Promoted H2 Production Research Articles

Effects of moisture content and CaO on municipal solid waste pyrolysis in a fixed bed reactor

Experiments of municipal solid waste (MSW) pyrolysis were carried out in a self-design fixed bed reactor. Polyethylene (PE), paper pulp and bamboo (chopsticks) were adopted to represent three major components in MSW in the experiments. The effects of moisture content (0, 50% and 66.7%) and CaO (0, 2g and 4g) on product composition and lower heating value (LHV) of syngas were investigated. The temperature was set at 900°C and each MSW sample was 4g in each test. The results indicated that increasing moisture content led to lower H2 concentration but higher tar yield in paper pulp and bamboo pyrolysis, but the influence was converse in PE pyrolysis; the addition of CaO promoted H2 production but reduced tar yield; the maximum LHV of syngas was achieved at zero moisture content in bamboo and paper pulp pyrolysis, while that was achieved at 66.7% moisture content in PE pyrolysis.

Hydrogen production by glycerol steam-reforming over nickel and nickel-cobalt impregnated on alumina

Hydrogen is a clean energy carrier, and its utilization will reduce environmental problems related to fossil fuels one. Biomass is an inexhaustible renewable source to generate biocompounds. Glycerol, obtained from a crescent biodiesel industry, is an abundant bio-substrate to produce hydrogen. The steam reforming of glycerol was studied employing 4Ni/Al2O3, 4Co–4Ni/Al2O3, and 12Co–4Ni/Al2O3 catalysts at 300, 500, and 700 °C, 1 atm, 10 h−1 WHSV, 6:1 water:glycerol molar ratio (WGMR), 0.17 ml min−1 glycerol solution feed flow rate and time-on-stream 8 h. The main product obtained was H2, followed by CO2, CO, and CH4 in smaller proportion. Co promotes H2 production and unfavors CO2 generation when temperature decreases; CH4 formation is observed at higher temperature. A low Co loading produces the largest H2 and CO2 amounts at the lowest temperature. A high Co loading improves H2 production at lower temperature, but this does not occur at high temperature.

Effect of gold loading and TiO2 support composition on the activity of Au/TiO2 photocatalysts for H2 production from ethanol–water mixtures

This paper systematically compares the activity of Au/TiO2 photocatalysts (Au loadings 0–10wt.%) for H2 production from ethanol–water mixtures under UV excitation. Degussa P25 TiO2 was used as the support phase. TEM analyses revealed that the average Au nanoparticle size at all loadings was 5±2nm, with the Au nanoparticles preferentially located at the interfacial sites between TiO2 crystallites. XRD, XRF, XPS, and UV–Vis measurements established that metallic Au was the only gold species on the surface of the photocatalysts. The Au/TiO2 photocatalysts showed an intense absorption maximum centred around 560–570nm due to the localised surface plasmon resonance (LSPR) of the supported gold nanoparticles. Photoluminescence measurements revealed that gold nanoparticles effectively suppress electron–hole pair recombination in TiO2, even at low Au loadings. All of the Au/TiO2 photocatalysts displayed high activity for H2 production from ethanol–water mixtures under UV irradiation, with the highest activities observed in the Au loading range 0.5–2wt.% (H2 production rate 31–34mmolg−1h−1). In order to deconvolute the role of the P25 TiO2 support in promoting H2 production, anatase and rutile nanoparticles were isolated from P25 TiO2 by selective chemical dissolution and then functionalised with gold nanoparticles (3wt.% loading, size 5±2nm). The H2 production activity of the resulting Au/anatase and Au/rutile photocatalysts was 22 and 10mmolg−1h−1, respectively, and substantially lower than the corresponding Au/P25 TiO2 photocatalyst (32mmolg−1h−1). The data provide strong evidence that synergistic electron transfer between the TiO2 polymorphs and supported Au nanoparticles is responsible for the high rates of H2 production observed in the Au/P25 TiO2 system. The interface between anatase and rutile crystallites, where gold nanoparticles preferentially deposit, is identified as a photocatalytic ‘hot spot’ for H2 production. High Au loadings reduce the efficiency of such ‘hot spots’.

