WO2022106308A1

WO2022106308A1 - Process for making water-soluble, nvp-containing copolymers in powder form

Info

Publication number: WO2022106308A1
Application number: PCT/EP2021/081476
Authority: WO
Inventors: Philipp VON TIEDEMANN; David Franz REISER; Ivan BOSNJAK; Alexander KRONAST; Christian Bittner
Original assignee: Basf Se
Priority date: 2020-11-23
Filing date: 2021-11-12
Publication date: 2022-05-27

Abstract

Process for making water-soluble, NVP-containing copolymers in powder form comprising an amount of residual water from 5 wt.-% to 25 wt.-% by radically polymerizing an aqueous solution comprising from 20 to 70 wt.-% of water-soluble ethylenically unsaturated monomers comprising at least acrylamide or derivatives thereof and NVP in the presence of suitable initiators for radical polymerization under adiabatic conditions thereby obtaining an aqueous polymer gel followed by comminuting the aqueous polymer gel obtained and drying it at a temperature of less than 80°C for less than 150 min. Use of NVP-containing copolymers made by such process in enhanced oil recovery.

Description

Process for making water-soluble, NVP-containing copolymers in powder form

The present invention relates to a process for producing water-soluble, NVP-containing copolymers in powder form comprising a residual amount of water from 5 wt.-% to 25 wt.-% by radically polymerizing an aqueous solution comprising from 20 to 70 wt.-% of water- soluble ethylenically unsaturated monomers comprising at least N-vinylpyrrolidone (NVP) and a water-soluble, monoethylenically unsaturated comonomer in the presence of suitable initiators for radical polymerization under adiabatic conditions, thereby obtaining an aqueous polymer gel followed by comminuting the aqueous polymer gel and drying it at a temperature of less than 80°C for less than 150 min. The invention furthermore relates to the use of NVP- containing polymers made by such process in enhanced oil recovery.

Water-soluble, NVP-containing copolymers are known in the art, in particular polyacrylamides comprising NVP. Polyacrylamides may be used for oifield applications, for example for enhanced oil recovery applications. Using NVP-containing polyacrylamides in particular is helpful, if the polymers are used at higher temperatures for a longer time period, for example in enhanced oil recovery operations in a subterranean formation having a relatively high formation temperature. Copolymers comprisng NVP and acrylamide and their use in oilfield applications have been described for example in H. L. Hsieh et al., Makromol. Chem., Macromol. Symp. 64, 121 - 135 (1992), US 5,080,809, WO 2010/133527 A2, WO 2013/108174 A1 , or WO 2014/166858 A1.

A common polymerization technology for manufacturing water-soluble, high molecular weight polymers, such as polyacrylamides is the so called “gel polymerization”. In gel polymerization, an aqueous monomer solution having a relatively high concentration of monomers, for example from 20 % by weight to 45 % by weight is polymerized by means of suitable polymerization initiators under essentially adiabatic conditions in an unstirred reactor thereby forming a polymer gel.

It is known in the art to dissolve such gels in water, thereby directly obtaining aqueous polymer solutions. However, for transporting and storing the polymers, the aqueous polymer gels are often dried thereby obtaining a free-flowing powder of such polymers, for example polyacrylamides. Such polymer powders may be transported to the location of use and dissolved in water for use.

The drying conditions are relevant for the amount of residual water in the obtained product. The higher the drying temperature and the longer the drying time, the less the amount of residual water in the product obtained.

WO 2010/133527 A2 discloses hydrophobically associating polymers, specifically hydrophobically associating polyacrylamides. NVP may be used as comonomer. The document also discloses gel polymerization. After the polymerization, the aqueous polymer gel obtained is comminuted and dried. The document discloses that drying should preferably take place at temperatures below 100°C. Examples 11 and 12 specifically disclose the manufacture of a copolymer comprising acrylamide, NVP, ATBS or a cationic monomer, acrylic acid, and an associative monomer. The monomers are polymerized in aqueous solution at a monomer concentration of about 50 %. The obtained aqueous polyacrylamide gel is dried in a drying chamber at 90 to 120°C in vacuum.

WO 2014/166858 A1 discloses water soluble polymers for oil and gas applications comprising acrylamide, NVP, and ATBS. The polymers are manufactured by adiabatic gel polymerization. The obtained aqueous gel is dried, however, the publication does not disclose any details about the conditions of drying.

WO 2019/081328 A1 discloses a process for producing hydrophobically associating polyacrylamides by adiabatic gel polymerization thereby obtaining an aqueous polyacrylamide gel. NVP may be used as comonomer. The obtained aqueous gels may be used directly without drying or they may be dried, however, the publication does not disclose any details about the conditions of drying.

US 5,080,809 discloses polymers useful in the recovery and processing of natural resources. Table LVIII discloses a polymer comprising N-vinylpyrrolidone, acrylamide, NaATBS and acrylic acid. Regarding the polymerization conditions the document discloses only that the polymers were made by conventional solution polymerization technology using total solids levels of 20 to 30 % in distilled water at ambient temperature with about 0.1 phm of initiator. The document does not comprise details about, how the polymers may be dried.

Our older applications WO 2021/037578 A1 and WO 2021/037579 A1 disclose water-soluble copolymers comprising acrylamide, ATBS, NVP and small amounts of polymerizable or non- polymerizable carboxylic acids. The documents mention that the aqueous polymer gels may be dried but don’t provide any details about drying.

WO 2012/069477 A1 discloses the manufacture of polyacrylamides comprising an associative monomer acrylamide and at least one further comonomer. NVP as comonomer has not been mentioned. It is suggested to dry the aqueous polymer gel at temperatures below 100°C. Specifically, the examples disclose the manufacture of a copolymer (“polymer 1”) comprising acrylamide, ATBS and an associative monomer by adiabatic gel polymerization The aqueous polymer gel obtained is dried in a fluid bed dryer at 55°C for 2 hours. WO 2012/069478 A1 and WO 2012/069438 A1 describe the synthesis of the same kind of polymers. Also, WO 2015/086468 A1 discloses the synthesis of polyacrylamides comprising acrylamide, ATBS and/or acrylic acid and an associative monomer by adiabatic gel polymerization and drying the aqueous polymer gel obtained at 55°C for 2 h in a fluid bed dryer. NVP has not been mentioned as a comonomer. EP 2 789670 A1 discloses water soluble polymers for oil and gas field applications comprising NVP, ATBS and acrylamide, wherein the amount of NVP is from 25 mol % to 45 mol %, and NVP and ATBS are used at equimolar amounts. The experimental part discloses the synthesis of such a polymer by gel polymerization, followed by drying thereby obtaining a powder with less than 15 % of water. The document provides no details about, how the gels are dried.

The inventors of the present invention found that the properties of NVP-containing polyacrylamides may be easily deteriorated by drying at high temperatures for longer times.

It was an object of the present invention to provide an improved process of making NVP- containing copolymers in powder form which avoids such a deterioration of properties in course of drying.

Surprisingly, it has been found that drying aqueous polymer gels comprising water-soluble NVP-containing copolymers at lower temperatures and a shorter drying time yields free- flowing powders of such NVP-containing copolymers with good application properties and good handling properties although the polymers still comprise significant amounts of residual water.

