Caprolactam Recovery from Nylon-6 Via Reactive Extrusion Previous Works

Caprolactam Recovery from Nylon-6 via Reactive Extrusion Previous Works

¾Ammonolysis ¾Hydrolysis Steam only Acid + steam Base + steam ¾Pyrolysis No catalyst Base-catalyzed Base-catalyzed Pyrolysis

% % Catalyst Reactor Time Temp. °C Pressure Yield Catalyst Purity

NaOH 1 semi-batch 4.5 hr 250 3 mmHg 90.5 unknown

K2CO3 0.5-2.5 semi-batch various 270-300 25 mbar 95 98

KOH on 5 w/w fludized bed < 1hr 330-360 - 85 90 alumina eutectic cycled 75-300 10 290-350 - 99 99 NaOH/KOH spheres mins

Mukherjee, A. K. et. al. J. of Appl. Poly. Sci. 22, 361-368 (1978). Nielinger, W. et.al. U.S. Patent 5,233,037 (1993). Czernik, S. et. al. J. of Anal.& Appl. Pyrol. 46, 51-54 (1998). Bockhorn, H. et. al. . J. of Anal.& Appl. Pyrol. 58-59 (2001) 79-94. Depolymerization Methods - Pyrolysis

National Renewable Energy Lab (NREL) CRNI TSE 2 minutes residence time

Nylon 6 carpet strips with K2CO3 67% crude yield Objectives

¾ Assess catalysts Different bases: same conditions Screen using dynamic Thermogravimetric Analysis (TGA) As little catalyst as possible

¾ Effective depolymerization reactor Catalyst Screening

¾ Mixed catalysts and pure nylon in Haake Rheomix® 600 240°C 5 mins

Under N2 10% wt of polymer ¾ Grind into powder ¾ Dynamic TGA 25-500°C Heating @ 10°/min TGA Results: Hydroxides TGA Results:Carbonates TGA Results: Selected Catalysts Kinetics from TGA

ASTM E 1641 – 99 ¾ Assumes 1st order ¾ Iterative process Activation Energy Pre-exponential

Time to 90% Conversion (min) @ 300 (°C) 325 (°C) 350 (°C) 375 (°C) 400 (°C) Pure 3.65E+04 6.15E+03 1197 264 65 1% KOH 21 7 2 0.9 0.3

1% K2CO3 130 42 15 6 2 cr Ca2CO3 1079 270 75 23 8 Reactor Design

¾ Extruders inherent capabilities: Good melting of polymers & temperature control Control over residence time distribution Excellent dispersive and distributive mixing Continuous processing

¾ Counter-rotating Non-intermeshing Twin Screw Extruder (CRNI TSE) High degree of backflow High interfacial area for devolatilization/Superior vent performance The Extruder Residence Time

Time to 90% Conversion (min) @ 300(°C) 325(°C) 350(°C) 375(°C) 400(°C) Pure 3.65E+04 6.15E+03 1197 264 65 1% KOH 21 7 2 0.9 0.3

1% K2CO3 130 42 15 6 2 cr Ca2CO3 1079 270 75 23 8 Product Collection 6.0

5.5 GC Results

ION TRACE. Flagging=Scan Number & Area. Max.Scan=1675#30:01.94. Integ=[Det:1%, Hgt:0.5V, Wid:3-50, Res:3%]. 5.0 Total Ion Current. Max.Int.=24.43895.