Hydrogen production from wood gasification promoted by waste eggshell catalyst

Bio-hydrogen renowned as a future potential hydrogen source and studies were devoted in developing the efficient way to obtain the hydrogen. Biomass gasification of Azadirachta excelsa wood was carried out with addition of naturally derived CaO catalyst using temperature-programmed gasification (TPG) technique. The reaction (TPG) was performed at 50–1000°C in 5% O2/He with flow rate 10 ml/min, and the product gas evolution (H2, CH4, CO and CO2) was detected by online mass spectrometer. The waste eggshell was chosen as a natural source of CaO, and the effect of catalyst loading was investigated in this study. All the fresh and used catalysts were characterized, and the physicochemical changes of the eggshell were observed through scanning electron microscopy, X-ray fluorescence and X-ray diffraction techniques. Hydrogen yield were increased along with the catalyst loading (20%, 40% and 60%) from 57 to 73%, respectively, compared to the reaction without catalyst. The additions of waste eggshell enhanced the catalytic activity and suppressed CO2 production through CaO absorption property which induced the water gas shift reaction that promotes H2 production at lower temperature. Copyright © 2013 John Wiley & Sons, Ltd.

Glycerol and bioglycerol conversion in supercritical water for hydrogen production

Catalytic transesterification of vegetable oils leads to biodiesel and an alkaline feed (bioglycerol and organic residues, such as esters, alcohols…). The conversion of bioglycerol into valuable organic molecules represents a sustainable industrial process leading to the valorization of a renewable organic resource. The physicochemical properties in the supercritical domain (T>374°C, P>22.1 MPa) transform water into a solvent for organics and a reactant favouring radical reactions. In this context, the conversion of bioglycerol in supercritical water (SCW) into platform molecules and/or high energetic gases (hydrogen, hydrocarbons) could represent an interesting valorization process. The reported research results concern the conversion of bioglycerol compared to pure glycerol. The experiments have been done in batch autoclaves (5 ml and 500 ml stirred). Solutions of pure (5 or 10 wt%) and crude (3.5 wt%) glycerol have been processed with or without catalyst (K2CO3 1.5 wt%) in the range of 450–600°C. The molecular formula of bioglycerol was determined as C4.3H9.7O1.8Na0.1Si0.08. Glycerol was partially decomposed in the batch systems during the heating (42% before reaching 420°C) and some intermediates (propanediol, ethylene glycol …) were quantified, leading to a proposition of a reaction pathway. Acrolein, a valuable platform molecule, was mainly produced in the absence of catalyst. No solid phase was recovered after SCW conversion of pure and bioglycerol in batch reactors. The optimal parameters for gasification were 600°C, 25 MPa for bioglycerol and 525°C, 25 MPa, for pure glycerol. In these operating conditions, 1 kg of pure or bioglycerol leads to 15 and, respectively, 10 mol of hydrogen. Supercritical water gasification of crude glycerol favoured the generation of light hydrocarbons, while pure glycerol promoted H2 production. SCW conversion of glycerol (pure and crude) allows to obtain simultaneously energetic gases (respectively 2600 and 4000 kcal/kg glycerol) and valuable platform molecules.

Effect of cosmic ray/X-ray ionization on supermassive black hole formation

We study effects of external ionization by cosmic rays (CRs) and X-rays on the thermal evolution of primordial clouds under strong far-ultraviolet (FUV) radiation. A strong FUV radiation dissociates H2 and quenches its cooling. Even in such an environment, a massive cloud with Tvir>10^4 K can contract isothermally at 8000 K by Lyman alpha cooling. This cloud collapses monolithically without fragmentation, and a supermassive star (>10^5 Msun) is believed to form at the center, which eventually evolves to a supermassive black hole (SMBH). However, candidates of FUV sources, including star-forming galaxies, are probably sources of strong CRs and X-rays, as well. We find that the external ionization promotes H2 production and elevates the threshold FUV intensity Jcr needed for the SMBH formation for CR energy density U_CR>10^-14 erg/cm^3 or X-ray intensity J_X>10^-24 erg/s/cm^2/sr/Hz at 1 keV. The critical FUV flux increases in proportion to U_CR^{1/2} (J_X^{1/2}) in the high CR (X-ray, respectively) limit. With the same value of FUV intensity at the Lyman limit (13.6 eV), the H^- photodissociation rate, with threshold of 0.755 eV, increases and the H2 molecules decrease with decreasing effective temperature of the FUV sources T*. The lower value of T* thus results in the lower critical FUV flux at 13.6 eV. Using an empirical relation between intensities of FUV and CR/X-ray from nearby star-forming galaxies, we find that external ionization effect remarkably enhances the critical FUV flux for sources with T* as high as 10^5 K and composed of stars with <100 Msun to a level that is not realized in any halo. This indicates that, to induce SMBH formation, the FUV sources must be either Pop II/I galaxies with low brightness temperature, Pop III galaxies with a very top-heavy IMF, or Pop III galaxies too young to harbor sources of CR/X-ray, e.g., supernova remnants or high-mass X-ray binaries.

