| PATENT ASSIGNEE'S COUNTRY | USA |
| UPDATE | 01.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 18.01.00 |
| PATENT TITLE |
Method of making 2,6-dimethylnaphthalene from other dimethylnaphthalene isomers and from dimethyltetralins/dimethyldecalins with a methyl group on each ring |
| PATENT 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. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 14.07.97 |
| PATENT REFERENCES CITED | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A method of making 2,6-dimethylnaphthalene comprising: (a) contacting a hydrocarbon feed comprising a dimethylnaphthalene isomer 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 fully hydrogenated counterparts thereof with a catalyst, the catalyst being a combination of an acidic catalyst with a metal, in the presence of hydrogen gas to obtain a hydroisomerized mixture comprising 2,6-dimethyltetralin, 2,6-dimethyldecalin; and (b) contacting the hydroisomerized mixture with a reforming catalyst to dehydrogenate the hydroisomerized mixture thus obtaining a dehydrogenated mixture comprising 2,6-dimethylnaphthalene. 2. The method of claim 1 further comprising recycling through step (a) and step (b) hydrocarbons other than 2,6-dimethylnaphthalene, 2,6-dimethyldecalin, and 2,6-dimethyltetralin from the hydroisomerized mixture produced in step (a) and/or hydrocarbons other than 2,6-dimethylnaphthalene from the dehydrogenated mixture of step (b) to yield additional 2,6-DMN. 3. The method of claim 1 further comprising contacting the feed mixture before and/or after step (a) with an acidic catalyst under conditions sufficient to maximize production of 2,6-DMN through intra-triad isomerization of DMN. 4. The method of claim 1 wherein the feed mixture is neat or in solution. 5. The method of claim 1 wherein the weight hourly space velocity is in a range from 0.1 to 100 hr.sup.-1. 6. The method of claim 1 wherein the molar ratio of hydrogen to hydrocarbon in step (a) is in a range from 0.1 to 100. 7. The method of claim 1 wherein step (a) is conducted at a temperature in a range from 300.degree. F. to 1000.degree. F. 8. The method of claim 1 wherein the acidic 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 of claim 1 wherein the metal in step (a) is selected from the group consisting of nickel, copper and a noble metal. 10. The method of claim 9 wherein the metal is in a range from 0.1 to 10% by weight of the catalyst in step (a). 11. The method of claim 9 wherein the metal is selected from the group consisting of palladium and platinum. 12. The method of claim 8 wherein the acidic catalyst in step (a) is selected from the group consisting of amorphous materials and zeolitic materials. 13. The method of claim 12 wherein the acidic catalyst in step (a) is selected from the group consisting of SAPO-11, Al/B/beta catalyst, Y zeolite and amorphous silica-aluminum catalyst. 14. The method of claim 1 wherein the catalyst in step (b) comprises a catalyst which is substantially non-acidic. 15. The method of claim 14 wherein the non-acidic catalyst in step (b) is selected from the group consisting of Pt/Na-ZSM-5 and Pt/Cs/B-SSZ-42. 16. The method of claim 14 wherein the non-acidic catalyst in step (b) is sulfided. 17. The method of claim 1 wherein the catalyst in step (b) comprises an acidic reforming catalyst. 18. The method of claim 17 wherein the acidic reforming catalyst in step (b) is Pt/Re on alumina. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION The present invention relates to a method for making 2,6-dimethylnaphthalene from a hydrocarbon feed comprising isomers of dimethylnaphthalene (DMN) and dimethyltetralins/dimethyldecalins (DMT/DMD) having a methyl group on each ring. BACKGROUND OF THE INVENTION There are ten different isomers of dimethyinaphthalene (DMN). Of these, nine of them can be grouped into three triads based on the relative ease of isomerization within a certain triad. Such an intra-triad isomerization can be done using a wide variety of solid acids as catalysts. This ease of isomerization within a triad is based on the fact that a methyl group on naphthalene shifts relatively easily from an alpha position to a beta position or vice versa on the same ring but does not shift easily from a beta position to another beta position on the same ring or from an alpha position to another alpha position. The three triad 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 doesn't fit into any of the three triads. Although isomerization of dimethylnaphthalenes within these triad groups is relatively easy, isomerization from one triad group to another triad group is much more difficult. Since certain of the isomers of dimethylnaphthalene are much more valuable than others for use in plastics synthesis, investigators are continually making attempts to find ways of converting from 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. Conversion of 2,7- and 1,7-dimethylnaphthalenes into 2,6-dimethylnaphthalene has been accomplished using certain zeolites such as ZSM-5. However, such