Systematic Optimization of Asphaltene Molecular Structure and Molecular Weight Using the Quantitative Molecular Representation Approach

Abstract

We describe results of the ongoing development of a computer algorithm to optimize asphaltene molecular weight (MW) by systematically deriving quantitative molecular representations (QMRs) for asphaltenes and a comparison to experimental data. The QMR method consists of the generation and optimization of molecular structures based on experimental data, including elemental analysis, nuclear magnetic resonance, and MW. In this case, we use the MW as a variable in the problem, keeping all other experimental variables constant, and systematically investigate the effect of an increasing MW on the quality of the model optimization, as measured by the penalty or objective function. In this fashion, we find an optimal value for the MW using the QMR algorithm. We observed a significant increase in the objective function when optimizing sets of increasing target MW. We then analyzed the individual contributions of the different properties of the optimized sets toward the objective function and tested a number of possible alterations to the sampling parameters in an attempt to reduce the value of the objective function. It was found that constructing a single set of molecules, prior to optimization, from smaller subsets that are generated using a variety of sampling parameters could yield a great reduction in the value of the objective function following optimization. The resulting asphaltene molecular structures may be used as input for molecular dynamics simulations.

Catalogue of Plausible Molecular Models for the Molecular Dynamics of Asphaltenes and Resins Obtained from Quantitative Molecular Representation

“…Seventeen molecules were chosen and published, with molecular weights ranging from 347 Da to 1625 Da, from a larger generated population by selecting the best fits to the chemical characterization data, which consisted of elemental analysis, GPC and 1 H - 13 The procedures of Sheremata et al 36 generated large archipelago-type structures by connecting building blocks only through alkyl chains. Boek et al 64,72,73 extended the approach by also including other linkages, generating continental structures with larger aromatic cores. The set of asphaltene and resin structures (examples provided in Figure 19) were simulated in heptane and toluene.…”

A Review of Kinetic Modeling Methodologies for Complex Processes

“…Several molecular reconstruction methods have been developed (Al Halwachi et al, 2012;Allen and Liguras, 1991;Alvarez-Majmutov et al, 2014Boek et al, 2009;Neurock et al, 1994;Peng, 1999;Pyl et al, 2011;Quann and Jaffe, 1992;Sheremata et al, 2004;Zhang, 1999). These methods can be classified into three groups according to the approach used to represent the molecular composition: approach by model molecule, deterministic molecular reconstruction approach, and stochastic molecular reconstruction approach.…”

Temperature and Moisture Impacts on Asphalt before and after Oxidative Aging Using Molecular Dynamics Simulations

“…2(a-d), respectively. However, other asphalt molecular structures are available in the literature (Al Halwachi et al 2012).…”