http://rulrepository.ru.ac.bd/handle/123456789/105 2026-04-07T21:46:24Z 2026-04-07T21:46:24Z Azad, Md. Abul Kalam http://rulrepository.ru.ac.bd/handle/123456789/1145 2025-07-15T08:56:44Z 2004-12-01T00:00:00Z

Synthesis and Characterization of Solid Catalysts Azad, Md. Abul Kalam Amorphous silica-alumina catalysts having different silicon aluminum ratios were prepared. The Brönsted surface acidity of these catalyst samples was measured by the base exchange method using aqueous CHCOONH solution and the results were compared with those measured by the base exchange method using NH4OH and KOH as adsorbates from aqueous solution. The amount of NH4' in CH3COONH4 and NH4OH and K in KOH adsorbed was determined by spectrophotometrically and titrimetrically respectively by measuring the concentration of NH4 and K in the solution before and after adsorption. Variation of surface acidity of catalyst samples-A (synthesized without pore regulating agent), sample-B (synthesized with tetramethylammonium bromide as a pore regulating agent) and sample-C (synthesized with pore regulating agent and base exchanged with NILCI solution to obtain H' form by calculation) have been studied using different concentrations of ammonium acetate, ammonium hydroxide and potassium hydroxide solutions. It has been observed that the surface acidity of a given size catalyst increases with the increasing of concentration of CH3COONH, NH4OH and KOH but dilute solutions of CHCOONH, NH4OH and KOH are sufficient to saturate the catalyst surface. It has been observed that the surface acidity of the catalyst samples found by using CHCOONI, is greater than that of NH4OH and KOH: Of the two bases NH4OH gives slightly greater surface acidity than that of given by KOH. At a given concentration of CH3COONH, NH4OH and KOH solutions the surface acidity was more pronounced when ammonium acetate solution was used as an adsorbate. A plausible explanation for this discrepancy is that with the use of NH4OH and KOII as bases considerable dealumination takes place with a consequent decrease of surface acidity of the catalyst samples. In all cases, the surface acidity was found to increase with the decrease of sample size. Surface acidity was also found to increase as the Al content of the catalyst was increased. The surface acidity of the catalyst samples-13 and C are greater than that of sample-A. But this increase of surface acidity is more noticeable in case of sample-C. Iron(III) dispersed on silica was prepared by the incipient wetness method and its surface acidity measured by CH3COONH, solutions was found negligibly small and was comparable to that of chromatographic silica and alumina. Finally, the Brönsted surface acidity of the catalyst sample-A measured by the base exchanged method using ammonium acetate has been found to be well correlated with the equilibrium pH of CH3COONH4 solution. This may therefore, be concluded that surface acidity of silica-alumina catalyst depends on its mode of preparation, sample size, ratio of Si:Al and concentration of titrants although very dilute solutions of titrants are sufficient to saturate the catalyst surface. A weak base like CH3COONH4 gives comparatively high values of surface acidity of all the silica-alumina catalyst samples where dealumination from the silica-alumina catalyst samples are supposed to be negligible. The total surface acidity of the silica-alumina catalyst sample was also determined by the Tamele method (Amine titration method). Considering the carcinogenic effect of benzene and toxicity of n-butylamine substitutes of benzene as a solvent and n- butylamine as a titrant have been sought. With this end in view attempts have been made to modify the Amine titration method by replacing benzene with cyclohexane or n-hexane or n-heptane and replacing n-butylamine by di-n-butylamine or di-iso- butylamine or sec-butylamine. For this parameters varied were concentration of di-n- butylamine, di-iso-butylamine, n-butylamine and sec-butylamine solutions, sample size of catalyst and types of catalyst samples. The results in