Suphan Kovenklioglu

Hollow fiber contained liquid membrane pervaporation system for the removal of toxic volatile organics from wastewater

A novel configuration of a hollow fiber contained liquid membrane (HFCLM) pervaporation system was used to separate organic solutes such as trichloroethylene and toluene from water. In this system the highly selective organic liquid membrane is contained in the shell side between two sets of hollow fibers packed in a shell-and-tube heat exchanger arrangement. Wastewater is fed into one set of hollow fibers and vacuum is applied in the other set of hollow fibers. The separation factors and solute recoveries for the HFCLM system were higher and water fluxes lower than in a conventional pervaporation system based on silicone rubber with vacuum applied outside the silicone rubber hollow fibers. The effluent concentration data for the HFCLM were satisfactorily correlated with a material balance where the mass flux was expressed in terms of an overall mass transfer coefficient based on resistances-in-series model.

Capillary Flow Behaviour of Microcrystalline Wax and Silicon Carbide Suspension

Suspensions of ceramic particles in low or high molecular weight polymers are shaped into various three-dimensional parts using various moulding and extrusion technologies. Such bodies are subsequently fired-up and sintered to remove the binder. The utilities of such three-dimensional ceramic bodies depend on the restrictions related to the shapeability of the ceramic suspension, hence to the flow and deformation behaviour of the suspension. In this study, factors affecting the flow and deformation behaviour of a 50% by volume of silicon carbide in a wax binder was investigated. Consistent with the previously observed behaviour of other highly filled materials, the ceramic suspension exhibited viscoplasticity, plug flow and wall slip. Furthermore, flow instabilities associated with the axial migration of the low viscosity binder under the imposed pressure gradient were observed. These results pinpoint to the various difficulties associated with the collection of rheological data and emphasize the relevance of various flow mechanisms, including wall slip and mat formation and filtration based flow instabilities, which would also occur in processing/shaping flows of such ceramic suspensions including extrusion and moulding.

Diffuse reflectance Fourier-transform IR studies on the role of catalyst support on selectivity in ethene oxidation

Abstract Infrared spectroscopy (DRIFTS) was used to study the role of adsorption on the support material on the selectivity to ethylene oxide in ethylene oxidation. With silver catalysts supported on high surface area alumina, no selectivity to ethylene oxide was observed. DRIFTS studies also showed that significant ethylene adsorption on the alumina support was occurring. Further studies on the high surface area alumina support indicated that hydroxyl groups play a major role in ethylene adsorption on the support. With catalysts where there was no evidence of ethylene adsorption on the support, such as silver on low surface area alumina and silver on silica, ethylene oxide was formed.

Formation of Aluminum Nanoparticles upon Condensation from Vapor Phase for Energetic Applications

A mathematical model of the nanoparticles formation process from deposition from the vapor phase process was developed and applied to the manufacture of alumina-coated aluminum nanoparticles. This process involves conversion of gaseous aluminum in the presence of helium carrier gas to solid aluminum nanoparticles. These activities effectively prepare the aluminum for reaction with oxygen gas to create an alumina coating in the remainder of the process. The basis of the calculations is the General Dynamic Equation for aerosols, which was formulated as an explicit numerical equation. The equation is solved over a user specified surface with particle volume (equivalent to particle diameter) and reactor holding time as the independent variables. The solution produces the number distribution function of the nanoparticles over the solution space. After all of the gaseous aluminum has solidified, a moment equation is employed to calculate the number of particles in each of the size distribution ranges. The mathematical model is useful to study the trends on the dependence of the nanoparticle size distribution on the operating parameters such as pressure and temperature profile in the reactor. A number of case studies are included to demonstrate the utility of the mathematical model.

Mathematical Model for a Fed-Batch Crystallization Process for Energetic Crystals to Achieve Targeted Size Distributions

In the manufacture of energetic materials including RDX, HMX, CL-20, it is a challenge to obtain the targeted size distribution. Generally blending is costly and regrinding of the crystals increases the defect densities to give rise to increased sensitivity. The ability to predict apriori the size distribution of various energetic crystalline materials upon recrystallization as a function of the operating conditions, allows the optimization of the process parameters to achieve the desired size distribution without having to regrind or blend different size populations. Here a comprehensive mathematical model of the fed-batch crystallization process consisting of two groups of equations is presented. These include first the dynamic material and energy equations, and second, a population balance model for the prediction of the number density of crystals as a function of time and size as functions of the nucleation and growth kinetics for the particles. A numerical solution to the general problem, which involves the alternate solution of the equations at each time step, was developed considering that the reactor volume changes with each time step. Typical results are presented to demonstrate the utility of the mathematical model of the recrystallization process.

