Process for acid hydrolysis of pure polylaurolactam

Abstract

An improved process can be used for the acid hydrolysis of polylaurolactam with sulfuric acid. An especially suitable starting material is polylaurolactam which is intended for recycling and which is characterized by a low laurolactam content.

Claims

1. A process for hydrolysis of polylaurolactam, the process comprising: cleaving the polylaurolactam with sulfuric acid at a temperature of from 125 C. to 190 C., to give o-aminolauric acid.

2. The process according to claim 1, wherein the polylaurolactam has a molar mass of 1,000 to 10.sup.6 g/mol.

3. The process according to claim 1, wherein the polylaurolactam has a content of laurolactam of <4.9% by weight.

4. The process according to claim 1, wherein the polylaurolactam has a content of -aminolauric acid of <4.9% by weight.

5. The process according to claim 1, wherein a pressure is 1 bar to 100 bar.

6. The process according to any claim 1, wherein a ratio of a weight of the sulfuric acid to a weight of the polylaurolactam is in a range of 1:0.1 to 1:1.

7. The process according to claim 1, further comprising: after 1-99% by weight of the polylaurolactam has reacted, adding alkali metal hydroxide to neutralize the sulfuric acid, and then adding further alkali metal hydroxide with which a remaining amount of the polylaurolactam is reacted.

8. The process according to claim 7, wherein after the neutralization of the sulfuric acid, the alkali metal hydroxide remains in such an amount that a ratio of a weight of unconverted polylaurolactam to a weight of a remaining amount of the alkali metal hydroxide is in a range of 1:0.1 to 1:1.

9. The process according to claim 7, wherein a temperature while adding the alkali metal hydroxide is in a range of 160 C. to 280 C.

10. The process according to claim 7, wherein a pressure while adding the alkali metal hydroxide is in a range of 1 bar to 100 bar.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) It has surprisingly been found that the hydrolysis of polylaurolactam with sulfuric acid proceeds with a higher yield compared to the processes described in the prior art.

(2) The polylaurolactam which is used in the process according to the invention is not subject to further restriction. Preference is given to using material intended for recycling (PA12 waste).

(3) The polylaurolactam is used in particular as a powder, since thereby the enlargement of the surface area can accelerate the hydrolysis. A suitable pulverulent PA12 is described for example in EP 0 911 142 A1, To this end, PA12 can be ground to powder by methods known to those skilled in the art before it is used in the process according to the invention.

(4) The PA12 used according to the invention comprises repeating units with the aforementioned structure (I), wherein the bond identified with (*) of one repeating unit binds to that identified with (**) of the adjacent repeating unit.

(5) The PA12 used according to the invention preferably has a molar mass of 1000 to 10.sup.6 g/mol, more preferably of 3000 to 200 000 g/mol, yet more preferably of 15 000 to 150 000 g/mol, more preferably still 25 000 to 120 000 g/mol, even more preferably 40 000 to 95 000 g/mol, even more preferably still 80 000 g/mol.

(6) The present invention is particularly suitable for the hydrolysis of polylaurolactam comprising a low content of laurolactam. Preferably, polylaurolactam is used which has a content of laurolactam of <4.9% by weight, preferably <4.0% by weight, more preferably <3.0% by weight, yet more preferably <1.0% by weight, even more preferably <0.01% by weight, based in each case on the sum of the masses of PA12 and laurolactam.

(7) The present invention is particularly suitable for the hydrolysis of polylaurolactam comprising a low content of -aminclauric acid. Preferably, polylaurolactam is used which has a content of -aminolauric acid of <4.9% by weight, preferably <4.0% by weight, more preferably <3.0% by weight, yet more preferably <1.0% by weight, even more preferably <0.3% by weight, based in each case on the sum of the masses of PA12 and -aminolauric acid.

(8) This distinguishes the present process in particular from the process in DE 3401415 A, in which residues from the production of laurolactam are hydrolysed, which leads to a high proportion of laurolactam in the reactant to be hydrolysed.

