Catalytic Reactors

Basudeb Saha, Basudeb Saha

• Publisher: De Gruyter
• Year: 2015
• ISBN:
  9783110390124
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

Catalytic Reactors presents several key aspects of reactor design in Chemical and Process Engineering. Starting with the fundamental science across a broad interdisciplinary field, this graduate level textbook offers a concise overview on reactor and process design for students, scientists and practitioners new to the field.

This book aims to collate into a comprehensive and well-informed work of leading researchers from north America, western Europe and south-east Asia. The editor and international experts discuss state-of-the-art applications of multifunctional reactors, biocatalytic membrane reactors, micro-flow reactors, industrial catalytic reactors, micro trickle bed reactors and multiphase catalytic reactors. The use of catalytic reactor technology is essential for the economic viability of the chemical manufacturing industry. The importance of Chemical and Process Engineering and efficient design of reactors are another focus of the book. Especially the combination of advantages from both catalysis and chemical reaction technology for optimization and intensification as essential factors in the future development of reactors and processes are discussed. Furthermore, options that can drastically influence reaction processes, e.g. choice of catalysts, alternative reaction pathways, mass and heat transfer effects, flow regimes and inherent design of catalytic reactors are reviewed in detail.

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• Focuses on the state-of-the-art applications of catalytic reactors and optimization in the design and operation of industrial catalytic reactors

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• Insights into transfer of knowledge from laboratory science to industry

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• For students and researchers in Chemical and Mechanical Engineering, Chemistry, Industrial Catalysis and practising Engineers

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Sanjay M. Mahajani and Basudeb Saha

1 Catalysis in Multifunctional Reactors

1.1Introduction

A multifunctional reactor is broadly defined as a multifaceted reactor system that combines a conventional reactor with any physical process to enhance the overall performance of the process to bring cost-effectiveness and/or compactness to a chemical plant. This multi-functionality can exist either on micro (catalyst) level or on macro (reactor) level [1]. There is substantial information available on several ways to achieve this task. Combining reaction with separation is one such popular approach. Here, when separation is performed in situ, several benefits like an increase in per-pass conversion and/or selectivity, energy integration, longer catalyst life, etc. are attained. When a separation process – e.g. distillation, adsorption, etc. – is to be performed simultaneously with a reaction, it imposes more restrictions on the reactor design so as to meet possible conflicting requirements that result from the reaction and separation. The existence of multiple phases as well as problems associated with heat and momentum transfer, mixing issues, etc. make the process complex, thereby attracting the attention of experts in reaction engineering, catalysis, modeling and simulation, and process design.

Since catalysts are an integral part of a reactor system, many efforts have been made to manipulate its design to meet the above-mentioned challenges. A few examples are inserting special catalyst-filled envelopes into a distillation column to reduce pressure drop, manipulating the hydrophobicity of ion exchange resin in reactive chromatography for selective separation, grafting the catalyst in membrane material, etc. In this chapter, we review the recent literature on catalysts and their modified forms used in multifunctional reactors that combine reaction and separation. We restrict ourselves to the four most studied multifunctional reactors: reactive distillation, reactive stripping, membrane reactors and chromatographic reactors.

1.2Reactive Distillation (RD)

Reactive distillation is a multifunctional reactor in which chemical reaction and a fractional distillation can be performed simultaneously. It is generally applied to a reversible reaction in which at least one of the products has a different volatility with respect to the other compounds. The most general configuration of a reactive distillation unit consists of: (i) a rectification section in the upper zone; (ii) a reactive section in the middle; and (iii) a stripping section in the lower zone. Due to the simultaneous operation of reaction and separation, this process offers smaller plant size, lower operating costs, higher yields and energy savings. The basic requirement for the success of reactive distillation is a reasonable reaction rate in the temperature and pressure ranges that are governed by the vapor-liquid equilibrium. It is particularly advantageous for equilibrium limited reactions in which the separation of at least one of the products as it is formed can drive the reaction to near completion. Reactive distillation allows the reaction to be carried out much closer to the stoichiometric ratio of the feed flows. Further, it is useful in the case of reactions in which a high concentration of the product or one of the reactants can cause undesired side reactions. Literature is replete with the information on various aspects of reactive distillation. Sharma and Mahajani [2] have reviewed various applications of reactive distillation. The important applications include etherification, dimerization, oligomerization, condensation, esterification, trans-esterification, hydrolysis of esters, hydration, hydro-desulfurization, alkylation, acetalization, ketalization, etc.

