MXPA00000333A - Method of making 2,6-dimethylnaphthalene from other dimethylnaphthalene isomers and from dimethyltetralins/dimethyldecalins with a methyl group on each ring - Google Patents

Abstract

The invention discloses a method of making 2,6-dimethylnaphthalene from any DMN with one methyl on each ring in a two-step hydroisomerization/dehydrogenation process. The catalyst used in the hydroisomerization step is an acidic catalyst such as a silica aluminum catalyst with a hydrogenation/dehydrogenation metal. The catalyst used in the dehydrogenation step is a reforming type catalyst.

Description

METHOD FOR PRODUCING 2, 6-DIMETHYLNAPHTHALENE FROM OTHER DIMETHYLNAFTALENE ISOMERS AND FROM DIMETILTETRALINAS / DIMETILDECALINAS WITH A METHYL GROUP IN EACH RING FIELD OF THE INVENTION _ The present invention relates to a method for producing 2,6-dimethylnaphthalene from a hydrocarbon feed comprising dimethylnaphthalene isomers (DMN) and dimethyltetralins / dimethyldecalins (DMT / DMD) having a methyl group in each ring.

BACKGROUND OF THE INVENTION There are ten different isomers of dimethylnaphthalene (DMF). Of which nine of these can be grouped into three trivalences based on the relative ease of isomerization within a certain trivalent. An intra-trivalent isomerization can be given using a wide variety of solid acids as catalysts. This isomerization facility within WF .: 323G5 A trivalent is based on the fact that a methyl group in naphthalene moves relatively easily from an alpha position to a beta position or vice versa in the same ring but does not easily move from a beta position to another position beta in the same ring or from an alpha position to another alpha position. The three trivalent groups are as follows: 2,7-, 1,7- and 1,8-dimethylnaphthalene; 2,6-, 1,6- and 1,5-dimethylnaphthalene; and 1,4-, 1,3- and 2,3-dimethylnaphthalene. 1,2-dimethylnaphthalene is the tenth isomer and does not displace in any of the three trivalences. Although the isomerization of dimethylnaphthalenes within these trivalent groups is relatively easy, isomerization from one trivalent group to another trivalent group is much more difficult. Since certain isomers of dimethylnaphthalene are much more valuable than others for use in plastics synthesis, researchers are continually making attempts to find ways to convert less useful to more useful isomers. A particularly valuable isomer is 2,6-dimethylnaphthalene. Certain processes for synthesizing dimethylnaphthalenes result in high yields of 2,7- and 1,7-dimethylnaphthalenes. The conversion of 2,7- and 1,7-dimethylnaphthalenes to 2,6-dimethylnaphthalene has been carried out using certain zeolites such as ZSM-5. However, such conversion has resulted in an excess of undesirable side products such as methylnaphthalenes, tri-ethylnaphthalenes and 1,4-, 1,3- and 2,3-dimethylnaphthalene via dealkylation, cracking and transalkylation. Usually, this isomerization catalyzed by acid is associated with deactivation of the catalyst when the reaction continues, resulting in a short life of the catalyst. It could be very useful to find an inexpensive way to convert 2,7- and 1,7-dimethylnaphthalene which is present with abundant products in synthesis of dimethylnaphthalene to 2,6-dimethylnaphthalene in a high yield. Other researchers have found methods to convert the isomers of dimethylnaphthalene, particularly 2,7-dimethylnaphthalene to it most useful, and therefore the most valuable isomer, 2,6-dimethylnaphthalene, but none of these conversion methods has been sufficiently simple and economic to guarantee the general use of such methods. U.S. Patent No. 3,890,403 (Shimada et al.) Discloses a method which can reportedly be used to obtain 2,6-dimethylnaphthalene from a mixture of dimethylnaphthalene containing the various isomers of dimethylnaphthalene. The method involves (a) partially hydrogenation of the di-ethylnaphthalene mixture to obtain dimethyltetralins (DMT) with a hydrogenation catalyst such as nickel, platinum, palladium, rhodium, copper-chromium, iridium or ruthenium; (b) the isomerization of the dimethyltetralins with a solid acid catalyst such as a zeolite catalyst so that the isomers of dimethyltetralin in which the two methyl groups are present in the same ring can be converted to the isomers of dimethyltetraline in the which the two methyl groups are present in opposite rings and the amount of isomers of dimethyltetralins in which the two methyl groups are present in opposite rings, is carried out near the thermodynamic equilibrium; (c) separating and collecting the dimethyltetralin isomers in which the two methyl groups are present in opposite rings from the isomers in which the two methyl groups are present in the same ring; (d) dehydrogenating the collected DMT mixture to convert it into a mixture of DMN; (e) separating and recovering 2,6-DMN from the recovered DMN mixture. Although this method obtains the desirable 2,6-DMN isomer from other DMN isomers, the method is time consuming and costly because it involves several widely separated and distinct steps. US Patent No. 3,803,253 (Suld) discloses a hydroisomerization / dehydrogenation process of a mixture of dimethylnaphthalenes, so that 2,6-dimethylnaphthalene can be obtained and isolated from the reaction mixture. Then the other remaining products are recirculated and the process is repeated to obtain more 2,6-dimethylnaphthalene. The catalyst used for the hydroisomerization / dehydrogenation step is described as a combination of a faujasite containing calcium and a hydrogenation / dehydrogenation catalyst component. The process step, with hydroisomerization and dehydrogenation carried out simultaneously in the same reaction vessel in the presence of the combination catalyst described, simplifies the process but makes the total efficiency and process yield very low. US Patent No. 3,928,482 (Hedge et al.), Which refers to the? 253 described above, describes a process of hydroisomerization portel which 2,6-DMT is obtained from a feed mixture which is rich in 2,7- or 1,7-DMT using an aluminosilicate zeolite containing polyvalent metal cations in exchange positions. It is intended that this process be incorporated as an improvement to the method of 253 described above but does not overcome the basic lack of success of this process to obtain 2,6-DMN with high yields in an expensive and cost effective manner.

An economic method to obtain 2,6-DMN from other isomers of DMN, especially isomers in the trivalent 2,7-DMN, with few steps and at relatively high yields, is necessary. The present inventors have found a method.

