US006147270A United States Patent [19] [11] Patent Number: 6,147,270 Pazzucconi et al. [45] Date of Patent: Nov. 14, 2000

[54] PROCESS FOR THE PREPARATION OF 5,670,704 9/1997 Hagen et al...... 585/471 2,6-DIMETHYLNAPHTHALENE USING A 5,672,799 9/1997 Perego et al...... 585/467 MTW ZEOLITIC CATALYST FOREIGN PATENT DOCUMENTS [75] Inventors: Giannino Pazzucconi, Broni; Carlo 2 246 788 2/1992 United Kingdom . Perego, Carnate; Roberto Millini, WO 90/03960 4/1990 WIPO. Cerro al Lambro; Francesco Frigerio, OTHER PUBLICATIONS Torre d’lsola; Riccardo Mansani, Sassari; Daniele Rancati, Porto Torres, “MTW”; internet search record, Dec. 1999. all of Italy Primary Examiner—Marian C. Knode [73] Assignee: Enichem S.p.A., S. Donato Milanese, Assistant Examiner—Thuan D. Dang Italy Attorney, Agent, or Firm—Oblon, Spivak, McClelland, Maier & Neustadt, PC. [21] Appl. No.: 09/281,961 [57] ABSTRACT [22] Filed: Mar. 31, 1999 A highly selective process is described for preparing 2,6 dimethylnaphthalene Which comprises reacting a naphtha [30] Foreign Application Priority Data lene hydrocarbon selected from naphthalene, Apr. 17, 1998 [IT] Italy ...... MI98A0809 methylnaphthalenes, dimethylnaphthalenes, trimethylnaphthalenes, polymethylnaphthalenes or their [51] Int. Cl.7 ...... C07C 15/12 mixtures With one or more benzene hydrocarbons selected [52] US. Cl...... 585/475; 585/471 from benzene, toluene, Xylenes, trimethylbenZenes, [58] Field of Search ...... 585/475, 471, tetramethylbenZenes, pentamethylbenZene and/or 585/470 heXamethylbenZene, under at least partially liquid phase conditions, in the presence of a Zeolite belonging to the [56] References Cited structural type MTW and optionally in the presence of a U.S. PATENT DOCUMENTS methylating agent.

5,003,122 3/1991 Fellman et al...... 585/467 36 Claims, No Drawings 6,147,270 1 2 PROCESS FOR THE PREPARATION OF naphthalene or 2-methyl-naphthalene the use of ZSM-5 is 2,6-DIMETHYLNAPHTHALENE USING A particularly preferred. To reduce undesired isomeriZation MTW ZEOLITIC CATALYST reactions Which result in the formation of 1-alkyl naphthalene, the Zeolitic catalyst is previously subjected to A highly selective process is described for preparing precarboniZation treatment. An example is provided of the 2,6-dimethylnaphthalene Which comprises reacting a naph alkylation of 2-methylnaphthalene With methanol, in gas thalene hydrocarbon selected from naphthalene, phase, catalyZed by ZSM-5: the conversion obtained methylnaphthalenes, dimethylnaphthalenes, betWeen 0.5 and 8 hours is from 5 to 7%, the yield to trimethylnaphthalenes, polymethylnaphthalenes or their dimethylnaphthalenes ranges from 4 to 5% and the 2,6 mixtures With one or more benZene hydrocarbons selected 10 dimethylnaphthalene isomer forms 50% of the dimethyl from benZene, toluene, xylenes, trimethylbenZenes, naphthalene fraction. tetramethylbenZenes, pentamethylbenZene and/or We have noW unexpectedly found a process for preparing hexamethylbenZene, under at least partially liquid phase 2,6-dimethylnaphthalene starting from naphthalene, conditions, in the presence of a Zeolite belonging to the methylnaphthalenes, dimethylnaphthalenes, trimethylnaph structural type MTW and optionally in the presence of a 15 thalenes and/or polymethylnaphthalenes carried out under at methylating agent. least partially liquid phase conditions and in the presence of 2,6-dimethylnaphthalene is an intermediate in the syn suitable aromatic hydrocarbons, catalyZed by a Zeolite of the thesis of 2,6-naphthalenedicarboxylic acid, used as mono structural type MTW (abbreviation IZA), Which alloWs mer in the preparation of PEN (polyethylnaphthalate). It is better results to be obtained in terms of yield, selectivity, knoWn that it can be recovered from fractions coming from 20 conversion to useful products in the time unit and life of the the reforming of kerosine (US. Pat. No. 4,963,248) or from catalyst, With respect to What is described in the prior art. In fractions of FCC oil (European Chemical NeWs, page 30, particular MTW Zeolites, When used under the conditions of Sep. 28, 1992). In the ?rst case, the dimethylnaphthalenes our invention, are more active not only than the same must be separated by distillation, then, the 2,6 isomer is Zeolites used under the conditions described previously, but isolated by means of selective absorptions and/or crystalli 25 also With respect to the BEA and MFI Zeolites already Zation. In the second case, there is an additional problem due described in the prior art as the best catalysts for the to the presence of nitrogen and sulfur Which poison the preparation of 2,6-dimethylnaphthalene. catalysts used for the separation and/or isomeriZation The present invention therefore relates to a process for phases. There is also a process (US. Pat. No. 4,990,717; preparing 2,6-dimethylnaphthalene Which comprises react US. Pat. No. 5,118,892; US. Pat. Nos. 5,073,670; 5,030, 30 ing a naphthalene hydrocarbon selected from naphthalene, 781; 5,012,024) Which, by means of alkenylation, methylnaphthalenes, dimethylnaphthalenes, cycliZation, dehydrogenation, isomeriZation, leads to the trimethylnaphthalenes, pentamethylnaphthalenes, hexam selective synthesis of 2,6-dimethylnaphthalene. This high ethylnaphthalenes or their mixtures With one or more ben number of passages obviously represents a burden from an Zene hydrocarbons selected from benZene, toluene, xylenes, economical point of vieW and in addition, each passage or 35 trimethylbenZenes, tetramethylbenZenes, pentamethylben chemical reaction involves secondary reactions requiring Zene and/or hexamethylbenZene, under at least partially separations to guarantee the purity of the intermediates or liquid phase conditions, in the presence of a Zeolite belong end-product. US. Pat. No. 5,043,501 describes a synthesis ing to the structural type MTW and optionally in the method of 2,6-dimethylnaphthalene in tWo steps. The ?rst presence of a methylating agent. comprises the alkylation of an alkylaromatic With a C5 ole?n 40 The naphthalene hydrocarbon is preferably selected from in the presence of a Zeolitic catalyst, the second comprises naphthalene, methylnaphthalenes, dimethylnaphthalenes, a dehydrocycliZation at 400—500° C. With a catalyst con trimethylnaphthalenes, or their mixtures. Aparticularly pre sisting of Pt/Ba/K on Zeolite L, obtaining a product con ferred aspect is that the reagent is naphthalene and/or taining dimethylnaphthalenes Which are then isomeriZed methylnaphthalene, optionally mixed With dimethylnaph mainly to 2,6 isomer. 45 thalenes and/or trimethylnaphthalenes. S. B. Pu and T. Inui describe in Applied Catalysis A, Fractions containing naphthalene, methylnaphthalenes General 146 (1996) 305—316, the alkylation With methanol and dimethylnaphthalenes, obtained by distillation from of methylnaphthalene, catalyZed by Zeolites of the BEA, FOC (Fuel Oil Cracking) or LCO (Light Cycle Oil) cracking FAU and MTW groups, carried out Without a solvent and in oils or obtained by the distillation of distilled oil from an exclusively gaseous phase. The best results are obtained pit-coal tar, can be used directly in the process of the present With beta Zeolite and faujasite. A. S. Loktev and P. S. invention. Chekriy, in Zeclites and Related Microporous Materials: According to a particularly preferred aspect of the State of art 1994, SSSC vol. 84, J. Weitkamp et al. (Eds) present invention, the process for the preparation of 2,6 describe the alkylation of naphthalene or methylnaphthalene dimethylnaphthalene is carried out in the presence of the With methanol catalyZed by ZSM-12, carried out in the 55 methylating agent Which can be selected from methanol, presence of paraffinic solvents and in gaseous phase. The dimethylether, dimethylcarbonate, dimethylsulfate, methyl yields to dimethylnaphthalenes, and to 2,6 isomer in iodide. Methanol is preferably used. particular, are Zero or in any case negligible. In addition, Operating according to our invention, a high selectivity high quantities of heavy by-products are obtained, due to the is unexpectedly obtained, Which, With respect to thermody reaction conditions and/or decomposition of the paraf?nic 60 namic equilibrium values, is unbalanced toWards the 2,6 solvents used. isomer: there are consequently kinetic control conditions of US. Pat. No. 4,795,847 discloses a process for the the reaction. The molar ratio betWeen the 2,6 and 2,7 isomers preparation of 2,6-dialkylnaphthalenes Which comprises the of dimethynaphthalene can also be considered as selectivity alkylation in gaseous phase of naphthalene or 2-alkyl index reached With our invention. Whereas the thermody naphthalene With an alkylating agent in the presence of a 65 namic ratio is about 1 (S. B. Pu and T. Inui, in Applied Zeolite selected from mordenite, EU-1, offretite, ZSM-12, Catalysis A, General 146 (1996) 305—316) in the case of ZSM-5 and ZSM-22. In the case of the methylation of Zeolitic catalysts With an MFI and BEA structure it is 1 and 6,147,270 3 4 1.3 respectively, in the case of MTW Zeolites used in gas The Zeolite can be used as such, pelletiZed in pure form, phase it is 1.2 and 1.5, in the case of MTW Zeolites used or extruded With suitable inorganic oxide ligands to form according to our invention, this ratio varies from 1.9 to 2.7. cylindrical, spherical pellets, or With other forms commonly For evaluating the selectivity Which can be reached With used, or obtained as microspheres by spray-drying after our invention, the selectivity to 2,6 or 2,6+1,6 isomer can mixing With a ligand. The ligands can be for example, also be considered. According to the thermodynamic equi aluminas, silicas, silicoaluminas, titania, Zirconia or clays. librium (calculated by S. B. Pu and T. Inui, in Applied Alumina is preferably used. In the bound catalyst the Zeolite Catalysis A, General 146 (1996) 305—316) there is 12% of and the ligand are in a Weight ratio ranging from 10:90 to the 2,6 isomer and 14% of the 1,6 isomer. With the process 