Polyethylene furanoate (PEF) is a polymer synthesized from the copolymerization of 2,5-furandicarboxylic acid (FDCA) with monoethylene glycol (MEG). Since both monomers can be obtained from biomass starting material, and the resulting PEF is 100% recyclable, PEF is considered a bio-based analogue to polyethylene terephthalate (PET). Also, PEF production is thought to have the potential to reduce greenhouse gas emissions compared to the production of PET.
Strong parallels are reported in the literature between the production of PET and PEF, to the point that existing PET assets may be used for PEF production. FDCA and MEG are polymerized in two steps (Figure 1) yielding bottle-grade PEF.
Melt-phase polymerization. MEG and FDCA are initially fed to the paste system, which prepares a uniform feed slurry batch-wise for melt-polymerization downstream. The mixture then passes through two agitated and jacketed reactors, in which esterification takes place, generating bis(2-hydroxyethyl)-2,5-furandicarboxylate (BHEF). Small amounts of water formed are removed, as well as the excess unreacted ethylene glycol that is boiled off and directed to the MEG recovery system.
BHEF is fed to an agitated, jacketed reactor. Here, vacuum and heat are applied for the removal of water and ethylene glycol, shifting the reaction equilibrium toward polymerition. Antimony glycolate is used as a catalyst. This pre-polymerization generates PEF oligomers. The ethylene glycol and water removed from the vessels by vacuum are directed to MEG recovery stage.
In the polycondensation step, the PEF oligomers undergo condensation reactions, increasing the degree of polymerization. The reaction occurs in a rotating-disc reactor under an even higher vacuum to remove water and excess MEG. Here, higher-molecular-weight PEF chains are generated, yielding a textile-fiber-grade PEF. Gaseous effluents from all reactors are condensed and fed to a distillation column, where MEG is recovered from the bottom and recirculated.
The previous melt-phase polymerization is concluded by a pelletizing step, in which the molten PEF is extruded, cooled and chopped into cylindrical shapes. The amorphous PEF chips are screened, classified, dried and then conveyed to a storage silo.
Solid-state polymerization. PEF chips are crystallized to prevent agglomeration due to high polymerization temperatures downstream. The particles are then polycondensed in the solid-state polymerization (SSP) reactor — a long cylindrical vessel.
The bottle-grade PEF chips are fed to a fluidized-bed cooler, which cools down the PEF and removes dust. The PEF chips are homogenized and packed in bags.
Because PEF production consists of the copolymerization of FDCA with MEG, different PEF manufacturing routes are related to different sources of these materials (Figure 2).
The total operating cost (raw materials, utilities, fixed costs and depreciation costs) estimated to produce PEF was about $2,700/ton in Q2 2015. The analysis was based on a plant constructed in the U.S. with the capacity to produce 300,000 metric ton per year of PEF.
This article was published on www.chemengonline.com