HYDROGENATION PROCESS

Abstract

A process for the production of heterocyclic quaternary ammonium salts or hydroxides is disclosed. The process comprises a continuous hydrogenation step, in which an unsaturated heterocyclic amine is reacted with hydrogen to form a saturated heterocyclic amine; a first continuous N-alkylation step, in which the saturated heterocyclic amine is alkylated to produce an intermediate saturated heterocyclic amine having an increased degree of substitution compared to the saturated heterocyclic amine; and one or more further N-alkylation steps in which the intermediate saturated heterocyclic amine is N-alkylated to the heterocyclic quaternary ammonium salt or hydroxide. A process of producing a saturated heterocyclic amine is also disclosed. The process comprises reacting an unsaturated heterocyclic amine with hydrogen in a vapour phase reaction at a pressure of not more than 70 bar and a temperature in the range of from 150° C. to 350° C. A process of N-alkylating a saturated heterocyclic amine is also disclosed. The process comprises N-alkylating the saturated heterocyclic amine in a vapour phase reaction at a temperature of at least 2° C.

Claims

1. A process of N-alkylating a saturated heterocyclic amine, the process comprising N-alkylating the saturated heterocyclic amine in a vapour phase reaction at a temperature of at least 220° C.

2. A process according to claim 1 wherein the process comprises reacting the saturated heterocyclic amine with dimethyl ether.

3. A process according to claim 2, wherein the dimethyl ether is generated in situ by the etherification of methanol.

4. A process according claim 3, wherein the saturated heterocyclic amine and the method are fed to the process at a molar ratio of from at least 1 mole of alkanol per mole of saturated heterocyclic amine to not more than 20 moles of alkanol per mole of saturated heterocyclic amine.

5. A process according claim 1, wherein the pressure is in the range of from 1 bar to 100 bar.

6. A process according to claim 1 wherein the gas hourly space velocity is in the range of from 20 h.sup.−1 to 200 h.sup.−1.

7. A process according to claim 1, wherein the saturated heterocyclic amine comprises a piperidine ring or a pryyolidine ring.

8. A process according to claim 7, wherein the saturated heterocyclic amine is selected from the group consisting of: piperidine, 2-methyl piperidine, 3-methyl piperidine, 4-methyl piperidine, 2,6 dimethylpiperidine, 3,5 dimethylpiperidine, pyrrolidine, 2-methyl pyrrolidine, 3-methyl pyrrolidine, 2,4-dimethyl pyrrolidine, and 2,5-dimethyl pyrrolidine.

9. A process according to claim 1, wherein the saturated heterocyclic amine is a fully saturated heterocyclic amine.

10. A process according to claim 1, wherein the saturated heterocyclic amine is 3,5 dimethylpiperidine and the process produces an N-alkylation product comprising 1,3,5 trimethylpiperidine.

11. A process according to claim 1 wherein the process comprises feeding gaseous saturated heterocyclic amine to a reactor, N-alkylating the saturated heterocyclic amine in a vapour phase reaction in the reactor to produce an N-alkylation product, wherein the reactor inlet temperature is at least 220° C., and withdrawing a product stream comprising the N-alkylation product from the reactor, wherein the feeding and withdrawing are continuous.

12. A process according to claim 11, wherein liquid saturated heterocyclic amine is fed to a vaporiser where it is vaporised along with an alkylating reagent to create a mixed gaseous stream of alkylating reagent and saturated heterocyclic amine that is then fed to the reactor.

13. A process according to claim 12, wherein the alkylating reagent is methanol.

14. A process according to claim 1, wherein the vapour phase reaction occurs over a catalyst comprising alumina.

15. A process according to claim 14, wherein the catalyst comprises λ-alumina.

16. A process according to claim 14, wherein the the catalyst also comprises silica.

17. A process for the production of heterocyclic quaternary ammonium salts or hydroxides, the process comprising a continuous hydrogenation step, in which an unsaturated heterocyclic amine is reacted with hydrogen to form a saturated heterocyclic amine; a first continuous N-alkylation step, in which the saturated heterocyclic amine is N-alkylated to produce an intermediate saturated heterocyclic amine having an increased degree of substitution compared to the saturated heterocyclic amine; and one or more further N-alkylation steps in which the intermediate saturated heterocyclic amine is N-alkylated to the heterocyclic quaternary ammonium salt or hydroxide.

18. A process according to claim 17, wherein the the process further comprises a counter ion swap step, in which a first counter ion on the heterocyclic quaternary ammonium salt or hydroxide is exchanged for a second counter ion.

