NEW METHOD FOR RECYCLING OF POLYURETHANE

Abstract

A new method for recycling polyurethane, in particular polyurethane foam via solvolysis can be performed. The new method includes a very efficient pre-treatment method of the polyurethane, wherein it is converted into a polyurethane dispersion. The method also includes providing the polyurethane, preparing a dispersion, and solvolyzing the dispersion. The polyurethane has an average particle size of 0.1 to 12 mm.

Claims

1. A method of solvolyzing a polyurethane, the method comprising: a. providing the polyurethane, b. preparing a dispersion from the polyurethane, and c. solvolyzing a polyurethane dispersion, wherein the polyurethane to be dispersed has an average particle size, measured by a laser diffraction analyzer, of 0.1 to 12 mm, and the polyurethane content in the dispersion after b. and/or the dispersion used for c. is in a range of from 4 to 20 percent by weight.

2. The method according to claim 1, wherein b. comprises b1. chopping, pulverizing, grinding, milling, cutting or otherwise comminuting the polyurethane provided in a. to obtain a polyurethane powder, b2. producing a dispersion from the polyurethane powder obtained in b1. by use of at least one device selected from the group consisting of colloid mills, single- or multi-stage rotor-stator systems with different geometries or fast running dissolver disk, and a sawtooth impeller in a stirred vessel.

3. The method according to claim 2, wherein a polyurethane powder to be dispersed has an average particle size measured by the laser diffraction analyzer of 0.2 to 4 mm and/or has a bulk density of higher than 30 kg/m.sup.3.

4. The method according to claim 2, wherein b1. is carried out in a temperature range between an ambient temperature and 120 C. and/or b2. is carried out at a temperature of 10 to 90 C.

5. The method according to claim 1, wherein a liquid or a mixture of liquid and other components, which is/are used as a reactant and/or a solvent in the solvolysis c. or a solvolysis reaction product of c., is used as a dispersing medium in b. and wherein the liquid or the mixture of liquid and other components is at least one selected from the group consisting of water, organic solvents, and a mixture comprising a base and water and/or a base and an organic solvent, and/or the polyurethane powder is mixed with the dispersing medium in a weight ratio of from 1:5 to 1:40, and/or the polyurethane content in the dispersion after b. and/or the dispersion used for c. is in a range of from 5 to 18 percent by weight, and/or the particle size of the polyurethane particles, measured by the laser diffraction analyzer, in the dispersion after b. and/or the dispersion used for c. is in a range of 10 to 2000 m.

6. The method according to claim 1, wherein b. is carried out, in a solvolysis reactor and the entire amount of the polyurethane is dispersed before the solvolysis reaction is started.

7. The method according to claim 1, wherein c. is carried out as a hydrolysis.

8. The method according to claim 7, wherein the hydrolysis in c. is carried out by contacting the polyurethane dispersion obtained in b. with water in the presence of a base-catalyst-combination (I), (II) or (III), wherein the base-catalyst-combination (I) comprises a base comprising an alkali metal cation and/or an ammonium cation and having a pKb value at 25 C. of from 1 to 10, and at least one catalyst selected from the group consisting of quaternary ammonium salts containing an ammonium cation containing 6 to 30 carbon atoms and organic sulfonates containing at least 7 carbon atoms, the base-catalyst-combination (II) comprises a strong inorganic base having a pKb value at 25 C. of <1, and as a catalyst a quaternary ammonium salt containing an ammonium cation containing 6 to 14 carbon atoms, or the base-catalyst-combination (III) comprises a strong inorganic base having a pKb value at 25 C. of <1, and as a catalyst a quaternary ammonium salt containing an ammonium cation containing 15 to 30 carbon atoms.

9. The method of claim 8, wherein the base comprising the alkali metal cation in base-catalyst-combination (I) is selected from the group consisting of alkali metal phosphates, alkali metal hydrogen phosphates, alkali metal carbonates, alkali metal silicates, alkali metal hydrogen carbonates, alkali metal acetates, alkali metal sulfites, ammonium hydroxide, and mixtures thereof.

