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Starting from formation properties of purines and pyrimidines, enthalpy of formation, Gibbs energy of formation, entropy of formation and heat capacity of several nucleosides, nucleotides and nucleotide-phosphates were calculated in dilute aqueous solution. For these calculations, the formation properties of ribose-1-phosphate were required and were calculated from data of various sources. Data for some enzymatic equilibrium constants were also used. To complete the set of formation properties of nucleosides and nucleotides, the energy contributions of some chemical bonds were calculated. The proposed values were reconciled with chemical and physical equilibrium data, validating the method of calculation used.

Changes in Gibbs energies of metabolic reactions of glycolysis and Krebs cycle have been calculated from literature data including ΔG, pK values, and complex formation constants values. Neutral, charged species and Mg-complexes are included in the data base. Results show that most of the reactions investigated proceed near thermodynamic equilibrium conditions whereas the reactions out of equilibrium are related to the metabolic regulation and seem associated with cyclic sequences or with parallel pathways. Examples of fructose 6-phosphate/fructose 1,6-diphosphate cycle and phosphotranferase system and hexokinase are presented.

A group-contribution method was used to estimate activity coefficients in biological liquid systems. The UNIFAC model, as modified by Larsen, was found the most convenient for aqueous systems containing saccharides and polyols. A Pitzer-Debye-Huckel term was added to handle aqueous mixtures containing solutes that ionize either completely or partially. The effect of ionic solvation involved the introduction of a hydration number for each ion. From activity coefficients, thermodynamic properties such as water activity, osmotic pressure, melting and boiling temperatures of mixtures and pH were calculated. It was found that, in buffered media, pH was not accurately predicted if only concentrations were calculated. Dissociation constants of acids or bases and of water were corrected by activity coefficients' estimations using the UNIFAC-Larsen-Pitzer-Debye-Huckel model, giving pH values within ± 0.01 pH unit.

Equations derived from the linear irreversible thermodynamics showed direct relationships between flow, pressure and chemical potential gradients. To predict flows, three coefficients (hydraulic permeability, solute permeability, and reflection coefficient) were introduced into the equations and measured experimentally for counter-current transfer of water and salt in agar gels. The reflection coefficient was less than 0.0003 indicating that the gel behaved as a non-selective membrane. To analyse the interactions, three interaction coefficients, for solute and water, solute and polymer network and water and polymer network were used, and expressed as a function of the former coefficients. Results showed that only salt and water interactions controlled the rate of transfer.

In many identification problems, the characterization of the system, i.e. the determination of the nature of the model from some specified response, is an important point. For an automatic characterization, a syntactic pattern recognition approach is related in this paper, which is based on the use of regular grammars and of a new grammatical inference algorithm. Linear dynamical systems with known impulse response are considered here, especially eight classes of models which are commonly encountered in the modelling of actual flow in chemical or biochemical reactors. The good results obtained for this application indicate the validity of this approach.

The influence of the stoichiometry of a reactive system involving a large number of components on the effectiveness factor of a catalyst has been studied. An adequate change of variables reduces the problem to solving a set of two non linear first-order differential equations describing the diffusion of a single component in the pores of the catalyst. The method is applied, as an example, to the oxidation of sulfur dioxide, in order to estimate errors predicted by the constant volume hypothesis, as functions of catalyst particle size, degree of conversion, and initial concentrations.

Resume La separation du melange n-heptane—toluene est realisee par pompage parametrique en mode direct fonctionnant en discontinu, c'est-a-dire a reflux total. La variable intensive utilisee est la temperature. L'adsorbant est du silica gel. Les resultats obtenus en faisant varier la duree du cycle, la difference de temperature d'un demi-cycle a l'autre et le volume des reservoirs confirment les resultats obtenus par Wilhelm et Sweed. L'analyse des resultats montre que l'hypothese considerant que l'equilibre est realise en chaque point de la colonne ne semble pas verifiee měme pour des durees de cycles de 120 minutes. Le modele propose par Grevillot et Tondeur, legerement modifie, permet de traduire les resultats experimentaux de facon satisfaisante au prix de deux parametres: nombre d'etages et volume mort dans les reservoirs. L'etude experimentale et les simulations mettent en evidence l'importance des effets d'extremites — melange dans les bacs, volumes morts — sur la separation.

Three bidimensional pseudo-homogeneous models are considered for estimation of heat transfer parameters in a fixed bed catalytic reactors. The Peclet and Biot numbers are obtained by identification of experimental and calculated temperatures profiles in a pilot plant reactor. Particular attention is drawn to sensivity of identification to experimental variables. The results obtained from the one parameter model proposed by Dewash and Froment are compared with experimental data, and influence of axial dispersion in catalytic bed is studied by comparison of different models.

