NOVEL PROCESS FOR FILTERING 2-ACRYLAMIDO-2-METHYLPROPANE SULFONIC ACID

Abstract

A continuous process for filtering a suspension of 2-acrylamido-2-methylpropane sulfonic acid crystals by means of a rotary pressure filter equipped with a drum, a surface of which is provided with cells covered with a filter medium, the drum rotating within a fixed concentric cylinder comprising at least three zones sealed from each other, respectively a filtration zone, a washing zone and a discharge zone, each zone opening onto the cells.

Claims

1. A continuous process for filtering a suspension of 2-acrylamido-2-methylpropane sulfonic acid crystals by means of a rotary pressure filter equipped with a drum, a surface of which is provided with cells covered with a filter medium, said drum rotating within a fixed concentric cylinder comprising at least three zones sealed from each other, respectively a filtration zone, a washing zone and a discharge zone, each zone opening onto the cells, the process comprising the following steps: a) supplying the filtration zone with a suspension of 2-acrylamido-2-methylpropane sulfonic acid crystals and filtering said suspension in the cells until a cake is formed, b) supplying the washing zone with a washing solution and washing the cake formed in the cells, c) discharging the washed cakes from the cells at the discharge zone; and wherein, a depth of the cells covering the filter medium is between 6 and 150 mm and in that a pressure of between 1 and 10 bars is applied in the filtration and washing zones.

2. The process of claim 1, wherein, the depth of the cells is between 10 and 100 mm, preferably between 15 and 70 mm, more preferably between 20 and 70 mm, even more preferably between 30 and 60 mm.

3. The process according to claim 1, wherein, the process comprises the following steps: a) supplying the filtration zone under pressure with a suspension of 2-acrylamido-2-methylpropane sulfonic acid crystals and simultaneously filtering said suspension in the cells until a cake is formed, b) supplying, under pressure, the washing zone with a washing solution and simultaneously washing the cake formed in the cells.

4. The process of claim 1, comprising at least one of the following two additional steps: between step b) and step c), drying the washed cake by injecting gas into a drying zone; after step c), washing the cells in a cleaning zone before resuming a filtration cycle.

5. The process of claim 4, wherein, a pressure is applied at least in the filtration, washing and drying zones, the pressure being different from one zone to another.

6. The process of claim 5, wherein, the pressure applied in the filtration zone is between 1.1 and 9, preferably between 1.5 and 7, even more preferably between 1.5 and 5, even more preferably between 2 and 4 bars.

7. The process of claim 5, wherein, the pressure applied in the washing zone is between 1.1 and 9, preferably between 1.5 and 9, even more preferably between 2 and 8, even more preferably between 3 and 7 bars.

8. The process of one of claim 5, wherein, the pressure applied in the drying zone is between 1.1 and 10, more preferably between 2 and 10, even more preferably between 3 and 10, even more preferably between 4 and 10 bars.

9. The process of claim 1, wherein, in step b) the washing is carried out with a solution containing at least 90% by mass of acrylonitrile.

10. The process of claim 4, wherein, the gas is at a temperature between 10° C. and 150° C. in the drying step.

11. Process according to claim 1, wherein, the suspension of 2-acrylamido-2-methylpropane sulfonic acid crystals comprises between 10 and 30% by mass of crystals of 2-acrylamido-2-methylpropane sulfonic acid.

12. The process of claim 1, wherein, the rotational speed of the drum is between 2 to 60 revolutions per minute.

13. The process of claim 1, wherein, a supply rate of the suspension of 2-acrylamido-2-methylpropane sulfonic acid crystals is between 1 m3/h and 30 m3/h.

14. The process of claim 1, comprising a drying step of the cake discharged until 2-acrylamido-2-methylpropane sulfonic acid crystals are obtained.

15. The process of claim 1, wherein, a cake of 2-acrylamido-2-methylpropane sulfonic acid crystals is obtained.

16. The process of claim 1, wherein, the cake of 2-acrylamido-2-methylpropane sulfonic acid crystals, comprising less than 60 ppm of IBSA and strictly less than 60 ppm of IBDSA.

17. The process of claim 1, wherein, a 2-Acrylamido-2-methylpropane sulfonic acid crystals is obtained.

18. The process of claim 1, wherein, a polymer is obtained from 2-acrylamido-2-methylpropane sulfonic acid crystals obtained.

19. An oil or gas recovery process comprising the preparation of an injection fluid containing the polymer obtained according to claim 18 and the injection of said fluid in an underground formation.

