WO2004087664A1

WO2004087664A1 - Process for preparing 2,6-divinylpyridine and 2-methyl-6-vinylpyridine from 2,6-lutidine over modified zeolites

Info

Publication number: WO2004087664A1
Application number: PCT/IN2003/000111
Authority: WO
Inventors: Shivanand Janardan Kulkarni; Madhavi Gangapuram; Vijaya Raghavan Kondapuram
Original assignee: Council Of Scientific And Industrial Research
Priority date: 2003-03-25
Filing date: 2003-03-31
Publication date: 2004-10-14
Also published as: US20040192925A1; US6897320B2

Abstract

The present invention relates to a process for the preparation of 2,6-divinylpyridine and 2-methyl-6-vinylpyridine over modified zeolite catalysts. In particular, it relates to the method for the synthesis of 2,6-divinylpyridine and 2-methyl-6-vinylpyridine from 2,6-lutidine and formaldehyde in vapour phase in an eco-friendly method with high yield and selectivity. This invention provides a non-corrosive, eco-friendly process, where the catalyst can be reused for many times. 2,6-divinylpyridine is useful starting material in polymer industry.

Description

PROCESS FOR PREPARING 2 , 6 -DIVINYLPYRIDINE AND 2-METHYL-6-VINYLPYRIDINE FROM

2 , 6-LUTIDINE OVER MODIFIED ZEOLITES

FIELD OF INVENTION

The present invention relates to a process for the preparation of 2,6- divinylpyridine and 2-methyl-6-vinylpyridine over modified zeolite catalysts. In particular, it relates to the method for the synthesis of 2,6-divinylpyridine and 2- methyl-6-vinylpyridine from 2,6-lutidine and formaldehyde in vapour phase in an eco- friendly method with high yield and selectivity. This invention provides a non- corrosive, eco-friendly process, where the catalyst can be reused for many times. 2,6- Divinylpyridine is useful starting material in polymer industry. BACKGROUND OF THE INVENTION

2,6-Divinylpyridine is used in the preparation of an aminated ion-exchange resins containing divinyl substituted heterocyclic co-monomers as cross-linkers. 2,6- Divinylpyridine (2,6-DVP) and 2-methyl-6-vinylpyridine (2M6VP) were synthesized by condensation of 2,6-lutidine and formaldehyde using potassium salts as catalysts. This method involves homogeneous conditions alongwith the high temperature and pressure [E.G. Martin, US 2,824,844 (1958); Chem. Abstract.52 (1958) 9482i; J. Michalski, K. Studniarski, Roczniki Chem. 29 (1955) 1141; Chem. Abstract. 51 (1957) 10530c and Chem. Abstract 62 (1965) 1627c].

2,6-DVP and 2M6VP were also prepared by oxidative dehydrogenation of dialkyl heteroaromatics over V₂O₅/MgO and MoO₃/MgO catalysts in the presence of O₂ [I.P. Belomestnykh, N.N. Rozhdestvenskaya, G.V. Isagulyants, Khim. Geterotsikl. Soedian. 6 (1994) 802; Chem. Abstract. 122 (1995) 31287r.]. We have reported the synthesis of 2-vinylpyridine and 4-vinylpyridine by side- chain alkylation of (2- and 4-methylpyridines) 2- and 4-picoline over modified basic zeolites. [Appl. Catal. (2003) in press]. OBJECTS OF THE INVENTION

The main object of the invention is to provide a process for the synthesis of 2,6-divinylpyridine and 2-methyl-6-vinylpyridine over modified zeolites in a heterogeneous eco-friendly method.

Another object of the invention is to provide a process for the preparation of

2,6-DVP and 2M6VP in high yield and high selectivity. SUMMARY OF THE INVENTION

The present invention relates to develop a process for the preparation of 2,6- divinylpyridine and 2-methyl-6-vinylpyridine from 2,6-lutidine and formaldehyde in vapour phase over zeolite/ molecular sieve catalysts. The catalyst comprises of particularly ZSM-5 (pentasil family) with sodium, potassium, rubidium, cesium, magnesium, calcium, strontium and/or barium, etc cation or their species.

