ETH Library Mechanisms of hydrodenitrogenation of amines over sulfided NiMo, CoMo, and Mo supported on Al₂O₂ Doctoral Thesis Author(s): Zhao, Yonggang Publication date: 2004 Permanent link: https://doi.org/10.3929/ethz-a-004779056 Rights / license: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information, please consult the Terms of use. Diss. ETH No. 15555 Mechanisms of Hydrodenitrogenation of Amines Over Sulfided NiMo, CoMo, and Mo Supported on Al O 2 3 A dissertation submitted to the SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH for the degree of DOCTOR OF CHEMICAL ENGINEERING Presented by Yonggang Zhao Bachelor and Master of Chemical Engineering, Fushun Petroleum Institute Born on 21 September 1974 in Jiangsu, China Accepted on the recommendation of Prof. Dr. Roel Prins, examiner Prof. Dr. Michèle Breysse, co-examiner Zürich, 2004 I CONTENTS Abstract................................................................................................................................V Zusammenfassung...........................................................................................................VII 1 Introduction..........................................................................................................................1 1.1 Hydrodenitrogenation..................................................................................................1 1.2 Structure of the catalysts..............................................................................................3 1.3 The role of H , H /H S and active sites.......................................................................8 2 2 2 1.4 Reaction mechanism..................................................................................................12 1.4.1 Aromatic C-N bond breaking............................................................................12 1.4.2 C-N bond cleavage of aliphatic amines............................................................15 1.4.3 C-N bond cleavage of hetero cyclic amines.....................................................18 1.5 Experimental..............................................................................................................21 1.5.1 Unit...................................................................................................................21 1.5.2 Product analysis................................................................................................24 1.5.3 Catalysts............................................................................................................24 1.5.4 Weight time.......................................................................................................25 1.5.5 Reactants and reaction conditions used in every chapter.................................25 1.6 References..................................................................................................................28 2 On the role of β-hydrogen atoms in the hydrodenitrogenation of 2-methylpyridine and 2-methylpiperidine.....................................................................................................35 2.1 Abstract......................................................................................................................35 2.2 Introduction................................................................................................................35 2.3 Results........................................................................................................................37 2.3.1 HDN of 2-methylpyridine.................................................................................37 2.3.2 HDN of 2-methylpiperidine..............................................................................39 2.3.3 Comparison of piperidine, 2-methylpyridine, and 2,6-dimethylpiperidine ...40 2.3.4 HDN of 1-aminohexane....................................................................................43 II 2.3.5 HDN of 2-aminohexane....................................................................................45 2.4 Discussion..................................................................................................................47 2.5 References..................................................................................................................51 3 Investigation of the mechanism of the hydrodenitrogenation of n-hexylamine over sulfided NiMo/γ-Al O .......................................................................................................53 2 3 3.1 Abstract......................................................................................................................53 3.2 Introduction................................................................................................................53 3.3 Results........................................................................................................................55 3.3.1 HDS of pentanethiol and hydrogenation of hexene..........................................55 3.3.2 HDN of hexylamine..........................................................................................58 3.3.3 HDN of dihexylamine.......................................................................................63 3.3.4 HDN of trihexylamine.......................................................................................66 3.4 Discussion..................................................................................................................69 3.4.1 Hexylamine.......................................................................................................69 3.4.2 Dihexylamine....................................................................................................71 3.4.3 Trihexylamine...................................................................................................74 3.4.4 General discussion.............................................................................................75 3.5 Conclusions................................................................................................................78 3.6 References..................................................................................................................79 4 Mechanisms of the hydrodenitrogenation of alkylamines with secondary and tertiary α-carbon atoms over sulfided NiMo/γ-Al O ...................................................................81 2 3 4.1 Abstract......................................................................................................................81 4.2 Introduction................................................................................................................81 4.3 Results........................................................................................................................82 