US2391160A - Refining operation - Google Patents

Description

Dec. 18, 1945.

C. A. HILLMAN ETAL REFINING OPERATION Filed day 2, 1942 Patented Dec.` 18, 1945 BEFINING OPERATION Charles A. Hillman, Sea Glrt, and Donald L.

Campbell. Short Bills, N. J., assignors to Standard (ill Development Company, a corporation oi Delaware 'Application May `2, 1942, Serial No. 441,518

1 Claim. (Cl. 260-680) bers by polymerizing di-oleiins obviously requires considerable quantities of the said di-olen's if the synthetic rubbers are to be produced in large quantities. The production of di-olelns in normal refinery practice is insufficient to'supply the demands for large scale synthetic rubber production using di-oleiins as starting materials, and in our present invention, we have devised means for producing di-oleiins such as butadiene from C4 saturated hydrocarbons lavailable in refinery practice or as eld butane, according to an im- .proved method which includes a -single stage catalytic dehydrogenation of normal butane followed by a precise fractionation of reaction products to recover a fraction consisting primarily of butadiene, iso-butane, iso-butane, and butene-1,

which fraction is thereafter subjected to solvent 'extraction to form an extract containing essentially only butadiene and a railinate containing the remainder of the said fraction, which rafilnate may be alkylated employing supplementary or extraneous iso-butane to form an aviation gasoline. Said supplementary iso-butane may be obtained by fractionation of the source material from which the above mentioned normal butane is obtained.

One object of the present invention is to dehydrogenate a hydrocarbon fraction containing normal butane to form substantial quantities of butadiene, and in orden to reduce the amount of material recycled to the dehydrogenation zone, the reaction products after extraction of the formed butadiene are alkylated so that principally normal butane and normal butenes are recycled to the dehydrogenation zone.

A more specific object of the present invention includes precisely fractionating reaction products from a single' stage dehydrogenation of `normal butane to separate and recycle to the dehydrogenation stage, a fraction containing y normal butane `and -butene-Z.v

butadiene and regeneration of the iso-butylene from the extract.

Other and further objects of our invention will appear from the following more detailed description and claim.

In order to afford a better understanding of our invention reference is madepto the accompanying drawing in which we have shown diagrammatically a form and arrangement of apparatus elements in which our invention may be carried into practical effect.

We shall now set forth a specific example illustrating our invention, and in so doing will refer to the drawing.

Referring therefore in` detail tothe drawing, i represents a charging line for normal butane. This butane is charged to a furnace 3 where it is heated to a temperature of 1330 F. and thereafter Withdrawn through line 5 and discharged into a reactor I0 containing catalyst C composed of 46% chromic oxide on alumina and preferably supported on spaced foraminous trays. The conditions maintained within the reactor I0 are the following:

Temperature Average 1230 F. Pressure Average mm. Hg absolute Contact time A second Due to the fact that the reaction is endothermic and the reactor is substantially adiabatic, the furnace outlet temperature will be somewhat higher than the average temperature in reactor i0). Alternatively heat may be supplied to the reactor.

'I'he reaction products are withdrawnl from reactor in through line I2 and'then discharged into a compressor i4 where the gases are compressed to a pressure of about 600 lbs./sq. in. whereupon they are Withdrawn and discharged into a fractionator I8 from which C3 andlighter hydrocarbons are withdrawn overhead through line 20, while the heavy bottoms comprising C4A l into an extraction tower 32. The solvent,l prei'- erably methyl amine, is discharged into tower' 32 through line 35, and this solvent dissolves out butadiene, an'd the extract thus formed is with- 'drawn through line I0. The extract is then discharged into a fractionating column 45 from which the butadiene is recovered through line I1, while the methyl amine is recovered through line 48 and recycled to line 35 leading into solvent extraction zone 32. Further details of this process, such as water extraction of solvent from the raiiln'ate and extract, are not shown because the process is well known.

The raiilnate for-med in solvent extraction zone 32- is withdrawn through line 50, and this ma tained. To this end therefore, the materials are discharged into a second treating tower 52 where they are treated with diluted sulfuric acid (about 65%) introduced into said tower through line 54 where at about 65 F. it extracts the isobutene. The material freed from isobutene is withdrawn from treating tower 52 through line 62 and discharged into alkylation plant 58. The isobutenesulfuric acid extract is withdrawn through line 53.

The details of the sulfuric acid a-lkylatlon are well known to the art and need not be `set forth at length here. It will be understood, of course, that instead of using sulfuric acid any alkylation catalyst, such as hydrogen fluoride, phosphoric acid, etc., may be used and the known expedients such as employing an excess of isoparaffin over olefin in a reaction -zone may. be

as stated, where the catalyst flows through the reaction zone in the form of a suspension or fluidized mass of catalyst intermixed with the reaction vapors, the catalyst after separation from the reaction vapors may be suspended inv air or the like and regenerated and thereaftervreturned to the reaction zone, thus maintaining the aforementioned continuity of operation. Also, since the dehydrogenation of butane is a reaction which requires careful temperature control in order to produce maximum yields of the desired products such as butadiene, it may be necessary to quench the reaction in i0 by means of a quenching medium, such as cold' butane gas, or even liquefied normal butane which may be charged into the reactor through line i5 or into line l2.

