Volume 13 (2011): Issue 4 (December 2011)

This paper presents the feasibility of the removal of hexavalent chromium ions from aqueous solutions by using activated carbon prepared from Cajanus Cajan(L) Milsp. It was carbonized and activated by treating it with concentrated sulfuric acid followed by heating for 5 h at 500°C. Batch adsorption experiments were carried out as a function of pH, contact time, initial concentration of the adsorbate, adsorbent dosage and temperature. The experimental data fitted well to the Freundlich isotherm. The thermodynamic parameters such as ΔH°, ΔS°, and ΔG° were calculated, which indicated that the adsorption was spontaneous and endothermic in nature. The adsorbent used in this study was characterized by FT-IR and SEM before and after the adsorption of metal ions. The results indicate that Cajanus Cajan(L) Milsp can be employed as a low cost alternative and commercial adsorbents in the removal of chromium (VI) from water and waste water.

Humic acid Leonardite IHSS standard was decomposed on TiO₂ and TiO₂ modified by FeC₂O₄ via the photocatalysis and photo-Fenton processes under UV irradiation. Humic acid (HA) were favorable adsorbed on TiO₂ surface and followed decomposition during UV irradiation faster on TiO₂ than on the modified samples. However, when H₂O₂ was added to the solution, the photo-Fenton process occurred on the prepared TiO₂ samples, contained iron together with photocatalysis and high acceleration of HA decomposition was observed. In this case the mineralization degree was much higher than in the applied photocatalysis only, around 75% HA (with concentration of 18 mg/L) was mineralized after 3 h of adsorption and 5 h of UV irradiation in the presence of H₂O₂ and modified TiO₂ whereas on TiO₂ mineralisation of HA occurred in around 45% only. The measured fluorescence spectra of HA solutions showed that in the presence of H₂O₂ polycyclic aromatics were rapidly oxidized to the lower size products such as alcohols, aldehydes, ketones and carboxylic acids, what accelerated the process of HA decomposition.

In this study, Aspergillus oryzae β galactosidase was immobilized on concanavalin A layered calcium alginate-cellulose beads as a bioaffinity support. Immobilized enzyme showed a remarkable broadening in temperature-activity profiles as compared to the native enzyme and exhibited 65% activity in the presence of 5% galactose. Michaelis constant (K_m) was 2.57 mM and 5.38 mM for the free and the immobilized β galactosidase, respectively. Crosslinked β galactosidase showed greater catalytic activity in the presence of Mg²⁺ and was more stable during storage at 4°C for 6 weeks. Immobilized enzyme hydrolyzed 67% lactose in milk in 8 h and 85% lactose in whey in 9 h in the stirred batch process at 50°C. The continuous hydrolysis of lactose by crosslinked β galactosidase in spiral bed reactor exhibited 93% and 88% hydrolysis of lactose at flow rate of 20 ml/h and 30 ml/h, after 1 month operation, respectively.

The paper presents determination of the effect of various chemical treatment on the strength of 288 tex jute yarn arisen from the plain weave fabric produced by LENTEX, Poland. The yarn was put to alternative treatments in: NaOH and KOH water solutions with various concentration (from 1 to 15%) and treatment duration (from 0.5 to 6 hours), vinyl acetate, methanol and toluene diisocyanate. After the treatment it was put to tensile tests. Yarn diameter and elementary fibre twist angle were also measured using MICRO PROF FRT optical profilographometer. The SEM micro-photographs have also been performed in order to evaluate the structural changes of the yarn after the treatment.

Optimal conditions of alcali-treatment are: 5% concentration and 2h duration for NaOH, 3% concentration and 4h duration for KOH. Such treatments give a growth in yarn rupture force up to 10% and they are well applicable in composite materials manufacturing. Also interaction with vinyl acetate and toluene diisocyanate has practically not negative influence on the mechanical performance of the yarn. Two effects were observed which can explain the influence of chemical treatment on mechanical performance of jute yarn: swelling and change in the orientation of elementary fibres.

A method was developed to attach 2,2-bipyridine (BP) onto a silica gel surface by a two-step reaction. The first step consisted of a reaction between the matrix and a silylating agent, 3-chloropropyltrimethoxysilane. In the second step of the reaction, a ligand molecule was attached onto Si-CPTS, yielding the product Si-BP. The modified material contained 0.431±0.01 mmol of 2,2-bipyridine per gram of modified silica, as confirmed by FT-IR spectra of the proposed structure. The surface modification was characterized by the BET technique, which revealed a decrease in the surface area from 614 to 450 m² g^-1. The series of adsorption isotherms for the metal ions were adjusted to fit a modified Langmuir equation. The maximum number of moles of copper, cadmium and lead ions adsorbed was 0.64, 0.53, and 0.54 mmol g^-1, respectively. The surface saturation was calculated as φ fraction and the values obtained, Cu(II) = 1.160, Cd(II) = 1.044 and Pb(II) = 0.997, suggest a type 1:1 metal-ligand complex.

The CFD modelling of heat transfer in the packed bed column in the laminar and turbulent flow regimes has been presented. Three numerical grids with different densities were generated for the packed bed column. The modelling was performed with the use of the Porous Media Model for treating the flow inside a porous structure. The standard k-ε model along with the logarithmic wall functions for the turbulent flow range was used. The influence of the mesh size on the accuracy of the fluid flow was studied. Both radial and axial direction temperature distributions have been compared with the experimental data¹ and the values calculated from a 2DADPF model. A good agreement between the experimental and the predicted values of the pressure drop, temperature distributions and heat transfer coefficient was obtained.

