US2344318A - Treatment of hydrocarbons - Google Patents

Description

Patented Mar. 14,1944

TREATMENT OF HYDROCAEBONS William J. Mattox, Chicago, 111., assignor to Universal -il Products Company, Chicago, corporation of Delaware No Drawing. Application December 28, 1939. Serial No. 311,306

8 Glaims.

This invention relates particularly to the conversion of straight chain hydrocarbons into closed chain or cyclic hydrocarbons.

More specifically it is concerned with a proccss involving the use of particular catalysts and specific conditions of operation in regard to temperature, pressure, and time of reaction whereby aliphatic hydrocarbons can be converted efii-e ciently into aromatic hydrocarbons.

In the straight pyrolysis of pure hydrocarbons or hydrocarbon mixtures, such as those encountered in fractions from petroleum or those occurring naturally or produced synthetically, the reactions involved which produce aromatics from paramns and olefins are of a complicated character and are diflicult'to control.

The search for catalysts to specifically control and accelerate desired conversion reactions amonghydrocarbons has been attended with the usual difilculties encountered in finding catalysts for other types of reactions since there are no basic laws or rules for predicting the efiectiveness of catalytic materials and the art as a whole is in a more or less empirical state. In using catalysts even in connection with conversion reactions among pure hydrocarbons and particularly in connection with the conversion of the relatively heavy distillates and-residua which are available for cracking; there is a general tendency for the decomposition reactions to proceed at a very rapid rate, necessitating the use of extremely short time factors and very accurate control of temperature and pressure to avoid too extensive decomposition. ,There are further dimculties encountered in maintaining the ciliciency of catalysts employed in pyrolysis since there is usually a rapid deposition of carbonaceous materials on their surfaces and in their pores.

The foregoing brief review of the art of hydrocarbon pyrolysis is given to furnish a general background for indicating the improvement in such processes which is embodied in the presentinvention, which may be applied to the treatment of pure paraflin or olefin hydrocarbons; hydrocarbon mixtures containing substantial per centages of paraffin hydrocarbons such as relatively close out fractions producible by distilling petroleum, and analogous fractions which con tain unsaturated as well as saturated straight chain hydrocarbons, such fractions resulting from cracking operations upon the heavier fractions of petroleum.

In one specific embodiment the present invention comprises a process tor producing aromatic reactions involving dehydrogenation, cyclization.

ing essentially a major proportion of thorium r ng closure with the production in the simplest oxide and a relatively minor proportion of on ides of elements selected from the members of the left-hand columns ofgroups 5 and 6 of the periodic table. I

According to the present invention aliphatic or straight chain hydrocarbons having 6 or more carbon atoms in chain arrangement in their structure are specifically dehydrogenated in such a way that the chain of carbon atoms undergoes case of benzene from n-hexane or n-hexene and in the case of higher molecular weight parafiins of various alkyl derivatives of benzene. Under properly controlled .conditions of temperature, pressure, and time of contact, very high yields of the order of '75 to of the benzene or aromatic compounds are obtainable which are far in excess of any previously obtained in the art either with or without catalysts. For the sake of illustrating and exemplifying the types of hydrocarbon conversion reactions which are specifically accelerated under the preferred conditionsby the present types of catalysts, the following structural equations are introduced:

fi fig on, on. on on H 4H2 CH1 CH1 CH CH n-Hcxane Benzene on, c-cHi 0H, CHr-CH: CH OH I 'II' 43: H: CH: H CH C a CH n-Heptane Toluene C31 /CH on, CHr-CH: CH f-cu: m

l H: QHlr-CH: H C-CH:

7 CH C n-Octanc o-Xylcnc Ethyl benzene and m-xylene and p-xylene are also formed from n-octane by a. combination of and isomerization, but no idea is oiiered as to the probable order in which these reactions occur.

In the foregoing table the structural formula of each of the primary parafiin hydrocarbons has been represented as a nearly closed ring instead of by the usual linear arrangement for the sake of indicating the possible mechanisms involved. No attempt has been made to indicate the possible intermediate existence of mono-olefins, dioleflns, hexarnethylenes or'alkylated hexamethylenes which might result from the loss of various amounts of hydrogen. It is not known at the present time whether ring closure occurs at the loss of one hydrogen molecule or whether dehydrogenation of the chain carbons occurs so that the first ring compound formed is an aromatic such as benzene or one of its derivatives. The above three equations are of a relatively simple character indicating generally the type of reactions involved but in the case of n-paraiiins or mono-olefins of higher molecular weight than the octane shown and in the case of branch chain compounds which contain various alkyl substituent groups in different positions along the G-carbon atom chain, more complicated reactions will be involved. For example, in the case of such a primary compound as '2,3-dimethyl hexane the principal resultant product is apparently o-xylene although there are concurrently produced definite yields of such compounds as ethyl benzene indicating an isomerization of two substituent methyl groups. In the case of nonanes which are represented by the compound 2,3,4-trimethyl hexanefithere is formation not only of mesitylene but also of such compounds as methyl ethyl benzene and various propyl benzenes.

