In this work, zeolite Beta was synthesized experimentally in order to be used as filler in fuel cell membranes in order to assess the proton conductivity of composite membranes. Effects of the Si/Al ratio, and synthesis time on yield, relative crystallinity, crystal size, and proton conductivity were investigated. Zeolite Beta with Si/Al ratio between 10 and 30 was synthesized with a batch formulation of 2.2Na2O:1Al2O3:ySiO2:4.6(TEA)2O:tH2O (where TEA&amp / #8801 / tetraethylammonium) at 150&deg / C for 5-15 days of synthesis time. Sodium aluminate, tetraethylammonium hydroxide (TEAOH) solution, sodium hydroxide pellets (NaOH), and deionized water were used for the preparation of the batch solution. Zeolite Na-Beta was calcined and treated with sulfuric acid solution at different concentrations in order to have zeolite H-Beta. Polyetherether ketone (PEEK) was sulfonated in order to have a proton conductive membrane and than zeolite H-Beta was incorporated resulting in a composite or nanocomposite membrane. X-ray diffraction (XRD) analysis helped to understand whether the synthesized material was zeolite Beta or not. The morphology and the crystal size of the crystals were observed as a result of the scanning electron microscopy (SEM) analysis. In order to see the effect of sulfuric acid treatment on the sodium (Na) content of the zeolite Beta, inductively coupled plasma (ICP) analysis was performed. Synthesis results indicate that as Si/Al ratio and synthesis time increased the yield of zeolite Beta increased. It was observed that Si/Al ratio from 10 to 30, and synthesis time between 5 to 15 days did not affect the crystal size significantly. For the sulfonation of PEEK, sulfuric acid was used. Sulfonated polyetherether ketone (SPEEK) was dissolved in a solvent that was dimethyl acetamide (DMAC), incorporated with zeolite Beta, and then solvent was removed in the vacuum oven. The proton conductivity was measured with a 2-probe impedance spectrometer. Initial results indicate that zeolite Beta at 10 and 20 wt % loadings did not affect the proton conductivity of the SPEEK membrane at 100 % relative humidity and room temperature.

Caffeine is a commercially important member of a group of purine alkaloids found in coffee, tea and cacao particularly. It is an important ingredient in beverages and most important chemical element of stimulating pharmaceuticals. Caffeine is either manufactured by total synthesis or as a by-product from the decaffeinated coffee manufacturing. To investigate the equilibrium relationship of caffeine in ion exchange systems, which are widely used for recovery and purification processes, was the aim of this study. The effects of initial caffeine concentration and pH of the solution on equilibrium were also investigated. Stock solutions of caffeine were prepared for screening of available adsorbents and cation exchange resins. A batch type operation was carried out in a shaker bath at 40 oC with 200 rpm agitation rate. After preliminary experiments, only Lewatit S100, which is a strongly acidic cation exchange resin with s-dvb copolymer matrix, was studied. For the analysis of samples, HPLC equipment with Shimadzu PDA Detector at 254 nm and Nucleosil 100 C18 column was used. As mobile phase, a mixture of 8% acetonitrile, 8% 2-Propanol, and 1% acetic acid was introduced at 1.5 mL/min flow rate. Results showed that, the caffeine uptake capacity of cation exchange resin was poor. A set of experiments were performed at three initial concentrations (0.005 M, 0.0075 M, and 0.01 M) and four different pH regions (acidic, slightly acidic, neutral, and basic). It was found that, at extreme pH conditions, the caffeine loading capacity of the resin was slightly increased. A significant effect of initial caffeine concentration, however, couldn&rsquo / t be observed. Due to the poor performance of gel type cation exchange resin and large molecular structure of caffeine molecule, Lewatit&rsquo / s SPC 112 macroporous resin was studied briefly for caffeine uptake performance. It was observed that SPC 112 has also poor but better loading capacity than S100 cation exchange resin.

Composite propellants are mainly composed of: crystalline oxidizer, metallic fuel, and polymeric binder. Additives, such as plasticizers, catalysts, bonding agents and curing agents may also be incorporated to propellant compositions in small amounts. These ingredients should be mixed rigorously in order to obtain a uniform microstructure throughout the cast propellant profile. The quality of the propellant mixture has to be determined quantitatively to improve the product quality and to reduce costs. In this study, it was aimed to develop an easy, cost effective and rapid test method for determining the optimum mixing conditions for the manufacturing process of solid rocket propellants. An analytical method used in the literature for assessing mixing quality in highly filled polymeric systems is wide-angle x-ray diffractometry (WA-XRD). After finding out the concentration distribution of the components indirectly by WA-XRD, degree of mixing was identified using statistical methods. To accomplish this, series of samples were taken from various locations of the mixing chamber and analyzed by WA-XRD. Degree of mixing calculations based on ratio of intensity arising from aluminum phase over total crystal intensity, and the ratio of intensity arising from ammonium perchlorate phase over total crystal intensity gave satisfactory results. Radial mixing efficiency of planetary mixer was determined, and it was found that mixing at the center was more effective than mixing at the outer regions. Also, by scanning electron microscopy technique (SEM), interactions between binder and solid loading during mixing process were observed. It was seen that polymeric matrix gradually encloses solid particles during mixing.

