CO2 Solutions Inc.
`Exhibit 2007
`Akermin, Inc. v. CO2 Solutions Inc.
`IPR2015-00880
`Page 1 of 50
`
`

`
`Copyright © 19.83. by Gordon and Breach, Science Publishers, Inc.
`
`Gordon and Breach, Science Publishers, Inc.
`. One Park Avenue
`New York, NY 10016
`
`Gordon and Breach Science Publishers Ltd.
`42 William IV Street
`'
`
`London, WC2N 4DE
`
`. _Gordon & Breach
`5 8, rue Lhomond
`75005 Paris
`
`5
`
`Library of Congress Cataloging in Publication Data
`
`Ramachandran, P. A.
`
`_
`
`Three-phase catalytic reactors.
`
`'
`
`(Topics in chemical engineering, ISSN 0277-5883‘;
`g V. 2)
`.
`Bibliography: p.
`Includes index.
`
`1. Chemical reactors. 2; Catalysis.
`' I.'Chaudhari, R. V.
`II. Title.
`III. Series:
`Topics in chemical engineering (Gordon and Breach Science
`Publishers); V. 2.
`'
`‘
`TP157‘.R3'
`660.2’995
`ISBN .0-677-05 650-8
`
`' 81-23521
`AACR2
`
`ISBN 0-677-05650-8. ISSN 0277-5883. All rights reserved. No part of this book may 4
`be reproduced or utilized in any form or by any ‘means, electronic or mechanical,
`including" photocopying, recording, or by any information storage or retrieval system
`\
`Without prior permission in writing from theppublishers. Printed in Great Britain.
`
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`

`
`
`
`I Introduction
`
`1.1 _ Areas of Application
`
`A THREE-PHASE catalytic reactor is a system in which gas and liquid
`phases are contacted with a solid-phase catalyst. In most applications,
`the reaction occurs between a dissolved gas and a liquid-phase reac-
`tant in presence of a solid catalyst. In some cases, the liquid is an inert
`medium and the reaction-takes place between the dissolved gases at
`the solid surface. These reactors have many diverse applications in‘
`catalytic processes and are becoming increasingly importantin the
`chemical-industry. Some of the important commercial applications of
`the three-phase reactors are described briefly below. (A more "com-
`plete discussion on some of these systems is presented in Chapter 12).
`
`_
`
`1.1.1 Hydrogenation of Unsaturated Oils
`
`Hydrogenation of industrial fats. and fatty oils is one of the important
`applications. A three-phase reactor is essential for this purpose
`because vaporization of fats‘ is a highly impracticable proposition. ‘
`The oils, such as cottonseed oil, soybean oil, corn oil, sunflower oil,
`etc., are hydrogenated in the presence of a nickel catalyst. The pro-
`. ducts obtained include oleomargarine stock, shortening, soap stock,
`and industrial greases. The reaction involves partial or complete sat-
`urationof carbon-carbon double bonds that are present hi the tri-
`glycerides (oils). .
`'
`
`1.1.2 Synthesis of Butynediol and Propargyl Alcohol
`
`Synthesis of butynediol from acetylene and aqueous formaldehyde
`solution is generally carried out using a supported copper acetylide
`catalyst in a three-phase reactor. This’ process is known as the Reppe
`
`1
`
`.
`
`.
`
`'
`
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`

`
`2
`
`THREE-PHASE CATALYTIC REACTORS
`
`process and the reaction can be represented as
`
`C21-12 + HCHO
`
`.3_‘fl’3’.‘i".d_C_"232; HocH~C=CH (11)
`2
`——-
`o
`propargyl alcohol
`
`HoCH2% CECH + HCHO
`
`supported Cu2C2
`—-——————>
`
`HOCH2—— CEC—CH2OH (1.2)
`2-butyne-1,4-diol
`
`The intermediate product, propargyl alcohol, formed in this reaction
`is also a useful raw material in many chemical processes and can be a
`major product at high acetylene pressures and low formaldehyde
`concentrations. An interesting feature of this process is that since the
`catalyst (copper acetylide) is explosive in the dry form, it is prepared
`. in situ.
`Butynediol may be further hydrogenated to butenediol or
`, butanediol. This operation is also normally carried out in a three-
`phase reactor in the presence of a supported Pd or Cu—Ni catalyst.
`
`1.1.3 Hydrodesulfurization of Petroleum Feedstocks
`
`The desulfurization of crude oils is gaining importance in industry.
`This process consists of removing sulfur-containing compounds in the
`oil by catalytic hydrogenation. The main reaction can be schemati-
`. Cally represented as
`
`supported
`
`(1.3)
`hydrocarbon + H28
`Qrganosulfur + H2
`Desulfurization of oils is necessary for two main reasons: (a) the ‘
`combustion of sulfur—containing fuels is the primary cause of pollu-
`tion of the atmosphere by S02 and (b) the sulfur compounds poison '
`the expensive precious metal catalysts used in the reforming proces-
`ses. Most of the commercial processes for hydrodesulfurizatlon em-
`ploy three-phase reactors.
`
`1.1.4 Hydrodenitrogenation
`
`This is another important’ example of a three-phase reaction that
`involves the removal of nitrogen compounds from oil feedstocks. The_
`
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`