19. A process according to claim 18, wherein the counter ion swap step is continuous.

20. A process according to claim 17, wherein the the hydrogenation step is in the vapour phase.

21. A process according to claim 17 13, wherein the the first continuous N-alkylation step is in the vapour phase.

22. A process according to claim 17, wherein the one or more further N-alkylation steps are continuous.

23. A process according to claim 17, wherein the unsaturated heterocyclic amine comprises a pyridine ring or a pyrrole ring, the saturated heterocyclic amine comprises a piperidine ring or a pyrrolidine ring, the intermediate saturated heterocyclic amine comprises a piperidine ring or a pyrrolidine ring, and the heterocyclic quaternary ammonium salt or hydroxide comprises a piperidinium ring or a pyrrolidinium ring.

24. A process according to claim 23, wherein the unsaturated heterocyclic amine is selected from the group consisting of: pyridine, 2-methyl pyridine, 3-methyl pyridine, 4-methyl pyridine, 2,6 lutidine, 3,5 lutidine, pyrrole, 2-methyl pyrrole, 3-methyl pyrrole, 2,4-dimethylpyrrole, and 2,5-dimethylpyrrole; the saturated heterocyclic amine is selected from the group consisting of: piperidine, 2-methyl piperidine, 3-methyl piperidine, 4-methyl piperidine, 2,6 dimethylpiperidine, 3,5 dimethylpiperidine, pyrrolidine, 2-methyl pyrrolidine, 3-methyl pyrrolidine, 2,4-dimethyl pyrrolidine, and 2,5-dimethyl pyrrolidine; the intermediate saturated heterocyclic amine is selected from the group consisting of: 1-methylpiperidine, 1,2-dimethyl piperidine, 1,3-dimethyl piperidine, 1,4-dimethyl piperidine, 1,2,6 trimethylpiperidine, 1,3,5 trimethylpiperidine, 1-methylpyrrolidine, 1,2-dimethyl pyrrolidine, 1,3-dimethyl pyrrolidine, 1,2,4-trimethyl pyrrolidine, and 1,2,5-trimethyl pyrrolidine; and the heterocyclic quaternary ammonium salt or hydroxide is selected from the group consisting of: 1,1-dimethylpiperidinium salt or hydroxide, 1,1,2-trimethylpiperidinium salt or hydroxide, 1,1,3-trimethylpiperidinium salt or hydroxide, 1,1,4-trimethylpiperidinium salt or hydroxide, 1,1,2,6 tetramethylpiperidinium salt or hydroxide, 1,1,3,5 tetramethylpiperidinium salt or hydroxide, 1,1-dimethylpyrrolidinium salt or hydroxide, 1,1,2-trimethylpyrrolidinium salt or hydroxide, 1,1,3-trimethylpyrrolidinium salt or hydroxide, 1,1,2,4-tetramethyl pyrrolidine salt or hydroxide, and 1,1,2,5-tetramethyl pyrrolidine salt or hydroxide.

25. A process according to claim 24, wherein the unsaturated heterocyclic amine is 3,5 lutidine, the saturated heterocyclic amine is 3,5 dimethylpiperidine, the intermediate saturated heterocyclic amine is 1,3,5 trimethylpiperidine and the heterocyclic quaternary ammonium salt or hydroxide is 1,1,3,5 tetramethylpiperidinium hydroxide.

26. A process according to claim 17, wherein the hydrogenation step comprises reacting an unsaturated heterocyclic amine with hydrogen in a vapour phase reaction at a pressure of not more than 70 bar and a temperature in the range of from 150° C. to 350° C.

27. A process according to claim 17, wherein the first N-alkylation step comprises N-alkylating the saturated heterocyclic amine in a vapour phase reaction at a temperature of at least 220° C.

28. A process according to claim 17, wherein the wherein the saturated heterocyclic amine is collected from the hydrogenation step as a condensed liquid and vaporised and fed to the first N-alkylation step.

29. A process according to claim 28 wherein the collection is carried out continuously.

30. A process according to claim 29, wherein the collection is carried out by passing a product stream from the hydrogenation step to a knock-out pot in which the saturated heterocyclic amine is condensed and separated from hydrogen in the product stream.

31. A process according to claim 17, wherein a product stream from the hydrogenation step, comprising the saturated heterocyclic amine and hydrogen, is fed directly to the first N-alkylation step.

32. A process according to claim 17, wherein the product stream is a gas stream and the product stream is kept in the gas phase and fed to the first N-alkylation step.

