New Catalytic Approaches to Produce Fuels from Algae

Transcription

1 Panel New Catalytic Approaches to Produce Fuels from Algae Chen Zhao, Johannes A. Lercher Department of Chemistry, Technische Universität München

2 Panel utline Introduction Fatty acid reduction to alkanes - Impacts of metal, support, and gas carrier - Hydrogenation-decarbonylation route over Ni/Zr 2 - Hydrodeoxygenation route over Ni/zeolite Microalgae oil conversion to alkanes Conclusions

3 Introduction Triglycerides (fats or oils) are important biomass resources for liquid fuels production. Microalgae oil has high potential to partially replace fossil oil. - Non-food feedstock, non-arable land culture - Triglyceride production rates are 1-2 times higher than terrestrial oil crops - il content in microalgae can attain 6-8 wt.% Y. Chisti, Biotech. Adv. 27, 25, 294. R. H. Wijffels, M. J. Barbosa, Science 21, 329, 796.

4 Techniques for biofuel production from triglyceride Transesterification KH Triglyceride + Methanol Biodiesel + Glycerol High oxygen content Poor flow property at low temperature Hydrotreating NiMoS Triglyceride + H 2 Green Diesel + H 2 /C x + C 3 H 8 Products contamination by sulfur Catalysts deactivation due to sulfur removal and produced H 2 Deoxygenation Pd/C Fatty acids Green Diesel + C 2 Expensive noble metal catalysts Relatively low activity for triglyceride conversion

5 bjectives Triglyceride Transesterification Glycerol + Biodiesel Reforming Liquid H 2 Fuels Hydrotreating Hydrocarbons R 1 R 3 R 2 hydrogenolysis fatty acids hydrodeoxygenation RDS hydrocarbons Triglycerides Develop economically effective nickel based catalysts Understand individual reaction steps in the deoxygenation of fatty acids Provide proof of principle for the alkanes production from microalgae oil

6 Composition of microalgae oil Fatty acids composition of microalgae oil [wt%] R 1 R 2 C 14: [a] C 16: C 18:2 C 18:1 C 18: C 2:4 C 2: C 22:6 C 22:4 C 22:1 C 22: C 24: Sterol R [a] The alkyl chain contains 14 carbons and C=C double bond Microalgae oil (Triglycerides) Microalgae oils are neutral lipids mainly including tri-, di- and mono-glycerides. Microalgae oils are highly unsaturated, and mainly are C 18 fatty acids.

7 utline Introduction Fatty acid reduction to alkanes - Impacts of metal, support, and gas atmosphere - Hydrogenation-decarbonylation route over Ni/Zr 2 - Hydrodeoxygenation route over Ni/zeolite Microalgae oil conversion to alkanes Conclusions

8 Impacts of metal and support on palmitic acid conversion Catalysts Metal loading (wt%) BET surface area (m 2 /g) Metal particle size (nm) Acidity (mmol g -1 ) Basicity (mmol g -1 ) Conv. (%) Selectivity (C%) n-c 15 n-c 16 Lighter C 16 -H Ester Raney Ni Pt/C Pd/C Ni/Zr Pt/Zr Pd/Zr Ni exhibited similar activity for fatty acid reduction to alkanes but stronger hydrocarbon hydrogenolysis ability compared to Pd and Pt. Zr 2 supported catalysts showed much higher activity, indicating strong support effect. Reaction conditions: 1 palmitic acid,.5 g catalyst (or.25 g Raney Ni), 26 o C, 12 bar H 2 (2 ml/min), 6h

9 Impact of gas atmosphere on palmitic acid conversion with Ni/Zr thers 8 Selectivity (C%) 6 4 Palmitone 6 4 Conversion (%) 2 2 1% H 2 at 26 o C 25% H 2 at 26 o C 1% H 2 at 26 o C 1% N 2 at 26 o C n-c 15 1% N 2 at 28 o C 1% N 2 at 3 o C 1% N 2 at 32 o C Ketonization: 2 C 15 H 31 CH C 15 H 31 -C-C 15 H 31 + C 2 + H 2 With altering the carrier gas from H 2 to N 2, the conversion of palmitic acid decreased dramatically, and the main product changed from n-pentadecane to palmitone. Palmitone was formed from the ketonization of palmitic acid on Zr 2. Reaction conditions: 1 palmitic acid,.5 g 5 wt% Ni/Zr 2, 12 bar flow gas (2 ml/min), 6h

10 Mechanism of palmitic acid ketonization The fatty acid is firstly adsorbed on the vacancies of metal oxides to form carboxylate species, followed by α-hydrogen atoms abstraction to form ketene intermediates. Subsequently the formed carboxylate species react with the adjoining ketene species to form ketone by eliminating 1 mole C 2. R. Pestman, et al., J. Catal. 1997, 168, 265. T. S. Hendren, et al., Catal. Today 23, 85, 333.