It will be seen from the foregoing that the scope of the present invention is preferably limited to the treatment of aliphatic hydrocarbons which contain at least 6 carbon atoms in straight chain arrangement. In the case of paraflin hydrocarbons containing less than G-carbon atoms in linear arrangement, some formation of aromatics may take place due to primary isomerization re- I actions although obviously the extent of these will vary considerably with the type of compound and the conditions of operation. The process is readily applicable to paramns from hexane up to dodecane and their corresponding olefins. With increase in molecular weight beyond this point the percentage of undesirable side reactions tends to increase and yields of the desired alkylated aromatics decrease in proportion.

The thorium oxide carrier referred to above has a relatively low dehydrogenating activity, while the oxides of the elements mentioned are of relatively high catalytic activity and furnish by far the greater proportion of the observed catalytic eflects. The oxides of these several elements vary somewhat in catalytic activity in any given reaction comprised within the scope of the invention and this variation will be greater in the case of different types of dehydrogenation and isomerization reactions.

In regard to the preparation of thoria employed as a carrier or support for the preparation of dehydrocyclization catalyst, it may be stated that thoria may be obtained by known methods from a number of minerals including thorite, orangite, and thorianite.

The catalytic dehydrogenating efiiciency of thorium is greatly improved by the presence of oxides of the preferred elements in relatively minor amounts. The oxides which constitute the principal active catalytic materials-may be deposited upon the surface and in the pores of stantly since the observed catalytic effects evidently' depend principally on surface action.

The oxide of vanadium which results from ignition of the nitrate, the hydroxide, or the carbonate is principally the pentoxide V205 which is reduced by hydrogen to form thetetroxide V204; or the corresponding dioxide V02 and then to the sesquioxide V203. In any case the primary deposition of vanadium compounds upon thoria granules may be made by the use of the soluble vanadyl sulfate or the nitrate and also solutions of ammonium and alkali metal vanadates may be employed, which furnish alkaline residues on ignition. It is probable that the sesquioxide 'is the principal compound which accounts for the catalytic activity observed with vanadium catalysts in reactions of the present character.

Columbium has several oxides which may be employed as catalyst; components supported by thoria although the lower oxides are most like-.

iv to exist under the conditions employed in the process. The pentoxide CbzOs results from the ignition of the pentahydroxidewhich may be precipitated from solutions of soluble compounds such as the mixed fluoride of columbium and potassium. Solutions of alkali metal columbates may also be employed as a source of catalytic material, these furnishing an alkaline residue on drying and ignition. The pentoxide is definitely reduced by hydrogen or by hydrocarbons at the preferred temperatures of operation so that the essential catalysts for the major proportion of a run will probably include the lower oxides CbOz. ch20: and C110.

Th element tantalum which has the highest atomic number of the fifth group of elements herein mentioned, also has the pentoxide TazOs, a tetroxide TazOq and probably a sesquioxide TazOa. The higher oxide is prepared by the ignition of the precipitated pentahydro'xide precipitated from soluble salts. The element chromium has three oxides, the trioxide CrOa, the dioxide CrOz, and the sesquioxide ClzOs, the last named being readily produced by heating the trioxide in hydrogen or hydrocarbon vapors at a temperature of 250 C. The dioxide has been considered to be an equimolecular mixture of the trioxide and the sesquioxide. The oxides are readily, developed on the surface and in the pores of thoria granule by utilizing primary solutions of chromic acid H2Cl04 or chromium nitrate Cr(NOa)a. The isnition of the chromic acid,the nitrate, or the precipitated trihydroxide produces primarily the trioxide which is then reduced to the sesquioxide to furnish an active catalyst for use in reactions of the present character.

The two most important oxides of molybdenum which are employed alternatively in the production of dehydrocyclization catalysts, according to the present invention, are the dioxide M002, and the sesquioxide M0203. Since thereduction of the trioxide by hydrogen begins at about 300 C. and the reduction is rapid at 450 just requisite to wet the carrier-granules uniformly and the mass is then dried and calcined.

