PROCESS AND PLANT FOR MANUFACTURING AQUEOUS POLYACRYLAMIDE GELS

Abstract

Process and a plant for making polyacrylamides by polymerizing an aqueous solution comprising at least acrylamide and acrylic acid or salts thereof in the presence of initiators for radical polymerization under adiabatic conditions, wherein acrylamide and acrylic acid are stored at the site of the plant as dilute aqueous solutions in pressure-resistant tanks and also the monomer mixing vessel and the polymerization vessel are pressure-resistant. The combination of using diluted monomer solutions and pressure-resistant tanks ensures that even in case of an unintended and uncontrolled polymerization, said vessels don't burst and there is no spill out of the plant to the environment.

Claims

1.-30. (canceled)

31. Process for making polyacrylamides by polymerizing an aqueous solution comprising at least acrylamide and acrylic acid or salts thereof in the presence of initiators for radical polymerization under adiabatic conditions, wherein the process comprises: [1] Providing an aqueous solution of acrylic acid or salts thereof in at least one pressure-resistant storage tank (1) having a volume of 10 to 500 m.sup.3 and comprising a heat-insulation layer and means for controlling the temperature of the aqueous solution, wherein the concentration of acrylic acid or their salts is from 2.5 mole/kg to 5 mole/kg of acrylic acid relating to the total of the aqueous solution, and wherein step [1] comprises at least the following sub-steps [1.1] providing in a transport unit a first liquid chemical product selected from pure acrylic acid, or an aqueous solution of acrylic acid or a salt thereof having a concentration of more than 5 mol/kg of acrylic acid relating to the total of the aqueous solution, [1.2] discharging the first liquid chemical product from the transport unit and diluting it with water in such a manner, that the resultant aqueous solution of acrylic acid or a salt thereof has a concentration from 2.5 mole/kg to 5 mole/kg of acrylic acid or salts thereof, relating to the total of the aqueous solution, and [1.3] transferring said aqueous solution of acrylic acid or salts thereof having a concentration from 2.5 mole/kg to 5 mole/kg of acrylic acid or salts thereof, to the at least one pressure-resistant monomer storage tank (1), and [2] providing an aqueous solution of acrylamide in at least one pressure-resistant storage tank (2) having a volume of 10 to 500 m.sup.3 and comprising a heat-insulation layer, means for controlling the temperature of the aqueous solution, wherein the concentration of the aqueous solution is from 2.5 mole/kg to 5 mole/kg of acrylamide relating to the total of the aqueous solution, and wherein step [2] comprises at least the following sub-steps [2.1] providing in a transport unit a second liquid chemical product which is an aqueous acrylamide solution having a concentration of more than 5 mol/kg of acrylamide, relating to the total of the aqueous solution, and [2.2] discharging the second liquid chemical product from the transport unit and diluting it with water in such a manner, that the resultant aqueous acrylamide solution has a concentration from 2.5 mole/kg to 5 mole/kg of acrylamide relating to the total of the aqueous solution, and [2.3] transferring said aqueous acrylamide solution to the at least one pressure-resistant monomer storage tank (2), [3] preparing an aqueous monomer mix comprising at least water, acrylamide and partially or fully neutralized acrylic acid in a pressure-resistant mixing vessel (3) having a volume of 10 to 150 m.sup.3, comprising a heat-insulation layer and means for controlling the temperature of the aqueous monomer solution, wherein step [3] comprises at least the following sub-steps [3.1] transferring an aqueous solution of acrylic acid or salts thereof from the pressure-resistant storage tank(s) (1) into the pressure-resistant mixing vessel (3), [3.2] transferring an aqueous solution of acrylamide from the pressure-resistant storage tank(s) (2) into the pressure-resistant mixing vessel (3), [3.3] optionally adding an aqueous base into the mixing vessel, while mixing the components in the pressure-resistant mixing vessel (3) and controlling the temperature of the mixture in the vessel (3) to maintain a temperature of not more than 40° C., wherein the amount of all monomers in the aqueous monomer mix is at least 2 moles/kg, relating to the total of all components of the aqueous monomer mix, and [4] transferring the aqueous monomer mix prepared in course of step [3] to a pressure-resistant polymerization unit (5) having a volume of 10 to 150 m.sup.3, adding initiators for radical polymerization and polymerizing it under adiabatic conditions, thereby obtaining an aqueous polyacrylamide gel.

32. Process according to claim 31, wherein the pressure-resistant storage tank (1) has a design pressure of at least 4 bar gauge, the pressure-resistant storage tank (2) has a design pressure of at least 4 bar gauge, the pressure-resistant mixing vessel (3) has a volume of 10 to 50 m.sup.2 and a design pressure of at least 8 bar gauge, and the pressure-resistant polymerization unit (5) has a design pressure of at least 4 bar gauge.

33. Process according to claim 31, wherein steps [1.2] and [2.2] are carried out by continuously mixing a flow of the respective liquid chemical product with a flow of water, thereby obtaining a flow of an aqueous monomer solution which is filled into the respective pressure-resistant monomer storage tank.