90:10, preferably from 25:75 to 75:25. of our invention, values are registered equal to 26—35% for 10 The benZene hydrocarbon is selected from benZene, the 2,6 isomer and 25—32% for the 1,6 isomer, depending on the reaction conditions: in any case the values are higher toluene, xylenes, trimethylbenZenes, tetramethylbenZenes, than the thermodynamic ones. pentamethylbenZene, hexamethylbenZene or their mixtures, Operating under the conditions of our invention, and in and is preferably trimethylbenZene. It is obviously necessary the presence of one or more of the particular benZene to operate in the presence of the methylating agent When hydrocarbons selected, Zeolites of the structural type MTW 15 only benZene is used as benZene hydrocarbon together With give better results than those of Zeolites of the MFI group, naphthalene alone as naphthalene substrate. The process of not only because they are more active, With a longer life and the present invention is completely different from the knoWn therefore greater productivity, but because they provide a simple alkylation processes of the prior art: in fact it is the product containing a higher percentage of 1,6 and 1,5 result of contemporaneous transalkylation, deproportioning, isomers Which can be easily converted to 2,6 isomer by 20 isomeriZation and alkylation reactions in Which all the types means of commercial processes or knoWn methods such as of methyl present in the reaction mixture unexpectedly those for example described in EP 519165 and US. Pat. No. participate, directly or indirectly, in the methylation of the 5,012,024. In addition, the MFI Zeolites produce signi?cant naphthalene substrate used and contribute to obtaining very quantities, Which tend to increase With deactivation, of high selectivities. Methyls present in the reaction mixture ethylnaphthalene Which on the other hand is not revealed by 25 refer to both those deriving from benZene hydrocarbon and GC analysis among the products obtained according to the also those possibly already present on one or more of the process of our invention. With respect to BEA Zeolites, the naphthalene substrates used. MTW Zeolites used according to our invention are more In accordance With this, at the end of the process, the selective, more active, With a longer life and produce less tri benZene hydrocarbon or mixture of benZene hydrocarbons and tetra-methylnaphthalenes (With the same conversion). 30 used Will produce a mixture of corresponding benZene Zeolites of the MTW structural type Which can be used in the present invention are for example: ZSM-12, CZH-5, hydrocarbons differently methylated both quantitatively and Nu-13, Theta-3 and TPZ-12. qualitatively, arising from the processes mentioned above. The Zeolite CZH-5 is described in GB 2079735A; Nu-13 The best results are obtained When a methylating agent is is described in EP59059; Theta-3 is described in EP 162719 used and consequently at least part of the methyls Which are and TPZ-12 in US. Pat. No. 4,557,919. 35 found in the 2,6-dimethylnaphthalene end-product derive The Zeolite of the MTW structural type Which is best directly or indirectly from this, ie by alkylation on the part suited for use in the resent invention is a silico-aluminate of the methylating agent of the aromatic hydrocarbon and With a molar ratio SiO2/Al2O3 greater than or equal to 20. subsequent transalkylation on the naphthalene substrate. This Zeolite and its preparation are described in A. Katovic The feeding of the benZene hydrocarbon is such as to and G. Giordano, Chem. Ind. (Dekker) (Synthesis of Porous 40 obtain a molar ratio betWeen the hydrocarbon and naphtha Materials) 1997 69, 127—137. The aluminum can be total or lene groups ranging from 1 to 100, more preferably from 3 partly substituted by B, Ga, Fe or their mixtures as described to 20, naphthalene groups referring to the naphthalene by Toktarev & Ione, in Chon et al., Progress in Zeolites and hydrocarbon used as substrate or, When several naphthalene Microporous Materials, SSSC, vol. 105, 1997. hydrocarbons are present, the sum of their moles. According to a preferred aspect the Zeolite ZSM-12 is 45 When the process of the present invention is carried out used, a porous crystalline material having in its calcined and in the presence of a methylating agent, preferably methanol, anhydrous form a molar composition of oxides correspond a molar ratio betWeen methylating agent and the naphthalene ing to the folloWing formula: groups of less than 30 is used, preferably ranging from 0.1 to 3. The reaction temperature ranges from 2000 C. to 450° C., Wherein M is H+ and/or a cation of an alkaline or earth preferably from 250 to 390° C., even more preferably from alkaline metal With valence n, W is selected from aluminum, 280 to 350° C., the WHSV space velocity ranges from 0.01 gallium or their mixtures, Y is selected from silicon or to 8 hours_1, preferably from 0.05 to 1 hours_1. germanium, Z is betWeen 0 and 60. M is preferably selected It should be pointed out that the combination of tempera from sodium, potassium, hydrogen or their mixtures. W is 55 ture and pressure conditions used should be such as to preferably aluminum and Y is preferably silicon. W can be guarantee that the synthesis of the 2,6-dimethylnaphthalene at least partially substituted by boron, iron or their mixtures. at least partly takes place in liquid phase, and even more The Zeolite ZSM-12 is described in Us. Pat. No. 3,832,449, preferably substantially in liquid phase. in Ernst et al., Zeolites, 1987, Vol. 7, September, and in The pressure used can vary from 3 to 60 atm. Toktarev & Ione, Chon et al., Progress in Zeolites and 60 The process of the present invention can be industrially Microporous Materials, SSSC, vol. 105, 1997. carried out in continuous, semicontinuous or batch; in order Aparticularly preferred aspect of the present invention is to keep the temperature Within a preferred range, the catalyst that the Zeolite of the MTW type used is in the form in Which can be arranged in the reactor in various layers. A quench the cation sites present in its structure are occupied for at With naphthalene, With the hydrocarbon or mixture of ben least 50% by hydrogen ions. It is particularly preferable for 65 Zene hydrocarbons used in the process itself, or With the at least 90% of the cation sites to be occupied by hydrogen methylating agent, preferably methanol, When present, can ions. be carried out betWeen one layer and another. 6,147,270 5 6 The temperature control can be carried out not only by trimethylnaphthalenes, tetramethylnaphthalenes, means of a quench of the reagents and/or inert products, but pentamethylnaphthalenes, hexamethylnaphthalene or their also by intercooling betWeen the layers, for example by mixtures With one or more benZene hydrocarbons selected means of the interpositioning of coolants. The synthesis of from benZene, toluene, xylenes, trimethylbenZenes, 2,6-dimethylnaphthalene can be conveniently carried out tetramethylbenZenes, pentamethylbenZene and/or either in a reactor in Which the catalyst is arranged in tWo or hexamethylbenZene, under at least partially liquid phase more beds or in tWo or more reactors in series, intercooled conditions, in the presence of a Zeolite belonging to the to control the temperature. MTW structural type and optionally in the presence of a When an alkylating agent is used, it can be fed in tWo or methylating agent, Wherein said regeneration method com more steps. The alkylating agent is preferably fed in tWo or 10 prises treating the exhausted catalyst With one or more of more steps along the catalytic beds of the reactor or betWeen these benZene hydrocarbons, at a temperature ranging from these, and/or betWeen the reactors situated in series. 200°to 450° C., more preferably from 250°to 400° C., even According to a preferred aspect, in order to maximiZe the more preferably from 280°to 370° C., said temperature production of 2,6-dimethylnaphthalene, the product being at least equal to that used during the preparation obtained according to the process of the present invention 15 process of 2,6-dimethylnaphthalene from Which the can be separated into: exhausted catalyst derives. The regeneration conditions are (a) a fraction containing benZene hydrocarbons, naphtha selected so as to operate in at least partially liquid phase, the lene and methylnaphthalene, (b) a fraction containing WHSV space velocity can range from 0.01 to 8 hours“1 and dimethylnaphthalenes and (c) a fraction containing the pressure can be selected from 5 to 60 atm. polymethylated naphthalenes. The desired 2,6 20 dimethylnaphthalene isomer is isolated from the frac EXAMPLE 1 tion (b) of dimethylnaphthalenes, Whereas the remain ing fraction (d) containing dimethylnaphthalenes Preparation of the Catalyst ZSM-12 different from the 2,6 isomer, and fractions a) and c), 2.4 grams of sodium aluminate at 56% of A1203 are are re-fed to the initial reactor Where they re-enter the 25 dissolved in 84 grams of aqueous solution of tetraethylam reactive cycle. Alternatively, fraction (d) and fractions monium hydroxide at 35%. The limpid solution thus (a) and (c), optionally enriched With naphthalene and/or obtained is poured, under stirring, into 200 grams of colloi methylnaphthalene, can be fed to a speci?c reactor dal silica Ludox HS 40. After brief stirring a limpid and Where they are reacted, under at least partially liquid homogeneous gel is obtained Which is poured into an phase conditions, in the presence of a Zeolite belonging 30 AISI316 steel autoclave equipped With an anchor stirrer. The to the MTW structural type, With one or more benZene gel is left to crystalliZe under hydrothermal conditions at hydrocarbons selected from benZene, toluene, xylenes, 165° C. for 90 hours. trimethylbenZenes, tetramethylbenZenes, pentamethyl At this point the autoclave is cooled and the solid sepa benZenes and/or hexamethylbenZene. The reaction tem rated from the mother liquor and Washed With demineraliZed