Low Temperature Catalytic Partial Oxidation (LTCPO) of methane to syngas for Gas-To-Liquids applications
Laboratory for Energy and Materials Cycles CH-5232 Villigen Switzerland
Phone: 0041-(0)56 310 2640 Fax: 0041-(0)56 310 2199 E-mail: stefan.rabe@psi.ch
S. Rabe, T.-B. Truong and F. Vogel
Results
RESULTS AND DISCUSSION
ATR
> 1000 °C CH4
O2 H2O
H2 + CO FT
LTCPO
< 800 °C CH4
O2 H2O
H2 + CO + CO2 AFT
Liquid Fuels Autothermal Reforming (ATR) and Fischer-Tropsch (FT)
Low Temperature Catalytic Partial Oxidation (LTCPO) and Advanced Fischer- Tropsch (AFT)
Liquid Fuels
66 66
EXPERIMENTAL
INTRODUCTION
Low Temperature Catalytic Partial Oxidation of methane (LTCPO)
• Proposed Technology Autothermal Reforming (ATR) operates at high temperatures ⇒ stable (and expensive) materials are needed
• LTCPO operates at low temperatures and higher steam-to-carbon ratios ⇒a CO2-rich syngas is produced
• Advanced Fischer Tropsch (AFT) Technology is currently developed (CO2active catalysts, dewatering membranes)
•LTCPO-AFT could be a low cost alternative to ATR-FT technology
Key Parameters for an efficient LTCPO – GTL Process
• High methane conversions (> 95 % are needed))
• M factor of 2.1
I) CATALYSTS FOR THE LTCPO OF METHANE
2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3
0 5 10 15 20 25 30
Number of Carbon Atoms Required H2 / C - Ratio (M factor)
FT - Synthesis of Paraffins: nCO + (2n+1) H2 → CnH2n+2 + n H2O
FT Diesel (H2-CO2) (CO+CO2) LTCPO: M =
Objectives
-To find suitable catalysts for the LTCPO of methane (noble metal catalysts) - Optimization of reaction conditions
- To study the methane activation on noble metal catalysts
-5 5 15 25 35 45 55 65 75 85 95
500 550 600 650 700
T / °C
XCH4;XH2O
XCH4: Thermodynamic Equilibrium Line
□:5%Ru/γ-Al2O3U: 0.3%Pt / γ-Al2O3+: 1%Pt / γ-Al2O3○: 0.6% Pt / SnO2 XH2O: Thermodynamic Equilibrium Line
p = 3 bar, O/C = 0.85; S/C = 2.9; WHSV = 96 g Feed/gcat/h
¾Pt catalysts: lower catalytic activity towards the LTCPO of methane (thermodynamic equilbrium was not achieved). M factors are too low for an efficient LTCPO- GTL process.
¾5%Ru/γ-Al2O3Catalyst: Activity close to the thermodynamic equilibrium
¾M factor is suitable for LTCPO-GTL.
¾A 1%Rh/5%Ce-ZrO2catalyst revealed similar performance.
¾Maximum conversion of 91 % was observed for the Ru catalyst at a pressure of 2 bars and an S/C ratio of 4-5.
II) ACTIVATION OF METHANE OVER Ru AND Rh CATALYSTS
PULSE TGA EXPERIMENTS OVER PRE-OXIDIZED RUTHENIUM CATALYSTS
0 10 20 30 40 50 60 70 80
5Ru/g-Al2O3 5Ru/5Ce-g-Al2O3 1Rh/5Ce-ZrO2 XCH4 / %
Equilibrium
0 10 20 30 40 50 60 70 80
5Ru/g-Al2O3 5Ru/5Ce-g-Al2O3 1Rh/5Ce-ZrO2 XCH4 / %
Equilibrium
SR: WHSV = 77 h-1, 650 °C, ptot= 3.1 bar, S / C = 2.9 CPO: WHSV = 57 h-1, 650 °C, ptot= 3.1 bar, O / C = 0.85 STEAM REFORMING (SR) DRY CATALYTIC PARTIAL OXIDATION (CPO)
5Ru/γ-Al2O35Ru/5Ce-γ-Al2O3 1Rh/5Ce-ZrO2 5Ru/γ-Al2O35Ru/5Ce-γ-Al2O31Rh/5Ce-ZrO2 1Rh/5Ce-ZrO2> 5Ru/γ-Al2O3> 5Ru/5Ce-γ-Al2O3 1Rh/5Ce-ZrO2≈ 5Ru/γ-Al2O3≈ 5Ru/5Ce-γ-Al2O3
¾Dry CPO: similar results were for Rh and Ru catalysts
¾SR: The 1%Rh/5%Ce-ZrO2Catalyst is more active.