Accordingly, the present invention provides a process for the simultaneous production of 2,6-divinylpyridine and 2-methyl-6-vinylpyridine comprising reacting 2,6-lutidine with formaldehyde in a catalytic zone containing a modified zeolite catalyst, the temperature of the catalytic zone being in the range of 200 to 450°C, the reaction being carried out at a weight hourly space velocity in the range of 0.25 to 1.0 h^"1, the molar ratio of 2,6-lutidine to formaldehyde being 1 :1 to 1:4.

In one embodiment of the invention, the modified zeolite catalyst comprises a modified ZSM-5 pentasil type zeolite catalyst, preferably modified by an alkali or alkaline earth metal ion selected from the group consisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺.

In another embodiment of the invention, the modified ZSM-5 catalyst is a two cation modified ZSM-5, such as Cs-K-ZSM-5.

In yet another embodiment of the invention, the weight percent of the alkali or alkaline earth metal ion in ZSM-5 is in the range of 1 wt % to 4 wt %.

In yet another embodiment of the invention, the ZSM-5 catalyst is modified by potassium ion, the potassium ion source being selected from the group consisting of KO'Bu, KOH, KF, KNO₃, K₃PO₄ and KOAc, to improve the yield and selectivity of 2,6-divinylpyridine. In a further embodiment of the invention, the modified zeolite is 3 wt% KZSM-

5, calcined at a temperature in the range of 400°C to 700°C.

In a further embodiment of the invention, the temperature of the catalytic zone is

300°C, the molar ratio of formaldehyde to 2,6-lutidine is 4:1 and the weight hourly space velocity in the process is 0.5 h^" . Another embodiment of the present invention provides a process for the preparation of 2,6-divinylpyridine and 2M6VP form 2,6-lutidine and formaldehyde in the presence of catalyst which comprises ZSM-5 containing one or two elements(s) from alkali and/ or alkaline earth metal ions like Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca ⁺, Sr²⁺, Ba etc which can be reused for several times. DETAILED DESCRIPTION OF THE INVENTION

The modified HZSM-5 catalyst was used in the development of the process. Each zeolite was pelleted without binder, crashed and sized 18-30 mesh before the impregnation. The ZSM-5 catalyst was modified by using required amount of alkali or alkaline earth cation nitrate by an impregnation method. In the case of potassium, different precursors like KO^lBu, KF, KOAc, K₃PO₄, KNO₃, or KOH were used to modify ZSM-5 (Siθ₂/Al₂O₃= 30) catalyst. The required amount of precursor was taken in the form of nitrate or other soluble salts in 30 ml of distilled water. 4.0 g of the meshed catalyst was added to it and kept for soaking for 12 h. Then it was dried at 110°C over night and calcined at 420°C for 4 h before using for the reaction.

In a typical procedure for the synthesis of KO^lBu modified ZSM-5 (30) catalyst is as follows; 7 g of HZSM-5 (30) was taken in 250 ml two-necked round bottom flask. Prior to modification the catalyst was predried in oven at 100°C for 1 h followed by flushing with nitrogen gas to remove water content present in the channels of the catalyst. In another round bottom flask required amount of KO^lBu was dissolved in dry DMSO solvent. This solution was added to HZSM-5 (30) catalyst and kept stirring for 24 h in presence of nitrogen atmosphere. After 24 h stirring the resultant mixture was filtered, dried at 120°C overnight and calcined at 400°C for 4 h. the reactions were carried out in a fixed bed, continuous, down-flow pyrex reactor with internal diameter of 20 mm at atmospheric pressure. All the catalysts were activated by calcination in a flow of air at 420°C for 4 h and brought to the reaction temperature in situ. A mixture of 2,6-lutidine and formaldehyde 37%wt/v was fed from a syringe pump at a rate of 2 ml. h^"1. The effluents from the reactor were cooled and periodically collected with an ice trap. The samples were analyzed by gas chromatography (SCHIMADZU-14B) fixed with an OV-17 (2 mm x 1/8" OD) on chromosorb W-HP column and flame ionization detector. The carrier gas was N₂ (100 kPa) and the column temperature programme was 90°C (5 min), 2°C. min^"1, 120°C (10 min), 180°C (injector) and 250°C (detector). Products were confirmed by GC-Ms and NMR techniques. 2,6-DVP and 2M6VP are formed as major products during side-chain alkylation of 2,6-lutidine and formaldehyde with all the catalysts studied here. Other products include 2-methyl-6- ethylpyridine and isomerized product 2,5-divinylpyridine.

