No description available.

No description available.

A laboratory scale delayed coking process was used to produce petrol precursors, diesel precursors, methane rich gas, green and calcined coke from five previously untested South African heavy petroleum residues. The ash content of the heavy petroleum residues was found to be detrimental to the microstructure of the green coke and Coefficient of Thermal Expansion (CTE) of the calcined coke. The sulphur content of the calcined cokes produced was found to be in-line with typical global anode grade cokes. De-ashing of the feedstock would be necessary to produce anode grade fillers for the aluminium industry. The local production of anode grade coke would serve to reduce imports and supply the aluminium smelters on the east coast of South Africa. The heavy petroleum residues (also known as heavy fuel oil) are currently used as bunker fuel in the shipping industry and are responsible for substantial air pollution. Delayed coking of these residues could extend the production of petrol and diesel per barrel of imported crude oil and reduce the effect on South Africa’s balance of payments deficit and impact the environment in a beneficial manner with respect to carbon dioxide and sulphur emissions. The research also evaluated the replacement of heavy fuel oil with marine diesel produced by delayed coking of the former. Marine diesel was found to emit less sulphur oxides and have a higher energy density per unit of carbon dioxide emitted. While seawater scrubbing of the heavy fuel oil would be more cost effective in reducing the sulphur oxide emissions, it would not contribute to carbon dioxide reductions. The research created a hypothetical scenario to determine the required value of Clean Development Mechanism credits for a marine diesel replacement, were shipping to be incorporated under the Kyoto Protocol in future

Agglomerate formation is a common phenomenon that can cause operating problems in the fluid coking reactor. When agglomerates form they provide longer diffusion paths of the reaction products through the liquid layers and liquid bridges within the agglomerate, which leads to higher mass transfer resistance, trapping of the reaction products and increasing the undesired coke formation reactions. Surviving agglomerates in the reactor can also cause fouling of the reactor interior and defluidization of the bed. The ultimate coke yield was determined for agglomerates of Athabasca vacuum residue and solid particles by heating on Curie-point alloy strips in an induction furnace at 503 oC and 530 oC and in a fluidized bed reactor at 500 oC until all toluene-soluble material was converted. Coke yields from agglomerates were compared to the results from reacting thin films of vacuum residue. The average coke yield from the agglomerates was 23%, while the coke yield from thin films of 20 m thickness was 11%, which supports the role of mass transfer in coke formation reactions. The ultimate coke yield was insensitive to vacuum residue concentration, agglomerate size, reaction temperature and agglomerate disintegration. The temperature profile within agglomerates was measured by implanting a thermocouple at the agglomerate center, and a heat transfer model was used to describe the temperature variation with time. The effective thermal diffusivity of the agglomerates was 0.20 x 10-6 m2/s. Control experiments on reactions in thin liquid films confirmed that heating rates in the range of 14.8 to 148 K/s had no effect on the ultimate yield of coke

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The alkylation of benzene with ethane was studied at 370 oC over two Pt-containing ZSM-5 catalysts with SiO2/Al2O3 ratios of 30 and 80. While the benzene and ethane conversion decreased with time-on-stream for the PtH-ZSM-5(30) catalyst, the PtH-ZSM-5(80) catalyst demonstrated a stable performance. The deactivation of the PtH-ZSM-5(30) catalyst was found to be more significant, when compared to the PtH-ZSM-5(80) catalyst as a result of differences in the formation of coke. Results from gas sorption and x-ray diffraction experiments showed that coke is preferentially formed within the channel segments of the PtH-ZSM-5(30) catalyst as opposed to coke deposition on the outside surface of the PtH-ZSM-5(80) crystallites, subsequently blocking entrance to the zeolite channels. <br /> The location of the coke deposition was found to affect the product selectivity of the two PtH-ZSM-5 catalysts. The accessibility functions, derived from nitrogen and argon sorption data, suggested that, with prolonged time-on-stream, the coke molecules build up from the middle of the zeolite crystallites outwards towards the surface, as the reaction was carried out over the PtH-ZSM-5(30) catalyst. Partial blockage of the internal pore structure of the PtH-ZSM-5(30) catalyst decreased the diffusion length within the crystallites. In contrast to the typical effect of coking, where the selectivity of para- isomers would be enhanced with coke deposition, the effect of the reduction in the diffusion length of the PtH-ZSM-5(30) crystallites is consistent with the decreasing para-selectivity of the diethylbenzene (DEB) isomers with time-on-stream. <br /> n investigation of the causes of coke locations was conducted, and the results suggested that, the spatial distribution of Pt metal was responsible for the different locations of coke observed. Surface reactions initiated coking in the intercrystalline region of the PtH-ZSM-5(80) catalyst, as the Pt particles on the surface of the PtH-ZSM-5(80) crystallites increased the difficulty of access for reactants to the interior of the crystallites. Within the PtH-ZSM-5(30) catalyst, ethane dehydrogenation and benzene alkylation took place in the micropore network as a result of preferential intracrystalline deposition of Pt metal. Further conversions on the active sites within the PtH-ZSM-5(30) crystallites thus lead intracrystalline coking.

