March 11, 2013
Make “green” p-xylene from 2,5-dimethylfuran and ethylene. The race to an economical process for making 100% renewable poly(ethylene terephthalate) (PET) carbonated soft drink bottles is under way. Currently, Coca-Cola offers “Plant” bottles that are ≈30% renewable because the monoethylene glycol used for making the PET comes from “green” ethylene made by cracking bioethanol. The comonomer terephthalic acid (PTA) comes from non-renewable sources.
To make a 100% renewable bottle, an economical route to green p-xylene (the PTA precursor) or directly to green PTA must be developed. Several biotech startups and well-established companies are working on this project, but the goal is proving to be difficult.
T. A. Brandvold discloses catalysts and operating conditions that allow the reaction of 2,5-dimethylfuran (DMF) and ethylene to produce p-xylene with good conversion and selectivity. This process has the potential to make 100% renewable p-xylene because DMF can be made from glucose, and ethylene can be made from bioethanol.
The inventor found that H3PO4-washed activated carbon is a good catalyst for the reaction of DMF and ethylene. The total oxygen content of the activated carbon catalyst ranges from 1% to 18%.
In the patent’s examples, DMF at 2.5, 5, or 10 cm3/h and ethylene at 30, 50, or 100 cm3/h are charged to a fixed bed of activated carbon catalyst. The pressure is 35 or 41 bar (gauge), and the temperature is in the range of 200–335 °C.
Under these conditions, the per-pass conversion of DMF to p-xylene is >30%. The overall yield ranges from 30% to 80% of theoretical. In experiments with no catalyst, the product contains only 3–4 wt% p-xylene. (UOP [Des Plaines, IL]. US Patent 8,314,267, Nov. 20, 2012; Jeffrey S. Plotkin)