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Identification, Conversion and Reactivity of Diolefins in Thermally Cracked Naphtha

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Identification, Conversion and Reactivity of Diolefins in Thermally Cracked Naphtha Identification, conversion and reactivity of diolefins in thermally cracked naphtha By Nidia Yohana Páez Cárdenas A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science In Chemical Engineering Deparment of Chemical and Materials Engineering University of Alberta © Nidia Yohana Páez Cárdenas, 2016 Abstract Bitumen extracted from Canadian oil-sands has a high viscosity, which limits its transportation. Field upgrading has become an option to overcome that limitation, without having to dilute the bitumen. During the field upgrading of bitumen, solvent deasphalting in combination with thermal cracking (visbreaking) can be used to produce a material ready to be transported for refining. In the thermal cracking process, mono-olefins and diolefins are generated especially in the light fractions. In many cases the olefin content exceeds the Canadian pipeline specification of <1% as 1-decene equivalent, required to have a product suitable for pipeline transportation. The usual treatment is hydrogenation, however, that treatment is not an option for a field upgrader facility due to the cost of H2 production and the size of the facility. Diolefins and especially conjugated diolefins are very reactive at high temperatures. They are capable of undergoing addition reactions to form molecules of high molecular weight better known as gums, that later could form coke. In previous research a non-conventional aromatic alkylation process was proposed to treat mono-olefins, but the conversion of diolefins at high temperatures contributed to catalyst deactivation by fouling. Therefore a hydrogen-free and low temperature alternative was sought to eliminate the diolefins. Three objectives were set in order to solve that problem: (1) to identify diolefins thermally cracked naphtha, (2) to explore alternative low temperature treatments for diolefins conversion and (3) to ii stablish a reactivity sequence of representative olefinic and diolefinic species present in cracked naphtha. The approach taken to develop the research involved three steps that corresponded to each objective. The identification of diolefins in thermally cracked naphtha was done by means of the gas chromatography-mass spectrometry (GC-MS) coupled with two chemical reactions: hydrogenation and Diels-Alder cycloaddition. This work was done in collaboration with Alberta Innovates Future Technologies (AITF), which analyzed the same sample using gas chromatography with vacuum ultra violet detector (GC-VUV). There was matrix interference due to the variety of compounds present in the naphtha. Four compounds were identified as diolefins, all of them with a conjugated structure: trans- 1,3-pentadiene, cis-1,3-pentadiene, 2-methyl-1,3- pentadiene and a cyclic diolefin of 7 carbons, possibly 5,5-dimethyl-1,3-cyclopentadiene. Five diolefins were identified by GC-VUV, two conjugated, two isolated and one cumulated: 2,3- dimethyl-1,3-butadiene, 3-methyl-1,3-pentadiene, trans-1,4-hexadiene, 1,7-octadiene and tetramethylallene. The low temperature treatment reactions explored were hydration and Diels-Alder cycloaddition. Hydration was first attempted on a model compound at 110ᵒC, 3 MPa and using four acid catalysts: sulfuric acid in aqueous solution, solid phosphoric acid, Siral-5 and H-ZSM-5. The model compound used was 2,5-dimethyl-2,4-hexadiene. The expected alcohol products of the water addition were not seen, instead a mixture of cracking, oxygenate and addition products was formed. The compounds present in the mixture were: trans-1,3-pentadiene, 1,5-hexadiene, 1,3- hexadiene, 1,3-cycloheptadiene, 2,5-dimethyl-2,4-hexadiene and cyclopentene and benzene as iii impurities. Conjugated and isolated linear diolefins underwent double bond and cis-trans isomerization. The disubstituted conjugated diolefin 2,5-dimethyl-2,4-hexadiene was converted into a cyclic ether. In the case of the Diels-Alder cycloaddition, the anticipated cyclohexene derivatives, were formed at the conditions of 60ᵒC and using 10 and 15% of AlCl3 as catalyst. The reaction was done using model compounds and a mixture of diolefins with two dienophiles: 3-buten-2-ol and methyl vinyl ketone (MVK). In the case of the model compounds, stereoisomers of 2,4-hexadiene were used, the diolefin trans-trans-2,4-hexadiene was the most reactive towards the dienophile. The mixture of diolefins was formed by 2,3-dimetyl-1,3-butadiene, 1,3-hexadiene, cis-3-methyl- 1,3- pentadiene, trans-3-methyl-1,3-pentadiene, 1,3-cycloheptadiene and 2,5-dimethyl-2,4-hexadiene. The diolefins of open chain were more prone to the cycloaddition, showing higher conversions than the cyclic diolefin. Similar to the reaction using model compounds, when