The element tungsten has three oxides: the trioxide W02, the dioxide W02, and the sesquioxide W203. The trioxide is readily soluble in aqueous ammonia from which it may be deposit- I ed upon thoria. granules and it is ordinarily re duccd preliminary to service by the action of hydrogen at a relatively high temperature. Tungstic acids may be precipitated from the hydrated oxides and these may be heated to drive ofi water and leave a residue of oxides on the carrier particles. I

In regard to uranium, which i the heaviest member of the present natural group of elements whose oxides are preferred as catalysts. it may merely be stated that while this element furnishes catalytic oxides having some order of catalytic activity, its scarcity and cost naturally preelude its extensive use in practice.

It has been found essential in the production of high yields of aromatics from parafilnic hydrocar-bons when using the preferred'types of dehydrocyclization catalysts that, depending upon the parafilnic hydrocarbon or mixture of hydrocarbons being treated, temperatures from 450 to 650 C. should be employed, contact times of approximately 0.1-60 seconds, and pressures approximating atmospheric. The use of subatmospheric pressure of the order of /4 atmos-- phere may be-beneflcial in that reduced pressure generally favors selective dehydrogenation reactions, but on the other hand moderately superatmospheric pressure, usually of the order of less than 100 pounds per square inch, increases the capacity of commercial plant equipment, so

that in practice a balance is struck between these two factors.

While the present process .is particularly applicable to the production of the corresponding aromatics from an aliphatic hydrocarbon or a mixture of aliphatic hydrocarbons the invention may be employed also to produce aromatics from olefinic hydrocarbon mixtures such as distillates from paraflinic or mixed-base crude petroleum. In this case the aromatic character of the distillate will be increased and as a rule the octane number of theproduct will be higher than that of the charging stock. If desired and found feasible on a basis of concentration, the aromatics produced in the hydrocarbon mixtures may be recovered as such by distillation to fractions of proper boiling range followed by chemical treatment with reagents capable of reacting selectively with them. Another method for concentrating aromatics will involve the use of selective sclvents such as liquid sulfur dioxide, furfural, chlorex, and alcohols.

to further contact with the dehydrocyclization catalyst so as to convert these olefins into further quantities of aromatics and form a substantially olefin-free aromatic product.

These catalysts consisting of thoria activated by oxides of the elements of the left-hand columns of groups 5 and 6-0f the periodic table may be composited with stabilizing oxides such as magnesium oxide to produce a catalyst composite which retains its aromatic-forming activity after many periods of use and reactivation by burning off carbonaceous deposits in an oxygen-contaming atmosphere. Composites of thoria and activating metal oxides such as are hereinabove described efiect a relatively high conversion of The process of this invention makes possible the production of aromatic concentrates or aromaltic-paraffinic hydrocarbon mixtures which are free from olefins and suitable for solvent extraction or other methods of separating pure aromatics, or which may be used directly for nitration Or for other chemical reactions to which the presence of olefins would be objectionable. By this process the olefins formed incidental to the CYOliZflltiOn reaction are converted into aromatics thereby increasing further the yield of these desirable hydrocarbons.

The following example is introduced to show results obtainable in the operation of the process,

although these data are not presented with the intention of unduly limiting the broad scope of the-invention:

EXAMPLE A catalystcontaining 8% by weight of chroamnic fraction is contacted, for example, with a material comprising granular activated thoria.

supporting 432% by weight of chromium sesquioxide. The'cyclicized material containing relatively small amounts of olefins may be recycled oxide was prepared b dissolving 84.2 parts by weight of crystalline chromic nitrate,

Cr (N03) 3.9H2O

and 385 parts by weight of thorium nitrate, Th(NO3)4.4H2O, in 8000 parts by weight of water, followed by precipitating the hydrated oxides by addition of 225 parts by weight of concentrated ammonium hydroxide solution. The precipitates were removed from the solution by filtration, wased with distilled water, dried at -200 0;, then pressed into cakes on a hydraulic press, and later broken and sized to produce 10-12 mesh particles which were calcined in a stream of dry air at 550 C. for one hour.

This granular calcined catalyst was employed as a filler in a tube through which normal heptane was passed at 550 C. at a charging rate corresponding to an hourly liquid space velocity of 2. Table 1 gives results obtained on normal heptane in the presence of the above described catalyst consisting of approximately 8% chromium sesquioxide and 92% thoria.

TABLE 1 Cycliaation of normal heptane in the presence of 8% chromium sesquioride and 92% thoria Yields, weight per cent of charge:

Total hydrocarbon 93.2 Toluene 24.2 Carbon a- 1.9 Gas, uncondensed 6.8

Yields, weight per cent of heptane decomposed:

Toluene 78.2

Gas 21.

Composition of hydrocarbon recovery, weight The results given in Table 1 show that a relatively high per cent of the heptane decomposed was converted into toluene in the presence of the chromium sesquioxide-thoria catalyst, the yields of toluene per pass being of the order of 26% by weight of the charge.