The present invention will be explained in more detail by the following examples, which do not limit the scope of the invention in any way. EXAMPLE 1: Synthesis of potassium modified SSM-5.

Four grams of calcined HZSM-5 having SiO₂/ Al₂O₃ molar ratio of 30 was taken in the form of 18-30 mesh size and soaked in 30 ml of the solution of potassium nitrate containing 0.4 g potassium for 12 h. Then it was dried at 110°C overnight and calcined at 420 C for 4 h before using for the reaction. EXAMPLE 2 : Synthesis of cesium modified ZSM-5.

Same procedure as given in Example 1 was used for the preparation of other metal ion ZSM-5 catalyst by using their inorganic salts as precursors. Cesium nitrate was used for Cs-ZSM-5. EXAMPLE 3: Modified ZSM-5 was used in the following reaction for the preparation of 2,6- divinylpyridine and 2-methyl-6-vinylρyridine. Cs-ZSM-5 (SiO2/ A12O3 = 30) (3 wt% Cs) catalyst was packed in a pyrex reactor having and inner diameter of 20 mm with the length of 30-40 cm and the catalytic zone was heated at 300°C. Then the mixture was fed from top of formaldehyde: 2,6-lutidine = 4: 1 molar. The weight hourly space velocity was 0.5 h^"1. The liquid product selectivities for 2,6-divinylpyridine (2,6-DVP) and 2-methyl-6-vinylpyridine (2M6VP) were 25.2 and 74.8 % at 37.1 wt% conversion of 2,6-lutidine (at time on stream (TOS) = 6 h) respectively. EXAMPLE 4:

Conversion of 2,6-lutidine and formaldehyde was carried out over K-ZSM-5 (3 wt% K) at 300°C with 0.5 h^'1 W.H.S.V. The catalyst was 4 g with 18-30 mesh size and feed rate of 2 ml. h^"1. 2,6-Lutidine to formaldehyde molar ratio was 1:4. The liquid product selectivities were 36.1 and 60.0 at 51.5 wt% conversion of 2,6-lutidine at TOS = 6 h. EXAMPLE 5: Reaction of 2,6-lutidine and formaldehyde was carried out over Rb-ZSM-5

(30) at 300°C with 0.5 h^"1 W.H.S.V. The catalyst was 4 g with 18-30 mesh size and feed rate of 2 ml. h^"1. 2,6-Lutidine to formaldehyde molar ratio was 1:4. The liquid product selectivities of 2,6-divinylpyridine and 2-methyl-6-vinylρyridien were 39.4 and 60.6 wt% at 62.3 wt% conversion of 2,6-lutidine at TOS = 6 h. EXAMPLE 6: Reaction of 2,6-lutidine and formaldehyde was carried out over Na-ZSM-5

(SiO₂/ Al₂O₃ = 30) at 300°C with 0.5 h^_1 W.H.S.V. The catalyst was 4 g with 18-30 mesh size and feed rate of 2 ml. h^"1. The molar ratio of 2,6-lutidine to formaldehyde 1:4. The liquid product selectivities were 30.4 and 69.6 % for 2,6-DVP and 2M6VP respectively, at 53.3 wt% conversion of 2,6-lutidine. EXAMPLE 7:

Reaction of 2,6-lutidine and formaldehyde was carried out over Sr-ZSM-5 (SiO₂/ Al₂O₃ =30) at 300°C with 0.5 h^"1 W.H.S.V. The catalyst was 4 g with 18-30 mesh size and feed rate of 2 ml. h^"1. The molar ratio of 2,6-lutidine: formaldehyde was 1:4. The liquid product selectivities were 24.9 and 75.1% of 2,6-DVP and 2M6VP respectively, at 32.5 wt% conversion of 2,6-lutidine at TOS= 6 h. EXAMPLE 8:

Reaction of 2,6-lutidine and formaldehyde was carried out over BaZSM-5 (30) at 300°C with 0.5 h^"1 W.H.S.V. The catalyst was 4 g with 18-30 mesh size and feed rate of 2 ml. h^"1. The molar ratio of 2,6-lutidine: formaldehyde was 1:4. The liquid product selectivity was >98% of 2,6-DVP at 21.9 % conversion of 2,6-lutidine at TOS= 6 h. EXAMPLE 9:

Reaction of 2,6-lutidine and formaldehyde was carried out over Cs-K-ZSM-5 (SiO₂/ Al₂O₃= 30) at 300°C with 0.5 h^_1 W.H.S.V. The catalyst was 4 g with 18-30 mesh size and feed rate of 2 ml. h^"1. The molar ratio of 2,6-lutidine; formaldehyde was 1:4. The liquid product selectivities were 31.0 and 67.8 wt% for 2,6-DVP and 2M6VP at 57.8 wt% conversion of 2,6-lutidine respectively, at TOS= 6 h. EXAMPLE 10:

The reaction of 2,6-lutidine and formaldehyde was carried out over K-ZSM-5 (30, 3 wt% K) in the reaction temperature range of 250 to 400°C. The catalyst was 4 g with 18-30 mesh size and feed rate 2 ml.h^"1. The molar ratio of 2,6-lutidine: formaldehyde was 1:4. The liquid product selectivities were 32.1 % 2,6-DVP and 67.9% 2M6VP at 16.1 wt% conversion of 2,6-lutidine at 250°C at TOS= 6 h. The liquid product selectivities were 36.1 %2,6-DVP and 60.0% 2M6VP at 51.5 wt% conversion of 2,6-lutidine at 300°C at TOS= 6 h. The liquid product selectivities were 45.0 % 2,6-DVP and 46.8 % 2M6VP at 60.4 wt% conversion of 2,6-lutidine at 350°C at TOS= 6 h. The liquid product selectivities were 29.1 % 2,6-DVP and 54.3 % 2M6VP at 55.3 wt% conversion of 2,6-lutidine at 400°C at TOS= 6 h. EXAMPLE 11:

The reaction of 2,6-lutidine and formaldehyde was carried out over K-ZSM-5 (30, 3 wt% K) at 300°C reaction temperature and W.H.S.V. =0.5 h^"1. The molar ratio of 2,6-lutidine: formaldehyde was varied in the range of 1:1 to 1:5. The catalyst was 4 g with 18-30 mesh size and feed rate 2 ml.h^"1. The liquid product selectivities were 30.9 % 2,6-DVP and 68.9 % 2M6VP at 39.3 wt% conversion of 2,6-lutidine for the molar ratio of lutidine: formaldehyde =1:1. The liquid product selectivities were 36.1 % 2,6-DVP and 60.0 % 2M6VP at 51.5 wt% conversion of 2,6-lutidine for the molar ratio of lutidine: formaldehyde =1: 4. The liquid product selectivities were 46.7 % 2,6- DVP and 49.1 % 2M6VP at 58.7 wt% conversion of 2,6-lutidine for the molar ratio of lutidine: formaldehyde =1:5. EXAMPLE 12: The reaction of 2,6-lutidine and formaldehyde was carried out over K-ZSM-5

(30, 4 wt% K by ion exchange method) at 300°C reaction temperature and weight hourly space velocity was varied in the range of 0.125 to 0.75 h^"1. The catalyst was 4 g with 18-30 mesh size and feed rate 2 ml.h^"1. The molar ratio of lutidine: formaldehyde was 1:4. The liquid product selectivities were 74.7 % 2,6-DVP and 23.4 % 2M6VP at 87.2 wt% conversion of 2,6-lutidine at 0.125 h^"1 and at TOS = 5 h. The liquid product selectivities were 61.8 % 2,6-DVP and 37.9 % 2M6VP at 74.4 wt% conversion of 2,6- lutidine at TOS = 6 h. EXAMPLE 13:

The calcination or activation temperature of the ZSM-5 catalyst was also varied in the temperature range of 420°C to 700°C. The reaction of 2,6-lutidine and formaldehyde was carried out over KZSM-5 (30, 3wt%). The liquid product selectivities were 36.1 % 2,6-DVP and 60.0 % 2M6VP at 51.5 wt% conversion of 2,6- lutidine at TOS = 6 h and calcination temperature was 420°C, 0.5 h^"1 W.H.S.V. The catalyst was 4 g with 18-30 mesh size and feed rate 2 ml.h^"1. The liquid product selectivities were 33.5 % 2,6-DVP and 66.2 % 2M6VP at 48.4 wt% conversion of 2,6- lutidine at TOS = 5+6 h. EXAMPLE 14:

The weight percent potassium impregnated in the HZSM-5 catalyst was also varied from 1 wt% to 4 wt%. The reaction of 2,6-lutidine and formaldehyde was carried out over K-ZSM-5 (30) at 300°C and 0.5 h^"1 W.H.S.V. The molar ratio of 2,6- lutidine: formaldehyde was 1:4. The weight of the catalyst was 4 g with 18-30 mesh size and feed rate 2 ml.h^"1. The liquid product selectivities were 24.3 % 2,6-DVP and 75.7 % 2M6VP at 34.0 wt% conversion of 2,6-lutidine at TOS = 6 h and for 1 wt% KZSM-5. The liquid product selectivities were 61.8 % 2,6-DVP and 37.9 % 2M6VP at 74.4 wt% conversion of 2,6-lutidine at TOS = 6 h for 4 wt% of potassium impregnation, KZSM-5. EXAMPLE 15:

The potassium precursor in the process of impregnation was also varied. The reaction of 2,6-lutidine and formaldehyde was carried out at 300°C and 0.5 h^"1 W.H.S.V. The molar ratio of 2,6-lutidine: formaldehyde was 1:4. The weight of the catalyst was 4 g with 18-30 mesh size and feed rate 2 ml.h^"1. The molar ratio of 2,6- lutidine to formaldehyde was 1:4. The liquid product selectivities were 49.8 % 2,6- DVP and 50.2 % 2M6VP at 64.7 wt% conversion of 2,6-lutidine at TOS = 6 h for KO*Bu as a precursor. Similarly the following precursors were studied, KNO₃, KF, KOAc, K₃PO₄ and KOH. The conversion of 2,6-lutidine was varied from 51% to 80% with 36 to 56 % of selectivity for 2,6-DVP.

Claims

We claim:

1. A process for the simultaneous production of 2,6-divinylpyridine and 2-methyl- 6-vinylpyridine comprising reacting 2,6-lutidine with formaldehyde in a catalytic zone containing a modified zeolite catalyst, the temperature of the catalytic zone being in the range of 200 to 450°C₃ the reaction being carried out at a weight hourly space velocity in the range of 0.25 to 1.0 h^"1, the molar ratio of 2,6- lutidine to formaldehyde being 1:1 to 1:4.

2. A process as claimed in claim 1 wherein the modified zeolite catalyst comprises a modified ZSM-5 pentasil type zeolite catalyst.

3. A process as claimed in claim 2 wherein the modified ZSM-5 catalyst is a ZSM- 5 catalyst modified by an alkali or alkaline earth metal ion selected from the group consisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺.

4. A process as claimed in claim 2 wherein the modified ZSM-5 catalyst is a two cation modified ZSM-5.

5. A process as claimed in claim 4 wherein the two cation modified ZSM-5 catalyst is Cs-K-ZSM-5.

6. A process as claimed in claim 3 wherein the weight percent of the alkali or alkaline earth metal ion in ZSM-5 is in the range of 1 wt % to 4 wt %.

7. A process as claimed in claim 3 wherein the ZSM-5 catalyst is modified by potassium ion, the potassium ion source being selected from the group consisting of KO'Bu, KOH, KF, KNO₃, K₃PO₄ and KOAc, to improve the yield and selectivity of 2,6-divinylpyridine.

8. A process as claimed in claim 2 wherein the modified zeolite is 3 wt% KZSM-5, calcined at a temperature in the range of 400°C to 700°C.

9. A process as claimed in claim 1 wherein the temperature of the catalytic zone is 300°C.

10. A process as claimed in claim 1 wherein the molar ratio of formaldehyde to 2,6- lutidine is 4:1.

11. A process as claimed in claim 1 wherein the weight hourly space velocity in the process is 0.5 h^"1.