33. A process according to claim 17, wherein the hydrogenation step and the first N-alkylation step are carried out in the same reactor.

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Description

DESCRIPTION OF THE DRAWINGS

[0058] Embodiments of the present invention will now be described, by way of example, and not in any limitative sense, with reference to the accompanying drawings, of which:

[0059] FIG. 1 is a flowsheet of a process according to the first aspect of the invention;

[0060] FIG. 2 is a graph of conversion and selectivity;

[0061] FIG. 3 is a graph of conversion and activity at a ratio of 800 moles hydrogen per mole of lutidine;

[0062] FIG. 4 is a graph of conversion and activity at a ratio of 600 moles hydrogen per mole of lutidine;

[0063] FIG. 5 is a graph of conversion and activity at a ratio of 400 moles hydrogen per mole of lutidine;

[0064] FIG. 6 is a graph of conversion and activity plotted against temperature;

[0065] FIG. 7 is a flowsheet of a process according to the second aspect of the invention;

[0066] FIG. 8 is a flowsheet of processes according to the first and second aspects of the invention;

[0067] FIG. 9 is a flowsheet of processes according to the first and second aspects of the invention;

[0068] FIG. 10 is a flowsheet of processes according to the third aspect of the invention;

[0069] FIG. 11 is a flowsheet of processes according to the first second and third aspects of the invention;

[0070] FIG. 12 is a graph of conversion against time;

[0071] FIG. 13 is a graph of conversion against pressure; and

[0072] FIG. 14 is a graph of conversion for 4 different catalysts.

DETAILED DESCRIPTION

[0073] In FIG. 1, hydrogen gas 102 is compressed 104 and fed to a vaporiser 105. Unsaturated heterocyclic amine, in this embodiment 3,5 lutidine 101, is pumped 103 into the vaporiser 105, where it is vaporised into the hydrogen gas. The stream exiting the vaporiser 105 comprises gaseous 3,5 lutidine and hydrogen gas and is heated 106 and fed to a reactor 107. In the reactor 107 a vapour phase reaction between the 3,5 lutidine and the hydrogen takes place and 3,5 dimethylpiperidine is formed. Preferably the pressure in the reactor 107 is not more than 70 bar and the inlet temperature of the reactor 107 is preferably in the range of from 150° C. to 350° C. Product from the reactor 107, which includes the 3,5 dimethylpiperidine is cooled, first by heat exchange 108 with a hydrogen recycle stream 114 and then by cooling 111, before being fed to a hydrogen knock-out pot 112. In hydrogen knock out pot 112, the product 3,5 dimethylpiperidine condenses and is produced as liquid 3,5 dimethylpiperidine 113, while the hydrogen remains as a gas and is produced overhead. The hydrogen is either compressed 109 and recycled in hydrogen recycle stream 114, or it is purged 110.

[0074] In FIG. 7, a feed comprising 3,5 dimethylpiperidine 201 and methanol 202 is fed to a vaporiser 203 in which the 3,5 dimethylpiperidine 201 and the methanol 202 are vaporised to form a mixed gas stream 204 comprising 3,5 dimethylpiperidine and methanol. The mixed gas stream 204 is fed to an N-alkylation reactor 205, where the methanol is converted to dimethyl ether and reacts with the 3,5 dimethylpiperidine, for example over an alumina catalyst, to produce 1,3,5 trimethylpiperidine, which is withdrawn in a product stream 206. The N-alkylation reactor 205 preferably has an inlet temperature of at least 220° C.

[0075] In FIG. 8, a stream comprising 3,5 lutidine 1101 is fed to a vaporiser 1105 where it is vaporised into a stream of hydrogen 1102. The resulting gas stream is fed to a hydrogenation reactor 1107, where the 3,5 lutidine is hydrogenated to 3,5 dimethylpiperidine, for example over a nickel catalyst. The pressure in the reactor 1107 is preferably not more than 70 bar and the inlet temperature of the reactor 1107 is preferably in the range of from 150° C. to 350° C. A product stream 1201 from the hydrogenation reactor 1107 is mixed with methanol 1202 and heated in heater 1207 before being passed to an N-alkylation reactor 1205. In the N-alkylation reactor 1205, the methanol forms dimethyl ether, which reacts with the 3,5 dimethylpiperidine, for example over an alumina catalyst, to produce 1,3,5 trimethylpiperidine, which is withdrawn in a product stream 1206. The N-alkylation reactor 1205 preferably has an inlet temperature of at least 220° C. Hydrogen is separated from the product stream 1206 and recycled via hydrogen recycle stream 1114.

