Single Stage Aldol Condensation and Hydrogenation of Acetone to MIBK in the Gas Phase

189 Pages·2008·2.27 MB·English

Single Stage Aldol Condensation
and Hydrogenation of Acetone to MIBK
in the Gas Phase
Zur Erlangung des akademischen Grades eines
DOKTORS DER INGENIEURWISSENSCHAFTEN (Dr.-Ing.)
von der Fakultät für Chemieingenieurwesen und Verfahrenstechnik der
Universität Fridericiana Karlsruhe (TH)
genehmigte
DISSERTATION
von
Dipl.-Ing. Gerrit Waters
aus Lahr / Schwarzwald
Tag des Kolloquiums: 28.08.2007
Referent: Prof. Dr. Bettina Kraushaar-Czarnetzki
Korreferent: Prof. Dr.-Ing. Elias Klemm
Ich versichere, dass die hier vorliegende Dissertation mit dem eingereichten und
genehmigten Exemplar der Doktorarbeit übereinstimmt.
Danksagung
Die vorliegende Arbeit entstand in den Jahren 2002 bis 2006 am Institut f(cid:128)r
Chemische Verfahrenstechnik der Universit(cid:129)t Karlsruhe (TH).
Mein besonderer Dank gilt Frau Prof. Dr. Bettina Kraushaar-Czarnetzki f(cid:128)r die
(cid:130)berlassung des Forschungsthemas und die wohlwollende Unterst(cid:128)tzung und
F(cid:131)rderung, die ich w(cid:129)hrend meiner T(cid:129)tigkeit am Institut erfahren habe.
Herrn Prof. Dr.-Ing. Elias Klemm von der Technischen Universit(cid:129)t Chemnitz danke
ich f(cid:128)r die freundliche (cid:130)bernahme des Korreferats.
Zum erfolgreichen Abschluss dieses Forschungsprojekts haben die studentischen
Mitarbeiter Dennis Campbell, Oliver Richter und (cid:132)zben Kutlu durch ihre Diplom –
bzw. Studienarbeiten einen bedeutenden Beitrag geleistet. F(cid:128)r ihre Mitwirkung
m(cid:131)chte ich mich deshalb ganz herzlich bedanken.
W(cid:129)hrend meiner Zeit am Institut f(cid:128)r Chemische Verfahrenstechnik habe ich stets die
freundliche Arbeitsatmosph(cid:129)re, die ausgepr(cid:129)gte Hilfsbereitschaft und die
wissenschaftliche Freiheit als besonders angenehm empfunden. Mein Dank gilt
deshalb allen Mitarbeitern des Instituts, die diese Erfahrung m(cid:131)glich gemacht haben.
Ausdr(cid:128)cklich m(cid:131)chte ich dem Land Baden-W(cid:128)rttemberg f(cid:128)r die Unterst(cid:128)tzung durch
ein Promotionsstipendium gem(cid:129)(cid:134) dem Landesgraduiertenf(cid:131)rderungsgesetz danken.

