• Energy Research

A new approach for the direct conversion of syngas into methanol has been proposed as alternative to the conventional process requiring WGS and/or PSA clean-up steps for syngas upgrading. A comparative thermodynamic equilibrium analysis of biogas reforming processes (dry reforming, steam reforming and oxy-steam reforming) has been performed using the Gibbs free energy minimization method. The calculations have been carried out under different biogas composition (CH4/CO2 ¼ 1e2.3), reaction temperature (400e900 C), S/CH4 (0.0e3.0) and O2/CH4 (0.0e0.2) molar ratios. The effects of process variables on the reforming performances as well as on the syngas quality, in term of CH4 and CO2 conversion, H2/CO and H2/CO2 ratios, coke deposition and energetic consumption, has been examined. Subsequently, methanol synthesis has been studied using the same mathematical approach, with the aim to identify the most adequate operating conditions for the direct conversion of the syngas obtained from reforming process into methanol. The simulations suggested that steam reforming of biogas, with high methane content, is the most appropriate route to produce a syngas quality suitable for the new proposed approach.

The sustainable production of H2 and its use as a new and alternative energy carrier are receiving growing attention as a valid alternative to fossil fuel exploitation, contributing to the development of the so-called H2 economy [1]. Traditionally, H2 is produced at industrial scale by steam reforming of natural gas; recently, membrane engineering is receiving considerable interest in this field as testified by a large literature about the membrane reactors (MRs), which represent alternative devices allowing the simultaneous generation of H2 and its purification in a unique stage process. The exploitation of biogas as a renewable source instead of natural gas to generate H2 in reforming processes could contribute to deplete the greenhouse gases pollution pursuing the net-zero carbon emission. This work focuses on the reforming of a CH4:CO2 = 60:40 mixture simulating biogas to produce a COx-free H2 stream in a tubular Pd-Ag MR, packed with a novel, non-commercial bimetallic catalyst, 0.5wt%Ru-7wt%Ni/La0,3Y0,3Zr0,4Ox, prepared by the solution combustion method. Preliminary XRD and TPR characterizations reveal the presence of weak and strong interactions between the support and the active phases (Ni and Ru). Mainly, the TPR analysis shows a complex reduction profile, characterized by multiple reduction peaks, located in the temperature range between 100 and 700°C, and ascribed to different ruthenium (ca. 130°C) and nickel species (ca. 200-700°C), Figure 1(a). As best result of the experimental reaction campaign, a CH4 conversion equal to 99% was reached in the MR (@ H2O/CH4 feed molar ratio = 2 and feed pressure of 250 kPa), with a COx-free H2 recovery of 37%. Globally, the MR behaved better than the traditional reactor (TR), reaching CH4 conversion more than 2.5 times greater than the former .

The glycerol steam reforming (GSR) reaction for hydrogen production was investigated over Rh-based catalysts supported on γ-Al2O3 modified with CeO2, MgO or La2O3. High specific surface area mesoporous supports (Al2O3, CeO2–Al2O3, MgO–Al2O3 and La2O3–Al2O3) were synthesized by the surfactant-assisted co-precipitation method using cetyltrimethylammonium bromide (CTAB) as template. Then, highly dispersed Rh-based catalysts were prepared by the wetness impregnation technique. The physico-chemical properties of the as-prepared supports and catalysts were investigated by N2-physisorption, XRD, ICP-AES, CO-chemisorption, TEM, H2-TPR, CO2-TPD and NH3-TPD measurements. Performance test experiments were carried out in a continuous flow fixed-bed reactor at water-to-glycerol feed ratio (WGFR) of 20:1 (molar), temperatures from 400 °C to 750 °C, weight hourly space velocity of 50,000 ml g−1 h−1 and atmospheric pressure. The stability of all catalysts was also investigated through 12 h time-on-stream (TOS) experiments at 600 °C using a WGFR of 9:1. All catalysts were remarkably stable during TOS with total glycerol conversion of ≈90%, glycerol conversion into gaseous products of ≈45% and H2 selectivity of ≈78%. The final H2 yield for all catalysts was 2.4–2.9 mol H2/mol glycerol. TEM experiments showed that the carbon formed onto the spent catalysts was amorphous and that sintering was mostly avoided during TOS, helping explain the excellent catalytic stability observed. The unpromoted catalyst seems to be following a different reaction pathway than and the promoted ones that depends strongly on the population and kind of acid and basic sites over its surface. MAG and NDC are grateful for financial support by the program THALIS implemented within the framework of Education and Lifelong Learning Operational Programme, co-financed by the Hellenic Ministry of Education, Lifelong Learning and Religious Affairs and the European Social Fund, Project Title: “Production of Energy Carriers from Biomass by Products: Glycerol Reforming for the Production of Hydrogen, Hydrocarbons and Superior Alcohols”. Peer reviewed

