PROCESS FOR PRODUCING POLYOXYMETHYLENE POLYMERS HAVING INTERMEDIATE CHAIN LENGTH

Abstract

A process for producing polyoxymethylene polymers comprises the reaction of aqueous formaldehyde solution with an aqueous solution of a base, wherein A) a starter solution comprising formaldehyde is initially charged and B) an aqueous formaldehyde solution and a base are added to the starter solution to obtain a reaction mixture. The starter solution in step A) has a temperature of ≥40° C. to ≤46° C. and the additions of the solutions in step B) are performed at a temperature of the reaction mixture of ≥40° C. to ≤46° C. The base is an alkali metal hydroxide and/or an alkaline earth metal hydroxide and the molar ratio of formaldehyde to base is ≥55:1 to ≤90:1 based on the total amounts of formaldehyde and base employed in the process. The base in step B) is added in aqueous solution.

Claims

1. A process for producing polyoxymethylene polymers, comprising the reaction of an aqueous formaldehyde solution and an aqueous solution of a base, wherein A) a starter solution comprising formaldehyde is initially charged and B) an aqueous formaldehyde solution and a base are added to the starter solution to obtain a reaction mixture, wherein the starter solution in step A comprises a temperature ≥40° C. to ≤46° C., the additions of the solutions in step B) are performed at a temperature of the reaction mixture of ≥40° C. to ≤46° C. and the base is an alkali metal hydroxide and/or an alkaline earth metal hydroxide, wherein: the molar ratio of formaldehyde to base is ≥55:1 to ≤90:1, based on the total amounts of formaldehyde and base employed in the process, and the base in step B) is added in the form of an aqueous solution.

2. The process according to claim 1, wherein the starter solution is an aqueous starter solution.

3. The process according to claim 1, wherein the starter solution further comprises a base.

4. The process according to claim 1, wherein the starter solution comprises a formaldehyde content from ≥35 weight-% up to ≤50 weight-%, in relation to the total weight of the solution.

5. The process according to claim 1, wherein the formaldehyde solution in step B) comprises a formaldehyde content of ≥50 weight-%, in relation to the total weight of the solution.

6. The process according to claim 1, wherein the starter solution and/or the formaldehyde solution in step B) comprise a methanol content of ≤1 weight-%, in relation to the total weight of the solution.

7. The process according to claim 1, wherein the temperature of the reaction mixture is decreased after the addition of the base solution is finished.

8. The process according to claim 1, wherein the process further comprises a delayed separation step, wherein a solid polyoxymethylene polymer and a mother liquor is obtained.

9. The process according to claim 8, wherein after the separation step at least a fraction of the mother liquor is concentrated and is used as starter solution in the reaction of the aqueous formaldehyde solution and the aqueous solution of the base.

10. The process according to claim 8, wherein the mother liquor obtained after the separation step and/or the concentrated mother liquor are treated with acidic and/or basic ion exchange resins.

11. The process according to claim 1, wherein the starter solution, the formaldehyde solution and/or the solution of the base additionally comprise a polyol.

12. The process according to claim 1, wherein the process is a continuous process.

13. A polyoxymethylene-polymer, obtainable by a process according to 1, comprising a water content of ≤1 weight-%, in relation to the total weight of the polymer.

14. The polyoxymethylene-polymer according to claim 13 comprising an average molecular weight from ≥1100 g/mol up to ≤3000 g/mol.

Description

EXAMPLE 1

[0066] A metal double jacketed vessel with approx. 12 ltr. capacity was used, which could be heated/cooled to the desired temperature by means of a thermostat. The vessel was equipped with a stirrer.

[0067] The starter solution was first prepared in this vessel. 1234 g of a low methanol aqueous formaldehyde solution containing 502 g of formaldehyde was added. To this solution, 11.6 ml of a 50% sodium hydroxide solution was added with stirring to obtain the starter solution. The reaction vessel and thus the solution were heated or cooled to 42° C. using the thermostat.

