Chemical Engineering @ChemengFiles.Com

To investigate the principles of Non-Equilibrium Thermodynamics, an experimental and theoretical study of a chemical reacting system is made. Nitric oxide, iodine, chlorine, iodine monochloride, and nitrosyl chloride in the gas phase are the macroscopic chemical species which comprise this system.

The system displays a coupling behavior which is uncommon to chemical reacting systems. However, this behavior may be useful in explaining some biological phenomena. The observed coupling effect results in a phenomenological coefficient matrix which is not diagonal.

To investigate the principles of Non-Equilibrium Thermodynamics, an experimental and theoretical study of a chemical reacting system is made. Nitric oxide, iodine, chlorine, iodine monochloride, and nitrosyl chloride in the gas phase are the macroscopic chemical species which comprise this system.

The system displays a coupling behavior which is uncommon to chemical reacting systems. However, this behavior may be useful in explaining some biological phenomena. The observed coupling effect results in a phenomenological coefficient matrix which is not diagonal.

This thesis presents a study of the morphological changes that occur in selected coal chars during oxidation at low temperature (725K-875K) and at high temperature (1400K-1600K). Gas adsorption and mercury porosimetry were the primary means by which these changes were monitored. An attempt was made to relate the observed reactivity of the char in oxygen to the evolving porous structure of the char. Initial pore structure was varied by using three different raw coals: a lignite, a subbituminous and high volatile A bituminous coal. In the case of the bituminous coal, pore structure was varied further by using different pyrolysis temperatures. Of course, while there were differences in the physical structure of the chars, there were differences in the chemical structure as well. In order to account for this, the chemical nature of the chars was monitored, using elemental analysis and oxygen chemisorption.

This thesis presents a study of the morphological changes that occur in selected coal chars during oxidation at low temperature (725K-875K) and at high temperature (1400K-1600K). Gas adsorption and mercury porosimetry were the primary means by which these changes were monitored. An attempt was made to relate the observed reactivity of the char in oxygen to the evolving porous structure of the char. Initial pore structure was varied by using three different raw coals: a lignite, a subbituminous and high volatile A bituminous coal. In the case of the bituminous coal, pore structure was varied further by using different pyrolysis temperatures. Of course, while there were differences in the physical structure of the chars, there were differences in the chemical structure as well. In order to account for this, the chemical nature of the chars was monitored, using elemental analysis and oxygen chemisorption.

Silicon nanoparticle-based floating gate metal-oxide-semiconductor (MOS) field effect devices have potential for terabit [...] density nonvolatile memory applications. Aerosol synthesis of silicon nanoparticles is an important route toward the formation of discontinuous silicon nanoparticle floating gate structures that affords excellent control over particle size and size distribution, particle density, and oxide passivation. We have fabricated nanoparticle memory devices in a conventional MOS ultra-large scale integration (ULSI) process with channel lengths from 0.2 - 10 [...] with a silicon nanoparticle floating gate fabricated by aerosol deposition.

Silicon nanoparticle-based floating gate metal-oxide-semiconductor (MOS) field effect devices have potential for terabit [...] density nonvolatile memory applications. Aerosol synthesis of silicon nanoparticles is an important route toward the formation of discontinuous silicon nanoparticle floating gate structures that affords excellent control over particle size and size distribution, particle density, and oxide passivation. We have fabricated nanoparticle memory devices in a conventional MOS ultra-large scale integration (ULSI) process with channel lengths from 0.2 - 10 [...] with a silicon nanoparticle floating gate fabricated by aerosol deposition.

This thesis describes a novel "microplasma" source that is suitable for microreactor applications. The high-pressure "microplasma" is a direct current microdischarge, formed between two metal electrodes: a cathode with a pin-hole (diameter~100 �m) and an anode of unspecified shape. Strong radial electric fields are produced in the microhollow cathode geometry, causing electrons to oscillate (Pendel effect). As a result of enhanced ionization processes, it is possible to produce a stable high-intensity discharge at pressures of 1 atmosphere or higher. We have utilized these microdischarges for several applications including pattern transfer, diamond deposition, excimer emission, and nanoparticle synthesis.

