US3153676A - Preparation of naphthalene and 2, 6-dimethylnaphthalene - Google Patents

Description

United States Patent Ofifice 3,i53,h? Patented Get. 20, 1964 3,153,676 PREPARATION OF NAPHTHALENE AND 2,6-DTHYLNAPHTHALENE Joseph G. Allen, Ridley Park, Pm, and Earl W. Mainsberg, Wilmington, Deh, assignors to un Gil Qompany,

Philadelphia, Pa, a corporation of New Jersey Filed June 27, 1961, Ser. No. 119,84? 6 Claims. (Cl. 260668) This invention relates to the preparation of condensed ring dicyclic aromatic hydrocarbons from charge stocks derived from gas oil and more specifically concerns an integrated process for producing naphthalene and 2,6- dimethylnaphthalene or, alternatively, a 2,6- and 2,7-dimethylnaphthalene concentrate.

Petroleum fractions which boil within the range of 400-550 F. generally contain substantial amounts of alkylnaphthalenes, such as mono-, diand trimethylnaphthalenes and in smaller quantity, the ethylnaphthalenes. Recycle fractions, which are formed in the cracking of petroleum stocks and which include this boiling range, often contain major proportions of aromatic hydrocarbons that are mainly alkylnaphthalenes. Such fractions typically may have aromatic contents varying within the range of 25-97% but usually contain between 50% and 95% aromatics depending upon the particular operation in which the petroleum fractions are produced. These hydrocarbon charge stocks are obtained in both catalytic and thermal cracking processes and in operations in which combinations of catalytic and thermal cracking steps are utilized. Stocks having high alkylnaphthalene contents can also be obtained by extracting straight run petroleum fractions of appropriate boiling ranges, such as kerosene, or catalytic fractions such as catalytic gas oil, with solvents, such as furfural or sulfur dioxide, or by selective adsorption with silica gel. These aromatic concentrates may contain up to 100% aromatic hydrocarbons.

The present invention is directed to the preparation of naphthalene and 2,6-dimethylnaphthalene, or a concentrate of mixed 2,6- and 2,7-dimethylnaphthalenes, from aromatic hydrocarbon charge stocks which comprise a mixture of alkylnaphthalenes and which can be derived from such sources as referred to above. The charge stock typically includes the two monomethylnaphthalenes, various dimethylnaphthalene isomers including 2,6-dirnethylnaphthalene and smaller amounts of the ethylnaphthalenes.

There are ten possible dimethylnaphthalene isomers and most if not all of these occur in charge stocks of the kind described above. Due to the close boiling points of these isomers, the separation from the mixture of any particular isomer in high concentration is a difficult task. A procedure for obtaining 2,6-dirnethylnaphthalene from such charge stocks is particularly desirable, since this isomer is especially useful as an intermediate in the preparation of high quality resins. The present invention provides an integrated process for obtaining the 2,6-isomer in amount greater than the content of this isomer in the charge, while simultaneously converting other alkylnaphthalenes to naphthalene.

In one embodiment of the invention anaromatic concentrate of the 440-525 F. boiling range, containing mainly monocyclic and dicyclic aromatic hydrocarbons, is subjected to a preconditioningstep involving hydrodesulfurization under conditions whereby sulfur is removed and the monocyclic aromatics largely are cracked to gasoline boiling range products. From the desulfurization product a fraction within the narrow boiling range of 500-510" F. is obtained by distillation under eflicient 'fractionating conditions. We have found that this fraction contains practically all of the 2,6- and 2,7-dimethylnaphthalenes that were present in the charge, together with substantial amounts of 1,3-, 1,6- and 1,7-dimethylnaphthalenes and a small amount of ethylnaphthalenes. This fraction is processed in a manner, hereinafter fully described, whereby a 2,6-dimethylnaphthalene concentrate is produced and part of the other dimethylnaphthalenes are isomerized to form more of the 2,6-isomer. Alkylnaphthalenes from the 500510 F. out which are not so isomerized are admixed with the portions of the desulfurization product boiling below 500 F. and above 510 F., and the mixture is subjected to high temperature hydrodealkylation to produce naphthalene. Thus substantially all of the alkylnaphthalenes in the charge are converted into either naphthalene or 2,6-dimethylnaphthalene.

The invention is described more specifically with reference to the accompanying drawing which is a schematic fiowsheet illustrating a combination process for producing naphthalene and 2,6-dimethyh1aphthalene from a hydrocarbon stock containing alkylnaphthalenes.