DESCRIPTION OF THE INVENTION - An object of the present invention is to provide an economical method for producing 2,6-dimethylnaphthalene in stable and relatively high yields. Another object of the present invention is to provide a method for using an isomer of dimethylnaphthalene or mixture of isomers selected from the group consisting of 1,6-dimethylnaphthalene, 1,5-dimethylnaphthalene, 2,7-dimethylnaphthalene, 1,7-dimethylnaphthalene, 1,8-dimethylnaphthalene and counterparts thereof partially or completely hydrogenated to produce 2,6-dimethylnaphthalene. Still another object of the present invention is to provide a method for producing 2,6-dimethylnaphthalene without significant formation of naphthalene, methylnaphthalenes, trimethylnaphthalenes and 1,4-, 1,3-, 2,3- and 1,2-dimethylnaphthalene. Still another object of the present invention is to provide a method for producing 2,6-dimethylnaphthalene using a two step hydroisomerization / dehydrogenation process. A further object of the present invention is to provide a method for producing 2,6-dimethylnaphthalene using a two step hydroisomerization / dehydrogenation process in conjunction with an intra-trivalent isomerization process in which 1,7- 'and 1,8 -DMN are converted to an acid catalyst at 2,7-DMN and 1,6- and 1,5-DMN are converted to an acid catalyst at 2,6-DMN, respectively, the 2,6-DMN is separated and the 2,7-DMN is then converted to 2,6-DMN with the hydroisomerization / dehydrogenation process. Another object of the present invention is to provide a method for using an acid catalyst in a hydroisomerization step followed by a reforming or dehydrogenation catalyst in a dehydrogenation step to convert the trivalent isomers of 2,7-dimethylnaphthalene (especially 2,7- and 1,7-DMN) to trivalent isomers of 2,6-dimethylnaphthalene (especially 2,6- and 1,6-DMN).

Other features and advantages of the invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph plotting the yields of the DMT and DMD products that result from the hydroisomerization function of 2,7-DMN at 204.4 ° C (400 ° F) against the time over current in which the products are analyzed online as described in Example 6. Figure 2 is a graph plotting the conversion of 2,7-DMN and yields of several products resulting from an acid-catalyzed isomerization of 2,7-DMN in H -ZSM-11 against time over current or flow time, as described in Example 11. Figure 3 is a similar graph plotting the conversion and selectivities against time over current when 1.5-, 1.6 - and 1,7-DMN -results as well as the unconverted 2,7-DMN are assumed to be recirculated and finally converted to 2,6-DMN.

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for producing 2,6-dimethylnaphthalene. Specifically, the invention relates to a method for using the isomer of dimethylnaphthalene or mixture of isomers selected from the group consisting of 1,6-dimethylnaphthalene, 1,5-di-ethylnaphthalene, 2,7-dimethylnaphthalene, 1,7-dimethylnaphthalene, 1,8-dimethylnaphthalene, and partially or totally hydrogenated counterparts thereof to obtain 2,6-dimethylnaphthalene. The invention also relates to the use of an acid catalyst (acidification of the catalyst is measured by the positive adsorption of the catalyst of ammonia, pyridine, and piperidine probed at its surface sites) with a metal in a hydroisomerization step followed by a reforming catalyst in a dehydrogenation step to obtain 2,6-dimethylnaphthalene from an isomer of dimethylnaphthalene or mixture of isomers selected from the group consisting of 1, 6-dimethylnaphthalene, 1,5-dimethylnaphthalene, 2,7-dimethylnaphthalene, 1,7-dimethylnaphthalene, 1,8-dimethylnaphthalene, and partially or totally hydrogenated counterparts thereof. The invention also relates to the use of a metal with an acid catalyst. This can be any metal that is effective as a catalyst in hydrogenation reactions, such as, for example, palladium, nickel, copper or platinum. In another preferred embodiment, the acid catalyst is used with a metal in a range from 0.1 to 30% by weight. In a preferred embodiment, the metal used with the acidic catalyst is palladium. In another preferred embodiment, the metal used with the acid catalyst is platinum. In still another preferred embodiment, the metal is sulfided. Non-limiting examples of hydroisomerization catalysts that can be used are PdS / Boron-Beta (in the presence of 500 ppm of aluminum), PtS / Boron-Beta (in the presence of 500 ppm of aluminum), PdS / Y, and Pd / Boron-Beta not sulfided (in the presence of 500 ppm of aluminum). PtS / Boro-SSZ-33 is not effective as a hydroisomerization catalyst because of its tendency to serve only as a function of hydrogenation and not to isomerize the various isomers of DMN to the 2, 6-DMD or -DMT isomer. A possible mechanism for the process of obtaining 2,6-dimethylnaphthalene from 2,7-, 1,7-, 1,8-, 1,5- and 1,6-dimethylnaphthalene with the acid catalyst and the noble metal it could be related to dimethylnaphthalenes that are partially or completely saturated to dimethyltetralins or di-ethyldecalins on or in the catalyst. According to this possible mechanism, once at least one of the aromatic rings in dimethylnaphthalenes is saturated, the beta-beta migration of methyl groups becomes much easier because of the energy barriers to such migration are raised by changing the reaction trajectories. It is evident, according to this mechanism, that if there is sufficient acidity on or in the catalyst, the saturated DMN 's will be isomerized close to equilibrium. After the above hydroisomerization, the saturated dimethylnaphthalenes should be reformed back to unsaturated dimethylnaphthalenes by dehydrogenation. For this, I work with high selectivity, that is, avoiding 2, 6-dimethylnaphthalenes, the reformation step must be carried out on a catalyst which avoids the transalkylation, dealkylation and cracking reactions. In a preferred embodiment, the catalysts that can be used in the reforming step are both acidic and non-acidic catalysts. A non-limiting example of an acid catalyst that can be used is a mixture of rhenium and platinum on alumina (Pt / Re / Al 2? 3 sulfurized). Non-limiting examples of a non-acid catalyst that can be used are sulfurized Pt / Na-ZSM-5 and PtS / Cs / Boro-SSZ-42. An alternative method to obtain 2,6-DMN from other DMN isomers, particularly those in the trivalent 2,7-DMN, is by means of an isomerization of acid catalyzed DMN. Unlike the two-step hydroisomerization / dehydrogenation process described above, this process proceeds in one step and does not involve the DMT and / or DMD forms of the partially or fully saturated intermediate. A non-limiting example of a catalyst that can be used for an acid-catalyzed isomerization is H-ZSM-11. This process is less preferred than the hydroisomerization / dehydrogenation process described above because it has a tendency to produce a pure or correct amount of methylnaphthalenes (MN) and trimethylnaphthalenes (TMN) as well as the undesirable isomers of DMN. Thus, the yield of 2,6-DMN is low compared to the hydroisomerization / dehydrogenation process. In all embodiments of the hydroisomerization / dehydrogenation process, the dimethylnaphthalene feed (pure or in solution) can be flowed over the catalyst together with hydrogen gas or the reaction can be carried out in the form of batches. In this process, the temperature needs to be high enough to hydrogenate the dimethylnaphthalene feed and isomerize the resulting DMD's and DMT's. The hydroisomerization reaction depends on both the hydrogenation / dehydrogenation activity and strong acid of the catalyst. Additionally, to generate a significant amount of DMT / DMD 's, the hydrogen pressure needs to be sufficiently high. Thermodynamically elevated temperatures direct the equilibrium towards DMN while high hydrogen pressures help to shift the equilibrium towards saturated species (DMD). The reaction kinetics, which depend on the type of catalyst, also have a strong influence on the selectivity of the product in relation to the hydrogenation / dehydrogenation activity and acid resistance of the catalyst. In a preferred embodiment, the yield of partially saturated species (DMT) of the hydroisomerization reaction should be at least 5 weight percent. In a more preferred embodiment, the yield of partially saturated species (DMT) should be at least 10 weight percent. Accordingly, the Space Speed per Hour in Weight (for its acronym in English, HSV) can be varied over a wide range (for example, approximately 0.1 to 100 h_1), the pressure can vary from 0 to 210.93 kg / cm2 gauge (0 to 3000 psi), the hydrogen / hydrocarbon molar ratio can vary from ~ 0.0 to 100, and the reactor temperature can vary from about 148.9 to 537.8 ° C (300 to 1000 ° F). The unreacted material and the partially hydrogenated products minus the 2,6-isomers can be recirculated back to the reactor or reformed back to DMN 's in a separate reactor. Several product separation schemes can be used at different points in the process. Also, in one embodiment, a more conventional isomerization process for interconverting isomers within trivalents can be used in conjunction with this process. In both the hydroisomerization and the reformation step, there are many variables to be optimized. These include: operating temperature, pressure, space velocity, and the catalyst itself. As shown below, when such variables are optimized, approximately 50% conversion from 2.7- to 2, 6-trivalents can be achieved. The resulting 2,6-DMN C-2 isomers can not be separated from the 2,6-DMN product and recirculated to the hydroisomerization reactor to be further converted to 2,6-DMN, increasing the production of 2,6-DMN. Additionally, little or no formation of 1,2-DMN, 1,3-DMN, 1,4-DMN, 2,3-DMN or TMN is found. There is also a relatively small formation of MN 's with the isomerization catalysts used. By taking measures to minimize hydrogenolysis during the isomerization reaction, such as by adding a little sulfur to the feed, MN 's formation can be further minimized. With the results achieved with the present invention, it is now possible to achieve large-scale isomerization of 2,7-, 1,7-, 1,8-, 1,5- and 1,6-DMN at 2,6-DMN . In addition, the yield of 2,6-DMN can also be increased through the improvement of the DMN feeds by incorporating the more conventional acid-catalyzed intra-trivalent isomerization of DMN's into the hydroisomerization / dehydrogenation process. Such intra-trivalent isomerization of DMN 's can be further associated with a recirculation step described above. In experiments described below, several hydroisomerization catalysts were used. In these experiments, there was little evidence of deactivation of the catalysts, in some cases after approximately three weeks of continuous use. It was also found in these experiments that the reformation step converts almost all of the saturated species back to DMN's. In effect, a species ratio of ~95 / 5 DMN / saturated or better can be achieved if several conditions are optimized.

