Biogas steam and oxidative reforming processes for synthesis gas and hydrogen production in conventional and microreactor reaction systems

In this work, a renewable source, biogas, was used for synthesis gas and hydrogen generation by steam reforming (SR) or oxidative reforming (OR) processes. Several Ni-based catalysts and a bimetallic Rh–Ni catalyst supported on magnesia or alumina modified with oxides like CeO₂ and ZrO₂ were used. For all the experiments, a synthetic biogas which consisted of 60% CH₄ and 40% CO₂ (vol.) was fed and tested in a fixed bed reactor system and in a microreactor reaction system at 1073 K and atmospheric pressure. The catalysts which achieved high activity and stability were impregnated in a microreactor to explore the viability of process intensification. For the SR process different steam to carbon ratios, S/C, varied from 1.0 to 3.0 were used. In the case of OR process the O₂/CH₄ ratio was varied from 0.125 to 0.50. Comparing conventional and microreactor reaction systems, one order of magnitude higher TOF and productivity values were obtained in the microreactors, while for all the tested catalysts a similar activity results were achieved. Physicochemical characterization of catalysts samples by ICP-AES, N₂ physisorption, H₂ chemisorption, TPR, SEM, XPS and XRD showed differences in chemical state, metal–support interactions, average crystallite sizes and redox properties of nickel and rhodium metal particles, indicating the importance of the morphological and surface properties of metal phases in driving the reforming activity.     

An experimental and theoretical approach for the biogas steam reforming reaction

An experimental and theoretical study for the biogas steam reforming reaction over 5%Ru/Al₂O₃ catalyst have been performed. An apparatus was constructed for the conduction of the experiments, the core of which was a tube reactor, filled with the catalyst in form of pellets. The inlet gas mixture consisted of CH₄ and CO₂ in various composition ratios as a model biogas and steam. A theoretical model of the process was developed. The experimental reactor was modelled as an isothermal pseudo homogeneous fixed bed reactor. Internal and external transport phenomena were neglected and appropriate effectiveness factors were employed instead. A physical properties model was used for the calculation of the physicochemical properties of the real mixture. Five reactant species, CH₄, CO₂, H₂O, CO and H₂, were included in the model, whereas the feed consisted of the first three. Steam reforming and water gas shift were the main reactions. Experimental results and theoretical predictions match closely, stability of the catalyst was assured and an optimal operational window was identified, at GHSV = 10,000–20,000 h⁻¹, T = 700–800 °C, CH₄/CO₂ = 1.0–1.5 and H₂O/CH₄ = 3.0–5.0.     

Carbon deposition behavior of a Co–Ni aerogel catalyst in CH4 oxy-CO2 reforming using various types of reactors

Carbon deposition behavior of a Co–Ni aerogel catalyst in CH₄ oxy-CO₂ reforming is investigated using a deactivation method in three types of reactors including a magnetic field assisted fluidized bed (MAFB) reactor, a conventional fluidized bed reactor and a fixed bed reactor. The spent catalysts are analyzed by TG/DSC and FESEM. It is found that the reactor influences the amount as well as type of carbon species on the spent catalysts. The amount of carbon on the spent catalyst in the MAFB reactor is 11.7 wt.%, which is 10.8 wt.% and 2.6 wt.% less than those in the fixed bed and conventional fluidized bed reactors. Fluidization behavior analysis reveals that agglomerate and bubble size of the catalyst are obviously decreased with the application of the MAFB, which should be accounted for the enhanced carbon resistance of the reactor.     

Hydrogen production from methane and natural gas steam reforming in conventional and microreactor reaction systems

Ni-based (over MgO and Al₂O₃) and noble metal-based (Pd and Pt over Al₂O₃) catalysts were prepared by wet impregnation method and thereafter impregnated in microreactors. The catalytic activity was measured at several temperatures, atmospheric pressure and different steam to carbon, S/C, ratios. These conditions were the same for conventional, fixed bed reactor system, and microreactors. Weight hourly space velocity, WHSV, was maintained equal in order to compare the activity results from both reaction systems. For microreactor systems, similar activities of Ni-based catalyst were measured in the steam methane reforming (SMR) activity tests, but not in the case of natural gas steam reforming tests. When noble metal-based catalysts were used in the conventional reaction system no significant activity was measured but all catalysts showed some activity when they were tested in the microreactor systems. The analysis by SEM and TEM revealed a carbon-free surface for Ni-based catalyst as well as carbon filaments growth in case of noble metal-based catalysts.     

