PROCESS FOR REDUCING FORMALDEHYDE CONTENT FROM CATIONIC MELAMINE-FORMALDEHYDE RESIN SOLUTION

Abstract

The present invention generally relates to a process for reducing formaldehyde content from cationic melamine-formaldehyde resin solution. Said process comprises the steps consisting of charging a starting solution to an ultrafiltration membrane system, separating said starting solution into a concentrate solution which mainly comprises cationic melamine-formaldehyde resin of high molecular weight, formaldehyde and water, and a permeate solution which mainly comprises cationic melamine-formaldehyde resin molecules of low molecular weight, formaldehyde, acid compounds and water and treating the permeate solution to reduce the free formaldehyde content of the permeate.

Claims

1. A process for reducing formaldehyde content from cationic melamine-formaldehyde resin solution, the process comprising the following steps: a) Charging a starting solution of a cationic melamine-formaldehyde resin to an ultrafiltration membrane system; b) Separating said starting solution into: i. a concentrate solution which mainly comprises cationic melamine-formaldehyde resin of high molecular weight, formaldehyde and water, and ii. a permeate solution which mainly comprises cationic melamine-formaldehyde resin molecules of low molecular weight, formaldehyde, acid compounds and water; c) Treating the permeate solution to reduce the free formaldehyde content of the permeate; d) Mixing the concentrate solution with treated permeate or with water.

2. The process according to claim 1, wherein the formaldehyde content of the starting solution is of between about 0.1% and 3.5%, by weight based on the weight of the starting solution.

3. The process according to claim 1, wherein the viscosity of the starting solution is between 10 cP.Math.s and 100 cP.Math.s.

4. The process according to claim 1, wherein the solid content of the starting solution is between 10% and 20%, by weight based on the weight of the starting solution.

5. The process according to claim 1, wherein the material of the ultrafiltration membrane system is selected from the group consisting of polysulphones, cellulose acetates, polyamides, vinyl chloride-acrylonitrile copolymers and poly(vinylidene fluoride).

6. The process according to claim 1, wherein the geometry of the ultrafiltration membrane system is selected from the group consisting of tubular, hollow fibre, spiral-wound, plate and frame.

7. The process according to claim 1, wherein the ultrafiltration membrane system has a pore size of between 5 kDa and 50 kDa.

8. The process according to claim 1, wherein the separation step (b) is operated at a pressure from 0.3 bar to 9.7 bar.

9. The process according to claim 8, wherein the pressure is applied with a pressure chamber with or without gas.

10. The process according to claim 1, wherein the staring starting solution is separated at a temperature from 15 C. to 30 C.

11. The process according to claim 1, wherein the concentrate solution comprises cationic melamine-formaldehyde resin of high molecular weight with a molecular weight higher than 50 kDa.

12. The process according to claim 1, wherein the permeate solution comprises cationic melamine-formaldehyde resin of low molecular weight with a molecular weight lower than 50 kDa.

13. The process according to claim 1, wherein the treatment step (c) comprises treating the permeate solution with a formaldehyde-free reducing agent selected from the group consisting of scavenging agent, precipitation agent and oxidizing agents.

14. The process according to claim 13, wherein the oxidizing agent is added in an amount of between 20% and 100% excess, by weight based on the weight of the permeate solution.

15. The process according to claim 1, wherein the permeate solution is treated during step (c) at a temperature from 15 C. to 100 C.

16. The process according to claim 1, wherein the permeate solution is cooled after step (c) at a temperature from 15 C. to 50 C.

17. The process according to claim 1, wherein the mixing step (d) is performed with water or with the treated permeate.

18. The process according to claim 1, wherein the concentrate solution is charged as part of the starting solution to another ultrafiltration membrane system and the process is repeated as many times as necessary to reach formaldehyde content less than 0.1%.

19. The process according to claim 1, wherein the ultrafiltration membrane systems regenerated by washing with water or with the treated permeate.

20. A cationic melamine-formaldehyde resin obtained from the process as defined in claim 1.

21.-24. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic diagram of the process according to one embodiment of the invention, without membrane washing.

[0023] FIG. 2 is a schematic diagram of the process according to another embodiment of the invention, with membrane washing.

