A study of the vapour phase pyrolysis and alkaline hydrolysis of chloroform

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The decomposition of chloroform at 510˚C was investigated in a continuous flow system, using nitrogen as the carrier gas. The main products of the reaction were hydrogen chloride, tetrachloroethylene, pentachloroethane and hexachloroethane; hydrogen and chlorine could not be detected. Neither the addition of a radical initiator (azobisisobutyroni trile) nor an inhibitor (phenol) affected the breakdown, and so we have rejected the idea that the main reaction mechanism is of a radical nature. From the results obtained by varying the surface to volume ratio of the reactor, the reaction appeared to be catalysed by the surface of the reactor, but pretreating the tube by steaming, soaking in water or EDTA solution did not affect the pyrolysis. The reaction appeared to be virtually unaltered when a tube made from very pure silica was used. Kinetic investigations showed that the reaction was first order with respect to chloroform, and exhibited an induction period. Carrying out the reaction in a carbonised tube resulted in a faster reaction, and an increase in the induction period. To account for the results obtained, a mechanism is suggested which involves the formation of a carbon polymer on the silica reactor. Chloroform could then be adsorbed onto the polymer where reaction could occur. In a carbonised tube a graphite-like carbon structure may begin to take over as the catalyst. The alkaline hydrolysis of chloroform was studied in aqueous 1,4-dioxane (32 % w/v), at 360C. The rate of disappearance of chloroform was followed by gas-liquid chromatography, whilst the sodium hydroxide concentration was determined by titration with dilute hydrochloric acid. The reaction was second order overall, first order with respect to each of the reactants. Data obtained at 25˚C, 31˚C, 36˚C and 41˚C was used to determine the activation parameters. Increasing the concentration of dioxane in the solvent decreased the reaction rate. The reaction showed a definite negative salt effect, sodium chloride exhibiting a greater effect than potassium nitrate. The reaction between deuterochloroform and sodium deuteroxide in deuterium oxide/dioxane was faster than the reaction in the corresponding proton system. Application of the Yagil approach suggested that the transition state is associated with seven water molecules. This led us to suggest an alternative mechanism for the reaction, involving nucleophilic attack by water on the trichloromethyl anion, formed by loss of a proton from chloroform. In order to apply the Yagil criterion the hydration number of diolane had to be determined; a value of 2.25 was obtained.Science Research Counci

Studies on the stability and antioxidant properties of butylated hydroxyanisoles

Butylated hydroxyanisole (BHA) is one of the most widely used synthetic antioxidants added to foodstuffs. BHA consists of a mixture of isomers, 3-tert-butyl-4- hydroxyanisole (3-BHA) and 2-tert-butyl-4-hydroxyanisole (2-BHA). [Continues.

