Xuân-Mi Meyer

An original kinetic model for the enzymatic hydrolysis of starch during mashing

Abstract This paper presents a kinetic model for the enzymatic degradation of the starch during mashing for beer production. Based on a new set of experiments, an original reaction scheme for the hydrolysis of starch by α- and β-amylases has been proposed. Here, the kinetics of the reactions involved in this scheme are described: starch gelatinisation, amylase activities and carbohydrate production. One originality of this model is the mathematical representation of the amylase activities temperature dependency. The model requires to know the initial composition of malt (starch concentration and amylase potential which are classically measured to qualify the raw material) and the operating conditions (temperature chart) to predict the evolutions of amylase activities, dextrins and fermentable carbohydrate concentrations during mashing. The model parameters have been estimated by fitting nine experiments performed on one malt variety. Five other experiments validate the model for different malt varieties.

Modelling of a dynamic multiphase flash: the positive flash. Application to the calculation of ternary diagrams

A general and polyvalent model for the dynamic simulation of a vapor, liquid, liquid-liquid, vapor-liquid or vapor-liquid-liquid stage is proposed. This model is based on the τ -method introduced as a minimization problem by Han & Rangaiah (1998) for steady-state simulation. They suggested modifying the mole fraction summation such that the same set of governing equations becomes valid for all phase regions. Thanks to judicious additional switch equations, the τ -formulation is extended to dynamic simulation and the minimization problem is transformed into a set of differential algebraic equations (DAE). Validation of the model consists in testing its capacity to overcome phase number changes and to be able to solve several problems with the same set of equations: calculation of heterogeneous residue curves, azeotropic points and distillation boundaries in ternary diagrams. Topical Heading Process System Engineering

Infinite/infinite analysis as a tool for an early oriented synthesis of a reactive pressure swing distillation

The study contributes to the characterization of an original reactive pressure swing distillation system. The methyl acetate (MeAc) transesterification with ethanol (EtOH) to produce methanol (MeOH) and ethyl acetate (EtAc) is shown as illustrative example. The streams outside the units are evaluated by the ∞/∞ analysis to provide insights on the process behavior. Two simpler systems with recycling stream are also presented. The ∞/∞ analysis allows checking the interrelation of the system streams without any column design consideration. Unfeasible regions, low limit values, multiplicity regions, discontinuities, control difficulties, recommendable operation conditions and column profile combinations are predicted and discussed. All these information are useful to establish an early and suitable system design strategy.

A Sequential and hierarchical approach for the feasibility analysis and the preliminary synthesis and design of reactive distillation processes

Abstract A procedure that combines feasibility analysis, synthesis and design of reactive distillation columns is introduced. The main interest of this methodology lies on a progressive introduction of the process complexity. From minimal information concerning the physicochemical properties of the system, three steps lead to the design of the unit and the specification of its operating conditions. This methodology which provides a reliable initialization point for the optimization of the process has been applied with success to different synthesis. The production of Methyl-Tert-Butyl-Ether (MTBE) is presented here as an example.

Dynamic simulation of batch crystallization process by using moving finite difference method

Publisher Summary This chapter discusses moving finite difference method combined with Weighted Essentially Non-Oscillatory (WENO) scheme for the dynamic simulation of batch crystallization processes described by hyperbolic-like Population Balance Equation (PBE) with a discontinuous initial condition. The accurate and stable WENO scheme shows an improvement of numerical results over conventional discretization methods (backward or central) on fixed grids as well as on moving grids. Owing to the moving grid method with the WENO scheme, which tracks well a steep front or shock, the physical model of PBEs could be numerically represented more exactly. Numerical results are compared with experimental results for the crystallization process of the potassium sulfate (K 2 SO 4 /H 2 O). The new approach is considered as an efficient numerical solution procedure for the verification of models described by hyperbolic-like Partial Differential Equations (PDEs).

Reactive distillation modelling and sensitivity analysis based on NEQ model

Abstract Firstly, a non-equilibrium model (or NEQ model)has implemented for multi component reactive separation processes. The mass transfer description is based on the Maxwell Stefan approach and the hydrodynamics on the film theory model. We have excluded other restrictive assumptions. The code calculation is implemented in the simulation software ProSim Plus TM . Secondly, an experimental packed reactive distillation pilot has been developed in order to obtain experimental. The experiments were performed for homogeneously catalysed esterification of acid acetic and methanol into methyl acetate and water. Five runs have been performed for which the inlet flow rate and compositions, as well as the concentration in catalyst are modified. For each run, the simulation results are in good agreement with the vapour composition and the liquid temperature profile, without any parameter adjustment. Finally, a sensitive analysis of the NEQ model parameters has been done. It seems for the various physical parameters (e.g. the liquid and vapour film thickness, the liquid hold-up and the interfacial area), that the interfacial area is the most sensitive. For the other parameters, their sensitivity depends where the reaction and the mass transfer resistance take place. Moreover, a step discretisation analysis in regard to the axial coordinates shows that the type of flow inside the column could be compared to a plug flow. In addition, the need of taking into account the reaction contribution in the diffusional layers is clearly shown.