Accordingly, the present invention relates to a process for producing water-soluble, NVP- containing copolymers in powder form by radically polymerizing an aqueous solution comprising from 20 to 70 wt.-% -relating to the total of all components of the aqueous solution- of water-soluble ethylenically unsaturated monomers in the presence of suitable initiators for radical polymerization under adiabatic conditions, thereby obtaining an aqueous polymer gel followed by drying the aqueous polymer gel, wherein the NVP-containing copolymers comprise at least

(A) 5 mole-% to 70 mole-% of N-vinylpyrrolidone,

(B) 30 mole-% to 95 mole-% of at least one water-soluble, monoethylenically unsaturated monomer, wherein the amounts of the monomers relate to the total of all ethylenically unsaturated monomers in the NVP-containing copolymer, wherein

• the aqueous polymer gel is comminuted into pieces,

• the obtained aqueous polymer gel pieces are dried at a temperature of less than 80°C for less than 150 min, and the obtained polymer powder comprises a residual amount of water from 5 wt.- % to 25 wt.-%, relating to the total of the polymer powder. In one embodiment, the monomers (B) comprise at least one monomer (B1) selected from the group of (meth)acrylamide, N-methyl(meth)acryl-amide, N,N'-dimethyl(meth)acrylamide or N-methylol(meth)acrylamide.

In another embodiment, the monomers (B2) comprise at least 2-acrylamido-2- methylpropanesulfonic acid or a salt thereof.

With regard to the invention, the following can be stated specifically:

In the process according to the present invention, an aqueous monomer solution comprising N-vinylpyrrolidone (A) and at least one further water-soluble, monoethylenically unsaturated comonomer (B) is used. Of course, further ethylenically unsaturated monomers, preferably monoethylenically unsaturated monomers may be present. The aqueous solution is polymerized in the presence of suitable initiators for radical polymerization under adiabatic conditions thereby obtaining an aqueous polymer gel.

Monomers

The water-soluble NVP-containing copolymers to be manufactured according to the process of the present invention comprise N-vinylpyrrolidone (monomer (A)), or abbreviated NVP. The amount of NVP is from 5 to 70 mole-%, relating to the total of all ethylenically unsaturated monomers in the polymer, preferably from 20 to 50 mole-%. Further embodiments are mentioned below.

In addition to monomer (A), the water-soluble, NVP-containing copolymers furthermore comprise at least one water-soluble, monoethylenically unsaturated monomer (B) different from monomer (A).

The term “water-soluble” in the context of this invention means that the monomers are to be soluble in the aqueous monomer solution to be used for polymerization in the desired use concentration. It is thus not absolutely necessary that the monomers to be used are miscible with water without any gap; instead, it is sufficient if they meet the minimum requirement mentioned. It has to be noted that the presence of the monomers mentioned above in the monomer solution might enhance the solubility of other monomers as compared to water only. In general, the solubility of water-soluble monomers in water at room temperature should be at least 50 g/l, preferably at least 100 g/l.

The amount of monomers (B) is from 30 to 95 mole-%, relating to the total of all ethylenically unsaturated monomers in the polymer, preferably from 50 to 80 mole-%. Further embodiments are mentioned below. The water-soluble, monoethylenically unsaturated monomers (B) are selected from the group of neutral monomers (B1), anionic monomers (B2) or cationic monomers (B3). Of course, two or more monomers (B) from different members of the group may be present.

Examples of monomers (B1) comprise (meth)acrylamide, N-methyl(meth)acryl-amide, N,N'- dimethyl(meth)acrylamide N-methylol(meth)acrylamide, N-vinylformamide, N- Vinylcaprolactam, N-vinylacetamide or monomers comprising hydroxy and/or ether groups, such as, for example, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, allyl alcohol, hydroxyvinyl ethyl ether or hydroxyl vinyl propyl ether.

In one embodiment of the invention, the monomers (B1) are selected from (meth)acrylamide, N-methyl(meth)acryl-amide, N,N'-dimethyl(meth)acrylamide or N-methylol(meth)acrylamide, preferably the monomers (B1) is (meth)acrylamide, especially acrylamide. If mixtures of different monomers (B1) are used, preferably at least 50 mole-% of the monomers (B1) should be (meth)acrylamide, preferably acrylamide. In one embodiment of the invention, the monomer (B1) is acrylamide.

The water-soluble, anionic monoethylenically unsaturated monomers (B2) comprise at least one acidic group or salts thereof. The acidic group is preferably at least one acidic group selected from the group of -COOH, -SO3H or -PO3H2 or salts thereof. Preference is given to monomers (B2) comprising -COOH groups and/or -SO3H groups or salts thereof.

Examples of monomers comprising -COOH groups include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid. Preference is given to acrylic acid.

Examples of monomers comprising sulfo groups include vinylsulfonic acid, allylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2-acrylamidobutanesulfonic acid, 3-acrylamido-3-methylbutanesulfonic acid and 2- acrylamido-2,4,4-trimethylpentanesulfonic acid. Preference is given to vinylsulfonic acid, allylsulfonic acid or 2-acrylamido-2-methylpropanesulfonic acid, and particular preference to 2-acrylamido-2-methylpropanesulfonic acid.

Examples of monomers comprising phosphonic acid groups include vinylphosphonic acid, allylphosphonic acid, N-(meth)acrylamidoalkylphosphonic acids and (meth)acryloyloxyalkyl- phosphonic acids, preference being given to vinylphosphonic acid.

In one embodiment, the monomers (B) are selected from the group of monomers (B1) and (B2). In one embodiment, the monomers (B) comprise at least monomers (B1) and monomers (B2).

The water-soluble, cationic monoethylenically unsaturated monomers (B3) comprise at least an ammonium group. Examples comprise quaternized derivatives of N-(o-aminoalkyl) (meth)acrylamides or co -ami noalkyl (meth)acrylic esters such a 3-trimethylammonium propylacrylamide chloride and 2-trimethylammonium ethyl methacrylate chloride.

In one embodiment, the water-soluble, NVP-containing copolymers additionally comprise besides the monomers (A) and (B) at least one monomer (C) selected from the group of monomers having the general formula

H₂C=C(R¹)-O-(-CH₂-CH(R²)-O-)k-R³ (I),

H₂C=C(R¹)-(C=O)-O-(-CH₂-CH(R²)-O-)k-R³ (II),

H₂C=C(R¹)-R⁴-O-(-CH₂-CH(R⁵)-O-)x-(-CH₂-CH(R⁶)-O-)_y-(-CH₂-CH₂O-)z-R⁷ (III), and

H₂C=C(R¹)-R⁴-O-(CH₂-CH₂-O-)a-(CH₂-CH(CH₃)-O-)b-R⁷ (IV).

Such monomers (C) comprise hydrophilic and hydrophobic moieties. When polymerized with water-soluble monomers, the polymerization yields water-soluble polymers comprising a small amount of side chains comprising hydrophobic moieties. In aqueous solution, said hydrophobic moieties may associate with each other, thereby yielding an aqueous solution having an increased viscosity as compared to the same polymer comprising no monomers (C). Polymers comprising such type of monomers are therefore also called “hydrophobically associating polymers”.

In the formulae (I), (II), (III), and (IV) R¹ is H or methyl, preferably H.

The R² moieties are each independently H, methyl or ethyl, preferably H or methyl, with the proviso that at least 70 mole % of the R² radicals are H. Preferably at least 80 mole % of the R² radicals are H, more preferably at least 90 mole %, and they are most preferably exclusively H. This block is thus a polyoxyethylene block which may optionally include certain proportions of propylene oxide and/or butylene oxide units, preferably a pure polyoxyethylene block.