the present investigation show that surface acidity of catalyst samples tends to increase with the decrease of catalyst sample size. Unlike Brönsted acidity for a given size of sample the total surface acidity tends to increase with the silicon content of the catalyst sample. For bases, the total surface acidity of various catalyst samples increase in the order of di-iso- butylamine<di-n-butylamine<sec-butylamine<n-butylamine. A concentration of 0.5N solutions of organic bases is sufficient to saturate the catalyst surface. Since the total surface acidity of all the catalyst samples are greater when cyclohexane is used as solvent compared to that when n-hexane and n-heptane are used as solvents a modified Tamele method has been suggested replacing benzene with cyclohexane as a solvent. It has been found that using dilute solutions of di-n-butylamine, di-iso-butylamine, n- butylamine and sec-butylamine in cyclohexane (or n-hexane or n-heptane) total surface acidity of silica-alumina catalyst can successfully be measured. Preferential heat of adsorption of pyridine in n-heptane solution on silica-alumina amorphous catalyst and Fe-SiO2 samples have been measured by a flow micro- calorimeter. For comparison preferential heats of adsorption of pyridine on a standard sample of ZSM-5 and SiO2 and Al2O3 have also been measured. The total surface acidity measured by the n-butylamine titration method of all the catalyst samples have been correlated with the integral heat of adsorption. A good correlation of surface acidity with the integral heat indicates that the flow micro-calorimeter method may be used as a standard technique for characterizing solid catalysts. Both in the base exchange method and amine titration method increase of concentration bases give increased values of surface acidity with surface acidity versus concentration of bases plots resembling BET type-1 (Langmuir type- monolayer) adsorption isotherms. Similarly, plots of integral heat of adsorption versus concentration of ammonium acetate for ZSM-5, Ferrisilicate-Fe-SiO2 and Aluminosilicate with Si:Al ratio of 90:10 resemble BET type-1 isotherms but aluminosilicate samples with Si:Al ratio of 70:30 and 50:50 give integral heat of adsorption versus concentration of ammonium acetate solution plots resembling BET type-II (multilayer) adsorption isotherms. This may, therefore, be concluded that the nature of interaction of the inorganic bases with the Brönsted acid sites remain the same for all types of catalyst. But organic bases like n-butylamine and pyridine are able to interact with both the Brönsted and the Lewis acid sites and their nature and extent of interaction with the catalyst sample varies with the type of catalysts. It may finally be concluded that for the measurement of Brönsted acidity ammonium acetate, CH3COONH4 as a base occupy a favorably distinct position so also for the amine titration method n-butylamine occupy a favorably distinct position. This is further concluded that the carcinogenic compound, benzene, may successfully be replaced by cyclohexane as solvent in the amine titration method (Tamele method). This Thesis is Submitted to the Department of Applied Chemistry and Chemical Engineering , University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD)

2004-12-01T00:00:00Z Singha, Hari Prosad http://rulrepository.ru.ac.bd/handle/123456789/1144 2025-07-15T08:54:06Z 2006-05-01T00:00:00Z

Some Physico-Chemical Properties of Cyanex 272 and Extraction of Some Metal Ions Singha, Hari Prosad Using a reported technique for purifying organophosphorous extractants, the as-received Cyanex 272 extractant containing 85% bis-2,4,4-trimethylpentyl- phosphinic acid [BTMPPA] has been purified to a purity of about 99% BTMPPA. The purified reagent has been characterized and compared to the literature values. A technique for the colorimetric estimation of purified Cyanex 272 has been developed. It consists of the digestion of pure sample or its aqueous solution (after evaporating out most of water) with concentrated HNO3 (70%) - HCIO (70%) mixture at 2:1 ratio