Process for producing aqueous polyacrylamide solutions

Abstract

Process for producing aqueous polyacrylamide solutions by polymerizing an aqueous solution comprising at least acrylamide thereby obtaining an aqueous polyacrylamide gel and dissolving said aqueous polyacrylamide gel in water, wherein the manufacturing steps are allocated to two different locations A and B and the process comprises the step of transporting an aqueous polyacrylamide gel hold in a transportable polymerization unit from a location A to a location B. Modular, relocatable plant for manufacturing aqueous polyacrylamide solutions wherein the units of the plant are located at two different locations A and B.

Claims

1. A process for producing an aqueous polyacrylamide solution comprising polymerizing an aqueous solution comprising at least acrylamide thereby obtaining an aqueous polyacrylamide gel and dissolving said aqueous polyacrylamide gel in water, characterized in that the process comprises at least the following steps: [1] preparing an aqueous monomer solution comprising at least water and 5% to 45% by weight—relating to the total of all components of the aqueous monomer solution—of water-soluble, monoethylenically unsaturated monomers at a location A, wherein said water-soluble, monoethylenically unsaturated monomers comprise at least acrylamide, [2] inerting and radically polymerizing the aqueous monomer solution prepared in step [1] in the presence of suitable initiators for radical polymerization under adiabatic conditions at a location A, wherein the polymerization is performed in a transportable polymerization unit having a volume of 1 m.sup.3 to 40 m.sup.3, the aqueous monomer solution has a temperature T.sub.1 not exceeding 30° C. before the onset of polymerization, and the temperature of the polymerization mixture raises in course of polymerization—due to the polymerization heat generated—to a temperature T.sub.2 of at least 45° C., thereby obtaining an aqueous polyacrylamide gel having a temperature T.sub.2 which is held in the transportable polymerization unit, [3] transporting the transportable polymerization unit filled with the aqueous polyacrylamide gel from location A to a different location B, [4] removing the aqueous polyacrylamide gel from the transportable polymerization unit at the location B, [5] comminuting and dissolving the aqueous polyacrylamide gel in an aqueous liquid at the location B, thereby obtaining an aqueous polyacrylamide solution.

2. The process according to claim 1, wherein the acrylamide is obtained by hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide.

3. The process according to claim 1, wherein the process comprises an additional step [0] conducted at location A comprising hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide, thereby obtaining an aqueous acrylamide solution, and wherein said aqueous acrylamide solution is used for step [1].

4. The process according to claim 3, wherein step [0] is performed in a relocatable bioconversion unit.

5. The process according to claim 1, wherein step [1] is performed in a relocatable monomer make-up unit.

6. The process according to claim 1, wherein step [2] is performed in a transportable polymerization unit having a volume from 5 m.sup.3 to 40 m.sup.3.

7. The process according to claim 1, wherein the initiators for radical polymerization to be used in course of step [2] comprise at least one redox initiator and at least one azo initiator.

8. The process according to claim 1, wherein T.sub.1 is from −5° C. to +5° C. and T.sub.2 is from 50° C. to 70° C.

9. The process according to claim 8, wherein the monomer concentration is from 15 to 24.9% by weight.

10. The process according to claim 1, wherein the monomer solution furthermore comprises at least one stabilizer for the prevention of polymer degradation.

11. The process according to claim 10, wherein the stabilizers are non-polymerizable stabilizers selected from the group of sulfur compounds, sterically hindered amines, N-oxides, nitroso compounds, aromatic hydroxyl compounds and ketones.

12. The process according to claim 11, wherein the amount of non-polymerizable stabilizers is from 0.1% to 2% by weight, relating to the sum of all monomers in the aqueous monomer solution.

13. The process according to claim 1, wherein step [2] is performed in a transportable polymerization unit P1 comprising a cylindrical upper part having a length of 4 m to 6 m and a diameter from 1.5 m to 2.5 m, a conical part at its lower end having a conus angle from 15° to 90°, feeds for the aqueous monomer solution, a bottom opening having a diameter from 0.2 to 0.8 m for removing the polyacrylamide gel, and means allowing to deploy the unit P1 in a vertical manner.

14. The process according to claim 13, wherein the volume of the polymerization unit P1 is from 20 m.sup.3 to 30 m.sup.3.

15. The process according to claim 1, wherein the aqueous polyacrylamide gel is removed from the transportable polymerization unit in course of step [4] by applying pressure onto the gel and pressing it through an opening in the polymerization unit, wherein the pressure onto the gel is applied by (i) means of gases, selected from the group of air, nitrogen, and argon and/or (ii) by means of aqueous fluids.