[0024] FIG. 3 is a graph comparing the performance of the formulations according to the Application Test, as percentage of TOG (Total Oil and Grease) Reduction.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The invention provides a process for reducing formaldehyde content from cationic melamine-formaldehyde resin solution comprising the following steps: [0026] a) Charging a starting solution of a cationic melamine-formaldehyde resin to a ultrafiltration membrane system; [0027] b) Separating said starting solution into: [0028] i. a concentrate solution which mainly comprises cationic melamine-formaldehyde resin of high molecular weight, formaldehyde and water, and [0029] ii. a permeate solution which mainly comprises cationic melamine-formaldehyde resin molecules of low molecular weight, formaldehyde, acid compounds and water; [0030] c) Treating the permeate solution to reduce the free formaldehyde content of the treated permeate; [0031] d) Mixing the concentrate solution with the treated permeate or with water.

[0032] Cationic melamine-formaldehyde resin is typically obtained by the hydroxy methylation reaction of melamine with formaldehyde and glyoxal followed by polymerization by condensation of methylol (hydroxymethyl) groups formed. The hydroxy-methylation is the step in which the amine (melamine) is transformed into compounds capable of polymerized with each other or with other melamine molecules that are not hydroxy-methylated yet.

[0033] Typically, the formaldehyde used in the synthesis of cationic melamine-formaldehyde resin contains 10% to 15% w/w of methanol which acts as an inhibitor of polymerization and antioxidant, and about 0.02% of free formic acid. During the synthesis, the complete dissolution of melamine in the reaction mass indicates the reaction of hydroxyl-methylation and the polymerization is characterized by an increase in viscosity. The presence of glyoxal in the polymer backbone increases the water dispersibility of the polymer formed.

[0034] Usually, a 40% solution of aqueous formaldehyde is heated at 70 C. to 75 C. and the melamine powder is then added. Once the melamine powder is completely dissolved and the solution is clear, the mixture is added to a dilute solution of acid and glyoxal.

[0035] According to the present invention, the cationic melamine-formaldehyde resin solution employed as a starting solution for the present process is an aqueous solution which may present an amount of free formaldehyde of between 0.1% and 3.5%, preferably between 0.8% and 3.0%, more preferably between 1.5% and 2.5%, by weight based on the weight of the starting solution. The free formaldehyde content can be determined using the colorimetric method with acetylacetone or iodometric titration.

[0036] The pH of the starting solution can be in the range of 3.0 to 4.0. The viscosity of the starting solution can be between 10 cP.Math.s and 100 cP.Math.s, preferably between 20 cP.Math.s and 60 cP.Math.s. Solid content of the starting solution can be between 10% and 20%, preferably between 11% and 15% and most preferably between 12% and 13%, by weight based on the weight of the starting solution.

[0037] In step (a), the starting solution is charged to an ultrafiltration membrane system.

[0038] An ultrafiltration membrane system with a suitable cut-off for retention of the desired high molecular weight fractions may be used in the present invention. The membranes can be selected from the group consisting of membranes whose material are polysulphones, cellulose acetates, polyamides, vinyl chloride-acrylonitrile copolymers and poly(vinylidene fluoride), preferably polyethersulphone. The geometry of the membrane system is selected from the group consisting of tubular, hollow fiber, spiral-wound, plate and frame, preferably the ultrafiltration membrane system is a spiral-wound module.

[0039] The geometry selection of the membrane depends on various factors such as characteristics of solution to be fractionated, ease of operation, cleaning and maintenance. For example, the hollow fiber module has high membrane surface per volume unit, is easy to operate and maintain, and its power consumption is low. The spiral-wound module has flow rate almost constant and turbulence promoter mechanisms present along the membrane surface, reducing the fouling and facilitating cleaning thereof.

[0040] The separation of substances depends on the cut-off membrane value, which is indicated by the size of the smallest molecule retained by the membrane. Thus the molecules smaller than the cut-off membrane value pass through, whereas larger are retained. Usually, ultrafiltration process involves the use of membranes that separate molecules having a molecular weight in the range of 1 to 200 kDa.

[0041] For cationic melamine-formaldehyde resins the desired high molecular weight fraction may be in the range of 5 to 50 kDa, preferably about 10 kDa and the separation is thus carried out to give essentially 95% of this fraction as the membrane-retained component, called herein as concentrate. Thus the membrane used in this invention can have a pore size of between 5 kDa and 50 kDa, preferably about 10 kDa.

[0042] In step (b), the starting solution is separated into two solutions, a concentrate and a permeate.

[0043] The concentrate solution according to the present invention comprises the melamine-formaldehyde resin of high molecular weight. The expression high molecular weight in the sense of the present invention covers all polymers with a molecular weight higher than 50 kDa.

