Nylon depolymerisation

X,9. DEPOLYMERISATION OF A HEXAMETHYLENE-DIAMINE-ADIPIC ACID POLYMER (NYLON 66 )... 

DuPont has recently announced plans to build a demonstration plant in Maitland, Ontario, to show that the quality of the recycled product is equivalent to the virgin material (64). BASF converts post-consumer carpet into caprolactam in Ontario. Rhodia has several European plants for depolymerising nylon 6. 

The problem of carpet recycling is considered and the different methods being proposed or commercially utilised are discussed. The main component of the carpet waste is fibres of nylon-6 and nylon-66. The review of the literature includes a limited amount of journal publications, which focus primarily on fundamental aspects, and a large number of patents, which describe the available technologies. The most promising recycling techniques (depolymerisation, extraction, melt blending and mechanical separation) are described. 48 refs. 

Disclosed is a process for recovering monomeric units of a nylon from whole carpet composed of fibres of the nylon and a backing composed of non-nylon components, the fibres being bound to the backing and the carpet containing between 15 and 35 wt.% of the nylon. It involves the steps of a) mechanically separating the whole carpet into a carpet mixture, which contains between 35 and 55 wt.% of nylon, and a depleted carpet mixture, and exposing the carpet mixture to conditions under which depolymerisation of the nylon is effected. 

A process for the depolymerisation of Nylon 6 carpet fibre in the presenee of steam under medium pressure (800 to 1500 KpA, 100 to 200 psig) is described. The feasibility of the seheme was demonstrated using a small laboratory apparatus and the best run produced a 95% yield of crude eaprolaetam. The data obtained were used to construct a computer model of the process for both batch and continuous flow stirred reactors. 6 refs. 

A method for the depolymerisation of PETP fibres using quarternary ammonium salt phase transfer catalysts in saponification processes at atmospheric pressure and temperatures as low as room temperature is reported. Terephthalic acid was produced in yields as high as 93%. Also reported are similar processes for the depolymerisation of nylon 66 and nylon 46 fibres. Nylon 46 oligomers produced were repolymerised using solid-state polymerisation to produce high molecular weight nylon 46. Nylon 66 was depolymerised to produce oligomers and adipic acid in reasonable yields. 11 refs. USA... 

This fall, the closed-loop Evergreen Nylon Recycling plant will start up in the US, a joint venture of DSM Chemicals North America and AlliedSignal. The facility will recover 45,000 m.t./year of caprolactam by depolymerising the fibres from 100,000 m.t./year of discarded nylon-6 carpets. Meanwhile in Germany, Lurgi is building the Polyamid 2000 AG facility. It will process 120,000 m.t./year of carpet waste and recover 10,000 m.t./ year of caprolactam from nylon-6 carpets and 13,000 m.t./ year of nylon-6-6 from nylon-6-6 carpets. 

AlliedSignal s Infinity, Forever Renewable Nylon, prepared by recycling of polyamide-6, is briefly described. The polyamide is treated by depolymerisation, purification of the caprolactam monomer and repolymerisation. The new resin is said to exhibit the same properties as those of virgin polyamide-6. ALLIEDSIGNAL... 

Large companies are taking a closer look at depolymerising nylon, polyester and PU produets that would otherwise end up in landfills. The most reeent project is a worldscale faeility to be built by DSM Chemicals North America and AlliedSignal that will produce about 100 million pounds of caprolactam per year by depolymerising nylon 6. The faeility will remove about 200 million pounds of earpet from landfills annually. DuPont says it has a proeess, ammonolysis, that ean depolymerise a combination of nylon 6 and 66. 

The present invention is for a method of preparing purified epsilon-caprolaetam from earpet waste containing nylon-6. Contaminated epsilon-eaprolaetam is obtained by depolymerising nylon-6 from earpet waste. A mixture of the contaminated epsilon-eaprolaetam and water is then hydrogenated in the presenee of hydrogen and a hydrogenation catalyst in order to produce purified epsilon-caprolactam. The amount of contaminated epsilon-caprolactam in the mixture ean be between 10 and 95% by weight. 

Polymers with hetero-atoms in the chain are suitable for chemical recycling of waste materials. In addition to depolymerisation (nylon 6) and solvolysis (nylon 6,6, PETP, PU) the degradation of aliphatic polyamides with dicarboxylic acids, diamines and cyclic anhydrides, especially trimellitic anhydride, becomes more and more important. The utilisation of the obtained fragments is described. 

Depolymerised Carpet printing/dyeing acid, metal-complex dyes Cotton, viscose vat, direct, azoic dyes Polyester disperse dyes Nylon acid, metal-complex dyes Acrylic fibres basic dyes... 

These technologies are exploited in indnstry. For example, the depolymerisation of Nylon 6 has been particnlarly well researched and has been practised since the 1960s [4], In 1997, DSM Chemicals North America and Allied Signal commissioned a worldscale facility to depolymerise Nylon 6 from carpet waste [5]. It opened in 1999 and 25% of these depolymerised monomer building blocks are nsed to make new nylon 6 compounds, marketed under the tradename AKULON ReCap with a particular focus towards their use in automotive applications [6]. 

---