Advances in ionic liquid pretreatment technologies: Impact on the economics of cellulosic biofuel production

Two new variants of IL pretreatment technologies have recently been developed at JBEI: one-pot (Shi et al.) and acidolysis (Sun et al.). Compared to previously envisaged IL pretreatment configurations (e.g., Klein-Marcuschamer et al., 2011), the one-pot process eliminates the need for an expensive water-wash step (by using IL tolerant enzymes), while the acidolysis process replaces enzymes altogether with acids. A comprehensive technoeconomic analysis of these processes was carried out to evaluate their economic potential (e.g., Minimum Ethanol Selling Price, MESP) and cost drivers. The one-pot process with IL tolerant enzymes was observed to be superior to the scenarios using commercial enzymes. The analysis revealed that until and unless the water used in water-wash step (to recover IL) is reduced to no more than 20 times the amount of biomass present, commercial enzyme scenarios will remain more expensive compared to the one-pot scenario. MESP for the one-pot process scenario was $5.1/gal, demonstrating its potential to be cost-competitive with the dilute-acid process ($6/gal for current technology and $3.3/gal for projected performance). At present, the main bottleneck in the one-pot system is the yield in the pretreatment reactor (~83%). In contrast to the one-pot process, the MESP in acidolysis based scenarios remained high (8 $/gal or more). The challenge with the acidolysis routes is to improve yield while reducing production costs. Cost drivers will be discussed in detail.

References:

• Klein-Marcuschamer et al. (2011). Biofpr, 5:562–569.
• Shi et al. (2013). Green Chemistry, 2579-2589.  
• Sun et al. (2013). Biotechnology for Biofuels, 6/39.