Hello
I want to pyrolyse some biomass to obtain biochar using Nitrogen gas but am not sure as to the purity of the gas to use for my laboratory scale pyrolysis.
The biochar obtained will be used for adsorption experiment
what is the recommended gas purity for pyrolysing biomass for adsorption experiment?
Any idea please ?
Depends upon types of pyrolysis.In the fast pyrolysis process, biomass is rapidly heated to a high temperature in the absence of oxygen. Typically on a weight basis, fast pyrolysis produces 60%–75% of oily products (oil and other liquids) with 15%–25% of solids (mainly bio char) and 10%–20% of gaseous phase depending on the feedstock used.so the purity of Nitrogen is must, Oxygen must be absent in Nitrogen.In market High purity Nitrogen is available up to 99.98%.Pyrolysis is the thermal decomposition of biomass occurring in the absence of oxygen. In this process; thermal decomposition of organic components in biomass starts at 350 °C–550 °C and goes up to 700 °C–800 °C in the absence of air/oxygen.
In other laboratories, a pure nitrogen (99 %)is used for pyrolysis, as the impurities may contaiminate the biofuels generated. I am not sure how it will effect biochar (e.g. if high molecular weight hyrdocarbon impurites are present, they may get adsorbed over the char even at high temperature decresing the adsorption uptake capcity of char ) but it may render the results difficult to reproduce, or invalid. A good idea is to stick to the purest nitrogen possible. Hope it will help.
Gas purity should be over 99vol%. 99.999vol% is too expensive for laboratory applications. So long as the O2 content is < 0.1vol%
Cordner Peacocke Dear sir, what purity of nitrogen would you recommend for a pilot-scale plant (25 TPD)?
Vivek. That is subject to the application. We were specifying 99.9vol%, but 99vol% is perfectly fine - if your gas us low in H2, you can use 98vol% N2. The OPEX is much lower for 98 or 99vol%.
For pyrolysis in an instrument like TGA, use the specified instrument grade nitrogen (99.999%). For bench and pilot scale pyrolysis you have to factor in the cost of nitrogen. It will be highly uneconomic to use 99.999 % grade on an experiment that will draw say 10 l/min of nitrogen for 2 hours. After-all pilot scale units are meant to simulate a real large-scale industrial setup, it will be uneconomic to use 99.999% grade in large industrial setup.
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