Difference between revisions of "Pyrolysis"
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== Process == | == Process == | ||
The pyrolysis is an endothermal process which requires the input of energy in form of heat which can either be directly (direct pyrolysis) applied via hot gases or indirectly (indirect pyrolysis) via external heating of the reactor. Compared to gasification, the process takes place in an atmosphere without oxygen or at least under a limitation of oxygen. | The pyrolysis is an endothermal process which requires the input of energy in form of heat which can either be directly (direct pyrolysis) applied via hot gases or indirectly (indirect pyrolysis) via external heating of the reactor. Compared to [[gasification]], the process takes place in an atmosphere without oxygen or at least under a limitation of oxygen. | ||
In general, pyrolysis can be divided into different steps which includes: | In general, pyrolysis can be divided into different steps which includes: | ||
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# Reaction and recombination of the molecules, and triggering of chain reactions through free radicals | # Reaction and recombination of the molecules, and triggering of chain reactions through free radicals | ||
The pyrolysis process and the formation of products can be controlled to a certain extend via different temperature ranges and reaction times as well as by utilising reactive gases, liquids, catalysts, alternative forms of heat application (e.g. via microwaves or plasma), and a variety of reactor designs. | The pyrolysis process and the formation of products can be controlled to a certain extend via different temperature ranges and reaction times as well as by utilising reactive gases, liquids, catalysts, alternative forms of heat application (e.g. via microwaves or plasma), and a variety of [[reactor designs]]. | ||
=== Reactions === | === Reactions === | ||
A range of different reactions occur during the process such as dehydration, depolymerisation, isomerisation, aromatisation, decarboxylation, and charring<ref name=":0">{{Cite journal|author=Hu, X. and Gholizadeh, M.|year=2019|title=Biomass pyrolysis: A review of the process development and challenges from initial researches up to the commercialisation stage|journal=Journal of Energy Chemistry|volume=39|issue=|page=109-143|doi=doi:https://doi.org/10.1016/j.jechem.2019.01.024}}</ref>. | A range of different reactions occur during the process such as [[dehydration]], [[depolymerisation]], [[isomerisation]], [[aromatisation]], [[decarboxylation]], and [[charring]]<ref name=":0">{{Cite journal|author=Hu, X. and Gholizadeh, M.|year=2019|title=Biomass pyrolysis: A review of the process development and challenges from initial researches up to the commercialisation stage|journal=Journal of Energy Chemistry|volume=39|issue=|page=109-143|doi=doi:https://doi.org/10.1016/j.jechem.2019.01.024}}</ref>. | ||
== Product == | == Product == | ||
A range of solid, liquid, and gaseous products can be obtained from the pyrolysis process including char, pyrolysis oil, and pyrolysis gas. Depending on the feedstock origin and composition as well as the pre-treatment and process the yield as well as the chemical and physical properties of the products can vary. | A range of solid, liquid, and gaseous products can be obtained from the pyrolysis process including [[char]], [[pyrolysis oil]], and [[pyrolysis gas]]. Depending on the feedstock origin and composition as well as the pre-treatment and process the yield as well as the chemical and physical properties of the products can vary. | ||
=== Char === | === Char === | ||
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=== Pyrolysis oil === | === Pyrolysis oil === | ||
[[File:Corn Stover Tar from Pyrolysis by Microwave Heating.jpg|thumb|upright|Pyrolysis oil from corn stover pyrolysis]] | [[File:Corn Stover Tar from Pyrolysis by Microwave Heating.jpg|thumb|upright|Pyrolysis oil from corn stover pyrolysis]] | ||
Produced pyrolysis oil is a multiphase emulsion composed of water and and hundrets of organic molecules such as acids, alcohols, ketones, furans, phenols, ethers, esters, sugars, aldehydes, alkenes, nitrogen- and oxygen- containing molecules. A longer storage or exposure to higher temperature increases the viscosity due to possible chemical reactions of the compounds in the oil which leads to the formation of larger molecules<ref name=":1">{{Cite journal|author=Czernik, S. and Bridgwater|year=2004|title=Overview of Applications of Biomass Fast Pyrolysis Oil|journal=Energy & Fuels|volume=18|issue=2|page=590-598|doi=10.1021/ef034067u}}</ref>. The presence of oligomeric species with a molecular weight >5000 decreases the stability of the oil<ref name=":0" />, furthermore the formation of aerosols from volatile substances accelerates the aging process in which the water content and phase separation increases. The application as fuel in standard equipment for petroleum fuels (e.g. boilers, engines, turbines) may be limited due to poor volatility, high viscosity, coking, and corrosiveness of the oil<ref name=":1" />. To overcome these problems the pyrolysis oil has to be upgraded in a post-treatment to be used as fuel and/or