34. Process according to claim 31, wherein steps [1.2] and [2.2] are carried out by discharging the respective liquid chemical product from the transport unit by means of a pump and pumping a flow of the respective liquid chemical product through a pipe to a mixing unit (4a) or (4b), wherein the pipe is equipped with a flow meter for controlling the flow and a valve for adjusting the flow, discharging water from a water storage tank by means of a pump and pumping a flow of water through a pipe to the mixing unit, wherein the pipe is equipped with a flow meter for controlling the stream and a valve for adjusting the flow, mixing the flow of water with the flow of the respective liquid chemical product in the mixing unit, adjusting the flow of water and the flow of the respective liquid chemical product by means of the valves, thereby adjusting the concentration of the respective monomer to the desired value in the range from 2.5 mole/kg to 5 mole/kg of the respective monomer, and transferring the resultant stream of an aqueous monomer solution to the respective pressure-resistant monomer storage tank.

35. Process according to claim 34, wherein the mixing unit comprises at least a T-fitting connecting the water pipe and the monomer pipe and a further pipe which is connected to the respective pressure-resistant monomer storage tank.

36. Process according to claim 35, wherein the mixing unit additionally comprises a static mixer.

37. Process according to claim 31, wherein temperature of the aqueous monomer solutions in the pressure-resistant monomer storage tank(s)(1) and the pressure-resistant monomer storage tank(s)(2) is maintained at ≤25° C.

38. Process according to claim 31, wherein the temperature of the aqueous monomer mix solution in the pressure-resistant mixing vessel is maintained at ≤5° C.

39. Process according to claim 31, wherein the first liquid chemical product is pure acrylic acid or an aqueous solution of acrylic acid and in course of step [3.3] an aqueous base is added into the pressure-resistant mixing vessel.

40. Process according to claim 31, wherein the concentration of all monomers in the aqueous monomer mix for polymerization is from 2.75 to 4.5 mole/kg, at relating to the total of all components of the aqueous monomer solution.

41. Process according to claim 31, wherein the pressure-resistant polymerization unit has a volume from 10 to 40 m.sup.3.

42. Process according to claim 31, wherein the polymerization unit comprises a cylindrical upper part, a conical part at its lower end, feeds for the aqueous monomer solution and a bottom opening for removing the polyacrylamide gel.

43. Process according to claim 31, wherein the process comprises additionally the following process steps: [5] removing the aqueous polyacrylamide gel from the polymerization unit, and [6] comminuting the aqueous polyacrylamide gel and mixing it with an aqueous liquid, thereby obtaining an aqueous polyacrylamide composition having a concentration of 0.01 to 14.9% by weight of polyacrylamides, relating to the total of all components of the aqueous polyacrylamide composition.

44. Process according to claim 43, wherein the process comprises additionally the following steps: [7] transporting the aqueous polyacrylamide composition in a transport unit having a volume from 1 m.sup.3 to 40 m.sup.3 by transport means selected from the group of trucks, railcars or ships from the manufacturing site (location A) to a different location B, and [8] removing the aqueous polyacrylamide composition from the transport unit at the location B.

45. Process according to claim 43, wherein the concentration of the polyacrylamides in the aqueous polyacrylamide composition is from 3.1 wt. % to 7 wt. %, relating to the total of all components of the aqueous composition.

46. Process according to claim 31, wherein the polymerization unit is a transportable polymerization unit, and the process comprises additionally the following process steps: [5a] transporting the polymerization unit filled with the aqueous polyacrylamide gel from the manufacturing site (location A) to a different location B, [6a] removing the aqueous polyacrylamide gel from the transportable polymerization unit at the location B, [7a] comminuting and dissolving the aqueous polyacrylamide gel in an aqueous liquid at the location B, thereby obtaining an aqueous polyacrylamide composition having a concentration of 0.01 to 14.9% by weight of polyacrylamides, relating to the total of all components of the aqueous polyacrylamide composition.

47. Process according to claim 31, wherein the pressure resistant storage tanks (1) and (2) have a volume from 10 to 200 m.sup.3 each.

48. Process according to claim 47, wherein the plant for carrying out the process is a modular, relocatable plant.

49. Process according to claim 31, wherein the pressure-resistant storage tank (1) has a design pressure of 6 bar to 8 bar gauge, and the concentration of the aqueous solution of acrylic acid or salts thereof in said monomer monomer tank is from 4.5 to 5 mole/kg, the pressure-resistant storage tank (2) has a design pressure of 6 to 8 bar gauge, and the concentration of the aqueous solution of acrylamide in said monomer tank is from 4.5 to 5 mole/kg, the pressure-resistant mixing vessel (3) has a design pressure of 15 to 20 bar gauge, and the pressure-resistant polymerization unit (5) has a design pressure of 15 to 20 bar gauge.

50. Process according to claim 31, wherein the pressure-resistant storage tank (1) has a design pressure of 3 bar to 4 bar gauge, and the concentration of the aqueous solution of acrylic acid or salts thereof in said monomer monomer tank is from 3.5 to 4.2 mole/kg, the pressure-resistant storage tank (2) has a design pressure of 3 to 4 bar gauge, and the concentration of the aqueous solution of acrylamide in said monomer tank is from 3.5 to 4.2 mole/kg, the pressure-resistant mixing vessel (3) has a design pressure of 11 to 15 bar gauge, and the pressure-resistant polymerization unit (5) has a design pressure of 11 to 15 bar gauge.