Refcoal is a refined carbon source obtained by extraction of coal with dimethylformamide (DMF). During the coking process, Refcoal goes through a mesophase (fluid) stage to form an anisotropic coke. In contrast, oxidised Refcoal does not undergo such a mesophase stage during the carbonisation process. Thus it does not yield an anisotropic coke, but forms an isotropic coke. The objective of this study is to produce an anisotropic coke from oxidised Refcoal. For this purpose, diabietic acid, a hydrogen donor, was considered as a suitable additive. Coking was performed in sealed glass capillary tubes as diabietic acid proved to be volatile at the carbonisation temperature of 500 °C. The resultant cokes were analysed using thermogravimetric analysis, Raman spectroscopy and optical microscopy. The results show that the degree of anisotropy increased with diabietic acid content (3, 5 and 10 mass %). / Dissertation (MSc (Chemistry))--University of Pretoria, 2008. / Chemistry / MSc / Unrestricted

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Este trabalho consiste no desenvolvimento de metodologia para a seleção de catalisadores de maior resistência ao coqueamento para serem aplicados à Tecnologia de Refino e de Petroquímica. Essa metodologia associada a outras determinações ajudará na seleção de catalisadores para as unidades de reforma a vapor e possibilitará maior atividade, estabilidade e menor geração de coque, o que se traduz em otimização do catalisador para a unidade. O catalisador para reforma a vapor é normalmente constituído de uma fase ativa de níquel, promovida ou não com metais refratários, alcalinos e outros, suportado em alumina, aluminato de cálcio ou aluminato de magnésio. Inicialmente os catalisadores foram submetidos ao processo de redução, permitindo uma percentagem e efeito similar, eliminando, portanto a influência da redução dos catalisadores na conversão dos mesmos. O desenvolvimento da metodologia empregou as técnicas termoanalíticas e a associação dessas com outras técnicas físico-quimicas e analíticas, por exemplo, cromatografia gasosa e/ou espectrometria de massa. No planejamento experimental 22 foram determinados e fixados os seguintes fatores para maximizar a formação de coque e, portanto selecionar os catalisadores mais resistentes ao coqueamento: i) massa de amostra: 10 mg; ii) granulometria: 24-48 mesh/Tyler; iii) temperatura do teste: 650°C; iv) razão de aquecimento 20°C.min-1 e tempo de coqueamento de 50 minutos; v) velocidade espacial 220 h-1 e mistura de alimentação (95)CH4/(5) H2 % mol/mol ; e vi) cadinho de Pt°. A análise geral dos resultados sugeriu que a metodologia, com os parâmetros selecionados, pode ser utilizada para a seleção de catalisadores mais resistentes ao coqueamento. No trabalho foram iniciados estudos da cinética do coqueamento, sobre a influência da temperatura no tipo de coque e a avaliação das características do coque nos diferentes catalisadores. / This work consists of the development of a methodology for the selection of catalysts of greater resistance to coking to be applied to the Refining Technology and Petrochemical. This methodology combined with other techniques should help in selection of catalysts for steam reforming units, which have better activity, stability and lower coke production. The catalyst for steam reforming normally is constituted of an active phase of nickel, promoted or not with refractory metals, alkali and others, supported on alumina, calcium aluminate or magnesium aluminate. Initially, the catalysts were subjected to the reduction process to the same degree, eliminating therefore the influence of this effect in their performance. The methodology developed here emploies thermoanalytics techniques and associated to other physical-chemistry and analytical techniques, for example, gas chromatography and / or mass spectrometry. In the experimental 22 planning were certain factors that could influence the results were identified and fixed such as: i) mass of sample: 10 mg; ii) size: 24- 48 mesh / Tyler, iii) test temperature: 650 ° C, iv) rate of heating 20 °C.min-1 And the coking time of 50 minutes, v) space velocity 220 h-1 and mixture of (95)CH4 /(5)H2% mol/mol; and vi) crucible of Pt. The general results suggest that the methodology, with the parameters selected, can be used for the selection of catalysts more resistant to coking. In the work it was initiated studies on the kinetics of coking, influence of temperature on the type of coke and evaluation of the characteristics of coke in different catalysts.