11 utline Introduction Fatty acid reduction to alkanes - Impacts of metal, support, and gas atmosphere - Hydrogenation-decarbonylation route over Ni/Zr 2 - Hydrodeoxygenation route over Ni/zeolite Microalgae oil conversion to alkanes Conclusions

12 Catalyst screening for stearic acid conversion Catalyst Rate a (mmol g -1 h -1 ) Conv. (%) Selectivity (C%) n-c 17 n-c 18 1-octadecanol Cracking Zr wt.%Ni/Zr wt.%Ni/Zr wt.%Ni/Zr wt.%Ni/Zr wt.%Ni/Ti wt.%Ni/Ce wt.%Ni/Al wt.%Ni/Si a initialhydrogenationrate Stearyl stearate Pure Zr 2 exhibited some hydrogenation ability. Zr 2, Ti 2 and Ce 2 supported Ni catalysts showed higher activity and selectivity to C 17 n-heptadecane than Al 2 3 and Si 2 supported catalysts. Reaction conditions: 1 g stearic acid,.5 g catalyst, 26 o C, 4 bar H 2, 8h

13 Stearic acid conversion over Ni/Zr 2 catalysts 1 1 Yields (C%) C 17 n-heptadecane C 18 1-ctadecanol Conversion (%) Yield of heptadecane(c%) o C 26 o C 25 o C 15 kj/mol Time (min) 1-ctadecanol was primary product and gradually converted to n-heptadecane. Reaction conditions: 1 g stearic acid,.5 g 1 wt% Ni/Zr 2, 26 o C (25, 27 o C), 4 bar H 2

14 Intermediate 1-octadecanol conversion 1 Yield of n-heptadecane (C%) Conversion (%) The yield of n-heptadecane increased linearly with 1-octadecanol conversion. Trace amount of octadecanal (<.5%) was observed. Possible reaction pathway: dehydrogenation followed by decarbonylation. C 17 H 35 -CH 2 -H C 17 H 35 -CH C 17 H 36 - C Reaction conditions: 1 g 1-octadecanol,.15 g 1 wt% Ni/Zr 2, 26 o C, 4 bar H 2

15 Impact of support on stearic acid hydrogenation 2 TF (h -1 ) Ni/Ti 2 Ni/Zr Ni/Ce 2 Ni/Al 2 3 Ni/Si Ni content (wt.%) The TFs for hydrogenation of stearic acid over Ni/Zr 2, Ni/Ti 2, and Ni/Ce 2 (12 h -1 ) were two-fold higher than those over Ni/Al 2 3 and Ni/Si 2, indicating the support plays an important role in the reductive conversion of stearic acid. Zr 2, Ti 2, and Ce 2 were reported for the selective reduction of carboxylic acid to aldehyde. Zr 2 indeed showed some hydrogenation ability. T. Yokoyama, et al., Appl. Catal. A: Gen. 21, 221, 227. T. Yokoyama, et al., Appl. Catal. A: Gen. 1992, 88, 149.

16 Reaction pathways for stearic acid reduction over Ni/Zr 2 Can we increase carbon-weight product by altering the reaction pathway from hydrogenation-decarbonylation to hydrodeoxygenation?