[0076] In FIG. 9, a stream of 3,5 lutidine 2101 is fed to a vaporiser 2105 where it is vaporised into a stream of hydrogen 2102. The resulting gas stream is fed to a hydrogenation reactor 2107, where the 3,5 lutidine is hydrogenated to 3,5 dimethylpiperidine, for example over a nickel catalyst. A product stream from the hydrogenation reactor 2107 is fed to a knock-out pot 2112, where hydrogen gas comes off overhead and is recycled via hydrogen recycle line 2114, and a 3,5 dimethylpiperidine stream 2201 comes off as a liquid. The 3,5 dimethylpiperidine stream 2201 is mixed with methanol 2202 and fed to a vaporiser 2203 before being passed to an N-alkylation reactor 2205. In the N-alkylation reactor 2205, the methanol forms dimethyl ether, which reacts with the 3,5 dimethylpiperidine, for example over an alumina catalyst, to produce 1,3,5 trimethylpiperidine, which is withdrawn in a product stream 2206. The N-alkylation reactor 2205 has an inlet temperature of at least 220° C.

[0077] In FIG. 10 a process for producing 1,1,3,5 tetramethylpiperidinium hydroxide involves a hydrogenation step 301, in which 3,5 lutidine is hydrogenated to 3,5 dimethylpiperidine, a first N-alkylation step 302, in which the 3,5 dimethylpiperidine is alkylated to 1,3,5 trimethylpiperidine, a second N-alkylation step 303 in which the 1,3,5 trimethylpiperidine is alkylated to one or more of 1,1,3,5 tetramethylpiperidinium methyl carbonate, 1,1,3,5 tetramethylpiperidinium hydrogen carbonate and 1,1,3,5 tetramethylpiperidinium hydroxide, and a counter-ion swap step 304, in which 1,1,3,5 tetramethylpiperidinium methyl carbonate and 1,1,3,5 tetramethylpiperidinium hydrogen carbonate are converted to 1,1,3,5 tetramethylpiperidinium hydroxide. In a particular embodiment, the hydrogenation step 301 and the N-alkylation step 302 are continuous vapour phase reactions. The hydrogenation step 301 and the first N-alkylation step 302, may for example be as described in relation to any of FIGS. 1 to 9 or 11 to 14.

[0078] In FIG. 11, hydrogen gas 3102 is compressed 3104 and fed to a vaporiser 3105. Unsaturated heterocyclic amine, in this embodiment 3,5 lutidine 3101, is pumped 3103 into the vaporiser 3105, where it is vaporised into the hydrogen gas. The stream exiting the vaporiser comprises gaseous 3,5 lutidine and hydrogen gas and is heated 3106 and fed to a reactor 3107. In the reactor 3107 a vapour phase reaction between the 3,5 lutidine and the hydrogen takes place and 3,5 dimethylpiperidine is formed. The pressure in the reactor 3107 is preferably not more than 70 bar and the inlet temperature of the reactor 3107 is preferably in the range of from 150° C. to 350° C. Product 3201 from the reactor 3107 is mixed with methanol 3202 which is fed via pump 3209 and heated in heat exchanger 3208 and heater 3207 before being fed to N-alkylation reactor 3205. In the N-alkylation reactor 3205, the methanol forms dimethyl ether, which reacts with the 3,5 dimethylpiperidine, for example over an alumina catalyst, to produce 1,3,5 trimethylpiperidine. The N-alkylation reactor 3205 has an inlet temperature of at least 220° C. The product from the N-alkylation reactor 3205, which includes the 1,3,5 trimethylpiperidine is cooled in heat exchanger 3208, heat exchanger 3106, heat exchanger 3108 and cooler 3111, before being fed to a hydrogen knock-out pot 3112. In hydrogen knock out pot 3112, the product 1,3,5 trimethylpiperidine condenses and is produced as liquid 1,3,5 trimethylpiperidine, while the hydrogen remains as a gas and is produced overhead. The hydrogen is either compressed 3109 and recycled in hydrogen recycle stream 3114, or it is purged 3110. The liquid 1,3,5 trimethylpiperidine is heated 3212 and passed to second N-alkylation reactor 3214, to which is also fed dimethyl carbonate 3210 via pump 3211 and heater 3213. In the second N-alkylation reactor 3214 the 1,3,5 trimethylpiperidine may react with the dimethyl carbonate to form a mixture of 1,1,3,5 tetramethylpiperidinium carbonate, 1,1,3,5 tetramethylpiperidinium hydrogen carbonate and 1,1,3,5 tetramethylpiperidinium hydroxide. The product from the second N-alkylation reactor 3214 is cooled 3215 and fed to a dimethyl carbonate decanter 3217, to which water 3218 is also supplied. In the dimethyl carbonate decanter 3217, the dimethyl carbonate is separated and recycled via pump 3216, while the mixture of 1,1,3,5 tetramethylpiperidinium carbonate, 1,1,3,5 tetramethylpiperidinium hydrogen carbonate and 1,1,3,5 tetramethylpiperidinium hydroxide is sent to the counter-ion swap 3222.