PORE FORMATION IN THE PYROLYSIS OF POLYMERS TO CERAMICS

Fabrication of a nonoxide ceramic SiC from pyrolysis of a polymer precursor, i.e. poly(carbosilane) was investigated. During pyrolysis the generation of small molecules such as hydrogen and methane results in the formation of pores. A mathematical model was developed to study the nucleation and growth of gas bubbles which lead to such pore formation. The mathematical model has the capability of predicting porosity and its distribution which is influenced by temperature, pressure, as well as the thickness, chemistry, and physical properties of the pyrolyzing object Thermogravimetric analysis and scanning electron microscopy were used to study the pore formation and possible cracking during pyrolysis. Submicron pores were observed in the thicker fibers. Based on the best estimate of physical properties, the mathematical model is capable of predicting the critical thickness of the pyrolyzing object for which there will be pore formation.

Transient study of cyclohexane dehydrogenation on PtAl2O3 catalyst in a Constant Flow Stirred Tank Reactor (CSTR)

Transient response data for the cyclohexane dehydrogenation reaction on a commercial Pt Al2O3 catalyst at 1.2 atm and in the temperature range of 555–672 °K was best correlated by a surface coverage type model with simultaneous catalyst deactivation followed by regeneration to the initial level of activity. The nature of the response can be exploited to yield kinetic information on the mechanistic steps of the overall reaction. Preliminary findings on the reaction kinetics indicate that surface reactions of the adsorbed hydrocarbon species and benzene desorption are very rapid (cyclohexane adsorption and hydrogen desorption are slow) and that hydrogen coverage impedes cyclohexane chemisorption.

Dissolution study of BAMO/AMMO thermoplastic elastomer for the recycling and recovery of energetic materials

Abstract This study involves the characterization and dissolution of a thermoplastic elastomer copolymer used as binder in the new generation of energetic materials. The thermoplastic binder is an oxetane based elastomer manufactured by Thiokol Corporation. Since the binder encapsulates other components in an energetic material formulation, its controlled dissolution is crucial to the recovery and recycle of all the energetic material ingredients. The polymeric binder was found to be highly soluble in ethyl acetate and THF. The dissolution rate data obtained under well defined flow dynamics was satisfactorily correlated with the film model. External mass transfer resistance was found to be generally important but became negligible for Reynolds numbers above 6.0×104. The mass transfer coefficients calculated on the basis of the film model were found to be an Arrhenius function of temperature. The activation energy for the dissolution rates was estimated to be 4.8 kcal/mol.

Effect of chemical reaction on particle to gas heat transfer

Abstract Particle to gas heat transfer studies were carried out by employing the endothermic cyclohexane dehydrogenation reaction. The calculated heat transfer coefficients were on the lower side of those previously reported in the literature for unreactive systems. Previous studies of other investigators with reactive systems suggest that particle to gas heat transfer coefficients may increase with exothermic reaction due to the product molecules leaving the catalyst surface with excess vibrational energy. For an endothermic reaction this effect would result in the calculation of a lower heat transfer coefficient.

Disposal of chemical munitions using concomitant neutralization, gelation and encapsulation

Abstract The disposal method developed at SIT involves the conversion of chemical munitions to safely transportable inert products. The main advantage is that the need for incineration at every location where currently munitions are stored is eliminated because the neutralized and encapsulated products are capable of safe transport. The method includes the continuous neutralization and gelation of the highly toxic chemicals and the continuous encapsulation of the neutralized products. A preferred embodiment of our disposal method includes a neutralization process which is accomplished by mixing the highly toxic chemicals along with any wash solution used to clean out the chemical storage containers or weapons with a neutralization agent specifically chosen to neutralize the particular chemical. The mixing occurs in both a mixing head and in a twin screw extruder designed to ensure thorough mixing. After neutralization, the neutralization products are encapsulated in a polymeric binder via a twin screw ext...