Recovery of cellulase activity after ethanol stripping in a novel pilot-scale unit
Recycling of enzymes has a potential interest during cellulosic bioethanol production as purchasing enzymes is one of the largest expenses in the process. By recycling enzymes after distillation, loss of sugars and ethanol are avoided, but depending on the distillation temperature, there is a potential risk of enzyme degradation. Studies of the rate of enzyme denaturation based on estimation of the denaturation constant K D was performed using a novel distillation setup allowing stripping of ethanol at 50–65 °C. Experiments were performed in a pilot-scale stripper, where the effect of temperature (55–65 °C) and exposure to gas–liquid and liquid–heat transmission interfaces were tested on a mesophilic and thermostable enzyme mixture in fiber beer and buffer. Lab-scale tests were included in addition to the pilot-scale experiments to study the effect of shear, ethanol concentration, and PEG on enzyme stability. When increasing the temperature (up to 65 °C) or ethanol content (up to 7.5 % w/v), the denaturation rate of the enzymes increased. Enzyme denaturation occurred slower when the experiments were performed in fiber beer compared to buffer only, which could be due to PEG or other stabilizing substances in fiber beer. However, at extreme conditions with high temperature (65 °C) and ethanol content (7.5 % w/v), PEG had no enzyme stabilizing effect. The novel distillation setup proved to be useful for maintaining enzyme activity during ethanol extraction.
KeywordsThermostable cellulases Distillation Gas–liquid interfaces Enzyme recycling Ethanol Denaturation constant (KD)
The fiber beer was a gift from Inbicon. The work was funded by the EU project HYPE, grant Agreement No. 213139, and the project Bio4Bio, which was financially supported by The Danish Council for Strategic Research.
- 5.Ghose TK (1987) Measurement of cellulase activities. Pure Appl Chem 59(2):257–268Google Scholar
- 12.Jensen E (2011) Rectification apparatus using a heat pump. US Patent No. US7972423 B2Google Scholar
- 19.Madsen P (2003) Ethanol distillation: the fundamentals. In: Jacques KA (ed) The alcohol textbook, 3rd edn. Notthingham University Press, UK, pp 319–336Google Scholar
- 22.Rahikainen J, Mikander S, Marjamaa K, Tamminen T, Lappas A, Viikari L, Kruus K (2011) Inhibition of enzymatic hydrolysis by residual lignins from softwood—study of enzyme binding and inactivation on lignin-rich surface. Biotechnol Bioeng 108(12):2823–2834. doi: 10.1002/bit.23242 PubMedCrossRefGoogle Scholar
- 23.Sellami-Kamoun A, Haddar A, Ali NEH, Ghorbel-Frikha B, Kanoun S, Nasri M (2008) Stability of thermostable alkaline protease from Bacillus licheniformis RP1 in commercial solid laundry detergent formulations. Microbiol Res 163(3):299–306. doi: 10.1016/j.micres.2006.06.001 PubMedCrossRefGoogle Scholar
- 24.Sipos B, Szilagyi M, Sebestyen Z, Perazzini R, Dienes D, Jakab E, Crestini C, Reczey K (2011) Mechanism of the positive effect of poly(ethylene glycol) addition in enzymatic hydrolysis of steam pretreated lignocelluloses. C R Biol 334(11):812–823. doi: 10.1016/j.crvi.2011.06.005 PubMedCrossRefGoogle Scholar