This thesis describes a novel "microplasma" source that is suitable for microreactor applications. The high-pressure "microplasma" is a direct current microdischarge, formed between two metal electrodes: a cathode with a pin-hole (diameter~100 �m) and an anode of unspecified shape. Strong radial electric fields are produced in the microhollow cathode geometry, causing electrons to oscillate (Pendel effect). As a result of enhanced ionization processes, it is possible to produce a stable high-intensity discharge at pressures of 1 atmosphere or higher. We have utilized these microdischarges for several applications including pattern transfer, diamond deposition, excimer emission, and nanoparticle synthesis.

Perchloric Acid is a substance resembling sulfuric acid in many respects. It is a strong acid, very stable in solution, and has a high boiling point. It possesses some advantages over sulfuric acid, such as being monobasic, and having relatively few insoluble salts. (K, Rb, Cs, and Tl perchlorates are only slightly soluble.) Hence a cheap way of making perchloric acid would be highly advantageous to the chemical industry. The present methods of its production are rather expensive, employing the electrolytic production of sodium perchlorate and the distillation of the latter with sulfuric acid under reduced pressure. The product, a 60% perchloric acid is now sold for $7 to $8 per pound. Ammonium perchlorate is obtainable at a fairly low cost, (about 2O [cents] per pound) and might be used as a basis for the cheaper preparation of perchloric acid.

Perchloric Acid is a substance resembling sulfuric acid in many respects. It is a strong acid, very stable in solution, and has a high boiling point. It possesses some advantages over sulfuric acid, such as being monobasic, and having relatively few insoluble salts. (K, Rb, Cs, and Tl perchlorates are only slightly soluble.) Hence a cheap way of making perchloric acid would be highly advantageous to the chemical industry. The present methods of its production are rather expensive, employing the electrolytic production of sodium perchlorate and the distillation of the latter with sulfuric acid under reduced pressure. The product, a 60% perchloric acid is now sold for $7 to $8 per pound. Ammonium perchlorate is obtainable at a fairly low cost, (about 2O [cents] per pound) and might be used as a basis for the cheaper preparation of perchloric acid.

It is well known that neutral or weakly acid solutions of alkali chlorates show no appreciable oxidizing power. However, it has been observed by K.A. Hofmann (Ber. 45,3329, 1912; 46, 1567, 1913) that, in the presence of very minute amounts of osmium tetroxide, the oxygen becomes readily available. Chlorate solutions activated in this way will, for example, oxidize hydrazine to free nitrogen, potassium iodide to iodine, and arsenic to arsenious acid.
Hoffman found that, in the oxidation of hydrazine sulfate, nitrogen is liberated quantitatively according to the equation [...].
The investigation of the mechanism of this reaction has been taken as the subject of this thesis.

It is well known that neutral or weakly acid solutions of alkali chlorates show no appreciable oxidizing power. However, it has been observed by K.A. Hofmann (Ber. 45,3329, 1912; 46, 1567, 1913) that, in the presence of very minute amounts of osmium tetroxide, the oxygen becomes readily available. Chlorate solutions activated in this way will, for example, oxidize hydrazine to free nitrogen, potassium iodide to iodine, and arsenic to arsenious acid.
Hoffman found that, in the oxidation of hydrazine sulfate, nitrogen is liberated quantitatively according to the equation [...].
The investigation of the mechanism of this reaction has been taken as the subject of this thesis.

The results of ballistic piston tests on methane and on n-hexane are described. In the case of methane the calculated reaction temperatures are 2500 to 3500[degrees]R. and maximum pressure range up to 100,000 pounds per square inch. The distribution of reaction products and the amount of reaction are correlated with the reaction conditions. For n-hexane the products are correlated with reaction conditions and in addition reaction rate coefficients were obtained. The decomposition reaction was found to be of apparent one half order with a low apparent activation energy. The range of reaction, temperatures investigated for n-hexane was 1600-2800[degrees]R. with maximum pressures up to 115,000 pounds per sqaure inch.

