid pyramiding of n-butane in the second stage.

tions of parains and steam will only slightly vary according to the composition of the product. Thus with a vapor mixture charge to said second stage containing 20 to 30 or more volume per cent of olens, the parainic hydrocarbon content may vary between 20 and 30 volume per cent while the steam component amounts to 40 to 60 volume per cent. These exemplary volume ratios, however, may be varied with specific operations on .diierent low-boilingl parafn feed stocks and within the terms of our disclosure.

'The` vapor eflluents from the second catalytic treatment are cooled to4 condense and separate Water andany high-boiling polymer or tar. The method of cooling may be designed to provide an )extremely rapid reduction of temperature such as the introduction of a quenching medium. After separation of the condensate, the hydrocarbon vapors are compressed and processed to remove C3 and lower-boiling hydrocarbons and other gases in one or a series of stripping and/or fraictionation operations.

The second stage of dehydrogenation is operated at low pressures of about atmospheric to pounds gage. Low total pressures' are desirable .to increase the yield of diolefin. Also, since 4the partial pressure of olens in the charge is ordinarily below 0.5 atmosphere, it is desirable to operate at low total pressures in order to have maximum volume concentrations of this component.

Higher temperatures are usually employed in the second Stage dehydrogenation than in the rst stage. I'hus, in order to obtain satisfactory conversion of butenes to butadiene, temperatures of about 1100 to 1300 F. are ordinarily employed. Flow rates used are between 1 and l0 liquid volumes of hydrocarbon charge per hour per volume of catalyst. In terms of the total vapor mixture charged to the catalyst, space velocities of 500 to5000 are satisfactory under proper conditions. The particular combination of flow rate and temperature for a specific operation will depend on the catalyst employed, the composition of the charge, and on the degree of conversion desired.

The catalysts used in the second stage are those of satisfactory activity in promoting selective olen dehydrogenation at temperatures in the range of 11.00 to i300" F. and in the presence of water vapor. Gf the greatest value are catalysts prepared by the treatment of bauxite with the hydroxides or oxides of barium and/ or strontium in such a manner that the adsorbent; mineral ore is impregnated with the metal compound. Such a catalyst and methods for manufacturing it have been disclosed in our co-pending application Serial No. 353,961 filed August 23, 1940. In the prior disclosure the application of the catalysts to butene dehydrogenation is described, but the present invention embodies a valuable additional development in the use of same in general olen dehydrogenation, particularly in View of the property of water-resistance disclosed herein.

The oxides of aluminum and magnesium have been found to give especially satisfactory catalysts, as have also those of zirconium and titanium. Both synthetic preparations of the substantially pure oxides, hydrated oxides, or hydroxides, and also natural mineral ores comprising these oxides, can yield satisfactory catalys'ts. High porosity, or specific surfaceand other qualifications of good catalysts are desirable in these materials, both before and after treatment to impart water-resistant qualities.

W e have found that various alkaline materials added to the untreated catalysts in such a manner as to impregnato the catalyst thoroughly,`

serve to impart the qualities of water resistance and selective olefin dehydrogenation to a Varying degree. While catalysts can be prepared by impregnating with alkali oxides,we have found the specic alkaline earth oxides and/or hydroxides of barium and strontium to be most satisfactory.

Catalysts prepared by impregnating bauxite with barium or strontium hydroxides and/or oxides are water-resistant and do not lose activity in contact with steam at elevated temperatures. Further, these catalysts promote selective dehydrogenation in the presence of steam to such an extent that the butane in a butano-butene mixed charge is relatively unconverted while excellent conversion of butenes to butadiene is obtained. Said catalysts are alsodeactivated with respect to craclring and/or polymerization reactions involving the hydrocarbon reactants or products.