`
`reaction can berepresented as
`
`INTRODUCTION 3
`
`in decreasing the‘
`Hydrodenitrogenation has become. important
`organonitrogen content of synthetic crudes extracted from oil shales,
`oils derived fromvlow-temperature pyrolysis of coal or low-grade
`naturally occurring petroleum which contain large amounts of both
`sulfur -and nitrogen (Satterfield et al., 1975). Denitrogenlation usually
`occurs simultaneously with desulfurization as organonitrogen com- .
`. pounds are generally present along with organosulfur compounds.
`
`1.1.5 Hydrocracking
`
`1
`
`Hydrocracking is a process in ‘which the heavy petroleum fraction is
`cracked in the presence of hydrogen using supported metal catalysts
`to yield products of lower molecular weight.
`I
`4
`
`V
`
`1.1.6 Fischer—Tropsch Synthesis '
`
`This generally refers to a class of reactions where carbon monoxide
`and hydrogen are reacted to produce certain specific products, such
`as methane, methanol, and higher hydrocarbons. Methanol synthesis
`is generally carried o'ut as- an gas—-solid reaction. However, a recent
`process using a three-phase reactor appears to provide some advan-
`tages (Sherwin and Frank, 1976). In this process, two gases (CO and
`H2) are bubbled through a medium of the product (methanol) con-
`taining the suspended catalyst. Here the liquid medium is inert and
`does not take part in the reaction. Synthesis of higher hydrocarbons
`from carbon monoxide and hydrogen was a well established process
`in Germany, Japan, and France before the second world war; these
`reactions were carriedlout in the three-phase mode. The process is
`likely to become commercially important once again due to the
`increasing need to locate alternate sourcesfof raw materials to crude
`oil. Currently" a large-scale Fischer-Tropsch process plant is operat-
`ing at SASOL_in "South Africa.
`
`p. Page 5 of 50
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`
`4
`
`THREE-PHASE CATALYTIC REACTORS
`
`1.1.7 Manufacture of Sorbitol from Glucose
`
`.
`
`is a commercially
`Catalytic hydrogenation of glucose to sorbitol
`important application of the three-phase reactor. Sorbitol is impor-
`tant in the manufacture of vitamin C. In this process, glucose is hyd-
`rogenated in the presence of a Raney nickel catalyst or a supported
`nickel catalyst. The reaction involves conversion of an aldehyde
`—CHO) group to an alcohol (-CH2OH).
`
`1.1.8 Hydrogenation of Cellulose
`
`Cellulose can be converted to liquid fuels by catalytic hydrogenation
`(Gupta et al. , 1976). The catalyst used is a nickel crystallite prepared
`in situ from nickel hydroxide. Paraffin oil is used as a medium of
`reaction. As this system involves the presence of two solid phases
`(cellulose and a catalyst), a liquid, and a gas, it is an example of a
`complex multi-phase reaction system.
`/*
`
`1.1.9 Pollution Control
`
`v
`
`Three-phase systems find some applications in the removal of pollut-
`ant gases, such as SO2 or H2S, by oxidation. For example, SO2
`removal from refinery tail gases or flue gases may be achieved by
`contacting them with water-containing activated carbon as a catalyst.
`Here the liquid medium is inert and reaction occurs between dis-
`solved S02 and O2 in the presence of a catalyst. Similarly, ’H2S may
`be oxidized to sulfur in an aqueous medium in the presence of
`activated carbon catalyst. Trace concentrations of liquid pollutants
`can also be removed by oxidation in a three-phase system.
`
`1.1.1!) Polymer-Bound Catalysis
`
`Liquid-phase homogeneous catalysts consisting of transition metal
`complexes offer possibilities of high selectivity for specific reactions. '
`The recovery of these expensive catalysts is, however, a difficult prob- _
`lem and also a major obstacle in commercial exploitation of these
`processes. The problem could be solved by heterogenizing these
`catalysts by binding them to polymers (Pittman et al., 1975). These
`
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`

