US2441663A - Process for purifying saturated hydrocarbons involving selective demethylation - Google Patents

Description

.May 18, 1948. V. HAENSEL ETAL 2,441,663

PROCESS FOR PURIFYING SATURATED HYDROCARBONS INVOLVING SELECTIVE DEMETHYLATION Filed Sept. 2l, 1946 Patented May 18, 1948 HYDROCARBONS INVOLVING 'IIVEA DEMETHYLATION SELEC- Vladimir Haensel, Clarendon Hills, and Vladimir' N. Ipatiefl, Chicago, Ill., assgnors to Universal Oil lProducts Company, Chicago, Ill., a corpo ration of Delaware Application September 21, 1946, Serial No. 698,442 y This application is a continuation-in-part of our co-pending application Serial No. 508,278, tiled October 30, 1943, now abandoned.

This invention relates to a process for purifying hydrocarbons. More specifically, the invention is concerned with a method for increasing the coi'/centration of a diiiicultly demethylatable hydrocarbon in a narrow boiling range mixture with a more readily demethylatable hydrocarbon.

An object of this invention is the production of a diflicultly demethylatable saturated hydrocarbon from a narrow boiling range hydrocarbon mixture containing said saturated hydrocarbon.

Another object of this invention is the treatment of a narrow boiling range hydrocarbon fraction containing a diilicultly demethylatable saturated hydrocarbon by reacting said fraction and hydrogen in the presence of a, hydrogenation catalyst at a temperature of from about 150 to about 350 C. and at which the more readily demethylatable hydrocarbons are demethylated more rapidly than thedescribed saturated hydrocarbons.

A further object of this invention is the treatment of a narrow boiling heptane fraction containing a major proportion of triptane with hydrogen in the presence of a hydrogenation catalyst at conditions of operation at which triptane vundergoes demethylation to only a small extent but at which other branched chain heptanes of closely related boiling points are demethylated substantially to parafnic hydrocarbons of lower molecular weight, and separating 'said parailinic hydrocarbons by fractional distillation from a higher boiling fraction containing a greater concentration of triptane than present in the heptane fraction charged to the process. A still further object of this invention is the treatment with hydrogen of a saturated hy`dro`- carbon fraction of narrow boiling range containing a major proportion of cyclohexane and smaller 7 claims. (ci. 26o-ess) tion comprises a process for increasing the concentration of a diiiicultly demethylatable V.hydrocarbon in a narrow boiling range mixture with a more readily demethylatable hydrocarbon which comprises subjecting said mixtureto reaction with hydrogen in the presence of a hydrogenation catalyst at a temperature of from about 150 C. to

about 350 C. to convert a substantial portion,v at least, of said more .readily demethylatable l hydrocarbon into lower boiling hydrocarbon, and fractionating the thus treated mixture to separate said lower boili-ng hydrocarbons yfronfr the unconverted difcultly demethylatable hydrocarbon.

Another embodiment of this inventioncomprises a process for increasing the concentration of a diicultly demethylatable saturated hydrocarbon in a narrow boiling range mixture with a more readily demethylatablev saturated hydrocarbon, which comprises subjecting said. mixture to reaction with hydrogen in the presence of a hydrogenation catalyst at a temperature of` from about 150 C. to about 350 C. to convert a substantial portion, at least, of said more readily demethylatable saturated hydrocarbon intov lower boiling saturated hydrocarbons, and fractionating the thus treated mixture to separate'said lower boiling saturated hydrocarbons from the unconverted diilicultly demethylatable saturated hydrocarbon.

A further embodiment of this invention comprises a process for increasing the concentration of a diiiicultly demethylatable saturated hydrocarbon in a narrow boiling range mixture with a more readily demethylatable saturated hydrocarbon, which comprises subjecting said mixture v portion, at least, of said more readily demethylatable saturated hydrocarbon into lower boiling saturated hydrocarbons, and fractionating the penta'nes and methyl hexanes in the presence of a hydrogenation catalyst at conditions of opera-"-4 tion at which cyclohexane undergoes demethylation to only a smallextent but at which the other saturated hydrocarbons admixed therewithv are demethylated to saturated hydrocarbons of .lower molecular weights and separating the said saturated hydrocarbons of lower molecularweight from a higher boiling fraction containing a greater concentration of cyclohexane than present in the saturated hydrocarbon fractioncharged to the process.

