Ratomir Paunović

Rapid computation of binary interaction coefficients of an equation of state for vapor—liquid equilibrium calculations. Application to the Redlich—Kwong—Soave equation of state

Abstract The sum of absolute relative deviations between calculated vapor and liquid component fugacities is proposed for use as the objective function in the minimization procedure for the determination of binary interaction coefficients. In contrast to the most widely used method based on the bubble point pressure criterion, the new method does not involve iterations in calculating objective function values, providing a considerable reduction in computing time requirement. The utility of the proposed procedure is demonstrated for coefficients Cij of the Redlich—Kwong—Soave equation of state. The Cijs values are evaluated comparatively using the two methods for twelve binary systems consisting of hydrocarbons, carbon dioxide, nitrogen, hydrogen and hydrogen sulfide. The results show that the differences between the Cij values in the proposed and the bubble point methods are tolerable, i.e., they do not have a significant effect on the accuracy of bubble point pressure predictions.

Applicability of a double-membrane reactor for thermal decomposition of water : a computer analysis

A theoretical study of applicability of double-membrane reactor for direct thermal decomposition of water is presented. The analysis is based on an isothermal, steady state, plug flow reactor model. One of the two membranes was supposed to be hydrogen permeable, and the other one, oxygen permeable. The simulations were performed for T=2000 K, it being the upper limit of temperatures of practical interest. With a high vacuum in separation zones, the double-membrane configuration theoretically enables complete conversion providing high values of Damkohler number and total rate ratio. When a sweep gas is introduced into separation zones, significant water conversions can also be provided by a countercurrent single membrane reactor, but considerably lower than those obtained in a double-membrane reactor. The double-membrane reactor seems to be a promising solution for the water splitting reaction, deserving experimental investigations.

Applicability of two-membrane reactors for reversible gas phase reaction. Effects of flow patterns and inerts

The objective of this study is a comparative analysis of single and two-membrane reactor performances for isothermal reversible gas phase reaction. The effects of flow patterns (ideal mixing, cocurrent and countercurrent plug flow) and the presence of inert components were investigated. It is shown by simulation that for the pure reactant feed in absence of inerts, the performance of a two-membrane reactor is not significantly affected by the flow patterns, providing the pressure ratio is kept close to zero. Concerning the conversion efficiency in the case when the reactant is the slowest permeating component, the advantage of a two-membrane reactor is evident, it being least significant for countercurrent plug flow. In the presence of inerts in the separation zone, the advantage of a two-membrane reactor is maintained, while it is diminished by increasing inert flow rate in the reaction zone.

Maximal extent of an isothermal reversible gas-phase reaction in single- and double-membrane reactors; direct thermal splitting of water

Abstract The maximal reactant conversions in isothermal double-membrane reactors are discussed theoretically, in comparison to single-membrane reactors. A method for calculating the limiting conversion is proposed and demonstrated on the elementary reversible gas-phase reaction aA=bB+cC. The criteria for approaching the limiting conversions are presented, in terms of values of dimensionless model parameters. The complete conversion of reactant can be realized in double-membrane reactors concerning the reactions with low equilibrium conversion and realistic process parameters. As to the applicability of double-membrane reactor model that assumes reaction equilibrium, that approximation could be reasonable only when the maximal attainable conversion is lower than the complete conversion of reactant. To demonstrate the validity of the conclusion that double-membrane configuration is superior to the single-membrane configuration considering the maximal attainable conversion, the results of simulation of thermal water splitting are presented.

