METHOD FOR THE CONTINUOUS PRODUCTION OF ANIONIC POLYMERS USING RADICALS

Abstract

The invention relates to a novel method for the continuous production of anionic polymers by radical polymerization. The polymers produced by said method have a controlled molecular weight.

Claims

1. A method for continuously preparing an anionic polymerby radical polymerization, the method comprising: introducing at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, and a mixture thereof; water; at least one initiator; and optionally at least one chain transfer agent into a tubular reactor, thus forming a fluid stream in the tubular reactor, carrying out a polymerization reaction in the tubular reactor, optionally with a heating means to initiate the polymerization reaction and with a residence time in the reactor of greater than 1 min, and obtaining the anionic polymer in solution in water at an outlet of the tubular reactor, wherein the at least one monomer is optionally partially neutralized, water is optionally hot water, the anionic polymer has a solids content of between 20% and 60% by weight, relative to a total weight of the anionic polymer, and a molecular weight Mw of less than 10 000 g/mol, the tubular reactor has a length L.sub.R of at least 5 m and comprises at least one tubular section of length L.sub.S and internal diameter D such that L.sub.S is at least 20 times larger than D, each tubular section comprises, over an entire length, a plurality of stationary baffles having holes, opposing the fluid stream, in a form of washers having a diameter identical to the internal diameter D of the tubular section, each tubular section is connected to a device, which subjects the fluid stream to an oscillatory movement, and the residence time in the tubular reactor, size of the holes in the baffles, spacing of the baffles, and movements of the device are chosen so as to provide, at any point in the tubular reactor, good homogeneity of the fluid stream.

2. The method of claim 1, wherein D is less than 20 cm.

3. The method of claim 1, wherein the baffles are spaced out, regularly or irregularly, by a distance ranging from 1D to 3D.

4. The method of claim 1, wherein the baffles comprise concentric annular holes such that a d2/d1 ratio varies from 1.2 to 5, wherein d2 is an external diameter of the washer and d1 the internal diameter of the washer.

5. The method of claim 4, wherein amplitude of the oscillatory movement varies from 0.3×d2 to 4×d2, and frequency of the oscillatory movement varies from 0.1 to 100 Hz.

6. The method of claim 1, wherein the reactor comprises one or more devices which provide or discharge heat so as to allow different temperatures from one area to the other.

7. The method of claim 1, wherein the at least one initiator is introduced at an inlet and/or downstream of the tubular reactor, one or more times.

8. The method of claim 1, wherein the at least one monomer is introduced at an inlet and/or downstream of the tubular reactor, one or more times.

9. The method of claim 1, wherein a catalyst based on water-soluble metal salts is also introduced, at an inlet and/or downstream of the tubular reactor, one or more times.

10. The method of claim 1, wherein at least one other ethylenically unsaturated monomer is provided, and the at least one other ethylenically unsaturated monomer is selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), maleic acid, fumaric acid, crotonic acid, itaconic acid, an unsaturated acrylic acid telomer, and a monomer of formula (I): ##STR00004## wherein: R.sub.a, R.sub.b and R.sub.c independently represent H or CH.sub.3, and n is an integer varying between 0 and 2.

11. The method of claim 1, wherein the at least one monomer is acrylic acid and the anionic polymer obtained is poly(acrylic acid) having a molecular weight Mw of from 1 000 to 10 000 g/mol and a polydispersity index of and from 1.5 to 4.

12. The method of claim 1, wherein a neutralizing agent is injected into the tubular reactor, in an area where a rate of conversion of the monomer is greater than 90%.

13. The method of claim 1, wherein the tubular reactor is connected, at an outlet, to another tubular reactor optionally equipped with an oscillatory device, to a stirred reactor, and/or to a flash distillation column.

Description

EXAMPLE 1

[0133] This example illustrates the continuous polymerization of acrylic acid in a tubular reactor having a length L=20 m and an internal diameter D=15 mm, equipped with a system that can oscillate at a frequency of from 0 to 10 Hz with an amplitude of between 0 and 5 cm. The oscillations are mechanically transmitted to the fluid present inside said reactor by means of an impermeable sliding piston. A Ni-Tech® reactor is used in this case.

