Sourcing Hydrogen from Complex Wastes

We explore the challenge of extracting hydrogen from complex wastes containing lignin and cellulose...
21 August 2012

Interview with 

Bushra Al-Dhuri, University of Birmningham


Meera -   Bushra uses water at high temperature and high pressure to chemically break down this complex waste and release hydrogen in a process known as water gasification.

Bushra -   My research area is in hydrothermal processing and this is the treatment of waste by using high temperature and high pressure in the presence of water.  We're talking about over 500 degrees and over 250 bars.  Hydrogen is actually an ultimate product that has to come out from a very complex starting material.

Meera -   And do you have an example say, perhaps of a breakdown to the kind of simple molecules that come out and then the complex ones that are left behind?

Bushra -   An initial waste biomass which is called scientifically, lignocellulose.  Now 'ligno' resembles lignin.  Cellulose is a very complex carbohydrate.  Cellulose is a subcomplex.  Ligno is another subcomplex and then the cellulose breaks down into sugars like sucrose and it also breaks down into other types of sugars that are not edible, but they are chemically sugars.  So, these cellulose can be treated in a process.  What treats cellulose is not enough to break lignin.

Meera -   This is where your work comes in.

Bushra -   Yes, because lignin is very complex.

Meera -   And at this say, high temperatures and high pressures, you're actually using water to get the hydrogen out of the lignin.

Bushra -   Yes.  Actually, this is, if you like, the advantage of it because when you treat waste biomass, you have to dry it first in order to burn it or to do like pyrolysis or gasification.  You have to actually dry it.  And this is a very costly process to get water out of it.  What we do, the water that wets biomass, that water acts as a medium.  It actually acts as a catalyst because when you compress it and heat it, it will actually dissolve all this.  It does facilitate the gasification and the word 'gasification' is turning all these chemical compounds, lignin, et cetera into, majorly, hydrogen.

Meera -   And the use of say, these high temperatures and high pressures, you're actually reaching a phase of the water known as 'super critical phase'.

Bushra -   Absolutely.  The super critical phase means it's the whole thing is actually in a gas phase, but more than that, it's a gas phase with different chemistry. I.e. it will follow different reaction paths to give us hydrogen.

Meera -   What do you hope perhaps will be, I guess almost the level of hydrogen you could achieve?  Do you imagine that this will be quite an efficient process?

Bushra -   The main attraction behind actually going to that level of temperatures and pressures is over 50% yield of hydrogen because this process does not give us any chars and tars.

Meera -   So, nice clean hydrogen gas at the end.

Bushra -   Yes.


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