Enhanced oxygen mobility and reactivity for ethanol steam reforming

AbstractThis article describes a strategy for increasing oxygen storage capacity (OSC) of ethanol steam reforming (ESR) catalysts. Sintering and carbon deposition are major defects of nickel‐based catalysts for ESR; tuning oxygen mobility (OM) of CeO2‐based supports can overcome these drawbacks and promote H2 production. We have successfully increased OSC and OM by adding Mg into the lattice of Ni/CeO2 to promote H2 production in ESR. The insertion of Mg into the CeO2 lattice efficiently promotes the reduction of Ce4+ according to X‐ray powder diffraction (XRD) and temperature‐programmed reduction (TPR) analysis. Mg‐modified Ni/CeO2 catalysts have larger OSC and smaller nickel crystallite size compared with bare Ni/CeO2. The optimal Mg addition is 7 mol % (Ni/7MgCe) with the best OM. We also present evidence indicating that Mg addition significantly promotes ethanol conversion and H2 production in ESR, and that Ni/7MgCe yields the best performance due to the high OM of the support. These Mg‐modified catalysts also produce less carbon deposition compared with Ni/CeO2, and the amount of deposited carbon decreases with increasing Mg addition. Ni/7MgCe has the best resistance to carbon deposition owing to the excellent OM. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Steam Reforming of Woody Biomass in a Fluidized Bed of Iron Oxide-Impregnated Porous Alumina

Steam reforming of woody biomass in a fluidized bed was performed at 773, 873, or 973 K. Nonporous silica sand, porous γ-alumina and iron oxide-impregnated porous γ-alumina (Fe-impregnated alumina) were used as bed materials. The addition of iron oxide to the alumina promoted H2 production at all the temperatures. Larger amounts of H2 were produced at higher temperatures. Tar evacuated during steam reforming was captured on the Fe-impregnated alumina, and the captured tar (referred to as coke) was reformed with steam to form H2. In addition to the reforming, a redox reaction occurred on the iron oxide: CO produced during steam reforming was consumed to reduce the iron oxide, and the reduced iron oxide came into contact with steam to form H2. The redox reaction, rather than reforming of the coke, was the predominant pathway of H2 formation at higher temperatures.

Gasification of Organic Waste with Subcritical Steam under the Presence of a Calcium-Based Carbon Dioxide Sorbent

“HyPr-RING” is a new H2 production process using carbonaceous fuels in which the fuel is reacted with subcritical steam and a calcium-based CO2 sorbent. We investigated the applicability of this process to organic matter by examining the performance of the process with fuels of differing volatility. The gasification rate and relative contributions of the volatile and “char” components to H2 production were investigated by using dried sewage sludge with a high volatile component concentration, coal with an intermediate volatile component concentration, and coal char with a low volatile component concentration. During the initial thermal decomposition, carbon in the fuels rapidly decreased with time and was converted to carbonaceous gas of CH4 and C2H6 in addition to H2. The amount of the decrease depended on the volatile content in the fuels. Following this initial rapid stage, the residual carbon appeared to become charlike, even for the high volatile content fuel. The gasification rate became slow, and the gasification shifted to favor H2 production in a molar ratio of H2 to CH4 that approximated the equilibrium composition for a char and steam reaction. NaOH catalytically promoted H2 production even for the sludge.

H2 Production from Algal Biomass by a Mixed Culture of Rhodobium marinum A-501 and Lactobacillus amylovorus.

To produce hydrogen from starch accumulated in an algal biomass, we used a mixed culture of the lactic acid bacterium, Lactobacillus amylovorus, and the photosynthetic bacterium, Rhodobium marinum A-501. In this system L. amylovorus, which possesses amylase activity, utilized algal starch for lactic acid production, and R. marinum A-501 produced hydrogen in the presence of light using lactic acid as an electron donor. Algal starch accumulated in the marine green alga Dunaliella tertiolecta, and the freshwater green alga Chlamydomonas reinhardtii, was more suitable for lactic acid fermentation by L. amylovorus than an authentic starch sample. Consequently, the yields of hydrogen obtained from starch contained in D. tertiolecta and C. reinhardtii were 61% and 52%, respectively, in the mixed culture of L. amylovorus and R. marinum A-501. These values were markedly superior to those obtained using a mixed culture of Vibrio fluvialis T-522 and R. marinum A-501 described previously. The yield and production rate of hydrogen by R. marinum A-501 from the lactic acid fermentates were higher than from authentic lactic acid, suggesting that the fermentates contain a factor(s) which promotes H2 production by this bacterium.