16. The process according to claim 15, wherein a polymerization unit P1 is used, and the aqueous polyacrylamide gel is removed through the bottom opening.

17. The process according to claim 1, wherein comminuting the aqueous polyacrylamide gel in course of step [5] is carried out by conveying the aqueous polyacrylamide gel through at least one comminuting unit thereby yielding pieces of aqueous polyacrylamide gel.

18. The process according to claim 17, wherein the aqueous polyacrylamide gel is conveyed through the at least one comminuting unit together with an aqueous liquid thereby yielding a mixture of pieces of aqueous polyacrylamide gel in an aqueous polyacrylamide solution.

19. The process according to claim 17 wherein the comminution unit comprises means for comminuting aqueous polymer gels selected from static cutting devices, moving cutting devices, perforated plates, static mixers, water-jet cutting devices and combinations thereof.

20. The process according to claim 17, wherein at least one of the comminuting units is a water-jet cutting device.

21. The process according to claim 1, wherein dissolution in course of step [5] is performed in a dissolution unit comprising at least a dissolution vessel and means for mixing the aqueous polyacrylamide gel with the aqueous liquid.

22. The process according to claim 21, wherein the dissolution unit is a relocatable dissolution unit.

23. The process according to claim 22, wherein the relocatable dissolution unit comprises at least a dissolution vessel, at least one stirrer, means for filling the dissolution unit with aqueous liquid and pieces of aqueous polyacrylamide gel and means for removing aqueous polyacrylamide solution.

24. The process according to claim 21 wherein at least two relocatable dissolution units are connected in series.

25. The process according to claim 1, wherein the aqueous polyacrylamide solution obtained in course of step [5] is transported from location B to a site-of-use which is distant from location B in a transport unit and removed from the transport unit at the site-of-use.

26. The process according to claim 25, wherein the aqueous polyacrylamide solution is transported in the transport unit is a concentrate having a concentration of 2.1% to 14.9% by weight.

27. The process according to claim 26, wherein—before use—the concentrate is further diluted with an aqueous liquid at the site-of-use.

28. A process for producing an aqueous polyacrylamide solution comprising polymerizing an aqueous solution comprising at least acrylamide thereby obtaining an aqueous polyacrylamide gel and dissolving said aqueous polyacrylamide gel in water, characterized in that the process comprises at least the following steps: [0] hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide, thereby obtaining an aqueous acrylamide solution at a location A, [1] preparing an aqueous monomer solution comprising at least water and 15% to 24.9% by weight—relating to the total of all components of the aqueous monomer solution—of water-soluble, monoethylenically unsaturated monomers at a location A, wherein said aqueous solution comprises at least the aqueous acrylamide solution prepared in course of step [0], [2] inerting and radically polymerizing the aqueous monomer solution prepared in step [1] in the presence of suitable initiators for radical polymerization under adiabatic conditions at a location A, wherein the polymerization is performed in a transportable polymerization unit having a volume of 5 m.sup.3 to 40 m.sup.3, the aqueous monomer solution has a temperature T.sub.1 from −5° C. to +5° C. before the onset of polymerization, and the temperature of the polymerization mixture raises in course of polymerization—due to the polymerization heat generated—to a temperature T.sub.2 from 50° C. to 70° C., thereby obtaining an aqueous polyacrylamide gel having a temperature T.sub.2 which is held in the transportable polymerization unit, [3] transporting the transportable polymerization unit filled with the aqueous polyacrylamide gel from location A to a different location B, [4] removing the aqueous polyacrylamide gel from the transportable polymerization unit at the location B, and [5] comminuting and dissolving the aqueous polyacrylamide gel in an aqueous liquid at the location B, thereby obtaining an aqueous polyacrylamide solution.

29. The process according to claim 1, wherein all process steps are carried out using relocatable units.

30. A process for producing an aqueous polyacrylamide gel comprising polymerizing an aqueous solution comprising at least acrylamide, characterized in that the process comprises at least the following steps: [1] preparing an aqueous monomer solution comprising at least water and 5% to 45% by weight—relating to the total of all components of the aqueous monomer solution—of water-soluble, monoethylenically unsaturated monomers at a location A, wherein said water-soluble, monoethylenically unsaturated monomers comprise at least acrylamide, [2] inerting and radically polymerizing the aqueous monomer solution prepared in step [1] in the presence of suitable initiators for radical polymerization under adiabatic conditions at a location A, wherein the polymerization is performed in a transportable polymerization unit having a volume of 1 m.sup.3 to 40 m.sup.3, the aqueous monomer solution has a temperature T.sub.1 not exceeding 30° C. before the onset of polymerization, and the temperature of the polymerization mixture raises in course of polymerization—due to the polymerization heat generated—to a temperature T.sub.2 of at least 45° C., thereby obtaining an aqueous polyacrylamide gel which is held in the transportable polymerization unit.