10. The method of claim 9, wherein the alkali metals are selected from the group consisting of Na, K, Li, and mixtures thereof.

11. The method of claim 8, wherein the strong inorganic base in base-catalyst-combination (II) or (III) is selected from the group consisting of alkali metal hydroxides, alkali metal oxides, alkaline earth metal hydroxides, alkaline earth metal oxides, and mixtures thereof.

12. The method of claim 11, wherein the alkali metals are selected from the group consisting of Na, K, Li, and mixtures thereof and/or the alkaline earth metals are selected from the group consisting of Be, Mg, Ca, Sr, Ba, and mixtures thereof.

13. The method of claim 8, wherein the catalyst is a quaternary ammonium salt having the general structure R.sub.1 R.sub.2 R.sub.3 R.sub.4 NX wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are the same or different and are at least one hydrocarbyl group selected from the group consisting of alkyl, aryl, and arylalkyl and X is at least one selected from the group consisting of halides, hydrogen sulfate, alkyl sulfate, carbonate, hydrogen carbonate, and carboxylate.

14. The method of claim 13, wherein for base-catalyst-combination (I) and (III) the catalyst is a quaternary ammonium salt having the general structure R.sub.1 R.sub.2 R.sub.3 R.sub.4 NX where R.sub.1 and R.sub.2 are the same or different and are alkyl groups with 1 to 12 carbon atoms, wherein the alkyl groups may be linear, branched, cyclic, saturated or unsaturated, R.sub.3 is at least one selected from the group consisting of alkyl groups with 1 to 12 carbon atoms, aryl groups with 6 to 14 carbon atoms, and aralkyl groups with 7 to 14 carbon atoms, wherein the alkyl groups may be linear, branched, cyclic, saturated or unsaturated and, R.sub.4 is at least one selected from the group consisting of alkyl groups with 3 to 12 carbon atoms, aryl groups with 6 to 14 carbon atoms, and aralkyl groups with 7 to 14 carbon atoms, wherein the alkyl groups may be linear, branched, cyclic, saturated or unsaturated, and X is selected from the group consisting of halides, hydrogen sulfate, alkyl sulfate, carbonate, hydrogen carbonate, acetate, and hydroxide and/or for base-catalyst-combination (II) the catalyst is a quaternary ammonium salt having the general structure R.sub.1 R.sub.2 R.sub.3 R.sub.4 NX where R.sub.1 to R.sub.3 are the same or different and are alkyl groups with 1 to 6 carbon atoms, wherein the alkyl groups may be linear, branched, cyclic, saturated or unsaturated, R.sub.4 is at least one selected from the group consisting of alkyl groups with 3 to 11 carbon atoms, aryl groups with 6 to 11 carbon atoms, and aralkyl groups with 7 to 11 carbon atoms, wherein the alkyl groups may be linear, branched, cyclic, saturated or unsaturated, and X is selected from the group consisting of halides, hydrogen sulfate, alkyl sulfate, carbonate, hydrogen carbonate, acetate, and hydroxide.

15. The method of claim 13, wherein for base-catalyst-combination (I) R.sub.1 to R.sub.4 are selected such that the sum of carbon atoms in the quaternary ammonium cation is 6 to 14 or R.sub.1 to R.sub.4 are selected such that the sum of carbon atoms in the quaternary ammonium cation is 15 to 30.

16. The method of claim 13, wherein for base-catalyst-combination (II) R.sub.4 is different from a benzyl residue and R.sub.1 to R.sub.4 are selected such that the sum of carbon atoms in the quaternary ammonium cation is 6 to 14 or R.sub.4 is a benzyl residue, R.sub.1 to R.sub.3 are selected such that the sum of carbon atoms in the quaternary ammonium cation is 6 to 12.