In the catalytic dehydrogenation of butenes over the above-mentioned catalysts certain benets have been noted from the use of water vapor as diluent. Thus, while the dehydrogenation of butenes proceeds with good conversion to butadiene, butane present in the mixture is relatively unconverted although operating temperatures are usually over 180 F. higher than those used for butane conversion in our rst stage.- Also, a prolonged period of maximum catalyst activity for butene dehydrogenation is obtained when the preferred conditions are maintained. These benets apparently are due to the use of steam in conjunction with water-resistant qualities of our preferred catalysts and to tne lunction of the water vapor in reducing tar and/or coke deposition on the `catalysts during the hydrocarbon conversion. This latter effect is responsible both for prolonged operating cycles and greatly reduced time requirements for reactivation.

The following examples will further illustrate specic applications of our process, vwithout implying any particular limitations thereto.

Example I Normal butane was dehydrogenated over a bauxite-chromium oxide catalyst containing 10 weight per cent of chromium oxide. The clehydrogenation was carried out at a temperature of 110D F. and 25 pounds gage pressure. At a ow rate of one liquid volume of charge per hour per Volume of catalyst, conversion amounted to 35 per cent per pass of the n-butane with an emciency of about 80 percent based on the butenes produced. The eilluent vapors from this rst dehydrogenation stage were cooled, compressed and fractionated to produce a C4 fraction containing about 30 mol per cent of butenes and about 70 mol per cent of n-butane with minor amounts of C3 hydrocarbons and butadiene.

This mixture which constituted make-up feed to a seconddehydrogenation stage was combined with a recycle stream predominantly comprising butenes from said second stage and diluted with steam to reduce the total butenes content to 30 volume per cent. The charge composition under recycle conditions was approximately as follows:

Volume per cent Butenes 30 n-Butane 2l Steam 49 I This charge was heated to 1185 F. and passed over a water-resistant catalyst consisting of bauxite impregnated with 4.5 weight per cent of barium hydroxide at a space velocity of 1150 and a pressure of 5 pounds gage. The eilluents were cooled by direct water injection and the steam Volume per cent Butadiene 9-19 Butenes -46 n-Butane d5 The product represented approximately 3() per cent per pass conversion of the butenes charged and about 50 per cent efciency in the couver sion to butadiene.

The Ci fraction was then submitted to selective solvent extraction for the separation of the n-butane, and the butenes-butadiene mixture was fractionated to separate overhead irst butene-l and nailysucstantially pure butadiene. The butene-i fraction contained some butadiene which was recovered by a chemical separation process utilizing a cuprous chloride reagent.

The butene-l and the butenes-Z bottoms from the final fractionation were combined as the recycle stream to the second dehydrogenation stage, while the n-b-utane previously separated was dehydrated and returned to the rst dehydrogenation stage. The make-up n-butane for the rst stage amounted to a. little more than 35 per cent of the total charge to that unit since there was substantially'no loss or conversion of n-butane in the second stage, The two-stage process as operated produced a 40 perv cent yield of butadiene based on make-up n-butane feed or a 50 per cent yield based on the butenes charge to the second stage.

Example Il' butadiene. Steam was added to the charge vapors at the inlet of a pre-heating furnace to produce a charge of the following composition:

Volume per cent Butenes 36 Butane 25 Steam 39 This charge leitl the preheater at 1185 F. and at the inlet to the catalyst chamber steam at 1200 F. was injected, in an amount equal to about 10 volume per cent of the resulting total mixture. This addition offset a slight drop in temperature in the transfer line and permitted correspondingly lower` temperature in the preheater to produce an initial reaction temperature of 1185 F. at the point of entry to. the lcatalyst case. Without steam addition at this point, the catalyst inlet temperature was about 1180 F.

During the passage of the vapors through the catalyst, an additional volume of steam at 1200? F. was injected at several points in the catalyst bed. The volume added amounted to about '7 volumeper cent of the resulting total vapor mixture. The exit temperature of the vapors was 1150 F. whereas without steamviniection and at equivalent space velocity the 4exit temperature was 1140" F. The higher average temperature throughout the bed produced a higher conversion of butenes to butadiene, and the additional incremental dilution of the eilluents increased the recovery of the diolen without adversely affecting the equilibrium in the oleiin-diolen conversion reaction.

