Process for producing aqueous polyacrylamide solutions

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 is conducted in a modular, relocatable plant and the process comprises at least the following steps:

[1] Preparing—in a relocatable monomer make-up unit—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, 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, wherein

the polymerization is performed in a relocatable polymerization unit having a volume of 1 m 3 to 100 m 3 ,

the aqueous monomer solution before the onset of polymerization has a temperature T 1 not exceeding 30° C., and

the temperature of the polymerization mixture raises in course of polymerization—due to the polymerization heat generated—to a temperature T 2 of at least 45° C.,

thereby obtaining an aqueous polyacrylamide gel having a temperature T 2 which is held in the relocatable polymerization unit,

[3] removing the aqueous polyacrylamide gel from the relocatable polymerization unit,

[4] comminuting the aqueous polyacrylamide gel by conveying the aqueous polyacrylamide gel through at least one relocatable comminuting unit, thereby obtaining aqueous polyacrylamide gel pieces, and

[5] dissolving the aqueous polyacrylamide gel pieces in an aqueous liquid in a relocatable dissolution unit, thereby obtaining an aqueous polyacrylamide solution.

2. The process according to claim 1 , wherein the acrylamide needed for the process is obtained by hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide, thereby obtaining an aqueous acrylamide solution.

3. The process according to claim 2 , wherein the manufacture of acrylamide by hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide is conducted at another location and the aqueous acrylamide solution is transported to the location of the modular, relocatable plant.

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

5. The process according to claim 1 , wherein the relocatable monomer make-up unit comprises a double-walled monomer make-up vessel having a volume of 10 m 3 to 150 m 3 and means for controlling the temperature of the aqueous monomer solution.

6. The process according to claim 1 , wherein the relocatable polymerization unit has a volume from 5 m 3 to 40 m 3 .

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

8. The process according to claim 7 , wherein the monomer concentration is from 15 to 24.9% by weight.

9. The process according to claim 1 , wherein the relocatable polymerization unit is a polymerization unit P 1 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 for deploying the unit P 1 in a vertical manner.

10. The process according to claim 9 , wherein the volume of the relocatable polymerization unit P 1 is from 20 m 3 to 30 m 3 .

11. The process according to claim 1 , wherein the aqueous monomer solution is inerted by injecting an inert gas into a monomer feed line connecting the monomer make-up unit with the relocatable polymerization unit and removing the gas from the polymerization unit.

12. The process according to claim 1 , wherein the aqueous monomer solution is inerted in the relocatable polymerization unit by bubbling an inert gas through the aqueous monomer solution.

13. The process according to claim 12 , wherein the relocatable polymerization unit is a polymerization unit P 1 and the inert gas is introduced into the aqueous monomer solution by nozzles in the conical part of polymerization unit P 1 or an additional cylindrical section connection the lower end of the conical section and the bottom opening.

14. The process according to claim 1 , wherein the aqueous polyacrylamide gel is removed from the relocatable polymerization unit in course of step [3] by applying pressure onto the gel and pressing it through an opening in the polymerization unit, wherein pressure onto the gel is applied by means of gases, selected from the group consisting of air, nitrogen, and argon and/or by means of aqueous fluids.

15. The process according to claim 14 , wherein a polymerization unit P 1 is used, and the aqueous polyacrylamide gel is removed through the bottom opening.

16. The process according to claim 1 , wherein in course of step [4] the aqueous polyacrylamide gel is conveyed through the relocatable comminuting unit and an aqueous liquid is fed into the comminution unit, thereby yielding a mixture of pieces of aqueous polyacrylamide gel in an aqueous polyacrylamide solution.

17. The process according to claim 1 , wherein the relocatable comminution unit comprises means for comminuting aqueous polyacrylamide gels selected from the group consisting of static cutting devices, moving cutting devices, perforated plates, static mixers, water-jet cutting devices and combinations thereof.

18. The process according to claim 1 , wherein the relocatable comminution unit comprises at least one water-jet cutting device.

19. The process according to claim 1 , wherein a relocatable polymerization unit P 1 is used and the relocatable comminution unit ( 34 ) is connected with the bottom opening ( 32 ) of the polymerization unit P 1 and aqueous polyacrylamide gel is conveyed from the polymerization unit P 1 through the comminution unit.

20. The process according to claim 1 , 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.

21. The process according to claim 20 , wherein at least two relocatable dissolution units are connected in series.

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

23. The process according to claim 22 , wherein the aqueous polyacrylamide solution transported in the transport unit is a concentrate having a concentration of 2.1% to 14.9% by weight of polyacrylamides relating to the total of all components of the concentrate.

24. The process according to claim 22 , wherein the site-of-use is at an oil well.

25. The process according to claim 1 , wherein the modular, relocatable plant is deployed on an oilfield.

26. The process according to claim 1 , wherein the modular, relocatable plant is deployed in a mining area.