FISCHER-TROPSCH STUDIES WITH ACETYLENIC COMPOUNDS AS PROBES by Li Hou B.S. in Chemical Engineering, Hefei University of Technology, China, 1997 M.S. in Chemical Engineering, Hefei University of Technology, China, 2000 Submitted to the Graduate Faculty of the School of Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Pittsburgh 2005 UNIVERSITY OF PITTSBURGH SCHOOL OF ENGINEERING This dissertation was presented by Li Hou It was defended on February 10, 2005 and approved by John W. Tierney, PhD, Professor James T. Cobb, PhD, Professor Badie I. Morsi, PhD, Professor Rachid Oukaci, PhD Dissertation Director: Irving Wender, PhD, Professor ii FISCHER-TROPSCH STUDIES WITH ACETYLENIC COMPOUNDS AS PROBES Li Hou, PhD University of Pittsburgh, 2005 Incorporation of probe molecules has been widely used in elucidation of the mechanism of the Fischer-Tropsch (F-T) reaction. In this study, we used acetylenic molecules, including 1- hexyne, 2-hexyne, 4-phenyl-1-butyne, and 1-phenyl-1-propyne as well as acetylene as probes with cobalt and iron catalysts. Experiments were carried out in a tubular microreactor of 3/8 inch diameter. Long chain alkynes were added via a saturator or a syringe pump. Acetylene was introduced from a cylinder containing carbon monoxide and hydrogen plus 1% of acetylene. We found that acetylenic compounds can initiate the F-T synthesis at temperatures more than 100oC lower than those at which normal F-T reactions are carried out. Since products obtained from linear alkyne-initiated F-T and those from normal F-T synthesis are indistinguishable, we used phenyl-substituted acetylenes as probes to distinguish the alkyne initiated products from normal F-T products. At low temperatures, only alkyne-initiated F-T reactions take place; at normal F-T temperatures, both alkyne initiated reactions and normal initiated F-T reactions occur. Although the degree of incorporation of internal alkynes is much less than that of the terminal alkynes, they can also initiate F-T chain growth to form mostly iii branched products. Under the same reaction conditions, internal olefins have little effect on the F-T reaction. When an acetylenic probe molecule is added to cobalt catalyzed F-T reactions, aldehydes or alcohols with one carbon more than the added probe molecule are the only oxygenates formed, perhaps by a hydroformylation type of reaction. Incorporation of alkynes (with carbon + number n) on iron catalysts increased the rate of formation of Cn+1 oxygenates, via Anderson- Schulz-Flory distribution. The F-T synthesis is a complex process in which a large number of hydrocarbon and oxygenated species are present on the catalyst surface. The nature of these adsorbates and how they react differ as reaction conditions and the nature of the catalyst changes. This work, combined with results of experiments on incorporation of ethylene, lends credence to the postulation that unsaturated two-carbon entity, possibly vinylidenes or ethylidynes, may be involved in initiation of the F-T synthesis. iv DESCRIPTORS Acetylene Acetylenic compounds Alkynes Chain initiation CO hydrogenation Cobalt Fischer-Tropsch synthesis Fixed-bed reactor 1-Hexyne 2-Hexyne Iron 1-Phenyl-1-propyne 4-Phenyl-1-butyne Probe molecules v TABLE OF CONTENTS ACKNOWLEDGEMENTS.......................................................................................................... xv 1.0 INTRODUCTION .................................................................................................................. 1 2.0 BACKGROUND .................................................................................................................... 7 2.1 F-T CATALYSTS .......................................................................................................... 7 2.2 F-T REACTION MECHANISMS................................................................................ 12 2.2.1 Schemes with hydrocarbon intermediates ............................................................ 13 2.2.2 Schemes with oxygenated intermediates .............................................................. 16 2.3 USE OF PROBE MOLECULES IN THE STUDY OF F-T MECHANISM ............... 18 2.3.1 F-T studies using alcohols as probes .................................................................... 19 2.3.2 F-T studies using alkenes as probes...................................................................... 21 2.3.3 F-T studies with C1 and C2 probes ...................................................................... 24 2.4 F-T vs. ETHYLENE POLYMERIZATION................................................................. 27 2.5 THE HYDROFORMYLATION REACTION ............................................................. 29 3.0 EFFECT OF STRAIGHT-CHAIN ALKYNES ON F-T SYNTHESIS ............................... 31 3.1 INTRODUCTION ........................................................................................................ 31 3.2 EXPERIMENTAL........................................................................................................ 32 3.2.1 Catalyst preparation .............................................................................................. 32 3.2.2 Experimental Setup............................................................................................... 33 3.2.3 Addition of alkynes............................................................................................... 35 vi 3.2.4 Product sampling and analysis.............................................................................. 36 3.3 RESULTS AND DISCUSSION................................................................................... 37 3.3.1 Incorporation of 1-hexyne addition with cobalt catalysts..................................... 37 3.3.1.1 Product distribution without/with 1-hexyne addition ................................... 37 3.3.1.2 Effect of temperatures on incorporation of 1-hexyne................................... 39 3.3.1.3 Comparison of 1-hexyne and 1-hexene incorporation.................................. 44 3.3.1.4 Time dependence of C7 oxygenates formation ........................................... 46 3.3.1.5 Deactivation of F-T synthesis in the presence of 1-hexyne ......................... 48 3.3.2 Incorporation of 1-heptyne and 1-decyne with cobalt catalysts ........................... 49 3.3.3 Incorporation of 2-hexyne and 2-hexene with cobalt catalysts ............................ 50 3.3.4 Effect of selective poisoning agents on cobalt catalysts....................................... 53 3.3.4.1 Effect of thiophene addition on cobalt catalysts........................................... 54 3.3.4.2 Effect of pyridine addition on cobalt catalysts. ............................................ 55 3.3.5 Incorporation of 1-hexyne with an iron catalyst................................................... 56 3.4 CONCLUSIONS........................................................................................................... 59 4.0 PHENYL-SUBSTITUTED ALKYNE PROBE MOLECULES AS MARKERS IN THE F-T SYNTHESIS................................................................................................................................. 61 4.1 INTRODUCTION ........................................................................................................ 61 4.2 EXPERIMENTAL........................................................................................................ 62 4.2.1 Catalyst preparation .............................................................................................. 62 4.2.2 Reactions Conditions ............................................................................................ 62 4.2.3 Addition of alkynes............................................................................................... 62 4.3 RESULTS AND DISCUSSION................................................................................... 63 4.3.1 Incorporation of 4-phenyl-1-butyne with cobalt catalysts.................................... 63 vii 4.3.2 Incorporation of 1-phenyl-1-propyne with cobalt catalysts.................................. 69 4.3.3 Incorporation of phenylacetylene with cobalt and iron catalysts.......................... 72 4.4 CONCLUSIONS........................................................................................................... 76 5.0 EFFECTS OF ACETYLENE ON F-T SYNTHESIS........................................................... 78 5.1 INTRODUCTION ........................................................................................................ 78 5.2 EXPERIMENTAL........................................................................................................ 79 5.2.1 Catalyst preparation .............................................................................................. 79 5.2.2 Reactions conditions ............................................................................................. 80 5.2.3 Addition of acetylene............................................................................................ 80 5.3 RESULTS AND DISCUSSION................................................................................... 81 5.3.1 Incorporation of acetylene with cobalt catalysts................................................... 81 5.3.1.1 Product distribution without/with acetylene addition .................................. 81 5.3.1.2 Effects of temperature on acetylene incorporation . ..................................... 86 5.3.1.3