• Energy Research

Thermodynamic analysis of gasification with air, steam, and mixed air-steam was performed over rice husk to determine the optimum conditions (i.e., equivalence ratio (ER), steam to biomass ratio (SBR) and operating temperature) that can maximize the yield of hydrogen production with low energy consumption. It was found that for air gasification, H2 production is always less than CO production and considerably decreased with increasing ER. For steam gasification, the simulation revealed that H2 production is greater than CO, particularly at high SBR and low temperature; furthermore, H2 yield increased steadily with increasing temperature and SBR until reaching SBR of 3.5-4.0, then the effect of steam on H2 yield becomes less pronounced. As for the mixed steam/air gasification, H2 production yield increased with increasing SBR, but decreased dramatically with increasing ER (up to 0.4). Among these three operations, the highest H2 production yield can be achieved from the steam gasification with SBR of 4.0. Nevertheless, by considering the system efficiency, the combined air-steam gasification provided significant higher hydrogen production efficiency than the other two operations. The optimum condition for combined air-steam gasification can be achieved at 900°C with ER of 0.1 and SBR of 2.5, which provided the efficiency up to 66.5 percent.

Abstract Catalytic activities of Ni- and Ni–Fe bimetallic based catalysts supported by palygorskite, MgO–Al 2 O 3 , La 0.8 Ca 0.2 CrO 3 , and La 0.8 Ca 0.2 CrO 3 /MgO–Al 2 O 3 toward the cracking and reforming of naphthalene and toluene (as biomass tar model compounds) as well as real biomass tar from pyrolysis of eucalyptus wood chips were studied. At 700-900 °C, the main products from the cracking of these hydrocarbons are H 2 , CH 4 , C 2 H 4 , C 2 H 6 , and C 3 H 6 . Among all catalysts, Ni–Fe supported by MgO–Al 2 O 3 and La 0.8 Ca 0.2 CrO 3 /MgO–Al 2 O 3 show the highest H 2 yield values and good resistance toward carbon deposition. Additions of H 2 O and CO 2 can promote steam and dry reforming, from which H 2 and CO were the major products from the reaction and the amount of carbon formation was considerably reduced. Importantly, the H 2 O/tar and CO 2 /tar ratios strongly affect the H 2 yield value, particularly for Ni–Fe/La 0.8 Ca 0.2 CrO 3 /MgO–Al 2 O 3 due to the presence of perovskite-based La 0.8 Ca 0.2 CrO 3 . At proper H 2 O/tar and CO 2 /tar ratios, La 0.8 Ca 0.2 CrO 3 behaves like the partly-reduced metal-oxide catalysts and promotes the reforming activity. Addition of O 2 along with H 2 O and/or CO 2 can further reduce the carbon formation and increase the H 2 yield. Nevertheless, excess O 2 could oxidize metal particles and combusted H 2 to H 2 O, which causes lower H 2 yield production.

Herein an ethanol production process from rice straw was optimized. Simultaneous saccharification and co-fermentation (SSCF) using Saccharomyces cerevisiae and Scheffersomyces stipitis co-culture was carried out to enhance ethanol production. The optimal saccharification solid loading was 5%. Key fermentation parameters for co-culture including cell ratio, agitation rate and temperature was rationally optimized using design of experiment (DoE). Optimized co-culture conditions for maximum ethanol production efficiency were at S. cerevisiae:S. stipitis cell ratio of 0.31, agitation rate of 116 rpm and temperature of 33.1°C. The optimized SSCF process reached ethanol titer of 15.2g/L and ethanol yield of 99% of theoretical yield, consistent with the DoE model prediction. Moreover, SSCF process under high biomass concentration resulted in high ethanol concentration of 28.6g/L. This work suggests the efficiency and scalability of the developed SSCF process which could provide an important basis for the economic feasibility of ethanol production from lignocelluloses.