The results of ballistic piston tests on methane and on n-hexane are described. In the case of methane the calculated reaction temperatures are 2500 to 3500[degrees]R. and maximum pressure range up to 100,000 pounds per square inch. The distribution of reaction products and the amount of reaction are correlated with the reaction conditions. For n-hexane the products are correlated with reaction conditions and in addition reaction rate coefficients were obtained. The decomposition reaction was found to be of apparent one half order with a low apparent activation energy. The range of reaction, temperatures investigated for n-hexane was 1600-2800[degrees]R. with maximum pressures up to 115,000 pounds per sqaure inch.

Due to the unique and difficult chemistry they perform, the aromatic ring-hydroxylating dioxygenases are of interest as industrial catalysts. Unfortunately, an application-specific array of problems limits their utility. To address these problems through laboratory evolution, I developed methods for high-throughput screening of tens of thousands of dioxygenase variants. These methods rely on a phenol detection reagent (Gibbs reagent) and can be applied to liquid cultures or to growing bacterial colonies expressing variant enzymes.

Due to the unique and difficult chemistry they perform, the aromatic ring-hydroxylating dioxygenases are of interest as industrial catalysts. Unfortunately, an application-specific array of problems limits their utility. To address these problems through laboratory evolution, I developed methods for high-throughput screening of tens of thousands of dioxygenase variants. These methods rely on a phenol detection reagent (Gibbs reagent) and can be applied to liquid cultures or to growing bacterial colonies expressing variant enzymes.

This dissertation discusses theoretical and experimental research on coal pyrolysis.

In the theoretical part, a mathematical model based on coal's chemical structure and its reactions is developed for computer simulation of pyrolysis. Firstly, the important organic functional groups of carbon, hydrogen and oxygen in medium and high rank coals are organized into a conceptual model for coal's chemical structure. Using the principles of thermochemistry of free radicals as guidelines, the important categories of chemical reactions in coal pyrolysis are postulated. A set of 41 series-parallel reactions represents the chemical change. It is concluded that there is no a priori distinction between volatiles and non-volatiles in a coal. They are both formed from the same chemical structure, and are basically an inevitable consequence of each other's formation.

This dissertation discusses theoretical and experimental research on coal pyrolysis.

In the theoretical part, a mathematical model based on coal's chemical structure and its reactions is developed for computer simulation of pyrolysis. Firstly, the important organic functional groups of carbon, hydrogen and oxygen in medium and high rank coals are organized into a conceptual model for coal's chemical structure. Using the principles of thermochemistry of free radicals as guidelines, the important categories of chemical reactions in coal pyrolysis are postulated. A set of 41 series-parallel reactions represents the chemical change. It is concluded that there is no a priori distinction between volatiles and non-volatiles in a coal. They are both formed from the same chemical structure, and are basically an inevitable consequence of each other's formation.

Experimental and theoretical studies in the field of fuel gas desulfurization at high temperatures are presented. The performance of different oxides as sorbents for high temperature H2S removal is evaluated. A fixed-bed microreactor was used for this purpose. Basically, streams containing different H2S concentrations were passed through the reactor and the outlet H2S concentration was measured as a function of time. Comparisons between observed and theoretical maximum conversion values are used as a measure of sorbent H2S removal efficiencies.

Experimental and theoretical studies in the field of fuel gas desulfurization at high temperatures are presented. The performance of different oxides as sorbents for high temperature H2S removal is evaluated. A fixed-bed microreactor was used for this purpose. Basically, streams containing different H2S concentrations were passed through the reactor and the outlet H2S concentration was measured as a function of time. Comparisons between observed and theoretical maximum conversion values are used as a measure of sorbent H2S removal efficiencies.