BACKGROUND OF THE INVENTION 1,5-dimethyltetralin is an intermediate material required in the preparation of polyethylenenaphthalate (PEN). 2,6-naphthalene dicarboxylic acid, which is a raw material for preparing polyethylenenaphthalate, is obtained by a multi-step process involving: (1) dehydrogenation of 1,5-dimethyltetralin to form 1,5- dimethylnaphthalene (DMN) ; (2) isomerization of 1,5-dimethylnaphthalene to form 2,6-dimethylnaphthalene ; and (3) oxidation of 2,6-dimethylnaphthalene to form 2,6- naphthalene dicarboxylic acid.

Polyethylenenaphthalate is known as a useful raw material for preparing products such as high capacity recording magnetic tape which can be used for a long

period of time, heat resistant condenser, beverage container, and so forth, because it is more stable than polyethyleneterephthalate (PET) in terms of mechanical, thermal and chemical properties. Therefore, there is a great demand for polyethylenenaphthalate, and a lot of research has been conducted in the preparation of 1,5-dimethyltetralin, which is an intermediate of the manufacturing process of polyethylenenaphthalate.

However, there is a problem in the prior arts in preparing 1,5-dimethyltetralin from the 5-ortho-tolylpentene in that an additional purifying process is required for removing impurities such as 1,5-dimethylnaphthalene isomers, 1,5-dimethyltetralin isomers, dimers and polymers. One of the above-mentioned dimers having a molecular weight of 320 is the dimer of 5-ortho-tolypentene and dimethltetraline or two 5-ortho-tolypentenes, which is displayed below.

U. S. Patent 4,950, 825 discloses a process for cyclization of 5-ortho- tolylpentene to 1,5-dimethyltetralin in the presence of a zeolite Y or a zeolite Y containing noble metals as a catalyst. However, there is a problem in the above process in that impurities of arylpentane, dimethylnaphthalene isomers such as 1,4-

dimethylnaphthalene and 1,7-dimethylnaphthalene, dimethyltetralin isomers, dimers and polymers are produced up to 10%. In particular, the selectivity and yield of 1,5- dimethyltetralin is low because dimers and polymers are formed over 5% and an additional purifying process is required.

In the process for cyclization of 5-ortho-tolylpentene to 1,5-dimethyltetralin provided by U. S. Patent 5,012, 024,5, 030,781, 5,073, 670 and 5,401, 892, an ultrastable zeolite Y is used as a catalyst. However, this process also generates impurities such as 1,5-dimethylnaphthalene isomers, 1,5-dimethyltetralin isomers and dimers. In addition, if the reaction temperature is lowered to prevent the production of impurities, the yield of 1,5-dimethyltetralin becomes reduced.

As mentioned above, if conventional catalysts are used in cyclization, impurities such as dimethyltetralin isomers or dimethylnaphthalene isomers are formed as a side-reaction and it is difficult to get rid of these compounds because of their similar boiling temperatures. In addition, since it is known that dimethylnaphthalene isomers are isomerized only within the same triad, it is almost impossible to remove undesirable isomers by isomerization.

KR Patent 10-0303246 provides a method for preparing 1,5-dimethyltetralin from 5-ortho-tolylpenten by using a zeolite beta catalyst. However, the mole ratio of Si02/Al203 in the zeolite beta catalyst in the above method is limited in the range of 10.0 to 30.0. Furthermore, the effect and supporting data of preventing the formation of dimers, which are the main by-products of the cyclization reaction, are not clear.

In addition, this method is not useful in the industrial field since the zeolite beta is in

powder form.

SUMMARY OF THE INVENTION The object of the present invention is to provide a preparation method for 1,5- dimethyltetralin with high selectivity and high yield by using a zeolite beta catalyst having a certain mole ratio of Si02/Al203 so as to reduce by-products or impurities such as dimethylnaphthalene isomers, dimethyltetralin isomers, dimers and polymers.

Further, the object of the present invention is to provide a method for preparing 1, 5-dimethyltetralin with an industrial applicability by using a zeolite beta catalyst in the form of pellets.

