Pyrolysis oil
Pyrolysis oil (also called "bio-oil" or "biocrudeoil") is a dark brown liquid that is obtained by pyrolysis of biomass at temperatures of around 500 ° C. Although of vegetable origin, pyrolysis oil, in contrast to vegetable oils, which are largely composed of fatty acids, consists of a large number of chemical compounds. In addition to being used as a biofuel , heating component or high-energy intermediate product, pyrolysis oil can be used as a raw material source for chemical applications.
process
The biomass is split into solid, liquid and gaseous components by pyrolysis. The solid components obtained include wood or activated charcoal, while the non-condensable components ( pyrolysis gas ) are hydrogen , carbon monoxide and dioxide, and methane . The liquid phase is condensed at room temperature and ambient pressure. The calorific value is between 15 and 30 MJ / kg and is therefore about half as high as that of natural gas or heating oil . When using wood as a pyrolysis raw material, the yield of pyrolysis oil is around 65 to 75%.
composition
Pyrolysis oil is made up of a variety of oxo components such as carboxylic acids , phenols , aldehydes, and ketones , including alcohols, furans, aldehydes, phenols, organic acids, and oligomeric carbohydrate and lignin products. Several hundred compounds can be detected, some of which are monomeric as well as polymeric lignin components. Up to 38% of the pyrolysis oil consists of water, which on the one hand consists of the water content of the biomass and, on the other hand, of the water of reaction produced when the chemical bonds are broken.
Typical properties
Pyrolysis oil is an acidic liquid that is dark red to dark brown in color. In contrast to mineral oil, it is not miscible with hydrocarbons; in ethanol it is infinitely miscible with water to a limited extent. The viscosity varies depending on the water content and the content of volatile components. The calorific value of pyrolysis oil is around 42% of that of heating oil.
The pour point is between −12 ° C and −33 ° C, the cloud point at around −21 ° C. The flash point is between 40 and 100 ° C. It is not self-igniting in a diesel engine; the cetane number is only around 10. Pyrolysis oil is not storage-stable for a long time. The viscosity increases due to polymerization and reaches a maximum after about 12 months. The oil oxidizes in the air and degasses over time. The smell of pyrolysis oil is slightly pungent and is reminiscent of smokehouse.
The following table shows typical properties of pyrolysis oil:
| property | unit | Typical values |
|---|---|---|
| density | kg / m³ | 1200 |
| Water content | % | 15-30 |
| viscosity | cP | 40-100 |
| PH value | without unity | 1.5-3.8 |
| calorific value | MJ / kg | 16-21 |
processing
Before use, pyrolysis oil must be prepared more or less comprehensively depending on the intended use. For use in engines, for example, engine manufacturers require compliance with limit values for particle content and size composition as well as for viscosity. Physical and chemical methods are available for processing.
Physical preparation
Contamination by solid particles is removed with multi- cyclones or hot gas filters in the flow of the hot pyrolysis gas before it condenses into pyrolysis oil. Cold filtration of the oil is also possible. The oil becomes thinner by adding water or low-alcohol alcohol.
Chemical processing
The (storage) stability of pyrolysis oil can be increased by hydrogenation (saturation of reactive double bonds with hydrogen). A higher proportion of hydrogen is also achieved through the process of hydrogenative cleavage ( hydrocracking or hydro-deoxygenation). This also reduces the oxygen content in the pyrolysis oil. The high proportion of oxygen in the starting product, however, results in a high consumption of hydrogen and therefore makes the process very expensive. Catalysts such as zeolites or other inorganic materials can remove oxygen from the oil by converting it into carbon dioxide, resulting in free and condensed aromatics.
Applications
There are various options for further processing the pyrolysis oil. In addition to the energetic use as fuel or heating component, it can also be used as a raw material source for chemical applications. The use of pyrolysis oil is largely an ongoing development.
Energetic use
Hydrogenation converts pyrolysis oil into fuel. In boilers, they can basically be burned in a similar way to heavy heating oil . Stationary diesel engines must be brought to operating temperature with conventional fuel before using pyrolysis oil. One negative aspect is the lack of lubricating properties. Several properties of pyrolysis oils such as a high ignition temperature, viscosity, acidity and thermolability as well as increased combustion emissions in the case of NO x and CO make their use difficult.
As a transportable intermediate product in the production of BtL fuel from biomass, pyrolysis oil plays an important role in the concept of a two-stage production of synthetic biofuels. In decentralized rapid pyrolysis plants, biomass from the local area will be processed into pastes or slurries made from pyrolysis oil and coke, which will then be transported to a central plant for the production of biofuels. Forschungszentrum Karlsruhe has been operating a pilot rapid pyrolysis system within the framework of this concept since 2007.
The use of pyrolysis oils in thermal power stations is being investigated in the context of industrial and politically funded projects.
Chemical processing
Chemical processing has so far been little researched. The only commercial application on a larger scale is currently the use as smoke flavoring (liquid smoke), subject to review by the EU Commission. Other options include isolating levoglucosan (the monomeric units of cellulose) to control certain chemical reactions, as well as using it as surfactants , biodegradable polymers and resins. It is also possible to isolate phenolic resins for glue. Unchanged pyrolysis oil can be used as a partial replacement for phenol and formaldehyde in chipboard, and as a reaction partner in the production of nitrogen fertilizers with delayed nutrient release.
swell
- Martin Kaltschmitt, Hans Hartmann and Hermann Hofbauer (eds.): Energy from biomass. Basics, techniques and procedures. Springer Verlag, 2nd edition, 2009, ISBN 978-3-540-85094-6 , pp. 685-690.
Individual evidence
- ↑ Long-term Stability, Catalytic Upgrading, and Application of Pyrolysis Oils (PDF; 17 kB)
- ^ Research Center Karlsruhe: Fast pyrolysis ( Memento from July 13, 2012 in the web archive archive.today ). Retrieved July 31, 2009.
- ↑ a b page no longer available , search in web archives: Flash pyrolysis for liquefying biomass - state of the art ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. , Status 2001 (PDF; 175 kB)
Web links
- Yellow straw instead of black gold in the innovation report
- Dietrich Meier, Oskar Faix: Heating oil and chemical raw materials made from wood - Flash pyrolysis opens up new possibilities (PDF; 322 kB)
- COMBIO Project (PDF; 385 kB)