Reaction kinetics of dolomite and portlandite

The reactions of dolomite with portlandite have been studied at well-spaced temperatures between 20 degrees C and 85 degrees C using XRD Rietveld, TG and SEM methods. The results show quantitatively the faster rates of reaction at higher temperature. Isothermal reaction has, at most, a short induction period after which the degree of reaction is linear with time. An exponential equation is presented to predict the initial rate of reaction as a function of temperature. The microstructure shows that large equant calcite crystals, up to 30 mu m, develop on the rhomboid cleavage surfaces of dolomite. Pressed pellets of dolomite develop calcite at both exterior surfaces and in the interior, where calcite develops as a secondary phase but is not morphologically well-formed crystals. Pellets remain coherent in the course of reaction. The porous pellets have much unfilled space inside and often exhibit portlandite agglomerates with development of Hadley grain structures at the sites of former dolomite crystals, especially when reacted at lower temperatures. The reaction is not topotactic but requires dissolution, transport, nucleation and growth. Transport occurs often over considerable distance relative to the sizes of crystals. (C) 2014 Elsevier Ltd. All rights reserved.

Micro-batch reactor for catching intermediates and monitoring kinetics of rapid and exothermic homogeneous reactions

Olivier Détraz, Madhvanand Namadeo Kashid, Lioubov Kiwi, Petra Prechtl, Albert Renken, Mireia Santacana Moya

The mechanism and kinetics of rapid and exothermic reactions is difficult to study using conventional offline techniques. This paper deals with experimental investigations of highly exothermic and fast model reaction (cyclisation of pseudoionone) using slug flow (micro-batches) microstructured reactor (MSR). The slug flow was obtained using a cross-junction and identifying suitable inert carrier fluid (perfluorohexane) immiscible with the species participating in the reaction. MSR provided short reaction time in a continuous slug-flow that allowed catching intermediates and monitoring the kinetics. The small reaction volumes suppress the temperature rise by removing the reaction heat. The kinetics has been studied under isothermal conditions and more reliable reaction network has been proposed. Finally, the mixing within the slugs and its influence on the obtained results was accessed. This methodology has a generic nature and can be applied for a wide variety of fast exothermic homogeneous reactions. (C) 2012 Elsevier B.V. All rights reserved.

Elsevier2013

Accumulation in fed-batch reactor with multiple reaction scheme

Charles Ibrahim Guinand

Nowadays, the fine chemical industry requires increasingly faster time-to-market as well as economically efficient and safe processes. In addition, the growing product variety needs more versatile production plants able to produce from small amounts up to several hundred tons per year. As a consequence, the time devoted to development is limited, and the production often takes place in multipurpose plants. This implies that a given process can run in different reactors making the process development a long and complicated task. As a matter of fact, the behaviour of a reactive system changes with scale and also changes from one equipment to another which often leads to difficulties in controlling a reactor at the industrial scale. In most cases, chemical incidents are caused by loss of control and wrong assessment of the thermal potential, resulting in runaway reactions or deviations in different units. These incidents could be foreseen and avoided or at least decreased with an appropriate process development and risk assessment. All processes should be optimised to achieve a fair productivity and still remain inherently safe. Such process characterization aims at providing a better understanding of reaction pathways and thermal behaviour. To reach this goal, save resources and effort, the real system dynamics can be reproduced by models where parameters are estimated from experimental calorimetric data. The dynamic behaviour of the reaction system can be represented by two models: 1) The reaction kinetics, based on an assumption of the reaction scheme considering different reactions occurring along the process course and 2) The reactor dynamics highlighting how the heating/cooling system controls the reaction course by adjusting its temperature and the adopted feed profile strategy. To acquire enough knowledge on the studied reaction system, several experiments have to be performed in a multiscale based approach to maximize the disturbances and explore the overall reaction kinetics. Nevertheless, even with this method, the investigation can be very long due to the increasingly complex models, involving a large number of parameters and amount of experiments. Therefore, a new approach to solve these issues has to be developed. The proposed approach is summarized in three steps: 1. Reaction Kinetic Investigation: Planning and minimize the number of experiments in a statistically optimal way to cover the experimental space efficiently and using a numerical method to extract the reaction kinetics based on the power rate law. 2. Reactor Dynamic Investigation: Planning the experiments in order to obtain information about the dynamic behaviour of the jacket together with its temperature controller and then use a numerical method to extract the parameters representing the reactor. 3. Risk assessment and Optimization: Combine the reaction kinetics and reactor dynamics to shape a Process Implementation model serving to predict the behaviour of the overall system and identify the optimal operating conditions the process inherently safe. This research establishes a new process scale-up methodology, regarding the assessment of the thermal potential. The results demonstrate that a multiscale approach joined with modelling and inherent safety, lead to a better understanding of the system. This approach also notably helps to optimise the operating conditions making the process inherently safe and remaining economically favourable.

EPFL2017

Accumulation in fed-batch reactor with multiple reaction scheme

Charles Ibrahim Guinand

EPFL2017