In order to achieve the above objects, the present invention provides a method for preparing 1,5-dimethyltetralin with high selectivity and high yield by cyclization of 5-ortho-tolylpenten, such as 5-ortho-tolyl-1-pentene, 5-ortho-tolyl-2-pentene, 5-ortho- tolyl-3-pentene, 5-ortho-tolyl-4-pentene and a mixture thereof in the presence of a zeolite beta in which the mole ratio of SiO2/AI203 exceeds 30.0 and the zeolite beta is preferably in the form of pellets.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the nature and objects of the present invention, the detailed description of the preferred embodiments will now be described.

The present invention of preparing 1,5-dimethyltetralin by cyclization of 5- ortho-tolylpenten, such as 5-ortho-tolyl-1-pentene, 5-ortho-tolyl-2-pentene, 5-ortho-

tolyl-3-pentene, 5-ortho-tolyl-4-pentene and a mixture thereof is characterized by the use of a zeolite beta catalyst in which the mole ratio of SiO2/Al203 exceeds 30.0.

The zeolite beta used in the present invention is substituted by a hydrogen ion and the mole ratio of SiO2/Al203 in the zeolite beta exceeds 30.0, preferably up to 300, and the content of Na2O is from 0.001 to 10 wt. %, preferably from 0.1 to 5 wt. %. If the zeolite beta in which the mole ratio of Si02/AI203 exceeds 30.0 is used, it is possible to prepare 1,5-dimethyltetralin with a higher yield and higher selectivity to dimethyltetralin or dimethylnaphthalene than the conventional method of using the zeolite Y catalyst or the zeolite beta catalyst in which the mole ratio of SiO2/Al203 is below 30.0.

In addition, the catalyst used in the present invention is characterized in the form of pellets.

For industrial use of a catalyst, the catalyst needs to be fixed in the reactor in order to reduce the loss of the catalyst. For the immobilization, the catalyst has to have a suitable size and structural strength. If the size of the catalyst is small, the density of the catalyst layer increases and then the pressure loss of the fluid flowing through the catalyst layer also increases. Accordingly, the pressure must be increased up to a higher level than needed in the reaction in order to maintain a suitable flowing speed of the fluid. If the structural strength of the catalyst is weak, the structure of the catalyst will be easily destroyed by the weight of the immobilization layer or pressure of the fluid, thus reducing the size of the catalyst and resulting in the loss of the catalyst by flowing out of the reactor.

Therefore, the catalyst used in the industrial field need to have a suitable size, especially beyond the diameter of 0.1 mm, and if the catalyst is in powder form it needs to be shaped to a specific form. Although it is possible to form the powder catalyst into a specific shape by itself, additional agents such as alumina, silica and polymer may be added for structural strength, and the activity of the catalyst may be changed by the additioned agents.

The above additional agents may be natural clay such as bentonite, kaolin, montmorillonite, halloysite, kaolinite, dickite, nacrite and anauxite or inorganic oxide such as alumina, silica and titania. In addition, one of the compounds such as silica- alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania, silica-alumina-thoria, silica-alumina-thoria, silica-alumina-magnesia, silica-magnesia- zirconia and so forth, may be used as the additional agents.

The content of the above additional agents relative to the catalyst is in the range of 1 wt. % to 90 wt. %, preferably from 2 wt. % to 80 wt. %. In one example of the present invention, alumina was used and its content was from 10 wt. % to 30 wt. %.

One of the catalysts used in the present invention is zeolite beta CP811E-75, which is in the form of pellets and purchased from Zeolyst Company. The data in the examples of U. S. Patent 5,012, 024,5, 030,781, 5,073, 670 and 5,401, 892, which employed a zeolite Y (CBV760) of Zeolyst Company are provided to be compared with the data of the present invention. The catalyst used in the comparative example of the present detailed description is zeolite beta (HSZ-930) in the form of powder or pellets purchased from Tosoh Company in Japan.

The method for preparing 1,5-dimethyltetralin by cyclization of 5-ortho- tolylpentene will be described in detail.

