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Difference between revisions of "Hydrolysis"
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== Process and technologies == | == Process and technologies == | ||
=== Chemical | === Chemical hydrolysis === | ||
Chemical pretreatments have been used extensively for removal of lignin surrounding cellulose and for destroying its crystalline structure. Even though chemical pretreatments are usually effective, they have disadvantages which should not be ignored [10]. These include use of specialized corrosion resistant equipment, need for extensive washing, and disposal of chemical wastes. Various chemical methods are discussed under several headings, namely, alkalis, acids, gases, oxidizing agents, cellulose solvents, extraction, and swelling agents. | Chemical pretreatments have been used extensively for removal of lignin surrounding cellulose and for destroying its crystalline structure. Even though chemical pretreatments are usually effective, they have disadvantages which should not be ignored [10]. These include use of specialized corrosion resistant equipment, need for extensive washing, and disposal of chemical wastes. Various chemical methods are discussed under several headings, namely, alkalis, acids, gases, oxidizing agents, cellulose solvents, extraction, and swelling agents. | ||
==== Acid ==== | ==== Acid hydrolysis ==== | ||
'''Acid hydrolysis''' is a hydrolysis process in which a protic acid is used to catalyze the hydrolysis reaction. Acids are used mainly for hydrolysis of cellulose [10]. 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 temperature and with high yield. Downsides are the high acid consumption and high corrosion potential. These downsides are circumvented with the use of '''diluted acid''' (2-5 %). However, in the latter case, higher temperature is required, which can lead to side product formation such as furfural and 5-hydroxymethyl-furfural.<ref name=":1">{{Cite book|author=Alessandra Verardi, Isabella De Bari, Emanuele Ricca and Vincenza Calabrò|year=2012|section_title=Hydrolysis of Lignocellulosic Biomass: Current Status of Processes and Technologies and Future Perspectives|editor=Marco Aurelio Pinheiro Lima and Alexandra Pardo Policastro Natalense|book_title=Bioethanol|publisher=IntechOpen}}</ref> | '''Acid hydrolysis''' is a hydrolysis process in which a protic acid is used to catalyze the hydrolysis reaction. Acids are used mainly for hydrolysis of cellulose [10]. 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 temperature and with high yield. Downsides are the high acid consumption and high corrosion potential. These downsides are circumvented with the use of '''diluted acid''' (2-5 %). However, in the latter case, higher temperature is required, which can lead to side product formation such as furfural and 5-hydroxymethyl-furfural.<ref name=":1">{{Cite book|author=Alessandra Verardi, Isabella De Bari, Emanuele Ricca and Vincenza Calabrò|year=2012|section_title=Hydrolysis of Lignocellulosic Biomass: Current Status of Processes and Technologies and Future Perspectives|editor=Marco Aurelio Pinheiro Lima and Alexandra Pardo Policastro Natalense|book_title=Bioethanol|publisher=IntechOpen}}</ref> | ||
Acid hydrolysis can be further improved by the addition of salts, such as metal salts or suphite salts. Metals such as aluminium, calcium, copper, iron and zincnc can be used to increase the sugar yield [6]. Similar to sulphite pulping, sulphites can be added to aid in lignin removal. . | |||
===== Sulfuric acid ===== | ===== Sulfuric acid ===== | ||
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''Elaborate more the reactions conditions and give some examples from literature.'' | ''Elaborate more the reactions conditions and give some examples from literature.'' | ||
==== | ==== Alkaline hydrolysis ==== | ||
'''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.<ref>{{Cite journal|title=Pretreatment of lignocellulosic sugarcane leaves and tops for bioethanol production|year=2020-01-01|journal=Lignocellulosic Biomass to Liquid Biofuels|page=301–324|doi=10.1016/B978-0-12-815936-1.00010-1|author=S. Niju, M. Swathika, M. Balajii|volume=}}</ref> | '''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.<ref>{{Cite journal|title=Pretreatment of lignocellulosic sugarcane leaves and tops for bioethanol production|year=2020-01-01|journal=Lignocellulosic Biomass to Liquid Biofuels|page=301–324|doi=10.1016/B978-0-12-815936-1.00010-1|author=S. Niju, M. Swathika, M. Balajii|volume=}}</ref> | ||
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''Elaborate more the reactions conditions and give some examples from literature.'' | ''Elaborate more the reactions conditions and give some examples from literature.'' | ||
=== Solvent === | === Solvent === | ||
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==== Organosolv ==== | ==== 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 H<sub>2</sub>SO<sub>4</sub>.<ref name=":2" /> For example, in '''acid-acetone''' pre-treatment biowaste is treated with an acid such as phophoric acid and then mixed with pre-cooled acetone.<ref name=":0" /> | 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 H<sub>2</sub>SO<sub>4</sub>.<ref name=":2" /> For example, in '''acid-acetone''' pre-treatment biowaste is treated with an acid such as phophoric acid and then mixed with pre-cooled acetone.<ref name=":0">{{Cite journal|title=A comprehensive review on pre-treatment strategy for lignocellulosic food industry waste: Challenges and opportunities|year=2016-01-01|journal=Bioresource Technology|volume=199|page=92–102|doi=10.1016/j.biortech.2015.07.106|author=Amit K. Jaiswal, Rajeev Ravindran}}</ref> | ||
==== Ionic Liquids ==== | ==== Ionic Liquids ==== | ||