perature ranges from 200 to 450° C., and the space 35 Water until the Washing Water has a pH of less than 9. velocity ranges from 0.01 to 8 hours_1. The solid is calcined at 550° C. in an atmosphere of air for According to another aspect of the present invention, to maximiZe the production of 2,6-methylnaphthalene, fraction 5 hours. It is then suspended in a solution of demineraliZed (d) containing dimethylnaphthalenes different from 2,6 Water and ammonium acetate, the latter in a molar quantity in excess, in particular 5 times, With respect to the aluminum dimethylnaphthalene, in particular the 1,6 and 1,5 isomer, is 40 subjected to isomeriZation, under at least partially liquid formally present from the synthesis. During this operation the sodium contained from the synthesis in the Zeolite is phase conditions, in the presence of a catalyst containing an substituted With the ammonium ion by ion exchange effect. MTW Zeolite, at a temperature ranging from 100 to 400° C., This ?rst exchange is folloWed by a Washing, a second more preferably from 120 to 250° C., even more preferably exchange using the same procedure and another Washing. from 130 to 200° C. 45 This particular isomeriZation process of 1,6 The solid is then de?nitely separated from the aqueous dimethylnaphthalene and 1,5-dimethylnaphthalene, pure or environment, dried and calcined for 5 hours at 550° C. in an mixed With other dimethylnaphthalene isomers, to give atmosphere of air. The Zeolitic catalyst is thus obtained in 2,6-dimethylnaphthalene, catalyZed by a Zeolite of the MTW acid form. XRD analysis is carried out on the end-sample type, is in itself innovative and represents a further object of Which shoWs the presence of only Zeolitic crystalline phase the present invention. of the MTW type, together With a chemical analysis on the The exhausted catalyst deriving from the process for basis of Which the residual sodium content proves to be less preparing 2,6-dimethylnaphthalene can be regenerated With than 50 ppm and the molar ratio SiO2/Al2O3 is 100. the knoWn combustion methods of coke or of its precursors EXAMPLE 2 to Which the deactivation of the solid acid materials Which 55 catalyZe reactions involving hydrocarbons, is due. We have 2 gr of ZSM-12 Zeolite of example 1 (molar ratio SiO2/ also unexpectedly found a method for regenerating this Al2O3=100) pelleted and granulated Within a range of 20—40 exhaused catalyst, Which is much simpler and more eco mesh, are charged into the isothermal Zone of a ?xed bed nomical. This neW method does not require, With respect to reactor, With quartZ above and beloW as inert ?lling. The the traditional regenerative methods, either removal of the 60 reactor is heated to 200° C. for at least 2 hours, under a catalyst from the reaction environment or the high tempera stream of nitrogen against atmospheric pressure. Maintain tures necessary for the combustion of coke. A further object ing under a stream of inert gas, the reactor is cooled to room of the present invention therefore relates to a method for temperature, and the reagents are then fed until the reactor regenerating the exhausted catalyst deriving from the pro is pressuriZed to 40 bars. cess for the preparation of 2,6-dimethylnaphthalene by the 65 The mixture of reagents fed consists of 1,2,4 reaction of a naphthalene hydrocarbon selected from trimethylbenZene, naphthalene, methanol in the folloWing naphthalene, methylnaphthalenes, dimethylnaphthalenes, molar ratios: 1,2,4-trimethylbenZene/naphthalene=10, 6,147,270 7 8 methanol/naphthalene=3. At this point the mixture is heated lated Within a range of 20—40 mesh, are charged into the and brought to a temperature of 350° C. In this test the isothermal Zone of a ?xed bed reactor, With quartZ above and conditions are therefore liquid phase, With respect to the beloW as inert ?ller. The reactor is heated to 200° C. for at state of reagents and products. The WHSV (hours_1) With least 2 hours, under a stream of nitrogen against atmospheric respect to the total mixture is 0.86. pressure. Maintaining under a stream of inert gas, the reactor The products leaving the reactor are cooled and analyZed is cooled to room temperature, and the reagents are then fed by gaschromatography. Samples are taken of the products at until the reactor is pressuriZed to 35 bars. regular time intervals (time on stream). The conversion of The mixture of reagents fed consists of 1,2,4 the methanol is alWays total. trimethylbenZene, naphthalene, methanol in the folloWing a) The conversion of naphthalene after 28.2 hours is equal to 10 molar ratios: 85.3% 1,2,4-trimethylbenZene/naphthalene 18, methanol/ The selectivities of each product With respect to the naphthalene=2. At this point the mixture is heated and naphthalene, de?ned as ratio betWeen the moles of said brought to a temperature of 320° C. In this test the product formed and the moles of naphthalene converted, are: conditions are therefore liquid phase, With respect to the selectivity dimethylnaphthalenes (% moles): 54.3 15 state of reagents and products. The WHSV (hours-1) With selectivity 2,6-dimethylnaphthalene (% moles): 16.0 respect to the total mixture is 0.43. The products leaving the reactor are cooled and analyZed selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): by gaschromatography. Samples are taken of the products at 33.4 regular time intervals (time on stream). The conversion of selectivity methylnaphthalenes (% moles): 34.6 20 the methanol is alWays total. selectivity polymethylnaphthalenes (% moles): 11.2 a) The conversion of naphthalene after 91 hours is equal to molar ratio 2,6-dimethylnaphthalene/total dimethylnaph 66.5% thalenes (% moles): 29.4 (the thermodynamic isomeri The selectivities With respect to naphthalene are: cal distribution, as described in S. B. Pu and T. Inui, selectivity dimethylnaphthalenes (% moles): 41.2 Applied Catalysis A, General 146 (1996) 305—316, 25 selectivity 2,6-dimethylnaphthalene (% moles): 13.0 foresees 12.0% of 2,6 isomer). selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim 26.8 ethylnaphthalenes (% moles): 61.5 (thermodynamic selectivity methylnaphthalenes (% moles): 53.7 ratio 32%) 30 selectivity polymethylnaphthalenes (% moles): 5.1 molar ratio 2,6/2,7 dimethylnaphthalene: 1.9 molar ratio 2,6-dimethylnaphthalene/total dimethylnaph (thermodymamic ratio 1) thalenes (% moles): 31.5 (the thermodynamic isomeric b) The conversion of naphthalene after 95.5 hours is equal distribution foresees 12.0% of 2,6 isomer) to 50.8% molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim The selectivities With respect to naphthalene are: ethylnaphthalenes (% moles): 65.1 (thermodynamic selectivity dimethylnaphthalenes (% moles): 32.5 ratio 32%) selectivity 2,6-dimethylnaphthalene (% moles): 9.0 molar ratio 2,6/2,7 dimethylnaphthalene: 2.1 selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): (thermodymamic 1) 18.6 b) The conversion of naphthalene after 241 hours is equal to selectivity methylnaphthalenes (% moles): 64.6 59.1% selectivity polymethylnaphthalenes (% moles): 2.9 The selectivities With respect to naphthalene are: molar ratio 2,6-dimethylnaphthalene/total dimethylnaph selectivity dimethylnaphthalenes (% moles): 36.8 thalenes (% moles): 27.5 selectivity 2,6-dimethylnaphthalene (% moles): 11.2 molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim 45 selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): ethylnaphthalenes (% moles): 57.2 23.3 molar ratio 2,6/2,7 dimethylnaphthalene: 2.0 selectivity methylnaphthalenes (% moles): 58.9 c) The test is then carried out halving the space velocity. The selectivity polymethylnaphthalenes (9 moles): 4.3 conversion of naphthalene after 102 hours is equal to 59.4% molar ratio 2,6-dimethylnaphthalene/total dimethylnaph The selectivities With respect to naphthalene are: thalenes (% moles): 30.5 selectivity dimethylnaphthalenes (% moles): 38.2 molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim selectivity 2,6-dimethylnaphthalene (% moles): 10.8 ethylnaphthalenes (% moles): 63.3 selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): molar ratio 2,6/2,7 dimethylnaphthalene: 2.3 22.5 55 c) At this point, in order to regenerate the catalyst only 1,2,4-trimethylbenZene is sent to the reactor at a WHSV of selectivity methylnaphthalenes (% moles) 56.7 1.32 hours“1 and a temperature of 360° C. (under liquid selectivity polymethylnaphthalenes (% moles): 5.1 phase conditions, pressure of 35 bars) for 24 hours. The molar ratio 2,6-dimethylnaphthalene/total dimethylnaph temperature is then brought to 320° C. and the initial mixture thalenes % moles): 28.3 60 With naphthalene and methanol is fed again. After 310 hours molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim of running (of Which 286 hours under a stream also con ethylnaphthalenes (% moles): 59.0 taining naphthalene) a sample is taken from the reactor and molar ratio 2,6/2,7 dimethylnaphthalene: 2.0 analyZed, as described above. The conversion of naphtha lene after 310 hours is equal to 70.9% EXAMPLE 3 The selectivities With respect to naphthalene are: 4 gr of ZSM-12 Zeolite (molar ratio SiO2/Al2O3=100), selectivity dimethylnaphthalenes (% moles): 45.7 prepared in accordance With example 1, pelleted and granu selectivity 2,6-dimethylnaphthalene (% moles): 14.4 6,147,270 9 10 selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): molar ratio 2,6-dimethylnaphthalene/total dimethylnaph 29.9 thalenes (% moles): 34.2 selectivity methylnaphthalenes (% moles): 47.9 molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim selectivity polymethylnaphthalenes (% moles): 6.4 ethylnaphthalenes (% moles): 65.4 molar ratio 2,6-dimethylnaphthalene/total dimethylnaph molar ratio 2,6/2,7 dimethylnaphthalene: 2.8 thalenes (% moles): 31.5 c) At this point, in order to regenerate the catalyst only molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim 1,2,4-trimethylbenZene is sent to the reactor at a WHSV of ethylnaphthalenes (% moles): 65.4 1.32 hours-1 and a temperature of 320° C. (under liquid phase conditions, pressure of 35 bars) for 60 hours. The molar ratio 2,6/2,7 dimethylnaphthalene: 2.3 10 temperature is then brought to 300° C. and the initial mixture The Washing With only benzene hydrocarbon unexpect With naphthalene and methanol is fed again. After 600 hours edly alloWed recovery of the catalytic activity, Without of running (of Which 540 hours under a stream also con resorting to the methods normally used in the ?eld of the taining naphthalene) a sample is taken from the reactor and combustion catalysis of coke or its precursors, Which is analyZed, as described above. The conversion of naphtha typically responsible for the deactivation of a solid acid 15 lene after 600 hours is equal to 43.6% Which catalyZes reactions involving hydrocarbons. The selectivities With respect to naphthalene are: EXAMPLE 4 selectivity dimethylnaphthalenes (% moles): 32.4 selectivity 2,6-dimethylnaphthalene (% moles): 9.7 4 gr of ZSM-12 Zeolite (molar ratio SiO2/Al2O3=100), prepared as in example 1, pelleted and granulated Within a 20 selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): 20.8 range of 20—40 mesh, are charged into the isothermal Zone of a ?xed bed reactor, With quartZ above and beloW as inert selectivity methylnaphthalenes (% moles): 67.6 ?lling. The reactor is heated to 200° C. for at least 2 hours, selectivity polymethylnaphthalenes (% moles): 0.0 under a stream of nitrogen against atmospheric pressure. 