for 1 h. The oxidizing mixed acid quantitatively converts Cyanex 272 to a clear solution of orthophosphate which can be easily estimated by the molybdenum blue colorimetric method at 830 nm. The method is sensitive with a molar extinction coefficient of 2.6 x 10 and reproducible within ± 2%. Applying this technique of analysis, the dimerization constant (K2), distribution or partition coefficient (K) and the ionization constant (K) of the purified Cyanex 272 ie. BTMPPA have been estimated to be 190, 53 and 5.52 x 10, respectively. Interactions of BTMPPA+ diluent (n-hexane cyclohexane / benzene / toluene / chloroform / carbon tetrachloride / 1,2-dichloroethane (DCE) / 1-heptanol) binary mixtures have been studied in terms of density and viscosity measurements and also in terms of derived properties such as excess molar volumes (V), excess viscosities (n) and excess Gibbs free energy changes of activation of flow (AGE). Variations of these values together with the variations of the Grunberg-Nissan interaction parameter (d) for BTMPPA diluent binary systems show that BTMPPA interacts with the diluents in varying degrees. However, no correlation between d, AGE, nor V and the Cu2+/ Fe3+ - extraction characteristics with BTMPPA could be noticed. - The interfacial adsorption property of Cyanex 272 (purified) at the 0.50 mol/dm3 H2SO4 (pH = 0.8) / BTMPPA - diluent (carbon tetrachloride / cyclohexane/ DCE/ n-hexane / toluene / kerosene / benzene / chloroform / 1-heptanol/ 1-hexanol) interface have been investigated. Applying the Gibbs adsorption isotherm to the y vs. log [BTMPPA] plots for each of the diluent used (y being the interfacial tension, mN/m), the apparent cross-sectional areas (A in A2) of BTMPPA molecules adsorbed at the interfaces have been estimated. A (A3) is found to vary in the order: CCl4 (157 A2) <cy-C6H12 (166 A3) < DCE (174 A3) <n-C6H14 (176 A2) < C6H5-CH3 (211 A2) = kerosene (211 A2) < C6H6 (262 A2) < CHCl3 (335 A2) < 1-CH1SOH (532 A2) < 1. C6H3OH (734 Å). When the measurements are done in identical conditions of interfaces, then the cross-sectional areas can be correlated with the metal extraction data. The extraction characteristics of Fe3+ from 0.10 mol/dm3 (H, Na*) SO,2 medium by BTMPPA in kerosene have been investigatied. The equilibration time is less than 25 min. The [Fe3] dependence curve at a constant equilibrium pH and concentrations of extractant and sulphate has a slope of -0.5 and zero at lower and higher concentration regions of Fe3. The pH dependence at lower pH region is 2; whereas, the extractant and sulphate ion dependences are 1 and -1, respectively. The pH dependence is decreased at higher pH regions due to hydrolysis of Fe3*. The temperature dependence of distribution ratio (D) indicates that the extraction process is exothermic with an average AH value of 30 kJ/mol. The extraction equilibrium reaction is suggested to be: Fe (HSO2)2+H2A2(0) Fe.HSO4-A2(0) + HSO4 + 2H* at the lower pH region of investigation. At higher pH region, the hydrolytic Fe3* species is involved. The extraction equilibrium constant (Ke) has been evaluated to be 10°23 The extracted complex can be stripped by 0.50 mol/dm3 H2SO4 solution; but a three- stage stripping (O/A = 1 in each stage) is needed for 99% Fe3 removal from the organic phase. The solvent extraction of Cu2 from 0.10 mol/dm3 sulphate medium by BTMPPA dissolved in distilled kerosene has been investigated. The equilibration time is less than 15 min. The distribution ratio is found to decrease appreciably with equilibrium Cu concentration in the aqueous phase, particularly, at its higher concentration region indicating some sort of association of Cu2+ species in either of the phases. The pH and the extractant concentration dependences on D are 1 and 1.2, respectively. D is almost independent of sulphate ion concentrations in the aqueous phase. The AH value is 27.3 ± 0.5 kJ/mol. The 60% extraction equilibrium reaction is suggested to be: CuHSO4 + H2A20) CuHSO4.A.0.5 H2A2(0)+H" and some 40% reaction is likely to occur via the reaction: CuHSO4+1.5 