[0134] The acrylic acid is polymerized in the presence of an initiating system composed of hydrogen peroxide, coupled with metal salts and also hydroxylamine sulfate. A transfer agent is used in order to limit the molecular masses of the poly(acrylic acid) produced. It is the DPTTC salt. The final solids content of poly(acrylic acid) is approximately 35%.

[0135] The reactants are separated in three distinct preparing tanks and are mixed just before they are introduced into the tubular reactor in order to be sure that the polymerization begins only inside said reactor. The reactants from the three tanks are mixed using a static mixer (of SMX® type) using three distinct pumps.

[0136] The flow rates for introducing the reactants into the static mixer and thus into the reactor located downstream are regulated such that the masses introduced are proportional to the values mentioned in the table below:

TABLE-US-00001 TABLE 1 Tank 1 Tank 2, thermostated at 80° C. Tank 3 100% Hydrox- Deminer- Hydrogen Deminer- 100% DPTTC Fe ylamine alized peroxide alized AA salt sulfate sulfate water 35% water (kg) (kg) (kg) (kg) (kg) (kg) (kg) 35 1.5 0.1 0.025 55 4.5 4 AA = acrylic acid

[0137] The flow rates of the three pumps connected to the three preparing tanks are then proportionately modified in order to adjust the residence time in the tubular reactor. Said residence time is measured visually by adding a colored tracer or by means of a conductor meter and a saline solution.

[0138] The polymer produced in this way can be collected in order to evaluate the physicochemical characteristics thereof. The product removed is an aqueous polymeric solution of low viscosity.

[0139] In addition to the overall flow rate (resulting from the sum of the flow rates of the three pumps), the frequency and also the amplitude transmitted by the oscillator can be modified. As soon as one of these parameters is modified, it is necessary to wait for a time at least equal to five times the residence time in the reactor before collecting a sample at the outlet of the reactor or at an intermediate collection point (this being in order to achieve the stationary conditions characteristic of a continuous method.

[0140] For the recipe of table 1, a residence time in the reactor of approximately four minutes makes it possible to obtain an acceptable rate of conversion. The flow rate of the three pumps is then fixed so that the overall flow rate is close to 40 kg per hour.

[0141] Under these operating conditions, the amplitude and the frequency of the oscillations are modified. In all situations, exothermia and also a pressure increase are observed in the reactor. The maximum temperature observed was 150° C. and the maximum pressure was 10 bar.

[0142] Characterization of the Polymers Obtained:

TABLE-US-00002 TABLE 2 Frequency Amplitude Conversion Mn Mw (Hz) (mm) (%) (g/mol) (g/mol) IP 1.25 25 94.9 1925 5570 2.9 1.25 50 98 2150 5980 2.8 2.5 12.5 95.2 1870 5405 2.9 2.5 25 94.8 1960 5485 2.8 2.5 50 92.1 1790 5650 3.2 5 25 96.3 1750 5040 2.9 5 50 94.8 1710 5320 3.1 10 25 95.6 1800 5460 3.0 10 50 97.3 1880 5190 2.8

[0143] Gel formation was not observed.

EXAMPLE 2

[0144] This example illustrates the continuous polymerization of acrylic acid in a tubular reactor having a length L=20 m and an internal diameter D=5 mm equipped with a system that can oscillate at a frequency of from 0 to 10 Hz with an amplitude of between 0 and 5 cm. The oscillations are mechanically transmitted to the fluid present inside said reactor using an impermeable sliding piston. A Ni-Tech® reactor is used in this case.

[0145] The recipe is similar to that used in example 1. The final solids content of poly(acrylic acid) is approximately 35%.

[0146] The flow rates for introducing the reactants into the static mixture and thus into the reactor located downstream are regulated such that the masses introduced are proportional to the values mentioned in table 1, example 1.

[0147] The residence time in the reactor is fixed at approximately two minutes and the flow rate of the three pumps is then fixed so that the overall flow rate is close to 80 kg per hour.