25 molar ratio 2,6-dimethylnaphthalene/total dimethylnaph Maintaining under a stream of inert gas, the reactor is cooled thalenes (% moles): 30.0 to room temperature, and the reagents are then fed until the molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim reactor is pressuriZed to 35 bars. The mixture of reagents fed ethylnaphthalenes (% moles): 64.2 consists of 1,2,4-trimethylbenZene, naphthalene, methanol in the folloWing molar ratios: 1,2,4-trimethylbenZene/ molar ratio 2,6/2,7 dimethylnaphthalene: 2.5 naphthalene 18, methanol/naphthalene=2. At this point the Also in this case, Washing With only benZene hydrocarbon mixture is heated and brought to a temperature of 300° C. In unexpectedly alloWed recovery of the catalytic activity, this test the conditions are therefore liquid phase, With Without resorting to the methods normally used in the ?eld respect to the state of reagents and products. The WHSV of the combustion catalysis of coke or its precursors, Which (hours-1) With respect to the total mixture is 0.43. is typically responsible for the deactivation of a solid acid 35 Which catalyZes reactions involving hydrocarbons. The products leaving the reactor are cooled and analyZed by gaschromatography. Samples are taken of the products at EXAMPLE 5 (COMPARATIVE) regular time intervals (time on stream). The conversion of the methanol is alWays total. 2 gr of beta Zeolite (molar ratio SiO2/Al2O3=20), prepared in accordance With Us. Pat. No. 3,308,069, pelleted and a) The conversion of naphthalene after 147 hours is equal to 40 46.6% granulated Within a range of 20—40 mesh, are charged into The selectivities With respect to naphthalene are: the isothermal Zone of a ?xed bed reactor, With quartZ above and beloW as inert ?ller. The reactor is heated to 200° C. for selectivity dimethylnaphthalenes (% moles): 30.6 at least 2 hours, under a stream of nitrogen against atmo selectivity 2,6-dimethylnaphthalene (% moles): 9.7 spheric pressure. Maintaining under a stream of inert gas, selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): 45 the reactor is cooled to room temperature, and the reagents 19.8 are then fed until the reactor is pressuriZed to 40 bars. The selectivity methylnaphthalenes (% moles): 69.4 mixture of reagents fed consists of 1,2,4-trimethylbenZene, selectivity polymethylnaphthalenes (% moles): 0.0 naphthalene, methanol in the folloWing molar ratios: 1,2,4 trimethylbenZene/naphthalene 10, methanol/naphthalene=3. molar ratio 2,6-dimethylnaphthalene/total dimethylnaph At this point the mixture is heated and brought to a tem thalenes (% moles): 31.7 (the thermodynamic isomeric perature of 350° C. In this test the conditions are therefore distribution foresees 12.0% of 2,6 isomer) liquid phase, With respect to the state of reagents and molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim products. The WHSV (hours-1) With respect to the total ethylnaphthalenes (% moles): 64.8 (thermodynamic mixture is 0.86. The products leaving the reactor are cooled ratio 32%) 55 and analyZed by gaschromatography. Samples are taken of molar ratio 2,6/2,7 dimethylnaphthalene: 2.5 the products at regular time intervals (time on stream). The (thermodymamic 1) conversion of the methanol is alWays total. b) The conversion of naphthalene after 506 hours is equal to The conversion of naphthalene after 95 hours is equal to 28.2% 26.1% The selectivities With respect to naphthalene are: 60 The selectivities With respect to naphthalene are: selectivity dimethylnaphthalenes (% moles): 17.9 selectivity dimethylnaphthalenes (% moles): 9.9 selectivity 2,6-dimethylnaphthalene (% moles): 6.1 selectivity 2,6-dimethylnaphthalene (% moles): 2.5 selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): 11.7 65 4.8 selectivity methylnaphthalenes (% moles): 80.0 selectivity methylnaphthalenes (% moles): 77.5 selectivity polymethylnaphthalenes (% moles): 2.0 selectivity polymethylnaphthalenes (% moles): 12.6 6,147,270 11 12 molar ratio 2,6-dimethylnaphthalene/total dimethylnaph 20—40 mesh, are charged into the isothermal Zone of a ?xed thalenes (% moles): 25.6 bed reactor, With quartZ above and beloW as inert ?ller. The molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim reactor is heated to 200° C. for at least 2 hours, under a ethylnaphthalenes (% moles): 48.9 stream of nitrogen against atmospheric pressure. Maintain molar ratio 2,6/2,7 dimethylnaphthalene: 1.3 ing under a stream of inert gas, the reactor is cooled to room From the results indicated above, it can be observed that temperature, and the reagents are then fed until the reactor beta Zeolite, under the same conditions as Zeolite ZSM-12, is pressuriZed to 30 bars. The mixture of reagents fed is less active, less selective to dimethylnaphthalenes, less consists of 1,2,4-trimethylbenZene, naphthalene, methanol selective to 2,6 isomer and 2,6—+1,6—+1,5-isomers, on the in the folloWing molar ratios: 1,2,4-trimethylbenZene/ contrary beta Zeolite is more selective With respect to the 10 naphthalene=10, methanol/naphthalene=3. At this point the formation of the undesired products tri- and tetramethyl mixture is heated and brought to a temperature of 400° C. In naphthalenes and is less favourable toWards the formation of this test the conditions are therefore gas phase. The WHSV 2,6 isomer With respect to the 2,7 isomer. (hours_1) With respect to the total mixture is 0.86. The EXAMPLE 6 (COMPARATIVE) products leaving the reactor are cooled and analyZed by 2.3 gr of Zeolite ZSM-5 (MFI) (PQ CBU3070E, molar 15 gaschromatography. Samples are taken of the products at ratio SiO2/Al2O3=30), in acid form, pelleted and granulated regular time intervals (time on stream). The conversion of Within a range of 20—40 mesh, are charged into the isother the methanol is alWays total. mal Zone of a ?xed bed reactor, With quartZ above and beloW a) The conversion of naphthalene after 28.5 hours is equal to as inert ?ller. The reactor is heated to 200° C. for at least 2 76.7% hours, under a stream of nitrogen against atmospheric pres 20 The selectivities With respect to naphthalene are: sure. Maintaining under a stream of inert gas, the reactor is selectivity dimethylnaphthalenes (% moles): 42.5 cooled to room temperature, and the reagents are then fed selectivity 2,6-dimethylnaphthalene (% moles): 10.5 until the reactor is pressuriZed to 40 bars. The mixture of selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): reagents fed consists of 1,2,4-trimethylbenZene, 22.1 naphthalene, methanol in the folloWing molar ratios: 1,2,4 25 trimethylbenZene/naphthalene=10, methanol/naphthalene= selectivity methylnaphthalenes moles): 44.0 3. At this point the mixture is heated and brought to a selectivity polymethylnaphthalenes (% moles): 13.6 temperature of 450° C. In this test the conditions are molar ratio 2,6-dimethylnaphthalene/total dimethylnaph therefore gas phase. The WHSV (hours-1) With respect to thalenes (% moles): 24.6 (it should be remembered that the total mixture is 0.75. The products leaving the reactor are 30 the thermodynamic isomeric distribution estimates cooled and analyZed by gaschromatography. Samples are 12.0% of 2,6 (PU)) taken of the products at regular time intervals (time on molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim stream). The conversion of the methanol is alWays total. ethylnaphthalenes (% moles): 52.1 (thermodynamic a) The conversion of naphthalene after 96 hours is equal to 35 32%) 21.8% molar ratio 2,6/2,7 dimethylnaphthalene: 1.5 The selectivities With respect to naphthalene are: (thermodynamic 1) The test is continued and the con selectivity dimethylnaphthalenes (% moles): 7.8 version of naphthalene after 95 hours is equal to 21.0% selectivity 2,6-dimethylnaphthalene (% moles): 3.6 The selectivities With respect to naphthalene are: selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): 40 selectivity dimethylnaphthalenes (% moles): 20.1 3.6 selectivity 2,6-dimethylnaphthalene (% moles): 4.1 selectivity methylnaphthalenes (% moles): 78.3 selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): selectivity polymethylnaphthalenes (% moles): 0.0 8.2 selectivity to ethylnaphthalenes (% moles): 14.0 selectivity methylnaphthalenes (% moles): 78.3 molar ratio 2,6-dimethylnaphthalene/total dimethylnaph 45 selectivity polymethylnaphthalenes (% moles): 1.7 thalenes (% moles): 26.3 molar ratio 2,6-dimethylnaphthalene/total dimethylnaph molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim thalenes (% moles): 20.6 (it should be remembered that ethylnaphthalenes (% moles): 46.3 the thermodynamic isomeric distribution estimates molar ratio 2,6/2,7 dimethylnaphthalene: 0.9 12.0% of 2,6 (PU)) From the results indicated above, it can be observed that molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim Zeolite ZSM-5 is less active than ZSM-12. In fact, to have comparable conversions the ZSM-5 must be used at much ethylnaphthalenes (% moles): 40.7 (thermodynamic higher temperatures (450° C. against 3500 C.) and under gas 32%) phase conditions. As Well as being less active, Zeolite molar ratio 2,6/2,7 dimethylnaphthalene: 1.2 ZSM-5 is more rapidly deactivated, With a considerable 55 (thermodynamic 1) formation of carbonaceous residues, it is less selective to It is further demonstrated that operating in gas phase dimethylnaphthalenes, less selective to 2,6 isomer and to provides Worse performances both in terms of the deactiva 2,6—+1,6—+1,5-isomers. ZSM-5 also produces a signi?cant tion rate of the catalyst and selectivity to 2,6 isomer and quantity of undesired ethylnaphthalenes, Whereas the molar 2,6—+1,6—+1,5 isomers. The formation of 2,6 isomer With ratio betWeen the 2,6 and 2,7 isomers of dimethylnaphtha 60 respect to 2,7 isomer is also less favourable. lene is practically the thermodynamic ratio and it is not EXAMPLE 8 (COMPARATIVE) unbalanced toWards the 2,6 isomer, Which is the isomer of particular interest. 