Catalysis : an Integrated Approach to Homogeneous ...

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8 - PREPARATION OF CATALYST SUPPORTS AND ZEOLITES 327 the case of catalysts the use of binders is restricted. If there is poor adherence the spheres are very weak and it will also be impossible to impregnate these spheres with a water-soluble salt. 8.5.4 Pelletization In this shaping process a powder is pressed between two punches in a pelleting press. The three different steps in the process are presented in Fig. 8.11. In step I the free-flowing powder is poured into the cylindrical hole. In step 11 the lower punch and the upper punch are moving towards each other and the powder is pressed at a pressure of about lo2 - 5 x lo3 atm and a pellet is formed. In step III the upper punch moves upwards and the lower punch pushes the pellet out of the hole. In the next step the pellet is moved away, the lower punch moves downwards and the hole is filled again. The schematic diagram shows that it is obvious that it is very important to use a free-flowing powder. The catalyst manufacturers use machines containing about 50 punches mounted in a circle. They produce 50,000 to 100,000 pellets/h. Because of the very rapid processing the hole must be filled in a reproducible way in less than one second. The filling of the hole determines the weight of the pellet. The grains of the free-flowing powder must be deformable during the pelleting process to form good pellets. Wear is an important problem and lubricants like graphite, stearic acid, aluminium stearate and talc are used to reduce this wear problem. These lubricants or plasticizers also act as a lubricant between the powder particles and improve the compacting of the powder and the formation of the pellet. .- I I1 I11 I Fig. 8.11. Three steps of the pelletization process.
328 8 -PREPARATION OF CATALYST SUPPORTS AND ZEOLITES The pellets are very uniform in size and shape and are mostly cylindrical. They have a high mechanical strength with a reasonable porosity. To increase the macroporosity one adds e.g. sawdust and (bio)polymers. After the pelletization process the pellets are calcined to burn out the lubricants and other combustible additives. It is also possible to make other shapes than just cylindrical ones. By using special dies one can make cylindrical pellets with a hole in the centre, corrugated cylinders, and even spheres. Pelletization is a rather expensive method as compared to the other shaping methods [3]. The modern machines with a very high pelletization speed have high maintenance costs. 8.5.5 Extrusion Extrusion is the most commonly applied shaping technique for catalysts or catalyst supports. Many types of extrusion equipment are used, some of which are very sophisticated, but the process is in principle very simple. A wet paste of the catalyst is fed to a screw transport system and the screw forces the paste through small holes in a die plate at the end of the extruder (see Fig. 8.12). This die can have holes in the form of a circle, rings, ovals, stars, three-lobed joined rings and many other shapes, so extrudates of different shapes and sizes can be made. As the ribbon of the extruded paste emerges from the hole in the die plate it begins to dry and harden sufficiently to maintain its shape. The ribbon is either cut into prescribed lengths by a knife rotating outside the end plate or allowed to break up in small pieces of irregular length when the material is dried and calcined in a drier or calciner. The extruder can be fed with a paste or a dry powder. In the case of a dry powder the extruder will have a kneading section where a liquid is add to the powder and the powder is kneaded to a paste. In the other case the paste is made in a separate kneader before feeding it into the extruder. The rheological proper- ties of the paste are very important, so the formulation of the paste is the most SLURRY i Fig. 8.12. Production of extrudates [13].
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Studies in Surface Science and Cata
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Studies in Surface Science and Cata
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Preface Catalysis is a fascinating
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industrial context of the features
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Contents Preface ..................
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4.3.4 P-Elimination and Deinsertion
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7.4.1 Scope .......................
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12.3 Adsorption Isotherms .........