Molecular pathways of degradation of wool-related peptides

The thermal and alkali-promoted reactions of A-acetyl-A-methylamides of alanine, cystine, glycine, histidine, methionine, phenylalanine, proline, serine, threonine, tryptophan and tyrosine have been studied as models for the reaction of heat and alkali on wool protein. The cystine model, iV,iV-diacetyl-L-cystine- N,N-dimethylamide (DCDMA), has been the principal substrate. The amino acid derivatives were usually heated either as wet solids at 125 “C or in aqueous solution buffered at pH 10-11 at 55“ and 100 “C. A brief photochemical study was conducted with DCDMA. Reactions were monitored by uv spectroscopy and HPLC. Products were isolated by preparative HPLC, characterised by spectroscopy and quantified by analytical HPLC. All the reactions with DCDMA give bright yellow product mixtures. The major components, however, are colourless, and include A,A-diacetyl-thiocystine-A,A- dimethylamide (DTCDMA), diastereoisomers of N,N- diacetyl lanthionine-A,A- dimethylamide (DLDMA) and A-acetyl-A-methylamides of cysteine (NACMA) and dehydroalanine (NADMA). Their formation is best explained by a p- elimination mechanism involving thiocysteinyl and dehydroalanyl derivative intermediates. The product distribution and yields from wet solid samples, however, differ significantly from those obtained with aqueous alkali. DTCDMA is the major product (65%) in wet solid-state conditions, and is formed so readily that it is usually present as a contaminant of the substrate. A-Acetylthio- cysteine-iV-methylamide (NATCMA) is also present amongst thermolysis products, but we could not determine its yield due to intrinsic instability. NADMA is the principal product formed in aqueous alkali (-58%) followed by DLDMA, DTCDMA and NACMA. NADMA is shown to be unstable under acid conditions and decomposes to methylpyruvamide (MPA) and acetamide. Elemental sulphur was isolated from the decomposition of DCDMA under both conditions. Yellow reaction mixtures of DCDMA show three regions of increased absorptions at 300, 385 and 455 nm. Results implicate methylthiopyruvamide as one of the pigments contributing to the yellowing and that polysulphides may also be involved. Of the monopeptides examined, A-acetyl-A-methylamides of histidine, serine, threonine, tryptophan, tyrosine and DCDMA both degrade and yellow in wet solid-state conditions. The derivative of cystine is by far the most reactive monopeptide on treatment with alkali. A-Acetylserine-A-methylamide is the only amino acid derivative which both degrades and yellows in dry solid-state conditions. The protection of the hydroxyl group by benzyl reduces thermal or alkaline yellowing but it remains ineffective against decomposition. Irradiation of DCDMA leads to a drop in pH, decomposition, and the formation of bright yellow solution with A-acetylcysteine-A-methylamide as the principal product. The derivatives of glycine, alanine, serine, and DTCDMA are also observed but in small amounts. Although the occurrence of the minor products is invoked as evidence for the cleavage of C-S bond, the cleavage of S-S bond appears to be predominant. The implications of the results from these model compounds for wool degradation are briefly discussed. The principal conclusion is that the ready formation of the thiocystinyl derivative in the thermal degradation of DCDMA suggests analogous structures within wool proteins play a far more significant role in their chemistry than has been considered hitherto

Posterior summaries of grocery retail topic models: Evaluation, interpretability and credibility

Understanding the shopping motivations behind market baskets has significant commercial value for the grocery retail industry. The analysis of shopping transactions demands techniques that can cope with the volume and dimensionality of grocery transactional data while delivering interpretable outcomes. Latent Dirichlet allocation (LDA) allows processing grocery transactions and the discovering of customer behaviours. Interpretations of topic models typically exploit individual samples overlooking the uncertainty of single topics. Moreover, training LDA multiple times show topics with large uncertainty, that is, topics (dis)appear in some but not all posterior samples, concurring with various authors in the field. In response, we introduce a clustering methodology that post-processes posterior LDA draws to summarise topic distributions represented as recurrent topics. Our approach identifies clusters of topics that belong to different samples and provides associated measures of uncertainty for each group. Our proposed methodology allows the identification of an unconstrained number of customer behaviours presented as recurrent topics. We also establish a more holistic framework for model evaluation, which assesses topic models based not only on their predictive likelihood but also on quality aspects such as coherence and distinctiveness of single topics and credibility of a set of topics. Using the outcomes of a tailored survey, we set thresholds that aid in interpreting quality aspects in grocery retail data. We demonstrate that selecting recurrent topics not only improves predictive likelihood but also outperforms interpretability and credibility. We illustrate our methods with an example from a large British supermarket chain

