Ethylene from renewable ethanol : process optimization and economic feasibility assessment

At present, ethylene is the most widely produced organic compound in the chemical industry. The main commercial way to obtain ethylene is by steam cracking of a wide range of hydrocarbon feedstocks, but biomass-derived ethanol can be catalytically dehydrated as a sustainable alternative route in order to exploit new renewable sources. The aim of this work is to design an optimal bioethanol-to-bioethylene plant, with a capacity of 445,652 ton/year, and to assess its economic feasibility. This design features an improved production capacity and intensified energy management. The main novelty of this study is the use of diluted bioethanol solutions, bypassing the energy intensive and expensive dehydration step. Moreover, while the first industrial bioethanol-to-bioethylene process uses NaOH to purify the outcoming flow from CO2, this plant uses diluted Methyldiethanolamine (MDEA), regenerated in situ. With this plant, the double of the capacity of the Braskem's plant, now the largest one, can be reached in an environmentally more sustainable manner. A pinch analysis was performed, in order to minimize the energy consumption of the process by optimizing the heat recovery systems. The economic analysis of the process consists of the evaluation of the total cost of the plant (TOC) including the sum of the CAPital EXpenditures (CAPEX) and the OPerating ones (OPEX), together with some sensitive profitability indexes (net yearly profit, net present value, net rate of return and cash flow analysis). The designed process presents an economically competitive solution compared to the current bioethylene production units. Assuming a premium price of between 0.293 $/kg for diluted bioethanol, the proposed plant is competitive with the lowest production cost for bioethylene (Brazil and India), while a sensitivity analysis on diluted bioethanol price evidenced that this option remains competitive still in Europe with a bioethanol cost 0.65 $/kg.