Environmental and economic analysis of low-moisture anhydrous ammonia (LMAA) as a pretreatment for cellulosic ethanol production

In the context of global energy supply, cellulosic ethanol plays an essential role due to being considered a renewable fuel and minimize environmental emissions when compared to the exploration and utilization of fossil fuels. However, the cellulosic ethanol production requires pretreatment before the fermentation process, which is considered an expensive procedure that makes the cellulosic ethanol production costly. Therefore, the main goal of this research was to evaluate the economic and environmental impacts of using low-moisture anhydrous ammonia (LMAA) pretreatment for five different scenarios, which were 1000 tonne (t) of feedstock per day (Scenario I), 2000 t/d (Scenario II), 3000 t/d (Scenario III), 5000 t/d (Scenario IV), and 10,000 t/d (Scenario V), for ethanol production from sugarcane bagasse by using SuperPro software. Life Cycle Assessment (LCA) and Techno-Economic Analysis (TEA) were used to evaluate the feasibility and environmental impacts of the scenarios simulated. From the results, the capital costs increased according to the increase of the feedstock amount to be processed, having the most significant investment to the largest facility simulated (10,000 t/d). Mostly all the scenarios presented material costs (sugarcane bagasse, enzyme, yeast, and ammonia costs) as the expenses that impacted the most the overall annual operating costs, where sugarcane bagasse and ammonia were the responsible for around 58% and 40% of the total investment for material costs. In addition, from utility costs, it was observed that electricity represented around 45% of the annual utility costs for almost all the scenarios simulated. All the scenarios resulted in negative profit, and sensitivity analysis showed that ethanol sale price was the parameter that presented the greatest sensitivity for sugarcane bagasse ethanol production under LMAA pretreatment conditions evaluated in this study. Related to environmental aspects, the LCA results showed that the 2000 t/d facility simulated (Scenario II) presented the lowest Global Warming Potential (GWP) for several electricity supply technologies analyzed and presented a significant reduction of CO2 equivalent emissions, representing more than 80% lower greenhouse gasses emissions (GHG) when compared to the 10,000 t/d facility simulated (Scenario V).

Automated summary

This study evaluated the economic and environmental impacts of using low-moisture anhydrous ammonia (LMAA) pretreatment for cellulosic ethanol production. Results showed that capital costs increased with higher feedstock processing volumes, and material costs (sugarcane bagasse, enzyme, yeast, and ammonia costs) had the most significant impact on overall annual operating costs.