Apparatus and method for preparing aldehyde-functionalized polymers

Abstract

The present invention provides an apparatus for preparing a solution of a nonionic, cationic, anionic or amphoteric polymer P2 by reacting a compound comprising at least one aldehyde functional group with at least one aqueous solution of a raw polymer P1 comprising at least one nonionic monomer, the apparatus comprising a reactor (1) equipped with a stirring system; and a recirculation loop (3), comprising a recirculation pump (12) located between the reactor outlet and the reactor inlet, a pH measuring probe (13), and an online pressure difference measuring device (14) in the form of a calibration tube, which is used to measure the pressure difference of the polymer P2 solution between the inlet and the outlet of the calibration tube, the calibration tube being located in a bypass of the recirculation loop.

Description

Technical Field

[0001] The present invention relates to a new apparatus and method for producing aldehyde-functionalized polymers which are advantageously used in paper or paperboard manufacturing processes. Background Art

[0002] Water-soluble aldehyde-functionalized polyacrylamides are widely used in papermaking processes, especially to improve the dry strength of these papers. These water-soluble polyacrylamides are mainly made of nonionic, cationic, anionic or amphoteric base polymers.

[0003] Aldehyde-functionalized polyacrylamide has two disadvantages:

[0004] - They are supplied in the form of dilute aqueous solutions containing 5 to 12% by weight of polymer. Therefore, their transfer to paper mills involves logistical constraints and considerable transportation costs.

[0005] The useful life of these polymers in aqueous solution is very short (10 to 40 days), after which the polymer solution gels.

[0006] Furthermore, during the production of glyoxalated polymers, it is necessary to monitor the progress of the reaction with the aldehyde functionalization. This consists in measuring the viscosity of the polymer using a viscometer by collecting regular samples of the reaction medium. This monitoring requires the permanent presence of an operator.

[0007] To overcome all these limitations, it would be possible to produce these aldehyde functionalized polymers directly from the equipment installed in the paper mill. The difficulty in making these polymers in the paper mill, then, is to set up equipment to automatically monitor the reaction of the aldehyde functionalization.

[0008] ACAT's patent US 2017 / 0306065 describes an in-situ glyoxalization (functionalization of polyacrylamide with glyoxal) device with control parameters:

[0009] - Turbidity monitoring

[0010] - pH adjustment according to temperature

[0011] - Adjust pH according to reaction time

[0012] - pH changes during the reaction

[0013] - Actual consumption of the recirculation pump.

[0014] The control parameters set in this patent are interesting. However, they have the disadvantage that they do not accurately reflect the changes in polymer molecular weight throughout the glyoxalation reaction (branching of the polymer structure is possible). In fact, turbidity measurements are sensitive to the quality of the water (contamination, substances in suspension) and the quality of the raw polymer (impurities, color...).

[0015] Therefore, controlling reactions by turbidity monitoring may result in:

[0016] - Obtaining low glyoxalation polymer (little reaction between glyoxal and base polymer). The resulting polymer solution has a low viscosity change during the entire reaction.

[0017] - A highly glyoxalated polymer is obtained in the form of an insoluble gel.

[0018] These are drawbacks associated with the aldehyde functionalization of polymers that need to be addressed. Summary of the invention

[0019] The applicant has developed a new device, including an online pressure difference measurement device (ΔP measurement) for continuous monitoring of the functionalization reaction of polymers with aldehydes. The device can effectively control the functionalization reaction and overcome the above-mentioned drawbacks.

[0020] Thus, when the change in the Δp value reaches a target value, the functionalization reaction of the polymer with the aldehyde-functionalized derivative can be stopped (by the addition of an acid).

[0021] Unlike turbidity measurements, Δp measurements are insensitive to both the quality of the water used and the quality of the polymer.

[0022] Another aspect of the present invention relates to a method for preparing a polymer solution functionalized with an aldehyde using the aforementioned apparatus.