The number of alkylene oxide units k is a number from 10 to 80, preferably 12 to 60, more preferably 15 to 50 and, for example, 20 to 40. It will be apparent to the person skilled in the art in the field of alkylene oxides that the values mentioned are mean values.

R³ is an aliphatic and/or aromatic, straight-chain or branched hydrocarbyl radical having 8 to 40 carbon atoms, preferably 12 to 32 carbon atoms. In one embodiment, the aliphatic hydrocarbyl groups are those having 8 to 22 and preferably 12 to 18 carbon atoms.

Examples of such groups include n-octyl, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl or n- octadecyl groups. In a further embodiment, the groups are aromatic groups, especially substituted phenyl radicals, especially distyrylphenyl groups and/or tristyrylphenyl groups.

In the monomers (C) of the formula (III), an ethylenic H₂C=C(R²)- group is bonded via a divalent linking -R⁴-O- group to a polyoxyalkylene moiety having block structure, wherein the -(-CH₂-CH(R⁵)-O-)X-, -(-CH₂-CH(R⁶)-O-)I- and optionally -(-CH₂-CH₂O-)_Z-R⁷ blocks are arranged in the sequence shown in formula (III). The transition between the two blocks may be abrupt or else continuous.

In formula (III), R¹ has the definition already defined, i.e. R¹ is H or a methyl group, preferably H.

R⁴ is a single bond or a divalent linking group selected from the group consisting of -(C_nH_2n)-, -O-(Cn'H₂n')- and -C(O)-O-(Cn"H_2n")-. In the formulae mentioned, n in each case is a natural number from 1 to 6; n¹ and n" are each a natural number from 2 to 6. In other words, the linking group comprises straight-chain or branched aliphatic hydrocarbyl groups which have 1 to 6 carbon atoms and may be joined directly, via an ether group -O- or via an ester group -C(O)-O- to the ethylenic H₂C=C(R²)- group. The -(C_nH_2n)-, -(Cn H₂n)- and -(C_n H_2n”)- groups are preferably linear aliphatic hydrocarbyl groups.

Preferably, the -(C_nH_2n)- group is a group selected from -CH₂-, -CH₂-CH₂- and -CH₂-CH₂- CH₂-, more preferably a methylene group -CH₂-.

Preferably, the -O-(C_n H₂n’)- group is a group selected from -O-CH₂-CH₂-, -O-CH₂-CH₂-CH₂- and -O-CH₂-CH₂-CH₂-CH₂-, more preferably -O-CH₂-CH₂-CH₂-CH₂-.

Preferably, the -C(O)-O-(C_n”H_2n”)- group is a group selected from -C(O)-O-CH₂-CH₂-, - C(O)O-CH(CH₃)-CH₂-, -C(O)O-CH₂-CH(CH₃)-, -C(O)O-CH₂-CH₂-CH₂-CH₂- and -C(O)O-CH₂- CH₂-CH₂-CH₂-CH₂-CH₂-, more preferably -C(O)-O-CH₂-CH₂- and -C(O)O-CH₂-CH₂-CH₂- CH₂-, and most preferably is -C(O)-O-CH₂-CH₂-.

More preferably, the R⁴ group is a -O-(C_n'H_2n')- group, most preferably a group -O-CH₂-CH₂-CH₂-CH₂-.

In the -(-CH₂-CH(R⁵)-O-)_X- block, the R⁵ radicals are independently H, methyl or ethyl, preferably H or methyl, with the proviso that at least 70 mole-% of the R⁵ radicals are H. Preferably at least 80 mole-% of the R⁵ radicals are H, more preferably at least 90 mole-%, and they are most preferably exclusively H. This block is thus a polyoxyethylene block which may optionally include certain proportions of propylene oxide and/or butylene oxide units, preferably a pure polyoxyethylene block.

The number of alkylene oxide units x is a number from 10 to 50, preferably 12 to 40, more preferably 15 to 35, even more preferably 20 to 30 and, for example, 23 to 26. It will be apparent to the person skilled in the art in the field of polyalkylene oxides that the numbers mentioned are mean values of distributions. In the second -(CH2-CH(R⁶)-O)_y- block, the R⁶ radicals are independently hydrocarbyl radicals of at least 2 carbon atoms, for example 2 to 10 carbon atoms, preferably 2 or 3 carbon atoms. This may be an aliphatic and/or aromatic, linear or branched carbon radical. Preference is given to aliphatic radicals.

Examples of suitable R⁶ radicals include ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl or n-decyl and phenyl. Examples of preferred radicals include ethyl, n-propyl, n-butyl, n-pentyl, especially ethyl and/or n-propyl radicals, and more preferably ethyl radicals. The -(-CH2-CH(R⁶)-O-)_y- block is thus a block consisting of alkylene oxide units having at least 4 carbon atoms.

The number of alkylene oxide units y is a number from 5 to 30, preferably 8 to 25.

In formula (III), z is a number from 0 to 10, preferably 0 to 5, i.e. the terminal block of ethylene oxide units is thus only optionally present. In one embodiment of the invention, z is a number > 0 to 10, especially > 0 to 10 and, for example, 1 to 4.

The R⁷ radical is H or a preferably aliphatic hydrocarbyl radical having 1 to 30 carbon atoms, preferably 1 to 10 and more preferably 1 to 5 carbon atoms. R⁷ is preferably H, methyl or ethyl, more preferably H or methyl and most preferably H.

In one embodiment of the invention, a mixture of at least two different monomers (C) of the formula (III) is used, where the radicals R¹, R⁴, R⁵, R⁶, and R⁷ and the indices x and y are the same in each case. In addition, z = 0 in one of the monomers, while z is a number > 0 to 10, preferably 1 to 4, in the other. Said preferred embodiment is thus a mixture of the following composition:

H₂C=C(R¹)-R⁴-O-(-CH2-CH(R⁵)-O-)x-(-CH₂-CH(R⁶)-O-)y-H (Illa) and

H₂C=C(R¹)-R⁴-O-(-CH2-CH(R⁵)-O-)x-(-CH2-CH(R⁶)-O-)y-(-CH2-CH₂O-)z-H (lllb), where the radicals and indices have the definition outlined above, including the preferred embodiments thereof, with the proviso that, in the formula (lllb), z is a number > 0 to 10.

Preferably, in the formulae (Illa) and (lllb), R¹ is H, R⁴ is -O-CH2CH2CH2CH2-, R⁵ is H, R⁶ is ethyl, x is 20 to 30, preferably 23 to 26, y is 12 to 25, preferably 14 to 18, and z is 3 to 5.

In the monomers (C) of the formula (IV), the radicals R¹, R⁴, and R⁷ have the same meaning as already defined above, including the preferred embodiments described above. In formula (IV), a is a number from 10 to 50, in particular 20 to 40, preferably 20 to 30, and b is a number from 10 to 125, in particular 35 to 125, preferably 40 to 100, and for example from 55 The monomers (C) of the formulae (I), (II), (III), and (IV), their preparation, copolymers comprising these monomers and the preparation thereof are known in principle to those skilled in the art, for example from WO 85/03510 A1 , WO 2010/133527 A1 , WO 2012/069478 A1 , WO 2014/095608 A1 , WO 2014/095621 A1 , WO 2015/086486 A1 , WO 2020/084033 A1 and in the literature cited therein.

