Preparation of N-vinyl carboxamides in a series of reactor units

Abstract

Disclosed herein is a process for producing polymers of an N-vinyl carboxamide, including the steps of flowing a reaction mixture containing an aqueous liquid containing at least one polymerization initiator, N-vinyl carboxamide monomer or a monomer mixture containing N-vinyl carboxamide into a reactor system, and polymerizing the monomer or monomer mixture to produce the polymer of a N-vinyl carboxamide. The polymers resulting therefrom may be hydrolyzed to provide polymers containing vinyl amine units. Also disclosed herein is an apparatus suitable for producing the polymers.

Claims

1. A process for producing a polymer of an N-vinyl carboxamide, the process comprising: flowing a reaction mixture comprising an aqueous liquid comprising at least one polymerisation initiator, N-vinyl carboxamide monomer or a monomer mixture comprising N-vinyl carboxamide into a reactor system; and polymerising the monomer or monomer mixture to produce the polymer of N-vinyl carboxamide, wherein: the reactor system comprises a series of reactor units comprising a combination of at least one mixed flow reactor and at least one single pass tubular reactor, in which i) the at least one mixed flow reactor comprises at least one vessel comprising an internal mixer, an external mixer, or both, and ii) the at least one single pass tubular reactor comprises a tubular section disposed between two ends, at least one inlet and at least one outlet in which the reaction mixture flows through the single pass tubular reactor only once; and substantially none of the reaction mixture exits the single pass tubular reactor less than 50% of a mean residence time of the reaction mixture in the single pass tubular reactor.

2. The process of claim 1, wherein the N-vinyl carboxamide is N-vinyl formamide, N-vinyl acetamide, or both.

3. The process of claim 1, wherein the reactor system comprises: i) from 1 to 10 mixed flow reactors; and ii) from 1 to 5 single pass tubular reactors.

4. The process of claim 1, wherein the at least one single pass tubular reactor is devoid of any internal mixing elements.

5. The process of claim 1, wherein the at least one mixed flow reactor comprises in series and in sequence a pump, static or dynamic mixer and a tubular vessel.

6. The process of claim 1, wherein the at least one mixed flow reactor comprises a continuous stirred tank reactor (CSTR).

7. The process of claim 5, wherein a recycle loop conveys a portion of the reaction mixture exiting the tubular vessel into reaction mixture entering the pump.

8. The process of claim 1, wherein: the at least one polymerisation initiator is added to the reaction mixture in at least two places; and each polymerisation initiator addition is before each at least one mixed flow reactor and each at least one single pass tubular reactor.

9. The process of claim 1, wherein the reaction mixture is passed through an in-line static or dynamic mixer following the addition of each at least one polymerisation initiator before the so treated reaction mixture flows into each at least one mixed flow reactor and each at least one single pass tubular reactor.

10. The process of claim 1, wherein the monomer or monomer mixture is polymerised at temperatures ranging from 1 to 120 C.

11. The process of claim 1, comprising: a) combining an optionally buffered aqueous liquid and the N-vinyl carboxamide monomer or monomer mixture comprising the N-vinyl carboxamide to form the reaction mixture, and optionally passing the reaction mixture through a static mixer; b) adding at least one polymerisation initiator into the reaction mixture either i) before feeding the reaction mixture into a first mixed flow reactor, in which the so treated reaction mixture is optionally passed through a static or dynamic mixer before entering said first mixed flow reactor; or ii) into the first mixed flow reactor in step (c); c) flowing reaction mixture into said first mixed flow reactor in which the monomer or monomer mixture in the reaction mixture polymerises as it passes through said first mixed flow reactor to form a partially polymerised reaction product within the reaction mixture; d) flowing a portion of the reaction mixture resulting from step (c) in a recycle loop to the reaction mixture prior to entering the first mixed flow reactor and adding further at least one polymerisation initiator to the remainder of the reaction mixture resulting from step (c) either i) before feeding the reaction mixture into a second mixed flow reactor, in which the so treated reaction mixture is optionally passed through a static or dynamic mixer before entering said second mixed flow reactor; or ii) into the second mixed flow reactor in step (e); e) flowing the reaction mixture resulting from step (d) into a second mixed flow reactor in which the monomer or monomer mixture in the reaction mixture polymerises as it passes through the second mixed flow reactor to form a further polymerised reaction product within the reaction mixture; f) flowing a portion of the reaction mixture resulting from step (e) in a recycle loop to the reaction mixture prior to entering the second mixed flow reactor and adding further at least one polymerisation initiator to the remainder of the reaction mixture resulting from step (e) either i) before feeding the reaction mixture into at least one single pass tubular reactor, in which the so treated reaction mixture is optionally passed through a static mixer before entering the single pass tubular reactor; or ii) into the at least one single pass tubular reactor in step (g); g) flowing the remaining reaction mixture of step (0 into the at least one single pass tubular reactor in which remaining monomer or monomer mixture in the reaction mixture polymerises as it passes through the at least one single pass tubular reactor to form the polymer of N-vinyl carboxamide.