51. Process according to claim 31, wherein the pressure-resistant storage tank (1) has a design pressure of 2 bar to 3 bar gauge, and the concentration of the aqueous solution of acrylic acid or salts thereof in said monomer monomer tank is from 3.5 to 4.2 mole/kg, the pressure-resistant storage tank (2) has a design pressure of 2 to 3 bar gauge, and the concentration of the aqueous solution of acrylamide in said monomer tank is from 3.5 to 4.2 mole/kg, the pressure-resistant mixing vessel (3) has a design pressure of 7 to 10 bar gauge, and the pressure-resistant polymerization unit (5) has a design pressure of 7 to 10 bar gauge.

52. Plant for manufacturing polyacrylamides by polymerizing an aqueous solution comprising at least acrylamide and partially or fully neutralized acrylic acid under adiabatic conditions thereby obtaining an aqueous polyacrylamide gel, comprising at least at least one storage tank for water (6), at least one pressure-resistant storage tank (1) for an aqueous solution of acrylic acid or a salt thereof, having a volume of 10 to 500 m.sup.3 and comprising a heat insulation layer and means for controlling the temperature of the aqueous solution, at least one pressure-resistant storage tank (2) for an aqueous acrylamide solution having a volume of 10 to 500 m.sup.3 and a heat insulation layer and comprising means for controlling the temperature of the aqueous solution, means for discharging a first liquid chemical product selected from pure acrylic acid or an aqueous solution of acrylic acid or a salt thereof from a transport unit and mixing it with water discharged from the storage tank for water (6) by means of a mixing unit (4a), thereby obtaining an aqueous solution of acrylic acid or a salt thereof, and means for transferring the aqueous solution obtained to the pressure-resistant storage tank (1), means for discharging a second liquid chemical product which is an aqueous acrylamide solution from a transport unit, and mixing it with water discharged from the storage tank for water (6) by means of a mixing unit (4b), thereby obtaining an aqueous acrylamide solution, and means for transferring the aqueous acrylamide solution obtained to the pressure-resistant storage tank (2), a pressure-resistant mixing vessel (3) for preparing an aqueous monomer mix comprising at least water, acrylamide and partially or fully neutralized acrylic acid, having a volume of 10 to 150 m.sup.3, means for transferring an aqueous solution of acrylic acid or salts thereof from the pressure-resistant storage tank(s) (1) to the pressure-resistant mixing vessel (3), means for transferring an aqueous solution of acryl amide from the pressure-resistant storage tank(s) (2) to the pressure-resistant mixing vessel (3), at least pressure-resistant polymerization unit (5) having a volume of 10 to 150 m.sup.3, and means for transferring the aqueous monomer mix from the pressure-resistant mixing vessel (3) to the pressure-resistant polymerization unit (5).

53. Plant according to claim 52, wherein the pressure-resistant storage tank (1) has a design pressure of at least 4 bar gauge, the pressure-resistant storage tank (2) has a design pressure of at least 4 bar gauge, the pressure-resistant mixing vessel (3) has a volume of 10 to 150 m.sup.2 and a design pressure of at least 8 bar gauge, and the pressure-resistant polymerization unit (5) has a design pressure of at least 4 bar gauge.

54. Plant according to claim 52, wherein the plant furthermore comprises at least one storage tank for an aqueous base (7), and means for transferring the aqueous base from the storage tank(s) for the aqueous base (7) to pressure-resistant mixing vessel (3).

55. Plant according to claim 52, wherein the mixing unit (4a) comprises a first inlet pipe connecting the mixing unit (4a) with the storage tank for water (6) comprising a pump, a second inlet pipe connecting the mixing unit (4a) with the transport unit for the first liquid chemical product comprising a pump, and an outlet pipe connecting the mixing unit (4a) with the pressure-resistant monomer storage tank (1), wherein each of the inlet pipes furthermore is equipped with a flow meter for controlling the flow through the pipe and a valve for adjusting the flow through the pipe, and wherein the mixing unit (4b) comprises a first inlet pipe connecting the mixing unit (4b) with the storage tank for water (6) comprising a pump, a second inlet pipe connecting the mixing unit (4b) with the transport unit for the second liquid chemical product comprising a pump, and an outlet pipe connecting the mixing unit (4b) with the pressure-resistant monomer storage tank (1), wherein each of the inlet pipes furthermore is equipped with a flow meter for controlling the flow through the pipe and a valve for adjusting the flow through the pipe.

56. Plant according to claim 55, wherein the mixing units (4a) and (4b) each comprise at least a T-fitting connecting the inlet pipe for water, the inlet pipe for the respective liquid chemical product and the outlet pipe connecting to the respective pressure-resistant monomer storage tank.

57. Plant according to claim 56, wherein the mixing unit additionally comprises at least a static mixer.

58. Plant according to claim 52, wherein the polymerization unit comprises a cylindrical upper part, a conical part at its lower end, feeds for the aqueous monomer solution and a bottom opening for removing the polyacrylamide gel.

59. Plant according to claim 52, wherein the pressure resistant storage tanks (1) and (2) have a volume from 10 to 200 m.sup.3 each.