[0044] The permeate solution according to the present invention comprises melamine-formaldehyde molecules of low molecular weight. The expression low molecular weight in the sense of the present invention covers all molecules with a molecular weight lower than 50 kDa.

[0045] Advantageously, after the separation step, the melamine-formaldehyde resin of high molecular weight is mainly comprised in the concentrate solution, and the permeate solution is free or essentially free of melamine-formaldehyde resin of high molecular weight.

[0046] The concentrate solution can have a solid content of 10% to 19% by weight based on the weight of the concentrate solution. The permeate solution can comprises a formaldehyde content of 0.1% to 2.5% by weight based on the weight of permeate solution. The concentrate solution can also comprise formaldehyde, with a content of 0.1% to 2.5% by weight based on the weight of concentrate solution.

[0047] The process can be generally operated at pressure ranging from 0.3 bar to 9.7 bar, preferably from 0.5 bar to 2.0 bar and it may be applied with a pressure chamber with or without gas, as nitrogen.

[0048] A turbulent and/or laminar flow can be imposed on the cationic melamine-formaldehyde resin solution in contact with the membrane. Both flows agitate the solution in contact with the membrane and it allows to obtain a concentrate with resin of high molecular weight and a permeate with molecules of low molecular weight. However, the turbulent flow may be preferably applied because it provides a higher permeability reducing the film formation on the membrane surface and thereby reducing the membrane cleaning cycles, required for its restoration.

[0049] The flux through the membranes can be improved by increasing the temperature. For the separation of cationic melamine-formaldehyde resin solution in the membranes of the present invention, the temperatures may vary from 15 C. to 30 C., preferably from 20 C. to 25 C.

[0050] Then, according to step (c) the permeate solution obtained in step (b) can be treated with a means for reducing free formaldehyde content. Said means may be any formaldehyde-free reducing agent, such as oxidizing agent, scavenging agent or precipitation agent.

[0051] According to a preferred embodiment, the permeate solution can be treated with an oxidizing agent, preferably hydrogen peroxide. The oxidizing agent may be added to the permeate solution in an amount of between 20% and 100% excess, preferably between 30% and 50% excess by weight based on the weight of the permeate solution. Then the permeate solution can be heated at a temperature from 15 C. to 100 C. preferably from 65 C. to 80 C. After that, the treated permeate can be cooled to a temperature from 15 C. to 50 C., preferably at 20 C. to 30 C. Heating allows that the formaldehyde in the permeate solution is converted to formic acid via an oxidation with excess of the oxidizing agent added. This reaction is exothermic, and the oxidizing agent residual is decomposed thermally while all the formaldehyde is oxidized.

[0052] The treated permeate solution, free or substantially free from formaldehyde, can be discharged or otherwise reused within the present process. The process according to the invention comprises a step (d) consisting in mixing the concentrated solution with the treated permeate or with water.

[0053] According to a preferred embodiment, the step (d) consists in mixing the concentrate solution with treated permeate. This reuse in the present process is possible because the formic acid levels generated in the oxidation and present in the permeate solution do not affect the characteristics and properties of the cationic melamine-formaldehyde resin solution and furthermore, this reuse generates less effluent.

[0054] According to another embodiment, the step (d) consists in mixing the concentrated solution with water. Then, if the treated permeate solution is not reused, it can be discharged in a wastewater, since the formaldehyde is not present in the solution there is no environmental risk involved.

[0055] If the process according to the invention is carried out successively several times, then the ultrafiltration combined with the mixing of the concentrate solution with another flow may be seen as a diafiltration. The diafiltration increases the permeation of no high molecular weight species across the membrane, thereby enabling the concentration of the high molecular weight species in the concentrate solution. This technique involves washing out the concentrate solution by adding water or the treated permeate at the same rate, i.e. volume, as permeate is being generated. As a result, the concentrate solution volume does not change during the diafiltration process and the purity enhances.

[0056] Preferably, the volume of water or the treated permeate solution added in this step is the same volume of the permeate solution which was separated in step (b). There may be a slight adjustment of this volume to keep the cationic melamine-formaldehyde resin solution at the end of the process with the same specified solid content, however, the mass balance is maintained.

[0057] In one embodiment of the present invention, following the mixing step (d), the concentrate solution can be charged as part of the starting solution to another ultrafiltration membrane system, and the process can be repeated as many times as necessary to reach adequate levels of formaldehyde, preferably less than 0.1% by weight.

