(9d) Demonstration of a Sustainable Pathway for Producing Fully Bio-Based Polyethylene Terephthalate (bio-PET)

We report the demonstration of a commercially scalable, environmentally sustainable, and economically viable pathway for producing fully bio-based polyethylene terephthalate (PET). Commercially available bio-PET contains only ~30% bio-content – the ethylene glycol is made from bioethanol, but terephthalic acid continues to be derived from fossil sources. In contrast, our approach uses low-quality fatty acids and triglycerides (e.g. waste cooking oils and brown grease) as feedstocks. Our process uses a novel, patented, and easily scalable vapor phase thermo-catalytic conversion of the waste oils to obtain high aromatic yields. Subsequently, the p-xylene is separated and converted to high purity terephthalic acid and polymerized with bio-ethylene glycol to obtain a 100% biobased PET product. Other methods to obtain bio-p-xylene rely on lignocellulosic biomass. Direct conversion of lignocellulose (e.g. via pyrolysis) results in low p-xylene yields and a complex mixture of xylene-like products that makes p-xylene purification difficult and potentially prohibitively expensive. As an alternative, production of p-xylene from lignocellulosic sugars or lignin have been explored; however, these approaches are predicated on commercially viable lignocellulosic biorefineries that do not yet exist. In contrast, waste oils are currently available, collected, and could be easily be incorporated into our process for bio-PET.

Our innovation for thermo-catalytic conversion of waste oil involves delivery of the feed into a hot reactor via an atomizer to allow the oils to vaporize rapidly and facilitate catalytic reactions in the vapor phase. As a result, our pyrolysis reactor generates products with high yields, high selectivity, and low coke formation on the catalyst. At the optimum reactor temperature of 500°C and a weight hourly space velocity of 6 h^-1, we have measured organic liquid product yields of 63% (relative to feed mass) with an aromatics content of 48%. Further, we have shown in-situ catalyst regeneration and reuse for 10 reaction runs without measurable impact on product yield; the duration of each run was 30 min. The product spectrum is similar to the mixture obtained from commercial petrochemical production and allows for easy p-xylene separation. We will present data on upstream conversion, downstream purification, and polymer synthesis to demonstrate a fully viable pathway for bio-PET by our process (see Figure below). Property comparisons of bio-PET and petro-PET will also be presented.