60. Plant according to claim 59, wherein the plant is a modular, relocatable plant.

Description

EXAMPLES

[0235] The following examples are deemed to further illustrate the invention:

[0236] Part a Storage of Aqueous Solutions of Acrylic Acid and Acrylamide

[0237] The data and formulae for the calculations which follow are taken from “VDI Wärmeatlas, 10.sup.th Edt, Springer-Verlag Berlin Heidelberg 2006”.

[0238] The vapor pressure of water was calculated according to the following formula of the “VDI Wärmeatlas”, page Da 13:

[00001]$\ln \frac{p_s}{p_c}=\frac{T_c}{T}\left[A\left(1-\frac{T}{T_c}\right)+{B\left(1-\frac{T}{T_c}\right)}^{1.5}+{C\left(1-\frac{T}{T_c}\right)}^3+{D\left(1-\frac{T}{T_c}\right)}^6\right]$

wherein the parameters have the following values:

TABLE-US-00002 A −7.71374 B   1.31467 C −2.51444 D −1.72542 Tc 647.1K pc 220.6 bar

[0239] T is the temperature of the water, and p.sub.s is the vapor pressure at the temperature T.

[0240] Furthermore, the following parameters were used for the calculation:

TABLE-US-00003 Neutralization heat acrylic acid/NaOH h_neutr. 58 kJ/mol (equimolar amounts) Polymerization heat of acrylic acid h_poly_GAA 78 kJ/mol Sum of neutralization heat and h_tot 136 kJ/mol polymerization heat Sum of neutralization heat and h_tot_s 1887 kJ/kg polymerization heat (other units) Polymerization heat of acrylamide h_poly_ACM 81 kJ/mol Polymerization heat of acrylamide h_poly_ACM 1140 kJ/kg (other units) Molar weights M_H.sub.2O 18 g/mol M_NaOH 40 g/mol M_GAA 72.06 g/mol M_ACM 71.08 g/mol Heat capacities cp_H.sub.2O 4.2 kJ/kgK cp_NaOH 1.5 kJ/kgK cp_GAA 2.1 kJ/kgK cp_ACM 2.6 kJ/kgK

Example 1

[0241] Pressure and Temperature Development of an Aqueous Acrylic Acid Solution Upon Polymerization

[0242] Using the formula and data as shown above the vapor pressure and temperature of an aqueous solution of acrylic acid after undesired polymerization was calculated. For the calculation, it was assumed that the polymerization takes place under ideal adiabatic conditions (i.e. there is no heat dissipation from the vessel), and that the polymerization proceeds to completion.

[0243] Table 2 shows the data for an initial temperature (i.e. the temperature of the aqueous acrylic acid solution before polymerization) of 25° C. In one embodiment of the present invention, the aqueous acrylic acid solutions are stored at 25° C., however, it is possible to store them also at higher temperatures, for example at 30° C. So, an initial temperature of 25° C. addresses a situation in which unintentional polymerization starts from a temperature at which the aqueous acrylic acid solution may be stored. The resulting pressures are also represented in FIG. 1.

[0244] Table 4 shows the data for an initial temperature of 50° C. A temperature of 50° C. relates to a worst-case-scenario assuming that the cooling system of a heat-insulated acrylic acid tank has a malfunction for a longer time and the insulated storage tank is exposed to intense sunlight also for a longer time so that the temperature of its contents increases significantly. The resulting pressures are also represented in FIG. 1.

[0245] Table 3 shows the data for an initial temperature of 40° C. An initial temperature of 40° C. relates to another worst-case-scenario assuming that the cooling system of an insulated acrylic acid tank has a malfunction for a longer time, however, the sunlight is not that intense to heat-up the storage tank completely to 50° C.

TABLE-US-00004 TABLE 2 Pressure and temperature of an aqueous solution of acrylic acid upon polymerization, initial temperature 25° C. resulting resulting Acrylic acid concentration pressure temperature mol/kg weight % bar gauge ° C. 2.78 20 0 82.3 3.47 25 0 98.6 4.16 30 0.7 116 4.50 32.4 1.3 124.6 4.58 33 1.5 126.9 4.86 35 2.1 134.3 5.00 36 2.4 138.1 5.55 40 4.3 153.9 6.24 45 7.8 174.6 6.94 50 13.5 196.8 8.33 60 36.9 245.9 9.71 70 88.1 302.5

TABLE-US-00005 TABLE 3 Pressure and temperature of an aqueous solution of acrylic acid upon polymerization, initial temperature 40° C. resulting resulting Acrylic acid concentration pressure temperature mol/kg weight % bar gauge ° C. 2.78 20 0 97.3 3.47 25 0.6 113.6 4.16 30 1.8 131.0 4.50 32.4 2.6 139.6 4.58 33 2.8 141.9 4.86 35 3.7 149.3 5.00 36 4.2 153.1 5.55 40 6.7 168.9

TABLE-US-00006 TABLE 4 Pressure and temperature of an aqueous solution of acrylic acid upon polymerization, initial temperature 50° C. resulting resulting Acrylic acid concentration pressure temperature mol/kg weight % barg ° C. 2.78 20 0.3 107.3 3.47 25 1.2 123.6 4.16 30 2.7 141 4.50 32.4 3.7 149.6 4.58 33 4.0 151.9 4.86 35 5.1 159.3 5.00 36 5.7 163.1 5.55 40 8.8 178.9 6.24 45 14.4 199.6 6.94 50 23 221.8 8.33 60 54.8 270.9 9.71 70 123.8 327.5

[0246] Both, tables 2 and 4 demonstrate, that undesired polymerization of aqueous solutions of acrylic acid at higher concentrations still yields a very significant temperature and pressure increase. An aqueous solution of 70 wt. % of acrylic acid gives rise to a pressure of about 88 bar gauge and a temperature of about 300° C. upon polymerization when starting at 25° C. (table 2), and nearly 125 bar gauge and a temperature of about 330° C. when starting at 50° C. (table 4). Such high pressures and temperatures are sufficient to burst the vessels in which aqueous acrylic acid solutions are stored, even when pressure resistant vessels as defined in the present invention are used.