`
`INTRODUCFION 5
`
`catalysts could then be used in a three-phase reactor. Possible appli-
`cations are in the field of carbonylation and hydroforrnylation rea‘c=
`tions. For example, the reaction of propylene, H2, and CO (oxo
`synthesis) to give butyraldehyde can be carried out using a Rh com-
`. plex catalyst bound to a. polystyrene—DVB support. Three-phase
`_reactors are likely to have potential applications in this emerging
`area.“-
`
`Three-phase reactors are also useful’ in many hydrogenation and
`oxidation reactions. A number of examples of these systems are pre?
`sented in Chapter 12.
`'
`
`1.2 Types of Three-Phase Reactors
`
`Three-phase reactors used in industry can be classified into two main
`categories:
`(a)- fixed-bed reactors in which the solid catalyst
`is
`stationary, and (b) slurry reactors in which the solid "catalyst
`is
`suspended and is in motion.
`
`1.2.1 Fixed-Bed Reactors
`
`G In this type of reactor, the two fluid phases move overa stationary
`bed of catalyst particles. The various modes of operation of fixed bed
`reactors are (a) cocurrent downflow of both gas and liquid, (b) down-
`flow of liquid and countercurrent upflow of gas, and (c) cocurrent
`upflow of both gas and liquid. These operations are schematically
`shown in Figure 1.1. The reactor in which liquid and gas_flow down-
`ward (category a) is conventionally referred to as a trickle-bed reac-
`tor (Satterfield, 1975). On the -other hand, a reactor with cocurrent
`upflow of gas and liquid (category c) is generally referred to as a
`packed bubble-bed reactor (Hofmann,'1978)’.
`In a trickle-bed reactor, the liquid is generally the dispersed phase"
`and flows downward in the form of rivulets or a thin film. The gas.
`phase is the continuous phase and flows either cocurrent or counter-
`current to the liquid. This reactor is commonly used‘ in industrial
`chemical processes.‘ Cocurrent operation is preferred as larger
`throughputst» of both gas and liquid phases are possible.
`(The
`throughput is not limited by flooding in cocurrent operation). For
`
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`

`
`_
`
`THREE-PHASE CATALYTIC REACTORS
`
`GAS
`
`LIQUID
`
`GAS
`
`LIQUID
`
`
`
`GAS ‘
`
`SOLID CATALYST *
`
`SOL ID CATALYST
`
`GAS BUBBLES
` LIQUID PHASE
`
`
`GAS
`
`GAS V
`
`(u) TRICKLE BED COCURRENT
`DOWNWARD OPERATION.
`
`(c) PACKED BUBBLE COLUMN
`REACTOR. (cocurrent upflow)
`FIGURE 1.1 Schematic diagrams of three-phase packed-bed reactors.
`
`lb) TRICKLE BED COUNTERCURRENT
`OPERATION .
`
`some specific situations (such as in pollution control where the gas
`phase leaving the reactor should have a very low solute content), the
`countercurrent mode is preferred.
`.
`.
`"The reactor with cocurrent upflow operation of both gas and liquid
`is commonly referred to as a packed bubble-bed reactor. In this reac-
`tor, the gas phase is generally the dispersed phase while the liquid is a
`continuous phase. At high gas rates and low liquid rates-, a phase
`reversal takes place and the gas phase becomes the continuous phase,
`but this mode of operation is not so common.
`/1
`
`1.2.2 Slurry Reactors
`
`Here the catalyst particles are in a suspended state. Depending on the
`mode by which the catalyst particles are suspended, it is possible to
`classify these reactors into three categories. Schematic diagrams of
`these reactors are shown in Figure 1.2.
`
`1.2.2.] Mechanically agitated slurry reactors
`
`Here the catalyst particles are kept in suspension by means of
`mechanical agitation.
`'
`‘
`
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`

`
`INTRODUCTION 7
`
`GAS
`
`‘
`
`3A5
`
`Lmum
`
`GAS " LIQUID
`» DISENGAGING
`zone
`
`LIQUID
`
`GAS BUBBLES
`CATALYST
`
`_.
`
`-
`
`;|_u|D|zED
`” zone
`
`3”""°’"
`PLATE~
`
`GAS
`
`‘
`
`_
`
`‘
`
`GAS
`
`
`
`
`
`
`LXQUID
`
`Uou”)
`
`(a) MECHANICALLY AGITATEQ
`SLURRY REACTOR
`
`. LIQUID
`(bl BUBBLE COLUMN
`SLURRY REACTOR
`
`LIQUID
`
`(C) THREE PHASE
`FLUIDIZED BED
`
`FIGURE 1.2 Schematic diagrams of three-phase slurry reactors.
`
`1.2.2.2 Bubble column slurry reactors
`
`In this type, the particles are suspended by meansof gas-induced
`agitation. Relatively small particles are used in this type of reactor.
`
`1.2.2.3 Three-phase fluidized-bed reactors
`
`Here the particles are suspended because of .the combined action of
`bubble movement and cocurrent liquid flow. The main difference in
`the fluidized bed and bubble column is that in the former the particles
`2 are suspended mainly due to liquid flow. Relatively larger particles
`can be used here.
`‘
`
`‘
`
`1.2.3 Comparison of Fixed-Bed and Slurry Reactors
`
`1.2.3.1 Overall rate of reaction,
`
`Due" to the hete'rogeneo_us nature of the three-phase system, a
`number of steps have to occur before a species can be converted to
`
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`