(9) In contrast, hydrolysis with sulfuric acid in the process according to the invention is particularly well suited to the use of material to be recycled which features a low content of laurolactam and -aminolauric acid.

(10) The hydrolysis can be performed by processes known to those skilled in the art.

(11) The temperature in the process according to the invention is 125 C. to 190 C., preferably 140 C. to 180 C., more preferably 150 C. to 170 C., even more preferably 160 C. to 165 C.

(12) The pressure in the process according to The invention is preferably in the range 1 bar to 100 bar, preferably 10 bar to 60 bar.

(13) Typically, the polylaurolactam to be hydrolysed is initially charged in a reaction vessel, for example an autoclave coated with a noble metal such as gold or stainless steel, and the sulfuric acid is added thereto.

(14) The sulfuric acid is in this case usually an aqueous solution, the content of sulfuric acid in the aqueous solution not being subject to further restriction.

(15) The content of sulfuric acid in the aqueous solution is preferably in the range 10% to 90% by weight, preferably 20% to 80% by weight, more preferably 30% to 50% by weight, even more preferably 35% to 40% by weight.

(16) The ratio of sulfuric acid used to polylaurolactam used is likewise not subject to further restriction. In particular, sulfuric acid is used in such an amount that the ratio of the weights of sulfuric acid used to PA12 used is in the range 1:0.1 to 1:1, preferably in the ramie 1:0.2 to 1:0.8, more preferably in the range 1:0.3 to 1:0.7, even more preferably in the range 1:0.4 to 1:0.6, even more preferably still in the range 1:0.45 to 1:0.51.

(17) The process according to the invention is preferably performed until at least 30% by weight, more preferably at least 50% by weight, even more preferably at least 70% by weight, more preferably still at least 90% by weight, even more preferably still at least 99% by weight of the PA12 used has reacted.

(18) In an alternative particular embodiment of the process according to the invention, after 1-99% by weight, preferably 30-90% by weight, more preferably 50-70% by weight, of the PA12 used has reacted, alkali metal hydroxide is added in order to neutralize the sulfuric acid (i.e. in particular to set a ph of 7 in the reaction mixture), and then further alkali metal hydroxide is added with which as hydrolysis catalyst the remaining PA12 is reacted.

(19) The alkali metal hydroxide used is especially lithium hydroxide, sodium hydroxide or potassium hydroxide, preferably potassium hydroxide.

(20) This alternative embodiment exploits the fact that the hydrolysis of PA12 having a low content of laurolactam or of the very similar -aminolauric acid functions very well with sulfuric acid. When the PA12 has decomposed to a certain extent, the remaining hydrolytic cleavage can then be performed in a subsequent step with alkali metal hydroxides.

(21) This subsequent step can then be preferably be performed as described in DE 3401415 A.

(22) In particular, alkali metal hydroxide is used in such an amount in the subsequent step that, after the neutralization of the sulfuric acid, alkali metal hydroxide remains in such an amount that the ratio of the weights of unconverted polylaurolactam to remaining alkali metal hydroxide is in the range 1:0.1 to 1:1, preferably in the range 1:0.2 to 1:0.8, more preferably in the range 1:0.3 to 1:0.7, even more preferably in the range 1:0.4 to 1:0.6, even more preferably still in the range 1:0.45 to 1:0.51.

(23) The temperature in the subsequent step is preferably in the range 160 C. to 280 C., preferably 180 C. to 250 C., more preferably 200 C. to 230 C.

(24) The pressure in the subsequent is preferably in the range 1 bar to 100 bar, preferably 10 bar to 60 bar.

(25) In the subsequent step the alkali metal hydroxide is preferably used as an aqueous solution, more preferably with a concentration of 1% to 10% by weight of alkali metal hydroxide.

(26) If the subsequent step is performed, the remaining workup of the cleaved PA12 can be performed as described in DE 3401415 A.

