PETpla.net Insider 10 / 2016

MATERIAL / RECYCLING 12 PET planet Insider Vol. 17 No. 10/16 www.petpla.net Comparison of MTR versus SSP Concepts for bottle grade PET by Martin Hittorff, Uhde Inventa-Fischer Product Management PET and HOD Process Department The challenges for the producers of PET are numerous including maturing consumption levels and the trend to light- weight bottles, the uncontrolled fluctuation of prices for raw materials and energy, the competition of mega-plants and regional protection duties. Uhde Inventa-Fischer in 2007 has given an answer to those challenges named Melt To Resin (MTR) technology. MTR is a completely integrated one-stage process providing bottle grade IV PET melt directly from the Discage reactor (finisher). PET is produced from the raw materials puri- fied terephthalic acid (PTA), isoph- thalic acid (PIA) and ethylene glycol (EG) using a melt polycondensation process. Conventional routes have in common that they require a second, subsequent solid-state post-conden- sation (SSP) step to further increase the molecular weight of the polymer. During this solid-stating, PET precur- sor chips are typically subjected to a temperature above 220°C under a counter-flow of purified nitrogen. However, the SSP stage is energy- consuming and, as it is an extra step, it also has the disadvantage of requir- ing additional plant equipment and operating personnel. Execution of MTR MTR technology requires a special design of the melt distribution system from the outlet of the Discage reac- tor to the cutters and a solid process- ing step called Chips Conditioning to achieve the final low acetaldehyde (AA) content of the resin. MTR technology is proven, since there is more than 3m t/a of PET resin capacity in operation. With MTR cus- tomers are able to produce at or over nominal capacity and downstream users of PET make use of specific features of MTR resin like low heat of fusion, low dust content, uniform IV in pellets and dust and low AA re-gener- ation. Recently the leading supplier for SSP technology introduced the use of an under-water cutting system to keep the temperature of the PET pellets on a high level. For the sake of easy distinction we shall name this process “new style” SSP, which will definitely reduce energy consumption compared to the “old style” SSP. However, even the “new style” SSP is using exter- nal energy input at the crystallisation stage and is operated at high temper- ature and under nitrogen atmosphere, which requires the operation of huge blowers, additional conveying systems and a nitrogen purification. In the subsequent diagrams the MTR technology is compared to “old style” and “new style” SSP technology. Investment (Capex) and Operational Cost (Opex) are based on realistic consumption figures published by the technology suppliers and site condi- tions for the case of a 750t/day site located in South-East Asia. The main driver for the lower Capex cost of the MTR technology is the fact that no investment is required for the SSP equipment, SSP building and SSP erection. Fig. 1: Process block diagram of the three competing concepts for production of bottle grade PET resin