A zeolite beta catalyst substituted by hydrogen ion and 5-ortho-tolylpentene, such as 5-ortho-tolyl-l-pentene, 5-ortho-tolyl-2-pentene, 5-ortho-tolyl-3-pentene, 5- ortho-tolyl-4-pentene and a mixture thereof were introduced into a liquid phase batch reactor and then nitrogen gas was injected into the reactor to purge away air. A cyclization reaction was performed at the temperature in the range of 70°C to 450°C, preferably from 90°C to 220°C, at a pressure range of 0.04 atm to 30 atm, preferably from 0.1 atm to 2 atm, in a reaction time range of 0.01 hours to 50 hours, preferably from 0.1 hours to 50 hours.

Zeolite beta was used after being dried to remove moisture. The amount of zeolite beta used was from 0.1 wt. % to 50 wt. %, preferably from 0.5 wt. % to 10 wt. % relative to those of the 5-ortho-tolylpentene.

The preparing method for 1.5-dimethyltetralin by cyclization of 5-ortho- tolylpentene of the present invention can be performed in a liquid phase or gas phase.

The reaction can be performed not only in a batch system but also in a semicontinuous system and a continuous system (CSTR or PFR). If the reaction is performed in a continuous system, nitrogen gas is injected into the reactor to purge away air and then the cyclization is performed at a temperature range of 70°C to 450°C, preferably from 70°C to 220°C and at a pressure range of 0.04 atm to 30 atm, preferably from 0.1 atm to 2 atm. The weight hourly space velocity (WHSV, 5-ortho- tolylpentene [g]/ (catalyst [g] x time [hr] )) is in the range of 0. 01/hr to 200/hr, preferably

from 0.1 to 10/hr.

The method of the present invention can add a diluent for the purpose of lowering the reaction heat and improving the selectivity and yield. The above diluent can be selected from the group consisting of nitrogen, carbon dioxide, hydrogen, argon, helium, aliphatic hydrocarbon, alicyclic hydrocarbon and aromatic hydrocarbon. The amount of said diluent is from 0.1 to 30 moles, preferably 1 to 20 moles per mole of 5- ortho-tolylpentene.

The conversion, yield and selectivity are defined in the following formula.

Conversion (%) = [ { (total amount of 5-OTP before the reaction)- (total amount of 5-OTP after the reaction)}/ (total amount of 5-OTP before the reaction) ] x 100 Selectivity (%) = [ { (amount of 1,5-DMT product) + (amount of 1, 5-DMN product)}/ { (total amount of 5-OTP before the reaction) - (total amount of the 5-OTP after the reaction)}] x 100 Yield (%) = (conversion (%)/100) x (selectivity (%)/100) x 100 The present invention will be explained in detail with the following examples.

These examples do not intend to limit the range of the present invention.

EXAMPLE 1 4g of a zeolite beta catalyst substituted by hydrogen ion and 100g of 5-ortho- tolylpentene were introduced into a liquid phase batch reactor and then nitrogen gas was sufficiently injected through the reactor to purge away air. After heating the reactor up to the temperature of 120°C, cyclization was performed by stirring at atmospheric pressure for 9.5 hours. The zeolite beta catalyst was in the form of pellets and the mole ratio of SiOs/AlzOs in the catalyst was 75. The moisture in said zeolite beta catalyst was removed by heating the catalyst to 250°C at an increasing rate of 5°C/min and then dried for 2 hours in the air atmosphere before introducing the catalyst into the reactor.

The conversion, selectivity and yield of the products were determined as 98.37%, 92.91% and 91.39%, respectively, by a gas chromatography analysis.

EXAMPLE 1-2 The conversion, selectivity and yield of products only containing up to 13 carbon atoms were analyzed from the result of example 1.

COMPARATIVE EXAMPLE 1 Cyclization was performed in the same manner as example 1, except that the zeolite beta catalyst substituted by hydrogen ion was changed by a zeolite Y catalyst (CBV 760 of Zeolyst Company) substituted by hydrogen ion, and the reaction time was 5 hours.

EXAMPLE 2 Cyclization was performed in the same manner as example 1, except that the 2g of the zeolite beta catalyst substituted by hydrogen ion and 100g of 5-ortho- tolylpentene were used, and the reaction was performed at the temperature of 140°C and at an atmospheric pressure for 9 hours.