(27) The examples which follow illustrate the invention, without limiting said invention in any way.

EXAMPLES

(28) The depolymerization of PA12 having a content of laurolactam and -aminolauric acid of in each case<1% was investigated with various catalysts and temperature conditions.

(29) The following catalysts were tested: KOH, H.sub.2SO.sub.4, H.sub.3PO.sub.4.

(30) The conversion rate was determined using .sup.1H NMR in CDCl.sub.2+trifluoroacetic anhydride.

(31) The following tests were carried out:

(32) 1. Comparative Test C1. H.sub.3PO.sub.4, 320 C.

(33) 6.66 mg of PA12 powder were placed in a gold-coated autoclave. Thereafter, 6.8 mg of H.sub.3PO.sub.4 (85) and 6.30 mg of water were added and the autoclave was sealed. The autoclave was heated in an oven to 320 C. and the reaction mixture was held at this temperature for 4 hours. The mixture was then cooled down to room temperature at a rate of 100 K/min. The reaction mixture was withdrawn from the reactor and neutralized by addition of 1 g of water and a stoichiometric amount of KOH. The mixture was dried at 80 C. and 200 mbar. The conversion rate of the PA12 was 96%.

(34) 2. Comparative Test C2: H.sub.3PO.sub.4, 300 C.

(35) 5.9 mg of PA12 powder were placed in a gold-coated autoclave. Thereafter, 4.25 mg of H.sub.3PO.sub.4 (85) and 5.23 mg of water were added and the autoclave was sealed. The autoclave was heated in an oven to 300 C. and the reaction mixture was held at this temperature for 4 hours. The mixture was then cooled down to room temperature at a rate of 100 K/min. The reaction mixture was withdrawn from the reactor and neutralized by addition of 1 g of water and a stoichiometric amount of KOH. The mixture was dried at 80 C. and 200 mbar. The conversion rate of the PA12 was 35%.

(36) 3. Comparative Test C3: H.sub.3PO.sub.4, 250 C.

(37) 7.17 mg of PA12 powder were placed in a gold-coated autoclave. Thereafter, 4.98 mg of H.sub.3PO.sub.4 (85%) and 6.23 mg of water were added and the autoclave was sealed. The autoclave was heated in an oven to 250 C. and the reaction mixture was held at this temperature for 4 hours. The mixture was then cooled down to room temperature at a rate of 100 K/min. The reaction mixture was withdrawn from the reactor and neutralized by addition of 1 g of water and a stoichiometric amount of KOH. The mixture was dried at 30 C. and 200 mbar. The conversion rate of the PA12 was 88%.

(38) 4. Comparative Test C4: H.sub.3PO.sub.4, 220 C.

(39) 6.95 mg of PA12 powder were placed in a gold-coated autoclave. Thereafter, 4.6 mg of H.sub.3PO.sub.4 (85%) and 6.30 mg of water were added and the autoclave was sealed. The autoclave was heated in an oven to 220 C. and the reaction mixture was held at this temperature for 4 hours. The mixture was then cooled down to room temperature at a rate of 100 K/min. The reaction mixture was withdrawn from the reactor and neutralized by addition of 1 g of water and a stoichiometric amount of KOH. The mixture was dried at 80 C. and 200 mbar. The conversion rate of the PA12 was 87%.

(40) 5. Comparative Test C5: H.sub.3PO.sub.4, 200 C.

(41) 7.27 mg of PA12 powder were placed in a gold-coated autoclave. Thereafter, 5.43 mg of H.sub.3PO.sub.4 (85%) and 6.20 mg of water were added and the autoclave was sealed. The autoclave was heated in an oven to 200 C. and the reaction mixture was held at this temperature for 4 hours. The mixture was then cooled down to room temperature at a rate of 100 K/min. The reaction mixture was withdrawn from the reactor and neutralized by addition of 1 g of water and a stoichiometric amount of KOH. The mixture was dried at 80 C. and 200 mbar. The conversion rate of the PA12 was 100%.