[0079] There, the mixture of 1,1,3,5 tetramethylpiperidinium carbonate, 1,1,3,5 tetramethylpiperidinium hydrogen carbonate and 1,1,3,5 tetramethylpiperidinium hydroxide is contacted with sodium hydroxide or calcium hydroxide 3219, to convert the 1,1,3,5 tetramethylpiperidinium carbonate and 1,1,3,5 tetramethylpiperidinium hydrogen carbonate into 1,1,3,5 tetramethylpiperidinium hydroxide. A solution of sodium or calcium carbonate 3220 and a solution of the 1,1,3,5 tetramethylpiperidinium hydroxide 3221 are withdrawn from the counter-ion swap step 3222.

Hydrogenation Examples

[0080] The process of FIG. 1 was tested in the following example run. Initially the reactor was charged with 115.8 g (equivalent to 150 ml) HTC 500RP, available from Johnson Matthey Plc, at a concentration of 0.772 g ml.sup.−1.

[0081] The catalyst was activated by ramping the temperature to 230° C. from room temperature over 12 hours at 50 psig under a hydrogen flow of 50 normal l/h. The recycle compressor was in operation during the reduction, generating an approximate recycle flow of 300 g/h.

[0082] A feed of 3,5 lutidine was then introduced with a reactor inlet temperature of 185° C., a reactor pressure of 60 barg, a liquid hourly space velocity (LHSV) based on the liquid feed of 3,5 lutidine to the vaporiser divided by the volume of the catalyst of 0.4 h.sup.−1 and a hydrogen: 3,5 lutidine ratio of 800 moles of hydrogen per mole of 3,5 lutidine. After approximately 40 hours on line the 3,5 lutidine conversion stabilised at approximately 99.91 wt %. After 70 hours on line the reactor inlet temperature was increased to 190° C. as the conversion had decreased to 99.88 wt %. This resulted in an increase in conversion to 99.97 wt %. After 143 hours on line the LHSV was increased to 0.5 h.sup.−1. The conversion stabilised at approximately 99.78 wt %. These conditions were maintained until 256 hours on line. The lutidine conversion and catalyst selectivity for these 256 hours on line is shown in FIG. 2.

[0083] Following an extended shutdown, the unit was re-started at a reactor inlet temperature of 190° C., a reactor inlet temperature of 195° C., a reactor pressure of 60 barg, a LHSV of 0.5 h.sup.−1 and a hydrogen: 3,5 lutidine ratio of 800 moles of hydrogen per mole of 3,5 lutidine.

[0084] The conversion and activity for this next period of the run are shown in FIG. 3. It can be seen that there was no evidence of any significant loss of activity on re-start. This suggesting that the catalyst is stable enough to tolerate an enforced plant shutdown. The catalyst retained activity throughout the run, with a very slow deactivation rate.

[0085] The recycle hydrogen gas was then reduced to produce a hydrogen: 3,5 lutidine ratio of 600 moles of hydrogen per mole of 3,5 lutidine, while all other parameters remained the same as before. The conversion and activity for this period are shown in FIG. 4, which demonstrates that there was no evidence of gross deactivation during this run.

[0086] To achieve a hydrogen: 3,5 lutidine ratio of 400 moles of hydrogen per mole of 3,5 lutidine while maintaining a high gas flow the LHSV was increased to 0.72 h.sup.−1 while keeping all other parameters the same as before. The conversion and activity for this period are shown in FIG. 5. There was no evidence of any significant increase in the rate of catalyst deactivation.

[0087] To simulate operation with an aged, less active catalyst, the LHSV was increased to 1.0, while maintaining a hydrogen: 3,5 lutidine ratio of 400 moles of hydrogen per mole of 3,5 lutidine.

[0088] After 660 hours on line this resulted in a 3,5 lutidine conversion of 92.76 wt %. There was no significant change in selectivity. For simplicity, assuming the drop-in conversion remains linear and starting at 99.5 wt % conversion then this is broadly equivalent to greater than 11000 hours on line, which is longer than the expected catalyst lifetime required for a commercial process.

