Analysis of the Coffee Cut Stems as Raw Material for the Production of Sugars for Acetone–Butanol–Ethanol (ABE) Fermentation: Techno-Economic Analysis

Lignocellulosic biomass is generally considered as a promising feedstock for the production of value added compounds, due to its availability, low cost and potential sustainable use. Coffee cut-stems (CCS) are a cut of 15–20 cm of length above the land where the coffee plant is cultivated and it is obtained at high quantities after crop renewal. Its high cellulose content makes it a potential sugar platform for different products. The objective of this work is to determine the potential of CCS as a raw material for acetone–butanol–ethanol (ABE) fermentation in technical, economic and environmental terms. The overall ABE fermentation was simulated using the commercial software Aspen Plus to obtain the mass and energy balances. Simulation included the composition of lignocellulosic residue, which was determined experimentally. The whole slurry obtained in the acid pretreatment was sent to enzymatic saccharification. Then the liquid fraction (rich in pentoses and hexoses) was used for fermentation step as carbon source. The process was proposed in this way to determine the influence of inhibitors in ABE fermentation yield through the comparison with other works that include detoxification step. The yield for the process was 140 kg ABE per ton of CCS. The operating costs were calculated using the software Aspen Economic Analyzer. The influence of the cost of the raw materials on the Net Present Value (NPV), the production cost of ABE solvents and the distribution cost by process stages were determined. Additionally, a scale analysis was performed to determine its influence on the NPV. The simulation demonstrated a Minimum Processing Scale for Economic Feasibility (MPSEF) of 64.6 ton/h of CCS. Finally, an environmental assessment using the Waste Reduction Algorithm (WAR) software was proposed to determine environmental impact.