the equipment for the end-application has to be adapted. | Produced pyrolysis oil is a multiphase emulsion composed of water and and hundrets of organic molecules such as acids, alcohols, ketones, furans, phenols, ethers, esters, sugars, aldehydes, alkenes, nitrogen- and oxygen- containing molecules. A longer storage or exposure to higher temperature increases the viscosity due to possible chemical reactions of the compounds in the oil which leads to the formation of larger molecules<ref name=":1">{{Cite journal|author=Czernik, S. and Bridgwater|year=2004|title=Overview of Applications of Biomass Fast Pyrolysis Oil|journal=Energy & Fuels|volume=18|issue=2|page=590-598|doi=10.1021/ef034067u}}</ref>. The presence of oligomeric species with a molecular weight >5000 decreases the stability of the oil<ref name=":0" />, furthermore the formation of aerosols from volatile substances accelerates the aging process in which the water content and phase separation increases. The application as fuel in standard equipment for petroleum fuels (e.g. boilers, engines, turbines) may be limited due to poor volatility, high viscosity, coking, and corrosiveness of the oil<ref name=":1" />. To overcome these problems the pyrolysis oil has to be upgraded in a [[post-treatment]] to be used as fuel and/or the equipment for the end-application has to be adapted. | ||
=== Pyrolysis gas === | === Pyrolysis gas === | ||
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=== Post-treatment === | === Post-treatment === | ||
* Fischer-Tropsch-Synthesis | * [[Fischer-Tropsch-Synthesis]] | ||
== Technology providers == | == Technology providers == | ||
Revision as of 10:18, 16 April 2021
Pyrolysis (from greek pyr, "fire" and lysis, "loosing/unbind") is a conversion technology that utilises a thermochemical process to convert organic compounds in presence of heat and absence of oxygen into valuable products which can be solid, liquid or gaseous. The chemical transformations of substances are generally accompanied by the breaking of chemical bonds which leads to the conversion of more complex molecules into simpler molecules which may also combine with each other to build up larger molecules again. The products of pyrolysis are usually not the actual building blocks of the decomposed substance, but are structurally modified (e.g. by cyclization and aromatisation or rearrangement).
Feedstock
Origin and composition
Since all kind of biowaste contains hydrocarbonaceous material it can also be processed via pyrolysis. However, the composition of the feedstock has an impact on the pyrolysis process and therewith on the products which can be obtained. Usually wood and herbaceous feedstocks are processed which are composed differently[1] which qualifies garden waste as suitable feedstock.
| Feedstock: | Corn stover | Switchgrass | Wood |
|---|---|---|---|
| Proximate analysis wt [%] | |||
| Moisture | 8.0 | 9.8 | 42.0 |
| Ash | 6.9 | 8.1 | 2.3 |
| Volatile matter | 69.7 | 69.1 | 47.8 |
| Fixed carbon | 15.4 | 12.9 | 7.9 |
| Elemental analysis [%] | |||
| Carbon | 49.7 | 50.7 | 51.5 |
| Hydrogen | 5.91 | 6.32 | 4.71 |
| Oxygen | 42.6 | 41.0 | 40.9 |
| Nitrogen | 0.97 | 0.83 | 1.06 |
| Sulphur | 0.11 | 0.21 | 0.12 |
| Chlorine | 0.28 | 0.22 | 0.02 |
| Structural organics wt [%] | |||
| Cellulose | 36.3 | 44.8 | 38.3 |
| Hemicellulose | 23.5 | 35.3 | 33.4 |
| Lignin | 17.5 | 11.9 | 25.2 |
Pre-treatment
The pre-treatment of the feedstock has an impact on the pyrolysis process, its efficiency, and the yield of certain products. The following pre-treatments may be considered [2]:
- Physical pre-treatments
- Sizing (e.g. chipping, grinding)
- Densification (e.g. pressure-densification)
- Steam explosion
- Drying (e.g. air drying, freeze-drying)
- Chemical pre-treatment
- Chemical extraction (e.g. acid and alkali treatment for the removal of minerals)
- Wet torrefaction
- Ammonia fibre expansion
- Decomposing (e.g. via fungi)
Process
The pyrolysis is an endothermal process which requires the input of energy in form of heat which can either be directly (direct pyrolysis) applied via hot gases or indirectly (indirect pyrolysis) via external heating of the reactor. Compared to gasification, the process takes place in an atmosphere without oxygen or at least under a limitation of oxygen.
In general, pyrolysis can be divided into different steps which includes:
- Evaporation and vapourisation of water and other volatile molecules which is induced at temperatures > 100 °C
- Thermal excitation and dissociation of the molecules induced at temperatures between 100-600 °C, which also may involve the production of free radicals as intermediate stage
- Reaction and recombination of the molecules, and triggering of chain reactions through free radicals
The pyrolysis process and the formation of products can be controlled to a certain extend via different temperature ranges and reaction times as well as by utilising reactive gases, liquids, catalysts, alternative forms of heat application (e.g. via microwaves or plasma), and a variety of reactor designs.
Reactions
A range of different reactions occur during the process such as dehydration, depolymerisation, isomerisation, aromatisation, decarboxylation, and charring[2].
