JSCS - Vol 63, No 4- Abstracts

J. Serb. Chem. Soc. 63(4) 237-249 (1998)
UDC 536.632:536.71:542.63
JSCS-2529
Original scientific paper

Cubic equation of state models for the liquid excess heat capacity calculations.
I. Mixing rules

MIRJANA LJ. KIJEVCANIN, BOJAN D. DJORDJEVIC, PETAR S. VESELINOVIC and SLOBODAN P. SERBANOVIC

Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, P. O. Box 35-03, Belgrade, Yugoslavia

(Received 26 November 1997)
Binary liquid excess heat capacities, c_p^E, were calculated by the PRSV EOS coupled with the van der Waals one fluid (vdW), the modified van der Waals one fluid (Schwartzentruber-Renon)(SR) and the Orbey-Sandler modificaiton of the Huron-Vidal mixing rule (HVOS). The HVOS mixing rule is used with the NRTL excess free energy model. In all the EOS models (PRSV-vdW, PRSV-SR and PRSV-HVOS), the binary parameters were assumed to be a linear function of temperature. The benzene-n-heptane binary system was chosen as the test system to check the capabilities of the investigated EOS models for the estimation of the excess heat capacity c_p^E.

Key words: excess heat capacity, cubic equation of state, mixing rule.

J. Serb. Chem. Soc. 63(4) 251-256 (1998)
UDC 536.632:536.71:62.001.54:541.123.2
JSCS-2530
Original scientific paper

Cubic equation of state models for liquid excess heat capacity calculations.
II. Applicability of the PRSV-SR and PRSV-HVOS models to complex binary mixtures

MIRJANA LJ. KIJEVCANIN, BOJAN D. DJORDJEVIC, MILUTIN M. ADAMOVIC and
SLOBODAN P. SERBANOVIC

Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, P. O. Box 35-03, Belgrade, Yugoslavia

(Received 26 November 1997)
Binary liquid excess heat capacities c_p^E for various kinds of complex binary systems measured by Conti and coworkers are well represented by the PRSV EOS modified van der Waals one fluid mixing rule proposed by Schwartzentruber and Renon (SR) and the Orbey-Sandler modification of the Huron-Vidal mixing rules (HVOS). The HVOS mixing rule is used with the NRTL excess free energy model. The binary parameters of both models (PRSV-SR and PRSV-HVOS) were assumed to be linear functions of temperature. Only for the system ethanol - cyclohexane the correlation obtained by the PRSV-SR model is not satisfactory.

Key words: excess heat capacity, cubic equation of state, mixing rule, polar compoound, binary mixture.

J. Serb. Chem. Soc. 63(4) 257-264 (1998)
UDC 661.183.6:577.153.6:66.097.5
JSCS-2531
Original scientific paper

Immobilization of lipase on a hydrophobic zeolite type Y

ZORICA KNEZEVIC, LJILJANA MOJOVIC, and BORIVOJE ADNADJEVIC*

Department of Biochemical Engineering and Biotechnologies, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, YU-11000 Belgrade and
*Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12, YU-11000 -Belgrade, Yugoslavia

(Received 12 August 1997, revised 14 January 1998)

Lipase from Candida cylindracea was immobilized by adsorption on a hydrophobic zeolite type Y. The maximal amount of bound protein of 8.2 mg g^-1 and an immobilization efficiency of 33% were achieved under optimum conditions. The kinetics of lipase binding to the zeolite were assessed using a general model of topochemical reactions. Based on the values of the parameters of the specific kinetic model, we propose that the adsorption process is controlled by surface kinetics. This was later experimentally confirmed. The activation energy for lipase adsorption on the zeolite is 43 kJ mol^-1.

Key words: Candida cylindracea lipase, zeolite, immobilization, kinetic model.

J. Serb. Chem. Soc. 63(4) 265-277 (1998)
UDC 661.183.6:62.001.54:542.6
JSCS-2532
Original scientific paper

Modelling of microporous diffusion in zeolite 5A

LJILJANA T. MARKOVSKA and VERA D. MESHKO

Faculty of Technology and Metallurgy, University "St. Cyril and Methodius", Skopje, Republic of Macedonia

(Received 16 July 1997, revised 19 January 1998)
Sorptive liquid-phase diffusion of two n-paraffins, C₁₀H₂₂ and C₁₁H₂₄, dissolved in iso-octane, onto the micropores of 5A zeolite was studied to assess multicomponent diffusion and competitive effects. The diffusion coefficients for the adsorbing components were determined from experimental batch reactor data. The experimental data indicate that diffusion through the microporous zeolite crystals is the primary diffusional resistance. A mathmematical model of the rate of adsorption of a solute from a liquid by a microporous adsorbent in a batch system was developed. The equation describing the mass transport by diffusion in a microporous adsorbent was solved in order to obtain theoretical uptake curves for systems in which the adsorption equilibrium isotherm is favourable and non-linear. The computer simulation of the microporous diffusion was performed by use of the ISIM-Interactive Simulation Language. The effects of the main term and cross-term coefficients of micropore diffusion for the system considered were investigated.

Key words: multicomponent diffusion, zeolite, micropore diffusion.