After processing the vapors to segregate n-butane for recycle to the first stage and a butenesbutadiene fraction, the latter fraction was treated by the scheme outlined in Example l, except that both the butene-l overhead fraction' and the butenes-2 bottoms fraction from the last two fractionation steps were combined ahead of the chemical extraction unit and treated for the recovery of butadiene. The butadiene yield was 55 volume per cent based on the butenes charged to the second dehydrogenation catalyst.

While the foregoing examples have served to illustrate specific applications of our invention, other modincations will be obvious and within the scope of our disclosure.

Butadiene separation may be carried out as indicated or by any satisfactory method or combination of methods such as the use of cuprous or other metal salt reagents and/0r extraction by sulfur dioxide, or by other selective solvents.

Further, although weV usually prefer to utilize a clean-up extraction on recycle streams to the olen dehydrogenation step, small amounts 'of butadiene may be'returned with said recycle streams.

The water resistant catalysts prepared and/or selected by the methods described may be reactivated over long periods of usey by treatment with oxidizing gases to, burn out carbonaceous residues responsible for decreased activity. In this connection it has been noted that in the reactivation of our preferred water-resistant catalysts, neither relatively high temperatures during reactivation nor the presence of relatively large -amounts of water vapor in the reactivating gas rigid temperature control during reactivation to avoid serious deterioration.

The terms water-sensitive" and water-resistant as applied to the dehydrogenation catalysts described herein are intended to indicate the degree to which said catalysts become polsoned and/or inactive due to the Presence of more than a trace of water vapor in the hydrocarbons undergoing the speciiied conversions.

While the foregoing disclosure has been relatively specinc to the treatment of C4 hydrocarbons, for the production of butadiene, we have found that equivalent results may be obtained from the application of our process to higher boiling paraiiins of live or six or more carbon atoms for the production of dioleiins.

We claim:

1. A pressure for the production of butadiene from normal butane which comprises contacting said normal butane with a dehydrogenation catalyst underl conditions effecting conversion of a portion of said normal butane to normal butenes, and passing the C4 hydrocarbon content of the resulting ellluent, without separation into its components, in admixture with steam into contact with a. catalyst consisting of bauxite rendered water resistant by incorporation of a minor proportion of a compound selected from the group consisting of the oxides and hydroxides of barium and strontium, under conditions effecting conversion of normal butenes to butadiene as the principal reactionwithout substantial conversion of normal butane.

2. A process for the production of butadiene from normal butane which comprises contacting said normal butane with a dehydrogenation catalyst under conditions effecting conversion of a portion of said normal butane to normal butenes, and passing the C4 hydrocarbon content of the resulting effluent, without separation into its com.. ponents, in 'admixture with steam into contact with a catalyst consisting of bauxite rendered water resistant by incorporation of a minor proportion of barium hydroxide, under conditions effecting conversion of normal butenes to butadiene as the principal reaction without substantial conversion of normal, butane.

3. A process for the production of butadiene from normal butane which comprises contacting said normal butane with a dehydrogenation catalyst under conditions eiecting conversion of a portion of said normal butane to normal butenes, and passing the C4 hydrocarbon content of the resulting eilluent, without separation into its components, in admixture with steam in amount sufcient to reduce the partial pressure of the butenes in the mixture to from 0.2 to 0.5 atmosphere into contact with a catalyst consisting of bauxite rendered water resistant by incorporation of a. minor proportion of a. compound selected from the group consisting of the oxides and hydroxides of barium and strontium, under conditions effecting conversion of normal butenes to butadiene as the principal reaction without substantial conversion of normal butane.

WALTER A. SCHULZE. J'OHN C. HILLYER. HARRY E. BRENNAN.

yCERTIFICATE oF CORRECTION. Patent No.'2,567,622 January 16, 19L5.

WALTER A. sCHUIzE, ET AL.

It is hereby certified 'that error appears `in the printed SPeCfiCatOn" `of"r:]:1eabove numbered patent requiring correction as follows: Page 1, second column, line 7, for .05 atmosphere read O.5.atmosphere; A line 2li, for "acting" read "active-F.; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the Case in the Patenteoffice.

Signed and sealed this 21|.th day of April, A. D. 1915.

Leslie Frazer (Seal) Acting Commissioner of Patent-s.

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