Porous carbons loaded with magnesium oxide were prepared through one-step process. Poly(ethylene terephthalate) and natural magnesite were used as carbon source and MgO precursor, respectively. An impact of a temperature and relative amounts of raw components used for preparations on the textural parameters of resulting hybrid materials is presented and discussed. As found, pore structure parameters tend to decrease along with MgO loading and temperature used during preparation process. Micropore area is the parameter being reduced primarily.

In this research, mathematical modeling of a duct heater has been performed using energy conservation law, Stefan-Boltzman law in thermal radiation, Fourier's law in conduction heat transfer, and Newton's law of cooling in convection heat transfer. The duct was divided to some elements with equal length. Each element has been studied separately and air physical properties in each element have been used based on its temperature. The derived equations have been solved using the finite difference method and consequently air temperature, internal and external temperatures of the wall, internal and external convection heat transfer coefficients, and the quantity of heat transferred have been calculated in each element and effects of the variation of heat transfer parameters have been surveyed. The results of modelling presented in this paper can be used for the design and optimization of heat exchangers.

The optimal conditions were determined for the precipitation of ammonium metavanadate from the solutions of ammonium nitrate with the use of sodium metavanadate. The experiments were performed with the molar ratio of salts NH₄NO₃: NaVO₃ 1.5:1 at temperatures 293, 303, 313 and 323 K. Based on the obtained results, the optimal time of the process was determined as 5 h at 293-303K. Under these conditions, the achieved yield of the precipitation process was ~98.7%, while the contents of the vanadium salts in the post - filtration solution was ~0.02%.

The activity of Pd/Al₂O₃ catalysts increases when Pd content is increased from 1% to 2%. Among these catalysts, 2%Pd/Al₂O₃ shows the highest methane combustion activity. In a reduced form, the catalyst displays a higher activity than in the oxidized form. 24-hour ageing at 600°C to 800°C lowers the catalytic activity of 2%Pd/Al₂O₃ due to Pd crystallite sintering. After 110-hour oxidation of 1% methane in air over 2%Pd/Al₂O₃, conversion decreases from 100% to 88%. Upon reduction with hydrogen (performed after 24-hour ageing at 700°C and 110-hour methane oxidation), the 2%Pd/Al₂O₃ catalyst regains its initial activity. The high activity of Pd catalysts renders them suitable for methane removal from coal mine ventilation air at high gas flow velocities and temperatures lower than 600°C.

The microporous carbon materials were prepared by chemical activation of Polish coal with potassium hydroxide using the simplex design method for planning the experiments. The experimental parameters were varied to identify the optimum conditions. Coal can be an excellent starting material for the preparation of high porous carbons for natural gas storage. The porosity of the resultant carbons was characterized by nitrogen adsorption (-196°C). Methane adsorption was investigated in a volumetric laboratory installation at range pressures from 1 to 3.5 MPa (25°C).

The best results of methane storage capacity (557 cm³ · g^-1) were obtained when using an impregnation ratio 3.41/1 KOH/precursor and temperature at 592°C, (S_LANG = 2091 m² · g^-1). The parameters of the preparation of high porosity and high methane adsorption carbon were determined by a fast and simple method.

High activity of copper based catalysts for C-O bond hydro-dehydrogenation and their poor activity for C-C bond cleavage1 have prompted an attempt to apply such catalysts in the hydrogenolysis of glycerol to 1,2- and 1,3-propanediol. In the present study the influence of hydrogen reduction time of the Cu/Al₂O₃ and CuCr₂O₄ copper catalysts on glycerol conversion and selectivity of transformation to propanediols and by-products was studied. At first a general comparison was made between the commercial catalysts and those prepared by the co-precipitation method. As better results were obtained in the presence of catalysts prepared by co-precipitation, they were selected for further detailed studies of the influence of reduction time. For both prepared catalysts Cu/Al₂O₃ and CuCr₂O₄ the reduction time of 8 h was optimal. In the presence of Cu/Al₂O₃ catalyst the conversion of glycerol was 59.0%, selectivity of transformation to 1,2-propanediol 77.4% and selectivity to 1,3-propanediol 1.9%. In the presence of CuCr₂O₄ the glycerol conversion was 30.3% and selectivity to 1,2-propanediol 67.3%.

Acrylic pressure-sensitive adhesives (PSA) are non electrical conductive materials. The electrical conductivity is incorporated into acrylic self-adhesive polymer after adding electrically conductive additives like carbon black, especially nano carbon black. After an addition of electrical conductive carbon black, the main and typical properties of pressure-sensitive adhesives such as tack, peel adhesion and shear strength, are deteriorated. The investigations reveals that the acrylic pressure-sensitive adhesives basis must be synthesised with ameliorated initial performances, like high tack, excellent adhesion and very good cohesion. Currently, the electrical conductive solvent-borne acrylic PSA containing carbon black are not commercially available on the market. They are promising materials which can be applied for the manufacturing of diverse technical high performance self-adhesive products, such as broadest line of special electrically conductive sensitive tapes.

A plant waste, rubber (Hevea brasiliensis) leaf powder was modified with carbon disulfide (xanthation) for the purpose of introducing sulfur groups, and the adsorbent performance in removing Pb(II) ion was evaluated. Pb(II) adsorption was confirmed by spectroscopic analysis, which involved Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The amount of Pb(II) adsorbed increased with increasing pH, contact time and concentration but slightly decreased with increasing ionic strength. Adsorption equilibrium was achieved in less than 60 min and followed the pseudo-second order model. The isotherm data indicated that Pb(II) adsorption on xanthated rubber leaf (XRL) fitted well with Langmuir isotherm model. The maximum adsorption capacity computed from the Langmuir isotherm model was 166.7 mg/g. Pb(II) adsorption occurred via ion-exchange and complexation mechanisms.