Product
A range of solid, liquid, and gaseous products can be obtained from the pyrolysis process including char, pyrolysis oil, and pyrolysis gas. Depending on the feedstock origin and composition as well as the pre-treatment and process the yield as well as the chemical and physical properties of the products can vary.
Char
As mentioned the functional properties of char may vary which includes carbon content, functional groups, heating value, surface area, and pore-size distribution. The application possibilities are versatile, the char can be used as soil amendment for carbon sequestration, soil fertility improvement, and pollution remediation. Furthermore the char can be used for catalytic purposes, energy storage, or sorbent for pollutant removal from water or flue-gas.
Pyrolysis oil
Produced pyrolysis oil is a multiphase emulsion composed of water and and hundrets of organic molecules such as acids, alcohols, ketones, furans, phenols, ethers, esters, sugars, aldehydes, alkenes, nitrogen- and oxygen- containing molecules. A longer storage or exposure to higher temperature increases the viscosity due to possible chemical reactions of the compounds in the oil which leads to the formation of larger molecules[3]. The presence of oligomeric species with a molecular weight >5000 decreases the stability of the oil[2], furthermore the formation of aerosols from volatile substances accelerates the aging process in which the water content and phase separation increases. The application as fuel in standard equipment for petroleum fuels (e.g. boilers, engines, turbines) may be limited due to poor volatility, high viscosity, coking, and corrosiveness of the oil[3]. To overcome these problems the pyrolysis oil has to be upgraded in a post-treatment to be used as fuel and/or the equipment for the end-application has to be adapted.
Pyrolysis gas
Syngas can be obtained from the pyrolysis gas which is composed of different gases such as carbon dioxide, carbon monoxide, hydrogen, methane, ethane, ethylene, propane, suphur oxides, nitrogen oxides, and ammonia[2]. The different gases can be fractionated from each other in the post-treatment to utilise them for different applications such as the production of chemicals, cosmetics, food, polymers or the utilisation as fuel or technical gas.
Post-treatment
Technology providers
BioBTX (ICCP technology)
Fortum (Combined Heat and Power plant, CHP; LignoCat?)
Fraunhofer UMSICHT (TCR-Process --> Susteen Technologies GmbH?)
Green Fuel Nordic
KIT (bioliq-Project)
Preem (Biozin; RenFuel)
Pyrocell
Statkraft (Silva Green Fuel)
VTT Technical Research Centre of Finland
Patents
References
Al Arni, S. 2018: Comparison of slow and fast pyrolysis for converting biomass into fuel. Renewable Energy, Vol. 124 197-201. doi:https://doi.org/10.1016/j.renene.2017.04.060
Czajczyńska, D., Anguilano, L., Ghazal, H., Krzyżyńska, R., Reynolds, A. J., Spencer, N. and Jouhara, H. 2017: Potential of pyrolysis processes in the waste management sector. Thermal Science and Engineering Progress, Vol. 3 171-197. doi:https://doi.org/10.1016/j.tsep.2017.06.003
Speight, J. 2019: Handbook of Industrial Hydrocarbon Processes. Gulf Professional Publishing, Oxford, United Kingdom.
Tan, H., Lee, C. T., Ong, P. Y., Wong, K. Y., Bong, C. P. C., Li, C. and Gao, Y. 2021: A Review On The Comparison Between Slow Pyrolysis And Fast Pyrolysis On The Quality Of Lignocellulosic And Lignin-Based Biochar. IOP Conference Series: Materials Science and Engineering, Vol. 1051 doi:10.1088/1757-899X/1051/1/012075
Waheed, Q. M. K., Nahil, M. A. and Williams, P. T. 2013: Pyrolysis of waste biomass: investigation of fast pyrolysis and slow pyrolysis process conditions on product yield and gas composition. Journal of the Energy Institute, Vol. 86 (4), 233-241. doi:10.1179/1743967113Z.00000000067
Zaman, C. Z., Pal, K., Yehye, W. A., Sagadevan, S., Shah, S. T., Adebisi, G. A., Marliana, E., Rafique, R. F. and Johan, R. B. 2017: Pyrolysis: A Sustainable Way to Generate Energy from Waste. IntechOpen
- ↑ a b Carpenter, D., Westover, T. L., Czernik, S. and Jablonski, W., 2014: Biomass feedstocks for renewable fuel production: a review of the impacts of feedstock and pretreatment on the yield and product distribution of fast pyrolysis bio-oils and vapors. Green Chemistry, Vol. 16, (2), 384-406. doi: https://doi.org/10.1039/C3GC41631C
- ↑ a b c d Hu, X. and Gholizadeh, M., 2019: Biomass pyrolysis: A review of the process development and challenges from initial researches up to the commercialisation stage. Journal of Energy Chemistry, Vol. 39, 109-143. doi: https://doi.org/doi:https://doi.org/10.1016/j.jechem.2019.01.024
- ↑ a b Czernik, S. and Bridgwater, 2004: Overview of Applications of Biomass Fast Pyrolysis Oil. Energy & Fuels, Vol. 18, (2), 590-598. doi: https://doi.org/10.1021/ef034067u