[0023] More specifically, the present invention relates to an apparatus for preparing a solution of a nonionic, cationic, anionic or amphoteric polymer P2 by reaction between a compound comprising at least one aldehyde function and at least one aqueous solution of a base polymer P1 comprising at least one nonionic monomer chosen from acrylamide, methacrylamide, N,N-dimethylacrylamide and acrylonitrile, said apparatus comprising a reactor equipped with a stirring system; and at least:

[0024] - a pipe for supplying water to the reactor, preferably in its upper part,

[0025] a pipeline equipped with a metering pump for supplying the reactor with an aqueous solution of polymer P1,

[0026] a conduit equipped with a metering pump for supplying the reactor with a compound comprising at least one aldehyde function,

[0027] - a pipeline equipped with a metering pump for supplying the reactor with base, preferably in its upper part,

[0028] - a pipeline equipped with a metering pump for supplying the reactor with acid, preferably in its upper part,

[0029] - A recirculation loop for recirculating the polymer P2 solution from the bottom of the reactor to the upper part of said reactor.

[0030] The device is characterized in that the recirculation loop includes a recirculation pump between the outlet of the reactor and the inlet of the reactor, a pH measurement probe, and an online pressure difference measurement device in the form of a calibration tube, which is used to measure the pressure difference of the polymer P2 solution between the inlet and the outlet of the calibration tube, and the calibration tube is located in the bypass of the recirculation loop.

[0031] In a preferred embodiment, the feeding of the aqueous solution of polymer P1 and the compound comprising at least one aldehyde function into the reactor is done in a recirculation loop.

[0032] In other words, the apparatus comprises a conduit connected to a recirculation loop and equipped with a metering pump for feeding the reactor with an aqueous solution of polymer P1; and a conduit equipped with a metering pump for feeding the reactor with a compound comprising at least one aldehyde functional group.

[0033] The base polymer P1 may be nonionic, cationic, anionic or amphoteric. Preferably, it is water-soluble.

[0034] The term "polymer" refers to homopolymers and copolymers.

[0035] The amphoteric polymer is a polymer containing cationic charges and anionic charges, preferably a polymer containing as many cationic charges as anionic charges.

[0036] As used herein, the term "water-soluble polymer" refers to a polymer that is soluble in water when heated to 20 g / L at 25°C. -1 The polymer was dissolved in water at a concentration of 1000 nm and stirred for 4 hours to obtain an aqueous solution free of insoluble particles.

[0037] The polymer P1 may contain a cationic monomer, preferably selected from the group consisting of quaternized or salified dimethylaminoethyl acrylate (DMAEA), quaternized or salified dimethylaminoethyl methacrylate (DMAEMA), dimethyldiallylammonium chloride (DMDAAC), acrylamidopropyltrimethylammonium chloride (APTAC), and methacrylamidopropyltrimethylammonium chloride (MAPTAC).

[0038] The polymer P1 may comprise anionic monomers, preferably selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, methacrylic acid, itaconic acid and / or salts thereof.

[0039] Optionally, the polymer P1 can be branched (structured) with a free radical branching agent, which can be selected from the group consisting of sodium allyl sulfonate, sodium methallyl sulfonate, sodium methallyl disulfonate, methylenebisacrylamide, triallylamine, triallylammonium chloride, ethylene glycol diacrylate, polyethylene glycol dimethacrylate, diacrylamide, methyl cyanoacrylate, ethyl vinyloxyacrylate or methacrylate. Preferably, the weight concentration of the branching agent in P1 is between 5 and 5000 ppm relative to the mass of the polymer.

[0040] The structuring of the polymer P1 can also be obtained with at least one polyfunctional compound comprising at least 3 heteroatoms selected from N, S, O, P and each having at least one mobile hydrogen atom. In particular, the polyfunctional compound can be a polyethyleneimine or a polyamine.

[0041] Preferably, the polymer P1 comprises at least 5 mol % of nonionic monomers selected from acrylamide, methacrylamide, N,N-dimethylacrylamide and acrylonitrile, preferably at least 70 mol %.

[0042] According to the invention, the "average molecular weight (weight average)" of the synthetic water-soluble polymer P is determined by measuring the intrinsic viscosity. The intrinsic viscosity can be measured by methods known to those skilled in the art, in particular, calculated from the reduced viscosity values ​​at different concentrations by a graphical method, which consists in plotting the reduced viscosity values ​​(on the ordinate axis) versus the concentration (on the abscissa axis) and by extrapolating the curve to zero concentration. The intrinsic viscosity values ​​are read on the ordinate axis or using the least squares method. Thereafter, the average molecular weight (weight average) can be determined by the Mark-Houwink equation:

[0043] [η] = KM α

[0044] [η] represents the intrinsic viscosity of the polymer determined by the viscosity measurement method in solution,

[0045] K represents the empirical constant,

[0046] M represents the molecular weight of the polymer,

[0047] α represents the Mark-Houwink coefficient,

[0048] α and K depend on the specific polymer-solvent system. Tables known to the person skilled in the art give the values ​​of α and K depending on the polymer-solvent system.