31. The process according to claim 30, wherein the process comprises an additional step [0] of hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide, thereby obtaining an aqueous acrylamide solution which is used for step [1].

32. A process for producing an aqueous polyacrylamide solution comprising dissolving an aqueous polyacrylamide gel in water, characterized in that the process comprises at least the following steps: [1a] providing an aqueous polyacrylamide gel comprising 5% to 45% by weight of a polyacrylamide obtainable by polymerization of an aqueous solution comprising water-soluble, monoethylenically unsaturated monomers comprising at least acrylamide, wherein the aqueous polyacrylamide gel is held in a transportable polymerization unit having a volume of 1 m.sup.3 to 40 m.sup.3, [2a] removing the aqueous polyacrylamide gel from the transportable polymerization unit, [3a] comminuting and dissolving the aqueous polyacrylamide gel in an aqueous liquid, thereby obtaining an aqueous polyacrylamide solution.

33. The process according to claim 32, wherein the transportable polymerization unit is a transportable polymerization unit P1 comprising a cylindrical upper part (30) having a length of 4 m to 6 m and a diameter from 1.5 m to 2.5 m, a conical part (31) at its lower end having a conus angle from 15° to 90°, feeds for the aqueous monomer solution, a bottom opening (32) having a diameter from 0.2 to 0.8 m for removing the polyacrylamide gel, and means (33) allowing to deploy the unit P1 in a vertical manner.

Description

EXAMPLES

(1) The invention is illustrated in detail by the examples which follow.

(2) I) Simulation of Gel Temperature in Polymerization Unit

(3) In order to better to demonstrate that the polyacrylamide gel cools down in the polymerization unit only very slowly, a mathematical simulation was run. For the simulation, the following parameters were used:

(4) TABLE-US-00002 Parameters: Polymerization unit: Cylindrical, length 6 m, diameter 2 m Volume: 18.8 m.sup.3 (completely filled with polyacrylamide gel) Starting temperature*: 90° C. Outside temperature: 20° C. Heat transfer coefficient on 10 W/m.sup.2 K the outside of the reactor wall: Polyacrylamide 70 wt. % acrylamide, 30 wt. % sodium acrylate Concentration of 30% polymer in water: Density of polymer gel: 1100 kg/m.sup.3 Heat capacity of polymer gel: 3.6 kJ/(kg*K) Thermal Conductivity: 0.43 W/(m K) Average temperature: volume-average temperature of gel in entire unit Maximum temperature: maximum temperature observed at time of observation anywhere in the polymerization unit. *temperature of the gel after polymerization, same starting temperature within entire reactor

(5) FIG. 7 shows the results of the simulation.

(6) As expected the average temperature decreases faster than the maximum temperature (the maximum temperature basically is observed in the center of the polymerization unit which is most apart from the walls). Basically, the temperature of the polymer gel only slowly decreases. Even after 5 days the average temperature still is about 65° C. and the maximum temperature still close to 90° C. After 10 days the average temperature is about 45° C. and the maximum temperature about 80° C. The simulation shows that at least parts of the gel still have a temperature of 80° C. even 10 days after polymerization.

(7) II) Gel Damage and Strategies to Avoid Gel Damage

(8) Test Series 1

(9) The first test series was performed with copolymers comprising 75 mole % acrylamide and 25 mole % sodium acrylate.

(10) Copolymer 1 is an unstabilized copolymer for which a monomer concentration of 30 wt. % relating to the sum of all components of the monomer solution was used. The acrylamide used was made by Cu-catalysis. The temperature in course of polymerization rose to 86° C.

(11) For copolymers 2, 3, and 4 the monomer concentration was reduced to 23 wt. % and the temperature in course of polymerization only rose to 60° C. Furthermore, bio acrylamide was used instead of Cu acrylamide.

(12) Copolymer 2 also was unstabilized, copolymer 3 comprised the stabilizer NaMBT, and copolymer 4 the polymerizable stabilizer MA-HPMP (which is a monoethylenically unsaturated monomer which polymerizes with the other monomers).

(13) Also for copolymer 5, the monomer concentration was 23% by wt., acrylamide obtained by Cu-catalysis from acrylonitrile was used. No stabilizer was used.

(14) Copolymer 1:

(15) Copolymer Comprising 69.4 Wt. % (75.0 Mole %) of Acrylamide and 30.6 Wt. % (25 Mole %) of Sodium Acrylate

(16) A 5 l beaker with magnetic stirrer, pH meter and thermometer was initially charged with 918.0 g of a 35% aqueous solution of Na-acrylate, and then the following were added successively: 1020.4 g of distilled water, 1457.4 g of acrylamide (52% by weight in water, Cu-catalysis), 26.3 g of 4,4′-azobis(4-cyanovaleric acid) solution (4% by weight in 5% sodium hydroxide solution) and 10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid, pentasodium salt.

