Loading...

Experimental Investigation for Enhancing the Lifetime of Co,Ru/La(γ-Al2O3) Catalyst in Fischer Tropsch Synthesis

Hemmati Mahmoudi, Mohammad Reza | 2012

1089 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 43213 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Kazemeini, Mohammad; Khorasheh, Farhad; Zarkesh, Jamshid
  7. Abstract:
  8. Fischer-Tropsch synthesis (FTS) is the main part of a Gas to Liquid (GTL) process. In this reaction which shall be done based upon iron or cobalt catalysts, H2 and CO molecules (namely Syngas) transform to long hydrocarbon chains. Regarding all of the advantages of cobalt catalysts in comparison with iron counterparts, Research Institute of Petroleum Industry (RIPI) began investigations since two decade ago. The present catalyst comprised of cobalt as active metal, ruthenium as activity promiter and lanthanum as support (gamma alumina) modifier. By the way, still some areas such as its lifetime duration and deactivation needs to be improved by complimentary researches. The present investigation is defined in RIPI to solve such problem. It is noteworthy that each route to enhance the catalyst lifetime should keep the selectivity intact or preferentially even improved. Also all solutions should comprise of the least possible changes in the catalyst preparation recipe, to make it possible to prepare the catalyst with least changes in the available equipments and raw materials.
    In this investigation three different routes were tested to enhance lifetime duration of the catalyst. The first route is to optimize the catalyst preparation recipe, by finding the optimum number of calcinations. The present recipe contains three calcinations in series but in some reports it is denoted that just one calcination is enough. The results shown that it is better to make three impregnations but just one calcination after the final impregnation. This method led to more appropriate physiochemical properties and also reactor test behavior. The reason is that the cobalt clusters get smaller (while still large enough to resist against oxidative effects of water) and hence the dispersion of the cobalt on the pore surfaces and also porosimetric properties get better. Also the reason of smaller size of cobalt during this recipe, is more tendency and better affiliation of precorsur's solution toward adsorption and crystallization on the cobalt oxide in comparison with cobalt nitrate. Lifetime of the best catalysts with this method (one calcination) is almost 1.4 time of the worst catalyst (with three calcinations) and opted as the reference catalyst.
    In the second step, two different ideas for utilization of nanotechnology in catalyst preparation were tested. The first idea was to cover the surface of alumina with carbon nanotubes (CNT) and the second one was to utilize Nano-Structured alumina. The results shown that both of these ideas will lead to more appropriate physicochemical and also reactor test results. Hovewer the best result was taken by combining these two ideas, i.e. covering the surface of Nano-Structured alumina with CNT. The reason could be enhancement in residence time of intermediate products, better reduction of cobalt at lower temperatures and also less interaction of cobalt and alumina. Porosimetric properties of Nano-Structured alumina is much better than regular gamma alumina but it is more sensitive towards calcination.
    Lifetime duration of the catalysts prepared in this steps: Nano-Structured alumina without CNT covering is 4.5 time, with CNT covering 9.0 times and regular gamma alumina with CNT covering 4.5 times of the reference catalyst. Also wax selectivity of all samples was much more than the primary catalyst.
    In the third step, lanthanum doping effect (before cobalt impregnation) was investigated. One of the main deactivation mechanisms of the catalyst is solid state reaction of the cobalt with the support to form cobalt aluminate spinel which leads to omitting some parts of the available cobalt from the reaction. Doping the catalyst with some amounts of lanthanum, will results in formation of a mixed oxide, which in turn lead to more lifetime duration of the catalysts. Reactor and physicochemical tests revealed that lanthanum doping up to 2.7% results in more lifetime duration of the catalysts. But lanthanum doping in comparison with nanotechnology has less improving effects. For example, catalysts with 1.1 and 2.7 weight percentages of lanthanum are 1.8 and 3.0 time more deactivation resistant compared to the reference catalysts.
    In coclusion, the catalyst with 3 impregnations and just one calcination, dope almost 3% of lanthanum utilizng Nano-Structured supports and cover the surface of supports with CNT reach a more deactivation resistant catalyst
  9. Keywords:
  10. Cobalt Catalyst ; Carbon Nanotubes ; Catalyst Deactivation ; Calcination ; Fischer-Tropsch Synthesis ; Nano-Structured Alumina ; Lanthanum

 Digital Object List

  • محتواي پايان نامه
  •   view

 Bookmark