`
`‘ 8
`
`THREE-PHASE CATALYTIC REACTORS
`
`i
`
`q
`
`products. The major steps are (a) mass transfer from gas to liquid, (b)
`mass transfer from bulk liquid to the catalyst »surface, and (c)
`intraparticle diffusion within the pores of the catalyst accompanied by
`chemical reaction. The overall rate of reaction in three-phase reactors
`is often limited by these factors. The rates of mass transfer processes
`are generally faster in slurry reactors than in fixed—bed reactors. This
`is because smaller particles can be used in slurry reactors; the rates of.
`liquid—to-solid mass transfer and intraparticle diffusion are therefore
`higher, leading to a more efficient utilization’ of the catalyst. The
`catalyst loading (amount per unit volume of the reactor) is, however,
`lower in slurry ‘systems. Since the rate of reaction is also proportional
`to the catalystloading, the rate per unit volume of reactor is generally
`higher in a packed-bed reactor except for highly active catalysts,
`where the mass transfer process dictates the overall rate. Thus the
`rate ofreaction. per unit volume of the reactor is lower in slurry V
`systems, while the rate per unit weight of the catalyst is likely to be 4
`higher. Homogeneous‘ side reactions contribute more in slurry reac=-
`tors than in fixed beds due to the relatively large liquid holdup.
`In addition to’ mass transfer, the rate of reaction is influenced by
`the mixing patterns of the liquid and gas phases. Two extreme situa-
`tions of mixing are (a) plug flow and (b) completely backmixed flow.
`4’ In plug flow, the concentration of a reactant decreases from the inlet
`to the outlet monotonically, while in a backmixed reactor the con-
`centration is the same throughout the reactor andequal to the outlet
`concentration. Backmixing generally lowers the reactor performance.
`« The liquid phase in a slurry reactor is generally backmixed while in
`the fixed-bed reactorthe liquid flow pattern approaches the plug flow
`behavior. Hence, when high conversion of the liquid reactant is
`desired, fixed-bed operation is preferable to slurry reactors.
`
`1.2.3.2 ~ Heat transfer
`
`\
`
`\ -
`Since heat transfer is more efficient in slurry reactors than in fixed
`beds, the control of temperature is easy in slurry reactors. This leads
`to uniform temperature at the active sitesof the catalyst and avoids
`formation ofhot spots. Large liquid holdup in slurry reactors also
`facilitates better temperature control due to the large heat capacity
`of the liquid‘ phase. A
`‘
`‘
`
`,
`
`3
`;
`
`‘
`
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`