Biogas dry reforming for hydrogen production over Ni-M-Al catalysts (M = Mg,Li, Ca,La, Cu,Co, Zn)

Biogas can be highlighted as a renewable raw material for the production of hydrogen. In this study, Ni-M-Al catalysts were evaluated to obtain hydrogen from the biogas reforming. The catalysts were synthesized by coprecipitation with Ni and Al with a molar percentage of 55 and 33%, respectively, varying the third component M = Mg, Li, Ca, La, Cu, Co, Zn, with a molar percentage of 11%. The reactions were carried out in a fixed bed tubular reactor using a synthetic biogas (70% of CH₄ and 30% of CO₂). The results showed that the CH₄ conversion increased with the temperature up to 700 °C for La11, Cu11, and Zn11 catalysts. CO₂ conversion increased for all catalysts in the range of 500–700 °C. The H₂/CO molar ratios observed in the reactions were higher than 1 due to the contribution of the CH₄ decomposition reaction. The catalyst containing La presented better stability in the reactions due to the stronger acid sites and high resistance to sintering. Carbon filaments were produced by all catalysts at 600 and 700 °C. Sintering was the main cause of deactivation of the catalysts, except for La11.     

Biogas dry reforming over Ni-Al catalyst: Suppression of carbon deposition by catalyst preparation and activation

Biogas dry reforming is as an alternative renewable route for the hydrogen production. However, the major drawback of this process is the catalyst deactivation by carbon deposition and sintering. In this work, Ni-Al catalysts were studied aiming to suppress the carbon deposition in the dry reforming of biogas. The catalysts were prepared by coprecipitation and evaluated the washing step. The reactions were carried out with unreduced and reduced catalysts in a fixed bed tubular reactor using a synthetic biogas (60% CH₄ and 40% CO₂). The washing and activation steps influenced the characteristics of the catalysts and the catalytic properties in the biogas reforming. The unwashed sample resulted in an oxide containing potassium nickelate with high basicity and low surface area. Both washed samples, reduced and unreduced, showed a high amount of carbon formation, whereas no carbon formation was observed in the unwashed samples for the reactions in the temperature range of 500–750 °C. The unwashed and unreduced sample was the only one that maintained the activity during all the reaction time at 700 °C (40% CH₄ conversion and 75% CO₂ conversion), low coke amount and no evidence of sintering, which was confirmed by XRD, TPO, and SEM analyses. The carbon suppression was related to the nickelate phase and to the Ni carbide formation in the unwashed and unreduced catalyst. In summary, the carbon deposition in biogas dry reforming was completely controlled between 600 and 750 °C using the unwashed and unreduced Ni-Al catalyst.     

An investigation of a stratified catalyst bed for small-scale hydrogen production from methanol autothermal reforming

This research project explored a methanol reforming system using a stratified catalyst bed. Commercially available catalysts were used within a single reactor and the system was run autothermally (fuel, steam and oxidizer). The investigation explored the fuel conversion and reactor temperature profile at various O₂/CH₃OH ratios. The experiments showed that the stratified system had fairly high conversions at low O₂/CH₃OH ratios. Additionally, it showed high selectivity towards hydrogen, and low selectivity for carbon monoxide. The experimental results gathered show a promising use of stratified catalyst beds for small-scale reforming systems.     

Development of a Co–Ni bimetallic aerogel catalyst for hydrogen production via methane oxidative CO2 reforming in a magnetic assisted fluidized bed

A novel nano-sized Co–Ni bimetallic aerogel catalyst was synthesized via the sol–gel process followed by the supercritical drying method. The catalyst exhibited at least 28% higher activity and 15% higher H₂ selectivity than those of a monometallic cobalt aerogel catalyst in methane oxidative CO₂ (Oxy-CO₂) reforming. Cold-model experiments revealed that channels were alleviated and the agglomerate size was reduced when the catalyst was applied in a magnetic assisted fluidized bed (MAFB). Owing to the improved fluidization quality of the catalyst in the MAFB reactor, CH₄ conversion was raised by 12% and 7% as compared with those in the fixed bed reactor and the conventional fluidized bed reactor, respectively. Furthermore, the catalytic performance was quite stable during a 50 h reaction. This stable performance can be illustrated both by the superior catalytic property of the Co–Ni bimetallic aerogel catalyst and the intensified gas–solid interaction in the MAFB reactor.     

