Techno-economic aspects of a safflower-based biorefinery plant co-producing bioethanol and biodiesel

Abstract

Safflower plant is a promising energy crop, which is compatible with arid and semi-arid climate conditions. This study is set to perform a techno-economic assessment of an integrated biorefinery located in Iran, using safflower seed and safflower straw as feedstock for production of bioethanol as the main product, biodiesel as the most valuable byproduct while biogas, glycerol, solid residue, and sodium sulfate are the other valuable byproducts. In the first Scenario (A), glucose, xylose, and arabinose are fermented into ethanol by using Zymomonas mobilis produced in a seed train unit. While in the other Scenario (B), Saccharomyces cerevisiae is supplied externally by a yeast production facility and is used to ferment glucose into ethanol. Both scenarios are simulated using Aspen Plus software and a cash flow analysis is performed using well-known economic indices for the biofuel industry presented by the National Renewable Energy Laboratory. The profitability index is 1.14 for Scenario A, showing its cost-effectiveness. However, this index is found to be 0.81 for Scenario B, revealing the fact that this approach is not economically-justified for implementation. More specifically, the use of Z. mobilis instead of S. cerevisiae as fermenting microorganism enhances the profitability of the project by lowering ethanol production cost from 0.12 $/L to 0.09 $/L and minimum ethanol selling price from 0.67 $/L to 0.43 $/L. Moreover, in both scenarios, biodiesel production boosts the total annual sale values by 39% and 55% for scenario A and B, respectively. In general, 1.86 and 2.44 times improvements in this economic index are respectively obtained for scenario A and B because of byproduct credits. The outcomes of sensitivity analysis also shows that the discount factor and safflower seed price have large impacts on the profitability of the developed biorefineries. Overall, Z. mobilis appears to be a preferred biocatalyst for bioethanol fermentation through the biorefinery platform from the techno-economic viewpoint.