MANUFACTURING OF 2,6-DIMETHYLNAPHTHALENE

Abstract: The invention is related to a process for making 2,6-dimethylnaphthalene from p-xylene and 1- or 2-butene or butadiene via 1-(p-tolyl)-2-methylbutane or 1-(p-tolyl)-2-methylbutene. 2,6-dimethylnaphthalene can be used for making polyethylenenaphthalate.

Description: MANUFACTURING OF 2.6-DIMETHYLNAPHTHALENE TECHNICAL AREA The invention is related to the manufacturing of 2,6-dimethylnaphthalene from p- xylene and 1- or 2-butene or butadiene via the intermediates l-(p-tolyl)-2-methyl- butane or l-(p-tolyl)-2-methylbutene. 2,6-dimethylnaphthalene can be used as a raw-material for manufacturing of polyethylenenaphthalate. TECHNICAL BACKGROUND Polyethylenenaphthalate (PEN) has got very good mechanical strength and heat resistance. Its known m-mufacturing processes, however, have not been competitive. Polyethylenenaphthalate is made from 2,6-naphthalenedicarboxylic acid, which is made by oxidizing 2,6-dimethylnaphthalene. Nowadays 2,6-dimethylnaphthalene is separated from hydrocarbon mixtures. In this way only small amounts are obtained. Furthermore also the separation and purification is difficult. It has also been suggested to manufacture 2,6-dimethylnaphthalene by cyclization of l-(p-tolyl)-2-methylbutane and/or l-(p-tolyl)-2-methylbutene. The manufacturing of 2,6-dimethylnaphthalene has been described in many patents. In some of these patents also the manufacturing of l-(p-tolyl)-2-methylbutane and/or l-(p-tolyl)-2-methylbutene is described. In some patents also the use of chromium oxide/aluminum oxide and its impregnation with potassium is mentioned. In GB- 1448136 (1976) the manufacturing of l-(p-tolyl)-2-methylbutane and/or 1- (p-tolyl)-2-methylbutene in many different ways is described. In most cases one component is p-xylene, the methyl group of which is alkylated with butene using a basic catalyst. In three examples the manufacturing of 2,6-dimethylnaphthalene using a Cr2θ3/AI-2θ3-catalyst poisoned with potassium is described. In the claims the amount of impregnated alkali metal oxide is 0.1-20 wt.% but in the examples the amounts of potassium are 2.1 and 3.5 wt.%. However, 3.1% and 5.0% of the total amount of dimethylnaphthalene is 2,7-dimethylnaphthalene which is very difficult to separate. In EP-430714A (1990) a chromium oxide / aluminum oxide catalyst poisoned with potassium is mentioned in one example but in the claims only the oxides are mentioned but not the amounts. In one example the components K.Cr.AL are in the proportions 7:11:100. In the same example the proportion of 2,6-dimethyl- naphthalene of the total amount of dimethylnaphthalenes is 98.6%. In EP-362507A (1989) p-xylene, 1-butene and carbon monoxide are used as raw- materials when making l-(p-tolyl)-2-methylbutane and/or l-(p-tolyl)-2-methyl- butene. When making the 2,6-dimethylnaphthalene Cr2θ3-5% K2O-AL2O3 is used as catalyst. The selectivity of 2,6-dimethylnaphthalene was reported to be 71%. Nothing is mentioned about the purity of the product. In the claims only aluminum oxide and silicon oxide are mentioned. EP-362651A (1989) is almost the same as EP-362507A regarding the dehydro- cyclization reaction. The only difference is that m-xylene, propylene and carbon monoxide are used for making 2,4-dimethyl-isobutyrophenone, which is cyclisized to 2,6-dimethylnaphthalene. In the patents mentioned above nothing is said about C12-alkylindanes and -indenes which are very difficult to separate because they are boiling at almost the same temperature as the dimethylnaphthalenes. DESCRIPTION OF THE INVENTION Now die process described in claim 1 has