Catalytic steam reforming of bio-oil aqueous fraction for hydrogen production over Ni–Mo supported on modified sepiolite catalysts

Hydrogen will be an important energy carrier in the future and hydrogen production has drawn a great deal of attention to its advantages in efficiency and environmental benefit. Catalytic steam reforming in this study was carried out in a fixed bed tubular reactor with sepiolite catalysts. Sepiolite catalysts modified with nickel (Ni) and molybdenum (Mo) were prepared using the precipitation method. Influential parameters such as temperature, catalyst, steam to carbon ratio (S/C), the feeding space velocity (WHSV), reforming length, and activity of catalyst were investigated and the yields of H₂, CO, CH₄, and CO₂ were obtained. The result of this experiment shows that the acidified sepiolite catalyst with addition of the Ni and Mo greatly improves the activities of catalyst and effectively increases the yield of hydrogen. The favorable reaction condition is as follows: reaction temperature is 700–800 °C; S/C is 16–18; the feeding space velocity is 1.5–2.2 h⁻¹, respectively.     

Comparative numerical evaluation of autothermal biogas reforming in conventional and split-and-recombine microreactors

A new microreactor design featuring embedded passive mixing elements was tested as a means to enhance autothermal reforming reaction of biogas over a novel ReNi/γ-Al₂O₃ catalyst. To determine an optimal condition that would result in completely converted biogas with H₂/CO product ratio of around one and minimal hot spot formation inside the reactor, use of various inlet O₂ and H₂O concentrations and inlet temperatures were numerically investigated. The influence of inlet reactant velocity on the reactor effectiveness was then studied at the optimal condition. Performance of a straight-channel microreactor was also studied and compared with that of the novel microreactor. The O₂:H₂O:CO₂:CH₄ ratio of 25:5:28:42% (v/v) and inlet temperature of 730 °C were noted as the optimal condition for the novel microreactor. Complete biogas conversion over a wider range of inlet Reynolds number, lower required catalyst loading to achieve the desired reactor performance, higher H₂ and CO selectivities and reduced hot spot formation were noted as the advantages of the novel microreactor.     

Simulative optimization of catalyst configuration for biogas dry reforming

Biogas dry reforming is a promising technology for converting biomass into high-value products and reducing greenhouse gas emissions. Recent improvements to biogas reforming have mainly focused on the preparation of functional catalysts; however, little attention has been paid to the effects of catalyst configuration in plug flow reactors. In this study, a Ni/MgO catalyst for biogas reforming was synthesized via the wet impregnation method. Parameters were optimized using an experimental rig and then simulations were performed using an Aspen HYSYS reaction simulator. We simulated loading the same amount of catalyst into 1, 2, 3, or 10 zones inside the reactor and compared performance parameters, including H₂ yield, CO yield, CH₄ conversion, and CO₂ conversion. The results of simulations showed that a 2-zone configuration with a catalyst ratio of 1:4 was optimal, with 88.2% H₂ yield, 83.5% CO yield, 96.4% CH₄ conversion, and 91.7% CO₂ conversion. Catalyst zone number, catalyst distribution, and catalyst zone position all had significant effects on catalytic behavior. The findings of this study provide new insights into the processes of biogas reforming and other heterogeneous catalysis reactions.     

Durability of a Ni based monolithic catalyst in the autothermal reforming of biogas

A Ni based catalyst supported on a cordierite monolithic substrate was applied to the autothermal reforming (ATR) of biogas to produce hydrogen. When the feed rates of oxygen and steam were constant, the Steam/CH₄ (S/CH₄) and O₂/CH₄ ratios changed because of an increase or decrease in the methane concentration of the biogas. The concentration of methane in the biogas fluctuates roughly between 35% and 65% according to factors such as the properties or amount of the waste. Therefore, the effect of S/CH₄ and O₂/CH₄ ratios on catalyst durability was confirmed by using actual biogas, which was produced by anaerobic fermentation of biomass at the biogasification bench-scale plant in Kyoto. Reforming reactions were carried out at ratios of S/CH₄ = 0–4, O₂/CH₄ = 0.5 and at S/CH₄ = 2, O₂/CH₄ = 0.6. The S/CH₄ range of 0–2.0 and the O₂/CH₄ range of 0.5–0.6 had no effect on the catalyst durability and a S/CH₄ ratio of more than 3.0 led to decreased catalytic performance.     

