Developing a stable catalyst for model waste oil upgrading in supercritical water

The United States alone produces 3 billion gallons of waste oils a year [1]. Addressing climate change will require production of sustainable alternatives to common chemicals derived from fossil fuels. Of these chemicals, benzene, toluene, ethylbenzene, and xylene (BTEX) specifically are highly valuable industrial precursors. Prior research has shown BTEX production from the breakdown of palmitic acid (PA)—a common component of waste oils. The use of nano-scale ZSM-5 was evaluated for chemical production in a reaction mixture consisting of palmitic acid and water at conditions near the critical point of water (400 °C, 23 ± 2 MPa). Nano ZSM-5 was selected to reduce diffusion limitations that contribute to coke formation. Supercritical water loading was included in the reaction mixture to reduce coke formation and at loading (15 wt%) much less than previous studies to improve catalyst reuse. Product distribution and time dependence and catalyst reuse were studied. Products favored single-ring aromatics, especially in the benzene-ethyl benzene-toluene-xylene family. Coke yields were approximately 1 wt%, a consequence of the effects of water. The catalyst was used four times, with some activity loss observed between the first and second cycle, and retention of activity for all subsequent cycles. Used catalysts were characterized for crystallinity, surface area, and acid properties, and these findings were consistent with reuse tests. These results provide new insight into the conversion of waste oils into chemicals using ZSM-5 in the presence of supercritical water component.

References

• United States Environmental Protection Agency, Learn About Biodiesel, August 2004. https://19january2017snapshot.epa.gov/www3/region9/waste/biodiesel/questions.html