Este trabalho consiste no desenvolvimento de metodologia para a seleção de catalisadores de maior resistência ao coqueamento para serem aplicados à Tecnologia de Refino e de Petroquímica. Essa metodologia associada a outras determinações ajudará na seleção de catalisadores para as unidades de reforma a vapor e possibilitará maior atividade, estabilidade e menor geração de coque, o que se traduz em otimização do catalisador para a unidade. O catalisador para reforma a vapor é normalmente constituído de uma fase ativa de níquel, promovida ou não com metais refratários, alcalinos e outros, suportado em alumina, aluminato de cálcio ou aluminato de magnésio. Inicialmente os catalisadores foram submetidos ao processo de redução, permitindo uma percentagem e efeito similar, eliminando, portanto a influência da redução dos catalisadores na conversão dos mesmos. O desenvolvimento da metodologia empregou as técnicas termoanalíticas e a associação dessas com outras técnicas físico-quimicas e analíticas, por exemplo, cromatografia gasosa e/ou espectrometria de massa. No planejamento experimental 22 foram determinados e fixados os seguintes fatores para maximizar a formação de coque e, portanto selecionar os catalisadores mais resistentes ao coqueamento: i) massa de amostra: 10 mg; ii) granulometria: 24-48 mesh/Tyler; iii) temperatura do teste: 650°C; iv) razão de aquecimento 20°C.min-1 e tempo de coqueamento de 50 minutos; v) velocidade espacial 220 h-1 e mistura de alimentação (95)CH4/(5) H2 % mol/mol ; e vi) cadinho de Pt°. A análise geral dos resultados sugeriu que a metodologia, com os parâmetros selecionados, pode ser utilizada para a seleção de catalisadores mais resistentes ao coqueamento. No trabalho foram iniciados estudos da cinética do coqueamento, sobre a influência da temperatura no tipo de coque e a avaliação das características do coque nos diferentes catalisadores. / This work consists of the development of a methodology for the selection of catalysts of greater resistance to coking to be applied to the Refining Technology and Petrochemical. This methodology combined with other techniques should help in selection of catalysts for steam reforming units, which have better activity, stability and lower coke production. The catalyst for steam reforming normally is constituted of an active phase of nickel, promoted or not with refractory metals, alkali and others, supported on alumina, calcium aluminate or magnesium aluminate. Initially, the catalysts were subjected to the reduction process to the same degree, eliminating therefore the influence of this effect in their performance. The methodology developed here emploies thermoanalytics techniques and associated to other physical-chemistry and analytical techniques, for example, gas chromatography and / or mass spectrometry. In the experimental 22 planning were certain factors that could influence the results were identified and fixed such as: i) mass of sample: 10 mg; ii) size: 24- 48 mesh / Tyler, iii) test temperature: 650 ° C, iv) rate of heating 20 °C.min-1 And the coking time of 50 minutes, v) space velocity 220 h-1 and mixture of (95)CH4 /(5)H2% mol/mol; and vi) crucible of Pt. The general results suggest that the methodology, with the parameters selected, can be used for the selection of catalysts more resistant to coking. In the work it was initiated studies on the kinetics of coking, influence of temperature on the type of coke and evaluation of the characteristics of coke in different catalysts.