The process as illustrated in the drawing involves a preliminary extraction step followed by a catalytic hydrocracking-desulfurization step adapted to condition the alkylnaphthalene charge material for use in the other steps of the process. The charge, which enters the system through line 10, is a gas oil fraction boiling in the range of 440-525 F. and containing alkylnaphthalenes including monomethylnaphthalenes and dimethylnaphthalenes together with saturated hydrocarbons. It is fed to extractor 11 wherein it'is countercurrently extracted with an aromatic-selective solvent, which preferably is furfural, under conditions that will produce a highly aromatic extract. Raifinate, which includes the bulk of the saturated hydrocarbons and part of the monocyclic aromatics, is removed as indicated by line 12, and extract is withdrawn via line 13. Conventional solvent separation means (not shown) are provided for recovering and recycling the solvent. The extract obtained from this step typically may contain about 60-65% dicyclic aromatics, 35% monocyclic aromatics and 0-5% saturates.

The heated extract, together with hydrogen from line 14, passes through line 15 to a catalytic desulfurizerhydrocracker 16 which contains a desulfurization catalyst such as cobalt molybdate on alumina or molybdenum disulfide on alumina. The conditions for conducting this catalytic conditioning step include a temperature within the range of 800-980" F., a pressure of -1000 p.s.i.g., with a range of 200-500 p.s.i.g. preferred, a hydrogen to hydrocarbon mole ratio of 3:1 to 25 :1 and preferably 5:1 to 15:1, and a liquid hourly space velocity of 0.5 to 10 (volumes of charge per hour per bulk volume of catalyst). The hydrogen consumption under these conditions should be between 65-500 s.c.f. per barrel of liquid feed per percent sulfur in the feed and preferably between 200 and 400 set. per barrel. This conditioning step effects cracking of most of the'saturates and some of the monocyclic aromatics and also converts most of the sulfur in the hydrocarbon stock to hydrogen sulfide.

From hydrocracker 16 the reaction product is sent through line 17 to fractionator 18 from which normally gaseous components are removed overhead through line H and a C -400 F. gasoline fraction is obtained from line 20. The 400+ P. fraction which contains the alkylnaphthalenes is removed via line 21 and passes to a fractionation section (hereinafter described) for obtaining the narrow fraction from which the 2,6-dimethylnaphthalene product is obtained.

Referring now to the high temperature dealkylation step for producing naphthalene, a stream of mixed materials, obtained as hereinafter specified and composed mainly of monomethyi and dim-ethylnaphthalenes and a small amount of ethylnaphthalenes, passes through line 22 together with hydrogen introduced Via line 23 into dealkylator 24. In a preferred embodiment the dealkylation is eifected thermally without a catalyst. The conditions for this operation include a pressure of 150-1000 p.s.i.g., preferably 200-500 p.s.i.g., a hydrogen to hydrocarbon mole ratio within the range of 3:1 to 25:1 and preferably 5:1 to 1, a residence time of 2-300 seconds with a preferred residence time of 10-60 seconds, and a temperature above 1000" R, preferably within the range of 12001400 F., suificient to effect dealkylation of alkylnaphthalenes. In this reaction only a partial dealkylation occurs. Hence the reaction product which leaves the reactor through line contains, in addition to the desired naphthalene, unreacted naphthalenes and partially dealkylated naphthalenes which can be recovered and recycled to the dealkylator.

Alternatively, the dealkylation reaction can be effected catalytically utilizing a desulfurizing catalyst such as cobalt molybdate or molybdenum disuifide. The presence of the catalyst in this step facilitates the dealkylation reaction and in some cases permits it to be carried out at a lower temperature than that required for thermal dealkylation. The catalyst also effects the conversion of any remaining sulfur into hydrogen sulfide and hence permits the preparation of naphthalene having negliglibe sulfur content. The conditions for the catalytic dealkylation step include a pressure of 150-1000 p.s.i.g. with a range of 200-500 p.s.i.g. preferred, a hydrogen to hydrocarbon mole ratio of 5:1 to 25:1, a liquid hourly space velocity of 0.2-5.0, and a temperature above 1000 F, usually between 1100 F. and 1200 F., sufiicient to dealkylate alkylnaphthalenes and convert any remaining sulfur mainly into hydrogen sulfide.

The reaction product from line 25 passes to fractionator 2.6 from which gases and a C -400" F. aromatic gasoline cut are removed, respectively, from lines 27 and 28. The desired naphthalene product is taken from line 29 as material boiling in the 400-450 F. range. Typically this fraction is composed predominantly of naphthalene and has a freezing point of 78.6 C. and a sulfur content that is practically negligible.