conversion has resulted in an excess of undesirable side products such as methylnaphthalenes, trimethylnaphthalenes and 1,4-, 1,3- and 2,3-dimethylnaphthalene via dealkylation, cracking and transalkylation. Usually, this acid-catalyzed isomerization is associated with catalyst deactivation as the reaction goes on, resulting in a short catalyst life. It would be very useful to find an economical way to convert 2,7- and 1,7-dimethylnaphthalene which occur as abundant products in dimethylnaphthalene synthesis to 2,6-dimethylnaphthalene in a high yield. Other investigators have found methods of converting the dimethylnaphthalene isomers, particularly 2,7-dimethynaphthalene to the most useful, and therefore most valuable isomer, 2,6-dimethylnaphthalene, but none of these conversion methods have been sufficiently simple and economical to warrant the general use of such methods. U.S. Pat. No. 3,890,403 (Shimada et al.) discloses a method which can reportedly be used to obtain 2,6-dimethylnaphthalene from a dimethylnaphthalene mixture containing the various isomers of dimethylnaphthalene. The method involves (a) partially hydrogenating the dimethylnaphthalene mixture to obtain dimethyltetralins (DMT) with a hydrogenation catalyst such as nickel, platinum, palladium, rhodium, copper-chromium, iridium or ruthenium; (b) isomerizing the dimethyltetralins with a solid acid catalyst such as a zeolite catalyst so that the dimethyltetralin isomers in which the two methyl groups occur on the same ring can be converted to the dimethyltetralin isomers in which the two methyl groups occur on opposite rings and the amount of dimethyltetralin isomers in which the two methyl groups occur on opposite rings is brought near to thermodynamical equilibrium; (c) separating and collecting the dimethyltetralin isomers in which the two methyl group occur on opposite rings from the isomers in which the two methyl groups occur on the same ring; (d) dehydrogenating the collected DMT mixture to convert it into a DMN mixture; (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 quite time-consuming and expensive because it involves several quite separate and distinct steps. U.S. Pat. No. 3,803,253 (Suld) discloses a process of hydroisomerization/dehydrogenation of a mixture of dimethylnaphthalenes, so that 2,6-dimethylnaphthalene can be obtained and isolated out from the reaction mixture. The other remaining products are then recycled 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 calcium-containing faujasite and a hydrogenation/dehydrogenation catalyst component. The process step, with hydroisomerization and dehydrogenation performed simultaneously in the same reaction vessel in the presence of the described combination catalyst, simplifies the process but makes the overall efficiency and yield of the process quite low. U.S. Pat. No. 3,928,482 (Hedge et al.), which is related to '253 discussed above, discloses a hydroisomerization process by 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. This process is intended to be incorporated as an improvement to the method of '253 discussed above but does not overcome the basic lack of success of that process for obtaining 2,6-DMN in high yields in a cost-effective way. An economical method of obtaining 2,6-DMN from other DMN isomers, especially isomers in the 2,7-DMN triad, with few steps and at relatively high yields is needed. The present inventors have found such a method. SUMMARY OF THE INVENTION One object of the present invention is to provide an economical method of making 2,6-dimethylnaphthalene in relatively high and stable yields. Another object of the present invention is to provide a method of utilizing a dimethylnaphthalene isomer 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 fully hydrogenated counterparts thereof to produce 2,6-dimethylnaphthalene. Still another object of the present invention is to provide a method of making 2,6-dimethylnaphthalene with no significant formation of naphthalene, methylnaphthalenes, trimethylnaphthalenes and 1,4-, 1,3-, 2,3- and 1,2-dimethylnaphthalene. Yet another object of the present invention is to provide a method of making 2,6-dimethylnaphthalene using a two-step hydroisomerization/dehydrogenation process. An additional object of the present invention is to provide a method of making 2,6-dimethylnaphthalene using a two-step hydroisomerization/dehydrogenation process in conjunction with an intra-triad isomerization process in which 1,7- and 1,8-DMN are converted on an acid catalyst to 2,7-DMN and 1,6- and 1,5-DMN are converted on an acid catalyst to 2,6-DMN, respectively, the 2,6-DMN is separated out 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 of utilizing an acid catalyst in a hydroisomerization step followed by a reforming or dehydrogenation catalyst in a dehydrogenation step to convert 2,7-dimethylnaphthalene triad isomers (especially 2,7- and 1,7-DMN) to 2,6-dimethylnaphthalene triad isomers (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 FIG. 1a shows in an expanded