Process for the selective production of N-methyl-2-pyrrolidone (NMP)

Abstract

This invention relates to an improved process for the selective production of N-methyl pyrrolidone (NMP) from gamma-butyrolactone and monomethyl amine preferably in aqueous form in the presence of a catalyst under comparatively milder conditions than the processes well known in the prior art of literature. The process is economically viable as it provides higher yield and selectivity for NMP which reduces the cost of separation of NMP from GBL. The catalyst shows good recyclability without significant loss in catalytic activity and no frequent regeneration is required.

Claims

1. A process for selective production of N-methyl-2-pyrrolidone (NMP) comprising: a) reacting feedstock monomethyl amine (MMA) and gamma-butyrolactone (GBL) in a single step in a continuously stirred tank reactor (CSTR) at a molar ratio of MMA to GBL in the range of 1 to 2, in the presence of catalyst wherein the catalyst comprises 5-15% of Al and consists of a bronsted acidic support which is a class of zeolitic material with SiO.sub.2 to Al.sub.2O.sub.3 molar ratio of 70 to 100 having specific surface area of 400 to 500 m.sup.2/g and modified by oxide of one or more metals selected from Zr and W to the percentage of metal loading of 1 to 30 parts by weight of the support with catalyst content between 1 to 10% of total feedstock, at operating condition of temperature 130 to 250 C. and pressure 5 to 70 at 500 to 1000 agitator speed, for a period of 30 to 180 minutes to obtain a reaction mixture; b) cooling the reaction mixture to a temperature in the range of 20 to 25 C.; c) separating the catalyst from the reaction mixture of step b) by known methods; d) separating the product from reaction mixture of step c) by evaporation or distillation to obtain NMP at selectivity to 99% at a conversion of GBL to 98%; and e) recycling the catalyst to reactor after repeating the steps a) to d) several times.

2. The process of claim 1, wherein said MMA is in aqueous form.

3. The process of claim 2, wherein said MMA is in concentration by weight of up to 40%.

4. The process of claim 1, wherein percentage weight of metal loading in catalyst is 5 to 20.

5. The process of claim 4, wherein percentage weight of metal loading in catalyst is 10 to 15.

6. The process of claim 1, wherein the support used in the formulation of the catalyst has SiO.sub.2 to Al.sub.2O.sub.3 molar ratio of 80 to 90 and specific surface area of 420 to 450 m.sup.2/g.

7. The process of claim 1, wherein amount of catalyst used with respect to the total feed is in a range of 1 to 5% by wt.

8. The process of claim 1, wherein the catalyst used is in the form of powder to a particle size of 20-30 mesh.

9. The process of claim 1, wherein the catalyst used for several runs is recycled back after stirring with a solvent at temperature 60-90 C. under reflux and drying in oven for a period of 6 to 12 hours at 80 to 110 C.

10. The process of claim 9, wherein the solvent used for the washing of the catalyst for recycled use is a low boiling chemical.

11. The process of claim 10, wherein the low boiling chemical is acetone, dimethylene chloride, benzene, or petroleum ether.

12. The process of claim 1, wherein purity of NMP is 99.99%.

13. The process of claim 1, wherein recovered unreacted monomethyl amine is recycled back.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) According to this invention, the process involves the production of N-methyl-2-pyrrolidone (NMP) by reacting monomethyl amine (MMA) preferably in aqueous form with gamma-butyrolactone in a batchwise operation in a single step in a typical CSTR in presence of a catalyst. In an alternative approach, MMA preferably in aqueous form is introduced into the reactor containing GBL and the catalyst premixed under a pressure of 5 to 70 bar preferably 20 to 30 bar. In another alternative approach, GBL is introduced into the reactor containing MMA preferably in aqueous form and the catalyst premixed under a pressure of 5 to 70 bar preferably 20 to 30 bar. The concentration of MMA in aqueous solution may be up to 40% by weight and the MMA is introduced to the reactor at a molar ratio to GBL of 1 to 2 more preferably 1 to 1.5 more particularly 1 to 1.15. The amount of the catalyst used is 1 to 20 parts preferably 1 to 10 parts more particularly 1 to 5 parts by weight of the total feed material. The reaction mixture is then heated to the desired temperature in the range of 130 to 250 C. preferably 150 to 200 C. and kept for residence time of 30 to 180 is minutes preferably 60 to 120 minutes under proper agitation. The reactor is then cooled down to room temperature and the catalyst is separated by filtration from the reaction product mixture. The reaction product collected is therefore subjected to either of the process of separation by evaporation or distillation to produce NMP at selectivity to 99% at a conversion of GBL to 98%.

(2) Accordingly, the present invention provides an improved process for the selective production of NMP at a milder condition than the processes mentioned in the prior art of literature in presence of a catalyst.

(3) In accordance with the present invention, the catalyst used is a typical acidic catalyst consisting of a bronsted acidic support and modified by oxide of one or in their combination among Al, Zr, W to the percentage of metal loading of 1 to 30 parts preferably 5 to 20 parts more particularly 10 to 15 parts by weight of the support.

(4) In accordance with the present invention, the catalyst used is prepared by conventional incipient wetness impregnation method by dissolving appropriate quantity of precursor salt of the metal in excess of a low boiling solvent preferably demineralized water and bringing the solution in contact of the support material preferably in powder form and stirring the mixture at temperature in the range of 40 to 60 C. until a slurry is obtained, followed by drying in oven at 110 C. for 6 to 12 hours preferably 8 to 10 hours and finally calcining at 450 C. for a period of 3 to 6 hours preferably 4 to 5 hours under continuous flow of air.