EXAMPLES The present invention will be further described with the following tables and figures showing the results of various experiments.

Hydrogenation without Isomerization The results of Examples 1-4 with PtS / Boron-SSZ-33 reveal that the effective hydroisomerization of DMN 's to DMT' s requires not only a sufficient hydrogenation / dehydrogenation function such as that of PtS but also sufficient acidity. since PtS / Boro-SSZ-33 tends to serve only as a function of hydrogenation and not to isomerize the resulting DMT's to other DMT isomers. Taking advantage of these results, the DMT isomers (1,5-, 1,6-, 2,5-, 1,7-, 2,8- and 2,7-DMT) produced in Examples 1-4, together with 1,4- and 2,6-DMT which are supplied as standards by Chemsampco and API / Carnegie Mellon University, respectively, are used to identify and quantify the major DMT isomers produced in the hydroisomerization step of this invention (see Example 8) on an expanded scale. It is beneficial to have the DMD's and main DMTs, especially DMTs identified in the hydroisomerization step since it provides approximately information on how many 2,6-isomers can be produced, useful for the prediction of 2,6-DMN performance even prior to the step of -reformation to be conducted after the hydroisomerization.

Example 1 Hydrogenation of 1,5-DMN with PtS / B-SSZ-33 An experiment was conducted to hydrogenate a hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 1,5-dimethylnaphthalene in a reactor with a PtS / Boro-SSZ-33 catalyst (0.5 g). The reaction was conducted at 204.4 ° C, 14.062 kg / cm2 gauge (400 ° F, 200_ lb / in2 manometric), 1 ml / hr feed and 40 ml / min H2. 96% of 1,5-DMN were converted, producing 88% of 1,5-DMT and 8% of DMD's and other C12's. No other DMT isomers were observed. The identification of the GC peaks was confirmed by GC / MS analysis. In this example and the following examples, the o-xylene diluent and its reaction products are subtracted from the performance data shown in the tables.

Example 2 Hydrogenation of 1, 6-DMN with PtS / B-SSZ-33 An experiment was conducted to hydrogenate a hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 1,6-dimethylnaphthalene in a reactor with a PtS / Boro-SSZ-33 catalyst (0.5 g). The reaction was conducted at 215.6 ° C, 14.062 kg / cm2 gauge (420 ° F, 200 lb / in2 gauge), 0.5 ml / hr feed and 40 ml / min H2. Depending on which the aromatic 1,6-DMN ring is hydrogenated, two different isomers of DMT, mainly 1,6-DMT and 2,5-DMT, were produced. Basically, no other DMTs were presented in the product. At a 100% conversion of 1, 6-DMN, 31% of 1,6-DMT and 23% of 2,5-DMT were produced with another 46% of DMD's and other C12 species. The identification of the GC peaks was confirmed by GC / MS analysis.