One specic embodiment of the present inventhus treated mixture tc separate said lower boiling saturated hydrocarbons from the unconverted Y 3 catalyst at a temperature of from about 150 to about 350 C. so maintained that methane is formed in approximately equivalent molecular proportion to the hydrogen consumed during the reaction. This process effects the removal of methane usually from the longest and least branched alkyl groups present in the hydrocarbon undergoing treatment. The more highly methylated hydrocarbons such as the polymethylalkanes are thus more stable under demethylating conditions than are other hydrocarbons with more nearly straight chain structures and, accordingly, we have found it possible to retreat a fraction containing more highly methylated hydrocarbons with hydrogen in another reactor containing a hydrogenation catalyst to obtain a hydrocarbon produ containing a still higher concentration oi' polymethylated hydrocarbons. The reaction products from such a treating step are then separated by fractional distillation from incompletely converted hydrocarbons, and the latter are l then recycled to further demethylation treatment.

By an alternative type of treatment, we are also able to obtain a fraction containing a high concentration of highly methylated hydrocarbons from a mixture oi demethylation products and unconverted hydrocarbons. In order to obtain a small fraction containing a relatively high concentration of the desired demethylated hydrocarbons, the low boiling hydrocarbons are removed from the demethylation reaction product by fractional distillation, and a part of the distillation residue consisting of a mixture of the desired demethylated hydrocarbons and unconverted hydrocarbons is recycled to further demethylation treatment. The other portion of said distillation residue is subjected to another distillation whereby desired demethylated hydrocarbons are recovered from unconverted hydrocarbons, and the latter vare also recycled to further demethylation treatment.

The attached drawing shows diagrammatical- 1y an arrangement of apparatus utilized in the production of a triptane fraction containing a relatively high concentration of this desirable diiiiculty demethylatable paramnic hydrocarbon. Other types of apparatus may be employed al- 4 ation reaction.

From reaction I5 the reaction mixture of hydrocarbons and gases, the latter comprising essentially hydrogen and methane, is directed through line I 5, and valve i1 to fractionator I8 of suitable design by which a mixture of hydrogen and methane is separated from normally liquid hydrocarbons. Said mixture of hydrogen and methane is discharged from fractionator I8 through line I3 containing valve 20 to waste, storage, or other use not illustrated in the drawing, but at least a portion of the mixture of hydrogen and methane which is being discharged through line I3 is directed therefrom through line 2| and valve 22 to compressor 23 which discharges through line 24 and valve 25 into line 4, already mentioned," through which the fresh hydrocarbon charging l stock and hydrogenmethane mixture are charged to the process.

From fractionator I8 the mixture of normally liquid hydrocarbons is withdrawn through line 25 and valve 21 by pump 28 which discharges through Aline 29 and valve 30 into fractionator 3l in which low boiling liquid hydrocarbons are separated from a mixture of heptanes and unconverted trimethylpentane hydrocarbons. 'I'he vapors of the low boiling liquid hydrocarbons are discharged from fractionator 3i through line 32 and valve 33 to condensation and cooling not illustrated in the diagrammatical drawing. 'Ihe higher boiling mixture of heptanes and unconverted trimethylpentane hydrocarbons is directed from fractionator 3i through line 34 and valve to pump 33 which discharges through line 31 and valve 38 into fractionator 39.