(17) After adjustment to pH 6.0 with a 50% by weight solution of sulfuric acid and addition of the rest of the water to attain the desired monomer concentration of 30% by weight (total amount of water 1069.6 g minus the amount of water already added, minus the amount of acid required), the monomer solution was adjusted to the initiation temperature of 0° C. The solution was transferred to a Dewar vessel, the temperature sensor for the temperature recording was inserted, and the flask was purged with nitrogen for 45 minutes. The polymerization was initiated with 17.5 g of a 4% methanolic solution of the azo initiator azo-bis-(isobutyronitrile)dihydrochloride, 1.68 g of a 1% t-BHPO solution and 0.84 g of a 1% sodium sulfite solution. With the onset of the polymerization, the temperature rose to 86° C. within about 50 min. A solid polymer gel was obtained.

(18) After the polymerization, the gel was incubated for 2 hours at 80° C. and the gel block was comminuted with the aid of a meat grinder. The comminuted aqueous polyacrylamide gel was kept for further testing without drying.

(19) Copolymer 2:

(20) Copolymer Comprising 69.4 Wt. % (75.0 Mole %) of Acrylamide and 30.6 Wt. % (25 Mole %) of Sodium Acrylate

(21) A 5 l beaker with magnetic stirrer, pH meter and thermometer was initially charged with 703.8 g of a 35% aqueous solution of Na-acrylate, and then the following were added successively: 1500 g of distilled water, 1074.4 g of acrylamide (52% by weight in water, bio acrylamide), 10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid, pentasodium salt, 2.8 g of a 1 wt. % aqueous solution of sodium hypophoshite hydrate.

(22) After adjustment to pH 6.4 with a 20% by weight solution of sulfuric acid and addition of the rest of the water to attain the desired monomer concentration of 23% by weight (total amount of water 1711.3 g minus the amount of water already added, minus the amount of acid required), the monomer solution was adjusted to the initiation temperature of 0° C. The solution was transferred to Dewar vessel, the temperature sensor for the temperature recording was inserted, and the flask was purged with nitrogen for 45 minutes. The polymerization was initiated with 21 g of a 10% aqueous solution of the water-soluble azo initiator 2,2′-azobis(2-methylpropionamidine) dihydrochloride (Wako V-50; 10 h t.sub.1/2 in water 56° C.), 1.75 g of a 1% t-BHPO solution and 1.05 g of a 1% sodium sulfite solution. With the onset of the polymerization, the temperature rose to 60° C. within about 50 min. A solid polymer gel was obtained.

(23) After the polymerization, the gel was incubated for 4 hours at 60° C. and the gel block was comminuted with the aid of a meat grinder. The comminuted aqueous polyacrylamide gel was kept for further testing without drying.

(24) Copolymer 3:

(25) Copolymer Comprising 69.4 Wt. % (75.0 Mole %) of Acrylamide and 30.6 Wt. % (25 Mole %) of Sodium Acrylate, Stabilized with 0.25% Wt. % NaMBT (Relating to Polymer)

(26) A 5 l beaker with magnetic stirrer, pH meter and thermometer was initially charged with 702.0 g of a 35% aqueous solution of Na-Acrylate, and then the following were added successively: 1500 g of distilled water, 1071.7 g of acrylamide (52% by weight in water, bio acrylamide) 10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid, pentasodium salt, 2.8 g of a 1 wt. % aqueous solution of sodium hypophoshite hydrate, and 4 g of a 50% aqueous solution of the stabilizer sodium 2-mercaptobenzothiazole (NaMBT).

(27) After adjustment to pH 6.4 with a 20% by weight solution of sulfuric acid and addition of the rest of the water to attain the desired monomer concentration of 23% by weight (total amount of water 1687.3 g minus the amount of water already added, minus the amount of acid required), the monomer solution was adjusted to the initiation temperature of 0° C. The solution was transferred to Dewar vessel, the temperature sensor for the temperature recording was inserted, and the flask was purged with nitrogen for 45 minutes. The polymerization was initiated with 21 g of a 10% aqueous solution of the water-soluble azo initiator 2,2′-azobis(2-methylpropionamidine) dihydrochloride (Wako V-50; 10 h t.sub.1/2 in water 56° C.), 1.75 g of a 1% t-BHPO solution and 1.05 g of a 1% sodium sulfite solution. With the onset of the polymerization, the temperature rose to 60° C. within about 50 min. A solid polymer gel was obtained.