[0058] The ultrafiltration membrane permeability after several filtration cycles may be compromised. Therefore, optionally, after each cycle the membrane can be washed with water or with treated permeate to restore its permeability.

[0059] According to an advantageous embodiment, the ultrafiltration membrane system may be regenerated by washing it with water or with the treated permeate solution obtained in step (c) at a temperature below 50 C.

[0060] The present invention also proposes a cationic melamine-formaldehyde resin with a free formaldehyde content of less than 0.1% and a cationic melamine-formaldehyde resin obtainable by the hydroxy methylation reaction of melamine with formaldehyde and glyoxal followed by polymerization by condensation of methylol groups having a free formaldehyde content of less than 0.1%.

[0061] The present invention also proposes the use of a cationic melamine-formaldehyde resin described above as reverse emulsion breaker, flocculating agent, textile finish, adhesion-promoting agent and moisture-resistant agent.

[0062] The present invention provides advantages over existing process for reducing formaldehyde content from cationic melamine-formaldehyde resin solution. The invention proposes an improved process to reduce levels of free formaldehyde by aligning the ultrafiltration with a treatment for reducing formaldehyde content. This process is advantageously operated at low temperatures without changing the cationic melamine-formaldehyde resin solution characteristics such as viscosity, color and solid content, indicating that the polymer chain is not broken by the treatment for reducing formaldehyde content. Cationic melamine-formaldehyde resin solution produced using the process according to the invention maintains preferably the same characteristics and properties of the starting solution and it can be applied in different applications requiring low formaldehyde levels, considering its reduced environmental, health and safety risks.

[0063] Other details or advantages of the invention will become more clearly apparent in the light of the examples given below.

EXAMPLES

Example 1: Membrane Permeability

[0064] The evaluation of membrane permeability was verified after three successive batch processes made according to the present invention, with or without membrane washing.

[0065] For the examples below, the cationic melamine-formaldehyde resin solution with reduced levels of free formaldehyde was obtained through an ultrafiltration membrane system with the following characteristics: polyethersulphone membrane with a hollow fiber module, 0.8 to 0.9 mm fiber outside diameter, tapped density of 800 m.sup.2/m.sup.3 and permeation area of 0.072 m.sup.2.

[0066] The starting solution of cationic melamine-formaldehyde resin, with a viscosity of 40.6 cP.Math.s, pH 2.98, and solid content of 12.70% w/w, was separated into two solutions, the concentrate and the permeate.

[0067] At each cycle the permeate solution was oxidized with 50% excess of hydrogen peroxide, at a temperature above 65 C., for 2 h, until complete consumption of formaldehyde and hydrogen peroxide.

Example 1.1: Evaluation without Membrane Washing

[0068] The treated permeate was added to the concentrate solution obtained in the same cycle to restore the original dispersion, as shown in FIG. 1. FIG. 1 is a schematic diagram of this process and its numbers represent the following descriptions:

1: Stating solution
2, 3, 4 and 5: Permeate solution
6: Concentrate solution

7: Membrane

[0069] 8: Conditions of the permeate solution treatment (H.sub.2O.sub.2 35%, 50% excess at 75 C. during 2 h)

TABLE-US-00001 TABLE 1 Parameters analyzed in each cycle Stream 1 6 Starting Final Parameters Solution 2 3 4 5 Solution Formaldehyde (%) 2.11 1.684 1.18 0.83 0.53 0.55 Hydrogen peroxide (%) 0.00 0.00 0.09 0.09 0.01 0.00 Viscosity (cP .Math. s) 40.60 2.70 1.50 1.65 0.75 46.40 pH 2.979 2.8 2.103 2.013 2.095 2.19 Solid content (%) 12.70 2.58 2.39 2.26 1.87 12.74 Acidity (mg KOH/g) 14.16 3.49 17.85 30.49 26.32 34.63 Total weight (g) 2000 700 700 600 500 2000

[0070] The results in table 1 show a decrease in formaldehyde concentration in relation to the total weight of the solutions obtained after each cycle. Moreover, the characteristics, as viscosity and solid content, have not changed compared to the starting solution.

[0071] In the starting solution 1, the amount of formaldehyde was 42 g (2.11% of the total weight), after the first cycle, the permeate solution 2 had 1.684% of formaldehyde, which is equivalent to 11.76 g of the total weight of the permeate solution 2 and the presence of the cationic melamine-formaldehyde resin was not detected in this solution. With the oxidation, the formaldehyde content is completely eliminated, therefore, after the mixing of the concentrate solution with the treated permeate solution, the total formaldehyde content in the system is reduced from 42 g to 30.24 g. Thus the cycles continue until the end of the process, separating the cationic melamine-formaldehyde resin of high molecular weight from the permeate solution, which is oxidized, avoiding its breakage.