(42) 6. Inventive Example I1: H.sub.2SO.sub.4, 180 C.

(43) 6.5 mg of PA12 powder were placed in a gold-coated autoclave. Thereafter, 8.62 mg of H.sub.2SO.sub.4 (35%) were added and the autoclave was sealed. The autoclave was heated in an oven to 180 C. and the reaction mixture was held at this temperature for 4 hours. The mixture was then cooled down to room temperature at a rate of 100 K/min. The reaction mixture was withdrawn from the reactor and neutralized by addition of 1 g of water and a stoichiometric amount of KOH. The mixture was dried at 80 C. and 200 mbar. The conversion rate of the PA12 was 100%.

(44) 7. Inventive Example I2: H.sub.2SO.sub.4, 160 C.

(45) 6.61 mg of PA12 powder were placed in a gold-coated autoclave. Thereafter, 8.63 mg of H.sub.2SO.sub.4 (35%) were added and the autoclave was sealed. The autoclave was heated in an oven to 160 C. and the reaction mixture was held at this temperature for 4 hours. The mixture was then cooled down to room temperature at a rate of 100 K/min. The reaction mixture was withdrawn from the reactor and neutralized by addition of 1 g of water and a stoichiometric amount of KOH. The mixture was dried at 80 C. and 200 mbar. The conversion rate of the PA12 was 98%.

(46) 8. Comparative Test C6 (Corresponding to DE 3407415 A1): KOH, 320 C. 30 g of PA12 powder were placed in a nickel-coated autoclave. Thereafter, 18.95 g of KOH solution (50%) in water were added and the autoclave was sealed. Nitrogen was then injected into the autoclave to 28 bar and it was heated to 320 C. The reaction mixture was held at this temperature for 4 hours. The mixture was then cooled down to room temperature at a rate of 100 K/min and the pressure was released. The reaction mixture was withdrawn from the reactor, dissolved in water and neutralized by addition of 13 g of sulfuric acid. The mixture was dried at and 100 mbar, The conversion rate of the PA12 was 94%.
9. Comparative Test C7 (Corresponding to DE 3407415 A1): KOH, 300 C.

(47) 7.42 mg of PA12 powder were placed in a gold-coated autoclave. Thereafter, 4.03 mg of KOH solution (50%) in water were added and the autoclave was sealed. The autoclave was heated in an oven to 300 C. The reaction mixture was held at this temperature for 4 hours and then cooled down to room temperature at a rate of 100 K/min. The mixture was subsequently cooled down to room temperature. The reaction mixture was withdrawn from the reactor and neutralized by addition of 1 g of water and a stoichiometric amount of phosphoric acid. The mixture was dried at and 100 mbar. The conversion rate of the PA12 was 78%.

(48) 10. Comparative Test C8 (Corresponding to DE 3407415 A1): KOH, 280 C.

(49) 7.17 mg of PA12 powder were placed in a gold-coated autoclave. Thereafter, 4.42 mg of KOH solution (50%) in water were added and the autoclave was sealed. The autoclave was heated in an oven to 280 C. The reaction mixture was held at this temperature for 4 hours and then cooled down to room temperature at a rate of 100 K/min. The mixture was subsequently cooled down to room temperature. The reaction mixture was withdrawn from the reactor and neutralized by addition of 1 g of water and a stoichiometric amount of phosphoric acid. The mixture was dried at and 100 mbar. The conversion rate of the PA12 was 78%.

(50) 11. Comparative Test C9 (Corresponding to DE 3407415 A1): KOH, 280 C.

(51) 6.80 mg of PA12 powder were placed in a gold-coated autoclave. Thereafter, 0.95 mg of KOH solution (50%) in water were added and the autoclave was sealed. The autoclave was heated in an oven to 320 C. The reaction mixture was held at this temperature for 4 hours and then cooled down to room temperature at a rate of 100 K/min. The mixture was subsequently cooled down to room temperature. The reaction mixture was withdrawn from the reactor and neutralized by addition of 1 g of water and a stoichiometric amount of phosphoric acid. The mixture was dried at and 100 mbar. The conversion rate of the PA12 was 2%.