`
`INTRODUCTION 9
`
`1.2.3.3 Separation and handling of Catalyst .
`
`Separation-of the catalyst poses difficulties in the continuous opera-.
`tion of slurry reactors: mainly due to thepprioblems of filtration‘, while
`in
`1. problem is’ not ienpcounteredbljlowever,
`the handling of catalyst is easy in slurry reactors compared .to4.fixe_cl
`beds due to the suspended state of the "particles. In processes ‘where
`fre‘qi1_ent'remova'1’ replacementiof thefcatalyst isnecessary, fixed-
`bed‘ readtofis Imayiinoti be suitable beciaiisefreplacement of catalyst
`generally;re'quires shutdown and dismantling of the reactor column.
`Also, the p"r‘ob1em“of‘bed plugging, experieiicedlin trickle beds (for
`example, in hydrodesulfurizatioii) due to the formation of nonvolatile
`residues, is eliminated ‘in slurry systems by-using small, free‘-moving
`Pafticles.
`'
`'
`
`I
`
`~
`
`-
`1.2.4 l Comparisoniof 1Fixed-Bed»-‘Reactors I
`The :corr_1p,arisQ11,..0f _t.r-iCl<_le..-bed andpacked bub-bl,e-.b6.d reactors" is
`discussed-below; :;-mm
`*
`'
`>-
`
`a)
`In a trickle-‘bed”re’act'or When" {c515e£a£é’d "at lovvliquid rates-, part.
`of the catalyst may not be Wetted and may only be exposed to the
`gas-phase reactant. -This can lead to many complications,_ such as hot- _
`spot formation, temperature run-away‘, and, in some cases, poorer’
`' utilization of theicatalyst. In a packed bubble-bedprepactor, the catalyst
`is ,co‘inplet‘ely Wetted and the above complications" may not exist.
`b) The pressure drop in downflow operation is less than that in
`upflow (the packed bubble-bed operation), thus reducing the pump-
`ing energy costs.
`_
`H
`i
`i
`'
`c) The higher liquid_..Iates in packed bubble, beds may be helpful
`in situations Where the catalyst gets deactivated by the deposition of
`tarry or polymericsubstances. These impurities aretmore effectively
`washed out from packed b.ubble bedsthan from trickle-bed reactors-».
`a-2d,)
`:Heat transfer efficiency and heatJi:errio‘va1 are better in" packed .
`bubl5_Ieyb“eds“ due 'to'.1§afger"<_lii:;1ui'd. ‘holdup ‘and-‘liquid ?\?elo"city than in‘ a
`'tfi\c1:=1evbed—.%>~
`.a
`’e)" we ‘i5“vv7él-iiquid'iii5i&{3p, the iicdntribiitioni er hoiimgeriecds
`liquid-‘phaseside reactions, which can be significant in some cases in
`packed bubble-bed reactors, is relatively small in trickle-bed reactors.
`
`..
`
`Page 11 of 50
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`

`
`.10
`THREE-PHASE CATALYTIC REACTORS
`1.2.5 Comparison of Slurry Reactors,
`
`'-
`
`. The comparison oftthree types. of slurry reactors is discussed below:.
`a) Theinechanically’ agitated reactor has_the' advantage higiher
`heat a‘rid'n1as‘s transfer “efficiencies compared‘ the bubble V.colu.1r_1Vn
`and threeéphase fluidized-bed reactor. .'
`i
`‘
`M _j
`.b) Catalyst attrition cianbe significant iniiniechanically ’ag1:ggg,d
`reactors, while thisiproblern is, not so serious in the othertwo types.
`» c) As there are no moving parts, the mechanical design’ of bubble
`columns andifluidizfed-bed reactors is simpler than that of agitated
`slurry yreactors which require suitable provision» for stirrer seals.
`A d) Catalyst separation is relatively easy in a three-phase fluidized I
`bed as the particleisize range used is larger than that in the other"two ’
`A types of reactors. »
`‘
`’
`'
`e) The power requirement is highest for a rnechanica-lly.agitated
`reactor and islowest for the bubble column.
`‘
`i
`The catalyst -distributioniis relatively uniform in vl‘a'n‘-’ agitated .
`slurry reactor, while in a bubble column and a three-phase-‘fluid bed,
`a nonuniform distribution of particles can exist. a;
`._.
`‘
`
`1.2.6 Modes of Operation
`
`Two modes of operation are common ‘for three-‘phase reactors. I
`
`'
`
`1.2.6.1
`
`Se;1ii-batch- operation P
`
`Here, there is no net inflow or outflow of liquid in the reactor, while
`the gas flows‘ continuously. Many hydrogenation reactors a’re“ope"r-
`ated in a semi-ba‘tch— manner. This mode is mainlyused for slow
`reactions and isconvenient ‘for ‘converting a batch of liquid“ reactant
`toproducts. Mechanically agitated or bubbleficolumn-slurry reactors _
`can be_ conveniently use_,cl'.yas-tsemisbiatch,reactors (see-Figure .14‘.-3a).
`Similar operation in a trickle bed would involve additional .equ_ip.-
`. [I16I1’i, ‘Sv,1.,1.<3l1:;:E!S.?l _P.1.1II1p_ for recycle ofi*.1iquid“(see Figure __1._3b).
`.
`.
`
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`

`
`INTRODUCTION 11
`
`GAS
`
`_
`
`LIQUID
`
`SOLID CATALYST s
`
`sN§
`
`(a) SEMIBATCH SLURRY
`
`REACTOR.
`
`‘
`
`G/ls
`
`SUPPORT FOR
`CATALYST
`
`
`
`
`
`PUMP
`
`L|QUlD SURGE
`TANK
`
`(b)‘SEMlBATCH PACKED BED REACTOR.
`
`FIGURE 1.3 Schematic of semi-batch reactors.
`
`1.2.6.2 Continuous operation
`
`In a continuous mode of operation, both the gas and liquid phases
`flow continuously in the reactor. This operation is preferred for rela-
`tively fast reactions where a significant per pass conversion can be
`achieved. Due to the ease of catalyst separation, trickle-bed, packed
`bubble-bed, and three-phase fluidized-bed reactors can be con-
`veniently operated in this Way. The continuous operation of an agi-
`tated and bubble column slurry reactors requires suitable means for
`separation of the catalyst. In some cases, a continuous operation
`with recycle of part of the effluent liquid is used in order to obtain a
`high concentration of the product in the outlet liquid. When the extent
`of conversion of the gas-phase reactant is small, the gas phase is often
`recycled with suitable makeup (Figure 1.4). This is a common prac-
`tice in large-scale hydrogenation reactors.
`°
`
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`