Content
1 Introduction 1
1.1 Introduction to industrial aldol condensation and hydrogenation 1
1.2 Background of the study and general outline 3
2 Theoretical background 5
2.1 The reaction scheme of aldol condensation and hydrogenation 5
of acetone
2.2 Active carbon 7
2.2.1 The application of active carbon 7
2.2.2 The production of active carbon 8
2.2.3 The structure of active carbon 10
2.2.4 Inorganic components of active carbon 12
3 Experimental procedure and data evaluation 13
3.1 The reaction units 13
3.1.1 Description of the Berty reactor unit 14
3.1.2 Description of the tubular reactor unit 17
3.2 Catalyst preparation 21
3.2.1 The catalyst notation 21
3.2.2 The active carbon support 21
3.2.3 CO – oxidation (similar to char activation) 22
2
3.2.4 Oxidation in air (calcination) 22
3.2.5 Liquid phase oxidation in nitric acid 22
3.2.6 Catalyst preparation: method 1 22
3.2.7 Catalyst preparation: method 2 25
3.3 Catalyst characterization 29
3.3.1 Argon physisorption 29
3.3.2 Temperature programmed desorption (TPD) of NH 29
3
3.3.3 Temperature programmed decomposition (TPDec) 30
3.3.4 Simplified mass titration 30
3.3.5 Mercury porosimetry 31
3.3.6 Quantitative analysis of the active carbon mineral content 31
3.4 Catalytic experiments in the Berty reactor 31
3.4.1 Pretreatment of the catalyst 31
3.4.2 Data acquisition 31
3.5 Catalytic experiments in the tubular reactor 33
3.5.1 Catalyst pretreatment prior to testing 33
3.5.2 Data acquisition 33
4 Examination of the reactor characteristics 35
4.1 The Berty reactor 35
4.1.1 Determination of a residence time distribution for the Berty reactor 35
4.2 The tubular reactor 37
4.2.1 Test for external mass transport limitations 37
4.2.2 Test for internal mass transport limitations 38
4.2.3 Evaluation of the axial dispersion 41
4.2.4 Influence of the wall slip on the reactor performance 43
4.2.5 Influence of the pressure drop on the reactor performance 44
5 Influence of oxidative treatment 45
on the surface chemistry of active carbon
6 Catalytic effect of acid-base surface sites of active carbon 52
6.1 Density and stability of oxygen functional groups (OFG) 52
6.2 Catalytic activity and selectivity in relation to the OFG surface density 57
6.3 The long-term performance 59
7 Influence of the hydrogenation function on 63
the catalyst performance
7.1 Comment on the metal loading procedure 63
7.2 Effect of the metal type on the catalytic activity and selectivity 65
7.3 Influence of the molar ratio of hydrogen to acetone in the feed 69
7.4 Effect of the amount of supported metal 73
7.5 Hydrogenation potential and product distribution 75
8 Comparison of different active carbon supports 77
8.1 Comparison of three active carbon support materials 77
8.2 Influence of additional MgO on the catalytic properties of R3E 83
9 Study of process conditions in a plug flow reactor 87
9.1 Influence of the temperature on the product distribution 87
9.2 Influence of the temperature on the catalyst activity 94
9.3 Influence of the reactor feed composition on the catalyst performance 98
9.4 The influence of water vapor on the course of reaction 101
9.5 Influence of the H /acetone ratio 103
2
9.6 Long-term testing 109
10 Proposal of a simplified power-law kinetics 115
10.1 The mathematical model 115
10.1.1 The program “MIBK_auto” 123
10.1.2 The program “MIBK_main” 123
10.1.3 The program “fit.m” 123
10.1.4 The program “n_solve.m” 124
10.1.5 The program “expXXX.m” 124
10.1.6 The program “equilibrium.m” 124
10.1.7 The program “n_DGL.m” 124
10.2 Simulation of a tubular fixed-bed reactor 125
(semi-homogeneous; 1-dimensional)
10.2.1 The program “SIM.m” 126
10.3 Discussion of the parameter fitting 126
10.4 Validity and limitations of the power-law kinetic model 131
11A Summary 135
11B Zusammenfassung 138
12 References 141
13 Appendix 146
Appendix A: List of symbols 146
Appendix B: Determination of conversion and selectivity values 150
Appendix C: Thermal decomposition of Mg(NO ) -6-hydrate and 154
3 2
Ni(NO ) -6-hydrate
3 2
Appendix D: The kinetic parameters 155
Appendix E: Display of confidence intervals for the fitted kinetic parameters 157
Appendix F: The MATLAB source code 160
Appendix G: Exploratory testing of extruded SiO as alternative 175
2
catalyst support
Appendix H: The mechanism of homogeneous aldol-condensation 178
1
Introduction
1.1 Introduction to industrial aldol condensation and
aaaahydrogenation
Condensation reactions of carbonyl compounds are of great industrial importance for
the production of a number of key substances. In combination with one or more
hydrogenation steps, aldol condensations yield branched, higher alcohols,
polyalcohols as well as branched ketones. With regard to production capacity, the
two most important products derived from aldol condensation with subsequent
hydrogenation are methyl isobutyl ketone (MIBK) (2003: 160000 t/year [1, 2]) and 2-
Ethylhexanol (1994: 2.3106 t/year [3]). MIBK is used as a solvent for a diversity of
applications including the production of paints, lacquers, stabilizers and resins. Apart
from that, it is used as an extracting agent for the dewaxing of mineral oils and for the
separation of mixtures of inorganic transition metal salts [3, 4]. 2-Ethylhexanol is
primarily used in the production of esters with different dicarboxylic acids like phthalic
or adipic acid. It is known to have considerable economical importance as a
precursor for the production of dioctylphthalat (DOP) which is an excellent nontoxic
standard plasticizer.