In a preferred embodiment of the invention, at least one of the monomers (C) is a monomer of the formula (III), preferably a mixture comprising at least the two monomers (Illa) and (lllb) is used.

If monomers (C) are present, their amount may be from 0.005 mole % to 1 mole %, in particular, from 0.005 mole % to 0.2 mole %, and for example from 0.005 mole % to 0.1 mole %.

In certain embodiments of the invention, the water-soluble, NVP-containing copolymers to be manufactured may optionally comprise additional, water-soluble ethylenically unsaturated monomers (D) different from the monomers (A), (B), and (C) mentioned above. Examples of monomers (D) comprise monomers comprising more than one ethylenically unsaturated group, i.e. crosslinking monomers. Such crosslinking monomers may be used in exceptional cases in limited amounts, however preferably, no such crosslinking monomers are used. If present at all, their amount should be less than 0.5 mole %, more preferably less than 0.1 mole % relating to the total of all ethylenically unsaturated monomers in the water-soluble, NVP-containing copolymers.

The water-soluble, NVP-containing copolymers manufactured according to the process of the present invention comprise at least

(A) 5 mole-% to 70 mole-%, preferably 5 mole-% to 50 mole-% of N-vinylpyrrolidone (A),

(B) 30 mole-% to 95 mole-%, preferably 50 mole-% to 95 mole-% of at least one water- soluble monoethylenically unsaturated monomer (B), wherein the amounts of the monomers relate to the total of all ethylenically unsaturated monomers in the NVP-containing copolymer.

In one preferred embodiment, the monomers (B) comprise at least one monomer (B1) selected from the group of (meth)acrylamide, N-methyl(meth)acryl-amide, N,N'- dimethyl(meth)acrylamide or N-methylol(meth)acrylamide, preferably the monomer (B1) is (meth)acrylamide, more preferably acrylamide.

In another preferred embodiment, the monomers (B) comprise at least one monomer (B2) comprising -COOH groups and/or -SO3H groups or salts thereof. Preferably, the monomer (B2) is 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof. In one embodiment of the invention, the water-soluble, NVP-containing copolymers manufactured comprise

(A) 5 mole-% to 70 mole-%, preferably 5 mole-% to 50 mole-%, more preferably 5 mole-% to 35 mole-% of N-vinylpyrrolidone, and

(B1) 30 mole-% to 95 mole-%, preferably 50 mole-% to 95 mole-%, more preferably 65 mole- % to 95 mole-% of at least one monomer (B1) selected from the group of (meth)acrylamide, N-methyl(meth)acrylamide, N,N'-dimethyl(meth)acrylamide or N- methylol(meth)acrylamide, wherein the amounts of the monomers relate to the total of all ethylenically unsaturated monomers in the copolymer.

In one embodiment of the invention, the water-soluble, NVP-containing copolymers manufactured comprise

(A) 5 mole-% to 70 mole-%, preferably 10 mole-% to 50 mole-%, more preferably 20 mole- % to 50 mole-% of N-vinylpyrrolidone, and

(B2) 30 mole-% to 95 mole-%, preferably 50 mole-% to 90 mole-%, more preferably 50 mole-% to 80 mole-% of a monomer (B2) which is 2-acrylamido-2- methylpropanesulfonic acid or a salt thereof, wherein the amounts of the monomers relate to the total of all ethylenically unsaturated monomers in the copolymer.

In yet another embodiment, the water-soluble, NVP-containing copolymers manufactured comprise

(A) 5 mole-% to 35 mole-%, preferably from 10 mol-% to 30 mol-% of N-vinylpyrrolidone,

(B1) 30 mole-% to 90 mole-%, preferably from 50 mole-% to 80 mole-% of at least one monomer (B1) selected from the group of (meth)acrylamide, N- methyl(meth)acrylamide, N,N'-dimethyl(meth)acrylamide or N- methylol(meth)acrylamide, and

(B2) 5 mole-% to 35 mole-%, preferably from 10 mol-% to 30 mol-% of 2-acrylamido-2- methylpropanesulfonic acid or a salt thereof, wherein the amounts of the monomers relate to the total of all ethylenically unsaturated monomers in the copolymer.

Aqueous monomer solution

For carrying out the process according to the present invention, an aqueous monomer solution comprising water-soluble ethylenically unsaturated monomers is used. At least the monomers (A) and (B) are used, preferably at least monomers (A), (B1), and/or (B2). Details of the monomers and their respective amounts have been mentioned above. The amounts of the monomers in the aqueous solution correspond to the amounts of monomers in the final copolymer.

Besides water, the aqueous monomer solution may also comprise additionally water-miscible organic solvents. However, as a rule the amount of water should be at least 70 % by wt. relating to the total of all solvents used, preferably at least 85 % by wt. and more preferably at least 95 % by weight. In one embodiment, only water is used as solvent.

The concentration of the aqueous monomers in the aqueous solution is from 20 to 70 wt.-% relating to the total of all components of the aqueous solution, preferably from 20 to 50 wt.-%, for example from 25 to 45 wt.-% or from 30 to 40 wt.-%.

Besides the monomers, further additives and auxiliaries may be added to the aqueous monomer solution. Examples of such further additives and auxiliaries comprise complexing agents, defoamers, surfactants, stabilizers, and bases or acids for adjusting the pH value. In certain embodiments of the invention, for polymerization the pH-value of the aqueous monomer solution is adjusted to values from pH 5 to pH 8, preferably from 5 to 7, and for example from pH 6 to pH 7. As will be detailed below, before polymerization suitable initiators for radical polymerization are added.

In one embodiment, the aqueous monomer solution comprises at least one stabilizer for the prevention of polymer degradation. Such stabilizers for the prevention of polymer degradation are what are called “free-radical scavengers”, i.e. compounds which can react with free radicals (for example free radicals formed by heat, light, redox processes), such that said radicals can no longer attack and hence degrade the polymer. Using such kind of stabilizers for the stabilization of aqueous solutions of polymers basically is known in the art, as disclosed for example in WO 2015/158517 A1 , WO 2016/131940 A1, or WO 2016/131941 A1.

The stabilizers may be selected from the group of non-polymerizable stabilizers and polymerizable stabilizers. Polymerizable stabilizers comprise a monoethylenically unsaturated group and become incorporated into the polymer chain in course of polymerization. Non-polymerizable stabilizers don’t comprise such monoethylenically unsaturated groups and are not incorporated into the polymer chain.

In one embodiment of the invention, stabilizers are non-polymerizable stabilizers selected from the group of sulfur compounds, sterically hindered amines, N-oxides, nitroso compounds, aromatic hydroxyl compounds or ketones.

Examples of sulfur compounds include thiourea, substituted thioureas such as N,N‘- dimethylthiourea, N,N‘-diethylthiourea, N,N‘-diphenylthiourea, thiocyanates, for example ammonium thiocyanate or potassium thiocyanate, tetramethylthiuram disulfide, and mercaptans such as 2-mercaptobenzothiazole or 2-mercaptobenzimidazole or salts thereof, for example the sodium salts, sodium dimethyldithiocarbamate, 2,2‘-dithiobis(benzothiazole), 4,4‘-thiobis(6-t-butyl-m-cresol).