the model mixture was used, the compounds with the trans configuration were more reactive. To stablish a reactivity sequence, hydrogenation was used as test reaction using Pt/C as catalyst. Eight compounds with different structure, but olefinic nature were selected. The order in reactivity found in this work from the most reactive to the least was: 1,4-pentadiene > 1-hexene > trans-1,3- pentadiene > 1-methylcyclohexene > 3-methyl-1,3-pentadiene > cyclohexene > 1,3- cylclohexadiene > vinylcyclopentane. According to the results, compounds with linear structure were more reactive, and the presence of branches or a cycle in the molecules decreased their reactivity for hydrogenation. iv Dedication To my parents, Carlos and Elvia and my sister, Claudia. You were not here physically but I could feel your presence in every supporting word. I love you. “Cuando crezcas, descubrirás que ya defendiste mentiras, te engañaste a ti mismo o sufriste por tonterías. Si eres un buen guerrero, no te culparás por ello, pero tampoco dejarás que tus errores se repitan.” (Pablo Neruda) v Acknowledgements I want to give special thanks to my supervisor, Dr. Arno De Klerk. Thanks for your time and your guidance during the development of this project; your patience and willingness to help in every step of the process made the difference in its culmination. I take advantage of this opportunity to express my sincere gratitude for the opportunity you gave me; besides the academic challenge , which is extremely important to me, this experience helped me to grow in a personal level. I would like to thank my lab co-workers. Thanks to all the people that had a word of encouragement when the stress could be seen in my face; those words helped me to keep going. Special thanks to Natalia, a fellow grad student, but more than that my friend; thank you for giving me your advice when I asked for it, for enriching the discussion by thinking differently and simply for being there along the way. To my friend, Yoshinori Casas, I think I would have never come here without that last push you gave me to make the final decision. Thank you. To my friends back home, Colombia. It has been wonderful to keep in touch. Thank you for being happy for me and encouraging me to continue. Special mention to Yu and Collazos, I remember a call from both of you in a very stressful and disappointing day, you both made me laugh and I treasure that. I want to do special mention of Nexen Energy ULC. Thanks for providing the financial support to carry out this research. vi TABLE OF CONTENTS CHAPTER 1-INTRODUCTION…………..……………………………………………………………….1 1. Background………………………………………..………………………………………………..…...1 2. Objectives and scope of work………………………………………………………………………… 4 CHAPTER 2-LITERATURE REVIEW………...………………………………………………………….7 1. Introduction………………………………………………………………...…………………………..7 2. General aspects of thermal cracking in partial upgrading of bitumen………..……………….………..7 2.1 Formation of alkenes during thermal cracking processes………………………………………….8 2.2 Implications of alkenes in light fractions…………………………………………………………..8 3. Alkenes identification………………………………………………………………………………….10 4. Chemistry of alkenes……………………………………………………………………………………13 4.1 Hydration …………………………………………………………………………………………14 4.2 Catalytic Hydrogenation…………………………………………………………………………...15 4.3 Diels-Alder reaction…………………………………………………………….………………….18 CHAPTER 3. IDENTIFICATION OF DIOLEFINS IN THERMALLY CRACKED NAPHTHA ....................................................................................................................................................... 26 1. Introduction............................................................................................................................ 26 2. Experimental .......................................................................................................................... 28 2.1 Materials ......................................................................................................................... 28 2.2 Equipment and procedure............................................................................................... 30 2.3 Analyses ......................................................................................................................... 31 2.4 Calibrations .................................................................................................................... 33 3. Results ................................................................................................................................... 33 3.1 Identification using GC-MS ........................................................................................... 33 3.2 Derivatization of the diolefins with maleic anhydride ................................................... 36 3.3 Model compound based identification ..........................................................................
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