A dynamic mathematical model for simulation of atmospheric circulating fluidized bed combustors has been developed on the basis of first principles and empirical correlations. The model accounts for dense and dilute zone hydrodynamics, volatiles release and combustion, char particles combustion and their size distribution, and heat transfer from/to gas, particles, waterwalls and refractory. Inputs to the model include configuration and dimensions of the combustor and its internals, air and coal flows, coal analysis, all solid and gas properties, inlet temperatures of air, cooling water, and feed solids, size distribution of feed solids / whereas outputs include transient values of combustor temperatures, gas concentrations, char and inert hold-ups and their size distributions. The solution procedure employs method of lines approach for the governing non-linear partial differential equations and combined bisection and secant rule for non-linear algebraic equations. The initial conditions required for the model are provided from the simultaneous solution of governing equations of dynamic model with all temporal derivatives set to zero. By setting all temporal derivatives to zero, model can also be utilized for steady state performance prediction. In order to assess the validity and predictive accuracy of the model, it was applied to the prediction of the steady state behavior of Technical University of Nova Scotia 0.3 MWt CFBC Test Rig and predictions were compared with measurements taken on the same rig. Comparison of model predictions at steady state conditions revealed that the predictions of the model are physically correct and agree well with the measurements and the model is successful in qualitatively and quantitatively simulating the processes taking place in a circulating fluidized bed combustor.

Acid Doped Polybenzimidazole Membranes for High Temperature Proton Exchange Membrane Fuel Cells Author: Ahmet &Ouml / zg&uuml / r Yurdakul One of the most popular candidates for high temperature PEMFC&rsquo / s is phosphoric acid doped polybenzimidazole (PBI) membrane due to its thermal and mechanical stability. In this study, high molecular weight PBI was synthesized by using PPA polymerization. The stirring rate of reaction solution was optimized to obtain high molecular weight. The inherent viscosity of polymer was measured at four points in 96 percent sulphuric acid solution at 30 degree centigrade by using an Ubbelohde viscometer. The highest average molecular weight was found as approximately 120,000 using the Mark-Houwink equation. The polymer was dissolved in N,N-dimethylacetamide at 70 degree centigrade with an ultrasonic stirrer. The membranes cast from this solution were doped with phosphoric acid solutions at different concentrations. The doping levels of the membranes were 6, 8, 10 and 11 moles phosphoric acid/PBI repeat unit. The mechanical strength of the acid doped membranes measured by tensile tests were found as 23, 16, 12 and 11 MPa, respectively. Conductivity measurements were made using the four probe technique. The membranes were placed in a conductivity cell and measurements were taken in humidity chamber with temperature and pressure control. The conductivity of membranes was measured at 110, 130 and 150 degree centigrade in both dry air and water vapor. The highest conductivity was 0.12 S/cm at 150 degree centigrade and 33 percent relative humidity for the membrane doped with 11 moles of H3PO4. The measurements showed that conductivity increased with increasing doping and humidity. Moreover, membranes had acceptable conductivity levels in dry air.

Zeolites are nanoporous crystalline aluminosilicates that are tasteless, odorless and nontoxic to humans. They can be tailored into antibacterial agents that are more cost effective than other conventional alternatives. Considering the increasing demand for enduring antibacterial agents, the potential uses of antibacterial zeolites are numerous in medical applications and for everyday household products. To produce antibacterial zeolites, the extra framework cations in the zeolite structures can be exchanged with silver ion (Ag+), the most commonly used antibacterial heavy metal ion due to its high stability, strong activity and broad spectrum. Utilization of antibacterial zeolite powders can be diversified when they are used as fillers in a polymer matrix. Polyurethanes (PU) are a class of polymers which can be prepared in wide range of physical structures with excellent mechanical properties. Ag+ loaded zeolites used as fillers in the PU matrix would contribute to the diversity and efficiency of the PU utilization in many applications including biomedical uses and consumer products. In this study, three types of zeolites, namely / zeolite Beta, X and A with different pores sizes and SiO2/Al2O3 ratios were synthesized hydrothermally and treated with Ag+ containing solution for the exchange of cations. Composites were prepared by incorporation of sieved Ag+ exchanged zeolite particles into biomedical grade PU prepolymers which were prepared either in film or as sponge forms. Films were prepared by molding and foams were prepared in the presence of water as the blowing agent. Liquid media antibacterial tests showed that all of the Ag+-zeolite powders were effective against E. coli at a concentration of 500 ppm zeolite in deionized water. To assess the antibacterial effect of composites against E. coli, disc diffusion tests were carried out. Bacterial growth inhibition zones formed around the composite samples were the evidence of the antibacterial activity in the vicinity of the surface. All three kinds of zeolites successfully introduced the desired antibacterial property to the biomedical grade PU both in elastomeric film and in the foam form. Mechanical characterization of the composites yield higher ultimate tensile strength, modulus of elasticity and elongation at break values compared to control PU. No significant change in thermal properties of the composites was observed. Hence mechanical and thermal characterization of the composites showed that zeolites serve for the reinforcement of the mechanical properties of the polymer and did not cause any deterioration in thermal properties.