been invented. Some preferrable process alternatives are presented in the claims. The reactions according to the invented process are described below: 2,5- imethylnaphthalene In reaction step 1 the alkylation ofthe benzyl side chain is done so that the amount of n-alkyl compounds is minimized. For this purpose some basic catalysts are therefore most appropriate. In reaction step 2 on the other hand the aromatic dehydrocyclization is done using a C12O3-, V2O5- or Pt-catalyst. According to the first aspect of the invention p-xylene is reacted with butene or butadiene to p-(2-methylbuthyl) toluene or p-(2-methylbuthenyl) toluene using an alkali metal as catalyst and this catalyst is preferably attached to a suitable support. As a catalyst one can use for instance potassium dispersed on the surface of graphite or sodium mixed with potassium carbonate at a high temperature. According to the second aspect ofthe invention p-(2-methylbuthyl) toluene or p-(2- methylbuthenyl) toluene are dehydrocyclicized selectively to 2,6-dimethyl- naphthalene in the presence of a catalyst. As catalyst one can use for instance chromium oxide (for instance Cr2θ3/AL2θ3) or platinum ( for instance Pt C, Pt Siθ2 or Pt/BaL-zeolite). The best choise is , however, to use a Cr2θ3-catalyst modified with potassium, for instance C12O3/AL2O3 impregnated with K2CO3. By impregnating the catalyst with potassium fragmentation becomes more favoured. Every methyl-group which is split off decreases the boiling point about 20°C. By fragmenting C12-alkyl-indanes and -indenes they can easily be separated from 2,6- di-methylnaphthalene. In this way 2,6-dimethylnaphthalene can be manufactured selectively and profitably. The amount of potassium in the catalyst can be 0.5 - 20 wt.% but preferably 4-10 wt.%. Below are some non-limiting examples which describe the invention: Example 1 Molten potassium was dissolved in xylene at 70°C (mixing at 200 RPM) and dispersed on the surface of graphite (weight ratio of potassium: graphite: xylene was 1:1:10). To the same autoclave were then added 1- or 2- butene or butadiene in a semi-batch mode during 6-8 hours. The reaction product was composed of 79% C6- alkyl (or alkenyl)- benzenes with a p-(2-methyl) buthyl(or buthenyl)toluene content of 67 wt.%. p-n-penthyltoluene was the biggest component which was not wanted but it was veiy easy to separate by distillation. Example 2 The Cr2θ3/AL-2θ3-catalyst was treated with a water solution of K2CO3 so that the potassium concentration ofthe catalyst was 4.7 wt%. This mixture was then kept at -20°C and dried in vacuum for 3 days. Then it was calcined in a reactor tube at 500°C. Example 3 The Cr2θ3/AL2θ3-catalyst (Chromium content 15%; Cr/AL, 0.12) was treated witii a water solution of K2CO3 so that the potassium concentration of the catalyst was 8.3 wt.%. This mixture was then dried at room temperature for 20 hours and after that in a drying oven at 100°C. The calcination was done in a reactor tube at 500°C. Example 4 The Cr2θ3/AL2θ3-catalyst was treated with a water solution of K2CO3 so that the potassium concentration of the catalyst was 2.1 and 8.1 wt.