To recapitulate, our present invention involves a process for producing butadiene by dehydrogenating normal butane catalytically with a onestage operation, and the process is characterized by the advantage that the reaction products are carefully fractionated to remove unreacted normal butane and butene-Z, and thereafter solvent extracting to remove butadiene and to form a recycle fraction. However, we propose to alkylate the recycled product to remove olens and iso-paramns so that the recycled product conemployed. Supplementary or extraneous isobutane is preferably discharged into the alkylation system through line 83 in order to maintain the proper excess of iso-'paramn over olefin so that high yields and high quality products may be obtained. The alkylate is withdrawn through line 84 and delivered to finishing equipment to produce a salable aviation gasoline. The alkyla` tionl reaction is carried out by so prooortioning the iso-paraiiin to olefin that substantially all of the iso-paraiiln and olefin `are converted to an alkylate, leaving only normal paramns. These normal paraffins are withdrawn from the alkylation system through liney 85 and recycled to the charging line I containing fresh feed.

In the 4previous. description, obviously many modifications of the process may be made without departing from the spirit thereof. For in- I stance. instead of using a stationary catalyst, it

is vwithin the purview of our invention to employ a powdered catalyst which is suspended inl the reaction vapors undergoing dehydrogenation. This type of operation has many advantages in that continuity of operation may be easily obtained, since the suspension of-reaction vapors may he withdrawn from the reaction zone and passed through separating devices where the catalyst may be separated from the vapors. regenerated and returned to the reaction zone. In the\modication shown in the drawing, it will be necessary periodically to discontinue the de hydrogenation reaction carried out in reactor I0 to regenerate the catalyst to remove coke. This regeneration may be readily accomplished by forcing an oxygen-containing gas under combustion conditions throughoutthe reactor to cause combustion and burning of the coke or carbonaceous deposits formed on the catalyst. However,

tains substantially only normal butane. Obviously, this alkylation step in our process has the decided advantage of cutting down the equipment necessary to carry out the dehydrogenation, for the recycle gases contain substantially only normal butane which is the desired starting material for dehydrogenation to produce butadiene. Consequently, our process is one which may be operated with less equipment and utilities than'heretofore accomplished. In the prior art with which we are aware, the entire C4 cut of the product after separation of butadiene was yrecycled to the reaction zone, and this product included iso-butane, iso-butene, butene-l, and other products. Not only do we require less equipment and consume less steam and other utilities in our process, but in reactor i0 we form less coke for a given conversion and, consequently, reactor I0 may be operated for a longer period of time without regeneration of catalyst than has been heretofore possible.

It will be understood that the several fractionating columns shown in the accompanying drawing are of conventional design and are provided with the usual reboiling and reflux equipment.

Many modifications of our invention not specifically mentioned herein will readily suggest themselves to those familiar with this art. For example, the conditions maintained within the reactor for dehydrogenating normal butane may be varied over a wide range say from 1000 to 1400 F. temperature, from 25 mm. Hg absolute to atmospheric pressure and from 0.05 to 2 seconds contact time. Also various catalysts may be usedwith some of which steam may be used as a diluent to give 25 mm. Hg absolute to atmospheric partial pressure for the reactants in the reactor while the total pressure in the reactor is superatmospheric.

By carrying out this process we obtain yields of 25 to 50 mois of butadiene per 100 mois of normal butane fresh feed to the system including the butadiene obtained. from the processing of the recycle streams described above. In addition there would lbe produced 10 to 25 mois of mono-olefins including iso-butene, butene-l and nonrecycled butene-2 land 4 to 12 mois of iso- 75 butane per 100 mois of normal butane fresh feed It is our intention w include in the scope of to the system including the amounts obtained from the processing of the recycle streams described above. Instead of using chromic oxide on alumina, activated or hydrated, we may use the oxides of vanadium, molybdenum, tungsten or in fact the oxides of the metals of the IV, V, VI, and VIII groups of the periodic system supported on alumina or some other known support.

As an alternative iso-butene may be extracted from the feed to the alkylation plant by contacting weak sulfuric acid with the liquid stream of C4 hydrocarbons andthe iso-butene regenerated from the extract licuid phase by means well known in the art. The raiiinate would contain substantially all the iso-butane and butene-l made in the dehydrogenation of the normal butane. This raffinate would be suitable for feed to the alkylation process above described. 'I'he iso-butene removed would be valuable as a feed to a polymerization process for making 4butyl rubber or Vistanex.u In the case of the manufacture of butyl rubber a small portion of the butadiene made from the combination process As another alternative the C4 hydrocarbons from which butadiene has been extracted may ybe processed through a selective catalytic polymerization process which removesbthe iso-butene and a portion of the' butene-l to make a polymer which can be hydrogenated to give a com'- ponent for high octane aviation gasoline. 'I'he the attached claim all o! the matter specifically described herein and all that included by necessary implication, except that matter excluded by the terms of said claim.

What we claim'is:

A continuous process for manufacturing butadiene from normal butane which-comprises heating the i butane to dehydrogenation temperatures, discharging the heated butane into a dehydrogenation zone where itis permitted to remain in contact with a catalyst, consisting of chromic oxide supported on alumina, for a period o'f time of from about 0.05 to 2 seconds,'at a temperature range from about 1000 F. to 1400 F.,

and at an average mm. mercury absolute l pressure, withdrawing the reaction products from the reaction zone, separating a portion of the butane and butene-Z from the reaction products by' fractionation, recycling said separated butane and butene2 to the dehydrogenation zone, treating the remainder ofthe C4 cut of the reaction products with methyl amine to remove butadiene extracting iso-butene with sulfuric a'cid from the reaction products remaining after butadiene removal, subjecting the residual mixture to alkylation conditions in the presence ofan alkylation catalyst whereby iso-butane and butenes are converted to alkylate, separating the alkylate from the normal butane and recycling the latter to the dehydrogenation zone.

CHARLES A. nnlLMAN. DONALD L. CAMPBELL.

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