Techno-Economic Evaluation of Producing Ethanol from Softwood: Comparison of SSF and SHF and Identification of Bottlenecks

Abstract

The aim of the study was to evaluate, from a technical and economic standpoint, the enzymatic processes involved in the production of fuel ethanol from softwood. Two base case configurations, one based on simultaneous saccharification and fermentation (SSF) and one based on separate hydrolysis and fermentation (SHF), were evaluated and compared. The process conditions selected were based mainly on laboratory data, and the processes were simulated by use of Aspen plus. The capital costs were estimated using the Icarus Process Evaluator. The ethanol production costs for the SSF and SHF base cases were 4.81 and 5.32 SEK/L or 0.57 and 0.63 USD/L (1 USD = 8.5SEK), respectively. The main reason for SSF being lower was that the capital cost was lower and the overall ethanol yield was higher. A major drawback of the SSF process is the problem with recirculation of yeast following the SSF step. Major economic improvements in both SSF and SHF could be achieved by increasing the income from the solid fuel coproduct. This is done by lowering the energy consumption in the process through running the enzymatic hydrolysis or the SSF step at a higher substrate concentration and by recycling the process streams. Running SSF with use of 8% rather than 5% nonsoluble solid material would result in a 19% decrease in production cost. If after distillation 60% of the stillage stream was recycled back to the SSF step, the production cost would be reduced by 14%. The cumulative effect of these various improvements was found to result in a production cost of 3.58 SEK/L (0.42 USD/L) for the SSF process.

Effect of Commercial Cellulase Enzymes on Ethanol Production from Pretreated Rice Straw at High Solid Loading

“…Ethanol production by FBP-SSF at 20% solid could produce ethanol of 35.76 g/L or 4.6% (v/v), which was close to benchmark level (above 4.0% (v/v)). This may be economically viable to produce in large scale [5,16,17]. The result showed that ethanol production by FBP-SSF was a good manner for cellulosic ethanol production.…”

“…Zhu et al [15] used liquefaction at 50 °C for 120 h before ethanol production by SSF. Although it could give high ethanol concentration over the benchmark level (above 4.0% (v/v)) [5,16,17], it might be economically viable to produce in large scale. However, almost of material pretreatment was used in high severity condition, especially high temperature, such as Chu et al [9] pretreated corn stover at 190 °C for 3 min, Zhu et al [15] pretreated aspen at 170 °C for 10 min, and Albuquerque-Wanderley et al [18] pretreated sugarcane bagasse at 200 °C for 7 min.…”

Continuous and Semicontinuous Reaction Systems for High-Solids Enzymatic Hydrolysis of Lignocellulosics

“…A critical economical issue for the enzymatic hydrolysis of lignocellulosic biomass is the final glucose concentration. It has been stated that the ethanol concentration in the broth entering distillation should be greater than 40 g L -1 (Wingren et al, 2003). Assuming an ethanol yield of 0.48 g(g G) -1 , a G concentration of at least 83 g L -1 would be required to reach this target.…”

“…However, solids loadings higher than 10% w/w are required to obtain cost-effective concentrations of sugars (Wingren et al, 2003). Due to the high water-holding capacity of solids, the reaction medium cannot be efficiently sheared and mixed at solids loadings higher than 10% w/w (Viamajala et al, 2009).…”

Economic Evaluation of Switchgrass Feedstock Production Systems Tested in Potassium-Deficient Soils

“…Harvest/N/K feedstock production system [37][38][39][40][41][42][43][44]. This range in biorefinery willingness to pay for feedstock is much lower than what will be required by farmers to grow switchgrass as a dedicated feedstock crop on their farms.…”