Theoretical Study of the Ti-Cl Bond Cleavage Reaction in TiCl4

In this work the kinetics of the TiCl4 TiCl3 + Cl reaction is studied theoretically. A variable-reaction coordinate transition-state theory (VRC-TST) is used to calculate the high-pressure limit rate coefficients. The interaction energy surface for the VRC-TST step is sampled directly at the CASPT2(6e,4o)/cc-pVDZ level of theory including an approximate treatment of the spin-orbit coupling. The pressure-dependence of the reaction in an argon bath gas is explored using the master equation in conjunction with the optimised VRC-TST transition-state number of states. The collisional energy transfer parameters for the TiCl 4-Ar system are estimated via a "one-dimensional minimisation" method and classical trajectories. The Ti-Cl bond dissociation energy is computed using a complete basis set extrapolation technique with cc-pVQZ and cc-pV5Z basis sets. Good quantitative agreement between the estimated rate constants and available literature data is observed. However, the fall-off behaviour of the model results is not seen in the current experimental data. Sensitivity analysis shows that the fall-off effect is insensitive to the choice of model parameters and methods. More experimental work and development of higher-level theoretical methods are needed to further investigate this discrepancy

An assessment of the viability of alternatives to biodiesel transport fuels

© 2019 Elsevier Ltd This work presents an economic feasibility study of using algae and biochar burial strategies to offset carbon emission from the use of conventional fossil-derived transport fuels. The economic feasibility is quantified on the basis that the final price of the decarbonised fossil-derived diesel should be lower or equal to the price of biodiesel which is deemed to be the next best alternative. The extra costs associated with the carbon capture/offset via algae and biochar burial are estimated for the most typical scenarios using the economic models developed as part of this work. In addition, High Dimensional Model Representation based global sensitivity analyses are performed in order to quantify the influence of key model parameters on the overall costs. It was found that using algae burial to offset carbon emissions is not viable for principle reasons such as the amount of water required and the burial of phosphate as well as more than doubling the current diesel price. This price is mainly due to the high costs of pumping dilute algae slurry underground. The biochar burial approach, on the other hand, was found to be much more economically viable as it only increases the conventional diesel price by a small amount. This comparably low price is due to the revenue generated from selling the electricity produced from the pyrolysis by-products. In addition, the global sensitivity analysis revealed that the overall costs were the most sensitive to the wood price, as the wood feedstock may either be an income or an expenditure

A kinetic mechanism for the thermal decomposition of titanium tetraisopropoxide

This work presents the first systematically derived and thermodynamically consistent mechanism to describe the thermal decomposition of titanium tetraisopropoxide (TTIP). The mechanism is based on an analogy between the decomposition of the isopropoxide branches and the decomposition of isopropanol. Flux and sensitivity analyses were used to identify the main reaction pathways in the proposed mechanism as the step-wise release of C3H6 via four-member ring transition states, the successive abstraction of CH3 radicals via C–C bond cleavage followed by hydrogen abstraction to form C = C double bonds, and hydrogen abstraction from the isopropoxide methyl groups followed by the release of C3H6. The final decomposition product was titanium hydroxide, Ti(OH)4. Rate constants were calculated using conventional and variational transition state theories for reactions in the first two pathways. The calculated rates are similar to the rates calculated for the corresponding isopropanol reactions, providing support for the analogy with isopropanol. The mechanism was used to simulate the ignition delay of isopropanol and TTIP. Excellent agreement was observed with experimental data for isopropanol. However, the mechanism over predicted the ignition delay for TTIP. The discrepancy was shown to be unlikely to be caused by the modest difference between the true reaction rates for the TTIP system and those assumed based on the analogy with isopropanol. It was found that the sensitivity of the TTIP decomposition to the presence of water must be caused by additional chemical pathways than the ones given by isopropanol analogy.This project is partly funded by the National Research Foundation (NRF), Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme. The authors thank Huntsman Pigments for financial support

A virtual laboratory to support chemical reaction engineering courses using real-life problems and industrial software

