Biomass can be converted into activated carbon by chemical or physical activation. The physical activation, especially using steam, produces a lot of pyrolytic oil and the yields are rather low. Using chemical activation the yields are much higher and little or no pyrolytic oil is formed.
What is removed by the physical activation but not by the chemical one? Do the ACs produced by chemical activation have more functional groups left compared to the ones produced by physical activation?
Production of Activated Carbon from Biochar Using Chemical and Physical Activation: Mechanism and Modeling
Ajay K. Dalai and Ramin Azargohar
Materials, Chemicals, and Energy from Forest BiomassChapter 29, pp 463–476 DOI: 10.1021/bk-2007-0954.ch029
Pyrolysis always involves chemical processes. The addition of other materials (catalysts or reagents) may alter the direction of the process, either by selectively increasing the rates of certain competing processes, OR by introducing completely new reaction paths. As for making activated carbon, activation by steam is still a chemical process, as the steam oxidises certain carbon atoms. If you are making a lot of pyrolytic oil, you did not start off with charcoal, but rather mildly charred biomass. The oil comes from the pyrolysis of lignin and polysaccharides. The addition of certain chemicals in the initial charring process will increase the conversion of polysaccharides to carbon simply by increasing the rate of dehydration reactions.
Starting material is in both cases virgin wood. One part undergoes carbonization and steam activation, the other part is impregnated with chemicals and undergoes thermal treatment. In which of the resulting carbons can we find more functional groups?
Henrik Romar
Sorry, but this is try and see. It tends to depend on exactly what you do, including heating rate, particle division, etc. Thus if you pass wood rapidly over a really hot surface it gasifies and you get NO carbon. There is no simple recipe. It depends on how you do it, and on what you do it on.
Ok. But normally the yields are higher for chem activation. Means that more is leaving in the physical activation. Most likely there should be more functional left after chem activation. I assume that carboxylic groups are leaving as CO2 and aldehydes leaves as CO. Both activations are performed using nitrogen flushing.
The below mentioned review discusses biomass pyrolysis and cites many helpful references. Best wishes.
https://www.researchgate.net/publication/325803601_Biomass_pyrolysis_past_present_and_future?_sg=uctHsEFk-uWqt2BGZz1K59-bi1t7VgNQEeXRDjXwvs2gsxu-Evn22Yb7YPx7DmkKLyzfP2k-9rjw3FbvbhEXHrYpY1-5eCp6PAMROxnl.NHWOapbTShJUMlZncKuCGor7UggmB3jS6JxupfrVf8zXykLkVKft9kzOsJwTPOdVbciIKza7L0ekkM8gUc4gaw
In the chemical activation case, I suggest to review the reaction mechanisms for each activation agent (H3PO4, H2SO4, HNO3, ZnCl2, NaOH, KOH, H2O2, K2CO3, CaCl2) this way you can see "what is removed" (products formed) from a fixed precursor at each temperature.
Definitely, different functional groups will be obtained from two different synthesis methods, you could try FTIR in order to identify them for a fixed precursor your material for both cases.
Attached you will find NaOH and KOH mechanism.
Kehila Yehudá Perez-Salcedo Do You have a good protocol for IR-measurments of activated carbons? It is a rather tricky sample having hight absorbance over the IR range. So what instrument and preparation methods are used?
- Badges
- Science topic
- Similar topics
- Engineering
- Petroleum Engineering
- Oil