[0068] Formaldehyde solution and sodium hydroxide solution were then added at 42° C. reaction temperature. The following table lists the amount of formaldehyde and sodium hydroxide solution at the respective times that had been dosed up to that point. The figure at zero minutes corresponds to the composition of the starter solution.

TABLE-US-00001 Formaldehyde- Calc. 100% 50% ige time solution Formaldehyde NaOH [min] [g] [g] [ml] 0 1234 502 11.6 45 2508 1279 29.6 80 4392 2428 56.3 130 6224 3603 83.3 215 8107 4751 110 260 10037 5926 137

[0069] After that, the reaction vessel was filled, the addition was stopped. A total of 197.3 mol formaldehyde and 2.6 mol NaOH were processed. This corresponds to a molar ratio of formaldehyde to base of 75.6:1.

[0070] After completion of the addition, the temperature in the double jacket vessel was started to be lowered by means of the thermostat. In about 4 hours, a temperature of about 20-22° C. was reached. After that, the reaction was allowed to continue for another 2-3 hours. Then the solution together with the precipitated solid was transferred to a suction filter with a suction flask of suitable size and sucked dry by applying a vacuum to the suction flask until nothing more dripped. The mother liquor thus obtained was removed from the suction flask and sent to vacuum distillation. The material on the suction filter was washed out with about 5 ltr. of water. The wash water must finally run off neutrally, i.e. it no longer contained any base. Afterwards, the solid was sucked dry and then dried in a dryer at low temperature (<45 ° C.) and at normal pressure to slight vacuum (approx. 200 mbar). The solid yield was up to 75.2% of the formaldehyde used, which showed a purity of 98.3% (formaldehyde titration) and a residual moisture of <0.1% (Karl-Fischer titration) in the analysis.

[0071] The mother liquor was evaporated in vacuo (boiling temperature 45° C./60-80 mbar). A 13% formaldehyde solution was obtained. The yield calculated over the solid and the recovered formaldehyde was 88.2%.

[0072] This experiment was repeated several times. The obtained samples were reacted with propylene oxide. Surprisingly, liquid products were obtained. On the basis of the evaluation of the substance consumptions as well as by the application of physical measuring methods, in particular .sup.1H-NMR and .sup.13C-NMR, molecular masses of approx. 1400 g/mol could be determined.

EXAMPLE 2

[0073] The same apparatus was used as in Example 1. In addition to the starter solution, a 50% sodium hydroxide solution and a high-percentage formaldehyde solution were used. The temperature in the reaction vessel was maintained at 42° C. by means of the thermostat. The following table lists the amount of formaldehyde and sodium hydroxide solution at the respective times that had been dosed up to that point. The figure at zero minutes corresponds to the composition of the starter solution.

TABLE-US-00002 Formaldehyde- Calc. 100% 50% ige time solution Formaldehyde NaOH [min] [g] [g] [ml] 0 1223 533 12.4 40 2487 1304 30.4 84 4370 2452 57.1 120 6263 3606 83.9 180 8217 4797 112 270 10757 6346 148

[0074] A total of 211.3 mol formaldehyde and 2.8 mol NaOH were processed. This corresponds to a molar ratio of formaldehyde to base of 75.0:1.

[0075] After completion of the addition, the temperature was lowered to 20° C. for 4 hours using the thermostat. After a further 5 hours post-reaction time, the work-up was carried out by means of a suction flask. After separating the mother liquor and washing out the solid cake on the suction filter and then drying the product, the following were obtained:

[0076] 4710 g of solid=74.2% with respect to formaldehyde with a purity of 98.5% and a water content of <0.1% and 3470 g of mother liquor with a formaldehyde content of 21.7%=753 g of formaldehyde or 11.8% of the original formaldehyde amount. 5900 g of wash water contained a further 8.5% formaldehyde=502 g formaldehyde. Thus, the fate of 94% of the formaldehyde used was detectable. 6% of the used formaldehyde was converted to formic acid and methanol by the Cannizzaro reaction and to sorbose and fructose by the saccharification reaction.