Th foregoing specification and example show clearly the character of the invention and the results to be expected in its application to aliphatic hydrocarbons including paraflins and olefins, although neither section is intended to unduly limit its generally broad scope.

I claim as my invention:

1. A process for producing aromatic hydrocarbons from aliphatic hydrocarbons containing at least six carbon atoms in straight chain arrangement which comprises dehydrogenating and cyclicizing said aliphatic hydrocarbons under dehydrocyclization conditions of temperature and pressure in the presence of a dehydrocyclization catalyst comprising essentially a major proportion of thorium oxide and relatively minor proportions or magnesium oxide and an oxide of an element selected from the members of the lefthand column of group 6 of the periodic table.

2. A process for producing aromatic hydrocarbons from aliphatic hydrocarbons containing straight chains of 6-12 carbon atoms per molecule which comprises dehydrogenating and cyclicizing said aliphatic hydrocarbons under dehydrocyclization conditions of temperature and pressure in the presence of a dehydrocyclization catalyst comprising essentially a major proportion of thorium oxide andv relatively minor proportions oi magnesium oxide and an oxide oi an element selected from the members or the left-hand column of group 6 of the periodic table.

3. A process for producing aromatic hydrocarbons from aliphatic hydrocarbons containing straight chains of 6-12 carbon" atoms per molecule which comprises dehydrogenating and cyclicizing said aliphatic hydrocarbons at a temperature of the order of 450-650 C. in the presence of a dehydrocyclization catalyst comprisingessentially a major proportion oi! thorium oxide and relatively minor proportions of magnesium oxide and an oxide of an element selected from the members of the left-hand column of group 6 or the periodic table.

' 4. A process for producing aromatic hydrocarbons from aliphatic hydrocarbons containing straight chains of 6-12 carbon atoms per molecule which comprises dehydrogenating and cyclicizing said aliphatic hydrocarbons at a temperature of the order of 450-650 C. under a pressure in the range of substantially atmospheric to approximately 100 pounds per square inch'in the presence of a dehydrocyclization catalyst comprising essentially a major proportion of th rium oxide and relatively minor proportions of mag:

nesium oxide and an oxide of an element selected 6 from the members of the left-hand column of group 6 of the periodic table.

5. A process for producing aromatic hydrocarbons from aliphatic hydrocarbons containing straight chains of 6-12 carbon atoms per molel cule which comprises dehydrogenating and cyclicizing said aliphatic hydrocarbons at a temperature of the order of 450-650 C. under a-pressure in the range of substantially atmospheric to approximately 100 pounds per square inch for an is average time of contact of approximately 0.1-60 seconds in the presence of a dehydrocyclization catalyst comprising essentially a major proportion of thorium oxide and relatively minor proportions of magnesium oxide and an oxide of an element selected from the members of the lefthand column of group 6 of theperiodic table consisting of chromium, molybdenum, tungsten, and uranium.

6. A process for producing aromatic hydrocar- 26 bons from aliphatic hydrocarbons containing straight chains of 6-12 carbon atoms per molecule which comprises dehydrogenating and cyclicizing said aliphatic hydrocarbons at a temperature of the order of 450-650 C. under a pressure in'the range of substantially atmospheric to approximately 100 pounds per. square inch for an average time oi contact of approximately 0.1-60 seconds in the presence of a dehydrocyclization catalyst comprising essentially a major proportion of thorium oxide and relatively'minor proportions of magnesium oxide and an oxide of chromium. 7. A process for producing aromatic hydrocarbons from aliphatic hydrocarbons containing straight chains of- 6- 2 carbon atoms per molecule which comprises dehydrogenating and cyclicizing said aliphatic hydrocarbons at a temperature of the order of 450-650 C. under a pressure in the range of substantially atmospheric to approximately 100 pounds per square inch for an average time of contact of approximately 0.1-

60 seconds in the presence 01 a dehydrocyclization catalyst comprising essentially a major pro-' portion of thorium oxide and relatively minor proportions of magnesium oxide and an oxide of molybdenum.

8. A process for producing aromatic hydrocarbons irom aliphatic hydrocarbons containing straight chains 01' 6-12 carbon atoms per molecule which comprises dehydrogenating and cyclicizing said aliphatic hydrocarbons at a temperature of the order of 450-650 C. under a pressure in the range of substantially atmospheric to approximately 100 pounds per square inch for an average time 01' contact of approximately 0.1-60 seconds in the presence of a dehydrocyclization catalyst comprising essentially a major proportion of thorium oxide and relatively minor proportions of magnesium oxide and an oxide or an element selected from the members 01 the lefthand column of group 6 of the periodic table consisting or chromium, molybdenum, tungsten'and uranium.

WILLIAM J. MA'I'IOX.