H2A210) CuHSO4.A.HzAzo) + H satisfying the extractant dependence of 1.2. The apparent extraction equilibrium constant (K) is estimated to be 10315. The loading capacity of BTMPPA is 13.47 g Cu2+/100 g BTMPPA. Among H2SO4, HCI and HNO3 solutions as stripping agent, 1 mol/dm3 H2SO4 solution is found to be the best; 99.6% Cu2+ in the organic phase can be stripped off in three stages (O/A = 1 in each stage). The Cu2* distribution ratio measured at pH = 4 in different diluents does not show good correlation with the cross sectional area of BTMPPA molecules at interfaces formed by different diluents at pH 0.80. This Thesis is Submitted to the Department of Applied Chemistry and Chemical Engineering , University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD)

2006-05-01T00:00:00Z Rahman, Md. Saidur http://rulrepository.ru.ac.bd/handle/123456789/1142 2025-07-15T08:44:16Z 2010-06-01T00:00:00Z

Solvent Extraction of Mn(II), Ni(II) and Zn(II) by Cyanex 272: Equilibrium and Kinetic Studies Rahman, Md. Saidur The solvent extraction systems: Mn(II)-SO, -Ac Cyanex 272-kerosene, Ni(II)- SO4-Ac Cyanex 272-kerosene and Zn(II)-SO4 Cyanex 272-kerosene have been thoroughly investigated from equilibrium and kinetic point of views. From the dependence of extraction ratio (at constant equilibrium values of other parameters) on various parametric concentrations, the equations for extraction ratios have been derived at 303 K as: log Dmn=-6.17+2 pHm) + log [H2Azam)-log (1 + 1.9 [SO"]) log Di-11.16+2 pH)+ log [H2A2)-log (1+ 6.92 [SO."])-log [Ac"]; at [H2A2]) <0.05 kmol/m log DN-11.56+2 pH)+3 log [H2A2km)-log (1+6.92 [SO, D)-log [Ac]; at [H2A2 >0.10 kmol/m log Dzn --3.11+2 pH)+ log [H2A2])-log (1+2 [SO,"]); at [H2A2] (en) <0.05 kmol/m3 log "Dzn -2.08 +2 pH() +2 log [H2A2](o)-log (1+2 [SO"]); at [H2A2]()>0.10 kmol/m where, the first terms on the right hand sides represent the logarithmic values of extraction equilibrium constants (Kex). The equilibrium extraction reactions in low concentration regions of extractant are suggested as M(II) + H2A2(0) [MA2](0) + 2 H; but disolvated and monosolvated species are extracted in the cases of Ni(II) and Zn(II), respectively, at high concentration regions of Cyanex 272 (H2A2). The extraction processes are found to be endothermic. The maximum loading capacities of the extractant are found to be 9.52 g Mn(II), 21.28 g Ni(II) and 11.5 g Zn(II) per 100 g extractant. The extracted species are strippable by dilute H2SO4, HNO3 and HCl solutions. In kinetics of forward extractions of the selected divalent metal ions by Cyanex 272, the rates have been measured the single falling drop technique at various extraction parametric concentrations in order to determine the orders of reaction with respect to various concentration terms and also to evaluate the log kr values. Rates have measured at various temperatures to determine E., AH* and AS* values at various parametric conditions for all systems under consideration. The rates of forward extractions of Mn(II), Ni(II) and Zn(II) at 303 K can be expressed respectively as: log F-3.6+ log [Mn(II)] +0.5 log [H2A2]()-log (1+ 105 [H])-log (1+1.58[SO"]) log Fr=-3.7+ log [Ni(11)] +0.5 log [H2A2](o)-log (1+ 10635 [H])-log (1+6.3[SO, ])-log (1 +0.55 [Ac"] log Fr=-8.4 + log [Zn(II)-log [H])+0.5 log [H2A2])+ log (1+ 1.07 [H2A]()) where, Fr represents flux of metal transfer from one phase to another and defined as rate per unit interfacial area. From the rate equations, the mechanisms of extractions are given. Invariably in all cases under investigation, the attachment of the first monomeric anion of the extractant (A') to the metal ion is the rate controlling (M2++ A slow [MA]'); which has been supported by high activation energy (>48 kJ/mol). However, in certain parametric conditions diffusions rather the chemical reaction stated become rate controlling, which is supported by low activation energy. In case of Ni(II) extraction, at high concentration region of extractant, the reaction: Ni2++ HA2 (int) → [NIHA2] becomes rate controlling. The highly negative AS* values in all cases suggest the