Patent Watch
November 2, 2009
This propylene is at least partly “green”. The concept of “green” chemicals and plastics has evolved over the past decade. Green plastics have historically implied biodegradability. Now, however, the term “green” is also used to indicate that a polymer is made from a renewable feedstock whether or not the plastic is biodegradable. A good example of this is green polyethylene produced by Braskem in Brazil. The properties of this polyethylene are similar to common commercially available polyethylene; the difference is that the ethylene used to make green polyethylene is made by dehydrating sugar-based ethanol.
Production of green propylene is more complicated than standard propylene because there are no readily available economic sources of biobased C3 feedstocks that can be easily converted to propylene. Glycerol would be a good candidate, but converting glycerol to propylene is not straightforward. [This is an active research area; see Patent Watch for October 12 for another example of using glycerol as a green feedstock.—Ed.]
D. Minoux and co-inventors disclose a method to make partially green propylene. Their technique consists of cracking fermentation-produced ethanol over a silicalite catalyst to make ethylene, then combining the ethylene with oil refinery–produced FCC C4 hydrocarbons and cracking the mixture over the same silicalite catalyst to give a mixture of ethylene and propylene. FCC is the fluidized catalytic cracking process.
In an example, bioethanol (containing 5% water) is fed to a fixed-bed reactor containing a silicalite catalyst at 380 °C, a liquid hourly space velocity of 7 h-1, and 0.35 bar (gauge) pressure. Ethanol conversion is 99.5%, and selectivity to ethylene is 97%. The effluent from this reactor, after water extraction, is combined with an FCC C4 cut that contains 56 wt% C4 olefins and 44 wt% paraffins. The composition of the combined fractions is 40 wt% ethylene, 36.6 wt% C4 olefins, and 26.4 wt% C4 paraffins. This feed is passed to a fixed-bed reactor containing the same silicalite catalyst as in the first step. Reaction conditions are 560 °C, weight hourly space velocity of 11 h-1, and 0.5 bar pressure. The effluent from this reactor consists of 30 wt% ethylene, 19 wt% propylene, 24.5 wt% C4+ olefins, and 25.1 wt% paraffins. (Total Petrochemicals Research Feluy [Belgium]. Eur. Pat. 2108637, Oct. 14, 2009; Jeffrey S. Plotkin)
View patent information from CAS.
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