[0089] To simulate a catalyst management strategy whereby the catalyst temperature is increased to offset the loss of activity with time the temperature was increased over time, with no discernible change in product selectivity throughout. This is shown in Table 1 and FIG. 6

TABLE-US-00001 TABLE 1 Effect of Temperature on Conversion and Activity Run 4 5 6 7 8 9 Temperature, 190 195 197 200 210 220 ° C. Time on 660 708 731 773 794 804 Line, h Conversion, 92.76 97.44 98.70 99.45 99.96 99.99 wt % Activity 2.62 3.67 4.33 5.17 6.22 6.91

[0090] It can be seen that acceptable conversions and activity are obtained across the temperature range.

[0091] The unit was returned to at a reactor inlet temperature of 190° C., a reactor inlet temperature of 195° C., a reactor pressure of 60 barg, a LHSV of 0.5 h.sup.−1 and a hydrogen: 3,5 lutidine ratio of 800 moles of hydrogen per mole of 3,5 lutidine. After 832 hours on line this resulted in a lutidine conversion of 99.58 wt % which equates to an activity of 2.80 suggesting that the catalyst has lost about 8% of activity over a period of at least 600 hours.

First N-Alkylation Examples

Vapour Phase N-Alkylation Example 1

[0092] An example vapour phase N-alkylation of 3,5 dimethylpiperidine to 1,3,5 trimethylpiperidine was carried out using a continuous vapour-phase process over a γ-alumina extrudate.

[0093] The reactor was operated at 190° C., with a pressure of 50 barg and a liquid hourly space velocity, based on the liquid feed rate of the 3,5 dimethylpiperidine prior to vaporisation divided by the volume of the catalyst, of 0.3 h.sup.−1. The hydrogen gas rate through the reactor was 240 normal I/h. The feed to the reactor contained 10.14 wt % methanol, 7.3 wt % cis 3,5 dimethylpiperidine, 2.65 wt % trans 3,5 dimethylpiperidine and 79.8 wt % cyclohexane. The cyclohexane was present as an inert diluent to aid with pumping control and plays no part in the reaction. After 49 hours on line of continuous operation this resulted in a 3.4 wt % selectivity to 1,3,5 trimethylpiperidine.

[0094] Keeping all other parameters the same, the temperature was increased to 195° C. After 90.2 hours on line of continuous operation this resulted in a slightly higher selectivity to 1,3,5 trimethylpiperidine of 4.1 wt %.

[0095] As the conversion to 1,3,5 trimethyl piperidine was low, the temperature was increased to 225° C. After 115 hours on line of continuous operation this afforded a selectivity to 1,3,5 trimethylpiperidine of 14.8 wt %, which is a significant increase from the selectivity of 4.1 wt % at 195° C.

[0096] The temperature was further increased to 235° C. and the gas rate was reduced by 50% (from 240 to 120 normal I/h) to simulate an increased bed volume; noting that the liquid hourly space velocity was still the same as the previous run. After 137 hours on line of continuous operation this afforded a selectivity to 1,3,5 trimethylpiperidine of 32.9 wt %.

[0097] The temperature was increased to 250° C. and the gas rate reduced to 80 normal I/h. After 161 hours on line of continuous operation this resulted in an increased selectivity to 1,3,5 trimethylpiperidine of 57.1 wt %.

[0098] The gas rate was further reduced to 40 normal I/h. After 178.9 hours on line of continuous operation, this resulted in a selectivity to 1,3,5 trimethyl piperidine of 67.7 wt %.

[0099] The same reactor was then operated at a temperature of 250° C. a pressure of 50 barg, a hydrogen flowrate of 40 normal I/h, a LHSV of 0.23 h.sup.−1 and a methanol to 3,5 dimethylpiperidine molar ratio of 8 moles methanol per mole of 3,5 dimethylpiperidine. After 195 hours on line this resulted in a conversion of about 80 wt % with 1,3,5 trimethylpiperidine isomers generated at high selectivity.

[0100] Keeping all other parameters the same, the temperature was increased to 275° C. After 223 hours on line this resulted in greater than 99 wt % conversion and good selectivity to 1,3,5 trimethylpiperidine isomers.