(28) After the polymerization, the gel was incubated for 4 hours at 60° C. and the gel block was comminuted with the aid of a meat grinder. The comminuted aqueous polyacrylamide gel was kept for further testing without drying.

(29) Copolymer 4:

(30) Copolymer Comprising 69.4 Wt. % (75.0 Mole %) of Acrylamide and 30.6 Wt. % (25 Mole %) of Sodium Acrylate, Stabilized with 0.05 wt. % MA-HPMP (Relating to Polymer)

1,2,2,6,6-pentamethyl-4-piperidinol methacrylate (MA-HPMP)

(31) ##STR00001##

(32) A 5 l beaker with magnetic stirrer, pH meter and thermometer was initially charged with 703.8 g of a 35% aqueous solution of Na-Acrylate, and then the following were added successively: 1500 g of distilled water, 1073.6 g of acrylamide (52% by weight in water, bio acrylamide), 10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid, pentasodium salt, 2.8 g of a 1 wt. % aqueous solution of sodium hypophoshite hydrate, and 4.0 g of a 10% aqueous solution of the polymerizable stabilizer (MA-HPMP).

(33) After adjustment to pH 6.4 with a 20% by weight solution of sulfuric acid and addition of the rest of the water to attain the desired monomer concentration of 23% by weight (total amount of water 1683.6 g minus the amount of water already added, minus the amount of acid required), the monomer solution was adjusted to the initiation temperature of 0° C. The solution was transferred to Dewar vessel, the temperature sensor for the temperature recording was inserted, and the flask was purged with nitrogen for 45 minutes. The polymerization was initiated with 21 g of a 10% aqueous solution of the water-soluble azo initiator 2,2′-azobis(2-methylpropionamidine) dihydrochloride (Wako V-50; 10 h t.sub.1/2 in water 56° C.), 1.75 g of a 1% t-BHPO solution and 1.05 g of a 1% sodium sulfite solution. With the onset of the polymerization, the temperature rose to 60° C. within about 50 min. A solid polymer gel was obtained.

(34) After the polymerization, the gel was incubated for 4 hours at 60° C. and the gel block was comminuted with the aid of a meat grinder. The comminuted aqueous polyacrylamide gel was kept for further testing without drying.

(35) Copolymer 5:

(36) Copolymer Comprising 69.4 Wt. % (75.0 Mole %) of Acrylamide and 30.6 wt. % (25 mole %) of Sodium Acrylate

(37) A 5 l beaker with magnetic stirrer, pH meter and thermometer was initially charged with 703.8 g of a 35% aqueous solution of Na-Acrylate, and then the following were added successively: 1500 g of distilled water, 1117.3 g of acrylamide (52% by weight in water, Cu-catalysis), 10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid, pentasodium salt and 7 g of a 0.1 wt. % aqueous solution of sodium hypophoshite hydrate.

(38) After adjustment to pH 6.4 with a 20% by weight solution of sulfuric acid and addition of the rest of the water to attain the desired monomer concentration of 23% by weight (total amount of water 1668.4 g minus the amount of water already added, minus the amount of acid required), the monomer solution was adjusted to the initiation temperature of 0° C. The solution was transferred to Dewar vessel, the temperature sensor for the temperature recording was inserted, and the flask was purged with nitrogen for 45 minutes. The polymerization was initiated with 21 g of a 10% aqueous solution of the water-soluble azo initiator 2,2′-azobis(2-methylpropionamidine) dihydrochloride (Wako V-50; 10 h t.sub.1/2 in water 56° C.), 1.75 g of a 1% t-BHPO solution and 1.05 g of a 1% sodium sulfite solution. With the onset of the polymerization, the temperature rose to 60° C. within about 50 min. A solid polymer gel was obtained.

(39) After the polymerization, the gel was incubated for 3 hours at 60° C. and the gel block was comminuted with the aid of a meat grinder. The comminuted aqueous polyacrylamide gel was kept for further testing without drying.

(40) Storage of the Polyacrylamide Gels at Various Temperatures:

(41) Test samples of the comminuted aqueous polyacrylamide gels to be tested were put into a vacuum bag, the vacuum bag purged with nitrogen for 15 min, the bags evacuated and heat-sealed. The bags filled with aqueous polyacrylamide gel were stored in a hot-air cabinet for up to 7 days at pre-defined temperatures.