Example 3 Hydrogenation of 1,7-DMN with PtS / B-SSZ-33 An experiment was conducted to hydrogenate a hydrocarbon feed of 5: 1 (weight: weight) o-xylene: 1,7-dimethylnaphthalene in a reactor with a PtS / Boro-SSZ-33 catalyst (0.5 g). The reaction was conducted at 215.6 ° C, 14.062 kg / cm2 gauge (420 ° F, 200 lb / in2 gauge), 0.5 ml / hr feed and 40 ml / min H2. Depending on which the aromatic 1,7-DMN ring is hydrogenated, two different isomers of DMT were produced, namely, 1,7-DMT and 2,8-DMT. Basically, no other DMTs were presented in the product. In a conversion of -100% of 1,7-DMN, 26% of 1,7-DMT and 28% of 2, 8-DMT occurred with the other 46% of DMD's and other C12 species. The identification of the GC peaks was confirmed by GC / MS analysis.

Example 4 Hydrogenation of 2,7-DMN with PtS / B-SSZ-33 An experiment was conducted to hydrogenate a hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 2,7-dimethylnaphthalene in a reactor with a PtS / Boro-SSZ-33 catalyst (0.5 g). The reaction was conducted at 193.3 ° C, 14,062 kg / cm 2 gauge (380 ° F, 200 lb / in 2 gauge), 1 ml / hr feed, and 40 ml / min H2. At a 100% conversion of 2,7-DMN, 75% 2,7-DMT was produced. Another 25% are DMD's and other C12's. No other DMT isomers were observed. The identification of the GC peaks was confirmed by GC / MS analysis.

Hydroisomerization without dehydrogenation Examples 5-10 describe the results of experiments performing the hydroisomerization step without a subsequent dehydrogenation of the hydroisomerization products.

Example 5 Hydroisomerization of 2,7-DMN with PdS / Y Three experiments were performed to hydroisomerize a hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 2,7-dimethylnaphthalene in a reactor with a PdS / Y to produce DMT's and DMN 's at 215.6, 204.4 and 176.7 ° C (420, 400 and 350 ° F), respectively. Other conditions were 14,062 kg / cm2 gauge (200 lb / in2 gauge), 1 ml / hr of feed, 40 ml / min of H2 and 0.5 g of catalyst. The compositions of the products are given in% by weight in Table V. No ethylnaphthalenes were detected. Essentially no cracking products were observed.

Table V Example 6 Hydroisomerization of 2,7-DMN with PdS / Y Four experiments were performed to hydroisomerize a hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 2,7-dimethylnaphthalene in a PdS / Y reactor at 500 psi (35.15 kg / cm2), 1 ml / hr of feed, 40 ml / min of H2 and 0.5 g of catalyst. The reaction temperature was 193.3, 204.4, 215.6 and 226.7 ° C (380, 400, 420 and 440 ° F), respectively. The compositions of the products were given in% by weight in Table VI. No methylnaphthalenes were detected. Essentially no cracking products were observed. Figure 1 shows the yields of DMT and DMD against the reaction time for operation at (400 ° F). After an initial period of about 70 hours, catalyst activity and selectivity became stable. For the next two weeks, this catalyst in the same reactor was continuously sieved under various conditions with several feeds containing several DMN isomers. The indicated results do not show the deactivation of the catalyst.

Table VI Example 7 Hydroisomerization of 2,7-DMN with PdS / Y Three experiments were performed to hydroisomerize a hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 2,7-dimethylnaphthalene in a PdS / Y reactor at 500 psig (500 psig), 2 ml / hr of feed, 40 ml / min and 0.5 g of catalyst. The reaction temperature was 204.4, 215.5 and 226.6 ° C (400, 420 and 440 ° F), respectively. The compositions of the products were given in% by weight in Table VII. No methylnaphthalenes were detected. Essentially products without cracking were observed.

Table VII Example 8 Hydroisomerization of 2,7-DMN with Pd / B / Al / Beta An experiment was performed to isomerize a hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 2,7-dimethylnaphthalene in a reactor with a Pd / Boron-Beta catalyst (0.5 g) containing 500 ppm of aluminum. The reaction conditions were: 216.1 ° C (475 ° F), 14.062 kg / cm2 gauge (200 psi), 1 ml / hr feed, 40 ml / min H. 89.2% of the product were DMT's. 8.7% of the product were DMD's and others. 2.1% of the product were DMN's.

Example 9 Hydroisomerization of 2,7-DMN with PdS / SAPO-11 Several experiments were done to hydroisomerize a hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 2,7-dimethylnaphthalene in a reactor with a PdS / SAPO-11 (0.5 g) with 40 ml / min H2 at a feed rate of 1 ml / hr. The results are shown in% by weight in Tables IXa-IXc.

Table IXa DMN: dimethylnaphthalene; DMT: dimethyltetralin; DMD: dimethyldecalin; MN: methylnaphthalene; TMN: trimethylnaphthalene.

Table IXb TABLE IXC Example 10 GC / MS Analysis of Hydroisomerization Products of 2,7-DMN with PdS / SAPO-11 Gas chromatography (GC) coupled with mass spectrometry was used to identify the products from a particular yield period (Experiment 5 in Example 9). The composition of the products of Experiment 5 at 371.1 ° C (700 ° F), 14.062 kg / cm2 manometric (200 lb / pg 2 gauge), 6 h_1 of WHSV is listed in% by weight in Tables Xa and Xb. The difference between the compositions determined by on-line GC (see Table IXb) and off-line GC / MS (see Tables Xa and Xb) is obviously. due to the different sensitivity of these two different analytical techniques.

TABLE Xa DMN: dimethylnaphthalene; DMT: dimethyltetralin; DMD: dimethyldecalin; MN: methylnaphthalene; C3I: Indane substituted with an alkyl group of C3; CeBz; benzene substituted with an alkyl group of Ce / C5T0I: toluene substituted with an alkyl group of C5.

TABLE Xb Isomerization of the Catalyst Acid without Hydrogenation Example 11 shows the results of an experiment in which an acid catalyst is used without combining it with a hydrogenation catalyst.

Example 11 Isomerization of 2,7-DMN with H-ZSM-11 An experiment was performed to isomerize a hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 2,7-dimethylnaphthalene in a reactor with an acid catalyst, H-ZSM-11 with non-carrier gas at 315.6 ° C. (600 ° F), -0.3515 kg / cm2 gauge (-5 lb / pg2 gauge), 1 ml / hr of feed and 0.2 'h 1 of WHSV. The results are shown in the graphical form in Figure 2. Assuming that the resulting 1,5-, 1,6- and 1,7-DMN as well as the unconverted 2,7-DMN are recirculated and can finally be converted At 2, 6-DMN, the desirable 2,6-DMN selectivities and other major byproducts such as MN 's and TMN' s can then be described as shown in Figure 3. It is evident that this isomerization class of catalyzed DMN with acid results in a significant amount of byproducts such as MN 's (meth- achenaphthalenes) and TMN's (trimethylnaphthalenes) which can be described as shown in Figure 3.

