Trickle Bed Reactors

Reactor Engineering and Applications

Vivek V. Ranade, Raghunath Chaudhari, Prashant R. Gunjal

• Publisher: Elsevier
• Year: 2011
• eBook ISBN: 9780080931449
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

This book provides a hybrid methodology for engineering of trickle bed reactors by integrating conventional reaction engineering models with state-of-the-art computational flow models. The content may be used in several ways and at various stages in the engineering process: it may be used as a basic resource for making appropriate reactor engineering decisions in practice; as study material for a course on reactor design, operation, or optimization of trickle bed reactors; or in solving practical reactor engineering problems. The authors assume some background knowledge of reactor engineering and numerical techniques.- Facilitates development of high fidelity models for industrial applications- Facilitates selection and application of appropriate models- Guides development and application of computational models to trickle beds

Chapter 1. Introduction

Fluids wander in the great void, some of these eject and some of these stray in voids, having found no group that they could belong to. A model and image of such wandering fluids is something we have daily before our eyes: Just look when rain fall on sand stones; you will see many tiny streams twisting and turning and moving here and there where the sunlight shows. It's as if they were in an unending conflict with squadrons coming and going in ceaseless battle, now forming groups, now scattering, and nothing lasting. From this you can imagine the agitation of these fluids in the great emptiness, so far at any rate as so small an example can give any hint of infinite events.

Modified version of De Rerum Natura

Trickle Bed Reactors

Trickle bed reactors are gas–liquid–solid contacting devices used in many diverse fields such as petroleum, petrochemical, fine chemicals, and biochemical industries. History of trickle bed reactors can be traced back to the eighteenth century with early applications mainly in wastewater treatment all over the world. Later on these reactors became quite popular in diverse chemical and petroleum industries because of a variety of their unique advantages for large volume processing. The worldwide capacity of materials processed via trickle bed reactors is approximately 1.6 billion metric tons/annum. The value of products processed through trickle bed reactors on an average is of the order of 300 billion US$/year (Sie & Krishna, 1998). The trickle bed reactors contribute significantly to manufacture cleaner fuels by hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions in refineries. Several other types of reactions involving hydrogenation, oxidation, alkylation, and chlorination are carried out advantageously in trickle bed reactors. Some examples of the industrial applications of trickle bed reactors are listed in Table 1. Current and future emphasis on cleaner fuels and increasing new applications of trickle bed reactors demand in-depth understanding of the engineering tools to enable manipulation and control of the trickle bed reactors for improved performance. In recent years, several variants of trickle bed reactors including micro reactors and mesh reactors have been introduced, while the attempts to further develop the design and scale-up methodologies continue. It is therefore essential to clearly understand the fundamentals of contacting gas and liquid reactants in “trickle bed” type of reactors to realize their full potential for existing and emerging applications. This book provides the basic understanding and a computational framework to simulate, manipulate, and control the performance of trickle bed reactors.

TABLE 1 Some Applications of Trickle Bed Reactors

Reaction Type	Process	Catalyst	Pressure (MPa)	Temperature (K)
Oxidation reactions	Ethanol oxidation	Pd/Al	2	343–373
	Wet oxidation of phenol	Pt/Al2O3	3–10	100–200
	Oxidation of formic acid/oxidation of organic matter in waste water treatment/oxidation of phenol	Co/SiO2–AlO2, CuO	0.1–1.5	300–403
Petroleum processing	Hydrodesulfurization Hydrodenitrification Hydrodemetallization	Mo–Ni	20–80	593–653
	Hydrodemetallization
	Catalytic hydrocracking/catalytic hydrofinishing
	Catalytic dewaxing, dearomatization
Hydrogenation reactions	Hydrogenation of various petroleum fractions, nitrocompounds, carbonyl compounds, carboxylic acids to alcohols (adipic acid to 1,6-hexanediol)	Pd, Pt, Ni, Cu	3–10	323–423
	Selective hydrogenation of acetylene to separate compound from C4 fraction in the presence of butadiene	Au/Al, Pd/Al2O3	0.1–2.5	313–523
	Hydrogenation of crotonaldehyde and α-methylstyrene to cumene	0.05% Pd on Al2O3	0.1–5	373–773
	Hydrogenation of 2-butyne-1,4-diol	Ni	10–30	350–450
	Hydrogenation of caprolactone and adipic acid	Cu	15–25	450–550
	Hydrogenation of aniline to cyclohexylaniline	Pd/Al2O3	3–20	298–313
	Hydrogenation of glucose to sorbitol	Ru/C	8	373–393
	Hydrogenation of maleic anhydride	Raney nickel, Pt/C	1–5	200–400
	Hydrogenation of acid esters to alcohols
	Hydrogenation of coal liquefaction extracts	Ni–Mo/Al2O3	7	593–623
Esterification	Esterification of acetone and butanol	Strong acidic ion exchange resin
F–T synthesis	Fischer–Tropsch reaction	Co/TiO2	10–50	450–650