[0247] Diluting acrylic acid to 2.5 mole/kg to 5 mole/kg and storing it at such a concentration in the pressure-resistant storage tank(s) (1) as provided for in the present application significantly limits the temperature and pressure development. If an acrylic acid solution comprising 5 mol/kg of acrylic acid (36 wt. %) is stored at 25° C. the pressure in course of unintended polymerization increases to 2.4 bar gauge only. With an initial temperature of 50° C. the pressure increases to 5.7 bar gauge in course of polymerization. A storage tank having a design pressure of 6 barg would withstand such a pressure. If an acrylic acid solution comprising 4.5 mol/kg of acrylic acid is stored at 25° C., the resulting pressure remains at less than 1.5 barg only and even at a starting temperature of 50° C., the resulting pressure remains at less than 4 barg, so that storage tanks having a design pressure of at least 4 barg are sufficient for aqueous solutions of acrylic acid having such a concentration.

Example 2

[0248] Pressure and Temperature Development of an Acrylamide Solution Upon Polymerization

[0249] In the same manner as explained above resulting pressures and temperatures were calculated for aqueous acrylamide solutions. As above, calculations were carried out for an initial temperature of 25° C., of 40° C. and of 50° C. The results are shown in tables 5, 6 and 7, and FIG. 2 shows the resulting pressures.

TABLE-US-00007 TABLE 5 Pressure and temperature of an aqueous solution of acryl amide upon polymerization, initial temperature 25° C. Resulting Resulting Acryl amide concentration pressure temperature mol/kg weight % barg ° C. 2.81 20 0.0 83.7 3.52 25 0.0 99.8 4.22 30 0.8 116.9 4.50 32 1.2 123.9 4.57 32.5 1.4 125.6 4.92 35 2.1 134.6 5.00 35.5 2.3 136.4 5.06 36 2.4 138.2 5.63 40 4.2 153 6.33 45 7.4 172.4 7.03 50 12.3 192.6

TABLE-US-00008 TABLE 6 Pressure and temperature of an aqueous solution of acryl amide upon polymerization, initial temperature 40° C. Resulting Resulting Acryl amide concentration pressure temperature mol/kg weight % barg ° C. 2.81 20 0 98.7 3.52 25 0.7 114.9 4.22 30 1.9 131.9 4.50 32 2.5 138.9 4.57 32.5 2.7 140.6 4.92 35 3.7 149.6 5.00 35.5 3.9 151.4 5.06 36 4.2 153.2

TABLE-US-00009 TABLE 7 Pressure and temperature of an aqueous solution of acryl amide upon polymerization, initial temperature 50° C. Resulting Resulting Acryl amide concentration pressure temperature mol/kg weight % barg ° C. 2.81 20 0.4 108.7 3.52 25 1.3 125 4.22 30 2.8 141.9 4.50 32 3.6 148.9 4.57 32.5 3.8 150.6 4.92 35 5.1 159.6 5.00 35.5 5.4 161.4 5.06 36 5.7 163.2 5.63 40 8.6 178 6.33 45 13.7 197.4 7.03 50 21.1 217.6

[0250] The results are similar as with acrylic acid. If an acryl amide solution comprising 4.92 mol/kg of acrylic acid (35 wt. %) is stored at 25° C. the pressure in course of unintended polymerization increases to 2.1 barg only. With an initial temperature of 50° C. the pressure increases to 5.1 barg in course of polymerization. A storage tank having a design pressure of 6 barg would withstand such a pressure.

Example 3

[0251] Pressure and Temperature Development of an Aqueous Acrylic Acid Solution Upon Polymerization and Neutralization

[0252] In course of step [3], i.e. the preparation of the aqueous monomer mix for polymerization, it is the worst-case scenario that acrylic acid unintentionally polymerizes in the same moment when it becomes neutralized with an NaOH solution (50 wt. % NaOH, used in equimolar amounts, i.e. complete neutralization), i.e. both, heat of polymerization and heat of neutralization are released simultaneously.

[0253] The vapor pressure and temperature of an aqueous solution of acrylic acid after undesired polymerization and neutralization was calculated as detailed above, including the heat of neutralization. It is important to note, that adding aqueous NaOH solution (50 wt. %) results in a dilution of the aqueous acrylic acid solution. Therefore, the acrylic acid concentration has been characterized as initial acrylic acid concentration in the table.

[0254] As above, three calculations were carried out, using initial temperatures of 25° C., 40° C. and 50° C. The results are shown in tables 8, 9 and 10, and in FIGS. 3 and 4.