[0148] Under these operating conditions, the amplitude and the frequency of the oscillations are modified. In all situations, exothermia and also a pressure increased are observed in the reactor. The maximum temperature observed was 150° C. and the maximum pressure was 10 bar.

[0149] Characterization of the Polymers Obtained:

TABLE-US-00003 TABLE 3 Frequency Amplitude Conversion Mn Mw (Hz) (mm) (%) (g/mol) (g/mol) IP 1.25 25 93.1 2050 6200 3.0 1.875 25 91.2 1950 6450 3.3 2.5 25 93.2 1840 5930 3.2 5 25 95.3 1910 6030 3.2 10 25 90.7 2020 6740 3.3

[0150] Gel formation was not observed.

EXAMPLE 3

[0151] This example illustrates the continuous polymerization of acrylic acid in a tubular reactor having a length L=20 m and an internal diameter of D=15 mm, equipped with a system that can oscillate at a frequency of from 0 to 10 Hz with an amplitude of between 0 and 5 cm. The oscillations are mechanically transmitted to the fluid present inside said reactor by means of an impermeable sliding piston. A Ni-Tech® reactor is used in this case.

[0152] The acrylic acid is polymerized in the presence of an initiating system composed of sodium persulfate, coupled with metal salts and also sodium hypophosphite. The latter acts as both a reducing agent and a transfer agent. The final solids content of poly(acrylic acid) is approximately 35%.

[0153] The reactants are separated in three distinct preparing tanks and are mixed just before they are introduced into the tubular reactor in order to be sure that the polymerization begins only inside said reactor. The reactants from the three tanks are mixed using a static mixture (of SMX type) using three distinct pumps.

[0154] The flow rates for introducing the reactants into the static mixer and thus into the reactor located downstream are regulated such that the masses introduced are proportional to the values mentioned in the table below:

TABLE-US-00004 TABLE 4 Tank 1 Tank 2, thermostated at 80° C. Tank 3 100% Iron Sodium De- Sodium De- AA sulfate hypophosphite mineralized persulfate mineralized (kg) (kg) (kg) water (kg) (kg) water (kg) 35 0.01 6.0 45 4 10

[0155] The flow rates of the three pumps connected to the three preparing tanks are then proportionately modified in order to adjust the residence time in the tubular reactor. Said residence time is measured visually by adding a colored tracer or using a conductometer and a saline solution.

[0156] The polymer produced in this way can be collected in order to evaluate the physicochemical characteristics thereof. The product removed is an aqueous polymeric solution of low viscosity.

[0157] In addition to the overall flow rate (resulting from the sum of the flow rates of the three pumps), the frequency and also the amplitude transmitted by the oscillator can be modified. As soon as one of these parameters is modified, it is necessary to wait for a time at least equal to five times the residence time in the reactor before collecting a sample at the outlet of the reactor or at an intermediate collection point (this being in order to achieve the stationary conditions characteristic of a continuous method).

[0158] In all situations, exothermia and also a pressure increase are observed in the reactor. The maximum temperature observed was 155° C. and the maximum pressure was approximately 11 bar.

[0159] For the recipe as described above, a residence time in the reactor of approximately three minutes makes it possible to obtain a very good rate of conversion. The flow rate of the three pumps is then fixed so that the overall flow rate is close to 60 kg per hour. Under these operating conditions, the amplitude and the frequency of the oscillations are modified.

[0160] Characterization of the Polymers Obtained:

TABLE-US-00005 TABLE 5 Frequency Amplitude Conversion Mn Mw (Hz) (mm) (%) (g/mol) (g/mol) IP 0.625 50 99.1 1540 4565 3.0 1.25 25 99.99 1535 6040 3.9 1.25 50 99.99 1445 5785 4.0 2.5 25 99.6 2210 8960 4.1 2.5 50 99.99 1750 6780 3.9 5 25 98.9 1830 6540 3.6 5 50 99.7 2150 7300 3.4 10 5 99.99 2130 7650 3.6 10 25 99.99 1970 6600 3.4 10 50 97.6 1630 5830 3.6

[0161] Gel formation was not observed.