chromatographic form the DMT isomers which are the product of the hydroisomerization run described in Example 8 and shown in a larger scale in FIG. 10b. FIG. 1b shows in chromatographic form the DMN, MN and EN isomers, which were measured using GC standards to identify the DMN products to be discussed in the next examples. FIG. 2a shows the composition in chromatographic form of the 1,5-DMN feed of the hydrogenation reaction described in Example 1. FIG. 2b shows the composition in chromatographic form of the 1,5-DMT product of the reaction. FIG. 3a shows the composition in chromatographic form of the 1,6-DMN feed of the hydrogenation reaction described in Example 2. FIG. 3b shows the composition in chromatographic form of the DMT isomers that are the product of the reaction. FIG. 4a shows the composition in chromatographic form of the 1,7-DMN feed of the hydrogenation reaction described in Example 3. FIG. 4b shows the composition in chromatographic form of the DMT isomers that are the product of the reaction. FIG. 5a shows the composition in chromatographic form of the 2,7-DMN feed of the hydrogenation reaction described in Example 4. FIG. 5b shows the composition in chromatographic form of the 2,7-DMT resulting from the reaction. FIG. 6a shows in chromatographic form the product of the first hydroisomerization run, performed at 420.degree. F., as described in Example 5. FIG. 6b shows in chromatographic form the product of the second hydroisomerization run, performed at 400.degree. F., as also described in Example 5. FIG. 6c shows in chromatographic form the product of the third hydroisomerization run, performed at 350.degree. F., as also described in Example 5. FIG. 7a shows in chromatographic form the product of the first hydroisomerization run, performed at 440.degree. F., as described in Example 6. FIG. 7b shows in chromatographic form the product of the second hydroisomerization run, performed at 420.degree. F., as also described in Example 6. FIG. 7c shows in chromatographic form the product of the third hydroisomerization run, performed at 400.degree. F., as also described in Example 6. FIG. 7d shows in chromatographic form the product of the fourth hydroisomerization run, performed at 380.degree. F., as also described in Example 6. FIG. 8 is a graph plotting the yields of DMT and DMD products resulting from the hydroisomerization run of 2,7-DMN at 400.degree. F. versus the time-on-stream at which the products were analyzed on-line as described in Example 6. FIG. 9a shows in chromatographic form the product of the first hydroisomerization run, performed at 440.degree. F., as described in Example 7. FIG. 9b shows in chromatographic form the product of the second hydroisomerization run, performed at 420.degree. F., as also described in Example 7. FIG. 9c shows in chromatographic form the product of the third hydroisomerization run, performed at 400.degree. F., as also described in Example 7. FIG. 10a shows the composition in chromatographic form of the 2,7-DMN feed of the hydroisomerization reaction described in Example 8. FIG. 10b shows the composition in chromatographic form of the resulting product of the reaction. FIG. 11a is a graph plotting the conversion of 2,7-DMN and yields of various products resulting from an acid-catalyzed isomerization of 2,7-DMN on H-ZSM-11 versus the time-on-stream, as described in Example 11. FIG. 11b is a similar graph plotting the conversion and selectivities versus the time-on-stream when the resulting 1,5-, 1,6- and 1,7-DMN as well as the unconverted 2,7-DMN are assumed to be recycled and finally converted to 2,6-DMN. FIG. 12b shows in chromatographic form the hydroisomerization product of 2,7-DMN used as feed in the hydrogenation run described in Example 18. FIG. 12a shows, as a comparison, the chromatographic form of the 2,7-DMN used as feed in the hydroisomerization reaction described in Example 18. FIG. 12c shows the results of the dehydrogenation in chromatographic form. FIG. 12e shows in an expanded scale chromatographic form the product of the dehydrogenation reaction described in Example 18. FIG. 12d shows, as a comparison to FIG. 12e, an expanded scale view of the chromatogram of the 2,7-DMN feed for the hydroisomerization described in Example 18. FIG. 13b shows in chromatographic form the hydroisomerization product of 2,7-DMN used as feed in the hydrogenation run described in Example 19. FIG. 13a shows, as a comparison, the chromatographic form of the 2,7-DMN used as feed in the hydroisomerization reaction described in Example 19. FIG. 13c shows the results of the dehydrogenation in chromatographic form. FIG. 13e shows in an expanded scale chromatographic form the product of the dehydrogenation reaction described in Example 19. FIG. 13d shows, as a comparison to FIG. 13e, in an expanded scale chromatographic form the 2,7-DMN feed for the hydroisomerization run of Example 19. FIG. 14a shows in chromatographic form the 2,7-DMN feed used for the hydroisomerization run described in Example 20. FIG. 14b shows in chromatographic form the