Molecular Characterisation and Modelling for Refining Processes

  • Luyi Liu

Student thesis: Phd


The highly competitive market in the oil refining industry forces refiners look for more detailed information of both feedstocks and products to achieve the optimal economic performance. Due to stricter environmental legislations, the molecular level characterisation has been investigated by various researchers and shows promising advantages in modern refinery design and operation. Although various molecular characterisation methods have been developed, there is an unavoidable trade-off between keeping astronomical molecule details and practicality in industrial applications. In the meantime, many of these methodologies have different characteristics and different focuses according to a particular application purpose. Our aim is hence to tackle the problems of developing manageable and practical technical solutions for molecular characterisation of petroleum fractions for vary refinery processes.A pseudo-component based approach is developed within a modified MTHS (Molecular Type Homologous Series) matrix framework (Peng, 1999) to represent the molecular information of a particular refining stream. This proposed methodology incorporates both molecular type and pseudo-component information by the conjunction of homologous series and boiling points in the matrix framework. To increase the usability of this method, a 3-parameter gamma distribution function is introduced to describe the composition of each structural molecular type. Typical PIONA (paraffin, iso-paraffin, olefin, naphthene, aromatic) analysis, ratios between each homologous types and the percentage of particular carbon type are considered as well as the distillation curve and the density of a stream. More strict product specifications and environmental legislations make strong restriction to the benzene and aromatics content in gasoline products, which motivate refiners to understand, characterise and simulate gasoline catalytic reforming on molecular-level. In this work, kinetic and reactor model of naphtha catalytic reforming is developed based on the proposed MTHS method. The naphtha feedstock composition is represented by the MTHS matrix, and a kinetic network is constructed according to conversions among matrix elements. A process model proposed by Wu (2010) is employed for reforming modelling. The proposed model is then applied to a bench-scale semi-regenerative catalytic reforming unit, which contains 3 fixed-bed reactors, for validation. The influences of essential operating conditions, such as reactor inlet temperature, pressure and weight hourly space velocity (WHSV), on the product distribution and quality are explored. The developed characterisation is also applied in gasoline blending modelling. A molecular-level nonlinear gasoline blending model is developed based on proposed MTHS method with validation. Key properties such as Octane Numbers (ONs) and RVP are blended by molecular matrix elements, and the influence of molecular composition on bulk properties is obvious. A case of recipe optimisation is studied to show the applicability of the proposed method.The implementation of the developed MTHS method for catalytic reforming and gasoline blending demonstrates the compatibility when characterising different petroleum streams, and provides a common platform to simulate and optimise refining operations on the same molecular basis.
Date of Award1 Aug 2015
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorNan Zhang (Supervisor)


  • MTHS matrix
  • Catalytic reforming
  • Gasoline blending
  • Petroleum characterisation
  • Molecular modelling

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