Kazuhiro Takahashi*, Kohki Satoh and Hidenori Itoh

Transcription

1 The 13th International Workshop on Advanced Plasma Processing and Diagnostics July 2011, Daejeon Convention Center, Daejeon, Korea Decomposition of an Artificial i Biogas by a Dielectric Barrier Discharge Kazuhiro Takahashi*, Kohki Satoh and Hidenori Itoh 1 Graduate School of Engineering, Muroran Institute of Technology, Mizumoto, Muroran, , Japan s @mmm.muroran-it.ac.jp Contents 1. Introduction -Background & Objective- 2. Experimental Apparatus & Conditions 3. Results 4C 4. Conclusions

2 Background Hydrogen is known as a source of clean energy, and various methods for hydrogen production, such as steam reforming of hydrocarbon, electrolysis of water, etc., are proposed [1]. Recently, the plasma reforming of biogas has attracted attention as a new technique to generate hydrogen. Biomass domestic animal wastes, sewage sludge, etc. methane fermentation ti Biogas CH 4 : 60 % CO 2 : 40 % H 2 S, SO 2 : ppm order [1] J. D. Holladay et al. Catalysis Today, 139, 244 (2004)

3 Background & Objective In plasma reforming of biogas, most of researches are intended to investigateand t and improve hydrogen generation efficiency. i However, by-products from the biogas are rarely investigated. Objective To investigate decomposition characteristics of an artificial biogas. We generated an atmospheric dielectric barrier discharge in an artificial biogas, investigated by-products from the biogas, and evaluated hydrogen generation efficiency.

4 Experimental Apparatus & Conditions mesh Applied voltage AC high voltage (15 kv p-p ) Input power : 30W wire path length:10m microsyring mixture ratio CH 4 /CO 2 = 60/40 % flow rate : 0.1slm purity CH 4, CO 2 : 99.5 % Identification and concentration measurement of by-products are carried out by agc-ms and FT-IR. The concentrations of the artificial biogas and hydrogen are measured by agc.

5 Infrared absorbance spectra (without discharge) abso orbance [a.u u.] without discharge CH 4 CO 2 CH 4 CO wavenumber [cm -1 ]

6 Infrared absorbance spectra (with and without discharge) abso orbance [a.u u.] C 2 H 2 without discharge with discharge CO HCHO, CH 3 CHO, (CH 3 ) 2 CO C 2 H 6, C 3 H 8 C 2 H 2 CH 3 OH, C 2 H 5 OH C 2 H 4 C 2 H wavenumber [cm -1 ] CO (carbon monoxide), C 2 H 2 (acetylene), C 2 H 4 (ethylene), C 2 H 6 (ethane), C 3 H 8 (propane), HCHO (formaldehyde), CH 3 CHO (acetaldehyde), CH 3 OH (methanol), C 2 H 5 OH (ethanol) and (CH 3 ) 2 CO (acetone) are produced from the biogas. Since the absorbance peaks at 2800 ~ 3200 cm - 1 are saturated due to high concentration or long optical path length, the concentrations of the by-products are aeca calculated cu ated from the teabso absorbance, ba which do not overlap those tose saturated ated peaks.

7 Chromatographic analysis of by-products (with discharge) 1.0x10 7 intensity [a a.u.] 7 5 m/z TIC x retention time [min]

8 Chromatographic analysis of by-products (with discharge) 1.0x10 7 intensity [a a.u.] 7 5 m/z TIC x retention time [min] relative inten nsity [%] ret. time min m/z [amu]

9 Chromatographic analysis of by-products (with discharge) 1.0x10 7 intensity [a a.u.] 7 5 CH 4, CO 2 m/z TIC x retention time [min] relative inten nsity [%] ret. time min [ref. methane*0.546]+[ref. carbon dioxide] 10 CH 4 20 m/z [amu] CO 2 50 Similarly, we make a search for reference mass spectra which are similar to the mass spectra of each peak.

10 Chromatographic analysis of by-products (with discharge) 1.0x10 7 intensity [a a.u.] 7 5 CH 4, CO 2 CH 3 CHCH 2 O (CH3 ) 2 CO CH 3 CHO C2 H 5 CHO HCHO (CH 3 ) 2 CHCHO CH 2 CHCHO C 3 H 7 CHO CH 3 CH(OH)CH 3 CH 3 OH CH 3 COC 2 H 5 m/z TIC C 2 H 5 OH 1.0x retention time [min] HCHO (formaldehyde), CH 3 CHO (acetaldehyde), C 2 H 5 CHO (propionaldehyde), C 3H 7 CHO (butyraldehyde butyraldehyde), y CH 2 CHCHO (acrylaldehyde acrylaldehyde), y (CH 3 3) 2 CHCHO (isobutyraldehyde), CH 3 CHCH 2 O (propylene oxide), CH 3 OH (methanol), C 2 H 5 OH (ethanol), CH 3 CH(OH)CH 3 (isopropyl alcohol), (CH 3 ) 2 CO (acetone) and CH 3 COC 2 H 5 (methyl ethyl ketone) are produced from the biogas. It is likely that these products are limited to only small quantities, since the intensities of these products are two or three orders of magnitude less than those of CH 4 and CO 2.

11 Concentrations of by-products product H 2 CO C 2 H 6 C 3 H 8 C 2 H 4 C 2 H 2 others concentration [%] less than 0.1 H 2, CO, C 2 H 6 and C 3 H 8 are major products, and the other products are minor products. It is probable that the concentration of by-product decreases with carbon chain length and bond multiplicity.

12 Comparison of experimental results Conversion rate of CH 4 [%] Conversion rate of CO 2 [%] present work Zou et al. [1] Zhang et al. [2] Zhou et al. [3] H 2 concentration [%] CO selectivity [%] H 2/CO ratio H 2 generation efficiency [g/kwh] For literatures, the entries in the table are the interpolated value at the mixture of CH 4 /CO 2 = 60/40 %. p 4 2 H 2 concentration and the conversion rates of CH 4 and CO 2 are equal to or lower than others. Ahigh H 2 /CO ratio is obtained as a result of low CO selectivity. H 2 generation efficiency is found to reach 1.82 g/kwh, and this is higher than others. [1] J. Zou et al. Plasma Chemistry and Plasma Processing, 23, 1, 69 (2003) [2] Y. Zhang et al. Fuel Processing Technology, 83, 101 (2003) [3] L. M. Zhou et al. Energy & Fuels, 12, 6, 1191 (1998)

13 Conclusions In this work, decomposition characteristics of an artificial biogas in an atmospheric dielectric barrier discharge are investigated. H 2, CO, C 2 H 2, C 2 H 4, C 2 H 6, C 3 H 8, HCHO, CH 3 CHO, C 2 H 5 CHO, C 3 H 7 CHO, CH 2 CHCHO, (CH 3 ) 2 CHCHO, CH 3 CHCH 2 O, CH 3 OH, C 2 H 5 OH, CH 3 CH(OH)CH 3, (CH 3 ) 2 CO and CH 3 COC 2 H 5 are produced from the biogas in the atmospheric dielectric barrier discharge. H 2, CO, C 2 H 6 and C 3 H 8 are major products, and the other products are minor products. The conversion rates of CH 4 respectively. and CO 2 come to 25 % and 19 %, The hydrogen concentration is found to reach approximately 11 %, and this corresponds to hydrogen generation efficiency of 1.82 g/kwh.