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Kinetic Monte Carlo (KMC) has been widely used in the simulation of polymeric reactions. The power of KMC is highlighted by its ability to keep track of the length and sequence of every radical or polymer chain, while it is computationally more expensive than deterministic kinetic models. This paper introduces an acceleration method that significantly reduces the computational cost of KMC simulations, while keeping the same features as the full kinetic Monte Carlo simulations. Case studies are used to demonstrate the general applicability of this method to free radical copolymerization. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4013-4021, 2017 [ABSTRACT FROM AUTHOR]

Abstract: Molecular simulations were used to screen a diverse collection of eight homochiral metal–organic frameworks (MOFs) for their ability to separate 19 chiral compounds by enantioselective adsorption. The simulation model was validated by comparison with available experimental data. It was found that high enantioselectivity is strongly correlated with a close match between the size of the pore and the size of the chiral sorbate molecule. However, there is also a possibility of no enantioselectivity even when the size of the pore matches with the size of the chiral sorbate molecule. A four-point model was used to explain this observation, and a solution to promote high enantioselectivity has been proposed. [Copyright &y& Elsevier]

Stochastic mechanistic models for gradient copolymerisation systems were developed based on a kinetic Monte Carlo algorithm. Due to the discrete nature of the simulations, chains were tracked as binary strings allowing for the storage of the complete sequence of each polymer chain, allowing for an unprecedented level of detail. Models were developed that simulated styrene/4-acetoxystyrene semi-batch gradient copolymer syntheses, and explicit sequence information was determined using simulation results. The chemical composition distribution was mapped for the copolymers, which is capable of providing a visual description of both the size and overall composition distributions of the copolymer and a qualitative description of the chain architecture. This methodology was expanded to track the explicit sequences of each chain that was used to determine the number and weight fraction sequence length distributions. Simulation results show that tail end compositional tapering was never fully achieved. Case studies were conducted to determine the major factors affecting tail end tapering, including increasing the initial batch fraction and varying the 4-acetoxystyrene flow rate. While an increase in initial batch fraction increases 4-acetoxystyrene significantly, head end tapering is lost, while a large increase in flow rate is not capable of fully tapering the tail end. [ABSTRACT FROM AUTHOR]

The potential application of a homochiral metal-organic framework (MOF) made from cadmium corners and BINOL-type linkers for enantioselective separations of chiral hydrocarbons was investigated using grand canonical Monte Carlo simulations. Adsorption of racemic mixtures of (R,S)-1,3-dimethyl-1,2-propadiene, (R,S)-1,2-dimethylcyclobutane and (R,S)-1,2-dimethylcyclopropane was simulated. The results show that an enantiomeric excess (ee) of over 50% can be achieved for 1,3-dimethyl-1,2-propadiene, while more moderate ee values were observed for the cyclic compounds. The adsorption sites, diastereomeric complexes and adsorption energies were analysed to understand the enantioselective adsorption. It is shown that the small zigzag pores of the homochiral MOF account primarily for the enantioselective adsorption, whereas the larger helical pores show almost no enantioselectivity. The results also demonstrate that both intrinsic enantioselectivity and accessibility of the adsorption sites are important for the overall enantioselective separation. [ABSTRACT FROM AUTHOR]

Knudsen dynamics simulations were performed in cylindrical pores with multiple sections of different diameters. The number and location of hits between particles and the pore walls can be related to the known distributions in the uniform diameter cases. Both sweep-gas and pass-through modes of operation were examined. The contact of the particles traveling inside the pores with the pore walls can be regulated by adjusting the aspect ratio (section length/section diameter) of the pore sections and the ratio of their cross-sectional areas. The results were found to be independent of the transition angle between sections except for very smooth transitions. Analytical expressions were developed to relate the transmission probability in pores of multiple sections to the transmission probabilities of the constituent sections. [Copyright &y& Elsevier]

Grand canonical Monte Carlo (GCMC) simulations demonstrate that catenation can be beneficial for improving hydrogen storage in metal–organic frameworks at cryogenic temperatures and low pressures but not necessarily at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: The three-point model and molecular simulation are used to understand the enantioselective adsorption of a homologous series of chiral compounds on a common chiral selector that is incorporated on a solid surface. We demonstrate how the enantioselectivity of homologous chiral compounds may go down, go up, remain the same, or even reverse. Conditions that lead to consistent enantioselectivity for homologous chiral compounds are also proposed. [Copyright &y& Elsevier]

Abstract: Conventional continuum mechanistic models for polymer degradation typically involve thousands of coupled differential-algebraic equations, requiring an efficient solver to solve the complex set of stiff model equations. This can be overcome by formulating the problem in terms of a stochastic simulation procedure, requiring only iterative operations to solve the model. The present work describes the detailed mechanistic modeling of pyrolysis of poly(styrene peroxide) (PSP) using kinetic Monte Carlo (KMC) simulation to predict the product yields and gain a better understanding of the product evolution pathways. The traditionally accepted mechanism of PSP pyrolysis proposed by Mayo and Miller, which involves the key reaction steps of peroxide bond fission, alkoxy radical recombination and disproportionation, and end chain β-scission, was initially tested using the KMC model to predict the peroxide concentration profile and the product yields. This model was only qualitatively able to predict the major products, benzaldehyde and formaldehyde, while the formation of minor products like α-hydroxy acetophenone, phenyl glycol, and phenyl glyoxal was not captured at all. Hence, a new mechanism that also incorporated hydrogen abstraction and β-scission was proposed and implemented in KMC. The final model tracked 949 reactions of 83 species. The rate coefficients for all the reaction steps were based on the existing literature reports, and hence no parameter estimation was done to fit the model against the experimental data. The revised model was quantitatively able to predict all the products of PSP pyrolysis, which was attributed to the stabilization of the alkoxy radicals by hydrogen abstraction, and the subsequent generation of additional alkoxy radicals by β-scission. KMC allowed the dominant pathways for the formation of minor products and dimers to be identified explicitly. Finally, the implications of this study in understanding the effect of trace peroxide bonds on poly(styrene) pyrolysis are outlined. [Copyright &y& Elsevier]