(5) In accordance with this invention, the support used in the formulation of the catalyst is a class of zeolitic material with SiO.sub.2 to Al.sub.2O.sub.3 mole ratio of 70 to 100 preferably 80 to 90 having specific surface area of 400 to 500 m.sup.2/g preferably 420 to 450 m.sup.2/g.

(6) In accordance with this invention, the catalyst used is in the form of powder to a particle size of 20 to 30 mesh.

(7) In accordance with this invention, the catalyst can be recycled back without any drastic change in activity after several runs.

(8) In accordance with this invention, the catalyst is thoroughly washed after number of experiments by stirring with a low boiling solvent like acetone, dimethylene chloride, benzene, methanol, petroleum ether etc. at temperature of 60 to 90 C. under reflux followed by drying in oven at 80 to 110 C. for a period of 6 to 12 hrs.

(9) In accordance with this invention the pure NMP is obtained after separation of water and MMA either by evaporation or distillation. The recovered MMA can further be used up in the process mentioned herein.

(10) The invention as described in detail in the examples given below which are provided by way of illustration only and therefore should not be construed to limit the scope of the present invention.

EXAMPLES

(11) The synthesis of NMP was carried out under the conditions indicated below in a batch CSTR consisting of a reactor vessel of volume 100 ml and made of high quality stainless steel. The reactor is fitted with an agitator which enables to mix the reactants with catalyst, a thermocouple inside the vessel that detects the reaction mixture temperature and a probe that detects the pressure inside the vessel. The pressure inside the vessel is maintained by using nitrogen gas supplied from a high pressure cylinder during the filling of reactants into the vessel. The external heating jacket enables to achieve the reaction temperature in the vessel very smoothly. For the safety precautions, the vessel is filled with reactants and catalyst up to 50% volume of the vessel. The agitator can be adjusted to a speed of maximum up to 3000 rpm in order to mix up the reactants with catalyst very well. Once the residence time gets over, the reaction is quenched by cooling the reactor vessel with ice water to bring the content of the vessel at room temperature. The pressure is released from vent valve and the content of the mixture is employed to filtration for the separation of the catalyst. Once the catalyst is separated, the product mixture is employed for evaporation of water and unreacted MMA from the solution. The catalyst so separated is directly used for recycle experiments The products left after evaporation of the lighters, are then analyzed by Gas Chromatography equipped with a FID detector precalibrated to measure the content of GBL, NMP and by-products to finally calculate the conversion of GBL and selectivity to NMP production as per:

(12) $\mathrm{Conversion}\left(\%\right)=\frac{\mathrm{moles}\mathrm{of}\mathrm{GBL}\mathrm{in}\mathrm{feed}\text{-}\mathrm{moles}\mathrm{of}\mathrm{GBL}\mathrm{in}\mathrm{product}}{\mathrm{moles}\mathrm{of}\mathrm{GBL}\mathrm{in}\mathrm{feed}}100$$\mathrm{selectivity}\left(\%\right)=\frac{\mathrm{moles}\mathrm{at}\mathrm{NMP}\mathrm{in}\mathrm{product}}{\mathrm{moles}\mathrm{of}\mathrm{GBL}\mathrm{in}\mathrm{feed}\text{-}\mathrm{moles}\mathrm{of}\mathrm{GBL}\mathrm{in}\mathrm{product}}100$

(13) The catalyst used is comprised of 15% of Al in the form of oxide loaded on H-ZSM-5 (SiO.sub.2 to Al.sub.2O.sub.3 molar ratio 80, typical surface area of 425 m.sup.2/g) in the reaction mentioned above. The catalyst is prepared by dissolving 21.2805 g of Al(NO.sub.3).sub.3.9H.sub.2O in about 40 ml of demineralized water and stirred with 10 g of powdered HZSM-5 at temperature 60 C. until a thick slurry is obtained. The slurry is then kept at room temperature for 24 hours and dried in oven at 110 C. for 12 hours. Final catalyst is obtained after calcination of the dried material in a tubular furnace by heating it up to temperature of 450 C. at a ramp of 2 C./min and keeping at 450 C. for 5 hours under a constant flow of air.

(14) Following are the condition and result of the experiments.

(15) TABLE-US-00001 Residence Agitator GBL Selectivity Experiment Temperature Pressure Molar ratio: time speed conversion for NMP No. ( C.) (bar) MMA to GBL (minute) (rpm) (%) (%) 1 150 30 1 120 500 99.876 99.94 2* 200 25 1 90 500 99.85 99.92 3* 200 25 1.15 120 500 99.55 99.65 4 200 30 1.15 120 1000 99.5 98.95 5 200 30 1.15 120 500 80.35 78.5 6 200 30 1.15 120 500 94.56 93.5 7 200 30 1.15 120 500 95.78 93.55 8 200 30 1.15 120 500 96.35 95.66 9 200 30 1.15 120 500 99.85 99.89 10 200 30 1.15 120 500 99.95 99.65 11 200 30 1.15 120 500 93.5 92.00 12 200 30 1.15 120 500 92.25 90.75 (*with recycled catalyst)

(16) The catalyst combination used for the above experiments:

(17) TABLE-US-00002 Catalyst content % Al loading in with respect to Experiment the form of oxide the total feed No. (% weight) content (% weight) 1 15 1 2* 15 1 3* 15 1 4 15 1 5 0 1 6 5 1 7 10 1 8 20 1 9 15 3 10 15 5 11 5 1 (% Zr loading in the form of oxide) 12 5 1 (% W loading in the form of oxide) (*with recycled catalyst)

Advantages of the Present Invention

(18) The present process produces NMP at high selectivity from MMA preferably in aqueous form and GBL at milder condition than that stated in prior art of literature. The present invention uses a catalyst that can be used for a number of runs at a stretch without necessity of regeneration frequently. The present invention provides a low cost process for the production of NMP.