`
`Page 14 of 50
`
`12
`
`THREE-PHASE CATALYTIC REACFORS
`
`GAS
`
`
`MAKEUP GAS
`
`
`
`
`
`PUMP
`
`, GA
`RECYCLE
`
`FIGURE 1.4 A continuous reactor with gas recycle.
`
`1.3 Scope of the ‘Work
`
`As discussed in Section 1.2.3.1, the three-phase reactors involve
`complexities due to the coupling of mass transfer andreaction. An
`' additional factor that needs ‘to be considered in these reactors is the
`backmixing of the ‘phases, In" some situations, nonisothermal effects
`are also important. The chemical reaction itself may follow a complex
`mechanism that leads to nonlinear kinetics and, in some cases, to
`series and parallel reactions. Hence, it is first necessary to analyze the
`influence of "mass transfer and intraparticle diffusion on the rate of
`reaction for variousrcomplex kinetics. The analysis ‘of differential
`. reactors is first essential to understand the effect of these complex-
`ities. This is becausepunder differentialconditions, the concentrations
`can be "assumed to be uniform in the reactor. Hence, the influence of
`backrnixing, nonisothermal effects, etc.’ are not so important here.
`
`Page 14 of 50
`
`

`
`]NI'RODUCI'ION 13
`
`Chapter 2 discusses the detailed theoretical analysis of the differential
`reactor.
`,
`C.
`In continuous reactors,
`two main additional complexities exist.
`First is the concentration change along the length of the reactor '
`leading to different reaction rates at different points. Second is the
`influence of backmixing of the gas and liquid phases. Hence, the
`design equations for continuous reactors should incorporate these
`factors in addition to mass transfer and reaction complexities. The
`modeling of continuousreactors is discussedlin Chapter 3 and the _
`design equations are developed for various cases.
`Many industrial three-phase reactors are operated in a semi-batch
`manner. In such cases, the concentration of the liquid-phase reactant
`is a function of time, hence the equations for a differential reactor
`have to be integrated over the entire time range to obtain the conver-
`' sion. Chapter 4 analyzes the design methods for semi-batch reactors.
`~ Having developed the design equations for continuous and semi-
`batch reactors, we require information on the mass transfer and the
`kinetic parameters. This is often determined by introducing a distur-
`bance (tracer) into the reactor (such as a pulse or a step change in the
`fluid concentration) and noting the transient responseof the system.
`To interpret the results of such experiments, it is necessary to under-
`stand the dynamic behavior of three-phase reactors. This knowledge
`is also useful in predicting the effect of disturbances on reactor per-
`formance and developing strategies for control of reactors. Chapter 5
`considers the theory of dynamics of three-phase systems.
`Various other techniques can also be used for evaluation of design
`parameters. Chapter 6 discusses the experimental methods that can
`be used to determine the various parameters required for analysis
`and design of three-phase reactors.
`_
`’
`Each reactor has some special characteristics and complexities of
`its own. For example, in a trickle-bed reactor, the catalyst may not be
`completely wetted at low liquid rates. In bubble columnsgthe dis-
`tribution of catalyst may be’ nonuniform. The mass transfer charac-
`teristics of each type of reactor are also influenced by the prevailing
`hydrodynamics. Hence, there is a necessity to study the hydrodynam-
`ics, mass transfer, heat transfer, and mixing characteristics of each
`reactor type. Chapters 7 to 11 cover these aspects for different types
`of three-phase reactors.
`.
`.
`T
`,
`_
`‘ Chapter 12 discusses some of the industrial applications of three-
`
`page 15 of 50 ;
`
`Page 15 of 50
`
`

`
`14 THREE-PHASE CATALYTIC REACTORS
`
`phase reactors. Some comfilexities of industrial systems are also
`pointed out, and the process design aspects and the choice of the type
`of reactor to be used for some of these systems are critically dis-
`cussed.
`A
`.
`‘
`
`_ Page 16 of 50
`
`Page 16 of 50
`
`