Hydroisomerization / Dehydrogenation Examples 12-25 describe experiments in which the product of the hydroisomerization step is then dehydrogenated with a separate catalyst.

Example 12 Hydroisomerization / Dehydrogenation of 2,7-DMN with PdS / SAPO-11 and PtS / Cs / B-SSZ-42 The experiments were conducted using a hydroisomerization / dehydrogenation system of two reactors. The first reactor facilitates the hydroisomerization function and the second reactor effects the dehydrogenation function of the saturated compounds back to DMN's. In the first reactor, a PdS / SAPO-11 catalyst (0.5 g) was used. In the second reactor, a PtS / Cs / Boro-SSZ-42 catalyst (0.45 g) was used. Tables Xlla and Xllb show results from the use of the two reactor system. The feed consists of o-xylene and 2,7-DMN in a ratio of 5: 1 (weight: weight).

TABLE XIIa DMN: dimethylnaphthalene; DMT: dimethyltetralin; DMD: dimethyldecalin; MN: methylnaphthalene; C3I: indane substituted with an alkyl group of C3.

TABLE XIIb Example 13 Analysis of GC / MS of Hydroisomerization / Dehydrogenation Products of 2,7-DMN with PdS / SAPO-11 and PtS / Cs / B-SSZ-42 Gas chromatography (GC) coupled with mass spectrometry (MS) it was used to identify the products from particular yield periods (shown in Example 12) after Reactor 2. The distributions without different DMNs in the products without DMN are listed in% by weight in Table XIII based on the results of GC / MS.

Table XIII MI: methyllindane; Ethylindane; DMD: dimethyldecalin; DMT: dimethyltetralin; MEI: methylethylindane; MEI =: methylethyldedene; MN: methylnaphthalene; C5T0I: toluene substituted with an alkyl group of C5; EN: ethylnaphthalene.

Example 14 Hydroisomerization / Dehydrogenation of 2,7-DMN with Pd / B / Al / Beta and PtS / Cs / B-SSZ-42 The experiments were conducted using a hydroisomerization / dehydrogenation system of two reactors. The first reactor facilitates the hydroisomerization function and the second reactor performs the function of dehydrogenation of saturated compounds back to DMN's. In the first reactor, a catalyst Pd / Boron / 500 ppm Al / beta (0.5) was used. In the second reactor, a catalyst PtS / Cs / Boro-SSZ-42 (0.45 g) was used. Table XIV shows the results for the example. In this example, the feed was composed of o-xylene and 2,7-DMN of a 5: 1 weight: weight ratio. The slightly high yield of MN 's after reactor 2 is probably related to the dealkylation of the resulting DMNs on PtS / Cs / B-SSZ-42.

Table XIV DMN: dimethylnaphthalene; DMT: dimethyltetralin; DMD: dimethyldecalin; MN: methylnaphthalene; C I: indane substituted with an alkyl group of C3.

Example 15 Hydroisomerization / Dehydrogenation of 2,7-DMN with Pd / B / Al / Beta and PtS / Cs / B-SSZ-42 Additional experiments were conducted using a similar two-reactor hydroisomerization / dehydrogenation system, Example 14. The first reactor facilitates the hydroisomerization function and the second reactor performs the function of dehydrogenation of saturated compounds back to DMN's. In the first reactor, a Pd / Boron / 500 ppm Al / beta catalyst (0.5 g) was used. In the second reactor, a PtS / Cs / Boro-SSZ-42 catalyst (0.45 g) was used. Table XV shows the results for the example. In this example, the feed was composed of o-xylene and 2,7-DMN of a 5: 1 ratio of pesorpeso. As described in Example 14, the slightly high yield of MN 's after reactor 2 is probably related to the dealkylation of the resulting DMNs on PtS / Cs / B-SSZ-42.

Table XV DMN: dimethylnaphthalene; DMT: dimethyltetralin; DMD: dimethyldecalin; MN: methylnaphthalene; C I: indane substituted with an alkyl group of C3.

Example 16 GC / MS Analysis of Hydroisomerization / Dehydrogenation Products of 2,7-DMN with Pd / B / Al / Beta and PtS / Cs / B-SSZ-42 Gas chromatography coupled with mass spectrometry was used to identify some of the products obtained from Example 15 described. The product of Experiment 1 of Example 15 was collected from Reactor 1 only and designated in this example as Experiment A. The product of Experiment 2 of Example 15 was collected from both Reactors 1 and 2 and designated in this example. as Experiment B. The results of the identification of the products of both experiments in% by weight are shown in Table XVI. The difference between the compositions determined by GC (see Table XV of Example 15) and GC / MS (see Table XVI of this example) is evidently due to the different sensitivities of these two different analytical techniques.

Table XVI Example 17 Hydroisomerization / Dehydrogenation of 2,7-DMN with PdS / Siral 40 and PtS / Cs / B-SSZ-42 The experiments were conducted using a hydroisomerization / dehydrogenation system of two reactors. The first reactor facilitates the function of hydroisomerization and the second reactor effects the dehydrogenation of saturated compounds back to DMN's. In the first reactor, a PdS / Siral 40 catalyst was used, consisting of sulfurized Pd deposited on commercial silica-alumina Siral 40 (0.5 g). In the second reactor, a PtS / Cs / Boro-SSZ-42 catalyst (0.45 g) was used. Tables XVIIa and XVIIb show the results in% by weight for the experiments. In these experiments, the feed was composed of o-xylene and 2,7-DMN in a 5: 1 ratio (weight: weight).

Table XVIla DMN: dimethylnaphthalene: DMT: dimethyltetraline; DMD: dimethyldecalin; MN: methylnaphthalene; C3I: indane with an alkyl group of C3; TMN: trimethylnaphthalene.

Table XVI Ib Example 18 Hydroisomerization / dehydrogenation of 2,7-DMN with Pd / B / Al / Beta and PtS / Na-ZSM-5 In Example 8, a hydrocarbon feed of 5: 1 (w / w) of o-xylene: 2,7-dimethylnaphthalene was hydroisomerized in a reactor with a Pd / Boron / Al / Beta catalyst (0.5 g) containing 500 ppm of aluminum at 216.1 ° C (475 ° F) and 14.062 kg / cm2 gauge (200 lb / pg2 gauge). The hydroisomerization products including the o-xylene solvent were collected and then dehydrogenated to be fed to PtS / Na-ZSM-5 in the reactor at 454.4 ° C (850 ° F), 7,031 kg / cm2 gauge (100 lb / pg2 gauge), 0.5 ml / hr of feed, 23 ml / min of H2 and 0.5 g of catalyst. The compositions of the feed for the dehydrogenation reaction (hydroisomerization products of 2,7-DMN in Example 8) and its dehydrogenation product are shown in% by weight in Table XVIII.