12. The process of claim 1, which is operated continuously.

13. The process of claim 1, wherein at least 60% by weight of the monomer has been converted to the polymer when the reaction mixture has exited the last at least one mixed flow reactor and before entering the first single pass tubular reactor.

14. An apparatus, comprising a reactor system suitable for producing a polymer of a N-vinyl carboxamide by polymerising an N-vinyl carboxamide monomer or a monomer mixture comprising N-vinyl carboxamide contained in an aqueous reaction mixture, wherein: the reactor system comprises a series of reactor units comprising a combination of at least one mixed flow reactor and at least one single pass tubular reactor, in which i) the at least one mixed flow reactor comprises at least one vessel comprising an internal mixer, an external mixer, or both, and ii) the at least one single pass tubular reactor comprises a tubular section disposed between two ends, at least one inlet and at least one outlet, in which the reactor system is arranged such that reaction mixture flows through the single pass tubular reactor only once; and the reactor system is provided in such a way that substantially none of the reaction mixture exits the single pass tubular reactor less than 50% of a mean residence time of the reaction mixture in the single pass tubular reactor.

Description

BRIEF DESCRIPTIONS OF THE FIGURES

(1) FIG. 1 is a diagram showing the reactor system used in examples 1 and 2.

(2) FIG. 2 is a graph showing the cumulative residence time distribution of the single pass tubular reactor section.

(3) The following examples illustrate the invention.

EXAMPLES

Example 1

(4) The reactor apparatus used for this example is illustrated in FIG. 1.

(5) FIG. 1 contains the following components: (1) aqueous buffer solution; (2) N-vinyl formamide feed; (3) static mixer; (4) initiator (V50) feed; (5) static mixer; (6) gear pump of first mixed flow reactor; (7) static mixer of first mixed flow reactor; (8) tubular vessel of first mixed flow reactor (R1); (9) recycle loop of first mixed flow reactor; (10) sampling port; (11) initiator (V50) feed; (12) gear pump of second mixed flow reactor; (13) static mixer of second mixed flow reactor; (14) tubular vessel of second mixed flow reactor (R2); (15) recycle loop of second mixed flow reactor; (16) sampling port; (17) initiator (V50) feed; (18) static mixer; (19) tubular vessel of first single pass reactor (R3); (20) initiator (V50) feed; (21) static mixer; (22) tubular vessel of second single pass reactor (R4); (23) polyvinyl formamide product.

(6) The apparatus contains a flow line with in series two mixed flow reactors followed by two single pass tubular reactors in series. The two mixed flow reactors are in each case, in sequence, a gear pump, a static mixer, a tubular vessel with recycle loop feeding reaction mixture back into the flow line ahead of the gear pump. The tubular vessels of the first and second mixed flow reactors, R1 and R2, are a cylindrical construction with a circular cross-section. The inner diameter of the tubular vessels of both mixed flow reactors are each 4 mm and the length of each are 10 m. The volume of the tubular vessels of both mixed flow reactors is 125.66 mL. The subsequent two single pass tubular reactors, R3 and R4 are formed from tubular vessels with a cylindrical construction, each with two ends, and inlet and outlet and in which both tubular vessels have a cylindrical cross-section with an internal diameter of 4 mm and a length of 5 m, providing a volume of 62.83 mL. Neither of the two single pass tubular reactors were equipped with recycle loops or internal mixing components. The reactor apparatus was equipped with sample ports between the first and second mixed flow reactors, between the second mixed flow reactor and the first single pass tubular reactor, and between the first and second single pass tubular reactors.

(7) All static mixers appearing in FIG. 1 are identical having a 7.75 mm diameter and contain 9 Fluitec CSE-X elements.

(8) Oxygen was stripped from the monomers by passing nitrogen through the monomers before they entered the reactor system. It is usually necessary to do this since the presence of oxygen in the monomer can inhibit or retard the polymerization reaction.

(9) The monomer N-vinylformamide was mixed by being passed through a static mixer with the aqueous buffer solution to form a reaction mixture before an azo initiator, V50 (2,2-azo bis (2-methylpropionamidine) dihydrochloride), available from Wako, was introduced into the reaction mixture and mixed using a static mixer. The reaction mixture entered the first mixed flow reactor as described above and the polymerisation proceeded.

(10) A portion of the reaction mixture containing partially polymerised product was recycled through the recycle loop. The recycled reaction mixture from the loop was fed into the reaction mixture and fed through the gear pump as above and mixed by the action of the aforementioned static mixer. The pump helps to push the product through the reactor and to feed the recycle loop. The pump adjustment determines the recycle ratio. Reaction mixture which was not recycled was passed into the second mixed flow reactor. Between the first and second mixed flow reactors additional V50 was added into the reaction mixture. The second mixed flow reactor functioned in the same way as the first mixed flow reactor. Reaction mixture containing partially polymerised product exiting the second mixed flow reactor and not recycled was passed into the aforementioned first single pass tubular reactor. Before the two single tubular pass reactors additional initiator V50 was fed into the reaction mixture and in each case mixed into the reaction mixture by flowing the reaction mixture through static mixers before entering each of the single pass tubular reactors.