Description

DESCRIPTION OF THE FIGURES

[0102] FIG. 1 schematically represents the different zones of the rotary pressure filter.

[0103] FIG. 2 schematically represents the various elements of a rotary pressure filter according to the invention.

[0104] More precisely, FIG. 1 represents a simplified cross section of the rotary pressure filter according to the invention showing the filtration zone (1), a first washing zone (2), a second washing zone (3), a drying zone (4), a discharge zone (5), and a cleaning zone (6).

[0105] More precisely, FIG. 2 represents a cross section of a rotary filter according to the invention not comprising a second washing zone (6). The rotary filter according to the invention comprises a fixed cylindrical casing (7), itself comprising a filtration zone (1), a washing zone (2), a drying zone (4), a discharge zone (5), and a cleaning zone (6). It also includes a rotating drum (8) and a central axis (9). The cylindrical casing comprises sealed separation elements for each zone (10), an inlet for the suspension to be filtered (11), an inlet for washing (12), an inlet for drying (13), a discharge zone (5), and an inlet for cleaning (14). The rotating drum comprises cells (15) provided with a filter (16).

EXAMPLARY EMBODIMENTS OF THE INVENTION

Example 1—Production of Crystal Suspensions of 2-Acrylamido-2-Methylpropane Sulfonic Acid

[0106] Several ATBS crystal suspensions are produced according to the operating conditions detailed in Table 1.

[0107] Acrylonitrile and sulfuric acid are continuously added into a first 1,000-liter stainless steel reactor.

[0108] This first reaction mixture is cooled to a temperature of −10° C.

[0109] A second 10,000-liter reactor is continuously supplied with the mixture described above, as well as with isobutylene. The temperature of this mixture is maintained at a given temperature, called the mixing temperature.

[0110] The crystal suspensions A to G of 2-acrylamido-2-methylpropane sulfonic acid are thus obtained.

TABLE-US-00001 TABLE 1 Operating conditions for obtaining ATBS crystal suspensions A to G. ATBS Acrylonitrile H2SO4 H2SO4 crystal flow rate concentration flow rate suspension (kg/h) (%) (kg/h) A 7586 101.13 927 B 3833 101.9 404 C 3000 99 443 D 3907 102.6 374 E 3231 99.8 498 F 2482 101.5 339 G 6546 102.2 750 ATBS Isobutylene Mixture Residence time crystal flow rate temperature in the 10 m.sup.3 Suspended suspension (kg/h) (° C.) reactor (h) solids rate A 487 45 1.1 20 B 261 43 2.2 21.5 C 279 44 2.7 27.7 D 219 40 2.2 18 E 270 40 2.5 25 F 178 38 3.3 22 G 247 41 1.3 20

[0111] In the following filtration examples, the size of the filters is adapted according to the flow rate which supplies the filter, itself depending on the raw material flow rates, the aim being to have a continuous process. Indeed, in Table 1, depending on the residence times in the 10 m.sup.3 reactor, the sum of the acrylonitrile, sulfuric acid and isobutylene flow rates is proportionally variable.

[0112] As such, in the following filtration examples, a filtration rate in kg of 2-acrylamido-2-methylpropane sulfonic acid per hour and per square meter of filtration surface is recalculated.

[0113] Filtration flow rate (kg/h/m.sup.2)=supply flow rate (kg/h)/filtration surface (m.sup.2)

Example 2—Filtration with a Rotating Pressurized Filter

[0114] The ATBS crystal suspensions A to G produced in Example 1 are supplied into the filtration zone of the rotary filter described above, and therefore the cells of the opposite drum. The suspension is supplied under pressure in order to subject the suspension to filtration.

[0115] Several series of tests are carried out. In the first five series, the supply pressure, also called the filtration pressure, the washing pressure and the drying pressure are different from each other. In a sixth series of tests, these pressures are identical to each other. In a seventh series of tests, the depth of the filtration cells is varied.

A) Different Pressures According to the Zones

[0116] In the first series of tests, the filter supply pressure is 7 bars. This pressure corresponds to the pressure applied in the filtration zone.

[0117] The rotating drum has a rotational speed of 30 revolutions per minute. The filtration cells have a depth of 50 mm and are covered by a polypropylene filter cloth with a mesh opening of 50 μm.

[0118] The cake formed in each of the filtration cells is then conveyed to the washing zone.