COMPARATIVE EXAMPLE 2 Cyclization was performed in the same manner as example 2, except that the zeolite beta catalyst substituted by hydrogen ion was changed by a zeolite Y catalyst (CBV 760 of Zeolyst Company) substituted by hydrogen ion.

COMPARATIVE EXAMPLE 3 2g of a zeolite Y substituted by hydrogen ion and 100g of 5-ortho-tolylpentene were introduced into the liquid phase batch reactor of 500 ml and then nitrogen gas was injected through the reactor to purge away air. After heating the reactor to a temperature of up to 168°C, cyclization was performed by stirring the catalyst at atmospheric pressure for 5 hours. The moisture in said zeolite Y catalyst was removed by heating the catalyst to 250°C at an increasing rate of 5°C/min and then dried for 2 hours with air atmosphere before introducing the catalyst to the reactor.

COMPARATIVE EXAMPLE 3-2 The conversion, selectivity and yield of products only containing up to 13 carbon atoms were determined from the result of comparative example 3.

COMPARATIVE EXAMPLE 4 For comparison purposes, the result of example 2 (ex. 2) of U. S. Patent 5,401, 892 was described in comparative example 4. The analysis of the compounds whose carbon number is 14 or more was excluded.

COMPARATIVE EXAMPLES 5,6 For comparison purposes, the results of example 79 (ex. 79) and the example 87 (ex. 87) of U. S. Patent 5,401, 892 were described in comparative examples 5 and 6, respectively.

1,5-dimethyltetralins obtained according to the above examples and comparative examples were analyzed by gas chromatography. These results are displayed in Table 1.

<Table 1> Example Compar Compar Compar Compar Compar Compar Feed Example Example Comper Example ative ative ative ative ative ative Feed 1-2a) Compar 2 Example Example Example Feed Example Example Example 2 3 3-2°'4''5 6 Reaction Temp 120 120 120 140 140 168 168 168 180 190 [°C] Reaction 9.5 9.5 5 9 9 5 5 6.8 3 4.5 Time [hr] OTP gl 25 25 25 50 50 50 50 50 83 83 Catalyst g Catalyst Zeolite Zeolite Zeolite Zeolite Zeolite Zeolite Zeolite Zeolite Zeolite Zeolite Type Beta Beta Y Beta Y Y Y Y Y Y CBV CBV CBV CBV LZ-CBV LZ-Y 760 760 760 706 Y72 706 72 union conteka carbide component 5-OTP 98.58% 1.61% 1.70% 1.84% 3.33% 1.77% 2.06% 2.18% 98.60% 0. 00% 0.20% 0.30% Saturated 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.20% 2.00% 1.90% 2.50% OTP 1,5- 0. 01% 89. 84% 95. 10% 87.71% 88. 05% 87.19% 87. 58% 92.84% 0.00% 93.50% 87.30% 85.80% DMT 1,5- 0. 02% 0.29% 0.31% 1.02% 0.37% 1.32% 1.26% 1.34% 0.00% 1.20% 0.80% 1.30% DMN DMT 0. 04% 1.96% 2.07% 1. 62% 2.49% 1.45% 2. 53% 2.68% 0.00% 0.60% 2.00% 3.10% isomers DMN 0% 0.05% 0.05% 0.38% 0.07% 0.43% 0.53% 0.56% 0.00% 0.00% 0.00% 0.10% isomers Lights 1. 21% 0.72% 0.76% 0.50% 0.39% 0.84% 0.37% 0.39% 0. 10% 0.00% 1.80% 0.10% (<C12) Dimers 5. 53%-6. 93% 5.30% 7.00% 5. 67%---3. 40% 4.60% Others 0.14% 1.10% 2.70% 2.50% 0.80% Total 100. 00 100. 00 100. 00 100. 00 100. 00 100. 00 100. 00 100. 00 100. 00 100. 00 99.90% 98.60% % % % % % % % % % % Conversion 100.00 Rate 98.37% 98. 27% 98. 13% 96. 62% 98. 20% 97. 91% 97.78% % 99, 80% 99. 70% [wt%] Selectivity 92. 91% 98. 45% 91. 68% 92. 79% 91.39% 92.01% 97. 67% 96.04% 89. 53% 88. 61% [wt%] Yield 91. 39% 96. 75% 89. 97% 89. 66% 89. 75% 90.09% 95. 50% 96.04% 89.35% 88. 34% [wt%] a) Analysis only for products containing up to 13 carbon atoms is performed

In comparative example 3, cyclization of 5-OTP was performed in the same manner as example 2 of US. Patent 5,401, 892, the result of which is described in comparative example 4 in the detailed description.

