Activated carbon and carbon molecular sieve preparation and new methods for pore size characterisation

Nguyen, Cuong (1999). Activated carbon and carbon molecular sieve preparation and new methods for pore size characterisation PhD Thesis, School of Chemical Engineering, The University of Queensland.

       
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Author Nguyen, Cuong
Thesis Title Activated carbon and carbon molecular sieve preparation and new methods for pore size characterisation
School, Centre or Institute School of Chemical Engineering
Institution The University of Queensland
Publication date 1999
Thesis type PhD Thesis
Supervisor Do, D.D
Total pages 126
Collection year 2002
Language eng
Subjects L
290600 Chemical Engineering
Formatted abstract

Microporous activated carbon is prepared from macadamia nutshell by pyrolysis followed by activation. It is then used as the precursor for the preparation of carbon molecular sieves by a sequence of controlled hydrocarbon cracking and gasification. The samples are characterised by the BET method using nitrogen adsorption at -196 °C. They are also subjected to adsorption studies of different adsorbates. Results of the characterisation indicate that the proposed method of preparation is feasible. The final product exhibits sieving effects against larger molecules while admitting smaller ones. Other methods such as the DS equation and a combination of the Langmuir and the modified Kelvin equation have also been tested and evaluated as viable means for porosity characterisation. These methods, however, can not fully characterise the distribution of the pore size, especially of those in the micro range, prompting the need for a different approach to the problem of pore size characterisation.

The objective of the second part of the thesis is the development of a new method of charactersation. In building the model, the importance of the pore adsorption enhancement is addressed. The influence of the pore wall on adsorption is accounted for via new concepts such as the pore-enhanced pressure, enhanced surface layering etc. The implication of the new concepts is a model, in which adsorption in micro and mesopores are unified, i.e. the same adsorption mechanism can be used for different pore ranges, which is a significant improvement. The model is first developed for adsorption of nitrogen at -196 °C in carbon slit like pores, because the results can be compared to those calculated using the Density Functional Theory, which are available in the literature. The model is then extended to the adsorption of other adsorbates at higher temperatures. The characterisation using other subcritical adsorbates shows some advantages over the method using adsorption of nitrogen at its liquid temperature. The model is further modified to describe adsorption of supercritical gases. Adsorption of methane and nitrogen onto a range of activated carbons are fitted using the model. A result of the fitting is the distribution of the micropore size. By changing the appropriate parameters, the model is also capable of describing adsorption in pores of other shapes. Adsorption of benzene in MCM-41, a model mesoporous adsorbent, is used to test the model for adsorption in cylindrical pores.

Since the dimension of micropores in carbon molecular sieve materials is not necessarily uniform and they are likely inkbottle shaped, a characterisation method based on equilibrium measurement is insufficient or inappropriate. A new dynamic model of adsorption into micropores of CMS materials is developed in the thesis. It describes the experimental uptake data fairly well...........................

Keyword microporous activated carbon
Adsorbate
characterisation

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
 
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Created: Wed, 05 Mar 2014, 10:21:02 EST by Mr Chinh Nguyen on behalf of Scholarly Communication and Digitisation Service