Abstract Liquid hot water (LHW) pretreatment of cellulosic feedstock improves its enzymatic digestibility by removing hemicellulose/lignin, thus making the remaining cellulose more accessible to cellulases. In this study, alkaline-catalyzed (NaOH) LHW pretreatment of rice straw was explored. Various NaOH concentrations (0.25–1.0%) were tested for removal of hemicellulose and lignin as well as enzymatic hydrolysis of the pretreated material at 140–160 °C for 5–20 min. It was found that glucose recovery from enzymatic hydrolysis was markedly higher for rice straw pretreated by LHW in the presence of NaOH compared with LHW pretreatment in the absence of NaOH. Alkaline catalysis of LHW pretreatment also increased removal of hemicellulose and lignin from solid residue and increased the pentose yield in the liquid phase. Under optimum LHW condition of 140 °C for 10 min in the presence of 0.25% NaOH, a maximum glucose yield of 71.8% was obtained from the enzymatic hydrolysis of pretreated rice straw; combined with hydrolyzed glucose in the liquid, this represents a maximum glucose recovery of 74.6% from rice straw. The results thus demonstrate the usefulness of NaOH catalyst for LHW pretreatment of rice straw for increasing sugar recovery and reducing energy requirement.

Abstract A detailed thermodynamic analysis is employed as a tool for prediction of carbon formation boundary for solid oxide fuel cells (SOFCs) fueled by methane. Three operating modes of SOFCs, i.e. external reforming (ER), indirect internal reforming (IIR) and direct internal reforming (DIR), are considered. The carbon formation boundary is determined by finding the value of inlet steam/methane (H2O/CH4) ratio whose equilibrium gas composition provides the value of carbon activity of one. It was found that the minimum H2O/CH4 ratio requirement for which the carbon formation is thermodynamically unfavorable decreases with increasing temperature. For SOFCs with the oxygen-conducting electrolyte, ER-SOFC and IIR-SOFC show the same values of H2O/CH4 ratio at the carbon formation boundary, independent of the extent of electrochemical reaction of hydrogen. In contrast, due to the presence of extra H2O from the electrochemical reaction at the anode chamber, DIR-SOFC can be operated at lower values of the H2O/CH4 ratio compared to the other modes. The difference becomes more pronounced at higher values of the extent of electrochemical reaction. For comparison purpose, SOFCs with the hydrogen-conducting electrolyte were also investigated. According to the study, they were observed to be impractical for use, regarding to the tendency of carbon formation. Higher values of the H2O/CH4 ratio are required for the hydrogen-conducting electrolyte, which is mainly due to the difference in location of water formed by the electrochemical reaction at the electrodes. In addition, with this type of electrolyte, the required H2O/CH4 ratio is independent on the SOFC operation modes. From the study, DIR-SOFC with the oxygen-conducting electrolyte seems to be the promising choice for operation.

Abstract In the present work, catalytic activities of sewage sludge char supported Re-Ni bimetallic catalyst toward cracking/reforming of naphthalene and biomass tar were studied. Several proportions of Re and Ni (i.e. 1:9, 3:7, 5:5, 7:3 and 9:1) were investigated and their activities were compared to char, Ni/char and Re/char catalysts. Among all catalysts, the highest naphthalene cracking conversion and H2 yield were achieved from Re-Ni/char with Re:Ni ratio of 3:7. From the post-reaction characterizations, the additional of Re into Ni not only improves the dispersion of Ni on char surface by preventing agglomeration of particles but also improve the catalyst resistance toward carbon deposition. The additional of steam and O2 along with naphthalene as steam and autothermal reforming were also carried out. The presences of suitable steam and O2 can further promote H2 production and significantly reduce the degree of carbon formation. Under optimum conditions at 800 °C with H2O/C and O2/C molar ratios of 1.5 and 0.3, the catalyst exhibited high biomass tar conversion with only 5% deactivation in H2 yield after 18 h operation. Therefore, this study indicates the successful development of catalyst and process for biomass tar conversion via cracking and reforming processes.