A portion of the mixture of heptanes and unconverted trimethylpentane hydrocarbons being transmitted through line 31'is directed therefrom through line 40 and valve 4I to recycle line and thence to line 4, already mentioned, through which.the fresh trimethylpentane frac- I ktion is charged to the process. By proper reguternately, and these various types of apparatus may also be utilized for treating other hydrocarbon fractions to increase their content of difnculty demethylatable hydrocarbons and accordingly the following description of the illustrative drawing is not limited to the treatment of trimethylpentanes to produce triptane.

A mixture of 2,2,3- and 2,3,4-trimethylpentane which is used as charging stock in the production of triptane is introduced through line I and valve 2 to pump 3 which discharges through line 4 and valve 5 into coil 5 which is heated by furnace 1. Simultaneously, hydrogen or a mixture of hydrogen and methane is directed through line 3 and valve 3 to compressor I Il which discharges through line II and valve I2 into line 4 and thence to coil 5, already mentioned. The mixture of hydrogen and trimethylpentane hydrocarbons which is so heated to a chosen reaction temperature isthen directed from coil 5 through line I3 and valve I4 to reactor I5 containing a demethylation catalyst of the type herein described. The temperature of the catalyst in reactor I5 is maintained substantially constant by suitable means, such as the useof a heat transfer liquid such as tetralin in a jacket surrounding reactor I5. For example, use of lation of valve 38, it is possible to control the amount of the hydrocarbon mixture to be returned through lines 40 and 60 to further demethylation treatment. The remainder of the mixture of demethylation product and unconverted trimethylpentane hydrocarbons which is directed to fractionator 33 is therein fractionally distilled and separated into demethylation products and unconverted trimethylpentanes.

Vapors of the demethylation products are di- 4B to receiver 41 provided with conventional gas release line 48 containing valve 43. From near the bottom of receiver 41 the liquid demethylation product is directed through line 50 and valve 5| .to pump 52 which discharges through line 53 and valve 54 to storage not illustrated in the drawing. In order to assist in controlling the temperature in fractionator 39 a portion of the demethylation product is directed from line 53 through line 55 and valve 55 to near the top of fractionatorl 39 to serve as reflux liquid therein. From near the bottom of fractionator 39 the higher boiling unconverted trimethylpentane hydrocarbons are withdrawn through line 51 and 'a pilling machine.

valve 58 by pump 59 which discharges through line 60 and valve 6| into line 4, already mentloned. As hereinabove described. a portion of the mixture of demethylation products and un` converted trimethylpentane hydrocarbon withdrawn from the bottom of fractionator 3l is also recycled by way of lines 34, 31, I0 and 60 to line 4.

Hydrogenation catalysts useful in our hydro`A carbon purification l,process comprise those catalysts which are commonly effctivejiri 'the hydrogenation of olenic hydrocarbons to parafnic hydrocarbons. The hydrogenation catalysts which we prefer in our process comprise -the metals and oxides of metals of the iron group and particularly nickel and cobalt. 'I'he metals iron, nickel, and cobalt or their oxides may be used as such, but they are preferably supported by a carrier such as-alumina, silica, diatomaceous earth, crushed porcelain, or some other refrac- 'tory material which has substantially no ad'- verse influence on the demethylation reaction. In some instances, it is also desirable to comrelatively low reaction temperatures.

comprise platinum, palladium; and also the oxides and sulfides of elements selected from the metals of the left hand'column of groups 5 and 6 of the periodic table and particularly the oxides and sulfldes of vanadium, chromium, molybdenum, tungsten, and uranium.

A highly active nickel catalyst which we have used in the present process contains approximately 66% by weight of total nickel, 30% of diatomacecus earth, and 4% of oxygen, the latter present as nickel oxide. by the general steps of suspending diatomaceous earth, also known as kieselguhr, in a dilute aqueous solution of nickel sulfate and then gradually adding thereto an excess of a hot saturated solution of sodium carbonate. This mixture of nickel sulfate soluton and diatomaceous earth is The resultant nickel-diatomaceous earth cata- .l

lyst is employed in powder form when demethylation is effected in batch type treatment or with uidized catalyst.

This catalyst is made.

