PETpla.net Insider 06 / 2018

MATERIALS / RECYCLING PET planet Insider Vol. 19 No. 06/18 www.petpla.net 20 thalic acid (IPA), monoethylene glycol, 1-2% diethylene glycol (DEG), and, depending on input source, also 1-3% cyclohexane dimethanol (CHDM) as well. The mother liquor is treated with equimolar amounts of sulfuric acid in order to pseparate the acids from the glycols and precipitate them. The papers do not describe how to sepa- rate TA from IPA. The process leaves substantial amounts of potassium sulphate left, insoluble impurities with adhering solvents, a blend of tereph- thalic acid and isophthalic acid, and, finally, the solvent containing MEG, DEG and maybe CHDM. These frac- tions have to be separated one by one to get PTA (purified terephthalic acid of 99.9-99.98% and 0.15% humid- ity), purified IPA, EG fibre grade, DEG and/or CHDM at the end. The metha- nol and dichloromethane solvents must be completely removed from the insoluble waste, like caps and labels, and purified quantitatively by distilla- tion or other means. Swiss company Gr3n has pub- lished a European project under the name Demeto which focuses on the chemical recycling of coloured PET bottles. Maurizio Grippa, CEO of Gr3n and one of the major stakehold- ers, is inventor of the process patent WO2013014650 (A1) - 2013-01-31, which seems to describe the technol- ogy of the new recycling process. The key element of this process is a microwave reactor, in which the hydrolysis of polyester waste, inter- mingled with MEG and water, takes place in the presence of alkaline-like sodium hydroxide (NaOH) or potas- sium hydroxide (KOH) to generate terephthalic acid alkaline salt and glycols. After the removal of insoluble waste by filtration the terephthalic acid is precipitated by neutralisation under addition of hydrochloric acid (HCl). The process by-products, sodium chloride (NaCl) or potassium chloride (KCl), are converted to NaOH or KOH by apply- ing chloralkali electrolysis. Chlorine (Cl 2 ) and hydrogen (H 2 ) gases recov- ered are reacted to form HCl, which is reused in the process. This means that the hydrolysis agents - NaOH or KOH - are recirculating as process aids. The process patent WO2013014650 does not disclose how the usual co- monomers like IPA, DEG or CHDM are separated from each other and purified to get the PTA and MEG (or their sepa- rated co-monomers) in commercial, industrial standard quality. The use of HCl raises some questions because the finished PTA, IPA, MEG and DEG must be completely free of chlorine ions. The companies Ioniqa and Accenture advertised their new polyester recycling process in 2016, thus: “Ioniqa invented a Magnetic Smart Process to recycle all kinds of colored PET polyester waste into ‘virgin quality’ raw materials, compet- ing with oil-base PET in both qual- ity and costs (….). In the last weeks (Oct 2016) the recycling process was scaled up successfully to a volume of 1,000l. This brings the world closer to an economical viable solution for tens of millions of tons of PET Polyester waste, currently down cycled, dumped or incinerated.” According to Ioniqa’s patent publica- tions the core of its recycling process is the application of a new generation of ionic liquids as decomposition catalysts, where the magnetic properties of the catalyst enable its removal by means of magnetic fields. This means that the catalyst can be repeatedly used in the decomposition process. The US patent 2018037710 (A1) - 2018-020 describes the theoretical background of the hydrolysis process catalysed by ionic liquids. Basic technical details such as how to separate the common bottle PET co-monomers, or how to remove the adhering ionic catalyst from the solid waste filtrates, are not covered in the publication. That is a short summary of some recently published activities and pro- jects to establish circular manufactur- ing approach to PET waste by chemi- cal loop recycling. 2. Which route leads to industrial scale plants? Looking at these new processes and considering a production of PTA, MEG and PET resins on an industrial scale raises some questions. The most obvious are: 2.1 What will the final PTA, MEG, IPA product quality be? 2.2 What will the PET waste input quality be? 2.3 What is the minimum feasible and economical plant capacity of such a chemical recycling project? 2.4 Are there any existing industrial scale chemical PET recycling pro- cesses already available? 2.5 What is to be done with the resulting non-PET-waste? 2.1 What will the final PTA, MEG, IPA product quality be? Everyone will, of cause, answer: “PTA, MEG and IPA will be produced in fibre or bottle grade quality”, mean- ing that these PET raw materials are Quality characteristics Specification 1 Apperance White crystalline powder 2 Colour, Hazen unit 10 Max 3 Colour index b 2.5 Max 4 Acid number, mg KOH/g of product from 673 to 677 inclusive 5 4-Carboxybenzaldehyde content, μg/g 25 Max 6 para-Toluic acid content, μg/g 150 Max 7 Benzoic acid content, μg/g 100 Max 8 Water content, % 0.2 Max 9 Ash content, μg/g 10 Max 10 Metals content*, μg/g - Fe, Mo, Cr, Ni, Mn, Co, Ti - Mg, Ca, Na, K, Al 3 Max 10 Max 11 Iron content, μg/g 2 Max 12 Particle size distribution, % - under 40 μm - over 250 μm 30 Max 18 Max * At the customer´s request Figure 1: PTA quality specification from SIBUR (Google: SIBUR+ terephthalic acid + specifications, 4th answer)