4 gr of Zeolite ZSM-12 (molar ratio SiO2/Al2O3=100), prepared in accordance With example 1, pelleted and granu EXAMPLE 7 (COMPARATIVE) 65 lated Within a range of 20—40 mesh, are charged into the 2 gr of Zeolite ZSM-12 (MTW), prepared in accordance isothermal Zone of a ?xed bed reactor, With quartZ above and With example 1, pelleted and granulated Within a range of beloW as inert ?ller. The reactor is heated to 200° C. for at 6,147,270 13 14 least 2 hours, under a stream of nitrogen against atmospheric EXAMPLE 9 pressure. Maintaining under a stream of inert gas, the reactor 4 gr of Zeolite ZSM-12 (molar ratio SiO2/Al2O3 is 100), is heated to a temperature of 320° C., and the reagents are prepared in accordance With example 1, pelleted and granu then fed into the reactor at atmospheric pressure. The lated Within a range of 20—40 mesh, are charged into the reaction therefore takes place under gas phase conditions. isothermal Zone of a ?xed bed reactor, With quartZ above and The mixture of reagents fed consists of methylnaphthalenes beloW as inert ?ller. The reactor is heated to 200° C. for at and methanol in the folloWing ratios: 2-methylnaphthalene/ least 2 hours, under a stream of nitrogen against atmospheric 1-methylnaphthalene 1.5; methanol/methylnaphthalenes pressure. Maintaining under a stream of inert gas, the reactor 0.1. is cooled to room temperature, and the reagents are then fed The WHSV (hours-1) With respect to the total mixture is 10 until the reactor is pressuriZed to 35 bars. The mixture of 0.20. The products leaving the reactor are cooled and reagents fed consists of 1,2,4-trimethylbenZene, analyZed by gaschromatography. Samples are taken of the naphthalene, 1-methylnaphthalene, methylnaphthalene, products at regular time intervals (time on stream). methanol in the folloWing molar ratios: 1,2,4 The conversion of the methanol is alWays total. trimethylbenZene/naphthalene groups=18, methanol/ a) The conversion of methylnaphthalene after 3 hours is naphthalene=2, methanol/methylnaphthalene=1. Naphtha equal to 13.56% lene groups refer to the sum in moles of naphthalene, The selectivities With respect to converted methylnaph 1-methylnaphthalene, 2-methylnaphthalene 30% of the thalene are: naphthalene groups consists of naphthalene, the remaining selectivity dimethylnaphthalenes (% moles): 70.0 70% consists of 30% of 1-methylnaphthalene and 70% of selectivity 2,6-dimethylnaphthalene (% moles): 7.3 2-methylnaphthalene. At this point the mixture is heated and brought to a temperature of 300° C. In this test the condi selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): tions are therefore liquid phase, With respect to the state of 19.7 reagents and products. The WHSV (hours-1) With respect to selectivity naphthalene (% moles): 11.2 the total mixture is 0.43. The products leaving the reactor are selectivity trimethylnaphthalenes (% moles): 13.5 25 cooled and analyZed by gaschromatography. Samples are selectivity heavy products (% moles) 5.3 taken of the products at regular time intervals (time on molar ratio 2,6-dimethylnaphthalene/total dimethylnaph stream). The conversion of the methanol is alWays total. thalenes (% moles): 10.5 The selectivities calculated With respect to the naphtha lene groups as if they all derived from simple naphthalene molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim 30 ethylnaphthalenes (% moles): 28.1 are: molar ratio 2,6/2,7 dimethylnaphthalene: 1.2 selectivity dimethylnaphthalenes (% moles): 40.3 The test is continued and the conversion of methylnaphtha selectivity 2,6-dimethylnaphthalene (% moles): 13.3 lene after 24 hours is equal to 3.0% selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): The selectivities With respect to methylnaphthalene are: 27.4 selectivity dimethylnaphthalenes (% moles): 94.6 selectivity methylnaphthalenes (% moles): 56.2 selectivity 2,6-dimethylnaphthalene (% moles): 9.2 selectivity polymethylnaphthalenes (% moles): 3.4 selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): molar ratio 2,6-dimethylnaphthalene/total dimethylnaph thalenes (% moles): 33.3 24.4 40 selectivity methylnaphthalenes (% moles): 1.9 molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim selectivity trimethylnaphthalenes (% moles): 3.2 ethylnaphthalenes (% moles): 67.9 molar ratio 2,6/2,7 dimethylnaphthalene: 2.5 selectivity heavy products (% moles)): 0.3 The mole % of dimethylnaphthalenes out of the total molar ratio 2,6-dimethylnaphthalene/total dimethylnaph 45 naphthalene groups is 33.2. thalenes (% moles): 9.7 Under the same experimental conditions and With the molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim same t.o.s., ie the deactivation of the catalyst, a mixture is ethylnaphthalenes (% moles): 25.8 reacted Which differs from the previous one in that it molar ratio 2,6/2,7 dimethylnaphthalene: 1.3 contains naphthalene alone as naphthalene substrate. The (thermodynamic 1) folloWing selectivities With respect to naphthalene corre It is evident that the preparation of 2,6 spond to a conversion of 32.9%: dimethylnaphthalene under the conditions of the prior art, selectivity dimethylnaphthalenes (% moles): 20.9 ie under gas phase conditions and Without a solvent, causes selectivity 2,6-dimethylnaphthalene (% moles): 7.1 a precocious and signi?cant deactivation of the catalyst. selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): The selectivity to total dimethylnaphthalenes is high, but 55 13.6 only When coinciding With very loW conversions of meth selectivity methylnaphthalenes (% moles): 79.1 ylnaphthalene and With a deactivated catalyst. The distribution of the isomers among the dimethylnaph selectivity polymethylnaphthalenes (% moles): 0.0 thalenes is different from that obtained When operating molar ratio 2,6-dimethylnaphthalene/total dimethylnaph according to the process of the present invention: in par 60 thalenes (% moles): 34.2 ticular the molar ratio betWeen the 2,6 isomer and total molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim dimethylnaphthalenes is much loWer (10 against 30—35), as ethylnaphthalenes (% moles): 65.2 is also that betWeen 2,6+1,6+1,5 and the total dimethylnaph molar ratio 2,6/2,7 dimethylnaphthalene: 2.6 thalenes (28 against 60—70). In addition there is the forma On comparing the tWo tests, it can be observed that at a tion of non-recoverable heavy products, such as dinaphth m 5 certain temperature, it is possible to increase the yield to ylmethanes possibly With from 1 to 3 methyl groups bound dimethylnaphthalenes substituting part of the naphthalene to the aromatic groups. With methylnaphthalenes. 6,147,270 15 16 EXAMPLE 10 These data are in accordance With a process in Which TWo tests are carried out under the following conditions: contemporaneous transalkylation, deproportioning, alkyla 4 gr of Zeolite ZSM-12 (molar ratio SiO2/Al2O3=100), tion and isomeriZation reactions take place. prepared in accordance With example 1, pelleted and granu Table AbeloW indicates the distribution in molar % of the lated Within a range of 20—40 mesh, are charged into the isomers of dimethylnaphthalene resulting from the ?rst test, isothermal Zone of a ?xed bed reactor, With quartz above and in Which the substrate used Was exclusively naphthalene: beloW as inert ?ller. The reactor is heated to 200° C. for at least 2 hours, under a stream of nitrogen against atmospheric TABLE A pressure. Maintaining under a stream of inert gas, the reactor is cooled to room temperature, and the reagents are then fed 10 isomer mol % until the reactor is pressuriZed to 35 bars. 2 6 28 6 In the ?rst test, the naphthalene hydrocarbon used is only 2:7 16' naphthalene and the reagent mixture fed consists of 1,2,4- 13 + 1,7 175 trimethylbenZene, naphthalene and methanol in the folloW- 1,6 27-2 ing molar ratios: 1,2,4-trimethylbenZene/naphthalene=18, 15 1>4 + 23 3-1 methanol/naphthalene=2. :7 In the second test, the naphthalene hydrocarbon fed 1:8 0 consists of 73.7% of naphthalene and the remaining 26.3% of dimethylnaphthalenes and the reagent mixture used con- ______Sists of 1,2,44rimethy1hehZehe, naphthalene, dimethyhlaph 20 Table B beloW indicates the distribution in molar % of the thalenes and methanol. The methanol is charged proportion- lsomefs of filmethylnaphthalene resulnng from the Second any to the naphthalene groups, according to the following test, in WhlCh the substrate' used consisted of 73.7% of criterium: 2 moles of methanol per mole of naphthalene, no naphlhalene and 263% of d1m§thY1naPhtha1ene§ (the table mole of methanol per mole of dimethylnaphthalene The also indicates the percentage distribution of the isomers in molar ratio 1,2,4-trimethylbenZene/naphthalene groups is 25 the dimethylnaphthalene fed) equal to 18. Naphthalene groups refer in this case to the sum in moles of naphthalene and dimethylnaphthalenes. The TABLE B operation is carried out at a temperature of 320° C., under f d_ d t liquid phase conditions, at a total WHSV of 0.43 hours-1. isomer £21115 pgoluf/os The tWo tests are carried out so that the equivalent 3O conversion- is- comparable, the equivalent- conversion- (% 2 > 6 — 22.6 . . . . 