Enzymatic processes
| Technology | |
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| Technology details | |
| Name: | Enzymatic processes |
| Category: | Biochemical processes and technologies |
| Feedstock: | Garden and park waste |
| Product: | Cellulose, hemicellulose, lignin |
Enzymatic processes utilise enzymes (/ˈɛnzaɪmz/) which are proteins that act as biological catalysts (biocatalysts).[1] In terms of lignocellulosic biomass valorisation, enzymes find two main applications: i) biomass pretreatment, and ii) polysaccharides hydrolysis. Biomass enzymatic pretreatment falls under the category of "biological pretreatment". Other pretreatment methods for lignocellulosic biomass includes, physical (e.g., mechanical), chemical (e.g., acid and alkali), physico-chemical (e.g., steam explosion and AFEX), and a combination thereof[2]. polysaccharides hydrolysis is a concept mostly applied in biorefineries as part of the hydrolysis of plant cell wall constituents like cellulose, hemicellulose, and lignin.
Feedstock
Origin and composition
Lignocellulosic biomass (LCB) can be collected as a waste material from forest residues, agricultural, and industrial activities. LCB is mainly characterized by the presence of two carbohydrate polymers, namely cellulose and hemicellulose, as well as an aromatic polymer called lignin. Other components in LCB, found in smaller amounts, are ash, pectin, and proteins. The percentage content of celluloce, hemicelllulose, and lignin are varied among different lignocellulosic materials. In general, the content of cellulose, hemicellulose, and lignin in LCB is in the range of 30-60%, 20-40%, and 15-25%, respectively.[3] The physical appearance and strenght of the biomass depend on the varying concentration of these polymers and therefore greatly influences the type of pre-treatment strategy applied for its deconstruction.
Structural features LCB:
Cellulose
Cellulose is a polysaccharide polymer of glucose disaccharide units, cellobiose, linked tightly by ß-1,4-glycoside bonds. Cellulose molecules are linked by hdyrogen bonds and have different orientations resulting in different levels of crystallinity. Its crystallinity plays a crucial role in the biodegradation of cellulose and in general the higher crystallinity level makes it harder to biodegrade the cellulose.
Hemicellulose
Hemicellulose is a random and branched heterogeneous polymer of different polysaccharides including pentoses (xylose and arabinose), hexoses (glucose, galactose, and mannose) and sugar acids. The branched nature of the hemicellulose allows it to form strong bonds with cellulose (through hydrogen bonds) and lignin (through covalent bonds).
Lignin
Lignin is a complex and large compound made out of phenylpropane units linked in a three-dimensional structure. The main monomers of lignin are p-hydroxyphenyl alcohol, coniferyl alcohol, and sinapyl alcohol. Lignin acts as a cementing material that links celluose and hemicellulose to from the rigid three-dimensional structure of the plant cell wall.
Pre-treatment
The following pre-treatments may be considered prior to enzymatic pre-treatment:
- Sizing (e.g., milling, grinding)
- Steam explosion (hybrid pre-treatment; e.g., combined with laccase pretreatment)[4]
The following pre-treatments may be considered prior to enzymatic hydrolysis[5],[6]:
- Physical (e.g., milling, grinding, ultrasonication, extrusion)
- Chemical (e.g., acid, alkali, ionic liquid, organosolv)
- Physico-chemical (e.g., steam explosion, hot water, AFEX, wet oxidation)
- Biological (e.g., microbial and enzymatic)
Process and technologies
Enzymatic pre-treatment (biological pre-treatment)
Pre-treatment of biomass is the first step in most, if not, all biorefinery related processes. For instance, it is the first and most challenging step in the bioethanol process, and is considered a critical step having a large impact on digestibility and downstream costs.
Enzymatic hydrolysis
Enzymatic hydrolysis processes allow to produce monomeric sugars from (ligno)cellulosic biomass by using specific enzymes (i.e. cellulases and hemicellulases) able to break down the chemical bonds in cellulose and hemicellulose polymers. Several factors can affect the efficiency of this process: accessible surface area and crystallinity of the biomass, as well as pH, time and temperatures of the process[7]. Enzymatic hydrolysis is gaining increased attention with respect to acid hydrolysis due to equipment corrosion, energy consumption, non-recyclability of reagents, fermentation inhibitors production during acid hydrolysis [8]. To increase the hydrolysis efficiency, a pretreatment step prior to enzymatic reaction is usually required due to the complex lignocellulosic biomass composition (Primary processing).
Product
Technology providers
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| Technology name: | Technology category: | Conversion (Biochemical processes and technologies) | |
| TRL: | Capacity: | kg·h-1 | |
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Open access pilot and demo facility providers
Patents
Currently no patents have been identified.
References
- ↑ , 2021: Enzyme , Last access 24-09-21. https://en.wikipedia.org/wiki/Enzyme
- ↑ E. Hosseini Koupaie, S. Dahadha, A.A. Bazyar Lakeh, A. Azizi, E. Elbeshbishy, 2018: Enzymatic pretreatment of lignocellulosic biomass for enhanced biomethane production - A review. Journal of Environmental Management, Vol. 233, 774-784. doi: https://doi.org/10.1016/j.jenvman.2018.09.106
- ↑ Sawatdeenarunat, C., Surendra, K., Takara, D., Oechsner, H., Khanal, S.K., 2015: Anaerobic digestion of lignocellulosic biomass: challenges and opportunities. Bioresour. Technol., Vol. 178, 178-186. doi: https://doi.org/10.1016/j.biortech.2014.09.103
- ↑ Weihua Qiu, Hongzhang Chen, 2012: Enhanced the ezymatic hydrolysis efficiency of wheat straw after combined steam explosion and laccase pretreatment. Bioresource Technology, Vol. 118, 8-12. doi: https://doi.org/10.1016/j.biortech.2012.05.033
- ↑ Rajeev Ravindran, Amit Kumar Jaiswal, 2016: A comprehensive review on pre-treatment strategy for lignocellulosic food industry waste: Challenges and opportunities. Bioresource Technology, Vol. 199, 92-102. doi: https://doi.org/10.1016/j.biortech.2015.07.106
- ↑ Bikash Kumar, Nisha Bhardwaj, Komal Agrawal, Venkatesh Chaturvedi, Pradeep Verma, 2019: Current perspective on pretreatment technologies using lignocellulosic biomass: An emerging biorefinery concept. Fuel Processing Technology, Vol. 199, . doi: https://doi.org/10.1016/j.fuproc.2019.106244
- ↑ Saverio Niglio, Alessandra Procentese, Maria Elena Russo, Giovanni Sannia, Antonio Marzocchella, 2019-06-01: Investigation of Enzymatic Hydrolysis of Coffee Silverskin Aimed at the Production of Butanol and Succinic Acid by Fermentative Processes. BioEnergy Research, Vol. 12, (2), 312–324. doi: https://doi.org/10.1007/s12155-019-09969-6
- ↑ Gabriela Piccolo Maitan-Alfenas, Evan Michael Visser, Valéria Monteze Guimarães, 2015-02-01: Enzymatic hydrolysis of lignocellulosic biomass: converting food waste in valuable products. Current Opinion in Food Science, Vol. 1, 44–49. doi: https://doi.org/10.1016/j.cofs.2014.10.001