A virtual laboratory has been developed to support chemical reaction engineering courses. Real-life engineering challenges that are difficult to address in a university laboratory give the opportunity to illustrate basic concepts of chemical reaction engineering such as the relationship between temperature and reaction rate, space time and conversion, and inert concentration and selectivity. Six virtual experiments covering topics from petroleum refining, diesel combustion, nanoparticle growth, and hydrogen combustion form the basis of the virtual laboratory. The characteristics embedded in the experiments include the use of economic analysis to give closure to open-ended problems, the solution of engineering problems with high environmental relevance and finally, the ability to solve complex engineering problems related to state-of-the-art technologies, for example the synthesis of functionalized nanoparticles. Trial tests with senior students, with continual feedback and freedom in terms of the delivery date were used to evaluate and improve the experiments. Subsequently, a classroom test with 45 undergraduate students with a fixed deadline was performed. The challenges and opportunities to use virtual experiments supported by industrial software to teach real-life problems to undergraduate students have been critically assessed

Uncovering the genomic basis of an extraordinary plant invasion

Invasive species are a key driver of the global biodiversity crisis, but the drivers of invasiveness, including the role of pathogens, remain debated. We investigated the genomic basis of invasiveness in Ambrosia artemisiifolia (common ragweed), introduced to Europe in the late 19th century, by resequencing 655 ragweed genomes, including 308 herbarium specimens collected up to 190 years ago. In invasive European populations, we found selection signatures in defense genes and lower prevalence of disease-inducing plant pathogens. Together with temporal changes in population structure associated with introgression from closely related Ambrosia species, escape from specific microbial enemies likely favored the plant's remarkable success as an invasive species.Peer reviewe

Question answering system for chemistry—A semantic agent extension

This paper introduces an extension of a previously developed question answering (QA) system for chemistry, operating on a knowledge graph (KG) called Marie. This extension enables the automatic invocation of semantic agents to answer questions when static data is absent from the KG. The agents are semantically described using the agent ontology, OntoAgent, to enable automated agent discovery and invocation. The natural language processing (NLP) models of the QA system need to be trained in order to interpret questions to be answered by new agents. For this purpose, we extend OntoAgent so that it becomes possible to automatically create training material for the NLP models. We evaluate the extended QA system with two example chemistry-related agents and an evaluation question set. The evaluation result shows that the extension allows the QA system to discover the suitable agent and to invoke the agent by automatically constructing requests from the semantic agent description, thereby increasing the range of questions the QA system can answer

Linking reaction mechanisms and quantum chemistry: An ontological approach

In this paper, a linked-data framework for connecting species in chemical kinetic reaction mechanisms with quantum calculations is presented. A mechanism can be constructed from thermodynamic, reaction rate, and transport data that has been obtained either experimentally, computationally, or by a combination of both. This process in practice requires multiple sources of data, which raises, inter alia, species naming and data inconsistency issues. A linked data-centric knowledge-graph approach is taken in this work to address these challenges. In order to implement this approach, two existing ontologies, namely OntoKin, for representing chemical kinetic reaction mechanisms, and OntoCompChem, for representing quantum chemistry calculations, are extended. In addition, a new ontology, which we call OntoSpecies, is developed for uniquely representing chemical species. The framework also includes agents to populate and link knowledge-bases created through the instantiation of these ontologies. In addition, the developed knowledge-graph and agents naturally form a part of the J-Park Simulator (JPS) – an Industry 4.0 platform which combines linked data and an eco-system of autonomous agents for cross-domain applications. The functionality of the framework is demonstrated via a use-case based on a hydrogen combustion mechanism.1. The National Research Foundation (NRF), Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme. 2. The European Union Horizon 2020 Research and Innovation Programme under grant agreement 724145. 3. Alexander von Humboldt foundation

Large haploblocks underlie rapid adaptation in the invasive weed Ambrosia artemisiifolia

Ambrosia artemisiifolia is an invasive weed and primary cause of pollen-induced hayfever. Here, the authors report its chromosome-level phased genome assembly, examine genome-wide variation among modern and historic accessions, and identify large haploblocks underling rapid adaptation