[0119] A washing solution, at a pressure of 1.5 bar, containing 95% by mass of acrylonitrile and 5% by mass of water supplies the washing zone of the rotary filter.

[0120] A nitrogen gas stream, at a pressure of 2 bars, supplies the drying zone of the rotary filter.

[0121] The cake thus washed and dried is then conveyed to the discharge zone. Pressurized nitrogen is applied from inside the drum in order to discharge the cake. In addition, a knife is inserted inside the cell to help scrape the cake. The cake obtained has residual moisture in acrylonitrile. An analysis by liquid chromatography of the crystals obtained makes it possible to complete the residual contents of IBSA and IBDSA.

[0122] The experimental conditions of the filtration tests of the suspensions A to G are recorded in Table 2. The analysis results on the cakes obtained are recorded in Table 3.

TABLE-US-00002 TABLE 2 Experimental filtration conditions for suspensions A to G with rotary pressure filter technology. ATBS Supply Filter Filtration Supply Filtration crystal rate surface rate pressure test suspension (kg/h) (m.sup.2) (kg/h/m.sup.2) (bars) 1 A 9000 14.4 625 7 2 B 4500 7 643 7 3 C 3720 5.6 664 7 4 D 4500 8 562 7 5 E 4000 6.8 588 7 6 F 3000 5 600 7 7 G 7550 12.5 604 7

TABLE-US-00003 TABLE 3 Analysis results on the cakes obtained with the rotary filter technology with a 7-bar supply pressure of the filtration zone. Filtration ATBS crystal Moisture of crystals IBSA IBDSA test suspension obtained (%) (ppm) (ppm) 1 A 23 55 59 2 B 22 53 62 3 C 21 51 52 4 D 24 58 64 5 E 22 59 58 6 F 23 51 59 7 G 24 62 64

[0123] In the second and third series of tests, the conditions are identical to those of the first series, except that the only parameter which changes is that of the supply pressure of the filter, i.e., the pressure applied in the filtration zone. Tables 4 and 5 summarize the results obtained respectively with a filter supply pressure of 5 bars (second series) and 2.5 bars (third series).

TABLE-US-00004 TABLE 4 Analysis results on the cakes obtained with the rotary filter technology with a 5-bar supply pressure of the filtration zone. Filtration ATBS crystal Moisture of crystals IBSA IBDSA test suspension obtained (%) (ppm) (ppm) 1 A 21 52 57 2 B 19 49 56 3 C 19 48 49 4 D 20 52 58 5 E 19 51 54 6 F 20 46 54 7 G 22 54 59

TABLE-US-00005 TABLE 5 Analysis results on the cakes obtained with the rotary filter technology with a 2.5-bar supply pressure of the filtration zone. Filtration ATBS crystal Moisture of crystals IBSA IBDSA test suspension obtained (%) (ppm) (ppm) 1 A 18 48 49 2 B 17 49 49 3 C 18 43 43 4 D 18 46 48 5 E 17 45 47 6 F 19 42 46 7 G 20 46 46

[0124] These results show that the IBSA and IBDSA impurity levels decrease when the pressure in the filtration zone goes from 7 bars to 5 bars then to 2.5 bars. This shows that an adjustment of the pressure in the filtration zone makes it possible to obtain a better purity of ATBS.

[0125] In a fourth series of tests, the same ATBS crystal suspensions A to G are supplied into the same rotating drum filter. The filtration conditions remain the same but the pressures applied are as follows. The supply pressure in the filtration zone is 7 bars, the pressure in the washing zone is 4 bars, and the pressure in the drying zone is 8 bars.

[0126] The analysis results on the cakes obtained are given in Table 6.

TABLE-US-00006 TABLE 6 Analysis results on the cakes obtained with the rotary filter technology with a 7-bar supply pressure in the filtration zone, a 4-bar washing pressure and an 8-bar drying pressure. Filtration ATBS crystal Moisture of crystals IBSA IBDSA test suspension obtained (%) (ppm) (ppm) 1 A 15 40 45 2 B 16 38 47 3 C 14 30 38 4 D 18 42 48 5 E 16 43 43 6 F 18 35 42 7 G 19 48 48

[0127] These results show that by adjusting the pressures in the washing zone and in the drying zone, respectively to 4 bars and 8 bars, the IBSA and IBDSA impurity levels further decrease compared to the previous tests, demonstrating the possibility to obtain higher purity ATBS crystals.

