Hydrocracking of short residue over unsupported and supported magnetite nanocatalysts.
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Date
2017
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Abstract
With the rapid depletion of crude oil and current cracking methods of heavy petroleum residue all resulting in the production of undesirable coke formation, a better solution must be found. This project investigated the use of an unsupported molybdenum-doped magnetite nano-catalyst, as well as a magnetite nanocatalyst on a mesoporous silica support, to determine if the use of these catalysts can be successful in cracking petroleum residue. Short residue from the vacuum distillation column supplied by SAPREF, was used throughout the experimental work.
A lot of effort went into the preparation of the feedstock due to the high viscosity of short residue. The solvent used during experimental work was toluene, which was used to dilute the short residue. A temperature range between 350˚C and 400˚C was used in order to determine temperature effects on product distribution from the cracking reaction. The feedstock to catalyst ratio was also varied, using the unsupported catalyst, in order to determine the effects of the amount of catalyst on the reaction. Kerosene and gas oil are the desired products due to their higher heating value and use as liquid fuels compared to the heavier residue. There is a strong interaction between temperature and catalyst to feedstock ratio. The high temperature-high catalyst combination gave improved gas oil yields over the low temperature-high catalyst combination. Results carried out at 400˚C with a high catalyst amount showed the most favourable results with a yield of 49.3% and 6% of gas oil and kerosene respectively. Aquaprocessing (catalytic splitting of water that occurs on the surface complexes of the iron-based catalyst, at a relatively low pressure) was simulated at the experimental conditions using kinetics from literature for a nickel-based catalyst. The simulated composition profiles proved that the unsupported magnetite nanocatalyst was much more efficient in upgrading residue than the nickel based catalyst, due to the presence of greater amounts of lighter components. Analysis of the catalyst after the cracking reaction shows that no major phase changes had taken place and that the catalyst could be regenerated to be used again.
The supported magnetite nanocatlyst was compared to conventional nickel-molybdenum and cobalt-molybdenum catalyst, in a fixed bed reactor set up. The supported catalyst proved to be the most consistent, and was able to shift the residue into the lighter fractions more effectively than the conventional catalysts. The supported catalyst was the most effective in cracking the vacuum residue, mostly into vacuum gas oil. The yields using the catalyst compared quite favourably with the unsupported catalyst, with the unsupported catalyst yielding more lighter components. The most favourable results implementing a supported catalyst were also at 400˚C, due to the extensive decrease in vacuum residue and a corresponding increase in lighter components.
Ultimately this investigation proved that hydrocracking can take place with the use of a supported and unsupported magnetite nanocatalyst, at lower temperatures than that of conventional methods and aquaprocessing. It was also proven that the process can be upscaled to industry level, as shown with the performance of the supported catalyst. A larger temperature range could give better clarity in the performance of the catalyst for future petroleum residue cracking.
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Masters Degree. University of KwaZulu-Natal, Durban.