The 450+ F. material withdrawn from fractionator 26 via line 30 is composed mainly of monornethyl and dimethylnaphthalenes. This stream also contains a small amount of material boiling above dimethylnaphthalenes which desirably should be removed. The stream is passed through line 30 to fractionator 3?. from which an alkylnaphthalene concentrate boiling in the range of 450-525 F. and suitable for recycling is obtained overhead through line 32. The higher boiling material unsuitable for recycling is removed as bottoms via line 33.

Referring now to the portion of the process for obtaining 2,6-dimethylnaphthalene, the 400+ F. fraction of the desulfurization product passes through line 21 to a distillation column 34 wherein a sharp separation is made at a cut point of about 500 F. The 400-500 F. distillate passes through lines 35 and 22 as part of the charge to dealkylation zone 24. The 500+ F. bottoms fraction is sent through line to distillation column 37 wherein a sharp fractionation is made to split out the narrow 500-510 P. out which is removed as distillate via line 38. The 510+ F. material obtained as bottoms passes through lines 39, 40 and 22 as additional charge to the dealkylator.

Each of the distillation columns 34 and 37 should be operated under efficient fractionating conditions employing, for example, 30-50 theoretical plates and reflux ratios of the order of 30:1 to :1. We have found that under these conditions the content of 2,6- plus 2,7-dimethylnaphthalenes in the 500-510 P. fraction will be of the order of 30-50%, with the remainder being the 1,3-, 1,6- and 1,7-isomers and ethylnaphthalenes. Practically all of the 1,2-, 1,4-, 1,5-, 1,8- and 2,3-dimethylnaphthalenes appear in the bottoms product withdrawn from column 37,

2,6-DMN isomer.

4 and these isomers are subsequently converted to naphthalene in dealkylator 24.

The 500-510 F. cut from column 38 will contain a major proportion of dimethylnaphthalenes (DMN) having the methyl groups on opposite rings of the naphthalene nucleus and minor proportions of ethylnaphthalene (EN) and DMN having methyl groups on the same ring of the naphthalene nucleus.

A typical composition of this material is as follows:

Percent Z-EN 1 8 l-EN 2 2,6-DMN 2 24 2,7-DMN 22 1,3 -DMN 13 1,7-DMN 17 1,6-DMN l4 1 Ethylnaphthalene. 2 Dimethylnaphthaleue.

This material is sent through lines 38 and 41 to a crystallizing and filtering zone 3-2 wherein the material is chilled to a temperature preferably in the range of 0-30" C. and is filtered at such temperature. This tends preferentially to crystallize the 2,6- and 2,7-DMN and gives a filtrate from line 43 which typically contains -30% of the EN and 60-75 of the 1,3-, 1, and 1,7-DMN that were present in the 500-510 F. cut. This procedure, by effecting removal of the bulk of the EN and 1,3-DMN, prevents these components from building up in the cyclic system hereinafter described. The filtrate passes from line 43 to lines 4-0 and 22 through which it is introduced to the dealkylator 24.

The filter cake obtained as indicated by line 44 is then subjected to a partial melting in zone .5. This is done by warming the cake to a temperature preferably of about -85 F. while pressing it to squeeze out the melted components which are filtered off through line 46. It has been found that this procedure will give a residual filter cake, indicated by line 47, which has a 2,6-DMN content of the order of -95% and which contains about 25-35% of the 2,6-DMN that was present in the material fed to zone 45.

The filtrate from zone 45 passes through line 46 to an isomerization zone 48 wherein it is subjected to conditions effective to cause a shift in position of methyl groups and thus produce a further amount of the desired A procedure for carrying out such isomerization reaction has been described in Seitzer application United States Serial No. 28,753, filed May 12, 1960. It involves contacting the alkylnaphthalenes with any solid acidic cracking catalyst such as silica-alumina, silica-magnesia, silica-zirconia and acid activated clays. The reaction temperature should be in the range of 300- 500 C. and more preferably 325-400 C. The liquid space velocity can vary between 0.1 and 20 volumes hydrocarbon per volume catalyst per hour and more preferably is maintained in the range of 0.5-6.0. It is desirable to conduct the isomerization at a low hydrocarbon partial pressure and generally in the range of 005-05 atmosphere, as otherwise coking tends to occur rapidly with resultant deactivation of the catalyst. The low partial pressure can be maintained either by holding a vacuum in isomerization zone 31 or by introducing an inert diluent along with the hydrocarbons, for example, nitrogen, hydrogen, methane, propane, butanes, and the like. Whenever the activity of the catalyst has dropped enough to require regeneration, this can be done in conventional manner merely by blowing air through the hot catalyst to burn off the coke deposits. Thereafter the catalyst can be re-used for further isomerization.

