Chemical Recycling of Aliphatic Polyamides by Microwave-Assisted Hydrolysis for Efficient Monomer Recovery

Abstract

We report on a simple and efficient chemical recycling process for aliphatic polyamides (PA 66, PA 1010, PA 11, and PA 12), whereby PAs are converted exclusively into their constituent monomers even in the presence of reinforcement additives, such as carbon- and glass-fibers. In this process, the rate of PA hydrolysis reaction, performed under microwave irradiation in the presence of HCl as an acid catalyst, depends on the PA type, the HCl/amide mole ratio, and the type and amount of reinforcement additives. PA 66 is completely converted into the constituent monomers at 200 °C and a 1.25 HCl/amide mole ratio in 10 min. Long-chain PAs (PA 11, PA 12, and PA 1010) and PAs containing glass- or carbon-fiber reinforcement additives need at the same experimental conditions longer reaction times. Alternatively, they can be completely hydrolyzed at 200 °C within a comparable reaction time at a higher HCl/amide mole ratio of 2.5. Complete and straightforward conversion of PAs into the constituent monomers in the absence of side reactions simplifies the isolation and purification of monomers and reinforcement additives, which have been recovered in high yields and quality comparable to those of commercially available chemicals.

Iron-based Lewis/Brønsted Deep Eutectic Solvents for thehydrolysis of nylon-6,6

“…In particular, the factor E, defined as the mass of waste for the mass of the product, was determined as well as the energy economy (ε) and the energy impact (ξ), calculated as the E/ε ratio (Table 1). a Virgin pellets, PA 66/system B1_1 1: Consistently with what previously reported in literature, [5,6,9] also in our case the values of E, ε and ξ are referred only to the depolymerization reaction. Although in some cases the depolymerization conditions are markedly different from those of this work (for example in the case of the hydrogenative depolymerization [10], or in the case of microwave irradiation [6]), making a strict comparison difficult, the values obtained for the LBDES are worth of attention and suggest the potential of these solvents for the effective depolymerization of PA-based waste.…”

Iron-based Lewis/Brønsted Deep Eutectic Solvents for thehydrolysis of nylon-6,6

“…In particular, the factor E, defined as the mass of waste for the mass of the product, was determined as well as the energy economy (ε) and the energy impact (ξ), calculated as the E/ε ratio (Table 1). a Virgin pellets, PA 66/system B1_1 1: Consistently with what previously reported in literature, [5,6,9] also in our case the values of E, ε and ξ are referred only to the depolymerization reaction. Although in some cases the depolymerization conditions are markedly different from those of this work (for example in the case of the hydrogenative depolymerization [10], or in the case of microwave irradiation [6]), making a strict comparison difficult, the values obtained for the LBDES are worth of attention and suggest the potential of these solvents for the effective depolymerization of PA-based waste.…”

Microwave Assisted Selective Hydrolysis of Polyamides from Multicomponent Carpet Waste

“…This is due to the higher melting temperature of PA‐66 and the longer alkyl segment between the amide bonds. [ 23 ] Interestingly, the same phenomenon with oligomeric versus monomeric products was observed, depending on the concentration of HCl, that is, at higher HCl concentration (C = 0.1 g mL −1 ), water soluble monomers were formed from both PA‐6 and PA‐66, Figure 2 .…”

Achieving 1060 mW cm −2 with 0.6 mg cm −2 Pt Loading Based on Imidazole‐Riched Semi‐Interpenetrating Proton Exchange Membrane at High‐Temperature Fuel Cells

“…This may be due to the disrupted NMBA crosslinked structure. [ 55,56 ] As previously discussed in the TGA section, the PBI‐V membranes retain only limited PVIm content after the purification treatment. The PA uptakes are ≈280% for all the PVIm membranes.…”

Iron-based Lewis/Brønsted Deep Eutectic Solvents for thehydrolysis of nylon-6,6

“…In particular, the factor E, defined as the mass of waste for the mass of the product, was determined as well as the energy economy (ε) and the energy impact (ξ), calculated as the E/ε ratio (Table 1). a Virgin pellets, PA 66/system B1_1 1: Consistently with what previously reported in literature, [5,6,9] also in our case the values of E, ε and ξ are referred only to the depolymerization reaction. Although in some cases the depolymerization conditions are markedly different from those of this work (for example in the case of the hydrogenative depolymerization [10], or in the case of microwave irradiation [6]), making a strict comparison difficult, the values obtained for the LBDES are worth of attention and suggest the potential of these solvents for the effective depolymerization of PA-based waste.…”

Microwave Assisted Selective Hydrolysis of Polyamides from Multicomponent Carpet Waste

“…This is due to the higher melting temperature of PA‐66 and the longer alkyl segment between the amide bonds. [ 23 ] Interestingly, the same phenomenon with oligomeric versus monomeric products was observed, depending on the concentration of HCl, that is, at higher HCl concentration (C = 0.1 g mL −1 ), water soluble monomers were formed from both PA‐6 and PA‐66, Figure 2 .…”

Achieving 1060 mW cm −2 with 0.6 mg cm −2 Pt Loading Based on Imidazole‐Riched Semi‐Interpenetrating Proton Exchange Membrane at High‐Temperature Fuel Cells

“…This may be due to the disrupted NMBA crosslinked structure. [ 55,56 ] As previously discussed in the TGA section, the PBI‐V membranes retain only limited PVIm content after the purification treatment. The PA uptakes are ≈280% for all the PVIm membranes.…”

Iron-based Lewis/Brønsted Deep Eutectic Solvents for thehydrolysis of nylon-6,6

“…In particular, the factor E, defined as the mass of waste for the mass of the product, was determined as well as the energy economy (ε) and the energy impact (ξ), calculated as the E/ε ratio (Table 1). a Virgin pellets, PA 66/system B1_1 1: Consistently with what previously reported in literature, [5,6,9] also in our case the values of E, ε and ξ are referred only to the depolymerization reaction. Although in some cases the depolymerization conditions are markedly different from those of this work (for example in the case of the hydrogenative depolymerization [10], or in the case of microwave irradiation [6]), making a strict comparison difficult, the values obtained for the LBDES are worth of attention and suggest the potential of these solvents for the effective depolymerization of PA-based waste.…”

Microwave Assisted Selective Hydrolysis of Polyamides from Multicomponent Carpet Waste

“…This is due to the higher melting temperature of PA‐66 and the longer alkyl segment between the amide bonds. [ 23 ] Interestingly, the same phenomenon with oligomeric versus monomeric products was observed, depending on the concentration of HCl, that is, at higher HCl concentration (C = 0.1 g mL −1 ), water soluble monomers were formed from both PA‐6 and PA‐66, Figure 2 .…”

Achieving 1060 mW cm −2 with 0.6 mg cm −2 Pt Loading Based on Imidazole‐Riched Semi‐Interpenetrating Proton Exchange Membrane at High‐Temperature Fuel Cells

“…This may be due to the disrupted NMBA crosslinked structure. [ 55,56 ] As previously discussed in the TGA section, the PBI‐V membranes retain only limited PVIm content after the purification treatment. The PA uptakes are ≈280% for all the PVIm membranes.…”