[0128] A fifth series of tests is carried out in which the same ATBS crystal suspensions A to G are supplied into the same rotating drum filter. The filtration conditions remain the same, but the pressures applied are as follows. The supply pressure in the filtration zone is 2.5 bars, the pressure in the washing zone is 4 bars, and the pressure in the drying zone is 8 bars.

[0129] The analysis results on the cakes obtained are shown in Table 7.

TABLE-US-00007 TABLE 7 Analysis results on the cakes obtained with the rotary filter technology with a 2.5-bar supply pressure in the filtration zone, a 4-bar washing pressure and an 8-bar drying pressure. Filtration ATBS crystal Moisture of crystals IBSA IBDSA test suspension obtained (%) (ppm) (ppm) 1 A 13 37 39 2 B 15 36 40 3 C 13 30 35 4 D 17 38 40 5 E 15 39 39 6 F 17 35 39 7 G 17 39 40

[0130] These results show that the choice of different and appropriate pressures in each of the zones makes it possible to obtain very low levels of IBSA and IBDSA impurities and, therefore, very high purity ATBS crystals.

B) Constant Pressures in the Zones

[0131] A sixth series of tests is carried out in which the same ATBS crystal suspensions A to G are supplied into the same rotating drum filter. The filtration conditions remain the same but the pressures applied are as follows. The supply pressure, also called the pressure in the filtration zone, the washing pressure and the drying pressure are equal to 2 bars.

[0132] The analysis results on the cakes obtained are shown in Table 8.

TABLE-US-00008 TABLE 8 Analysis results on the cakes obtained with the rotary filter technology with a pressure in the filtration, washing and drying zone equal to 2 bars. Filtration ATBS crystal Moisture of crystals IBSA IBDSA test suspension obtained (%) (ppm) (ppm) 1 A 18 44 47 2 B 17 47 46 3 C 18 40 40 4 D 18 42 45 5 E 17 42 45 6 F 19 41 43 7 G 20 43 45

C) Variation in Cell Depth

[0133] Finally, a seventh and final series of tests is carried out by varying the depth of the cells. In this series of tests, the same suspensions of ATBS crystal suspensions A and C are supplied into the same rotating drum filter in which the cells have varying depths. The pressures applied are as follows. The supply pressure in the filtration zone is 2.5 bars, the pressure in the washing zone is 4 bars, and the pressure in the drying zone is 8 bars.

[0134] The rotating drum has a rotational speed of 30 revolutions per minute. The filtration cells have a different depth and are covered by a polypropylene filter cloth with a mesh opening of 50 μm.

[0135] The analysis results on the cakes obtained are given in Table 9.

TABLE-US-00009 TABLE 9 Analysis results on cakes obtained with rotary filter technology with variable cell depth. ATBS crystal Cell depth Moisture of crystals IBSA IBDSA suspension (mm) obtained (%) (ppm) (ppm) A 12 13 44 48 A 20 13 45 49 A 50 13 37 39 A 80 14 52 54 A 120 15 68 75 A 200 22 113 162 C 12 13 43 45 C 20 14 45 49 C 50 13 30 35 C 80 15 53 56 C 120 15 69 88 C 200 23 109 158

[0136] Tests with 5-mm cell depths were carried out but the results are not satisfactory because the productivity is strongly affected which makes the process not industrially sustainable.

[0137] These results show that an adjustment of the cell depth makes it possible to obtain a better purity of ATBS.

Example 3—Filtration with a Vacuum Belt Filter

[0138] The ATBS crystal suspensions A, C and E produced in Example 1 are supplied to a vacuum belt filter having a given filtration zone. The interior of the belt filter is maintained under a 300-mbar vacuum.

[0139] The vacuum belt filter is equipped with a polypropylene filter cloth having a mesh opening of 50 μm.

[0140] The cake formed on the filter is then conveyed to the washing zone.

[0141] A washing solution at a 1.5-bar pressure, containing 95% by mass of acrylonitrile and 5% by mass of water, is sprayed onto the cake.

[0142] A nitrogen gas stream, at a pressure of 2 bars, supplies the drying zone of the vacuum belt filter.

[0143] The cake thus washed and dried is then discharged using a scraper knife.

[0144] An analysis by liquid chromatography of the crystals obtained makes it possible to complete the residual contents of IBSA and IBDSA.

[0145] The experimental conditions of filtration tests 8 to 10 of suspensions A, C and E are recorded in Table 10. The analysis results on the cakes are recorded in Table 11.

