Design Projects 2015: Biomass to Ethylene (B2)
Executive Summary The purpose of this report is to present a sustainable and efficient process for the production of ethylene. The main process feed is corn stover, which is treated through milling and acid hydrolysis followed by neutralization and co-fermentation with the organism Zymomonas Mobilis. The ethanol is then purified and sent to a fixed bed catalytic reactor train using aluminum oxide on gamma-alumina. Ethylene purification is achieved through the introduction of an entrainer,
... an entrainer, tri-ethylene glycol, primarily to separate water from the mixture. The plant capacity is 2000 MT/day of corn stover and will be located in Sioux City, Iowa. Iowa is a domestic leader in production of corn and thus serves as an optimal location for obtaining corn stover along with other various economic incentives. The plant will produce 260 MT/day polymer-grade purity ethylene. The major challenge is the production of wastewater, which approaches production of 2000 MT/day. Several treatment options are discussed in the report and should be considered carefully before process implementation. Major design tradeoffs were considered for the development of this process. The choice of organism is left for implementation, but the results presented in this report include usage of Zymomonas Mobilis. A traditional yeast strain for fermentation would be considerably easier to control and maintain constant growth. Additionally, the number of reactors in the fixed bed reactor train is considered as well as the ethylene purification method. An economic evaluation of this process was conducted and shows extreme viability for development and implementation. After summarizing various costs, a yearly profit was determined to approach eight million dollars. The net present value of the process is around 150 million dollars with an internal rate of return of thirty-five percent. These values illustrate the feasibility and attractiveness of the process design that supplement the previously mentioned sustainability and efficiency. Going forward, laboratory-scale testing should be conducted in order to assess the physical feasibility of process scale-up. Additionally, this process assumed a deal with a waste treatment contractor in order to treat the large amount of wastewater that the process produces. This option proves economically unsound, and it would be more prudent to develop an on-site waste treatment facility. In conclusion, this process achieves desired goals of creating a sustainable, environmentally sound method of producing ethylene without petroleum as a starting ingredient. The design and development of this process is considered a success for the field of process design and should be expanded upon and possibly implemented in the future.