4.3.1 2-Pentylamine and 2-pentanethiol.....................................................................82 4.3.2 3-Methyl-2-butylamine and 3-methyl-2-butanethiol........................................85 4.3.3 3,3-Dimethyl-2-butylamine...............................................................................88 4.3.4 2-Methylcyclohexylamine.................................................................................90 4.3.5 2-Methyl-2-butylamine and 2-methyl-2-butanethiol........................................91 4.4 Discussion..................................................................................................................94 III 4.4.1 HDN and HDS mechanism...............................................................................94 4.4.1.1 Acid-base mechanism...........................................................................94 4.4.1.2 Metal-like mechanism...........................................................................96 4.4.2 HDN of amines with secondary α-carbon atoms..............................................99 4.4.3 HDN of 2-methyl-2-butylamine and benzylamine.........................................102 4.5 Conclusions..............................................................................................................103 4.6 References................................................................................................................105 5 Mechanisms of HDN of Alkylamines and HDS of alkanethiol on NiMo/Al2O3, CoMo/Al2O3, and Mo/Al2O3.........................................................................................107 5.1 Abstract....................................................................................................................107 5.2 Introduction..............................................................................................................107 5.3 Results......................................................................................................................109 5.3.1 Simultaneous reaction of pentylamine and hexanethiol.................................111 5.3.2 Simultaneous reaction of 2-hexylamine and 2-pentanethiol...........................116 5.3.3 2-Methyl-2-butylamine and 2-methyl-2-butanethiol......................................122 5.4 Discussion................................................................................................................124 5.4.1 Pentylamine.....................................................................................................124 5.4.2 2-Hexylamine..................................................................................................126 5.4.3 2-Methyl-2-butylamine...................................................................................128 5.5 Conclusion...............................................................................................................130 5.6 References................................................................................................................131 6 Mechanism of the hydrodenitrogenation of adamantylamine and neopentylamine over sulfided NiMo/γ-Al O .............................................................................................133 2 3 6.1 Abstract....................................................................................................................133 5.2 Introduction..............................................................................................................133 6.3 Results......................................................................................................................134 6.3.1 Neopentylamine..............................................................................................134 6.3.2 Adamantylamines and adamantanethiol.........................................................136 6.4 Discussion................................................................................................................138 6.4.1 HDN of neopentylamine.................................................................................138 IV 6.4.2 HDN of AdNH and HDS of AdSH................................................................140 2 6.5 Conclusion................................................................................................................143 6.6 References................................................................................................................144 7 Mechanism of the direct hydrodenitrogenation of naphthylamine over sulfided NiMo/γ-Al O ....................................................................................................................147 2 3 7.1 Abstract....................................................................................................................147 7.2 Introduction..............................................................................................................147 7.3 Results......................................................................................................................149 7.4 Discussion................................................................................................................154 7.4.1 Direct denitrogenation.....................................................................................154 7.4.2 Direct desulfurization......................................................................................160 7.5 Conclusions..............................................................................................................162 7.6 References................................................................................................................162 8 Concluding remarks.........................................................................................................165 8.1 Conclusion................................................................................................................165 8.2 Outlook.....................................................................................................................167 8.3 References................................................................................................................170 Acknowledgements Publications Curriculum Vitae V Abstract The hydrodenitrogenation (HDN) of alkylamines has been studied over sulfided NiMo, CoMo, and Mo catalysts supported on γ-Al O at reaction conditions in the range of 3-5 MPa, 2 3 270-350 °C, and 10-100 kPa H S. The heterocyclic amines 2-methylpyridine and 2,6- 2 dimethylpyridine as well as the alkylamines of n-hexylamine, 2-pentylamine, and 2-methyl-2- butylamine were chosen as HDN models. The corresponding alkanethiols were studied as well. In the HDN of 2-methylpiperidine, the products 2-methylpyridine, 