[0049] The average molecular weight of the polymer P1 is preferably greater than or equal to 100,000 Daltons, even more preferably greater than or equal to 200,000 Daltons. Preferably, it is less than or equal to 2 million Daltons, even more preferably less than 1 million Daltons. Preferably, the average molecular weight of the polymer P1 is preferably between 100,000 Daltons and 2 million Daltons, even more preferably between 200,000 Daltons and 1 million Daltons.

[0050] The compound containing at least one aldehyde functional group that reacts with P1 to obtain P2 is preferably selected from: glyoxal, glutaraldehyde, furan dialdehyde, 2-hydroxyadipaldehyde, succinaldehyde, dialdehyde starch, 2,2-dimethoxyacetaldehyde, or a combination thereof. Even more preferably, the compound containing at least one aldehyde functional group is glyoxal.

[0051] Preferably, the pressure difference online measuring device is in a bypass of the recirculation loop on either side of the recirculation pump.

[0052] In a particular embodiment, the differential pressure inline measuring device is presented in the form of a loop, with an inlet point upstream of the recirculation pump and an outlet point downstream of the pH measuring probe.

[0053] When the aqueous polymer P1 solution and the compound comprising at least one aldehyde functional group are added to the reactor via a recirculation loop, the outlet point of the differential pressure online measuring device is located downstream of the supply point of polymer P1 and the compound comprising at least one aldehyde functional group.

[0054] Preferably, the pressure difference online measuring device further comprises:

[0055] - a control valve that allows to maintain a constant flow rate in a calibrated tube,

[0056] -Flowmeter that allows measuring and regulating the flow rate downstream of the control valve.

[0057] According to another preferred example, the pressure difference online measuring device comprises, preferably downstream of the control valve, a two-stage filter with a mesh size between 5 and 50 μm.

[0058] According to another preferred embodiment, the pressure difference online measuring device includes a pulsation damper of the recirculation loop, preferably located between the two-stage filter and the control valve.

[0059] Preferably, the base flowing in the conduit is sodium hydroxide (soda) in aqueous solution.

[0060] Preferably, the acid flowing in the conduit is sulfuric acid in aqueous solution.

[0061] Preferably, the apparatus of the present invention comprises a turbidity meter directly connected to the upper part of the reactor.

[0062] The invention also relates to a process for preparing a solution of a nonionic, cationic, anionic or amphoteric polymer P2, derived from the reaction between a compound comprising at least one aldehyde function and at least one aqueous solution of a base polymer P1 comprising at least one nonionic monomer selected from acrylamide, methacrylamide, N,N-dimethylacrylamide and acrylonitrile, by means of a device according to the invention, comprising the following successive steps:

[0063] - add water to the reactor and activate the recirculation pump,

[0064] - adding polymer P1 to the reactor, preferably to the recirculation loop, and activating the stirring system,

[0065] - adding a compound comprising at least one aldehyde function to the reactor, preferably to a recirculation loop,

[0066] - adding base to the reactor and stopping the addition when the pH measuring probe indicates a pH between 8 and 12,

[0067] - measuring the differential pressure of the polymer P2 solution circulating in the recirculation loop with an online differential pressure measuring device,

[0068] - optionally continuously measuring the turbidity of the polymer P2 solution in the reactor,

[0069] When the change in the differential pressure of the polymer P2 solution reaches a value between 100% and 500%, acid is added to the reactor and the addition of acid is stopped when the pH measuring probe indicates a pH between 2.5 and 5.

[0070] Preferably, the compound comprising at least one aldehyde function is added in a concentration of 1-30% by weight.

[0071] Preferably, the acid is added to the reactor when the pressure difference of the polymer P2 solution changes between 200% and 400%.