Further examples include dicyandiamide, guanidine, cyanamide, paramethoxyphenol, 2,6-di- t-butyl-4-methylphenol, butylhydroxyanisole, 8-hydroxyquinoline, 2,5-di(t-amyl)- hydroquinone, 5-hydroxy-1,4-naphthoquinone, 2,5-di(t-amyl)hydroquinone, dimedone, propyl 3,4,5-trihydroxybenzoate, ammonium N-nitrosophenylhydroxylamine, 4-hydroxy-2, 2,6,6- tetramethyoxylpiperidine, (N-(1 ,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and

1.2.2.6.6-pentamethyl-4-piperidinol.

Preference is given to sterically hindered amines such as 1 ,2,2,6,6-pentamethyl-4-piperidinol and sulfur compounds, preferably mercapto compounds, especially 2-mercaptobenzothiazole or 2-mercaptobenzimidazole or the respective salts thereof, for example the sodium salts, and particular preference is given to 2-mercaptobenzothiazole or salts thereof, for example the sodium salts.

The amount of such non-polymerizable stabilizers -if present- may be from 0.1 % to 2.0 % by weight, relating to the total of all monomers in the aqueous monomer solution, preferably from 0.15 % to 1.0 % by weight and more preferably from 0.2 % to 0.75 % by weight.

In another embodiment of the invention, the stabilizers are polymerizable stabilizers substituted by a monoethylenically unsaturated group. Examples of stabilizers comprising monoethylenically unsaturated groups comprise (meth)acrylic acid esters of 1, 2,2,6, - pentamethyl-4-piperidinol or other monoethylenically unsaturated groups comprising

1.2.2.6.6-pentamethyl-piperidin-4-yl groups. Specific examples of suitable polymerizable stabilizers are disclosed in WO 2015/024865 A1, page 22, lines 9 to 19. In one embodiment of the invention, the stabilizer is a (meth)acrylic acid ester of 1 ,2,2,6,6-pentamethyl-4- piperidinol.

The amount of polymerizable stabilizers -if present- may be from 0.01 to 2% by weight, based on the total sum of all the monomers in the aqueous monomer solution, preferably from 0.02 % to 1 % by weight, more preferably from 0.05 % to 0.5 % by weight.

In one embodiment, the aqueous monomer solution comprises at least one non- polymerizable surfactant. Examples of suitable surfactants including preferred amounts have been disclosed in WO 2015/158517 A1, page 19, line, 23 to page 20, line 27. In the manufacture of hydrophobically associating polymers, the surfactants lead to a distinct improvement of the product properties. If present, such non-polymerizable surfactant may be used in an amount of 0.1 to 5% by weight, for example 0.5 to 3 % by weight based on the amount of all the monomers used. Gel Polymerization

According to the present invention, the aqueous monomer solution is polymerized in the presence of suitable initiators for radical polymerization under adiabatic conditions thereby obtaining an aqueous polymer gel.

Such a polymerization technique is also briefly denominated by the skilled artisan as “adiabatic gel polymerization”. Reactors for adiabatic gel polymerization are unstirred. Due to the relatively high monomer concentration, the aqueous monomer solution used solidifies in course of polymerization thereby yielding an aqueous polymer gel. The term “polymer gel” has been defined for instance by L. Z. Rogovina et al., Polymer Science, Ser.

C, 2008, Vol. 50, No. 1, pp. 85-92. According to Rogovina et al., gels may be chemically crosslinked, or the gels may be physical gels.

“Adiabatic” is understood by the person skilled in the art to mean that there is no exchange of heat with the environment. This ideal is naturally difficult to achieve in practical chemical engineering. In the context of this invention, “adiabatic” shall consequently be understood to mean “essentially adiabatic”, meaning that the reactor is not supplied with any heat from the outside during the polymerization, i.e. is not heated, and the reactor is not cooled during the polymerization. However, it will be clear to the person skilled in the art that - according to the internal temperature of the reactor and the ambient temperature - certain amounts of heat can be released or absorbed via the reactor wall because of temperature gradients.

Naturally, this effect plays an ever-lesser role with increasing reactor size.

The polymerization of the aqueous monomer solution generates polymerization heat. Due to the adiabatic reaction conditions the temperature of the polymerization mixture increases in course of polymerization.

Suitable reactors for performing adiabatic gel polymerizations are known in the art. For example, cylindrical reactors may be used. Particularly advantageously, the polymerization can be conducted using (partly) conical reactors, as described, for example, by US 5,633,329 or US 7,619,046 B2. In one embodiment of the invention, the reactor comprises a cylindrical upper part and a conical part at its lower end. At the lower end, there is a bottom opening which may be opened and closed. After polymerization, the aqueous polymer gel formed is removed through the opening.

The polymerization is performed in the presence of suitable initiators for radical polymerization. Suitable initiators for radical polymerization, in particular for adiabatic gel polymerization are known to the skilled artisan.

In a preferred embodiment, redox initiators are used for initiating. Redox initiators can initiate a free-radical polymerization even at temperatures of less than +5°C. Examples of redox initiators are known to the skilled artisan and include systems based on Fe²⁺/Fe³⁺- H2O2, Fe²⁺/Fe³⁺ - alkyl hydroperoxides, alkyl hydroperoxides - sulfite, for example t-butyl hydroperoxide - sodium sulfite, peroxides - thiosulfate or alkyl hydroperoxides - sulfinates, for example alkyl hydroperoxides/ hydroxymethane-sulfinates, for example t-butyl hydroperoxide - sodium hydroxymethanesulfinate.

Furthermore, water-soluble azo initiators may be used. The azo initiators are preferably fully water-soluble, but it is sufficient that they are soluble in the monomer solution in the desired amount. Preferably, azo initiators having a 10 h ti/2 in water of 40°C to 70°C may be used. The 10-hour half-life temperature of azo initiators is a parameter known in the art. It describes the temperature at which, after 10 h in each case, half of the amount of initiator originally present has decomposed.

Examples of suitable azo initiators having a 10 h ti/2 temperature between 40 and 70°C include 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (10 h ti/2 (water): 44°C), 2,2'-azobis(2-methylpropionamidine) dihydrochloride (10 h ti/2 (water): 56°C), 2,2'-azobis[N- (2-carboxyethyl)-2-methylpropionamidine hydrate (10 h ti/2 (water): 57°C), 2,2'-azobis{2-[1- (2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride (10 h ti/2 (water): 60°C), 2,2'- azobis(1-imino-1-pyrrolidino-2-ethylpropane) dihydrochloride (10 h ti/2 (water): 67°C) or azobis(isobutyronitrile) (10 h ti/2 (toluene): 67°C).

In one embodiment of the invention a combination of at least one redox initiator and at least one azo initiator is used. The redox initiator efficiently starts polymerization already at temperatures below +5°C. When the reaction mixture heats up, also the azo initiators decompose and also start polymerization.

In the following, the temperature of the aqueous monomer solution before the onset of polymerization shall be denominated as T1 and the peak temperature of the aqueous polymer gel in course of polymerization shall be denominated as T2. It goes without saying that T2 > T1. The term “peak temperature” refers to the highest temperature reached in course of polymerization. In an ideal adiabatic system, the temperature should stay at the highest temperature also after polymerization, however, in “the real world” after polymerization, the temperature may start decreasing a bit from the peak temperature due to some unavoidable loss of heat.

Within the context of the present invention, the temperature T1 should not exceed 30°C. In particular, T1 should not exceed 25°C, preferably not 15°C and more preferably, T1 should not exceed 5°C. In one embodiment, T1 is in the range from -5°C to +5°C, for example from -5°C to 0°C.