Trickle bed reactors comprise a family of reactors in which gas and liquid phase reactants flow in downward direction (toward the direction of gravity) over a bed of solid catalyst particles. The gas phase may flow in upward or downward direction depending on the type of application. The liquid phase, however, always flows or “trickles” over the solid catalyst in a downward direction. The word “TRICKLE” itself describes its operational characteristics in which liquid intermittently flows over the solid catalyst in the form of films or rivulets or droplets. Conventionally, solid catalyst particles (may be of different shapes) are randomly packed in a bed through which gas and liquid phases flow. However, different variants of trickle bed reactors, comprising structured catalytic beds like monoliths in which the catalyst is coated on the interior surface of small channels or a mesh reactor in which the catalyst is coated on the mesh, have been used. In all these cases, catalyst loading in the reactor is substantially higher than other multiphase reactors (solid volume fraction is usually larger than 0.4 in trickle bed reactors). In most of the industrial trickle bed reactors, catalyst particles are generally porous and are of different shapes such as spherical, cylindrical, extrudates, trilobes, or multilobes (Fig. 1). The reactions carried out in trickle bed reactors are often exothermic and energy liberated because of chemical reactions is transported by flowing gas and liquid components. Management of this liberated energy from the catalytic bed without causing undesired effects on the performance is often a crucial task in the design of trickle bed reactors.

FIGURE 1 Schematic shapes of catalyst particles used in practice (from Palmisano, Ramachandran, Balakrishnan, & Al-Dahhan, 2003).

The overall performance of trickle bed reactors depends on several issues like characteristics of catalytic bed (packing configuration, porosity, particle size/coating thickness), flow maldistribution, wetting of catalyst particles and local interphase heat (including beds to wall) and mass transfer rates, intraparticle mass and heat transfer, and reaction kinetics. The configuration and characteristics of the catalytic bed influence the underlying fluid dynamics and therefore the local transport rates, wetting, and mixing of fluid phases in trickle bed reactors. The innovation and competitive edge of any technology based on trickle bed reactors therefore rests on how well the underlying fluid dynamics is understood and optimized to suit the specific process requirements. The complex fluid dynamics of trickle bed reactors often makes the scale-up or scale-down of trickle bed reactors quite difficult. Despite knowing this for several years, conventional methods used for design and optimization of trickle bed reactors often rely on experiments and empirical models. However, experimental measurements of design parameters have limitations due to severe operating conditions (high pressure and temperature) and difficulties because of the opaque and inaccessible nature of the packed beds, especially on pilot or large-scale reactors. The correlations and basic reaction engineering models based on mass and energy balances for designing of trickle bed reactors have been discussed extensively in a review by Satterfield (1975) and in a classic book by Ramachandran and Chaudhari (1983). In the last couple of decades, extensive research on various aspects of the trickle bed reactors and new developments in experimental as well as theoretical approaches has been carried out to get better insight into the complexities of trickle bed reactors. For example, new experimental techniques like Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) can provide more details on porosity and gas–liquid...

Table of contents

• Cover Image
• Table of Contents
• Front Matter
• Copyright
• Preface
• Chapter 1. Introduction
• Chapter 2. Hydrodynamics and Flow Regimes
• Chapter 3. Reaction Engineering of Trickle Bed Reactors
• Chapter 4. Flow Modeling of Trickle Beds
• Chapter 5. Reactor Performance and Scale-Up
• Chapter 6. Applications and Recent Developments
• Notations
• Author Index
• Subject Index