17 utline Introduction Fatty acid reduction to alkanes - Impacts of metal, support, and gas atmosphere - Hydrogenation-decarbonylation route over Ni/Zr 2 - Hydrodeoxygenation route over Ni/HBEA Microalgae oil conversion to alkanes Conclusions

18 Catalysts properties and screening Catalyst Metal Content [wt%] Si/Al [mol/mol] BET surface area [m 2 /g] Acid density [mmol/g] d Ni(111) [nm] d Ni(2) [nm] Conv. [%] Selectivity [C%] n-c 18 iso-c 18 n-c 17 iso-c 17 Cracking Ni/HZSM Ni/HZSM Ni/HZSM Ni/HBEA Ni/HBEA Ni/HBEA Ni/HBEA Reaction conditions: stearic acid (1. g), dodecane (1 ml), Ni/zeolite (.2 g), H 2 (4 bar at 26 o C), 8 h, stirred at 6 rpm. 1 wt% Ni/HBEA (Si/Al=18) showed good activity and high selectivity to n-octadecane. As the acid strengths are similar (TPD), the higher degree of cracking on HBEA compared to HZSM-5 is caused by a higher effective residence time due to the narrower pores of HZSM-5. Reaction conditions: 1 g stearic acid,.2 g Ni/zeolite, 26 o C, 4 bar H 2, 8h

19 Stearic acid conversion over 1 wt% Ni/HBEA (Si/Al=18) 1 8 C 18 n-ctadecane Yields (C%) C 17 n-heptadecane hydrogenation C 17 H 35 -CH C 17 H 35 -CH decarbonylation C 17 H 36 C C 17 H 35 -CH 2 H dehydration hydrogenation C 18 H 38 H 2 H 2 iso-c Conversion (%) The yields of C 18 and C 17 alkanes increased linearly as a function of conversion. ctadecanal (<.2%) and 1-octadecanol (<.1%) were observed in traces. Reaction pathway: sequential hydrogenation followed by dehydration to C 18 alkanes (major), or hydrogenation-decarbonylation to C 17 alkanes (minor). Reaction conditions: 1 g stearic acid,.2 g 1% Ni/HBEA (Si/Al=18), 26 o C, 4 bar H 2

20 Impact of H 2 pressure with Ni/HBEA Yields (C%) n-c 17 iso-c 18 n-c Pressure (bar) Yield of octadecane (C%) bar 4 bar 15 bar Time (min) The higher H 2 pressure leads to a larger reaction rate and a higher yield of n-c 18 alkanes, which is caused by the equilibrium shift from octadecanal to 1-octadecanol. hydrogenation C 17 H 35 -CH C 17 H 35 -CH decarbonylation C 17 H 36 C C 17 H 35 -CH 2 H dehydration hydrogenation C 18 H 38 H 2 H 2 Reaction conditions: 1 g stearic acid,.2 g 1 wt% Ni/HBEA 36, 26 o C

21 Impact of reaction temperature with Ni/HBEA 1 Yields (C%) n-c 17 iso-c 18 n-c Temperature ( o C) Yield of n-octadecane (C%) o C 26 o C 25 o C Time (min) The higher reaction temperature leads to increases of n-c 17 and iso-c 18 yields but comparable n-c 18 yield. - either because of longer contact of the intermediates - or due to the higher apparent activation energies of decarbonylation and isomerization Reaction conditions: 1 g stearic acid,.2 g 1% Ni/HBEA (Si/Al=18), 4 bar H 2, 8h

22 Intermediate 1-octadecanol conversion with Ni/HBEA 8 C 18 n-ctadecane Yields (C%) Distearyl ether C 17 n-heptadecane Conversion (%) The reaction pattern of 1-octadecanol is similar as the reaction of stearic acid. The dehydration rate of 1-octadecanol (8.64 mmol g -1 h -1 ) is ca. 4 times larger than the reaction rate of stearic acid conversion (2.15 mmol g -1 h -1 ), which suggests that the hydrogenation of stearic acid is the rate determining step. Reaction conditions: 1 g 1-octadecanol,.5 g 1 wt% Ni/HBEA (Si/Al=18), 26 o C, 4 bar

23 utline Introduction Fatty acid reduction to alkanes - Impacts of metal, support, and gas atmosphere - Hydrogenation-decarbonylation route over Ni/Zr 2 - Hydrodeoxygenation route over Ni/zeolite Microalgae oil conversion to alkanes Conclusions

24 Transformation of microalgae oil over Ni/Zr 2 8 Total hydrocarbons Yields / wt% C 17 n-heptadecane C 18 Stearic acid C 18 1-ctadecanol Time / min The hydrogenation of fatty acid to aldehyde is the rate determining step. Reaction conditions: 1 g microalgae oil,.5 g 1 wt% Ni/Zr 2, 27 o C, 4 bar H 2