TABLE-US-00010 TABLE 8 Pressure and temperature of an aqueous solution of acrylic acid with and without neutralization upon polymerization, initial temperature 25° C. Initial acrylic acid acrylic acid only with NaOH concentration pressure temperature pressure temperature mol/kg weight % [barg] [° C.] [barg] [° C.] 2.78 20 0 82.3 0.6 114.1 3.47 25 0 98.6 2.1 135.1 4.16 30 0.7 116 4.5 155.5 4.50 32.4 1.3 124.6 5.1 159.5 4.86 35 2.1 134.3 8 175.5 5.00 36 2.4 138.1 8.9 179.5 5.55 40 4.3 153.9 13 195 6.24 45 7.8 174.6 19.7 214.1 6.94 50 13.5 196.8 28.4 232.8

TABLE-US-00011 TABLE 9 Pressure and temperature of an aqueous solution of acrylic acid with and without neutralization upon polymerization, initial temperature 40° C. Initial acrylic acid acrylic acid only with NaOH concentration pressure temperature pressure temperature mol/kg weight % [barg] [° C.] [barg] [° C.] 2.78 20 0 97.3 1.2 123.4 3.47 25 0.6 113.6 2.9 143.0 4.16 30 1.8 131.0 6.5 162.1 4.50 32.4 2.6 139.6 8.1 171.2 4.86 35 3.7 149.3 9.2 180.8 5.00 36 4.2 153.1 10.1 184.5 5.55 40 6.7 168.9 14.3 199.1

TABLE-US-00012 TABLE 10 Pressure and temperature of an aqueous solution of acrylic acid with and without neutralization upon polymerization, initial temperature 50° C. Initial acrylic acid acrylic acid only with NaOH concentration pressure temperature pressure temperature mol/kg weight % [barg] [° C.] [barg] [° C.] 2.78 20 0.3 107.3 2.2 135.5 3.47 25 1.2 123.6 4.5 155.6 4.16 30 2.7 141 8 175.3 4.5 32.4 3.7 149.6 10.1 184.5 4.86 35 5.1 159.3 12.8 194.5 5.00 36 5.7 163.1 14.0 198.2 5.55 40 8.8 178.9 19.3 213.2 6.24 45 14.4 199.6 27.8 231.5 6.94 50 23 221.8 38.4 249.4

[0255] Tables 8 to 10 clearly demonstrate, that the pressure and temperature increase in course of unintentional polymerization is significantly higher if concentrated NaOH is added to the acrylic acid solution as compared to the case in which only acrylic acid is present, because simultaneously the polymerization heat and neutralization heat become released. For that reason, the design pressure of the pressure-resistant mixing vessel needs to be higher than that of the pressure-resistant storage vessels.

[0256] Part B Polymerization

[0257] Manufacture of a copolymer comprising 75 mole % of acrylamide and 25 mole % of sodium acrylate by adiabatic gel polymerization

[0258] (monomer concentration 23 wt. % regarding all components of the aqueous solution, scheduled quantity 3.5 kg)

[0259] General Polymerization Procedure

[0260] A 5 L beaker with magnetic stirrer, pH meter and thermometer was charged with 1600 g of distilled water, 702.04 g of sodium acrylate (35% by weight in water), and 1071.69 g of acrylamide (52% by weight in water). Then 10.5 g of diethylenetriamine-pentaacetic acid penta-sodium salt (Trilon C; 5% by weight in water), and 4 g of the stabilizer sodium 2-mercapto-benzothiazole (NaMBT; 50% by weight in water) were added.

[0261] After adjusting the pH value of the monomer solution to 6.4 with sulfuric acid (20% by weight in water) the desired monomer concentration of 23% by weight was adjusted by adding water (total amount of water 1690.08 g minus the amount of water already added, minus the amount of acid required), and the temperature of the monomer solution was adjusted approx. —3° C. The solution was transferred to a Dewar vessel, a sensor for recording the temperature was inserted, and the monomer solution in the Dewar vessel was purged with nitrogen for 45 minutes. The polymerization was initiated at 0° C. with 21 g of a 10% aqueous solution of 2,2′-azobis(2-methylpropionamidine) dihydrochloride (Wako V-50; 10h t.sub.1/2 in water 56° C.), 1.75 g of t-butyl hydroperoxide (1% by weight in water) and 1.05 g of a 1% sodium sulfite solution. With the onset of the polymerization, the temperature rose to >60° C. within about 60 min. A solid polymer gel block was obtained. After polymerization, the gel block was incubated 4 hours at 60° C. The block was cut into larger pieces and sealed in plastic bags until further testing.

[0262] Sample Preparation and Characterization Methods

[0263] Composition of pH 7 Buffer.sup.2* and pH 7 Buffer.sup.1*

[0264] A 5 L volumetric flask is charged with 583.3±0.1 g sodium chloride, 161.3±0.1 g disodium hydrogenphosphate•12 H.sub.2O, 7.80±0.01 g sodium dihydrogenphosphate•2 H.sub.2O and 4 L of distilled water. The solution is stirred until full dissolution and filled up to the 5 L graduation mark with distilled water. The pH value should be 7.0±0.1.

[0265] The concentrated pH 7 buffer.sup.2* solution was diluted 1:1 with distilled water to obtain the simple pH 7 buffer.sup.1*.