Durability characteristics of asphalt mixtures containing bioditives

This thesis is focused on determining the durability characteristics of asphalt mixtures containing bio-based additives for the purpose of more effective use of recycled materials. Fifty mixtures were evaluated by Cantabro Mass Loss testing in their virgin state, after 1 year of field aging, and after laboratory conditioning to determine the effectiveness of bioditives in dense graded asphalt and sand asphalt mixtures. Key findings from this work demonstrated that considerable amounts of recycled asphalt shingles (i.e. 5% of the total mixture) significantly affect the brittleness of dense graded asphalt mixtures when used in conjunction with reclaimed asphalt pavement (RAP). Furthermore, brittleness was not improved with the use of bioditives at high dosages (e.g. greater than 7.5% of the total binder content), but was improved in some cases at lower dosage rates (e.g. 2.5-5%). Additional testing of similar mixtures and bioditives evaluated in this thesis are recommended

New insights in vulcanization chemistry using microwaves as heating source

La vulcanització per microones és un procés madur i no hi ha dubte sobre la seva eficiència per produir articles de cautxú d'alta qualitat. Les microones són conegudes no només per la seva capacitat d'accelerar els processos i augmentar la eficiència de la transferència energètica, sinó que també són capaces en certs casos de canviar els camins de reacció. Hi ha evidències, basades en canvis en propietats físiques al comparar productes vulcanitzats amb el mètode convencional i amb microones, que indiquen que alguns canvis poden succeir al treballar amb diferents fonts d'escalfament. No obstant això, hi ha una falta d'informació sobre els efectes que les microones tenen en la química de la vulcanització. Per tant, el principal objectiu d'aquesta tesi es basa en estudiar la vulcanització assistida amb microones des d'una nova perspectiva, centrant-se en els efectes d'aquesta radiació en els ingredients principals de les formulacions de cautxú, en el mecanisme de vulcanització, en la reticulació de la xarxa polimèrica i també en el procés de devulcanització.La primera part de la feina va consistir en desenvolupar i optimitzar tots els mètodes analítics necessàris per explorar totes les etapes del procés de vulcanització i identificar tots els intermedis formats. Estudis de Model Compound Vulcanization (MCV) utilitzant esqualè com a molècula model s'han realitzat per entendre millor la influència d'aquesta radiació en el mecanisme de la reacció, encara que alguns experiments també s'han realitzat amb mostres de cautxú natural. Tècniques com HPLC-MS, MALDI-TOF o GPC s'han utilitzat per caracteritzar les mostres de MCV, mentre que mesures d'inflament, de tensió-elongació, compressió i duresa s'han realitzat per caracteritzar les mostres de cautxú natural.Dos dels sistemes de vulcanització més comuns han estat estudiats (sulfenamides i tiurams). A més, s'ha donat un especial èmfasi a l'estudi de la influència de les microones en el sistema activador, intentant reduir el contingut de ZnO i cercar, a través de diverses estratègies, substituts més amigables amb el medi ambient. Finalment, tot el coneixement adquirit en aquests estudis s'ha utilitzat per optimitzar el comportament devulcanitzant del disulfur de difenil (DPDS) amb l'ajut de les microones, demostrant que les microones poden ajudar a avançar en la recerca d'una solució al problema del reciclatge dels residus de cautxú.La vulcanización por microondas es un proceso maduro y no cabe duda sobre su eficiencia para producir artículos de caucho de alta calidad. Las microondas son conocidas no sólo por su capacidad de acelerar los procesos y aumentar la eficiencia de la transferencia energética, sino que también son capaces en ciertos casos de cambiar los caminos de reacción. Hay evidencias, basadas en cambios en propiedades físicas al comparar productos vulcanizados con el método convencional y con microondas, que indican que algunos cambios pueden suceder al trabajar con diferentes fuentes de calentamiento. Sin embargo, hay una falta de información sobre los efectos que las microondas tienen en la química de la vulcanización. Por lo tanto, el principal objetivo de esta tesis se basa en estudiar la vulcanización asistida por microondas desde una nueva perspectiva, centrándose en los efectos de esta radiación en los ingredientes principales de las formulaciones de caucho, en el mecanismo de vulcanización, en la reticulación de la red polimérica y también en el proceso de