Hydrolysis
Hydrolysis (/haɪˈdrɒlɪsɪs/; from Ancient Greek hydro- 'water', and lysis 'to unbind') is a chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.[1] In lignocellulosic biomass, the cellulose and hemicellulose breaks down into individual sugars, where hemicellulose is easier to hydrolyse than cellulose.[2] The result of hydrolysing hemicellulose and cellulose is sugars (glucose, xylose, mannose, and galactose) and organic acids (formic acid and acetic acid).[3]
Feedstock
Hydrolysis can be performed as a pretreatment on any biowaste with a high lignocellulose content. Lignocellulose is typically the nonedible part of a plant, composed of a complex of cellulose, hemi-cellulose and lignin. In order to make the celluloses available for further processing, in the form of its monomeric sugars, they can be hydrolysed. Suitable feedstocks include grasses, straw, leaves, stems, shells, manure, paper waste, and others. The ratio between cellulose, hemi-cellulose and lignin varies wildly depending on the specific feedstock.[4]
Process and technologies
Acid
Acid hydrolysis is a hydrolysis process in which a protic acid is used to catalyze the hydrolysis reaction. A strong acid, such as formic, hydrochloric, nitric, phosphoric, or sulphuric acid can be used in concentrated or diluted form. Concentrated acid (10-30 %) can penetrate the lignin structure and break down the cellulose and hemicellulose to individual sugars at low temperatures and high yields. Downsides are the high acid consumption and high corrosion potential. These downsides are circumvented with the use of diluted acid (2-5%). However, higher temperatures are required, which can lead to side product formation such as furfural and 5-hydroxymethyl-furfural.[4]
Alkali
Alkaline hydrolysis refers to hydrolysis reactions using hydroxide, commonly from sodium hydroxide or calcium hydroxide. The hydroxide breaks down the lignin bonds to make the cellulose more accessible. The reaction proceeds at lower temperature and pressure and residual alkali can be recycled. However, the pretreatment does result in irrecoverable salts in the product.[5]
Salt
Hydrolysis can be further improved by the addition of salts, such as metal salts or sulphite salts.
Metals salts
Acid hydrolysis can be stimulated by the addition of metal chlorides. Metals such as aluminium, calcium, copper, iron, and zinc can be used to increase the sugar yield.[6]
Sulphite salt
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Solvent
Solvents can be added to improve the hydrolysis process. This is similar to arganosolv pulping, but without the delignification as goal.[7]
Organosolv
In an organosolv hydrolysis organic solvents are added to the process, usually performed at high temperatures (100-250 °C). This can be combined with a catalyst such as HCl or H2SO4.[7] For example, in acid-acetone pre-treatment biowaste is treated with an acid such as phophoric acid and then mixed with pre-cooled acetone.[6]
Product
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Technology providers
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Valmet Oyj
| General information | |||
| Company: | Valmet Oyj | 
| |
| Country: | |||
| Contact: | |||
| Webpage: | https://www.valmet.com/ | ||
| Technology and process details | |||
| Technology name: | BioTrac | Technology category: | Conversion (Thermochemical processes and technologies) |
| TRL: | 9 | Capacity: | biomass feed up to 800 tonne/day kg·h-1 |
| Atmosphere: | Catalyst: | Acid conditions | |
| Heating: | Pressure: | Up to 25 bar bar | |
| Reactor: | Horizontal tube reactor | Temperature: | High temperature °C |
| Other: | |||
| Feedstock and product details | |||
| Feedstock: | All lignocellulosic biomass, including wood and forest residues, wheat straw, corn stover and bagasse | Product: | |
Patents
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References
- ↑ Wikipedia, 2002: Hydrolysis 2002, Last access 2021. https://en.wikipedia.org/wiki/Hydrolysis
- ↑ P. Lenihan, A. Orozco, E. O’Neill, M.N.M. Ahmad, D.W. Rooney, G.M. Walker, 2010-01-15: Dilute acid hydrolysis of lignocellulosic biomass. Chemical Engineering Journal, Vol. 156, (2), 395–403. doi: https://doi.org/10.1016/j.cej.2009.10.061
- ↑ Katarzyna Świątek, Stephanie Gaag, Andreas Klier, Andrea Kruse, Jörg Sauer, David Steinbach, 2020-04-17: Acid Hydrolysis of Lignocellulosic Biomass: Sugars and Furfurals Formation. Catalysts, Vol. 10, (4), 437. doi: https://doi.org/10.3390/catal10040437
- ↑ a b Alessandra Verardi, Isabella De Bari, Emanuele Ricca and Vincenza Calabrò, 2012: Hydrolysis of Lignocellulosic Biomass: Current Status of Processes and Technologies and Future Perspectives. Bioethanol. Marco Aurelio Pinheiro Lima and Alexandra Pardo Policastro Natalense (Ed.). IntechOpen, {{{place}}}.
- ↑ S. Niju, M. Swathika, M. Balajii, 2020-01-01: Pretreatment of lignocellulosic sugarcane leaves and tops for bioethanol production. Lignocellulosic Biomass to Liquid Biofuels, Vol. , 301–324. doi: https://doi.org/10.1016/B978-0-12-815936-1.00010-1
- ↑ a b Amit K. Jaiswal, Rajeev Ravindran, 2016-01-01: 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
- ↑ a b Valery B. Agbor, Nazim Cicek, Richard Sparling, Alex Berlin, David B. Levin, 2011-11: Biomass pretreatment: Fundamentals toward application. Biotechnology Advances, Vol. 29, (6), 675–685. doi: https://doi.org/10.1016/j.biotechadv.2011.05.005