17. The method of claim 7, wherein at least 0.5 weight percent of the quaternary ammonium salt is used as phase transfer catalysts based on the weight of the polyurethane.

18. The method of claim 1, further comprising separating and recovering the reaction products of the solvolysis.

19. The method of claim 1, wherein the solvolysis in c. is carried out at a temperature of from 80 C. to 200 C. and/or for 1 minute to 14 hours.

20. The method of claim 1, wherein the solvolysis in c. is carried out at atmospheric pressure or under an elevated pressure.

Description

EXAMPLES

Example 1: Preparation of an Aqueous Dispersion

[0135] As raw material polyurethane foam cubes based on 100% polyol were used, with edge lengths of approx. 162424 cm. The cubes were cut by hand into coarse pieces and dosed into a cutting mill of the company Condux (type CS 230/220/N1). The mill was equipped with a sieve layer with a 2 mm square perforation. A snow like fluffy powder was obtained from the cutting mill, which was dispersed in water. This was done in a colloid mill of the company IKA (type MK 2000/5), which was equipped with a cone insert (type MKO). The polyurethane snow was dosed together with water in a weight ratio of 1:20 into the colloid mill and dispersed in passage operation mode over 10 passages. A measurement of the particle sizes at the end of the process resulted in an average particle size of d.sub.50=592 m. The achieved opening of the foam cell structure is shown in FIG. 2a, 2b. The dispersion thus obtained was used for the subsequent hydrolysis reaction.

Example 2: Preparation of a Dispersion in Aqueous Potassium Carbonate Solution

[0136] As raw material polyurethane foam cubes based on 100% polyol were available, with edge lengths of approx. 162424 cm. The cubes were cut by hand into coarse pieces and dosed into a cutting mill of the company Condux (type CS 230/220/N1). The mill was equipped with a sieve layer with a 4 mm square perforation. A snow like fluffy powder was obtained from the cutting mill, which was dispersed in a colloid mill of Fa IKA (type MK 2000/5) with cone insert (type MKO). A 40 wt. % K.sub.2CO.sub.3 solution in water was used as a dispersing medium. The K.sub.2CO.sub.3 solution was mixed with the additive Tomadol 1-5, wherein the proportion was calculated so that based on the dry amount of the polyurethane 1% of the additive was used. For the preparation of the dispersion, 50 g of polyurethane (dry) snow and 1.5 kg of K.sub.2CO.sub.3 solution were used, which in turn contained 0.5 g of Tomadol 1-5.

[0137] The components were simultaneously metered into the colloid mill and then dispersed in passages over 10 passages. The measurement of the particle sizes at the end of the process resulted in an average particle size of d.sub.50=525 microns. A dispersion was used for the subsequent hydrolysis reaction.

Example 3: Preparation of a Dispersion in Aqueous Potassium Carbonate Solution

[0138] In a modification of the experiment described in Example 2, the dispersion was finally filtered via a 300 m sieve to separate excess dispersing fluid before using the dispersion for hydrolysis. The amount of the dispersing fluid was, thus, reduced by about 50%.

Example 4: Preparation of a Dispersion in Aqueous Potassium Carbonate Solution by Means of Recirculation

[0139] Example 2 was repeated with the following modifications:

[0140] The polyurethane snow obtained from the cutting mill was dispersed in the colloid mill in the recirculation mode rather than in the passage mode. A pump was installed in the liquid drain of the colloid mill to pump back the dispersing medium into a feed tank above the mill. The feed tank was filled with the dispersing medium, this time including Tomadol 1-5 and the mill was started. While pumping the dispersing medium through the mill and back to the feed tank, the required amount of polyurethane snow was continuously metered into the liquid circuit. After reaching the polyurethane target concentration, the dispersion was circulated in the liquid circuit for a short time and then withdrawn for further use. A measurement of the particle sizes at the end of the process resulted in an average particle size of d.sub.50=694 m.

