October 28, 2013
What is the definition of “green” plastic? Is it biodegradable? Is it made from a renewable resource? The answers to these questions are “yes” and “yes”. Fifteen or more years ago, “green” only meant biodegradable, but today it can also mean that the feedstocks are renewable.
Braskem in Brazil is developing green polyethylene by dehydrating sugar-fermentation bioethanol to ethylene. This ethylene is polymerized to polyethylene, which is labeled as a green plastic even though it is identical to petrochemical-based polyethylene.
Likewise, Coca-Cola sponsored a project in which bioethanol-derived ethylene is converted to monoethylene glycol that is copolymerized with petrochemical-derived terephthalic acid to give ≈30%-green poly(ethylene terephthalate) for making water bottles. Coke markets this type of bottle as the “Plant” bottle.
W. Yang and co-inventors disclose process conditions that promote the reaction of bioethanol with benzene to give ethylbenzene in one step. The ethanol does not have to be cracked first to ethylene.
In one of the patent’s examples, a catalyst that consists of ZSM-5 molecular sieves and 2.0 wt% La2O3 is first steamed and then treated with 1.5 M aq H3PO4 at 50 ºC for 5 h. The reaction of EtOH and benzene over this catalyst is carried out in the gas phase in a fixed-bed reactor at 390 ºC, 1.2 MPa pressure, a benzene/EtOH mol ratio of 6.5:1, and a weight-hourly space velocity of 0.8 h–1.
EtOH conversion ranges from 97.2 to 99.8%; selectivity to ethylbenzene ranges from 97.9 to 99.8%. Dehydrogenation of this ethylbenzene will give partially green styrene. (China Petroleum & Chemical [Beijing]; Sinopec [Shanghai]. US Patent 8,519,208, Aug 27, 2013; Jeffrey S. Plotkin)
What do you think of Patent Watch? Let us know.