[0266] Dissolution Method

[0267] A 400 mL beaker was charged with 256.52 g of pH 7 buffer.sup.1* and 43.48 g of a 23% polymer gel, which was cut in tiny pieces, to obtain a stock solution with a specific concentration. The mixture with less than 1% concentration was stirred for 12 h with an overhead stirrer equipped with a paddle-type stirrer approx. 1.5 cm smaller than the diameter of the beaker. The mixing speed was 200 rpm. The evaporated water was replenished, and the solution stirred for additional 60 minutes. The solution was filtered over a 194 μm sieve prior to use. The mixture with more than 1% concentration was stirred on a tumble wheel.

[0268] The desired concentration for the specific measurement was obtained by a second dilution step using an overhead stirrer.

[0269] MPFR Determination

[0270] The polymer solution was diluted to 1000 ppm with pH 7 buffer.sup.1*. Subsequently this solution was stirred for 1 h at 200 rpm with the same overhead stirrer as described above. 200 mL of this polymer solution is placed into a Sartorius filtration cell equipped with a 5 μm polycarbonate nucleo pore filter (aka Millipore). After closure of the cell, 2 bar of air is applied and the weight of the filtrate measured over time. When the filtration is finished, the filtrate weight is plotted against the time of filtration and the deviation from linearity is calculated by regression analysis. Values <1.3 are within the specification for Modular Solution polymers.

[0271] Measurement of Brookfield RS Viscosity

[0272] A 5000 ppm solution was prepared. The viscosity was measured at room temperature with a Brookfield R/S device equipped with a 45 mm bob and cup geometry at a shear rate of 100 s.sup.−1. An average value is taken after 3 minutes of measurement.

[0273] Error range: ±5 mPas.

[0274] Measurement of Intrinsic Viscosity

[0275] The polymer solution was diluted to 350 ppm with pH 7 buffer.sup.1* and injected either manually or automatically. Further four dilutions were done automatically. The viscosity at five different concentrations was measured at 25° C. with an automatic Lauda iVisc LMV830 equipped with an Ubbelohde capillary tube and manual injection, unless otherwise noted. The IV value [dL/g] was taken at infinite dilution. The error range is: ±2 dL/g.

[0276] Storing in Fresh Water

Comparative Example 1 (100% Acrylic Acid)

[0277] Pure 100% acrylic acid was stored for 4 weeks at ambient temperature, then neutralized with an aqueous NaOH solution (50 wt. %) and diluted with water to obtain a solution comprising 35 wt. % of sodium acrylate (3.72 mol/kg). The obtained solution was used for making a copolymer of sodium acrylate and acrylamide according to the general polymerization procedure as detailed above.

[0278] 3 polymerizations were carried out.

[0279] The results and properties of the obtained polymer are shown in table 7.

Example 4 (35 wt. % Aqueous Solution of Acrylic Acid)

[0280] 100% acrylic acid was diluted with desalinated water to obtain an aqueous acrylic acid solution comprising 35 wt. % of acrylic acid (4.86 g/mol). The obtained aqueous acrylic acid solution was stored at ambient temperature for 4 weeks. Thereafter, the solution was neutralized with an aqueous NaOH solution (50 wt. %) and used for making a copolymer of sodium acrylate and acrylamide according to the general polymerization procedure as detailed above. The amounts of water added were adjusted as compared to the general procedure to obtain a final concentration for polymerization of 23 wt. %. Except for that, the polymerization was carried out as described above.

[0281] The results and properties of the obtained polymer are shown in table 11.

Example 5 (30 wt. % Aqueous Solution of Acrylic Acid)

[0282] Example 5 was carried out as example 4, except that the acrylic acid was diluted to 30 wt. % (4.16 mol/kg) and stored for 4 weeks. The amounts of water used for making the monomer solution for polymerization were adjusted accordingly.

[0283] The results and properties of the obtained polymer are shown in table 11.

Example 6 (25 wt. % Aqueous Solution of Acrylic Acid)

[0284] Example 6 was carried out as example 4, except that the acrylic acid was diluted to 25 wt. % (3.47 mol/kg) and stored for 4 weeks. The amounts of water used for making the monomer solution for polymerization were adjusted accordingly.

[0285] The results and properties of the obtained polymer are shown in table 11.

TABLE-US-00013 TABLE 11 Results of comparative example 1 and examples 4, 5, and 6 AA conc. in course of T.sub.max Ø T.sub.max RS Ø RS IV.sup.a No. storage [° C.] [° C.] [mPas] [mPas] [dL/g] MPFR Ø MPFR C1 100%  55.4 55.6 76 77 — 1.21 1.18 55.6 80 — 1.26 55.9 76 32.1 1.07 4 35% 56.5 55.3 76 77 — 1.14 1.09 55.2 75 30.4 1.09 54.2 79 — 1.05 5 30% 55.8 55.7 82 80 — 1.06 1.09 55.8 79 32.7 1.09 55.6 80 — 1.11 6 25% 56.1 55.1 79 80 — 1.10 1.19 56.1 77 32.5 1.28 53.2 83 — 1.19

[0286] The results of comparative example 1 and the examples 4, 5, and 6 show, that the number of T.sub.max obtained in course of polymerization are —within typical ranges of error—the same and the same holds true for the viscosities and the MPFR of the copolymers obtained. So, diluting the acrylic acid and storing the diluted solution for 4 weeks does not negatively affect polymerization and also not the properties of the copolymer obtained.