[0072] Preferably, after the process is completed, the obtained polymer P2 solution is transferred to a storage tank equipped with a device for detecting the level of the polymer P2 solution by a recirculation pump. Then, when the detected level of the storage tank is below a threshold, all pipes and reactors are flushed with water to restart the process as described above.

[0073] Advantageously, the invention also relates to a process for obtaining paper or board, said process comprising adding to a fiber suspension a solution of a polymer P2 obtained according to the process described above.

[0074] Typically, the dry matter of the fiber suspension is based on, preferably consists of, cellulose fibers and charges. The term "cellulose fibers" includes any cellulose entity, including fibers, fine particles, microfibers or nanofibers. A fiber suspension is understood to be a thick or thin slurry based on water and cellulose fibers.

[0075] The polymer P2 is added to the papermaking process before or after the formation of the paper, board sheet or the like. Thus, the cellulosic material can be contacted with the polymer of the invention in different ways, in particular according to typical methods known to those skilled in the art. The polymer P2 can be applied by an impregnation technique, it can be added directly to the fiber suspension at any point in the papermaking process where dry strength agents are usually introduced.

[0076] Thus, the polymer P2 can be introduced into a thick stock (or thick stock) or into a thin stock (or thin stock). It can be added in a mixing pump or a filter screen. Preferably, the polymer P2 will be introduced before the headbox.

[0077] Preferably, the polymer according to the invention is injected into the fiber suspension industrially, ie before dilution with white water (thick stock).The consistency of the pulp is in the range of 2-5% by weight of cellulose fibers.

[0078] The papermaking process according to the invention can be carried out using any type of pulp, such as virgin fiber pulp (Kraft pulp, bisulfite pulp), recycled fiber, deinked pulp, mechanical and thermomechanical pulp.

[0079] Advantageously, the polymer P2 is prepared according to the process of the invention using an apparatus of the invention close to a paper machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 It is a schematic diagram of the device of the present invention. DETAILED DESCRIPTION

[0081] The following examples illustrate the invention without limiting its scope.

[0082] Example 1

[0083] Figure 1 It is a schematic diagram of the device of the present invention.

[0084] The apparatus essentially comprises a reactor (1) provided with a stirring system (2), said reactor being connected to a recirculation loop (3). The recirculation loop (3) is in the form of a pipe protruding from the bottom (4) of the reactor (1), also referred to as the "outlet" of the recirculation loop, and having its opposite end connected to the upper level (5) of the reactor (1).

[0085] The apparatus also has a conduit for supplying the reactor with reactants for obtaining the final product.

[0086] These consist of pipes (7), (8) and (9) which supply water, acid and base respectively to the top of the reactor.

[0087] The polymer and the compound comprising at least one aldehyde function are introduced into the recirculation loop (3) via conduits (10) and (11), respectively.

[0088] According to an essential feature of the plant according to the invention, the recirculation loop (3) has different elements in sequence from the outlet (4) of the reactor to the inlet (5) in the reactor, namely a recirculation pump (12), a pH probe (13) and finally an online pressure differential measurement device (14).

[0089] The device (14) includes, in the flow direction of the polymer: a control valve (15) capable of maintaining a constant flow rate; a flow meter (16) capable of measuring and adjusting the flow rate downstream of the control valve (15), a calibration tube (17) for generating a pressure drop, and a differential pressure measuring device (18) located between an inlet and an outlet of the calibration tube, wherein the differential pressure measuring device (18) is capable of measuring the pressure drop of the fluid after the fluid passes through the calibration tube.

[0090] The apparatus of the invention also comprises a turbidity meter (19) connected to the recirculation loop (3).

[0091] The device (14) is located in a bypass of the recirculation loop between a point (20) upstream of the recirculation pump and a point (21) downstream of the reactant inlets (10) and (11).

[0092] Finally, the device comprises a tank (22) provided with means for detecting the level of the polymer P2 solution, capable of triggering the supply of water to the reactor (1) when the detected level of the tank falls below a threshold level.

[0093] Example 2

[0094] Preparation of polymer P1a solution (AM / DADMAC (95 / 5 mol%)): Polymerization of P1a was initiated using SPS and filtered acrylamide solution.