`
`
`
`8 Fixed-Bed) Reactor with Cocurrent if
`Upflow,
`
`\
`
`8.1
`
`Introduction
`
`‘
`
`THIS CHAPTER reviews the important design features of a fixed-bed
`, catalytic reactor with a cocurrent upflow of gas and liquid. A common
`mode of operation of such reactors is to have a continuous liquid
`_ phase with a dispersed gas phase. Such a reactor is also ‘referred to as
`> a packed bubble column reactor. This type of reactor is used when a
`relatively small amount of gas is to be processed with a large amount
`of liquid. Also, when a large residencetime for the liquid phase is
`desired, this operation is preferred. lln this operation, the catalyst
`particles are completely Wetted, and the entire catalyst surface can be
`, utilized effectively. The mass and heat transfer efficiencies in packed
`bubble~bed reactors are also higher than those of trickle-bed reactors.
`« A disadvantage compared to a trickle bed, however, is that the liquid
`backmixing is significant in this reactor, which reduces the reactor .
`efficiency. Also, as the liquid holdup is large compared to trickle-bed
`reactors, homogeneous side reactions may occur in the liquid in some
`situations. Some examples of the "application of packed bubble bed
`reactors are hydrodesulfurization of heavy petroleum oil, hydrogen-
`ation of nitrocompounds, amination of alcohols, and ethynylation 0:
`formaldehyde in butynediol synthesis. Design aspects of the fixed-bec‘
`reactors with cocurrent upflow have been reviewed recently b}
`Hofmann (1978) and Shah (1979). An illustrative sketch of this type
`of reactor (based on the work‘of Fukushirna and Kusaka, 1979) '
`along with gas and liquid distributors and a gas—liquid separator, 1'
`shown in Figure 8.1.
`
`"256 ‘
`
`Page 17 of 50 1
`
`Page 17 of 50
`
`

`
`FIXEAD-BED REACTOR WITH COCURRENT UPFLOW 257 .
`
`1 GAS our
`
`
`
`GAS - LIQUID
`DISENGAGING ZONE
`
`STAINLESS STEEL
`GRID
`
`PACKED SECTION
`
`STAINLESS STEEL
`GRID
`
`LIQUID
`OUT
`
`‘Ii:-:o.o-0.-.o.u.n'o‘rv-.2.-0:1 -
`
`7 GAS W
`
`eE
`
`I LIQUID IN
`
`fly
`:4
`
`O'
`
`1mm DIA. HOLE r-‘on GAS
`
`:
`
`‘‘
`' .AYAV.4L.'AV.A.
`
`.:;;m;;m;;.
`‘.n.'A‘.n_'A,n\,".
`v¢v£;gg¢v 10mm DlA.TUBE FOR LIQUID
`.
`
`
`P|TCH= 15mm
`
`FIGURE-8.1 A sketch of a fixed-bed reactor with cocurrent upflow (Fukushima and
`Kusaka, 1979).
`
`8.2 Flow Regimes
`\
`
`In a fixed-bed reactor with cocurrent iipflow of gas and liquid, the
`existence of different flew regimes was ‘first indicated by Eisenklam
`
`Page 18 of 50
`
`Page 18 of 50
`
`

`
`
`
`Page 19 of 50
`
`
`
`9
`
`5 9. Mechanically Agitated Slurry
`
`Reactors
`
`A
`
`9.1
`
`Introduction
`
`MECHANICALLY AGITATBD slurry reactors arevused in many chemical
`‘ processes. Some of the industrial examples include hydrogenation of
`unsaturated oils and hydrogenation of nitrocompounds. These’
`' reactors are convenient for use in batch processes. They have some
`specific advantages over other three-phase reactors because a high
`efficiency for mass and heat transfer is achieved. As small particle
`sizes .can be used,
`the intraparticle diffusional resistance is also
`minimal, thus leading to maximum utilization of the catalyst. In view
`of the higher mass and heat transfer rates obtained in these reactors,
`they are-also most suitable for kinetic studies in the laboratory. The
`disadvantages are the large power requirement for mechanical
`agitation,
`significant
`liquid_ backmixing, and difficulties in the
`separation of catalyst in continuous operations.
`This chapter, discusses the various parameters required for the‘
`design of mechanically‘ agitated slurry reactors. The correlations for
`predicting these have also been summarized and compared.
`A schematic diagram of a mechanically agitated reactor ‘and the
`stirrer design commonly used are shown in Figure 9.1. The type of
`agitator generally employed is a radial flow impeller of the turbine-
`type. In the design of mechanically agitated reactors, an- optimum
`‘ ratio for the diameter of the impeller to the diameter of the tank
`exists for which the solid particles in both the central and peripheral
`parts of the reactor move at the same speed. This optimum ratio for
`vessels of different shapes is given below (see Nagata, 1975).
`
`0.45 — 0.5 4
`
`for flat bottom vessel
`
`d,/dT = 0.4
`0.35
`
`,
`
`for dished bottom vessel
`‘for spherical bottom vessel
`
`281
`
`Page 19 of 50
`
`