Alternatively, the isomerization in zone 31 can be effected at low temperature using TIP-8P as catalyst. In practicing the isomerization in this manner, the alkylnaphthalenes from line 4-6 are first dissolved in a suitable solvent, such as benzene or heptane, and the mixture is contacted with the catalyst at a temperature preferably in the range of -30 C. and generally for several hours. Only a small amount of Bitneed be used and the HF can be present in a large molar excess over the B1 to provide sufiicient catalyst volume for good contact. After the isomerization the solvent can be removed by distillation (not shown). Generally, some amount of tarry material may be formed during this type of isomerizing operation and it also can be removed by distillation.

By either of the above-described procedures for effecting isomerization, the dimethylnaphthalenes which have methyl groups on opposite rings of the naphthalene nucleus will be converted to an equilibrium mixture of DMNs also having methyl groups on opposite rings, and those having both methyl groups on the same ring will be converted to an equilibrium mixture or" DMNs likewise having methyl groups on the same ring. In other words a shift of methyl groups from one ring to the other does not occur. Thus the 1,3-isomer present in the 500-510 P. out does not constitute a source for formation of the 2,6-DMN, and hence the 1,3-isomer and any of the isomers to which it is converted in isomerizer 48, such as the 1,4- and 2,3-isomers, eventually are converted to naphthalene in dealkylator 24.

The isomerization product from zone 43 passes from line 49 to a distillation column 50 from which a distillate boiling up to 510 F. is taken overhead. This material, which contains essentially all of the 2,6- and 2,7-DMN and part of the 1,3-, 1,6- and 1,7-isomers, is recycled through lines 51 and 41 to the crystallizer-filter 42. The higher boiling material obtained as bottoms through line 52 is essentially free of the 2,6- and 2,7- DMN and contains the remainder of the 1,3-, 1,6- and 1,7-isomers along with any higher boiling isomers formed during the isomerization reaction. This material is sent through lines 52, 40 and 23 to dealkylator 24 for conversion to naphthalene.

From the foregoing description it can be seen that essentially all of the alkylnaphthalenes present in the charge are utilized to produce either naphthalene or 2,6- DMN as the two chemical products of the process. In addition the process produces gasoline which is highly aromatic and hence has a high antiknock rating.

The above-described process can be modified, if desired, to obtain a concentrate of mixed 2,6- and 2,7-DMN instead of the 2,6-DMN concentrate. This can be done by first crystallizing the mixed feed to crystallizer-filter 42 at a relatively low temperature, such as -lO C. to C. The filtrate from this step, which is enriched in EN and also contains part of the 1,3-, 1,6- and 1,7- DMN, is sent to the dealkylator. The filter cake is then warmed in zone 45 to a temperature in the range of 65 C. while pressing and filtering. The resulting cake will contain a major proportion of 2,6- and 2,7-DMN. For example, the combined contents of these materials typically is 60-65% when the cake is warmed at C. and 70-75% when it is warmed to 50 C. The resulting 2,6- and 2,7-concentrate can be separately processed, if desired, to obtain each of the isomers in concentrated form. The filtrate from zone 45 passes to isomerizer 48 to equilibrate the DMNs and produce additional amounts of the 2,6- and 2,7-iso1ners for recycling by means of line 51.

We claim:

1. In a process involving hydrodesulfurizing a gas oil fraction boiling mainly in the range of 440-525 F. and containing mainly monocyclic and dicyclic aromatic hydrocarbons including monomethyl and dimethylnapthalene, separating from the desulfurization product material containing alkylnaphthalene and subjecting such material to a dealkylation reaction at a temperature above 1000 F. to produce naphthalene, the steps for recovering 2,6- dimethylnaphthalene as an additional product which comprises: (l) separating from said desulfurization product a fraction boiling essentially in the range of 500-5l0 F. and composed of a major proportion of dimethylnaphthalene having the methyl groups on opposite rings of the naphthalene nucleus and minor proportions of ethylnaphthalene and dimethylnaphthalene having methyl groups on the same ring of the naphthalene nucleus; (2) chilling said product to a temperature sufiiciently low to crystallize most of the 2,6- and 2,7-dimethylnaphthalene; (3) separating a filtrate enriched in ethylnaphthalene from the crystallized material; (4) increasing the temperature of the crystallized material to effect partial melting; (5) separating melted components from a cake constituting a 2,6-dimethylnaphthalene concentrate; (6) isomerizing said melted components; (7) fractionating the isomerizate to obtain an overhead fraction boiling up to about 510 F. and composed mainly of dimethylnaphthalene having methyl groups in opposite rings of the naphthalene nucleus and a bottoms fraction boiling above 510 F; (8) recycling said overhead fraction to step (2); and (9) passing the filtrate from step (3), the bottoms fraction from step (7) and materials from step (1) boiling below 500' F. and above 510 F. to said dealltylation reaction for conversion to naphthalene.