The result of comparative example 3 shows that a large quantity of dimer components of 5.67% was produced, and thus, the selectivity and yield was low when cyclization of 5-OTP was performed using a zeolite Y catalyst.

For reference, the result of comparative example 3-2, wherein the compounds whose number of carbons is 14 or more are excluded from the result of comparative example 3, is nearly identical to the result of comparative example 4.

It is also known that heavy components and dimer components were formed in the reaction from the results of comparative examples 5 and 6, which are examples 79 and 87 (ex. 79 and ex. 87) of US. Patent 5,401, 892.

In example 1 and comparative example 1, the cyclization conditions such as the reaction temperature being 120°C and the weight ratio of 5-OTP to the catalyst being 25 are identical except the catalyst. From the results of those examples, it is known that the content of the dimers produced was decreased from 6.92% of comparative example 1 to 5.53% of example 1 by 1.39% and the selectivity was increased from 91.68% of comparative example 1 to 92.91% of example 1 by 1.23%.

Moreover, the yield of the products in example 1 was increased to 91.38% from 89. 97% of comparative example 1 by 1.42%.

The conversion, selectivity and yield of products only containing up to 13 carbon atoms were analyzed from the result of example 1 in order to be compared with

the result of comparative example 4 and described in example 1-2.

In example 2 and comparative example 2, the cyclization conditions such as the reaction temperature being 140°C and the weight ratio of 5-OTP to the catalyst being 50 are identical except the catalyst. From the results of those examples, it is known that the content of the dimers produced was decreased from 7.00% of comparative example 2 to 5.50% of example 2 by 1. 72%, and the selectivity was increased from 91. 39% of comparative example 2 to 92.79% of example 2 by 1.40%.

Meanwhile, although the yield of the products in example 2 was slightly lower than comparative example 2 due to the conversion, an improvement of the conversion and the yield can be expected if the reaction time is increased. The selectivity is equal to the yield when un-reacted 5-ortho-tolylpentene is recycled back into the reactor, and if the recycling is performed, an increase in selectivity can be expected, accompanied with an increase in yield.

EXAMPLE 11 4g of a zeolite beta catalyst substituted by hydrogen ion and 100g of 5-ortho- tolylpentene were introduced into a liquid phase batch reactor and then nitrogen gas was sufficiently injected into the reactor to purge away air. After heating the reactor to a temperature of up to 150°C, cyclization was performed by stirring the mixture at atmospheric pressure for 5 hours. The zeolite beta used was in the form of pellets and the mole ratio of Si02/A1203 in the zeolite beta was 75. The moisture in the above zeolite beta catalyst substituted by hydrogen ion was removed by heating the

catalyst to 250°C at an increasing rate of 5°C/min and then dried for 2 hours in the air atmosphere before introducing the catalyst into the reactor.

COMPARATIVE EXAMPLE 11 Cyclization was performed in the same manner as example 11, except that the zeolite beta catalyst in which the mole ratio of the S1O2/A12O31S 75 was changed by a zeolite beta in pellet form (HSZ-930 of Tosoh Company in Japan) wherein the mole ratio of the Si02/Al203 is 27.

EXAMPLE 12 Cyclization was performed in the same manner as example 11 except that the reaction temperature was changed from 150°C to 110°C.

COMPARATIVE EXAMPLE 12 Cyclization was performed in the same manner as example 12 except that the zeolite beta catalyst of example 11 in which the mole ratio of the Si02/Al203 is 75 was changed by a zeolite beta in the form of pellets (HSZ-930 from Tosoh Company in Japan) wherein the mole ratio of the Si02/Al203 is 27.

EXAMPLE 13 Cyclization was performed in the same manner as example 11 except that the reaction temperature was changed from 150°C to 90°C and the weight ratio of the 5-

OTP/catalyst was changed from 25 to 12.5.