`
`
`
`282
`
`THREE-PHASE CATALY'I‘IC REACTORS
`
`
`
`FIGURE 9.1 A schematic diagram of agitated reactor with stirrer design (Rushton
`etal.,
`d1 = 617/2, [7 : dT/5,1
`dTl4, L = dz‘, C =
`t0
`and BW = 0.1617‘.
`
`The other dimensions important in design are given by Rushton et al.
`(1950) and are shown in Figure 9.1. For uniform suspension of the
`catalyst particles, use of baffles is generally recommended. The
`standard baffles are 1/10-1/12 of the tank diameter, and four
`baffles are sufficient in most cases. The use of baffles is also necessary
`for proper distribution of the gas and to avoidthe formation of a
`vortex at the free surface of the liquid. The gas inlet pipe should be as
`close to the impeller blade as possible, and the gas should be
`dispersed through a ring sparger rather than from a single nozzle”.
`The width of the sparger should be about 0.8/times the impeller
`diameter.
`_
`’
`_
`A reactor with multiple agitators, a schematic diagram of which is
`shown in Figure 9.2,
`is often used for the hydrogenation of oils.
`Additionally, horizontal partitions can be introduced at various
`positions in the reactor in order to reduce the overall backmixing in
`continuous operation.
`
`'
`
`‘Page 20 of 50
`
`Page 20 of 50
`
`

`
`Page 21 of 50
`
`, MECHANICALLY AGITATED SLURRY REACTORS
`
`
`
`-‘o7ooo‘- -v—‘o‘o‘6oooo:ooo_oo-
`i-,oAoAooooo9‘o_o_o_a‘oo -V-i
`
`1
`
`2
`
`3
`
`4
`
`TURBINE IMPELLER
`
`BAFFLE
`
`"
`
`cooume AND HEATING COILS
`
`PERFORATED RING FOR HYDROGEN SUPPLY
`
`~ FIGURE 9.2 A reactor with multiple agitator arrangement (Bern et al., 1976).
`(Reproduced with permission of the Amer. Oil. Chem. Society.)
`
`‘
`
`9.2 Suspension of Catalyst Particles
`
`It is necessary to keep the entire solid mass suspended for maximum
`utilization of the catalyst; in an ideal operation, no catalyst should
`settle at the bottom. A certain minimum. degree of agitation is
`~ required to achieve this, and it is necessary to calculatethe minimum
`agitation required to ensure complete suspension, so that proper
`
`Page 21 of 50
`
`

`
`284 THREE-PHASE CATALYTIC REACTORS
`
`operating conditions can be chosen. An extensive examination of the
`conditions for complete suspension has been done by Zwietering
`(1958), who stated that a suspension can be considered to be com-
`plete if no particle remains at the bottom of the reactor for longer
`than 1 or 2 s. Zwietering (1958) proposed the following correlation
`to predict the minimum speed required forcomplete suspension.
`N = B2dp0.2#L0.lg0.45(pp _ ‘pL)l0.45W’0.13-
`9 1
`m
`pL0.S5dIO.85
`»
`q
`‘
`
`)
`
`(
`
`where w’ is the percentage catalyst loading, g/ 100 g solution, N”, is
`the minimum stirrer speed required for complete suspension, and
`[32 is a constant.
`The constant /32 was presented by Zwietering (1958) as a graph of
`/32 VS dT_/d, for Various agitator arrangements. Nienow (1968, 1975)
`has shown that an approximate Value of B2 for a disc turbine is
`given by
`
`»
`
`dT 1.33
`
`_
`
`‘
`
`" _
`
`~.B2 “
`
`(9-2)
`
`Kolar (1967) and.Narayan er al. (1969) have proposedtheoretical
`equations for Nm. However, these do not agree with the empirical
`correlation of Zwietering. Recently, Baldi et al.
`(1978) have
`proposed a model to explain the mechanism of complete suspension
`of particles in a cylindrical, flat—bottomed Vessel. The model is based
`on the assumption that the suspension of particles is due to eddies
`of a certain critical scale. Eddies with lower scales than the critical
`Value do not have the energy necessary to suspend thepparticles at E’
`rest at the bottom. Eddies of a larger scale have a lower frequency,
`. and hence less_ probability of hitting and suspending the particles.
`The correlation proposed by Baldi et al. (1978) is
`
`’
`
`Nm.
`
`_ ,