Example 5: Hydrolysis of Polyurethane Snow Dispersion

[0141] From the 50 g polyurethane snow dispersion of example 1 an excess of the water phase was separated by filtration and 490 g of a 40 wt. % K.sub.2CO.sub.3 solution in water was added to the dispersion. The resulting dispersion was further mixed with 2.5 g of the quaternary ammonium salt Tetrabutylammoniumhydrogensulfate (C=16). The suspension is added to a pressure-resistant reactor. In the reactor, sufficient mixing is ensured.

[0142] By means of connected thermostats in the reactor jacket, the stirred mixture is heated to the desired reaction temperature and cooled after the completion of the reaction. The reaction was carried out at 150 C. internal temperature and increased pressure (equal to or higher than boiling pressure of the reaction mixture). The reaction was interrupted by discharging the reaction solution from the reactor after 30 minutes.

[0143] The conversion rate was measured by weighing the dried residue of the organic fraction of the reaction mixture and is shown in Table 1. For this the organic phase and DMSO soluble solids were dissolved in DMSO. Undissolved solids, i.e. remaining PU and K.sub.2CO.sub.3, were filtered and washed with HCl. By washing with HCl, potassium carbonate is dissolved and only unreacted PU remains on the filter.

Comparative Example 1

[0144] The procedure described in Example 5 was repeated in Comparative Example 1. Instead of an inventive polyurethane snow dispersion, polyurethane foam cubes were used for hydrolysis, which were obtained by hot compression of the same raw polyurethane foam at 160 C. and 10 min holding time and cutting the hot compressed polyurethane into cubes with an average size of approximately 112 cm. The conversion rate was determined at different times and is shown in Table 1.

TABLE-US-00001 TABLE 1 Comparative Reaction time Example 1 Example 5 min Conversion rate [%] Conversion rate [%] 30 69 100 75 93 90 97

[0145] As can be seen in Table 1, the inventive dispersion of Example 5, which was obtained by use of steps b1. (cutting mill) and b2. (dispersing step) can be converted completely within 30 min. In contrast thereto an identical polyurethane foam, which was treated by hot compressing and cutting, as suggested in the prior art, could be converted to only 97% even after 90 minutes reaction time.

Comparative Example 2

[0146] In Example 1 of US 2016/00347927, 500 g rigid PU was grinded. During grinding in sum 500 g recycle polyol was added and a mixture comprising 50% by wight grinded PU powder in polyol was obtained. US '927 does not provide details of the used grinder. Thus a direct reproduction of the example is impossible.

[0147] To, nevertheless, compare the grinded material of US '927 with the present invention, pre-grinded polyol was added to 100 ml (97 g) of polyol under stirring until the resulting mixture forms a wetted powder rather than a dispersion, i.e. until the reaction mixture can no longer be pumped through a pipe. It was found that after addition of 30 g grinded PU a wet powder as shown in FIG. 3 was obtained. Even under pressure no liquid could be pressed out of the wetted powder.

[0148] This shows that a mixture of grinded PU and polyol having a PU content of 30 or more percent by weight, as the grinded powder obtained in Example 1 of US '927, cannot be regarded as dispersion, in particular not as pumpable dispersions as those of the present invention. A mixture of grinded PU in polyol with such high solid content must be treated and conveyed with conveying means for solids like screw conveyors or conveyor belts and cannot be pumped through pipes with small diameters.

[0149] An attempt to produce a mixture of grinded PU in polyol with a solvent content of 30% by weight in a grinder resulted in a wetted powder, too. The wet powder sticked to the walls of the mill and caused a high effort to clean the mill after the experiment. Continuous operation of the mill with such material is impossible.

[0150] Hydrolysis experiments conducted with the wetted powder obtained in Comparative Example 2 under conditions as described in Comparative Example 1 led to incomplete conversion even if the reaction time was 50% longer compared to the use of dispersions according to the invention.