[0095] In a 1 liter reactor equipped with a mechanical stirrer, a thermometer, a refrigerant and a nitrogen plunger, 333.8 g of water, 50.1 g of diallyldimethylammonium chloride (DADMAC, 64% by weight in water) are introduced. The pH of the solution is adjusted to 2.5 with sulfuric acid. Under a water bath, the medium is heated and the temperature is maintained at 79 to 81° C. 535.8 g of filtered acrylamide solution (50% by weight solution) are incorporated for 90 minutes and sodium persulfate solution (SPS, 10% by weight aqueous solution) are incorporated for 90 minutes after two consecutive castings. After aging for 30 minutes, 0.26 g of sodium bisulfite (40% by weight solution) is added to react any residual monomers. Fresh aging is carried out for 60 minutes before cooling. The polymer P1a solution obtained has a pH of 5.0, a polymer mass concentration of 30.1%, and a Brookfield viscosity (LV3 modulus, 12 rpm, 25° C.) of 8500 centipoise (cps).

[0096] Preparation of polymer P2a solution (reaction monitoring by turbidimeter)

[0097] In a 1-liter reactor equipped with a mechanical stirrer, 46.4 g of polymer P1a polymer and 748.4 g of water were added. The reactor was equipped with a pH probe. After stirring for 10 minutes, 5.22 grams of 40% glyoxal (by weight in water) were added, and the pH was then adjusted to 10.2 with a 10% soda solution (by weight in water). The temperature was maintained between 20 and 22°C. The progress of the reaction was monitored by turbidity. Once the turbidity change (Hanna turbidimeter) of the polymer P2a solution was equal to +2NTU, the reaction was stopped by adding sulfuric acid (92% by weight in water) to reduce the pH to less than 3.5. The Brookfield viscosity (LV1 modulus, 60rpm, 25°C) of the polymer P2a solution (weight concentration: 2%) obtained in this way was 55cps.

[0098] Preparation of polymer P2b solution (reaction monitoring by pressure difference ΔP measurement)

[0099] In a 1-liter reactor equipped with a mechanical stirrer, 46.4 g of polymer P1a polymer and 748.4 g of water were added. The reactor was equipped with a pH probe. After stirring for 10 minutes, 5.22 g of 40% glyoxal (by weight in water) was added, and the pH was then adjusted to 10.2 with a 10% soda solution (by weight in water). The temperature was maintained between 20 and 22°C. The progress of the reaction was monitored by measuring the ΔP of the polymer P2b solution (pressure difference measurement device: calibrated tube with a diameter of 2 mm and a length of 2.2 m, P2b solution flow rate: 21 mL.min -1). Once the ΔP changes by +300%, the reaction is stopped by lowering the pH to less than 3.5 by adding sulfuric acid (92 wt. % in water). The Brookfield viscosity (LV1 modulus, 60 rpm, 25° C.) of the polymer P2b solution obtained in this way (weight concentration: 2%) is 54 cps.

[0100] Example 3

[0101] Preparation of polymer P1b solution (AM / DADMAC (95 / 5 mol%)): Polymerization of P1b was initiated using SPS and unfiltered acrylamide solution.

[0102] In a 1 liter reactor equipped with a mechanical stirrer, a thermometer, a refrigerant and a nitrogen plunger, 333.8 g of water, 50.1 g of diallyldimethylammonium chloride (DADMAC, 64% by weight in water) and 500 ppm of biocatalyst / arylamide are introduced. The pH of the solution is adjusted to 2.5 with sulfuric acid. Under a water bath, the medium is heated and the temperature is maintained at 79 to 81° C. Over two continuous casts, 535.8 g of filtered acrylamide solution (50% by weight in solution) are incorporated for 90 minutes and sodium persulfate solution (SPS, 10% by weight in water) for 90 minutes. After aging for 30 minutes, 0.26 g of sodium bisulfite (40% by weight solution) is added to react possible residual monomers. A new aging of 60 minutes is carried out before cooling. The obtained polymer P1b solution had a pH of 4.8, a polymer mass concentration of 29.9%, and a Brookfield viscosity (LV3 modulus, 12 rpm, 25° C.) of 8,900 centipoise (cps).