2. Process according to claim 1 wherein the temperature in step (2) is in the range of 0-30 C.

3. Process according to claim 2 wherein the temperature is increased to 70-85 C. in step (4).

4. in a process involving hydrodesulfurizing a gas oil fraction boiling mainly in the range of 440-525 F. and containing mainly monocyclic and dicyclic aromatic hydrocarbons including monomethyl and dimethylnaphthalene, separating from the desulturization product material containing alkylnaphthalene and subjecting such material to a dealkyla ion reaction at a temperature above 1000 F. to produce naphthalene, the steps for recovering a concentrate of mixed 2,6- and 2,7-dimethylnaphthalenes as an additional product which comprises: (1) separating from said desulfurization product a fraction boiling essentially in the range of 500-510 F. and composed of a major proportion of dimethylnaphthalene having the methyl groups on opposite rings of the naphthalene nucleus and minor proportions of ethylnaphthalene and dimethylnaphthalene having methyl groups on the same ring of the naphthalene nucleus; (2) chilling said product to a temperature sufiiciently low to crystallize most of the 2,6- and 2,7-dimethylnaphthalene; (3) separating a filtrate enriched in ethylnaphthalene from the crystallized material; (4) increasing the temperature of the crystallized material to eilect partially melting; (5) separating melted components from a cake constituting a concentrate of mixed 2,6- and 2,7-dimethylnaphthalenes; (6) isomerizing said melted components; (7) fractionating the isomerizate to obtain an overhead fraction boiling up to about 510 F. and composed mainly of dimethylnaphthalene having methyl groups in opposite rings of the naphthalene nucleus and a bottoms fraction boiling above 510 F.; (8) recycling said overhead fraction to step (2); and (9) passing the filtrate from step (3), the bottoms fraction from step (7) and materials from step (1) boiling below 500 F. and above 510 F. to said dealkylation reaction for conversion to naphthalene.

5. Process according to claim 4 wherein the temperature in step (2) is in the range of 10 F. to +15 C.

6. Process according to claim 5 wherein the temperature is increased to 20-65 C. in step (4).

References Cited in the file of this patent UNITED STATES PATENTS 2,577,788 McAteer et al Dec. 11, 1951 2,741,646 Clark Apr. 10, 1956 2,910,514 Scott et al. Oct. 27, 1959 2,920,115 Friedman Jan. 5, 1960 3,001,932 Pietsch Sept. 26, 1961

Claims (1)

1. IN A PROCESS INVOLVING HYDRODESULFURIZING A GAS OIL FRACTION BOILING MAINLY IN THE RANGE OF 440-525* F. AND CONTAINING MAINLY MONOCYCLIC AND CICYCLIC AROMATIC HYDROCARBONS INCLUDING MONOMETHYL AND DIMETHYLNAPTHALENE, SEPARATING FROM THE DESULFURIZATON PRODUCT MATERIAL CONTAINING ALKYLNAPHTHALENE AND SUBJECTING SUCH MATERIAL TO A DEALKYLATION REACTION AT A TEMPERATURE ABOVE 1000* F. TO PRODUCE NAPHTHALENE, THE STEPS FOR RECOVERING 2,6DIMETHYLNAPHTHALENE AS AN ADDITIONAL PRODUCT WHICH COMPRISES: (1) SEPARATING FROM SAID DESULFURIZATION PRODUCT A FRACTION BOILING ESSENTIALLY IN THE RANGE OF 500-510*F. AND COMPOSED OF A MAJOR PROPORTION OF DIMETHYLNAPHTHALENE HAVING THE METHYL GROUPS ON OPPOSITE RINGS OF THE NAPHTHALENE NUCLEUS AND MINOR PROPORTIONS OF ETHYLNBAPHTHALENE AND DIMETHYLNAPHTHALENE HAVING METHYL GROUPS ON THE SAME RING OF THE NAPHTHALENE NUCLEUS; (2) CHILLING SAID PRODUCT TO A TEMPERATURE SUFFICIENTLY LOW TO CRYSTALLIZE MOST OF THE 2,6- AND 2,7-DIMETHYLNAPHTHALENE; (3) SEPARATING A FILTRATE ENRICHED IN ETHYLNAPHTHALENE FROM THE

Images