Peter O. Osifo

The influence of the degree of cross-linking on the adsorption properties of chitosan beads.

The influence of the degree of cross-linking (DCL) on chitosan beads was studied. Chitosan was prepared from the exoskeleton of Cape rock-lobsters, collected from the surroundings of Cape Town, South Africa. The chitosan beads were characterized; the beads water contents and pKa varied in the range of 90-96% and 4.3-6.0, respectively, and were found to decrease with increasing DCL (0.0-34.0%). A pH-model, which described the reversibility of the metal adsorbed onto the beads, was used to predict the equilibrium properties of copper adsorption onto the cross-linked beads. The model accounts for the effect of pH and the important model parameters, the equilibrium adsorption constant (Kads) and to a lesser extent the adsorbent adsorption capacity (qmax) showed to decrease with the DCL. The adsorbent capacity and the adsorption constant were determined as 3.8-5.0mmol/g chitosan and (9-90)x10(-4), respectively. The adsorption kinetics could be described using a shrinking core model and the effective diffusion coefficient (Deff) was determined as (8.0-25.8)x10(-11)m2/s. It was found that Deff decreases with the DCL mainly due to the decreased in water content of the beads at high DCL.

The adsorption of copper in a packed-bed of chitosan beads: Modeling, multiple adsorption and regeneration

In this study, exoskeletons of Cape rock lobsters were used as raw material in the preparation of chitin that was successively deacetylated to chitosan flakes. The chitosan flakes were modified into chitosan beads and the beads were cross-linked with glutaraldehyde in order to study copper adsorption and regeneration in a packed-bed column. Five consecutive adsorption and desorption cycles were carried out and a chitosan mass loss of 25% was observed, after the last cycle. Despite the loss of chitosan material, an improved efficiency in the second and third cycles was observed with the adsorbent utilizing 97 and 74% of its adsorbent capacity in the second and third cycles, respectively. The fourth and fifth cycles, however, showed a decreased efficiency, and breakage of the beads was observed after the fifth cycle. In the desorption experiments, 91-99% of the adsorbed copper was regenerated in the first three cycles. It was also observed that the copper can be regenerated at a concentration of about a thousand fold the initial concentration. The first cycle of adsorption could be accurately described with a shrinking core particle model combined with a plug flow column model. The input parameters for this model were determined by batch characterization methods, with as only fitting parameter, the effective diffusion coefficient of copper in the bead.

The Influence of Chitosan Membrane Properties for Direct Methanol Fuel Cell Applications

The chitosan membranes with different degrees of deacetylation (dda), prepared from Cape rock lobster collected from the surroundings of Cape Town, South Africa were characterized for suitability in methanol fuel cell applications. A comparison of chitosan membranes characteristics and that of conventional Nafion 117 membranes were made. Following this, the chitosan membranes were chemically modified with sulfuric acid to improve its proton conductivity and mechanical properties. A mass balance on proton transfer across the membrane resulted in a second order differential equation. Experimental data fitted into the equation gives a linear curve that was used to determine the membrane resistance. It was found that the dda of the chitosan membranes affected the water uptake, thereby affecting the proton flow. At a temperature of 20°C, chitosan membranes with a difference of 10% dda have a difference of about 5% water content. Chitosan membranes with a lower dda were found to have higher water content resulting in lower membrane resistances to proton flow. The water content of chitosan membranes was higher than Nafion membranes. The average resistance to proton flow for chitosan membrane was 53 min/cm and a Nafion membrane was 78 min/cm. Thermogravimetry analysis shows that chitosan membrane with higher dda is more thermally stable than chitosan with lower dda, Nafion membranes were more stable at higher temperature than chitosan membranes, Nafion membranes could decompose at temperature of 320 °C while chitosan membranes at 230 °C. Methanol permeability through chitosan membrane of higher dda was more than with one lower dda, however, the permeability through chitosan was three times lower when compares to Nafion membranes under the same temperature and pressure conditions. The performance of chitosan membranes and Nafion 117 membranes measured from a single cell DMFC with Pt-Ru/C anode catalysts and Pt/ C cathode catalysts showed that Nafion membranes have a better performance. This was because the current and peak power densities determined for Nafion membranes were 0.56 A/cm 2 and 0.075 W/cm 2 , respectively, and for Chit-I, were 0.22 A/cm 2 and 0.0274 W/cm 2 respectively, and for Chit-II membrane, were 0.26 A/cm 2 and 0.0424 W/cm 2 , respectively.

