November 28, 2011
Convert byproduct glycerol to propylene glycol. Renewables-to-chemicals process technologies are receiving much attention in established industrial laboratories, biotech startups, government labs, and academia. Whereas many innovative processes for taking biofeedstocks to chemicals and polymers are available, these processes will be sustainable in the long term only if their economics are competitive with existing petrochemicals-based processes.
One route with potential attractive economics is the conversion of biodiesel-derived glycerol to C3-based chemicals because the price of propylene, the key C3 petrochemical building-block, has risen dramatically. High propylene prices are being driven by supply-side and demand-side trends.
On the supply side, US steam crackers are cracking more ethane to take advantage of low ethane pricing that is driven by the abundance of shale gas. The result is that less byproduct propylene is being made.
On the demand side, the demand for polypropylene is growing strongly and is increasing the demand for propylene. Limited supply coupled with strong demand is pushing propylene prices to historic highs. Glycerol, a byproduct of biodiesel manufacture, presents a unique opportunity to convert a relatively low-priced C3 feedstock to C3 compounds ordinarily made from costly propylene.
H. Kouno, S. Ozawa, and N. Yoshimura disclose catalysts and operating conditions that foster the liquid-phase conversion of glycerol to propylene glycol in high yields. The catalysts contain zinc oxide, silica, and copper oxide.
Of the patent’s 42 examples, the first one is representative of the efficacy of the invention. Glycerol (24 g), distilled water (6 g), and the catalyst system are sealed in a 100-mL autoclave. The catalyst system consists of two materials, 1.0 g F10G (50 wt% CuxO and 50 wt% ZnO) and 0.20 g E35S (67 wt% CuxO, 27 wt% of SiO2, and 6 wt% binder). (The inventors do not specify the oxidation state of copper in the oxide.) After the autoclave is flushed with nitrogen, it is filled with hydrogen and pressurized to 10 MPa at room temperature. It is then heated to 200 °C and stirred at 450 rpm for 12 h.
Glycerol conversion is 91.1%, and the propylene glycol yield is 86%. A key finding is that it is not necessary to vaporize glycerol to effect the hydrogenolysis, a potentially significant cost savings. (Mitsui Chemicals [Minato-ku Japan]. US Patent 8,053,608, Nov. 8, 2011; Jeffrey S. Plotkin)