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Modelling and optimisation of batch distillation involving esterification and hydrolysis reaction systems. Modelling and optimisation of conventional and unconventional batch distillation process: Application to esterification of methanol and ethanol using acetic acid and hydrolysis of methyl lactate system.
Batch distillation with chemical reaction when takes place in the same unit is referred to
as batch reactive distillation process. The combination reduces the capital and operating
costs considerably. Among many different types of batch reactive distillation column
configurations, (a) conventional (b) inverted (c) semi-batch columns are considered
here.
Three reaction schemes such as (a) esterification of methanol (b) esterification of
ethanol (c) hydrolysis of methyl lactate are studied here. Four different types of
dynamic optimisation problems such as (a) maximum conversion (b) maximum
productivity (c) maximum profit and (d) minimum time are formulated in this work.
Optimal design and or operation policies are obtained for all the reaction schemes.
A detailed rigorous dynamic model consisting of mass, energy balances, chemical
reaction and thermodynamic properties is considered for the process. The model was
incorporated within the dynamic optimisation problems. Control Vector
Parameterisation (CVP) technique was used to convert the dynamic optimisation
problem into a nonlinear programming problem which was solved using efficient SQP
(Successive Quadratic Programming) method available within the gPROMS (general
PROcess Modelling System) software.
It is observed that multi-reflux ratio or linear reflux operation always led to better
performance in terms of conversion, productivity for all reaction schemes compared to
that obtained using single reflux operation.
Feed dilution (in the case of ethanol esterification) led to more profit even though
productivity was found to be lower. This was due to reduction in feed price because of
feed dilution. Semi-batch reactive distillation opertation (for ethanol esterification) led
to better conversion compared to conventional batch distillation, however, the total
amount of acetic acid (reactant) was greater in semi-batch operation. Optimisation of
design and operation (for ethanol esterification) clearly showed that a single cloumn
will not lead to profitable operation for all possible product demand profile. Also
change in feed and /or product price may lead to adjust the production target to
maximise the profitability.
In batch distillation, total reflux operation is recommended or observed at the begining
of the operation (as is the case for methnaol or ethanol esterification). However, in the
case of hydrolysis, total reflux operation was obseved at the end of the operation. This
was due to lactic acid (being the heaviest) was withrawn as the final bottom product.Libyan Petroleum Institut
Improvement of Batch Distillation Separation of Azeotropic Mixtures
La distillation est le procédé de séparation le plus répandu dans l'industrie chimique. Pour la séparation des mélanges azéotropiques, une méthode spéciale de distillation doit être appliquée. Le but de mon travail était d'améliorer la séparation des mélanges azéotropiques par distillation discontinue (DD). Un nouvel algorithme a été présenté pour la détermination de la séquence des produits de DD pour des mélanges multicomposants azéotropiques. Contrairement aux méthodes publiées précédemment, cet algorithme n'a pas besoin des paramètres d'équilibre. Configurations non-conventionnelles de DD ont été étudiées par simulation rigoureuse avec un accent sur l'opération fermée. Nombreux modes d'opération fermés étaient proposés, lesquelles diffèrent en l'opération de réservoir supérieur. Les effets du recyclage des fractions sur un procédé de séparation existant de 6 lots d'un mélange déchet azéotropique ont été étudiés. Les études ont été étendues pour un procédé de distillation extractive discontinue (DED). Un volume minimal de pré-fraction doit être incinéré. Le cas optimal de DED a donné un profit plus grand que celui de DD. DED a été étudié pour la séparation des deux mélanges azéotropiques. La séparation a été infaisable ou le rendement a été bas par DD, mais DED et le procédé hybride ont donné des rendements élevés. Une nouvelle politique de DED a été aussi proposée. Un modèle généralisé de la distillation hétéroazéotropique discontinue avec une rétention variable de décanteur a été développé. Dans une analyse de faisabilité, toutes les politiques opérationnelles possibles ont été identifiées. Ce modèle a été étendu pour la distillation extractive hétérogène discontinue. ABSTRACT : Distillation is the most widespread method for separating liquid mixtures. The separation of azeotropic mixtures requires a special distillation method. My aim was to improve the batch distillation separation of azeotropic mixtures. A new algorithm was presented for the determination of product sequences of batch distillation of multicomponent azeotropic mixtures. Non-conventional configurations were studied by simulation with emphasis on closed operation. The effects of off-cut recycle on a six-batch separation process of a waste solvent mixture were also investigated. Batch extractive distillation was studied for the separation of two azeotropic mixtures. A new extractive policy was also proposed. A generalised model of batch heteroazeotropic distillation with variable decanter hold-up was developed. This model was extended for batch heterogeneous extractive distillation