When pelleted or formed and reduced to give an active cobalt-diatomaceous earth catalyst, utilizable in the form of powder or-pellets in essentially the same manner' as the nickel-diatomaceous earth catalyst.

In order to obtain relatively high yields of desired demethylation products from a higher boiling saturated or aromatic hydrocarbon charging stock, it is necessary to carry out the process under correlated conditions of temperature, pressure, and partial pressure of hydrogen.

With such correlated operating conditions, de-

methylation of the saturated hydrocarbons occurs as the principal reaction of the process. We have also found that the temperature of the demethylation reaction isv controlled more readyily when the partial pressure of hydrogen does not undergo considerable change throughout the reaction zone., Thus the normal excess of hydrogen relative to the hydrocarbon undergoingv treatment appears to assist in dissipating the' relatively high exothermic heat of reaction. The addition of methane and recycling of methanehydrogen mixtures are other means of controlling the reaction temperature.

The following examples are given to illustrate the process of the invention although with no intention of unduly limiting the broad scope of the invention.

EXAMPLE I A heptane fraction containing'approxirnately 74% of triptane and 26% of essentially 2,2-dimethylpentane and- 2,4-dimethylpentane vwas mixed with hydrogen and passed through a layer. of granular nickel-diatomaceous earth catalyst containedy in a steel reactor maintained at a temperature of 279 C. and at a pressure of 14.5 atmospheres. The heptane fraction which was charged at a rate of 1.7 liquid volumes per hour` per volume of catalyst was thus treated with 4 molecular proportions of hydrogen and a liquid product was obtained ina yield of about 94% by volume of the heptane fraction charged to the process. Distillation of the recovered liquid products separated therefrom' 25.6% by volume -of hydrocarbons boiling below '75 C. and 74.4% cf higher boiling hydrocarbons with a` refractive index, 11.02, of 1.3880. The 74.4% of higher boil- `ing hydrocarbons crystallized upon being cooled to -'l8 C. and, accordinglyQcontained at leastL 83% of'triptane' as it is known that atleast 83% catalyst particles are desired, the powdered mix.

-water and then treated lwith an excess of a hot saturated solution of sodium carbonate. The mixture of cobalt nitrate solution andjdiatomaceous earth suspended therein was agitated vigorously while the sodium carbonate solution was added thereto to form a precipitate which was then removed by filtration and washed, dried,

before it will freeze at 78 C.

Upon the basisy of our experimental results, we

" have calculated that 16.5% of the triptane and 51.5% of the other heptanes present in the triptane fraction demethylated in the above-mentioned run.

These results show that it is possible to remove less branched hydrocarbons .from a mixture with more branched hydrocarbons and thereby to con. centrate the more highly branched hydrocarbons into a single fraction. As herein described, this reaction is not limited to a mixture of parafllnic hydrocarbons but is also applicable to a mixture of paraflins and cycloparains.

' EXAMPLE II A fraction containing about '74% of triptane and 26% of dimethylpentanes, namely, 2.2,- and 2,4-dimethylpentane, was mixed with hydrogen and subjected to demethylation treatment at 282 C. catalyst temperature and at a pressure of 14 atmospheres 4in the same apparatus and in the presence of thecatalyst as referred to in Ex- 5.,, ample I. Results of this run (run No. 2) are given in Table I which also contains experimental results obtained by recycling the product to further demethylation treatment in the presence of the same catalyst.

Tanta I Treatment of triptGne-dimethylpentane mixture with hydrogen in the presence of a nickel-diatomaceous earth catalyst Run No H dro Heptanc molar ratio Hurlyglaixluid space velocity of heptane..

gist in oi run, hours ol. percent yield based on charge...