(42) With the stored gels, the following tests were performed:

(43) Viscosity in Aqueous Solution

(44) Measurements were performed in “pH 7 buffer”: For 10 l of pH 7 buffer fully dissolve 583.3±0.1 g sodium chloride, 161.3±0.1 g disodium hydrogenphosphate.12H.sub.2O and 7.80±0.01 g sodium dihydrogenphosphate.2H.sub.2O in 10 l dist. or deionized water. A 5000 ppm polymer solution was obtained by dissolving the appropriate amount of polymer gel in pH 7 buffer until being fully dissolved.

(45) Filtration Ratio

(46) Determination of MPFR (Millipore Filtration Ratio)

(47) The filterability of the polymer solutions was characterized using the MPFR value (Millipore filtration ratio). The MPFR value characterizes the deviation of a polymer solution from ideal filtration characteristics, i.e. when there is no reduction of the filtration rate with increasing filtration. Such a reduction of the filtration rate may result from the blockage of the filter in course of filtration.

(48) To determine the MPFR values, about 200 g of the relevant polyacrylamide solution having a concentration of 1000 ppm were filtered through a polycarbonate filter have a pore size of 5 μm at a pressure of 2 bar and the amount of filtrate was recorded as a function of time.

(49) The MPFR value was calculated by the following formula
MPFR=(t.sub.180 g−t.sub.160 g)/(t.sub.80 g−t.sub.60 g).

(50) T.sub.x g is the time at which the amount solution specified passed the filter, i.e. t.sub.180 g is the time at which 180 g of the polyacrylamide solution passed the filter. According to API RP 63 (“Recommended Practices for Evaluation of Polymers Used in Enhanced Oil Recovery Operations”, American Petroleum Institute), values of less than 1.3 are acceptable.

(51) Gel Fraction

(52) A 5000 ppm polymer solution in pH 7 buffer is diluted to 1000 ppm with pH 7 buffer. The gel fraction is given as mL of gel residue on the sieve when 250 g 1000 ppm polymer solution are filtered over 200 μm sieve and consequently washed with 2 l of tab water.

(53) The test results for copolymer 1 are summarized in table 1, the results for copolymers 2 to 5 are summarized in table 2.

(54) TABLE-US-00003 TABLE 1 Results of gel storage tests. Viscosity measured at 5000 ppm in pH 7 buffer at RT, 50 s−1. MPFR measured at 1000 ppm in pH 7 buffer, 2 bar. Gel Acrylamide Storage Viscosity volume No. Copolymer Stabilizer type Duration T [°] [mPas] MPFR [ml] Remarks 1 1 — Cu 0 days — 78 1.08 <1 2 1 — Cu 1 day 30° C. 80 1.15 1 3 1 — Cu 7 days 30° C. 83 1.08 <1 4 1 — Cu 14 days 30° C. 71 1.15 1 5 1 — Cu 0 days — 78 1.08 1 6 1 — Cu 1 day 60° C. 79 1.04 <1 7 1 — Cu 3 days 60° C. 74 1.4 2 8 1 — Cu 7 days 60° C. 68 1.47 4 9 1 — Cu 14 days 60° C. 61 — 31 No MPFR measurement possible 10 1 — Cu 0 days — 68 1.1 1 11 1 — Cu 1 day 90° C. 65 2.5 3-4 12 1 — Cu 3 days 90° C. 60 — 12 No MPFR measurement possible 13 1 — Cu 7 days 90° C. 62 — 12 No MPFR measurement possible

(55) TABLE-US-00004 TABLE 2 Results of gel storage tests. Viscosity measured at 5000 ppm in pH 7 buffer at RT, 100 s−1. MPFR measured at 1000 ppm in pH 7 buffer, 2 bar. Mean Mean Acrylamide Storage viscosity Mean gel volume No. Copolymer Stabilizer type Duration T [°] [mPas] MPFR [ml] Remarks 14 2 — bio 4 h 60° C.  55 (1)* 1.1 0 15 2 — bio 7 days 50° C. 57 (8) 1.1 0 16 2 — bio 7 days 60° C. 52 (2) 1.1 0 17 2 — bio 7 days 70° C. 46 (4) 1.2 0 18 3 NaMBT bio 4 h 60° C. 54 (2) 1.1 0 19 3 NaMBT bio 7 days 50° C. 63 (2) 1.1 0 20 3 NaMBT bio 7 days 60° C. 55 (2) 1.2 0 21 3 NaMBT bio 7 days 70° C. 60 (2) 1.1 0 22 4 MA-HPMP bio 4 h 60° C. 54 (1) 1.0 0 23 4 MA-HPMP bio 7 days 50° C. 54 (3) 1.1 0 24 4 MA-HPMP bio 7 days 60° C. 55 (4) 1.1 0 25 4 MA-HPMP bio 7 days 70° C. 52 (7) 1.2 0 26 5 — Cu 4 h 50° C. 53 1.1 0 27 5 — Cu 1 day 50° C.  37 (7)** 1.0 0 28 5 — Cu 4 days 50° C. 38 (1) 1.0 0 29 5 — Cu 8 days 50° C. 44 (6) 1.0 0 30 5 — Cu 4 h 60° C. 53 1.1 0 31 5 — Cu 1 day 60° C. 45 (0) 1.0 0 32 5 — Cu 4 days 60° C. — — — gel no longer soluble 33 5 — Cu 4 h 70° C. 53 1.1 0 34 5 — Cu 1 day 70° C. 37 (8) 1.1 0 35 5 — Cu 4 days 70° C. — — — gel no longer soluble (*in brackets: standard deviation for viscosity, mean value out of three independent samples, **in brackets: standard deviation for viscosity, mean value out of two independent samples)