chemical rate determining step occurs via SNo2 mechanism. The kinetics of stripping of metal ions from highly metal ion loaded organic phases by sulphuric acid solutions have been investigated by the single falling drop technique to derive respective stripping rate equations at 303 K. The stripping rate equations derived for stripping of Mn(II), Ni(II) and Zn(II), respectively, are: log F1 = -4.88 + log [MnA2])- 0.5 log (1+0.002 [H]') + log (1 +5.129 [SO,")) log F-4.35+ log [Ni-H2A2 complex])-log (1 + 1042 [H])-log ([H2A2])+2.5 [H2A2])+ log (1+6 [SO, ])+ log (1 + 3.2 [Ac']) log F-5.24+ log [Zn-HA, complex]) + log [H]-0.5 log [H2A2]) + log (1 +1.5 log [SO."]) The rate equations have been analyzed to give stripping mechanisms. It is found that the dissociation of second anion ligand from [MA2](o) is rate determining which occurs in the bulk aqueous phase (MA slow M2++ A), which is, supported by high Eq. values. This mechanism is valid for Mn(II) and Zn(II) covering all concentration region of free extractant in the organic phase; and also for Ni(II) in low concentration region of extractant, but at its high concentration region, the dissociation of dimeric anion (HA2) from [Ni(HA2)2. H2A2] (0) appears as rate determining. However, low E, value suggests this step occurs via SN2 mechanism. The extraction equilibrium constants (Ke) for Mn(II) and Zn(II) derived from equilibrium studies are matchable to those from respective kinetic studies (Kex = kr/k). But in the case of Ni(II), a deviation by a factor of 10 is obtained, which may be attributed to the loss buffer action resulting the change of interfacial pH. The possibilities of separations of the metal ions under consideration from their mixtures by Cyanex 272 have been theoretically evaluated and it has been shown that the mutual almost complete separation of this metal ion by single or by at least two stage extractions by Cyanex 272 solution in kerosene is possible. This Thesis is Submitted to the Department of Applied Chemistry and Chemical Engineering , University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD)

2010-06-01T00:00:00Z Saha, Joykrisna http://rulrepository.ru.ac.bd/handle/123456789/1104 2023-08-29T08:05:36Z 0221-01-01T00:00:00Z

Modification of cotton fabric with Natural antimicrobial agents for Ecofriendly protective textiles Saha, Joykrisna In recent time‘s health and hygiene issues have achieved the greatest attention among the awareness people of all over the world. Health and hygiene are the primary obligations for human beings to live comfortably and work with maximum safety. The aim of the present work is to develop environment friendly protective textiles using Aloe vera, chitosan and sericin on bleached cotton woven fabrics for medical and health care apparel against gram-positive Staphylococcus aureus and gram-negative Escherichia coli bacteria. Aloe vera, chitosan and silk sericin are natural biopolymer which exhibited different significant biological property. Aloe vera extract was prepared from Aloe vera leaves through methanol solvent using a rotary evaporator. Chitosan was made from shrimp shell through several steps of alkali and acid treatments and silk sericin powder was obtained from a boiled water solution of silk cocoons through ethanol precipitation. Extracted Aloe vera, chitosan and sericin powder were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Energy dispersive spectroscopy (EDS), UV-visible spectrophotometer, X-ray diffraction (XRD). Solubility, degree of deacetylation, antibacterial activity, antioxidant property and UV protection factor were also analyzed. Both quantitative and qualitative methods were used to assay the antimicrobial activity. The antioxidant activity was evaluated by 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radicals. Chitosan was found to have a 90% degree of deacetylation.----- This Thesis is Submitted to the Department of Applied Chemistry and Chemical Engineering , University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD)

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