2,7 17.2 13.7 mole) referring to the ratio, multiplied by 100, betWeen the 1 3 + 1 7 _ 26 sum of moles of methylnaphthalenes, dimethylnaphthalenes, 1,6 _ 21 trimethylnaphthalenes, and polymethylnaphthalenes among 1,4 + 2,3 82-8 10-6 products,the products comprising and the total therefore moles also of naphthalenes the naphthalene. among the 35 1’8 :_ 0' The equivalent conversion is then calculated as if all the na hthalene rou s fed, meth lated and non-meth lated, are _ - p 1 hg p y y Comparison betWeen the tables shoWs that the 2,3 s1mp e nap thalene groups. _ _ . . dimethylnaphthalene fully entered the reactive system; the In the ?rst test the following results are obtained: 40 ...... same can be said for the 2,7 1somer, as there is no registra convers1on=78.4% composition of the products % mol (after . f . 1 . removal of the 1 2 4-trimethylbenZene)' Hon 0 Its accumu anon' . . . ’ ’ ' Table C below summarizes the molar % composition of the products relating to the tWo tests discussed above: the ?rst and second columns refer respectively to the feeding of naphthalene 216 45 naphthalene alone as naphthalene substrate and to the com rriethylnaphthalenes 27-4 position in molar % of products and isomers obtained in the slmetglllyllnapgtiallenes jg ?rst test; the third and fourth columns refer respectively to nme y nap a enes the composition of the naphthalene substrate and the com position in molar % of products and isomers obtained in the In the second test the results obtained are the following: 50 second test. conversion=80.8% composition of the products % mol (Without the benZene TABLE C hydrocarbon): (composition in % moles) 55 Feeding Products Feeding Products naphthalene 19.2 Naphthalene 100 21.6 73.7 19.2 methylnaphthalenes 25.3 1-methylnaphthalene — 8.5 — 7.7 dimethylnaphthalenes 39.2 2-methylnaphthalene — 18.9 — 17.6 trimethylnaphthalenes 16.4 60 Methylnaphthalenes — 27.4 — 25.3 Dimethylnaphthalenes — 36 26.3 39.2 2,6 isomer — 10.3 — 8.9 Comparison of the data indicated in the previous tables 2,7 isomer — 5.8 4.3 5.4 demonstrates that the distribution of the main products in 1>3 _+ 1>7 isomers — 6-3 — 101 - - - - 1,6 isomer — 9.8 — 8.2 both cases is very similar and consequently the d1methyl- 1 4 + 23 isomers _ 1 1 21 8 4 1 naphthalenes fed entered the reaction cycle Without simple 65 1:5 iSOI’ner _ 1:7 ' 1:3 accumulation, i.e. inert behaviour, or only additional alky- 1,2 isomer — 1.1 — 1.1 lation. 6,147,270

TABLE C-continued -continued (composition in % moles) Methylnaphthalenes 35-10 Dimethylnaphthalenes 11.20 Feeding Products Feeding Products 5 2,6 isomer O-OO 2,7 isomer 4.90 1,8 isomer — 0 — 0 1,3 + 1,7 isomers 0.00 Trimethylnaphthalenes 15 — 16.4 1,6 isomer 0.00 1,4 + 2,3 isomers 5.70 1,5 isomer 0.00 Also in this table it can be seen that 2,3 10 1,2 isomer 0.50 -dimethylnaphthalene fully enters the reactive system; the 13? lsomer 0'00 same can be said. for the 2,7 isomer,. as there is. no registra. Trimethylnaphthalenes 0.00 tion of its accumulation. The reagent mixture fed also contains 1,2,4 EXAMPLE 11 15 trimethylbenZene and methanol. The methanol is charged proportionally to the naphthalene groups, according to the Using the same procedure as the previous example, the folloWing criterium: tWo moles of methanol per mole of folloWing experimentations are carried out at 300° C. and 35 naphthalene, one mole of methanol per mole of bars. The total WHSV is 0.43 hours-1. In the ?rst test the methylnaphthalene, no mole of methanol per mole of dim naphthalene hydrocarbon used is naphthalene alone and the 20 ethylnaphthalene. The molar ratio 1,2,4-trimethylbenZene/ reagent mixture fed consists of 1,2,4-trimethylbenZene, naphthalene groups is equal to 18. Naphthalene groups refer naphthalene and methanol in the folloWing molar ratios: to the sum in moles of naphthalene, methylnaphthalenes and 1,2,4-trimethylbenZene/naphthalene=18, methanol/ dimethylnaphthalenes. naphthalene=2. The results obtained in this second experimentation, The results obtained, expressed as composition in moles, 25 expressed as composition in % moles, are indicated in Table are the following: D beloW, ?rst column, Where they are compared With the spectrum of products obtained starting from naphthalene alone as naphthalene substrate (second column), With the Equivalent conv. % 67.10 same equivalent conversion. Naphthalene 32.90 30 1-methylnaphthalene 10.50 TABLE D 2-methylnaphthalene 24.20 Methylnaphthalenes 34.80 Equivalent conv. % 89.00 89.30 Dimethylnaphthalenes 29.20 Naphthalene 11.00 10.70 2,6 isomer 9.40 1-methylnaphthalene 7.50 7.30 2,7 isomer 4.00 35 2-methylnaphthalene 17.60 16.60 1,3 + 1,7 isomers 4.60 Methylnaphthalenes 25.10 23.90 1,6 isomer 8.50 Dimethylnaphthalenes 49.80 50.20 1,4 + 2,3 isomers 0.80 2,6 isomer 15.00 15.20 1,5 isomer 1.30 2,7 isomer 8.10 8.40 1,2 isomer 0.50 1,3 + 1,7 isomers 8.50 8.40 1,8 isomer 0.00 40 1,6 isomer 13.60 14.10 Trimethylnaphthalenes 3.10 1,4 + 2,3 isomers 1.50 1.10 1,5 isomer 2.20 2.30 1,2 isomer 1.10 0.70 In the second test a feeding is used Which repeats the 1,8 isomer 0.00 0.00 spectrum of products obtained from the ?rst Trimethylnaphthalenes 14.10 15.20 experimentation, except that: 45 the 2,6-dimethylnaphthalene, 1,6-dimethylnaphthalene As can be seen from the above table, from the test Which and 1,5-dimethylnaphthalene (belonging to the same simulates the recycling, there is a spectrum of products isomeriZation group as de?ned in EP 519165) are (column 1) Which is practically undistinguishable from that replaced by an equal quantity in moles of naphthalene; obtained, With the same equivalent conversion, starting from 50 the 1,3, 2,3 and 1,4 isomers (as they belong to the same naphthalene alone (column 2): these data shoW that the isomeriZation group as de?ned in EP 519165) are dimethylnaphthalenes fed have entered the reaction cycle, as replaced by the 2,3 isomer; there is no simple accumulation, i.e. inert behaviour, or only additional alkylation, and they are also in accordance With a the 1,7 isomer, Which is not anlaytically separated from process in Which transalkylation, deproportioning, alkyla the 1,3 isomer, and cannot therefore be quanti?ed, is 55 tion and isomeriZation reactions contemporaneously con substituted With the 2,3 isomer. tribute to the formation of the desired product 2,6 This second test therefore simulates a recycling of prod dimethylnaphthalene. ucts and isomers Which are different from the desired product in the synthesis reactor of 2,6-dimethylnaphthalene. EXAMPLE 12 The composition in % moles of the naphthalene substrate 60 Using the same procedure as the previous example, a test used in the second test is therefore the folloWing: is carried out at 300° C. and 35 bars. The total WHSV is 0.43 hours_1. Methylnaphthalene is used as naphthalene hydrocarbon, consisting of 70% of 2-methylnaphthalene and Naphthalene 53.70 30% of l-methylnaphthalene. The reagent mixture fed con 1-methylnaphthalene 10. 60 65 sists of 1,2,4-trimethylbenZene, methylnaphthalene and 2-methylnaphthalene 24.50 methanol in the folloWing molar ratios: 1,2,4 trimethylbenZene/methylnaphthalene= 10, methanol/ 6,147,270 19 20 methylnaphthalene=0.5. The methylnaphthalene fed con phase, With respect to the state of reagents and products. The sists of 70% of 2-methylnaphthalene and 30% of WHSV (h_1) (With respect to the total mixture) is 0.86. The 1-methylnaphthalene. products at the output the reactor are cooled and analyZed by During the test tWo samplings are taken, With relative GC gaschromatography. Samples are taken of the products at analysis of the products, and the results are indicated in the regular time on stream intervals. following table: The conversion of the methanol is alWays total. The conversion of the naphthalene after 95 h is 21.7%. The selectivities With respect to the naphthalene are:

time time 10 selectivity dimethylnaphthalenes (% moles): 14.8 on on selectivity 2,6-dimethylnaphthalene (% moles): 1.4 stream stream (hours) (hours) Feeding selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): 92 130 _ 3.9