The assessment of reformation in a porous medium-catalyst hybrid reformer under excess enthalpy condition

A porous medium-catalyst hybrid reformer for hydrogen-rich syngas production by dry autothermal reforming (DATR) was investigated in this study. In the reforming process, the reaction under excess enthalpy was explored by visualization in packed-bed catalyst reactor. The hybrid design was arranged with a porous medium (PM) in the upstream of the catalyst packed-bed. In the arrangement, the reactants were preheated by internal heat recirculation and the selectivity of H₂-rich syngas was enhanced by the catalyst surface reaction. Controlled parameters included CO₂/CH₄ and O₂/CH₄ ratios, gas hourly space velocity (GHSV) with or without porous medium. The experimental results demonstrated that the reforming reaction with the hybrid reformer could achieve excess enthalpy under the tested parameters. The excess enthalpy ratio was between 0.15 and 0.55. The temperature measurement along the axial position and image observation of the catalyst packed-bed indicated that the flame was stably held at the interface of the PM and the catalyst bed, and this enhanced fuel conversion and reforming efficiencies, especially in the low methane conversion condition. In the dry autothermal reforming process, part of the chemical energy released from the reaction supplies the energy required for a self-sustaining reaction. Therefore, the selection of the parameters was determined to achieve high reforming efficiency and low energy loss percentage. The results showed that the energy loss percentage was between 12.7 and 24.6% and reforming efficiency was between 64.4 and 79.5% with the best reforming parameter settings (O₂/CH₄ = 0.7–0.9 and CO₂/CH₄ = 0.0–2.0).     

Fixed beds of Rh/Al2O3-based catalysts for syngas production in methane SCT-CPO reactors

The present experimental work deals with methane short contact time (SCT) CPO in a fixed bed reactor considering CH₄ conversion and H₂ and CO selectivity in a wide range of weight hourly space velocity (WHSV). Two different Rh/Al₂O₃-based catalysts both loaded with 0.5% by weight of Rh were developed: one catalyst carrying Rh on the external support surface (Egg-Shell configuration), and the other one with Rh embedded into the porous support (Egg-Yolk configuration). The goal was the design of the optimal fixed bed structure (not only considering beds made of egg-shell or egg-yolk catalysts alone, but also their various combinations), able to either attain the best performance or maintain a reaction temperature along the bed without excessive variations with WHSV. The highest CH₄ conversion (>90%) and H₂ selectivity (>98%), moreover stable despite the WHSV variation of about 3.6 times, and reactor working temperature with not too large variations (maximum of about 16%) by increasing WHSV were obtained with the fixed bed of Egg-Yolk catalyst alone. Instead, the fixed bed of Egg-Shell catalyst alone showed the worst performance: CH₄ conversion and H₂ selectivity were lower of about 15% and 10%, respectively, and decreasing with the increase of WHSV; on the contrary, the CO selectivity remained practically the same, only a slightly decrease being observed. Suitable combinations of the two catalysts in the fixed bed produced intermediate performance between those of the catalysts alone. The different performance of the two catalyst types was probably due to the different structure of the particles and to the Rh position on the carrier itself. Finally, thermal and performance durability tests up to 16 working hours showed that the Egg-Yolk catalyst employed alone in the fixed bed was able to maintain the CH₄ partial oxidation activity with practically disregardable decrease.     

Optimization of tri-reformer reactor to produce synthesis gas for methanol production using differential evolution (DE) method

This paper presents a study on optimization of a fixed bed tri-reformer reactor (TR). This reactor has been used instead of conventional steam reformer (CSR) and auto thermal reformer (CAR). A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methane conversion, hydrogen production and desired H₂/CO ratio as a synthesis gas for methanol production. A mathematical heterogeneous model has been used to simulate the reactor. The process performance under steady state conditions was analyzed with respect to key operational parameters (inlet temperature, O₂/CH₄, CO₂/CH₄ and steam/CH₄ ratios). The influence of these parameters on gas temperature, methane conversion, hydrogen production and H₂/CO ratio was investigated. Model validation was carried out by comparison of the reforming model results with industrial data of CSR. Differential evolution (DE) method was applied as a powerful method for optimization. Optimum feed temperature and reactant ratios (CH₄/CO₂/H₂O/O₂) are 1100 K and 1/1.3/2.46/0.47 respectively. The optimized TR has enhanced methane conversion by 3.8% relative to industrial reformers in a single reactor. Methane conversion, hydrogen yield and H₂/CO ratio in optimized TR are 97.9%, 1.84 and 1.7 respectively. The optimization results of tri-reformer were compared with the corresponding predictions from process simulation software operated at the same feed conditions.     