3,4,5,6- tetrahydropyridine, and 2-hexylamine as well as hydrocarbons were formed. Only a trace of hexylamine was observed. As the reactivity of 2-hexylamine was much higher than that of hexylamine at the same reaction conditions, the ring opening of 2-methylpiperidine occurred preferentially between the nitrogen atom and the methylene group, instead of between the nitrogen atom and the carbon atom bearing the methyl group. It demonstrates that β-hydrogen atoms are not involved in the HDN of 2-methylpiperidine. This was confirmed with the much higher HDN conversion of piperidine than 2-methylpiperidine and 2,6-dimethylpiperidine. The HDN of hexylamine, dihexylamine, and trihexylamine was studied between 300 and 340 °C, 3 and 5 MPa total pressure, 5 and 20 kPa amine pressure, and 10 and 150 kPa H S 2 pressure over a sulfided Ni-Mo/γ-Al O catalyst. The conversion of hexylamine and 2 3 dihexylamine decreased slightly with H S pressure, but that of trihexylamine increased 2 substantially. The conversion increased with the H pressure and decreased with increasing 2 partial pressure of the hexylamines. In the HDN of n-hexylamine, a substantial amount of hexenes and hexanethiol was formed by elimination and nucleophilic substitution. Two methods were used to distinguish between elimination and nucleophilic substitution. One is to test the initial product selectivities at short weight time. The initial alkene selectivities were low and accounted for only a minor part of the n-alkylamine conversion. Furthermore, the simultaneous reactions of hexylamine and pentanethiol show that the hexenes/hexane ratio in the HDN of the hexylamine was almost equal to the pentenes/pentane ratio in the hydrodesulfurization (HDS) of pentanethiol. Therefore, it was concluded that the majority of the hexene in the HDN of hexylamine originates from hexanethiol formed by nucleophilic substitution of hexylamine with H S. 2 VI The HDN of alkylamines with secondary and tertiary α-carbon atoms and benzylamine as well as the HDS of the corresponding alkanethiols was studied over sulfided NiMo/Al O 2 3 CoMo/Al O and Mo/Al O catalysts. The similar alkenes/alkane ratios in the HDN of the 2 3 2 3 alkylamines and HDS of the corresponding alkanethiols confirm that nucleophilic substitution is the predominant reaction in the HDN of the amine group attached to secondary carbon atoms. 2-Methyl-2-butylamine and benzylamine reacted much faster than the amines with secondary α-carbon atoms. In the HDN of 2-methyl-2-butylamine and benzylamine, hydrocarbons were formed. Only a trace of the relevant thiol was formed and this amount did not increase much with increasing H S pressure. The much higher 2 methylbutenes/methylbutane ratios in the HDN of 2-methyl-2-butylamine as in the HDS of 2- methyl-2-butanethiol demonstrate that 2-methyl-2-butylamine and the activated benzylamine react by means of an E1 mechanism. The HDN of 1-adamantylamine, 2-adamantylamine and neopentylamine and the HDS of 1-adamantanethiol were studied. The adamantanethiols and neopentanethiol were formed as the primary products of the adamantylamines and neopentylamine by substitution of the NH 2 group with H S. Adamantane and neopentane were secondary products, demonstrating that 2 hydrogenolysis can hardly take place. Furthermore, elimination cannot take place and a classic S 2 substitution is not possible for the adamantylamines either. It is proposed that the N NH -SH substitution in adamantylamine takes place by adsorption of the amine group at the 2 metal sulfide surface and by shifting the adamantyl group to a neighbouring sulfur atom. 1-Naphthylamine was studied to test the direct hydrogenolysis in hydrodenitrogenation. Tetralin, naphthalene, 1,2-dihydronaphthalene and 5,6,7,8-tetrahydro-1-naphthylamine were formed in the HDN of naphthylamine. The reactions of the intermediates 1,2,3,4-tetrahydro- 1-naphthylamine, 1,2-dihydronaphthalene and 5,6,7,8-tetrahydro-1-naphthylamine were studied as well. 1-Naphthylamine reacts to 1,2,3,4-tetrahydro-1-naphthylamine by hydrogenation, and then it reacts by NH elimination to 1,2-dihydronaphthalene. 1,2- 3 dihydronaphthalene subsequently reacts to tetralin as well as naphthalene. This direct denitrogenation of naphthylamine to naphthalene could take place by hydrogenation of 1- naphthylamine to 1,2-dihydro-1-naphthylamine, followed by NH elimination or followed by 3 a Bucherer-type NH -SH exchange, dehydrogenation and C-S bond hydrogenolysis. 2 VII Zusammenfassung Die Hydrodenitrogenierung (HDN) von Alkylaminen wurde über sulfidierten, auf γ- Al O geträgerten NiMo, CoMo, und Mo Katalysatoren unter Reaktionsbedingungen von 3-5 2 3 MPa, 270-350 °C und 10-100 kPa H S untersucht. Als Modellverbindungen für die HDN 2 wurden sowohl die heterocyclischen Amine 2-Methylpyridin und 2,6-Dimethylpyridin als auch die Alkylamine n-Hexylamin, 2-Pentylamin, und 2-Methyl-2-butylamin gewählt. Ebenfalls untersucht wurden die entsprechenden Alkylthiole. Während der HDN von 2-Methylpiperidin wurden die Produkte 2-Methylpyridin, 3,4,5,6- Tetrahydropyridin und 2-Hexylamin sowie Kohlenwasserstoffe gebildet. Hexylamin ist nur in Spuren beobachtet worden. Da die Reaktivität von 2-Hexylamin unter denselben Reaktionsbedingungen viel höher war als die von Hexylamin, fand die Ringöffnung von 2- Methylpiperidin bevorzugt zwischen dem Stickstoffatom und der Methylengruppe statt, anstatt zwischen dem Stickstoffatom und dem methylsubstituierten Kohlenstoff. Dies zeigt, dass β-Wasserstoffatome in der HDN von 2-Methylpiperidin nicht involviert sind. Der viel höhere HDN Umsatz von Piperidin verglichen mit dem Umsatz von 2-Methylpiperidin bestätigt dies. Die HDN von Hexylamin, Dihexylamin und Trihexylamin wurde über sulfidiertem Ni- Mo/γ-Al O Katalysator zwischen 300-340 °C, 3-5 MPa Totaldruck, 5-20 kPa 2 3 Aminpartialdruck und 10-150 kPa Schwefelwasserstoffpartialdruck untersucht. Während der Umsatz von Hexylamin und Dihexylamin mit zunehmendem H S Druck leicht abnahm, 2 nahm derjenige von Trihexylamin deutlich zu. Der Umsatz nahm mit zunehmendem H Druck 2 zu und mit zunehmendem Partialdruck der Hexylamine ab. Während der HDN von n- Hexylamin bildete sich durch Eliminierung und nucleophile Substitution eine erhebliche Menge an Hexenen und Hexanthiol. Für die Unterscheidung zwischen Eliminierung und nucleophiler Substitution wurden zwei Methoden angewendet. Die eine besteht darin, die anfänglichen Produktselektivitäten nach kurzer Kontaktzeit zu untersuchen. Die anfänglichen Alkenselektivitäten waren klein und trugen nur wenig zum Umsatz von n-Alkylamin bei. Weiter zeigte die gleichzeitige Reaktion von Hexylamin und Pentanthiol, dass das Hexene/Hexan Verhältnis in der HDN von Hexylamin beinahe gleich war wie das Verhältnis Pentene/Pentan in der Hydrodesulfurisierung (HDS) von Pentanthiol. Daraus wurde