The techno-economic feasibility of three biogas utilization processes was assessed through computer simulations on commercial process simulator Aspen HYSYS: HPC (biogas to methanol), BioCH (biogas to biomethane) and CHP (biogas to heat & electricity). The last two processes are already used commercially with the aid of subsidy policies. The economic analysis indicates that, without these policies, none of these attain economic self-sustainability due to high overall manufacturing costs. The estimated minimum support cost (MSCs) were 108, 62 and 109 EUR/MWh for the HPC, BioCH and CHP processes, respectively. The model could explain currently practised government subsidies in Italy and Germany. It was seen that the newly proposed HPC process is economically comparable to the traditional CHP process. Therefore, the HPC process is a possible alternative to biogas usage. A support policy was proposed: 50, 66, 158 and 148 EUR/MWh for available heat, methane, electricity and methanol (respectively); the proposed energy policy results in a 10% OpEx rate of return for any of the processes, thus avoiding a disparity in the production of different products.

This work focuses on the utilization of a novel Ru-Ni foam structured catalysts housed in a Pd-Ag membrane reactor to generate decarbonized H2 by steam reforming of synthetic biogas, analysing from energy/exergy point of views the whole MR based plant, including also the ancillary devices (condenser, boiler, pump etc.). The influence of the wall temperature in the reforming process has been studied to determine the temperature profile along the foam structured membrane reactor. In addition, the overall process efficiency as well as an economic study to determine the cost of the decarbonised hydrogen production have been analysed with the further objective of contributing to meet the European Green Deal policies in the framework of renewable energy carriers production respecting the net zero gas emissions by 2050. The experimental campaign has been realized between 673 and 773 K and varying the pressure between 100 and 200 kPa, reaching 74 % CH4 conversion, 95 % hydrogen recovery and 55 % yield at 773 K and 200 kPa, S/C = 2/1 and WHSV = 0.6 h−1, and a total exergy efficiency of 85 %. The purity of the hydrogen stream recovered in the foam structured membrane reactor was superior to 99.999 % in the whole range of operating conditions analyzed in this work, meeting the expected values of the European Clean Hydrogen Agency (Targets-2030: hydrogen recovery = 95 %, hydrogen purity = 99.99 %)

The application of ceramic foams as structured catalyst supports is clearly expanding due to their interesting specific properties (large exchange area, low pressure drops, high mass and heat transfer properties). In the present work, alumina open-cell foams (OCFs) with different pore density (20,30 and 40 ppi) were coated with Rh/CeO2 catalyst via a two steps synthesis method involving i) the solution combustion synthesis (SCS) to in-situ deposit the CeO2 carried and the ii) wet impregnation (WI) of the Rh active phase. The coated structures were characterized by SEM/EDX and TEM analysis to analyze the morphological characteristics of the deposited films; the mechanical stability was analyzed using ultrasound tests; the permeability and form coefficient were derived from the pressure drop data. The activity and stability of the structured catalysts were investigated towards the steam reforming (SR) and oxy-steam reforming (OSR) of biogas at atmospheric pressure varying temperature (700-900°C), space velocity (35,000-230,000 Nmlog-1oh-1) and time-on-stream (up to 200 h). Catalytic tests were carried out at S/CH4=3 for SR experiments and S/CH4=1 and O2/CH4=0.2 for OSR experiments. Homogeneous, thin (5-40 ?m) and high-resistance coating layers were obtained. Structured catalysts showed high activity, following the order 20 ppi < 30 ppi ? 40 ppi. External mass transfer diffusion, evaluated by Damköhler and Carberry numbers, could be improved by reducing the pore diameter of the OCF structures, whereas Damköhler and Weisz-Prater numbers confirmed the absence of internal mass transport limitation due to thin coating thickness provided by SCS method. Good stability was observed over 200 h for both SR and OSR processes.

Monoliths and foams have received growing attention as catalyst supports in both academic research and industrial applications due to their interesting specific properties (high geometric surface area, low pressure drops, high mass and heat transfer properties). Structured catalysts can operate at high space velocity, achieving a good contact between gas phase and surface reactions. All these characteristics are highly desirable for both exothermic (methanation reaction) and endothermic reactions (reforming processes) [1]. The solution combustion synthesis (SCS) method is a suitable procedure to deposit uniform, thin and high-strength catalytic layers on ceramic monoliths and foams [2,3]. In this work, the catalytic phase was in-situ deposited by the SCS on commercial cordierite monoliths (400-500 cpsi) and alumina foams (20,30,40 ppi). The activity and stability results were investigated towards Steam Reforming (SR) and Oxy-Steam Reforming (OSR) of different fuels (CH4, biogas, n-dodecane) and CO2 methanation reaction. Then, the catalyst scale-up was investigated to evaluate the goodness and the reproducibility of the coating method.