COnV. MN % 65.9 64.4 — selectivity methylnaphthalenes (% moles): 84.1 Select. DMNi (mol %) 85.2 86.5 15 selectivity polymethylnaphthalenes (% moles): 1.1 Select. 2,6 DMN (mol %) 29.6 30.2 Select. 2,6.1,6-1,5 60 61.2 molar ratio 2,6-dLmethylnaphthalene/total dimethylnaph DMNi (mol %) thalenes (% moles): 9.7 Select. N (mol %) 1.8 1.8 Select. PMNi (mol %) 12.9 11.7 molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim 2,6—DMN/t0tal DMNi 34.7 34.9 20 ethylnaphthalenes (% moles): 26.5 (mol %) molar ratio 2,6/2,7 dimethylnaphthalene: 1.1 2,6-1,6-1,5-DMN/total 70.4 70.7 From the results indicated above it can be observed that DNMi (mol %) Molar ratio 2,6/2,7-DMN 2.5 2.6 Y Zeolite, With respect to ZSM-12 Zeolite, under the same Composition in Weight % (solvent free) conditions, is less active, less selective to 25 dimethylnaphthalenes, less selective to the 2,6 isomer and to N 1 1 1-MN 9.7 10.2 30 the 2,6—+1,6—+1,5-isomers. In addition it is much less 2-MN 22.1 23.1 70 selective toWards the formation of the 2,6 isomer With MNi 31.9 33.3 100 respect to the 2,7 isomer (ratio close to the thermodynamic EtNi 0 0 ratio) and much less selective toWards the formation of the DMNi 57.6 57.3 30 2,6 isomer With respect to the other isomers of dimethyl 2,6-DMN 20 20 2,7-DMN 8 7.8 naphthalenes. 1,3-1,7-DMN 7.6 7.4 1,6-DMN 17.7 17.7 EXAMPLE 14 (COMPARATIVE) 1,4-2,3-DMN 0.6 0.6 TWo grams of ZSM5 Zeolite (MEI) (PQ CBU3070E, ratio 1,5-DMN 2.9 2.8 35 1,2-DMN 0.8 1 SiO2/Al2O3=30), in acid form, pelleted and granulated 1,8-DMN 0 0 Within a range of 20—40 mesh, are charged into the isother TMNI 9.5 8.4 mal Zone of a ?xed bed reactor, With quartZ above and beloW as inert ?ller. The temperature of the reactor is brought to In the above table N=naphthalene; 200° C. for at least 2 hours, under a stream of nitrogen MN=methylnaphthalene; MNi=methylnaphthalenes; EtNi= 40 against atmospheric pressure. Maintaining under a stream of ethylnaphthalenes; DMN=dimethylnaphthalene; DMNi inert gas, the reactor is cooled to room temperature, and the dimethylnaphthalenes; TMNi=trimethylnaphthalenes; reagents are then fed until the reactor is pressuriZed to 40 PMNi=polymethylnaphthalenes. bars. The mixture of reagents fed consists of 1,2,4 trimethylbenZene, naphthalene, methanol in the folloWing Under these conditions there is a very high selectivity to 45 dimethylnaphthalenes, Whereas the distribution of the iso molar ratios: 1,2,4-trimethylbenZene/naphthalene=10, mers internally does not differ from the previous examples. methanol/naphthalene=3. At this point the mixture is heated The high total selectivity to total DMNi, is re?ected in a and brought to a temperature of 350° C. Therefore in this test greater Weight % production of 2,6-DMN than the previous the conditions are of liquid phase, With respect to the state examples. of reagents and products. The WHSV (h_1) (With respect to the total mixture) is 0.86. The products at the output of the EXAMPLE 13 (COMPARATIVE) reactor are cooled and analyZed by gaschromatography. Samples are taken of the products at regular time on stream TWo grams of Y Zeolite (FAU) (TOSOH HSZ 330 HUA, intervals. molar ratio SiO2/Al2O3=6), in acid form, pelleted and granu The conversion of the methanol is alWays total. lated Within a range of 20—40 mesh, are charged into the 55 isothermal Zone of a ?xed bed reactor, With quartZ above and The conversion of the naphthalene after 49 h is 6.7%. beloW as inert ?ller. The temperature of the reactor is The selectivities With respect to the naphthalene are: brought to 200° C. for at least 2 hours, under a stream of selectivity dimethylnaphthalenes (% moles): 24.5 nitrogen against atmospheric pressure. Maintaining under a selectivity 2,6-dimethylnaphthalene (% moles): 6.6 stream of inert gas, the reactor is cooled to room 60 selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): temperature, and the reagents are then fed until the reactor 6.6 is pressuriZed to 40 bars. The mixture of reagents fed consists of 1,2,4-trimethylbenZene, naphthalene, methanol selectivity methylnaphthalenes (% moles): 57.3 in the folloWing molar ratios: 1,2,4-trimethylbenZene/ selectivity to ethylnaphthalenes (% moles): 18.2 naphthalene=10, methanol/naphthalene=3. At this point the 65 selectivity polymethylnaphthalenes (% moles): 0.0 mixture is heated and brought to a temperature of 350° C. molar ratio 2,6-dimethylnaphthalene/total dimethylnaph Therefore, in this test We are in the conditions of liquid thalenes (% moles): 27.0 6,147,270 21 22 molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim molar ratio 2,6-dimethylnaphthalene/total dimethylnaph ethylnaphthalenes (% moles): 27.0 thalenes (% moles): 10.8 molar ratio 2,6/2,7 dimethylnaphthalene: 0.5 molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim ethylnaphthalenes (% moles): 28.0 EXAMPLE 15 molar ratio 2,6/2,7 dimethylnaphthalene: 1.0 The experimental data obtained With ZSM-12 Zeolite (prepared according to example 1) operating under the same EXAMPLE 17 conditions as example 2 and the previous comparative TWo grams of ZSM12 Zeolite (MTW) (prepared as example, after 49 hours of time on stream, are provided 10 described in example 1) pelleted and granulated Within a hereunder. range of 20—40 mesh, are charged into the isothermal Zone Conversion of naphthalene: 75.8%. of a ?xed bed reactor, With quartZ above and beloW as inert The selectivities With respect to the naphthalene are: ?ller. The temperature of the reactor is brought to 200° C. for selectivity dimethylnaphthalenes (% moles): 47.9 at least 2 hours, under a stream of nitrogen against atmo 15 spheric pressure. Maintaining under a stream of inert gas, selectivity 2,6-dimethylnaphthalene (% moles): 13.8 the reactor is cooled to room temperature, and the reagents selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): are then fed until the reactor is pressuriZed to 40 bars. The 29.2 mixture of reagents fed consists of 1,2,4-trimethylbenZene selectivity methylnaphthalenes (% moles): 44.3 and naphthalene. The molar ratio 1,2,4-trimethylbenZene/ selectivity polymethylnaphthalenes (% moles): 7.8 20 naphthalene=10. In this example methanol is not present in molar ratio 2,6-dimethylnaphthalene/total dimethylnaph the reaction mixture. After pressuriZing the reactor, it is heated and brought to a temperature of 350° C. Therefore in thalenes (% moles): 28.9 this test the conditions are of liquid phase, With respect to the molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim state of reagents and products. The WHSV (h_1) (With ethylnaphthalenes (% moles): 61.0 25 respect to the total mixture) is 0.86. The products at the molar ratio 2,6/2,7 dimethylnaphthalene: 1.9 output of the reactor are cooled and analyZed by gaschro On comparing the above data With those of the previous matography. Samples are taken of the products at regular example 14, it can be observed that ZSM-5 Zeolite, With time on stream intervals. respect to ZSM-12 Zeolite, under the same conditions, is The conversion of the naphthalene after 95 h is 49.5%. much less active, less selective to dimethylnaphthalenes, 30 The selectivities With respect to the naphthalene are: less selective to 2,6 isomer, less selective to 2,6—+1,6—+1, 5-isomers. In addition it produces a large quantity of selectivity dimethylnaphthalenes (% moles): 32.5 ethylnaphthalenes, Which are absent in the spectrum of selectivity 2,6-dimethylnaphthalene (% moles): 9.0 ZSM-12 products. The molar ratio betWeen 2,6 and 2,7 selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): isomers is far from the thermodynamic ratio and is deci 35 19.0 sively unbalanced toWards 2,7. selectivity methylnaphthalenes (% moles): 64.8 EXAMPLE 16 (COMPARATIVE) selectivity polymethylnaphthalenes (% moles): 2.7 molar ratio 2,6-dimethylnaphthalene/total dimethylnaph TWo grams of Y Zeolite (FAU) (TOSOH HSZ 330 HUA, thalenes (% moles): 27.7 molar ratio SiO2/Al2O3=6), in acid form, pelleted and granu 40 lated Within a range of 20—40 mesh, are charged into the molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total dim isothermal Zone of a ?xed bed reactor, With quartZ above and ethylnaphthalenes (% moles): 57.6 beloW as inert ?ller. The temperature of the reactor is molar ratio 2,6/2,7 dimethylnaphthalene: 2.0 brought to 200° C. for at least tWo hours, under a stream of On comparing the data of example 17 above With the data nitrogen against atmospheric pressure. Maintaining under a 45 of the previous comparative example 16, both carried out stream of inert gas, the reactor is cooled to room Without methanol, it can be observed that Y Zeolite, With temperature, and the reagents are then fed until the reactor respect to ZSM-12 Zeolite, under the same conditions, is less is pressuriZed to 40 bars. The mixture of reagents fed active, less selective to dimethylnaphthalenes, less selective consists of 1,2,4-trimethylbenZene and naphthalene. The to 2,6 isomer and to 2,6—+1,6—+1,5-isomers. In addition it is molar ratio 1,2,4-trimethylbenZene/naphthalene=10. In this much less selective toWards the formation of 2,6 isomer With example methanol is not present in the reaction mixture. respect to 2,7 isomer (ratio close to the thermodynamic After pressuriZing the reactor, it is heated and brought to a ratio) and much less selective toWards the formation of 2,6 temperature of 350° C. Therefore, in this test the conditions isomer With respect to the other isomers of dimethylnaph are of liquid phase, With respect to the state of reagents and thalenes. products. The WHSV (h_1) (With respect to the total 55 mixture) is 0.86. The products at the output of the reactor are EXAMPLE 18 (COMPARATIVE) cooled and analyZed by gaschromatography. Samples are TWo grams of ZSM12 Zeolite (MTW) (prepared as taken of the products at regular time on stream intervals. The described in example 1), pelleted and granulated Within a conversion of the naphthalene after 95 h is 22.9%. range of 20—40 mesh, are charged into the isothermal Zone The selectivities With respect to the naphthalene are: of a ?xed bed reactor, With quartZ above and beloW as inert selectivity dimethylnaphthalenes (% moles): 15.6 ?ller. The temperature of the reactor is brought to 200° C. for at least tWo hours, under a stream of nitrogen against selectivity 2,6-dimethylnaphthalene (% moles): 1.7 atmospheric pressure. Maintaining under a stream of inert selectivity 2,6/1,6/1,5-dimethylnaphthalene (% moles): gas, the reactor is cooled to room temperature, and the 4.4 65 reagents are then fed until the reactor is pressuriZed to 40 selectivity methylnaphthalenes (% moles): 83.1 bars. The mixture of reagents fed consists of selectivity polymethylnaphthalenes (% moles): 1.3 1-methylnaphthalene (liquid at room temperature and also at 6,147,270 23 24 350° C., 40 bars) and methanol. The molar ratio methanol/ ing of aluminum, gallium, and their mixtures, Y is selected 1-methylnaphthalene is equal to 0.5. After pressuriZing the from the group consisting of silicon, and germanium, Z reactor, it is heated and brought to a temperature of 350° C. ranges from 0 to 60. The WHSV (h_1) (With respect to the total mixture) is 0.75. 9. The process according to claim 8, Wherein W is at least The products at the output of the reactor are cooled and partially substituted by boron, iron or their mixtures. analyZed by gaschromatography. Samples are taken of the 10. The process according to claim 8, Wherein W is products at different time on stream intervals. aluminum and Y is silicon. The conversion of the methanol is alWays total. 