Lizeth Ortiz Advisor: Dr. Ben Church Materials Science and Engineering Performance of alumina forming alloys under repeated coking and de-coking cycles Lizeth Ortiz Advisor: Dr. Ben Church Materials Science and Engineering

Ethylene production Steam crackers are made of alloys that provide: High temperature mechanical strength Chemical resistance to attack under the aggressive carbon-rich conditions Production facilities are periodically taken off-line Reactor systems can be “de-coked” Loss of production efficiency (~2-8% of annual capacity) Blockages of coke formed inside a serpentine furnace tube.* Steam crackers Ethane Propane Ethylene

Alloy composition in wt%. Cyclic test Pre-Oxidation 100% Steam 12 hours at 850 °C 1 hour at 915 °C Coking 30:1 H2:C2H6 Temp: 950 °C Time: 12 hours Decoking Temp: 850 °C Finish cycle 10 Alloy composition in wt%.

RESULTS: Cyclic Test G3606 – 3.2% Al G3610 – 3.9% Al HP-Nb Coking De-Coking HP-Nb Average of 3 samples/material All mass changes are relative to the mass after pre-oxidation

This work is sponsored by ARPA-E; DE-AR0000690 SUMMARY Mass changes showed that the HP-Nb alloy had the highest gain in mass compare to the AFA alloys both for pre-oxidation and coking/de- coking cycles. AFA alloys showed an stabilization on their change in mass after the 4th cycle while HP-Nb continued gaining mass. Oxide layer and coke layer are seen in SEM pictures for each alloy. Overall, alumina-forming alloys are showing better resistance to cyclic conditions than chromia-forming alloy. Future work will focus on: Cyclic conditions with alloys of different Aluminum content Study of longer cyclic effects as well as thermogravimetric analysis. Comparative studies of alloy behavior of alternative feedstocks. This work is sponsored by ARPA-E; DE-AR0000690 Electron microscopy conducted in the UW-Milwaukee Advanced Analysis Facility