[0287] Storing in Well Water

[0288] Storing of the monomers was also tested in well water. For the test a well water having the composition as shown in the following table 12 was used:

TABLE-US-00014 TABLE 12 Composition of the well water used (all data in mg/kg) Cl.sup.− NO.sub.3.sup.− SO.sub.4.sup.2− 438.0 26.7 300.5 Al B Ba Ca Fe K Li Mg Na S Si Sr 0.05 1.03 0.04 217.9 0.01 9.12 0.08 35.6 217.8 104.5 18.9 2.41

Comparative Example 2 (100% Acrylic Acid, No Storage, Desalinated Water)

[0289] Pure 100% acrylic acid was neutralized with an aqueous NaOH solution (50 wt. %) and diluted with water to obtain a solution comprising 35 wt. % of sodium acrylate (3.72 mol/kg). The obtained solution was used for making a copolymer of sodium acrylate and acrylamide according to the general polymerization procedure as detailed above.

[0290] 3 polymerizations were carried out.

[0291] The results and properties of the obtained polymer are shown in table 13.

Comparative Example 3 (100% Acrylic Acid, No Storage, Well Water)

[0292] 100% acrylic acid was neutralized with an aqueous NaOH solution (50 wt. %) and diluted with well water having the composition shown in table 12 to obtain a solution comprising 35 wt. % of sodium acrylate (3.72 mol/kg). The obtained solution was used for making a copolymer of sodium acrylate and acrylamide according to the general polymerization procedure as detailed above, except that well water was used.

[0293] 3 polymerizations were carried out.

[0294] The results and properties of the obtained polymer are shown in table 13.

Example 7 (35 wt. % Acrylic Acid, 30 wt. % Acrylamide, Storage in Well Water)

[0295] 100% acrylic acid was diluted with well water to obtain an aqueous acrylic acid solution comprising 35 wt. % of acrylic acid (4.86 g/mol). The obtained aqueous acrylic acid solution was stored at ambient temperature for 4 weeks.

[0296] An aqueous solution comprising 52 wt. % of acrylamide was diluted with well water to obtain an aqueous acrylamide acid solution comprising 30 wt. % of acryl amide (4.22 mole/kg). The obtained aqueous acrylamide solution was stored at ambient temperature for 4 weeks.

[0297] After 4 weeks, the acrylic acid solution was neutralized with an aqueous NaOH solution (50 wt. %). Both, the neutralized acrylic acid solution and the acrylamide solution were used for making a copolymer of sodium acrylate and acrylamide according to the general polymerization procedure as detailed above. The amounts of well water added were adjusted as compared to the general procedure to obtain a final concentration for polymerization of 23 wt. %. Except for that, the polymerization was carried out as described above. 3 polymerizations were carried out. The results and properties of the obtained polymer are shown in table 13.

Example 8 (30 wt. % Acrylic Acid, 30 wt. % Acrylamide, Storage in Well Water)

[0298] Example 8 was carried out as example 7, except that the acrylic acid was diluted to 30 wt. % (4.16 mol/kg). Acrylamide was diluted to 30 wt. % (4.22 mole/kg) in the same manner as in example 7. The amounts of well water used for making the monomer solution for polymerization were adjusted accordingly.

[0299] The results and properties of the obtained polymer are shown in table 13.

Example 9 (25 wt. % Acrylic Acid, 30 wt. % Acrylamide, Storage in Well Water)

[0300] Example 9 was carried out as example 7, except that the acrylic acid was diluted to 30 wt. % (3.47 mol/kg). Acrylamide was diluted to 30 wt. % (4.22 mole/kg) in the same manner as in example 7. The amounts of well water used for making the monomer solution for polymerization were adjusted accordingly.

[0301] The results and properties of the obtained polymer are shown in table 13.

TABLE-US-00015 TABLE 13 Results of comparative examples C2 and C3 and of examples 7, 8, and 9 Monomer concentration T.sub.max Ø T RS Ø RS IV Ø No. and storage Water [° C.] [° C.] [mPas] [mPas] [dL/g] MPFR MPFR C2 100% AA desalinated 55.0 53.9 71 69 32.3 1.14 1.14 no storage 54.2 64 31.7 1.14 52.4 73 35.2 1.13 C3 100% AA well 56.1 56.2 72 72 31.4 — — no storage 56.4 73 — 56.2 72 — 7 35% AA well 55.0 54.4 72 72 37.0 1.04 1.07 30% AM 54.3 71 1.08 4 weeks storage 53.9 73 1.08 8 30% AA well 58.0 56.8 72 72 36.0 1.04 1.05 30% AM 55.1 70 1.00 4 weeks storage 57.2 75 1.12 9 25% AA well 54.8 55.0 75 75 1.13 1.13 30% AM 55.3 76 37.2 1.07 4 weeks storage 54.9 75 1.18

[0302] The results show that the copolymers obtained by polymerization in well water show slightly higher Brookfield RS and intrinsic viscosities (IV) but the MPFR values are still sufficient (a number of more than 1.3 is usually no longer considered as sufficient). Storage of the monomers for 4 weeks in well water does not negatively affect the properties of the polymer obtained.