(56) TABLE-US-00005 TABLE 3 Results of gel storage tests. Viscosity measured at 5000 ppm in pH 7 buffer at RT, 100 s−1. MPFR measured at 1000 ppm in pH 7 buffer, 2 bar. Mean Mean Acrylamide Storage viscosity Mean gel volume No. Copolymer Stabilizer type Duration T [°] [mPas] MPFR [ml] Remarks 36 3 NaMBT bio 4 h 60° C.  48 (1)* 1.08 0 37 3 NaMBT bio 1 day 80° C. 47 (1) 1.12 0 38 3 NaMBT bio 2 days 80° C. 53 (1) 1.08 0 39 3 NaMBT bio 3 days 80° C. 50 (1) 1.09 0 40 3 NaMBT bio 7 days 80° C. 49 (0) 1.07 0 41 3 NaMBT bio 14 days 80° C. 51 (1) 1.16 0 42 3 NaMBT bio 21 days 80° C. 48 (3) 1.28 0 (*in brackets: standard deviation for viscosity, mean value out of three independent samples)

(57) The tests with copolymer 1 demonstrate that it is possible to store an unstabilized aqueous polyacrylamide gel (acrylamide made by Cu catalysis) at 30° C. for 14 days without significant deterioration of its properties. At 60° C. one day storage is possible. After 3 days already some deterioration is observed. The 7 days and 14 days data indicate a very pronounced increase on insoluble fraction, indicating crosslinking. The 90° C. data show that there is a pronounced deterioration already after 1 day.

(58) Summarizing the results, the unstabilized aqueous polyacrylamide gel comprising copolymer 1 may be transported at 30° C. without problems, at 60° C. quick transports with transporting times of less than 3 days seems possible, while a transport at 90° C. seems to be not possible.

(59) The aqueous gel comprising copolymer 2 was synthesized with another recipe thereby limiting the temperature increase to temperature to 60° C. Furthermore, bio acrylamide was used. It also was unstabilized. The gel could be stored at 50° C. and 60° C. for 7 days without deterioration of its properties. At 70° C. after 7 days a slight increase in the MPFR and a decrease in viscosity is observed.

(60) Copolymer 3 was synthesized in the same manner as copolymer 2, except that the stabilizer NaMBT was added. Adding the stabilizer yields an increased stability also at 70° C. and the same holds true for MA-HPMP (Copolymer 4). In both cases the drop in viscosity after 7 days as compared to copolymer 2 may be avoided.

(61) Finally, the tests with copolymer 5 demonstrate the advantages of using bio acrylamide as compared to acrylamide made by copper catalysis for the process according to the present invention. The tests at 50° C. show that the viscosity decreases upon storing but the gel remains soluble and no gel fractions are formed. However, storing the gels at 60° C. and at 70° C. for 4 days yielded gel which no longer were soluble. So, the gels seemed to have been crosslinked.

(62) Table 3 demonstrates that aqueous polyacrylamide gels stabilized with NaMBT may also be stored at 80° C. for at least 7 days. The viscosity remained more or less the same (with the errors of measurement) for 21 days. Also the MPFR remained stable for about 7 days and then began to increase slightly. However, even after 21 days it was slightly below the value of 1.3.

(63) Test Series 2

(64) Further tests were conducted with another type of polyacrylamide copolymer, namely a copolymer comprising about 33.3 wt. % of acrylamide and 66.7 wt. % of sodium acrylate.

(65) For copolymer 6, the monomer concentration was 35% by weight and the temperature rose to 86° C. in course of polymerization. No stabilizer was used.

(66) For copolymer 7, the monomer concentration was 28% by weight and the temperature rose to 73° C. in course of polymerization. MA-HPMP was used as stabilizer.