Table XVIII Example 19 Hydroisomerization / dehydrogenation of 2,7-DMN with PdS / Y and PtS / Na-ZSM-5 In Example 6, a hydrocarbon feed of 5: 1 (w / w) of o-xylene: 2,7-di-ethylnaphthalene was hydroisomerized in a reactor with a PdS / Y catalyst (0.5 g) at 204.4 ° C ( 400 ° F) and 35.15 kg / cm2 gauge (500 lb / pg2 gauge). The hydroisomerization products including the o-xylene solvent were collected and then dehydrogenated to be fed as PtS / Na-ZSM-5 in a reactor at 454.4 ° C (850 ° F), 7,031 kg / cm2 gauge (100 lb / pg2 gauge), 0.5 ml / hr of feed, 23 ml / min of H ^ and 0.5 g of catalyst. The feed compositions (hydroisomerization products of 2,7-DMN in Example 6) and their dehydrogenation product are shown in% by weight in Table XIX. The dehydrogenation catalyst was stable under this condition for at least 9 days.

Table XIX Example 20 Hydroisomerization / dehydrogenation of 2,7-DMN with PdS / Y and PtS / Re / Al203 A hydrocarbon feed of 5: 1 (weight / weight) of o-xylene: 2,7-dimethylnaphthalene was hydroisomerized in a reactor with PdS / Y catalyst 176. 7-216.1 ° C (350-475 ° F) and 14,062 kg / cm2 gauge (200 lb / pg2 gauge), 1.0 ml / hr of feed, 40 ml / min of H2 and 0.5 g of catalyst. The hydroisomerization product including the o-xylene solvent was collected and then dehydrogenated to be fed to a sulfurized Pt / Re / Al203 catalyst (0.3 wt.% Pt, 0.3 wt.% Re, 1.1 wt.% of Cl over A1203) in a reactor at 454.4 ° C (850 ° F), 7.031 kg / cm2 gauge (100 lb / pg2 gauge), 0.3 ml / hr of feed, 23 ml / min of H2 and 0.5 g of catalyst. It appears that due to the acid properties of the Pt / Re / Al203 catalyst a significant amount of methylnaphthalenes were produced as by-products in the dehydrogenation step when Pt / Re / Al203 was used as the dehydrogenation catalyst. The compositions of the 2,7-DMN feed (for hydroisomerization), the dehydrogenation feed (2,7-DMN hydroisomerization products) and the dehydrogenation product are shown in wt% in Table XX. Table XX Example 21 Hydrogenation / dehydrogenation of 1,5-DMN with PtS / B-SSZ-33 and PtS / Na-ZSM-5 In Example 1, a hydrocarbon feed of 5: 1 (weight / weight) of o-xylene: 1,5-dimethylnaphthalene was hydrogenated in a reactor with a PtS / Boro-SSZ-33 catalyst (0.5 g) at 204.4 ° C (400 ° F) and 14,062 kg / cm2 gauge (200 lb / pg2 gauge). The hydrogenation products including the o-xylene solvent were collected and then dehydrogenated to be fed to PtS / Na-ZSM-5 in a reactor at 454.4 ° C. (850 ° F), 7,031 kg / cm2 gauge (100 lb / pg2 gauge), 0.5 ml / hr of feed, 23 ml / min of H2 and 0.5 g of catalyst. As described in Example 1, in the hydrogenation step, 96% of 1,5-DMN was converted, yielding 88% of 1,5-DMT and 8% of DMD's and other C12's. No DMT isomers were observed. In the dehydrogenation step of this example, the resulting dehydrogenation product had the following composition: -0% of DMD's and other C12's, 0.9% of 1, 5-DMT, 1.3% of other DMT's, 96.5% of 1.5- DMN, 1.3% of 1,6 / 1,7-DMN. No MN's were detected. Since PtS / Na-ZSM-5 works for the "volumetric" 1, 5-isomers as demonstrated in this example, this catalyst apparently also works for the dehydrogenation of other DMN isomers.

Example 22 Hydroisomerization / dehydrogenation of 1,5-DMN with PdS / Y and PtS / Na-ZSM-5 A hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 1,5-dimethylnaphthalene was hydroisomerized in a reactor with u? PdS / Y catalyst at 226.7 ° C (440 ° F), 35.15 kg / cm2 gauge (500 lb / pg2 gauge), 0.5 ml / hr feed, 40 ml / min H2 and 0.5 g catalyst. The hydroisomerization products including the o-xylene solvent were collected and then dehydrogenated by being fed to PtS / Na-ZSM-5 in a reactor at 454.4 ° C (850 ° F), 7,031 kg / cm2 gauge (100 lb / pg2) gauge), 0.5 ml / hr of feed, 23 ml / min of H2 and 0.5 g of catalyst. The compositions of the 1,5-DMN feed (for hydroisomerization), the dehydrogenation feed (hydroisomerization products of 1,5-DMN), and the dehydrogenation product are shown in% by weight in Table XXII.

Table XXII Example 23 Hydroisomerization / dehydrogenation of 1,6-DMN with PdS / Y and PtS / Na-ZSM-5 A hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 1,6-dimethylnaphthalene was hydroisomerized in a reactor with a PdS / Y catalyst 226. 7 ° C (440 ° F), 35.15 kg / cm2 gauge (500 lb / pg2 gauge), 0.5 ml / hr of feed, 40 ml / min of H2 and 0.5 g of catalyst. Hydroisomerization products including the o-xylene solvent were collected and then dehydrogenated by being fed to a PtS / Na-ZSM-5 in a reactor at 454.4 ° C (850 ° F), 7,031 kg / cm2 gauge (100 lb / pg2 gauge), 0.5 ml / hr of feed, 23 ml / min of H2 and 0.5 g of catalyst. The compositions of the 1,6-DMN feed (for hydroisomerization), the dehydrogenation feed (hydroisomerization products of 1,6-DMN), and the dehydrogenation product are shown in% by weight in Table XXIII.