As the polymerization is carried out under adiabatic conditions, the temperature T2 reached in course of polymerization is not influenced by external heating or cooling but only depends on the polymerization parameters chosen. By suitable choice of the polymerization parameters, the skilled artisan can adjust T2. Because the reaction is adiabatic, the temperature increase in course of polymerization basically depends on the heat of polymerization generated in course of polymerization, the heat capacity of the contents of the polymerization unit and the temperature T1 of the monomer solution, i.e. the temperature before the onset of polymerization. Due to high water contents of the mixture for polymerization the heat capacity of the mixture for polymerization is dominated by the heat capacity of water and it may of course be measured. The polymerization heat per mole for common monoethylenically unsaturated monomers is known in the art and may therefore be gathered from the scientific literature. Of course, it may also be measured. So, it is possible for the skilled artisan to calculate at least roughly the heat of polymerization for specific monomer compositions and specific monomer concentrations. The higher the concentration of the monoethylenically unsaturated monomers in the aqueous solution the more heat of polymerization is generated. T2 may be roughly calculated from the parameter mentioned above by the formula T2 = T1 + [(polymerization heat) I (heat capacity)].

According to the invention, the starting temperature T1 and the concentration of the monomers in the aqueous monomer solution is selected such, that the temperature T2 is from 45°C to 95°C, in particular from 80°C to 95°C, preferably from 50°C to 70°C, for example from 55°C to 70°C.

In one embodiment, T1 is from -5°C to + 5°C and T2 is from 45°C to 80°C, preferably from 50°C to 80°C, more preferably from 50°C to 70°C and for example from 55°C to 70°C.

Before polymerization oxygen from the reactor and the aqueous monomer solution to be polymerized is removed in basically known manner. Deoxygenation is also known as inertization. By the way of example, inert gases such as nitrogen or argon may be injected into the reactor filled with the aqueous monomer solution.

Polymerization processes

The polymerization can be carried out as batch polymerization or as continuous polymerization.

In a batch polymerization, the polymerization reactor is filled with the aqueous monomer solutions, the monomers are polymerized, and after polymerization the aqueous polymer gel is removed from the reactor. Advantageously, the aqueous polymer gel may be removed by applying pressure onto the gel and pressing it through an opening in the polymerization reactor. By the way of example, pressure may be generated by mechanical means such as a piston, by means of gases such as compressed air, nitrogen, argon or by means of aqueous fluids, in particular water. In continuous polymerization, the polymerization reactor continuously is fed with a monomer solution, the monomers are polymerized while moving through the reactor and aqueous polymer gel is continuously removed from the reactor. Preferably, for continuously polymerization, cylindrical reactor or a reactor having at least cylindrical sections may be used. For example, a vertical reactor having an upper cylindrical section and a lower conical section comprising a bottom opening may be used. The monomer solution may be fed at the upper end and the aqueous polymer gel is removed at the lower end through the bottom opening. In such a reactor, the transport of the polymerizing mixture through the reactor is affected by gravity and it may be supported by gas pressure.

A continuous polymerization may be a 2-step process, comprising a pre-polymerization in a first reactor and continuing the polymerization in a second reactor. In the pre-polymerization step typically not more than 25 % of the monomers are polymerized, so that the product from the first reactor is somewhat viscos but not yet a solid gel. In continuous polymerization there is always the risk, that the low viscosity monomer solution bypasses the aqueous polymer gel, for example at the reactor wall. The risk of bypassing is significantly diminished by feeding a higher viscos pre-polymerized solution.

In particular, a continuous polymerization may comprise at least the following sub-steps

• feeding aqueous monomer solution as described above through an inlet into a first reactor device comprising a positive displacement pump and partially polymerizing the aqueous monomer solution while transferring it from the inlet to an outlet of the first reactor device to provide a partially polymerized product, in which no more than 25% of the monomers have been polymerized as it exits the outlet;

• transferring the partially polymerized product to a second reactor device, and

• feeding the partially polymerized product into the second reactor device through an inlet, continuing the polymerization in the second reactor device and removing an aqueous polymer gel from the outlet of the second reactor device.

Preferably, the positive displacement pump is a progressive progressive cavity pump.

A continuous 2-step polymerization process in which a pre-polymerization is carried out in a first reactor device comprising a positive displacement pump is described in more detail in WO 2014/049513 A1.

Because no solvent is added or removed in course of adiabatic polymerization, the amount of water and optionally further solvents corresponds to the amounts in the aqueous solution used as starting material. Post-Processing the aqueous polymer gel

Comminution

Further processing of the aqueous polymer gel comprises at least comminution and drying of the aqueous polymer gel, thereby obtaining water-soluble, NVP-containing copolymers in powder form.

The size of the aqueous polymer gel pieces obtained in course of comminuting is not specifically limited. In an embodiment of the invention, the aqueous polymer gel pieces should conveniently have a size such that at least two dimensions are no more than 1 cm, preferably no more than 0.5 cm. Preferably three dimensions of the aqueous polymer gel pieces should be no more than 1 cm, preferably no more than 0.5 cm.

Basically, any kind of comminution means may be used for disintegrating the aqueous polymer gel into smaller pieces. Examples of suitable means for comminuting aqueous polymer gels include cutting devices such as knives or perforated plates, or crushers.

Drying

In course of drying not all of the water is removed. As will be outlined below, the powders obtained from the process according to the present invention still comprise certain amounts of water and are still free flowing. So, a complete removal of water is not necessary to obtain free-flowing powders which of course saves time and energy.

After comminution, the obtained aqueous polymer gel pieces are dried at a temperature of less than 80°C for less than 150 min, thereby obtaining a polymer powder which comprises an amount of residual water from 5 wt.-% to 25 wt.-%, relating to the total of the polymer powder.

The drying temperature is less than 80°C, preferably from 35°C to 75°C, more preferably from 35 to 55°C.

The drying time is less than 150 min, in particular from 20 to 120 min, preferably from 20 min to 60 min and for example from 20 min to 50 min.

Drying may be preferably be carried out at normal pressure but it may also be carried out at reduced pressure.

Basically, any kind of dryers may be used for carrying out the drying process, for example drum dryers, belt dryers or fluid bed dryers. Also, any kind of equipment for vacuum drying may be used although it is preferred not to use reduced pressure. In one embodiment of the invention, drying is carried out at standard pressure.

In one embodiment of the invention, a fluid bed dryer may be used.

The polymer powder obtained from the process according to the present invention still comprise -due to the mild drying conditions- residual amounts of water. Despite the residual amount of water, the powders are free flowing.

According to the invention, the amount of residual water in the water-soluble, NVP-containing copolymers in powder form is from 5 wt.-% to 25 wt.-%, relating to the total of the polymer powder, in particular from 5 wt.-% to 20 wt.-%. In certain embodiments, the amount may be from 8 to 20 wt.-%, in particular from 10 to 20 wt.-% and for example from 10 to 15 wt.-%.

Further steps

The dried product may be further processed, for example by grinding and sieving.

Use of water-soluble. NVP-containing polymers in powder form

The water-soluble NVP-containing polymers in powder form manufactured according to the process according to the present invention may be used for various purposes, for example for mining applications, oilfield applications, water treatment, waste-water cleanup, paper making or agricultural applications. Examples of oilfield applications include enhanced oil recovery, oil well drilling or the use as friction reducers, for example friction reducers for fracturing fluids.