[0103] Preparation of polymer P2c solution (reaction monitoring by turbidimeter)

[0104] In a 1-liter reactor equipped with a mechanical stirrer, 46.4 g of polymer P1b polymer and 748.4 g of water were added. The reactor was equipped with a pH probe. After stirring for 10 minutes, 5.22 grams of 40% glyoxal (by weight in water) were added, and the pH was then adjusted to 10.2 with a 10% soda solution (by weight in water). The temperature was maintained between 20 and 22°C. The progress of the reaction was monitored by turbidity. Once the turbidity change (Hanna turbidimeter) of the polymer P2c solution was equal to +2NTU, the reaction was stopped by adding sulfuric acid (92% by weight in water) to reduce the pH to less than 3.5. The Brookfield viscosity (LV1 modulus, 60rpm, 25°C) of the polymer P2c solution (weight concentration: 2%) obtained in this way was 15cps.

[0105] Preparation of polymer P2d solution (reaction monitoring by pressure difference ΔP measurement)

[0106] In a 1-liter reactor equipped with a mechanical stirrer, 46.4 g of polymer P1b polymer and 748.4 g of water were added. The reactor was equipped with a pH probe. After stirring for 10 minutes, 5.22 g of 40% glyoxal (by weight in water) was added, and the pH was then adjusted to 10.2 with a 10% soda solution (by weight in water). The temperature was maintained between 20 and 22°C. The progress of the reaction was monitored by measuring the ΔP of the polymer P2d solution (pressure difference measurement device: calibrated tube with a diameter of 2 mm and a length of 2.2 m, P2d solution flow rate: 21 mL.min -1 ). Once the ΔP changed by +300%, the reaction was stopped by lowering the pH to less than 3.5 by adding sulfuric acid (92 wt. % in water). The Brookfield viscosity (LV1 modulus, 60 rpm, 25° C.) of the polymer P2d solution obtained in this way (weight concentration: 2%) was 53 cps.

[0107] Example 4

[0108] Preparation of polymer P1c solution (AM / DADMAC (95 / 5 mol%)): Polymerization of P1c was initiated using V50 and filtered acrylamide solution.

[0109] In a 1 liter reactor equipped with a mechanical stirrer, a thermometer, a refrigerant and a nitrogen plunger, 333.8 g of water, 50.1 g of diallyldimethylammonium chloride (DADMAC, 64% by weight in water) are introduced. The pH of the solution is adjusted to 2.5 with sulfuric acid. Under a water bath, the medium is heated and the temperature is maintained at 79 to 81 ° C. Over two continuous castings, 535.8 g of filtered acrylamide solution (50% by weight solution) are incorporated for 90 minutes and V50 (2,2'-azobis 2-methylpropionamide dihydrochloride, 10% by weight aqueous solution) solution is incorporated for 90 minutes. After aging for 30 minutes, 0.26 g of sodium bisulfite (40% by weight solution) is added to react possible residual monomers. A new aging of 60 minutes is carried out before cooling. The obtained polymer P1c solution had a pH of 5.0, a polymer mass concentration of 30.1%, and a Brookfield viscosity (LV3 modulus, 12 rpm, 25° C.) of 8,420 centipoise (cps).

[0110] Preparation of polymer P2e solution (reaction monitoring by turbidimeter)

[0111] In a 1 liter reactor equipped with a mechanical stirrer, 46.4 g of polymer P1c polymer and 748.4 g of water were added. The reactor was equipped with a pH probe. After stirring for 10 minutes, 5.22 g of 40% glyoxal (by weight in water) was added, and the pH was then adjusted to 10.2 with 10% soda solution (by weight in water). The temperature was maintained between 20 and 22°C. The progress of the reaction was monitored by turbidity. No turbidity change with n was observed for the polymer P2e solution (Hanna turbidimeter). The polymer P2e solution gelled rapidly.

[0112] Preparation of polymer P2f solution (reaction monitoring by pressure difference ΔP measurement)

[0113] In a 1 liter reactor equipped with a mechanical stirrer, 46.4 g of polymer P1c polymer and 748.4 g of water were added. The reactor was equipped with a pH probe. After stirring for 10 minutes, 5.22 g of 40% glyoxal (by weight in water) was added, and the pH was then adjusted to 10.2 with a 10% soda solution (by weight in water). The temperature was maintained between 20 and 22°C. The progress of the reaction was monitored by measuring the ΔP of the polymer P2f solution (pressure difference measurement device: calibrated tube with a diameter of 2 mm and a length of 2.2 m, P2f solution flow rate: 21 mL.min -1 ). Once the ΔP changes by +300%, the reaction is stopped by lowering the pH to less than 3.5 by adding sulfuric acid (92 wt. % in water). The Brookfield viscosity (LV1 modulus, 60 rpm, 25° C.) of the polymer P2f solution obtained in this way (weight concentration: 2%) is 57 cps.