25 Impact of H 2 pressure on microalgae oil reaction over Ni/Zr 2 75 Yield of n-heptadecane / wt% Accelarating hydrogenolysis of triglycerides and hydrogenation of fatty acids Suppressing decarbonylation of alcohol H 2 Pressure / bar Hygrogenolysis-hydrogenation Equilibrium R 1 = R 2 = R1 R 2 H 2 H2 R 3 = R 3 R-CH R-CH R-CH 2 -H Microalgae oil (Triglycerides) Hydrogenated triglycerides RH Reaction conditions: 1 g microalgae oil,.5 g 1 wt% Ni/Zr 2, 26 o C, 8h

26 Transformation of microalgae oil over Ni/HBEA 8 Theoretical Total hydrocarbons R 1= R 2= R = H 2 (r 1 ) R H 2 (r 2 ) R 1 hydrogenation R 2 hydrogenolysis Yields / wt% Stearic C 18 ctadecane C 17 Heptadecane H 2 (r 3 ) R-CH R-CH 2 hydrogenation 3 + C 3 H 8 microalgae oil 1 -C(r 4 ) decarbonylation n-rh Time / min R-CH 2 H R 1=,R 2=,R = :unsaturatedalkylchain Methanation:C +3H 2 =CH 4 +H 2 C 2 +4H 2 =CH 4 +2H 2 Red: carbon distribution in products Reaction pathway: hydrogenolysis-hydrodeoxygenation (major); hydrogenolysis-decarbonylation (minor) The hydrogenation of fatty acid to aldehyde is the rate determining step. Reaction conditions: 1 g microalgae oil,.2 g 1 wt% Ni/HBEA (Si/Al=18), 27 o C, 4 bar H 2

27 Microalgae oil conversion in continuous flow trickle bed reactor Back pressure regulator PIC Waste Bottle Vent Heat exchanger 16 ports sampling loop TIC Reactor Hydrogen Feed Bottle HPLC pump

28 Catalyst stability wt.% Ni/Zr 2 Total hydrocarbons wt% Ni/HBEA (Si/Al=18) Total hydrocarbons Yields / wt% C 17 n-heptadecane Yields / wt% C 18 n-ctadecane TS / h TS / h The performance of continuous flow reactor is identical to the batch reactor. Both Ni/Zr 2 and Ni/HBEA catalysts are stable. Reaction conditions: 26 o C, microalgae oil in dodecane (1.33 wt%, liquid flow speed:.2 ml/min), H 2 (4 bar, gas flow rate: 5 ml/min), 1 wt% Ni/Zr2 (.5 g) or 1 wt% Ni/HBEA (.2 g).

29 Upgrading of microalgae oil to diesel range oil Route 1: hydrodeoxygenation (Angew. Chemie. Int. Ed. 212, 51, 272) Cover paper Route 2: hydrogenation-decarbonylation (J. Am. Chem. Soc. 212, 134, 94)

30 Conclusions Two routes, i.e., hydrogenation-decarbonylation over Ni/Zr 2 and hydrodeoxygenation over Ni/zeolite, are developed for microalgae oil upgrading. The metallic Ni catalyzes the hydrogenolysis of triglyceride, the decarbonylation of aldehyde, and the hydrogenation of functional groups (that is, -CH, -CH, C=C). The rate determining hydrogenation of the fatty acid is either catalyzed solely by metallic Ni to form aldehyde, or catalyzed by synergistic Ni and the Zr 2 support through ketene-like intermediate. The acid function catalyzes the dehydration of alcohol intermediates. Microalgae oil can be efficiently transformed into diesel-range alkanes with Ni based catalysts. R 1= R 2= microalgae oil R 1=, R 2=, R = : unsaturated alkyl chain R = H 2 R H 2 hydrogenation R 1 R 2 hydrogenated triglyceride hydrogenolysis R-CH + Propane H 2 - H 2 R-CH R-CH 2 H R'=CH 2 hydrogenation (de)hydrogenation dehydration decarbonylation - C n-rh Ni/Zr 2 H 2 isomerization cracking iso-rh iso-rch 3 lighter alkanes H 2 hydrogenation n-rch 3 Ni/BEA

31 Panel Acknowledgements