Vapour Phase N-Alkylation Example 2

[0101] A further run was conducted, again using a continuous vapour-phase process over a γ-alumina extrudate. A feed of 29.78 wt % methanol and 68.66 wt % 3,5 dimethylpiperidine was fed to a reactor having an inlet temperature of 262° C., a reactor pressure of 10 barg, a liquid hourly space velocity based on the volumetric flowrate of liquid 3,5 dimethylpiperidine fed to the vaporiser of 0.79 h.sup.−1. The methanol: 3,5 dimethylpiperidine molar ratio was thus 1.5:1. After 176 hours on line of continuous operation this afforded a 3,5 dimethylpiperidine conversion of 99.16 wt % with a product selectivity of 94.67 wt %.

[0102] Keeping all other parameters the same, the methanol: 3,5 dimethylpiperidine molar ratio was reduced to 1:1. After 212 hours on line of continuous operation this afforded a 3,5 dimethylpiperidine conversion of 96.28 wt % with a selectivity to the desired product of 92.82 wt %. The decrease in conversion is thought to be as a result of the absence of a molar excess of methanol to generate dimethyl ether. However, the conversion is still acceptable and this is thought to be because although 2 moles of methanol are needed to generate dimethyl ether, 1 mole of methanol is regenerated in the N-alkylation process and a 1:1 methanol: 3,5 dimethylpiperidine molar ratio therefore still gives an adequate result.

[0103] At 220 hours on line of continuous operation the feed was returned to a methanol: 3,5-dimethylpiperidine molar ratio of 1.5:1 and the LHSV increased to 1.0 h.sup.−1. The reactor inlet temperature was reduced to 233° C. After 260 hours on line of continuous operation this resulted in a 3,5 dimethylpiperidine conversion of 99.33 wt % and selectivity of 97.39 wt %.

[0104] At 265 hours on line of continuous operation the LHSV was increased to 1.1 h.sup.−1 with the other parameters remaining unchanged. After 308 hours on line of continuous operation this resulted in a 3,5-dimethylpiperidine conversion of 99.09 wt % and selectivity to 1,3,5-trimethylpiperidine of 94.26 wt %.

[0105] At 310 hours on line of continuous operation the LHSV was returned to 0.8 h.sup.−1 with a methanol: 3,5-dimethylpiperidine molar ratio of 1.5:1 at a reactor inlet temperature of 261° C. These conditions were maintained for approximately 350 hours to generate catalyst deactivation data. After 683 hours on line of continuous operation this afforded a 3,5-dimethylpiperidine conversion of 99.15 wt % and a selectivity to 1,3,5-trimethylpiperidine of 92.50 wt %.

[0106] As shown in FIG. 12 the catalyst performance was very stable with only a slight decrease in activity seen.

Vapour Phase N-Alkylation Example 3

[0107] Three runs at a methanol: 3,5 dimethylpiperidine molar ratio of 2:1, an inlet temperature of 260° C., an LHSV of 2.2 h.sup.−1 and pressures of 5 barg, 10 barg and 20 barg respectively were carried out in the continuous vapour phase reactor. These three runs show the impact of pressure on the process. For each run, two different silica/alumina catalysts having 3% silica were used. Both catalysts showed adequate conversion. The results for conversion in wt %, which are shown in FIG. 13, indicate that by increasing the pressure the 3,5 dimethylpiperidine conversion increases, although adequate conversion is observed at all pressures.

Vapour Phase N-Alkylation Example 4

[0108] A further experiment was carried out to compare 4 different catalysts. Catalysts A and B are silica/alumina catalysts having 3% silica, while catalysts C and D are alumina catalysts. The catalysts were used in a continuous vapour phase N-alkylation process at a methanol: 3,5 dimethylpiperidine molar ratio of 5:1, an inlet temperature of 260° C., an LHSV of 0.7 h.sup.−1 and a pressure of 10 barg. The results in FIG. 14 show that the average conversion for both types of catalyst was acceptable, but that the silica/alumina catalysts A and B had higher average conversions.

Vapour Phase Hydrogenation and N-Alkylation

[0109] A combined vapour phase hydrogenation and first N-alkylation may be achieved by the addition of methanol to the feed to the hydrogenation reactor to promote the gas phase N-alkylation reaction co-current with the hydrogenation reaction, via a dimethyl ether intermediate. This may be advantageous in reducing the number of reactors required. However, the formation of methane and water would potentially require a large purge from the hydrogen gas recycle to maintain an appropriate recycle gas molecular weight.

