Oxidative Ring-Opening of Aromatics

  • Author / Creator
    Montoya Sanchez, Natalia
  • The increased production of heavy and extra-heavy oils has changed the quality of the feedstocks processed in refineries. Conversion of heavier aromatic-rich materials using traditional upgrading technologies is possible but modifications are needed. There is a growing interest from industry and academia to develop new approaches to deal with the upgrading of heavier oils. The objective of this work was to explore a new conversion strategy: oxidative ring-opening of multinuclear aromatics.The oxidative ring-opening strategy refers to the oxidation of multinuclear aromatics using oxygen (in air) as oxidant to produce ring-opened hydrocarbons products that do not contain oxygen. This concept involves three steps: (i) oxidation of multinuclear aromatics to produce quinonoids, (ii) further oxidation and ring-opening to produce aromatic carboxylic acid species, and (iii) decarboxylation of aromatic carboxylic acids to yield the ring-opened product. Ultimately, the structure of the multinuclear aromatic feed is simplified and the H:C ratio of the product increased. The conversion chemistry of the individual steps was investigated.The oxidation chemistry of atoms that are part of an aromatic ring using air as oxidant was reviewed. Emphasis was placed on reactions leading to selective cleavage of C–C bonds as well as on competing non-selective oxidation reactions. The application of the Clar-formalism to multinuclear aromatics guided the discussion of fundamental aspects of aromatic oxidation. The need to adopt a catalytic approach for the oxidative ring-opening of multinuclear aromatics became evident.Patent literature dealing with air oxidation of heavy feedstocks was also reviewed. Claims stating that the non-catalytic low-temperature oxidation of asphaltenes is able to produce liquid products of petrochemical value were found; their validity was questioned and explored in an experimental study. Under all conditions studied, little asphaltenes oxidative degradation was observed. No increase in the yield of the maltenes fraction took place. These observations were consistent with expectations based on free radical oxidation fundamentals.The oxidation of multinuclear aromatic model compounds over metal oxide catalysts was studied. Liquid-phase autoxidation and catalytic oxidation of anthracene and 9,10-anthraquinone in the presence of V2O5, MoO3, Fe2O3, and NiO were conducted. It was confirmed that catalytic oxidation of both compounds took place by transfer of lattice oxygen from V2O5 and that catalytic oxidation led to ring-opening. The contribution of thermal cracking and the competition of ring-opening and ring-closing reactions affected the selectivity towards ring-opened products.Effective removal of the carboxylic acid functionality is necessary to produce ring-opened hydrocarbons. Thermal decomposition of aromatic carboxylic acids produced by the oxidative ring-opening of multinuclear aromatics was studied in order to understand how to manipulate the reaction selectivity. Analysis of the reaction network showed that ketonization and dehydration, i.e., undesirable ring-closing reactions, compete with decarboxylation. Two strategies to limit the contribution of the ring-closing reactions were suggested: (i) carboxylic acid decomposition using a catalyst that favors decarboxylation to produce CO2, and (ii) decomposition in the presence of water to suppress reactions involving dehydration.Catalytic decomposition of aromatic carboxylic acids was studied using metal carboxylates as catalytic surrogates. The study of zinc biphenyl carboxylates demonstrated the potential selectivity benefit of catalytic decomposition over thermal decomposition. It also highlighted possibles changes in the temperature and chemistry of decomposition depending on the metal used to facilitate the decarboxylation reaction. Decompositon using selected alkali, alkaline earth, and transition metals was investigated. The base knowledge for the catalytic behavior of specific metals was expanded (empirical contribution). The need for a systematic approach to predict which materials are suitable for carboxylic acid decarboxylation became evident.Decomposition of aromatic carboxylic acids in the presence of water was investigated. Production of ring-opened products was favored indicating the beneficial effect of water on the reaction selectivity. The latter was found to be sensitive to the mass transport of water. For the overall oxidative ring-opening process, this finding emphasized that the success of the strategy relies not only on the conversion chemistry, but also on the reaction engineering.The critical review of the literature on aromatic oxidation in combination with experimental work on the oxidation of multinuclear aromatics and the decarboxylation of aromatic carboxylic acids contributed to the advancement of the oxidative ring-opening concept.

  • Subjects / Keywords
  • Graduation date
    Spring 2018
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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