feed for the dehydrogenation reaction described in Example 20. The result of the dehydrogenation is shown in chromatographic form in FIG. 14c. FIG. 14e shows in an expanded scale chromatographic form the product of the dehydrogenation reaction described in Example 20. FIG. 14d shows, as a comparison to FIG. 14e, an expanded scale view of the chromatogram of the 2,7-DMN feed for the hydroisomerization run of Example 20. FIG. 15b shows in chromatographic form the product of the dehydrogenation reaction described in Example 21. FIG. 15a shows, as a comparison to FIG. 15b, an expanded view of the chromatogram of the 1,5-DMN feed for the hydrogenation run described in Examples 1 and 21. The result of the dehydrogenation is shown in chromatographic form in FIG. 15c. FIG. 16a shows in chromatographic form the 1,5-DMN feed used for the hydroisomerization run described in Example 22. FIG. 16b shows in chromatographic form the feed for the dehydrogenation reaction described in Example 22. The result of the dehydrogenation is shown in chromatographic form in FIG. 16c. FIG. 16e shows in a closer scale chromatographic form the product of the dehydrogenation reaction described in Example 22. FIG. 16d shows, as a comparison to FIG. 16e, a closer scale view of the chromatogram of the 1,5-DMN feed for the hydroisomerization run of Example 22. FIG. 17a shows in chromatographic form the 1,6-DMN feed used for the hydroisomerization run described in Example 23. FIG. 17b shows in chromatographic form the feed for the dehydrogenation reaction described in Example 23. The result of the dehydrogenation is shown in chromatographic form in FIG. 17c. FIG. 17e shows in a closer scale chromatographic form the product of the dehydrogenation reaction described in Example 23. FIG. 17d shows, as a comparison to FIG. 17e, a closer scale view of the chromatogram of the 1,6-DMN feed for the hydroisomerization run of Example 23. FIG. 18a shows in chromatographic form the 1,7-DMN feed used for the hydroisomerization run described in Example 24. FIG. 18b shows in chromatographic form the feed for the dehydrogenation reaction described in Example 24. The result of the dehydrogenation is shown in chromatographic form in FIG. 18c. FIG. 18e shows in a closer scale chromatographic form the product of the dehydrogenation reaction described in Example 24. FIG. 18d shows, as a comparison to FIG. 18e, a closer scale view of the chromatogram of the 1,7-DMN feed for the hydroisomerization run of Example 24. FIG. 19a shows in chromatographic form the DMN mixture feed used for the hydroisomerization run described in Example 25. FIG. 19b shows in chromatographic form the feed for the dehydrogenation reaction described in Example 25. The result of the dehydrogenation is shown in chromatographic form in FIG. 19c. FIG. 19e shows in a closer scale chromatographic form the product of the dehydrogenation reaction described in Example 25. FIG. 19d shows, as a comparison to FIG. 19e, a closer scale view of the chromatogram of the DMN mixture feed for the hydroisomerization run of Example 25. DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method of making 2,6-dimethylnaphthalene. Specifically, the invention relates to a method of using dimethylnaphthalene isomer 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 fully hydrogenated counterparts thereof to obtain 2,6-dimethylnaphthalene. The invention also relates to using an acid catalyst (the catalyst's acidity being measured by the catalyst's positive adsorption of ammonia, pyridine, and piperidine probes on 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 a dimethylnaphthalene isomer 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 fully hydrogenated counterparts thereof. The invention further 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 of from 0.1 to 30 weight %. In one preferred embodiment, the metal used with the acid catalyst is palladium. In another preferred embodiment, the metal used with the acid catalyst is platinum. In yet another preferred embodiment, the metal is sulfided. Non-limiting examples of hydroisomerization catalysts which can be used are PdS/Boron-Beta (in the presence of 500 ppm aluminum), PtS/Boron-Beta (in the presence of 500 ppm aluminum), PdS/Y, and non-sulfided Pd/Boron-Beta (in the presence of 500 ppm aluminum). PtS/Boron-SSZ-33 is not as effective as a hydroisomerization catalyst because of its tendency to serve only a hydrogenating function and not to isomerize the various DMN isomers 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 could relate to dimethylnaphthalenes being partially or fully saturated to dimethyltetralins or dimethyldecalins 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 the energy barriers for such a migration are lifted by changing the reaction pathways. It appears, according to this mechanism, that if there is sufficient acidity on or in the catalyst, the saturated DMN's will isomerize near to equilibrium. After the above hydroisomerization, the saturated dimethylnaphthalenes must be reformed