In one embodiment, the water-soluble NVP-containing polymers in powder form are used for enhanced oil recovery.

Accordingly, the present invention also relates to the use of water-soluble, NVP-containing polymers in powder form for producing mineral oil from underground mineral oil deposits by dissolving said NVP-containing polymer powders in an aqueous liquid, thereby obtaining an aqueous injection fluid and injecting the aqueous injection fluid into a mineral oil deposit through at least one injection well and withdrawing crude oil from the deposit through at least one production well.

For the method of enhanced oil recovery, at least one production well and at least one injection well are sunk into the mineral oil deposit. In general, a deposit will be provided with a plurality of injection wells and with a plurality of production wells. An aqueous injection fluid is injected into the mineral oil deposit through at least one injection well, and mineral oil is withdrawn from the deposit through at least one production well. By virtue of the pressure generated by the aqueous injection fluid injected, called the “polymer flood”, the mineral oil flows in the direction of the production well(s) and is produced through the production well(s). In this context, the term “mineral oil” does not of course just mean a single-phase oil; instead, the term also encompasses the customary crude oil-water emulsions.

The water-soluble, NVP-containing copolymers according to the present invention may be used for any kind of subterranean formation. They are in particular suitable for mineral oil deposits having a formation temperature of at least 60°C. The mineral oil deposit may have a formation temperature from 40°C to 120°C, preferably from 60°C to 120°C, for example from 60°C to 100°C.

The aqueous liquid used for making the aqueous injection fluid, may be selected from freshwater, tap water or river water or from water comprising salts, such as seawater or formation water or mixtures thereof. In one embodiment, the aqueous injection fluid has a salinity of 10,000 ppm to 240,000 ppm, for example from 30,000 ppm to 200,000 ppm, relating to the total of all components of the aqueous injection fluid. In other embodiments, the aqueous injection fluid has a salinity from 100,000 ppm to 200,000 ppm.

In general, the concentration of the water-soluble, NVP-containing polymers in the injection fluid is 0.02 to 2% by weight based on the sum total of all the components in the aqueous formulation. The amount is preferably 0.05 to 1 % by weight, for example from 0.1 to 0.5% by weight.

The aqueous injection fluid may of course optionally comprise further components. Examples of further components include biocides, stabilizers, free-radical scavengers, initiators, surfactants, cosolvents, bases and complexing agents.

Using the water-soluble NVP-containing polymers in powder form manufactured according to the process according to the present invention has advantages for using them in enhanced oil recovery. As detailed in the experimental part, aqueous solutions obtained by dissolving the polymer powders prepared according to the process of the present invention have low filtration ratios, while other samples dried at higher temperatures have higher filtration ratios. A higher filtration ratio indicates beginning plugging of the filter due to insoluble portions in the solution, for example caused by beginning crosslinking of the polymer in course of drying. Such insoluble portions can also plug subterranean formations in course of enhanced oil recovery operations which is highly undesired.

Examples

The invention is illustrated in detail by the examples which follow. Polymer synthesis

Copolymer comprising 37.8 wt.-% (59.2 mole-%) acrylamide, 19.7 wt.-% (19,7 mole-%) N- vinylpyrrolidone (NVP), 40.6 wt.-% (21.0 mole-%) 2-acrylamido-2-methylpropanesulfonic acid, sodium salts (Na-ATBS), and 1.9 wt.-% (0.1 mole-%) of an associative macromonomer (H₂C=CH-O-(CH₂)4-O-(EO)24.5-(BuO)i6-(EO)3.5 ) (solid contents: 37.4 wt.-%)

1^st step: Gel polymerization

To 1000 g of water 1036.01 g of an aqueous Na-ATBS solution (50 mass% in water), 944.78 g of an aqueous acrylamide solution (51 mass% in water), 251.46 g NVP, 27.9 g of an aqueous solution of the macromonomer H₂C=CH-O-(CH₂)4-O-(EO)₂4.5-(BuO)i6-(EO)3.5 (87 mass% in water), 1.1 g of an aqueous solution of the trisodium salt of methylglycinediacetic acid (Trilon® M) (25 mass% in water), 21.5 g Sodium propionate (35 mass% in water), 31.2 g of the surfactant iCi3-(EO)i₂ Lutensol TO 129 (85 mass% in water) and 3.5 g of a commercially available silicon defoamer (Xiameter® AFE-0400) were added.

The pH value was adjusted to 6.0 (using 4.14 g of H₂SO4, 20 mass% aq.), and the residual amount of water (152.96 g) was added. The mixture was cooled to 0°C and then transferred into a thermos flask and degassed with nitrogen for 45 minutes. While purging, 21 g of the water soluble azo initiator 2, 2’-Azobis(2-methylpropionamidine)dihydrochloride (Wako V50; 10 mass% in water), 2.8 g of tert-Butylhydroperoxide (t-BHP) (1 mass% in water) were also added. The polymerization was initiated upon addition of 5.6 g of sodium sulfite (1 mass% in water) and then the nitrogen sparge pipe was carefully removed. Time/temperature readings were recorded until the polymerization was finished (polymerization peak temperature (~78 °C) was reached after ~16 minutes). An aqueous polymer gel was obtained.

After the polymerization, the thermocouple probe was removed, and the aqueous polymer gel was placed in a heated cabinet at 80 °C for 2 hours to allow the reduction of the residual monomer levels by the thermal initiator. For the drying tests, the obtained aqueous polymer gel was divided into portions of about 130 g to 150 g and sealed in polyethylene bags until use.

2^nd step: Drying

Each of the portions of aqueous polymer gel was minced with a meat mincer and dried in a fluid bed dryer at different temperatures and times. Details of the drying conditions chosen are provided below.

The basic Model 501 Fluid Bed Dryer (Sherwood Scientific, Ltd.) incorporates an air pump, heating coil, and temperature measurement (with control and timer). Air is drawn through an inlet filter, passed over a heating element and forced through a support filter (which holds the weight of the sample) and a tub inlet filter (selected for pores smaller than the sample particle size). The air passes through the sample contained within a 2 L glass tub, and finally through an outlet filter (filter bag). Bag material is selected to be chemically inert to emitted sample vapors. After drying the dried gel was milled to a particle size below 1 mm to produce a solid powder.

Characterization methods

Brine compositions

The following section explains the typical brine compositions that were used for all kinds of analyses.

Table No. 1: Brine no. 1.

Total dissolved solids (TDS) = 208020 mg/L,

Effective TDS (TDS without crystallization water) = 180353 mg/L, pH adjusted to 6,0

Millipore Filtration Ratio (MPFR) determination

The polymer (approx. 200 g) solution was diluted to 3500 with brine no. 1. Subsequently, the solution was stirred for 1 h at 200 rpm with the same overhead stirrer as described above and was filtered through a 190 pm sieve. 200 mL of this polymer solution was placed into a Sartorius filtration cell equipped with a 3 or 5 pm polycarbonate nucleo pore filter (aka Millipore). After closure of the cell, 2 bar of air was applied and the weight of the filtrate was measured over time. When the filtration was finished, the weight of the filtrate was plotted against the filtration time and the deviation from linearity was calculated by regression analysis. The flow rate is measured by following the filtrated mass of polymer solution over time. From these data the filtration ratio, MPFR, was calculated by inserting the times needed to collect a fixed mass of the filtrate into the following equation I:

Measurement of Anton-Paar viscosity The polymer solution was diluted to 3500 ppm and filtered through a 190 pm sieve for measurements in the reservoir brine no 1 (see composition above). The viscosity was measured with a double-gap system at 25 °C with an Anton-Paar rheometer (MCR-series, DG26.7) at a shear rate of 7.0 s’¹.