(11) The tubular vessels of both mixed flow reactors and of both single pass reactors were all placed in a thermal bath filled with thermal oil. The temperature was kept constant over the reactor length and reaction time.

(12) The feed streams had the following composition: 1) Monomer N-vinylformamide: 99 mass % in water 2) Aqueous buffer solution (Buffer): 0.27 mass % phosphoric acid+0.13 mass % sodium hydroxide in water 3) Azo initiator Wako V50 (Initiator): 1 mass % in water

(13) The temperature was 75 C. in the first and second mixed flow reactors and 85 C. in the first and second single pass tubular reactors. The mean residence time was 1 hour in each of the first and second mixed flow reactors and 30 min in each of the first and second single pass tubular reactors. The total mean residence time in the whole reactor system was 3 hours. These conditions as well as the corresponding volume flow rates and the volume fraction recycled in the first and second mixed flow reactors are summarized in Table 1.

(14) TABLE-US-00001 TABLE 1 Process Conditions for Example 1 Average Volume residence fraction Volume flowrate Temperature time recycled Monomer Buffer Initiator [ C.] [h] [%] [mL/h] [mL/h] [mL/h] R1 75 1.0 97 34.4 103.9 6.8 R2 75 1.0 97 2.9 R3 85 0.5 6.8 R4 85 0.5 6.8

(15) The experiment ran for 24 hours and the results of the analysis of the product exiting the first and second mixed flow reactors and the second single pass reactor are shown below in Table 2.

(16) TABLE-US-00002 TABLE 2 Results for Example 1 Residual Monomer Polymer monomer content conversion content K value [%] [%] [mass %] [] R1 57.9 R2 83.0 R3 R4 0.4 99.6 20.8 87

Example 2

(17) The reactor apparatus used in Example 2 is shown in FIG. 1. The apparatus used in Example 2 only differed from the apparatus used in Example 1 in that the two tubular vessels of both mixed flow reactors have an inner diameter of 6 mm but hold the same volume.

(18) The process of Example 2 was carried out using the same starting materials including monomer, buffer and initiator and in the same way and under the same conditions as employed in Example 1.

(19) The results of the analysis of the product exiting the first and second mixed flow reactors and the second single pass reactor are shown below in Table 3 and in Table 4. In Table 4 it can be seen that the residual monomer content is very stable over the duration of the experiment.

(20) TABLE-US-00003 TABLE 3 Results for Example 2 Residual Monomer Polymer monomer content conversion content K value [%] [%] [mass %] [] R1 63.8 R2 89.3 R3 R4 0.3 99.7 21.0 95

(21) TABLE-US-00004 TABLE 4 Time evolution of the residual monomer content for Example 2 Time after start of Residual experiment monomer content [hour] [%] 6 0.35 9 0.34 12 0.34 18 0.35 21 0.34

(22) The cumulative residence time distribution of the single pass tubular reactor section was measured under non-reactive conditions by means of a step experiment with a colored tracer. During the whole procedure, 148.0 mL/h of deionized water were directly fed to static mixer (18) and nothing was added via feed (20). During the first 3 hours, nothing was added via feed (17) so as to flush the system and achieve stable starting conditions. After that period, the measurement phase itself was initiated by adding 6.8 mL/h of a colored tracer solution via feed (17). Samples were collected at the outlet of the second single pass tubular reactor (23) at regular time intervals and the corresponding concentration of tracer was determined via UV spectroscopy. From these concentration measurements, the cumulative residence time distribution was computed according to usual formulae (e.g., O. Levenspiel, Chemical Reaction Engineering, 3.sup.rd edition, John Wiley and Sons, 1999.) and is shown in FIG. 2. Less than 4% of the mixture exits the single pass tubular reactor section in less than 0.5 of the mean residence time of the mixture in the single pass tubular reactor section. A graph showing the cumulative residence time distribution of the single pass tubular reactor section is shown in FIG. 2.

Analytics for Both Examples

(23) Solid contents were measured in a forced draft oven at 140 C. Typically a sample of about 1 g was exactly weighed then dried for 2 hours and finally weighed again.

(24) K-Values were measured according to Fikentscher (Cellulosechemie, Band 13, 48-64 und 71-74) in aqueous solution at a concentration of 0.5% Residual monomer content was determined using an iodine titration method. About 0.5 g of the sample was weighed exactly and diluted with 250 ml of water then acidified with sulfuric acid and treated with an excess of a 0.05 molar iodine solution so that a visible coloration occurred. After 20 min reaction time the excess of iodine was titrated with a 0.1 molar solution of thiosulfate. Starch was used as indicator.