Table XXIII Example 24 Hydroisomerization / dehydrogenation of 1,7-DMN with PdS / Y and PtS / Na-ZSM-5 A hydrocarbon feed of 5: 1 (weight: weight) of o-xylene: 1,7-dimethylnaphthalene was hydroisomerized in a reactor with a PdS / Y catalyst 226. 7 ° C (440 ° F), 35.15 kg / cm2 gauge (500 lb / pg2 gauge), 0.5 ml / hr of feed, 40 ml / min of H2 and 0.5 g of catalyst. Hydroisomerization products including the o-xylene solvent were collected and then dehydrogenated by being fed to PtS / Na-ZSM-5 in a reactor at 454.4 ° C (850 ° F), 7,031 kg / cm2 gauge (100 lb / pg2) gauge), 0.1 ml / hr of feed, 23 ml / min of H2 and 0.5 g of catalyst. The compositions of the 1,7-DMN feed (for hydroisomerization), the dehydrogenation feed (hydroisomerization products of 1,7-DMN), and the dehydrogenation product are shown in% by weight in Table xxv.

Table XXIV Example 25 Hydroisomerization / dehydrogenation of a mixture of DMN with PdS / Y and PtS / Na-ZSM-5 A hydrocarbon feed of 5: 1 (weight: weight) of o-xylene mixture of DMN (approximately 2,7-DMN: 1, 7-DMN: 1, 6-DMN: 1, 5-DMN = 2: 2: 2: 1 by weight) was hydroisomerized in a reactor with PdS / Y catalyst to 215. 6 ° C (420 ° F), 35.15 kg / cm2 gauge (500 lb / pg2 gauge), 1.0 ml / hr of feed, 40 ml / min of H2 and 0.5 g of catalyst. Hydroisomerization products including the o-xylene solvent were collected and then dehydrogenated by being fed to PtS / Na-ZSM-5 in a reactor at 454.4 ° C (850 ° F), 7,031 kg / cm2 gauge (100 lb / pg2) gauge), 1.0 ml / hr of feed, 23 ml / min of H2 and 0.5 g of catalyst. Compositions of food of mix of DMN (for hydroisomerization), food for dehydrogenation (hydroisomerization products of DMN blend), and the dehydrogenation product are shown in% by weight in Table XXV.

Table XXV Although a few embodiments of the invention have been described in detail above, it will be appreciated by those skilled in the art that various modifications and alterations can be made to the particular embodiments, shown, without starting material, from the novel teachings and advantages. of the invention. Accordingly, it is understood that all modifications and alterations are included within the spirit and scope of the invention as defined by the following claims.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention Oomo antecede claims as property what is contained in the following

Claims (54)

1. A method for producing 2,6-dimethylnaphthalene characterized in that it comprises: (a) contacting a hydrocarbon feed comprising an isomer of dimethylnaphthalene or mixture of isomers selected from the group consisting of 1,6-dimethylnaphthalene, 1.5 - dimethylnaphthalene, 2,7-dimethylnaphthalene, 1,7-dimethylnaphthalene ', 1,8-dimethylnaphthalene, and partially or completely hydrogenated counterparts thereof - with an acid catalyst in the presence of hydrogen gas to obtain a hydroisomerized mixture comprising 6-dimethyltetralin, 2,6-dimethyldecalin; and (b) contacting the hydroisomerized mixture with a reforming catalyst to dehydrogenate the hydroisomerized mixture thereby obtaining a dehydrogenated mixture comprising 2,6-dimethylnaphthalene.

2. The method according to claim 1, characterized in that it further comprises recirculation through step (a) and step (b) of hydrocarbons minus 2,6-dimethylnaphthalene, 2,6-dimethyldecalin, and 2,6-dimethyltetraline from of the hydroisomerized mixture produced in step (a) and / or hydrocarbons other than 2,6-dimethylnaphthalene from the dehydrogenated mixture of step (b) to give additional 2,6-DMN.

3. The method according to claim 1, characterized in that it further comprises contacting the feed mixture before and / or after step (a) with an acid catalyst under conditions sufficient to maximize the production of 2,6-DMN through of intra-trivalent isomerization of DMN.

4. The method according to claim 1, characterized in that the feed mixture is pure or in solution.

5. The method according to claim 1, characterized in that the space velocity per hour is in a range of 0.1 to 100 hr-1.

6. The method according to claim 1, characterized in that the molar ratio of hydrogen to hydrocarbon in step (a) is in the range of 0.1 to 100.

7. The method according to claim 1, characterized in that step (a) is conducted at a temperature in a range from 148.9 ° C (300 ° F) to 537.8 ° C (1000 ° F).

8. The method according to claim 1, characterized in that the catalyst in step (a) is selected from the group consisting of oxides of silica, boron, aluminum, gallium, germanium, iron, chromium, zirconium and mixtures thereof.

9. The method according to claim 8, characterized in that the catalyst in step (a) further comprises a noble metal.

10. The method according to claim 9, characterized in that the noble metal is in the range from 0.1 to 10% by weight of the catalyst in step (a).

11. The method according to claim 9, characterized in that the noble metal is selected from the group consisting of palladium and platinum.

12. The method according to claim 8, characterized in that the catalyst in step (a) is selected from the group consisting of amorphous materials and zeolitic materials.

13. The method according to claim 12, characterized in that the catalyst in step (a) is selected from the group consisting of SAPO-11, A / B / beta catalyst, Y zeolite and amorphous silica-aluminum catalyst.

14. The method according to claim 1, characterized in that the catalyst in step (b) comprises a catalyst which is not substantially acidic.

15. The method according to claim 14, characterized in that the non-acid catalyst in step (b) is selected from the group consisting of Pt / Na-ZSM-5 and Pt / Cs / B-SSZ-42.

16. The method according to claim 14, characterized in that the non-acid catalyst in step (b) is sulfided.

17. The method according to claim 1, characterized in that the catalyst in step (b) comprises a reforming catalyst, acid.

18. The method according to claim 17, characterized in that the acid reforming catalyst in step (b) is Pt / Re on alumina.

19. A method that does not use 2,6-dimethylnaphthalene to obtain 2,6-dimethylnaphthalene, characterized in that it comprises: (a) contacting a hydrocarbon feed comprising an isomer of dimethylnaphthalene or "mixture of isomers selected from the group consisting of of 1, 6-dimethylnaphthalene, 1,5-dimethylnaphthalene, 2,7-dimethylnaphthalene, 1,7-dimethylnaphthalene, 1,8-dimethylnaphthalene, and counterparts thereof partially or completely hydrogenated with an acid catalyst in the presence of hydrogen gas to obtain a hydroisomerized mixture comprising 2,6-dimethyldecalin 2, 6-dimethyltetralin, and (b) contacting the hydroisomerized mixture with a reforming catalyst to dehydrogenate the hydroisomerized mixture, thereby obtaining a dehydrogenated mixture comprising 2,6- dimethylnaphthalene.

