Techno-economic evaluation of 2nd generation bioethanol production from sugar cane bagasse and leaves integrated with the sugar-based ethanol process

Abstract

BackgroundBioethanol produced from the lignocellulosic fractions of sugar cane (bagasse and leaves), i.e. second generation (2G) bioethanol, has a promising market potential as an automotive fuel; however, the process is still under investigation on pilot/demonstration scale. From a process perspective, improvements in plant design can lower the production cost, providing better profitability and competitiveness if the conversion of the whole sugar cane is considered. Simulations have been performed with AspenPlus to investigate how process integration can affect the minimum ethanol selling price of this 2G process (MESP-2G), as well as improve the plant energy efficiency. This is achieved by integrating the well-established sucrose-to-bioethanol process with the enzymatic process for lignocellulosic materials. Bagasse and leaves were steam pretreated using H3PO4 as catalyst and separately hydrolysed and fermented.ResultsThe addition of a steam dryer, doubling of the enzyme dosage in enzymatic hydrolysis, including leaves as raw material in the 2G process, heat integration and the use of more energy-efficient equipment led to a 37 % reduction in MESP-2G compared to the Base case. Modelling showed that the MESP for 2G ethanol was 0.97 US$/L, while in the future it could be reduced to 0.78 US$/L. In this case the overall production cost of 1G + 2G ethanol would be about 0.40 US$/L with an output of 102 L/ton dry sugar cane including 50 % leaves. Sensitivity analysis of the future scenario showed that a 50 % decrease in the cost of enzymes, electricity or leaves would lower the MESP-2G by about 20%, 10% and 4.5%, respectively.ConclusionsAccording to the simulations, the production of 2G bioethanol from sugar cane bagasse and leaves in Brazil is already competitive (without subsidies) with 1G starch-based bioethanol production in Europe. Moreover 2G bioethanol could be produced at a lower cost if subsidies were used to compensate for the opportunity cost from the sale of excess electricity and if the cost of enzymes continues to fall.

High-Throughput Profiling of the Fiber and Sugar Composition of Sugarcane Biomass

“…Its sugar has been used for firstgeneration biofuels in the last 10 to 20 years, while its lignocellulosic biomass has only recently been exploited for second-generation biofuels. Sugarcane lignocellulosic biomass is derived mostly from its millable stalk and partially from leaves and green tops, estimated to be two thirds of the total sugarcane biomass produced [39][40][41]. Hence, developing sugarcane varieties with a desirable fiber/sugar ratio within this biomass fraction, from the current diverse germplasm collections, is essential and should be advanced in parallel a b c d…”

Anaerobic digested sludge: a new supplementary nutrient source for ethanol production

“…However, in some articles, second-generation ethanol from lignocellulosic residues is investigated from this point of view (Macrelli et al 2012). For instance, by targeting the ethanol production of 45 l per dry ton of sugarcane and estimating the costs as follows: enzymes (0.341 US $/l), acid (0.08 US $/l), base (0.02 US $/l), water consumption (0.045 US $/l), vinasse sales (-0.003 US $/l), labor, maintenance, and insurance (0.148 US $/l), electricity (0.357 US $/l), and capital cost (0.56 US $/l), the minimum ethanol selling price would be calculated as 1.548 US $/l (Macrelli et al 2012). Although this estimation contains the cost of pretreatments in which either of chemicals or energy is required, the price of other nutrients such as yeast extract and synthetic salts which can increase the costs substantially is not included.…”

Feedstock Crop Production Costs and Biofuel Feedstock Input Costs Associated with the Production of Energy Cane and Sweet Sorghum in the Southeastern USA

“…This study identified the Midwest and South as the regions of the country with the greatest potential for feedstock crop production, with emphasis on sweet sorghum and energy cane. Macrelli et al evaluated the technical and economic prospects of bioethanol produced from the lignocellulosic portions of sugar cane (bagasse and leaves) associated with the production of sugar cane bioethanol on Brazil [6]. Utilizing simulation analysis, results indicated that production of second generation bioethanol from sugar cane bagasse and leaves in Brazil was currently economically competitive starch-based bioethanol production in Europe and, further, that sugar cane bioethanol could be produced at a lower cost with enzyme costs continuing to decline and if subsidies were used to compensate for the opportunity cost from the sale of excess electricity.…”