The steam activation or chemical activation with phosphoric acids requires to subject the biomass to extremely high temperature ofter higher than 800 degrees. I am looking for some other methods which I can follow with the limited facilities in my lab.
In this way Controll of pH will be more benificial and more effective..
Along with Phosphoric acid some salts of Phosphoric acid (Like sodium Phosphate) can be added.
There is no need of advanced technology
You can use direct activation in air. In this condition, 400°C is generally enough. However this method is almost never used, as there is almost no control of the activation rate. Therefore, reproducibility is low, and the pore size distribution is not optimal by this technique. Pores are indeed wider than with usual techiques, so surface areas are lower. But at least you can significantly improve the surface area of any charcoal, and hence the resultant product can be used as adsorbent for example.
Alain
Let me add that phosphoric acid activation of biomass only requires 550°C and can be carried out without problem in air. Therefore, a simple mufle furnace without inert gas can be used for that purpose with excellent results. Just have a look on our papers published on lignin activation. I recommend this method, more than the previous one: if you can heat in air at 400°C, you can probably heat up to 550°C. Then, you just have to control the impregnation ratio and the time to get reproducible results.
Alain
addition of phosphoric acid and heating upto 550 in muffle furnace in air will give proper activation of charcoal if wooden material is used
Wanted to add some "alchemy" to the equation. In the 1970s, worked as Food and Drug Chemist. In doing gravimetric analyses of a drug by extraction in a separatory funnel, often the colorless drug would have a color. Often, we would pass a chloroform solution of the drug through activated charcoal. Some activated charcoal would work for one specific dye, a different activated charcoal would work for a different dye. Some worked for one specific purpose, others did not. Clearly the difference was due to the process used to make the activated charcoal. A criteria that could be optimized in making charcoal is yield. Dehydration from CH-CHOH going to CH=CH will result in loss of mass. Oxidation to CO2 however will result in loss of carbon. . . Don't know how that can be optimized except experimentally. . .
I am in Beltsville, MD. Albany, CA and Wynmoor, PA are the two ARS process engineering centers.
We do a little charcoal research in Beltsville related to adding charcoal to soil as a mechanism to sequester carbon. Actually makes more sense than storing carbon in the fully oxidized state (CO2 or as carbonate salt).
Dear Dr. Schmidt
It was interesting to sequester carbon in the soil by addition of charcoal. But after some time will the carbon be released back into the atmosphere? Ideally how long we can sequester carbon in the form of charcoal if added to the soil?
Arun,
It is not a mass balance equation as much as it is a kinetics equation.
Trees sequester carbon. Harvesting trees and burning them for fuel produces the CO2 more rapidly than for example if the same trees had been burnt in forest fire. Thus in fact burning some trees at the right place and right time such that a forest fire burns only a fraction of the forest would have net positive effect on the environment: release of CO2 from combustion of wood would be slower.
The chemistry of carbon in soils is rather interesting. Biochemically there are anabolic processes and catabolic processes. Basically, anabolic processes add hydrogen to the molecular formulas in soil; catabolism adds oxygen to the molecular formula in soils. A third process is the chemical loss of water, i.e. CH-CHOH -> CH=CH, which is neither anabolic or catabolic.
An analogous process occur with N containing compounds: Ammonia (NH3) is fully reduced, nitrate (NO3 minus 2) is fully oxidized. Oxidation and reduction are occurring ubiquitously all the time. Oxidations spends energy, reduction stores energy. This is why diesel fuel is a better fuel than coal: the CH=CH bonds in coal chemically are already partially oxidized (again CH=CH is simply CH-CHOH minus a water molecule). Burning coal or wood is simply burning material that is already partially burnt. Converting wood to charcoal is not actually burning anything: it is just chemically dehydrating wood.
If one adds charcoal to soil where microbe are living, they can either use the matter as fuel (oxidizing it further) or as building blocks, the chemical source of C and H to manufacture other chemicals increasing the amount of biomass.
Biomass always sequesters carbon. Burning trees faster than they grow is the kinetics by which CO2 levels will always measurably increase. Growing perennial plants in place of annuals does the same, living longer sequesters carbon longer.
Human behavior always affects global processes in larger as well as [perhaps even much] smaller ways.
Walter.
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