[0114] The results of Examples 1 to 3 are summarized in Table 1.

[0115] Table 1

[0116]

[0117] The difference between the solutions of polymers P1a and P1b is that the P1b solution contains a biocatalyst (a common impurity from the enzymatic process for obtaining acrylamide). Therefore, monitoring the glyoxalation of these polymers by turbidity results in polymers with different Brookfield viscosities, whereas when the reaction is monitored by measuring the change in differential pressure, the polymers obtained have equivalent Brookfield viscosities.

[0118] When the primers used to obtain the polymers were varied (P1a and P1c), this had an impact on the monitoring of the glyoxalation reaction of these polymers by turbidity. The polymers obtained were different: a solution (P2a) and a gel (P2e).

[0119] However, when the glyoxalation reaction was monitored by measuring the change in differential pressure, the polymers obtained had equivalent Brookfield viscosities.

[0120] Example 5: Application test of polymer P2

[0121] For these examples, pulp of recycled fibers was used.

[0122] The wet pulp was obtained by disintegration of dry pulp to obtain a final aqueous solution concentration of 1% by weight. It consisted of pulp at neutral pH, 100% consisting of recycled paperboard fibers.

[0123] Each polymer P2 was metered in an amount of 2.5 dry kg / ton of paper.

[0124] Drainage (DDA) performance assessment

[0125] The DDA (Dynamic Drainage Analyzer) automatically determines the time (in seconds) required to drain the fiber suspension under vacuum. The polymer was added to the wet pulp (0.6 L pulp, 1.0 wt%) in the DDA drum under stirring at 1,000 rpm:

[0126] T=0s:Start stirring the pulp

[0127] T = 10s: Add polymer P2

[0128] T = 30 s: stop stirring and drain under vacuum of 200 mBar for 60 s

[0129] The pressure under the fabric is recorded over time. Once all the water has been drained from the mat, air is forced through the mat, resulting in a slope breakpoint in the curve that represents fabric pressure over time. The time (in seconds) reported at this slope breakpoint corresponds to the drainage time. Therefore, the shorter the time, the better the vacuum drainage.

[0130] Performance in DSR (dry strength) applications, grammage 80g.m -2

[0131] Take the required amount of pulp to obtain a final weight of 80 g.m. -2 of sheet.

[0132] The wet pulp is introduced into the barrel of the dynamic sheet former and kept stirred. The different components of the system are injected into this pulp according to a predefined sequence. Typically, the contact time between each polymer addition is 30 to 45 seconds.

[0133] The sheet former is made with an automatic sheet former: the blotting paper and the forming fabric are placed in the drum of the dynamic sheet former before starting the drum rotation at 1000 rpm and building a water wall. The processed pulp is distributed on the water wall to form a fiber mat on the forming fabric.

[0134] Once the water has been drained off, the fiber mat is recovered, pressed in a press with an output of 4 bar and then dried at 117° C. The sheets obtained are conditioned overnight in a room with controlled humidity and temperature (relative humidity 50% and 23° C.). The dry strength properties of all the sheets obtained by this procedure are then measured.

[0135] The burst resistance is measured with a Messmer Buchel M 405 burst tester according to standard TAPPI T403 om-02. The result is expressed in kPa. The burst resistance index is determined by dividing this value by the grammage of the sheet being tested, expressed in kPa.M 2 / g indicates.

[0136] The dry breaking length is measured in the machine direction using the tensile equipment Testmetry AX according to standard TAPPI T494 om-01. The results are expressed in km.

[0137] The results of the application tests of polymer P2 obtained in Examples 1 to 3 are summarized in Table 2 (% increase relative to the control).

[0138] Table 2

[0139] polymer % Burst Index %DBL MD %drain P2a 21.4 16.2 34.8 P2c 15.8 10.6 19.4 P2b 21.4 16.2 34.8 P2d 21.9 16.2 34.2 P2f 21.9 16.5 35.1

[0140] Compared to the polymer obtained in the same way but monitoring the glyoxalation reaction by measuring the differential pressure (P2d), polymer P2c (containing impurities (biocatalyst) and whose glyoxalation reaction was monitored by turbidity) has lower performance in terms of burst resistance, dry strength and vacuum drainage.

