Ryuzo Tanaka

Structural Relaxation Behaviors of Three Different Asphaltenes Using MD Calculations

Abstract For asphaltene obtained from vacuum residues of three different kinds of crude oils (Khafji, Maya, and Iranian-Light), the energy-minimum conformation calculated by molecular mechanics–dynamics simulations showed that aggregated structures of asphaltene molecules through noncovalent interactions are the most stable conformation. Changes of aggregated structures by heating or solvent treatment were investigated by using the molecular dynamics calculation. For Khafji and Iranian-Light asphaltenes, the simulation showed that the aggregated structure was dissociated at 673K, while for Maya asphaltene the dissociation behavior was not observed, showing that Maya asphaltene seems difficult to be dissociated by heating, compared to other asphaltenes. In contrast, the simulation of relaxation of the Maya aggregates in quinoline showed that at 573K a part of aggregates was dissociated more easily than Khafji and Iranian-Light asphaltenes. These results above suggest that the effects of heating and solvent treatment on the structural relaxation of asphaltene aggregates can be different.

Molecular Dynamics Simulation of Structural Relaxation of Asphaltene Aggregates

Abstract For asphaltene obtained from vacuum residue of Khafji crude oil, the energy-minimum conformation calculated by molecular mechanics–dynamics simulations showed that aggregated structures of asphaltene molecules through noncovalent interactions are more stable. Changes induced in aggregated structures by pretreatment with solvents were investigated using molecular dynamics calculations. The simulation showed that in quinolin at 573 K, some staking interactions could be disrupted, while, in 1-methylnaphthalene it was not observed. Autoclave experiments showed that the coke yield after pyrolysis at 713 K was decreased when the asphaltene was pretreated with quinoline at 573 K for 1 h, compared to the yield without the pretreatment. While, in the case of pretreatment in 1-methylnaphthalene, the coke yield did not change significantly. The simulations results above can be related to the difference in coke yield between two solvents; in quinoline some aromatic–aromatic stacking interactions could be disrupted and mobility of molecules was increased. This resulted in prevention of the asphaltenes from polymerizing, as in condensation reactions among aromatic rings. Consequently, the coke yield after the pretreatment with quinoline was decreased.

Supra-Molecular Asphaltene Relaxation Technology

The asphaltene components of heavy oil can become serious problems during fractionation, particularly the toluene-soluble and pentane-insoluble fractions. Asphaltenes are composed of mixtures of thousands of different molecules with complicated chemical structures that form three-dimensionally entangled macromolecular structures. In general, a “supra-molecule” refers to a molecular assembly in which each molecule cooperatively interacts with the others through different types of noncovalent bonds. The resulting supramolecule can express several complicated and specific properties. Asphaltene may form such a supramolecular structure, because asphaltene molecules interact cooperatively with each other through interactions related to poly-aromatic rings such as aromaticaromatic and charge-transfer ones. Every asphaltene supra-molecule exhibits distinct, characteristic properties and different reactivities. The chemical reactions of each individual molecule determine the reactivity of the entire assembly. Therefore, an understanding of these molecular and supra-molecular structures is essential for developing strategies to control their reactivity. Although structural analyses have been performed on asphaltenes, the true molecular weight of asphaltenes has not yet been determined. Vapor pressure osmometry (VPO) and size exclusion chromatography (SEC) 61 Journal of the Japan Petroleum Institute, 56, (2), 61-68 (2013)

A framework for developing a structure-based lumping kinetic model for the design and simulation of refinery reactors

Abstract This study represents a systematic framework supporting the development of a structure-based lumping kinetic model useful for designing, simulating, and optimizing refinery reactors. Utilizing the wealth of the available data and information provided by petroleomics, the framework comprises strategies for analyzing and reducing a large and complicated elementary kinetic reaction model as well as generating lumps in light of the structure and reactivity of the species included in the feedstock and product mixtures. A structure-based model developed by applying the framework cannot only predict yield but can also provide the structure-based composition of the product mixture. A case study on the hydrodesulfurization of light gas oil (LGO-HDS) was used to illustrate the applicability of the framework. The developed LGO-HDS structure-based kinetic model can describe reaction behavior and predict product distribution with high accuracy.