4.5

575 4.0 9.97618E07

3.5

3.0

2.5

Intensity (%age) Intensity 2.0 1169 1191 1467 1513 1.5 1018 1.0 357 393 706

0.5

0.0 5:00 10:00 15:00 20:00 25:00 30:00 Retention Time MS Results 100

SCAN GRAPH. 90 Scan 571#10:13.76 - 576#10:19.15. Sub=579#10:22.37 - 591#10:35.28. 100% Int.=0.20936. EI. POS. 0.209360.20936 113.1

55.1 80

84.1 50 42.1 85.1

40 Intensity (%age)

67.1 10 68.1 51.1

0 40 50 60 70 80 90 100 110 120 130 140 150 Low Resolution M/z Key Parameters and Variables

¾Screw configuration ¾Barrel temperatures ¾Vacuum level ¾Product rate/Screw speed ratio Summary

¾ Pure nylon: degradation onset ~ 400°C ¾ With catalyst: onset between 250-300°C ¾ Hyroxides CsOH & KOH most effective ¾ Carbonates

Cs2CO3 and K2CO3 most effective Carpet Ratio CaCO3 decreases onset ¾ Cs+ bases more expensive than K + bases

KOH and K2CO3 seem to be the best candidates • 10% KOH and K2CO3 have similar onset Temperature • 1% catalyst as effective as 10% ¾ Twin screw extruder as reactor Sufficient residence time Pure caprolactam Still trying to optimize the yield Fin Miscellaneous

Specifications ε-caprolactam ¾ caprolactam $0.90- $ Freezing point (dry basis) (°C) 69.0 (minimum) Percen transmission at 410 nm (65wt 92.0 (minimum) 0.98/lb % aq. sol'n) Permnganate number 7 (maximum) ¾ K2CO3 $0.40/lb ¾ vapor pressure of Moisture (%) 0.10 (maximum) caprolactam 1.9 E-3 Iron (as Fe) (ppm) 0.5 (maximum) mm Hg at 25 °C Volatile bases (as NH3) (ppm) 5 (maximum) Ignition residue (ppm) 10 (maximum)

Water insoluble passes test

Cyclohexanone omine (ppm) 10 (maximum)

Free alkalinty (meq kg-1) 0.04 (maximum)

Chemical Week, 3/7/2007, Vol. 169 Issue 8, p26-26 http://www.epa.gov/ttn/atw/hlthef/caprolac.html Chemical market reporter Oct. 28, 2004 Sneell F. D. and C. L. Clifford. Encyclopedia of Industrial Chemical Analysis. Vol. 4 (120-128) and Vol. 8 (410-419). SBR 10%

CaCO3 30% Nylon 53%

PP 7% Purity

SCAN100 GRAPH. Scan 642#11:28.44. EI. POS. Probe T =29. GC Temp =186. 113.1 90

80 55

84.1 50

41.9

Intensity (%age) Intensity 40 56

67.1 10

0 30 40 50 60 70 80 90 100 110 120 130 140 150 Low Resolution M/z Depolymerization Methods - Ammonolysis

¾Nylon in ammonia at high temperatures and pressures ¾81% monomer recovery ¾ Numerous by-products

Bodrero, S. et. al. 4th Annual conference on recycling of Fibrous Textile and Carpet Waste. Dolton, GA, May 1999. Hendrix, J. A. et. al. U.S. Patent 5,668,277 (1997). McKinney, R. J. “Ammonoylsis of Nylon”. U. S. Patent 5,302,756 (1994) Depolymerization Methods - Hydrolysis

¾ Non-catalyzed: steam only Less than 10% contaminant 3 hours 94.4% pure caprolactam, but only 89.7% overall yield Further purification required ¾ Acid Catalyzed: 5-35wt% mineral acids with steam 96.4% yield Cannot be used with mixed material ¾ Base catalyzed: alkali and alkaline earth oxides, hydroxides, carbonates, etc. with steam 98% yield By-products present

Miller, B. U.S. Patent 2,840,606 (1958) Thomissen, P.J. H. European Patent 0,875,504, A1 (1998) Braun, M. et. al. Polym.-Plastics Tech. & Engr. 38 (3) 471-484 (1999). Moran, E.F., E.I. Dupont de Nemours. U.S. Patent 5,310,905 (1994). Andrady, A. ed. Polymers and the environment: a Handbook, Wiley-Interscience, New York (2002).