COMPARATIVE EXAMPLE 13 Cyclization was performed in the same manner as example 13 except that the zeolite beta catalyst of example 11 in which the mole ratio of the SiO2/A1203 iS 75 was changed by a zeolite beta in the form of pellets (HSZ-930 from Tosoh Company in Japan) wherein the mole ratio of the SiO2/A1203 is 27.

COMPARATIVE EXAMPLE 14 Cyclization was performed in the same manner as example 13 except that the zeolite beta catalyst of example 11 in which the mole ratio of the SiOz/AlzOs is 75 was changed by a zeolite beta in powder form (HSZ-930 from Tosoh Company in Japan) wherein the mole ratio of the SiOz/AlzOs is 27 and the weight ratio of 5-OTP/catalyst was changed from 25 to 100.

1,5-dimethyltetralins obtained according to the above examples and comparative examples were analyzed by gas chromatography. These results are displayed in Table 2.

<Table2> Example Comparative Example Comparative Example Comparative Comparative 11 Example 11 12 Example 12 13 Example 13 Example 14 Zeolite beta Zeolyst Tosoh Zeolyst Tosoh Zeolyst Tosoh Tosoh CP81 le-HSZ-930 CP811e-HSZ-930 CP811e-HSZ-930 HSZ-930 Catalyst 75 Pellet form 75 Pellet form 75 Pellet form Powder form Pellet Pellet Pellet form form form Mole ratio of 75 27 75 27 75 27 27 the Si/Al Reaction 150 150 110 110 90 90 90 Temp (°C) OTP/catalyst 25 25 25 25 12.5 12. 5 100 (wt%) Reaction 5 5 20 20 30 30 5 Time (hr) Component (wt%) O-X 0.04 0.24 0.04 0.07 0.19 0.13 0.11 5-OPT-2 1.97 2.72 1.90 1.53 1.79 2.39 1.93 1,5-DMT 87. 19 83. 27 91.09 89.19 91.62 90.81 93.74 1,5-DMN 0.88 1.31 0.18 0.41 0.09 0. 14 0.05 Lights 0.12 0.03 0.02 0.13 0.02 0.02 0.02 Intermediates 1.65 1.74 1.92 1.64 1.90 1.80 1.53 Dimers 8.29 10.69 4.93 7.01 4.37 4.70 2.62 Total 100. 00 100.00 100.00 100.00 100.00 100.00 100.00 Conversion 98.00 97.24 98.08 98.45 98.18 97.57 98.04 1,5-DMT Selectivity (wt%) 90.09 86.86 94.13 91.90 94.65 94.39 96.97 1,5-DMT+ 1, 5-DMN Selectivity 90. 98 88.23 94. 31 92.30 94.72 94.52 97.00 (wt%) Yield (t%) 89. 16 85.79 92.50 90.87 93.00 92.23 95. 11

From the above description, it is apparent that cyclization of 5-ortho- tolylpentene in the present invention wherein a zeolite beta catalyst in which the mole ratio ofthe SiO2/A1203 exceeds 30.0 is used can produce 1,5-dimethyltetralin with higher selectivity and higher yield than that of the conventional cyclization process wherein a zeolite Y catalyst or a zeolite beta catalyst in which the mole ratio of the SiO2/A1203 is below 30.0 is used.

However, when example 13 in which the mole ratio of SiO2/A1203 is 75 is compared with comparative example 14 in which the mole ratio of SiO2/A1203 is 27, it is known that the selectivity and yield of example 13 are slightly lower than those of comparative example 14. This is thought to result from the fact that the surface area of the pellet form catalyst is less than that of the powder form catalyst and thus the activity of the pellet form of the catalyst is lowered. Nevertheless, the pellet form catalyst is required for industrial application and the improvement of selectivity and yield can be achieved by the extension of the reaction time.

Cyclization of 5-ortho-tolylpentene in the present invention can provide a preparing process of 1,5-dimethyltetralin with immediate industrial applicability by using the pellet form zeolite beta catalyst in which SiO2/A1203 exceeds 30.0.

Furthermore, the present preparing method can produce 1,5-dimethyltetralin with a high selectivity and yield by reducing the formation of the by-products.