20. The method according to claim 19, characterized in that it further comprises recirculation through step (a) and step (b) of hydrocarbons other than 2,6-dimethylnaphthalene, 2,6-dimethyldecalin, and 2,6-dimethyltetralin a Starting from the hydroisomerized mixture produced in step (a) and / or hydrocarbons other than 2,6-dimethylnaphthalene from the dehydrogenated mixture of step (b) to give additional 2,6-DMN.

21. The method according to claim 19, characterized in that it further comprises contacting the feed mixture before and / or after step (a) with an acid catalyst under conditions sufficient to maximize the production of 2,6-DMN and 2, 7-DMN through intra-trivalent isomerization of DMN.

22. The method according to claim 19, characterized in that the feed mixture is pure or in solution.

23. The method according to claim 19, characterized in that the space velocity per hour is in a range of 0.1 to 100 hr "1.

24. The method according to claim 19, characterized in that the molar ratio of hydrogen to hydrocarbon in step (a) is in a range of 0.1 to 100.

25. The method according to claim 19, characterized in that step (a) is conducted at a temperature in a range from 300 ° F to? ° ° F.

26. The method according to claim 20, characterized in that the catalyst in step (a) is selected from the group consisting of oxides of silica, boron, aluminum, gallium, germanium, iron, chromium, zirconium and mixtures thereof.

27. The method according to claim 26, characterized in that the catalyst in step (a) further comprises a noble metal.

28. The method according to claim 27, characterized in that the noble metal is in the range from 0.1 to 10% by weight of the catalyst in step (a).

29. The method according to claim 27, characterized in that the noble metal is selected from the group consisting of palladium and platinum.

30. The method according to claim 26, characterized in that the catalyst in step (a) is selected from the group consisting of amorphous materials and zeolitic materials.

31. The method according to claim 30, characterized in that the catalyst in step (a) is selected from the group consisting of SAPO-11, A / B / beta catalyst, Y zeolite and amorphous silica-aluminum catalyst.

32. The method according to claim 19, characterized in that the catalyst in step (b) comprises a non-acid catalyst.

33. The method according to claim 32, characterized in that the non-acid catalyst in step (b) is selected from the group consisting of Pt / Na-ZSM-5 and Pt / Cs / B-SSZ-42.

34. The method according to claim 33, characterized in that the non-acid catalyst in step (b) is sulfided.

35. The method according to claim 19, characterized in that the catalyst in step (b) comprises an acid reforming catalyst.

36. The method according to claim 35, characterized in that the acid reforming catalyst in step (b) is Pt / Re in alumina.

37. A method for using an acid catalyst in a hydroisomerization step followed by a non-acid reforming catalyst in a dehydrogenation step to obtain 2,6-dimethylnaphthalene from an isomer of dimethylnaphthalene or mixture of isomers selected from the group consisting of 1, 6-dimethylnaphthalene, 1,5-dimethylnaphthalene, 2,7-dimethylnaphthalene, 1,7-dimethylnaphthalene, 1,8-dimethylnaphthalene, and partially or totally hydroisomerized counterparts thereof, characterized in that it comprises: (a) contacting a hydrocarbon feed comprising an isomer of dimethylnaphthalene or mixture of isomers selected from the group consisting of 1,6-dimethylnaphthalene, 1,5-dimethylnaphthalene, 2,7-dimethylnaphthalene, 1,7-dimethylnaphthalene, 1,8- dimethylnaphthalene, and counterparts thereof partially or completely hydrogenated with an acid catalyst in the presence of hydrogen gas to obtain a hydroisomerized mixture comprising e 2, 6- dimethyldecaline and 2,6-dimethyltetralin; and (b) contacting the hydroisomerized mixture with a reforming catalyst to dehydrogenate the hydroisomerized mixture, thereby obtaining a dehydrogenated mixture comprising 2,6-dimethylnaphthalene.

38. The method according to claim 37, characterized in that it further comprises recirculation through step (a) and step (b) of hydrocarbons other than 2,6-dimethylnaphthalene, 2,6-dimethyldecalin, and 2,6-dimethyltetralin a Starting from the hydroisomerized mixture produced in step (a) and / or hydrocarbons other than 2,6-dimethylnaphthalene from the dehydrogenated mixture of step (b) to give additional 2,6-DMN.

39. The method according to claim 37, further comprising contacting the feed mixture before and / or after step (a) with an acid catalyst under conditions sufficient to maximize the production of 2,6-DMN through intra-trivalent isomerization of DMN.

40. The method according to claim 37, characterized in that the hydrocarbon feed is pure or in solution. '

41. The method according to claim 37, characterized in that the hydrocarbon feed in step (a) is flowed at a space velocity per hour in a range of 0.1 to 100 hr "1.

42. The method according to claim 37, characterized in that the molar ratio of hydrogen to hydrocarbon in step (a) is in a range of 0.1 to 100.

43. The method according to claim 37, characterized in that step (a) is conducted at a temperature in a range from 300 ° F to 1000 ° F.

44. The method according to claim 37, characterized in that the catalyst in step (a) is selected from a group consisting of oxides of silica, boron, aluminum, gallium, germanium, iron, chromium, zirconium and mixtures thereof.

45. The method according to claim 37, characterized in that the catalyst in step (a) further comprises a noble metal.

46. The method according to claim 45, characterized in that the noble metal is in a range from 0.1 to 10% by weight of the catalyst in step (a).

47. The method according to claim 45, characterized in that the noble metal is selected from the group consisting of palladium and platinum.

48. The method according to claim 44, characterized in that the catalyst in step (a) is selected from the group consisting of amorphous materials and zeolitic materials.

49. The method according to claim 48, characterized in that the catalyst in step (a) is selected from the group consisting of SAPO-11, A / B / beta catalyst, Y zeolite and amorphous silica-aluminum catalyst.

50. The method according to claim 37, characterized in that the catalyst in step (b) comprises a non-acid catalyst.

51. The method according to claim 50, characterized in that the non-acid catalyst in step (b) is selected from the group consisting of Pt / Na-ZSM-5 and Pt / Cs / B-SSZ-42.

52. The method according to claim 51, characterized in that the non-acid catalyst in step (b) is sulfided.

53. The method according to claim 37, characterized in that the catalyst in step (b) comprises an acid reforming catalyst.

54. The method according to claim 53, characterized in that the acid reforming catalyst in step (b) is Pt / Re in alumina.