I. VOCs real-time monitoring by Proton Transfer Reaction – Time of Flight – Mass Spectrometry

1. Experimental investigation on the cleaning of biogas from anaerobic digestion as fuel in an anode-supported SOFC under direct dry-POx reforming. I. VOCs real-time monitoring by Proton Transfer Reaction – Time of Flight – Mass Spectrometry Biogas production from the Organic Fraction of Municipal Solid Waste in a pilot plant (OFMSW) Real-time monitoring of VOCs Dynamic gas dilutionsystem for VOCsquantification Measured mass spectra for biogas contaminants • VOCs from a dry anaerobic digestion pilotplant (Ambientaliasrl) are detected by direct injection mass spectrometry (PTR-ToF-MS 8000, IoniconAnalytik GmbH, Innsbruck, Austria). This innovative technique enables for the real-time monitoring of the biogas contaminants (from 10 to 400 amu). The real-time evolution of selected compounds also enable to study in detail the anaerobic digestion mechanisms (e.g., MT and DMS shift to H2S during the digestion process). • To overcame quantification problems related with compounds with proton affinity (e.g., H2S) close to that of water (H3O+ as ion source), a dynamic gas dilution system was used to perform accurate calibrations. Biogas II. Biogas cleaning on activated carbons Fig.1 – AD pilot plant in San Michele a/A (IT) Fig.4 – Gas calibration unit Fig.3 – Measured mass spectra at day 1 of the AD biogas production process • A clean biogas is required to feed the SOFC. Especially, sulfur compounds must be removed. Two different type of activated carbons, Sulfatrap R8 (TDA Research inc.) and RGM3 (Norit) (Table 1), were tested using a simulated biogas with selected contaminants in it (Table 2) at a GHSV of 27657 h-1.Figs. 6 – 7 give breakthrough curves for 1 g of activated carbons. • The threshold concentration of 1ppmv is reached at: • 230 min for H2S and 174 min for C2H6S, using Sulfatrap R8 adsorbent; • 155 min for H2S and 20 min for C2H6S, using RGM3 adsorbent. Fig.2 – PTR-ToF-MS instrument1 Fig.6 – Breakthrough curve for H2S on activated carbons Fig.7 – Breakthrough curve for DMS on activated carbons Fig.5 – VOCs time evolution during the AD process III. Experimental tests on planar anode supported SOFCs Biogas with residual H2S contentcoming from the gas cleaningsection Biogas direct internal reforming – CH4 partial oxidation (POx) adding air at the anode compartment After an initial voltage decrease, POx of CH4 showed stable cell performance for more than 100h. By adding 1 ppmv of sulfur (H2S) to the main gas stream, the cell voltage started decreasing steadily. However, after sulfur was removed from the biogas feed, the initial performance was restored. Overall stable performance under POX direct reforming exceeded 200 h. The effect of the POx ratio on cell performance was also studied (Fig. 10). Ohmic losses are almost constant (0.12 W*cm2) either feeding the cell with clean biogas or biogas with 1 ppmv of H2S. The total ASR increased with sulfur from 0.45 to 0.70 W*cm2. However, upon sulfur removal, the initial ASR (pre-H2S) was restored pointing out how a hydrogen sulfide breakthrough brings a reversible degradation at the 1 ppmv level. Fig.10 – Effect of the air/biogas ratio on the cell performance The ohmic ASR remains constant (0.09 W*cm2) immediately after switching from H2 to CH4(POx); after ~50 h of test a shift occurred yielding an ohmic ASR of 0.13 W*cm2. At later times, also the total ASR increased most likely due to microstructural changes on Nickel anode structure (Fig. 11). Fig.8 – C-H-O ternary diagram for gas mixtures selected Fig.8 allows to choose the POx ratio to avoid the carbon deposition zone from thermochemicalequilibriumevaluations. Fig.9 – Galvanostatic experiment with direct biogas POx Fig.11 – EIS during the experiment with POx and POx + H2S Conclusions References [1] Courtesy of IoniconAnalytik GmbH, Austria [2] Altepkin, G.O., 2004. Sorbents for Desulfurization of Natural Gas, LPG and Transportation Fuels. Sixth Annual SECA Workshop Pacific Grove, California. [3] Takahashi, Y., Shiratori, Y., Furuta, S. and Sasaki, K., 2012. Thermo-mechanical reliability and catalytic activity of Ni-Zirconia anode supports in internal reformingSOFC running on biogas. Solid State Ionics. • VOCs from AD of OFMSW were monitored using a PTR-ToF-MS instrument. Several compounds are found: sulfur compounds (H2S 18-200ppmv, CH4S 0-47ppmv, C2H6S 0-35ppmv), carbonyl compounds (C4H8O 2-78ppmv) and terpenes (C10H16 11-213ppmv) were detected and quantified using a dynamic gas dilution system. • Preliminary studies on the gas cleaning were made using two different adsorbents (SulfatrapR8 and RGM3); results suggest that a mixture of the two activated carbons would provide a satisfactory gas quality to feed fuel cells. • Stable performance with DIRECT-POX of biogas were tested for over 200 h. At the 1 ppmv level of H2S (kept for 25 h and simulating a breakthrough of the adsorbent filter), a reversible degradation was observed.