%. This mixture was then dried at 100°C for 2 hours and calcined at 500°C. Example 5 A Siθ2-carrier (Grace Siθ2 432) was dried and pre-calcined at 300°C. Pt (acac) 2 was then dissolved in THF by heating shghtly and the dried Siθ2-carrier was impregnated with this Pt-THF-solution at 120°C. The impregnated Siθ2-carrier was aged for 1 day after which it was calcined at 300°C for 4h. Example 6 The Pt Siθ2-catalyst (Pt 1%) made according to Example 5 was put into a 4 ml (9mm inner diameter) quartz tube which was used as a reactor. Then 96% l-(p- tolyl)-2-methylbutane (LHSV, 0.25h " ) with hydrogene as a carrier gas (3 mol H2/1 mol l-(p-tolyl)-2-methylbutane) was pumped through the reactor. The reaction conditions were: temperature 510°C; pressure 1 bar; contact time 5.2 s. A sample was taken lh after starting the experiment and the results are presented below: Conversion 58.2% Selectivity of converted l-(p-tolyl)-2-methylbutane (mol%) C6 - C11 39.4 l-(p-tolyl)-2-methylbutene 14.2 C 12-alkyl-indanes and -indenes 8.1 2 - methylnaphthalene 10.1 dimethylnaphthalenes 24.9 (2,6 - dimethylnaphthalene 23.6) Example 7 The catalyst made according to Example 2 was put into a 4 ml (9mm inner diameter) steel tube which was used as a reactor. Then 96% l-(p-tolyl)-2- methylbutane (LHSV, 0.25 h ) with nitrogene as a carrier gas (1.8 mol N2/ 1 mol l-(p-tolyl) -2-methylbutane) was pumped through the reactor. The reaction conditions were: temperature 510°C; pressure 1 bar; contact time 7.7 s. A sample was taken 1 h after starting the experiment and the results are presented below: Conversion 83.4% Selectivity of converted l-(p-tolyl)-2-methylbutane (mol%) C6 - C11 72.9 1 -(p-tolyl)-2-methylbutenes 2.1 C12-alkyl-indanes and -indenes 0.4 2 - methylnaphthalene 5.7 dimethylnaphthalenes 18.5 (2,6 - dimethylnaphthalene 18.3) Example 8 The dehydrocyclization was done according to Example 6 except for the following changes: LHSV, 0.5h _1 ; contact time, 4 s; 1.3 mol H2/1 mol l-(p-tolyl)-2- methylbutane. The results are presented below: Conversion 58.2% Selectivity of converted l-(p-tolyl)-2-methylbutane (mol%) C6 - C11 70.8 l-(p-tolyl)-2-methylbutane 5.2 C 12-alkyl-indanes and -indenes 1.4 2 - methylnaphthalene 3.8 dimethylnaphthalenes 16.7 (2,6 - dimethylnaphthalene 16.2) Example 9 The dehydrocyclization was done according to Example 6 except for the following changes: LHSV, l.Oh ; contact time, 1.9 s. The results are presented below: Conversion 38.3% Selectivity of converted l-(p-tolyl)-2-methylbutane (mol%) C6 - C11 64.7 l-(ρ-tolyl)-2-methylbutenes 11.9 C 12-alkyl-indanes and -indenes 3.6 2 - methylnaphthalene 2.3 dimethylnaphthalenes 15.6 (2,6 - dimethylnaphthalene 14.9) Example 10 The dehydrocyclization was done according to Example 8 except for the catalyst which was pure Cr2θ3/AL2θ3. The results are presented below: Conversion 54.8% Selectivity of converted l-(p-tolyl)-2-methylbutane (mol%) C6 - C11 32.9 1 -(p-tolyl)-2-methylbutenes 21.5 C 12-alkyl-indanes and -indenes 6.4 2 - methylnaphthalene 1.2 dimethylnaphthalenes 35.4 (2,6 - dimethylnaphthalene 33.8) Example 11 The dehydrocyclization was done according to Example 9 except for the following changes: temperature 450°C; contact time 7.3 s. The results are presented below: Conversion 54.7% Selectivity of converted l-(p-tolyl)-2-methylbutane (mol%) C6 - C11 39.0 l-(p-tolyl)-2-methylbutenes 33.9 C12-alkyl-indanes and -indenes 6.0 2 - methylnaphthalenes 0.3 dimethylnaphthalenes 16.2 (2,6 - dimethylnaphthalene 15.3) Example 12 , The catalyst made in Example 3 was put into a 4 ml (9 mm inner diameter) quartz tube which was used as a reactor. Then 96% l-(p-tolyl)-2-methylbutane (LHSV, Oh ) with nitrogene as a carier gas (1.8 mol N2/I mol l-(p-tolyl)-2- methylbutane) was pumped through the reactor. The reaction conditions were: temperature 510°C; pressure 1 bar; contact time 1.7 s. A sample was taken lh after starting the experiment and the results are presented below: Conversion 26.7% Selectivity of converted l-(p-tolyl)-2-methylbutane (mol%) C6 - C11 67.6 l-(p-tolyl)-2-methylbutenes 13.7 C12-alkyl-indanes and -indenes 2.8 2 - methylnaphthalene 2.1 dimethylnaphthalenes 11.5 (2,6 - dimethylnaphthalene 11.5) Example 13 The dehydrocyclization was done according to Example 12 except for the following changes: temperature 450°C; LHSV 0.3h " ; contact time 7.3 s. The results are presented below: Conversion: 22.6% Selectivity of converted l-(p-tolyl)-2-methylbutane (mol%) C6 - Cl l 63.3 l-(p-tolyI)-2-methylbutenes 22.0 C12-alkyl-indanes and -indenes 0.6 2 - methylnaphthalene 0.3 dimethylnaphthalenes 10.8 (2,6 - dimethylnaphthalene 10.4) Example 14 The dehydrocyclization was done according to Example 6 except for the LHSV which was 0.5 h . The results are presented below: Conversion: 42.0% Selectivity of converted 1 -(p-tolyl)-2-methylbutane (mol%) C6 - C1 1 33.5 l-(p-tolyl)-2-methylbutenes 27.3 C12-alkyl-indanes and -indenes 9.8 2 - methylnaphthalene 4.0 dimethylnaphthalenes 19.2 (2,6 - dimethylnaphthalene 18.2) Example 15 The dehydrocyclization was done according to Example 6 except for the LHSV which was lh " . The results are presented below: Conversion: 58.2% Selectivity of converted l-(p-tolyl)-2-methylbutane (mol%) C6 - C11 28.6 l-(p-tolyl)-2-methylbutenes 38.6 C12-alkyl-indanes and -indenes 11.3 2 - methylnaphthalene 2.0 dimethylnaphthalenes 14.4 (2,6 - dimethylnaphthalene 13.9) Example 16 The Pt/BaL-zeolite catalyst was put into a 3 ml (9mm inner diameter) quartz tube which was used as a reactor. Then 96% l-(p-tolyl)-2-methylbutane (LHSV, 1.7h ) with hydrogene as carrier gas (3 mol H2/1 mol l-(p-tolyl)-2-methylbutane). The reaction conditions were: temperature 510°C; pressure 1 bar; contact time 0.8 s. A sample was taken 1 h after starting the experiment and the results are presented below: Conversion 71.4% Selectivity of converted l-(p-tolyl)-2-methylbutane (mol%) C6 - C11 40.2 l-(p-tolyl)-2-methylbutenes 6.2 C 12-alkyl-indanes and -indenes 3.3 2 - methylnaphthalene 17.6 dimethylnaphthalenes 14.9 (2,6 - dimethylnaphthalene 13.5)

Claims: CLAIMS 1. Process for making 2,6 dimethylnaphthalene, in two steps, wherein - the first step is a reaction p-xylene and butene or butadiene to obtain p-(2- mehylbuthyl)toluene or p-(2-methylbuthenyl)-toluene using a catalyst which is potassium or sodium on the surface of a suitable support or mixed with a suitable substance, and - the second step is a selective hydrocyclization of the intermediate to 2,6- dimethylnaphthalene using a supported chromium dioxide catalyst which has been modified with a potassium compound or a supported paltinum catalyst. 2. Process according to claim 1 , wherein the catalyst used in the first step is potassium dispersed on the surfase of graphite or sodium mixed with potassium carbonate. 3. Process according to claims 1 and 2, wherein the catalyst used in the second step is Cr2θ3 supported on AI2O3 and impregnated with K2CO3. 4. Process according to claim 3, wherein the concentration of potassium in the catalyst is 0.5-20 wt.% and preferably 4-10 wt.%. 5. Process according to claim 1 and 2, wherein the catalyst used in the second step is platinum supported on a graphite-, Siθ2- or BaL-zeolite-support.

Inventors: CSICSERY SIGMUND M, HALME ERKKI, KOSKIMIES SALME, LAATIKAINEN MARKKU, NIEMI VESA, VAHTERISTO KARI, CSICSERY, SIGMUND, M., HALME, ERKKI, KOSKIMIES, SALME, LAATIKAINEN, MARKKU, NIEMI, VESA, VAHTERISTO, KARI
Applicants: CSICSERY SIGMUND M, HALME ERKKI, KOSKIMIES SALME, LAATIKAINEN MARKKU, NIEMI VESA, OPTATECH OY, VAHTERISTO KARI, CSICSERY, SIGMUND, M., HALME, ERKKI, KOSKIMIES, SALME, LAATIKAINEN, MARKKU, NIEMI, VESA, VAHTERISTO, KARI
Application year: 1996
Main classification: C07C15
IPC codes: C07C2, C07C5, C07C15