In the course of this study, the production of MIBK from acetone and hydrogen was
chosen as an exemplary reaction for the investigation of aldol condensation with
subsequent hydrogenation in the gas phase. Thereby, this work is meant to promote
the development of an industrial single-stage process operated at low pressure. It is
1
anticipated that the insight gained in this study will be helpful for the conversion of
carbonyl compounds other than acetone.
In the advent of commercial MIBK production, the state-of-the-art process consisted
of three stages. After initial acetone self-addition homogeneously catalyzed by acids
or bases in the liquid phase, the resulting addition product diacetonealcohol (DAA)
was separated and transferred to the second stage. Again in liquid medium, the acid-
catalyzed dehydration was conducted to form the ,-unsaturated mesityl oxide
(MO). The step was followed by subsequent hydrogenation of mesityl oxide in the
gas phase over Ni or Cu chromite or noble metal catalysts. The disadvantages of this
process were numerous, including equilibrium limitations, corrosion and the disposal
of significant amounts of inorganic salts. The latter results from the use of acids and
bases like Ba(OH) , Ca(OH) , NaOH, KOH, H PO , H SO either as catalysts in the
2 2 3 4 2 4
aldol condensation or as neutralization agents. For industrial aldol condensation and
hydrogenation, single-stage process variants have emerged to cope with some of the
mentioned disadvantages. Therefore, today’s MIBK demand is covered by a single-
step process conducted in a trickle bed reactor with the reaction taking place in the
liquid phase. Typical operation conditions are pressures of 10-100 bar and
temperatures ranging from 120 to 160 (cid:138)C [5, 6]. Operation around 100 bar is usually
favored in order to enhance the mass transfer of hydrogen from the gas to the liquid
phase. Since the hydrogenation of mesityl oxide can be considered irreversible under
these conditions, equilibria in the formation of DAA and MO don’t represent a
limitation for the single stage process. On the other hand, trickle-bed operation in
combination with high hydrogen pressures requires a high cost reactor inventory.
Several groups have described suitable heterogeneous catalysts for the application
in a three-phase (G/L/S) process. Typically, palladium is used as a hydrogenating
component in combination with supports such as Nb O /SiO [7], CaO-MgO-SrO-
2 5 2
Al O [8], Nb O [9-11], Ti-, Zr-, Cr-oxide or hydroxide with carbon [12], Ce-, Hf-, Ta-
2 3 2 5
oxide or hydroxide with Al O [13]. Several of these catalysts enable high MIBK
2 3
selectivities, e.g. more than 90 %, at acetone conversions ranging from 25 to 35 %.
In addition, remarkably long lifetimes are reported [7, 9].
The attractiveness of a gas phase process with a simple fixed-bed reactor has
caused a shift of scientific interest away from three-phase operation. In recent years,
research focused on the single-stage conversion of gaseous acetone to MIBK. The
catalysts under investigation are usually bi- or multifunctional materials involving one
2