Percent distilling below 75 C Percent residue Triptane content oi charge Triptane content of residue Exit gas, volume percent: ercent Hydrogenercent methane. tiiimfarmv'v Demo y ono p c, reen Dcmethylation o1 the dimet ylpentanes,

percent product and had the following composition:

Per cent by volume Condensible gas (butanes and neopentane) 4.6 Isopentane Neohexane Y 2,3-Dimethylbutane and 2-methylpentane-- Total 100.00

EXAMPLEIII A sample of technical cyclohexane containing approximately 89% of cyclohexane and 11% of a mixture of l2,4-dimethylpentane, 2,2-dimethylpentane, 3methylhexane, normal hexane and methylcyclopentane was subjected to fractional distillation. .Approximatelyl 3% o! the material boiled below 79 C. and about 95% distilled in the' range of 19 to 81 C. A fraction taken at about the midpoint of the 'J9-81 C. plateau had a refractive index. nu, of .1.4239 and a melting point of -1.6 C. Another sample oi' the original technical cyclohexane was then passed over a nickel on kieselguhr catalyst at 299 C. and 14.6 atmospheres in the presence of 4.1 moles of hydrogen per mole cf hydrocarbon. The space velocity employed was 1 volume of liquid charge per volume of catalyst. 97.4% by volume of the liquid charge was recovered .and subjected to fractional distillation. Approximately 18% of the product boiled below 79 C. and the remainder distilled in the range of '19 to 80.5 C. A fraction taken at about the midpoint of the 'iQ-80.5 C. plateau had a refractive index, un, of 1.4253 and a melting point of +2.5 C. Another cut boiling at 80.5 C. had a refractive index, un, of 1.4260

the refractive indices and melting points. the calculated purity of the fraction distilled from the original charge was 92% while the two cuts obtained from the product had purities oi' 97 and 98.8% respectively.

We claim as our invention:

1. A process for increasing the concentration of triptane in a. mixture of the latter with 2,2-dimethylpentane and 2,4-dimethylpentane, which comprises subjecting said mixture to reaction with hydrogen in the presence of a hydrogenation catalyst at a temperature of from about 150 C. to labout 350 C. to convert a substantial portion, at mast, or said dimetnymentenes into lower bouing hydrocarbons,A and fractionating the thus treated mixture to separatelsaid lower` bom hydrocarbons from the unconverted triptane.

2. The process as detlned in claim 1 further characterized in that said catalyst comprisei; a metal of the iron group.

3. The process as deilned in claim l further characterized in that said catalyst comprises nickel.

4. A process for increasing the concentration of cyclohexane in a narrow boiling range mix re of the latter with methylcyclopentane, dime lr pentanes, and methylhexane which comprises subjecting said Amixture to reaction with hydrogen in the presence of a hydrogenation catalyst at a temperature of from about 150 C. to about 350 C. to convert a substantial portion, at least, of said methylcyclopentane. dimethylpentanes, and methylhexane into lower boiling hydrocarbons, and fractionating the thus treated mixture to separate said lower boiling hydrocarbons from the unconverted cyclohexane.

5. The processv as deflned'in claim 4 further characterized in that said catalyst comprises a metal of the iron group.

6. The process as'dened in claim 4 further characterized in that said catalyst comprises nickel.

7. A process, for the treatment of a hydrocarbon mixture comprising 2,2-dlmethy1pentane, 2,4-dimethylpentane and a saturated hydrocarbon selected from the group consisting of triptane and cyclohexane to increase the concentration of said* saturated hydrocarbon; said process comprising subjecting said mixture to reaction with hydrogen `in the presence of a hydrogenaticn catalyst at a temperature of from about 150 C. to about 350 C. to convert a substantial portion, at least, of said dimethylpentanes into lower boiling hydrocarbons,` and fractionating the thus treated mixture to separate said lower boiling hydrocarbons from the unconverted portion of said saturated hydrocarbon. l VLADIMIR HAENSEL.

VLADIMIR N. IPATIEFF.

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

UNITED STATES PATENTS Number Name Date j 2.303.118 Frey Nov. 24, 1942 2,342,074 Deanesly et al. Feb. 15, 1944 OTHER REFERENCES and` a melting point of +43' C. On the basis 0I '(6 .596-7 (1939).

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