Plasma-Catalysis: A Novel Technology for Bioenergy Applications

Transcription

1 Plasma-Catalysis: A Novel Technology for Bioenergy Applications Xin Tu Department of Electrical Engineering and Electronics University of Liverpool, UK xin.tu@liv.ac.uk Coaxial DBD Packed Bed DBD Gliding Arc (GA) Rotating GA Supergen Bioenergy Annual Assembly, 25 th October 2017, Belfast, UK 1/36

2 Outline I. Introduction II. III. IV. Plasma-catalytic gas cleaning process for the removal of tars from the gasification of biomass waste Plasma-catalytic conversion of biogas (CO 2 and CH 4 ) into liquid fuels and chemicals at ambient conditions Summary 2/36

3 Energy and environment challenges Total global energy demand 70% increase Increasing energy demand and pressure on supply depletion of fossil fuels! Energy use and its impact on the environment Greenhouse gas effect and global warming! UK: 470M tonnes CO 2 /year 3/36

4 Energy and environment challenges Biomass: promising sustainable feedstock Thermo-chemical conversion of biomass 4/36

5 Non-thermal plasmas (cold plasma) low temperature (as low as room temperature) generation of highly energetic electrons (1-10 ev)/chemically reactive species (free radicals O, OH, excited atoms, molecules and ions) instant reaction/fast start and shut down (combined with renewable energy such as wind or solar) size: microsystem large scale; compact and mobile system flexibility to combine with other technologies, e.g. plasma/uv, plasma/catalysis, plasma/adsorption, plasma/biochemical Plasma-catalysis (advantages) synergistic effect (interactions between plasma and catalysts) reduced metal particle size and enhanced metal dispersion improved selectivity, yield and energy efficiency minimise the formation of unwanted by-products overcome trade-off between conversion and energy efficiency 5/36

6 Plasma-catalytic reforming of tar model compounds Working conditions C 7 H 8 content: 15.0 g/nm 3 ; C 10 H 8 content: 1.1 g/nm 3 Carrier gas: N 2; Total gas flow: 3.5 L/min Steam/carbon molar ratio: 1.5 Preheating temperature: 300 o C Catalysts 2 g x wt.% Ni- y wt.% Co/γ- Al 2 O 3, denoted as: 15Ni, 7.5Ni7.5Co, 15 Co 6/36

7 Effect of Ni-Co bimetallic catalyst The highest tar conversion of 93.7% (toluene) was achieved when using the 7.5Ni7.5Co bimetallic catalyst in the plasma at a discharge power of 56 W. The corresponding energy efficiency was 37 g/kwh. 7/36

8 Possible mechanisms of toluene decomposition i) Radical generating reactions: e N N e * 2 2 e H2O OH H e N H O OH H N * ii) Toluene destruction reactions: C6H5CH3 e C6H5CH2 H e iii) Radical termination reactions: OH CO CO2 H H CH3 N2 CH4 N2 H OH N2 H2O N2 H H M H2 M C6H5CH3 e C6H5 CH3 e C H CH N (A ) C H CH H N u C H CH N (A ) C H CH N u C H CH N (A ) C H CH H N u C H CH N (a ) C H C H N ' u C H CH OH C H CH H O C6H5CH3 OH N2 C6H 5(OH)CH 3 H2O N2 8/36

9 Reforming of tar model compound in simulated producer gas using a rotating gliding arc 9/36

10 Destruction efficiency (%) Energy efficiency (g/kw h) Gas composition (%) Reforming of tar model compound (toluene) in simulated producer gas Input H2O concentration (%) C 7 H 8 Content: 10 g/nm 3 ; Total flow rate: 10 L/min; Power: ~380 W The maximum conversion of toluene was 87.4% at a steam concentration of 16%. The volume fraction of H 2 and CO in the gas products increased (the volume fraction of CO 2 and CH 4 decreased) after the plasma reforming of toluene %H 2, 10%CO, 13%CO 2, 3%CH 4, 61%N 2 Input H2O concentration (%) H2 CO CO2 CH4 10/36

11 Integrated system combining biomass gasification and plasma-catalytic tar reforming (University of Leeds) Experimental set-up Water syringe Nitrogen Insulator Plasma reactor SPA tar sampling port Condensers 11/36

12 III. Plasma-catalytic direct conversion of biogas into liquid fuels and chemicals Unique route 12/36

13 Experimental setup Power/Temperature Discharge power: 10 W Temperature: ~30 o C Working gas CH 4 /CO 2 = 3:1 1:2 Flow rate: 40 ml/min Catalysts (2g) 15 wt.% Cu/Al 2 O 3 1 wt.% Pt/Al 2 O 3 1 wt.% Au/Al 2 O 3 Argon DBD calcination DBD reactor (cooled) Gas gap: 3 mm; Length: 45 mm Electrode: stainless steel rod/ water electrode AC Power supply Frequency: 9 khz Voltage: up to 30 kv 13/36

14 Effect of CH 4 /CO 2 ratio (Plasma-alone) Products: Acetic acid Methanol Ethanol Acetone Formaldehyde Wang et al., Angew. Chem. Int. Ed. 2017, 56, Acetic acid CH 3 COOH 100% atom economy 14/36

15 Effect of CH 4 /CO 2 ratio Wang et al., Angew. Chem. Int. Ed. 2017, 56, /36

16 Different operating modes: plasma alone, catalysis alone and plasma-catalysis (CH 4 /CO 2 =1:1) Products: Acetic acid Methanol Ethanol Acetone Formaldehyde Acetic acid 100% atom economy Wang et al., Angew. Chem. Int. Ed. 2017, 56, /36

17 Possible reaction pathways 17/36

18 Summary Plasma-catalytic process has been demonstrated to be effective for the reforming of tars from biomass gasification. The combination of the plasma with the catalysts showed much better performance compared to that using plasma alone. We have developed an integrated process combining biomass gasification and plasma-catalytic process. Direct conversion of biogas (CO 2 and CH 4 ) into value-added liquid fuels and chemicals has been achieved using a cold plasma reactor at ambient conditions (~30 o C, 1 atm). Acetic acid, methanol and ethanol are the main liquid products in this process, while HCHO can only be formed in the presence of noble catalysts. This process can be integrated with renewable energy sources for decentralised system for chemical energy storage. 18/36

19 Acknowledgement University of Liverpool Dr. Li Wang Miss. Shiyun Liu Mr. Fengsen Zhu Miss. Bryony Ashford University of Leeds Prof. Paul Williams Dr. Mohamad Nahil University of Hull Dr. Chunfei Wu 19/36

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