Preparation of bagasse ash/CaO/ammonium acetate sorbent and modelling their desulphurization reaction

The influence of siliceous and hydration agents additives on the preparation of calcium-based sorbents for dry flue-gas desulphurization at low temperature was studied. The key reaction variables investigated are: quantity of bagasse ash, hydration temperature, quantity of ammonium acetate and hydration time. Their effect on the surface area of the sorbent was determined and a central composite design was used as a statistical tool. A polynomial model was established to correlate the sorbent preparation parameters to the sorbent surface area. The desulphurization experiments performed with the thermogravimetric analyser indicate higher SO2 removal when bagasse ash and ammonium acetate are used. The kinetics of desulphurization reaction was fitted using the unreacted shrinking core model and the results show that the rate-limiting step was diffusion over the product layer.

The use of impregnated perlite as a heterogeneous catalyst for biodiesel production from marula oil

In this study, biodiesel was produced from marula (Sclerocarya birrea) oil using impregnated perlite with potassium hydroxide (KOH) as a heterogeneous catalyst. The effect of experimental variables such as temperature (°C), reaction time (h), methanol to oil ratio (mass %), and catalyst to oil ratio (mass %) on the transesterification process were investigated. Using a central composite design (CCD), a mathematical model was developed to correlate the experimental variables with the percentage yield of biodiesel. The model showed that optimum conditions for biodiesel production were as follows: catalyst to oil ratio of 4.7 mass %, temperature of 70.4°C, methanol to oil ratio of 29.9 mass %, and reaction time of 3.6 h. The yield of 91.4 mass % of biodiesel was obtained. It was also possible to recycle and reuse the modified perlite up to three times without any significant change in its catalytic activity. The X-ray diffraction (XRD) and the Brunauer-Emmett-Teller (BET) surface area showed no modifications in the perlite structure. The results show that the important fuel properties of marula biodiesel meet the American Society for Testing and Materials (ASTM) biodiesel standard properties.

Evaluation of pyrolytic oil from used tires and natural rubber (Hevea brasiliensis)

ABSTRACT The pyrolysis of used tires, UT, and natural rubber (Hevea brasiliensis), NR obtained from Nigerian NIG800 clonal rubber tree, was performed and the effects of process conditions on product yield were investigated. An optimum yield was attained at operating temperature of 600°C, a heating rate of 15°C min−1, for a feed size of 6 mm. The UT and NR gave maximum pyrolytic oil yield of 34.40 and 75.93 wt%, respectively. The pyrolytic oil was characterized using Fourier transform infrared, nuclear magnetic resonance, and gas chromatography–mass spectrometry (GC–MS). Results obtained reveal the pyrolytic oil to be a complex mixture, mainly of aliphatic and aromatic compounds, which can serve as feedstock for industrial application. Nevertheless, a comparative evaluation of the physical and chemical properties of the UT and NR pyrolytic oil showed that NR had hydrocarbon composition of 80% aliphatics, 12% aromatics (with less than 2% polycyclic aromatic hydrocarbon concentration). However, the UT pyrolytic oil had 42% aliphatic and 34% aromatic compounds (with polycyclic aromatic hydrocarbons concentrations of 18%). Also, NR pyrolytic oil had better physical properties such as density, viscosity, flash point, pour point, and higher heating value than that produced from UT in this study, and comparable with that of commercial diesel. Moreover, sulfur content, which is a limiting factor in the direct combustion of UT pyrolytic liquid, was absent in NR pyrolytic oil. Hence, it is technologically feasible for NR from H. brasiliensis to be a suitable source of pyrolytic oil than UT.