TABLE-US-00010 TABLE 10 Experimental filtration conditions for suspensions A, C and E with vacuum belt filter technology. Filtration ATBS crystal Supply rate Filter surface Filtration rate test suspension (kg/h) (m.sup.2) (kg/h/m.sup.2) 8 A 9000 23.9 377 9 C 3720 10.1 368 10 E 4000 10.8 370

TABLE-US-00011 TABLE 11 Analysis results on cakes obtained with vacuum belt filter technology. Filtration ATBS crystal Moisture of crystals IBSA IBDSA test suspension obtained (%) (ppm) (ppm) 8 A 28 120 190 9 C 26 110 170 10 E 25 127 183

Example 4—Filtration with a Continuous Decanter with a Full Cylindrical-Conical Bowl

[0146] The ATBS crystal suspensions A, B and F produced in Example 1 are supplied into a continuous decanter with a full cylindrical-conical bowl.

[0147] The bowl is rotated at a speed of 4,400 revolutions per minute, and the internal conveying screw is rotated at a speed of 4,420 revolutions per minute.

[0148] The cake formed inside the bowl is conveyed by the internal screw to the discharge zone. A solid bowl decanter does not allow washing the cake. Consequently, no washing of the cake is carried out.

[0149] An analysis by liquid chromatography of the crystals obtained makes it possible to complete the residual contents of IBSA and IBDSA.

[0150] The experimental conditions of filtration tests 11 to 13 of suspensions A, B and F are recorded in Table 12. The analysis results on the cakes are recorded in Table 13.

TABLE-US-00012 TABLE 12 Experimental filtration conditions for suspensions A, B and F with a continuous decanter with a full cylindrical-conical bowl. Filtration ATBS crystal Supply rate Filter surface Filtration rate test suspension (kg/h) (m.sup.2) (kg/h/m.sup.2) 11 A 9000 21.5 419 12 B 4500 9.65 466 13 F 3000 6.89 435

TABLE-US-00013 TABLE 13 Analysis results on the cakes obtained with a continuous decanter with a solid cylindrical-conical bowl. Filtration ATBS crystal Moisture of crystal IBSA IBDSA test suspension obtained (%) (ppm) (ppm) 11 A 54 375 450 12 B 48 366 419 13 F 63 398 459

[0151] The cakes obtained have a muddy appearance, they are difficult to transport with the solids conveying techniques known to a person skilled in the art.

Example 5—Filtration with a Continuous Decanter with a Cylindrical-Conical Bowl Having a Solid Bowl Zone and a Perforated Bowl Zone

[0152] In filtration test No. 14, crystal suspension A supplies a cylindrical-conical bowl continuous decanter having a solid bowl zone and a perforated bowl zone. The total surface of the bowl is 25 m.sup.2 and the perforated bowl zone has a mesh size of 500 μm.

[0153] The supply rate of the crystal suspension is 9,000 kg/h.

[0154] The bowl is rotated at a speed of 4,400 revolutions per minute, and the internal conveying screw is rotated at a speed of 4,420 revolutions per minute.

[0155] The cake formed inside the bowl is conveyed by the internal screw to the zone of the perforated bowl. A washing solution at a pressure of 1.5 bar containing 95% by mass of acrylonitrile and 5% by mass of water is supplied and sprayed onto the cake.

[0156] The cake obtained has an acrylonitrile residual moisture of 65% by mass, and a muddy appearance. The cake is difficult to transport with the solids conveying techniques known to a person skilled in the art.

[0157] In addition, 50% of the cake has passed through the filter and is found in suspension in the liquid filtrate. This represents a direct loss, and therefore yield, of 2-acrylamido-2-methylpropane sulfonic acid.

[0158] Analysis by liquid chromatography of the crystals obtained shows that the latter have an IBSA content of 300 ppm and an IBDSA content of 280 ppm.

[0159] The filtration rate of the crystal suspension is 498 kg/m.sup.2/h.

[0160] In conclusion, these examples show that the filtration process according to the invention makes it possible to obtain 2-acrylamido-2-methylpropane sulfonic acid crystals having much lower levels of IBSA and IBDSA than those obtained with other filtration processes. Thus, the process according to the invention provides a continuous process making it possible to significantly improve the purity of the 2-acrylamido-2-methylpropane sulfonic acid crystals while retaining excellent filtration performance and residual moisture in acrylonitrile of the crystals. Furthermore, it should be noted that this improvement is accompanied by an increase in the filtration rate, and therefore in productivity.