Zeolite membrane synthesis is conventionally carried out in batch systems. Recently, several attempts have been performed to synthesize zeolite membranes in flow systems which can allow preparation of membranes with large specific surface areas. Membranes synthesized in the recirculating flow system had comparable N2/SF6 and n- C4H10/i-C4H10 ideal selectivities with the membranes prepared in the batch system, indicating that good quality membranes can be produced by this method. The objective of this study is to separate organic/water mixtures by pervaporation by using MFI type membranes synthesized in the flow system. Effect of number of synthesis steps and synthesis method on the separation factor and flux was investigated. Membranes were synthesized from clear solutions with a molar composition of 80SiO2:16TPAOH:1536H2O at 95oC and atmospheric pressure. The synthesis solution was recirculated through the tubular alumina support with a flow rate of 6 ml/min for 72 h. The membranes were characterized by X-ray diffraction for phase identification and scanning electron microscopy for morphology determination. Single gas permeances of N2, H2, CH4, CO2, n-C4H10 and i-C4H10 were measured between 25 and 200oC. Mixtures of 5 wt% ethanol/water, 2-propanol/water and acetone/water were separated by pervaporation at different temperatures. The single gas permeances decreased with increasing temperature for weakly adsorbed gases. For n-C4H10 the permeance passed through a maximum and i-C4H10 permeance was nearly constant. For a membrane synthesized by two consecutive synthesis steps, the ideal selectivity for n-C4H10/i-C4H10 was 132 at 200oC. The selectivity in the pervaporation separation of ethanol-water mixture was 43 with a permeate flux of 0.2 kg/m2h at 25oC. With increasing temperature, selectivity decreased but the flux increased, the selectivity was 23 and the flux was 1.9 kg/m2h at 85oC. 2-propanol/water and acetone/water separation factors were 36 and 1024 with 0.2 and 0.1 kg/m2h fluxes, respectively. The separation factors and fluxes for membranes synthesized in the flow system were comparable with membranes synthesized in the batch system.

The world&rsquo / s being alerted to the global warming danger and the depletion of fossil fuel resources, has increased the importance of the clean and renewable hydrogen energy. Bioethanol has high potential to be used as a resource of hydrogen since it is a non-petroleum feedstock and it is able to produce hydrogen rich mixture by steam reforming reactions. Discovery of mesoporous MCM-41 type high surface area silicate-structured materials with narrow pore size distributions (20-100 &Aring / ) and high surface areas (up to 1500 m2/g) opened a new avenue in catalysis research. Catalytic activity of such mesoporous materials are enhanced by the incorporation of active metals or metal oxides into their structure. Nickel and copper are among the most active metals to be used in steam reforming of ethanol to produce hydrogen. In this study, copper and nickel incorporated MCM-41 type catalytic materials were tested in the steam reforming of ethanol. Two Ni-MCM-41 samples having different Ni/Si ratios were prepared by high temperature direct synthesis method and two Cu-MCM-41 samples having same Cu/Si ratios were synthesized by two different methods namely, high temperature direct synthesis method and impregnation method. The synthesized materials characterized by XRD, EDS, SEM, N2 physisorption and TPR techniques. XRD results showed that Ni-MCM-41 and Cu-MCM-41 catalysts had typical MCM-41 structure. The d100 and lattice parameter values of Ni-HT (I) (Ni-MCM-41 sample having 0.036 Ni/Si atomic ratio) was obtained as 3.96 and 4.57 nm., respectively. In addition Ni-HT (I) was found to have a surface area of 860.5 m2/g and 2.7 nm pore diameter. The d100 and lattice parameter values for a typical Cu-MCM-41 prepared by impregnation method having Cu/Si atomic ratio of 0.19 were obtained as 3.6 and 4.2 nm., respectively. This sample also has a 631 m2/g surface area and 2.5 nm pore diameter. Steam reforming of ethanol was investigated in the vapor phase by using Ni-MCM-41 and Cu-MCM-41 catalysts between 300&deg / C and 550&deg / C. Results proved that Ni incorporated MCM-41 type catalytic materials were highly active in hydrogen production by steam reforming of ethanol and actualized almost complete ethanol conversion for Ni-MCM-41 having Ni/Si atomic ratio of 0.15 over 500&deg / C . The side products obtained during reforming are methane and formaldehyde. Although the Cu-MCM-41 samples were not as active as Ni-MCM-41, it was observed that Cu-MCM-41 catalyst synthesized by the impregnation method showed an ethanol conversion of 0.83. However, the main product was ethylene with the copper incorporated catalysts. Effects of space time, the operating conditions (reaction temperature), metal/Si ratio of the catalyst and the preparation method on the product distributions were also investigated and best reaction conditions were searched.