back to unsaturated dimethylnaphthalenes by dehydrogenation. For this step to work with high selectivity, i.e., avoiding non-2,6-dimethylnaphthalenes, the reforming step should be done over a catalyst which avoids transalkylation, dealkylation, and cracking reactions. In a preferred embodiment, catalysts that can be used in the reforming step are both acidic and non-acidic catalysts. A non-limiting example of an acidic catalyst that can be used is a mixture of rhenium and platinum on alumina (sulfided Pt/Re/Al.sub.2 O.sub.3). Non-limiting examples of a non-acidic catalyst that can be used are sulfided Pt/Na-ZSM-5 and PtS/Cs/Boron-SSZ42. An alternative method of obtaining 2,6-DMN from other DMN isomers, particularly those in the 2,7-DMN triad, is by means of an acid-catalyzed DMN isomerization. Unlike the hydroisomerization/dehydrogenation two-step process discussed above, this process proceeds in one step and does not involve the partially or fully saturated intermediate DMT and/or DMD forms. A non-limiting example of a catalyst that can be used for such an acid-catalyzed isomerization is H-ZSM-11. This process is less preferred than the hydroisomerization/dehydrogenation process discussed above because it has a tendency to produce a fair amount of methylnaphthalenes (MN) and trimethyinaphthalenes (TMN) as well as the undesired isomers of DMN. Thus, its yield of 2,6-DMN is low in comparison to the hydroisomerization/dehydrogenation process. In all the embodiments of the hydroisomerization/dehydrogenation process, the dimethylnaphthalene feed (neat or in solution) can be flowed over the catalyst along with hydrogen gas or the reaction can be performed batchwise. In this process, the temperature needs to be high enough to hydrogenate the dimethylnaphthalene feed and to isomerize the resulting DMD's and DMT's. The hydroisomerization reaction depends on both the hydrogenation/dehydrogenation activity and acid strength of the catalyst. Additionally, in order to generate a significant amount of DMT/DMD's, the hydrogen pressure needs to be sufficiently high. Thermodynamically, higher temperatures drive the equilibrium towards DMN while higher hydrogen pressures help shift the equilibrium towards the saturated species (DMD). The reaction kinetics, which are dependent on the catalyst type, also have a strong influence on the product selectivity in relation to the hydrogenation/dehydrogenation activity and acid strength of the catalyst. In a preferred embodiment, the yield of partially saturated species (DMT) from 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 Weight Hourly Space Velocity (WHSV) can be varied over a broad range (e.g., about 0.1 to 100 h.sup.-1), the pressure can vary from 0 to 3000 psig, the hydrogen/hydrocarbon molar ratio can vary from .about.0.0 to 100, and the reactor temperature can vary from about 300 to 1000.degree. F. The unreacted material and the partially hydrogenated products other than 2,6-isomers can be recycled back to the reactor or reformed back to DMN's in a separate reactor. Various product separation schemes can be used at different points of the process. Also, in one embodiment, a more conventional isomerization process to interconvert isomers within triads can be used in conjunction with this process. In both the hydroisomerization and the reforming step, there are many variables to be optimized. These include: run temperature, pressure, space velocity, and the catalyst itself. As shown below, when such variables are optimized, approximately 50% conversion of 2,7- to 2,6-triad can be achieved. The resulting non-2,6-DMN C.sub.12 -isomers can be separated from 2,6-DMN product and recycled to the hydroisomerization reactor to be further converted to 2,6-DMN, boosting the 2,6-DMN production. Furthermore, little or no formation of 1,2-DMN, 1,3-DMN, 1,4-DMN, 2,3-DMN or TMN is encountered. There is also relatively little 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, formation of MN's can be minimized even further. With such 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 to 2,6-DMN. In addition, the yield of 2,6-DMN can be also increased through enhancing the DMN feedstocks by incorporating the more conventional, acid-catalyzed intra-triad isomerization of DMN's into the hydroisomerization/dehydrogenation process. Such intra-triad isomerization of DMN's may be further associated with a recycling step described above. In experiments described below, various hydroisomerization catalysts were used. In these experiments, there was little evidence of deactivation of the catalysts, in some cases after up to approximately three weeks of continuous use. It was also found in these experiments that the reforming step converted almost all of the saturated species back to DMN's. In fact, a ratio of .about.95/5 DMN/saturated species or better can be achieved if the various conditions are optimized. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
|
Want more information ? Interested in the hidden information ? Click here and do your request. |