January 27, 2014
Ethanol-to-propylene process may lead to “green” polypropylene. The concept of “green” plastics is attractive to many consumer product manufacturers. Plastics made from renewable resources allow producers to make claims that their products are environmentally friendly.
One of the more visible “green” packages in the marketplace is Coca-Cola’s “PlantBottle”. This polyester bottle is made from sugar-based ethylene glycol (EG) and conventional petroleum-based terephthalic acid. This green version of EG is produced from ethylene made by cracking fermentation-based ethanol. Braskem also produces green polyethylene from bioethylene.
Green plastics based on propylene would be attractive, but there is no economical route to green propylene. Y. Liu and co-inventors disclose a catalyst and operating conditions that are capable of converting ethanol to propylene. Their key finding is that rhenium-modified ZSM-5 zeolite is a good catalyst for this transformation.
The reactor used in the inventors’ examples is a stainless steel tube 6 in. long and 025 in. diam. For each trial, 200 mg of a catalyst based on ReOx/ZSM-5, was loaded into the tube reactor. Reaction temperatures ranged from 300 to 400 ºC. EtOH was fed into the reactor at 3 mg/min.
At 300 ºC, the best run had the following selectivities: ethylene (38.6%), propylene (8.8%), and butenes (13.2%). Other products included ethane, propane, butanes, and aromatics. Propylene selectivity improved at 400 ºC: ethylene (18.9%), propylene (20.1%), and butenes (14.1%). The propylene selectivity is still modest, but it is higher than values reported up to now. (Dow Global Technologies [Midland, MI]. US Patent 8,598,399, Dec. 3, 2013; Jeffrey S. Plotkin)