[0110] A feed composition of 9.6 wt % 3,5 lutidine, 10.1 wt % methanol and the remainder cyclohexane was vaporised and fed to a reactor operated at a temperature of 190° C., a pressure of 50 barg, an LHSV based on the volumetric liquid flow rate of 3,5 lutidine to the vaporiser divided by the volume of catalyst in the reactor of 0.3 h.sup.−1, a gas rate through the reactor of 240 normal l/h and a hydrogen: 3,5 lutidine ratio of 800 moles of hydrogen per mole of 3,5 lutidine. The cyclohexane is an inert diluent to allow for pumping control and plays no part in the reaction.

[0111] After 360 hours on line of continuous operation, this resulted in a 3,5 lutidine conversion of 98.77 wt %, with 31.7 wt % selectivity to 1,3,5 trimethylpiperidine, 50.0 wt % selectivity to cis 3,5 dimethylpiperidine and 18.3 wt % selectivity to trans 3,5 dimethylpiperidine.

[0112] Keeping all other parameters the same, the feed was changed to 10.1 wt % 3,5 lutidine and 89.8 wt % methanol. After 396 hours on line of continuous operation, this resulted in a 3,5 lutidine conversion of 99.23 wt % with 93.5 wt % selectivity to 1,3,5 trimethylpiperidine, 4.65 wt % selectivity to cis 3,5 dimethylpiperidine and 1.85 wt % selectivity to trans 3,5 dimethylpiperidine. The unit was operated at these conditions until 538 hours on line of continuous operation, at which point the 3,5 lutidine conversion was 99.80 wt % suggesting no loss of activity over this period of operation.

Comparative Example of Batch N-Alkylation

[0113] 20 ml 3,5 dimethylpiperidine was transferred into 200 g hot dimethyl carbonate at 200° C. in a 300 ml autoclave via a pump. Transferring the 3,5 dimethylpiperidine into the already hot dimethyl carbonate avoided the formation of unwanted carbamate when heating the autoclave. Samples were taken from a submerged dip-leg and analysed by gas chromatography (GC). The results are in table 2 below.

TABLE-US-00002 TABLE 2 Batch Liquid-Phase First N-Alkylation GC wt % 1,3,5- Cis-3,5 Trans-3,5 3,5 dimethyl- 1,3,5 trimethyl- Time Dimethyl trimethyl- dimethyl- dimethyl- 3,5 piperidine piperidine (mins) Methanol carbonate piperidine piperidine piperidine Lutidine Carbamate Total conversion wt % selectivity wt % 0 0.34 99.29 0.04 0.18 0.03 0.01 0.06 99.61 1 0.81 33.95 1.12 45.77 15.85 0.13 1.66 98.48 5 2.29 81.22 4.25 6.82 2.48 0.03 2.72 97.52 10 2.38 90.18 3.33 0.67 0.26 0.08 2.84 97.36 89.97 46.88 15 2.37 90.25 3.47 0.66 0.22 0.06 2.70 97.36 90.47 49.19 30 2.53 89.86 3.50 0.71 0.24 0.03 2.84 97.19 89.80 48.03 60 2.81 90.21 3.63 0.12 0.01 0.05 2.71 96.74 98.62 56.11 120 3.28 90.05 3.36 0.06 0.00 0.06 2.55 96.09 99.29 56.21

[0114] The samples are not representative of the autoclave contents until the 10-minute sample, because the 3,5 dimethylpiperidine was fed into the autoclave via the same dip-leg that was used to take the samples. The 3,5 dimethylpiperidine conversion reached 99.3 wt % after 120 minutes. However, the selectivity to the target 1,3,5 trimethylpiperidine was only 56.2 wt %, with significant losses to the carbamate species. There was also a quantity of solid precipitate produced during the test. This is likely the 1,1,3,5-tetramethylpiperidinium methyl carbonate salt that is formed by the second methylation step. This precipitate accounted for as much as 10 wt % of the samples taken.

[0115] Compared to the vapour phase N-alkylation example above, which affords a high conversion of 3,5 dimethylpiperidine and a high selectivity to 1,3,5 trimethylpiperidine, the batch autoclave N-alkylation was not very selective to the target 1,3,5 trimethylpiperidine and formed significant quantities of unwanted carbamate.

[0116] It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example, while the above examples use 3,5 lutidine as a feed to the hydrogenation, other unsaturated heterocyclic amines are contemplated as part of the invention. As explained above, the same deactivation issues that occur with 3,5 lutidine hydrogenation in the liquid phase would be expected to occur with other unsaturated heterocyclic amines and would be expected to be solved in the same manner by the process of the invention. Similarly, the advantages demonstrated above in relation to vapour phase N-alkylation of 3,5 dimethylpiperidine would be expected to apply to N-alkylation of other saturated heterocyclic amines.