**4. Conclusion: Challenges and opportunities**

From the discovery of PET in 1940s and the start of PET chemical recycling in 1950s that attracted great interest from the research community, PET glycolysis has gone a long way,

They attained 100 % PET conversion with 71.2% BHET yield by performing the glycolysis at 190 ⁰C for 2 hours with EG/PET molar ratio of 10 and catalyst/PET weight ratio of 0.05 (Yue et al., 2011). As can be deduced in this study, the recoverability and reusability of ionic

In 1997, Güçlü et al. added xylene in the zinc acetate catalyzed PET glycolysis reaction, and obtained 80% BHET yield, which was higher than the yield from that without xylene. The main objective of xylene was initially to provide mixability to the PET-glycol mixture. At temperatures between 170 ⁰C and 225 ⁰C, EG dissolves sparingly in xylene while it dissolves readily in PET. Meanwhile, the glycolysis products are soluble in xylene. Therefore, as the reaction progressed, the glycolysis products moved from the PET-glycol phase to the xylene phase, shifting the reaction to the direction of depolymerization (Güçlü et al., 1997). Sole publication is available for this PET glycolysis technique. Further investigations may have been prevented by the reason that organic solvents are harmful to the environment and

The use of supercritical conditions has been explored earlier in PET hydrolysis (Sato et al., 2006) and methanolysis (Minoru et al., 2005; Yang et al., 2002), but only recently for glycolysis (Imran, et al., 2010). The main advantage of the use of supercritical fluids in a reaction is the elimination of the need of catalysts, which are difficult to separate from the reaction products. It is also environment friendly. Our group investigated the use of EG in its supercritical state (Tc = 446.70 ⁰C, Pc = 7.7 MPa) (Imran et al., 2010). Supercritical process was carried out at 450 ⁰C and 15.3 MPa, and the results were compared with those from the subcritical processes carried out at 350 ⁰C and 2.49 MPa, and 300 ⁰C and 1.1 MPa. Compared to the subcritical process, the BHET-dimer equilibrium was achieved much earlier for supercritical process: a maximum BHET yield of 93.5 % was reached in mere 30 minutes. Owing to high temperature and pressure, supercritical glycolysis delivered a very high yield of BHET while suppressing the yield of the side products (0.69% DEG yield and almost negligible formation of oligomers, BHET dimer, and TEG). If economically feasible,

Beyond eco-friendly catalysts, Pingale and Shukla extended their study to the use of unconventional heating source of microwave radiations. The employment of microwave radiations as heating source drastically decreased the time for the completion of reaction from 8 hours to just 35 minutes. However, it did not increase the BHET monomer yield (Pingale and Shukla, 2008). The use of more efficient catalyst along with microwave irradiation heating may

From the discovery of PET in 1940s and the start of PET chemical recycling in 1950s that attracted great interest from the research community, PET glycolysis has gone a long way,

liquid catalyst permits the use of higher amount of catalyst.

massive use of these solvents is not a very attractive idea.

supercritical glycolysis may be able to replace catalyzed glycolysis.

be able to increase the BHET yield while decreasing the reaction time.

**4. Conclusion: Challenges and opportunities** 

**3.2 Solvent-assisted glycolysis** 

**3.3 Supercritical Glycolysis** 

**3.4 Microwave-assisted glycolysis** 

back when zinc acetate was first used as catalyst to obtain about 60% BHET yield after 8 hours of reaction until when silica nanoparticle-supported metal oxide catalysts were applied to obtain at least 90% yield after 80 minutes. Studies have already dealt with most of the problems dealing with PET glycolysis, including unfeasibility of operation due to long reaction times, low yields, severe conditions, and pollution problems. Researchers have developed catalysts to increase the rate and BHET monomer yield, catalysts that are environmentally friendly, catalysts that can be recovered and reused, a method that does not require catalysts, and many others.

However, PET glycolysis is still far from its peak. Though researchers have found ways to solve each problem separately, there is still no way to solve them all simultaneously. For instance, eco-friendly catalysts deliver lower yields compared to the not-so-eco-friendly ones (e.g. metal oxides). The main challenge that stands now is to deliver an efficient, sustainable, environment friendly, and less energy demanding way to chemically recycle PET. This may be an opportunity for researchers try to develop efficient and highly selective catalysts that can be recovered and reused. There may be many other ways to break the boundaries, and with the rapid advancement of technologies like nanotechnology, solutions may be discovered in the near future. We believe that by exploring the possibilities of technologies that have not yet been applied, great advancements on PET glycolysis can be made. For instance, it has been reported that ultrasound can induce the scission of polymer chains (Kuijpers et al., 2004). Ultrasound assisted depolymerization has been applied to other depolymerization processes before (Sayata & Isayev, 2002; Sayata et al., 2004; Shim et al., 2002), but it has not been explored in PET glycolysis yet. Nanotechnology, which is growing by leaps and bounds may also be exploited to develop more highly efficient glycolytic depolymerization of PET.

#### **5. Acknowledgement**

This work was supported by the Resource Recyling R&D Center sponsored by 21C Frontier R&D Program, the Center for Ultramicrochemical Process Systems sponsored by KOSEF, the Basic Science Research Program through a National Research Foundation of Korea (NRF) grant funded by the Ministry of Education, Science and Technology (2010-0025671).

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**3** 

**Overview on Mechanical** 

**of POSTC-PET Bottles** 

**Recycling by Chain Extension** 

\*Doina Dimonie1, Radu Socoteanu2, Simona Pop1, Irina Fierascu1,

Radu Fierascu1, Celina Petrea3, Catalin Zaharia3 and Marius Petrache1

The post consumer poly(ethylene therephtalate) bottles (POSTC-PET) can be recycled by chemical or / and mechanical processes. The POSTC-PET chemical recycling is widespread in Europe and is based on depolycondensation of secondary polymers and usage of the resulted products for the purposes of the fibre and unwoven material industry. The POST - PC mechanical recycling requires a phase transformation (melting) and can be attained without or with polymer up-gradation (Mancini, 1999; Akovali, 1988; Belletti, 1997; Ehrig, 1992; Erema, 2002; Firas, 2005; Sandro & Mari, 1999; Scheirs, 1998; Awaja,

The well-known worldwide POSTC-PET mechanical and chemical recycling ways are:

1. **Resorption back into the bottles manufacture.** After getting flakes, POSTC-PET is mechanically and /or chemically recycled into bottles for non-food products (soap, cosmetics, and cleaning agents). In 2004, around 50 % of the PET recycled in this way

2. **Re-use in the fibre and un-woven materials industry** for obtaining insulation membranes for roofs, shoe soles, filters, covers for car inner compartments. This

3. **Processing into thin sheets for thermoforming** refer only to the flakes resulted from POSTC-PET selective collected by colour. It is appreciated that the sheets obtained from such material can undergo a high degree of stretching during thermoforming in order to shape packaging cases such as transport trays for tomatoes, eggs and strawberries

4. **Up-gradation by melt processing compounding.** Although PET has excellent usage properties, because of certain characteristics such as low glass transition, low crystallization speed (for certain types) and low impact resistance, in order to be

*1Research and Development national Institute for Chemistry and Petrochemistry –ICECHIM, Spl.Independentei,* 

*2"IC Murgulescu" Institute, Spl.Independentei, sector 6, Bucharest, Romania 3"Politehnica"University, Clea Victoriei, Bucharest, Romania*

direction is the most popular in Europe (Monika, 2007; Morawiec, 2002);

**1. Introduction**

was processed;

*sector 6, Bucharest, Romania* 

etc.;

2005).