This paper deals with the comparison of theoretical reactor performance and measurements in an actual non-adiabatic non-isothermal fixed bed. The experimental scheme relies mainly on the measurement of radial temperature profiles at various axial distances and of the average outlet conversion for a set of nine different experiments. The intrinsic reaction rate and internal diffusion coefficients have been determined separately on a laboratory integral reactor. Heat transfer parameters were obtained from temperature profiles without reaction in the pilot plant reactor. The results given by three different reactor models are analysed. Good agreement is observed between the experiments and results computed from a heterogeneous two-dimensional model. Two simpler models are also assessed and it is shown that the one-dimensional one fails to represent the experimental results.

Un modele bidimensionnel pseudo-homogene est utilise pour l'etude de comportement d'un reacteur catalytique a lit fixe d'oxydation du propene en acroleine. Les lois de vitesses utilisees sont les fonctions puissance de pressions partielles en oxygene et en propene. Les valeurs des parametres thermiques Pehr et Bi necessaires a la simulation sont obtenues directement a l'aide des profils de temperature en l'absence de reaction. Le modele est integre par une methode de collocation orthogonale. Les resultats du modele, a savoir les profils de temperatures et la concentration a la sortie du reacteur, sont compares avec ceux obtenus experimentalement. A bidimensional pseudo homogeneous model is developed to explain the behaviour of a fixed bed catalytic reactor for oxydation of propene to acrolein. The rate of the main reaction and of side reaction are expressed as power fonctions of partial pressures of oxygene and propene. Heat transfer parameter (Pehr et Bi) necessary for simulation are obtained by the help of temperature profiles in the absence of reaction. The integration of the model has been done by orthogonal collocation and the results i.e. temperature profiles and outlet concentration are compared with experimental data.

The response of an amperometric oxygen electrode is studied theoretically and experimentally for the case of significant liquid film resistance at the outer side of the membrane. The behaviour of the probe in a gas stream is predicted by using a transfer function which involves an electrode model including oxygen diffusion within the electrode. The effects of the liquid film which exists at the membrane surface when dissolved oxygen concentrations are measured, are taken into account by modifying the transfer function. The new expression obtained is used to model the step response of the probe in a 2-1 stirred tank fermentor filled with water or xanthane solutions at different concentrations. First, the results are used to correct automatically the steady-state voltage readings of the probe. Secondly, the probe transfer function is used to evaluate k 1 a by dynamic measurements: the response to a step change in the gas concentration is transformed via the fast Fourier transform algorithm and k 1 a is identified in the Fourier domain by a Gauss-Newton algorithm. Data acquisition, Fourier transform and k 1 a identification are implemented on-line on a HP-87 computer. This method of obtaining k 1 a values appears to be a generalized moment method. It is shown that it is necessary to consider the liquid film dynamics around the probe in the actual fermenting conditions to evaluate k 1 a successfully.

This work concerns energy consumption and aeration efficiency in a 15 dm 3 concentric cylinder gas-lift fermentor with the ejector nozzle located at the base of the central tube. Pressures are measured at ejector input and output and in the fermentor, and are compared with those predicted using Bernoulli's theorem and momentum balance at different points in the apparatus. Energy consumption per unit volume is the sum of isothermal expansion and gas-jet kinetic energy terms, the second of which becomes dominant at volumetric aeration rates above 2 vvm (volume of gas per liquid volume per min). Energy consumed is always lower than that for a classical agitated aerated fermentor. Oxygen transfer rate is determined by the sodium sulphite technique (with cobalt catalyst). Transfer can be strongly enhanced by the chemical reaction. The specific interfacial area for mass transfer, a′, depends on the power dissipated according to a′ = 3.66 (E/V l ) 0.73 (S.I. units) This correlation accounts for results obtained by other authors for larger fermentors (0.06 – 2 m 3 ).

Resume Cet article presente un modele statique bidimensionnel de reacteur catalytique a lit fixe qui permet de prendre en consideration les transferts massiques et thermiques s'effectuant par: 1. -diffusion axiale et radiale dans le fluide reactionnel 2. -convection 3. -echange de matiere et de chaleur entre la masse reactionnelle et les grains de catalyseur 4. -echange thermique avec la paroi du reacteur 5. -generation de matiere au niveau du catalyseur. 6. L'integration du modele implique la resolution numerique de deux equations aux derivees partielles elliptiques couplees non lineairement. Cette resolution est obtenue a la convergence de deux processus iteratifs enchevetres: 7. -l'un concerne la resolution de la partie lineaire du systeme par la methode de Gauss-Seidel, 8. -l'autre permet d'eviter la resolution de la partie non lineaire due a la loi de vitesse. 9. Deux coefficients de relaxation, l'un concernant la temperature et l'autre la concentration sont choisis de facon a optimaliser la convergence de l'algorithme. 10. La methode ne n'applique qu'aux modeles statiques contrairement a d'autres methodes 18,19 . En revanche elle a l'avantage d'etre beaucoup plus rapide et donc de presenter de l'interet pour l'identification parametrique des modeles. 11. Les resultats de la simulation—profils de concentration et de temperature—pour une reaction exothermique reversible, sont compares avec les resultats experimentaux obtenus sur un reacteur pilote.