A NEW METHOD OF CHARACTERIZATION OF POROUS SOLIDS USING MONTE CARLO SIMULATION

Luis Herrera Diaz (2011). A NEW METHOD OF CHARACTERIZATION OF POROUS SOLIDS USING MONTE CARLO SIMULATION PhD Thesis, School of Chemical Engineering, The University of Queensland.

       
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Author Luis Herrera Diaz
Thesis Title A NEW METHOD OF CHARACTERIZATION OF POROUS SOLIDS USING MONTE CARLO SIMULATION
School, Centre or Institute School of Chemical Engineering
Institution The University of Queensland
Publication date 2011-04
Thesis type PhD Thesis
Supervisor Professor Duong Do
Total pages 219
Total colour pages 39
Total black and white pages 180
Subjects 09 Engineering
Abstract/Summary The characterization of porous solids is an important topic because of the significant role that they play in many industries and everyday life. For example, activated carbon is used in water purification and in odor removal from air, carbon molecular sieves are used for the separation of gases with similar molecular dimensions but different structures and zeolites are used in the petro-chemistry for the cracking processes. Choosing the best porous material for a specific process is a challenging task for scientists and engineers. The selection of a particular porous solid is carried out by matching the physical and chemical properties of the solid with the requirements of the process, for example, when the separation of gases using molecular sieves, the pore size distribution is compared with the size of gas molecules for the selection of a proper adsorbent. This is why the proper characterization of porous solids is critical for its potential applications. This has been recognized by the scientific community since the early 19th and in 1958 the first symposium to discuss in particular the characterization of porous solids was organized. Currently the importance of this topic is still being recognized, and this is evidenced in the IUPAC’s sub-committee dedicated exclusively to the characterization of porous solids and the two main symposia on characterization: Characterization of Porous Solids (COPS) and Characterization of Porous Materials Workshop. Currently, there is a wide range of methods for the characterization of porous solids; however these methods are somewhat ambiguous and do not agree with each other. Among all these methods gas adsorption is the preferable method, because it is inexpensive and can be carried out in most laboratories. That is why the main aim of this work is to study the characterization of porous solids by using adsorption. Molecular simulation and particularly Monte Carlo simulation has shown great potential for the study of gas adsorption. This is because Monte Carlo in its grand canonical ensemble mimics the process carried out in a volumetric apparatus. In this study grand canonical Monte Carlo simulation is used to derive the adsorption isotherms that are used subsequently to characterize the porous solids structures. This work proposes that the key concept for the characterization of porous solids is accessibility. What that entails is that the physical properties of a porous solid vary with the probe molecule used, and this is completely consistent with the molecular sieving concept, which is failed to be recognized by the conventional characterization methods. For example the void spaces in a porous solid are different if they are measured with argon and xenon; this is because these two probe molecules are different in size and approach the solid surface differently. The accessible properties presented here are accessible volume, accessible geometrical surface area and accessible pore size distribution. These properties are based on the accessible volume proposed recently by Do and co-workers. Two main approaches to the characterization of porous solids are presented. One is for the characterization of solids whose structures are known such as metal-organic frameworks and another is for solids whose structures are unknown such as porous carbons. The first approach is developed based on a Monte Carlo integration method, while the second is based on the new concept of using the total amount that is introduced into a volumetric adsorption apparatus. These two approaches are tested with the characterization of different porous solids. The characterization methods proposed here are robust and unambiguous and they show great potential as a new standard for the characterization of porous solids. The final part of this study considers the computer synthesis of a char structure. A Monte Carlo simulation method is proposed to obtain a number of char structures. The computer synthesis of the char structure is carried out by mimicking the experimental process. The resultant simulated char structures are characterized by using the above characterization methods and the results agree well with the experimental properties of char.
Keyword Accessibility
Characterization
Molecular Simulation
Pore Size Distribution
Porous Solids

 
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Created: Tue, 17 May 2011, 09:24:43 EST by Mr Luis Herrera Diaz on behalf of Library - Information Access Service