IRON OXIDE BASED OXYGEN CARRIERS FOR HYDROGEN PRODUCTION
BY CHEMICAL LOOPING REFORMING
Lidia Protasova, Marijn Gysen, Myrjam Mertens, Frans Snijkers
Flemish Institute for Technological Research (VITO), Boeretang 200, 2400 Mol,
Belgium. Tel.: + 32 14 33 56 72, Fax: + 32 14 32 11 86
During hydrocracking process, heavy gas oil molecules are cracked into distillate
and gasoline in the presence of hydrogen and catalyst. Increased reliance on
hydrocracking for clean fuels production has also led to a rise in hydrogen
consumption. Hydrogen plays a critical role in this process, and its demand has
increased with the introduction of low-sulphur gasoline and diesel fuels.
Chemical-looping reforming (CLR) is an alternative process to produce hydrogen,
where fuel is oxidized using oxygen from a solid oxygen carrier (OC) material
instead of gaseous oxygen. In CLR, methane is partially oxidized to synthesis gas
by the lattice oxygen of the OC (reduction), and then reduced OC is re-oxidized by
water (oxidation) to produce hydrogen. The key issue in CLR is the OC
performance. Particle size distribution, porosity, strength, and reactivity define the
performance of the OC particles. The OC materials of first generation were Nibased. Recently, a search for Ni-free OC’s with similar or superior properties was
initiated because of the toxicity and high cost of nickel.
In this work, iron oxide based OC particles were prepared from commercial raw
materials by the spray-drying technique, that is well suited for preparation of
particles with high sphericity, attrition resistance, and homogeneity. In order to
obtain OC particles with sufficient mechanical strength, sintering was performed at
1000-1200°C.
The OC’s were tested in CLR at different temperatures (850-900°C) and redox
cycle lengths (35-120 min). A few compositions (Fe-Al, Fe-Al-Zr, Fe-Zr oxides)
were screened in order to find an OC with the best performance. The influence of
the composition and sintering temperature was studied. The full conversion of
methane was achieved using the Fe-Al and Fe-Al-Zr OC’s. Morphology, crushing
strength, redox properties, porosity of OC’s were analysed before and after CLR
runs. Stability tests of Fe-Al and Fe-Al-Zr OC’s showed no deactivation of the
material after more than 150 hours time-on-stream. Some impurity of hydrogen due
to carbon monoxide formation was observed during the reduction step. The
composition of OC’s was improved by addition of ceria; moreover the effect of the
reaction conditions (CH4-to-steam ratio) was studied.
The work is done in the frame of Sener Conacyt project No. 177007 “Recovery of
matricial oil and density improvement of heavy crude oils by in-situ oil
hydroprocessing”.