Results

The aqueous polyacrylamide gel (fractions of 130-150 g) obtained as above were dried in the fluid bed dryer as described above at different temperatures and at different times. All polymers were dried at 80% air flow. Testing was done in brine 1. The drying conditions and the results obtained are summarized in table 3.

Table 1. Data and drying conditions in course of making NVP-containing polymers.

The examples and comparative examples show that the drying temperature has a significant influence on the properties of the obtained water-soluble, NVP-containing copolymers in powder form. While the water content decreases with increasing temperature, the properties of the NVP-containing polymers deteriorate. At 80°C and more, the MPFR-value significantly increases. The larger the MPFR-value the more likely the polymer solution will clog the mineral oil deposit. Using shorter drying times at 120°C (comparative examples 6 and 7) does not improve the MPFR value. Only the combination of short drying times with low drying temperatures yields a good product. The residual amount of water in the obtained polymer powders is from 5.5 wt.-% to 14.7 wt.-% in the examples according to the present invention.

Claims

25 Claims:

1. Process for producing water-soluble, NVP-containing copolymers in powder form by radically polymerizing an aqueous solution comprising from 20 to 70 wt.-% -relating to the total of all components of the aqueous solution- of water-soluble, ethylenically unsaturated monomers in the presence of suitable initiators for radical polymerization under adiabatic conditions, thereby obtaining an aqueous polymer gel followed by drying the aqueous polymer gel obtained, wherein the NVP-containing copolymers comprise at least

(A) 5 mole-% to 70 mole-% of N-vinylpyrrolidone,

(B) 30 mole-% to 95 mole-% of at least one water-soluble monoethylenically unsaturated monomer, wherein the amounts of the monomers relate to the total of all ethylenically unsaturated monomers in the NVP-containing copolymer, and wherein

• the aqueous polymer gel is comminuted into pieces,

• the obtained aqueous polymer gel pieces are dried at a temperature of less than 80°C for less than 150 min, and

• the obtained polymer powder comprises an amount of residual water from 5 wt.-% to 25 wt.-%, relating to the total of the polymer powder.

2. Process according to claim 1 , wherein the temperature of drying is from 35°C to 75°C.

3. Process according to claim 1, wherein the temperature of drying is from 35°C to 55°C.

4. Process according to any of claims 1 to 3, wherein the drying time is from 20 min to 120 min.

5. Process according to any of claims 1 to 3, wherein the drying time is from 20 min to 60 min.

6. Process according to any of claims 1 to 5, wherein the amount of residual water is from 10 wt.-% to 15 wt.-%.

7. Process according to any of claims 1 to 6, wherein drying is carried out by means of a fluid bed dryer.

8. Process according to any of claims 1 to 7, wherein the monomers (B) comprise at least one monomer (B1) selected from the group of (meth)acrylamide, N-methyl(meth)acryl- amide, N,N'-dimethyl(meth)acrylamide or N-methylol(meth)acrylamide.

9. Process according to any of claims 1 to 7, wherein the monomers (B) comprise at least water-soluble, monoethylenically unsaturated monomers (B2) comprising -COOH groups and/or -SO3H groups or salts thereof.

10. Process according to claim 9, wherein the monomers (B2) comprise at least 2- acrylamido-2-methylpropanesulfonic acid or a salt thereof.

11 . Process according to any of claims 1 to 7, wherein the NVP-containing polymers comprise from

(A) 5 mole-% to 35 mole-% of N-vinylpyrrolidone,

(B1) 30 mole-% to 90 mole-% of at least one monomer selected from the group of (meth)acrylamide, N-methyl(meth)acrylamide, N,N'-dimethyl(meth)acrylamide or N-methylol(meth)acrylamide,

(B2) 5 mole-% to 35 mole % of 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof, wherein the amounts of the monomers relate to the total of all ethylenically unsaturated monomers in the NVP-containing copolymer.

12. Process according to claim 11 , wherein the amounts of (A), (B1), and (B2) are from

(A) 50 mole-% to 80 mole-%,

(B1) 10 mole-% to 25 mole-%, and

(B2) 10 mol-% to 25 mole-%.

13. Process according to any of claims 1 to 12, wherein the NVP-containing polymers comprise additionally at least one monoethylenically unsaturated monomer (C) selected from the group of

H₂C=C(R¹)-O-(-CH₂-CH(R²)-O-)k-R³ (I),

H₂C=C(R¹)-(C=O)-O-(-CH₂-CH(R²)-O-)k-R³ (II),

H₂C=C(R¹)-R⁴-O-(-CH₂-CH(R⁵)-O-)x-(-CH₂-CH(R⁶)-O-)_y-(-CH₂-CH₂O-)z-R⁷ (III), and H₂C=C(R¹)-R⁴-O-(CH₂-CH₂-O-)a-(CH₂-CH(CH₃)-O-)b-R⁷ (IV), wherein the radicals and indices are defined as follows: R¹: H or methyl;

R²: independently H, methyl or ethyl, with the proviso that at least 70 mole-% of the R² radicals are H,

R³: aliphatic and/or aromatic, linear or branched hydrocarbyl radicals having 8 to

40 carbon atoms,

R⁴: a single bond or a divalent linking group selected from the group consisting of

-(C_nH2_n)-, -O-(Cn'H2n')- and - C(O)-O-(Cn"H2n")-, where n is a natural number from 1 to 6, and n¹ and n" are a natural number from 2 to 6,

R⁵: independently H, methyl or ethyl, with the proviso that at least 70 mole-% of the R⁵ radicals are H,

R⁶: independently hydrocarbyl radicals of at least 2 carbon atoms,

R⁷: H or a hydrocarbyl radical having 1 to 30 carbon atoms, k a number from 10 to 80, x a number from 10 to 50, y a number from 5 to 30, z a number from 0 to 10, a a number from 10 to 50, and b a number from 10 to 125.

14. Use of water-soluble, NVP-containing polymers in powder form comprising at least

(A) 5 mole-% to 70 mole-% of N-vinylpyrrolidone,

(B) 30 mole-% to 95 mole-% of at least one water-soluble monoethylenically unsaturated monomer, wherein the amounts of the monomers relate to the total of all ethylenically unsaturated monomers in the NVP-containing copolymer, wherein the NVP-containing copolymer powder comprises an amount of residual water from 5 wt.-% to 25 wt.-%, relating to the total of the polymer powder, for producing mineral oil from underground mineral oil deposits by dissolving said NVP- containing polymer powders in an aqueous liquid, thereby obtaining an aqueous injection fluid and injecting the aqueous injection fluid into a mineral oil deposit through at least one injection well and withdrawing crude oil from the deposit through at least one production well, wherein water-soluble, NVP-containing polymers in powder form are manufactured by a process according to any of claims 1 to 13. 28 Use according to claim 14, wherein the mineral oil deposit has a formation temperature of at least 60°C. Use according to claim 14 or 15, wherein the aqueous injection fluid has a salinity from 100,000 ppm to 200,000 ppm, relating to the total of all components of the aqueous injection fluid.