[0077] The mother liquor could be freed from both caustic soda and formic acid by means of ion exchange resins. First, the sodium hydroxide solution was removed. A strongly acidic ion exchange resin was used for this purpose. After passing through the resin, an acidic reacting solution was obtained in which a formic acid content of 1.3% was determined by acid titration. From this, a conversion of about 3% of the formaldehyde used, corresponding to the Cannizzaro reaction to formic acid and methanol, is calculated. Likewise, a further 3% of the formaldehyde used must have reacted to form sorbose and fructose, since 94% of the formaldehyde is in the form of polymer and aqueous solution.

[0078] The formic acid was also removed by means of a strongly basic ion exchange resin, resulting in a neutral solution. This could be used for the production of so-called “impregnating resins” for the manufacture of specialty papers by adding the solution according to the formulations applicable there. To reduce the formaldehyde content in the wash water and to increase the amount of mother liquor, provision could be made to dry the moist filter cake in an industrial-scale plant by applying a good vacuum by means of a water ring pump before the washing process was initiated.

[0079] The conclusion of this experiment is that a different molar mass of the products was obtained by the different formaldehyde concentration than in Example 1 (determined by propoxylation to about 2000 g/mol).

EXAMPLE 3

[0080] The test was carried out as in Example 1. In addition, 1 g of 1,1,1-trimethylolpropane was added to each 30 g of formaldehyde (calculated as 100%). The TMP was added proportionally to the starter solution. A total of 6014 g formaldehyde in the form of a 60.8% aqueous solution, 155 ml of a 50% sodium hydroxide solution and 200 g 1,1,1-trimethylolpropane were added to the reaction vessel at 42° C. within 5.3 hours.

[0081] 200.3 mol formaldehyde and 3.0 mol NaOH were processed. This corresponds to a molar ratio of formaldehyde to base of 67.8:1.

[0082] After the end of the reaction, the solution was filtered to isolate the solid. After washing out the adherent solution and drying the solid, 3392 g of a polymeric formaldehyde was obtained corresponding to a yield of 54.6% based on the sum of formaldehyde 100% and 1,1,1-trimethylolpropane. The formaldehyde content of the solid was 95.4% and the residual moisture was 0.04%. These analytical results demonstrate that the 1,1,1-trimethylolpropane was incorporated into the polymer chain of the formaldehyde. Consequently, this polymer chain is no longer straight but branched. The mother liquor contained 23.8% formaldehyde.

EXAMPLE 4

[0083] The test was carried out as in Example 1. In addition, 1 g of 1,1,1-trimethylolpropane was added to each 13.3 g of formaldehyde (100%). The TMP was added proportionally to the starter solution. A total of 5777 g of formaldehyde in the form of a 61.1% aqueous solution, 135 ml of a 50% sodium hydroxide solution and 432 g of 1,1,1-trimethylolpropane were added to the reaction vessel at 42° C. within 5 hours. Thus, 192.4 moles of formaldehyde and 2.6 moles of NaOH were processed. This corresponds to a molar ratio of formaldehyde to base of 74.8:1.

[0084] After the end of the reaction, the solution was filtered to isolate the solid. After washing out the adherent solution and drying the solid, 3643 g of a polymeric formaldehyde was obtained corresponding to a yield of 56.4% based on the sum of formaldehyde 100% and 1,1,1-trimethylolpropane. The formaldehyde content of the solid was 92.3% and the residual moisture was 0.2%. These analytical results demonstrate that the 1,1,1-trimethylolpropane was incorporated into the polymer chain of the formaldehyde. Consequently, this polymer chain is no longer straight but branched, and more so than in Example 3.