Example 1.2: Evaluation with Membrane Washing

[0072] The treated permeate was passed through the membrane for 15 minutes to remove any obstructions formed during each cycle, which reduce its permeability. This treated permeate from the membrane washing was added to the concentrate solution obtained in the same cycle to restore the original dispersion, as shown in FIG. 2. FIG. 2 is a schematic diagram of this process and its numbers represent the following descriptions:

9: Starting solution
10, 11 and 12: Permeate solution
14: Concentrate solution

15: Membrane

[0073] 16: Conditions of the permeate solution treatment (H.sub.2O.sub.2 35%, 50% excess at 75 C. during 2 h)

[0074] The results in table 2 show a decrease in formaldehyde concentration in relation to the total weight of the solutions obtained after each and the filtration time remained almost constant. As well as for the previous example, the characteristics, as viscosity and solid content, have not changed compared to the starting solution.

TABLE-US-00002 TABLE 2 Parameters analyzed in each cycle Stream 9 14 Starting Final Parameters Solution 10 11 12 Solution Formaldehyde (%) 2.11 1.56 1.06 0.67 0.67 Hydrogen peroxide (%) 0.00 0.00 0.00 0.04 0.00 Viscosity (cP .Math. s) 40.60 2.40 0.60 0.55 47.80 pH 2.98 2.49 2.05 1.95 2.17 Solid content (%) 12.70 2.94 2.50 2.14 12.24 Acidity (mg KOH/g) 14.16 8.47 25.60 36.59 37.00 Total weight (g) 2000 707 707 656.5 2000

[0075] When compared with the Example 1.1 the washing steps in Example 1.2 is advantageous because the duration and the number of treatment cycles are reduced.

Example 2: Application TestReverse Demulsifier

[0076] The evaluation of demulsification performance was verified by the TOG (Total Oil and Grease) Reduction test described below.

[0077] To implement the TOG Reduction test, an oily water sample was prepared in laboratory by adding slowly 50 drops of crude oil to 6 liters of deionized water, under high shear mixing (Ultra Turrax) at 2000 rpm, maintaining the mixing during 10 minutes, until the total dispersion of oil in water.

[0078] A solution 10% (v/v) of each proposed formulation (reverse demulsifier) below was prepared, using fresh water as solvent and the cationic melamine-formaldehyde resin, referred as polyelectrolyte in the table 3. Table 3 presents a description and free formaldehyde level of each proposed formulation.

TABLE-US-00003 TABLE 3 Description of each proposed formulation Free formaldehyde Identification (%) Description Formulation #1 1.4 Untreated polyelectrolyte - starting material for formulations #2 and #3 Formulation #2 0.2 Treated polyelectrolyte, according to the invention, adding water in the step d) (6 cycles) Formulation #3 0.2 Treated polyelectrolyte, according to the invention, adding the treated permeate in the step d) (6 cycles)

[0079] To each vessel containing 1 liter of oily water was added a volume of each formulation corresponding to the assessed concentration, as described in table 4. The solutions of each vessel were mixed. During the first minute, the rotation was maintained at 80 rpm, after the first minute, the rotation was decreased to 8 rpm and it was maintained during 10 minutes. Then, after this time, the mixing process was stopped and the solutions were allowed to stand for additional 30 minutes.

[0080] For the quantification of TOG by using ultraviolet-visible spectrophotometry analysis, 25 mL of water was collected from the bottom of each vessel with attention to the oil located at the surface. To each 25 mL of water it was added 25 mL of chloroform (CHCl.sub.3), in order to extract all oil and grease from water. This mixture was transferred to a separation funnel and then, only the organic fraction was collected.

[0081] This fraction was evaluated in UV Vis Spectrophotometer at 400 nm, using the calibration curve data previously prepared to measure the TOG value.

[0082] Considering that water quality may change significantly in the oilfield, it is suggested to compare the final results of the analysis starting from the same level of TOG and presenting the results as percentage of TOG reduction, as shown in the FIG. 3.

[0083] The results shown in FIG. 3 demonstrate that the three proposed formulations exhibit the same performance in reducing the TOG value, about 30%, when the concentration tested is up to 10 ppm. And for the cases tested with higher concentrations, the formulations #2 and #3 show a slightly better performance comparing with the formulation #1.