¾The presence of cerium seems to inhibit the SR activity of the ruthenium based catalysts
CH4+ H2O → CO + 3 H2 CH4+ 0.5 O2→ CO + 2 H2
ACTIVATION OVER REDUCED Ru- AND Rh-CATALYSTS: TG-FTIR EXPERIMENTS
-2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0
150 250 350 450 550 650 750 850
T / °C
TG / %
5% Ru - 5% Ce / Al2O3 1% Ru / Al2O3 5% Ru / Al2O3 1% Rh - 5% Ce / ZrO2 5% Ru / Al2O3 0.1% Rh / ZrO2 1% Ru / TiO2 5% Rh / Al2O3
I) METHANE DECOPMOSITION: CH4→C + 2 H2 II) TPO: C + O2→CO2
-5 0 5 10 15 20 25 30 35 40
0 100 200 300 400 500 600 700 800
Temp / ºC
Absorbance / A.U.
5% Ru - 5% Ce /Al2O3 1% Ru /Al2O3 5% Ru /Al2O3 1% Rh -5% Ce / ZrO2 5% Ru /Al2O3 0.1% Rh / ZrO2 1% Ru / TiO2 5% Rh /Al2O3
¾Activation / decomposition of methane to carbon (CH4 →C + 2 H2 ) occurs on reduced rhodium catalysts at much lower temperatures as on reduced ruthenium materials (450 °C compared to 675 °C)
¾Steam reforming activity seems to be strongly affected by the methane decomposition on reduced catalytic sites
¾In contrast, no correlation between dry CPO activity and methane activation is observed. The presence of oxygen therefore seems to influence the methane activation pathway
¾Temperature Programmed Oxidation (TPO) studies of the carbon deposits on the different catalysts revealed that the oxidation of the deposited carbon is enhanced on ceria/zirconia supports
Catalyst Preparation
¾Rhodium and ruthenium catalysts were prepared by impregnation of the support material with aqueous noble metal nitrate solutions. Platinum catalysts were prepared from a PtII(NH3)4(OH)2solution
¾Calcination in air at 550 °C for 3 h
LTCPO, Dry CPO and Steam Reforming Experiments
¾Continuous flow fixed-bed microreactor (glass lined stainless steel tube, 4 mm inner diameter) using air as oxidant
¾Catalyst particle size: 125-250 µm, dilutor: sea sand
¾Products were analyzed by on-line gas chromatography TG-FTIR Experiments
¾A Netzsch STA 409 thermogravimetric analyser coupled with a Bruker FTIR spectrometer was used
¾Pre-reduced catalyst (50 mg, 10 % H2in Ar, 650 °C, 1h)
¾After cooling to RT in an argon flow, the sample was heated up to 800 °C (10 °C / min) in a methane / argon flow (20 % CH4). The weight change was recorded
¾After cooling in an argon flow, temperature programmed oxidation (TPO) was performed (20 % O2in Ar).
Carbon dioxide was monitored by FTIR spectroscopy
5%Rh/γ-Al2O3
1%Rh/5%Ce-ZrO2
5%Rh/γ-Al2O3 1%Rh/5%Ce-ZrO2
0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00
0 20 40 60 80 100
t / min Int. CO2 / a.u.
-0.10 0.00 0.10 0.20 0.30 0.40 0.50
Int. CO / a.u.
98.6 98.8 99 99.2 99.4 99.6 99.8 100 100.2 100.4
TG / %
0.55 0.56 0.57 0.58 0.59 0.6 0.61 0.62 0.63 0.64 0.65
DTA / uV/mg
TG DTA Change from exothermic to endothermic
CO/CO2- Formation
Reaction Conditions
¾CH4: 0.5 ml/Pulse
¾T=550 °C
¾Pre-oxidized Ru Catalyst
¾Fully oxidized ruthenium surface (RuO2): Total Oxidation (CH4+ n RuO2→ CO2+ 2 H2O + 2 Ru ), Exothermic
¾Partially reduced ruthenium surface: CO formation (RuO(2-x)+ (2-x) CH4→ (2-x) CO + 2 (2-x) H2,, Endothermic
¾From TG-DTA: RuO0.27is most efficient for CO formation