(67) Copolymer 6:

(68) Copolymer Comprising 33.3 Wt. % (39.8 Mole %) of Acrylamide and 66.7 Wt. % (60.2 Mole %) of Sodium Acrylate

(69) A 1 μl beaker with magnetic stirrer, pH meter and thermometer was initially charged with 266.8 g of a 35% aqueous solution of Na-Acrylate, and then the following were added successively: 35.1 g of distilled water, 89.7 g of acrylamide (52% by weight in water, bio acrylamide), 2.04 g of 4,4′-Azobis(4-cyanovaleric acid) solution (4% by weight in 5% sodium hydroxide solution) and 1.2 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid, pentasodium salt.

(70) After adjustment to pH 6.7 with a 20% by weight solution of sulfuric acid and addition of the rest of the water to attain the desired monomer concentration of 35% by weight (total amount of water 40 g minus the amount of water already added, minus the amount of base required), the monomer solution was adjusted to the initiation temperature of 0° C. The solution was transferred to Dewar vessel, the temperature sensor for the temperature recording was inserted, and the flask was purged with nitrogen for 45 minutes. The polymerization was initiated 0.12 g of a 1% t-BHPO solution and 0.24 g of a 1% sodium sulfite solution. With the onset of the polymerization, the temperature rose to 86° C. within about 60 min. A solid polymer gel was obtained.

(71) After the polymerization, parts of the gel was comminuted with the aid of a meat grinder. The other part of the gel was incubated at 90° C. vacuum sealed under nitrogen for 24 hours and then comminuted with the aid of a meat grinder.

(72) Copolymer 7:

(73) Copolymer Comprising 33.3 Wt. % (39.8 Mole %) of Acrylamide and 66.7 Wt. % (60.2 Mole %) of Sodium Acrylate, Stabilized with 0.05 wt. % MA-HPMP (Relating to Polymer)

(74) A 5 l beaker with magnetic stirrer, pH meter and thermometer was initially charged with 1867.6 g of a 35% aqueous solution of Na-Acrylate, and then the following were added successively: 900 g of distilled water, 626.6 g of acrylamide (52% by weight in water, bio acrylamide) 4.9 g of a 10% by weight methanolic MA-HPMP solution and 10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid, pentasodium salt.

(75) After adjustment to pH 6.9 with a 10% by weight solution of sodium hydroxide and addition of the rest of the water to attain the desired monomer concentration of 28% by weight (total amount of water 968.3 g minus the amount of water already added, minus the amount of base required), the monomer solution was adjusted to the initiation temperature of 0° C. The solution was transferred to Dewar vessel, the temperature sensor for the temperature recording was inserted, and the flask was purged with nitrogen for 45 minutes. The polymerization was initiated with 21 g of a 10% aqueous solution of the water-soluble azo initiator 2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (Wako VA-044; 10 h t.sub.1/2 in water 44° C.), 1.05 g of a 1% t-BHPO solution and 2.1 g of a 1% sodium sulfite solution. With the onset of the polymerization, the temperature rose to 73° C. within about 60 min. A solid polymer gel was obtained.

(76) After the polymerization, the gel was comminuted with the aid of a meat grinder. A fraction of the gel granules obtained were dried in a fluidized bed drier at 55° C. for two hours, another fraction was kept as aqueous polyacrylamide gel for further testing.

(77) Tests

(78) The tests of the polyacrylamide gels were performed in the same manner as described above. The data are summarized in table 4.

(79) TABLE-US-00006 TABLE 4 Results of gel storage tests. Viscosity measured at 5000 ppm in 0.1M NaOH at RT, 300 s−1. Gel fraction: ml gel in 5000 ppm solution filtered over 190 μm sieve. Mean Mean Acrylamide Storage viscosity gel volume No. Copolymer Stabilizer type Duration T [°] [mPas] [ml] comment 43 6 — bio gel 0 h —  74 (9)* 0 44 6 — bio gel 24 h 90° C. 56 (4) 25 extremely high gel fraction 45 7 MA-HPMP bio gel 0 h 70° C. 52 (2) 0 46 7 MA-HPMP bio powder 0 h 70° C. 50 (1) 0 47 7 MA-HPMP bio gel 24 h 70° C. 51 (1) 0 48 7 MA-HPMP bio powder 24 h 70° C. 53 (1) 0 (*in brackets: standard deviation for viscosity, mean value out of three independent samples). Powder sample is generated from gel as described above for comparative purposes.

(80) Storing the unstabilized copolymer 6 only 1 day at 90° C. yields a significant decrease in viscosity and very pronounced amounts of gel are formed. Such a product were no longer suitable for oilfield uses and other uses.

(81) Copolymer 7 synthesized with an adapted recipe and stabilized with MA-HPMP could be stored for 24 h without any decrease in viscosity and without any gel formation.