Metal foam-supported Pd–Rh catalyst for steam methane reforming and its application to SOFC fuel processing

Pd–Rh/metal foam catalyst was studied for steam methane reforming and application to SOFC fuel processing. Performance of 0.068 wt% Pd–Rh/metal foam catalyst was compared with 13 wt% Ni/Al₂O₃ and 8 wt% Ru/Al₂O₃ catalysts in a tubular reactor. At 1023 K with GHSV 2000 h⁻¹ and S/C ratio 2.5, CH₄ conversion and H₂ yield were 96.7% and 3.16 mol per mole of CH₄ input for Pd–Rh/metal foam, better than the alumina-supported catalysts. In 200 h stability test, Pd–Rh/metal foam catalyst exhibited steady activity. Pd–Rh/metal foam catalyst performed efficiently in a heat exchanger platform reactor to be used as prototype SOFC fuel processor: at 983 K with GHSV 1200 h⁻¹ and S/C ratio 2.5, CH₄ conversion was nearly the same as that in the tubular reactor, except for more H₂ and CO₂ yields. Used Pd–Rh/metal foam catalyst was characterized by SEM, TEM, BET and CO chemisorption measurements, which provided evidence for thermal stability of the catalyst.     

Syngas production by CO2 reforming of coke oven gas over Ni/La2O3–ZrO2 catalysts

Syngas production by CO₂ reforming of coke oven gas (COG) was studied in a fixed-bed reactor over Ni/La₂O₃–ZrO₂ catalysts. The catalysts were prepared by sol–gel technique and tested by XRF, BET, XRD, H₂-TPR, TEM and TG–DSC. The influence of nickel loadings and calcination temperature of the catalysts on reforming reaction was measured. The characterization results revealed that all of the catalysts present excellent resistance to coking. The catalyst with appropriate nickel content and calcination temperature has better dispersion of active metal and higher conversion. It is found that the Ni/La₂O₃–ZrO₂ catalyst with 10 wt% nickel loading provides the best catalytic activity with the conversions of CH₄ and CO₂ both more than 95% at 800 °C under the atmospheric pressure. The Ni/La₂O₃–ZrO₂ catalysts show excellent catalytic performance and anti-carbon property, which will be of great prospects for catalytic CO₂ reforming of COG in the future.     

Deactivation and regeneration of Ni catalyst during steam reforming of model biogas: An experimental investigation

This paper presents detailed study of biogas reforming. Model biogas with different levels of H₂S is subjected to reforming reaction over supported Ni catalyst in a fixed bed reactor at 700 °C and 800 °C. In order to understand the poisoning effects of H₂S the reactions have been initially carried out without H₂S in the feed stream. Three different H₂S concentrations (20, 50 and 100 ppm) have been considered in the study. The H₂O to CH₄ ratio is maintained in such as way that CO₂ also participates in the reforming reaction. After performing the poisoning studies, regeneration of the catalyst has been studied using three different techniques i) removal of H₂S from the feed stream ii) temperature enhancement and iii) steam treatment. Poisoning at low temperature is not recoverable just by removal of H₂S from the feed stream. However, poisoning at high temperature is easily reversed just by removal of H₂S from the feed stream. Unlike some previous reports by Li et al. (2010) and Rostrup-nielsen (1971) [1,2], catalyst regeneration is achieved in shorter time frames for all the regeneration techniques attempted.     

A novel catalyst–sorbent system for an efficient H2 production with in-situ CO2 capture

This paper presents an experimental investigation for an improved process of sorption-enhanced steam reforming of methane in an admixture fixed bed reactor. A highly active Rh/Ce_αZr_1−αO₂ catalyst and K₂CO₃-promoted hydrotalcite are utilized as novel catalyst/sorbent materials for an efficient H₂ production with in situ CO₂ capture at low temperature (450–500 °C). The process performance is demonstrated in response to temperature (400–500 °C), pressure (1.5–6.0 bar), and steam/carbon ratio (3–6). Thus, direct production of high H₂ purity and fuel conversion >99% is achieved with low level of carbon oxides impurities (<100 ppm). A maximum enhancement of 162% in CH₄ conversion is obtained at a temperature of 450 °C and a pressure of 6 bar using a steam/carbon molar ratio of 4. The high catalyst activity of Rh yields an enhanced CH₄ conversion using much lower catalyst/sorbent bed composition and much smaller reactor size than Ni-based sorption enhanced processes at low temperature. The cyclic stability of the process is demonstrated over a series of 30 sorption/desorption cycles. The sorbent exhibited a stable performance in terms of the CO₂ working sorption capacity and the corresponding CH₄ conversion obtained in the sorption enhanced process. The process showed a good thermal stability in the temperature range of 400–500 °C. The effects of the sorbent regeneration time and the purge stream humidity on the achieved CH₄ conversion are also studied. Using steam purge is beneficial for high degree of CO₂ recovery from the sorbent.