Successful commercialization of RD technology requires special attention to the hardware design. This means that standard designs used for conventional distillation may not work in the case of RD. The column should provide favorable conditions for both reaction and distillation. The catalyst used in RD columns (RDCs) can be either homogeneous or heterogeneous. The homogeneous catalysts generally offer a high activity; however, a separation of the catalyst from the product mixture incurs an additional cost. However, heterogeneous catalysts such as anion and cation exchangers, zeolites, etc. are preferred over their homogeneous counterparts. These catalysts offer various advantages that include the elimination of separation and recycling of catalysts, elimination of acid disposal problems, exactly defined position of the height of the reaction zone in the column, less corrosion problems, lower investment costs and relatively easier operation. The challenge in heterogeneously catalyzed reactive distillation is the decision of how, where and which type of catalyst should be placed in the reactor to achieve the desired performance. The location of the reaction zone inside the column depends on the type of reaction and the relative volatilities of the components. The column internals for reactive distillation should be designed in such a way that there is an efficient contact between solid catalysts and the liquid phase; one achieves efficient separation by distillation with a high capacity and low pressure drop. A liquid hold-up higher than what is necessary for normal distillation columns is required if the reaction is slow [3, 4]. The optimal solution must be a compromise between these requirements. The mechanical arrangement of the catalyst inside the column and its shape are of primary importance in achieving an optimal performance for both the reaction and distillation. In the following section, RD column hardware for both homogeneous reactions and heterogeneous reactions are explained.

1.2.1Homogeneous catalysis

RD columns, in which a reaction takes place in the liquid phase, are operated counter-currently; a sufficient degree of staging can be achieved in a multi-tray column or in a column with random or structured packing. The packing in this case is inert and serves only to provide even liquid distribution in the column and to suppress liquid phase back-mixing. To increase the productivity of an RD column, it is important to maximize the liquid hold-up in the column as the Hatta number is usually less than unity in most cases [5]. Packed columns usually have much lower hold-up than tray columns, so for a homogeneous RD, tray columns are preferred. The tray column can be operated in the spray, mixed froth or bubbly flow regimes. As higher liquid hold-up and higher residence time are desired, the preferred regime of operation is the bubbly flow regime; it can be achieved by operating the column at lower superficial vapor velocities. The higher weir height ensures higher liquid hold-up on the tray. The bubble cap trays provide higher liquid hold-up, and reverse flow trays with additional sumps can be used to increase the liquid residence time. Eastman Kodak uses a specially designed tray for the manufacture of methyl acetate [6]. Computational fluid dynamics (CFD) can provide better insight into the flow pattern and hence the column performance based on liquid hold-up, pressure drop, residence time distribution and mass transfer aspects. It can predict whether ...

Table of contents

• Cover
• Title
• Copyright
• List of contributing authors
• About the editor
• Preface
• Contents
• 1 Catalysis in Multifunctional Reactors
• 2 Biocatalytic membrane reactors (BMR)
• 3 Metallic nanoparticles made in flow and their catalytic applications in micro-flow reactors for organic synthesis
• 4 Application of multi-objective optimization in the design and operation of industrial catalytic reactors and processes
• 5 Design of catalytic micro trickle bed reactors
• 6 Three-phase catalytic reactors for hydrogenation and oxidation reactions
• 7 Design and modeling of laboratory scale three-phase fixed bed reactors
• Index