EXAMPLE 5 (COMPARISON EXAMPLE): REACTION AT 33° C. AND A 34% FORMALDEHYDE SOLUTION

[0085] A starter solution containing a 34% formaldehyde solution and sodium hydroxide solution was added. The molar ratios to each other were the same as in Example 1. The temperature of the solution was set to 33° C. and the addition of further formaldehyde solution and aqueous sodium hydroxide solution was also carried out at this temperature. Samples were titrated for formaldehyde content by removing small amounts of liquid and separating any solid material formed by filtration. The rate of addition of the two components to the mixture was chosen so that the formaldehyde content did not rise appreciably above 30%. The purpose of this measure was to avoid supercooling of the added high-percentage formaldehyde solution and thus uncontrolled precipitation of sticky paraformaldehyde.

[0086] The reaction rate decreased to about 40% compared to working at 42° C. with an approximately 40% formaldehyde solution, so that the reaction time increased by 2.5 times. A total of 4333 g of formaldehyde (calculated as 100%) and 101 ml of a 50% sodium hydroxide solution were dosed. 2903 g of solid were obtained, corresponding to a yield of 67% formaldehyde. The purity was 98.1% and the residual moisture was 0.1%. Because of the total duration of the experiment of more than 14 hours and the poorer yield, this method of operation was not pursued further. A higher purity compared to the product from Example 1 could also not be determined.

EXAMPLE 6 (COMPARISON EXAMPLE): REACTION AT 55° C. AND A 60.1% FORMALDEHYDE SOLUTION

[0087] The experiment was carried out in the same way as in Example 1, but with a 60.1% formaldehyde solution and at 55° C. The solution was then used for the test. The amount of caustic solution was selected as in example 1. The solution turned yellowish shortly after the start of the reaction. The reaction rate—measured by titration of the formaldehyde concentration in the solution—was about 1.5 times faster than in experiment 1, so the dosing rate was increased accordingly. After the addition of 5342 g formaldehyde (100%) and 126 ml of a 50% sodium hydroxide solution, the precipitated solid was filtered off and dried. 2243 g of solid was obtained, corresponding to a yield of 41.9%. The mother liquor was clearly yellowish in color. The purity was 96.2%, the residual moisture 0.2%. Consequently, this test result is significantly worse than the result from Example 1.

EXAMPLE 7 (COMPARISON EXAMPLE): REACTION AT 42° C. AND HIGHER SODIUM HYDROXIDE AMOUNT IN COMPARISON TO EXAMPLE 1

[0088] The experiment was carried out as in Example 1. The formaldehyde solution used had a content of 62.0%. 5337 g formaldehyde (100%) were dosed and 173 ml of a 50% sodium hydroxide solution. 3929 g of solid were obtained, corresponding to a yield of 64.6%. 177.7 mol of formaldehyde and 3.3 mol of NaOH were processed. This corresponds to a molar ratio of formaldehyde to base 53.9:1.

[0089] The purity was 99.0%, the residual moisture 0.07%. Conclusion: Increasing the amount of sodium hydroxide leads to a worse yield than in example 1.

EXAMPLE 8 (COMPARISON EXAMPLE): REACTION AT 42° C. AND LOWER SODIUM HYDROXIDE AMOUNT IN COMPARISON TO EXAMPLE 1

[0090] The experiment was carried out as in Example 1. The formaldehyde solution used had a content of 61.0%. 5858 g formaldehyde (100%) were dosed and 110.9 ml of a 50% sodium hydroxide solution. 4081 g of solid were obtained corresponding to a yield of 69.7% based on formaldehyde. 195.1 mol of formaldehyde and 2.1 mol of NaOH were processed. This corresponds to a molar ratio of formaldehyde to base of 92.3:1.

[0091] The purity was 98.8%, the residual moisture 0.05%. Conclusion: Reducing the amount of sodium hydroxide leads to a poorer yield than in example 1.

[0092] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.