devulcanización.La primera parte del trabajo consistió en desarrollar y optimizar todos los métodos analíticos necesarios para explorar todas las etapas del proceso de vulcanización y identificar todos los intermedios formados. Estudios de Model Compound Vulcanization (MCV) utilizando escualeno como molécula modelo se han realizado para entender mejor la influencia de esta radiación en el mecanismo de la reacción, aunque algunos experimentos también se han realizado con muestras de caucho natural. Técnicas como HPLC-MS, MALDI-TOF o GPC se han utilizado para caracterizar las muestras de MCV, mientras que medidas de inflamiento, de tensión-elongación, compresión y dureza se han realizado para caracterizar las muestres de caucho natural.Dos de los sistemas de vulcanización más comunes han sido estudiados (sulfenamidas y tiuramos). Además, se ha dado un especial énfasis al estudio de la influencia de las microondas en el sistema activador, intentando reducir el contenido en ZnO y buscar, a través de diversas estrategias, substitutos más amigables con el medio ambiente. Finalmente, todo el conocimiento adquirido en estos estudios se ha utilizado para optimizar el comportamiento devulcanitzante del disulfuro de difenilo (DPDS) con ayuda de las microondas, demostrando que las microondas pueden ayudar a avanzar en la búsqueda de una solución al problema del reciclaje de los residuos de caucho.Microwaves vulcanization is a mature process and there is no doubt about its efficiency on producing high quality goods. Microwaves are found not only to speed up the processing and increase the energy transfer efficiency, but also to be in some cases able to change reaction pathways. There are some evidences, based on changes in physical properties when comparing conventional and microwaves vulcanization, that suggest that some changes occur when working with different heating sources. However, there is a lack of information of the effects of MW in vulcanization chemistry. Therefore, the principal aim of this thesis consists of studying microwave-assisted vulcanization from a new perspective, focusing on the effects of this radiation in the main ingredients of a rubber compound, in the vulcanization mechanism, in the final crosslinked network and also in the devulcanization process.The first part of the work consisted in developing and optimizing all the analytical methods necessary to explore all the steps of vulcanization process and identifying all the intermediates formed. Model Compound Vulcanization (MCV) studies, using squalene as a model molecule, have been used to understand better the influence of this radiation in the reaction mechanism, even though some tests have been also performed in natural rubber samples. Techniques as HPLC-MS, MALDI-TOF or GPC have been used to characterize the MCV samples, whereas swelling measurements, stress-strain measurements, compression set or hardness have been used to characterized natural rubber samples. Two of the most common vulcanizing systems have been studied (using sulfenamide and/or thiuram accelerator types). In addition, a special emphasis has been given to the study of the microwaves influence on the activator system, trying to reduce ZnO contents and finding more environmental friendly substitutes through different strategies. Finally, all the knowledge acquired in all these studies has been used to optimize the devulcanizing behavior of diphenyl disulfide (DPDS) with the help of microwaves, proving that microwaves can help to advance in the search of a solution to the problem of waste rubber recycling

Design aspects of explosive mixtures in a vehcile interstage final report

Prevention and control of explosive mixture of hydrogen and oxygen within vehicle interstag

CRITICAL REVIEW OF THE SUITABILITY OF SULPHUR AS A COMPONENT IN VARIOUS CIVIL ENGINEERING APPLICATIONS

Sulphur Extended Asphalt (SEA) mixtures were used commercially in the 1970s and 1980s. Increases in sulphur prices, however, rendered SEA mixes uneconomical. Handling and safety issues also were of concern, as molten sulphur was difficult to use and occasionally generated H2S. Sulphur is a major waste of by-product from gas and oil production that has potential for encapsulation in civil engineering purposes mainly concentrating in road pavements

The making of nickel and nickel-alloy shapes by casting, powder metallurgy, electroforming, chemical vapor deposition, and metal spraying

Casting, powder metallurgy, electroforming, metal spraying, and chemical vapor deposition techniques for producing nickel and nickel-alloy shape