J. Serb. Chem. Soc. 63(4) 279-287 (1998)
UDC 661.728.892:532.7
JSCS-2533
Original scientific paper

Viscoelastic properties of Na-carboxymethylcellulose solutions

JOVA HRABAR, DEJAN POLETI, SASA DRMANIC, ZORICA GALOVIC*, and LJILJANA MAJDANAC

Faculty of Technology and Metallurgy, P. O. Box 494, YU-11001 Belgrade and
*Chemical Industry "Milan Blagojevic", Lucani, Yugoslavia

(Received 25 August, revised 30 December 1997)
The rheological characteristics of 5% solutions of Na-carboxymethylcellulose (CMC) of various origin were investigated. Depending on the molar mass (1.25 - 1.94 × 10⁵ g mol^-1), i.e., the degree of polymerization (545-851) and degree of substitution (0.748-1.039), as well as the electrolyte (NaCl) content (0.55 - 36.40%), it was found that microgel particles appear in some cases, while in other cases there are entanglements or isolated particles of CMC macromolecules in solution. Stronger macromolecular interactions were observed when the degree of polymerization was greater than about 600 and the degree of substitution was higher than approximately 0.8. The rheological characteristics of the investigated samples are discussed in relation to the macromolecular structure (defined by X-ray powder diffraction and FT-IR spectroscopy) in the solid state.

Key words: Na-carboxymethylcellulose, rheological characteristics, degree of polymerization, degree of substitution, microgel particles, entanglement.

J. Serb. Chem. Soc. 63(4) 289-300 (1998)
UDC 543.424:578.746:542.9
JSCS-2534
Original scientific paper

A Raman spectroscopical study of redox reactions onelectrochemically synthesized polyaniline

LJUBOMIR ARSOV, KATICA COLANCESKA and NEDKA PETROVSKA

Faculty of Technology and Metallurgy, University "St. Cyril and Methodius", 91000 Skopje, Macedonia

(Received 28 November 1997)
The redox reactions of electrochemically synthesized polyaniline, at differents values of anodic and cathodic potentials during cyclisation, have been studied employing in-situ electrochemical and Raman spectroscopical techniques. Aniline was polymerized on a Pt surface in sulfuric acid solution containing various concentrations of added aniline. The Raman bands were assigned for each CV peak and a discussion of the redox mechanisms is given.

Key words: electropolymerization, cyclic voltammetry, polyaniline, redox reactions, Raman spectroscopy.

J. Serb. Chem. Soc. 63(4) 301-314 (1998)
UDC 549.7:621.785.4
JSCS-2535
Original scientific paper

Ferrite transformation on annealing at 1050 and 1150°C in surface melted dupex stainless steel

ZORICA M. CVIJOVIC, DRAGINJA V. MIHAJLOVIC and VIDA R. KNEZEVIC

Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, P. O. Box 494, YU-11001 Belgrade, Yugoslavia

(Received 24 November 1997, revised 13 January 1998)
Three different microstructure morphologies: lathy ferrite (LF), vermicular ferrite (VF) and intercellular austenite (IA) were achieved in duplex stainless steel by surface melting using the GTA technique. The cooling rates were of the order of 10¹-10³ ° C s^-1. All three structures are exceptionally fine. On annealing at 1050 and 1150°C, the structures proved to be highly unstable. The process kinetics depend only on the attained degree of the thermodynamic equilibrium. The structure morphology, via the d/g boundary characteristics considerably influence the type of secondary austenite, g₂, which can be formed in the interior of ferrite, g_2i, and on existing d/g boundaries, g_2b. The precipitation of highly dispersed g_2iparticles causes a very large increase in the parameters S_v_d-g and S_v_dg/V_g(_d₎. With increasing time of annealing intensive coarsening of the structure by coalescence and rounding of the boundaries decreases the effect of the change of the phase composition. At 1050 °C the s-phase is also observed, but at 1150 °C only the d->Žg transformation and a coarsening processes occur.

Key words: duplex stainless steel, surface melting, microstructural morphology, geometrical parameters, metastable ferrite transformation.

J. Serb. Chem. Soc. 63(4) 315-318 (1998)
UDC 547.93:543.062:636.4
JSCS-2536
Note

NOTE
Determination of the bile acids content in pig gall bladder bile

KSENIJA KUHAJDA, JULIJAN KANDRAC, SVETLANA TRAJKOVIC* and JOVAN HRANISAVLJEVIC*

Institute of Chemistry, Faculty of Science, Trg D. Obradovica 3, YU-21000 Novi Sad, and
*Institute of General and Physical Chemistry, Studentski trg 12, P. O. Box 551, YU-11000 Belgrade, Yugoslavia

(Received 26 February 1997, revised 15 October 1997)
High-performance liquid chromatography with a C₁₈ reverse phase column and a mixture of methanol-water-acetate buffer (pH=4.3) as the mobile phase was used to separate conjugated bile acids isolated from pig gall bladder bile of animals of different age. No essential animal age dependent difference in the content of conjugated bile acids was found. The developed method of high-performance liquid chromatography under conditions of strictly controlled mobile phase pH is simple, rapid and reproducible, so that it may be suitable for routine analyses.

Key words: bile acids, glyco and tauro conjugates, pig bile, HPLC.

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