Non-isothermal two-membrane reactors for reversible gas phase reactions

Abstract The performance of a non-isothermal two-membrane reactor for reversible chemical reactions in gas phase has been analyzed by numerical simulation. The analyzed reactions were of the form: aA = bB + cC . Two membranes, that are permeable to all the components of the reaction mixture, are supposed to be the most permeable to one of the two reaction products, satisfying the condition of reverse products permselectivities. The reactant is taken to be the slowest permeating component. A negative temperature influence on the permeabilities of components has been assumed. Co-current plug flow pattern has been accepted. It has been shown that it is possible to enhance reactant conversion above that of a conventional reactor for both endothermic and exothermic reversible reactions, including adiabatic and non-adiabatic case. By using a two-membrane reactor, considerable lowering of feed temperatures is enabled for an endothermic reaction. For endothermic reactions, there is the optimum feed temperature, whereas for exothermic reactions, the higher the temperature, the lower is the attained conversion. In reactor design, the optimal external heat exchange for both endothermic and exothermic reactions can be determinated.

Applicability of two membranes for improving performance of a membrane reactor

Abstract The applicability of the two-membrane reactor concept is demonstrated on a simple perfectly mixed reactor model. The two-membrane reactor has the advantage over the single membrane one, when both high conversion and mutual separation of products are required. By introducing the second membrane, the overall process efficiency (high conversion and high separation of components) could be improved, if the reactant was the slowest of the permeating components.

Citrate process for SO2 recovery: Vapour-liquid data and correlation

Abstract Precise knowledge of the quantitative data of equilibrium vapour pressure of SO2 over aqueous sodium citrate solution is of considerable technological importance for the design of both absorber and regenerator. The absence of such data prompted a series of measurements to determine them. The ranges of experimental conditions used for measurements of vapour-liquid equilibrium data were: gas flow rate, 1.60–1.701 min−1; SO2 concentration in inlet gases, 0.50–6.00 vol%; temperature, 40–70°C at atmospheric pressure and citrate buffer with the molar ratio CNaOH/CH3Ci of 0.50/1 .00, 1 .00/1 .00 and 2.00/1.00. The equilibrium vapour-liquid data were correlated by the extended two-parameter model. Good agreement between experimental results and those predicted by the suggested model was obtained for the whole investigated region of interest for SO2 absorption.

Analysis of a model of hollow-fiber bioreactor wastewater treatment

Abstract In this work, the effect of neglecting fiber lumen radial concentrations gradients in the one-dimensional mathematical model of isothermal anaerobic acetate biodegradation in hollow-fiber bioreactor has been analyzed. The results show a significant increase of the error resulting from neglection of radial lumen concentration gradients with increase of hollow-fiber diameter value. The limiting fiber diameter value above which the inclusion of lumen concentration profile is recommendable is proposed. To provide a stable convergence in the whole domain of real model solutions, a self-starting procedure based on a shooting method has been developed.

A discussion of maximal extent of an isothermal reversible gas phase reaction in double-membrane reactors ☆

The maximal reactant conversions in cocurrent isothermal double-membrane reactors are discussed theoretically, in comparison to single-membrane reactors. A method for calculation of the limiting conversion is proposed and demonstrated on the elementary reversible gas phase reaction A=B+C. Owing to the disturbing separation and reaction equilibrium, double-membrane reactor without sweep gas could provide complete conversion. When the sweep gas is introduced, large but not infinite sweep gas flow enables complete conversion. The criteria for approaching the limiting conversions are presented, in terms of values of dimensionless model parameters. To demonstrate the validity of the conclusion that double-membrane configuration is superior to the single-membrane configuration considering the maximal attainable conversion, the results of simulation of thermal water splitting are presented. As to the applicability of double-membrane reactor model that assumes reaction equilibrium, that approximation could be reasonable only when the maximal attainable conversion is lower than unity.

Conversion enhancement of equilibrium-limited reactions in a two-membrane reactor

Abstract Analysis of two-membrane reactor performance is carried out on a simple, perfectly mixed reactor model. The influence of the design and operating parameters and physical properties of the system on conversion for equilibrium reactions of the type A ↞ B + C have been studied. Also, the effects of the presence of inerts at both the reaction and permeation sides of the reactor have been discussed. It has been shown that the two-membrane reactor exhibits superior performance as compared to the single-membrane reactor.