[0141] Furthermore, polymers P2b and P2f, obtained by glyoxalation of polymers P1a and P1c, respectively, with different primers (V50 / SPS) during polymerization, had equivalent performance in terms of paper dry strength and vacuum drainage when the glyoxalation reaction was monitored by measuring the pressure difference.

Claims

1. An apparatus for preparing a solution of a nonionic, cationic, anionic or amphoteric polymer P2 by reaction between a compound comprising at least one aldehyde functional group and at least one aqueous solution of a base polymer P1 comprising at least one nonionic monomer selected from acrylamide, methacrylamide, N,N-dimethylacrylamide and acrylonitrile, the apparatus comprising a reactor (1) equipped with a stirring system; and at least: - a pipe (7) for supplying water to the reactor (1), a conduit I (11) equipped with a metering pump for supplying the reactor (1) with an aqueous solution of the polymer P1, a conduit II (10) equipped with a metering pump for supplying the reactor (1) with a compound comprising at least one aldehyde function, - a pipe III (9) equipped with a metering pump for supplying the reactor (1) with alkali, a conduit IV (8) equipped with a metering pump for supplying the reactor (1) with acid, The reactor (1) comprises a recirculation loop (3) for recirculating a polymer P2 solution from the bottom (4) of the reactor (1) to the upper part (5) of the reactor (1), wherein: The recirculation loop (3) comprises a recirculation pump (12) between the outlet of the reactor (1) and the inlet of the reactor (1), a pH measuring probe (13), and an online pressure difference measuring device (14) in the form of a calibration tube for measuring the pressure difference of the polymer P2 solution between the inlet and the outlet of the calibration tube, the calibration tube being located in a bypass of the recirculation loop.

2. The device according to claim 1, characterized in that The pressure difference online measuring device (14) is located on either side of the recirculation pump.

3. The device according to claim 1, characterized in that The pressure difference online measuring device (14) further comprises: - a control valve (15) allowing a constant flow rate to be maintained in the calibrated tube (17), - A flow meter (16) allowing the flow rate downstream of the control valve (15) to be measured and regulated.

4. The device according to claim 3, characterized in that The differential pressure online measuring device (14) comprises: downstream of the control valve, a two-stage filter with a mesh size between 5 and 50 μm.

5. The device according to claim 4, characterized in that The differential pressure online measuring device (14) comprises: a pulsation damper of the recirculation loop located between the two-stage filter and the control valve.

6. The device according to claim 1, characterized in that The apparatus comprises a turbidity meter (19) connected directly to the recirculation loop of the reactor (1).

7. A method for preparing a solution of a nonionic, cationic, anionic or amphoteric polymer P2, derived from the reaction between a compound comprising at least one aldehyde function and at least one aqueous solution of a base polymer P1 comprising at least one nonionic monomer selected from acrylamide, methacrylamide, N,N-dimethylacrylamide and acrylonitrile, by means of an apparatus as claimed in claim 6, comprising the following successive steps: - Add water to the reactor (1) and activate the recirculation pump, - Add polymer P1 to reactor (1) and activate the stirring system, - adding a compound comprising at least one aldehyde functional group to the reactor (1), - adding alkali to the reactor (1) and stopping the addition when the pH measuring probe indicates a pH between 8 and 12, - measuring the differential pressure of the polymer P2 solution circulating in the recirculation loop using an online differential pressure measuring device (14), - continuously measuring the turbidity of the polymer P2 solution in the reactor (1), When the change in the differential pressure of the polymer P2 solution reaches a value between 100% and 500%, acid is added to the reactor (1) and the addition of acid is stopped when the pH measuring probe indicates a pH between 2.5 and 5.

8. The method for preparing a polymer P2 solution according to claim 7, characterized in that The following steps are also included: - transferring the polymer P2 solution obtained by means of a recirculation pump to a storage tank equipped with a device for detecting the level of the polymer P2 solution, - When the detected liquid level in the liquid storage tank falls below a threshold value, all pipes and the reactor (1) are flushed with water to restart the process as previously described.

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