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List of contributors E.B.M. Doesbur
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Introductory section
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Chapter 1 History of catalysis 1.1
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1 -HISTORY OF CATALYSIS 5 One of th
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1 - HISTORY OF CATALYSIS 7 was disc
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1 -HISTORY OF CATALYSIS exlenaed em
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1 -HISTORY OF CATALYSIS 11 aromatiz
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1 -HISTORY OF CATALYSIS 13 had a gr
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1 - HISTORY OF CATALYSIS 15 The new
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1 -HISTORY OF CATALYSIS 17 1960 law
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1 - HISTORY OF CATALYSIS TABLE 1.2
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1 -HISTORY OF CATALYSIS 21 1900 195
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Chapter 2 Catalytic processes in in
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2 - CATALYTIC PROCESSES IN INDUSTRY
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2 - CATALYTIC PROCESSES IN INDUSTRY
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flue gaa t c t air Vacuum gas ol 2
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2 -CATALYTIC PROCESSES IN INDUSTRY
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2 -CATALYTIC PROCESSES JN INDUSTRY
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Chapter 3 Chemical kinetics of cata
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3 - CHEMICAL KINETICS OF CATALYSED
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3 -CHEMICAL KINETICS OF CATALYSED R
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Fundamental catalysis
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Chapter 4 Bonding and elementary st
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4 -BONDING AND ELEMENTARY STEPS IN
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Chapter 5 Heterogeneous catalysis 5
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5 -HETEROGENEOUS CATALYSIS 161 a. _
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5 -HETEROGENEOUS CATALYSIS 163 appr
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5 -HETEROGENEOUS CATALYSIS 165 In r
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5 - HETEROGENEOUS CATALYSIS 167 lit
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5 - HETEROGENEOUS CATALYSIS 169 An
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5 -HETEROGENEOUS CATALYSIS 171 A ma
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5 - HETEROGENEOUS CATALYSIS 173 2 L
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5 - HETEROGENEOUS CATALYSIS 175 (3)
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5 -HETEROGENEOUS CATALYSIS 177 20 '
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5 -HETEROGENEOUS CATALYSIS 179 with
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5 - HETEROGENEOUS CATALYSIS 181 In
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5 -HETEROGENEOUS CATALYSIS 183 Info
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5 -HETEROGENEOUS CATALYSIS 185 0 20
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5 - HETEROGENEOUS CATALYSIS 187 TAB
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5 -HETEROGENEOUS CATALYSIS 189 i)U
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5 -HETEROGENEOUS CATALYSIS 600 560
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5 -HETEROGENEOUS CATALYSIS 193 b H
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Chapter 6 Homogeneous catalysis wit
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6 -HOMOGENEOUS CATALYSIS WlTH TRANS
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6 - HOMOGENEOUS CATALYSIS WlTH TRAN
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6 -HOMOGENEOUS CATALYSIS WITH TRANS
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6 -HOMOGENEOUS CATALYSIS WTH TRANSI
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Applied catalysis
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Chapter 7 Catalytic reaction engine
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7 -CATALYTIC REACTION ENGINEERING 2
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7 - CATALYTIC REACTION ENGINEERING
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Page 326 and 327: Ca ta I ys t preparation
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I0 -CATALYST CHARACTERJZATION WITH
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Chapter 11 Temperature programmed r
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Chapter 12 The use of adsorption me
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12 -ADSORPTION METHODS 421 pairs of
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12 -ADSORPTION METHODS 423 of multi
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12 -ADSORPTION METHODS 425 son of t
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12 - ADSORPnON METHODS 427 equation
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12 - ADSOWON METHODS / Fig. 12.4. T
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12 - ADSOFSTION METHODS 431 - a i-
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12 -ADSORPTION METHODS 433 uptake o
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12 - ADSOlU'TION METHODS 435 gives
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12 - ADSOFSTION METHODS 437 condens
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Future trends
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Chapter 13 Future trends The large
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13 - FUTURE TRENDS 443 control of t
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13 -FUTURE TRENDS 445 the conversio
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Subject Index x-Acceptor Iigands, 2
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SUBJECT INDEX 449 - see also Extend
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SUBJECr INDEX 451 Ethane, 143 Ethen
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SUBJECT INDEX 453 Hydrogen peroxide
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SDJJTT INDEX 455 Octane number, 24,
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SUBJECT INDEX 457 RBS, 383 Reaction
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SUBJECT INDEX 459 - see also Ruther
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STUDIES IN SURFACE SCIENCE AND CATA
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Volume 35 Volume 36 Volume 37 Volum
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Volume 70 Volume 71 Volume 72 Volum
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