This paper investigated the performance of a bioethanol-fed Solid Oxide Fuel Cell (SOFC) system integrated with a distillation column (SOFC-D). Excess heat from the SOFC system was directly utilized in the distillation column where bioethanol (5 mol%) was purified to a desired concentration before feeding to the SOFC system consisting of an air heater, an ethanol/water heater, a reformer, an SOFC preheater, an SOFC stack and an afterburner. The SOFC-D system was simulated using Aspen PlusTM for the distillation portion and MatlabTM for the SOFC portion. The effects of operating parameters; i.e., ethanol concentration, ethanol recovery, fuel utilization and operating voltage on the performance and energy involved in the SOFC-D system (e.g. distillation energy: QD and the net exothermic heat of the SOFC system: QSOFC,Net) were examined. In addition, the performance of the SOFC-D system at the energy sufficient point where QD = QSOFC,Net was considered. The integration of the distillation column with the SOFC system was found to offer superior SOFC performance. The ethanol recovery and fuel utilization significantly influenced the overall electrical efficiency and power density. Quite low performances are obtained when one operated the SOFC-D without an external heat source. The maximum overall efficiency and power density (~35% and 0.22 W cm-2) occured at an ethanol recovery of 80% and Uf of 90%.

Abstract Catalytic activities of trimetallic ReNiMo sulfide supported on γ-Al2O3 toward the deoxygenation of oleic acid, palm fatty acid distillate (PFAD), refined palm stearin (RPS) and refined palm olein (RPO) were studied. Relevant monometallic and bimetallic (i.e. Mo-, W-, Re-, ReMo-, ReW-, NiMo-) sulfides were also tested for comparison. Experiments revealed that, among all catalysts, ReNiMo sulfide catalyst exhibited the highest diesel yield of 76.5% from oleic acid, 72.5% from PFAD, 69.7% from RPS and 69.5% from RPO. Furthermore, the catalyst could maintain constant diesel yield level for at least six consecutive runs, whereas significant deactivation was observed from other catalysts due to high carbon deposition. Importantly, glycerol was also successfully employed as a hydrogen donor for deoxygenation reaction over this catalyst. From the catalyst characterizations, additional of Re increased the NiMo surface area by 20.4%, furthermore, it reduced the metal particle size and promote the metal dispersion on the support.

Abstract The electrochemical performance of solid oxide electrolysis cells (SOECs) having barium strontium cobalt ferrite (Ba0.5Sr0.5Co0.8Fe0.2O3−δ) and composite lanthanum strontium manganite–yttria stabilized zirconia (La0.8Sr0.2MnO3−δ–YSZ) oxygen electrodes has been studied over a range of operating conditions. Increasing the operating temperature (973 K to 1173 K) significantly increased electrochemical performance and hydrogen generation efficiency for both systems. The presence of water in the hydrogen electrode was found to have a marked positive effect on the EIS response of solid oxide cell (SOC) under open circuit voltage (OCV). The difference in operation between electrolytic and galvanic modes was investigated. Cells having BSCF oxygen electrodes (Ni–YSZ/YSZ/BSCF) showed greater performance than LSM-YSZ-based cells (Ni–YSZ/YSZ/LSM-YSZ) over the range of temperatures, in both galvanic and electrolytic regimes of operation. The area specific resistance (ASR) of the LSM-YSZ-based cells remained unchanged when transitioning between electrolyser and fuel cell modes; however, the BSCF cells exhibited an overall increase in cell ASR of ∼2.5 times when entering electrolysis mode. Durability studies of cells in electrolysis mode were made over 20 h periods. Significant degradation of the BSCF cell was observed (0.02 V h−1) while the LSM-YSZ cell exhibited more stable performance under the same operating conditions (0.3 A cm−2, 1123 K, and H2O/H2 = 70/30). Increasing the electrolysis current density accelerated performance degradation. Electrochemical impedance spectroscopy measurements and microstructure analysis were used to investigate the cause of performance degradation, with evidence emerging of microstructural change in the case of the BSCF electrode.