During the last decades, batch distillation is preferably used with an increasing demand over continuous one, to separate fine chemicals in chemical and petroleum industries, due to its advantages like, flexibility and high product purity. Consequently, packed distillation columns, with newly generated packing materials, are advantageous compared to plate columns because of their smaller holdups, resistivity to corrosive materials and their higher separation efficiencies. Also, in many industrial applications, mathematical models of distillation systems are frequently used in order to design effective control systems, to train operating personnel and to handle fault diagnostics. Thus, the main objective of this study is to develop a mathematical model for a multicomponent batch distillation column, which is used to separate mixtures at low operating pressures, packed with random packing materials. In multicomponent batch packed distillation, operation with optimum reflux ratio profile is important for efficiency to maximize the amount of the distillate with a specified concentration, for a given time. Therefore, it is also aimed to find the optimum reflux ratio profile for the multicomponent batch packed distillation column. A simulation algorithm is written with the aid of MATLAB and FORTRAN programming languages by taking into account pressure drop and variation of physical properties. The selected incremental bed height, &amp / #916 / z, to be used in the simulation program has an effect on the accuracy of the results. This is analyzed and the optimal incremental height is found to be 3.5 cm for a 1.5m bed height. The change in distillate compositions with a given constant reflux ratio is found to be similar with those of previous studies. The simulation code is also used to obtain responses in distillate compositions for different reflux ratios, condenser holdups and reboiler duties and compared with similar studies found from literature and found to be adequate. Finally, experiments are conducted to verify simulation algorithm by using a lab-scale packed distillation column for the separation of a polar mixture of ethanol and water. It is observed that, there is a good agreement between the experimental and simulation results. After the verification of dynamic model, optimum operation policy to maximize product amount is investigated numerically by using capacity factor approach. The column is operated with and without recycling of the holdups of the slop cut tanks, in order to examine the effect of recycling on capacity factor, CAP. It is observed that, recycling of the molar holdups of the slop cut tanks is resulted in a 28% increase in the separation efficiency.

Co-firing of biomass with coal in fluidized bed combustors is a promising alternative which leads to environmentally friendly use of coal by reducing emissions and provides utilization of biomass residues. Therefore, effect of biomass share on gaseous pollutant emissions from fluidized bed co-firing of various biomass fuels with high calorific value coals have extensively been investigated to date. However, effect of co-firing of olive residue, hazelnut shell and cotton residue with low calorific value lignites having high ash and sulfur contents has not been studied in bubbling fluidized bed combustors to date. In this thesis study, co-firing of typical Turkish lignite with olive residue, hazelnut shell and cotton residue in 0.3 MWt METU Atmospheric Bubbling Fluidized Bed Combustion (ABFBC) Test Rig was investigated in terms of combustion and emission performance and ash behavior of different fuel blends. The results reveal that co-firing of olive residue, hazelnut shell and cotton residue with lignite increases the combustion efficiency and freeboard temperatures compared to those of lignite firing with limestone addition only. O2 and CO2 emissions are not found sensitive to increase in olive residue, hazelnut shell and cotton residue share in fuel blend. Co-firing lowers SO2 emissions considerably while increasing CO emissions. Co-firing of olive residue and hazelnut shell has no significant influence on NO emissions, however, reduces N2O emissions. Co-firing cotton residue results in higher NO and N2O emissions. Regarding to major, minor and trace elements partitioning, co-firing lignite with biomasses under consideration shifts the partitioning of these elements from bottom ash to fly ash. No chlorine is detected in both EDX and XRD analyses of the ash deposits. In conclusion, olive residue, hazelnut shell and cotton residue can easily be co-fired with high ash and sulfur containing lignite without agglomeration and fouling problems.