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Hydrotreating is the response to the necessity of a cleaner feed for downstream processes and reduced pollution. Hydrotreating catalysts are vital in this process; hence catalyst deactivation is a key issue. The principal objective of this research was the experimental study of hydrotreating catalyst deactivation due to arsenic compounds. The hydrotreating of light gas oil, in the presence and absence of an arsenic compound over a commercial NiMoS catalyst, was investigated in a trickle bed reactor (temperature 315-360˚C, space velocity = 1-3 h-1, pressure = 3MPa). Kinetics of first order for nitrogen and sulphur were found and activation energies values of 32 kj/mol and 76 kj/mol respectively. Studies of activity changes, suggested that arsenic mainly affects the conversion of sulfur compounds; which might indicate that arsenic prefers mainly the S edge of the catalysts. Activation energy values decreased after arsenic introduction, which may suggest pore plugging of the catalyst. / Chemical Engineering

Thesis (M. Eng.)(Chemical)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (M.Eng. (Chemical Engineering)) -- University of Pretoria, 2007. / Includes bibliographical references.

Thesis (M.Eng. (Chemical Engineering)) -- Universiteit van Pretoria, 2006. / Includes bibliographical references.

Thesis (M.Eng.(Chemical Engineering))--University of Pretoria, 2004. / Title from opening screen (viewed March 18, 2005). Includes summary. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xii, 119 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 114-119).

Biodiesel is a re-emerging biofuel as an alternative to the traditional petroleum derived diesel. There are however, several factors that currently hinder the widespread uptake. Majority of the biodiesel are currently produced from edible oils thereby sparking the food versus fuel debate, the cost of feedstock is significantly high, there are problems experienced in the traditional production process and the resulting fuel is of inadequate quality. This work focused on addressing the issue of poor cold flow properties to improve the overall quality of biodiesel. The skeletal isomerisation of linear fatty acid methyl esters (FAMEs) into branched chain isomers, using solid acid catalysts, appears to be the most comprehensive solution in enhancing the cold flow properties of biodiesel. However, obtaining high branched chain yields, mitigation of undesired side reactions, achieving shorter reaction times, using fewer processing steps and lower operating conditions have still not been achieved to a large extent. Moreover, no studies were found to date investigating isomerisation of FAMEs as a continuous process. A trickle bed reactor (TBR) system has been identified to be an effective continuous reactor. Its key features of being a three phase system and allowing a high degree of contact between the reactant and the catalyst offering a high conversion per unit volume provides an encouraging opportunity to lower reaction times, reaction steps and conditions whilst increasing branched chain yields. This thesis explores the use of the TBR system, for the first time, to enhance the cold flow properties of biodiesel through molecular modification using zeolite beta catalyst with Si/Al ratios of 180 and 12.5. A range of reactions have been investigated including isomerisation, dewaxing (hydroisomerisation and hydrocracking) and decarboxylation on biodiesels derived from camelina, palm and coconut oils. Significant progress has been made in this research area with a 7 °C drop in MP being achieved upon the dewaxing of the coconut biodiesel at 250 °C, 1.01 bar pressure, 0.2 ml/min LF and 37.5 ml/min GF. To achieve greater drops in melting points it has been suggested to investigate mesoporous catalysts as they will ensure greater facilitated molecular access to the active sites, resulting in a higher conversion by preventing pore blockages. All in all, a series of key findings and serendipitous discoveries have brought to surface an array of new challenges as well as paving the way for a host of exciting opportunities for future research. The ability to continuously produce high quality renewable fuel offers a fascinating prospective for various industrial associates such as Argent Energy, Olleco, Neste Oil and ConocoPhillips.