(52) 12. Comparative Test C10: Without Catalyst, 320 C.

(53) 7.62 mg of PA12 powder were placed in a nickel-coated autoclave. Thereafter, 3.91 mg of water were added and the autoclave was sealed. The autoclave was heated in an oven to 320 C. The reaction mixture was held at this temperature for 4 hours and then cooled down to room temperature at a rate of 100 K/min. The reaction mixture was withdrawn from the reactor and dried at 80 C. and 200 mbar. The conversion rate of the PA12 was 6%.

(54) Table 1 below summarizes the results of the tests and comparative tests.

(55) TABLE-US-00001 TABLE 1 Amount of catalyst based on Amount of amount of PA-12 PA-12 in Test in mg Catalyst % by weight Temperature Yield C1 6.66 H.sub.3PO.sub.4 86.7 320 C. 96% C2 5.9 H.sub.3PO.sub.4 61.2 300 C. 85% C3 7.17 H.sub.3PO.sub.4 59.0 250 C. 88% C4 6.95 H.sub.3PO.sub.4 56.3 220 C. 87% C5 7.27 H.sub.3PO.sub.4 63.5 200 C. 100% I1 6.5 H.sub.2SO.sub.4 46.4 180 C. 100% I2 6.61 H.sub.2SO.sub.4 45.7 160 C. 98% C6 30000.0 KOH 31.6 320 C. 94% C7 7.42 KOH 27.1 300 C. 78% C8 7.17 KOH 30.8 280 C. 78% C9 6.8 KOH 6.99 320 C. 2% C10 7.62 320 C. 6%

(56) It is evident from the results that the addition of H.sub.2SO.sub.4 results in almost quantitative conversion at particularly low temperatures, i.e. as low as at 190 C. and 160 C.

(57) 13. Temperature Dependence of the Hydrolysis of PA12 with Sulfuric Acid

(58) In order to investigate the temperature dependence of the hydrolysis of PA12 with sulfuric acid, the following series of tests was carried out:

(59) PA12 powder and H.sub.2SO.sub.4 (35%) were added to a gold-coated autoclave in the amounts respectively indicated in Table 2 below. The autoclave was then sealed. The autoclave was heated in an oven to the respective temperature T indicated in Table 2 below (heating rate 5 K/min) and the reaction mixture was held at this temperature for 4 hours. The mixture was then cooled down to room temperature at a rate of 5 K/min. The residual content of PA12 was subsequently determined.

(60) TABLE-US-00002 TABLE 2 Amount of Added Residual PA-12 amount of Temperature content Test in mg 35% H.sub.2SO.sub.4 in mg T of PA12 C11 5.33 5.08 80 C. 90.5% I3 5.47 5.33 125 C. 7.3% I4 5.7 4.99 158 C. 6.3% I5 6.22 5.32 190 C. 5.3% C12 6.3 5.1 230 C. 10.5% C13 6.74 12.68 80 C. 7.2% I6 5.60 12.07 125 C. <0.1% I7 5.03 13.04 158 C. 1.3% I8 6.78 12.07 190 C. 0.7% C14 5.74 13.23 230 C. 3.2%

(61) It is apparent from the test results shown in Table 2 that the hydrolysis of PA12 with sulfuric acid in the temperature range from 125 C. to 190 C. (13 to 15; 16 to 18) proceeds surprisingly efficiently. In comparison, hydrolysis at a temperature of 80 C. (comparative tests C11, C13) performed in the prior art (U.S. Pat. No. 4,170,588 A) is not productive. Comparative tests C12 and C14 additionally demonstrate that at a temperature of 230 C. the residual content of PA12 rises again; hence the efficiency of the conversion decreases again.