11. The process according to claim 1 Wherein the cation sites of the Zeolite are occupied by at least 50% of hydrogen The conversion of 1-methylnaphthalene, after 20 hours of time on stream is equal to 16.8%. 10 ions. 12. The process according to claim 11, Wherein at least The molar ratio 2,6-dimethylnaphthalene/total dimethyl 90% of the cation sites is occupied by hydrogen ions. naphthalenes is 7.7 13. The process according to claim 1, Wherein the Zeolite The molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total is used pure in pelletiZed form, or extruded With inorganic dimethylnaphthalenes is 25.7 15 oxide ligands to form cylindrical, spherical pellets, or in the The molar ratio 2,6/2,7 dimethylnaphthalene is 0.9 form of microspheres obtained by spray-drying. The conversion of 1-methylnaphthalene, after 23 hours of 14. The process according to claim 13, Wherein the ligand time on stream is equal to 12.0%. is selected from the group consisting of aluminas, silicas, The molar ratio 2,6-dimethylnaphthalene/total dimethyl silico-aluminas, titania, Zirconia, and clays. naphthalenes is 6.1 20 15. The process according to claims 13 or 14, Wherein the Zeolite and the ligand are in a Weight ratio of 10:90 to 90:10. The molar ratio 2,6-1,6-1,5-dimethylnaphthalene/total 16. The process according to claim 15, Wherein the Weight dimethylnaphthalenes is 27.1 ratio of said Zeolite to said ligand varies from 25:75 to 75:25. The molar ratio 2,6/2,7 dimethylnaphthalene is 1.0 17. The process according to claim 1, Wherein the benZene What is claimed is: 25 hydrocarbon is trimethylbenZene. 1. Aprocess for preparing 2,6-dimethylnaphthalene Which 18. The process according to claim 1, Wherein the molar comprises reacting a naphthalene hydrocarbon selected from ratio betWeen the benZene hydrocarbon and the maphthalene the group consisting of naphthalene, methylnaphthalenes, hydrocarbon ranges from 1 to 100. dimethylnaphthalenes, trimethylnaphthalenes, 19. The process according to claim 18, Wherein the molar tetramethylnaphthalenes, pentamethylnaphthalenes, 30 ratio betWeen the benZene hydrocarbon and the naphthalene hexamethylnaphthalenes, and their mixtures With one or hydrocarbon ranges from 3 to 20. more benZene hydrocarbons selected from the group con 20. The process according to claim 1, Wherein the molar sisting of benZene, toluene, xylenes, trimethylbenZenes, ratio betWeen the methylating agent and the naphthalene tetramethylbenZenes, pentamethylbenZene, and hydrocarbon is less than 30. hexamethylbenZene, under at least partially liquid phase 35 21. The process according to claim 20, Wherein the molar conditions, in the presence of a Zeolite having a MTW ratio betWeen methylating agent and naphthalene hydrocar structure Which has cation ion sites and optionally in the bon ranges from 0.1 to 3. presence of a methylating agent. 22. The process according to claim 1, Wherein the process 2. The process according to claim 1, Wherein the naph is carried out at a reaction temperature ranging from 200° C. thalene hydrocarbon is selected from the group consisting of 40 to 450° C. naphthalene, methylnaphthalenes, dimethylnaphthalenes, 23. The process according to claim 22, Wherein the trimethylnaphthalenes, and their mixtures. temperature ranges from 280° C. to 350° C. 3. The process according to claim 2, Wherein the naph 24. The process according to claim 1, Wherein the process thalene hydrocarbon is selected from the group consisting of is carried out at a WHSV ranging from 0.01 to 8 hours-1. naphthalene, methylnaphthalene and their mixtures, option 45 25. The process according to claim 24, Wherein the ally mixed With dimethylnaphthalenes, trimethylnaphtha WHSV ranges from 0.05 to 1 hours_1. lenes and their mixtures. 26. The process according to claim 1, Wherein the process 4. The process according to claim 1, Wherein the methy is carried out at a pressure ranging from 3 to 60 atm. lating agent is selected from the group consisting of 27. The process according to claim 1, Wherein the methy methanol, dimethylether, dimethylcarbonate, lating agent is fed in at least tWo steps. dimethylsulfate, and methyl iodide. 28. The process according to claim 1, Wherein there are 5. The process according to claim 4, Wherein the methy tWo or more catalytic beds or tWo or more reactors in series. lating agent is methanol. 29. The process according to claim 28, Wherein the 6. The process according to claim 1, Wherein the MTW methylating agent is fed betWeen the catalytic beds or the Zeolite is a silico-aluminate With a molar ratio SiO2/Al2O3 55 reactors in series in at least tWo steps. greater than or equal to 20. 30. The process according to claim 1, Wherein the process 7. The process according to claim 6, Wherein the alumi is carried out in substantially liquid phase. num in the Zeolite is totally or partly substituted by B, Ga, 31. A process for preparing 2,6-dimethylnaphthalene Fe or their mixtures. Which comprises 8. The process according to claim 1 or 6, Wherein the 1) reacting, under at least partially liquid phase Zeolite is a ZSM-12 having in its calcined and anhydrous conditions, in the presence of a Zeolite having a MTW form a molar composition of oxides corresponding to the structure and optionally a methylating agent, a naph folloWing formula: thalene hydrocarbon selected from the group consisting of naphthalene, methylnaphthalenes, 65 dimethylnaphthalenes, trimethylnaphthalenes, Wherein M is H+ and/or a cation of an alkali or alkaline earth tetramethylnaphthalenes, pentamethylnaphthalenes, metal With valence n, W is selected from the group consist hexamethylnaphthalenes, and their mixtures With one 6,147,270 25 26 or more benzene hydrocarbons selected from the group benZene hydrocarbons selected from the group consist consisting of benzene, toluene, xylenes, ing of benZene, toluene, xylenes, trimethylbenZenes, trimethylbenZenes, tetramethylbenZenes, tetramethylbenZenes, pentamethylbenZene, and hexam pentamethylbenZene, and hexamethylbenZene to pro ethylbenZene. duce a product; 33. A process for preparing 2,6-dimethylnaphthalene 2) separating the product obtained in step (1) into frac Which comprises tions comprising (a) a fraction containing benZene 1) reacting, under at least partially liquid phase aromatic hydrocarbons, naphthalene and conditions, in the presence of a Zeolite having a MTW methylnaphthalene, (b) a fraction containing dimethyl structure and optionally a methylating agent, a naph naphthalenes a_nd (C) a fracnon Contammg pen/meth- 10 thalene hydrocarbon selected from the group consisting ylnaphtllalenes’_ _ _ _ _ of naphthalene, methylnaphthalenes, 3) separating fraction (b) into a fraction containing 2,6- dimethylnaphthalenes, trimethylnaphthalenes, dlmethylnaph.thalene and a fracnon (d) .contalmng, 1’5 tetramethylnaphthalenes, pentamethylnaphthalenes, and/Or 1’6_dlmethylnaphthalenes’ opnonany mlxed 15 hexamethylnaphthalenes, and their mixtures With one With other isomers of dimethylnaphthalene; and or more benZene hydrocarbons selected from the group 4) feeding fractions (a), (c) and (d) to step 1). consisting of benZene, toluene, xylenes, 32. A process for preparing 2,6-dimethylnaphthalene trimethylbenZenes, tetramethylbenZenes, Which comprises pentamethylbenZene, and hexamethylbenZene to pro 1) reacting, under at least partially liquid phase 20 duce a product; conditions, in the presence of a Zeolite having a MTW 2) separating the product obtained in step (1) into frac structure and optionally a methylating agent, a naph tions comprising (a) a fraction containing benZene thalene hydrocarbon selected from the group consisting aromatic hydrocarbons, naphthalene and 0 f n a P h t h a 16 n e > m 6 th Y1 n 211) h t h a 16 n e S > methylnaphthalene, (b) a fraction containing dimethyl dimethylnaphthalenes> trimethylnaphthalenes> 25 naphthalenes and (c) a fraction containing polymeth tetramethylnaphthalenes, pentamethylnaphthalenes, ylnaphthalenes; hexamethylnaphthalenes, and their mixtures With one 3) Separating fraction (b) into a fraction Containing 2,6_ or mo_re benzene hydrocarbons Selected from the group dimethylnaphthalene and a fraction (d) containing 1,5 cqnslstlng of benzene’ toluene’ xylenes’ and/or 1,6-dimethylnaphthalenes, optionally mixed trlmethylbenzenes’ tetramethylbenzenes’ 30 With other isomers of dimethylnaphthalene' pentamethylbenZene, and hexamethylbenZene to pro- ______’ duce a product; 4) SllblCCtlIlg fraction (d) to fSQIIlGIlZaIlOIl, under at least _ _ _ _ partially liquid phase conditions, in the presence of an 2) separating the product obtained in step (1) into frac- MTW Zeolite at a temperature ranging from 100 to tions comprising (a) a fraction containing benZene 400° C‘ ’ aromatlc hydrocarbons,’ naphlhfllenp and 35 34. The process according to claim 33, Wherein step 4) is methylnaphthalene, (b) a fraction containing dimethyl- Carried out at a temperature ranging from 120 to 250° C‘ naphthalenes and (C) a fraction Containing polymeth' 35. The process according to claim 34, Wherein step 4) is ylnaphthalenes; carried out at a temperature ranging from 130 to 200° C. 3) Separating fraction (b) into a fraction Containing 2,6‘ 4O 36. The process according to claim 1, Wherein the naph dimethylnaphthalene and a fraction (d) containing 1,5 thalene hydrocarbons are naphthalene, methylnaphthalenes and/or 1,6-dimethylnaphthalenes, optionally mixed and dimethylnaphthalenes, and said hydrocarbons are con With other isomers of dimethylnaphthalene; tained in a fraction obtained by distillation from FOC or 4) reacting fractions (a), (c) and (d), optionally enriched LCO cracking oils, or obtained by the distillation of distilled With naphthalene and/or methylnaphthalene, under at oil from pit-coal tar. least partially liquid phase conditions, in the presence 45 of a Zeolite having a MTW structure, With one or more * * * * *